Reducing the content of NOX and no2 in the offgas from firing plants operated with nh3

Abstract

The invention relates to reducing the content of NOX and N2O in the offgas (flue gas) from a firing plant operated with NH3 which is integrated into a plant for catalytic decomposition of NH3 into N2 and H2. To this end, the firing plant preferably comprises a combustion means in which NH3 is burnt to produce combustion heat and an NH3-decomposition means which is in heat exchange with the combustion means and in which NH3 is catalytically decomposed to afford N2 and H2. The heat required for the catalytic decomposition of NH3 in the NH3-decomposition means is provided by the combustion of NH3 in the combustion means. The combustion means preferably comprises at least one burner and a combustion space. The firing plant is preferably configured analogously to a primary reformer.

Description

__________________________________________________________________________________ Reduction of NO X and N2O in the exhaust gas of NH3-fired combustion plants for the catalytic decomposition of NH3__________________________________________________________________________________

[0001] Priorities are claimed from European patent application No. 22216421.2, filed on December 23, 2022, from European patent application No. 23165192.8, filed on March 29, 2023, and from German patent application No. 102023118563.2, filed on July 13, 2023.

[0002] The invention relates to the reduction of NOX and N2O content in the exhaust gas (flue gas) of a combustion plant operated with NH3, which is integrated into a plant for the catalytic decomposition of NH3 into N2 and H2. For this purpose, the combustion plant preferably comprises a combustion device in which NH3 is burned to generate heat of combustion, as well as an NH3 decomposition device which is in heat exchange with the combustion device and in which NH3 is catalytically decomposed into N2 and H2. The heat required for the catalytic decomposition of NH3 in the NH3 decomposition device is provided by the combustion of NH3 in the combustion device. The combustion device preferably comprises at least one burner and a combustion chamber. The combustion plant is preferably designed analogously to a primary reformer.

[0003] H2 can be extracted from H2O using renewable energy and then converted into NH3 with N2. NH3 can be stored and transported much more safely than H2. NH3 can then be decomposed back into H2 and N2. After N2 is separated, H2 finds a wide variety of industrial applications.

[0004] The decomposition of NH3 to N2 and H2 is an endothermic reaction (ΔH° = 45.9 kJ∙mol-1) in which the amount of substance doubles (2 NH3 ↔ N2 + 3 H2). Therefore, the reaction is generally favored by high temperatures and low pressures. The higher the pressure, the higher the temperature must be to achieve satisfactory reaction yields. A variety of materials have been proposed as catalysts for the decomposition of NH3, which are active at different temperatures (see, for example, Il. Lucentini et al., Ind. Eng. Chem. Res. 2021, 60, 18560-18611).

[0005] During the catalytic decomposition of NH3, a product gas is obtained which contains H2 in a mixture with N2 and possibly other gaseous components, e.g., undecomposed NH3. However, many industrial applications require H2 in high purity, so that purification of the product gas is necessary before H2 can be supplied to industrial applications. While the purification of H2 is basically possible using various processes, e.g., cryogenic processes or Membrane processes, cleaning by pressure swing adsorption is particularly economical on an industrial scale.

[0006] The catalytic decomposition of NH3 into N2 and H2 takes place at high temperature and medium pressure in the gas phase. NH3 is stored in liquid form in cooled tanks at atmospheric pressure and -32.8°C. NH3 is fed into the plant by a pump at system pressure. Due to the increased system pressure, the boiling point of the NH3 rises, e.g., at 27.8 bar a to approximately 62.2°C. To convert NH3 into the gas phase, heat is required to evaporate the NH3.

[0007] Conventional processes for the catalytic decomposition of NH3 generate significant amounts of heat, which can be used to evaporate NH3.

[0008] US 4704267 A concerns the production of high-purity H2 from liquid, anhydrous NH3. NH3 is vaporized and then separated into its components. The resulting dissociated gas stream is fed to an adiabatic metal hydride purification unit to absorb the H2 present in the stream. The adsorbed H2 is then recovered as a high-purity product.

[0009] FR 1469045 A relates to an apparatus comprising a preheater fed with NH3, a tube bundle enclosing a catalyst for splitting NH3 and, optionally, a cell for purifying H2 by diffusion, which are interconnected and located in a single housing containing heating means.

[0010] CN 111957270 A relates to an NH3 decomposition device comprising an NH3 decomposition unit and a combustion unit acting on the NH3 decomposition unit. NH3 enters the NH3 decomposition unit via a first purified gas inlet to perform a decomposition reaction of the NH3. Produced mixed gas is discharged via a second purified gas outlet and then enters the combustion unit via a second purified gas inlet. The mixed gas comprises N2, H2, and undecomposed NH3. The mixed gas enters the combustion unit to provide heat for the decomposition reaction of the NH3 of the NH3 decomposition unit, thus realizing heat self-sufficiency in the NH3 decomposition-H2 production system. No additional fuel is required for energy supply and the cost of the NH3 decomposition H2 production system is reduced.

[0011] CN 113896168 A relates to a process for producing H2 or reducing gas by cracking NH3 using a two-stage process, comprising the following steps: The liquid NH3 of the raw material is fully gasified and heated by a heat exchange gasification system and then enters a first-stage heat exchange NH3 cracking reaction system to generate a partial NH3 cracking reaction. The reaction gas from the first-stage heat exchange NH3 cracking reaction system enters a second-stage high-temperature NH3 cracking reaction system to perform a residual NH3 cracking reaction. The second-stage high-temperature NH3 cracking reaction gas sequentially enters the second-stage heat exchange NH3 cracking reaction system. first stage and the heat exchange gasification system to gradually recover heat so that the reducing gas is obtained.

[0012] WO 2001 / 087770 A1 relates to the autothermal decomposition of NH3 to produce high-purity H2.

[0013] WO 2011 / 107279 A1 relates to an NH3-based H2 production reactor comprising an NH3 cracking chamber with an NH3 cracking catalyst, an inner combustion chamber with a combustion or oxidation catalyst which is in thermal contact with the NH3 cracking chamber, an NH3 gas preheating chamber and an outer shroud for heat recovery from the combustion products emerging from the combustion chamber, wherein the cracking chamber, the inner combustion chamber, the preheating chamber and the heat recovery shroud are arranged concentrically.

[0014] WO 2017 / 160154 A1 relates to a method for generating power using a gas turbine, comprising the following steps: (i) evaporating and preheating liquid NH3 to produce preheated NH3 gas; (ii) introducing the preheated NH3 gas into an NH3 cracking device suitable for converting NH3 gas into a mixture of H2 and N2; (iii) converting the preheated NH3 gas into a mixture of H2 and N2 in the device; (iv) cooling the mixture of H2 and N2 to obtain a cooled H2 and N2 mixture; (v) introducing the cooled H2 and N2 mixture into a gas turbine; and (vi) combusting the cooled H2 and N2 mixture in the gas turbine to generate power.

[0015] WO 2019 / 038251 A1 relates to a process for producing a product gas containing N2 and H2 from NH3, comprising the steps of non-catalytic partial oxidation of NH3 with an O2-containing gas to a process gas containing N2, water, amounts of nitrogen oxides and residual amounts of NH3; cracking at least a portion of the residual amounts of NH3 to H2 and N2 in the process gas by contact with a nickel-containing catalyst and simultaneously reducing the amounts of nitrogen oxides to N2 and water by reaction with a portion of the H2 formed during the cracking of the process gas by contact of the process gas with the nickel-containing catalyst; and withdrawing the product gas containing H2 and N2.

[0016] WO 2012 / 039183 A1 relates to an NH3 decomposition device that produces H2 as a combustion enhancer and an NH3 oxidation device that reacts a portion of the introduced NH3 with O2 using an oxidation catalyst, causing combustion to provide the heat required for an NH3 decomposition reaction.

[0017] WO 2012 / 090739 A1 relates to an H2 generator comprising a decomposition device that decomposes a compound containing an H atom and an N atom and generates H2; a compound supply device that supplies the compound to the decomposition device; and an O2 supply device that supplies O2 to the decomposition device.

[0018] WO 2020 / 095467 A relates to an apparatus for generating H2 gas, comprising: an NH3 evaporator that heats liquid NH3 to generate NH3 gas; a main thermal decomposition device that causes combustion of a fuel gas, thereby heating and decomposing the NH3 gas generated by the NH3 evaporator into N2 gas and H2 gas; a cooler that cools a decomposition gas containing the N2 gas and the H2 gas generated by the decomposition by the main thermal decomposition device; and a separator that separates the H2 gas from the cooled decomposition gas.

[0019] WO 2021 / 257944 A1 relates to the recovery of H2 from an NH3 cracking process in which the cracked gas is purified in a PSA device. The use of a membrane separator for the PSA off-gas improves the recovery.

[0020] WO 2022 / 096529 A1 relates to a process for cracking NH3, producing H2 and generating electric power, comprising electrolysis of water in supplied NH3, evaporation, preheating and cracking of NH3 using NH3 synthesis catalysts at low temperatures.

[0021] WO 2022 / 243410 A1 relates to a process for the synthesis of H2 via the catalytic cracking of NH3; wherein an NH3-containing stream is subjected to a catalytic cracking step in the presence of heat to obtain a combusted gas and a thermally cracked stream containing N2, H2 and possibly residual NH3 and optionally water; wherein the thermally cracked stream is subjected to an H2 recovery step to obtain a high-purity H2 stream.

[0022] WO 2022 / 265647 A1 relates to the recovery of a renewable H2 product from an NH3 cracking process, in which the cracked gas is purified in a first PSA device and at least a portion of the first PSA tail gas is recycled as fuel to reduce the carbon intensity of the renewable H2 product.

[0023] WO 2022 / 265648 A1 relates to the removal of NOX contaminants by selective catalytic reduction (SCR) from a flue gas produced in an NH3 cracking process, using an aqueous NH3 solution produced by cooling the compressed exhaust gas from an H2-PSA device for cleaning the cracked gas.

[0024] WO 2022 / 265649 A1 concerns the reduction of the water content of the NH3 used in an NH3 cracking process, which enables the use of water-incompatible cracking catalysts. The water removal process can also be used to recover and recycle NH3 from the cracking gas.

[0025] WO 2022 / 265650 A1 relates to an NH3 cracking process in which cracking gas is purified in a PSA system. Residual NH3 in a first cracking gas is converted into further H2 and N2 by feeding PSA residual gas or a gas derived therefrom to a secondary cracking reactor and further processing a second cracking gas.

[0026] WO 2022 / 265651 A1 relates to a process in which residual NH3 is removed from NH3 cracking gas in an H2-PSA system using a non-zeolitic adsorbent such as activated carbon, activated alumina or silica gel.

[0027] US 2003 / 0143142 A1 and US 2017 / 0334722 A1 describe processes for reducing NO X -concentration and the N2O concentration of the residual gas from nitric acid production.

[0028] CN 114412668 A relates to ammonia fuel engines, in particular to an ammonia-hydrogen fusion type hybrid energy system and engine.

[0029] JP 2023026798A, published on March 1, 2023, relates to an exhaust gas processing system of an ammonia engine, comprising as a first catalyst an oxidation catalyst comprising a catalyst layer containing Pt and zeolite, and as a second catalyst a denitration catalyst comprising a catalyst layer containing zeolite ion-exchanged with Cu, Co or Fe ions.

[0030] YK Park, Chemical Engineering Journal, Volume 461, 141958, published on April 1, 2023 is a review on the catalytic removal of nitrogen oxides (NO, NO2, N2O) from exhaust gas generated when ammonia is used as a fuel.

[0031] KR 2023095308 A, published on June 29, 2023, relates to a plant comprising a catalytic reactor; a storage tank for liquid ammonia; a first distributor for supplying at least a portion of the ammonia supplied from the storage tank to a catalytic reactor as decomposition ammonia; wherein the ammonia supplied to the catalytic reactor is contacted with an ammonia cracking catalyst to generate nitrogen and hydrogen. A second distributor supplies remaining ammonia that has passed through the first distributor to a denitrification reactor and a mixer.

[0032] NH3 has a comparatively low calorific value and a low flame propagation rate, and poses the risk of flame extinction, resulting in incomplete combustion. Furthermore, the combustion of NH3 carries the risk of increased emissions of nitrogen oxides (particularly NO, NO2, N2O), which affects its suitability as a combustion gas. Gaseous ammonia / hydrogen / air mixtures have been proposed, in which a certain proportion of hydrogen is used as a combustion accelerator, which could be generated, for example, by catalytic or heat-assisted NH3 dissociation.

[0033] Previous research has focused on optimizing the combustion of ammonia itself, particularly with regard to energy yield and economic efficiency, but also with regard to the formation of undesirable nitrogen oxides. However, it can be assumed that the formation of NO X(ie NO and NO2) and N2O cannot be completely suppressed during the combustion process.

[0034] Emissions of NO X However, emissions of N2O, and possibly other components that may be present in combustion gases (e.g., CO, HCN, or NH3) must be avoided or at least reduced as much as possible to protect health, the environment, and the climate. Many industrialized countries have therefore issued corresponding regulations.

[0035] In addition, the combustion of hydrocarbons (CH4, natural gas, etc.) in the presence of NH3 produces exhaust gases that may contain hydrogen cyanide (HCN, hydrogen cyanide). Even small amounts of HCN are problematic because it is classified as highly toxic, and correspondingly low limits for HCN emissions into the environment must be observed. Exhaust gases contaminated with HCN can, in principle, be purified using various measures. Cyanides can be formed and separated through alkaline scrubbing, but these, in turn, must then be disposed of as highly toxic compounds. Using special oxidation catalysts based on precious metals, HCN can be converted to CO2, H2O, N2, and various nitrogen oxides. However, this entails considerable processing and cost expenditure. The resulting nitrogen oxides must be broken down in a further process step, e.g., using SCR. Passing the cyanide through special catalysts, e.g.,based on TiO2, for the hydrolysis of HCN according to HCN + H2O. CO + NH3 is described. In this case, further oxidation using appropriate separate oxidation catalysts is also necessary. Therefore, there is a need for purification processes for HCN-contaminated exhaust gases that are characterized by simple and cost-effective operation and low equipment (cost). Furthermore, these processes should convert HCN into non-toxic substances that do not require further treatment.

[0036] Another problem is the incomplete combustion of ammonia, which means that the exhaust gases from combustion plants using ammonia as fuel can contain significant amounts of unburned ammonia (so-called NH3 slip, NH3 breakthrough). Acceptable limits for ammonia to be released into the atmosphere are comparatively strict. Therefore, in such cases, it is necessary to ensure that ammonia is oxidized to nitrogen before the exhaust gas is released into the atmosphere. So-called ammonia slip catalysts (ASCs) have been developed for this purpose, which are usually based on precious metals from the platinum group (i.e., Ru, Rh, Pd, Os, Ir, Pt). Such catalysts are not only cost-intensive but also poorly selective (i.e., they form NO from NH3, possibly X or N2O) and susceptible to chlorine and chlorine compounds.

[0037] There is therefore a need for measures that are suitable for reducing nitrogen oxides (especially N2O and NO X (ie NO and NO2)), - any excess NH3, and - any other environmentally harmful components of the exhaust gases (such as CO or HCN), which are contained in the exhaust gases of combustion plants operating with NH3 as a result of combustion, so that the exhaust gases can then be released into the ambient air in compliance with all environmental regulations.

[0038] The combustion plants preferably comprise a combustion device in which NH3 is burned to generate combustion heat, as well as an NH3 decomposition device which is in heat exchange with the combustion device and in which NH3 is catalytically decomposed into N2 and H2.

[0039] In this context, the special circumstances resulting from the most efficient combustion of NH3 for the operation of combustion plants, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2, must be taken into account. In addition to the varying composition of the exhaust gas, key parameters include, in particular, the pressure and temperature of the exhaust gas. These parameters can differ considerably from those of other exhaust gases for which measures for the removal of NOX and N2O have been developed to date.

[0040] For example, in the industrial production of nitric acid, NH3 is deliberately oxidized to NOx, which is then converted into nitric acid by reaction with water in an absorption tower. Special catalysts made of precious metals are used for the oxidation, and the reaction often takes place at elevated pressure. The goal of NH3 combustion is to achieve the highest possible NOx yield, and typical water contents in the exhaust gas range from approximately 1 to 3 vol%.

[0041] In contrast, during combustion in combustion plants, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2, NH3 is preferably only oxidized to the N2 stage, for which no catalysts are usually necessary, and this conversion usually takes place at atmospheric pressure. Typical water contents in the exhaust gas are well above 3 vol. For example, the combustion of pure NH3 in air with a residual oxygen content of 3 mol.% produces more than 28 mol.% water. The main aim of the combustion of NH3 is to generate the energy required for the catalytic decomposition reaction of NH3 into N2 and H2.Low levels of nitrogen oxides in the exhaust gas formed during combustion are advantageous because only a comparatively small exhaust gas treatment system is then required to reduce the nitrogen oxide content in the flue gas and thus meet the official requirements regarding permissible emissions, and because only then can sufficiently low residual concentrations be achieved using known processes for nitrogen oxide reduction.

[0042] In contrast to conventional exhaust gas treatment systems, such as those used for exhaust gases from plants for the production of HNO3, the combustion of NH3, preferably in a mixture with H2, associated with the catalytic decomposition of NH3 to H2, has special features that require special measures.

[0043] On the one hand, the pressure-free conditions and, on the other hand, the very high water content are essential. Pressure-free means that when using conventional catalyst beds based on bulk particulate matter, etc., the pressure losses could potentially be too great. The high water content, due to the hydrothermal stress on the catalysts in the exhaust gas treatment system, particularly in the case of zeolite material, combined with high temperatures, may lead to progressive deactivation of the catalysts. The maximum temperature should therefore be limited. Apart from aging, the chemical reduction of NOX is hardly affected by the high water content, while the degradation of N2O by decomposition and / or chemical reduction is significantly impaired by the high water content.

[0044] A further difference between the exhaust gases to be treated according to the invention compared to the production of HNO3 is the relatively high NOX content, which can amount to several thousand ppmv. The NOX content depends on the conditions of the combustion of NH3, in particular on the NH3 content, any other combustible gases present (H2 and / or CH4 (natural gas)) and the air ratio λ. Due to the high temperatures during combustion of up to 1000°C and more, the NOX is initially present almost exclusively as NO, i.e. with a very high proportion of NO and a very low proportion of NO2. Due to the preferential cooling in the downstream heat exchanger, only a small proportion of the NO is converted into NO2 due to the slow formation kinetics of NO2 at high temperatures. This means that the degree of oxidation (β) of the NOX, i.e.the molar fraction of NO2 in the total NOX (β = n (NO2) / (n (NO) + n (NO2)) is small when the exhaust gas enters the exhaust gas treatment system, typically <5 vol.%. This in turn means that the desired selective catalytic NOX reduction can actually only proceed very poorly or slowly, corresponding to the slow so-called normal SCR.

[0045] These are fundamental differences to established exhaust gas purification in HNO3 plants, in which the residual gas containing N2O and NOX is gradually heated under an overpressure of usually 4-10 bar after leaving the absorption tower from a "cold" state (the thermodynamic NOX equilibrium lies almost entirely on the side of NO2). Thus, the NOX oxidation level of residual gases in HNO3 production before entering the corresponding exhaust gas treatment plant is typically between 30 and 70 vol.%, i.e., close to the ideal stoichiometric ratio for NO X-Reduction according to the very fast SCR.

[0046] The high NO X content, combined with a very low NO X The high degree of oxidation and high water content combined with low operating pressure (near atmospheric pressure) poses particular challenges to the effectiveness of the exhaust gas treatment system according to the invention. Added to this is the challenge and necessity of eliminating the Exhaust gases contain N2O, which cannot be reduced using conventional SCR processes based on V2O5 / TiO2 catalysts.

[0047] The objectives and the reaction products obtained during the combustion of NH3 therefore sometimes differ considerably.

[0048] In conventional plants for the production of nitric acid, the exhaust gas often has, at comparatively high pressure, - a comparatively low NOX content; - a comparatively high NO2 content; - a comparatively high N2O content; - a comparatively low water content; and - no unburned NH3 content (NH3 slip).

[0049] In contrast, in combustion plants, preferably comprising combustion devices and NH3 decomposition devices for splitting NH3 into N2 and H2, the exhaust gas often has, at comparatively low pressure, - a comparatively high NOX content; - a comparatively low NO2 content; - a comparatively low N2O content; - a significantly higher water content; - possibly a not insignificant proportion of unburned NH3 (NH3 slip); and - possibly a not negligible proportion of HCN, if NH3 is burned together with CH4 (natural gas).

[0050] These special circumstances must be taken into account when removing NOX and N2O from exhaust gases, which presents a particular challenge.

[0051] It is an object of the invention to reduce the content of NOX (i.e., NO and NO2), N2O and possibly NH3, CO and / or HCN in exhaust gases produced by NH3-operated combustion plants, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2. In doing so, it should be possible to reduce, if necessary, a very large amount of NO X and also to reduce N2O in order to reduce the respective content.

[0052] This problem is solved by the subject matter of the patent claims.

[0053] A first aspect of the invention relates to a method for reducing the content of NO Xand N2O in the exhaust gas of a combustion plant operated with NH3, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2, the method comprising the following steps: (a) Combustion of NH3 (optionally in a mixture with one or more other combustible gases, such as H2, CH4, etc.) to operate the combustion plant, preferably comprising a combustion device for burning NH3 (preferably comprising at least one burner and a combustion chamber) and an NH3 decomposition device for splitting NH3 into N2 and H2, producing an exhaust gas which contains N2, H2O, NOX and N2O and optionallyHCN and which leaves the combustion plant, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment plant; (d) reducing the N2O content in the exhaust gas by (d1) decomposition of N2O on an N2O decomposition catalyst and / or (d2) chemical reduction of N2O with reducing agent on an N2O reduction catalyst; (e) reducing the NOX content in the exhaust gas by chemical reduction of NOX with reducing agent on an NOX reduction catalyst; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

[0054] The order of steps (d) and (e) is arbitrary; according to the invention, all possibilities are encompassed, from sequentially in any order to simultaneously or mixed forms thereof.

[0055] The invention preferably relates to a method for reducing the content of NOX and N2O in the exhaust gas of a combustion plant operated with NH3 and H2, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2, wherein the method comprises the following steps: (a) Combustion of NH3 and H2 for operating the combustion plant, preferably comprising a combustion device for burning NH3 (preferably comprising at least one burner and a combustion chamber) and an NH3 decomposition device for splitting NH3 into N2 and H2, producing an exhaust gas which contains N2, H2O, NO Xand N2O and which leaves the combustion plant, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger, which is arranged downstream of the combustion plant in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment plant, which is arranged downstream of the combustion plant and optionally of the at least one heat exchanger in the flow direction of the exhaust gas; (d) reducing the N2O content in the exhaust gas by (d1) decomposition of N2O on an N2O decomposition catalyst and / or (d2) chemical reduction of N2O with reducing agent on an N2O reduction catalyst; (e) reducing the NO content X in the exhaust gas by chemical reduction of NO Xwith reducing agent on a NOX reduction catalyst; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

[0056] It was found that the content of NO Xin the flue gas can be advantageously used. For example, in the exhaust gas treatment plant, during the chemical reduction of NOX with a reducing agent, preferably with NH3, a considerable amount of heat is generated, which can be transferred to a suitable heat transfer medium with the help of one or more heat exchangers. Water or steam is preferably used as the heat transfer medium, which has advantages with regard to safety, among other things. The heat absorbed by the heat transfer medium is then preferably used to heat NH3, which is fed as a feed stream to the NH3 decomposition plant. Alternatively or additionally, the heat can also be used to preheat combustion air.

[0057] Experimental findings and simulation calculations indicate that the heat released during the chemical reduction of NOX with a reducing agent, preferably with NH3, heats the exhaust gas relatively by up to 70 K, preferably up to 50 K, i.e. that the gas temperature at the outlet from the exhaust gas treatment system is up to 70 K, preferably up to 50 K higher than at the inlet to the exhaust gas treatment system.

[0058] Furthermore, it was found that the amount of nitrogen oxides formed in the exhaust gas during the combustion of NH3 can depend on numerous factors, including the mixing ratio of H2 : NH3, the air ratio λ, the preheating of the combustion air, the design of the burners, etc.

[0059] The catalytic decomposition of NH3 serves to form H2 as a product. A further aspect of the invention therefore relates to a process for producing H2 by catalytic decomposition of NH3, comprising the process according to the invention for reducing the NOX and N2O content in the exhaust gas of a combustion plant operated with NH3, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2. This aspect preferably relates to a process for producing H2 by catalytic decomposition of NH3, comprising the process according to the invention for reducing the NO content. X and N2O in the exhaust gas of a combustion plant operated with NH3 and H2, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2.

[0060] The exhaust gas treatment system according to the invention comprises at least - a N2O reduction catalyst and / or a N2O decomposition catalyst; and - a NO X -reduction catalyst; which may be the same or different depending on the given functionality or multiple functionality and may be present in common or separate reaction zones (catalyst beds).

[0061] In preferred embodiments, the exhaust gas treatment system according to the invention comprises - a N2O reduction catalyst; - a N2O decomposition catalyst; and - a NO X -reduction catalyst; which may be the same or different depending on the given functionality or multiple functionality and may be present in common or separate reaction zones (catalyst beds).

[0062] In preferred embodiments, the exhaust gas treatment system according to the invention additionally comprises at least one further catalyst or one of the above-mentioned N2O reduction, N2O decomposition or NOX reduction catalysts fulfills at least one further functionality selected from - NH3 oxidation catalyst; - HCN degradation catalyst; and - CO oxidation catalyst.

[0063] The NH3 oxidation catalyst is preferably used when the proportion of unburned NH3 in the exhaust gas (NH3 slip) is greater than the demand for NH3 as a reducing agent for NOX and / or N2O in the exhaust gas treatment system, so that after passing through steps (d1) and / or (d2) and (e), the exhaust gas still contains residual amounts of NH3 that should not or must not be released into the environment. These residual amounts of NH3 can then be broken down by oxidation of NH3 with the help of the downstream NH3 oxidation catalyst.

[0064] The HCN degradation catalyst is preferably used when the fuel contains hydrocarbons (CH4, natural gas, etc.) in addition to NH3, and the exhaust gas formed during combustion contains certain amounts of HCN. The resulting HCN can then be degraded with the help of the HCN degradation catalyst by hydrolysis of the HCN and oxidation of the resulting hydrolysis products (hydrolysates), i.e., NH3 and CO, with NO, preferably contained in the exhaust gas. X and N2O are broken down (removed).

[0065] It was surprisingly found that HCN in water-containing exhaust gases, which simultaneously contain NOX and N2O in a molar amount which is greater than or equal to the molar amount of HCN, can be degraded to N2, H2O and CO2 by passing the exhaust gas over a zeolitic catalyst loaded with transition metals, e.g. a pack of catalyst pellets containing an iron-loaded zeolitic material of the structure type BEA, at temperatures of 300 to 600°C (preferably 350 to 550°C).

[0066] In contrast to known processes, this method allows for complete removal of HCN, ie, conversion into non-toxic substances, in a single step, ie, in one process step, without the need for expensive precious metal catalysts. To remove excess NO X and N2O can be added to HCN, NO XIn addition, NH3 is added to the exhaust gas containing NOX and N2O to reduce NOX and N2O, and if necessary, CO or hydrocarbons such as CH4 or propane to reduce N2O. The amount of reducing agent in this case is based on the molar input quantities of N2O and NO. X , each reduced by the molar amount of HCN contained in the exhaust gas. If excess amounts of N2O are present in the exhaust gas, which are to be reduced with NH3 or CO or hydrocarbon, the NO X The CO content must be reduced to zero (or close to zero) using NH3 in any case. If CO or hydrocarbons are used as additional reducing agents, an additional CO oxidation catalyst can be used downstream of the zeolite catalyst to eliminate any CO emissions.

[0067] The CO oxidation catalyst is preferably used when (i) hydrocarbons (CH4, natural gas, etc.) are used as reducing agents for N2O; and / or (ii) an HCN degradation catalyst is used to degrade HCN, the degradation products of which contain CO. Any CO produced in this process can then be degraded to CO2 by oxidation with the help of the downstream CO oxidation catalyst.

[0068] If the exhaust gas treatment system according to the invention comprises an NH3 oxidation catalyst, it may be preferable according to the invention to first cool the exhaust gas within the exhaust gas treatment system using a heat exchanger to a lower temperature than at the inlet to the exhaust gas treatment system, so that the NH3 oxidation catalyst can optimally develop its effect. In preferred embodiments, the exhaust gas treatment system according to the invention therefore additionally comprises one or more heat exchangers.

[0069] For the purpose of description, "and / or" means either "or" or "and", so that, for example, "A and / or B" has the following three meanings: (i) only A but not B, (ii) only B but not A, and (iii) both A and B.

[0070] For the purpose of description, "NOX" includes nitric oxide (NO) and nitrogen dioxide (NO2), but not nitrous oxide (N2O).

[0071] Catalysts accelerate certain chemical reactions by lowering their activation energies.

[0072] Unless expressly stated otherwise, all data in ppm are by volume, i.e., ppmv. Unless expressly stated otherwise, all percentages with respect to the gas composition are by volume, i.e., vol%. Unless expressly stated otherwise, all other percentages are by weight, i.e., wt%.

[0073] Steps (b) and (f) of the process according to the invention are independently optional and preferred.

[0074] Steps (a), optionally (b), and (c) of the process according to the invention are carried out successively in alphabetical order, followed by steps (d) and (e) in basically any desired order. Step (d) can therefore be carried out before step (e) or after step (e) or simultaneously with step (e). Mixed forms of partial simultaneity are also possible. This can be particularly relevant when one and the same catalyst material is capable of catalyzing multiple reactions. Such embodiments are particularly preferred according to the invention. These reactions then take place simultaneously according to the invention, although the kinetics of the respective reactions can vary, so that a first reaction can be completed earlier or have achieved a higher conversion than a second reaction proceeding in parallel. The optional step (f) is carried out after steps (d) and (e).

[0075] Steps (d1) and (d2) are considered separately for the purpose of description, but both serve the common purpose of reducing the N2O content in the exhaust gas.

[0076] Steps (d1), (d2) and (e) can also be carried out in any order, whereby mixed forms of partial simultaneity are also possible in this regard.

[0077] In preferred embodiments, the process according to the invention comprises steps (a), optionally (b), (c), (d1), (e) and optionally (f); steps (a), optionally (b), (c), (d2), (e) and optionally (f); or steps (a), optionally (b), (c), (d1), (d2), (e) and optionally (f).

[0078] In preferred embodiments, the exhaust gas passes through the steps of the process according to the invention in one of the following orders: (i) (a) → (c) → (d1) → (e); (ii) (a) → (c) → (e) → (d2); (iii) (a) → (c) → (e) → (d2) → (d1); (iv) (a) → (c) → (e) → (d1+d2); or (v) (a) → (c) → (e) → (d1).

[0079] In preferred embodiments, the exhaust gas passes through the steps of the process according to the invention in one of the following orders: (vi) (a) → (b) → (c) → (d1) → (e); (vii) (a) → (b) → (c) → (e) → (d2); (viii) (a) → (b) → (c) → (e) → (d2) → (d1); (ix) (a) → (b) → (c) → (e) → (d1+d2); or (x) (a) → (b) → (c) → (e) → (d1).

[0080] In preferred embodiments, the exhaust gas passes through the steps of the process according to the invention in one of the following sequences: (xi) (a) → (b) → (c) → (d1) → (e) → (f); (xii) (a) → (b) → (c) → (e) → (d2) → (f); (xiii) (a) → (b) → (c) → (e) → (d2) → (d1) → (f); (xiv) (a) → (b) → (c) → (e) → (d1+d2) → (f); or (xv) (a) → (b) → (c) → (e) → (d1) → (f).

[0081] Here (d1+d2) means that both step (d1) and step (d2) are carried out, whereby the execution of these two steps (d1) and (d2) takes place at least partly simultaneously, ie both steps run in parallel.

[0082] Between these steps, additional, not explicitly mentioned, steps may occur. Material flows:

[0083] For the purpose of the description, the following material flows are distinguished, among others: - NH3 (educt), which is used as starting material for the catalytic decomposition and is preferably fed to the NH3 decomposition device for this purpose; - intermediate product gas, which, in the case of NH3 decomposition devices connected in series, leaves an upstream NH3 decomposition device (pre-reactor) and is fed to a downstream NH3 decomposition device (main reactor); in the case of several pre-reactors, if necessary.a distinction is made between several intermediate product gases; the intermediate product gas contains the products of a partial catalytic decomposition of NH3, typically H2, N2 and comparatively large amounts of undecomposed NH3; - product gas obtained by the catalytic decomposition of NH3, typically H2, N2 and comparatively small amounts of undecomposed NH3; in the case of several NH3 decomposition devices connected in series, the product gas is the gas mixture leaving the last of the NH3 decomposition devices connected in series; - combustion gas which is combusted in the combustion plant according to the invention, preferably in the combustion device, to generate combustion heat; the combustion gas contains NH3 and H2, optionallyadditionally N2; - combustion air, which is supplied to the combustion plant according to the invention, preferably the combustion device, so that the combustion gas can burn in a mixture with the combustion air; the combustion air contains O2 and N2; - exhaust gas, which is formed during the combustion of the combustion gas in a mixture with the combustion air; the exhaust gas contains N2, H2O, NO. X and N2O.

[0084] It is an essential object of the invention to reduce the NO content in this exhaust gas X and reduce N2O. Step (a):

[0085] In step (a) of the process according to the invention, NH3 is burned to operate a combustion plant. In step (a) of the process according to the invention, NH3 is preferably burned, optionally in a mixture with other components (e.g., H2 or CH4). The combustion plant preferably comprises a combustion device in which NH3 is burned to generate combustion heat, as well as an NH3 decomposition device which is in heat exchange with the combustion device and in which NH3 is catalytically decomposed into N2 and H2. During combustion, an exhaust gas is generated which contains N2, H2O, NO X and N2O. Residues of unburned NH3 may also be present. The exhaust gas leaves the combustion plant, preferably the combustion device, and is then fed to optional step (b) or directly to step (c) of the process according to the invention.

[0086] "Combustion plants" within the meaning of the invention generate heat through combustion processes. The combustion plants preferably comprise a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2. Heat is generated by burning combustion gases. "Combustion plants" or the "combustion plants" encompassed therein within the meaning of the invention are any plants in which NH3 or a fuel containing NH3 is oxidized with O2 (preferably from combustion air) with the aim of producing, in particular, N2 and H2O as the main products. Plants in which NH3 is oxidized with O2 with the aim of producing, as the main products, nitrogen compounds with higher oxidation numbers (e.g., NOX), as is the case, for example, in the production of nitric acid, are neither combustion plants nor combustion plants within the meaning of the invention.Catalysts are typically required to produce such nitrogen compounds with higher oxidation numbers as the main products. According to the invention, the combustion plant according to the invention is preferably not equipped with a catalyst, i.e., the combustion of NH3 and H2 according to the invention is preferably not catalyzed.

[0087] The combustion of NH3 means the oxidation of NH3 with O2. According to the invention, this conversion does not have to be complete, so that the exhaust gas may contain residual, unburned (unoxidized, unconverted) NH3 (NH3 slip, NH3 breakthrough). The same applies if NH3 is not burned in its pure form, but together with other combustible gases, in particular H2 and / or CH4 (natural gas). The O2 used for combustion can be used in the form of combustion air, which may optionally be enriched with O2.

[0088] In preferred embodiments, in step (a) of the process according to the invention, the combustion of NH3 takes place in a combustion plant comprising a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2. The combustion of NH3 in the combustion device serves to heat the NH3 decomposition device, preferably a reactor filled with catalyst, for cracking NH3 into N2. and H2. According to the invention, the splitting of NH3 into N2 and H2 takes place as a catalytic decomposition of NH3 on an NH3 decomposition catalyst.

[0089] According to the invention, the catalytic decomposition of NH3 results in the formation of N2 and H2, occasionally referred to in the art as "cleavage" or "cracking." The terms "catalytic decomposition," "decomposition," "catalytic cleavage," "cleavage," "catalytic cracking," and "cracking" of NH3 are used interchangeably for the purpose of description. According to the invention, the catalytic decomposition of NH3 preferably takes place in the absence of O2.

[0090] The combustion plant according to the invention preferably comprises a combustion device and an NH3 decomposition device, which exchange heat with one another. In the combustion device, a combustion gas containing NH3 and preferably H2 is combusted together with combustion air containing O2, generating combustion heat. The combustion heat thus generated is at least partially supplied as a heat flow to the NH3 decomposition device (or transferred to the NH3 decomposition device) in order to supply the heat required for the endothermic catalytic decomposition of NH3 to H2 and N2. Furthermore, the combustion heat is preferably used according to the invention to preheat the NH3 to be decomposed, the combustion gas, and the combustion air to an elevated temperature.

[0091] "Incinerator" and "furnace" are used as interchangeable synonyms for descriptive purposes.

[0092] The NH3 decomposition device is preferably a tubular reactor, which is designed analogously to a primary reformer for producing synthesis gas or hydrogen from natural gas. The basic construction of such a fired tubular reactor, which is designed analogously to a primary reformer, includes one or more tubes containing the NH3 decomposition catalyst, which are arranged in a combustion chamber, into which flames from burners extend, and in which the radiant heat and convection heat of the flames and the hot exhaust gas effect heat transfer to the NH3 (process gas) flowing through the NH3 decomposition catalyst. The combustion device thus preferably comprises a combustion chamber and one or more burners, preferably several burners. The NH3 decomposition device (parallel-arranged tubes) is then located within the combustion device (combustion chamber, combustion chamber).To ensure a uniform energy input and to define the flame shape, the exhaust gas is removed from the combustion device through an imposed pressure gradient, for example, through the use of compressors in the combustion air supply or the exhaust gas discharge. To ensure sufficient heat transfer across the length of the NH3 decomposition catalyst bed within the tubes, the exhaust gas must still have a sufficiently high temperature at the end of the NH3 decomposition catalyst bed, i.e., at the end of the tubes, to allow a significant release of radiant heat. The exhaust gas leaves the combustion device (combustion chamber). Therefore, high temperatures are required, which in the case of a tubular reactor designed analogously to a primary reformer can exceed 1000°C. Typically, the proportion of heat transferred to the endothermic catalytic decomposition of NH3 is about 40-60% of the total energy generated by combustion of the combustion gas. The remaining heat can be used for other purposes.

[0093] After being removed from the combustion device (combustion chamber), the exhaust gas is preferably passed through an exhaust duct which preferably fulfils three essential tasks: 1. Utilisation of the heat from the combustion of NH3 which is not used by the endothermic catalytic decomposition of NH3 to N2 and H2 with the aim of avoiding energy waste and increasing energy efficiency; 2. Preheating of material flows (e.g. NH3, combustion gas, combustion air) with the aim of improving energy integration and increasing hydrogen yield; and 3. Reducing the content of nitrogen oxides (in particular NO, NO2 and N2O) through suitable reaction control with the aim of minimising their emissions and complying with regulatory limits.

[0094] Preferably, step (a) of the process according to the invention, ie the combustion of NH3 and preferably H2 for operating the combustion plant to produce an exhaust gas which leaves the combustion plant, comprises the following sub-steps: (a1) optionally and preferably heating and evaporating (liquid) NH3; (a2) optionally and preferably heating combustion air (preferably comprising N2 and O2); (a3) ​​combustion of combustion gas (comprising NH3 and preferably H2) and combustion air (comprising O2) in a combustion plant, preferably a combustion device, whereby an exhaust gas (comprising N2, H2O, NOX and N2O) is produced and combustion heat is released, whereby at least part of the combustion heat flows into an NH3 decomposition device; and (a4) catalytic decomposition of NH3 in the NH3 decomposition device on an NH3 decomposition catalyst, wherein combustion heat from sub-step (a3) ​​is absorbed and a product gas is produced (comprising H2 and N2).Combustion of combustion gas and combustion air: .

[0095] In preferred embodiments, NH3 is burned as the sole fuel, ie, no other gas is burned besides NH3. In other preferred embodiments, In some embodiments, NH3 is burned in a mixture with H2. In further preferred embodiments, NH3 is burned in a mixture with CH4 (natural gas). These gases or mixtures are also referred to as "combustion gas" for the purposes of this description. In addition to NH3 and possibly H2 and / or CH4, the combustion gas may contain other components, e.g., N2.

[0096] According to the invention, heat is provided by the combustion of a combustion gas in a combustion system, preferably in a combustion device. The combustion device preferably has one or more burners, preferably at least two burners, more preferably at least three burners.

[0097] The combustion gas contains a mixture of H2 and NH3, partly because this mixture produces a medium flame temperature and has better combustion properties than pure NH3. The nitrogen oxide content can also be influenced by a suitable mixture ratio of H2 and NH3.

[0098] Preferably, the combustion of NH3, ie the oxidation of NH3 with O2 (or the mixture of NH3 with another combustible gas, such as H2, CH4, etc.), does not take place on a catalyst, ie the combustion is not carried out in the presence of a heterogeneous catalyst.

[0099] Particularly preferably, the H2 present in the combustion gas in a mixture with the NH3 to be burned is formed by thermal and / or catalytic decomposition of NH3 (substep (a4)). The integrated combustion of NH3 with O2 preferably provides the energy for the catalytic decomposition (cracking). Therefore, in step (a), the combustion of NH3 is preferably integrated into a process for the thermal and / or catalytic decomposition of NH3 into N2 and H2.

[0100] The composition of the exhaust gas formed during combustion depends on the combustion gas used. In preferred embodiments, sufficient H2 is added to NH3 to modify the combustion properties of the combustion gas such that a largely quantitative conversion is achieved during combustion. In other preferred embodiments, the combustion gas used is a mixture of the effluent from a separation unit for purifying the H2, preferably from the off-gas of a pressure swing adsorption device or the retentate of a membrane unit, preferably a pressure swing adsorption device, and a portion of the NH3 or the H2 produced as a product.

[0101] If the catalytic decomposition of NH3 is incomplete, the product gas (i.e. the product of the catalytic decomposition) contains, in addition to N2 and H2, residual, unreacted NH3. Preferably, the H2, which is present in the combustion gas in a mixture with the NH3 to be burned, is formed by catalytic decomposition of NH3 and then, if necessary in a mixture with residual NH3 and / or N2, separated from the product gas formed during the catalytic decomposition of NH3, preferably by pressure swing adsorption (PSA). Thus, the product of the catalytic decomposition According to the invention, the product gas obtained from NH3 and an NH3 decomposition catalyst is preferably separated by pressure swing adsorption - into high-purity H2 on the one hand (product hydrogen) and - into a gas mixture (off-gas of the pressure swing adsorption) on the other hand.

[0102] The gas mixture separated from the H2 (off-gas of pressure swing adsorption) contains, in addition to N2, possibly residual, non-catalytically decomposed NH3, as well as a certain amount of H2. Thus, the separation efficiency of the device for purifying the H2 determines how much H2 is contained in the off-gas of the pressure swing adsorption device or in the retentate of the membrane unit and therefore also influences the composition of the exhaust gas formed during combustion. The quantitative separation of the entire amount of H2 is not technically possible or not economical, which is why the separated gas mixture (off-gas of pressure swing adsorption) often contains a certain amount of H2. In this way, a mixture of NH3 and H2 is obtained, which can either be burned directly as such or first enriched with additional NH3 (or H2).

[0103] This gas mixture separated from the product gas by pressure swing adsorption is therefore preferably used as combustion gas according to the invention. Depending on the NH3 and H2 content, the separated gas mixture can be used unchanged as combustion gas, or an appropriate amount of NH3 or H2 can be added to adjust the desired NH3 to H2 ratio. If the catalytic decomposition is complete or almost complete, the NH3 content in the separated gas mixture (off-gas of pressure swing adsorption) may still be too low, and the required amount of NH3 must still be added.

[0104] The exact composition of the exhaust gas produced during combustion depends on the composition of the combustion gas and the combustion air. A key parameter in describing the combustion properties of the combustion gas, the emission of pollutants, and the composition of the exhaust gas is the mixing ratio of NH3 to H2.

[0105] The following table shows the composition of the combustion gas and the resulting exhaust gas based on simulation calculations for five different process configurations #1 to #5, assuming the same combustion air composition. The molar flows are standardized to a calorific value of 1 MW to ensure comparison. In process configurations #1 to #3 (comparative examples), pure CH4, pure NH3, or pure H2 are used as the combustion gas. In process configurations #4 and #5 (inventive examples), mixtures of H2 and NH3 (process configuration #4) or H2, NH3, N2, and H2O are used as the combustion gas (process configuration #5; off-gas of a pressure swing adsorption device (PSA)): #1 #2 #3 #4 #5 CH4 NH3 H2 Start-up Normal operation operation Combustion gas: CH4 Mol% 100.00 0 0 0 0 H2 Mol% 0 0 100.00 10.00 26.4 N2 Mol% 0 0 0 0 62.7 NH3 Mol% 0 100.00 0 90.00 10.6 H2O Mol% 0 0 0 0 0.2 Molar flow kmol / h 4.49 11.36 14.89 11.64 36.95 Combustion air: N2 Mol% 77.48 77.48 77.48 77.48 77.48 O2 Mol% 20.78 20.78 20.78 20.78 20.78 Ar Mol% 0.91 0.91 0.91 0.91 0.91 CO2 mol% 0.03 0.03 0.03 0.03 0.03 H2O mol% 0.80 0.80 0.80 0.80 0.80 Molar flow kmol / h 49.63 47.40 40.56 46.86 50.72 Air ratio 1.15 1.16 1.13 1.15 1.35 Flue gas: N2 mol% 71.06 68.84 65.47 68.63 80.93 O2 mol% 2.48 2.15 2.05 2.15 2.52 Ar mol% 0.83 0.70 0.77 0.70 0.43 CO2 mol% 8.32 0.03 0.03 0.03 0.02 H2O mol% 17.31 28.29 31.69 28.50 16.11 molar flow kmol / h 54.12 61.60 48.00 60.54 108.24

[0106] As the data in the table above illustrate, in the inventive process #5 (off-gas of the PSA), almost twice as much exhaust gas flows through the exhaust duct as in a hydrogen-fired reformer (process #3), and only slightly less than twice as much compared to a methane-fired reformer (process #1).

[0107] Therefore, the inventive process #5 has a significantly flatter temperature profile in the exhaust duct than the other process scenarios and can therefore include more heat integration steps, including those possible at low flue gas temperatures. As process scenarios #5 to #7 illustrate, this enables (almost) complete energy integration.

[0108] For reformers fired with hydrogen or methane, the temperature profile in the exhaust duct would have to be significantly steeper because of the small volume of exhaust gas available. Since the heat exchangers in the exhaust duct require a minimum temperature difference to be designed economically, steep temperature profiles significantly increase the risk of leaving residual heat unused due to the required temperature difference. In any case, the exhaust gas entering the exhaust duct is significantly hotter in these cases, requiring the use of more complex materials.

[0109] Preferably, a mixing ratio of NH3 and H2 is set in the combustion gas that is optimized for subsequent combustion. The proportion of H2 is preferably at most 80 mol%, more preferably at most 70 mol%, even more preferably at most 60 mol%, most preferably at most 50 mol%, and in particular at most 40 mol%. The proportion of H2 is preferably at most 30 mol%, more preferably at most 20 mol%, even more preferably at most 15 mol%, most preferably at most 10 mol%, and in particular at most 5 mol%.

[0110] Preferably, the proportion of H2 is at least 1 mol%, more preferably at least 2 mol%, even more preferably at least 3 mol%, most preferably at least 4 mol%, and especially at least 5 mol%. Preferably, the proportion of H2 is at least 10 mol%, more preferably at least 20 mol%, even more preferably at least 30 mol%, most preferably at least 40 mol%, and especially at least 50 mol%.

[0111] In particularly preferred embodiments, the molar ratio of H2:NH3 in the mixture is in the range from 45:55 to 90:10, preferably 50:50 to 85:15, more preferably 55:45 to 80:20, even more preferably 60:40 to 75:25, most preferably 65:35 to 70:30 or 70:30 to 75:25. Since, according to the invention, the separated gas mixture of a gas exchange adsorption plant is preferably used as the combustion gas, the molar ratio of H2:NH3 depends mainly on its hydrogen yield and can, in extreme cases, be approximately 15:1.

[0112] During combustion of the mixture of combustion gas and combustion air, the air ratio λ for combustion is preferably in the range from 0.9 to 1.7, more preferably 1.0 to 1.6, even more preferably 1.1 to 1.5, and most preferably 1.2 to 1.4. Another very preferred range for the air ratio λ is between 1.0 and 1.2.

[0113] In particularly preferred embodiments, the air ratio is in the range of 1.06±0.06, preferably 1.06±0.05, more preferably 1.06±0.04, even more preferably 1.06±0.03, most preferably 1.06±0.02, and in particular 1.06±0.01.

[0114] The air / fuel ratio λ (i.e., the combustion air ratio) specifies the mass ratio of combustion air to combustion gas relative to the stoichiometrically ideal ratio for a theoretically complete combustion process. It is defined as the ratio of air to fuel that contains a sufficient mass of oxygen to achieve complete combustion of a given mass of fuel (see, for example, K. Soman, Thermal Engineering, PHI, 2011, page 224, no. 5.4.2). In principle, the ratio can be expressed in terms of mass or amount of substance (see, for example, P. Majumdar, Design of Thermal Energy Systems, Wiley 2021, page 66, no. 2.13.5.2). For descriptive purposes, the ratio is mass-based. If a combustion process is carried out using another oxygen-containing gas instead of air, then "air" must strictly speaking be replaced by "oxygen carrier".However, the parameter λ is still used in the above definition.

[0115] In preferred embodiments, the equivalence ratio NH3 / H2(Φ) (not to be confused with the inverse of the air ratio 1 / λ) is in the range from 0.55 to 1.40, more preferably 1.05 to 1.20. The formation of nitrogen oxides depends, among other things, on the residual oxygen content in the exhaust gas, which can be, for example, 3 mol% or 1 mol%. For example, to achieve a residual oxygen content of 1 mol%, an air ratio of approximately 1.1 is required.

[0116] The concentration of nitrogen oxides (particularly NO, NO2, and N2O) and the dew points of condensable components are two parameters that are of great importance for the technical design and equipment of the exhaust duct. These parameters are also largely determined by the composition of the exhaust gas. The exhaust gas from tubular reactors, which are designed similarly to a primary reformer, contains nitrogen oxides produced during the combustion reaction. In many countries, the emission of nitrogen oxides is regulated, and if permissible limits are exceeded, it must be reduced using appropriate technologies.

[0117] Nitrogen oxides (particularly NO, NO2, and N2O) are formed in combustion reactions through various mechanisms. In tubular reactors, which are designed analogously to a primary reformer, a combustion gas containing no NH3 produces exclusively so-called "thermal nitrogen oxides." This is achieved through the recombination of nitrogen radicals with oxygen, the formation of which is favored at high temperatures. With a combustion gas containing NH3, nitrogen oxides can form via various reaction pathways in the complex kinetics of NH3 combustion, so-called "kinetic nitrogen oxides."

[0118] In plants for the production of H2 from NH3, both thermal nitrogen oxides and kinetic nitrogen oxides can be formed. The presence of H2 in the combustion gas increases the flame temperature, and the addition of NH3 increases the tendency to form kinetic nitrogen oxides. Numerous cases are described in the literature in which the combustion of mixtures of NH3 and H2 leads to significantly higher emissions of nitrogen oxides than is the case with conventional primary reformers. The emission of nitrogen oxides depends not only on the composition of the combustion gas, specifically the mixing ratio of NH3 and H2, but also on various other parameters, in particular - the preheating temperature of the combustion air and the combustion gas; - the excess combustion air during combustion; and - the design and geometry of the burner used.

[0119] The exact emissions of nitrogen oxides are therefore far more dependent on the individual case than is the case with conventional primary reformers. Typical emissions of NO X (i.e., NO and NO2) are in the range 100–10,000 ppmv. An example of an exhaust gas with a comparatively low nitrogen oxide content contains 500 ppmv NO, 10 ppmv NO2, and 10 ppmv N2O (Case A). An example of an exhaust gas with a comparatively high nitrogen oxide content contains 5,000 ppmv NO, 10 ppmv NO2, and 50 ppmv N2O (Case B).

[0120] During plant start-up, using a combustion gas rich in NH3 would result in comparatively low NO emissions, but comparatively high N2O emissions. This case must be taken into account in the design of the equipment, even if it is of no major importance for the plant's mass balance during normal operation, ie, after the start-up phase has been completed.

[0121] In addition, when considering the exhaust duct of a plant for the production of H2 from NH3, two dew points are of interest: the dew point of H2O and the dew point of NH4NO3.

[0122] The dew point of H2O depends on the partial pressure of H2O in the exhaust gas. In process variants where the off-gas from the pressure swing adsorption (PSA) device or the retentate from a membrane unit is fed into the combustion gas system, the exhaust gas contains mainly N2 and only a comparatively small amount of H2O, which generally leads to rather low dew points.

[0123] The following table shows the water content of the exhaust gas and the dew point of water for the process variants already introduced: Molar fraction H2O Partial pressure H2O Dew point [mol%] [bar] [°C] CH4 17.31 0.16 54.78 NH3 28.29 0.25 65.40 H2 31.69 0.29 67.97 90 mol% NH3 10 mol% H2 28.5 0.26 65.57 PSA offgas + NH3 16.11 0.14 53.29

[0124] If this dew point of H2O is reached during system operation, droplets will form. Since a temperature change in the exhaust gas is caused by the heat dissipation in a heat exchanger, condensed water can precipitate on the surface of the tubes, impairing heat transfer. If droplets enter an exhaust fan, this can damage the rotor. Condensation of liquid H2O is therefore undesirable. To avoid influencing system operation and damaging it, a distance of 25 K between the minimum exhaust gas temperature and the dew point should be maintained in the exhaust duct. According to the invention, the exhaust gas is therefore preferably not cooled below approximately 81-88°C in the exhaust duct, depending on the specific conditions. This temperature is therefore the technically achievable minimum, and the internal energy of the exhaust gas cannot be further utilized.This is therefore an unavoidable energy loss.

[0125] The dew point of NH4NO3 is relevant because systems for removing nitrogen oxides from exhaust gases (exhaust gas treatment systems) can exhibit a slip of incompletely degraded nitrogen oxides, usually NO. The NH3 added to the exhaust gas treatment system as a reducing agent is often also not fully converted, resulting in the slip of small amounts of NO and NH3. Cooling of the exhaust gas in the exhaust duct can cause the temperature of NH4NO3 to fall below the dew point, which can precipitate on the tubes of a heat exchanger. This precipitation poses a threat to the safe operation of the system because it is sensitive to impact and can react explosively. The table shows the dew points of NH4NO3 at various typical residual contents of NO and NH3 in the flue gas: Pressure [bar a] 1.00 1.00 1.00 1.00 Residual NH3 [ppmv v] 10 10 50 10 Residual NOX [ppmv v] 10 10 10 50 Ratio NO2 / NO 1 9 1 1 Dew point NH4NO3 [°C] 71 79 79 79

[0126] To reach the critical temperature for the precipitation of NH4NO3, the gas flow does not necessarily have to reach or fall below this temperature; the wall temperature of a heat exchanger tube can also be sufficient and lead to the precipitation of NH4NO3. Since the combustion system requires combustion air, which is usually drawn in at ambient temperature, there is a risk of NH4NO3 precipitation on the tubes of a heat exchanger for preheating combustion air under normal operating conditions.

[0127] Unlike the dew point of H2O, maintaining a minimum temperature for the exhaust gas is therefore not a sufficient solution. To avoid the risk of NH4NO3 precipitation, the device for removing nitrogen oxides (exhaust gas treatment system) is operated according to the invention in such a way that the slip is either from NO X or NH3, or ideally both, is reduced to a maximum of 1 ppmv. This can be achieved according to the invention by suitable reaction control during the chemical reduction of NOX with NH3, and preferably with a reactor for the post-oxidation of NH3 with residual oxygen from the exhaust gas. Catalytic decomposition of NH3 into H2 and N2:

[0128] The catalytic decomposition of NH3 generally proceeds thermally, but is accelerated by the use of an NH3 decomposition catalyst. According to the invention, the catalytic decomposition of NH3 can be carried out under various conditions using different NH3 decomposition catalysts and with various configurations using different reactor types.

[0129] According to the invention, the catalytic decomposition of NH3 is preferably carried out by supplying heat in the presence of an NH3 decomposition catalyst. Important parameters for the catalytic decomposition of NH3 are the type of NH3 decomposition catalyst, the reaction temperature, and the reaction pressure.

[0130] According to the invention, various materials can be considered as NH3 decomposition catalysts. The reaction temperature at which the catalytic decomposition of NH3 occurs is determined in particular by the choice of the NH3 decomposition catalyst.

[0131] Suitable processes for the thermal and / or catalytic decomposition of NH3 into N2 and H2 are known to those skilled in the art. Suitable catalysts for the catalytic decomposition of NH3 into N2 and H2 are, for example, Ru supported on Al2O3 or SiO2, Fe, Co, Ni supported on MgAl2O4, Cu or Ru, or Co3Mo3N (A. Boisen et al., Journal of Catalysis 230 (2005) 309-312; I. Lucentini et al., Ind. Eng. Chem. Res. 2021, 60, 18560-18611; HJ Lee et al., Catalysts 2022, 12, 1203).

[0132] In preferred embodiments of the invention, a nickel-based NH3 decomposition catalyst is used. The reaction temperature and pressure determine the equilibrium conversion. At 900°C and 20 bar pressure, the decomposition of NH3 is almost quantitative. At 650°C, the NH3 conversion is approximately 98.5%, and at 500°C, only approximately 95%.

[0133] In preferred embodiments, reaction temperatures are set in the range of about 550°C to about 900°C, preferably about 550°C to about 700°C, so that a high conversion is achieved.

[0134] In other preferred embodiments, reaction temperatures are set in the range of about 600°C to about 900°C, preferably about 600°C to about 700°C, so that a high conversion is achieved.

[0135] In terms of energy balance and conversion, optimal reaction temperatures are in the range of approximately 630°C to 640°C. Nickel-based NH3 decomposition catalysts are advantageous despite the comparatively high reaction temperature. Due to the high conversion, the remaining content of undecomposed NH3 in the product gas is comparatively low, so separate separation of undecomposed NH3 for its recovery is preferable. Instead, N2 and undecomposed NH3 are combined from the product gas by pressure swing adsorption during the purification of H2.

[0136] Preferably, the NH3 decomposition catalyst comprises supported nickel. Preferred support materials are selected from the group consisting of Al2O3, MgO, SiO2, mesoporous SiO2 (e.g. MCF-17, MCM-41, SBA-15), zeolite (e.g. HY, H-ZSM-5), BaMnO3, BaTiO3, BaZrO3, CaMnO3, CaTiO3, CaZrO3, CeO2, Gd2O3, GdAlO3, KNbO3, La2O3, LaAlO3, MnO2, NaNbO3, Nb2O5, Sm2O3, SmAlO3, SrMnO3, SrTiO3, SrZrO3, TiO2, Y2O3, ZrO2, carbon (e.g. CNTs, SWCNTs, AX-21, MSC-30, MESO-C, GNP, activated carbon, Graphene, graphene oxide), attapulgite, hydrocalumite, sepiolite, and mixtures thereof.

[0137] In other preferred embodiments of the invention, a ruthenium-based NH3 decomposition catalyst is used. For this purpose, reaction temperatures in the range of approximately 450°C to approximately 500°C are preferably set according to the invention, although somewhat lower conversions of, for example, approximately 95% can be achieved, so that the remaining residual content of undecomposed NH3 in the product gas is higher.

[0138] Alternatively, other NH3 decomposition catalysts can also be used at even lower reaction temperatures. The lower the reaction temperature, the lower the conversion and the more undecomposed NH3 must be separated from the product gas and recycled.

[0139] According to the invention, the reaction pressure is preferably between about 15 bar a and about 25 bar a. The stoichiometry of the reaction (2 NH3 → N2 + 3 H2) increases the volume, which is why an increased reaction pressure generally has a negative effect on the conversion. On the other hand, it is advisable to operate the entire process at higher pressures in order to limit the container volume and thus the investment costs. With a reaction pressure of only 1 bar, conversions of more than 99% could be achieved at reaction temperatures above 400°C. However, since a reaction pressure of 1 bar is only practical for very small plants, the plant according to the invention is preferably operated at a higher reaction pressure, even if this means accepting a certain loss in conversion.

[0140] The reaction pressure is determined in particular by the design of the H2 purification. The pressure swing adsorption (PSA) preferred according to the invention for the purification of H2 can preferably be operated effectively at a pressure in the range from about 15 bar to about 25 bar. The pressure of the product gas upon leaving the NH3 decomposition device is preferably in the range from about 15 to about 25 bar a, more preferably about 18 bar a to about 22 bar a, even more preferably about 19 bar a to about 21 bar a. In this way, a good balance is found between the requirements of pressure swing adsorption on the one hand and the achieved conversion on the other.

[0141] The catalytic decomposition of NH3 can basically take place in different reactor types.

[0142] In adiabatic reaction conditions, the internal heat of the reaction gas is used as the energy source for the reaction. Suitable reactors for this are autothermal reformers and secondary reformers, which operate with internal energy generation. Combustion air is added to the process gas, and a portion of the reaction gas is combusted to raise the temperature so that the desired temperature is reached at the reactor outlet. A disadvantage is the presence of water in the process gas produced during combustion, which must be removed by condensation. Some of the undecomposed NH3 then dissolves in the condensed water and is lost. In addition, the high temperatures lead to the formation of significant amounts of nitrogen oxides.

[0143] According to the invention, these disadvantages are avoided by the product gas preferably being physically separated from the combustion gas and the exhaust gas formed therefrom. The product gas is formed in the NH3 decomposition device of the combustion plant according to the invention by the decomposition of NH3 and preferably leaves the NH3 decomposition device via its own outlet. The combustion gas is combusted together with combustion air in the combustion device of the combustion plant, and the exhaust gas formed thereby preferably also leaves the combustion device via its own outlet, preferably into an exhaust duct. Product gas and exhaust gas are preferably not mixed with each other, but remain physically separated from each other. During combustion The heat of combustion generated during the combustion gas flow flows into the NH3 decomposition device as a heat stream and thus provides the heat required to maintain the endothermic catalytic decomposition of NH3.

[0144] The catalytic decomposition of NH3 is preferably carried out isothermally, quasi-isothermally, or in a mixed isothermal and adiabatic process. In isothermal reaction conditions, the gas temperature remains largely unchanged.

[0145] In preferred embodiments of the invention, the catalytic decomposition of NH3 takes place in a reactor analogous to a primary reformer. For this purpose, the reactor comprises both the NH3 decomposition device according to the invention and the combustion device according to the invention.

[0146] For this purpose, the NH3 decomposition catalyst is preferably arranged in at least one tube through which NH3 flows, more preferably at least two tubes, even more preferably at least three tubes. The at least one tube contains the NH3 decomposition catalyst. NH3 preferably flows through the at least one tube from top to bottom. In a physically separate combustion chamber, a mixture of NH3 and H2 is preferably combusted together with combustion air as the combustion gas (combustion device). The N2 formed alongside H2 during the catalytic decomposition of NH3 is inert and serves as an additional heat carrier. The combustion heat generated by the combustion process in the combustion chamber of the combustion device is used to heat the NH3 decomposition device, preferably the tube or tubes through which the NH3 to be decomposed is passed. For this purpose, a heat flow is passed from the combustion device into the NH3 decomposition device.

[0147] In particularly preferred embodiments of the invention, NH3 is preheated before entering the NH3 decomposition device according to the invention. As a result of this preheating, the temperature of the NH3 before entering the NH3 decomposition device according to the invention is preferably at least about 600°C, preferably at least about 630°C. The temperature of the NH3 is preferably at most about 850°C, more preferably at most about 820°C. Particularly preferably, the temperature of the NH3 upon entering the NH3 decomposition device according to the invention is about 780°C to 820°C, preferably about 800°C. The NH3 decomposition device according to the invention and the combustion device according to the invention preferably form a reactor designed analogously to a primary reformer. The NH3 decomposition catalyst is preferably nickel-based.In preferred embodiments, the reaction temperature in the NH3 decomposition device, preferably in the at least one tube containing the NH3 decomposition catalyst and through which the NH3 is passed, is preferably about 630°C to about 670°C, preferably about 650°C. In other preferred embodiments, this temperature is about 660°C to 700°C, preferably about 680°C. The product gas leaves the reactor (the NH3 decomposition device) preferably at a pressure of about 15 bar a to about 25 bar a, preferably about 20 bar a.

[0148] In further particularly preferred embodiments of the invention, the decomposition of NH3 takes place in two stages in two successively flowing NH3 decomposition devices. In a pre-reactor (first NH3 decomposition device), only a portion of the NH3 is initially decomposed. The remaining decomposition of NH3 up to the maximum conversion achieved then takes place in a second NH3 decomposition device. For this purpose, the second NH3 decomposition device, together with the combustion device according to the invention, preferably forms a reactor, as described in more detail above, designed analogously to a primary reformer.

[0149] Preferably, the NH3 is preheated before being introduced into the pre-reactor (first NH3 decomposition device). The temperature of the NH3 after heating and upon entry into the pre-reactor (first NH3 decomposition device) is preferably approximately 620°C to approximately 680°C, more preferably approximately 650°C. The preheated NH3 then enters the pre-reactor, which contains an NH3 decomposition catalyst and in which a catalytic decomposition of NH3 to N2 and H2 occurs to a certain extent. An intermediate product gas is formed, which still contains significant residual amounts of undecomposed NH3, but also already formed N2 and H2. Due to the endothermic decomposition of NH3, the intermediate product gas cools preferentially.

[0150] Preferably, the conversion of decomposed NH3 in the pre-reactor is at most 30%, more preferably at most 25%, even more preferably at most 20% of the total conversion achieved.

[0151] Preferably, the conversion of decomposed NH3 in the pre-reactor is at least 10%, more preferably at least 15% of the total conversion achieved.

[0152] After leaving the pre-reactor, the intermediate gas is preferably reheated before entering the downstream, second NH3 decomposition device.

[0153] In preferred embodiments, the temperature of the intermediate gas after reheating and upon entry into the second NH3 decomposition device is about 550°C to about 680°C, more preferably about 580°C.

[0154] In other preferred embodiments, the temperature of the intermediate gas after reheating and upon entry into the second NH3 decomposition device is about 620°C to about 680°C, more preferably about 650°C.

[0155] The remaining decomposition of NH3 then takes place in the second NH3 decomposition device until the total conversion is achieved.

[0156] In this preferred embodiment of the invention, with the same total conversion, the temperature of the intermediate product gas upon entry into the pre-reactor (first NH3 decomposition device) and upon entry into the second NH3 decomposition device can each be lower than the temperature of the NH3 in single-stage decomposition of NH3, i.e. when only a single NH3 decomposition device is used. Because of the lower temperature, nitriding of the pipes occurs to a lesser extent, thereby increasing the service life of the steel that comes into contact with NH3.

[0157] The NH3 decomposition catalyst in the first NH3 decomposition device (pre-reactor) is preferably the same as in the second NH3 decomposition device. Properties of the exhaust gas upon leaving the combustion plant:

[0158] By burning combustion gas with combustion air, an exhaust gas is generated in the combustion plant, preferably the combustion device, which leaves the combustion plant, preferably into an exhaust gas duct.

[0159] In preferred embodiments, the exhaust gas has one or more of the following properties when leaving the combustion plant, preferably the combustion device, and when entering the exhaust gas duct:

[0160] In preferred embodiments, the exhaust gas has a NOX content that is greater than the N2O content. Preferably, the NOX content is at least twice as high, more preferably at least three times as high, even more preferably at least four times as high, most preferably at least seven times as high, and in particular at least ten times as high as the N2O content. Preferably, the molar ratio of NOX:N2O is more than 10:1, more preferably at least 20:1, even more preferably at least 30:1, most preferably at least 40:1, and in particular at least 50:1.

[0161] In preferred embodiments, the exhaust gas has a NO content that is greater than the N2O content. Preferably, the NO content is at least twice as high, more preferably at least three times as high, even more preferably at least four times as high, most preferably at least seven times as high, and in particular at least ten times as high as the N2O content.

[0162] In preferred embodiments, the exhaust gas has a NO2 content that is greater than the N2O content. Preferably, the NO2 content is at least twice as high, more preferably at least three times as high, even more preferably at least four times as high, most preferably at least seven times as high, and in particular at least ten times as high as the N2O content.

[0163] Preferably, the exhaust gas has a content of NO X of at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 30 ppmv, even more preferably at least 40 ppmv, and in particular at least 50 ppmv.

[0164] The exhaust gas preferably has a NOX content of at least 75 ppmv, preferably at least 100 ppmv, more preferably at least 150 ppmv, even more preferably at least 200 ppmv, and in particular at least 250 ppmv.

[0165] Preferably, exhaust gas contains NO Xof at least 500 ppmv, preferably at least 1000 ppmv, more preferably at least 2000 ppmv, even more preferably at least 3000 ppmv, and in particular at least 3500 ppmv.

[0166] The exhaust gas preferably has an N2O content of at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 30 ppmv, even more preferably at least 40 ppmv, and in particular at least 50 ppmv.

[0167] Preferably, the exhaust gas has an N2O content of at least 75 ppmv, preferably at least 100 ppmv, more preferably at least 150 ppmv, even more preferably at least 200 ppmv, and in particular at least 250 ppmv.

[0168] Preferred exhaust gases have a content of NO X in the range of 1500 to 3000 ppmv, preferably 2000 to 3000 ppmv, and an N2O content in the range of 20 to 100 ppmv.

[0169] In preferred embodiments, the exhaust gas has an H2O content of more than 4.0 vol.%; preferably at least 5.0 vol.%, more preferably at least 6.0 vol.%, even more preferably at least 7.0 vol.%, most preferably at least 8.0 vol.%, and in particular at least 9.0 vol.%.

[0170] In further preferred embodiments, the exhaust gas has an H2O content of at least 10 vol.%; preferably at least 12 vol.%, more preferably at least 14 vol.%, even more preferably at least 16 vol.%, most preferably at least 18 vol.%, and in particular at least 20 vol.%.

[0171] In preferred embodiments, the exhaust gas has an H2O content in the range of 10±8 vol.%; preferably in the range of 10±7 vol.%, more preferably in the range of 10±6 vol.%, even more preferably in the range of 10±5 vol.%, most preferably in the range of 10±4 vol.%, and in particular in the range of 10±3 vol.%.

[0172] In preferred embodiments, the exhaust gas has an H2O content in the range of 15±8 vol.%; preferably in the range of 15±7 vol.%, more preferably in the range of 15±6 vol.%, even more preferably in the range of 15±5 vol.%, most preferably in the range of 15±4 vol.%, and in particular in the range of 15±3 vol.%.

[0173] In preferred embodiments, the exhaust gas has an H2O content in the range of 20±8 vol.%; preferably in the range of 20±7 vol.%, more preferably in the range of 20±6 vol.%, even more preferably in the range of 20±5 vol.%, most preferably in the range of 20±4 vol.%, and in particular in the range of 20±3 vol.%.

[0174] In preferred embodiments, the exhaust gas has a H2O content in the range of 25±8 vol.%; preferably in the range of 25±7 vol.%, more preferably in the range of 25±6 vol.%, still more preferably in the range of 25±5 vol%, most preferably in the range of 25±4 vol%, and in particular in the range of 25±3 vol%.

[0175] In preferred embodiments, the exhaust gas has an H2O content in the range of 30±8 vol.%; preferably in the range of 30±7 vol.%, more preferably in the range of 30±6 vol.%, even more preferably in the range of 30±5 vol.%, most preferably in the range of 30±4 vol.%, and in particular in the range of 30±3 vol.%.

[0176] The exhaust gas preferably has an N2 content of at most 95 vol.%, preferably at most 90 vol.%, more preferably at most 85 vol.%, even more preferably at most 80 vol.%, most preferably at most 75 vol.%, and in particular at most 70 vol.%.

[0177] The exhaust gas preferably has an N2 content of at least 40 vol.%, preferably at least 50 vol.%, more preferably at least 60 vol.%, even more preferably at least 70 vol.%, most preferably at least 80 vol.%, and in particular at least 90 vol.%.

[0178] Preferably, the exhaust gas, when leaving the combustion plant, preferably the combustion device, has a temperature T1 of at least 500°C, more preferably at least 600°C, even more preferably at least 700°C, most preferably at least 800°C, and in particular at least 900°C.

[0179] Preferably, the exhaust gas, when leaving the combustion plant, preferably the combustion device, has a temperature T1 of at most 1100°C, more preferably at most 1000°C, even more preferably at most 900°C, most preferably at most 800°C, and in particular at most 700°C.

[0180] Preferably, the exhaust gas has a pressure of at most 1.5 bar upon leaving the combustion plant, preferably the combustion device; preferably atmospheric pressure.

[0181] Preferably, the exhaust gas, when leaving the combustion plant, preferably the combustion device, has an oxidation degree of NOX of at least 10%, more preferably at least 20%, even more preferably at least 30%, most preferably at least 40%, and in particular at least 50%.

[0182] Preferably, the exhaust gas has an oxidation level of NO when leaving the combustion plant, preferably the combustion device. X of at most 90%, more preferably at most 80%, even more preferably at most 70%, most preferably at most 60%, and in particular at most 50%.

[0183] Preferably, the exhaust gas leaving the combustion plant, preferably the combustion device, has an O2 content of less than 2.0 vol.%. Step (b):

[0184] In the optional and preferred step (b) of the method according to the invention, the temperature T1 of the exhaust gas at the outlet of the combustion plant, preferably the combustion device, is preferably measured and modified using suitable devices so that the exhaust gas, upon entering the exhaust gas treatment plant, has a temperature T2 that is optimized under the given conditions for carrying out steps (d) and (e) of the method according to the invention within the exhaust gas treatment plant. The optimized temperature depends on the selected configuration of steps (d) and (e), i.e., on the type and sequence of the individual process steps for N2O reduction and NO X -reduction and in particular according to the type of catalyst materials used for the N2O decomposition catalyst and / or N2O reduction catalyst as well as the NO X -reduction catalyst.

[0185] Suitable devices for changing the temperature of the exhaust gas are known to a person skilled in the art and include, in particular, heat exchangers, which can be designed, for example, as plate heat exchangers or tube heat exchangers.

[0186] In the optional and preferred step (b) of the process according to the invention, the cooling of the exhaust gas preferably takes place in at least one heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas.

[0187] The exhaust gas from a tubular reactor designed similarly to a primary reformer contains significant amounts of internal energy. The process for producing H2 from NH3 requires the supply of process streams at high temperatures. According to the invention, the exhaust gas is used to preheat these process streams and is cooled in the process. This has the advantage of reducing the plant's demand for combustion gas and increasing the yield of hydrogen product.

[0188] The effectiveness of different process variants can be measured by the hydrogen yield, which is defined as follows: ×

[0189] The hydrogen yield of the plant is the ratio of the mole flow of H2 leaving the plant as a product compared to the mole flow of NH3 entering the plant as a feed stream, including any bypass to the combustion gas.

[0190] A number of process streams are available for absorbing heat from the exhaust gas: - Preheating and evaporation of NH3 (also possible indirectly); - Further heating of evaporated NH3 and intermediate product gas; - Heating of combustion air; - Preheating of boiler feed water; - Heating of water; - Heating of combustion gas; - Evaporation of boiler feed water to generate steam; - Superheating of steam; - Auxiliary streams (heat transfer medium for preheating NH3 or for the evaporator of an NH3 desorption unit).

[0191] The target temperature of the process streams to be heated usually determines the order in which they are heated. Large temperature differences between the exhaust gas and the heat-absorbing process stream reduce the required size of the heat exchangers.

[0192] However, it is advantageous to maintain a temperature difference across all components that should not be undercut. This prevents an increase in the temperature difference at one heat exchanger, and thus its reduction, which would be "paid for" by an increase in the size of all other heat exchangers. To enable an economical design of the heat exchangers in the exhaust duct, according to the invention, a temperature difference of 45 K between the inlet of the hot stream and the outlet of the cold stream, or between the inlet of the cold stream and the outlet of the hot stream, whichever pair of values ​​is smaller, is preferably not undercut.

[0193] Another key factor in developing an effective solution for the exhaust duct of a tubular reactor designed analogously to a primary reformer is setting the required temperatures for the unit for removing nitrogen oxides from the exhaust gas.

[0194] Theoretically, it is possible to utilize the heat of the exhaust gas in numerous different configurations. In a plant for producing H2 from NH3, the stream of product gas generated in the NH3 decomposition device provides another significant heat source. It is advantageous and preferred according to the invention to utilize the heat contained in the product gas for the following heat integration measures: - generation of steam; - preheating of NH3; - preheating of H2O for the generation of steam; and / or - cooling of the product gas with subsequent heat integration of the cooling water.

[0195] Furthermore, it is advantageous and preferred according to the invention to use the heat contained in the exhaust gas for the following heat integration measures: - preheating of the NH3 to the inlet temperature for the NH3 decomposition device; - preheating of boiler feed water; and / or - preheating of combustion air.

[0196] Due to the mechanical limitations of the heat exchangers used in the exhaust duct, the required energy quantities, and the temperature profiles of the exhaust gas and the process streams to be heated, such configurations often leave usable but non-integrable residual heat in the exhaust gas. This results in a high inlet temperature of the exhaust gas into the flue stack. Internal energy contained in this stream is lost to the process and ultimately reduces the yield of H2.

[0197] To reduce the loss of heat via the exhaust gas and to increase the yield of H2, further integration stages in the exhaust gas duct are possible and preferred according to the invention: - preheating of NH3 to the inlet temperature for a first pre-reactor (preferably an adiabatic fixed-bed reactor); - preheating of NH3 to the inlet temperature for a second pre-reactor (preferably an adiabatic fixed-bed reactor); - two-stage preheating of the combustion air; - preheating of the combustion gas (preferably the effluent from the purification plant for H2, preferably the off-gas of a pressure swing adsorption device or the retentate of a membrane unit); and / or - preheating of an auxiliary stream for the integration of usable residual heat.

[0198] Heat exchangers according to the invention serve to transfer heat from one medium to another without the media being mixed together. For the purposes of description, with regard to an "A / B heat exchanger," the heat-emitting medium A is mentioned first, followed by the heat-absorbing medium B. Accordingly, for example, an "exhaust gas / NH3 heat exchanger" serves to transfer heat contained in the exhaust gas to NH3. For this purpose, the exhaust gas / NH3 heat exchanger is wired accordingly, i.e., its warmer side is traversed by exhaust gas, whereas its cooler side is traversed by NH3. For reasons of simplicity, "NH3" is used in the nomenclature for starting material as well as for any intermediate gas that still contains significant amounts of NH3. Heat exchangers with the same functionality may be designated by a different name for distinguishability.Numbered, whereby a specific number does not necessarily mean that all heat exchangers with the same functionality but with a lower number must be present at the same time. It is therefore possible, for example, that a second exhaust gas / combustion air heat exchanger is present, while a first exhaust gas / combustion air heat exchanger is not.

[0199] Each heat exchanger according to the invention can be independent of one another, possibly as an individual heat exchanger of the described design or configuration, or possibly also as part of a plurality of several, e.g., two or three heat exchangers connected directly in series with the same functionality of the described design or configuration. The heat-emitting medium and the heat-absorbing medium are then the same in the plurality of heat exchangers with the same functionality. This division of a single heat exchanger into, for example, two heat exchangers connected in series with the same functionality can have structural and / or design advantages.

[0200] The exhaust gas leaves the combustion plant, preferably the combustion device, at a temperature T1 and is cooled in step (b) preferably to a temperature T2 at which the exhaust gas which is then subsequently transferred to the exhaust gas treatment system. Preferably, both the at least one heat exchanger and the exhaust gas treatment system are arranged in one exhaust gas duct.

[0201] In preferred embodiments, a single heat exchanger is arranged downstream of the combustion plant in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place (see Figure 2).

[0202] In other preferred embodiments, at least two heat exchangers are arranged in the flow direction of the exhaust gas downstream of the combustion plant, in which the exhaust gas is cooled one after the other (see Figures 3, 5 and 6).

[0203] In further preferred embodiments, at least three heat exchangers are arranged in the flow direction of the exhaust gas downstream of the combustion plant, in which the exhaust gas is cooled one after the other (see Figure 4).

[0204] The cooling of the exhaust gas in the at least one heat exchanger takes place by transferring heat from the exhaust gas to a heat transfer medium.

[0205] According to the invention, NH3 is preferably used as the heat transfer medium, which is then subsequently fed to the catalytic decomposition in an NH3 decomposition device on an NH3 decomposition catalyst.

[0206] In preferred embodiments, in step (b) of the process according to the invention, the exhaust gas is cooled in at least one first exhaust gas / NH3 heat exchanger, which is arranged downstream of the combustion plant in the flow direction of the exhaust gas. Preferably, an NH3 decomposition device is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the NH3, in which a catalytic decomposition of the heated NH3 takes place on an NH3 decomposition catalyst to produce a product gas. The NH3 is heated in the first exhaust gas / NH3 heat exchanger by absorbing heat from the exhaust gas (see Figure 2).

[0207] In other preferred embodiments, in step (b) of the process according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / NH3 heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas, and - in a second exhaust gas / NH3 heat exchanger which is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas.

[0208] Preferably, a first NH3 decomposition device (pre-reactor) is arranged in the flow direction of the NH3 downstream of the first exhaust gas / NH3 heat exchanger, in which a partial catalytic decomposition of the heated NH3 takes place on an NH3 decomposition catalyst to produce an intermediate gas. Preferably, the second exhaust gas / NH3 heat exchanger is arranged downstream of the first NH3 decomposition device (pre-reactor) in the flow direction of the NH3.

[0209] Preferably, a second NH3 decomposition device (main reactor) is arranged in the flow direction of the NH3 downstream of the second exhaust gas / NH3 heat exchanger, in which a catalytic decomposition of the heated NH3 takes place on an NH3 decomposition catalyst to produce a product gas.

[0210] The NH3 (or the intermediate product gas) is heated in the first exhaust gas / NH3 heat exchanger and in the second exhaust gas / NH3 heat exchanger by absorbing heat from the exhaust gas.

[0211] The exhaust gas first flows through the first exhaust gas / NH3 heat exchanger and then through the second exhaust gas / NH3 heat exchanger.

[0212] The NH3 (or the intermediate product gas) first flows through the first exhaust gas / NH3 heat exchanger, where it absorbs heat from the exhaust gas. The heated NH3 then flows into the first NH3 decomposition device, where partial catalytic decomposition of the heated NH3 occurs on an NH3 decomposition catalyst, producing an intermediate product gas. The intermediate product gas thus formed, which still contains significant amounts of undecomposed NH3, then flows through the second exhaust gas / NH3 heat exchanger, where it again absorbs heat from the exhaust gas. Finally, the heated intermediate product gas flows into the second NH3 decomposition device, where catalytic decomposition of the heated NH3 occurs on an NH3 decomposition catalyst, producing a product gas (see Figures 3, 5, and 6).

[0213] In further preferred embodiments, in step (b) of the method according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / NH3 heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas, - in a second exhaust gas / NH3 heat exchanger which is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas, and - in a third exhaust gas / NH3 heat exchanger which is arranged downstream of the second exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas.

[0214] Preferably, a first NH3 decomposition device (first pre-reactor) is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the NH3, in which a partial catalytic decomposition of the heated NH3 takes place on an NH3 decomposition catalyst to produce a first intermediate gas. Preferably, the second exhaust gas / NH3 heat exchanger is arranged downstream of the first NH3 decomposition device (first pre-reactor) in the flow direction of the NH3.

[0215] Preferably, a second NH3 decomposition device (second pre-reactor) is arranged in the flow direction of the NH3 downstream of the second exhaust gas / NH3 heat exchanger, in which a further partial catalytic decomposition of the heated NH3 (first intermediate product gas) takes place on an NH3 decomposition catalyst to produce a second intermediate product gas. The third exhaust gas / NH3 heat exchanger is arranged downstream of the second NH3 decomposition device (second pre-reactor) in the flow direction of the NH3.

[0216] Preferably, a third NH3 decomposition device (main reactor) is arranged in the flow direction of the NH3 downstream of the third exhaust gas / NH3 heat exchanger, in which a catalytic decomposition of the heated NH3 (second intermediate product gas) takes place on an NH3 decomposition catalyst to produce a product gas.

[0217] The NH3 (or the first intermediate product gas or the second intermediate product gas) is heated in the first exhaust gas / NH3 heat exchanger, in the second exhaust gas / NH3 heat exchanger and in the third exhaust gas / NH3 heat exchanger by absorbing heat from the exhaust gas.

[0218] The exhaust gas first flows through the first exhaust gas / NH3 heat exchanger, then the second exhaust gas / NH3 heat exchanger and finally the third exhaust gas / NH3 heat exchanger.

[0219] The NH3 (or the first intermediate product gas or the second intermediate product gas) first flows through the first exhaust gas / NH3 heat exchanger and absorbs heat from the exhaust gas therein. The heated NH3 then flows into the first NH3 decomposition device, in which a partial catalytic decomposition of the heated NH3 takes place on an NH3 decomposition catalyst to produce a first intermediate product gas. The first intermediate product gas thus formed, which still contains considerable amounts of undecomposed NH3, then flows through the second exhaust gas / NH3 heat exchanger and again absorbs heat from the exhaust gas therein. The heated first intermediate product gas then flows into the second NH3 decomposition device, in which a further partial catalytic decomposition of the heated NH3 takes place on an NH3 decomposition catalyst to produce a second intermediate product gas.The resulting second intermediate gas, which still contains significant amounts of undecomposed NH3, then flows through the third exhaust gas / NH3 heat exchanger, where it again absorbs heat from the exhaust gas. Finally, the heated second intermediate gas flows into the third NH3 decomposition device, where catalytic decomposition of the heated NH3 takes place on an NH3 decomposition catalyst to produce a product gas (see Figure 4).

[0220] In step (b), the exhaust gas is preferably cooled to a temperature T2, at which the exhaust gas is then transferred to the exhaust gas treatment plant.

[0221] Preferably, the temperature T2 is at least 360°C, more preferably at least 370°C, even more preferably at least 380°C, most preferably at least 390°C, and in particular at least 400°C.

[0222] Preferably, the temperature T2 is at most 500°C, more preferably at most 480°C, even more preferably at most 460°C, most preferably at most 440°C, and in particular at most 420°C.

[0223] Preferably, the temperature T2 is in the range of 400 to 450°C, more preferably 400 to 420°C. The ideal temperature T2 depends on the NO X -Inlet concentration and the associated heat emission. Per 1000 ppmv NO X A ΔT of around 12 K is to be expected. For example, if the exhaust gas contains 7000 ppmv NO X , this would correspond to around 80-90 K. The outlet temperature should not be too high, because the stability of the catalysts in the exhaust gas treatment system is a critical factor due to the high water content of the exhaust gas.

[0224] At very high NO XFor high concentrations, the invention preferably provides a multi-stage arrangement of catalyst beds with multi-stage NH3 feed and intermediate heat exchangers. This avoids excessively high temperatures. Furthermore, this enables significantly higher NOX and N2O degradation (with the same catalyst volume).

[0225] Preferably, the exhaust gas has a temperature T2 on entry into the exhaust gas treatment plant which is relatively at least 20°C, preferably at least 40°C, more preferably at least 60°C, even more preferably at least 80°C, most preferably at least 100°C, and in particular at least 120°C below the temperature T1 which the exhaust gas has on leaving the combustion plant, preferably the combustion device.

[0226] Preferably, the temperature T2 is relatively lower than the temperature T1 by at least 50°C, more preferably at least 100°C, even more preferably at least 150°C, most preferably at least 200°C, and especially at least 250°C. Step (c):

[0227] In step (c) of the process according to the invention, the optionally cooled exhaust gas is transferred to an exhaust gas treatment plant, ie from the combustion plant from step (a) or from the at least one heat exchanger from the optional and preferred step (b) to an exhaust gas treatment plant.

[0228] In step (c) of the process according to the invention, the exhaust gas which has left the combustion plant, preferably the combustion device, and has possibly been cooled in step (b), is transferred to an exhaust gas treatment plant.

[0229] This can be achieved, for example, by means of pipelines connecting the outlet of the combustion system, preferably the combustion device, to the inlet of the exhaust gas treatment system. This connection is preferably established via an exhaust duct. Since the method according to the invention is preferably carried out at atmospheric pressure, such pipelines or the walls of the exhaust duct are typically not subject to any special requirements with regard to possible compressive stress.

[0230] However, the pipes or walls of the exhaust duct should be able to withstand the temperatures which the exhaust gas has when leaving the combustion plant, preferably the combustion device, or when entering the exhaust gas treatment plant.

[0231] In the exhaust gas treatment system according to the invention, steps (d) and (e) of the process according to the invention take place. For this purpose, the exhaust gas treatment system is equipped with the N2O decomposition catalyst for step (d1) and / or with the N2O reduction catalyst for step (d2), as well as with the NO X -reduction catalyst for step (e).

[0232] If the exhaust gas treatment system according to the invention additionally comprises at least one further catalyst or one of the aforementioned N2O reduction, N2O decomposition or NOX reduction catalysts fulfills at least one further functionality, at least one of the following steps (g1) to (g4) is preferably additionally carried out in the exhaust gas treatment system according to the invention: (g1) Cooling the exhaust gas in at least one heat exchanger, which is preferably arranged within the exhaust gas treatment system; preferably upstream of the NH3 oxidation catalyst in the flow direction of the exhaust gas; (g2) Reducing the NH3 content in the exhaust gas by oxidation with an oxidizing agent on an NH3 oxidation catalyst; wherein the oxidizing agent preferably comprises O2; (g3) Reducing the HCN content in the exhaust gas by hydrolysis and oxidation of the hydrolysates with an oxidizing agent on an HCN degradation catalyst; wherein the oxidizing agent preferably comprises NOX and / or N2O;and (g4) reducing the CO content in the exhaust gas by chemical oxidation with an oxidizing agent on a CO oxidation catalyst; wherein the oxidizing agent preferably comprises O2. Step (d): ;

[0233] In step (d) of the process according to the invention, the N2O content in the exhaust gas is reduced. This can be achieved by (d1) decomposition of N2O on an N2O decomposition catalyst and / or (d2) chemical reduction of N2O with a reducing agent on an N2O reduction catalyst.

[0234] During the decomposition of N2O, N2 and O2 are formed according to the following overall reaction: 2 N2O → 2 N2 + O2.

[0235] Decomposition of N2O therefore means decomposition into N2 and O2. A "N2O decomposition catalyst" within the meaning of the invention catalyzes the decomposition of N2O. The achievable reduction of N2O by catalytic decomposition depends not only on the type, ie the chemical nature and physical design of the N2O decomposition catalyst and the prevailing pressure and temperature conditions, but also, above all, on the selected space velocity, ie the ratio of exhaust gas volume flow to the catalyst volume. However, the catalytic activity of an N2O decomposition catalyst does not have to be limited exclusively to this reaction. It is therefore entirely possible and, according to the invention, also preferred for the N2O decomposition catalyst to also catalyze other reactions, for example, the chemical reduction of N2O and / or the chemical reduction of NOX. Whether such further reactions actually take place depends on the conditions of the individual case, in particular the type of catalyst, and the kinetics of any parallel processes, for example, the presence or amount of the reducing agent and the presence or amount of other reactants.

[0236] During the chemical reduction of N2O with a reducing agent, different reaction products are formed depending on the reducing agent.

[0237] In the case of the reducing agent NH3 which is preferred according to the invention, N2 and H2O in particular are formed during the chemical reduction of N2O, e.g. according to: 3 N2O + 2 NH3 → 4 N2 + 3 H2O or 4 N2O + 4 NH3 + O2 → 6 N2 + 6 H2O or also in the joint reduction with NO according to 2 NO + N2O + 2 NH3 → 3 N2 + 3 H2O.

[0238] In the case of hydrocarbons, which are also preferred as reducing agents according to the invention, in particular CO and H2O are formed during the chemical reduction of N2O, e.g. according to (2n+1) N2O + CnH2n+2 → (2n+1) N2 + n CO + (n+1) H2O or also CO2 and H2O according to 4n N2O + CnH2n+2 → 4n N2 + n CO2 + 2n H2O.

[0239] CO is also preferred as a reducing agent according to the invention. It can react further with N2O to form CO2, e.g., according to: N2O + CO → N2 + CO2.

[0240] An "N2O reduction catalyst" within the meaning of the invention catalyzes the chemical reduction of N2O with a reducing agent. However, the catalytic activity of an N2O reduction catalyst does not have to be limited exclusively to this reaction. Thus, it is entirely possible and preferred according to the invention for the N2O reduction catalyst to also catalyze other reactions, for example, the decomposition of N2O and / or the chemical reduction of NO. X Whether such further reactions actually take place depends on the conditions of the individual case, in particular the type of catalyst, and the kinetics of any parallel processes, for example the presence or amount of the reducing agent and the presence or amount of other reactants. Step (s):

[0241] In step (e) of the process according to the invention, the NO content is reduced Xin the exhaust gas by chemical reduction of NO X with reducing agent on a NO X -reduction catalyst.

[0242] Preference is given to such NO X -Reduction catalysts, which, if possible, enable the selective catalytic reduction (SCR) of the nitrogen oxides contained in the exhaust gas, in particular NO X enable, ie the NOX reduction catalysts primarily catalyze the oxidation of NH3 with NOX and not or secondarily the oxidation of NH3 with free oxygen (O2) possibly present in the exhaust gas.

[0243] In the chemical reduction of NO XWith reducing agents, different reaction products are formed depending on the reducing agent. In the case of the reducing agent NH3, which is preferred according to the invention, N2 and H2O in particular are formed during the chemical reduction of NOX, depending on the type of NOX reduction catalyst and the ratio of NO to NO2, e.g., according to: 4 NH3 + 2 NO + 2 NO2 → 4 N2 + 6 H2O (so-called fast SCR) 4 NH3 + 4 NO + O2 → 4 N2 + 6 H2O (so-called normal SCR) 8 NH3 + 6 NO2 → 7 N2 + 12 H2O (so-called NO2 SCR).

[0244] The joint selective catalytic reduction is called so-called fast SCR and is generally much faster than the so-called normal SCR or NO2 SCR.

[0245] A "NOX reduction catalyst" within the meaning of the invention catalyzes the chemical reduction of NOX with a reducing agent. However, the catalytic activity of a NOX reduction catalyst does not have to be limited exclusively to this reaction. Thus, it is entirely possible and, according to the invention, also preferred for the NOX reduction catalyst to also catalyze other reactions, for example, the decomposition of N2O, the chemical reduction of N2O and / or the establishment of the NOX equilibrium, or even the selective oxidation of excess NH3 with free O2. Whether such further reactions actually occur depends on the conditions of the individual case and the kinetics of any parallel processes, for example, the presence or amount of the reducing agent and the presence or amount of other reactants. Catalysts

[0246] N2O decomposition catalysts are known per se, and a wide variety of substance classes can be used. Preferred N2O decomposition catalysts are those that exhibit high catalytic activity for the decomposition of N2O into N2 and O2, for example, in the temperature range of 350 to 600°C.

[0247] Preferred examples of N2O decomposition catalysts according to the invention are metal-loaded zeolite catalysts, for example zeolite catalysts loaded with copper or cobalt or, in particular, with iron, noble metal catalysts, or transition metal oxide catalysts, such as catalysts containing cobalt oxide. Examples of suitable catalysts are described, inter alia, by Kapteijn et al. in Appl. Cat. B: Environmental 9 (1996), 25-64, in US-A-5,171,553, in Actes du 2ieme Congres International sur la Catalyse, Technip, Paris 1961, 1937-1953, and in WO-A-01 / 58,570. When iron-loaded zeolite catalysts are used in the first catalyst bed, the NO still present in the gas accelerates. X As expected, the desired N2O decomposition is achieved by an activating effect (co-catalytic effect), as is the case for different N2O / NO X -relations were described by Kögel et al. in Catal. Comm.2 (2001) 273-276.

[0248] Further preferred examples of N2O decomposition catalysts according to the invention are catalysts whose N2O decomposition activity is significantly limited by the presence of NOX. Such N2O decomposition catalysts are also referred to as "NOX-sensitive N2O decomposition catalysts" for the purposes of this description. These catalysts contain one or more catalytically active compounds of elements selected from groups 5 to 11 of the Periodic Table of Elements (PSE). Particular preference is given to compounds of the elements from groups 9 to 11 of the PSE. Of these, compounds of the elements Co, Pt, Pd, Ir, Rh, Ni and / or Cu are in turn preferred, preferably Co, Rh, Ni and / or Cu, and in particular Co or Rh.Preferably, the N2O decomposition catalyst is based on noble metals, which are preferably supported on refractory oxides, or on mixtures of transition metal oxides, in particular mixed oxides or simple transition metal oxides, in each case either supported or preferably as unsupported catalysts.

[0249] The catalytically active compounds themselves can be metallic and / or oxide compounds, the latter being present either as singular oxides or as binary, ternary, or polynary mixed oxides of various structural types, such as perovskites or spinels. Such compounds are described, for example, in Catalysis Letters 35 (1995) 372-382, Applied Catalysis 73 (1991) 165-171, Catal. Rev.-Sci. Eng.; 34(4), 409-425 (1992), or Actes du 2ieme Congres International sur la Catalyse 97 (1961) 1937-1953. Mixtures of various catalytically active compounds can also be used. Examples of particularly preferred catalytically active compounds are metallic rhodium, rhodium oxides such as RhO2 or Rh2O3, CoO, Co2O3, Co-containing spinels such as Co3O4, CuxCo3-xO4 or Co-containing perovskites such as LaCoO3 or Co-containing perovskites substituted on A and B sites.

[0250] The catalytically active compounds can be contained in the catalysts in pure form or applied to or mixed with suitable support materials. In the first case, these are so-called full catalysts, which, in addition to active compounds, also contain may contain known additives such as binders or other manufacturing-related additives such as plasticizers, pore formers, fiber reinforcements or pressing aids.

[0251] The methods for producing such catalysts are known to those skilled in the art. In the case of "supported catalysts," the catalytically active compounds are applied to the support material. This disperses and stabilizes the catalytically active compound against both mechanical and thermal stress. The methods for producing such catalysts are also known to those skilled in the art. The support materials are preferably refractory oxides, such as SiO2, TiO2, ZrO2, or Al2O3, or mixtures of two or more thereof, or materials that themselves exhibit a certain catalytic activity for N2O decomposition, such as MgO, zeolites, hydrotalcites, or mixtures of two or more thereof. Preference is given to using catalysts that contain no or essentially no zeolites, preferably less than 15% by weight of zeolites, in particular less than 5% by weight of zeolites.

[0252] Preferred support materials for Rh-containing compounds are ZrO2, TiO2, Al2O3, hydrotalcites, or zeolites, e.g., of the MFI structure type. These are described, for example, in Chemical Engineering and Technology 24 (2001) 281-285 or in Catalysis Today 35 (1997) 113-120. Particularly preferred supports for Rh-containing compounds are ZrO2, TiO2, and hydrotalcites. The Rh content of these catalysts is preferably 0.1 to 10 wt.%, more preferably 0.5 to 5 wt.%. Particularly preferably, Rh-containing catalysts contain CeO2 in addition to Rh. The proportion of CeO2 is preferably 5 to 50 wt.%, in particular 10 to 30 wt.%.

[0253] Preferred supports for Co-containing compounds are zeolites, or the preferred supports contain magnesium oxide. In the case of zeolites, Si-rich structural types such as MFI, BEA, FER, MEL, or MOR are particularly preferred. The preparation of such Co-doped zeolites is known to the person skilled in the art. In the case of magnesium oxide supports, these can be pure MgO or MgO-containing compounds such as hydrotalcites. Such catalysts are described, for example, in Appl. Catal. B: Environmental 7 (1996) 397-406 or Appl. Catal. B: Environmental 13 (1997) 69-79.

[0254] Particular preference is given to catalysts which consist essentially of at least one oxidic magnesium compound and at least one oxidic cobalt compound, wherein the content of oxidic cobalt compounds is in the range from 0.1 to 50 wt.% and the content of oxidic magnesium compounds is in the range from 50 to 99.9 wt.%, in each case based on the total mass of the catalyst, and at least 30 wt.% of the Co atoms present in the catalyst are in the chemically trivalent state. Such catalysts and their preparation are described in EP 1257 347 B1. Also particularly preferred when using oxidic Co compounds as the active component are catalysts having a support which consists of at least 50 wt.% MgO or of a mixed oxide which consists of at least 50 wt.% MgO, and wherein a cerium oxide functional layer is applied to the support.Such catalysts and their preparation are described in DE 102007038711 A1.

[0255] The N2O decomposition catalyst can be in the form of a shaped body of any size and geometry, preferably in geometries with a high surface-to-volume ratio and with the lowest possible pressure drop during flow. Typical geometries are all known in catalysis, such as cylinders, hollow cylinders, multi-hole cylinders, rings, granular fragments, trilobes, or honeycomb structures.

[0256] N2O reduction catalysts and NO XReduction catalysts are also known per se, and a wide variety of material classes can be used. Examples include metal-loaded zeolite catalysts, such as copper- or cobalt-loaded zeolite catalysts, or, in particular, iron-loaded zeolite catalysts, or precious metal catalysts or catalysts used in the well-known SCR (Selective Catalytic Reduction) processes.

[0257] Preferably, the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NOX reduction catalyst independently of one another contain a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably, independently of one another, an iron-loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU and / or MEL.

[0258] Preferably, each of the N2O decomposition catalyst and / or the N2O reduction catalyst and the NOX reduction catalyst independently comprise a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably, independently of one another, an iron-loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU, and / or MEL.

[0259] These can be different catalysts or the same catalysts. Iron-loaded zeolite catalysts used particularly preferably according to the invention contain essentially, preferably > 50 wt.%, in particular > 70 wt.%, of one or more iron-loaded zeolites. For example, in addition to an Fe-ZSM-5 zeolite, another iron-containing zeolite, such as an iron-containing FER-type zeolite, can be present in the catalyst used according to the invention.

[0260] In addition, the catalyst used according to the invention may contain further additives known to the person skilled in the art, such as binders.

[0261] The iron content of the preferred zeolites can be up to 25% based on the mass of zeolite, but preferably 0.1 to 10%.

[0262] The process according to the invention also includes the use of zeolites in which the lattice aluminum is partially isomorphously substituted by one or more elements, for example by one or more elements selected from B, Be, Ga, Fe, Cr, V, As, Sb and Bi. Also included is the use of zeolites in which the lattice silicon is substituted by one or more is isomorphously substituted by several elements, for example, by one or more elements selected from Ge, Ti, Zr, and Hf. Precise details on the composition or structure of the zeolites preferably used according to the invention are given in the Atlas of Zeolite Structure Types, Elsevier, 4th revised Edition 1996, which is hereby expressly incorporated by reference.

[0263] Zeolite catalysts that have been treated with steam ("steamed" catalysts) are very particularly preferably used in the process according to the invention. Such a treatment dealuminizes the zeolite lattice; this treatment is known per se to the person skilled in the art. These hydrothermally treated zeolite catalysts are characterized by particularly high activity in the process according to the invention. Preference is given to using hydrothermally treated zeolite catalysts that have been loaded with iron and in which the ratio of extra-lattice aluminum to lattice aluminum is at least 1:2, preferably 1:2 to 20:1.

[0264] The N2O decomposition catalyst and / or the N2O reduction catalyst as well as the NOX reduction catalyst preferably each independently comprise transition metal-loaded zeolites, more preferably each iron-loaded zeolites (Fe zeolites), even more preferably each iron-loaded zeolites of the same structural type, most preferably with the same external shape (e.g. honeycomb or pellet).

[0265] In preferred embodiments, the N2O decomposition catalyst and the N2O reduction catalyst are made of the same material.

[0266] In preferred embodiments, the N2O decomposition catalyst and the NOX reduction catalyst are made of the same material.

[0267] In preferred embodiments, the N2O reduction catalyst and the NOX reduction catalyst are made of the same material.

[0268] In preferred embodiments, the N2O decomposition catalyst, the N2O reduction catalyst and the NOX reduction catalyst are made of the same material.

[0269] Preferably, the exhaust gas is cooled after leaving the combustion plant, preferably the combustion device, during the optional and preferred step (b) of the process according to the invention, wherein steps (d1) and / or (d2) and / or (e) can introduce new heat. Preferred catalysts for the degradation of N2O and NO X

[0270] The inventive N2O decomposition catalysts, N2O reduction catalysts, and NO X Reduction catalysts independently preferably contain zeolitic materials (for the purpose of description also "zeolites") which are reacted with at least one transition metal (atomic numbers 21-30, 39-48, 57-80, 89-112) and / or with at least one lanthanide (also "lanthanide"). nid"; atomic numbers 57-71). For the purpose of description, transition metals and lanthanides are referred to collectively as "transition metals" for simplicity. Preferred transition metals are iron ("Fe zeolites"), copper ("Cu zeolites"), and cobalt ("Co zeolites"). Iron-loaded zeolitic materials (i.e., Fe zeolites) are particularly preferred and, in addition to iron, may also be loaded with or contain other transition metals, for example manganese, vanadium, chromium, nickel, or mixtures thereof.

[0271] The zeolitic materials according to the invention preferably exhibit high hydrothermal resistance. Particular preference is given to SiO2-rich zeolites, so-called "high-silica zeolites," which have a molar ratio of [SiO2] to [AlO2] units, and thus a molar Si / Al ratio, of at least 8, preferably at least 9, more preferably at least 10, even more preferably at least 11, most preferably at least 12, and especially at least 13.

[0272] Zeolitic materials preferred according to the invention essentially have a zeolite structure of the BEA, MFI, MOR, MEL, or FER structure type, more preferably of the MFI and BEA structure type, and even more preferably of the BEA structure type. For the MFI structure type, the ZSM-5 type is particularly preferred. Further information on the designation of the structure types of zeolitic materials and their composition can be found in the Atlas of Zeolite Structure Types, Elsevier, 4th revised edition 1996.

[0273] Particularly preferred N2O decomposition, N2O reduction, or NOx reduction catalysts according to the invention contain, independently of one another, at least 50 wt.% Fe zeolite based on the total weight of the zeolitic material, more preferably at least 70 wt.% Fe zeolite, wherein a single structural type or multiple structural types may be present. In preferred embodiments, in addition to Fe-BEA zeolite, another Fe zeolite of a different structural type is present, preferably Fe-MOR zeolite.

[0274] The loading (doping) of the zeolitic materials with the transition metals / lanthanides can be carried out using relevant methods for loading or doping zeolites with transition metals / lanthanides, which are known to those skilled in the art. Loading is preferably carried out starting from the commercially available H form or, preferably, NH4 form of the zeolitic materials by ion exchange with corresponding salts of the transition metals, either in the aqueous phase or by solid-state reaction. The loaded zeolitic materials thus obtained are subsequently calcined, preferably in air in an oven at temperatures in the range of 400 to 650°C. After calcination, the loaded zeolitic materials are thoroughly washed in distilled water, and the filtered-off loaded zeolitic materials are then dried.The loaded zeolitic materials thus obtained are preferably admixed with suitable binders, such as aluminosilicates, boehmite, or silica sol, and optionally with auxiliary agents for plasticizing or for producing slurries, and mixed. In preferred embodiments, the resulting mixtures are extruded into catalyst bodies (full catalysts) and then calcined. In other preferred embodiments, the resulting mixtures are coated on catalyst supports (supported catalysts) and finally calcined. These methods are also known to those skilled in the art and established in many technical applications.

[0275] The inventive N2O decomposition, N2O reduction, NO XReduction, NH3 oxidation, HCN degradation, and CO oxidation catalysts can be present independently of one another as shaped bodies of any size and geometry, preferably in geometries that have a high surface-to-volume ratio and through which the lowest possible pressure drop is generated. Typical geometries are all geometries known in catalysis, such as cylinders, hollow cylinders, multi-hole cylinders, rings, trilobes, or star-shaped extrudates. Monolithic catalyst elements with parallel channels, such as monolithic honeycombs, so-called "catalyst honeycombs," as known, for example, from the purification or denitrification of power plant or automotive exhaust gases, are particularly preferred. Catalyst honeycombs, honeycomb bodies, and honeycomb modules

[0276] The exhaust gas treatment system according to the invention or the catalyst beds comprised therein preferably comprises catalyst honeycombs, preferably a plurality of catalyst honeycombs, which are arranged parallel to one another in the exhaust duct, each with honeycomb channels aligned longitudinally to the flow direction of the exhaust gas. The geometry of the cross-sectional area of ​​the catalyst honeycombs (perpendicular to the flow direction of the exhaust gas) is, in principle, freely selectable. The catalyst honeycombs preferably have a rectangular or, in particular, square cross-sectional area, but other cross-sectional areas are also possible, in particular hexagonal, triangular, trapezoidal, etc. Suitable geometries are known to those skilled in the art. Accordingly, the term "honeycomb" is not limited, according to the invention, to a rectangular or square cross-sectional area.

[0277] If the exhaust gas treatment system according to the invention comprises a first reaction zone (first catalyst bed) and a second reaction zone (second catalyst bed) downstream in the flow direction of the exhaust gas, which is preferred according to the invention, the first and second reaction zones (the first and second catalyst beds) preferably have a plurality of catalyst honeycombs which are arranged parallel to one another with honeycomb channels each aligned longitudinally to the flow direction of the exhaust gas in the exhaust gas channel.

[0278] In preferred embodiments, several catalyst honeycombs, i.e., several monolithic honeycomb bodies, are combined to form a honeycomb module, preferably by a metal frame that is open in the direction of exhaust gas flow. Preferably, two, four, or six honeycomb bodies, preferably monolithic honeycomb bodies, are combined to form a honeycomb module. This modular design allows for effective utilization of the available cross-sectional area of ​​the exhaust duct and easy replacement of defective or deactivated honeycomb bodies.

[0279] The honeycomb bodies preferably have a rectangular cross-section. Preferably, the Rectangular cross-section, a first edge length (perpendicular to the flow direction of the exhaust gas) in the range of 5 to 20 cm, more preferably 10 to 15 cm, and a second edge length (also perpendicular to the flow direction of the exhaust gas) in the range of 5 to 20 cm, preferably 10 to 15 cm. The height of a honeycomb body (flow direction of the exhaust gas) is preferably in the range of 5 to 25 cm, preferably in the range of 7.5 to 15 cm.

[0280] The so-called cell density, i.e., the density of the channels of a single catalyst honeycomb, is preferably 150 to 500 cpsi, more preferably 180 to 450 cpsi (cells per square inch). 100 cpsi, i.e., 100 cells or honeycomb channels per square inch, correspond to approximately 15.5 catalyst channels per cm2.

[0281] The individual honeycomb modules are preferably stacked one above the other and next to each other in the direction of flow and secured by suitable holders so that the best possible use of the inflow area, i.e. cross-sectional area of ​​the exhaust duct, is achieved. Bypass flows between the individual honeycomb modules or in the outer edge region between the outer edge of the honeycomb modules and the inner wall of the exhaust duct should be avoided. For this purpose, suitable sealing materials are preferably applied between the individual honeycomb modules and between the outer honeycomb modules and the inner wall. In the case of larger wall distances, cover plates are used which are attached to the inner wall of the exhaust duct in the direction of flow in front of and / or behind the packing of the honeycomb modules. The cover plates are preferably covered with seals at the contact points with the honeycomb modules.Preferably, the honeycomb modules are arranged and sized so that the usable inflow area of ​​the catalyst is preferably at least 60% of the inner cross-sectional area of ​​the exhaust duct, more preferably at least 70%, even more preferably at least 80%.

[0282] In circular exhaust ducts or exhaust pipes, the gaps created in the edge area of ​​the honeycomb module packing, unless they can easily be filled with rectangular honeycomb modules, are preferably not filled with specially cut honeycomb modules, but rather closed with blanking plates. This has the advantage that when replacing used honeycomb modules, only standardized honeycomb modules need to be replaced, and no special adaptations are required.

[0283] When using exhaust pipes, individual, larger honeycomb bodies with a circular inflow cross-section adapted to the pipe cross-section can also be used. In a preferred embodiment, several of these bodies can also be arranged one behind the other in the flow direction. In this case, it is not necessary to combine several honeycomb bodies parallel to one another to form honeycomb modules.

[0284] In preferred embodiments, the honeycomb bodies or honeycomb modules are arranged in several layers offset along the longitudinal axis in the flow direction of the exhaust gas. Preferably, the honeycomb bodies or honeycomb modules are arranged in 2 to 5 layers, particularly preferably in 2 to 3 layers. Between the layers, i.e. between the end faces of the honeycomb bodies or honeycomb body modules, a distance is preferably provided, preferably in the range of 3 to 30 mm, more preferably 4 to 20 mm. The distance can enable intermediate, in particular radial, mixing of the gas stream emerging from a first layer of the honeycomb bodies or honeycomb body modules. Furthermore, it can be prevented that a possible slippage of unreacted reducing agent and / or of its not yet fully oxidized reaction products from the first layer of the honeycomb bodies propagates into a subsequent, second layer of the honeycomb bodies.

[0285] The supply and distribution of reducing agents for NO Xand optionally N2O is preferably carried out via a multiply branched piping system provided with a large number of openings or nozzles, which is arranged in the exhaust gas duct or in the exhaust gas line in the flow direction upstream of the respective catalyst bed, preferably the packing of the catalyst honeycombs as honeycomb bodies or honeycomb body modules.

[0286] The distribution pipes are preferably designed in the form of grids or in the form of concentrically connected circles, which extend as far as possible over the cross-sectional area of ​​the exhaust gas duct or the inflow area of ​​the catalyst bed.

[0287] The specific design and dimensioning of these distributors, including suitable outlet nozzles, is part of the expertise in catalytic exhaust gas purification technology and is widely used, for example, in the exhaust gas purification of coal-fired power plants. NH3 oxidation catalyst

[0288] NH3 oxidation catalysts are known to experts.

[0289] The NH3 oxidation catalyst is preferably platinum group metal-free, more preferably noble metal-free.

[0290] For the purposes of this description, "platinum group metal-free" means that it contains essentially no platinum group metals (i.e., Ru, Rh, Pd, Os, Ir, Pt). However, analytically detectable traces of platinum group metals may be present. For the purposes of this description, "precious metal-free" means that it contains essentially no precious metals. However, analytically detectable traces of precious metals may be present.

[0291] The NH3 oxidation catalyst is preferably an iron- or copper-loaded zeolite; preferably an iron- or copper-loaded zeolite of the MFI, BEA, FER, MOR, FAU, AEI, and / or MEL structural type (hereinafter referred to as "NH3 oxidation-active, iron- or copper-loaded zeolite catalyst").

[0292] Preferred platinum group metal-free NH3 oxidation catalysts are selected from transition metal oxides (e.g. of Fe, Mn, Cu, Cr, Co, Ni ...), metal-loaded zeolites, e.g. described ben in Handbook of Heterogeneous Catalysis, Wiley-VCH, Edited by Ertl, Knötzinger, Schüth, Weitkamp, ​​2nd Ed. 2008, Volume 5, Chapter 11.5 “Solid Catalysts for the Oxidation of Volatile Organic Compounds”.

[0293] Preferred NH3 oxidation catalysts include - cobalt-containing catalysts; in particular Co3O4; mixed oxides derived from Co3O4 (Co3-yMyO4), which preferably crystallize in the spinel structure like Co3O4, where M is preferably selected from Zn, Cu, Fe, Mn, and V; cobalt-loaded zeolites, preferably of the structure type MFI, BEA, FER, Mor, FAU, CHA, or AFI; - manganese-containing catalysts; in particular MnO X with x = 1-2; of MnO X derived mixed oxides (Mn x-y M y O x), where M is preferably selected from Zn, Cu, Fe and Mn; manganese-loaded zeolites, preferably of the structure type MFI, BEA, FER, Mor, FAU, CHA or AFI; - copper-containing catalysts; in particular CuOX with x = 0.5-1; mixed oxides derived from CuOX (Cux-yMyOx), where M is preferably selected from Zn, Co, Fe and Mn; copper-loaded zeolites, preferably of the structure type MFI, BEA, FER, Mor, FAU, CHA, AFI; - silver-containing catalysts; in particular supported, preferably supported on Al2O3, TiO2, or SiO2, more preferably e.g. X% Ag / TiO2, X% Ag / Al2O3, or X% Ag / SiO2, each with X=1-10.

[0294] In preferred embodiments, the device according to the invention contains no further NH3 oxidation catalyst besides the iron or copper loaded zeolite.

[0295] In preferred embodiments, the NH3 oxidation catalyst, preferably the NH3 oxidation-active, iron-loaded zeolite catalyst, has a molar ratio of iron to zeolitic aluminum n(Fe) / n(Al) of less than 0.50 to greater than 0.05; preferably less than 0.40 to greater than 0.05, more preferably less than 0.25 to greater than 0.05, even more preferably less than 0.15 to greater than 0.05.

[0296] In preferred embodiments, the NH3 oxidation catalyst, preferably the NH3 oxidation-active, copper-loaded zeolite catalyst, has a molar ratio of copper to zeolitic aluminum n(Cu) / n(Al) of less than 1.00 to greater than 0.10; preferably less than 0.80 to greater than 0.10, more preferably less than 0.50 to greater than 0.10, even more preferably less than 0.30 to greater than 0.10.

[0297] Surprisingly, it was found that iron- or copper-loaded zeolites, in which only a part of the potentially available cation sites are occupied by Fe or Cu ions, so that the remaining cation sites are essentially saturated by protons, exhibit a significantly increased activity for the oxidation of NH3 with free oxygen.

[0298] The ratio of iron or copper to zeolitic aluminum can be adjusted by selecting the Al content during the synthesis of the zeolitic material, in particular by the proportions of the selected Si and Al starting materials, as well as by the subsequent loading with iron or copper ions.

[0299] In the synthesis of zeolites, the selected Si and Al starting materials are usually heated in an alkaline solution, often under elevated pressure, which causes crystallization to form microporous aluminosilicates, the zeolites, composed of three-dimensionally linked AlO2 and SiO2 units. By carefully selecting the synthesis conditions, for example by adding structure-directing reagents such as organic cations, not only the Si / Al ratio and thus the Al content, but also the structural type of the zeolite can be specifically adjusted or controlled. The synthesis methods are industrially established. Zeolites of various structural types with different Si / Al ratios and loaded with different cations, e.g. in Na or NH4 form, are commercially available.

[0300] Using suitable methods known to those skilled in the art, such as liquid-phase or solid-state ion exchange, the cations contained in the zeolite, such as NH4+, can be specifically exchanged for other cations, such as iron or copper ions (J. Weitkamp, ​​L. Puppe, Catalysis and Zeolites – Fundamental and Applications, Springer-Verlag Berlin Heidelberg New York, 1999 or Kucherov, AV Slinkin, A. a.: Solid state reactions as a method of introducing transition metals cations into high-silica zeolites, Russ. Chem. Rev. 1992, Vol. 61, No. 9, pp. 925-943). If all of the negative charges generated by the AlO2 units are compensated by cations, the so-called degree of exchange is 100%.

[0301] The exact Al content of the zeolitic material or the catalyst moldings produced from it, as well as the Fe content, can be determined by X-ray fluorescence analysis (XRF). This is conveniently performed according to DIN EN 169-2 (Section 5) after determining the loss on ignition and after lithium tetraborate digestion.

[0302] If the Al content of the underlying zeolitic material is to be subsequently determined on the finished molded body, it must be noted that the molded body may also contain Al-based binder components that cannot be distinguished from zeolitic Al by XRF. In this case, an additional investigation of the molded body is required, e.g., using 27Al solid-state NMR, which allows differentiation between the Al bound in the zeolite structure and the extra-lattice Al. Details on the principles, implementation, and evaluation of such investigations are known to experts (J. Weitkamp, ​​L. Puppe, Catalysis and Zeolites – Fundamental and Applications, Springer-Verlag Berlin Heidelberg New York, 1999, Chapter 4.2 (NMR Spectroscopy; especially sections 4.2.4.1( 29 Si MAS NMR Spectroscopy of SiO4 Tetrahedra in the Zeolite Framework) and 4.3.4.2 ( 27 Al NMR Spectroscopy of Framework and Non-Framework Aluminum in Zeolites)).

[0303] Preferably, the NH3 oxidation catalyst, preferably the NH3 oxidation-active, iron-loaded zeolite catalyst, has a total iron content (expressed as the mass content of Fe2O3) of less than 10.0 wt.% to greater than 2.0 wt.%, preferably of less than 7.0 wt.% to greater than 2.0 wt.%, more preferably of less than 5.0 wt.% to greater than 2.0 wt.% and even more preferably of less than 4.0 wt.% to greater than 2.0 wt.%.

[0304] Preferably, the NH3 oxidation catalyst, preferably the NH3 oxidation-active, copper-loaded zeolite catalyst, has a total copper content (expressed as mass content of Cu2O) from less than 9.0 wt.% to greater than 1.5 wt.%; preferably from less than 6.5 wt.% to greater than 1.5 wt.%, more preferably from less than 4.5 wt.% to greater than 1.5 wt.% and even more preferably from less than 3.5 wt.% to greater than 1.5 wt.%.

[0305] In preferred embodiments, the NH3 oxidation catalyst, preferably the NH3 oxidation-active, iron- or copper-loaded zeolite catalyst, is configured for the selective oxidation of NH3 with O2 to N2 and H2O, and is filled as a particulate bed, the particles of which have an equivalent diameter of 3.5 to 5.5 mm, which is defined as the diameter of a spherical particle of the same volume, and wherein the ratio of the outer, geometrically detectable surface of the particles to the volume of the particulate bed is 1000 m2 / m3 to 1500 m2 / m3, in an amount of 8.0±0.5 mL in an isothermally operated, axially flowing tubular reactor with an inner diameter of 20±3 mm, subjected to a volume flow of a gas mixture consisting of 500±50 ppmv NH3, 2.5±0.1 vol% O2 and 0.30±0.05 vol% H2O in N2 at a space velocity of 10 based on standard conditions (0°C; 1.01325 bara).000±500 h-1, a total pressure of 6±0.5 bara and a temperature of 380°C±5 K an NH3 conversion of at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80%, in particular at least 90%.

[0306] In preferred embodiments, the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NOX reduction catalyst and / or the NH3 oxidation catalyst independently of one another have a honeycomb-shaped monolithic structure.

[0307] In preferred embodiments, the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NOX reduction catalyst and / or the NH3 oxidation catalyst independently of one another have a honeycomb-shaped monolithic structure.

[0308] In preferred embodiments, the NH3 oxidation catalyst and the N2O decomposition catalyst are made of the same material.

[0309] In preferred embodiments, the NH3 oxidation catalyst and the N2O reduction catalyst are made of the same material.

[0310] In preferred embodiments, the NH3 oxidation catalyst and the NOX reduction catalyst are made of the same material.

[0311] In preferred embodiments, the NH3 oxidation catalyst, the NOX reduction catalyst, and the N2O decomposition catalyst are made of the same material. Preferred variants of combinations of steps (d) and (e):

[0312] In preferred embodiments, steps (d1) and / or (d2) and / or (e) of the process according to the invention are carried out at different temperatures, ie at different temperatures carried out at different levels, whereby a step carried out earlier in time or upstream in the flow direction of the exhaust gas preferably takes place at a higher temperature than a step carried out later in time or downstream in the flow direction of the exhaust gas.

[0313] Depending on the type of catalyst used, however, the steps may not be completely separable from one another, neither spatially nor temporally. If a catalyst used is suitable for catalyzing several of the steps (d1), (d2) and (e) at the same time, these steps may occur simultaneously and / or sequentially. In the flow direction of the exhaust gas, individual segments of one and the same catalyst can be considered, through which the exhaust gas flows one after the other and on which different reactions may dominate. Which reaction dominates in which segment depends in particular on the respective reaction kinetics, the local temperature and the local concentrations of the reactants, possibly including the concentration of reducing agent and possibly including the concentration of co-catalytically active species.

[0314] The exhaust gas treatment system according to the invention serves in particular to carry out steps (d) and (e) of the process according to the invention. However, it is also possible for further steps to be carried out within the exhaust gas treatment system in addition to steps (d) and (e), and for chemical reactions to take place.

[0315] This preferably relates to the installation of a catalyst bed arranged downstream in the flow direction of the exhaust gas for the oxidation of incompletely converted reducing agents or their incompletely oxidized reaction products, e.g., for the oxidation of NH3 (NH3 oxidation catalyst) or CO (CO oxidation catalyst; when using hydrocarbons as reducing agents). In such embodiments, the exhaust gas is preferably cooled before being introduced into the downstream catalyst bed, i.e., the oxidation of NH3 and / or CO preferably takes place at a lower temperature than steps (d) and (e).

[0316] When carrying out steps (d) and (e) of the process according to the invention, there are various preferred variants of the process according to the invention, which may differ from one another with regard to the sequence of the reactions taking place, the catalysts used, the reducing agents used, the space velocities and other reaction conditions.

[0317] In preferred embodiments, these reactions are carried out in a common reaction zone (catalyst bed) which is equipped upstream with a device for metering reducing agent into the exhaust gas.

[0318] In other preferred embodiments, these reactions are carried out in two successively arranged, separate reaction zones (catalyst beds), of which preferably at least one reaction zone, preferably both reaction zones independently of one another, are equipped upstream with a device for metering reducing agent into the exhaust gas. is or are. The exhaust gas then flows first through the first reaction zone and then through the second reaction zone.

[0319] Particularly preferred variants / embodiments include [a] (d2) the chemical reduction of N2O with NH3 and (e) the chemical reduction of NO X with NH3, preferably together in one reaction zone; [b] (d2) the chemical reduction of N2O with hydrocarbon (CH4, natural gas, etc.) and (e) the chemical reduction of NO Xwith NH3, preferably together in one reaction zone; [c] (d1) the decomposition of N2O and (e) the chemical reduction of NO Xwith NH3, preferably together in one reaction zone; [d] (d1) the decomposition of N2O and (d2) the chemical reduction of N2O with NH3 and (e) the chemical reduction of NOX with NH3, preferably together in one reaction zone; [e] (d1) the decomposition of N2O and (d2) the chemical reduction of N2O with hydrocarbon (CH4, natural gas, etc.) and (e) the chemical reduction of NOX with NH3, preferably together in one reaction zone; [f] (d1) the decomposition of N2O, preferably in a first reaction zone; and subsequently (e) the chemical reduction of NOX with NH3, preferably in a second reaction zone; [g] (d1) the incomplete decomposition of N2O, preferably in a first reaction zone; and subsequently (d2) the chemical reduction of residual N2O with NH3 and (e) the chemical reduction of NOX with NH3, preferably in a second reaction zone; [h] (d1) the incomplete decomposition of N2O, preferably in a first reaction zone; and subsequently (d2) the chemical reduction of residual N2O with hydrocarbon (CH4, natural gas, etc.) and (e) the chemical reduction of NOX with NH3, preferably in a second reaction zone; [i] (d1) the incomplete decomposition of N2O, preferably in a first reaction zone; and subsequently (d1*) the decomposition of residual N2O and (e) the chemical reduction of NOX with NH3, preferably in a second reaction zone; [j] (d1) the incomplete decomposition of N2O, preferably in a first reaction zone; and subsequently (d1*) the decomposition of residual N2O and (d2) the chemical reduction of residual N2O with NH3 (e) and the chemical reduction of NOX with NH3, preferably in a second reaction zone; [k] (d1) the incomplete decomposition of N2O, preferably in a first reaction zone; and subsequently (d1*) the decomposition of residual N2O and (d2) the chemical reduction of residual N2O with hydrocarbon (CH4, natural gas, etc.) and (e) the chemical reduction of NO. Xwith NH3, preferably in a second reaction zone; [l] (e) the incomplete chemical reduction of NO X , preferably in a first reaction zone; and subsequently (d1) the decomposition of N2O and (e*) the chemical reduction of residual NO X with NH3, preferably in a second reaction zone; [m] (e) the incomplete chemical reduction of NO X , preferably in a first reaction zone; and subsequently (d1) the decomposition of N2O and (d2) the chemical reduction of N2O with NH3 and (e*) the chemical reduction of residual NOX with NH3, preferably in a second reaction zone; or [n] (e) the incomplete chemical reduction of NO X , preferably in a first reaction zone; and subsequently (d1) the decomposition of N2O and (d2) the chemical reduction of N2O with hydrocarbon (CH4, natural gas, etc.) and (e*) the chemical reduction of residual NO Xwith NH3, preferably in a second reaction zone.

[0320] However, this does not mean that the explicitly mentioned reactions must be the only reactions that take place in the respective reaction zone. Depending on the catalyst used, it is rather preferred according to the invention that additional reactions also take place simultaneously, which are not explicitly mentioned but can proceed in parallel. The explicitly mentioned reactions are therefore only those reactions that at least take place in the respective variant / embodiment.

[0321] When NOX, N2O, and NH3 are present in the mixture and the catalyst used catalyzes both the chemical reduction of NOX with NH3 and the chemical reduction of N2O with NH3, the chemical reduction of NOX with NH3 is typically significantly faster than the chemical reduction of N2O with NH3. If the catalyst used also catalyzes the decomposition of N2O, the decomposition of N2O is typically superimposed on the chemical reduction of N2O with NH3, whereby the extent of the chemical reduction of N2O can be increased by increasing the amount of NH3 added.

[0322] For the purpose of description, "*" indicates a process sub-step which was previously only incompletely carried out in a similar process sub-step, whereby the process sub-step marked with "*" subsequently continues the previously only incompletely carried out process sub-step, possibly however in a different reaction zone or a different catalyst bed. As with all other process steps, unless expressly stated otherwise, the result achieved at the end of all process sub-steps is not quantitatively determined. Thus, if, for example, NOX is chemically incompletely reduced in a first process sub-step (e), the fact that process sub-step (e*) is subsequently carried out does not necessarily require that at the end of process sub-step (e*) the total amount of NO Xmust have been completely chemically reduced, ie down to 0.0 ppmv. Rather, it is quite possible that at the end of process step (e*) a residual amount of NO X is present.

[0323] The exhaust gas treatment system includes at least one injection point for reducing agents. The exhaust gas treatment system may include multiple injection points for reducing agents.

[0324] The type of introduction of the reducing agent into the exhaust gas stream to be treated can be freely designed according to the invention, as long as this is in front of the N2O reduction catalyst or NO X-reduction catalyst. The reducing agent can be introduced in the form of a gas or a liquid or aqueous solution, which evaporates in the exhaust gas stream to be treated. It is fed in through a suitable device, such as a corresponding pressure valve or appropriately designed nozzles, which leads into a mixer for the exhaust gas stream to be treated and the supplied reducing agent. When using different reducing agents for NOX and N2O, the feed and introduction into the exhaust gas can take place separately or together.

[0325] When the catalyst beds are designed as a packing of catalyst honeycombs or honeycomb modules, the supply and distribution of the reducing agents for NOX and optionally N2O to the one or more reaction zones (catalyst beds) is preferably carried out via a multiply branched pipe system provided with a plurality of openings or nozzles, which is arranged in the flow direction of the exhaust gas upstream of the respective reaction zone (catalyst bed), ie the packing of the catalyst honeycombs or honeycomb modules.

[0326] The distributors are preferably designed in the form of grids or concentrically connected circles, which extend as far as possible over the cross-sectional area of ​​the exhaust gas duct or the inflow area of ​​the reaction zone (catalyst bed).

[0327] The specific design and dimensioning of these distributors, including suitable outlet nozzles, is part of the specialist knowledge in catalytic exhaust gas purification technology and is widely used, for example, in the exhaust gas purification of coal-fired power plants.

[0328] The exhaust gas treatment system according to the invention can comprise a single reaction zone. In this case, the catalyst used in this single reaction zone serves as an N2O decomposition catalyst and / or N2O reduction catalyst as well as a NOx reduction catalyst. In this case, steps (d) and (e) of the process according to the invention take place essentially simultaneously within this reaction zone. However, it should be noted that the kinetics of the individual reactions can be quite different. For example, depending on the catalyst material used, the chemical reduction of NO Xwith NH3 as a reducing agent, for example, can be significantly faster than the chemical reduction of N2O with NH3. Therefore, if NOX and N2O are present in the mixture and NH3 is fed in as a reducing agent, different reactions take place in the front section of the single reaction zone than in the rear section of the single reaction zone. Due to the faster kinetics, the chemical reduction of NO predominantly occurs in the front section. X and only in the rear section, when the majority of the NO X is degraded, the chemical reduction of N2O takes place.

[0329] Alternatively, the exhaust gas treatment system can comprise multiple reaction zones, which is preferred according to the invention. If multiple reaction zones are included, they are preferably arranged one behind the other, i.e., the exhaust gas flows through them successively, first through the first reaction zone, then through the second reaction zone, and optionally subsequently through the third reaction zone.

[0330] In preferred embodiments, the reaction zones are each spatially separated catalyst beds.

[0331] In preferred embodiments, the exhaust gas passes through the steps of the process according to the invention in one of the following orders: (i) (a) → (b) → (c) → (d1) → (e); wherein step (d1) preferably takes place in a first reaction zone; and step (e) takes place in a second reaction zone; (ii) (a) → (b) → (c) → (e) → (d2); wherein step (e) preferably takes place in a first reaction zone; and step (d2) takes place in a second reaction zone; (iii) (a) → (b) → (c) → (e) → (d2) → (d1); wherein step (e) preferably takes place in a first reaction zone; step (d2) takes place in a second reaction zone; and step (d1) takes place in a third reaction zone; (iv) (a) → (b) → (c) → (e) → (d1)+(d2); wherein preferably step (e) takes place in a first reaction zone; and step (d1) and step (d2) take place in a second reaction zone; (v) (a) → (b) → (c) → (e) → (d1); wherein preferably step (e) takes place in a first reaction zone;and step (d1) takes place in a second reaction zone; (vi) (a) → (b) → (c) → (d1)+(e) → (e*); wherein preferably step (d1) and incomplete step (e) take place in a first reaction zone; and the remaining step (e*) takes place in a second reaction zone; (vii) (a) → (b) → (c) → (d1)+(e) → (e*)+(d2); wherein preferably step (d1) and incomplete step (e) take place in a first reaction zone; and step (d2) and the remaining step (e*) take place in a second reaction zone; (viii) (a) → (b) → (c) → (d1)+(d2)+(e) → (d1*)+(d2*)+(e*); wherein preferably incomplete step (d1) and incomplete step (d2) and incomplete step (e) take place in a first reaction zone, which preferably contains no zeolitic material as catalyst; and the remaining step (d1*) and the remaining step (d2*) and the remaining step (e*) take place in a second reaction zone, which preferably contains zeolitic material as catalyst;(ix) (a) → (b) → (c) → (d1)+(d2)+(e) → (d1*)+(d2*)+(e*); wherein preferably incomplete step (d1) and incomplete step (d2) and incomplete step (e) take place in a first reaction zone which preferably contains zeolitic material as catalyst; and the remaining step (d1*) and the remaining step (d2*) and the remaining step (e*) take place in a second reaction zone which preferably contains an NO as catalyst; X -sensitive N2O decomposition catalyst; (x) (a) → (b) → (c) → (d1) → (d1*)+(d2)+(e); wherein step (d1) preferably takes place incompletely in a first reaction zone which preferably contains zeolitic material as catalyst; and the remaining step (d1*) as well as step (d2) and step (e) take place in a second reaction zone which preferably contains zeolitic material as catalyst; (xi) (a) → (b) → (c) → (d1) → (d1*)+(d2)+(e); wherein step (d1) preferably takes place incompletely in a first reaction zone which preferably contains a NOX-sensitive N2O decomposition catalyst as catalyst; and the remaining step (d1*) as well as step (d2) and step (e) take place in a second reaction zone which preferably contains zeolitic material as catalyst.

[0332] However, it is also possible for multiple reaction zones to be realized by a single catalyst bed. Two reaction zones on a common catalyst bed can be formed, in particular, by feeding reducing agent into the center (or another position along the longitudinal extent) of the catalyst bed. Upstream of the feed point, no reducing agent is then present, so that steps (d2) and (e) of the process according to the invention cannot take place in the absence of reducing agent. The decomposition of N2O then essentially takes place upstream according to step (d1) (first reaction zone). Downstream of the feed point, reducing agent is present, so that steps (d2) and (e) of the process according to the invention can take place, optionally overlaid by step (d1) of the process according to the invention (second reaction zone).In this case too, due to the different reaction kinetics, different reactions may occur in the front section of each reaction zone than in the rear section of each reaction zone; however, the first reaction zone and the second reaction zone differ from each other in that, in the absence of reducing agent, no chemical reduction of N2O and no chemical reduction of NOX takes place in the first reaction zone.

[0333] In particularly preferred embodiments, the exhaust gas treatment system comprises a first reaction zone and a second reaction zone. Additional reaction zones may be present.

[0334] In preferred embodiments, the first reaction zone and the second reaction zone are spatially separated from one another. In this case, they are preferably separate catalyst beds. With spatial separation of the catalyst beds, it is possible to adjust the temperature of the second catalyst bed or of the gas stream entering it by removing or adding heat so that it is lower or higher than that of the first catalyst bed. The temperature of an individual catalyst bed can conveniently be determined as the arithmetic mean of the temperature of the gas stream at the inlet and outlet of the catalyst bed.

[0335] In preferred embodiments, the temperature in the first reaction zone (in the first catalyst bed) is higher than the temperature in the second reaction zone (in the second catalyst bed).

[0336] Preferably, the temperature in the first reaction zone is at least 450°C, more preferably at least 500°C, even more preferably at least 550°C, most preferably at least 600°C and in particular at least 650°C.

[0337] Preferably, the temperature in the second reaction zone (in the second catalyst bed) is at most 600°C, more preferably at most 550°C, even more preferably at most 500°C, most preferably at most 450°C and in particular at most 400°C.

[0338] In preferred embodiments, the temperature in the first reaction zone (in the first catalyst bed) is relatively higher by at least 20°C, more preferably by at least 40°C, even more preferably by at least 60°C, most preferably by at least 80°C and in particular by at least 100°C than the temperature in the second reaction zone (in the second catalyst bed).

[0339] In other preferred embodiments, the temperature in the second reaction zone (in the second catalyst bed) is relatively higher than the temperature in the first reaction zone (in the first catalyst bed) by at least 20°C, more preferably by at least 40°C, even more preferably by at least 60°C, most preferably by at least 80°C and in particular by at least 100°C.

[0340] In preferred embodiments, the temperature in the first reaction zone (in the first catalyst bed) is relatively higher than the temperature in the second reaction zone (in the second catalyst bed) by at least 120°C, more preferably by at least 140°C, even more preferably by at least 160°C, most preferably by at least 180°C and in particular by at least 200°C.

[0341] In other preferred embodiments, the temperature in the second reaction zone (in the second catalyst bed) is relatively higher than the temperature in the first reaction zone (in the first catalyst bed) by at least 120°C, more preferably by at least 140°C, even more preferably by at least 160°C, most preferably by at least 180°C and in particular by at least 200°C.

[0342] Preferably, the temperature of the exhaust gas at the inlet into the first reaction zone (into the first catalyst bed) is at least 400°C, more preferably at least 425°C, even more preferably at least 450°C, most preferably at least 500°C.

[0343] Preferably, the temperature of the exhaust gas at the outlet from the second reaction zone (from the second catalyst bed) is at most 600°C, more preferably at most 550°C, even more preferably at most 500°C.

[0344] In preferred embodiments, the temperature of the exhaust gas at the inlet into the first reaction zone (into the first catalyst bed) is relatively higher by at least 20K, more preferably by at least 40K, even more preferably by at least 60K, most preferably by at least 80K and in particular by at least 100K than the temperature of the exhaust gas at the inlet into the second reaction zone (into the second catalyst bed).

[0345] In preferred embodiments, the temperature of the exhaust gas at the inlet into the second reaction zone (into the second catalyst bed) is relatively higher by at least 10K, more preferably by at least 20K, even more preferably by at least 30K, most preferably by at least 40K and in particular by at least 50K than the temperature of the exhaust gas at the inlet into the first reaction zone (into the first catalyst bed).

[0346] In preferred embodiments, the temperature in the first reaction zone (in the first catalyst bed) is relatively higher by at least 120K, more preferably by at least 140K, even more preferably by at least 160K, most preferably by at least 180K and in particular by at least 200K than the temperature in the second reaction zone (in the first catalyst bed).

[0347] In preferred embodiments, the temperature in the second reaction zone (in the second catalyst bed) is relatively higher by at least 120K, more preferably by at least 140K, even more preferably by at least 160K, most preferably by at least 180K and in particular by at least 200K than the temperature in the first reaction zone (in the first catalyst bed).

[0348] In other preferred embodiments, the first reaction zone and the second reaction zone are spatially connected to one another. In this case, they preferably comprise a common catalyst bed, with external influences causing the division into reaction zones, particularly the location of the reducing agent feed, so that reducing agent is not present equally throughout the catalyst bed.

[0349] Preferably, the first reaction zone and the second reaction zone are arranged in a common container.

[0350] Preferably, the temperature of the exhaust gas in the first reaction zone and in the second reaction zone is, independently of one another, at most 500°C, preferably, independently of one another, it is in the range from 350 to 450°C.

[0351] In preferred embodiments, the space velocity in the first reaction zone is greater than the space velocity in the second reaction zone. Preferably, the space velocity in the first reaction zone is at least a factor of 1.2, more preferably at least a factor of 1.4, even more preferably at least a factor of 1.6, most preferably at least a factor of 1.8, and in particular at least a factor of 2.0 greater than the space velocity in the second reaction zone.

[0352] In other preferred embodiments, the space velocity in the second reaction zone is greater than the space velocity in the first reaction zone. Preferably, the space velocity in the second reaction zone is at least a factor of 1.5, more preferably at least a factor of 2.0, even more preferably at least a factor of 3.0, most preferably at least a factor of 5.0, and especially at least a factor of 10.0 greater than the space velocity in the first reaction zone.

[0353] For the purposes of the invention, "space velocity" is understood as the quotient of the volume flow of the gas mixture passed through the catalyst bed (measured at 0 °C and 1.014 bara and usually expressed in Nm3 h-1) relative to the volume of the catalyst or catalyst bed. The space velocity can thus be adjusted via the volume flow of the gas and / or the amount of catalyst.

[0354] Preferably, the exhaust gas has a temperature of at least 300°C, more preferably at least 350°C, even more preferably at least 400°C, most preferably at least 425°C, and in particular at least 450°C when entering the exhaust gas treatment plant.

[0355] Preferably, the exhaust gas has a temperature of at least 500°C, more preferably at least 550°C, even more preferably at least 600°C, most preferably at least 625°C, and in particular at least 650°C when entering the exhaust gas treatment plant.

[0356] Preferably, the exhaust gas has a temperature of at most 825°C, more preferably at most 800°C, even more preferably at most 775°C, most preferably at most 750°C, and in particular at most 725°C when entering the exhaust gas treatment plant.

[0357] Preferably, the exhaust gas has a temperature of at most 700°C, more preferably at most 650°C, even more preferably at most 600°C, most preferably at most 550°C, and in particular at most 500°C when entering the exhaust gas treatment plant.

[0358] In preferred embodiments, the exhaust gas has a pressure of at most 1.4 bara, preferably of at most 1.3 bara, more preferably of at most 1.2 bara upon entering the exhaust gas treatment system.

[0359] In other preferred embodiments, the exhaust gas has a negative pressure upon entering the exhaust gas treatment system, preferably of approximately -5 mbar. This has the advantage that, in the event of any leaks, no gas is released into the environment.

[0360] Preferably, the exhaust gas upon entry into the exhaust gas treatment plant has an oxidation degree of NOX of at least 10%, more preferably at least 20%, even more preferably at least 30%, most preferably at least 40%, and in particular at least 50%.

[0361] Preferably, the exhaust gas has an oxidation level of NO when entering the exhaust gas treatment system X of at most 90%, more preferably at most 80%, even more preferably at most 70%, most preferably at most 60%, and in particular at most 50%.

[0362] Depending on the combustion temperature, the degree of oxidation can also be significantly lower, with the degree of oxidation decreasing with increasing combustion temperature. Preferably, the exhaust gas entering the exhaust gas treatment system has an oxidation degree of NO X of at most 15%, more preferably at most 12.5%, even more preferably at most 10%, most preferably at most 7.5%, and in particular at most 5.0%.

[0363] Preferably, the exhaust gas has an O2 content of less than 2.0 vol.% upon entry into the exhaust gas treatment system.

[0364] Preferably, the exhaust gas has an O2 content of more than 4.0 vol.% upon entry into the exhaust gas treatment system.

[0365] In step (d) of the process according to the invention, the N2O content in the exhaust gas is reduced. This can be achieved in various ways, namely by (d1) decomposition of N2O on an N2O decomposition catalyst and / or by (d2) chemical reduction of N2O with a reducing agent on an N2O reduction catalyst. Step (d) of the process according to the invention is carried out in the exhaust gas treatment system.

[0366] In preferred embodiments, step (d) comprises reducing the content of N2O in the exhaust gas by (d1) decomposing N2O on a N2O decomposition catalyst.

[0367] In preferred embodiments, the N2O decomposition catalyst comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU, and / or MEL.

[0368] In other preferred embodiments, the N2O decomposition catalyst is a NOX-sensitive N2O decomposition catalyst within the meaning of the invention, which has already been described in more detail above. In this case, the exhaust gas preferably first undergoes step (e), i.e., the NOX content in the exhaust gas is first reduced, preferably quantitatively, by chemical reduction of NOX with a reducing agent on a NOX reduction catalyst, before the exhaust gas subsequently comes into contact with the NOX-sensitive N2O decomposition catalyst.

[0369] Preferably, the N2O decomposition catalyst is arranged in a radial basket through which the flow is axial.

[0370] Preferably, the N2O decomposition catalyst is particulate and comprises at least 50 particles.

[0371] In preferred embodiments, step (d) comprises reducing the N2O content in the exhaust gas by (d2) chemically reducing N2O with reducing agent on an N2O reduction catalyst; preferably wherein the N2O reduction catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU and / or MEL.

[0372] Preferably, the N2O reduction catalyst is arranged in a radial basket through which the flow is axial.

[0373] Preferably, the N2O reduction catalyst is particulate and comprises at least 50 particles.

[0374] In preferred embodiments, step (d) comprises reducing the N2O content in the exhaust gas - both by (d1) decomposition of N2O on an N2O decomposition catalyst; preferably wherein the N2O decomposition catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU and / or MEL; - thus also by (d2) chemical reduction of N2O with reducing agent on an N2O reduction catalyst; preferably wherein the N2O reduction catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite;more preferably an iron-loaded zeolite of the structural type MFI, BEA, FER, MOR, FAU and / or MEL. ;

[0375] Preferably, the reducing agent in step (d2) is selected from NH3, hydrocarbons, CO, H2 and mixtures thereof; preferably NH3.

[0376] In preferred embodiments, the reducing agent in step (d2) is NH3, which is preferably used in an amount of 0.5 to 2.0 molar parts, more preferably in an amount of 0.8 to 1.8 molar parts, based on a molar proportion of N2O to be chemically reduced, ie based on the amount of N2O at the inlet into the catalyst bed of the N2O reduction catalyst.

[0377] In preferred embodiments, the reducing agent in step (d2) is NH3, which is preferably used in an amount of 0.5 to 2.0 molar fractions, more preferably in an amount of 0.8 to 1.8 molar fractions, based on the molar amount of N2O in the exhaust gas at the inlet to the catalyst bed of the N2O reduction catalyst. This amount is additive to any amount of NH3 required for NOX reduction, provided that step (e) also takes place in the catalyst bed of the N2O reduction catalyst.

[0378] In other preferred embodiments, the reducing agent is a hydrocarbon or a mixture of several hydrocarbons, which are preferably used in an amount of 0.2 to 1.0 molar fractions, more preferably 0.2 to 0.7 molar fractions, based on the molar amount of N2O in the exhaust gas at the inlet to the catalyst bed of the N2O reduction catalyst. This amount is also additive to the possibly required amount of NH3 for NO.X -reduction, provided that step (e) also takes place in the catalyst bed of the N2O reduction catalyst.

[0379] Likewise, the reducing agent may already be present in the exhaust gas, e.g. as residual combustion gases and / or their oxidation products. The process according to the invention then not only reduces the content of nitrogen oxides (NO X and N2O), but also the content of these contaminants (residual combustion gases and / or their oxidation products).

[0380] In step (e) of the process according to the invention, the content of NO X (ie NO and NO2) in the exhaust gas. This is achieved by chemical reduction of NO X with reducing agent on a NO X Reduction catalyst. Step (e) of the process according to the invention is also carried out in the exhaust gas treatment plant.

[0381] Preferably, the NO contains X-Reduction catalyst comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt or copper loaded zeolite; more preferably an iron loaded zeolite; even more preferably an iron loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU and / or MEL.

[0382] Preferably, the NOX reduction catalyst is arranged in a radial basket through which the flow is axial.

[0383] Preferably, the NOX reduction catalyst is particulate and comprises at least 50 particles.

[0384] Preferably, the reducing agent in step (e) is selected from NH3, hydrocarbons, CO, H2 and mixtures thereof; preferably NH3.

[0385] Preferably, the reducing agent in step (e) is NH3, which is used in an amount of 0.9 to 2.5 molar parts, preferably 1.0 to 1.4 molar parts, more preferably 1.0 to 1.2 molar parts, based on a molar part of NOX to be chemically reduced.

[0386] In preferred embodiments, the reducing agent in step (d2) is the same as the reducing agent in step (e); preferably NH3.

[0387] In addition to NH3, other nitrogen-containing reducing agents are also suitable in steps (d2) and / or (e) of the process according to the invention, for example hydrogen compounds of nitrogen, such as azanes, hydroxyl derivatives of azanes, and amines, oximes, carbamates, urea or urea derivatives. Examples of azanes are hydrazine and, in particular, ammonia. Examples of hydroxyl derivatives of azanes are hydroxylamine. Examples of amines are primary aliphatic amines, such as methylamine. An example of carbamates is ammonium carbamate. Examples of urea derivatives are N,N'-substituted ureas, such as N,N'-dimethylurea. Ureas and urea derivatives are preferably used in the form of aqueous solutions. Particular preference is given to ammonia or substances that release ammonia upon introduction, such as urea or ammonium carbamate.

[0388] Particularly preferred process procedures according to the invention are explained in more detail below: DeNO X -DeN2O - Variant 1

[0389] In preferred embodiments, the exhaust gas treatment system comprises a first reaction zone and a second reaction zone arranged downstream thereof, through which the exhaust gas flows one after the other; wherein reducing agent is added to the exhaust gas upstream of the first reaction zone; wherein initially in the first reaction zone the NOX content in the exhaust gas is reduced by chemical reduction of NOX with reducing agent on a NOX reduction catalyst (step (e)), (DeNO X-stage); wherein optionally the N2O content in the exhaust gas is additionally reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)); wherein optionally further reducing agent is added to the exhaust gas upstream of the second reaction zone; and wherein subsequently in the second reaction zone the N2O content in the exhaust gas is reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)) (DeN2O stage); wherein optionally the NOX content in the exhaust gas is additionally further reduced by chemical reduction of NOX on an NOX reduction catalyst (step (e)).

[0390] Preferably, the NOX reduction catalyst in the first reaction zone comprises a conventional, preferably non-zeolitic SCR catalyst, e.g. based on V2O5-WO3- / TiO2.

[0391] Preferably, the temperature of the exhaust gas upon entry into the first reaction zone is at most 400°C, preferably at most 350°C.

[0392] Preferably, the N2O decomposition catalyst in the second reaction zone comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU, and / or MEL structure type.

[0393] The temperature of the exhaust gas upon entry into the second reaction zone is preferably in the range from 300 to 550°C, preferably 350 to 500°C.

[0394] Preferably, the exhaust gas after leaving the first reaction zone and before entering the second reaction zone has a content of NO X in the range of 0 to 200 ppmv, preferably 1 to 200 ppmv, and an N2O content in the range of 200 to 2000 ppmv. DeNOX-DeN2O - Variant 2

[0395] In other preferred embodiments, the exhaust gas treatment system also comprises a first reaction zone and a second reaction zone arranged downstream thereof, through which the exhaust gas flows one after the other; wherein reducing agent is added to the exhaust gas upstream of the first reaction zone; where initially in the first reaction zone the content of NO X in the exhaust gas by chemical reduction of NO X with reducing agent on a NO X -reduction catalyst; (step (e)) (DeNO X-stage); wherein optionally the N2O content in the exhaust gas is additionally reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)); wherein optionally further reducing agent is added to the exhaust gas upstream of the second reaction zone; and wherein subsequently in the second reaction zone the N2O content in the exhaust gas is reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)) (DeN2O stage); wherein optionally the NOX content in the exhaust gas is additionally further reduced by chemical reduction of NOX on an NOX reduction catalyst (step (e)).

[0396] Preferably, the NOX reduction catalyst in the first reaction zone comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU, and / or MEL structure type.

[0397] Preferably, the temperature of the exhaust gas upon entry into the first reaction zone is at least 300°C, more preferably at least 350°C, even more preferably at least 400°C. Preferably, the temperature of the exhaust gas upon entry into the first reaction zone is at most 600°C, more preferably at most 550°C.

[0398] Preferably, the N2O decomposition catalyst in the second reaction zone comprises a NOX-sensitive N2O decomposition catalyst according to the invention, which has already been described in more detail above.

[0399] Preferably, the temperature of the exhaust gas upon entry into the second reaction zone is at least 300°C, more preferably at least 350°C, even more preferably at least 400°C. Preferably, the temperature of the exhaust gas upon entry into the second reaction zone is at most 600°C, more preferably at most 550°C.

[0400] Preferably, the exhaust gas after leaving the first reaction zone and before entering the second reaction zone has a content of NO X of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv and an N2O content in the range of 200 to 2000 ppmv. Particularly preferred embodiments of DeNO X -DeN2O - Variant 2

[0401] In particularly preferred embodiments, the exhaust gas treatment system according to the invention comprises a first catalyst bed and a second catalyst bed spatially separated therefrom; wherein the first catalyst bed is arranged upstream of the second catalyst bed in the flow direction of the exhaust gas is arranged; wherein optionally and preferably upstream of the first catalyst bed, a first device with a first control valve for metering NH3 into the exhaust gas is arranged; wherein downstream of the first catalyst bed and upstream of the second catalyst bed, a second device with a second control valve for metering NH3 into the exhaust gas is arranged, with which further NH3 is metered into the exhaust gas; wherein both the first catalyst bed and the second catalyst bed each contain an iron-loaded zeolite catalyst; wherein (i) in the first catalyst bed (d1) N2O is decomposed; and (e) NO Xis incompletely chemically reduced with NH3, wherein optionally and preferably at least a portion of the NH3 originates from incomplete combustion of NH3 in step (a) (NH3 slip); and (ii) in the second catalyst bed (d2) residual N2O is chemically reduced with NH3 and optionally (d1*) residual N2O is decomposed; and (e*) residual NO X is chemically reduced with NH3.

[0402] Preferably, the catalytic decomposition of N2O in the first catalyst bed is co-catalyzed by NOX present in the exhaust gas.

[0403] Preferably, the incomplete chemical reduction of NOX with NH3 in the first catalyst bed leads to a predetermined residual NOX content sufficient to cause a co-catalytic effect on the decomposition of N2O in the first catalyst bed. Since the chemical reduction of NOX with NH3 in the first catalyst bed typically proceeds significantly faster than the chemical reduction of N2O with NH3, and not the entire amount of NOX is chemically reduced in the first catalyst bed, the extent of any parallel chemical reduction of N2O with NH3 in the first catalyst bed is typically negligible.

[0404] Preferably, additional NH3 is metered into the exhaust gas via the first device for NOX reduction; preferably under feedback control, i.e. a specific value for the NOX concentration at the outlet of the first catalyst bed is specified as the target value (setpoint) and the actual NOX concentration at the outlet of the first catalyst bed is measured (actual value). If there is a difference between the setpoint and actual value (control difference), the control level of the first control valve is changed in order to minimize the difference. Preferably, the setpoint of the NOX concentration at the outlet of the first catalyst bed and thus the amount of additional NH3 is selected such that the residual NOX concentration at the outlet of the first catalyst bed is at most 1000 ppmv, preferably at most 500 ppmv, more preferably at most 100 ppmv.Preferably, the target value of the NOX concentration at the outlet of the first catalyst bed and thus the amount of additional NH3 is selected so that the residual concentration of NO. X at the outlet of the first catalyst bed is at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 40 ppmv. The expected specific consumption of NH3 for the chemical reduction of NO X in the first catalyst bed is typically in the range of 0.9 to 1.1 mol NH3 per mol reduced NO X and is thus significantly smaller than the expected specific (mol / mol) consumption of NH3 in the second catalyst bed.

[0405] Preferably, the temperature of the exhaust gas at the outlet from the first catalyst bed is in the range of 400 to 550°C.

[0406] Preferably, the exhaust gas at the outlet from the first catalyst bed has a pressure which is greater than atmospheric pressure, ie ≥ 1.0 bara, but at most 1.2 bara, more preferably at most 1.1 bara.

[0407] Preferably, the exhaust gas at the outlet from the first catalyst bed has an oxidation degree of NOX of at least 5.0%, preferably at least 7.5%, more preferably at least 10%, even more preferably at least 12.5%, most preferably at least 15%, and in particular at least 17.5%.

[0408] In preferred embodiments, the exhaust gas at the outlet from the first catalyst bed has an oxidation level of NOX in the range of 30 to 50%.

[0409] In other preferred embodiments, the exhaust gas at the outlet from the first catalyst bed has an oxidation level of NOX in the range of 15 to 35%, preferably 15 to 30%.

[0410] In further preferred embodiments, the exhaust gas at the outlet from the first catalyst bed has an oxidation level of NOX in the range of 10 to 20%.

[0411] In other preferred embodiments, the exhaust gas at the outlet from the first catalyst bed has an oxidation level of NOX in the range of 5 to 15%.

[0412] Preferably, residual N2O is decomposed in the second catalyst bed to a residual N2O concentration at the outlet of the second catalyst bed of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv, most preferably at most 2 ppmv.

[0413] Preferably, residual NOX is decomposed in the second catalyst bed to a residual concentration of NOX at the outlet of the second catalyst bed of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv, most preferably at most 2 ppmv.

[0414] Preferably, the additional NH3 is metered in using the second device under feedforward control, i.e. the concentrations of NOX and optionally preferably of N2O are measured at the outlet of the first catalyst bed or optionally at the inlet to the second catalyst bed; taking into account the amount of exhaust gas entering the second catalyst bed, the amount of NH3 required for NOX reduction and optionally preferably the sum of the amounts of NH3 required for NOX reduction and N2O reduction is calculated using stored ratios, e.g. molar ratios (mol / mol) of NH3 / NOX and optionally preferably of NH3 / / N2O or factors derived therefrom; and the control level of the second control valve is changed using the calculated result (control variable) in order to meter in the required amount of NH3.

[0415] According to the invention, the molar NH3 concentration [NH3] of the exhaust gas at the inlet to the second catalyst bed is preferably in the range of the sum of 0.7 x [N2O] and 1.0 x [NO X ] to the sum of 4.0 x [N2O] and 2.0 x [NO X ], more preferably in the range of the sum of 1.0 x [N2O] and 1.1 x [NO X ] to the sum of 3.0 x [N2O] and 1.6 x [NO X ], more preferably in the range from the sum of 1.5 x [N2O] and 1.2 x [NOX] to the sum of 2.5 x [N2O] and 1.4 x [NOX], where [N2O] is the molar concentration of N2O and [NOX] is the molar concentration of NOX, respectively, in the exhaust gas at the inlet to the second catalyst bed.

[0416] For feedforward control of the NH3 dosage into the second catalyst bed with regard to NOX reduction, a molar ratio of NH3 / NOX in the range of 1.0 to 2.0; preferably 1.1 to 1.6; more preferably 1.2 to 1.4 is selected.

[0417] For feedforward control of the NH3 dosage into the second catalyst bed with respect to N2O reduction, a molar ratio of NH3 / N2O in the range of 0.7 to 4.0; preferably 1.0 to 3.0; more preferably 1.5 to 2.5 is preferably selected.

[0418] Preferably, the additional NH3 is not metered in with the second device under feedback control, since the aim is to achieve the most complete chemical reduction of NOX in the second catalyst bed, ie no or only very low residual concentrations of NOX and N2O result, which would be difficult to use as control variables in terms of control technology.

[0419] Preferably, the amount of catalyst, ie the space velocity (= ratio of exhaust gas volume flow under standard conditions to catalyst volume) is selected such that in the first catalyst bed a degradation of N2O of at least 50% takes place, more preferably at least 70%, even more preferably at least 80%, based on the concentration of N2O at the inlet to the first catalyst bed.

[0420] Preferably, the amount of catalyst and the amount of additional NH3 are selected such that at the outlet of the first catalyst bed the molar ratio of NOX / N2O is at least 5, more preferably at least 10, even more preferably at least 20.

[0421] Preferably, the space velocity of the first catalyst bed is in the range of 5,000 h-1 to 100,000 h-1, more preferably 10,000 h-1 to 50,000 h-1, even more preferably 15,000 h-1 to 45,000 h-1.

[0422] If the molar ratio of NOX / N2O at the outlet of the first catalyst bed is at least 10, then the addition of NH3 into the second catalyst bed via the second device can preferably be adjusted solely in relation to the amount of NO entering. X take place.

[0423] Preferably, the temperature of the exhaust gas upon entry into the first catalyst bed is at least 400°C, more preferably at least 425°C, even more preferably at least 450°C. Preferably, the temperature of the exhaust gas upon entry into the first catalyst bed is at most 550°C, more preferably at most 525°C, even more preferably at most 500°C. The temperature can be adjusted by measures which are known to experts, in particular the design of heat exchangers and the conditions for the combustion of NH3.

[0424] Depending on the heat of the chemical reactions taking place in the first catalyst bed and in the second catalyst bed, the inlet temperature of the exhaust gas into the first catalyst bed is preferably selected such that the temperature of the exhaust gas at the outlet of the second catalyst bed is at most 600°C, more preferably at most 550°C, even more preferably at most 520°C.

[0425] Preferably, the space velocity of the second catalyst bed is in the range of 5,000 h-1 to 100,000 h-1, more preferably 10,000 h-1 to 50,000 h-1, even more preferably 15,000 h-1 to 45,000 h-1.

[0426] Preferably, the ratio of the catalyst volumes (V1 kat / V2 kat ) from the first catalyst bed V1 kat to the second catalyst bed V2 kat in the range of 1 / 2 to 20 / 1, more preferably 1 / 2 to 10 / 1, even more preferably 1 / 1 to 4 / 1.

[0427] In preferred embodiments, at least one, several or all of the following conditions are met: ^ the pressure of the exhaust gas upon entry into the first catalyst bed is at most 5 bara, more preferably at most 4 bara, even more preferably at most 1.3 bara, most preferably at most 1.2 bara and in particular at most 1.1 bara; ^ the H2O content in the exhaust gas upon entry into the first catalyst bed is at least 5 vol.%, more preferably at least 10 vol.%, even more preferably at least 15 vol.%, most preferably at least 20 vol.% and in particular at least 25 vol.%; ^ the NO content Xin the exhaust gas upon entry into the first catalyst bed is at least 500 ppmv, more preferably at least 1000 ppmv, even more preferably at least 1500 ppmv, most preferably at least 2000 ppmv, and in particular at least 2500 ppmv; ^ the N2O content in the exhaust gas upon entry into the first catalyst bed is at most < 500 ppmv, more preferably at most 200 ppmv, even more preferably at most 100 ppmv, but at least 5 ppmv, preferably at least 10 ppmv, more preferably at least 50 ppmv; ^ the exhaust gas upon entry into the first catalyst bed contains unburned residues of NH3 from the combustion of NH3; ^ the N2O decomposition catalyst and / or the N2O reduction catalyst is in the form of a honeycomb body; ^ the NOX reduction catalyst is in the form of a honeycomb body; ^ the first catalyst bed contains Fe zeolite; ^ the second catalyst bed contains Fe zeolite; ^ the exhaust gas flows through a heat exchanger before entering the first catalyst bed and is heated therein; ^ the NOX content at the outlet of the first catalyst bed is at most 1000 ppmv, more preferably at most 500 ppmv, even more preferably at most 300 ppmv, most preferably at most 100 ppmv; but preferably at least 10 ppmv, more preferably at least 20 ppm, even more preferably at least 40 ppmv, most preferably at least 100 ppmv, and in particular at least 250 ppmv; ^ the N2O content at the outlet of the first catalyst bed is at most 20 ppmv, more preferably at most 15 ppmv, even more preferably at most 10 ppmv, most preferably at most 5 ppmv and in particular at most 2 ppmv; ^ after leaving the first catalyst bed and until entering the second catalyst bed, there is no intermediate cooling of the exhaust gas;^ the molar ratio of N2O : NOX upon entry into the first catalyst bed is at most 0.5, more preferably at most 0.2, even more preferably at most 0.1; ^ the molar ratio of N2O : NO; X at the outlet from the first catalyst bed is at most 0.20, more preferably at most 0.1, even more preferably at most 0.05; ^ the feeding of NH3 into the exhaust gas in the flow direction of the exhaust gas upstream of the first catalyst bed is optional; if feeding takes place, this is preferably substoichiometric with regard to the NO content X at the inlet to the first catalyst bed; ^ the feeding of NH3 into the exhaust gas in the flow direction of the exhaust gas downstream of the first catalyst bed and upstream of the second catalyst bed is mandatory, preferably over-stoichiometric with regard to the total NO content X and N2O at the inlet to the second catalyst bed.

[0428] The process described above using Fe-zeolite catalysts in two catalyst beds enables, in comparison to classical DeNOX processes using V2O5 / TiO2 catalysts, - the complete or almost complete degradation of large amounts of NOX without the risk of NH3 slip; as well as - the simultaneous, complete or almost complete degradation of N2O at comparatively small catalyst volumes, i.e. at comparatively high space velocities.

[0429] This is achieved not only by the inventive method of operation but also by the oxidative properties of the Fe-zeolite catalysts used in the invention. Thus, in the first catalyst bed, the molar ratio of NO to NO2 is adjusted as close as possible to the thermodynamic The NO XThe degree of oxidation (molar ratio of NO2 / (NO + NO2)) before entering the first catalyst bed is expected to be less than 5% due to the upstream NH3 combustion at very high temperatures and the slow establishment of equilibrium in the gas phase during the cooling of the exhaust gas in the subsequent heat exchanger(s), and is thus significantly below the thermodynamic equilibrium applicable for the inlet temperature into the first catalyst bed. However, this is very disadvantageous for efficient chemical reduction of NO. X , as this only removes a small part of the NO present in the exhaust gas X can be reduced according to an almost SCR and a large part of the NO X or the remaining NO must be broken down according to the significantly slower normal SCR.

[0430] Due to the selected operating mode of limited NH3 dosing in the first catalyst bed and the ability of the Fe-zeolite catalysts to oxidize NO and / or to catalytically accelerate the equilibrium process, a significantly faster, i.e., more efficient, chemical reduction of NOX is achieved in the first catalyst bed, while simultaneously setting the maximum possible NOX oxidation level of the escaping residual NOX. This also enables efficient chemical reduction of NOX in the second catalyst bed right from the start.

[0431] It was found that large amounts of NH3, which are necessary for the complete chemical reduction of high concentrations of NOX, inhibit the establishment of the NOX equilibrium on the Fe-zeolite catalyst, similar to water.

[0432] Furthermore, the chemical reduction of NOX itself is also inhibited by NH3 itself at sufficiently high NH3 dosages. This means that, depending on temperature, catalyst quantity, and NOX content, with increasing NH3 addition, no further increase in NOX degradation occurs beyond a certain amount of NH3. With further increases in NH3 addition, a decrease in NOX degradation may even be observed, accompanied by a simultaneous NH3 slip.

[0433] By chemically reducing the NOX in the first catalyst bed, the amount of NH3 required for chemically reducing NOX in the second catalyst bed is significantly reduced.

[0434] In this way, together with the above-described setting or permanent tracking of the NO X -equilibrium, also in the second catalyst bed a very efficient chemical reduction of NO Xeven with the inventive overstoichiometric dosing of NH3 possible.

[0435] The fact that this occurs according to the invention without or only with a negligible NH3 slip of preferably at most 10 ppmv, more preferably at most 5 ppmv, even more preferably at most 3 ppmv, is also due to the oxidative properties of the Fe-zeolite catalysts used according to the invention. If the inlet temperature of the exhaust gas into the second catalyst bed is preferably at least 400°C, more preferably at least 425°C, even more preferably at least 450°C, then The NH3 dosed in excess within the limits of the invention is selectively oxidized to N2 and H2O by the residual oxygen content of the exhaust gas.

[0436] All of these advantages cannot be realized when using conventional V2O5 / TiO2-based SCR catalysts, such as those typically used for denitrification of exhaust gases from natural gas-fired reformers, in a single or multi-stage configuration. For stability reasons, these conventional SCR catalysts typically cannot be operated at temperatures above 400°C, which limits the achievable reaction rates of the degradation reaction. Furthermore, conventional SCR catalysts exhibit only very limited oxidation activity, so neither adjustment nor permanent tracking of the NOX balance is possible, nor do these catalysts enable effective and N2-selective oxidation of excess NH3. In fact, there is a risk of undesirable N2O formation.

[0437] In a preferred variant of the embodiments described above, the first catalyst bed and the second catalyst bed contain the same catalyst. In preferred embodiments, the second device with a second control valve for metering NH3 into the exhaust gas is omitted, wherein the spatial separation of the first catalyst bed from the second catalyst bed is preferably omitted - there is then in fact only one common catalyst bed, wherein a first device with a first control valve for metering NH3 into the exhaust gas is preferably arranged upstream of this common catalyst bed. Additional NH3 is preferably metered into the exhaust gas via the first device; preferably under feedforward control, i.e.The concentration of NOX, N2O, and NH3 in the exhaust gas upstream of the common catalyst bed is measured; taking into account the amount of exhaust gas entering the common catalyst bed, the additional amount of NH3 still required is calculated; and the calculated result (manipulated variable) is used to change the control level of the first control valve in order to meter in the additional amount of NH3 still required. In such embodiments, an NH3 oxidation catalyst is preferably arranged downstream of the common catalyst bed in order to reduce possible NH3 slip. Simultaneous combustion of NH3 and CH4 - reduction of the hydrogen cyanide content.

[0438] In preferred embodiments, in step (a) a mixture of CH4 and NH3 is burned with air and / or oxygen to produce an exhaust gas which, in addition to NO X and N2O also contains CO2, CO and HCN.

[0439] In these cases, the first catalyst bed preferably takes over the additional function of catalytic decomposition of HCN by hydrolysis with water present in the exhaust gas into the products CO and NH3 according to HCN + H2O ↔ CO + NH3. The resulting products CO and NH3 can then subsequently with regard to NH3preferentially to NO X -reduction in the first catalyst bed and with regard to CO preferentially to N2O reduction in the second catalyst bed as a reducing agent for the removal of N2O and NO X used in the exhaust gas.

[0440] Due to its toxicity, longevity in the atmosphere, and absorption in the infrared, HCN as a pollutant and greenhouse gas must be limited or eliminated in its concentration in exhaust gases. The fact that during the inventive degradation of HCN on zeolite catalysts in the first catalyst bed, CO and NH3 decomposition products are formed, which can be used as reducing agents for the further exhaust gas aftertreatment of NOX and N2O in the second catalyst bed completes the uniqueness of the inventive exhaust gas treatment using zeolite catalysts. Conventional SCR catalysts based on vanadium oxide exhibit almost no activity for HCN hydrolysis and are therefore unsuitable for removing HCN from exhaust gases. In this case, a downstream oxidation catalyst would have to be used. DeN2O-DeNOX

[0441] In further preferred embodiments, the exhaust gas treatment system comprises a first reaction zone and a second reaction zone arranged downstream of it, through which the exhaust gas flows one after the other; wherein reducing agent is added to the exhaust gas between the first reaction zone and the second reaction zone; wherein firstly in the first reaction zone the N2O content in the exhaust gas is reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)) (DeN2O stage); and wherein subsequently in the second reaction zone the NOX content in the exhaust gas is reduced by chemical reduction of NOX with reducing agent on an NOX reduction catalyst (step (e)) (DeNOX stage); wherein optionally additionally the N2O content in the exhaust gas is further reduced by further decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)).

[0442] Preferably, no reducing agent is added to the exhaust gas before the first reaction zone.

[0443] Such a process is particularly preferred according to the invention. It allows the relative NO content to be determined without the consumption of reducing agent. X and N2O. While the absolute NO X In the first reaction zone, the N2O content in the exhaust gas is selectively reduced by decomposition, while the N2O content remains virtually unchanged. This can be done to the extent required to achieve the desired relative content of NOX and N2O. For economic reasons, the amount of N2O decomposition catalyst is preferably not selected so large that a quantitatively complete reduction of the N2O content in the exhaust gas occurs through decomposition (0 ppmv), but rather a compromise is found between the decomposition rate and the dimensioning of the N2O decomposition catalyst.

[0444] In preferred embodiments, the N2O decomposition catalyst in the first reaction zone comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU, and / or MEL structure type.

[0445] In other preferred embodiments, the N2O decomposition catalyst in the first reaction zone comprises a NO X -sensitive N2O decomposition catalyst according to the invention, which has already been described above.

[0446] In preferred embodiments, the NOx reduction catalyst in the second reaction zone comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU, and / or MEL structure type.

[0447] Preferably, the first reaction zone and the second reaction zone are operated at different temperature levels.

[0448] Preferably, the N2O decomposition catalyst in the first reaction zone comprises a NOX-sensitive N2O decomposition catalyst; wherein the temperature of the exhaust gas in the first reaction zone is preferably at least 450°C, more preferably at least 500°C, even more preferably at least 550°C, most preferably at least 600°C; and the NOX reduction catalyst in the second reaction zone comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU and / or MEL; wherein the temperature of the exhaust gas in the second reaction zone is preferably at most 550°C, more preferably at most 500°C, even more preferably at most 450°C, most preferably at most 400°C;and wherein, in addition to the chemical reduction of NOX, a further reduction of the (residual) N2O content preferably takes place in the second reaction zone by decomposition and / or chemical reduction. ;

[0449] Preferably, the space velocity in the first reaction zone is adjusted such that in the first reaction zone the N2O content in the exhaust gas is reduced by at most 95%, preferably by at most 90%, more preferably by at most 85%, based on the N2O content in the exhaust gas upon entry into the first reaction zone.

[0450] In preferred embodiments, the N2O content in the exhaust gas after leaving the first reaction zone and before entering the second reaction zone is at least 20 ppmv, more preferably at least 40 ppmv, more preferably at least 60 ppmv, most preferably at least 80 ppmv and especially at least 100 ppmv.

[0451] In preferred embodiments, the N2O content in the exhaust gas after leaving the first reaction zone and before entering the second reaction zone is at most 400 ppmv, more preferably at most 300 ppmv, even more preferably at most 200 ppmv, most preferably at most 100 ppmv and in particular at most 50 ppmv.

[0452] Preferably, the space velocity in the second reaction zone is adjusted such that a further reduction of the N2O content in the exhaust gas occurs in the second reaction zone by at least 30%, preferably by at least 40%, more preferably by at least 50%, based on the N2O content in the exhaust gas upon entry into the second reaction zone. Since reducing agent is present in the second reaction zone, the further reduction of the N2O content in the second reaction zone can occur both by decomposition on an N2O decomposition catalyst (step (d1)) and by chemical reduction with reducing agent on an N2O reduction catalyst (step (d2)).

[0453] Preferably, in the second reaction zone, a further reduction of the N2O content in the exhaust gas takes place by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)).

[0454] In addition, the NOX content is reduced in the second reaction zone by chemical reduction with a reducing agent on a NOX reduction catalyst. This reduction typically has rapid kinetics and, according to the invention, preferably proceeds virtually quantitatively. Step (f):

[0455] In the optional and preferred step (f) of the process according to the invention, the exhaust gas is cooled in at least one heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

[0456] In preferred embodiments, a single heat exchanger is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place.

[0457] In other preferred embodiments, at least two heat exchangers are arranged in the flow direction of the exhaust gas downstream of the exhaust gas treatment system, in which the cooling of the exhaust gas takes place one after the other (see Figures 2, 3 and 4).

[0458] In further preferred embodiments, at least three heat exchangers are arranged in the flow direction of the exhaust gas downstream of the exhaust gas treatment system, in which the cooling of the exhaust gas takes place one after the other (see Figure 5).

[0459] In other preferred embodiments, at least four heat exchangers are arranged in the flow direction of the exhaust gas downstream of the exhaust gas treatment system, in which the cooling of the exhaust gas takes place one after the other.

[0460] In further preferred embodiments, at least five heat exchangers are arranged in the flow direction of the exhaust gas downstream of the exhaust gas treatment system, in which the cooling of the exhaust gas takes place one after the other (see Figure 6).

[0461] The cooling of the exhaust gas in the at least one heat exchanger takes place by transferring heat from the exhaust gas to a heat transfer medium.

[0462] According to the invention, the heat transfer medium used is preferably a heat transfer medium selected from the group consisting of water, steam, combustion air, NH3, and combinations thereof. Water or steam is particularly preferred as the heat transfer medium, among other things for safety reasons.

[0463] In preferred embodiments, in step (f) of the process according to the invention, the exhaust gas is cooled in a first exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. The H2O is heated in the first exhaust gas / H2O heat exchanger by absorbing heat from the exhaust gas. The heated H2O, which can be in liquid form and / or as water vapor, is preferably used to heat NH3. For this purpose, an H2O / NH3 heat exchanger is preferably arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the H2O, in which NH3 is heated by absorbing heat from the H2O (see Figures 2-6).

[0464] In preferred embodiments, in step (f) of the process according to the invention, the exhaust gas is cooled in a first exhaust gas / combustion air heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. The combustion air is heated in the first exhaust gas / combustion air heat exchanger by absorbing heat from the exhaust gas. The heated combustion air is preferably used to burn NH3 and H2 in the combustion device, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the combustion air (see Figures 2-6).

[0465] In other preferred embodiments, in step (f) of the method according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / H2O heat exchanger described above, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, and - in a first exhaust gas / combustion air heat exchanger described above, which is also arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas; preferably downstream of the first exhaust gas / H2O heat exchanger (cf. Figures 2-6).

[0466] In further preferred embodiments, in step (f) of the method according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, and - in a second exhaust gas / combustion air heat exchanger which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas.

[0467] The combustion air is heated in the first exhaust gas / combustion air heat exchanger and in the second exhaust gas / combustion air heat exchanger by absorbing heat from the exhaust gas. The exhaust gas preferably first flows through the first exhaust gas / combustion air heat exchanger and then through the second exhaust gas / combustion air heat exchanger. The combustion air preferably first flows through the second exhaust gas / combustion air heat exchanger and then through the first exhaust gas / combustion air heat exchanger, which is why the first exhaust gas / combustion air heat exchanger is preferably arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the combustion gas. The heated combustion air is preferably used to burn NH3 and H2 in the combustion device, which for this purpose is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the combustion air (see Figures 5 and 6).

[0468] In other preferred embodiments, in step (f) of the method according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger described above, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas (cf. Figures 4-6).

[0469] The exhaust gas then preferably flows first through the first exhaust gas / combustion air heat exchanger, then the first exhaust gas / H2O heat exchanger, and then the second exhaust gas / combustion air heat exchanger.

[0470] In preferred embodiments, in step (f) of the method according to the invention, the cooling of the exhaust gas takes place in at least one exhaust gas / combustion gas heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the above-described first exhaust gas / combustion air heat exchanger, the above-described first exhaust gas / H2O heat exchanger, and / or the above-described second exhaust gas / combustion air heat exchanger. The combustion gas is heated in the exhaust gas / combustion gas heat exchanger by absorbing heat from the exhaust gas. The heated combustion gas is preferably used for combustion in the combustion device, which is arranged downstream of the exhaust gas / combustion gas heat exchanger in the flow direction of the combustion gas (see Figure 6).

[0471] In preferred embodiments, in step (f) of the process according to the invention, the exhaust gas is cooled in at least one second exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the above-described first exhaust gas / combustion air heat exchanger, the above-described first exhaust gas / H2O heat exchanger, and / or the above-described second exhaust gas / combustion air heat exchanger. The H2O is heated in the second exhaust gas / H2O heat exchanger by absorbing heat from the exhaust gas (see Figure 6).

[0472] In other preferred embodiments, in step (f) of the method according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger described above, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / combustion gas heat exchanger described above, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas (see Figure 6).

[0473] In further preferred embodiments, in step (f) of the method according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger described above, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / H2O heat exchanger described above, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas (see Figure 6).

[0474] In other preferred embodiments, in step (f) of the method according to the invention, the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger described above, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger described above, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion gas heat exchanger described above, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / H2O heat exchanger described above,which is arranged downstream of the exhaust gas / combustion gas heat exchanger in the flow direction of the exhaust gas (see Figure 6).

[0475] High exhaust gas temperatures lead to significant stress on the material used due to the setting of high wall temperatures, at least at the heat exchangers located upstream in the direction of exhaust gas flow, in the exhaust duct. This can lead to a reduced service life or a change to a more complex and cost-intensive material. Therefore, one factor in considering the effectiveness of an exhaust duct configuration is the inlet temperature of the exhaust gas into the duct. The preheating of the NH3 must be carried out to a temperature determined by the process requirements. In contrast, the temperature of the combustion air preheating, for example, represents a degree of freedom in the design, since it is not subject to any direct requirements other than efficient energy integration.The inlet temperature of the exhaust gas into the exhaust gas duct is therefore limited downwards by the preheating temperatures specified in the tube reactor designed analogously to a primary reformer or possible pre-reactors (preferably adiabatic fixed bed reactors) due to the requirements of the process.

[0476] Heterogeneous catalysts achieve higher reaction rates at higher temperatures by accelerating diffusion and kinetics. However, their operation is often limited by their decreasing stability against deactivation at high temperatures. Therefore, there is an optimal operating window for the exhaust gas treatment system, within which high reaction rates are achieved, which in turn translates into high permissible space velocities of the feed gas, which in turn reduces the required catalyst volume. However, this window lies below the range in which operation leads to deactivation and a loss of catalytic effectiveness. A further criterion for evaluating efficient energy integration is therefore whether the inlet temperature of the exhaust gas into the exhaust gas treatment system lies within this optimal window.

[0477] The third factor in evaluating the effectiveness of a flue duct configuration is the flue gas inlet temperature into the stack. Together with the flue gas mass flow, this determines the energy loss through the flow compared to the theoretical optimum, achieved at the dew point of water plus the required safety margin of 25 K.

[0478] The H2 yield should be as high as possible to increase the economic efficiency of the plant. A high yield is typically directly linked to a low flue gas inlet temperature in the stack. However, if this goal cannot be achieved without minimizing the required flue gas inlet temperature in the stack or providing a suitable inlet temperature for the flue gas treatment system, the selected flue duct design will be less than successful.

[0479] Regardless of the respective process control, the process according to the invention is preferably regulated.

[0480] In preferred embodiments, depending on the design of the combustion system, preferably the combustion device, for controlling the method according to the invention, at least one parameter is measured as the first measured variable, which is characteristic of the current operating state of the combustion system, preferably the combustion device. This first measured variable or parameter is preferably selected from the group consisting of combustion temperature and NH3 consumption of the combustion system, preferably the combustion device.

[0481] Depending on the nature of the exhaust gas leaving the combustion plant, preferably the combustion device, in particular - NOX content in the exhaust gas; - NOX oxidation level in the exhaust gas; - N2O content in the exhaust gas; - content of other components in the exhaust gas, such as H2O, O2, and N2; - temperature of the exhaust gas; - pressure of the exhaust gas; and - volume flow of the exhaust gas; the process conditions can be optimized to achieve an efficient and economical reduction of the NO content. X and N2O in the exhaust gas.

[0482] In preferred embodiments, therefore, for the control of the method according to the invention, at least one parameter is measured as a second measurement variable at the outlet from the combustion plant, preferably the combustion device, and / or at the inlet into the exhaust gas treatment plant, either in addition to the first measurement variable or instead of the first measurement variable, which is characteristic of the current state of the exhaust gas before entering the exhaust gas treatment plant. This is preferably second measured variable or parameter selected from the group consisting of NO content X in the exhaust gas; degree of oxidation of NO X in the exhaust gas; content of N2O in the exhaust gas; content of other components in the exhaust gas, such as H2O, O2, and N2; temperature of the exhaust gas; pressure of the exhaust gas; and volume flow of the exhaust gas.

[0483] In preferred embodiments, for the control of the method according to the invention, at least one parameter which is characteristic of the current state of the exhaust gas at the outlet of the exhaust gas treatment system is measured as a third measured variable at the outlet of the exhaust gas treatment system, either in addition to the first measured variable or instead of the first measured variable, and either in addition to the second measured variable or instead of the second measured variable. This third measured variable or parameter is preferably selected from the group consisting of NOX content in the exhaust gas; degree of oxidation of NOX in the exhaust gas; N2O content in the exhaust gas; content of other components in the exhaust gas, such as H2O, O2, and N2; temperature of the exhaust gas; pressure of the exhaust gas; and volume flow of the exhaust gas.

[0484] In preferred embodiments, in particular when the exhaust gas treatment system comprises a first reaction zone and a second reaction zone through which the exhaust gas flows one after the other, wherein reducing agent is fed between the first reaction zone and the second reaction zone, for the control of the method according to the invention at the outlet from the first reaction zone and before entering the second reaction zone as a fourth measured variable, either in addition to the first measured variable or instead of the first measured variable, and either in addition to the second measured variable or instead of the second measured variable, and either in addition to the third measured variable or instead of the third measured variable, at least one parameter is measured which is characteristic of the current state of the exhaust gas after leaving the first reaction zone and before entering the second reaction zone. This fourth measured variable orthe parameter selected from the group consisting of NOX content in the exhaust gas; degree of oxidation of NOX in the exhaust gas; N2O content in the exhaust gas; content of other components in the exhaust gas, such as H2O, O2, and N2; temperature of the exhaust gas; pressure of the exhaust gas; and volume flow of the exhaust gas. .

[0485] Depending on the first measured variable and / or the second measured variable and / or the third measured variable and / or the fourth measured variable, at least one manipulated variable is preferably changed to regulate or control the method according to the invention. Therefore, the method is preferably regulated or controlled based on the first measured variable and / or the second measured variable and / or the third measured variable and / or the fourth measured variable by deliberately changing the manipulated variable (control variable), preferably by deliberately changing the added amount of reducing agent.

[0486] With regard to preferred control variables, a distinction must be made between - process conditions which cannot be changed at short notice or only with greater equipment expenditure, and - Procedural conditions which can be changed at short notice and are therefore better suited to regulating the procedure.

[0487] According to the invention, the following are preferred: - the dimensioning of the exhaust gas treatment device; - the type, quantity and flow direction of the N2O decomposition catalyst and / or N2O reduction catalyst; - the type, quantity and flow direction of the NO X -reduction catalyst; - the type of reducing agent; - the pressure of the exhaust gas; - the position of the reducing agent feed; and - the arrangement of the first reaction zone and second reaction zone relative to one another are not control variables, ie these parameters preferably remain constant during the implementation of the process according to the invention.

[0488] However, these parameters can be selected or adjusted during the planning and design of the exhaust gas treatment system so that the process according to the invention can be controlled within wide limits. This allows for responses to even short-term changes, for example, with regard to the exhaust gas to be treated. An efficient and economical reduction of the NOX and N2O content in the exhaust gas is ensured without undesirable breakthrough of reducing agent (so-called slippage).

[0489] Preferred control variables according to the invention are: - the amount of reducing agent; - if applicable, the temperature of the exhaust gas; and - if applicable, the temperature of the catalysts.

[0490] Preferably, the exhaust gas leaves the exhaust gas treatment plant and has a residual NOX content of at most 20 ppmv, preferably at most 15 ppmv, more preferably at most 10 ppmv, even more preferably at most 7.5 ppmv, most preferably at most 5.0 ppmv, and in particular at most 2.5 ppmv.

[0491] Preferably, the exhaust gas leaves the exhaust gas treatment plant and has a residual N2O content of at most 20 ppmv, preferably at most 15 ppmv, more preferably at most 10 ppmv, even more preferably at most 7.5 ppmv, most preferably at most 5.0 ppmv, and in particular at most 2.5 ppmv.

[0492] A further aspect of the invention relates to a device comprising (i) an NH3 firing system, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2, and (ii) an exhaust gas treatment system; wherein the device is configured to carry out the method according to the invention described above.

[0493] The device according to the invention is preferably a plant complex for producing pure hydrogen, comprising - one (or more) NH3 decomposition device(s) for the catalytic decomposition of NH3 into N2 and H2, preferably a reactor filled with catalyst; - a combustion device for directly or indirectly heating the NH3 decomposition device(s), preferably comprising a combustion chamber and at least one burner for burning a fuel with (atmospheric) oxygen, wherein the fuel contains NH3 or consists essentially thereof; - a device for purifying a product stream of the NH3 decomposition device, preferably by PSA;- an exhaust gas treatment system for cleaning the exhaust gases of the combustion device comprising one or more catalyst beds for the reduction of NOX, optionally for N2O reduction and / or N2O decomposition, and preferably for the oxidation of unreacted reducing agents and / or their incompletely oxidized reaction products (preferably a downstream catalyst bed with NH3 oxidation catalyst).

[0494] Preferred embodiments of the invention are summarized below as sentences: Sentence 1: A method for reducing the content of NOX and N2O in the exhaust gas of a combustion plant operated with NH3, the method comprising the following steps: (a) burning NH3 to operate the combustion plant, preferably a furnace, preferably comprising a combustion device and NH3 decomposition device, for the catalytic decomposition of NH3 into N2 and H2, to produce an exhaust gas which comprises N2, H2O, NOX and N2O and which leaves the combustion plant; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment plant;(d) reducing the N2O content in the exhaust gas by (d1) decomposition of N2O on an N2O decomposition catalyst and / or (d2) chemical reduction of N2O with reducing agent on an N2O reduction catalyst; (e) reducing the NO content; X in the exhaust gas by chemical reduction of NO X with reducing agent on a NO X - reduction catalyst; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. Sentence 2: The process according to sentence 1 for reducing the NO content X and N2O in the exhaust gas of a combustion plant operating with NH3 and H2, which is fed into a plant for the catalytic decomposition of NH3 to N2 and H2, the process comprising the following steps: (a) burning NH3 and H2 to operate the combustion plant (preferably in a combustion device) to produce an exhaust gas which contains N2, H2O, NO X and N2O and leaves the combustion plant; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment plant which is arranged downstream of the combustion plant and optionally of the at least one heat exchanger in the flow direction of the exhaust gas; (d) reducing the N2O content in the exhaust gas by (d1) decomposition of N2O on an N2O decomposition catalyst and / or (d2) chemical reduction of N2O with reducing agent on an N2O reduction catalyst; (e) reducing the NO content Xin the exhaust gas by chemical reduction of NOX with reducing agent on a NOX reduction catalyst; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. Sentence 3: The method according to one of the preceding sentences, wherein a single heat exchanger is arranged downstream of the combustion system in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place. Sentence 4: The method according to one of the preceding sentences, wherein at least two heat exchangers are arranged downstream of the combustion system in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place one after the other. Sentence 5: The method according to one of the preceding sentences, wherein at least three heat exchangers are arranged downstream of the combustion system in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place one after the other.Sentence 6: The method according to one of the preceding sentences, wherein in step (b), the cooling of the exhaust gas takes place in the at least one heat exchanger by releasing heat from the exhaust gas to a heat transfer medium, wherein NH3 preferably serves as the heat transfer medium, which is then subsequently fed to the catalytic decomposition in an NH3 decomposition device on an NH3 decomposition catalyst. Sentence 7: The method according to one of the preceding sentences, wherein in step (b), the cooling of the exhaust gas takes place in at least one first exhaust gas / NH3 heat exchanger, which is arranged downstream of the combustion plant in the flow direction of the exhaust gas.Sentence 8: The method according to one of the preceding sentences, wherein in step (b) the cooling of the exhaust gas takes place - in a first exhaust gas / NH3 heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas, and - in a second exhaust gas / NH3 heat exchanger which is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas. Sentence 9: The process according to one of the preceding sentences, wherein in step (b) the cooling of the exhaust gas takes place - in a first exhaust gas / NH3 heat exchanger, which is arranged downstream of the combustion plant in the flow direction of the exhaust gas, - in a second exhaust gas / NH3 heat exchanger, which is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas, and - in a third exhaust gas / NH3 heat exchanger, which is arranged downstream of the second exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas. Sentence 10: The process according to one of the preceding sentences, wherein the exhaust gas in step (b) is cooled to a temperature T2 in the range from 400 to 450°C, more preferably 400 to 420°C. Sentence 11: The process according to one of the preceding sentences, wherein the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NO X-reduction catalyst independently comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably, independently of one another, an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU and / or MEL type. Sentence 12: The process according to any one of the preceding sentences, wherein the N2O decomposition catalyst and the N2O reduction catalyst are made of the same material. Sentence 13: The process according to any one of the preceding sentences, wherein the N2O decomposition catalyst and the NOX reduction catalyst are made of the same material. Sentence 14: The process according to any one of the preceding sentences, wherein the N2O reduction catalyst and the NOX reduction catalyst are made of the same material.Sentence 15: The process according to any one of the preceding sentences, wherein the N2O decomposition catalyst, the N2O reduction catalyst, and the NOX reduction catalyst are made of the same material. Sentence 16: The process according to any one of the preceding sentences, wherein in step (a) the combustion of NH3 does not take place over a catalyst. Sentence 17: The process according to any one of the preceding sentences, wherein the proportion of H2 in the mixture with NH3 is at most 80 mol%, more preferably at most 70 mol%, even more preferably at most 60 mol%, most preferably at most 50 mol%, and in particular at most 40 mol%. Sentence 18: The process according to any one of the preceding sentences, wherein the proportion of H2 in the mixture with NH3 is at least 10 mol%, more preferably at least 20 mol%, even more preferably at least 30 mol%, most preferably at least 40 mol%, and in particular at least 50 mol%.Sentence 19: The process according to any one of the preceding sentences, wherein the molar ratio of H2:NH3in the mixture is in the range of 45:55 to 90:10, preferably 50:50 to 85:15, more preferably 55:45 to 80:20, even more preferably 60:40 to 75:25, most preferably 65:35 to 70:30. Sentence 20: The process according to any one of the preceding sentences, wherein the air ratio λ is in the range of 0.9 to 1.7, more preferably 1.0 to 1.6, even more preferably 1.1 to 1.5, most preferably 1.2 to 1.4. Sentence 21: The process according to one of the preceding sentences, wherein the combustion plant, preferably the furnace (preferably comprising a combustion device and a NH3 decomposition device), is integrated into a plant for the thermal and / or catalytic decomposition of NH3 into N2 and H2. Sentence 22: The process according to one of the preceding sentences, wherein the exhaust gas has a NO content. X which is greater than the content of N2O; preferably wherein the content of NO Xat least twice as large, more preferably at least three times as large, even more preferably at least four times as large, most preferably at least seven times as large and in particular at least ten times as large as the N2O content. Sentence 23: The process according to one of the preceding sentences, wherein the exhaust gas has an NO content which is greater than the N2O content; preferably wherein the NO content is at least twice as large, more preferably at least three times as large, even more preferably at least four times as large, most preferably at least seven times as large and in particular at least ten times as large as the N2O content.Sentence 24: The process according to one of the preceding sentences, wherein the exhaust gas has an NO2 content which is greater than the N2O content; preferably wherein the NO2 content is at least twice as high, more preferably at least three times as high, even more preferably at least four times as high, most preferably at least seven times as high and in particular at least ten times as high as the N2O content. Sentence 25: The process according to one of the preceding sentences, wherein the exhaust gas has an N2O content which is greater than the NOX content; preferably wherein the N2O content is at least twice as high, more preferably at least three times as high, even more preferably at least four times as high, most preferably at least seven times as high and in particular at least ten times as high as the NOX content.Sentence 26: The process according to one of the preceding sentences, wherein the exhaust gas has an N2O content which is greater than the NO content; preferably wherein the N2O content is at least twice as high, more preferably at least three times as high, even more preferably at least four times as high, most preferably at least seven times as high and in particular at least ten times as high as the NO content. Sentence 27: The process according to one of the preceding sentences, wherein the exhaust gas has an N2O content which is greater than the NO2 content; preferably wherein the N2O content is at least twice as high, more preferably at least three times as high, even more preferably at least four times as high, most preferably at least seven times as high and in particular at least ten times as high as the NO2 content. Sentence 28: The process according to one of the preceding sentences, wherein the exhaust gas has an NO content. Xof at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 30 ppmv, even more preferably at least 40 ppmv, and in particular at least 50 ppmv. Sentence 29: The process according to one of the preceding sentences, wherein the exhaust gas contains NO X of at least 75 ppmv, preferably at least 100 ppmv, more preferably at least 150 ppmv, even more preferably at least 200 ppmv, and in particular at least 250 ppmv. Sentence 30: The process according to one of the preceding sentences, wherein the exhaust gas has a NO Xof at least 500 ppmv, preferably at least 1000 ppmv, more preferably at least 2000 ppmv, even more preferably at least 3000 ppmv, and in particular at least 3500 ppmv. Sentence 31: The process according to any one of the preceding sentences, wherein the exhaust gas has an N2O content of at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 30 ppmv, even more preferably at least 40 ppmv, and in particular at least 50 ppmv. Sentence 32: The process according to any one of the preceding sentences, wherein the exhaust gas has an N2O content of at least 75 ppmv, preferably at least 100 ppmv, more preferably at least 150 ppmv, even more preferably at least 200 ppmv, and in particular at least 250 ppmv. Sentence 33: The process according to any one of the preceding sentences, wherein the exhaust gas has an N2O content of at least 500 ppmv, preferably at least 1000 ppmv, more preferably at least 2000 ppmv, even more preferably at least 3000 ppmv, and in particular at least 3500 ppmv.Sentence 34: The process according to one of the preceding sentences, wherein the exhaust gas has an H2O content of less than 2.0 vol.%. Sentence 35: The process according to one of the preceding sentences, wherein the exhaust gas has an H2O content of more than 4.0 vol.%; preferably at least 5.0 vol.%, more preferably at least 6.0 vol.%, even more preferably at least 7.0 vol.%, most preferably at least 8.0 vol.%, and in particular at least 9.0 vol.%. Sentence 36: The process according to one of the preceding sentences, wherein the exhaust gas has an H2O content of at least 10 vol.%; preferably at least 12 vol.%, more preferably at least 14 vol.%, even more preferably at least 16 vol.%, most preferably at least 18 vol.%, and in particular at least 20 vol.%. Sentence 37: The process according to one of the preceding sentences, wherein the exhaust gas has an H2O content in the range of 10±8 vol.%; preferably in the range of 10±7 vol%, more preferably in the range of 10±6 vol.-%, more preferably in the range of 10±5 vol.%, most preferably in the range of 10±4 vol.%, and in particular in the range of 10±3 vol.%. Sentence 38: The process according to any one of the preceding sentences, wherein the exhaust gas has an H2O content in the range of 15±8 vol.%; preferably in the range of 15±7 vol.%, more preferably in the range of 15±6 vol.%, even more preferably in the range of 15±5 vol.%, most preferably in the range of 15±4 vol.%, and in particular in the range of 15±3 vol.% Sentence 39: The process according to any one of the preceding sentences, wherein the exhaust gas has an H2O content in the range of 20±8 vol.%; preferably in the range of 20±7 vol.%, more preferably in the range. of 20±6 vol.%, more preferably in the range of 20±5 vol.%, most preferably in the range of 20±4 vol.%, and in particular in the range of 20±3 vol.%. Sentence 40: The process according to any one of the preceding sentences, wherein the exhaust gas has an H2O content in the range of 25±8 vol.%; preferably in the range of 25±7 vol.%, more preferably in the range of 25±6 vol.%, even more preferably in the range of 25±5 vol.%, most preferably in the range of 25±4 vol.%, and in particular in the range of 25±3 vol.%. Sentence 41: The process according to any one of the preceding sentences, wherein the exhaust gas has an H2O content in the range of 30±8 vol.%; preferably in the range of 30±7 vol.%, more preferably in the range of 30±6 vol.%, even more preferably in the range of 30±5 vol.%, most preferably in the range of 30±4 vol.%, and in particular in the range of 30±3 vol.%. Sentence 42: The process according to one of the preceding sentences, wherein the exhaust gas has an N2 content of at most 95 vol.%, preferably at most 90 vol.-%, more preferably at most 85 vol.%, even more preferably at most 80 vol.%, most preferably at most 75 vol.%, and in particular at most 70 vol.%. Sentence 43: The process according to one of the preceding sentences, wherein the exhaust gas has an N2 content of at least 40 vol.%, preferably at least 50 vol.%, more preferably at least 60 vol.%, even more preferably at least 70 vol.%, most preferably at least 80 vol.%, and in particular at least 90 vol.%. Sentence 44: The process according to one of the preceding sentences, wherein the exhaust gas comprises further gaseous constituents; preferably selected from the group consisting of O2, CO, CO2, NH3, CH4 and mixtures thereof.Sentence 45: The method according to one of the preceding sentences, wherein the exhaust gas on leaving the firing system, preferably the furnace, more preferably the combustion device has a temperature of at least 500°C, more preferably at least 600°C, even more preferably at least 700°C, most preferably at least 800°C, and in particular at least 900°C. Sentence 46: The method according to one of the preceding sentences, wherein the exhaust gas on leaving the firing system, preferably the furnace, more preferably the combustion device has a temperature of at most 1100°C, more preferably at most 1000°C, even more preferably at most 900°C, most preferably at most 800°C, and in particular at most 700°C. Sentence 47: The process according to one of the preceding sentences, wherein the exhaust gas upon leaving the combustion plant, preferably the furnace, more preferably the combustion device, has a pressure of at most 1.5 bar; preferably atmospheric pressure.Sentence 48: The process according to one of the preceding sentences, wherein the exhaust gas has an oxidation level of NO when leaving the combustion plant, preferably the furnace, more preferably the combustion device. X of at least 10%, more preferably at least 20%, even more preferably at least 30%, most preferably at least 40%, and in particular at least 50%. Sentence 49: The process according to one of the preceding sentences, wherein the exhaust gas upon leaving the combustion plant, preferably the furnace, more preferably the combustion device, has an oxidation level of NO Xof at most 90%, more preferably at most 80%, even more preferably at most 70%, most preferably at most 60%, and in particular at most 50%. Sentence 50: The process according to one of the preceding sentences, wherein the exhaust gas has an O2 content of less than 2.0 vol.% upon leaving the combustion plant, preferably the furnace, more preferably the combustion plant. Sentence 51: The process according to one of the preceding sentences, wherein the exhaust gas has an O2 content of more than 4.0 vol.% upon leaving the combustion plant, preferably the furnace, more preferably the combustion plant. Sentence 52: The process according to one of the preceding sentences, wherein the exhaust gas has a temperature of at least 300°C, more preferably at least 350°C, even more preferably at least 400°C, most preferably at least 425°C, and in particular at least 450°C upon entering the exhaust gas treatment plant.Sentence 53: The method according to one of the preceding sentences, wherein the exhaust gas has a temperature of at least 500°C, more preferably at least 550°C, even more preferably at least 600°C, most preferably at least 625°C, and in particular at least 650°C upon entering the exhaust gas treatment plant. Sentence 54: The method according to one of the preceding sentences, wherein the exhaust gas has a temperature of at most 825°C, more preferably at most 800°C, even more preferably at most 775°C, most preferably at most 750°C, and in particular at most 725°C upon entering the exhaust gas treatment plant. Sentence 55: The process according to any one of the preceding sentences, wherein the exhaust gas has a temperature of at most 700°C, more preferably at most 650°C, even more preferably at most 600°C, most preferably at most 550°C, and in particular at most 500°C upon entry into the exhaust gas treatment plant.Sentence 56: The method according to one of the preceding sentences, wherein the exhaust gas on entering the exhaust gas treatment plant has a temperature which is at least 20°C, preferably at least 40°C, more preferably at least 60°C, even more preferably at least 80°C, most preferably at least 100°C, and in particular at least 120°C lower than the temperature which the exhaust gas has on leaving the firing plant, preferably the furnace, more preferably the combustion device. Sentence 57: The method according to one of the preceding sentences, wherein the exhaust gas on entering the exhaust gas treatment plant has a pressure of at most 1.2 bar; preferably atmospheric pressure. Sentence 58: The method according to one of the preceding sentences, wherein the exhaust gas on entering the exhaust gas treatment plant has an oxidation degree of NO. X of at least 10%, preferably at least 20%, more preferably at least 30%, most preferably at least 40%, and in particular at least 50%. Sentence 59: The process according to one of the preceding sentences, wherein the exhaust gas has an oxidation level of NO upon entry into the exhaust gas treatment plant. Xof at most 90%, more preferably at most 80%, even more preferably at most 70%, most preferably at most 60%, and in particular at most 50%. Sentence 60: The process according to one of the preceding sentences, wherein the exhaust gas has an O2 content of less than 2.0 vol.% upon entering the exhaust gas treatment plant. Sentence 61: The process according to one of the preceding sentences, wherein the exhaust gas has an O2 content of more than 4.0 vol.% upon entering the exhaust gas treatment plant.Sentence 62: The process according to any one of the preceding sentences, wherein step (d) comprises reducing the content of N2O in the exhaust gas by (d1) decomposing N2O on an N2O decomposition catalyst; preferably wherein the N2O decomposition catalyst comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt or copper, loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the type MFI, BEA, FER, MOR, FAU and / or MEL.Sentence 63: The process according to any one of the preceding sentences, wherein step (d) comprises reducing the N2O content in the exhaust gas by (d2) chemically reducing N2O with a reducing agent over an N2O reduction catalyst; preferably wherein the N2O reduction catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the type MFI, BEA, FER, MOR, FAU and / or MEL. Sentence 64: The process according to any one of the preceding sentences, wherein the reducing agent in step (d2) is selected from NH3, hydrocarbons, CO, H2 and mixtures thereof; preferably NH3.Sentence 65: The process according to any one of the preceding sentences, wherein the reducing agent in step (d2) is NH3, which is used in an amount of 0.5 to 2.0 molar parts, preferably 0.8 to 1.8 molar parts, based on a molar proportion of N2O to be chemically reduced. Sentence 66: The process according to any one of the preceding sentences, wherein the reducing agent in step (d2) is a hydrocarbon or a mixture of several hydrocarbons, which are preferably used in an amount of 0.2 to 1.0 molar parts, more preferably 0.2 to 0.7 molar parts, based on a molar proportion of N2O to be degraded. Sentence 67: The process according to any one of the preceding sentences, wherein the NO. X-reduction catalyst comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt or copper loaded zeolite; more preferably an iron loaded zeolite; even more preferably an iron loaded zeolite of the MFI, BEA, FER, MOR, FAU and / or MEL type. Sentence 68: The process according to any one of the preceding sentences, wherein the reducing agent in step (e) is selected from NH3, hydrocarbons, CO, H2, and mixtures thereof; preferably NH3. Sentence 69: The process according to any one of the preceding sentences, wherein the reducing agent in step (e) is NH3, which is used in an amount of 0.9 to 2.5 molar fractions, preferably 1.0 to 1.4 molar fractions, more preferably 1.0 to 1.2 molar fractions, based on a molar fraction of NO to be chemically reduced. XSentence 70: The process according to one of the preceding sentences, wherein the reducing agent in step (d2) is the same as the reducing agent in step (e); preferably NH3. Sentence 71: The process according to one of the preceding sentences, wherein the exhaust gas treatment plant comprises a first reaction zone and a second reaction zone arranged downstream thereof, through which the exhaust gas flows one after the other; wherein reducing agent is added to the exhaust gas upstream of the first reaction zone; wherein firstly in the first reaction zone the NOX content in the exhaust gas is reduced by chemical reduction of NOX with reducing agent on a NOX reduction catalyst; (step (e)); wherein optionally additionally the N2O content in the exhaust gas is reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2));wherein optionally further reducing agent is added to the exhaust gas upstream of the second reaction zone; and wherein subsequently, in the second reaction zone, the N2O content in the exhaust gas is reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2));wherein optionally the NOX content in the exhaust gas is further reduced by chemical reduction of NOX on a NOX reduction catalyst (step (e)). Sentence 72: The process according to sentence 71, wherein the NOX reduction catalyst in the first reaction zone comprises a conventional SCR catalyst, preferably based on V2O5-WO3- / TiO2. Sentence 73: The process according to sentence 71 or 72, wherein the temperature of the exhaust gas upon entry into the first reaction zone is at most 400°C, preferably at most 350°C. Sentence 74: The process according to any one of sentences 71 to 73, wherein the N2O decomposition catalyst in the second reaction zone comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite;more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU and / or MEL type. Sentence 75: The process according to any one of Sentences 71 to 74, wherein the temperature of the exhaust gas upon entry into the second reaction zone is in the range from 300 to 550°C, preferably 350 to 500°C. Sentence 76: The process according to any one of Sentences 71 to 75, wherein the NO; X -reduction catalyst in the first reaction zone comprises a zeolitic material; preferably a transition metal (one- finally lanthanide), in particular a zeolite loaded with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU and / or MEL type. Sentence 77: The process according to any one of sentences 71 to 76, wherein the temperature of the exhaust gas upon entering the first reaction zone is at least 300°C, more preferably at least 350°C, even more preferably at least 400°C. Sentence 78: The process according to any one of sentences 71 to 77, wherein the temperature of the exhaust gas upon entering the first reaction zone is at most 600°C, more preferably at most 550°C. Sentence 79: The process according to any one of sentences 71 to 78, wherein the N2O decomposition catalyst in the second reaction zone comprises a NOX-sensitive N2O decomposition catalyst.Sentence 80: The process according to any one of sentences 71 to 79, wherein the temperature of the exhaust gas on entering the second reaction zone is at least 300°C, more preferably at least 350°C, even more preferably at least 400°C. Sentence 81: The process according to any one of sentences 71 to 80, wherein the temperature of the exhaust gas on entering the second reaction zone is at most 600°C, more preferably at most 550°C. Sentence 82: The process according to any one of sentences 71 to 81, wherein the exhaust gas after leaving the first reaction zone and before entering the second reaction zone has a NOX content in the range from 0 to 200 ppmv, preferably 1 to 200 ppmv, and an N2O content in the range from 200 to 2000 ppmv.Sentence 83: The process according to any one of Sentences 71 to 82, wherein the exhaust gas after leaving the first reaction zone and before entering the second reaction zone has a NOX content of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv and a N2O content in the range from 200 to 2000 ppmv.Sentence 84: The method according to one of the preceding sentences, wherein the exhaust gas treatment system comprises a first reaction zone and a second reaction zone arranged downstream of it, through which the exhaust gas flows one after the other; wherein reducing agent is added to the exhaust gas between the first reaction zone and the second reaction zone; wherein firstly in the first reaction zone the N2O content in the exhaust gas is reduced by decomposition of N2O on an N2O decomposition catalyst (step (d1)); and wherein subsequently in the second reaction zone the NOX content in the exhaust gas is reduced by chemical reduction of NOX with reducing agent on an NOX reduction catalyst (step (e)); wherein optionally in addition the N2O content in the exhaust gas is further reduced by further decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)).Clause 85: The process according to clause 84, wherein no reducing agent is added to the exhaust gas before the first reaction zone. Sentence 86: The process according to sentence 84 or 85, wherein the N2O decomposition catalyst in the first reaction zone comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the type MFI, BEA, FER, MOR, FAU and / or MEL. Sentence 87: The process according to any one of sentences 84 to 86, wherein the N2O decomposition catalyst in the first reaction zone comprises a NO X -sensitive N2O decomposition catalyst. Sentence 88: The process according to any one of Sentences 84 to 87, wherein the NO X-reduction catalyst in the second reaction zone comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU and / or MEL type. Sentence 89: The process according to any one of sentences 84 to 88, wherein the space velocities in the first reaction zone and in the second reaction zone are adjusted such that in the first reaction zone the N2O content in the exhaust gas is reduced by at most 95%, preferably at most 90%, based on the N2O content in the exhaust gas upon entry into the first reaction zone.Sentence 90: The process according to any one of sentences 84 to 89, wherein in the second reaction zone a further reduction in the N2O content in the exhaust gas takes place by at least 30%, preferably at least 40%, more preferably at least 50%, based on the N2O content in the exhaust gas upon entry into the second reaction zone. Sentence 91: The process according to any one of sentences 84 to 90, wherein in the second reaction zone a further reduction in the N2O content in the exhaust gas takes place by chemical reduction of N2O with reducing agent on an N2O reduction catalyst (step (d2)). Sentence 92: The process according to any one of sentences 71 to 91, wherein the first reaction zone and the second reaction zone are spatially separated. Sentence 93: The process according to any one of sentences 71 to 92, wherein the first reaction zone and the second reaction zone are spatially connected to one another.Sentence 94: The process according to any one of sentences 71 to 93, wherein the first reaction zone and the second reaction zone are arranged in a common vessel. Sentence 95: The process according to any one of sentences 71 to 94, wherein the temperature of the exhaust gas in the first reaction zone and in the second reaction zone is at most 500°C, preferably in the range from 350 to 450°C. Sentence 96: The process according to any one of sentences 71 to 95, wherein the space velocity in the first reaction zone is greater than in the second reaction zone; preferably by at least a factor of 1.2, more preferably at least a factor of 1.4, even more preferably at least a factor of 1.6, most preferably at least a factor of 1.8, and in particular at least a factor of 2.0. Sentence 97: The process according to any one of sentences 71 to 96, wherein the space velocity in the first reaction zone is lower than in the second reaction zone; preferably by at least a factor of 1.5, more preferably at least a factor of 2.0, even more preferably at least a factor of 3.0, most preferably at least a factor of 5.0, and especially at least a factor of 10.0. Sentence 98: The process according to any one of sentences 71 to 97, wherein the temperature in the first reaction zone is at least 450°C, more preferably at least 500°C, even more preferably at least 550°C, most preferably at least 600°C, and especially at least 650°C. Clause 99: The process according to any one of clauses 71 to 98, wherein the temperature in the second reaction zone is at most 600°C, more preferably at most 550°C, even more preferably at most 500°C, most preferably at most 450°C and in particular at most 400°C.Sentence 100: The process according to any one of sentences 71 to 99, wherein the temperature in the first reaction zone is relatively higher than the temperature in the second reaction zone by at least 20°C, more preferably by at least 40°C, even more preferably by at least 60°C, most preferably by at least 80°C, and in particular by at least 100°C. Sentence 101: The process according to any one of sentences 71 to 100, wherein the temperature in the first reaction zone is relatively higher than the temperature in the second reaction zone by at least 120°C, more preferably by at least 140°C, even more preferably by at least 160°C, most preferably by at least 180°C, and in particular by at least 200°C.Sentence 102: The process according to one of the preceding sentences, wherein the exhaust gas leaves the exhaust gas treatment plant and has a residual NOX content of at most 20 ppmv, preferably at most 15 ppmv, more preferably at most 10 ppmv, even more preferably at most 7.5 ppmv, most preferably at most 5.0 ppmv, and in particular at most 2.5 ppmv. Sentence 103: The process according to one of the preceding sentences, wherein the exhaust gas leaves the exhaust gas treatment plant and has a residual N2O content of at most 20 ppmv, preferably at most 15 ppmv, more preferably at most 10 ppmv, even more preferably at most 7.5 ppmv, most preferably at most 5.0 ppmv, and in particular at most 2.5 ppmv. Sentence 104: The process according to one of the preceding sentences, wherein the N2O decomposition catalyst is arranged in a radial basket through which flow occurs axially. Sentence 105: The process according to any one of the preceding sentences, wherein the N2O decomposition catalyst is particulate and comprises at least 50 particles.Sentence 106: The process according to any one of the preceding sentences, wherein the N2O reduction catalyst is arranged in a radial basket through which flow is axial. Sentence 107: The process according to any one of the preceding sentences, wherein the N2O reduction catalyst is particulate and comprises at least 50 particles. Sentence 108: The process according to any one of the preceding sentences, wherein the NO. X -reduction catalyst is arranged in a radial basket through which the flow is axial. Sentence 109: The procedure according to one of the preceding sentences, where the NO X-reduction catalyst is particulate and comprises at least 50 particles. Sentence 110: The method according to one of the preceding sentences, wherein in the combustion plant at least one parameter is measured as a first measured variable which is characteristic of the current operating state of the combustion plant. Sentence 111: The method according to sentence 110, wherein the first measured variable is selected from the group consisting of combustion temperature, NH3 consumption, possibly rotational speed, and noise level of the combustion plant. Sentence 112: The method according to one of the preceding sentences, wherein before entering the exhaust gas treatment plant at least one parameter is measured as a second measured variable which is characteristic of the current state of the exhaust gas before entering the exhaust gas treatment plant.Sentence 113: The method according to sentence 112, wherein the second measured variable is selected from the group consisting of NOX content in the exhaust gas; degree of oxidation of the NOX in the exhaust gas; N2O content in the exhaust gas; content of other components in the exhaust gas, such as H2O, O2, and N2; temperature of the exhaust gas; pressure of the exhaust gas; and volume flow of the exhaust gas. Sentence 114: The method according to one of the preceding sentences, wherein at least one parameter which is characteristic of the current state of the exhaust gas at the outlet of the exhaust gas treatment system is measured as a third measured variable. Sentence 115: The method according to sentence 114, wherein the third measured variable is selected from the group consisting of NOX content in the exhaust gas; degree of oxidation of the NOX in the exhaust gas; N2O content in the exhaust gas; content of other components in the exhaust gas, such as H2O, O2, and N2; temperature of the exhaust gas; pressure of the exhaust gas; and volume flow of the exhaust gas.Sentence 116: The method according to one of the preceding sentences, wherein the exhaust gas treatment system comprises a first reaction zone and a second reaction zone through which the exhaust gas flows one after the other, wherein reducing agent is fed between the first reaction zone and the second reaction zone, and wherein after leaving the first reaction zone and before entering the second reaction zone, at least one parameter is measured as a fourth measured variable, which is characteristic of the current state of the exhaust gas after leaving the first reaction zone and before entering the second reaction zone. Sentence 117: The method according to sentence 116, wherein the fourth measured variable is selected from the group consisting of NO content. X in the exhaust gas; degree of oxidation of NO Xin the exhaust gas; N2O content in the exhaust gas; content of other components in the exhaust gas, such as H2O, O2, and N2; temperature of the exhaust gas; pressure of the exhaust gas; and volume flow of the exhaust gas. Sentence 118: The method according to one of sentences 110 to 117, wherein the control of the method is carried out based on the first measured variable and / or based on the second measured variable and / or based on the third measured variable and / or based on the fourth measured variable by targeted modification of a manipulated variable. Sentence 119: The method according to Sentence 118, wherein the manipulated variable is the metered amount of reducing agent. Sentence 120: The method according to one of the preceding sentences, wherein a single heat exchanger is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place. Sentence 121: The method according to one of the preceding sentences, wherein at least two heat exchangers are arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place one after the other. Sentence 122: The method according to one of the preceding sentences, wherein at least three heat exchangers are arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, in which the cooling of the exhaust gas takes place one after the other. Sentence 123: The method according to one of the preceding sentences, wherein at least four heat exchangers are arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas,in which the exhaust gas is cooled one after the other. Sentence 124: The method according to one of the preceding sentences, wherein at least five heat exchangers are arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, in which the exhaust gas is cooled one after the other. Sentence 125: The method according to one of the preceding sentences, wherein in step (f), the cooling of the exhaust gas in the at least one heat exchanger takes place by releasing heat from the exhaust gas to a heat transfer medium; wherein the heat transfer medium is preferably selected from the group consisting of water, water vapor, combustion air, NH3, and combinations thereof. Sentence 126: The method according to one of the preceding sentences, wherein in step (f), the cooling of the exhaust gas takes place in a first exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. Sentence 127: The method according to one of the preceding sentences,wherein in step (f) the cooling of the exhaust gas takes place in a first exhaust gas / combustion air heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. Sentence 128: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / H2O heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, and - in a first exhaust gas / combustion air heat exchanger which is also arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas; preferably downstream of the first exhaust gas / H2O heat exchanger Sentence 129: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, and - in a second, Exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas. Sentence 130: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas.Sentence 131: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place in at least one exhaust gas / combustion gas heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the first exhaust gas / combustion air heat exchanger, the first exhaust gas / H2O heat exchanger, and / or the second exhaust gas / combustion air heat exchanger. Sentence 132: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place in at least one exhaust gas / combustion gas heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the first exhaust gas / combustion air heat exchanger, the first exhaust gas / H2O heat exchanger, and / or the second exhaust gas / combustion air heat exchanger.Sentence 133: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place in at least one second exhaust gas / H2O heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the first exhaust gas / combustion air heat exchanger, the first exhaust gas / H2O heat exchanger, and / or the second exhaust gas / combustion air heat exchanger.Sentence 134: The method according to one of the preceding sentences, wherein in step (f) of the method the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - in an exhaust gas / combustion gas heat exchanger which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas.Sentence 135: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first off-. gas / H2O heat exchanger, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / H2O heat exchanger, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas.Sentence 136: The method according to one of the preceding sentences, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, - in an exhaust gas / combustion gas heat exchanger, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas / combustion gas heat exchanger.Sentence 137: A device comprising (i) a combustion plant operated with NH3; preferably a furnace (preferably comprising a combustion device and NH3 decomposition device) for catalytically decomposing NH3 into N2 and H2; and (ii) an exhaust gas treatment plant; wherein the device is configured to carry out the method according to one of the preceding sentences.

[0495] Particularly preferred embodiments of the invention are explained below with reference to the figures. In all these embodiments, NH3 is preferably preheated with steam and steam condensate, optionally exclusively or additionally.

[0496] Figure 1 schematically shows a preferred embodiment of the invention. NH3 is fed into an NH3 decomposition device (1), which is designed analogously to a primary reformer, and therein catalytically decomposed on an NH3 decomposition catalyst into a product gas comprising H2+N2+NH3. In parallel, a combustion gas comprising NH3+N2+H2 is mixed with combustion air comprising N2+O2 in a combustion device (2) and burned. The combustion heat generated thereby fires the NH3 decomposition device (1). The exhaust gas produced during combustion, comprising N2+H2O+NOX+N2O, enters an exhaust duct (3) and is fed to an exhaust gas treatment system (4), in which the NOX and N2O content is virtually completely removed. The exhaust gas leaving the exhaust gas treatment system, comprising N2+H2O, passes through a fan (5) and exits the system through a chimney (6).The product gas comprising H2+N2+NH3 formed during the catalytic decomposition is separated in a pressure swing adsorption plant (7) into H2 as product and an off-gas comprising NH3+N2+H2, which is used as the combustion gas, if necessary after dosing in additional NH3.

[0497] Figure 2 schematically shows a preferred embodiment of the invention (process variant #1). The exhaust duct contains a first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, in which NH3 absorbs heat from the exhaust gas and is then fed to the NH3 decomposition device. The exhaust gas treatment system is arranged downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas. A first exhaust gas / H2O heat exchanger (Q5) is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, in which water absorbs heat from the exhaust gas. Downstream of the first exhaust gas / H2O heat exchanger (Q5) in the flow direction of the exhaust gas is a second exhaust gas / combustion air heat exchanger (Q6) in which combustion air absorbs heat from the exhaust gas and is then fed to the combustion device.

[0498] Figure 3 schematically shows a preferred embodiment of the invention (process variant #2). The exhaust duct contains a first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, in which NH3 absorbs heat from the exhaust gas and is then fed to a first pre-reactor (NH3 decomposition device) for the partial catalytic decomposition of NH3. The intermediate product gas is preferably cooled, for example, from 650°C at the inlet of the first pre-reactor to 360°C at the outlet of the first pre-reactor. Downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, a second exhaust gas / NH3 heat exchanger (Q2) is arranged. In the second exhaust gas / NH3 heat exchanger, in which intermediate product gas absorbs heat from the exhaust gas and is then fed to the NH3 decomposition device for the catalytic decomposition of NH3. In the flow direction of the exhaust gas, the exhaust gas treatment system is arranged downstream of the second exhaust gas / NH3 heat exchanger (Q2).Downstream of the exhaust gas treatment system, in the direction of flow of the exhaust gas, a first exhaust gas / H2O heat exchanger (Q5) is arranged, in which water absorbs heat from the exhaust gas. Downstream of the first exhaust gas / H2O heat exchanger (Q5) is arranged a second exhaust gas / combustion air heat exchanger (Q6), in which combustion air absorbs heat from the exhaust gas and is then fed to the combustion device.

[0499] Figure 4 schematically shows a preferred embodiment of the invention (process variant #3). The exhaust duct contains a first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, in which NH3 absorbs heat from the exhaust gas and is then fed to a first pre-reactor (NH3 decomposition device) for the partial catalytic decomposition of NH3. The first intermediate product gas is preferably cooled, for example, from 650°C at the inlet of the first pre-reactor to 480°C at the outlet of the first pre-reactor. Downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, a second exhaust gas / NH3 heat exchanger (Q2) is arranged. In the flow direction of the exhaust gas, the intermediate product gas absorbs heat from the exhaust gas and is then fed to a second pre-reactor (NH3 decomposition device) for the partial catalytic decomposition of NH3.The second intermediate gas is preferentially cooled, for example, from 630°C at the inlet of the second pre-reactor to 510°C at the outlet of the second pre-reactor. A third exhaust gas / NH3 heat exchanger (Q2) is located downstream of the second exhaust gas flow direction. An exhaust gas / NH3 heat exchanger (Q3) is arranged in which intermediate product gas absorbs heat from the exhaust gas and is then fed to the NH3 decomposition device for the catalytic decomposition of NH3. The exhaust gas treatment system is arranged downstream of the third exhaust gas / NH3 heat exchanger (Q3) in the flow direction of the exhaust gas. A first exhaust gas / H2O heat exchanger (Q5) is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, in which water absorbs heat from the exhaust gas. A second exhaust gas / combustion air heat exchanger (Q6) is arranged downstream of the first exhaust gas / H2O heat exchanger (Q5) in the flow direction of the exhaust gas, in which combustion air absorbs heat from the exhaust gas and is then fed to the combustion device.

[0500] Figure 5 schematically shows a preferred embodiment of the invention (process variant #4). The exhaust duct contains a first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, in which NH3 absorbs heat from the exhaust gas and is then fed to a first pre-reactor (NH3 decomposition device) for the partial catalytic decomposition of NH3. The intermediate product gas is preferably cooled, for example, from 650°C at the inlet of the first pre-reactor to 360°C at the outlet of the first pre-reactor. Downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, a second exhaust gas / NH3 heat exchanger (Q2) is arranged. In the second exhaust gas / NH3 heat exchanger, in which intermediate product gas absorbs heat from the exhaust gas and is then fed to the NH3 decomposition device for the catalytic decomposition of NH3. In the flow direction of the exhaust gas, the exhaust gas treatment system is arranged downstream of the second exhaust gas / NH3 heat exchanger (Q2).Downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, a first exhaust gas / combustion air heat exchanger (Q4) is arranged, in which combustion air absorbs heat from the exhaust gas. Downstream of the first exhaust gas / combustion air heat exchanger (Q4) in the flow direction of the exhaust gas, a first exhaust gas / H2O heat exchanger (Q5) is arranged, in which water absorbs heat from the exhaust gas. Downstream of the first exhaust gas / H2O heat exchanger (Q5) in the flow direction of the exhaust gas, a second exhaust gas / combustion air heat exchanger (Q6) is arranged, in which combustion air absorbs heat from the exhaust gas, is then fed to the first exhaust gas / combustion air heat exchanger (Q4) and subsequently to the combustion device. The heating of the combustion air thus takes place in two stages, first in the second exhaust gas / combustion air heat exchanger (Q6) and then in the first exhaust gas / combustion air heat exchanger (Q4).

[0501] Figure 6 schematically shows three preferred embodiments of the invention, which are similar to one another (process variants #5, #6, and #7). In all three process variants, the exhaust gas channel contains a first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, in which NH3 absorbs heat from the exhaust gas and is then fed to a first pre-reactor (NH3 decomposition device) for the partial catalytic decomposition of NH3. In this process, the intermediate product gas is preferably cooled, for example, from 650°C at the inlet of the first pre-reactor to 360°C at the Outlet of the first pre-reactor. A second exhaust gas / NH3 heat exchanger (Q2) is arranged downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas. Intermediate gas in the second exhaust gas / NH3 heat exchanger is then fed to the NH3 decomposition device for the catalytic decomposition of NH3. The exhaust gas treatment system is arranged downstream of the second exhaust gas / NH3 heat exchanger (Q2) in the flow direction of the exhaust gas. A first exhaust gas / combustion air heat exchanger (Q4) is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. Combustion air in the second exhaust gas / NH3 heat exchanger is arranged downstream of the exhaust gas treatment system. In the flow direction of the exhaust gas, a first exhaust gas / H2O heat exchanger (Q5) is arranged downstream of the first exhaust gas / combustion air heat exchanger (Q4), in which water absorbs heat from the exhaust gas.Downstream of the first exhaust gas / H2O heat exchanger (Q5) in the direction of flow of the exhaust gas, a second exhaust gas / combustion air heat exchanger (Q6) is arranged. In this second exhaust gas / combustion air heat exchanger, the combustion air absorbs heat from the exhaust gas, is then fed to the first exhaust gas / combustion air heat exchanger (Q4) and then to the combustion device. The combustion air is thus heated in two stages, first in the second exhaust gas / combustion air heat exchanger (Q6) and then in the first exhaust gas / combustion air heat exchanger (Q4). Downstream of the second exhaust gas / combustion air heat exchanger (Q6) in the direction of flow of the exhaust gas, an exhaust gas / combustion gas heat exchanger (Q7) is arranged. In this second exhaust gas / combustion gas heat exchanger, the combustion gas, namely the off-gas of the pressure swing adsorption device, absorbs heat from the exhaust gas and is then fed to the combustion device.In the flow direction of the exhaust gas, a second exhaust gas / H2O heat exchanger (Q8) is arranged downstream of the exhaust gas / combustion gas heat exchanger (Q7), in which water absorbs heat from the exhaust gas.

[0502] In process variant #5, the residual heat remaining in the exhaust gas is removed with water in the second exhaust gas / H2O heat exchanger (Q8) and transferred to NH3, which is thus preheated from the liquid state (storage temperature -33.5°C) to, for example, -8°C.

[0503] In process variant #6, heat is removed with water in the first exhaust gas / H2O heat exchanger (Q5) and transferred to NH3, which is thus preheated from the liquid state to, for example, 30°C. The residual heat remaining in the exhaust gas is removed with water in the second exhaust gas / H2O heat exchanger (Q8) and also transferred to NH3, which is thus heated to, for example, 45°C.

[0504] In process variant #7, heat is removed in the first flue gas / H2O heat exchanger (Q5) with water and transferred to NH3, which is thus preheated from the liquid state to, for example, 30°C. The residual heat remaining in the flue gas is removed in the second flue gas / H2O heat exchanger (Q8) with water and also transferred to NH3, which is thus heated to, for example, 39°C. The amount of preheated boiler feedwater is increased compared to the amount required to produce steam. The excess boiler feedwater is stored below of an NH3 evaporator into a stream of water vapor condensate and serves as an additional heat carrier.

[0505] Mass balances and temperature profiles for process variants #1 to #7 are summarized in the following tables. All data are scaled for a plant capacity of 1000 mtpd NH3. The numbers 1 to 28 shown in bold refer to the correspondingly marked positions in Figure 7. Two cases, A and B, are distinguished, each of which contains different levels of nitrogen oxides in the exhaust gas. In case A, the exhaust gas contains a comparatively low level of nitrogen oxides of 500 ppmv NO, 10 ppmv NO2, and 10 ppmv N2O. In case B, the exhaust gas contains a comparatively high level of nitrogen oxides of 5000 ppmv NO, 10 ppmv NO2, and 50 ppmv N2O.

[0506] Process variant #1: Process variant 1A 1 2 3 4 5 6 7 8 9 1 0 CO2 mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % Ar mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % H2 mol.- 0.00 0.00 0.00 0.00 0.00 74.29 0.00 28.81 % N2 mol.- 0.00 0.00 0.00 0.00 24.76 0.00 68.55 % NH3 mol.- 99.81 99.81 99.81 99.81 0.86 99.81 2.37 % O2Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % H2O Mol.- 0.19 0.19 0.19 0.19 0.10 0.19 0.26 % NO ppmv 0 0 0 0 0 0 0 NO2ppmv 0 0 0 0 0 0 0 N2O ppmv 0 0 0 0 0 0 0 Mass flow kg / h 3685 3685 3685 3685 36856 4776 3131 6 6 6 6 2 molar kmol / h 2164 2164 2164 2164 4287 280 1547 current temperature °C 272.0 580.0 579.9 580.0 680.0 22.8 27.0 11 12 13 14 15 24 25 26 27 2 8 CO2 mol.- 0.00 0.03 0.03 0.02 0.02 0.00 0.00 % Ar mol.- 0.00 0.90 0.90 0.53 0.53 0.00 0.00 % H2 mol.- 24.39 0.00 0.00 0.00 0.00 0.00 0.00 % N2 mol.- 58.03 75.30 75.30 74.10 74.10 0.00 0.00% NH3 Mol.- 17.32 0.00 0.00 0.00 0.00 0.00 0.00 % O2Mol.- 0.00 20.21 20.21 1.00 0.99 0.00 0.00 % H2O mol.- 0,25 3,56 3,56 24,30 24,36 100,0 100,0 % 0 0. NO ppmv 0 0 0 476 0 0 0 NO2 ppmv 0 0 0 5 0 0 0 N2O ppmv 0 0 0 10 0 0 0 Massestrom kg / h molars kmol / h 1828 2489 2489 4173 4175 1512 1512 Current Temperature °C 26.1 44.3 500.0 870.0 310.2 130.5 230.0 Process variable 1B 1B 0 CO2Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % The Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % H2Mol.- 74.29 0.00 28.81 % N2 Mol.- 0.00 0.00 0.00 0.00 24.76 0.00 68.55 % NH3Mol.- 99.81 99.81 99.81 99.81 0.81 99.8 19.7% O Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % H2O Mol.- 0.19 0.19 0.19 0.19 0.10 0.19 0.26 % NO ppmv 0 0 N2O ppmv 0 0 0 0 0 0 0 Massestrom kg / h 3641 3641 3641 3641 36414 4895 3093 4 4 4 4 6 molar kmol / h 1529 Current Temperature °C 267.4 580.0 579.9 580.0 680.0 22.8 27.0 11 12 13 14 15 24 25 26 27 2 8 CO2Mol.- 0.00 0.00 30.00.20. 0.00 0.00 % Ar Mol.- 0.00 0.90 0.90 0.54 0.54 0.00 0.00 % H2Mol.- 24.25 0.00 0.00 0.00 0.00 0.00 0.00 % N2 Mol.- 57.70 75.30 75.30 73.80 73.84 0.00 0.00 % NH3Mol.- 17.79 0.00.00.00. 0.00 0.00 0.00 % O2 Mol.- 0.00 20.21 20.21 1.00 0.87 0.00 0.00 % H2O Mol.- 0.25 3.56 3.56 24.15 24.74 0.00 % ppm NO 0 0 0 4951 1 0 0 NO2 ppmv 0 0 0 5 0 0 0 N2O ppmv 0 0 0 10 0 0 0 Massestrom kg / h 3583 7285 7285 10868 10903 27237 27237 19237 1 1 9 molar kmol / h 1816 2549 2549 4226 4252 1512 1512 Current Temperature °C 26.0 44.3 500.0 870.2 366.4 130.5 230.0 .

[0507] Process Variant #2: Prozessvariant 2A 1 2 3 4 5 6 7 8 9 1 0 CO2Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % Ar Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % H2Mol.- 0.00 0.00 33.06 33.06 74.29 0.00 28.81 % N2 Mol.- 0.00 0.00 11.02 11.02 24.76 0.00 68.55 % NH3Mol.- 99.81 99.81 55.77 55.77 0.86 99.81 2.37 % O2 Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % H2O Mol.- 0.19 0.19 0.15 0.15 0.10 0.19 0.26 % NO ppmv 0 0 0 0 0 0 0 NO2 ppmv 0 0 0 0 0 0 0 N2O ppmv 0 0 0 0 0 0 0 Massestrom kg / h 3766 3766 3766 3766 37669 3963 3200 9 9 9 9 3 molarer kmol / h 2212 2212 2837 2837 4382 233 1582 Strom Temperatur °C 280.2 650.0 360.0 580.0 0.0 27.0 680.0 22.8 27.0 11 12 13 14 15 24 25 26 27 2 8 CO2Mol.- 0.00 0.03 0.03 0.02 0.02 0.00 0.00 % Ar Mol.- 0.00 0.90 0.90 0.52 0.52 0.00 0.00 % H2Mol.- 25.12 0.00 0.00 0.00 0.00 0.00 0.00 % N2 Mol.- 59.76 75.30 75.30 74.61 74.62 0.00 0.00 % NH3Mol.- 14.87 0.00 0.00 0.00 0.00 0.00 0.00 % O2 Mol.- 0.00 20.21 20.21 1.00 0.99 0.00 0.00 % H2O Mol.- 0.25 3.56 3.56 23.79 23.85 100.0 100.0 % 0 0 NO ppmv 0 0 0 499 0 0 0 NO2 ppmv 0 0 0 5 0 0 0 N2O ppmv 0 0 0 5 kg / h 3596 6658 6658 10255 10258 27237 27237 6 6 6 2 6 molars kmol / h 1814 2330 2330 3984 3987 1512 1512 Current Temperature 24.36 °C, 246.3 919.7 200.9 130.5 230.0 Process Variant 2B 1 2 3 4 5 6 7 8 9 1 0 CO2Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % Mol. 0.00 0.00 0.00 0.00 % H2Mol.- 0.00 0.00 33.06 33.06 74.29 0.00 28.81 % N2 Mol.- 0.00 0.00 11.02 11.02 2.00 8.56 %. NH3 Mol.- 99,81 99,81 55,77 55,77 0,86 99,81 2,37 % O2Mol.- 0,00 0,00 0,00 0,00 0,00 0,00 0,00 % H2O Mol.- 0,19 0,19 0,15 0,15 0,10 0,19 0,26 % NO ppmv 0 0 0 0 0 0 0 NO2ppmv 0 0 0 0 0 0 0 N2O ppmv 0 0 0 0 0 0 0 Massestrom kg / h 3750 3750 3750 3750 37500 3826 3185 0 0 0 0 9 molarer kmol / h 2202 2202 2824 2824 4362 225 1574 Strom Temperatur °C 278,5 650,0 360,0 580,0 680,0 22,8 27,0 11 12 13 14 15 24 25 26 27 2 8 CO2 Mol.- 0,00 0,03 0,03 0,02 0,02 0,00 0,00 % Ar Mol.- 0,00 0,90 0,90 0,53 0,52 0,00 0,00 % H2 Mol.- 25,22 0,00 0,00 0,00 0,00 0,00 0,00 % N2Mol.- 59,99 75,30 75,30 74,47 74,50 0,00 0,00 % NH3 Mol.- 14,54 0,00 0,00 0,00 0,00 0,00 0,00 % O2Mol.- 0,00 20,21 20,21 1,00 0,87 0,00 0,00 % H2O Mol.- 0,26 3,56 3,56 23,48 24,09 100,0 100,0 % 0 0 NO ppmv 0 0 0 5019 1 0 0 NO2ppmv 0 0 0 5 0 0 0 N2O ppmv 0 0 0 10 0 0 0 Massestrom kg / h 3568 6683 6683 10251 10285 27237 27237 5 0 0 5 6 molarer kmol / h 1799 2339 2339 3976 4001 1512 1512 Strom Temperatur °C 26,2 44,3 351,5 919,6 225,8 130,5 230,0

[0508] Process Variant #3: Process Variant 3A 1 2 3 4 5 6 7 8 9 1 0 CO2 Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % Ar Mol.- 0, 0.00 0.00.00. 0.00 0.00 0.00 0.00 0.00 % H2 Mol.- 0.00 0.00 21.45 21.45 33.48 33.48 74.28 0.00 28.81 % N2Mol. 11.16 24.76 0.00 68.54 % NH3 Mol.- 99.81 99.81 71.23 71.23 55.21 55.21 0.86 99.81 2.39 % O2Mol.- 0.00 0.00 0.00.00. 0.00 0.00 0.00 0.00 % H2O Mol.- 0.19 0.19 0.16 0.16 0.15 0.15 0.10 0.19 0.26 % NO ppmv 0 0 N2O ppmv 0 0 0 0 0 0 0 0 0 Massestrom kg / h 3722 3722 3722 3722 37228 37228 37228 4403 3163 8 8 8 8 0 molar kmol / h Strom Temperature °C 276.3 650.0 480.0 630.0 510.0 580.0 680.0 22.8 27.0 11 12 13 14 15 24 25 26 26 27 2 8 CO2Mol.- 0.00.30.30. 0.02 0.00 0.00 % Ar Mol.- 0.00 0.90 0.90 0.53 0.53 0.00 0.00 % H2Mol.- 24.72 0.00 0.00 0.00 0.00 0.00 0.00 % N28 - 5.8 Mol. 75.30 75.30 74.33 74.33 0.00 0.00 % NH3Mol.- 16.21 0.00 0.00 0.00 0.00 0.00 0.00 % O2 Mol.- 0.00 20.21 10.20 .90 .90 0.00 0.00 % H2O Mol.- 0.25 3.56 3.56 24.07 24.13 100.0 100.0 % 0 0 NO ppmv 0 0 0 499 0 0 0 NO2 ppmv 0 0 0 Massestrom kg / h 3603 6906 6906 10509 10513 27237 27237 3 3 3 6 1 molars kmol / h 44.3 436.0 1030.1 262.1 130.5 230.0 Process variant 3B 1 2 3 4 5 6 7 8 9 1 0 CO2Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % Ar Mol.- 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 % H2Mol.- 0,00 0,00 21,45 21,45 33,48 33,48 74,28 0,00 28,81 % N2 Mol.- 0,00 0,00 7,15 7,15 11,16 11,16 24,76 0,00 68,54 % NH3 Mol.- 99,81 99,81 71,23 71,23 55,21 55,21 0,86 99,81 2,39 % O2Mol.- 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 % H2O Mol.- 0,19 0,19 0,16 0,16 0,15 0,15 0,10 0,19 0,26 % NO ppmv 0 0 0 0 0 0 0 0 0 NO2ppmv 0 0 0 0 0 0 0 0 0 N2O ppmv 0...

Claims

Patent claims:

1. A method for reducing the content of NO X and N2O in the exhaust gas of a combustion plant operated with NH3, the method comprising the following steps: (a) burning NH3 to operate the combustion plant, preferably comprising a combustion device and an NH3 decomposition device, for catalytically decomposing NH3 into N2 and H2, producing an exhaust gas which contains N2, H2O, NO Xand N2O and which leaves the combustion plant; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment plant; (d) reducing the N2O content in the exhaust gas by (d1) decomposition of N2O on an N2O decomposition catalyst and / or (d2) chemical reduction of N2O with reducing agent on an N2O reduction catalyst; (e) reducing the NOX content in the exhaust gas by chemical reduction of NOX with reducing agent on an NOX reduction catalyst; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the exhaust gas treatment plant in the flow direction of the exhaust gas. 2.The method according to claim 1, for reducing the content of NOX and N2O in the exhaust gas of a combustion plant operated with NH3 and H2, which is integrated into a plant for the catalytic decomposition of NH3 to N2 and H2, wherein the method comprises the following steps: (a) burning NH3 and H2 to operate the combustion plant (preferably in a combustion device) to produce an exhaust gas which comprises N2, H2O, NOX and N2O and leaves the combustion plant; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment plant which is arranged downstream of the combustion plant and optionally of the at least one heat exchanger in the flow direction of the exhaust gas; (d) reducing the N2O content in the exhaust gas by (d1) decomposition of N2O on a N2O decomposition catalyst and / or. (d2) chemical reduction of N2O with a reducing agent on a N2O reduction catalyst; (e) reducing the NO content X in the exhaust gas by chemical reduction of NO X with reducing agent on a NO X-reduction catalyst; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

3. The method according to one of the preceding claims, wherein in step (b), the cooling of the exhaust gas in the at least one heat exchanger takes place by releasing heat from the exhaust gas to a heat transfer medium, wherein NH3 preferably serves as the heat transfer medium, which is then subsequently fed to the catalytic decomposition in an NH3 decomposition device on an NH3 decomposition catalyst.

4. The method according to one of the preceding claims, wherein in step (b), the cooling of the exhaust gas takes place in at least one first exhaust gas / NH3 heat exchanger, which is arranged downstream of the combustion system in the flow direction of the exhaust gas. 5.The method according to one of the preceding claims, wherein in step (b) the cooling of the exhaust gas takes place - in a first exhaust gas / NH3 heat exchanger which is arranged downstream of the combustion plant in the flow direction of the exhaust gas, and - in a second exhaust gas / NH3 heat exchanger which is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas.

6. The method according to any one of the preceding claims, wherein in step (b) the cooling of the exhaust gas takes place - in a first exhaust gas / NH3 heat exchanger, which is arranged downstream of the combustion plant in the flow direction of the exhaust gas, - in a second exhaust gas / NH3 heat exchanger, which is arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas, and - in a third exhaust gas / NH3 heat exchanger, which is arranged downstream of the second exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas. 7.The process according to any one of the preceding claims, wherein the exhaust gas in step (b) is cooled to a temperature T2 in the range of 400 to 450°C, more preferably 400 to 420°C.

8. The process according to any one of the preceding claims, wherein the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NO X -reduction catalyst independently comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt or copper loaded zeolite; more preferably an iron loaded zeolite; even more preferably, independently of one another, an iron loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU and / or MEL.

9. The process according to any one of the preceding claims, wherein the N2O decomposition catalyst and / or the N2O reduction catalyst and the NO X-reduction catalyst each independently comprise transition metal-loaded zeolites, more preferably each iron-loaded zeolites (Fe zeolites), even more preferably each iron-loaded zeolites of the same structural type, most preferably with the same external shape.

10. The process according to any one of the preceding claims, wherein the N2O decomposition catalyst and the N2O reduction catalyst are made of the same material.

11. The process according to any one of the preceding claims, wherein the N2O decomposition catalyst and the NOX reduction catalyst are made of the same material.

12. The process according to any one of the preceding claims, wherein the N2O reduction catalyst and the NOX reduction catalyst are made of the same material.

13. The process according to any one of the preceding claims, wherein the N2O decomposition catalyst, the N2O reduction catalyst, and the NOx reduction catalyst are made of the same material. 14.The process according to any one of the preceding claims, wherein in step (a) the combustion of NH3 does not take place over a catalyst.

15. The process according to any one of the preceding claims, wherein in step (a) NH3 is burned in a mixture with H2 and wherein the proportion of H2 in the mixture with NH3 is at most 80 mol%, more preferably at most 70 mol%, even more preferably at most 60 mol%, most preferably at most 50 mol%, and in particular at most 40 mol%.

16. The process according to any one of the preceding claims, wherein in step (a) NH3 is burned in a mixture with H2 and wherein the proportion of H2 in the mixture with NH3 is at least 10 mol%. more preferably at least 20 mol%, even more preferably at least 30 mol%, most preferably at least 40 mol%, and in particular at least 50 mol%.

17. The process according to claim 15 or 16, wherein the molar ratio of H2:NH3 in the mixture is in the range from 45:55 to 90:10, preferably 50:50 to 85:15, more preferably 55:45 to 80:20, even more preferably 60:40 to 75:25, most preferably 65:35 to 70:

30.

18. The process according to any one of the preceding claims, wherein the air ratio λ is in the range from 0.9 to 1.7, more preferably 1.0 to 1.6, even more preferably 1.1 to 1.5, most preferably 1.2 to 1.

4.

19. The method according to any one of the preceding claims, wherein the combustion plant comprises a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2. 20.The process according to any one of the preceding claims, wherein the exhaust gas has a NOX content which is greater than the N2O content; preferably wherein the NOX content is at least twice as great, more preferably at least three times as great, even more preferably at least four times as great, most preferably at least seven times as great, and in particular at least ten times as great as the N2O content; preferably wherein the molar ratio of NOX:N2O is more than 10:1, more preferably at least 20:1, even more preferably at least 30:1, most preferably at least 40:1, and in particular at least 50:

1. 21.The process according to any one of the preceding claims, wherein the exhaust gas has a NO content which is greater than the N2O content; preferably wherein the NO content is at least twice as great, more preferably at least three times as great, even more preferably at least four times as great, most preferably at least seven times as great and in particular at least ten times as great as the N2O content.

22. The process according to any one of the preceding claims, wherein the exhaust gas has a NO2 content which is greater than the N2O content; preferably wherein the NO2 content is at least twice as great, more preferably at least three times as great, even more preferably at least four times as great, most preferably at least seven times as great and in particular at least ten times as great as the N2O content.

23. The process according to any one of the preceding claims, wherein the exhaust gas has a NO content. Xof at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 30 ppmv, even more preferably at least 40 ppmv, and in particular at least 50 ppmv.

24. The method according to any one of the preceding claims, wherein the exhaust gas has a content of NO Xof at least 75 ppmv, preferably at least 100 ppmv, more preferably at least 150 ppmv, even more preferably at least 200 ppmv, and in particular at least 250 ppmv.

25. The process according to any one of the preceding claims, wherein the exhaust gas has a NOX content of at least 500 ppmv, preferably at least 1000 ppmv, more preferably at least 2000 ppmv, even more preferably at least 3000 ppmv, and in particular at least 3500 ppmv.

26. The process according to any one of the preceding claims, wherein the exhaust gas has an N2O content of at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 30 ppmv, even more preferably at least 40 ppmv, and in particular at least 50 ppmv.

27. The process according to any one of the preceding claims, wherein the exhaust gas has an N2O content of at least 75 ppmv, preferably at least 100 ppmv, more preferably at least 150 ppmv, even more preferably at least 200 ppmv, and in particular at least 250 ppmv. 28.The process according to any one of the preceding claims, wherein the exhaust gas has an H2O content of more than 4.0 vol.%; preferably at least 5.0 vol.%, more preferably at least 6.0 vol.%, even more preferably at least 7.0 vol.%, most preferably at least 8.0 vol.%, and in particular at least 9.0 vol.%.

29. The process according to any one of the preceding claims, wherein the exhaust gas has an H2O content of at least 10 vol.%; preferably at least 12 vol.%, more preferably at least 14 vol.%, even more preferably at least 16 vol.%, most preferably at least 18 vol.%, and in particular at least 20 vol.%.

30. The process according to any one of the preceding claims, wherein the exhaust gas has an H2O content in the range of 10±8 vol.%; preferably in the range of 10±7 vol%, more preferably in the range of 10±6 vol%, even more preferably in the range of 10±5 vol%, most preferably in the range of 10±4 vol%, and especially in the range of 10±3 vol%. 31.The process according to any one of the preceding claims, wherein the exhaust gas has a H2O content in the range of 15±8 vol%; preferably in the range of 15±7 vol%, more preferably in the range of 15±6 vol%, even more preferably in the range of 15±5 vol%, most preferably in the range of 15±4 vol%, and in particular in the range of 15±3 vol%.

32. The process according to any one of the preceding claims, wherein the exhaust gas has an H2O content in the range of 20±8 vol.%; preferably in the range of 20±7 vol.%, more preferably in the range of 20±6 vol.%, even more preferably in the range of 20±5 vol.%, most preferably in the range of 20±4 vol.%, and in particular in the range of 20±3 vol.% 33. The process according to any one of the preceding claims, wherein the exhaust gas has an H2O content in the range of 25±8 vol.%; preferably in the range of 25±7 vol.%, more preferably in the range of 25±6 vol.%, even more preferably in the range of 25±5 vol.%, most preferably in the range of 25±4 vol.%, and in particular in the range of 25±3 vol.%.

34. The process according to any one of the preceding claims, wherein the exhaust gas has a H2O content in the range of 30±8 vol.%; preferably in the range of 30±7 vol.%, more preferably in the range of 30±6 vol.%, even more preferably in the range of 30±5 vol.%, most preferably in the range of 30±4 vol.-%, and in particular in the range of 30±3 vol.%.

35. The process according to any one of the preceding claims, wherein the exhaust gas has an N2 content of at most 95 vol.%, preferably at most 90 vol.%, more preferably at most 85 vol.%, even more preferably at most 80 vol.%, most preferably at most 75 vol.%, and in particular at most 70 vol.%.

36. The process according to any one of the preceding claims, wherein the exhaust gas has an N2 content of at least 40 vol.%, preferably at least 50 vol.%, more preferably at least 60 vol.%, even more preferably at least 70 vol.%, most preferably at least 80 vol.%, and in particular at least 90 vol.%.

37. The process according to any one of the preceding claims, wherein the exhaust gas comprises further gaseous constituents; preferably selected from the group consisting of O2, CO, CO2, NH3, CH4 and mixtures thereof. 38.The method according to one of the preceding claims, wherein the exhaust gas has a temperature of at least 500°C, more preferably at least 600°C, even more preferably at least 700°C, most preferably at least 800°C, and in particular at least 900°C upon leaving the combustion plant, preferably the combustion plant.

39. The method according to one of the preceding claims, wherein the exhaust gas has a temperature of at most 900°C upon leaving the combustion plant, preferably the combustion plant. 1100°C, more preferably at most 1000°C, even more preferably at most 900°C, most preferably at most 800°C, and in particular at most 700°C.

40. The method according to any one of the preceding claims, wherein the exhaust gas upon leaving the firing plant, preferably the combustion device, has a pressure of at most 1.5 bar; preferably atmospheric pressure.

41. The method according to any one of the preceding claims, wherein the exhaust gas upon leaving the firing plant, preferably the combustion device, has an oxidation degree of NO Xof at least 10%, more preferably at least 20%, even more preferably at least 30%, most preferably at least 40%, and in particular at least 50%.

42. The method according to any one of the preceding claims, wherein the exhaust gas, upon leaving the combustion plant, preferably the combustion device, has an oxidation degree of NOX of at most 90%, more preferably at most 80%, even more preferably at most 70%, most preferably at most 60%, and in particular at most 50%.

43. The method according to any one of the preceding claims, wherein the exhaust gas, upon leaving the combustion plant, preferably the combustion device, has an O2 content of less than 2.0 vol.%.

44. The method according to any one of the preceding claims, wherein the exhaust gas, upon leaving the combustion plant, preferably the combustion device, has an O2 content of more than 4.0 vol.%. 45.The method according to one of the preceding claims, wherein the exhaust gas has a temperature of at least 300°C, more preferably at least 350°C, even more preferably at least 400°C, most preferably at least 425°C, and in particular at least 450°C on entry into the exhaust gas treatment plant.

46. The method according to one of the preceding claims, wherein the exhaust gas has a temperature of at least 500°C, more preferably at least 550°C, even more preferably at least 600°C, most preferably at least 625°C, and in particular at least 650°C on entry into the exhaust gas treatment plant.

47. The method according to one of the preceding claims, wherein the exhaust gas has a temperature of at most 825°C, more preferably at most 800°C on entry into the exhaust gas treatment plant. more preferably at most 775°C, most preferably at most 750°C, and in particular at most 725°C.

48. The method according to any one of the preceding claims, wherein the exhaust gas, upon entering the exhaust gas treatment plant, has a temperature of at most 700°C, more preferably at most 650°C, even more preferably at most 600°C, most preferably at most 550°C, and in particular at most 500°C.

49. The method according to any one of the preceding claims, wherein the exhaust gas, upon entering the exhaust gas treatment plant, has a temperature which is at least 20°C, preferably at least 40°C, more preferably at least 60°C, even more preferably at least 80°C, most preferably at least 100°C, and in particular at least 120°C lower than the temperature which the exhaust gas has upon leaving the combustion plant, preferably the combustion device.The method according to any one of the preceding claims, wherein the exhaust gas has a pressure of at most 1.4 bara upon entering the exhaust gas treatment system, preferably of at most 1.3 bara, more preferably of at most 1.2 bara.

51. The method according to any one of the preceding claims, wherein the exhaust gas has a NOX oxidation level of at most 15%, more preferably of at most 12.5%, even more preferably of at most 10%, most preferably of at most 7.5%, and in particular of at most 5.0% upon entering the exhaust gas treatment system.

52. The method according to any one of the preceding claims, wherein the exhaust gas has an O2 content of less than 2.0 vol.% upon entering the exhaust gas treatment system.

53. The method according to any one of the preceding claims, wherein the exhaust gas has an O2 content of more than 4.0 vol.% upon entering the exhaust gas treatment system. 54.The process according to any one of the preceding claims, wherein step (d) comprises reducing the content of N2O in the exhaust gas by (d1) decomposing N2O on an N2O decomposition catalyst; preferably wherein the N2O decomposition catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanide), in particular with iron, cobalt or copper; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the structure type MFI, BEA, FER, MOR, FAU and / or MEL.

55. The process according to any one of the preceding claims, wherein step (d) comprises reducing the N2O content in the exhaust gas by (d2) chemically reducing N2O with a reducing agent over an N2O reduction catalyst; preferably wherein the N2O reduction catalyst comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU, and / or MEL structural type.

56. The process according to any one of the preceding claims, wherein the reducing agent in step (d2) is selected from NH3, hydrocarbons, CO, H2, and mixtures thereof; preferably NH3. 57.The process according to any one of the preceding claims, wherein the reducing agent in step (d2) is NH3, which is used in an amount of 0.5 to 2.0 molar parts, preferably 0.8 to 1.8 molar parts, based on a molar proportion of N2O to be chemically reduced.

58. The process according to any one of the preceding claims, wherein the reducing agent in step (d2) is a hydrocarbon or a mixture of several hydrocarbons, which are preferably used in an amount of 0.2 to 1.0 molar parts, more preferably 0.2 to 0.7 molar parts, based on a molar proportion of N2O to be degraded. 59.The process according to any one of the preceding claims, wherein the NOx reduction catalyst comprises a zeolitic material; preferably a transition metal (including lanthanide), in particular iron, cobalt, or copper-loaded zeolite; more preferably an iron-loaded zeolite; even more preferably an iron-loaded zeolite of the MFI, BEA, FER, MOR, FAU, and / or MEL structural type.

60. The process according to any one of the preceding claims, wherein the reducing agent in step (e) is selected from NH3, hydrocarbons, CO, H2, and mixtures thereof; preferably NH3.

61. The process according to any one of the preceding claims, wherein the reducing agent in step (e) is NH3, which is used in an amount of 0.9 to 2.5 molar parts, preferably 1.0 to 1.4 molar parts, more preferably 1.0 to 1.2 molar parts, based on a molar part of NO to be chemically reduced. X .

62. The method according to any one of the preceding claims, wherein the reducing agent in step (d2) is the same as the reducing agent in step (e); preferably NH3.

63. The method according to any one of the preceding claims, wherein the exhaust gas treatment system comprises a first catalyst bed and a spatially separate second catalyst bed; wherein the first catalyst bed is arranged upstream of the second catalyst bed in the flow direction of the exhaust gas; optionally, wherein preferably upstream of the first catalyst bed, a first device with a first control valve for metering NH3 into the exhaust gas is arranged; wherein downstream of the first catalyst bed and upstream of the second catalyst bed, a second device with a second control valve for metering NH3 into the exhaust gas is arranged, with which further NH3 is metered into the exhaust gas;wherein both the first catalyst bed and the second catalyst bed each contain an iron-loaded zeolite catalyst; wherein (i) in the first catalyst bed (d1) the N2O content in the exhaust gas is reduced by catalytic decomposition of N2O; and (e) the NOX content in the exhaust gas is incompletely reduced by catalytic chemical reduction of NOX with NH3, wherein at least part of the NH3 originates from incomplete combustion of NH3 in step (a) (NH3 slip); and (ii) in the second catalyst bed (d2) the residual N2O content is reduced by catalytic chemical reduction of N2O with NH3; (d1*) optionally the residual N2O content is reduced by catalytic decomposition of N2O;and (e*) the residual NOX content is reduced by catalytic chemical reduction of NOX with NH3.

64. The process according to claim 63, wherein in the first catalyst bed the catalytic decomposition of N2O is co-catalyzed by NOX present in the exhaust gas.

65. The process according to claim 63 or 64, wherein the incomplete chemical reduction of NO; X with NH3in the first catalyst bed up to a specified residual NO content X which is sufficient to cause a co-catalytic effect on the decomposition of N2O in the first catalyst bed.

66. The method according to any one of claims 63 to 65, wherein additional NH3 is metered into the exhaust gas via the first device; preferably under feedback control; wherein preferably a specific value for the concentration of NO X at the outlet of the first catalyst bed as a target value (setpoint) and the actual concentration of NO Xis measured at the outlet of the first catalyst bed (actual value); and wherein, in the event of a difference between the setpoint and actual value (control difference), the control level of the first control valve is changed to minimize the difference.

67. The method according to claim 66, wherein the amount of additional NH3 is selected such that the residual concentration of NO Xat the outlet of the first catalyst bed is at most 1000 ppmv, preferably at most 500 ppmv, more preferably at most 100 ppmv.

68. The process according to claim 66 or 67, wherein the amount of additional NH3 is selected such that the residual NOX concentration at the outlet of the first catalyst bed is at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 40 ppmv.

69. The process according to any one of claims 63 to 68, wherein residual N2O in the second catalyst bed is degraded to a residual N2O concentration at the outlet of the second catalyst bed of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv, most preferably at most 2 ppmv. 70.The method according to any one of claims 63 to 69, wherein residual NOX in the second catalyst bed is broken down to a residual NOX concentration at the outlet of the second catalyst bed of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv, most preferably at most 2 ppmv.

71. The method according to any one of claims 63 to 70, wherein the further NH3 is metered in using the second device under feedforward control; wherein preferably the concentration of NOX and N2O at the outlet of the first catalyst bed is measured; taking into account the amount of exhaust gas entering the second catalyst bed, the required amount of NH3 is calculated; and the control level of the second control valve is changed using the calculated result (control variable) in order to meter in the required amount of NH3.

72. The process according to any one of claims 63 to 71, wherein the molar ratio of NH3 / (NO. X+N2O) at the inlet to the second catalyst bed is in the range of 1.7 to 6.0; preferably 2.1 to 4.6; more preferably 2.7 to 3.

9.

73. The process according to any one of claims 63 to 72, wherein the molar ratio of NH3 / NO Xat the inlet to the second catalyst bed is in the range of 1.0 to 2.0; preferably 1.1 to 1.6; more preferably 1.2 to 1.

4.

74. The process according to any one of claims 63 to 73, wherein the molar ratio of NH3 / N2O at the inlet to the second catalyst bed is in the range of 0.7 to 4.0; preferably 1.0 to 3.0; more preferably 1.5 to 2.

5.

75. The process according to any one of claims 63 to 74, wherein the further NH3 is not metered in with the second device under feedback control.

76. The process according to any one of claims 63 to 75, wherein the amount of catalyst is selected such that a degradation of N2O of at least 50%, more preferably at least 70%, and even more preferably at least 80%, based on the concentration of N2O at the inlet to the first catalyst bed, occurs in the first catalyst bed. 77.The process according to any one of claims 63 to 76, wherein the amount of catalyst and the amount of additional NH3 are selected such that at the outlet of the first catalyst bed the molar ratio of NOX / N2O is at least 5, more preferably at least 10, even more preferably at least 20.

78. The process according to any one of claims 63 to 77, wherein the space velocity of the first catalyst bed is in the range of 5,000 h-1 to 100,000 h-1, more preferably 10,000 h-1 to 50,000 h-1, even more preferably 15,000 h-1 to 45,000 h-1.

79. The process according to any one of claims 63 to 78, wherein the molar ratio of NOX / N2O at the outlet of the first catalyst bed is at least 10, and the addition of additional NH3 via the second device occurs solely in relation to the amount of incoming NOX. 80.The process according to any one of claims 63 to 79, wherein the temperature of the exhaust gas upon entering the first catalyst bed is at least 400°C, more preferably at least 425°C, even more preferably at least 450°C.

81. The process according to any one of claims 63 to 80, wherein the temperature of the exhaust gas upon entering the first catalyst bed is at most 550°C, more preferably at most 525°C, even more preferably at most 500°C.

82. The process according to any one of claims 63 to 81, wherein, depending on the heat of the chemical reactions taking place in the first catalyst bed and in the second catalyst bed, the inlet temperature of the exhaust gas into the first catalyst bed is selected such that the temperature of the exhaust gas at the outlet of the second catalyst bed is at most 600°C, more preferably at most 550°C, even more preferably at most 520°C.

83. The process according to any one of claims 63 to 82, wherein the space velocity of the second catalyst bed is in the range from 5,000 h-1 to 100,000 h-1, more preferably 10,000 h-1 to 50,000 h-1, even more preferably 15,000 h-1 to 45,000 h-1.

84. The process according to any one of claims 63 to 83, wherein the ratio of the catalyst volumes (V1kat / V2kat) of the first catalyst bed V1kat to the second catalyst bed V2kat is in the range from 1 / 2 to 20 / 1, more preferably 1 / 2 to 10 / 1, even more preferably 1 / 1 to 4 / 1. 85.The process according to any one of claims 63 to 84, wherein at least one, several or all of the following conditions are met: - the pressure of the exhaust gas on entry into the first catalyst bed is at most 5 bara, more preferably at most 4 bara, even more preferably at most 1.3 bara, most preferably at most 1.2 bara and in particular at most 1.1 bara; - the H2O content in the exhaust gas on entry into the first catalyst bed is at least 5 vol.%, more preferably at least 10 vol.%, even more preferably at least 15 vol.%, most preferably at least 20 vol.% and in particular at least 25 vol.%; - the NO content. Xin the exhaust gas upon entry into the first catalyst bed is at least 500 ppmv, more preferably at least 1000 ppmv, even more preferably at least 1500 ppmv, most preferably at least 2000 ppmv, and in particular at least 2500 ppmv; - the N2O content in the exhaust gas upon entry into the first catalyst bed is at most < 500 ppmv, more preferably at most 200 ppmv, even more preferably at most 100 ppmv, but at least 5 ppmv, preferably at least 10 ppmv, more preferably at least 50 ppmv; - the exhaust gas upon entry into the first catalyst bed contains unburned residues of NH3 from the combustion of NH3; - the N2O decomposition catalyst and / or the N2O reduction catalyst is in the form of a honeycomb body; - the NOX reduction catalyst is in the form of a honeycomb body; - the first catalyst bed contains Fe zeolite; - the second catalyst bed contains Fe zeolite; - the exhaust gas flows through a heat exchanger before entering the first catalyst bed and is heated therein; - the NO content Xat the outlet of the first catalyst bed is at most 1000 ppmv, more preferably at most 500 ppmv, even more preferably at most 300 ppmv, most preferably at most 100 ppmv; but preferably at least 10 ppmv, more preferably at least 20 ppm, even more preferably at least 40 ppmv, most preferably at least 100 ppmv, and in particular at least 250 ppmv; - the N2O content at the outlet of the first catalyst bed is at most 20 ppmv, more preferably at most 15 ppmv, even more preferably at most 10 ppmv, most preferably at most 5 ppmv and in particular at most 2 ppmv; - after leaving the first catalyst bed and until entering the second catalyst bed, no intermediate cooling of the exhaust gas takes place; - the molar ratio of N2O:NOX upon entry into the first catalyst bed is at most 0.5, more preferably at most 0.2, even more preferably at most 0.1;- the molar ratio of N2O:NOX at the outlet from the first catalyst bed is at most 0.20, more preferably at most 0.1, even more preferably at most 0.05; - the feeding of NH3 into the exhaust gas in the flow direction of the exhaust gas upstream of the first catalyst bed is optional; if feeding takes place, this is preferably substoichiometric with regard to the NOX content at the inlet to the first catalyst bed; and / or - the feeding of NH3 into the exhaust gas in the flow direction of the exhaust gas downstream of the first catalyst bed and upstream of the second catalyst bed is mandatory, preferably superstoichiometric with regard to the total NO content; X and N2O at the inlet to the second catalyst bed.

86. The process according to any one of the preceding claims, wherein the N2O decomposition catalyst and / or the N2O reduction catalyst and the NO X-reduction catalyst are present independently of one another as monolithic catalyst elements with parallel channels running through them, preferably as monolithic honeycomb bodies 87. The process according to one of the preceding claims, wherein the exhaust gas leaves the exhaust gas treatment plant and has a residual NOX content of at most 20 ppmv, preferably at most 15 ppmv, more preferably at most 10 ppmv, even more preferably at most 7.5 ppmv, most preferably at most 5.0 ppmv, and in particular at most 2.5 ppmv.

88. The process according to one of the preceding claims, wherein the exhaust gas leaves the exhaust gas treatment plant and has a residual N2O content of at most 20 ppmv, preferably at most 15 ppmv, more preferably at most 10 ppmv, even more preferably at most 7.5 ppmv, most preferably at most 5.0 ppmv, and in particular at most 2.5 ppmv.

89. The method according to any one of the preceding claims, wherein in step (f), the cooling of the exhaust gas in the at least one heat exchanger takes place by releasing heat from the exhaust gas to a heat transfer medium; wherein the heat transfer medium is preferably selected from the group consisting of water, water vapor, combustion air, NH3, and combinations thereof.

90. The method according to any one of the preceding claims, wherein in step (f), the cooling of the exhaust gas takes place in a first exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

91. The method according to any one of the preceding claims, wherein in step (f), the cooling of the exhaust gas takes place in a first exhaust gas / combustion air heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas. 92.The method according to one of the preceding claims, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, and - in a first exhaust gas / combustion air heat exchanger, which is also arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas; preferably downstream of the first exhaust gas / H2O heat exchanger 93. The method according to one of the preceding claims, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, and - in a second exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas. 94.The method according to one of the preceding claims, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / combustion air heat exchanger which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas.

95. The method according to one of the preceding claims, wherein in step (f), the cooling of the exhaust gas takes place in at least one exhaust gas / combustion gas heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the first exhaust gas / combustion air heat exchanger, the first exhaust gas / H2O heat exchanger, and / or the second exhaust gas / combustion air heat exchanger.

96. The method according to one of the preceding claims, wherein in step (f), the cooling of the exhaust gas takes place in at least one exhaust gas / combustion gas heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the first exhaust gas / combustion air heat exchanger, the first exhaust gas / H2O heat exchanger, and / or the second exhaust gas / combustion air heat exchanger. 97.The method according to one of the preceding claims, wherein in step (f), the cooling of the exhaust gas takes place in at least one second exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, preferably downstream of the first exhaust gas / combustion air heat exchanger, the first exhaust gas / H2O heat exchanger, and / or the second exhaust gas / combustion air heat exchanger. 98.The method according to one of the preceding claims, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - in an exhaust gas / combustion gas heat exchanger which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas. 99.The method according to one of the preceding claims, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas. - in a second exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / H2O heat exchanger, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas. 100.The method according to one of the preceding claims, wherein in step (f) the cooling of the exhaust gas takes place - in a first exhaust gas / combustion air heat exchanger, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - in a first exhaust gas / H2O heat exchanger, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - in a second exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, - in an exhaust gas / combustion gas heat exchanger, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - in a second exhaust gas / H2O heat exchanger, which is arranged downstream of the exhaust gas / combustion gas heat exchanger in the flow direction of the exhaust gas is. 101.A device comprising (i) a combustion plant operated with NH3, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2; and (ii) an exhaust gas treatment plant; wherein the device is configured to carry out the method according to one of the preceding claims.

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