Reducing NOx and N2O content in exhaust gases from combustion plants operating with NH3

Abstract

The invention relates to reducing the NOx and N2O content in the exhaust gas (flue gas) of an NH3-operated combustion system integrated into a system for catalytic decomposition of NH3 into N2 and H2. To this end, the combustion system preferably comprises a combustion device, in which NH3 is combusted to generate combustion heat, and an NH3 decomposition device, which exchanges heat with the combustion device, 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 combusting NH3 in the combustion device. The combustion device preferably comprises at least a combustor and a combustion chamber. The combustion system is preferably configured like a primary reformer.

Description

[0001] This application claims priority to European patent application No. 22216421.2 filed on December 23, 2022, European patent application No. 23165192.8 filed on March 29, 2023, and German patent application No. 102023118563.2 filed on July 13, 2023.

[0002] The present invention relates to the reduction of NO in the exhaust gas (flue gas) of an NH3-operated firing system integrated into a system for the catalytic decomposition of NH3 into N2 and H2. X and N2O content. To this end, the combustion system preferably includes a combustion device and an NH3 decomposition device. NH3 is burned in the combustion device to generate combustion heat, and the NH3 decomposition device performs heat exchange with the combustion device. In the NH3 decomposition device, NH3 is catalytically decomposed into N2 and H2. The heat required for catalytically decomposing NH3 in the NH3 decomposition device is provided by burning NH3 in the combustion device. The combustion device preferably includes at least a burner and a combustion chamber. The combustion system is preferably constructed similarly to a primary reformer.

[0003] H2 can be obtained from H2O using renewable energy and then converted with N2 into NH3. NH3 is much safer to store and transport than H2. NH3 can then be decomposed again into H2 and N2. After separation from N2, H2 has a wide range of industrial applications.

[0004] The decomposition of NH3 into N2 and H2 is an endothermic reaction (ΔH°=45.9kJ·mol -1 ), where the molar amount is doubled Therefore, this reaction is fundamentally favored by high temperatures and low pressures. The higher the pressure, the higher the temperature must be to obtain a satisfactory reaction yield. 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] The catalytic decomposition of NH₃ provides a product gas containing H₂ in a mixture with N₂ and possibly other gaseous components (e.g., undecomposed NH₃). However, many industrial applications require high-purity H₂, necessitating purification of the product gas before it can be used in industrial applications. While H₂ purification can be achieved through various methods, such as membrane or cryogenic methods, purification by pressure swing adsorption is particularly economical and viable on an industrial scale.

[0006] The catalytic decomposition of NH3 into N2 and H2 occurs in the gas phase at high temperatures and moderate pressures. NH3 is stored as a liquid in refrigerated tanks at atmospheric pressure and -32.8°C. A pump is used to feed NH3 into the system at system pressure. The increased system pressure causes the boiling point of NH3 to rise, for example, to approximately 62.2°C at 27.8 bar. To convert NH3 to the gas phase, heat is supplied to evaporate the NH3.

[0007] Conventional methods for catalytically decomposing NH 3 generate a considerable amount of heat, which can be used to evaporate NH 3 .

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

[0009] FR 1 469 045 A relates to an apparatus consisting of a preheater fed with NH 3 , a shell-and-tube system enclosing a catalyst for cracking NH 3 and optionally a small cell for cleaning H 2 by diffusion, the preheater fed with NH 3 , the shell-and-tube system enclosing a catalyst for cracking NH 3 and optionally the small cell being connected to one another and being present in a single housing containing a heating device.

[0010] CN 111 957 270A 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 inlet for purified gas to undergo a decomposition reaction of the NH3. The resulting mixed gas is discharged via a second outlet for purified gas and then enters the combustion unit via a second inlet for purified gas. The mixed gas contains N2, H2, and undecomposed NH3. The mixed gas enters the combustion unit to provide heat for the decomposition reaction of NH3 in the NH3 decomposition unit, thereby achieving heat self-sufficiency in the H2 production system through NH3 decomposition. No additional fuel is required for energy supply, and the cost of the H2 production system is reduced by NH3 decomposition.

[0011] CN 113 896 168A relates to a method for producing H2 or reducing gas by cracking NH3. The method is carried out using a two-stage process comprising the following steps: liquid NH3 in the feedstock is fully vaporized and heated in a heat exchange gasification system, and then enters a heat exchange NH3 cracking reaction system in the first stage to produce a partial NH3 cracking reaction. The reaction gas from the heat exchange NH3 cracking reaction system in the first stage enters a high-temperature NH3 cracking reaction system in the second stage to undergo a residual NH3 cracking reaction. The high-temperature NH3 cracking reaction gas from the second stage then enters the heat exchange NH3 cracking reaction system and the heat exchange gasification system in sequence to gradually recover heat, thereby producing reducing gas.

[0012] WO 2001 / 087770 A1 is concerned with the autothermal decomposition of NH 3 for the production of high-purity H 2 .

[0013] WO 2011 / 107279 A1 relates to an NH3-based H2 production reactor, comprising an NH3 cracking chamber having an NH3 cracking catalyst, an inner combustion chamber having a combustion or oxidation catalyst in thermal contact with the NH3 cracking chamber, an NH3 gas preheating chamber and an outer shell ring for recovering heat from combustion products leaving the combustion chamber, wherein the cracking chamber, the inner combustion chamber, the preheating chamber and the heat recovery shell ring are in a concentric arrangement.

[0014] WO 2017 / 160154A1 relates to a method for generating energy 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 unit suitable for converting the NH3 gas into a mixture of H2 and N2; (iii) converting the preheated NH3 gas into a mixture of H2 and N2 in the unit; (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) burning the cooled H2 and N2 mixture in the gas turbine for generating energy.

[0015] WO 2019 / 038251 A1 relates to a method for preparing a product gas containing N2 and H2 from NH3, comprising the following steps: non-catalytic partial oxidation of NH3 with a gas containing O2 to obtain a process gas containing N2, water, a certain amount of nitrogen oxides and a residual amount of NH3; cracking at least a portion of the residual NH3 in the process gas into H2 and N2 by contact with a nickel-containing catalyst, and simultaneously reducing a certain amount of nitrogen oxides into N2 and water by reacting with a portion of H2 formed in the process of cracking the process gas by contacting the process gas with the nickel-containing catalyst; and extracting a product gas containing H2 and N2.

[0016] WO 2012 / 039183 A1 relates to an NH3 decomposition device that generates H2 as a combustion improver and to an NH3 oxidation device that uses an oxidation catalyst to react a portion of introduced NH3 with O2, which causes combustion to provide heat required for the NH3 decomposition reaction.

[0017] WO 2012 / 090739 A1 relates to an H2 generator comprising a decomposition device for decomposing a compound containing hydrogen atoms and nitrogen atoms and generating H2; a compound feeding device for feeding the compound to the decomposition device; and an O2 feeding device for feeding O2 to the decomposition device.

[0018] WO 2020 / 095467A relates to a device for producing H2 gas, comprising: an NH3 evaporation device for heating liquid NH3 to produce NH3 gas; a main device for thermal decomposition, which causes combustion of fuel gas, whereby the NH3 gas produced by the NH3 evaporation device is heated and decomposed into N2 gas and H2 gas; a cooler for cooling the gas produced by the decomposition, the gas containing N2 gas and H2 gas produced by decomposition by the main device for thermal decomposition; and a separator for separating H2 gas from the cooled gas produced by the decomposition.

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

[0020] WO 2022 / 096529 A1 relates to a method for cracking NH3, generating H2 and generating electricity, comprising electrolyzing water in feed NH3, evaporating, preheating and cracking NH3 at low temperature using an NH3 synthesis catalyst.

[0021] WO 2022 / 243410 A1 relates to a process for the synthesis of H2 via catalytic cracking of NH3; wherein a stream containing NH3 is subjected to a catalytic cracking step in the presence of heat to obtain combustion gas and a thermal cracking stream containing N2, H2 and possibly residual NH3 and with or without water; wherein the thermal cracking stream is subjected to an H2 recovery step to obtain a high-purity H2 stream.

[0022] WO 2022 / 265647 A1 relates to an NH3 cracking process to recover a renewable H2 product, wherein the cracked gas is purified in a first PSA unit and at least some 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 NO from flue gases produced in an NH3 cracking process using aqueous NH3 solution by selective catalytic reduction (SCR) X The impurity, aqueous NH3 solution is produced by cooling compressed off-gas from an H2 PSA unit used to clean the cracked gas.

[0024] WO 2022 / 265649 A1 relates to reducing the water content of NH3 used in NH3 cracking processes, which enables the use of cracking catalysts that are incompatible with water. 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 the cracked gas is purified in a PSA system. Residual NH3 in the first cracked gas is converted into additional H2 and N2 by supplying the PSA tail gas or a gas derived therefrom to a secondary cracking reactor and further treating the second cracked gas.

[0026] WO 2022 / 265651 A1 relates to a process in which residual NH 3 in an H 2 PSA system is removed from NH 3 cracking gas using a non-zeolitic adsorbent (eg activated carbon, activated alumina or silica gel).

[0027] US2003 / 0143142 A1 and US2017 / 0334722 A1 describe methods for reducing NO in tail gas from nitric acid production. X concentration and N2O concentration.

[0028] CN 114 412 668A relates to an ammonia fuel engine, in particular to an ammonia-hydrogen fusion type hybrid energy system and engine.

[0029] JP 2023 026798A published on March 1, 2023 relates to an exhaust gas treatment system for an ammonia engine, which includes an oxidation catalyst as a first catalyst and a denitration catalyst as a second catalyst, wherein the oxidation catalyst includes a catalyst layer containing Pt and zeolite, and the denitration catalyst includes a catalyst layer containing zeolite that has been 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 of the catalytic removal of nitrogen oxides (NO, NO2, N2O) from exhaust gases formed when ammonia is used as a fuel.

[0031] KR 2023 095308A, published on June 29, 2023, relates to a plant comprising a catalytic reactor, a storage tank for liquid ammonia, and a first distributor for supplying at least a portion of the ammonia supplied from the storage tank to the catalytic reactor as decomposed ammonia. The ammonia supplied to the catalytic reactor contacts an ammonia cracking catalyst to produce nitrogen and hydrogen. A second distributor supplies residual ammonia that has passed through the first distributor to a denitrification reactor and a mixer.

[0032] NH3 has a relatively low calorific value and a low flame propagation velocity, and there is a risk of flame extinction due to incomplete combustion. Furthermore, the combustion of NH3 carries the risk of increased emissions of nitrogen oxides (particularly NO, NO2, and N2O), which affects its suitability as a combustion gas. Gaseous ammonia / hydrogen / air mixtures have been proposed, in which a certain hydrogen content acts as a combustion promoter. These mixtures can be produced, for example, by catalytic or thermally assisted dissociation of NH3.

[0033] To date, the focus of research has been on the optimization of ammonia combustion itself, in particular with regard to energy yield and economic feasibility, but also with regard to the formation of undesirable nitrogen oxides. However, it can be assumed that it is not possible to completely suppress NO in the combustion process. X (i.e. the formation of NO and NO2) and the formation of N2O.

[0034] However, in order to protect health, the environment and the climate, NO should be avoided or at least reduced as much as possible. X , N2O and other components that may be present in the combustion gases (such as CO, HCN or even NH3). Therefore, many industrialized countries have implemented corresponding regulations.

[0035] Furthermore, the combustion of hydrocarbons (CH4, natural gas, etc.) in the presence of NH3 produces exhaust gases that may contain hydrogen cyanide (HCN, hydrocyanic acid). Even small amounts of HCN are problematic, as it is classified as highly toxic, and corresponding low limit values ​​for HCN emissions into the environment must be adhered to. HCN-contaminated exhaust gases can, in principle, be purified using various methods. Alkaline scrubbing operations can form and separate cyanides, but these, in turn, must be handled as highly toxic compounds. Specific oxidation catalysts based on precious metals can be used to convert HCN into CO2, H2O, N2, and various nitrogen oxides. However, this involves considerable procedural complexity and costs. For example, the nitrogen oxides formed must be decomposed in further process steps, such as by means of SCR. Treatment over specific catalysts, such as those based on TiO2, for the hydrolysis of HCN as follows: HCN + H2O → CO + NH3 has also been described. In this case, subsequent further oxidation over a corresponding separate oxidation catalyst is also necessary. Therefore, there is a need for a cleanup process for HCN-contaminated exhaust gases that is characterized by a simple and inexpensive operating mode and low equipment expenditure. 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, the effect of which is that the exhaust gases from combustion systems operating with ammonia as fuel may contain considerable amounts of unburned ammonia (known as NH3 slip, NH3 breakthrough). The acceptable limits for ammonia released into the atmosphere are relatively strict. Therefore, in this case, it must be ensured that the ammonia is oxidized to nitrogen before the exhaust gases can be released into the atmosphere. For this purpose, so-called ammonia slip catalysts (ASCs) have been developed, which are typically based on platinum group noble metals (i.e. Ru, Rh, Pd, Os, Ir, Pt). Such catalysts are not only expensive but also not very selective (i.e. they cannot form NO from NH3). X or N2O) and is sensitive to chlorine and chlorine compounds.

[0037] Therefore, measures are needed that can at least partially eliminate:

[0038] -Nitrogen oxides (especially N2O and NO X (i.e. NO and NO2)),

[0039] - any excess NH3, and

[0040] - any other components in the exhaust gas that are harmful to the environment (such as CO or HCN),

[0041] It is present in the exhaust gases of NH 3 -operated combustion systems for combustion-related reasons, so that the exhaust gases can then be discharged into the ambient air in compliance with all environmental regulations.

[0042] These combustion systems preferably include a combustion device in which NH3 is burned to generate combustion heat, and an NH3 decomposition device in which NH3 is catalytically decomposed into N2 and H2, and which exchanges heat with the combustion device.

[0043] It is necessary to take into account the special circumstances arising from the maximum combustion efficiency of NH3 for operating a combustion system, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2. Important parameters are not only the different compositions of the exhaust gases, but also, in particular, the pressure and temperature of the exhaust gases. These parameters can be compared with the NOx removal methods that have been developed so far. X The parameters of other exhaust gases are very different from those of N2O measures.

[0044] For example, in the industrial production of nitric acid NH3, it is intentionally oxidized to NO X , so that nitric acid can be obtained from it by reaction with water in an absorption tower. Special catalysts made of precious metals are used for oxidation, and the reaction is often carried out under high pressure. The purpose of the NH3 combustion here is to achieve NO X The maximum yield is achieved with a typical water content of about 1-3% by volume in the off-gas.

[0045] In contrast, NH3 is oxidized during combustion, preferably only to the N2 level for operating the combustion system, which preferably includes a combustion device for burning the NH3 and an NH3 decomposition device for splitting the NH3 into N2 and H2. Catalysts are generally not required, and the reaction is usually carried out at atmospheric pressure. The typical water content in the exhaust gas is well above 3% by volume. For example, the combustion of pure NH3 in air with a residual oxygen content of 3 mol% provides more than 28 mol% of water. The main purpose of the NH3 combustion is to generate the energy required for the catalytic decomposition reaction of NH3 into N2 and H2. The low level of nitrogen oxides in the exhaust gas formed during combustion is advantageous here because, in this case, only a relatively small exhaust gas treatment system is required to reduce the nitrogen oxide level in the flue gas and thus comply with the regulatory requirements for permissible emissions, or because only in this case can sufficiently low residual concentrations be achieved using known nitrogen oxide reduction methods.

[0046] Compared to conventional exhaust gas treatment systems used (for example in the case of exhaust gases from plants for the production of HNO3), the inventive combustion of NH3 (preferably in a mixture with H2) combines the catalytic decomposition of NH3 to H2 and offers special features that require special measures.

[0047] Essential features are firstly ambient pressure conditions and secondly very high water contents. The term "ambient pressure" means that the pressure drop can be too great when using conventional catalyst beds based on granular beds, for example. Due to the hydrothermal load on the catalyst in the exhaust gas treatment system (especially in the case of zeolite materials), high water contents combined with simultaneously high temperatures can lead to a gradual deactivation of the catalyst. Therefore, the maximum temperature should be limited. In addition to aging, NO X The chemical reduction of N2O is hardly affected by high water content, whereas the decomposition of N2O by decomposition and / or chemical reduction is significantly impaired by high water content.

[0048] A further difference of the exhaust gas to be treated according to the invention is the relatively high NO X Content, NO X The content can be several thousand ppmv. X The content depends on the conditions of NH3 combustion, in particular on the NH3 content, the presence of any other combustible gases (H2 and / or CH4 (natural gas)) and the air ratio λ. Due to the high temperatures of up to 1000°C or more in combustion, NO X Initially, it is also almost entirely present as NO, i.e. the proportion of NO is very high and the proportion of NO2 is very low. Due to the slow kinetics of NO2 formation at high temperatures and due to the preferred cooling in the downstream heat exchanger, only a small part of the NO is converted into NO2. This means that when the exhaust gas enters the exhaust gas treatment system, NO X The degree of oxidation (β) (i.e. NO2 in the total NO X The molar ratio (β = n(NO2) / (n(NO) + n(NO2))) in the reaction is small, typically <5 vol%. This in turn means that the desired selective catalysis of NO is not sufficient, according to normal SCR, which occurs at a slow rate. X The restore may actually proceed very poorly or slowly.

[0049] There is a fundamental difference between these and the established exhaust gas cleaning in HNO3 systems, where exhaust gas is removed from the “cold” state (thermodynamic NO X After leaving the absorption tower, the mixture containing N2O and NO is gradually heated under a positive pressure of usually 4-10 bar. X For example, in the production of HNO3, the tail gas NO X The oxidation level before entering the corresponding exhaust gas treatment system is typically between 30% and 70% by volume, i.e. close to the NO in a very fast SCR. X The ideal stoichiometric ratio for reduction.

[0050] Therefore, in this case, high NO X Very low NO content XThe combination of oxidation levels and high water content with low operating pressures (near atmospheric pressure) presents particular challenges to the effectiveness of the exhaust gas treatment system of the present invention. Furthermore, there is the challenge or need to eliminate N2O, which is also present in the exhaust gas and cannot be reduced by conventional SCR methods based on V2O5 / TiO2 catalysts.

[0051] Therefore, the purpose and the resulting reaction products in the combustion of NH3 are sometimes very different from each other.

[0052] In conventional plants for the production of nitric acid, the waste gases often have at relatively high pressure:

[0053] - Relatively low levels of NO X ;

[0054] - relatively high proportion of NO2;

[0055] - Relatively high content of N2O;

[0056] - relatively low levels of water; and

[0057] - Zero proportion of unburned NH3 (NH3 slip).

[0058] In contrast, in a combustion system (preferably comprising a combustion device and an NH3 decomposition device for cracking NH3 into N2 and H2), the exhaust gas often has at a relatively low pressure:

[0059] - Relatively high levels of NO X ;

[0060] - relatively small proportion of NO2;

[0061] - Relatively low content of N2O;

[0062] - Significantly higher water content;

[0063] - a possibly non-negligible proportion of unburned NH3 (NH3 slip); and

[0064] - If NH3 is burned together with CH4 (natural gas), a non-negligible proportion of HCN may be produced.

[0065] Eliminating NO from exhaust gas X These special circumstances must be taken into account when analyzing N2O and NH3, which poses special challenges.

[0066] One object of the present invention is to reduce NO in the exhaust gases obtained in NH3-operated combustion systems X(i.e. NO and NO2), N2O and, if necessary, NH3, CO and / or HCN, the combustion system preferably comprises a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2. If necessary, it should be possible to degrade very large amounts of NO in this context. X and additional N2O to reduce their respective contents.

[0067] This object is achieved by the subject matter of the claims.

[0068] A first aspect of the present invention relates to the reduction of NO in the exhaust gas of an NH3-operated combustion system. X and N2O content, the combustion system preferably comprises a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2, wherein the method comprises the following steps:

[0069] (a) burning NH3 (optionally mixed with one or more other combustible gases, such as H2, CH4, etc.) to operate a combustion system, preferably the combustion system comprises a combustion device for burning NH3 (preferably comprising at least one burner and a combustion chamber) and an NH3 decomposition device for cracking NH3 into N2 and H2 to produce a gas containing N2, H2O, NO X and N2O and the exhaust gas leaving the combustion system (with or without HCN), preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2;

[0070] (b) optionally and preferably cooling the exhaust gases in at least one heat exchanger, which is arranged downstream of the combustion system in the flow direction of the exhaust gases;

[0071] (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment system;

[0072] (d) reducing the N2O content in the exhaust gas by the following steps

[0073] (d1) decomposing N2O on an N2O decomposition catalyst, and / or

[0074] (d2) chemically reducing N2O using a reducing agent on an N2O reduction catalyst;

[0075] (e) By X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content; and

[0076] (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.

[0077] The order of steps (d) and (e) is desired; according to the present invention, all options from sequential in time to simultaneous in any order or a mixture thereof are included.

[0078] The present invention is preferably concerned with reducing NO in the exhaust gases of NH3- and H2-operated combustion systems. X and N2O content, the combustion system preferably comprises a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2, wherein the method comprises the following steps:

[0079] (a) burning NH3 and H2 to operate a combustion system, preferably the combustion system comprises a combustion device for burning NH3 (preferably comprising at least one burner and a combustion chamber) and an NH3 decomposition device for cracking NH3 into N2 and H2 to produce a gas containing N2, H2O, NO X and N2O and the exhaust gas leaving the combustion system, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2;

[0080] (b) optionally and preferably cooling the exhaust gases in at least one heat exchanger, which is arranged downstream of the combustion system in the flow direction of the exhaust gases;

[0081] (c) transferring the optionally cooled exhaust gases to an exhaust gas treatment system which is arranged downstream of the combustion system in the flow direction of the exhaust gases and, if appropriate, downstream of the at least one heat exchanger;

[0082] (d) reducing the N2O content in the exhaust gas by the following steps

[0083] (d1) decomposing N2O on an N2O decomposition catalyst, and / or

[0084] (d2) chemically reducing N2O using a reducing agent on an N2O reduction catalyst;

[0085] (e) By X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content; and

[0086] (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.

[0087] It has been found that NO in flue gases can be advantageously utilized X Therefore, in the exhaust gas treatment system, a reducing agent (preferably NH3) is used to reduce NO X The chemical reduction generates a considerable amount of heat, which can be released to a suitable heat transfer medium with the aid of one or more heat exchangers. The heat transfer medium used herein is preferably water or steam, which offers particular safety advantages. The heat absorbed by the heat transfer medium is then preferably used to heat NH3, which is supplied as a feed stream to the NH3 decomposition unit. Alternatively or additionally, the heat can also be used to preheat the combustion air.

[0088] Experimental results or simulation calculations show that, relatively speaking, when using a reducing agent (preferably NH3) to reduce NO X The heat released in the ongoing chemical reduction heats the exhaust gas by up to 70 K, preferably up to 50 K, ie the temperature of the gas leaving the exhaust gas treatment system is up to 70 K, preferably up to 50 K, higher than the temperature of the gas entering the exhaust gas treatment system.

[0089] It has also been found that the amount of nitrogen oxides formed in the exhaust gas during NH3 combustion may depend on many factors, including the H2:NH3 mixture ratio, the air ratio λ, the preheating of the combustion air, the design of the burner, etc.

[0090] The catalytic decomposition of NH3 is used to form H2 as a product. Therefore, another aspect of the present invention relates to a method for producing H2 by catalytic cracking of NH3, comprising the method of the present invention for reducing NO in the exhaust gas of an NH3-operated combustion system. X The method for reducing NO in the exhaust gas of an NH3- and H2-operated combustion system is preferably provided by a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2. This aspect preferably relates to a method for producing H2 by catalytic cracking of NH3, comprising the method of the present invention for reducing NO in the exhaust gas of an NH3- and H2-operated combustion system. X and N2O content, the combustion system preferably includes a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2.

[0091] The exhaust gas treatment system of the present invention comprises at least:

[0092] - N2O reduction catalyst and / or N2O decomposition catalyst; and

[0093] -NO X Reduction catalyst;

[0094] They may be identical or different depending on the given function or functions and may be present in common or separate reaction zones (catalyst beds).

[0095] In a preferred embodiment, the exhaust gas treatment device of the present invention comprises:

[0096] -N2O reduction catalyst;

[0097] - N2O decomposition catalyst; and

[0098] -NO X Reduction catalyst;

[0099] They may be identical or different depending on the given function or functions and may be present in common or separate reaction zones (catalyst beds).

[0100] In a preferred embodiment, the exhaust gas treatment system of the present invention further comprises at least one additional catalyst, or the aforementioned N2O reduction catalyst, N2O decomposition catalyst or NO having at least one additional function selected from the group consisting of: X One of the reduction catalysts:

[0101] -NH3 oxidation catalyst;

[0102] - an HCN decomposition catalyst; and

[0103] -CO oxidation catalyst.

[0104] When the proportion of unburned NH3 in the exhaust gas (NH3 slip) is greater than the amount of NO in the exhaust gas treatment system X When there is a need for NH3 as a reducing agent for N2O and / or N3, an NH3 oxidation catalyst is preferably used so that the exhaust gas still contains residual amounts of NH3 that should not or must not be released into the environment after passing through steps (d1) and / or (d2) and (e). Then, a downstream NH3 oxidation catalyst can be used to decompose these residual amounts of NH3 by oxidation of NH3.

[0105] When the fuel (in addition to NH3) contains hydrocarbons (CH4, natural gas, etc.) and the exhaust gas formed during combustion contains a certain amount of HCN, an HCN decomposition catalyst is preferably used. The HCN decomposition catalyst can then be used to hydrolyze the HCN and oxidize the hydrolysis products (hydrolysates) formed (i.e., oxidation of NH3 and CO, preferably using NO present in the exhaust gas). X and N2O) to decompose (eliminate) the resulting HCN.

[0106] It was surprising to find that while containing NO XHCN in an aqueous exhaust gas containing N2 and N2O (each in a molar amount greater than or equal to the molar amount of HCN) can be decomposed into N2, H2O and CO2 by passing the exhaust gas over a transition metal-loaded zeolite catalyst (for example a package of catalyst pellets comprising an iron-loaded zeolite material of the BEA structure type) at a temperature of 300 to 600°C (preferably 350 to 550°C).

[0107] Thus, in contrast to known methods, the complete elimination of HCN (i.e., conversion into non-toxic substances) can be achieved in a one-stage process, i.e., in one process step without expensive noble metal catalysts. X and N2O, which can be additionally added for the reduction of NO X and NH3 of N2O, and optionally for reducing N2O to HCN-, NO X - and N2O- in the exhaust gas of CO or hydrocarbons (such as CH4 or propane). In this case, the amount of reducing agent should be based on the amount of N2O and NO X If excess N2O is present in the exhaust gas and is reduced with NH3 or CO or hydrocarbons, in each case NO X The content should be reduced to zero (or close to zero) by means of NH3. If CO or hydrocarbons are used as additional reducing agents, any CO emissions can be eliminated by using an additional CO oxidation catalyst downstream of the zeolite catalyst.

[0108] A 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 decomposition catalyst is used to decompose HCN and CO is present in its degradation products. In each case, any CO obtained can then be decomposed by oxidation to CO2 with the aid of a downstream CO oxidation catalyst.

[0109] If the exhaust gas treatment system of the present invention includes an NH3 oxidation catalyst, it is preferred according to the present invention to first cool the exhaust gas to a lower temperature than when it enters the exhaust gas treatment system using a heat exchanger within the exhaust gas treatment system, so that the NH3 oxidation catalyst can optimally exert its effect. Therefore, in a preferred embodiment, the exhaust gas treatment system of the present invention further includes one or more heat exchangers.

[0110] For the purposes of this 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.

[0111] For descriptive purposes, "NO X ” includes nitric oxide (NO) and nitrogen dioxide (NO)2, but not nitrous oxide (N2O).

[0112] Catalysts speed up certain chemical reactions by lowering their activation energy.

[0113] Unless expressly stated otherwise, all figures in ppm are based on volume, i.e. ppmv. Unless expressly stated otherwise, all percentages relating to gas composition are based on volume, i.e. vol%. Unless expressly stated otherwise, all other percentages are based on weight, i.e. wt%.

[0114] Steps (b) and (f) of the process of the present invention are independently optional and preferred.

[0115] The steps (a), optionally (b) and (c) of the method of the present invention are carried out in alphabetical order, and steps (d) and (e) are then carried out in any order. Therefore, step (d) can be carried out before step (e) or after step (e) or simultaneously with step (e). It can also be a mixed form of parts at the same time. When a single and identical catalyst material is capable of catalyzing multiple reactions, this may be particularly relevant. According to the present invention, such an embodiment is particularly preferred. Then, according to the present invention, these reactions may occur simultaneously, although the kinetics of each reaction can vary, so that the first reaction can end earlier than the second reaction carried out in parallel or can achieve a higher conversion rate. The optional step (f) is after steps (d) and (e).

[0116] For the purpose of description, steps (d1) and (d2) are considered separately, but both serve the common purpose of reducing the N2O content in the exhaust gas.

[0117] Steps (d1), (d2) and (e) can likewise be carried out in any order, although a partially simultaneous mixed form is also possible in this respect.

[0118] In a preferred embodiment, the method of the present 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).

[0119] In a preferred embodiment, the exhaust gas undergoes the steps of the method of the present invention in one of the following orders:

[0120] (i)(a)→(c)→(d1)→(e);

[0121] (ii) (a)→(c)→(e)→(d2);

[0122] (iii)(a)→(c)→(e)→(d2)→(d1);

[0123] (iv) (a) → (c) → (e) → (d1 + d2); or

[0124] (v)(a)→(c)→(e)→(d1).

[0125] In a preferred embodiment, the exhaust gas undergoes the steps of the method of the present invention in one of the following orders:

[0126] (vi)(a)→(b)→(c)→(d1)→(e);

[0127] (vii)(a)→(b)→(c)→(e)→(d2);

[0128] (viii)(a)→(b)→(c)→(e)→(d2)→(d1);

[0129] (ix) (a) → (b) → (c) → (e) → (d1 + d2); or

[0130] (x)(a)→(b)→(c)→(e)→(d1).

[0131] In a preferred embodiment, the exhaust gas undergoes the steps of the method of the present invention in one of the following orders:

[0132] (xi)(a)→(b)→(c)→(d1)→(e)→(f);

[0133] (xii)(a)→(b)→(c)→(e)→(d2)→(f);

[0134] (xiii)(a)→(b)→(c)→(e)→(d2)→(d1)→(f);

[0135] (xiv) (a) → (b) → (c) → (e) → (d1 + d2) → (f); or

[0136] (xv)(a)→(b)→(c)→(e)→(d1)→(f).

[0137] (d1+d2) means that both steps (d1) and (d2) are performed, although the two steps (d1) and (d2) are performed at least partially simultaneously, ie the two steps are performed in parallel.

[0138] Between these steps, there may be additional steps that are not explicitly specified.

[0139] Material flow:

[0140] For the purposes of the description, in particular the following substance streams are distinguished:

[0141] NH 3 (reactant), which serves as starting material for the catalytic decomposition and is preferably supplied to the NH 3 decomposition device;

[0142] an intermediate product gas which, in the case of NH3 decomposition devices connected in series, leaves the upstream NH3 decomposition device (preliminary reactor) and is supplied to the downstream NH3 decomposition device (main reactor); in the case of a plurality of preliminary reactors, a plurality of intermediate product gases can be distinguished; the intermediate product gas comprises products of the partial catalytic decomposition of NH3, typically H2, N2 and relatively large amounts of undecomposed NH3;

[0143] - a product gas obtained by the catalytic decomposition of NH 3 , typically H 2 , N 2 and relatively small amounts of undecomposed NH 3 ; in the case of a plurality of NH 3 decomposition units connected in series, the product gas is the gas mixture leaving the last NH 3 decomposition unit connected in series;

[0144] - combustion gas which is combusted in the combustion system of the invention, preferably in the combustion device, to generate combustion heat; the combustion gas comprises NH3 and H2 and optionally additional N2;

[0145] - combustion air, which is supplied to the combustion system of the invention, preferably to the combustion device, so that the combustion gases can be burned in a mixture with the combustion air; the combustion air contains O2 and N2;

[0146] - exhaust gases formed during the combustion of combustion gases in a mixture with combustion air; exhaust gases contain N2, H2O, NO X and N2O.

[0147] The main purpose of this invention is to reduce the NO X and N2O content.

[0148] Step (a):

[0149] In step (a) of the method of the present invention, the combustion of NH3 is used for the operation of the combustion system. Preferably, in step (a) of the method of the present invention, NH3 is burned, optionally in a mixture with other components (such as H2 or CH4). These combustion systems preferably include a combustion device and an NH3 decomposition device, in which NH3 is burned to generate combustion heat, and the NH3 decomposition device is heat-exchanged with the combustion device, and in which NH3 is catalytically decomposed into N2 and H2. The combustion produces a gas containing N2, H2O, NOX and N2O. Residues of unburned NH3 may also be present. The waste gas leaves the combustion system, preferably the combustion device, and is then supplied to optional step (b) of the process of the invention or directly to step (c).

[0150] In the context of the present invention, a "combustion system" generates heat by a combustion process. The combustion system preferably comprises a combustion device for burning NH3 and an NH3 decomposition device for splitting NH3 into N2 and H2. The combustion of the combustion gases generates heat. In the context of the present invention, a "combustion system" or "combustion device" covers any plant in which NH3 or a fuel containing NH3 is oxidized by O2 (preferably from the combustion air) in order to produce N2 and H2O, in particular to produce N2 and H2O as the main products. In the context of the present invention, a plant in which NH3 is oxidized by O2 in order to produce nitrogen compounds with a higher oxidation number (e.g. NO X A system in which nitrogen compounds are produced as the main product (e.g., in the production of nitric acid) is neither a combustion system nor a combustion device. The production of such nitrogen compounds, which have a higher oxidation number than the main product, generally requires a catalyst. Preferably, according to the invention, the combustion system according to the invention is not equipped with a catalyst, i.e., the combustion of NH and H according to the invention (preferably according to the invention) is uncatalyzed.

[0151] Combustion of NH3 means oxidation of NH3 with O2, wherein, according to the invention, this reaction does not have to be complete, so that the exhaust gas may contain residual unburned (unoxidized, unconverted) NH3 (NH3 slip, NH3 breakthrough). This also applies if NH3 is not burned in pure form, but is burned 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, wherein the combustion air can optionally be enriched with O2.

[0152] In a preferred embodiment, in step (a) of the method of the present invention, NH3 is combusted in a combustion system comprising a combustion device for combusting NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2. The combustion of NH3 in the combustion device is used to heat the NH3 decomposition device, preferably a reactor filled with a catalyst, for cracking NH3 into N2 and H2. The cracking of NH3 into N2 and H2 is carried out according to the present invention as catalytic decomposition of NH3 over an NH3 decomposition catalyst.

[0153] According to the present invention, the catalytic decomposition of NH3 refers to the formation of N2 and H2, which is occasionally also referred to as "cracking" in the prior art. For descriptive purposes, the terms "catalytic decomposition," "decomposition," "catalytic cracking," and "cracking" of NH3 are used as interchangeable synonyms. Preferably, according to the present invention, the catalytic decomposition of NH3 is preferably carried out in the absence of O2.

[0154] The combustion system of the present invention preferably includes a combustion device and an NH3 decomposition device that exchange heat with each other. In the combustion device, combustion gas containing NH3 and preferably H2 is combusted with combustion air containing O2, generating combustion heat. The generated combustion heat is at least partially supplied as a heat stream to the NH3 decomposition device (or transferred to the NH3 decomposition device) to provide the heat required for the endothermic catalytic decomposition of NH3 into H2 and N2. Furthermore, according to the present invention, the combustion heat is preferably used to preheat the NH3 to be decomposed, the combustion gas, and the combustion air to an elevated temperature.

[0155] For the purposes of this description, "combustion device" and "furnace" are used as interchangeable synonyms.

[0156] The NH3 decomposition device is preferably a tubular reactor configured similarly to a primary reformer used to produce synthesis gas or hydrogen from natural gas. The basic structure of this fired tubular reactor, constructed similarly to a primary reformer, includes one or more tubes containing an NH3 decomposition catalyst. These tubes are arranged in a combustion chamber and extend into the burner flame. Within the tubes, radiative and convective heat from the flame and hot exhaust gases transfers heat to the NH3 (process gas) flowing through the NH3 decomposition catalyst. Therefore, the combustion device preferably includes a combustion chamber and one or more burners, preferably multiple burners. The NH3 decomposition device (parallel tubes) is then positioned within the combustion device (combustion chamber). To ensure uniform energy input and a defined flame shape, exhaust gases are removed from the combustion device via an applied pressure gradient, for example, by using a compressor for the combustion air supply or exhaust gas removal. To ensure sufficient heat transfer over the length of the NH3 decomposition catalyst bed within the tubes, the exhaust gas must still be at a sufficiently high temperature at the end of the NH3 decomposition catalyst bed (i.e., at the end of the tubes) to allow for significant release of radiative heat. The exhaust gases therefore leave the combustion device (combustion chamber, combustion chamber) at high temperatures, which in the case of a tubular reactor configured similarly to a primary reformer can be above 1000° C. Typically, the proportion of heat transferred to the endothermic catalytic decomposition of NH 3 is approximately 40-60% of the total energy generated by the combustion of the combustion gases. The remaining heat can be used for other purposes.

[0157] After the exhaust gases have been discharged from the combustion device (combustion chamber, combustion chamber), the exhaust gases preferably pass through an exhaust gas duct, which preferably fulfills three main tasks:

[0158] 1. Utilize the unused heat from the combustion of NH3 by endothermic catalytic decomposition of NH3 into N2 and H2, in order to avoid energy waste or improve energy efficiency;

[0159] 2. Preheating of material streams (e.g. NH3, combustion gases, combustion air) in order to improve energy integration and increase hydrogen yield; and

[0160] 3. Reduction of nitrogen oxides (particularly NO, NO2 and N2O) through suitable reaction schemes, with the aim of minimizing emissions or complying with regulatory limits.

[0161] Preferably, step (a) of the process of the present invention (i.e., burning NH3 and preferably H2 to operate the combustion system while producing exhaust gases leaving the combustion system) comprises the following constituent steps:

[0162] (a1) optionally and preferably heating and evaporating (liquid) NH3;

[0163] (a2) optionally and preferably heating the combustion air (preferably comprising N2 and O2);

[0164] (a3) burning the combustion gas (containing NH3 and preferably H2) and the combustion air (containing O2) in a combustion system (preferably a combustion device) to produce an exhaust gas (containing N2, H2O, NO X and N2O) and releases heat of combustion, at least some of which flows into an NH3 decomposition unit; and

[0165] (a4) catalytically decomposing NH3 over an NH3 decomposition catalyst in an NH3 decomposition unit, absorbing the combustion heat from step (a3) ​​and producing a product gas (comprising H2 and N2).

[0166] Combustion of combustion gas and combustion air:

[0167] In a preferred embodiment, NH 3 is burned as the sole fuel, meaning that preferably no other gas is burned besides NH 3. In another preferred embodiment, NH 3 is burned in a mixture with H 2. In a further preferred embodiment, NH 3 is burned in a mixture with CH 4 (natural gas). For descriptive purposes, these gases or mixtures are also referred to as "combustion gas." In addition to NH 3 and optionally H 2 and / or CH 4, the combustion gas may optionally contain further components, such as N 2.

[0168] According to the present invention, heat is provided by the combustion of combustion gas in a combustion system, preferably in a combustion device. For this purpose, the combustion device preferably comprises one or more burners, preferably at least two burners, more preferably at least three burners.

[0169] The combustion gas contains a mixture of H2 and NH3 because, in one reason, the mixture produces a moderate flame temperature and has better combustion properties than pure NH3. A suitable mixing ratio of H2 and NH3 can additionally affect the nitrogen oxide content.

[0170] Preferably, the combustion of NH 3 (or a mixture of NH 3 and another combustible gas (eg H 2 , CH 4 , etc.) (ie the oxidation of NH 3 with O 2 ) is not carried out over a catalyst, ie the combustion is not carried out in the presence of a heterogeneous catalyst.

[0171] More preferably, the H2 present in the combustion gas in a mixture with the NH3 to be combusted is formed by thermal and / or catalytic decomposition of NH3 (constituting step (a4)). The integrated combustion of NH3 with O2 preferably provides energy for the catalytic decomposition (cracking). Therefore, preferably, in step (a), the combustion of NH3 is preferably integrated into a process for the thermal and / or catalytic cracking of NH3 into N2 and H2.

[0172] The composition of the exhaust gas formed during combustion depends on the combustion gas used. In a preferred embodiment, sufficient H2 is added to the NH3 to modify the combustion properties of the combustion gas, thereby achieving a substantial quantitative conversion during the combustion process. In other preferred embodiments, the combustion gas used is a mixture of the output from a separation unit for H2 purification, preferably the exhaust gas from a pressure swing adsorption unit or the retentate of a membrane unit (preferably a pressure swing adsorption unit), and a proportion of NH3 or a proportion of H2 produced as a product.

[0173] If the catalytic decomposition of NH3 is not complete, the product gas (i.e., the product of the catalytic decomposition) will still contain residual unconverted NH3 in addition to N2 and H2. Preferably, the H2 present in the combustion gas in a mixture with the NH3 to be combusted is formed by the catalytic decomposition of NH3 and subsequently separated, possibly in a mixture with residual NH3 and / or N2. The product gas formed from the catalytic decomposition of NH3 is preferably obtained by pressure swing adsorption (PSA). Thus, the product gas obtained in the catalytic decomposition of NH3 (preferably according to the invention) and the catalytic decomposition of NH3 is separated by pressure swing adsorption into:

[0174] - On the one hand, high purity H2 (product hydrogen) and

[0175] - On the other hand, gas mixtures (offgases from pressure swing adsorption).

[0176] In addition to N₂, the gas mixture separated from H₂ (offgas from the pressure swing adsorption) may contain residual NH₃ that has not been catalytically decomposed and a certain amount of H₂. Therefore, the separation efficiency of the device used to purify H₂ determines how much H₂ is present in the offgas of the pressure swing adsorption device or in the retentate of the membrane unit, and thus also influences the composition of the offgas formed therefrom during combustion. For production reasons or economic reasons in terms of production, quantitative separation of the total amount of H₂ is not possible, and therefore the separated gas mixture (offgas from the pressure swing adsorption) usually contains a certain amount of H₂. In this way, a mixture of NH₃ and H₂ is obtained, which can be burned directly as is or first enriched with additional NH₃ (or H₂).

[0177] Therefore, according to the present invention, the gas mixture separated from the product gas by pressure swing adsorption is preferably used as the combustion gas. Depending on the NH3 and H2 contents, the separated gas mixture can be used as the combustion gas in its original form, or appropriate amounts of NH3 or H2 can be metered in to establish the desired NH3 to H2 ratio. If the catalytic decomposition is complete or almost complete, the NH3 content in the separated gas mixture (pressure swing adsorption offgas) may still be too low, and the required amount of NH3 may need to be added.

[0178] The exact composition of the exhaust gas formed during the combustion of the combustion gas depends on the composition of the combustion gas and the combustion air. An essential parameter 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.

[0179] The following table shows the composition of the combustion gas and the exhaust gas formed for the same combustion air composition based on simulation calculations for five different process solutions #1 to #5. The molar streams are normalized to a 1 MW calorific value stream to make them comparable. For process solutions #1 to #3 (comparative examples), pure CH4, pure NH3, and pure H2 are used as combustion gases. For process solutions #4 and #5 (embodiments of the present invention), H2 and NH3 (process solution #4) or a mixture of H2, NH3, N2, and H2O are used as combustion gases (process solution #5; exhaust gas from a pressure swing adsorption unit (PSA)):

[0180]

[0181]

[0182] As shown in the data in the above table, in process scheme #5 of the present invention (offset gas of PSA), the amount of offset gas flowing through the offset conduit is almost twice that in the case of the hydrogen-fired reformer (process scheme #3), and only slightly less than twice that of the methane-fired reformer (process scheme #1).

[0183] Thus, process variant #5 of the present invention has a much flatter temperature profile in the flue gas duct than the other process variants and can therefore include more steps for heat integration, including those possible at low flue gas temperatures. This allows for (almost) complete energy integration, as shown in process variants #5 to #7.

[0184] In the case of hydrogen- or methane-fired reformers, the temperature profile in the exhaust duct must be much steeper due to the smaller available exhaust gas volume. Since heat exchangers in the exhaust duct require a minimum temperature difference for economical design, the risk of unused, non-transferable waste heat due to the required temperature difference is significantly greater with steep temperature profiles. In any case, the exhaust gas entering the exhaust duct is significantly hotter in these cases, necessitating the use of more expensive materials.

[0185] It is preferred to establish a mixing ratio of NH 3 and H 2 in the combustion gas that is optimized for the subsequent combustion. The proportion of H 2 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 H 2 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 %.

[0186] The proportion of H2 is preferably at least 1 mol%, more preferably at least 2 mol%, even more preferably at least 3 mol%, most preferably at least 4 mol%, and in particular at least 5 mol%. The proportion of H2 is preferably 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%.

[0187] In a particularly preferred embodiment, the molar ratio of H2:NH3 in 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, and most preferably 65:35 to 70:30 or 70:30 to 75:25. Since the combustion gas used (preferably according to the present invention) is a separated gas mixture from a gasswing adsorption system, the molar ratio of H2:NH3 depends primarily on its hydrogen yield and can be about 15:1 in extreme cases.

[0188] When a mixture of combustion gas and combustion air is burned, the air ratio λ for combustion is preferably 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. Another very particularly preferred range for the air ratio λ is between 1.0 and 1.2.

[0189] In a particularly preferred embodiment, 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.

[0190] The air ratio λ (i.e., the combustion air ratio) indicates the mass ratio of the combustion air to the combustion gas relative to the stoichiometric ideal ratio of the theoretical complete combustion process. It is defined as the ratio of air to fuel that contains enough 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 molar amount (see, for example, P. Majumdar, Design of Thermal Energy Systems, Wiley 2021, page 66, No. 2.13.5.2). For the purpose of description, the ratio is based on mass. If another oxygen-containing gas is used for the combustion operation instead of air, strictly speaking, "air" should be changed to "oxygen carrier". However, the λ parameter is still used in the above definition.

[0191] In a preferred embodiment, the equivalent ratio NH 3 / H 2 (Φ) (not to be confused with the inverse of the air ratio 1 / λ) is in the range of 0.55 to 1.40, more preferably 1.05 to 1.20. The formation of nitrogen oxides depends on several factors, including 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 about 1.1 is required.

[0192] Nitrogen oxides (especially NO, NO2, and N2O) and the dew point of condensable components are two parameters of great significance for the technical implementation and installation of the exhaust gas line. These parameters are also largely determined by the composition of the exhaust gas. The exhaust gas from tubular reactors (which are similar in design to primary reformers) contains nitrogen oxides formed in the combustion reaction. In many countries, nitrogen oxide emissions are regulated, and if the permitted limits are exceeded, they must be reduced using appropriate technologies.

[0193] Nitrogen oxides (especially NO, NO2, and N2O) are formed by various mechanisms during combustion reactions. In tubular reactors designed similarly to primary reformers, NH3-free combustion gases exclusively produce so-called "thermal NOx," which are formed by the recombination of nitrogen radicals with oxygen, preferably at high temperatures. Due to the complex kinetics of NH3 combustion, NH3-containing combustion gases can form NOx via various reaction pathways, known as "kinetic NOx."

[0194] In plants producing H₂ from NH₃, both thermal and kinetic NOx can be formed. The presence of H₂ in the combustion gas increases the flame temperature, and the admixture of NH₃ increases the tendency to form kinetic NOx. The literature describes numerous cases where the combustion of mixtures of NH₃ and H₂ results in NOx emissions significantly higher than in conventional primary reformers. NOx emissions depend not only on the composition of the combustion gas, in particular the mixing ratio of NH₃ and H₂, but also on various other parameters, in particular:

[0195] - preheat temperature of combustion air and combustion gases;

[0196] - Excess combustion air during combustion; and

[0197] - The design and geometry of the burners used.

[0198] The exact nitrogen oxide emissions therefore depend more strongly on the individual circumstances than with conventional primary reformers. X Typical emissions of nitrogen oxides (i.e., NO and NO2) range from 100 to 10,000 ppmv. An example of an exhaust gas with a relatively low nitrogen oxide content includes 500 ppmv of NO, 10 ppmv of NO2, and 10 ppmv of NO (Case A). An example of an exhaust gas with a relatively high nitrogen oxide content includes 5,000 ppmv of NO, 10 ppmv of NO2, and 50 ppmv of NO (Case B).

[0199] During the startup of a system using NH3-rich combustion gases, relatively low NO emissions will result, but relatively high N2O emissions will result. This must be taken into account in the design and installation, even if it is not significant for the mass balance of the plant during normal operation (i.e. after the startup operation).

[0200] Furthermore, when considering the exhaust gas conduit of a system for producing H 2 from NH 3 , two dew points are of interest: the dew point of H 2 O and the dew point of NH 4 NO 3 .

[0201] The dew point of H2O depends on the partial pressure of H2O in the offgas. In process variants in which the offgas of a pressure swing adsorption plant (PSA) or the retentate of a membrane unit is fed into the combustion gas system, the offgas contains predominantly N2 and only relatively little H2O, which generally results in a relatively low dew point.

[0202] The following table shows the water content of the exhaust gas and the water dew point for the process variants that have been introduced:

[0203]

[0204] If the dew point of H2O is reached during system operation, liquid droplets will form. Since temperature changes in the exhaust gas are caused by the heat outflow from the heat exchanger, condensed water may deposit on the tube surfaces and deteriorate heat transfer. If the droplets enter the exhaust fan, the rotor may be damaged. Therefore, condensation of liquid H2O is undesirable. To avoid affecting the operation of the system and causing damage to it, a minimum exhaust gas temperature of 25K margin relative to the dew point should be maintained in the exhaust gas duct. Therefore, according to the present invention, the exhaust gas is preferably not cooled below approximately 81-88°C in the exhaust gas duct, depending on the respective given conditions. This temperature is therefore the lowest technically achievable, and the internal energy of the exhaust gas cannot be used. This, therefore, represents an unavoidable energy loss.

[0205] The dew point of NH4NO3 is relevant because the devices for removing nitrogen oxides from the exhaust gas (exhaust gas treatment systems) may have an escape of incompletely degraded nitrogen oxides (usually NO). NH3 metered into the exhaust gas treatment system as a reducing agent is often also incompletely converted, resulting in the escape of small amounts of NO and NH3. By cooling the exhaust gas in the exhaust gas duct, the temperature can drop below the dew point of NH4NO3, and NH4NO3 can deposit on the tubes of the heat exchanger. This deposit poses a risk to the safe operation of the system, as it is shock-sensitive and can react explosively. The following table shows the dew point of NH4NO3 for various typical residual contents of NO and NH3 in the exhaust gas:

[0206] pressure [bar a] 1.00 1.00 1.00 1.00 <![CDATA[Residual NH3]]> [ppmv v] 10 10 50 10 <![CDATA[Residual NO X > [ppmv v] 10 10 10 50 <![CDATA[NO2 / NO ratio]]> 1 9 1 1 <![CDATA[Dew point of NH4NO3]]> [℃] 71 79 79 79

[0207] In order to reach the critical temperature for NH4NO3 deposition, the gas flow does not have to be at or below this temperature; even the wall temperature of the heat exchanger tubes may be sufficient and lead to NH4NO3 deposition. Since combustion plants require combustion air that is usually drawn in at ambient temperature, there is a risk of NH4NO3 deposition on the heat exchanger tubes used to preheat the combustion air under normal operating conditions.

[0208] Therefore, unlike the dew point of H2O, observing the minimum temperature of the exhaust gas is not an appropriate solution. In order to avoid the risk of NH4NO3 deposition, the device for removing nitrogen oxides (exhaust gas treatment system) should be operated according to the invention so that NO X or NH3 or ideally both to a maximum of 1 ppmv. This can be achieved according to the invention by using NH3 to reduce NO X A suitable reaction scheme for chemical reduction is implemented, preferably with a reactor for post-oxidation of NH3 using residual oxygen in the exhaust gas.

[0209] NH3 is catalytically decomposed into H2 and N2:

[0210] The catalytic decomposition of NH3 is carried out thermally in principle, but is accelerated by using an NH3 decomposition catalyst. According to the invention, the catalytic decomposition of NH3 can be carried out under various conditions using various interconnections with different reactor types and using various NH3 decomposition catalysts.

[0211] According to the present invention, the catalytic decomposition of NH3 is preferably achieved 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.

[0212] Useful NH3 decomposition catalysts according to the present invention include various materials. The reaction temperature for carrying out the catalytic decomposition of NH3 is determined in particular by the choice of the NH3 decomposition catalyst.

[0213] Suitable methods for the thermal and / or catalytic decomposition of NH to form N and H are known to those skilled in the art. Suitable catalysts for the catalytic decomposition of NH to form N and H are, for example, AlO or SiO-supported Ru, MgAlO-supported Fe, Co, Ni, Cu or Ru, or CoMoN (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).

[0214] In a preferred embodiment of the present invention, a nickel-based NH3 decomposition catalyst is used. The equilibrium conversion rate is determined by the reaction temperature and pressure. At 900°C and a pressure of 20 bar, NH3 decomposition occurs almost quantitatively. At 650°C, the NH3 conversion rate is approximately 98.5%, while at 500°C, it is only approximately 95%.

[0215] In a preferred embodiment, a reaction temperature of about 550°C to about 900°C, preferably about 550°C to about 700°C, is employed in order to achieve high conversion.

[0216] In other preferred embodiments, a reaction temperature of about 600°C to about 900°C, preferably about 600°C to about 700°C, is employed in order to achieve high conversions.

[0217] In terms of energy balance and conversion, the optimal reaction temperature is in the range of approximately 630°C to 640°C. Despite the relatively high reaction temperature, nickel-based NH3 decomposition catalysts are advantageous. Due to the high conversion, the residual content of undecomposed NH3 in the product gas is relatively low, so it is preferred not to perform any separate separation of undecomposed NH3 for its recovery. Instead, a combined separation of N2 and undecomposed NH3 from the product gas is then performed by pressure swing adsorption in the H2 purification process.

[0218] 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), zeolites (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, GNPs, activated carbon, graphene, graphene oxide), attapulgite, diaspore, sepiolite, and mixtures thereof.

[0219] In a further preferred embodiment of the invention, a ruthenium-based NH decomposition catalyst is used. For this purpose, it is preferred according to the invention that the reaction temperature is in the range of about 450° C. to about 500° C., although slightly lower conversions (e.g., about 95%) can also be achieved, resulting in a greater residual content of undecomposed NH in the product gas.

[0220] Alternatively, other NH3 decomposition catalysts can optionally 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.

[0221] According to the present invention, the reaction pressure is preferably about 15 bara to about 25 bara. The stoichiometric reaction (2NH3 → N2 + 3H2) increases the volume, so the increased reaction pressure has a fundamental adverse effect on the conversion rate. On the other hand, it is recommended to operate the entire process at a higher pressure to limit the container volume and therefore the capital cost. At a reaction pressure of only 1 bar, a conversion rate of more than 99% can be achieved at a reaction temperature higher than 400°C. However, since a reaction pressure of 1 bar is only useful for the smallest systems, the system of the present invention is preferably operated at a higher reaction pressure, even if a certain loss in conversion rate must be accepted as a result.

[0222] The reaction pressure is defined, in particular, by the H2 purification process. The preferred pressure swing absorption (PSA) system for H2 purification according to the present invention can be effectively operated preferably at a pressure of about 15 bar to about 25 bar. The pressure of the product gas leaving the NH3 decomposition unit is preferably in the range of about 15 to about 25 bara, more preferably about 18 to about 22 bara, and even more preferably about 19 to about 21 bara. In this way, a good balance is achieved between the requirements of the pressure swing adsorption system on the one hand and the conversion achieved on the other.

[0223] The catalytic decomposition of NH 3 can in principle be carried out in different reactor types.

[0224] In adiabatic reaction schemes, the internal heat of the reaction gases is used as the energy source for the reaction. Suitable reactors for this purpose 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 burned to raise the temperature to the desired temperature at the reactor outlet. A disadvantage is the presence of water formed during combustion in the process gas, which must be removed by condensation. A portion of the undecomposed NH3 then dissolves in the condensed water and is lost. Furthermore, the high temperatures lead to the formation of large amounts of nitrogen oxides.

[0225] According to the invention, these disadvantages are avoided, wherein the product gas is preferably physically separated from the combustion gas and the exhaust gas formed therefrom. The product gas is formed in the NH3 decomposition device of the present invention in a combustion system by decomposing NH3 and leaving the NH3 decomposition device (preferably via a dedicated outlet). The combustion gas is burned in the combustion device of the combustion system together with the combustion air, and the exhaust gas formed leaves the combustion device (preferably also via a dedicated outlet), preferably into the exhaust gas duct. The product gas and the exhaust gas are preferably not mixed with each other, but are kept physically separated from each other. The combustion heat formed in the combustion of the combustion gas flows as a heat flow into the NH3 decomposition device, thereby providing the heat required to maintain the endothermic catalytic decomposition of NH3.

[0226] Preferably, the catalytic decomposition of NH3 is carried out in an isothermal, quasi-isothermal or mixed isothermal and adiabatic process scheme.In an isothermal reaction scheme, the temperature of the gas remains substantially unchanged.

[0227] In a preferred embodiment of the present invention, the catalytic decomposition of NH3 is carried out in a reactor similar to a primary reformer. For this purpose, the reactor comprises an NH3 decomposition device according to the invention and a combustion device according to the invention.

[0228] For this purpose, the NH3 decomposition catalyst is preferably arranged in at least one tube, more preferably at least two tubes, and even more preferably at least three tubes, through which NH3 flows. The at least one tube contains the NH3 decomposition catalyst. Preferably, NH3 passes through the at least one tube from top to bottom. In the physically separated combustion chamber, the combustion gas burned is preferably a mixture of NH3 and H2 together with combustion air (combustion device). In the catalytic decomposition of NH3, in addition to H2, N2 is also formed, which 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 through which the NH3 to be decomposed passes. For this purpose, the heat flow is directed from the combustion device to the NH3 decomposition device.

[0229] In a particularly preferred embodiment of the present invention, the NH3 is preheated before entering the NH3 decomposition device of the present invention. As a result of this preheating, the temperature of the NH3 before entering the NH3 decomposition device of the present 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, preferably at most about 820°C. More preferably, the temperature of the NH3 upon entering the NH3 decomposition device of the present invention is between about 780°C and 820°C, preferably about 800°C. In this case, the NH3 decomposition device of the present invention and the combustion device of the present invention preferably form a reactor designed similarly to a primary reformer. The NH3 decomposition catalyst is preferably a nickel-based catalyst. In a preferred embodiment, 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 conducted, is preferably between about 630°C and about 670°C, preferably about 650°C. In other preferred embodiments, the temperature is between about 660°C and 700°C, preferably about 680°C. The product gas preferably leaves the reactor (NH3 decomposition unit) at a pressure of about 15 bara to about 25 bara, preferably about 20 bara.

[0230] In a further particularly preferred embodiment of the present invention, the decomposition of NH3 is carried out in two stages in two NH3 decomposition units through which the fluid passes continuously. In the primary reactor (the first NH3 decomposition unit), only a portion of the NH3 is initially decomposed. The remaining NH3 is then decomposed in the second NH3 decomposition unit until the maximum conversion rate is achieved. Preferably, for this purpose, the second NH3 decomposition unit, together with the combustion unit of the present invention, forms a reactor having a design similar to that of the primary reformer, as described in detail above.

[0231] NH3 is preferably preheated before being introduced into the preliminary reactor (first NH3 decomposition device). The temperature of the NH3 after heating and upon entering the preliminary reactor (first NH3 decomposition device) is approximately 620°C to approximately 680°C, preferably approximately 650°C. The preheated NH3 then enters the preliminary reactor containing an NH3 decomposition catalyst, where a certain degree of catalytic decomposition of the NH3 into N2 and H2 occurs. This forms an intermediate product gas that still contains a considerable residual amount of undecomposed NH3, as well as N2 and H2 that have already been formed. As a result of the endothermic decomposition of NH3, the intermediate product gas is preferably cooled.

[0232] Preferably, the conversion of NH3 decomposed in the preliminary reactor is at most 30%, more preferably at most 25%, even more preferably at most 20% of the total conversion achieved.

[0233] Preferably, the conversion of NH3 decomposed in the preliminary reactor is at least 10%, more preferably at least 15% of the total conversion achieved.

[0234] After leaving the preliminary reactor, the intermediate product gas is preferably reheated before it enters the downstream second NH3 decomposition unit.

[0235] In a preferred embodiment, the temperature of the intermediate product after reheating and upon entering the second NH3 decomposition device is about 550°C to about 680°C, more preferably about 580°C.

[0236] In other preferred embodiments, the temperature of the intermediate product after reheating and upon entering the second NH3 decomposition device is about 620°C to about 680°C, more preferably about 650°C.

[0237] Then, in the second NH 3 decomposition device, the remaining decomposition of NH 3 continues until the total conversion is achieved.

[0238] In this preferred embodiment of the present invention, for the same overall conversion rate, the temperature of the intermediate product gas upon entering the preliminary reactor (the first NH3 decomposition device) and upon entering the second NH3 decomposition device can each be lower than the temperature of NH3 in the case of single-stage NH3 decomposition (i.e., when passing through only a single NH3 decomposition device). Due to the lower temperature, the degree of nitriding of the pipeline is lower, which increases the service life of the steel that comes into contact with NH3.

[0239] The NH 3 decomposition catalyst in the first NH 3 decomposition device (preliminary reactor) is preferably the same as that in the second NH 3 decomposition device.

[0240] Properties of exhaust gases when leaving the combustion system:

[0241] The combustion of the combustion gas and the combustion air generates exhaust gas in the combustion system, preferably the combustion device, and the exhaust gas leaves the combustion system, preferably into an exhaust gas duct.

[0242] In a preferred embodiment, the exhaust gas when leaving the combustion system, preferably the combustion device, and entering the exhaust gas conduit has one or more of the following properties:

[0243] In a preferred embodiment, the NO X The content is greater than the N2O content. Preferably, NO X The content is at least twice, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times the N2O content. X The molar ratio of NH:N2O is greater than 10:1, more preferably at least 20:1, even more preferably at least 30:1, most preferably at least 40:1, and especially at least 50:1.

[0244] In a preferred embodiment, the NO content of the exhaust gas is greater than the N2O content. Preferably, the NO content is at least two times, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times, the N2O content.

[0245] In a preferred embodiment, the NO2 content of the exhaust gas is greater than the N2O content. Preferably, the NO2 content is at least two times, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times the N2O content.

[0246] Preferably, the exhaust gas NO X The content is 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.

[0247] Preferably, the exhaust gas NO XThe content is 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.

[0248] Preferably, the exhaust gas NO X The content is 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.

[0249] Preferably, the N2O content of the exhaust gas is 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.

[0250] Preferably, the N2O content of the exhaust gas is 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.

[0251] Preferred exhaust gases have NO in the range of 1500 to 3000 ppmv, preferably 2000 to 3000 ppmv. X content and N2O content in the range of 20 to 100 ppmv.

[0252] In a preferred embodiment, the H2O content of the offgas is greater 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%.

[0253] In a further preferred embodiment, the H2O content of the offgas is at least 10% by volume; preferably at least 12% by volume, more preferably at least 14% by volume, even more preferably at least 16% by volume, most preferably at least 18% by volume, and in particular at least 20% by volume.

[0254] In a preferred embodiment, the H2O content of the exhaust gas is 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.-%.

[0255] In a preferred embodiment, the H2O content of the exhaust gas is 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.-%.

[0256] In a preferred embodiment, the H2O content of the exhaust gas is 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.-%.

[0257] In a preferred embodiment, the H2O content of the exhaust gas is 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.-%.

[0258] In a preferred embodiment, the H2O content of the exhaust gas is 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.-%.

[0259] Preferably, the N2 content of the offgas is at most 95% by volume; preferably at most 90% by volume, more preferably at most 85% by volume, even more preferably at most 80% by volume, most preferably at most 75% by volume, and in particular at most 70% by volume.

[0260] Preferably, the N2 content of the exhaust gas is at least 40% by volume; preferably at least 50% by volume, more preferably at least 60% by volume, even more preferably at least 70% by volume, most preferably at least 80% by volume, and in particular at least 90% by volume.

[0261] Preferably, the exhaust gases leaving the combustion system, preferably the combustion device, are at 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.

[0262] Preferably, the exhaust gases leaving the combustion system, preferably the combustion device, are at 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.

[0263] Preferably, the exhaust gases leaving the combustion system, preferably the combustion device, are at a pressure of at most 1.5 bar; preferably at atmospheric pressure.

[0264] Preferably, the NO of the exhaust gas leaving the combustion system, preferably the combustion device, X The degree of oxidation is 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%.

[0265] Preferably, the NO of the exhaust gas leaving the combustion system, preferably the combustion device, X The degree of oxidation is 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%.

[0266] Preferably, the O2 content of the exhaust gas leaving the combustion system, preferably the combustion device, is less than 2.0% by volume.

[0267] Step (b):

[0268] In the optional and preferred step (b) of the method of the present invention, the temperature T1 of the exhaust gas is preferably measured when leaving the combustion system, preferably the combustion device, and is changed by suitable means so that the exhaust gas is at a temperature T2 when entering the exhaust gas treatment system, which temperature T2 is optimized under the given conditions for carrying out steps (d) and (e) of the method of the present invention in the exhaust gas treatment system. The optimized temperature depends on the selected configuration of steps (d) and (e), i.e. the N2O reduction and NO X The type and sequence of the individual process steps for the reduction, in particular for the N2O decomposition catalyst and / or N2O reduction catalyst and NO X The type of catalyst material of the reduction catalyst.

[0269] Suitable devices for changing the exhaust gas temperature are known to those skilled in the art and include, in particular, heat exchangers which can be designed, for example, as plate heat exchangers or tube heat exchangers.

[0270] In optional and preferred step (b) of the process according to the invention, the exhaust gases are preferably cooled in at least one heat exchanger arranged downstream of the combustion system in the flow direction of the exhaust gases.

[0271] The exhaust gases from tubular reactors, similar in design to primary reformers, contain considerable internal energy. The process of producing H from NH requires supplying process streams at high temperatures. According to the present invention, the exhaust gases are simultaneously cooled and used to preheat these process streams. This has the advantage of reducing the plant's demand for combustion gases and increasing the yield of hydrogen product.

[0272] The effectiveness of different process variants can be measured by the hydrogen yield. This is defined as follows:

[0273]

[0274] The hydrogen productivity of a plant refers to the ratio of the molar flow rate of H2 leaving the plant as product compared to the molar flow rate of NH3 entering the plant in the feed stream (including any branching of the combustion gases).

[0275] Many process streams can be used to absorb heat from exhaust gases:

[0276] - preheating and evaporation of NH3 (possibly also indirectly);

[0277] - Further heating and evaporation of NH3 and intermediate product gases;

[0278] - Heating of combustion air;

[0279] -Preheating of boiler feed water;

[0280] - water heating;

[0281] - Heating of combustion air;

[0282] - Evaporation of boiler feed water to produce steam;

[0283] - superheating of water vapor;

[0284] - Auxiliary streams (heat transfer medium for preheating NH3 or for the evaporator of the NH3 desorption unit).

[0285] The target temperatures of the process streams to be heated generally dictate the order in which they are heated.The high temperature difference between the exhaust gas and the heat absorbing process stream reduces the required size of the heat exchanger.

[0286] However, it is advantageous to maintain a minimum temperature difference across all components. This prevents an increase in the temperature difference within a heat exchanger, and thus a reduction in its size is "compensated" by an increase in the size of all other heat exchangers. To achieve an economical design of the heat exchanger in the exhaust gas duct, preferably according to the invention, a minimum temperature difference of 45 K is present 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 is smaller.

[0287] Another essential factor in developing an efficient solution for the exhaust gas conduit of a tubular reactor of similar design to the primary reformer is the setting of the required temperature of the unit for removing nitrogen oxides from the exhaust gas.

[0288] The heat of the exhaust gas can theoretically be used in many different configurations. In plants for producing H₂ from NH₃, the product gas stream generated in the NH₃ decomposition unit provides a further important source of heat. According to the invention, it is advantageous and preferred to utilize the heat present in the product gas for the following measures of heat integration:

[0289] - Generation of water vapor;

[0290] - preheating of NH3;

[0291] - preheating of H2O to generate water vapor; and / or

[0292] - Cooling of the product gas with subsequent heat integration into cooling water.

[0293] According to the invention, the following measures for utilizing the heat present in the exhaust gas for heat integration are also advantageous and preferred:

[0294] -NH3 is preheated to the inlet temperature of the NH3 decomposition unit;

[0295] - Preheating of boiler feed water; and / or

[0296] - Preheating of combustion air.

[0297] Due to the mechanical limitations of the heat exchangers used in the exhaust duct, the amount of energy required, and the temperature profiles of the exhaust and process streams to be heated, in this configuration, waste heat that can be utilized but not integrated often remains in the exhaust. This manifests as a high inlet temperature of the exhaust gas entering the chimney of the exhaust duct. The internal energy present in this stream is lost to the process, ultimately reducing the H2 yield.

[0298] According to the invention, for reducing heat losses via the exhaust gas and for increasing the yield of H 2 , further integration steps in the exhaust gas duct are possible and preferred:

[0299] - NH3 is preheated to the inlet temperature of the first preliminary reactor (preferably an adiabatic fixed bed reactor);

[0300] - NH3 is preheated to the inlet temperature of the second preliminary reactor (preferably an adiabatic fixed bed reactor);

[0301] - Two-stage preheating of combustion air;

[0302] - preheating of the combustion gases (preferably from the output of the H2 purification plant, more preferably from the off-gas of a pressure swing adsorption unit or from the retentate of a membrane unit); and / or

[0303] - Preheating of auxiliary streams to integrate available waste heat.

[0304] The heat exchanger of the present invention is used to transfer heat from one medium to another without mixing the media. For descriptive purposes, with respect to an "A / B heat exchanger," the heat-releasing medium A is mentioned first, followed by the heat-absorbing medium B. Thus, for example, an "exhaust gas / NH3 heat exchanger" is used to release the heat present in the exhaust gas to NH3. For this purpose, the exhaust gas / NH3 heat exchangers are interconnected accordingly, i.e., the exhaust gas flows through their warmer sides, while NH3 flows through their cooler sides. For simplicity, the nomenclature "NH3" is used for the feedstock and any intermediate product gases that still contain significant amounts of NH3. Heat exchangers with the same function may be numbered to distinguish them, but a particular number does not necessarily mean that all heat exchangers with the same function having a lower number must be present at the same time. Thus, it is possible, for example, for a second exhaust gas / combustion air heat exchanger to be present without a first exhaust gas / combustion air heat exchanger.

[0305] Each heat exchanger of the present invention can exist independently, perhaps as a single heat exchanger of the described design or interconnection, or alternatively as part of a plurality, for example, two or three, heat exchangers of the described design or interconnection, having the same function and connected directly in series. In each of the plurality of heat exchangers having the same function, the heat-releasing medium and the heat-absorbing medium are identical. This separation of a single heat exchanger into, for example, two serially connected heat exchangers having the same function can have structural and / or design advantages.

[0306] The exhaust gas leaves the combustion system, preferably the combustion device, at a temperature T1 and is preferably cooled in step (b) to a temperature T2 before the exhaust gas is transferred to the exhaust gas treatment system at a temperature T2. Preferably, both the at least one heat exchanger and the exhaust gas treatment system are arranged in the exhaust gas conduit.

[0307] In a preferred embodiment, the exhaust gases are cooled in a single heat exchanger arranged in the flow direction of the exhaust gases downstream of the combustion system (see Figure 2 ).

[0308] In a further preferred embodiment, the exhaust gases are cooled continuously in at least two heat exchangers arranged downstream of the combustion system in the flow direction of the exhaust gases (see Figure 3 、 5 and 6).

[0309] In a further preferred embodiment, the exhaust gases are cooled in at least three heat exchangers arranged in the flow direction of the exhaust gases downstream of the combustion system (see Figure 4 );

[0310] The exhaust gas is cooled in at least one heat exchanger by releasing heat from the exhaust gas to a heat transfer medium.

[0311] Preferably, according to the present invention, the heat transfer medium used is NH 3 , which is then supplied to the catalytic decomposition in the NH 3 decomposition device over an NH 3 decomposition catalyst.

[0312] In a preferred embodiment, in step (b) of the method according to the invention, the exhaust gas is preferably cooled in at least one first exhaust gas / NH3 heat exchanger arranged downstream of the combustion system in the flow direction of the exhaust gas. In the NH3 decomposition device, preferably in the NH3 decomposition device arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the NH3, catalytic decomposition of the heated NH3 is carried out on the NH3 decomposition catalyst to produce product gas. The NH3 is heated in the first exhaust gas / NH3 heat exchanger by absorbing heat from the exhaust gas (see Figure 2 ).

[0313] In a further preferred embodiment, the exhaust gas is cooled in step (b) of the process according to the invention in the following apparatus:

[0314] a first exhaust gas / NH3 heat exchanger arranged downstream of the combustion system in the flow direction of the exhaust gases, and

[0315] a second exhaust gas / NH 3 heat exchanger, which is arranged downstream of the first exhaust gas / NH 3 heat exchanger in the flow direction of the exhaust gases.

[0316] In the first NH3 decomposition device (preliminary reactor), preferably located downstream of the first exhaust gas / NH3 heat exchanger in the direction of NH3 flow, partial catalytic decomposition of the heated NH3 is achieved over the NH3 decomposition catalyst to produce an intermediate product gas. The second exhaust gas / NH3 heat exchanger is preferably located downstream of the first NH3 decomposition device (preliminary reactor) in the direction of NH3 flow.

[0317] In the second NH3 decomposition device (main reactor), preferably arranged downstream of the second exhaust gas / NH3 heat exchanger in the flow direction of NH3, catalytic decomposition of the heated NH3 is carried out on the NH3 decomposition catalyst to produce product gas.

[0318] By absorbing heat from the exhaust gas, the NH 3 (or the intermediate product gas) is heated in the first exhaust gas / NH 3 heat exchanger and in the second exhaust gas / NH 3 heat exchanger.

[0319] The exhaust gas flows first through the first exhaust gas / NH 3 heat exchanger and then through the second exhaust gas / NH 3 heat exchanger.

[0320] NH3 (or intermediate product gas) first flows through the first exhaust gas / NH3 heat exchanger and absorbs heat from the exhaust gas therein. Thereafter, the heated NH3 flows into the first NH3 decomposition device, in which a partial catalytic decomposition of the heated NH3 is carried out on the NH3 decomposition catalyst to produce an intermediate product gas. The intermediate product gas thus formed (which still contains a considerable amount of undecomposed NH3) then flows through the second exhaust gas / NH3 heat exchanger and absorbs heat from the exhaust gas therein again. Finally, the heated intermediate product gas flows into the second NH3 decomposition device, in which a catalytic decomposition of the heated NH3 is carried out on the NH3 decomposition catalyst to produce a product gas (see Figure 3 、 5 and 6).

[0321] In a further preferred embodiment, the exhaust gas is cooled in step (b) of the process according to the invention in the following apparatus:

[0322] a first exhaust gas / NH 3 heat exchanger, which is arranged downstream of the combustion system in the flow direction of the exhaust gases,

[0323] 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

[0324] 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 gases.

[0325] In the first NH3 decomposition device (first preliminary reactor), preferably located downstream of the first exhaust gas / NH3 heat exchanger in the direction of NH3 flow, partial catalytic decomposition of the heated NH3 is achieved over the NH3 decomposition catalyst to produce a first intermediate product gas. The second exhaust gas / NH3 heat exchanger is preferably located downstream of the first NH3 decomposition device (first preliminary reactor) in the direction of NH3 flow.

[0326] In the second NH3 decomposition device (second preliminary reactor), preferably located downstream of the second exhaust gas / NH3 heat exchanger in the direction of NH3 flow, partial catalytic decomposition of the heated NH3 (intermediate product gas) is achieved over the NH3 decomposition catalyst to produce a second intermediate product gas. The third exhaust gas / NH3 heat exchanger is preferably located downstream of the second NH3 decomposition device (second preliminary reactor) in the direction of NH3 flow.

[0327] In the third NH3 decomposition device (main reactor), preferably arranged downstream of the third exhaust gas / NH3 heat exchanger in the flow direction of NH3, catalytic decomposition of heated NH3 (second intermediate product gas) is carried out on the NH3 decomposition catalyst to produce product gas.

[0328] By absorbing heat from the exhaust gas, NH 3 (or the first intermediate product gas or the second intermediate product gas) is heated in the first exhaust gas / NH 3 heat exchanger, the second exhaust gas / NH 3 heat exchanger and the third exhaust gas / NH 3 heat exchanger.

[0329] The exhaust gas flows first through the first exhaust gas / NH 3 heat exchanger, then through the second exhaust gas / NH 3 heat exchanger, and then through the third exhaust gas / NH 3 heat exchanger.

[0330] NH3 (or the first intermediate product gas or the second intermediate product gas) first flows through a first exhaust gas / NH3 heat exchanger, where it absorbs heat from the exhaust gas. The heated NH3 then flows into a first NH3 decomposition unit, where the heated NH3 undergoes partial catalytic decomposition over an NH3 decomposition catalyst to produce a first intermediate product gas. The resulting first intermediate product gas (which still contains a significant amount of undecomposed NH3) then flows through a second exhaust gas / NH3 heat exchanger, where it again absorbs heat from the exhaust gas. The heated first intermediate product gas then flows into a second NH3 decomposition unit, where further partial catalytic decomposition of the heated NH3 occurs over an NH3 decomposition catalyst to produce a second intermediate product gas. The resulting second intermediate product gas (which still contains a significant amount of undecomposed NH3) then flows through a third exhaust gas / NH3 heat exchanger, where it again absorbs heat from the exhaust gas. Finally, the heated second intermediate product gas flows into the third NH3 decomposition device, where the heated NH3 is catalytically decomposed on the NH3 decomposition catalyst to produce a product gas (see Figure 4 ).

[0331] The exhaust gas is cooled to a temperature T2 in step (b), and then the exhaust gas is transferred to an exhaust gas treatment system at the temperature T2.

[0332] Preferably, 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.

[0333] Preferably, 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.

[0334] Preferably, the temperature T2 is in the range of 400 to 450° C., more preferably in the range of 400 to 420° C. The ideal temperature T2 depends on the NO X Inlet concentration and related exotherm. For every 1000 ppmv NO X For example, ΔT is expected to be about 12 K. If the exhaust gas contains, for example, 7000 ppmv NO X , which would correspond to approximately 80-90 K. The outlet temperature should not be too high, since the stability of the catalyst in the exhaust gas treatment system is a critical factor due to the high water content of the exhaust gas.

[0335] At very high NO X In the case of a high concentration of NO, it is preferred according to the invention to provide a multi-stage arrangement of the catalyst bed with multi-stage NH3 feed and intermediate heat exchangers. In this way, excessively high temperatures are avoided. In addition, this allows (for the same catalyst volume) NO X and N2O can be decomposed significantly more.

[0336] Preferably, the exhaust gas entering the exhaust gas treatment system is at a temperature T2 which is relatively lower than the temperature T1 of the exhaust gas leaving the combustion system, preferably leaving the combustion device, by at least 20°C, preferably by at least 40°C, more preferably by at least 60°C, even more preferably by at least 80°C, most preferably by at least 100°C, and in particular by at least 120°C.

[0337] Preferably, relatively speaking, temperature T2 is at least 50°C lower than temperature T1, more preferably at least 100°C, even more preferably at least 150°C, most preferably at least 200°C, and in particular at least 250°C.

[0338] Step (c):

[0339] In step (c) of the process of the invention, the optionally cooled offgas is transferred to an offgas treatment system, ie from the combustion system from step (a) or from the at least one heat exchanger from optional and preferred step (b).

[0340] In step (c) of the process of the invention, the exhaust gases which have left the combustion system, preferably the combustion plant, and which have optionally been cooled in step (b) are transferred to an exhaust gas treatment system.

[0341] This can be achieved, for example, by connecting the outlet pipe of the combustion system, preferably the combustion device, to the inlet of the exhaust gas treatment system. This connection is preferably established via the exhaust gas conduit. Since the method according to the invention is preferably carried out at atmospheric pressure, there are typically no special requirements on the walls of the exhaust gas conduit or such conduit with regard to possible compressive stresses.

[0342] However, the walls or pipes of the exhaust gas duct should be able to withstand the temperature of the exhaust gas when it leaves the combustion system, preferably the combustion device, or enters the exhaust gas treatment system.

[0343] Steps (d) and (e) of the method of the present invention are carried out in the exhaust gas treatment system of the present invention. For this purpose, the exhaust gas treatment system is equipped with an N2O decomposition catalyst for step (d1) and / or an N2O reduction catalyst for step (d2), and is equipped with a NO X Reduction catalyst.

[0344] If the exhaust gas treatment system of the present invention additionally comprises at least one further catalyst, either the aforementioned N2O reduction catalyst, N2O decomposition catalyst or NO X At least one of the reduction catalysts has at least one further function, at least one of the following steps (g1) to (g4) is preferably additionally implemented in the exhaust gas treatment system of the present invention:

[0345] (g1) cooling the exhaust gas in at least one heat exchanger, which is preferably arranged in the exhaust gas treatment system; preferably upstream of the NH3 oxidation catalyst in the flow direction of the exhaust gas;

[0346] (g2) reducing the NH 3 content in the exhaust gas by oxidation with an oxidizing agent over an NH 3 oxidation catalyst; wherein the oxidizing agent preferably comprises O 2 ;

[0347] (g3) reducing the HCN content in the exhaust gas by hydrolysis and oxidation of the hydrolysis product with an oxidant over an HCN decomposition catalyst; wherein the oxidant preferably comprises NO X and / or N2O; and

[0348] (g4) Reducing the CO content in the exhaust gas by chemical oxidation with an oxidant over a CO oxidation catalyst; wherein the oxidant preferably comprises O2.

[0349] Step (d):

[0350] In step (d) of the method according to the present invention, the N2O content in the exhaust gas is reduced. This can be achieved by (d1) decomposing N2O over an N2O decomposition catalyst and / or (d2) chemically reducing N2O with a reducing agent over an N2O reduction catalyst.

[0351] The decomposition of N2O forms N2 and O2 according to the following empirical reaction:

[0352] 2N2O→2N2+O2.

[0353] The decomposition of N2O therefore means the decomposition into N2 and O2. In the context of the present invention, an "N2O decomposition catalyst" catalyzes the decomposition of N2O. The decomposition of N2O achievable by catalytic decomposition depends not only on the type of N2O decomposition catalyst (i.e. chemical properties and physical configuration) and the pressure and temperature conditions present, but also, in particular, on the selected space velocity, i.e. the ratio of the exhaust gas volume flow rate to the catalyst volume. However, the catalytic activity of the N2O decomposition catalyst is not necessarily limited to this reaction. For example, according to the present invention, it is entirely possible and indeed preferred that the N2O decomposition catalyst can also additionally catalyze further reactions, such as the chemical reduction of N2O and / or NO X Whether this further reaction actually takes place depends on the conditions of the individual case, in particular the type of catalyst, and the kinetics of any processes occurring in parallel, for example on the presence or amount of reducing agent and the presence or amount of other co-reactants.

[0354] Depending on the reducing agent, the chemical reduction of N2O with the reducing agent forms different reaction products.

[0355] In the case of the NH 3 reducing agents preferred according to the invention, the chemical reduction of N 2 O forms N 2 and H 2 O, in particular, for example as follows:

[0356] 3N2O+2NH3→4N2+3H2O or

[0357] 4N2O+4NH3+O2→6N2+6H2O

[0358] or in a combined reduction with NO, as follows:

[0359] 2NO+N2O+2NH3→3N2+3H2O.

[0360] In the case of hydrocarbons, which are likewise preferred according to the invention as reducing agents, the chemical reduction of N2O to form CO and H2O is carried out, in particular, for example as follows:

[0361] (2n+1)N2O+C n H 2n+2 →(2n+1)N2+n CO+(n+1)H2O

[0362] Alternatively, CO2 and H2O are formed as follows:

[0363] 4n N2O+C n H 2n+2 →4n N2+n CO2+2n H2O.

[0364] According to the present invention, CO is also preferred as a reducing agent. It can further react with N2O to obtain CO2, for example according to:

[0365] N2O+CO→N2+CO2.

[0366] In the context of the present invention, an "N2O decomposition catalyst" catalyzes the chemical reduction of N2O with a reducing agent. However, the catalytic activity of the N2O reduction catalyst is not necessarily limited to this reaction. For example, according to the present invention, it is entirely possible and indeed preferred that the N2O reduction catalyst can also additionally catalyze further reactions, such as the decomposition of N2O and / or NO X Whether this further reaction actually takes place depends on the conditions of the individual case, in particular the type of catalyst, and the kinetics of any processes occurring in parallel, for example on the presence or amount of reducing agent and the presence or amount of other co-reactants.

[0367] Step (e):

[0368] In step (e) of the method of the present invention, by X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content.

[0369] It is preferred here to be able to reduce the nitrogen oxides (especially NO X ) for those NO that undergo selective catalytic reduction (SCR) X Reduction catalyst, i.e. NO X The reduction catalyst mainly catalyzes NO X The oxidation of NH3 is performed and does not catalyze or only to a minor extent catalyzes the oxidation of NH3 with any free oxygen (O2) present in the exhaust gas.

[0370] According to the reducing agent, the reducing agent is used to reduce NO X The chemical reduction carried out forms different reaction products. In the case of the NH3 reducing agent preferred according to the invention, NO X Chemical reduction to form N2 and H2O, especially depending on NO X The type of reduction catalyst and the ratio of NO to NO2 are, for example, as follows:

[0371] 4NH3+2NO+2NO2→4N2+6H2O (fast SCR)

[0372] 4NH3+4NO+O2→4N2+6H2O (normal SCR)

[0373] 8NH3+6NO2→7N2+12H2O (NO2 SCR).

[0374] A common selective catalytic reduction is called "fast SCR" and is typically much faster than normal SCR or NO2 SCR.

[0375] In the context of the present invention, "NO X Reduction catalyst" catalyzes the reduction of NO with a reducing agent X However, NO X The catalytic activity of the reduction catalyst is not necessarily limited to this reaction. For example, according to the present invention, it is entirely possible and indeed preferred that NO X The reduction catalyst may also additionally catalyze further reactions, such as the decomposition of N2O, the chemical reduction of N2O and / or NO X The establishment of equilibrium or the selective oxidation of excess NH 3 with free O 2 . Whether this further reaction actually occurs depends on the conditions of the individual case and on the kinetics of any processes occurring in parallel, for example on the presence or amount of reducing agent and the presence or amount of other co-reactants.

[0376] catalyst

[0377] N2O decomposition catalysts are known per se, and a variety of material classes can be used. Preferred are N2O decomposition catalysts having high catalytic activity, for example, N2O decomposition catalysts having high catalytic activity in the temperature range of 350-600°C for decomposing N2O into N2 and O2.

[0378] Examples of preferred NO decomposition catalysts according to the invention are metal-loaded zeolite catalysts, for example copper- or cobalt-loaded or in particular iron-loaded zeolite catalysts, noble metal catalysts or other transition metal oxide catalysts, for example catalysts containing cobalt oxide. Examples of suitable catalysts are described in particular 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 an iron-loaded zeolite catalyst is used in the first catalyst bed, as expected, NO still present in the gas is X Accelerate the desired N2O decomposition through activation effect (promoter effect), such as et al. in Catal. Comm. 2 (2001) 273-276 for different N2O / NO X described by the ratio.

[0379] Another example of a preferred N2O decomposition catalyst according to the present invention is a catalyst having an activity factor for N2O decomposition. X For the purpose of description, this N2O decomposition catalyst is also referred to as "NO X -sensitive N2O decomposition catalysts". These catalysts contain one or more catalytically active compounds of elements from groups 5 to 11 of the Periodic Table of the Elements (PTE). Particular preference is given to compounds of elements from groups 9 to 11 of the PTE. In particular, preference is given in that order to compounds of the elements Co, Pt, Pd, Ir, Rh, Ni and / or Cu, preferably compounds of Co, Rh, Ni and / or Cu, in particular compounds of Co or Rh. Preference is given to N2O decomposition catalysts based on noble metals, preferably supported on refractory oxides, or based on mixtures of transition metal oxides, in particular mixed oxides or simple transition metal oxides, in each case in supported form or preferably as unsupported catalysts.

[0380] The catalytically active compounds themselves can be metal and / or oxidic compounds, the latter in the form of single oxides or in the form of binary, ternary or multinary mixed oxides of different structural types, such as perovskites or spinels. These 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 different catalytically active compounds can also be used. Examples of particularly preferred catalytically active compounds are metallic rhodium, rhodium oxides (e.g. RhO2 or Rh2O3), CoO, Co2O3, Co-containing spinels (e.g. Co3O4), Cu x Co 3-x O4 or Co-containing perovskite (such as LaCoO3) or Co-containing perovskite substituted at the A and B sites.

[0381] The catalytically active compounds may be present in pure form in the catalyst or may be applied to or mixed with a suitable support material. In the former case, these are so-called unsupported catalysts which, in addition to the active compounds, may also contain additives known to those skilled in the art, such as binders or other production-related additives, such as plasticizers, pore formers, fiber reinforcements or compression aids.

[0382] Methods for preparing such catalysts are known to those skilled in the art. In the case of a "supported catalyst," the catalytically active compound is already applied to a support material. As a result, the catalytically active compound undergoes dispersion and stabilization, resisting mechanical and thermal stresses. Methods for preparing such catalysts are also known to those skilled in the art. The support material is preferably a refractory oxide, such as SiO2, TiO2, ZrO2, or Al2O3, or a mixture of two or more of these, or a material that itself has some catalytic activity for the decomposition of NO, such as MgO, zeolite, hydrotalcite, or a mixture of two or more of these. Preferably, a catalyst that is substantially free of zeolite is used, and if zeolite is present, it preferably contains less than 15% by weight of zeolite, in particular less than 5% by weight of zeolite.

[0383] Preferred support materials for Rh-containing compounds are ZrO , TiO , Al 2 O , hydrotalcite or zeolite, for example, support materials having an MFI structure. These are described, for example, in Chemical Engineering and Technology 24 (2001) 281-285 or Catalysis Today 35 (1997) 113-120. Particularly preferred supports for Rh-containing compounds are ZrO , TiO , and hydrotalcite. The Rh content of these catalysts is preferably 0.1 to 10% by weight, preferably 0.5 to 5% by weight. In addition to Rh, the Rh-containing catalyst more preferably also contains CeO . The proportion of CeO is preferably 5 to 50% by weight, in particular 10 to 30% by weight.

[0384] Preferred supports for the Co-containing compound are zeolites, or preferably supports comprising magnesium oxide. In the case of zeolites, particularly preferred are Si-rich structures such as MFI, BEA, FER, MEL, or MOR. The production of such co-doped zeolites is known to those skilled in the art. The magnesium oxide support may be pure MgO or a compound containing MgO, such as hydrotalcite. Such catalysts are described, for example, in Appl. Catal. B: Environmental 7 (1996) 397-406 or Appl. Catal. B: Environmental 13 (1997) 69-79.

[0385] Particularly preferred are catalysts consisting essentially of at least one magnesium oxide compound and at least one cobalt oxide compound, wherein the content of the cobalt oxide compound is in the range of 0.1% to 50% by weight, and the content of the magnesium oxide compound is in the range of 50% to 99.9% by weight, in each case based on the total mass of the catalyst, and at least 30% by weight of the Co atoms present in the catalyst are in the chemically trivalent state. Such catalysts and their preparation are described in EP 1 257 347 B1. When using a cobalt oxide compound as the active component, particularly preferred are catalysts having a support composed of at least 50% by weight of MgO or a support composed of a mixed oxide composed of at least 50% by weight of MgO, and wherein a cerium oxide functional layer has been applied to the support. Such catalysts and their preparation are described in DE 10 200 7 038 711 A1.

[0386] The N2O decomposition catalyst can take the form of shaped bodies of any size and geometry, preferably having a high surface area to volume ratio that produces a minimum pressure drop when traversed. All geometries known for catalysts are typical, such as cylinders, hollow cylinders, porous cylinders, rings, crushed particles, trilobes or honeycomb structures.

[0387] N2O reduction catalyst and NO X Reduction catalysts are likewise known per se, and various substance classes can likewise be used. Examples of these are metal-loaded zeolite catalysts, for example copper- or cobalt-loaded zeolite catalysts, or in particular iron-loaded zeolite catalysts, or noble metal catalysts or catalysts used in the known SCR (Selective Catalytic Reduction) process.

[0388] Preferably, the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NO X The reduction catalyst independently comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an iron, cobalt or copper loaded zeolite; more preferably, an iron loaded zeolite; even more preferably, an iron loaded zeolite independently of the MFI, BEA, FER, MOR, FAU and / or MEL structure type.

[0389] Preferably, both the N2O decomposition catalyst and / or the N2O reduction catalyst and the NO X The reduction catalyst independently comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an iron, cobalt or copper loaded zeolite; more preferably, an iron loaded zeolite; even more preferably, an iron loaded zeolite independently of the MFI, BEA, FER, MOR, FAU and / or MEL structure type.

[0390] These can be different catalysts or the same catalyst. The iron-loaded zeolite catalyst used particularly preferably according to the invention essentially preferably contains >50% by weight, in particular >70% by weight, of one or more iron-loaded zeolites. For example, in addition to the Fe-ZSM-5 zeolite, further iron-containing zeolites, for example of the FER type, may be present in the catalyst used according to the invention.

[0391] Furthermore, the catalysts used according to the invention may comprise further additives known to those skilled in the art, such as binders.

[0392] The zeolites preferably used may have an iron content of up to 25%, but preferably from 0.1% to 10%, based on the mass of the zeolite.

[0393] The process of the present invention also includes the use of zeolites in which the lattice aluminum has been partially isomorphously substituted with one or more elements, for example with one or more elements selected from the group consisting of B, Be, Ga, Fe, Cr, V, As, Sb and Bi. It also includes the use of zeolites in which the lattice silicon has been isomorphously substituted with one or more elements, for example with one or more elements selected from the group consisting of Ge, Ti, Zr and Hf. The exact details of the formation or structure of the zeolites preferably used according to the present invention are given in Atlas of Zeolite Structure Types, Elsevier, 4th revised edition 1996, which is expressly incorporated herein by reference.

[0394] In the process of the present invention, very particular preference is given to zeolite catalysts that have been treated with steam ("steamed" catalysts). This treatment results in dealumination of the zeolite crystal lattice; such treatments are known per se to those skilled in the art. These hydrothermally treated zeolite catalysts have particularly high activity in the process of the present invention. Preference is given to using hydrothermally treated zeolite catalysts loaded with iron in which the ratio of extracrystalline aluminum to lattice aluminum is at least 1:2, preferably from 1:2 to 20:1.

[0395] Preferably, the N2O decomposition catalyst and / or the N2O reduction catalyst and the NO X The reduction catalysts each independently comprise a transition metal-loaded zeolite, preferably each comprise an iron-loaded zeolite (Fe zeolite), even more preferably each comprise an iron-loaded zeolite of the same structural type, most preferably having the same external shape (eg, honeycomb or pellet).

[0396] In a preferred embodiment, the N2O decomposition catalyst and the N2O reduction catalyst are made of the same material.

[0397] In a preferred embodiment, the N2O decomposition catalyst and NO XThe reduction catalyst is made of the same material.

[0398] In a preferred embodiment, the N2O reduction catalyst and the NO X The reduction catalyst is made of the same material.

[0399] In a preferred embodiment, the N2O decomposition catalyst, the N2O reduction catalyst and the NO X The reduction catalyst is made of the same material.

[0400] During optional and preferred step (b) of the process of the invention, the exhaust gases are preferably cooled after leaving the combustion system, preferably the combustion device, wherein steps (d1) and / or (d2) and / or (e) can introduce new heat.

[0401] Used to decompose N2O and NO X The preferred catalyst

[0402] Preferably, the N2O decomposition catalyst, N2O reduction catalyst and NO X The reduction catalyst independently comprises a zeolite-type material (also referred to as a "zeolite" for the purposes of this specification) loaded with at least one transition metal (atomic numbers 21-30, 39-48, 57-80, 89-112) and / or at least one lanthanide (also referred to as "lanthanide group elements", atomic numbers 57-71). For the purposes of description, for simplicity, transition metals and lanthanides are collectively referred to as "transition metals". The transition metals are preferably iron ("Fe zeolite"), copper ("Cu zeolite") and cobalt ("Co zeolite"). Zeolite materials loaded with iron (i.e., Fe zeolite) are particularly preferred and can be loaded or contain not only iron but also other transition metals, such as manganese, vanadium, chromium, nickel or a mixture thereof.

[0403] The zeolite material of the present invention preferably has high hydrothermal stability. Particularly preferred are SiO2-rich zeolites, known as "high silica zeolites," which have a [SiO2] and [AlO2] - ] units, thus having a Si / Al molar 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 in particular at least 13.

[0404] Preferred zeolitic materials according to the present invention essentially have a zeolitic structure of the BEA, MFI, MOR, MEL or FER structure type, more preferably the MFI and BEA structure types, even more preferably the BEA structure type. In the case of the MFI structure type, the ZSM-5 type is particularly preferred. Further details of the structure types of zeolitic materials and the nomenclature of their structures can be found in Atlas of Zeolite Structure Types, Elsevier, 4th revised edition, 1996.

[0405] According to the present invention, particularly preferred N2O decomposition catalysts, N2O reduction catalysts or NO X The reduction catalyst independently comprises at least 50 wt. % of Fe zeolite, preferably at least 70 wt. % of Fe zeolite, relative to the total weight of the zeolitic material, wherein a single structure type or several structure types may be present. In a preferred embodiment, in addition to the Fe-BEA zeolite, another Fe zeolite of a different structure type, preferably an Fe-MOR zeolite, is present.

[0406] The zeolite material loaded (doped) with a transition metal / lanthanide element can be achieved by a method related to loading or doping zeolite with a transition metal / lanthanide element, which is known to those skilled in the art. Preferably, the zeolite material is loaded from a commercially available H form or preferably an NH4 form by ion exchange with an appropriate salt of a transition metal in an aqueous phase or by solid-state reaction. The loaded zeolite material thus obtained is then calcined, preferably at a temperature of 400-650°C in air in a furnace. After calcination, the loaded zeolite material is vigorously washed in distilled water, and the loaded zeolite material is filtered out and then dried. A suitable binder (such as aluminosilicate, boehmite or silica sol) and an optional auxiliary agent for plasticizing or for producing lubricants (slips) are preferably added to the loaded zeolite material thus obtained and mixed therewith. In a preferred embodiment, the mixture thus obtained is extruded into a catalyst body (unsupported catalyst) and finally calcined. In other preferred embodiments, the mixture thus obtained is applied to a catalyst support (supported catalyst) and finally calcined. These methods are also well known to those skilled in the art and have been established in many technical applications.

[0407] According to the present invention, the particularly preferred N2O decomposition catalyst, N2O reduction catalyst, NO X The reduction catalyst, the NH3 oxidation catalyst, the HCN decomposition catalyst and the CO oxidation catalyst can independently take the form of shaped bodies of any size and geometry, preferably having a large surface-to-volume ratio and generating a minimum pressure drop when the stream flows through them. Typical geometries are all those known in catalysis, such as cylinders, hollow cylinders, porous cylinders, rings, trilobes or star-shaped extrudates. Particularly preferred are monolithic catalyst elements permeated by parallel channels, such as monolithic honeycombs (referred to as "catalyst honeycombs"), as are known, for example, from the cleaning or denitrification of power plant exhaust gases or automobile exhaust gases.

[0408] Catalyst honeycombs, honeycomb bodies and honeycomb body modules

[0409] The exhaust gas treatment system of the present invention or the catalyst bed contained therein preferably comprises catalyst honeycombs arranged parallel to one another, preferably a plurality of catalyst honeycombs, wherein the honeycomb channels in the exhaust gas duct are longitudinally aligned with 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) can in principle be freely selected. 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. Therefore, according to the present invention, the term "honeycomb" is not limited to rectangular or square cross-sectional areas.

[0410] If the exhaust gas treatment system of the present invention includes 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 present invention), the first reaction zone and the second reaction zone (first catalyst bed and second catalyst bed) preferably have a plurality of catalyst honeycombs arranged parallel to each other, wherein the honeycomb channels in the exhaust gas duct are longitudinally aligned with the flow direction of the exhaust gas.

[0411] In a preferred embodiment, several catalyst honeycombs (i.e., several monolithic honeycomb bodies) are combined to form a honeycomb module, preferably using 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 optimal utilization of the available cross-sectional area of ​​the exhaust gas line and simple replacement of defective or inactivated honeycomb bodies.

[0412] The honeycomb body preferably has a rectangular cross-section. The rectangular cross-section preferably has a first edge length (perpendicular to the direction of exhaust gas flow) in the range of 5 to 20 cm, more preferably in the range of 10 to 15 cm, and a second edge length (also perpendicular to the direction of exhaust gas flow) in the range of 5 to 20 cm, preferably in the range of 10 to 15 cm. The height of the honeycomb body (in the direction of exhaust gas flow) is preferably in the range of 5 to 25 cm, preferably in the range of 7.5 to 15 cm.

[0413] The so-called cell density (i.e., the channel density of a single catalyst honeycomb) is preferably 150 to 500 cpsi, preferably 180 to 450 cpsi (cells per square inch). 100 cpsi (i.e., 100 cells or honeycomb channels per square inch) corresponds to approximately 15.5 catalyst channels per square centimeter.

[0414] The individual honeycomb modules are preferably stacked on top of each other and arranged side by side in the direction of flow and secured by suitable mounting means in such a manner as to maximize utilization of the inflow area (i.e., the cross-sectional area of ​​the exhaust gas duct). Bypass flows between individual honeycomb modules or in the outer edge regions between the outer edges of the honeycomb modules and the inner wall of the exhaust gas 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 spacings, cover plates are used, which are attached to the inner wall of the exhaust gas duct in the direction of flow, in front of and / or behind the charge of the honeycomb modules. The cover plates are preferably covered by seals at the points of contact with the honeycomb modules. The honeycomb modules are preferably arranged and dimensioned so that the available inflow area for the catalyst preferably represents at least 60%, more preferably at least 70%, and even more preferably at least 80% of the inner cross-sectional area of ​​the exhaust gas duct.

[0415] In the case of round exhaust gas ducts or exhaust gas pipes, gaps that occur in the edge region of the honeycomb module charge (unless they can be easily filled by rectangular honeycomb modules) are preferably not filled with specially customized honeycomb bodies, but rather closed with blanking plates. This has the advantage that when replacing a used honeycomb body, only a standardized honeycomb body needs to be replaced without any special adjustments.

[0416] When using an exhaust gas duct, it is also advantageous to use a single, larger honeycomb body adapted to the duct cross section with a circular inflow cross section, wherein a plurality of honeycomb bodies can also be arranged in series in the direction of flow in a preferred configuration. In this case, it is not necessary to combine a plurality of honeycomb bodies parallel to one another to form a honeycomb module.

[0417] In a preferred embodiment, the honeycomb bodies or honeycomb modules are arranged in several layers offset along the longitudinal axis in the direction of exhaust gas flow. The honeycomb bodies or honeycomb modules are preferably arranged in 2 to 5 layers, more preferably in 2 to 3 layers. Preferably, a margin is provided between the layers (i.e., between the end faces of the honeycomb bodies or honeycomb modules), preferably with a size of 3 to 30 mm, preferably 4 to 20 mm. This margin enables intermediate mixing, in particular radial mixing, of the gas flow exiting the first layer of the honeycomb body or honeycomb module. Furthermore, any possible escape of unreacted reducing agent and / or its incompletely oxidized reaction products from the first layer of the honeycomb body to the subsequent second layer of the honeycomb body can be prevented.

[0418] For NO XThe reducing agent and optionally N2O are preferably supplied and distributed via a manifold pipe system having a plurality of openings or nozzles, which are arranged in the exhaust gas channel or in the exhaust gas duct in the flow direction or upstream of the corresponding catalyst bed, preferably in the exhaust gas channel or in the exhaust gas duct upstream of the filling material of the catalyst honeycombs as a honeycomb body or honeycomb body module.

[0419] The distributor pipes are preferably designed in the form of a grid, 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.

[0420] The specific design and dimensions of these distributors, including suitable outlet nozzles, are part of the know-how of catalytic exhaust gas cleaning technology and are widely used, for example, in the treatment of exhaust gases from coal-fired power plants.

[0421] NH3 oxidation catalyst

[0422] NH3 oxidation catalysts are known to those skilled in the art.

[0423] The Nh3 oxidation catalyst is preferably free of platinum group metals, preferably free of precious metals.

[0424] For the purposes of this description, "free of platinum group metals" means that platinum group metals (i.e., Ru, Rh, Pd, Os, Ir, Pt) are substantially absent. However, minimal analytically detectable traces of platinum group metals are possible. For the purposes of this description, "free of precious metals" means that precious metals are substantially absent. However, minimal analytically detectable traces of precious metals are possible.

[0425] 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 structure type (hereinafter referred to as "NH3 oxidation active iron- or copper-loaded zeolite catalyst").

[0426] Preferred platinum group metal-free NH oxidation catalysts are selected from transition metal oxides (e.g., Fe, Mn, Cu, Cr, Co, Ni, ...), metal-loaded zeolites, such as those described in Handbook of Heterogeneous Catalysis, Wiley-VCH, edited by Ertl, Schsis, Weitkamp, ​​2nd Ed. 2008, Volume 5, Chapter 11.5 "Solid Catalysts for the Oxidation of Volatile Organic Compounds".

[0427] Preferred NH3 oxidation catalysts include:

[0428] - cobalt catalysts; in particular Co3O4; Co3O4-derived mixed oxides (Co 3-y M y O4), preferably crystallized in a spinel structure like Co3O4, wherein M is preferably selected from Zn, Cu, Fe, Mn and V; a cobalt-loaded zeolite, preferably having an MFI, BEA, FER, MOR, FAU, CHA or AFI structure type;

[0429] - Manganese catalysts; especially MnO X , where x = 1-2; MnO X -derived mixed oxides (Mn x-y M y O x ), wherein M is preferably selected from Zn, Cu, Fe and Mn; a manganese-loaded zeolite preferably having an MFI, BEA, FER, MOR, FAU, CHA or AFI structure type;

[0430] - Copper catalysts; especially CuO X , where x = 0.5-1; CuO X -derived mixed oxides (Cu x-y M y O x ), wherein M is preferably selected from Zn, Co, Fe and Mn; copper-loaded zeolite, preferably having MFI, BEA, FER, MOR, FAU, CHA, AFI structure type;

[0431] - Silver catalyst; in particular in supported form, preferably on Al2O3, TiO2 or SiO2, for example, more preferably X% Ag / TiO2, X% Ag / Al2O3 or X% Ag / SiO2, in each case X=1-10.

[0432] In a preferred embodiment, the device of the invention does not contain any additional NH3 oxidation catalyst other than the iron-loaded or copper-loaded zeolite.

[0433] In a preferred embodiment, the NH3 oxidation catalyst, preferably the NH3 oxidation active iron-loaded zeolite catalyst, has a molar ratio of iron to zeolite 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.

[0434] In a preferred embodiment, the NH3 oxidation catalyst, preferably the NH3 oxidation active copper-loaded zeolite catalyst, has a molar ratio of copper to zeolite 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.

[0435] Thus, it was surprisingly found that iron- or copper-loaded zeolites in which only some of the potentially available cationic sites are occupied by Fe or Cu ions, leaving the remaining cationic sites essentially satisfied by protons, have significantly increased activity for the oxidation of NH 3 with free oxygen.

[0436] The ratio of iron or copper to zeolitic aluminum can be adjusted by selecting the Al content in the synthesis of the zeolitic material, in particular via the ratio of the selected Si and Al starting materials, and also by subsequent loading with iron or copper ions.

[0437] In the synthesis of zeolites, the selected Si and Al starting materials are usually heated in an alkaline solution, usually under elevated pressure, which causes crystallization to occur to obtain a zeolite consisting of three-dimensional chains of AlO2. - Zeolites are microporous aluminosilicates formed by SiO2 units. By controlling the selection of synthesis conditions, for example by adding structure-directing agents such as organic cations, not only the Si / Al ratio and thus the Al content, but also the structure type of the zeolite can be specifically adjusted or controlled. The synthesis method is industrially established. Zeolites of different structure types with different Si / Al ratios and loaded with different cations (e.g., in the form of Na or NH4) are commercially available.

[0438] Suitable methods known to those skilled in the art (such as liquid phase or solid state ion exchange) can result in the cations present in the zeolite (such as NH +) Controlled exchange for other cations (e.g., iron or copper ions) (J. Weitkamp, ​​L. Puppe Catalysis and Zeolites—Fundamentals and Applications, Springer-Verlag Berlin Heidelberg New York, 1999 or Kucherov, A.V. Slinkin, A.A.: Solid state reactions as method of introducing transition metal cations into high-silicazeolites, Russ. Chem. Rev. 1992, vol. 61, no. 9, p. 925-943). If all the negative charges generated by the AlO2 units have been compensated by cations, the so-called exchange level is 100%.

[0439] It is known that the exact Al content and Fe content of zeolitic materials or catalyst shaped bodies produced therefrom can be determined by X-ray fluorescence analysis (XRF). This is suitably carried out according to DIN EN 169-2 (Section 5) after determining the loss on ignition and lithium tetraborate digestion.

[0440] If the intention is to subsequently determine the Al content of the parent zeolite material on finished shaped bodies, it should be noted that the shaped bodies may also contain Al-based binder components that cannot be distinguished from the zeolite Al by XRF. In this case, additional investigation of the shaped bodies is required, for example by 27 Al solid-state NMR, which allows the distinction between Al bound in the zeolite structure and extra-lattice Al. Those skilled in the art will be familiar with the details of the basic principles, implementation and evaluation of these studies (J. Weitkamp, ​​L. Puppe Catalysis and Zeolites—Fundamentals 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)and4.3.4.2( 27Al NMR Spectroscopy of Framework and Non-Framework Aluminum inZeolites)).

[0441] Preferably, the NH3 oxidation catalyst, preferably the NH3 oxidation active iron-loaded zeolite catalyst has a total iron content (reported as mass content of Fe2O3) of less than 10.0 wt% to more than 2.0 wt%, preferably less than 7.0 wt% to more than 2.0 wt%, more preferably less than 5.0 wt% to more than 2.0 wt%, even more preferably less than 4.0 wt% to more than 2.0 wt%.

[0442] Preferably, the NH3 oxidation catalyst, preferably the NH3 oxidation active copper-loaded zeolite catalyst, has a total copper content (reported as mass content of Cu2O) of less than 9.0 wt% to more than 1.5 wt%, preferably of less than 6.5 wt% to more than 1.5 wt%, more preferably of less than 4.5 wt% to more than 1.5 wt%, even more preferably of less than 3.5 wt% to more than 1.5 wt%.

[0443] In a preferred embodiment, the NH3 oxidation catalyst, preferably an NH3 oxidation active iron or copper loaded zeolite catalyst, is configured for the selective oxidation of NH3 to N2 and H2 with O2 and is introduced in the form of a bed of particles having an equivalent diameter (defined as the diameter of a spherical particle of equal volume) of 3.5 to 5.5 mm and wherein the ratio of the external geometrically detectable surface area of ​​the particles to the volume of the particle bed is 1000 m 2 / m 3 Up to 1500m 2 / m 3 , in an isothermally operated tubular reactor with an axial flow having an inner diameter of 20±3 mm, in an amount of 8.0±0.5 ml with a gas mixture consisting of 500±50 ppmv of NH3, 2.5±0.1% by volume of O2 and 0.30±0.05% by volume of H2O in N2 at a space velocity of 10000±500 h-1 based on standard conditions (0°C; 1.01325 bara) -1 , a total pressure of 6±0.5 bara, a temperature of 380°C±5K, and a conversion rate of NH3 to produce at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80%, and especially at least 90%.

[0444] In a preferred embodiment, the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NO X The reduction catalyst and / or the NH 3 oxidation catalyst independently have a honeycomb monolithic structure.

[0445] In a preferred embodiment, the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NO X The reduction catalyst and / or the NH 3 oxidation catalyst independently have a honeycomb monolithic structure.

[0446] In a preferred embodiment, the NH 3 oxidation catalyst and the N 2 O decomposition catalyst are made of the same material.

[0447] In a preferred embodiment, the NH 3 oxidation catalyst and the N 2 O reduction catalyst are made of the same material.

[0448] In a preferred embodiment, the NH3 oxidation catalyst and the NO X The reduction catalyst is made of the same material.

[0449] In a preferred embodiment, the NH3 oxidation catalyst, NO X The reduction catalyst and the N2O decomposition catalyst are made of the same material.

[0450] Preferred variants of the combination of steps (d) and (e):

[0451] In a preferred embodiment, steps (d1) and / or (d2) and / or (e) of the method of the present invention are carried out at different temperatures (i.e. at different temperature levels), wherein the step carried out earlier or upstream in the flow direction of the exhaust gas is preferably carried out at a higher temperature than the step carried out subsequently or downstream in the flow direction of the exhaust gas.

[0452] However, depending on the properties of the catalyst used, these steps may not be completely separated from one another locally or in time. If the catalyst used is simultaneously suitable for catalyzing two or more of steps (d1), (d2), and (e), these steps can be carried out simultaneously and / or sequentially. For this purpose, it is possible to consider, in the direction of exhaust gas flow, individual sections of one or the same catalyst through which the exhaust gas flows in sequence, and in which different reactions may predominate. Which reaction predominates in which section depends, in particular, on the respective reaction kinetics, the local temperature, and the local concentrations of the reactants, which may include the concentration of the reducing agent and, possibly, the concentration of the catalytically active substance.

[0453] The exhaust gas treatment system of the present invention is particularly useful for carrying out steps (d) and (e) of the method of the present invention. However, in addition to steps (d) and (e), further steps and chemical reactions may also be carried out within the exhaust gas treatment system.

[0454] This preferably involves a catalyst bed arranged downstream in the direction of exhaust gas flow for oxidizing incompletely converted reducing agent or its not yet completely oxidized reaction products, i.e., for example, for oxidizing NH 3 (NH 3 oxidation catalyst) or CO (CO oxidation catalyst; when hydrocarbons are used as reducing agent). In such an embodiment, the exhaust gas is preferably cooled before it is introduced into the downstream catalyst bed, i.e., the oxidation of NH 3 and / or CO is preferably carried out at a lower temperature than in steps (d) and (e).

[0455] In the embodiment of steps (d) and (e) of the process according to the invention, there are different preferred variants of the process scheme according to the invention, which can differ from one another with regard to the sequence of reactions carried out, the catalysts used, the reducing agents used, the space velocity and other reaction conditions.

[0456] In a preferred embodiment, these reactions are carried out in a common reaction zone (catalyst bed) which is equipped upstream with a device for metering the reducing agent into the exhaust gas.

[0457] In a further preferred embodiment, the reactions are carried out in two separate reaction zones (catalyst beds) arranged in series, wherein preferably at least one reaction zone, preferably both reaction zones, is independently equipped upstream with a device for metering the reducing agent into the exhaust gas. In this case, the exhaust gas first flows through the first reaction zone and then through the second reaction zone.

[0458] Particularly preferred variants / embodiments include

[0459] [a] (d2) Chemical reduction of N2O with NH3 and (e) Chemical reduction of NO with NH3 X The chemical reduction is carried out, preferably together in one reaction zone;

[0460] [b] (d2) Chemical reduction of N2O with hydrocarbons (CH4, natural gas, etc.) and (e) Chemical reduction of NO with NH3 X The chemical reduction is carried out, preferably together in one reaction zone;

[0461] [c] (d1) Decomposition of N2O and (e) Reaction of NO with NH3 X The chemical reduction is carried out, preferably together in one reaction zone;

[0462] [d] (d1) Decomposition of N2O and (d2) Chemical reduction of N2O with NH3 and (e) Chemical reduction of NO with NH3 X The chemical reduction is carried out, preferably together in one reaction zone;

[0463] [e] (d1) Decomposition of N2O and (d2) Chemical reduction of N2O with hydrocarbons (CH4, natural gas, etc.) and (e) Reduction of NO with NH3 X The chemical reduction is carried out, preferably together in one reaction zone;

[0464] [f] (d1) decomposition of N2O, preferably in a first reaction zone; followed by (e) reaction of NO with NH3 X Chemical reduction is carried out, preferably in a second reaction zone;

[0465] [g] (d1) incomplete decomposition of N2O, preferably in a first reaction zone; followed by (d2) chemical reduction of residual N2O with NH3 and (e) chemical reduction of NO with NH3 X Chemical reduction is carried out, preferably in a second reaction zone;

[0466] [h] (d1) incomplete decomposition of N2O, preferably in a first reaction zone; followed by (d2) chemical reduction of residual N2O with hydrocarbons (CH4, natural gas, etc.) and (e) chemical reduction of NO with NH3 X Chemical reduction is carried out, preferably in a second reaction zone;

[0467] [i] (d1) incomplete decomposition of N2O, preferably in a first reaction zone; subsequently (d1 * ) Decomposition of residual N2O and (e) use of NH3 to remove NO X Chemical reduction is carried out, preferably in a second reaction zone;

[0468] [j] (d1) incomplete decomposition of N2O, preferably in a first reaction zone; then (d1 * ) Decomposition of residual N2O and (d2) Chemical reduction of residual N2O with NH3 and (e) Chemical reduction of NO with NH3 X Chemical reduction is carried out, preferably in a second reaction zone;

[0469] [k] (d1) incomplete decomposition of N2O, preferably in a first reaction zone; subsequently (d1 * ) decomposition of residual N2O and (d2) chemical reduction of residual N2O with hydrocarbons (CH4, natural gas, etc.) and (e) reduction of NO with NH3 X Chemical reduction is carried out, preferably in a second reaction zone;

[0470] [l](e)NO X Incomplete chemical reduction, preferably in a first reaction zone; followed by (d1) decomposition of N2O and (e * ) Use NH3 to remove residual NO XChemical reduction is carried out, preferably in a second reaction zone;

[0471] [m](e)NO X Incomplete chemical reduction, preferably in a first reaction zone; followed by (d1) decomposition of N2O and (d2) chemical reduction of N2O with NH3 and (e * ) Use NH3 to remove residual NO X Chemical reduction is carried out, preferably in a second reaction zone;

[0472] [n](e)NO X Incomplete chemical reduction, preferably in a first reaction zone; followed by (d1) decomposition of N2O and (d2) chemical reduction of N2O with hydrocarbons (CH4, natural gas, etc.) and (e * ) Use NH3 to remove residual NO X Chemical reduction is carried out, preferably in a second reaction zone;

[0473] However, this does not mean that the reactions explicitly mentioned must be the only reactions occurring in the respective reaction zone. Depending on the catalyst used, it is preferred according to the invention that other reactions also occur simultaneously, which are not explicitly mentioned but can be carried out in parallel. Therefore, the reactions explicitly mentioned are only those reactions that occur at least in the respective variant / embodiment.

[0474] If NO X , N2O and NH3 are present in the mixture, and the catalyst used catalyzes the reaction of NO with NH3 X The chemical reduction of N2O is also catalyzed by NH3, and the chemical reduction of NO is catalyzed by NH3. X The chemical reduction that takes place is typically much faster than the chemical reduction of N2O with NH3. If the catalyst used additionally catalyzes the decomposition of N2O, the decomposition of N2O typically overlaps with the chemical reduction of N2O with NH3, wherein the extent of the chemical reduction of N2O can be increased by increasing the amount of NH3 metered in.

[0475] For the purposes of the description, a "*" indicates a component process step that has previously been carried out only partially in a component process step of the same type, wherein the component process step then identified by "*" continues the component process step that was previously carried out only partially, but possibly in a different reaction zone or in a different catalyst bed. As with all other process steps, the results obtained at the end of all component process steps are not quantified unless expressly stated otherwise. For example, if NO X In the first composition method step (e), the incomplete chemical reduction is followed by the composition method step (e * ) does not necessarily mean that in the constituent method steps (e* ) End NO X The total amount of must have been completely chemically reduced (ie to 0.0 ppmv). On the contrary, it is entirely possible that in the composition process step (e * ) at the end of the experiment, there is still a residual amount of NO X .

[0476] The exhaust gas treatment system comprises at least one injection site for a reducing agent.The exhaust gas treatment system may comprise several injection sites for a reducing agent.

[0477] According to the invention, the mode of introduction of the reducing agent into the stream of the exhaust gas to be treated is freely configurable, provided that this is done in the direction of flow between the N2O reduction catalyst or the NO X The reducing agent can be introduced in the form of a gas or liquid or aqueous solution that evaporates in the stream of exhaust gas to be treated. The feeding is achieved by suitable means, such as a suitable pressure valve or a suitably designed nozzle, which leads to a mixer for the stream of exhaust gas to be treated and the supplied reducing agent. When using different X When using N2 as a reducing agent, they can be supplied and introduced into the exhaust gas separately or together.

[0478] In the case where the catalyst bed is constructed as a catalyst honeycomb or a filling material of a honeycomb module, the catalyst bed is used for NO X The supply and distribution of the reducing agent and optionally N2 to one or more reaction zones (catalyst beds) is preferably achieved by a manifold piping system having multiple openings or nozzles, which is arranged upstream of the corresponding reaction zone (catalyst bed) in the flow direction of the exhaust gas, i.e. upstream of the filling material of the catalyst honeycomb or honeycomb module.

[0479] The distributor is preferably designed in the form of a grid, or concentrically connected circles, which extends as far as possible over the cross-sectional area of ​​the exhaust gas duct or the inflow area of ​​the reaction zone (catalyst bed).

[0480] The specific design and dimensions of these distributors, including suitable outlet nozzles, are part of the know-how of catalytic exhaust gas cleaning technology and are widely used, for example, in the treatment of exhaust gases from coal-fired power plants.

[0481] The exhaust gas treatment system of the present invention may include a single reaction zone. In this case, the catalyst used in the single reaction zone acts as an N2O decomposition catalyst and / or an N2O reduction catalyst and acts as a NO X In this case, steps (d) and (e) of the process of the invention are carried out essentially simultaneously in the reaction zone. However, it should be noted that the kinetics of the individual conversions can be very different. For example, the reaction of NO with NH3 as a reducing agent may be very different depending on the catalyst material used. XThe chemical reduction of NO can be much faster than the chemical reduction of N2O with NH3. X When N2O and NH3 are in a mixture and NH3 is fed as a reducing agent, different reactions will occur in the front of a single reaction zone than in the back of a single reaction zone. In the front, due to faster kinetics, NO X chemical reduction, and once most of the NO X It has been decomposed and only chemical reduction of N2O is carried out in the latter stage.

[0482] Alternatively, the exhaust gas treatment system may comprise several reaction zones, which is preferred according to the invention. If several reaction zones are comprised, they are preferably arranged in series, so that the exhaust gas flows through them one after another: first the first reaction zone, then the second reaction zone, and if appropriate, then the third reaction zone.

[0483] In a preferred embodiment, the reaction zones are each spatially separated catalyst beds.

[0484] In a preferred embodiment, the exhaust gas undergoes the steps of the method of the present invention in one of the following orders:

[0485] (i) (a) → (b) → (c) → (d1) → (e); wherein step (d1) is preferably carried out in the first reaction zone; and step (e) is carried out in the second reaction zone;

[0486] (ii) (a) → (b) → (c) → (e) → (d2); wherein step (e) is preferably carried out in the first reaction zone; and step (d2) is carried out in the second reaction zone;

[0487] (iii) (a) → (b) → (c) → (e) → (d2) → (d1); wherein step (e) is preferably carried out in the first reaction zone; step (d2) is carried out in the second reaction zone; and step (d1) is carried out in the third reaction zone;

[0488] (iv) (a) → (b) → (c) → (e) → (d1) + (d2); wherein step (e) is preferably carried out in the first reaction zone; and steps (d1) and (d2) are carried out in the second reaction zone;

[0489] (v) (a) → (b) → (c) → (e) → (d1); wherein step (e) is preferably carried out in the first reaction zone; and step (d1) is carried out in the second reaction zone;

[0490] (vi)(a)→(b)→(c)→(d1)+(e)→(e * ); wherein step (d1) and step (e) are (incompletely) carried out in the first reaction zone; step (e* ) is carried out in a second reaction zone;

[0491] (vii)(a)→(b)→(c)→(d1)+(e)→(e * )+(d2); wherein step (d1) and step (e) are (incompletely) carried out in the first reaction zone; step (d2) and step (e * ) is carried out in a second reaction zone;

[0492] (viii)(a)→(b)→(c)→(d1)+(d2)+(e)→(d1 * )+(d2 * )+(e * ); wherein preferably step (d1) (incompletely) and step (d2) (incompletely) and step (e) (incompletely) are carried out in a first reaction zone, which first reaction zone preferably does not contain a zeolitic material as a catalyst; and step (d1 * ) and the remainder of step (d2 * ) and the remainder of step (e * ) is carried out in a second reaction zone, which preferably contains a zeolitic material as a catalyst;

[0493] (ix)(a)→(b)→(c)→(d1)+(d2)+(e)→(d1 * )+(d2 * )+(e * ); wherein preferably step (d1) (incompletely) and step (d2) (incompletely) and step (e) (incompletely) are carried out in a first reaction zone, which first reaction zone preferably contains a zeolitic material as a catalyst; and step (d1 * ) and the remainder of step (d2 * ) and the remainder of step (e * ) is carried out in a second reaction zone, which preferably contains NO X -Sensitive N2O decomposition catalyst as catalyst;

[0494] (x)(a)→(b)→(c)→(d1)→(d1 * )+(d2)+(e); wherein preferably step (d1) is (incompletely) carried out in a first reaction zone, which preferably contains a zeolitic material as a catalyst; and step (d1 * ) and step (d2) and step (e) are carried out in a second reaction zone, which preferably contains a zeolitic material as catalyst;

[0495] (xi)(a)→(b)→(c)→(d1)→(d1 * )+(d2)+(e); wherein preferably step (d1) is carried out (incompletely) in a first reaction zone, which preferably contains NO X - a sensitive N2O decomposition catalyst as a catalyst; and step (d1 * ) and step (d2) and step (e) are carried out in a second reaction zone, which preferably contains a zeolitic material as catalyst.

[0496] However, it is also possible to realize two or more reaction zones by means of a single catalyst bed. In particular, two reaction zones on a common catalyst bed can be formed by feeding the reducing agent in the middle of the catalyst bed (or at another position along the longitudinal extent). Upstream of the feeding point, there is no reducing agent, so that steps (d2) and (e) of the process according to the invention cannot be carried out due to the lack of reducing agent. What then takes place upstream is essentially the decomposition of N2O in step (d1) (first reaction zone). Downstream of the feeding point, there is a reducing agent, so that steps (d2) and (e) of the process according to the invention can be carried out, possibly overlapping with step (d1) (second reaction zone) of the process according to the invention. In this case as well, due to different reaction kinetics, different reactions may occur in the front section of each reaction zone and in the back section of each reaction zone; however, the first reaction zone and the second reaction zone will in any case differ from one another, since no chemical reduction of N2O and NO2 is carried out in the first reaction zone due to the lack of reducing agent. X Chemical reduction.

[0497] In a particularly preferred embodiment, the exhaust gas treatment system comprises a first reaction zone and a second reaction zone. Possibly, further reaction zones are present.

[0498] In a preferred embodiment, the first reaction zone and the second reaction zone are spatially separated from each other. In this case, they are preferably separate catalyst beds. In the case of spatial separation of the catalyst beds, the temperature of the second catalyst bed or the gas stream entering it can be adjusted by removing or supplying heat so that it is lower or higher than the temperature of the first catalyst bed. The temperature of a single catalyst bed can be appropriately determined as the arithmetic mean of the temperature of the gas stream at the inlet and outlet of the catalyst bed.

[0499] In a preferred embodiment, 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).

[0500] 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 especially at least 650°C.

[0501] 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.

[0502] In a preferred embodiment, the temperature in the first reaction zone (in the first catalyst bed) is, relatively speaking, at least 20°C higher than the temperature in the second reaction zone (in the second catalyst bed), more preferably at least 40°C higher, even more preferably at least 60°C higher, most preferably at least 80°C higher, and in particular at least 100°C higher.

[0503] In other preferred embodiments, the temperature in the second reaction zone (in the second catalyst bed) is, relatively speaking, at least 20°C higher than the temperature in the first reaction zone (in the first catalyst bed), more preferably at least 40°C, even more preferably at least 60°C, most preferably at least 80°C, and in particular at least 100°C higher.

[0504] In a preferred embodiment, the temperature in the first reaction zone (in the first catalyst bed) is, relatively speaking, at least 120°C higher than the temperature in the second reaction zone (in the second catalyst bed), more preferably at least 140°C, even more preferably at least 160°C, most preferably at least 180°C, and in particular at least 200°C higher.

[0505] In other preferred embodiments, the temperature in the second reaction zone (in the second catalyst bed) is, relatively speaking, at least 120°C higher than the temperature in the first reaction zone (in the first catalyst bed), more preferably at least 140°C, even more preferably at least 160°C, most preferably at least 180°C, and in particular at least 200°C higher.

[0506] Preferably, the temperature of the off-gas upon entering the first reaction zone (entering 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.

[0507] Preferably, the temperature of the off-gas on leaving the second reaction zone (leaving the second catalyst bed) is at most 600°C, more preferably at most 550°C, even more preferably at most 500°C.

[0508] In a preferred embodiment, relatively speaking, the temperature of the exhaust gas upon entering the first reaction zone (entering the first catalyst bed) is at least 20K higher than the temperature of the exhaust gas upon entering the second reaction zone (entering the second catalyst bed), more preferably at least 40K, even more preferably at least 60K, most preferably at least 80K, and in particular at least 100K.

[0509] In a preferred embodiment, relatively speaking, the temperature of the exhaust gas upon entering the second reaction zone (entering the second catalytic bed) is at least 10K higher than the temperature of the exhaust gas upon entering the first reaction zone (entering the first catalytic bed), more preferably at least 20K, even more preferably at least 30K, most preferably at least 40K, and in particular at least 50K.

[0510] In a preferred embodiment, the temperature in the first reaction zone (in the first catalyst bed) is, relatively speaking, at least 120 K higher than the temperature in the second reaction zone (in the first catalyst bed), more preferably at least 140 K higher, even more preferably at least 160 K higher, most preferably at least 180 K higher, and in particular at least 200 K higher.

[0511] In a preferred embodiment, the temperature in the second reaction zone (in the second catalyst bed) is, relatively speaking, at least 120 K higher than the temperature in the first reaction zone (in the first catalyst bed), more preferably at least 140 K, even more preferably at least 160 K, most preferably at least 180 K, and in particular at least 200 K higher.

[0512] In a further preferred embodiment, the first reaction zone and the second reaction zone are spatially connected to one another. In this case, the catalyst bed is preferably a common catalyst bed, wherein external influences lead to a division into a plurality of reaction zones, in particular by the injection points of the reducing agent, so that the reducing agent is present unevenly across the catalyst bed.

[0513] Preferably, the first reaction zone and the second reaction zone are provided in a common vessel.

[0514] Preferably, the temperature of the offgas in the first reaction zone and in the second reaction zone is in each case independently at most 500°C, preferably in each case independently in the range from 350°C to 450°C.

[0515] In a preferred embodiment, 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 1.2 times greater than the space velocity in the second reaction zone, more preferably at least 1.4 times, even more preferably at least 1.6 times, most preferably at least 1.8 times, and in particular at least 2.0 times greater.

[0516] 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 1.5 times greater than the space velocity in the first reaction zone, more preferably at least 2.0 times, even more preferably at least 3.0 times, most preferably at least 5.0 times, and in particular at least 10.0 times greater.

[0517] In the context of the present invention, "space velocity" means the quotient of the volumetric flow rates of the gas mixture through the catalyst bed, based on the volume of the catalyst or catalyst bed (measured at 0°C and 1.014 bara, typically in standard m / s). 3 ·h -1 Report). Thus, the space velocity can be adjusted by the volumetric flow rate of the gas and / or the amount of catalyst.

[0518] Preferably, the exhaust gas entering the exhaust gas treatment system is at 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 especially at least 450°C.

[0519] Preferably, the exhaust gas entering the exhaust gas treatment system is at 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 especially at least 650°C.

[0520] Preferably, the exhaust gas entering the exhaust gas treatment system is at 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.

[0521] Preferably, the exhaust gas entering the exhaust gas treatment system is at 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.

[0522] Preferably, the pressure of the exhaust gas entering the exhaust gas treatment system is at most 1.4 bara, preferably at most 1.3 bara, more preferably at most 1.2 bara.

[0523] In a further preferred embodiment, the exhaust gas is at a reduced pressure, preferably about -5 mbar, when entering the exhaust gas treatment system. This has the advantage that in the event of a possible leak, no gas is released into the environment.

[0524] Preferably, the NO of the exhaust gas entering the exhaust gas treatment system X The degree of oxidation is 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%.

[0525] Preferably, the NO of the exhaust gas entering the exhaust gas treatment system X The degree of oxidation is 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%.

[0526] Depending on the combustion temperature, the degree of oxidation can also be significantly lower, and the degree of oxidation decreases with increasing combustion temperature. Preferably, the exhaust gas NO X The degree of oxidation is 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%.

[0527] Preferably, the O2 content of the exhaust gas when entering the exhaust gas treatment system is less than 2.0% by volume.

[0528] Preferably, the O2 content of the exhaust gas when entering the exhaust gas treatment system is greater than 4.0% by volume.

[0529] In step (d) of the method of the present invention, the NO content in the exhaust gas is reduced. This can be achieved in various ways, namely, by (d1) decomposing NO over an NO decomposition catalyst and / or (d2) chemically reducing NO with a reducing agent over an NO reduction catalyst. Step (d) of the method of the present invention is carried out in an exhaust gas treatment system.

[0530] In a preferred embodiment, step (d) comprises reducing the N2O content in the exhaust gas by (d1) decomposing N2O over an N2O decomposition catalyst.

[0531] In a preferred embodiment, the N2O decomposition catalyst comprises a zeolitic material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0532] In other preferred embodiments, the N2O decomposition catalyst is NO in the context of the present invention. X -sensitive N2O decomposition catalyst, which has been described in detail above. In this case, the exhaust gas is preferably first passed through step (e), i.e. first through the NO X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content, preferably quantitatively, and then the exhaust gas is mixed with NO X -Contact with sensitive N2O decomposition catalyst.

[0533] Preferably, the N2O decomposition catalyst is arranged in a radial basket through which the flow passes axially.

[0534] The N2O decomposition catalyst is preferably in granular form and comprises at least 50 particles.

[0535] In a preferred embodiment, step (d) comprises reducing the N2O content in the exhaust gas by (d2) chemically reducing N2O with a reducing agent over a N2O reduction catalyst; preferably, wherein the N2O reduction catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including a 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 structure type.

[0536] Preferably, the N2O reduction catalyst is disposed in a radial basket through which the flow passes axially.

[0537] The N2O reduction catalyst is preferably in a granular form and comprises at least 50 particles.

[0538] In a preferred embodiment, step (d) comprises reducing the N2O content in the exhaust gas by:

[0539] - decomposing N2O by (d1) over an N2O decomposition catalyst; preferably, wherein the N2O decomposition catalyst comprises a zeolitic material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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

[0540] - in turn by chemically reducing the N2O with a reducing agent over a N2O reduction catalyst (d2); preferably, wherein the N2O reduction catalyst comprises a zeolitic material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0541] Preferably, the reducing agent in step (d2) is selected from NH3, hydrocarbons, CO, H2 and mixtures thereof; preferably NH3.

[0542] In a preferred embodiment, the reducing agent in step (d2) is NH3, preferably, used in an amount of 0.5 to 2.0 parts by mole based on the molar ratio of N2O to be chemically reduced (i.e., based on the amount of N2O at the inlet of the catalyst bed entering the N2O reduction catalyst), preferably 0.8 to 1.8 parts by mole.

[0543] In a preferred embodiment, the reducing agent in step (d2) is NH3, preferably used in an amount of 0.5 to 2.0 parts by mole, preferably 0.8 to 1.8 parts by mole, based on the molar amount of N2O in the exhaust gas at the inlet to the catalyst bed of the N2O reduction catalyst. If step (e) is also carried out in the catalyst bed of the N2O reduction catalyst, this amount plus the amount for NO X Any desired amount of added NH3 for reduction.

[0544] In other preferred embodiments, the reducing agent is a hydrocarbon or a mixture of two or more hydrocarbons, and its amount is preferably 0.2 to 1.0 parts by mole, more preferably 0.2 to 0.7 parts by mole, based on the molar amount of NO in the exhaust gas at the inlet of the catalyst bed of the NO reduction catalyst. If step (e) is also carried out in the catalyst bed of the NO reduction catalyst, this amount is also added to the amount used for NO X Any desired amount of added NH3 for reduction.

[0545] The reducing agent may also already be present in the exhaust gas, for example in the form of residual combustion gases and / or their oxidation products. In this case, the method according to the invention not only reduces nitrogen oxides (NO X and N2O), and also reduce the content of these impurities (residual combustion gases and / or their oxidation products).

[0546] In step (e) of the method of the present invention, NO in the exhaust gas is reduced. X (i.e. NO and NO2) content. This is determined by the NO X Reduction of NO by using a reducing agent on a catalyst X The step (e) of the method of the present invention is also carried out in the exhaust gas treatment system.

[0547] NO X The reduction catalyst preferably comprises a zeolitic material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0548] Preferably, NO X The reduction catalyst is disposed in radial baskets through which the flow passes axially.

[0549] Preferably, NO X The reduction catalyst is in a granular form and comprises at least 50 particles.

[0550] Preferably, the reducing agent in step (e) is selected from NH3, hydrocarbons, CO, H2 and mixtures thereof; preferably NH3.

[0551] Preferably, the reducing agent in step (e) is NH3, and its amount is based on the NO to be chemically reduced. X The molar ratio is 0.9 to 2.5 parts by mole, preferably 1.0 to 1.4 parts by mole, and preferably 1.0 to 1.2 parts by mole.

[0552] In a preferred embodiment, the reducing agent in step (d2) is the same as the reducing agent in step (e); preferably NH3.

[0553] In step (d2) and / or (e) of the inventive method, in addition to NH 3 , other nitrogen-containing reducing agents are also suitable in principle, for example nitrogen hydrogen compounds, such as azane, hydroxy derivatives of azane and amines, oximes, carbamates, ureas or urea derivatives. An example of an azane is hydrazine, and very particularly ammonia. An example of a hydroxy derivative of azane is hydroxylamine. An example of an amine is an aliphatic primary amine, for example methylamine. An example of a carbamate is ammonium carbamate. An example of a urea derivative is N,N '-substituted urea, for example N,N '-dimethylurea. Urea and urea derivatives are preferably used in the form of an aqueous solution. Particularly preferred is ammonia or a substance that releases ammonia when introduced, for example urea or ammonium carbamate.

[0554] The particularly preferred process scheme of the present invention is described in detail below:

[0555] DeNO X -deN2O-transformer 1

[0556] In a preferred embodiment, the exhaust gas treatment system comprises a first reaction zone through which the exhaust gas passes in series and a subsequent second reaction zone;

[0557] wherein a reducing agent is added to the exhaust gas upstream of the first reaction zone;

[0558] Among them, in the first reaction zone, first by NO X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X Content (step (e)) (deNO X 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 a reducing agent on an N2O reduction catalyst (step (d2));

[0559] wherein optionally, additional reducing agent is added to the exhaust gas upstream of the second reaction zone; and

[0560] wherein the N2O content in the exhaust gas is then reduced in a second reaction zone by decomposing N2O on an N2O decomposition catalyst (step (d1)) and / or by chemically reducing N2O with a reducing agent on an N2O reduction catalyst (step (d2)) (deN2O stage); wherein optionally, by X NO reduction catalyst X Chemical reduction (step (e)) is performed to additionally further reduce NO in the exhaust gas. X content.

[0561] Preferably, the NO in the first reaction zone X The reduction catalyst comprises a conventional, preferably non-zeolitic SCR catalyst, for example based on V2O5-WO3- / TiO2.

[0562] Preferably, the temperature of the off-gas upon entering the first reaction zone is at most 400°C, preferably at most 350°C.

[0563] Preferably, the N2O decomposition catalyst in the second reaction zone comprises a zeolitic material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0564] Preferably, the temperature of the off-gas upon entering the second reaction zone is in the range of 300 to 550°C, preferably 350 to 500°C.

[0565] Preferably, the off-gas after leaving the first reaction zone and before entering the second reaction zone has a NO in the range of 0 to 200 ppmv, preferably 1 to 200 ppmv. X content and an N2O content in the range of 200 to 2000 ppmv.

[0566] DeNO X -deN2O-transformer 2

[0567] In other preferred embodiments, the exhaust gas treatment system also comprises a first reaction zone and a subsequent second reaction zone through which the exhaust gas passes continuously;

[0568] wherein a reducing agent is added to the exhaust gas upstream of the first reaction zone;

[0569] Among them, in the first reaction zone, first by NO X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X Content (step (e)) (deNO Xwherein 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 a reducing agent on an N2O reduction catalyst (step (d2));

[0570] wherein optionally, additional reducing agent is added to the exhaust gas upstream of the second reaction zone; and

[0571] wherein the N2O content in the exhaust gas is then reduced in a second reaction zone by decomposing N2O on an N2O decomposition catalyst (step (d1)) and / or by chemically reducing N2O with a reducing agent on an N2O reduction catalyst (step (d2)) (deN2O stage); wherein optionally, by X NO reduction catalyst X Chemical reduction (step (e)) is performed to additionally further reduce NO in the exhaust gas. X content.

[0572] Preferably, the NO in the first reaction zone X The reduction catalyst comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0573] Preferably, the temperature of the off-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. Preferably, the temperature of the off-gas upon entering the first reaction zone is at most 600°C, more preferably at most 550°C.

[0574] Preferably, the N2O decomposition catalyst in the second reaction zone comprises NO in the context of the present invention. X - a sensitive N2O decomposition catalyst, which has been described in detail above.

[0575] Preferably, the temperature of the off-gas upon entering 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 off-gas upon entering the second reaction zone is at most 600°C, more preferably at most 550°C.

[0576] Preferably, the off-gas after leaving the first reaction zone and before entering the second reaction zone has a NO content of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv. X content and an N2O content in the range of 200 to 2000 ppmv.

[0577] DeNO X Particularly preferred embodiments of deN2O variant 2

[0578] In a particularly preferred embodiment, the exhaust gas treatment system of the present invention comprises a first catalyst bed and a spatially separated second catalyst bed; wherein the first catalyst bed is arranged upstream of the second catalyst bed in the flow direction of the exhaust gas; wherein optionally and preferably, a first device having a first control valve for metering NH3 into the exhaust gas is arranged upstream of the first catalyst bed; wherein a second device having a second control valve for metering NH3 into the exhaust gas is arranged downstream of the first catalyst bed and upstream of the second catalyst bed, the second device being used to meter additional NH3 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 X incomplete chemical reduction with NH3, wherein optionally and preferably at least part of the NH3 comes 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 (d1*) residual N2O is optionally decomposed; and (e*) residual NO X Chemically reduced with NH3.

[0579] Preferably, the catalytic decomposition of N2O in the first catalyst bed is carried out by the presence of NO in the exhaust gas. X Catalytic promoter.

[0580] Preferably, NH3 is used to convert NO into X Incomplete chemical reduction of NO leads to a predetermined residual NO X content, the residual NO X The content is sufficient to promote the decomposition of N2O in the first catalyst bed. X The chemical reduction is usually much faster than the chemical reduction of N2O with NH3, and the chemically reduced NO in the first catalyst bed X The amount is not the entire amount and the extent of any parallel chemical reduction of N2O with NH3 in the first catalyst bed is typically negligible.

[0581] Preferably, for NO X Reduction Additional NH3 is metered into the exhaust gas by the first device; preferably under feedback control; ie NO X A specific value of the concentration is defined as a target value (set point) and the NO Xand, in the event of a difference between the set point and the actual value (control difference), changing the output of the first control valve so as to minimize the difference. X The set point for the concentration and therefore the amount of additional NH3 is chosen so that upon leaving the first catalyst bed NO X The residual concentration of NO is at most 1000 ppmv, preferably at most 500 ppmv, more preferably at most 100 ppmv. X The set point for the concentration and therefore the amount of additional NH3 is chosen so that upon leaving the first catalyst bed NO X The residual concentration of NO in the first catalyst bed is at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 40 ppmv. X The expected specific consumption of chemically reduced NH3 is typically per mole of reduced NO X The amount of NH3 in the catalyst bed is 0.9-1.1 mol, which is therefore significantly less than the expected specific (mol / mol) consumption of NH3 in the second catalyst bed.

[0582] Preferably, the temperature of the exhaust gas as it leaves the first catalyst bed is in the range of 400 to 550°C.

[0583] Preferably, the off-gas on leaving the first catalyst bed has a pressure greater than atmospheric pressure, ie ≥ 1.0 bara, but at most 1.2 bara, more preferably at most 1.1 bara.

[0584] Preferably, the NO X The degree of oxidation is 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%.

[0585] In a preferred embodiment, the NO content of the exhaust gas leaving the first catalyst bed is X The degree of oxidation is in the range of 30% to 50%.

[0586] In other preferred embodiments, the NO content of the exhaust gas leaving the first catalyst bed is X The degree of oxidation is in the range of 15% to 35%, preferably 15% to 30%.

[0587] In a further preferred embodiment, the NO content of the exhaust gas leaving the first catalyst bed is X The degree of oxidation is in the range of 10% to 20%.

[0588] In other preferred embodiments, the NO content of the exhaust gas leaving the first catalyst bed isX The degree of oxidation is in the range of 5% to 15%.

[0589] Preferably, residual N2O is decomposed in the second catalyst bed such that the residual concentration of N2O leaving the second catalyst bed is at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv, most preferably at most 2 ppmv.

[0590] Preferably, residual NO X decomposed in the second catalyst bed so that NO X The residual concentration is at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv, most preferably at most 2 ppmv.

[0591] Preferably, additional NH3 is metered in under feedforward control by a second means, namely NO X The concentration of N2O and optionally preferably N2O is measured in each case upon leaving the first catalyst bed or optionally in each case upon entering the second catalyst bed; the amount of exhaust gas entering the second catalyst bed is taken into account to calculate the amount of NO X The amount of reduced NH3 and optionally preferably by means of the stored ratio (ie for example NH3 / NO X The molar ratio (mol / mol) of NH3 / N2O and optionally preferably a factor derived therefrom) for NO X The sum of the required reduction and N2O reduction; and the calculation result (manipulated variable) is used to change the output of the second control valve in order to meter the required amount of NH3.

[0592] Preferably, according to the present invention, the molar NH3 concentration [NH3] of the exhaust gas entering the second catalyst bed is between 0.7x [N2O] and 1.0x [NO X ] to 4.0x[N2O] and 2.0x[NO X ], more preferably within the range of 1.0x[N2O] and 1.1x[NO X ] to 3.0x[N2O] and 1.6x[NO X ], even more preferably in the range of 1.5x[N2O] and 1.2x[NO X ] to 2.5x[N2O] and 1.4x[NO X ], where [N2O] is the molar concentration of N2O, and [NO X ] is NO X The molar concentrations of , both are the concentrations in the exhaust gas when entering the second catalyst bed.

[0593] Preferably, relative to NO XFor the feedforward control of the metered addition of NH3 to the second catalyst bed, an NH3 / NO ratio in the range of 1.0 to 2.0 is selected; preferably 1.1 to 1.6; more preferably 1.2 to 1.4. X molar ratio.

[0594] Preferably, for the feedforward control of the metered addition of NH 3 to the second catalyst bed relative to the N 2 O reduction, a molar ratio of NH 3 / N 2 O is selected in the range of 0.7 to 4.0; preferably 1.0 to 3.0; more preferably 1.5 to 2.5.

[0595] Preferably, additional NH3 is not metered with the second device under feedback control, since the aim is to maximize the chemical reduction of NO in the second catalyst bed. X , which means that the result is zero or only a very small residual concentration of NO X and N2O, which have limited utility as control variables.

[0596] Preferably, the amount of catalyst, i.e. the space velocity (= ratio of the exhaust gas volume flow rate under standard conditions to the catalyst volume) is selected so that the decomposition of N2O in the first catalyst bed is at least 50%, preferably at least 70%, more preferably at least 80%, based on the N2O concentration when entering the first catalyst bed.

[0597] Preferably, the amount of catalyst and the amount of additional NH3 are selected so that upon leaving the first catalyst bed, NO X The molar ratio of N2O to N2O is at least 5, more preferably at least 10, even more preferably at least 20.

[0598] Preferably, the space velocity of the first catalyst bed is 5000h -1 Up to 100,000 hours -1 In the range of 10000h, more preferably 10000h -1 Up to 50,000 hours -1 , even more preferably 15000h -1 Up to 45000h -1 .

[0599] If NO leaves the first catalyst bed X The molar ratio of NH3 to N2O is at least 10, and the NH3 metered addition to the second catalyst bed via the second device can preferably only react with the incoming NO X The amount is related.

[0600] Preferably, 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. Preferably, 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. The temperature can be adjusted by measures known to those skilled in the art, in particular the design of the heat exchanger and the conditions of the NH combustion.

[0601] Depending on the exothermicity of the chemical reactions carried out in the first catalyst bed and in the second catalyst bed, the inlet temperature of the exhaust gas entering the first catalyst bed is preferably selected so that the temperature of the exhaust gas when leaving the second catalyst bed is at most 600°C, more preferably at most 550°C, even more preferably at most 520°C.

[0602] Preferably, the space velocity of the second catalyst bed is 5000h -1 Up to 100,000 hours -1 In the range of 10000h, more preferably 10000h -1 Up to 50,000 hours -1 , even more preferably 15000h -1 Up to 45000h -1 .

[0603] Preferably, the first catalyst bed V1 cat With the second catalyst bed V2 cat The catalyst volume ratio (V1 cat / V2 cat ) is in the range of 1 / 2 to 20 / 1, preferably 1 / 2 to 10 / 1, more preferably 1 / 1 to 4 / 1.

[0604] In a preferred embodiment, at least one, more than one, or all of the following conditions are met:

[0605] the pressure of the exhaust gas upon entering the first catalyst bed is at most 5 bara, preferably at most 4 bara, more preferably at most 1.3 bara, most preferably at most 1.2 bara, and in particular at most 1.1 bara;

[0606] the H2O content of the offgas upon entry into the first catalyst bed is at least 5% by volume, preferably at least 10% by volume, more preferably at least 15% by volume, most preferably at least 20% by volume and in particular at least 25% by volume;

[0607] NO in the exhaust gas entering the first catalyst bed X A content of 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;

[0608] the N2O content of the off-gas upon entering 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;

[0609] The exhaust gas contains unburned NH3 residues from NH3 combustion when entering the first catalyst bed;

[0610] The N2O decomposition catalyst and / or the N2O reduction catalyst is in the form of a honeycomb body;

[0611] NO X The reduction catalyst is in the form of a honeycomb;

[0612] The first catalyst bed comprises Fe zeolite;

[0613] The second catalyst bed comprises Fe zeolite;

[0614] The exhaust gas passes through a heat exchanger and is heated therein before entering the first catalyst bed;

[0615] NO when leaving the first catalyst bed X The content is at most 1000 ppmv, preferably at most 500 ppmv, more preferably at most 300 ppmv, most preferably at most 100 ppmv; but preferably at least 10 ppmv, more preferably at least 20 ppm, more preferably at least 40 ppmv, most preferably at least 100 ppmv, and especially at least 250 ppmv;

[0616] a NO2 content on leaving the first catalyst bed of 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;

[0617] There is no intermediate cooling of the exhaust gas between leaving the first catalyst bed and entering the second catalyst bed;

[0618] N2O:NO when entering the first catalyst bed X The molar ratio of is at most 0.5, more preferably at most 0.2, even more preferably at most 0.1;

[0619] N2O:NO when leaving the first catalyst bed X The molar ratio of is at most 0.20, more preferably at most 0.1, even more preferably at most 0.05;

[0620] Feeding of NH3 into the exhaust gas upstream of the first catalyst bed in the direction of exhaust gas flow is optional; if present, it is preferably at a relative concentration to NO on entry into the first catalyst bed. XThe content is substoichiometric;

[0621] It is necessary to feed NH3 into the exhaust gas downstream of the first catalyst bed and upstream of the second catalyst bed in the direction of exhaust gas flow, and preferably relative to NO3 on entry into the second catalyst bed. X The total content of N2O is superstoichiometric.

[0622] Compared with conventional deNO using V2O5 / TiO2 catalyst X Compared to the above process, the above process using an Fe zeolite catalyst in two catalyst beds enables, at relatively low catalyst volumes (i.e. at relatively high space velocities):

[0623] - Complete or almost complete decomposition of large amounts of NO X , there is no risk of NH3 escape; and

[0624] - Simultaneous, complete or almost complete decomposition of N2O.

[0625] In addition to the inventive method of operation, this is achieved by the oxidizing properties of the Fe zeolite catalyst used according to the invention. Thus, in the first catalyst bed, according to the invention, the molar ratio of NO to NO2 is such that it is as close as possible to the thermodynamic equilibrium position. For example, due to the combustion of NH3 upstream at very high temperatures and the slow establishment of equilibrium in the gas phase as the exhaust gas cools in any downstream heat exchanger, the NO2 before entering the first catalyst bed is X The degree of oxidation (molar ratio of NO2 / (NO+NO2)) is lower than the expected 5% and is therefore well below the thermodynamic equilibrium applicable to the inlet temperature of the first catalyst bed. X This is very disadvantageous for efficient chemical reduction of NO, since as a result, only a small fraction of the NO present in the exhaust gas X It can be decomposed by fast SCR, and most of the NO X Or the remaining NO must be broken down by the significantly slower normal SCR.

[0626] The selected mode of operation of limited metered addition of NH3 in the first catalyst bed and the ability of the iron zeolite catalyst to oxidize NO or catalytically accelerate the establishment of equilibrium leads to a significantly faster (ie more efficient) NO X Chemical reduction, and at the same time the residual NO X NO X This allows NO to be oxidized from the outset in the second catalyst bed as well. X Perform efficient chemical reduction.

[0627] It has therefore been found that, similar to water, large amounts of NH3 (such as the complete chemical reduction of high concentrations of NO X required) to suppress NO on iron zeolite catalysts X Establishment of balance.

[0628] In addition, at relatively high doses of NH3, NO X The chemical reduction of NH3 is also inhibited by NH3 itself. As a result, depending on the temperature, the amount of catalyst and NO X As the amount of NH3 added increases and exceeds a certain amount of NH3, the NO X No further increase in decomposition occurred. With further increase in NH3 addition, it is even possible that in some cases NO2 can be observed simultaneously with NH3 slip. X Reduced decomposition.

[0629] The previous NO in the first catalyst bed X The chemical reduction of NO is significantly reduced in the second catalyst bed. X The amount of NH3 required.

[0630] According to the invention, in this way, together with the above-mentioned establishment or permanent readjustment of NO X Balance, a very efficient NO X Chemical reduction is also possible in the second catalyst bed even with superstoichiometric addition of NH 3 .

[0631] This is additionally achieved according to the invention with no or only negligible NH3 slip, preferably with an NH3 slip of at most 10 ppmv, more preferably at most 5 ppmv, even more preferably at most 3 ppmv, a fact also due to the oxidizing properties of the Fe zeolite catalyst 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 within the limits of the invention, the excess NH3 is selectively oxidized to N2 and H2O by the residual oxygen content of the exhaust gas present.

[0632] When using conventional SCR catalysts based on V2O5 / TiO2 (typically also used for denitrification of exhaust gases from natural gas combustion reformers), all of these advantages cannot be achieved in a single-stage or multi-stage arrangement. Therefore, for stability reasons, these conventional SCR catalysts typically cannot be operated at temperatures above 400°C, which limits the achievable rate of the decomposition reaction. It is also the case that conventional SCR catalysts have only very limited oxidation activity, so NO XEstablishing an equilibrium or permanently resetting it is not possible, nor can these catalysts efficiently and selectively oxidize the stoichiometric excess of NH 3 . On the contrary, there is even the risk of the undesirable formation of N 2 O.

[0633] In a variant of the above-described preferred embodiment according to the invention, the first catalyst bed and the second catalyst bed contain the same catalyst. In a preferred embodiment, the second device with the second control valve for metering NH3 into the exhaust gas is omitted, and preferably the spatial separation of the first catalyst bed from the second catalyst bed is omitted - in that case, there is actually only a single common catalyst bed, the first device with the first control valve for metering NH3 into the exhaust gas being 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. NO X The concentrations of NO, N₂O, and NH₃ are measured in the exhaust gas upstream of the common catalyst bed; the amount of exhaust gas entering the common catalyst bed is taken into account to calculate the additional amount of NH₃ still required; and the result of the calculation (the manipulated variable) is used to change the output of the first control valve to meter the additional amount of NH₃ still required. Preferably, in such an embodiment, the NH₃ oxidation catalyst is disposed downstream of the common catalyst bed to reduce possible NH₃ slip.

[0634] Simultaneous combustion of NH3 and CH4 - reduction of hydrogen cyanide content

[0635] In a preferred embodiment, in step (a), a mixture of CH4 and NH3 is combusted with air and / or oxygen to produce a mixture containing additionally CO2, CO and HCN and NO X and N2O exhaust gases.

[0636] In these cases, the first catalyst bed preferably assumes the additional function of catalyzing the cracking of HCN to give CO and NH3 products by hydrolysis with water present in the exhaust gas, as follows: HCN+ The CO and NH3 products formed can then be used, preferably (in the case of NH3), to reduce NO in the first catalyst bed. X , and preferably (for CO) used as a reducing agent to reduce N2O in the second catalyst bed to eliminate N2O and NO in the exhaust gas X .

[0637] As a pollutant and greenhouse gas, HCN content in exhaust gases must be limited or eliminated due to its toxicity, lifetime in the atmosphere, and absorption in the infrared. The cracking products formed when HCN is decomposed according to the invention with CO and NH3 in a first catalyst bed over a zeolite catalyst are suitable as catalysts for the second catalyst bed to remove NO. XThe fact that the vanadium oxide-based SCR catalysts are a reducing agent for further exhaust gas post-treatment with N2O completes the inventive concept of the present invention for exhaust gas treatment over zeolite catalysts. Conventional SCR catalysts based on vanadium oxide have virtually no HCN hydrolysis activity and are therefore unsuitable for HCN removal from exhaust gases. In this case, a downstream oxidation catalyst must be used.

[0638] DeN2O-deNO X.

[0639] In a further preferred embodiment, the exhaust gas treatment system comprises a first reaction zone and a subsequent second reaction zone through which the exhaust gas passes continuously;

[0640] wherein a reducing agent is added to the exhaust gas between the first reaction zone and the second reaction zone;

[0641] wherein, in the first reaction zone, the N2O content in the exhaust gas is first reduced by decomposing N2O on an N2O decomposition catalyst (step (d1)) (deN2O stage); and

[0642] In the second reaction zone, the X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X Content (step (e)) (deNO X wherein optionally, the N2O content in the exhaust gas is additionally further reduced by further decomposition of N2O on an N2O decomposition catalyst (step (d1)) and / or by chemical reduction of N2O with a reducing agent on an N2O reduction catalyst (step (d2));

[0643] Preferably, no reducing agent is added to the exhaust gas upstream of the first reaction zone.

[0644] According to the present invention, such a process scheme is particularly preferred. This makes it possible to first adjust the NO X and the relative content of N2O without consuming the reducing agent. The absolute NO in the first reaction zone X While the content remains almost unchanged, the N2O content in the exhaust gas is selectively reduced by decomposition. This can achieve the goal of establishing NO X The amount of N2O decomposition catalyst selected is preferably not too large to achieve a quantitative complete reduction of the N2O content in the exhaust gas by decomposition (0 ppmv) for economic reasons; rather, a compromise is found between the size of the N2O decomposition catalyst and the decomposition rate.

[0645] In a preferred embodiment, the N2O decomposition catalyst in the first reaction zone comprises a zeolitic material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0646] In other preferred embodiments, the N2O decomposition catalyst in the first reaction zone comprises NO in the context of the present invention. X - a sensitive N2O decomposition catalyst, which has been described in detail above.

[0647] In a preferred embodiment, the NO in the second reaction zone X The reduction catalyst comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0648] Preferably, in this context, the first reaction zone and the second reaction zone are operated at different temperature levels.

[0649] Preferably,

[0650] - The N2O decomposition catalyst in the first reaction zone contains NO X - a sensitive N2O decomposition catalyst; wherein the exhaust gas temperature 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

[0651] - NO in the second reaction zone X The reduction catalyst is a zeolitic material; preferably a zeolite loaded with a transition metal (including lanthanides), in particular 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 structure type; wherein the exhaust gas temperature 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 NO X In addition to the chemical reduction, preferably the (residual) N2O content is further reduced in the second reaction zone by decomposition and / or chemical reduction.

[0652] Preferably, in the first reaction zone, the space velocity is set such that the N2O content in the offgas is reduced in the first reaction zone by at most 95%, preferably at most 90%, preferably at most 85%, based on the N2O content in the offgas when entering the first reaction zone.

[0653] In a preferred embodiment, the N2O content in the offgas after leaving the first reaction zone and before entering the second reaction zone is at least 20 ppmv, more preferably at least 40 ppmv, even more preferably at least 60 ppmv, most preferably at least 80 ppmv, and in particular at least 100 ppmv.

[0654] In a preferred embodiment, the N2O content in the offgas 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.

[0655] Preferably, in the second reaction zone, the space velocity is set so that the NO content in the exhaust gas is further reduced by at least 30%, preferably at least 40%, and more preferably at least 50%, based on the NO content in the exhaust gas upon entering the second reaction zone. Due to the presence of the reducing agent in the second reaction zone, further reduction of the NO content in the second reaction zone can be achieved by decomposition on the NO decomposition catalyst (step (d1)) and by chemical reduction with the reducing agent on the NO reduction catalyst (step (d2)).

[0656] Preferably, in the second reaction zone, the N2O content in the exhaust gas is further reduced by chemical reduction of N2O over an N2O reduction catalyst (step (d2)).

[0657] In addition, in the second reaction zone, by X Chemical reduction of NO by using a reducing agent on a reduction catalyst X This reduction typically has rapid kinetics and preferably proceeds practically quantitatively according to the invention.

[0658] Step (f):

[0659] In 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.

[0660] In a preferred embodiment, the exhaust gas is cooled in a single heat exchanger which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

[0661] In a further preferred embodiment, the exhaust gas is cooled continuously in at least two heat exchangers arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas (see Figure 2 、 3 and 4).

[0662] In a further preferred embodiment, the exhaust gas is cooled in at least three heat exchangers arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas (see Figure 5 );

[0663] In a preferred embodiment, the exhaust gas is cooled successively in at least four heat exchangers which are arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

[0664] In a further preferred embodiment, the exhaust gas is cooled in at least six heat exchangers arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas (see Figure 6 );

[0665] The exhaust gas is cooled in at least one heat exchanger by releasing heat from the exhaust gas to a heat transfer medium.

[0666] Preferably, according to the present invention, the heat transfer medium used is selected from the group consisting of water, steam, combustion air, NH3 and combinations thereof. In particular, for reasons such as safety, water or steam is particularly preferred as the heat transfer medium.

[0667] In a preferred embodiment, in step (f) of the method according to the invention, the exhaust gas is preferably 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. Preferably, the heated H2O (which may be in liquid form and / or in the form of water vapor) is used to heat the NH3. Preferably, for this purpose, an H2O / NH3 heat exchanger is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the HO, wherein the NH3 is heated by absorbing heat from the HO (see Figure 2-6 ).

[0668] In a preferred embodiment, in step (f) of the method according to the invention, the exhaust gas is preferably 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. Preferably, the heated combustion air is used for the combustion of NH3 and H2 in a 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 Figure 2-6 ).

[0669] In a further preferred embodiment, the exhaust gas is cooled in step (f) of the process according to the invention in the following apparatus:

[0670] - a first exhaust gas / H2O heat exchanger as described above, which is arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, and

[0671] - the 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 (see Figure 2-6 ).

[0672] In a further preferred embodiment, the exhaust gas is cooled in step (f) of the process according to the invention in the following apparatus:

[0673] 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 gases, and

[0674] 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 gases.

[0675] The combustion air is heated in the first exhaust gas / combustion air heat exchanger and the second exhaust gas / combustion air heat exchanger, respectively, by absorbing heat from the exhaust gas. Preferably, the exhaust gas first flows through the first exhaust gas / combustion air heat exchanger and then through the second exhaust gas / combustion air heat exchanger. Preferably, the combustion air 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 gases. Preferably, the heated combustion air is used for the combustion of NH3 and H2 in a 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 Figure 5 and 6 ).

[0676] In a further preferred embodiment, the exhaust gas is cooled in step (f) of the process according to the invention in the following apparatus:

[0677] - the 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 gases,

[0678] - a first exhaust gas / H2O heat exchanger as described above, which is arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gases, and

[0679] - the 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 ( Figure 4-6 ).

[0680] The exhaust gas then preferably flows first through the first exhaust gas / combustion air heat exchanger, then through the second exhaust gas / H 2 O heat exchanger and subsequently through the second exhaust gas / combustion air heat exchanger.

[0681] In a preferred embodiment, in step (f) of the method according to the invention, the exhaust gas is cooled 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 described above, the first exhaust gas / H2O heat exchanger described above and / or the second exhaust gas / combustion air heat exchanger described above. The combustion gas is heated in the first exhaust gas / combustion gas heat exchanger by absorbing heat from the exhaust gas. Preferably, the heated combustion gas is used for combustion in a combustion device which, for this purpose, is arranged downstream of the exhaust gas / combustion gas heat exchanger in the flow direction of the combustion gas (see Figure 6 ).

[0682] In a preferred embodiment, in step (f) of the method according to the invention, the exhaust gas is cooled in at least one second exhaust gas / H2O heat exchanger 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 described above, the first exhaust gas / H2O heat exchanger described above and / or the second exhaust gas / combustion air heat exchanger described above. By absorbing heat from the exhaust gas, the H2O is heated in the second exhaust gas / H2O heat exchanger (see Figure 6 ).

[0683] In a further preferred embodiment, the exhaust gas is cooled in step (f) of the process according to the invention in the following apparatus:

[0684] - the 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 gases,

[0685] - the 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 gases,

[0686] - a second exhaust gas / combustion air heat exchanger as described above, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gases, and

[0687] - an exhaust gas / combustion gas heat exchanger as described above, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gases (see Figure 6 ).

[0688] In a further preferred embodiment, the exhaust gas is cooled in step (f) of the process according to the invention in the following apparatus:

[0689] - the 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 gases,

[0690] - the 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 gases,

[0691] - a second exhaust gas / combustion air heat exchanger as described above, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gases, and

[0692] - the 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 ).

[0693] In a further preferred embodiment, the exhaust gas is cooled in step (f) of the process according to the invention in the following apparatus:

[0694] - the 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 gases,

[0695] - the 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 gases,

[0696] - a second exhaust gas / combustion air heat exchanger as described above, which is arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gases,

[0697] - an exhaust gas / combustion gas heat exchanger as described above, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gases, and

[0698] - the 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 ).

[0699] Since high wall temperatures build up in the flow direction of the exhaust gases in the exhaust gas duct, at least in the upstream heat exchanger, the high exhaust gas temperatures lead to considerable stresses on the materials used, which can lead to a shortened service life or replacement with more complex and more expensive materials. One factor that should be considered for the effectiveness of the exhaust gas duct configuration is therefore the inlet temperature of the exhaust gases entering the duct. The NH3 must be preheated to a temperature defined by the process requirements. On the other hand, the preheating temperature of the combustion air, for example, constitutes a degree of freedom in the design, since it is not subject to any direct requirements other than efficient energy integration. Therefore, the inlet temperature of the exhaust gases into the exhaust gas duct is limited at the lower end by the preheating temperature imposed by the process requirements in a tubular reactor of a similar design to the primary reformer or possibly the primary reactor (preferably an adiabatic fixed-bed reactor).

[0700] Heterogeneous catalysts achieve higher reaction rates at higher temperatures by accelerating diffusion and kinetics. However, their operation is often limited by their reduced stability against deactivation at high temperatures. Therefore, for exhaust gas treatment systems, there exists an optimal operating window within which they achieve high reaction rates, which in turn manifests as a high permissible space velocity for the supplied gas, which in turn reduces the required catalyst volume. However, this window lies below the region where operation leads to deactivation and loss of catalytic effectiveness. Therefore, another criterion for evaluating efficient energy integration is whether the inlet temperature of the exhaust gas entering the exhaust gas treatment system is within this optimal window.

[0701] The third factor in evaluating the effectiveness of the exhaust duct configuration is the inlet temperature of the exhaust gas entering the chimney. Together with the mass flow of the exhaust gas, this determines the energy loss through the stream compared to the theoretical optimum, which is obtained at the dew point of water plus a required safety margin of 25K.

[0702] The H2 yield should be as high as possible to increase the economic viability of plant operation. High yields are typically directly correlated with low exhaust gas inlet temperatures into the chimney. However, if this goal cannot be achieved without minimizing the required exhaust gas inlet temperature into the chimney or providing the exhaust gas treatment system with an appropriate inlet temperature, the selected exhaust gas duct design will not be very successful.

[0703] Closed-loop control

[0704] Irrespective of the respective process scheme, the process according to the invention is preferably under closed-loop control.

[0705] In a preferred embodiment, depending on the configuration of the combustion system, preferably the combustion device, used for the closed-loop control of the method according to the invention, the first measured variable is at least one parameter characterizing the current operating state of the combustion system, preferably the combustion device. Preferably, the first measured variable or parameter is selected from the group consisting of combustion temperature and NH3 consumption of the combustion system, preferably the combustion device.

[0706] Depending on the characteristics of the exhaust gases leaving the combustion system, preferably the combustion device, in particular:

[0707] - NO in exhaust gas X content;

[0708] - NO in exhaust gas X degree of oxidation;

[0709] -N2O content in exhaust gas;

[0710] - the content of other components in the exhaust gas, such as H2O, O2 and N2;

[0711] - exhaust gas temperature;

[0712] - exhaust gas pressure; and

[0713] - exhaust gas volume flow rate;

[0714] Process conditions can be optimized to achieve efficient and economically viable reduction of NO in exhaust gases X and N2O content.

[0715] Therefore, in a preferred embodiment, for controlling the method according to the invention, in addition to or instead of the first measured variable, at least one parameter characteristic of the current state of the exhaust gas before entering the exhaust gas treatment system is measured upon leaving the combustion system, preferably the combustion device, and / or as a second measured variable upon entering the exhaust gas treatment system. Preferably, this second measured variable or parameter is selected from the group consisting of: NO in the exhaust gas; X Content; NO in exhaust gas X the degree of oxidation; the N2O content in the exhaust gas; the content of other components in the exhaust gas, such as H2O, O2 and N2; the exhaust gas temperature; the exhaust gas pressure; and the volume flow rate of the exhaust gas.

[0716] Therefore, in a preferred embodiment, for controlling the method according to the invention, in addition to or instead of the first measured variable and in addition to or instead of the second measured variable, at least one parameter characteristic of the current state of the exhaust gas when leaving the exhaust gas treatment system is measured as a third measured variable. Preferably, this third measured variable or parameter is selected from the group consisting of: NO in the exhaust gas; X Content; NO in exhaust gasX the degree of oxidation; the N2O content in the exhaust gas; the content of other components in the exhaust gas, such as H2O, O2 and N2; the exhaust gas temperature; the exhaust gas pressure; and the volume flow rate of the exhaust gas.

[0717] In a preferred embodiment, in particular when the exhaust gas treatment system comprises a first reaction zone and a second reaction zone through which the exhaust gas passes in sequence, wherein the reducing agent is fed between the first reaction zone and the second reaction zone, in order to control the method according to the invention, in addition to or instead of the first measured variable, and in addition to or instead of the second measured variable, and in addition to or instead of the third measured variable, at least one parameter characteristic of the current state of the exhaust gas before leaving the first reaction zone and before entering the second reaction zone is measured as a fourth measured variable. Preferably, this fourth measured variable or parameter is selected from the group consisting of: NO in the exhaust gas; X Content; NO in exhaust gas X the degree of oxidation; the N2O content in the exhaust gas; the content of other components in the exhaust gas, such as H2O, O2 and N2; the exhaust gas temperature; the exhaust gas pressure; and the volume flow rate of the exhaust gas.

[0718] Preferably, at least one manipulated variable is modified for the open-loop or closed-loop control of the method according to the invention as a function of the first measured variable and / or the second measured variable and / or the third measured variable and / or the fourth measured variable. Thus, preferably, the open-loop or closed-loop control of the method is 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 means of a controlled variation of the manipulated variable (control variable), preferably by means of a controlled variation of the amount of metered reducing agent.

[0719] In terms of preferred manipulated variables, it is necessary to distinguish:

[0720] - process conditions that can be changed at short notice only with relatively high plant complexity, if at all, and

[0721] - Process conditions that can be changed within a short time and are therefore better suited to the control of the process.

[0722] Preferably, according to the present invention,

[0723] - Dimensions of the exhaust gas treatment equipment;

[0724] - the nature, amount and flow direction of the N2O decomposition catalyst and / or N2O reduction catalyst;

[0725] -NO X the nature, amount and flow direction of the reduction catalyst;

[0726] - Type of reducing agent;

[0727] - Exhaust gas pressure;

[0728] - the feeding location of the reducing agent; and

[0729] - Relative arrangement of the first reaction zone and the second reaction zone

[0730] These parameters are not manipulated variables, ie they are preferably kept constant during the performance of the method of the invention.

[0731] However, these parameters can be selected or adjusted during the planning and design of the exhaust gas treatment system so that control of the method according to the invention is possible within a wide range. In this way, changes, for example with respect to the exhaust gas to be treated, can also be reacted to within a short time. Efficient and economically viable reduction of NO in exhaust gases X and N2O content without causing an undesirable breakthrough of the reducing agent (known as slip).

[0732] The preferred manipulated variables (controlled variables) according to the present invention are:

[0733] - the amount of reducing agent;

[0734] - exhaust gas temperature, if applicable; and

[0735] - If applicable, the temperature of the catalyst.

[0736] Preferably, the exhaust gas leaving the exhaust gas treatment system has a residual NO 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. X content.

[0737] Preferably, the exhaust gas leaving the exhaust gas treatment system 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.

[0738] Another aspect of the present invention relates to an apparatus comprising:

[0739] (i) an NH3 combustion system, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2; and

[0740] (ii) exhaust gas treatment system;

[0741] The device is configured to execute the above-described method of the present invention.

[0742] The device according to the invention is preferably a plant complex for producing pure hydrogen, comprising:

[0743] - one (or more) NH3 catalytic decomposition device for catalytically decomposing NH3 into N2 and H2, preferably a reactor filled with a catalyst;

[0744] a combustion device for directly or indirectly heating the NH3 decomposition device, preferably comprising a combustion chamber and at least one burner for burning a fuel with (air) oxygen, wherein the fuel contains NH3 or consists essentially of NH3;

[0745] - a device for purifying the product stream from the NH3 decomposition unit, preferably by means of PSA;

[0746] - Exhaust gas treatment system for cleaning exhaust gases from combustion plants, comprising a system for reducing NO X , optionally one or more catalyst beds for N2O reduction and / or N2O decomposition, preferably for the oxidation of unconverted reducing agent and / or its incompletely oxidized reaction products (preferably with a downstream catalyst bed of an NH3 oxidation catalyst).

[0747] The preferred embodiment of the present invention is summarized in the following paragraphs:

[0748] Sentence 1: A method for reducing NO in the exhaust gas of an NH3-operated combustion system X and N2O content, the method comprising the following steps: (a) burning NH3 to operate a combustion system, preferably a furnace, the combustion system preferably comprising a combustion device and an NH3 decomposition device for catalytically decomposing NH3 into N2 and H2, generating an exhaust gas, the exhaust gas containing N2, H2, NO X and N2O and leaves the combustion system; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger, the heat exchanger being arranged downstream of the combustion system in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas into an exhaust gas treatment system; (d) reducing the N2O content in the exhaust gas by (d1) decomposing N2O on an N2O decomposition catalyst and / or (d2) chemically reducing N2O with a reducing agent on an N2O reduction catalyst; (e) X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger, the heat exchanger being arranged downstream of the exhaust gas treatment system along the flow direction of the exhaust gas.

[0749] Sentence 2: The method according to sentence 1, which is used to reduce NO in the exhaust gas of an NH2- and H2-operated combustion system integrated into a system for the catalytic decomposition of NH3 into N2 and H2. X and N2O content, the method comprising the following steps: (a) burning NH3 and H2 for operating the combustion system (preferably in a combustion device) to produce an exhaust gas containing N2, H2O, NO X and N2O and leaves the combustion system; (b) optionally and preferably cooling the exhaust gas in at least one heat exchanger, the heat exchanger being arranged downstream of the combustion system in the flow direction of the exhaust gas; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment system, the exhaust gas treatment system being arranged downstream of the combustion system in the flow direction of the exhaust gas and optionally downstream of the at least one heat exchanger; (d) reducing the N2O content in the exhaust gas by (d1) decomposing N2O on an N2O decomposition catalyst and / or (d2) chemically reducing N2O with a reducing agent on an N2O reduction catalyst; (e) X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content; and (f) optionally and preferably cooling the exhaust gas in at least one heat exchanger, the heat exchanger being arranged downstream of the exhaust gas treatment system along the flow direction of the exhaust gas.

[0750] Clause 3: A method according to any preceding clause, wherein the exhaust gases are cooled in a single heat exchanger arranged downstream of the combustion system in the direction of flow of the exhaust gases.

[0751] Clause 4: The method according to any of the preceding clauses, wherein the exhaust gas is cooled successively in at least two heat exchangers arranged downstream of the combustion system in the flow direction of the exhaust gas.

[0752] Clause 5: The method according to any of the preceding clauses, wherein the exhaust gas is cooled successively in at least three heat exchangers arranged downstream of the combustion system in the flow direction of the exhaust gas.

[0753] Sentence 6: A method according to any of the preceding sentences, wherein in step (b), the exhaust gases are cooled in the at least one heat exchanger by releasing heat from the exhaust gases to a heat transfer medium, wherein the heat transfer medium used is preferably NH3, and the heat transfer medium is then supplied to the catalytic decomposition in the NH3 decomposition device on an NH3 catalyst.

[0754] Sentence 7: The method according to any of the preceding sentences, wherein in step (b) the exhaust gas is cooled in at least one first exhaust gas / NH3 heat exchanger arranged downstream of the combustion system in the flow direction of the exhaust gas.

[0755] Sentence 8: A method according to any one of the preceding sentences, wherein in step (b), the exhaust gas is cooled in: a first exhaust gas / NH3 heat exchanger arranged downstream of the combustion system in the flow direction of the exhaust gas; and a second exhaust gas / NH3 heat exchanger arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas.

[0756] Sentence 9: A method according to any one of the preceding sentences, wherein in step (b), the exhaust gas is cooled in: - a first exhaust gas / NH3 heat exchanger arranged downstream of the combustion system in the flow direction of the exhaust gas, - a second exhaust gas / NH3 heat exchanger arranged downstream of the first exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas, - a third exhaust gas / NH3 heat exchanger arranged downstream of the second exhaust gas / NH3 heat exchanger in the flow direction of the exhaust gas.

[0757] Clause 10: A method according to any preceding clause, wherein in step (b) the off-gas is cooled to a temperature T2 in the range of 400 to 450°C, more preferably 400 to 420°C.

[0758] Clause 11: A method according to any of the preceding clauses, wherein the N2O decomposition catalyst and / or the N2O reduction catalyst and / or the NO X The reduction catalyst independently comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an iron, cobalt or copper loaded zeolite; more preferably, an iron loaded zeolite; even more preferably, an iron loaded zeolite independently of the MFI, BEA, FER, MOR, FAU and / or MEL structure type.

[0759] Clause 12: The method of any preceding clause, wherein the N2O decomposition catalyst and the N2O reduction catalyst are made of the same material.

[0760] Clause 13: The method of any preceding clause, wherein the N2O decomposition catalyst and the NO X The reduction catalyst is made of the same material.

[0761] Clause 14: The method of any preceding clause, wherein the N2O reduction catalyst and the NO X The reduction catalyst is made of the same material.

[0762] Clause 15: The method of any preceding clause, wherein the N2O decomposition catalyst, the N2O reduction catalyst, and the NO X The reduction catalyst is made of the same material.

[0763] Clause 16: A method according to any preceding clause wherein in step (a), the combustion of NH3 is not over a catalyst.

[0764] Sentence 17: A process according to any 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%.

[0765] Sentence 18: A process according to any preceding sentence, wherein the proportion of H 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%.

[0766] Sentence 19: A method according to any preceding sentence, wherein the molar ratio of H2:NH3 in the mixture is from 45:55 to 90:10, preferably from 50:50 to 85:15, more preferably from 55:45 to 80:20, even more preferably from 60:40 to 75:25, most preferably from 65:35 to 70:30.

[0767] Clause 20: The method of any preceding clause wherein the air ratio λ is in the range of 0.9 to 1.7, preferably 1.0 to 1.6, even more preferably 1.1 to 1.5, most preferably 1.2 to 1.4.

[0768] Clause 21: The method according to any of the preceding clauses, wherein the combustion system, preferably a furnace (preferably comprising a combustion device and an NH3 decomposition device) is integrated into a system for the thermal and / or catalytic decomposition of NH3 into N2 and H2.

[0769] Clause 22: A method according to any preceding clause, wherein the NO X The content is greater than the N2O content; preferably, wherein NO X The content is at least twice, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times the N2O content.

[0770] Sentence 23: A method according to any of the preceding sentences, wherein the NO content of the exhaust gas is greater than the N2O content; preferably, wherein the NO content is at least twice the N2O content, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times.

[0771] Sentence 24: A method according to any of the preceding sentences, wherein the NO2 content of the exhaust gas is greater than the N2O content; preferably, wherein the NO2 content is at least twice the N2O content, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times.

[0772] Clause 25: A method according to any preceding clause, wherein the N2O content of the exhaust gas is greater than NO X content; preferably, wherein the N2O content is NO X The amount is at least twice, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times greater.

[0773] Sentence 26: A method according to any of the preceding sentences, wherein the N2O content of the exhaust gas is greater than the NO content; preferably, wherein the N2O content is at least twice the NO content, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times.

[0774] Sentence 27: A method according to any of the preceding sentences, wherein the N2O content of the exhaust gas is greater than the NO2 content; preferably, wherein the N2O content is at least twice the NO2 content, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times.

[0775] Clause 28: A method according to any preceding clause, wherein the NO X The content is 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.

[0776] Clause 29: A method according to any preceding clause, wherein the NO X The content is 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.

[0777] Clause 30: A method according to any preceding clause, wherein the NO XThe content is 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.

[0778] Clause 31: A method according to any preceding clause, 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 especially at least 50 ppmv.

[0779] Clause 32: A method according to any preceding clause, 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 especially at least 250 ppmv.

[0780] Clause 33: A method according to any preceding clause, 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 especially at least 3500 ppmv.

[0781] Clause 34: The method of any preceding clause wherein the off-gas has an H2O content of less than 2.0 vol%.

[0782] Sentence 35: A method according to any of the preceding sentences, wherein the H2O content of the off-gas is greater 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%.

[0783] Sentence 36: A method according to any of the preceding sentences, wherein the H2O content of the off-gas is 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%.

[0784] Sentence 37: A method according to any of the preceding sentences, wherein the H2O content of the exhaust gas is in the range of 10±8 volume %; preferably in the range of 10±7 volume %, more preferably in the range of 10±6 volume %, even more preferably in the range of 10±5 volume %, most preferably in the range of 10±4 volume %, and in particular in the range of 10±3 volume %.

[0785] Sentence 38: A method according to any of the preceding sentences, wherein the H2O content of the exhaust gas is in the range of 15±8 volume %; preferably in the range of 15±7 volume %, more preferably in the range of 15±6 volume %, even more preferably in the range of 15±5 volume %, most preferably in the range of 15±4 volume %, and in particular in the range of 15±3 volume %.

[0786] Sentence 39: A method according to any of the preceding sentences, wherein the H2O content of the exhaust gas is in the range of 20±8 volume %; preferably in the range of 20±7 volume %, more preferably in the range of 20±6 volume %, even more preferably in the range of 20±5 volume %, most preferably in the range of 20±4 volume %, and in particular in the range of 20±3 volume %.

[0787] Sentence 40: A method according to any of the preceding sentences, wherein the H2O content of the exhaust gas is in the range of 25±8 volume %; preferably in the range of 25±7 volume %, more preferably in the range of 25±6 volume %, even more preferably in the range of 25±5 volume %, most preferably in the range of 25±4 volume %, and in particular in the range of 25±3 volume %.

[0788] Sentence 41: A method according to any of the preceding sentences, wherein the H2O content of the exhaust gas is in the range of 30±8 volume %; preferably in the range of 30±7 volume %, more preferably in the range of 30±6 volume %, even more preferably in the range of 30±5 volume %, most preferably in the range of 30±4 volume %, and in particular in the range of 30±3 volume %.

[0789] Sentence 42: A method according to any of the preceding sentences, wherein the N2 content of the exhaust gas is at most 95 volume %; preferably at most 90 volume %, more preferably at most 85 volume %, even more preferably at most 80 volume %, most preferably at most 75 volume %, and in particular at most 70 volume %.

[0790] Sentence 43: A method according to any of the preceding sentences, wherein the exhaust gas N2 content is at least 40 volume %; preferably at least 50 volume %, more preferably at least 60 volume %, even more preferably at least 70 volume %, most preferably at least 80 volume %, and in particular at least 90 volume %.

[0791] Clause 44: A method according to any preceding clause, wherein the off-gas comprises an additional gaseous component; preferably selected from the group consisting of O2, CO, CO2, NH3, CH4 and mixtures thereof.

[0792] Sentence 45: A method according to any of the preceding sentences, wherein the exhaust gases leaving the combustion system, preferably the furnace, more preferably leaving the combustion device are at 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.

[0793] Sentence 46: A method according to any of the preceding sentences, wherein the exhaust gases leaving the combustion system, preferably the furnace, more preferably leaving the combustion device are at 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.

[0794] Clause 47: A method according to any preceding clause, wherein the flue gases exiting the combustion system, preferably furnace, more preferably the combustion device, are at a pressure of at most 1.5 bar; preferably atmospheric pressure.

[0795] Clause 48: A method according to any preceding clause, wherein the NO X The degree of oxidation is 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%.

[0796] Clause 49: A method according to any preceding clause, wherein the NO X The degree of oxidation is 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%.

[0797] Clause 50: A method according to any preceding clause, wherein the O2 content of the flue gas exiting the combustion system, preferably furnace, more preferably the combustion apparatus, is less than 2.0% by volume.

[0798] Clause 51: A method according to any preceding clause, wherein the O2 content of the flue gas leaving the combustion system, preferably furnace, more preferably leaving the combustion device is greater than 4.0% by volume.

[0799] Sentence 52: A method according to any preceding sentence, wherein the exhaust gas entering the exhaust gas treatment system is at 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.

[0800] Sentence 53: A method according to any of the preceding sentences, wherein the exhaust gas entering the exhaust gas treatment system is at 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.

[0801] Sentence 54: A method according to any preceding sentence, wherein the exhaust gas entering the exhaust gas treatment system is at 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.

[0802] Sentence 55: A method according to any preceding sentence, wherein the exhaust gas entering the exhaust gas treatment system is at 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.

[0803] Sentence 56: A method according to any of the preceding sentences, wherein the exhaust gas entering the exhaust gas treatment system is at a temperature which is relatively lower than the temperature of the exhaust gas leaving the combustion system, preferably the furnace, more preferably leaving the combustion device, by 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.

[0804] Clause 57: A method according to any preceding clause wherein the exhaust gas is at a pressure of at most 1.2 bar on entering the exhaust gas treatment system; preferably atmospheric pressure.

[0805] Clause 58: A method according to any preceding clause, wherein the NO X The degree of oxidation is 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%.

[0806] Clause 59: A method according to any preceding clause, wherein the NO X The degree of oxidation is 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%.

[0807] Clause 60: The method of any preceding clause wherein the O2 content of the exhaust gas entering the exhaust treatment system is less than 2.0% by volume.

[0808] Clause 61: The method of any preceding clause wherein the exhaust gas entering the exhaust treatment system has an O2 content greater than 4.0% by volume.

[0809] Sentence 62: A method according to any of the preceding sentences, wherein step (d) comprises reducing the N2O content in the exhaust gas by (d1) decomposing N2O over an N2O decomposition catalyst; preferably, wherein the N2O decomposition catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including a 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.

[0810] Sentence 63: A method according to any of the preceding sentences, wherein step (d) comprises reducing the N2O content in the exhaust gas by (d2) chemically reducing the 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 a 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.

[0811] Sentence 64: The method of any preceding sentence wherein the reducing agent in step (d2) is selected from NH3, hydrocarbons, CO, H2 and mixtures thereof; preferably NH3.

[0812] Sentence 65: The method of any preceding sentence, wherein the reducing agent in step (d2) is NH3 in an amount of 0.5 to 2.0 parts by mole, preferably 0.8 to 1.8 parts by mole, based on the molar ratio of N2O to be chemically reduced.

[0813] Sentence 66: A method according to any of the preceding sentences, wherein the reducing agent in step (d2) is a hydrocarbon or a mixture of several hydrocarbons, and its amount is preferably 0.2 to 1.0 mole parts, more preferably 0.2 to 0.7 mole parts based on the molar proportion of N2O to be decomposed.

[0814] Clause 67: A method according to any preceding clause wherein the NO X The reduction catalyst comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0815] Sentence 68: The method of any preceding sentence wherein the reducing agent in step (e) is selected from the group consisting of NH3, hydrocarbons, CO, H2, and mixtures thereof; preferably NH3.

[0816] Sentence 69: A method according to any preceding sentence, wherein the reducing agent in step (e) is NH3 in an amount based on the NO to be chemically reduced. X The molar ratio of the present invention is 0.9 to 2.5 parts by mole, preferably 1.0 to 1.4 parts by mole, more preferably 1.0 to 1.2 parts by mole.

[0817] Clause 70: The process of any preceding clause wherein the reducing agent in step (d2) is the same as the reducing agent in step (e); preferably NH3.

[0818] Sentence 71: The method of any of the preceding sentences, wherein the exhaust gas treatment system comprises a first reaction zone through which the exhaust gas passes in series and a subsequent second reaction zone; wherein a reducing agent is added to the exhaust gas upstream of the first reaction zone; wherein, in the first reaction zone, the reducing agent is first introduced into the exhaust gas by the addition of a reducing agent to the exhaust gas upstream of the first reaction zone; X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction is performed to reduce NO in the exhaust gas X wherein optionally, the N2O content in the exhaust gas is further reduced by decomposing N2O on an N2O decomposition catalyst (step (d1)) and / or by chemically reducing N2O with a 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, then, in the second reaction zone, the N2O content in the exhaust gas is further reduced by decomposing N2O on an N2O decomposition catalyst (step (d1)) and / or by chemically reducing N2O with a reducing agent on an N2O reduction catalyst (step (d2)); wherein optionally, the N2O content in the exhaust gas is further reduced by decomposing N2O on an N2O decomposition catalyst (step (d1)) and / or by chemically reducing N2O with a reducing agent on an N2O reduction catalyst (step (d2)); X Chemical reduction of NO on reduction catalysts X To further reduce NO in the exhaust gas X content (step (e)).

[0819] Clause 72: The method of clause 71, wherein the NO in the first reaction zone X The reduction catalyst comprises a conventional SCR catalyst, preferably based on V2O5-WO3- / TiO2.

[0820] Sentence 73: The process of sentence 71 or 72 wherein the temperature of the off-gas upon entering the first reaction zone is no greater than 400°C, more preferably no greater than 350°C.

[0821] Sentence 74: A 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 a 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.

[0822] Clause 75: The process of any of clauses 71 to 74 wherein the off-gas temperature upon entering the second reaction zone is in the range of 300 to 550°C, preferably 350 to 500°C.

[0823] Clause 76: The process of any one of clauses 71 to 75 wherein the NO in the first reaction zone X The reduction catalyst comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0824] Clause 77: The process of any of clauses 71 to 76 wherein the off-gas temperature upon entering the first reaction zone is at least 300°C, more preferably at least 350°C, even more preferably at least 400°C.

[0825] Clause 78: The process of any of clauses 71 to 77 wherein the off-gas temperature upon entering the first reaction zone is at most 600°C, preferably at most 550°C.

[0826] Clause 79: The process of any one of clauses 71 to 78 wherein the N2O decomposition catalyst in the second reaction zone comprises NO X -Sensitive N2O decomposition catalyst.

[0827] Clause 80: The process of any of clauses 71 to 79 wherein the off-gas temperature upon entering the second reaction zone is at least 300°C, more preferably at least 350°C, even more preferably at least 400°C.

[0828] Clause 81 . The process of any of clauses 71 to 80 wherein the off-gas temperature upon entering the second reaction zone is at most 600°C, preferably at most 550°C.

[0829] Clause 82: The process of any one of clauses 71 to 81, wherein the off-gas after leaving the first reaction zone and before entering the second reaction zone has a NO in the range of 0 to 200 ppmv, preferably 1 to 200 ppmv. Xcontent and an N2O content in the range of 200 to 2000 ppmv.

[0830] Clause 83: A process according to any one of clauses 71 to 81, wherein the off-gas after leaving the first reaction zone and before entering the second reaction zone has a NO content of at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv. X content and an N2O content in the range of 200 to 2000 ppmv.

[0831] Sentence 84: A method according to any of the preceding sentences, wherein the exhaust gas treatment system also comprises a first reaction zone and a subsequent second reaction zone through which the exhaust gas passes continuously; wherein a reducing agent is added to the exhaust gas between the first reaction zone and the second reaction zone; wherein, in the first reaction zone, the NO content in the exhaust gas is first reduced by decomposing NO on an NO decomposition catalyst (step (d1)); and wherein, in the second reaction zone, the NO content in the exhaust gas is then reduced by decomposing NO on an NO decomposition catalyst (step (d2)). X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction is performed to reduce NO in the exhaust gas X wherein optionally, the N2O content in the exhaust gas is additionally further reduced by further decomposing N2O on the N2O decomposition catalyst (step (d1)) and / or by chemically reducing N2O with a reducing agent on the N2O reduction catalyst (step (d2)).

[0832] Clause 85: The method of clause 84 wherein no reducing agent is added to the exhaust gas upstream of the first reaction zone.

[0833] Sentence 86: A process according to any of sentences 84 to 85, wherein the N2O decomposition catalyst in the first reaction zone comprises a zeolitic material; preferably, a zeolite loaded with a transition metal (including a 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.

[0834] Clause 87: The method of any one of clauses 84 to 86 wherein the N2O decomposition catalyst in the first reaction zone comprises NO X -Sensitive N2O decomposition catalyst.

[0835] Clause 88: The process of any one of clauses 84 to 87 wherein the NO in the second reaction zone XThe reduction catalyst comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

[0836] Sentence 89: A method according to any one of sentences 84 to 88, wherein in the first reaction zone and the second reaction zone, the space velocity is set so that the N2O content in the exhaust gas in the first reaction zone is reduced by at most 95%, preferably at most 90%, based on the N2O content in the exhaust gas when entering the first reaction zone.

[0837] Sentence 90: A method according to any one of sentences 84 to 89, wherein in the second reaction zone, the N2O content in the exhaust gas is reduced by at least 30%, preferably at least 40%, more preferably at least 50% based on the N2O content in the exhaust gas when entering the second reaction zone.

[0838] Clause 91: A method according to any of clauses 84 to 89, wherein in the second reaction zone, the N2O content in the exhaust gas is further reduced by chemically reducing the N2O with a reducing agent over an N2O reduction catalyst (step (d2)).

[0839] Clause 92: The method of any one of clauses 71 to 91 wherein the first reaction zone and the second reaction zone are spatially separated.

[0840] Clause 93: The method of any one of clauses 71 to 92 wherein the first reaction zone and the second reaction zone are spatially connected to each other.

[0841] Clause 94: The process of any one of clauses 71 to 93 wherein the first reaction zone and the second reaction zone are disposed in a common vessel.

[0842] Sentence 95: A process according to any one of sentences 71 to 94 wherein the off-gas temperature in the first reaction zone and in the second reaction zone is at most 500°C, preferably in the range of 350 to 450°C.

[0843] Sentence 96: A method according to any one of sentences 71 to 95, wherein the space velocity in the first reaction zone is greater than the space velocity in the second reaction zone; preferably at least 1.2 times greater, more preferably at least 1.4 times greater, even more preferably at least 1.6 times greater, most preferably at least 1.8 times greater, and in particular at least 2.0 times greater.

[0844] Sentence 97: A method according to any one of sentences 71 to 96, wherein the space velocity in the first reaction zone is less than the space velocity in the second reaction zone; preferably at least 1.5 times less, more preferably at least 2.0 times less, even more preferably at least 3.0 times less, most preferably at least 5.0 times less, and in particular at least 10.0 times less.

[0845] Sentence 98: A 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.

[0846] Sentence 99: A process according to any one of sentences 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.

[0847] Sentence 100: A process according to any one of sentences 71 to 99, wherein the temperature in the first reaction zone is at least 20°C higher than the temperature in the second reaction zone, more preferably at least 40°C, even more preferably at least 60°C, most preferably at least 80°C, and in particular at least 100°C.

[0848] Sentence 101: A process according to any one of sentences 71 to 100, wherein the temperature in the first reaction zone is at least 120°C higher than the temperature in the second reaction zone, more preferably at least 140°C, even more preferably at least 160°C, most preferably at least 180°C, and in particular at least 200°C.

[0849] Clause 102: The method of any preceding clause, wherein the exhaust gas exits the exhaust gas treatment system and has a residual NO 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 especially at most 2.5 ppmv. X content.

[0850] Sentence 103: A method according to any preceding sentence, wherein the exhaust gas leaves the exhaust gas treatment system 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.

[0851] Clause 104: The method of any preceding clause wherein the N2O decomposition catalyst is disposed in radial baskets through which flow passes axially.

[0852] Clause 105: The method of any preceding clause wherein the N2O decomposition catalyst is granular and comprises at least 50 particles.

[0853] Clause 106: The method of any preceding clause wherein the N20 reduction catalyst is disposed in a radial basket through which flow is axially passed.

[0854] Clause 107: The method of any preceding clause wherein the N2O reduction catalyst is granular and comprises at least 50 particles.

[0855] Clause 108: The method of any preceding clause wherein the NO X The reduction catalyst is disposed in radial baskets through which the flow passes axially.

[0856] Clause 109: A method according to any preceding clause wherein the NO X The reduction catalyst is in a granular form and comprises at least 50 particles.

[0857] Clause 110: The method of any of the preceding clauses, wherein at least one parameter characteristic of a current operating state of the combustion system is measured in the combustion system as a first measured variable.

[0858] Clause 111: The method of clause 110, wherein the first measured variable is selected from the group consisting of: combustion temperature, NH3 consumption, rotational speed (if applicable), and volume of the combustion system.

[0859] Clause 112: The method of any of the preceding clauses, wherein at least one parameter characteristic of a current state of the exhaust gas is measured before entering the exhaust gas treatment system as a second measured variable before entering the exhaust gas treatment system.

[0860] Clause 113: The method of clause 110, wherein the second measured variable is selected from the group consisting of: NO in the exhaust gas X Content; NO in exhaust gas X the degree of oxidation; the N2O content in the exhaust gas; the content of other components in the exhaust gas, such as H2O, O2 and N2; the exhaust gas temperature; the exhaust gas pressure; and the volume flow rate of the exhaust gas.

[0861] Clause 114: A method according to any of the preceding clauses, wherein at least one parameter characteristic of the current state of the exhaust gas upon leaving the exhaust gas treatment system is measured as a third measured variable upon leaving the exhaust gas treatment system.

[0862] Clause 115: The method of clause 114, wherein the third measured variable is selected from the group consisting of: NO in the exhaust gas X Content; NO in exhaust gas X the degree of oxidation; the N2O content in the exhaust gas; the content of other components in the exhaust gas, such as H2O, O2 and N2; the exhaust gas temperature; the exhaust gas pressure; and the volume flow rate of the exhaust gas.

[0863] Sentence 116: A method according to any of the preceding sentences, wherein the exhaust gas treatment system includes a first reaction zone and a second reaction zone through which the exhaust gas flows in sequence, wherein a 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 characteristic of the current state of the exhaust gas after leaving the first reaction zone and before entering the second reaction zone is measured as a fourth measurement variable.

[0864] Clause 117: The method of clause 116, wherein the fourth measured variable is selected from the group consisting of: NO in the exhaust gas X Content; NO in exhaust gas X the degree of oxidation; the N2O content in the exhaust gas; the content of other components in the exhaust gas, such as H2O, O2 and N2; the exhaust gas temperature; the exhaust gas pressure; and the volume flow rate of the exhaust gas.

[0865] Sentence 118: Method according to any of sentences 110 to 117, wherein control of the method is 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 means of a controlled change of a manipulated variable.

[0866] Paragraph 119: The method of paragraph 118, wherein the manipulated variable is the amount of metered reducing agent.

[0867] Clause 120: The method of any preceding clause, wherein the exhaust gas is cooled in a single heat exchanger disposed downstream of the exhaust gas treatment system in the direction of flow of the exhaust gas.

[0868] Clause 121: The method of any preceding clause, wherein the exhaust gas is cooled successively in at least two heat exchangers arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

[0869] Clause 122: The method of any preceding clause, wherein the exhaust gas is cooled successively in at least three heat exchangers arranged downstream of an exhaust gas treatment system in the flow direction of the exhaust gas.

[0870] Clause 123: The method of any preceding clause, wherein the exhaust gas is cooled successively in at least four heat exchangers arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas.

[0871] Clause 124: The method of any preceding clause, wherein the exhaust gas is cooled successively in at least five heat exchangers arranged downstream of an exhaust gas treatment system in the flow direction of the exhaust gas.

[0872] Sentence 125: A method according to any of the preceding sentences, wherein in step (f), the exhaust gas is cooled in the at least one heat exchanger by releasing heat from the exhaust gas to a heat transfer medium; wherein the heat transfer medium is preferably selected from water, steam, combustion air, NH3 and combinations thereof.

[0873] Sentence 126: A method according to any of the preceding sentences, wherein in step (f), 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.

[0874] Sentence 127: A method according to any of the preceding sentences, wherein in step (f), 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.

[0875] Sentence 128: A method according to any of the preceding sentences, wherein in step (f), the exhaust gas is cooled in the following devices: - a first exhaust gas / H2O heat exchanger arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas; and - a first exhaust gas / combustion air heat exchanger 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.

[0876] Sentence 129: A method according to any of the preceding sentences, wherein in step (f), the exhaust gas is cooled in the following devices: - a first exhaust gas / combustion air heat exchanger arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas; and - a second exhaust gas / combustion air heat exchanger also arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas.

[0877] Sentence 130: A method according to any of the preceding sentences, wherein in step (f), the exhaust gas is cooled in the following devices: - a first exhaust gas / combustion air heat exchanger arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - a first exhaust gas / H2O heat exchanger arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - a second exhaust gas / combustion air heat exchanger arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas.

[0878] Sentence 131: A method according to any of the preceding sentences, wherein the exhaust gas is cooled in step (f) in at least one exhaust gas / combustion gas heat exchanger, and the at least one exhaust gas / combustion gas heat exchanger 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.

[0879] Sentence 132: A method according to any of the preceding sentences, wherein the exhaust gas is cooled in step (f) in at least one exhaust gas / combustion gas heat exchanger, and the at least one exhaust gas / combustion gas heat exchanger 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.

[0880] Sentence 133: A method according to any of the preceding sentences, wherein the exhaust gas is cooled in step (f) in at least one exhaust gas / H2O heat exchanger, and the at least one exhaust gas / H2O heat exchanger 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.

[0881] Sentence 134: A method according to any of the preceding sentences, wherein in step (f) the exhaust gas is cooled in: - a first exhaust gas / combustion air heat exchanger arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - a first exhaust gas / H2O heat exchanger arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - a second exhaust gas / combustion air heat exchanger arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - a exhaust gas / combustion gas heat exchanger arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas.

[0882] Sentence 135: A method according to any of the preceding sentences, wherein in step (f), the exhaust gas is cooled in the following devices: - a first exhaust gas / combustion air heat exchanger arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - a first exhaust gas / H2O heat exchanger arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - a second exhaust gas / combustion air heat exchanger arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, and - a second exhaust gas / H2O heat exchanger arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas.

[0883] Sentence 136: A method according to any of the preceding sentences, wherein in step (f), the exhaust gas is cooled in the following devices: - a first exhaust gas / combustion air heat exchanger arranged downstream of the exhaust gas treatment system in the flow direction of the exhaust gas, - a first exhaust gas / H2O heat exchanger arranged downstream of the first exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, - a second exhaust gas / combustion air heat exchanger arranged downstream of the first exhaust gas / H2O heat exchanger in the flow direction of the exhaust gas, - a exhaust gas / combustion gas heat exchanger arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gas, and - a second exhaust gas / H2O heat exchanger arranged downstream of the exhaust gas / combustion gas heat exchanger in the flow direction of the exhaust gas.

[0884] Sentence 137: An apparatus comprising (i) an NH3-operated combustion system, preferably a furnace (preferably comprising a combustion device and an NH3 decomposition device) for catalytically decomposing NH3 into N2 and H2; and (ii) an exhaust gas treatment system; wherein the apparatus is configured to perform a method according to any of the preceding sentences.

[0885] In the following, particularly preferred embodiments of the present invention will be described with reference to the accompanying drawings. In all these embodiments, NH3 is preferably preheated with water vapor or water vapor condensate alone or in addition.

[0886] Figure 1 A schematic diagram of a preferred embodiment of the present invention is shown. NH3 is fed into an NH3 decomposition device (1) having a similar structure to a primary reformer and catalytically decomposed therein on an NH3 decomposition catalyst into a product gas containing H2+N2+NH3. Simultaneously, the combustion gas containing NH3+N2+H2 is mixed with combustion air containing N2+O2 in a combustion device (2) and combusted. The combustion heat generated therein ignites the NH3 decomposition device (1). The exhaust gas (containing N2+H2O+NO X+N2O) enters the exhaust gas conduit (3) and is supplied to the exhaust gas treatment system (4), where NO X The content of N2O is almost completely removed. The exhaust gas (containing N2+H2O) leaving the exhaust gas treatment system passes through a ventilator (5) and leaves the system through a chimney (6). The product gas (containing H2+N2+NH3) formed in the catalytic decomposition is separated in a pressure swing adsorption system (7) into H2 as product and an exhaust gas containing NH3+N2+H2 (which, if necessary, can be used as combustion gas after metering in additional NH3).

[0887] Figure 2 A schematic diagram of a preferred embodiment of the present invention is shown (process variant #1). The exhaust gas conduit includes a first exhaust gas / NH3 heat exchanger (Q1) in the direction of exhaust gas flow, in which NH3 absorbs heat from the exhaust gas and is then supplied to the NH3 decomposition device. An exhaust gas treatment system is provided downstream of the first exhaust gas / NH3 heat exchanger in the direction of exhaust gas flow. A first exhaust gas / H2O heat exchanger (Q5) is provided downstream of the exhaust gas treatment system in the direction of exhaust gas flow, in which water absorbs heat from the exhaust gas. A second exhaust gas / combustion air heat exchanger (Q6) is provided downstream of the first exhaust gas / H2O heat exchanger (Q5) in the direction of exhaust gas flow, in which combustion air absorbs heat from the exhaust gas and is then supplied to the combustion device.

[0888] Figure 3 A schematic diagram of a preferred embodiment of the present invention is shown (process variant #2). The exhaust gas conduit includes a first exhaust gas / NH3 heat exchanger (Q1) in the direction of exhaust gas flow, in which NH3 absorbs heat from the exhaust gas and is then fed to a first preliminary reactor (NH3 decomposition unit) for partial catalytic decomposition of NH3. This preferably cools the intermediate product gas, for example from 650°C at the inlet of the first preliminary reactor to 360°C upon exiting the first preliminary reactor. A second exhaust gas / NH3 heat exchanger (Q2) is provided downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the direction of exhaust gas flow, in which the intermediate product gas absorbs heat from the exhaust gas and is then fed to the NH3 decomposition unit for catalytic decomposition of NH3. An exhaust gas treatment system is provided downstream of the second exhaust gas / NH3 heat exchanger (Q2) in the direction of exhaust gas flow. Water absorbs heat from the exhaust gas in a first exhaust gas / H2O heat exchanger (Q5) provided downstream of the exhaust gas treatment system in the direction of exhaust gas flow. A second exhaust gas / combustion air heat exchanger (Q6) is provided downstream of the first exhaust gas / H2O heat exchanger (Q5) in the flow direction of the exhaust gas, in which the combustion air absorbs heat from the exhaust gas and is then supplied to the combustion device.

[0889] Figure 4A schematic diagram of a preferred embodiment of the present invention is shown (process variant #3). The exhaust gas conduit includes 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 supplied to a first preliminary reactor (NH3 decomposition device) for the partial catalytic decomposition of NH3. This preferably cools the first intermediate product gas, for example from 650°C at the inlet of the first preliminary reactor to 480°C upon leaving the first preliminary reactor. A second exhaust gas / NH3 heat exchanger (Q2) is provided downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the flow direction of the exhaust gas, in which the intermediate product gas absorbs heat from the exhaust gas and is then supplied to a second preliminary reactor (NH3 decomposition device) for the partial catalytic decomposition of NH3. This preferably cools the intermediate product gas, for example from 630°C at the inlet of the second preliminary reactor to 510°C upon leaving the second preliminary reactor. A third exhaust gas / NH3 heat exchanger (Q3) is provided downstream of the second exhaust gas / NH3 heat exchanger (Q2) in the direction of exhaust gas flow, wherein the intermediate product gas absorbs heat from the exhaust gas and is then supplied to an NH3 decomposition device for catalytically decomposing NH3. An exhaust gas treatment system is provided downstream of the third exhaust gas / NH3 heat exchanger (Q3) in the direction of exhaust gas flow. In a first exhaust gas / H2O heat exchanger (Q5) provided downstream of the exhaust gas treatment system in the direction of exhaust gas flow, water absorbs heat from the exhaust gas. A second exhaust gas / combustion air heat exchanger (Q6) is provided downstream of the first exhaust gas / H2O heat exchanger (Q5) in the direction of exhaust gas flow, wherein the combustion air absorbs heat from the exhaust gas and is then supplied to the combustion device.

[0890] Figure 5A schematic diagram of a preferred embodiment of the present invention is shown (process variant #4). The exhaust gas conduit includes a first exhaust gas / NH3 heat exchanger (Q1) in the direction of exhaust gas flow, in which NH3 absorbs heat from the exhaust gas and is then fed to a first preliminary reactor (NH3 decomposition unit) for partial catalytic decomposition of NH3. This preferably cools the intermediate product gas, for example from 650°C at the inlet of the first preliminary reactor to 360°C upon exiting the first preliminary reactor. A second exhaust gas / NH3 heat exchanger (Q2) is provided downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the direction of exhaust gas flow, in which the intermediate product gas absorbs heat from the exhaust gas and is then fed to the NH3 decomposition unit for catalytic decomposition of NH3. An exhaust gas treatment system is provided downstream of the second exhaust gas / NH3 heat exchanger (Q2) in the direction of exhaust gas flow. A first exhaust gas / combustion air heat exchanger (Q4) is provided downstream of the exhaust gas treatment system in the direction of exhaust gas flow, in which the combustion air absorbs heat from the exhaust gas. A first exhaust gas / H2O heat exchanger (Q5) is provided downstream of the first exhaust gas / combustion air heat exchanger (Q4) in the direction of exhaust gas flow, in which water absorbs heat from the exhaust gas. A second exhaust gas / combustion air heat exchanger (Q6) is provided downstream of the first exhaust gas / H2O heat exchanger (Q5) in the direction of exhaust gas flow, in which combustion air absorbs heat from the exhaust gas and is then supplied to the first exhaust gas / combustion air heat exchanger (Q4) and then to the combustion device. Thus, the combustion air is 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).

[0891] Figure 6Schematic diagrams of three similar preferred embodiments of the present invention (process variants #5, #6, and #7) are shown. In all three process variants, the exhaust gas conduit includes a first exhaust gas / NH3 heat exchanger (Q1) in the direction of exhaust gas flow, in which NH3 absorbs heat from the exhaust gas and is then fed to a first preliminary reactor (NH3 decomposition unit) for the partial catalytic decomposition of NH3. This preferably cools the intermediate product gas, for example, from 650°C at the inlet of the first preliminary reactor to 360°C upon exiting the first preliminary reactor. A second exhaust gas / NH3 heat exchanger (Q2) is provided downstream of the first exhaust gas / NH3 heat exchanger (Q1) in the direction of exhaust gas flow, in which the intermediate product gas absorbs heat from the exhaust gas and is then fed to the NH3 decomposition unit for the catalytic decomposition of NH3. An exhaust gas treatment system is provided downstream of the second exhaust gas / NH3 heat exchanger (Q2) in the direction of exhaust gas flow. A first exhaust gas / combustion air heat exchanger (Q4) is provided downstream of the exhaust gas treatment system in the direction of exhaust gas flow, in which the combustion air absorbs heat from the exhaust gas. A first exhaust gas / H2O heat exchanger (Q5) is provided downstream of the first exhaust gas / combustion air heat exchanger (Q4) in the direction of exhaust gas flow, in which water absorbs heat from the exhaust gas. A second exhaust gas / combustion air heat exchanger (Q6) is provided downstream of the first exhaust gas / H2O heat exchanger (Q5) in the direction of exhaust gas flow, in which combustion air absorbs heat from the exhaust gas, is then supplied to the first exhaust gas / combustion air heat exchanger (Q4), and then to the combustion device. Thus, the combustion air is 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). An exhaust gas / combustion gas heat exchanger (Q7) is provided downstream of the first exhaust gas / combustion air heat exchanger (Q6) in the direction of exhaust gas flow, in which combustion gas (i.e., exhaust gas from the pressure swing adsorption device) absorbs heat from the exhaust gas and is then supplied to the combustion device. In a second exhaust gas / H2O heat exchanger (Q8) arranged downstream of an exhaust gas / combustion gas heat exchanger (Q7) in the flow direction of the exhaust gas, water absorbs heat from the exhaust gas.

[0892] In process variant #5, the residual heat remaining in the off-gas is removed with water in a second off-gas / H2O heat exchanger (Q8) and released to NH3, whereby for example NH3 is preheated from liquid state (storage temperature -33.5°C) to -8°C.

[0893] In process variant #6, heat is removed with water in the first flue gas / H2O heat exchanger (Q5) and released to NH3, so that, for example, NH3 is preheated from the liquid state to 30° C. The residual heat remaining in the flue gas is removed with water in the second flue gas / H2O heat exchanger (Q8) and likewise released to NH3, so that, for example, NH3 is heated to 45° C.

[0894] In process variant #7, heat is removed with water in the first flue gas / H₂O heat exchanger (Q5) and released to the NH₃, thereby preheating the NH₃ from the liquid state to, for example, 30°C. The residual heat remaining in the flue gas is removed with water in the second flue gas / H₂O heat exchanger (Q8) and likewise released to the NH₃, thereby heating the NH₃ to, for example, 39°C. The amount of preheated boiler feed water is increased compared to the amount required to generate steam. The excess boiler feed water is fed into the steam condensate stream below the NH₃ evaporator and serves as additional heat transfer medium.

[0895] The mass balance and temperature profile characteristics for process variants #1 to #7 are compiled in the table below. All data are scaled for a plant capacity of 1000 mtpd NH3. The numbers 1 to 28 in bold refer to Figure 7 The correspondingly marked positions in FIG. In each case, a distinction is made between two cases A and B in which the exhaust gas contains different nitrogen oxide contents. In case A, the exhaust gas contains a relatively low nitrogen oxide content of 500 ppmv NO, 10 ppmv NO₂, and 10 ppmv N₂O. In case B, the exhaust gas contains a relatively high nitrogen oxide content of 5000 ppmv NO, 10 ppmv NO₂, and 50 ppmv N₂O. Crafting Variant #1:

[0896]

[0897]

[0898] Crafting Variant #2:

[0899]

[0900]

[0901] Crafting Variant #3:

[0902]

[0903]

[0904] Crafting Variant #4:

[0905]

[0906]

[0907] Crafting Variant #5:

[0908]

[0909]

[0910] Crafting Variant #6:

[0911]

[0912]

[0913] Crafting Variant #7:

[0914]

[0915]

[0916] The mass balance and temperature profile characteristics are summarized in the following table:

[0917]

[0918] By selecting the appropriate heat exchanger and configuring it appropriately within the exhaust gas conduit, the present invention allows heat recovery from the exhaust gas conduit up to the theoretical maximum value of the water dew point plus a safety margin. A clear correlation is observed between heat recovery and H₂ production. A highly integrated heat recovery system can increase H₂ production by more than 4%.

[0919] The flat temperature profile that allows for significant heat integration also reduces the required exhaust gas inlet temperature into the exhaust duct. This reduces surface temperatures in upstream heat exchangers and allows the use of simpler materials.

[0920] Reference Mark List:

[0921] (Q1) First exhaust gas / NH3 heat exchanger

[0922] (Q2) Second exhaust gas / NH3 heat exchanger

[0923] (Q3) Third exhaust gas / NH3 heat exchanger

[0924] (Q4) First exhaust gas / combustion air heat exchanger

[0925] (Q5) First exhaust gas / H2O heat exchanger

[0926] (Q6) Second exhaust gas / combustion air heat exchanger

[0927] (Q7) Exhaust gas / combustion gas heat exchanger

[0928] (Q8) Second exhaust gas / H2O heat exchanger

[0929] (1) NH3 decomposition device

[0930] (2) Combustion device

[0931] (3) Exhaust gas duct

[0932] (4) Waste gas treatment system

[0933] (5) Ventilator

[0934] (6) Chimney

[0935] (7) Pressure swing adsorption device

Claims

1. A method for reducing NO in the exhaust gas of NH3-operated combustion systems X and N2O content, the method comprising the following steps: (a) burning NH3 to operate the combustion system, the combustion system preferably comprising a combustion device and an NH3 decomposition device for catalytically decomposing NH3 into N2 and H2, generating an exhaust gas containing N2, H2, NO X and N2O, and exit the combustion system; (b) optionally and preferably cooling the exhaust gases in at least one heat exchanger, which is arranged downstream of the combustion system in the flow direction of the exhaust gases; (c) transferring the optionally cooled exhaust gas to an exhaust gas treatment system; (d) reducing the N2O content in the exhaust gas by the following steps (d1) decomposing N2O on an N2O decomposition catalyst, and / or (d2) chemically reducing N2O using a reducing agent on an N2O reduction catalyst; (e) By X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content; 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.

2. The method according to claim 1 for reducing NO in the exhaust gas of an NH3- and H2-operated combustion system integrated into a system for the catalytic decomposition of NH3 into N2 and H2. X and N2O content, the method comprising the following steps: (a) burning NH3 and H2 for operating the combustion system (preferably in a combustion device) to produce an exhaust gas containing N2, H2O, NO X and N2O, and exit the combustion system; (b) optionally and preferably cooling the exhaust gases in at least one heat exchanger, which is arranged downstream of the combustion system in the flow direction of the exhaust gases; (c) transferring the optionally cooled exhaust gases to an exhaust gas treatment system which is arranged downstream of the combustion system in the flow direction of the exhaust gases and, if appropriate, downstream of the at least one heat exchanger; (d) reducing the N2O content in the exhaust gas by the following steps (d1) decomposing N2O on an N2O decomposition catalyst, and / or (d2) chemically reducing N2O using a reducing agent on an N2O reduction catalyst; (e) By X Reduction of NO by using a reducing agent on a catalyst X Chemical reduction to reduce NO in exhaust gas X content; 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 claim 1 , wherein in step (b), the exhaust gases are cooled in the at least one heat exchanger by releasing heat from the exhaust gases to a heat transfer medium, wherein the heat transfer medium used is preferably NH 3 , which is then supplied to the catalytic decomposition in the NH 3 decomposition device over an NH 3 catalyst.

4. The method according to any one of the preceding claims, wherein in step (b), the exhaust gas is cooled 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 any one of the preceding claims, wherein in step (b), the exhaust gas is cooled in: a first exhaust gas / NH3 heat exchanger arranged downstream of the combustion system in the flow direction of the exhaust gases, and a second exhaust gas / NH 3 heat exchanger, which is arranged downstream of the first exhaust gas / NH 3 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 exhaust gas is cooled in: a first exhaust gas / NH 3 heat exchanger, which is arranged downstream of the combustion system in the flow direction of the exhaust gases, 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 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 gases.

7. The method according to any one of the preceding claims, wherein in step (b) the off-gas is cooled to a temperature T2 in the range of 400 to 450°C, more preferably 400 to 420°C.

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

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

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

11. The method of any one of the preceding claims, wherein the N2O decomposition catalyst and the NO X The reduction catalyst is made of the same material.

12. The method of any one of the preceding claims, wherein the N2O reduction catalyst and the NO X The reduction catalyst is made of the same material.

13. The method of any one of the preceding claims, wherein the N2O decomposition catalyst, the N2O reduction catalyst and the NO X The reduction catalyst is made of the same material.

14. The process according to any one of the preceding claims, wherein in step (a), the combustion of NH3 is not over a catalyst.

15. The process as claimed in any one of the preceding claims, wherein in step (a) NH3 is combusted 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 as claimed in any one of the preceding claims, wherein in step (a) NH3 is combusted 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 method of claim 15 or 16, wherein the molar ratio of H2:NH3 in the mixture is from 45:55 to 90:10, preferably from 50:50 to 85:15, more preferably from 55:45 to 80:20, even more preferably from 60:40 to 75:25, most preferably from 65:35 to 70:

30.

18. The method of any one of the preceding claims, 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.

19. The method according to any one of the preceding claims, wherein the combustion system comprises a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2.

20. The method of any one of the preceding claims, wherein the NO X The content is greater than the N2O content; preferably, wherein NO X The content is at least twice, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times the N2O content; preferably, wherein NO X The molar ratio of NH:N2O is greater than 10:1, more preferably at least 20:1, even more preferably at least 30:1, most preferably at least 40:1, and especially at least 50:

1.

21. The method of any one of the preceding claims, wherein the NO content of the exhaust gas is greater than the N2O content; preferably, wherein the NO content is at least twice, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times, the N2O content.

22. The method of any one of the preceding claims, wherein the NO2 content of the exhaust gas is greater than the N2O content; preferably, wherein the NO2 content is at least twice, more preferably at least three times, even more preferably at least four times, most preferably at least seven times, and in particular at least ten times, the N2O content.

23. The method of any one of the preceding claims, wherein the NO X The content is 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 of any one of the preceding claims, wherein the NO X The content is 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 method of any one of the preceding claims, wherein the NO X The content is 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 method of any of the preceding claims, wherein the N2O content of the exhaust gas is 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 method according to any one of the preceding claims, wherein the N2O content of the exhaust gas is 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 method of any of the preceding claims, wherein the H2O content of the off-gas is greater than 4.0% by volume; preferably at least 5.0% by volume, more preferably at least 6.0% by volume, even more preferably at least 7.0% by volume, most preferably at least 8.0% by volume, and in particular at least 9.0% by volume.

29. The method of any of the preceding claims, wherein the HO content of the off-gas is at least 10% by volume; preferably at least 12% by volume, more preferably at least 14% by volume, even more preferably at least 16% by volume, most preferably at least 18% by volume, and in particular at least 20% by volume.

30. The method according to any of the preceding claims, wherein the HO content of the offgas is 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.-%.

31. The method according to any of the preceding claims, wherein the H2O content of the offgas is 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 method according to any of the preceding claims, wherein the H2O content of the offgas is 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 method according to any of the preceding claims, wherein the H2O content of the offgas is 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 method according to any of the preceding claims, wherein the H2O content of the offgas is 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 as claimed in any one of the preceding claims, wherein the N2 content of the off-gas is at most 95% by volume; preferably at most 90% by volume, more preferably at most 85% by volume, even more preferably at most 80% by volume, most preferably at most 75% by volume and in particular at most 70% by volume.

36. The method of any of the preceding claims, wherein the N2 content of the off-gas is at least 40% by volume; preferably at least 50% by volume, more preferably at least 60% by volume, even more preferably at least 70% by volume, most preferably at least 80% by volume, and in particular at least 90% by volume.

37. A method as claimed in any preceding claim, wherein the exhaust gas comprises additional gaseous components; preferably selected from the group consisting of O2, CO, CO2, NH3, CH4 and mixtures thereof.

38. The method of any of the preceding claims, wherein the exhaust gases leaving the combustion system, preferably the combustion device, are at 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.

39. The method of any of the preceding claims, wherein the exhaust gases leaving the combustion system, preferably the combustion device, are at 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.

40. A method as claimed in any preceding claim, wherein the exhaust gases exiting the combustion system, preferably the combustion apparatus, are at a pressure of at most 1.5 bar; preferably atmospheric pressure.

41. The method according to any one of the preceding claims, wherein the NO X The degree of oxidation is 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 NO X The degree of oxidation is 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 of any of the preceding claims, wherein the O2 content of the exhaust gases leaving the combustion system, preferably the combustion device, is less than 2.0% by volume.

44. The method of any of the preceding claims, wherein the O2 content of the exhaust gases leaving the combustion system, preferably the combustion device, is greater than 4.0% by volume.

45. The method of any of the preceding claims, wherein the exhaust gas entering the exhaust gas treatment system is at 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.

46. ​​The method of any of the preceding claims, wherein the exhaust gas entering the exhaust gas treatment system is at 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.

47. The method of any of the preceding claims, wherein the exhaust gas entering the exhaust gas treatment system is at 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.

48. The method of any of the preceding claims, wherein the exhaust gas entering the exhaust gas treatment system is at 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. A method as claimed in any one of the preceding claims, wherein the exhaust gas entering the exhaust gas treatment system is at a temperature which is relatively lower than the temperature of the exhaust gas leaving the combustion system, preferably leaving the combustion device, by 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.

50. The method of any preceding claim, wherein the pressure of the exhaust gas entering the exhaust gas treatment system is at most 1.4 bar, preferably at most 1.3 bar, more preferably at most 1.2 bar.

51. The method of any one of the preceding claims, wherein the NO X The degree of oxidation is 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%.

52. The method of any of the preceding claims, wherein the O2 content of the exhaust gas entering the exhaust treatment system is less than 2.0% by volume.

53. The method of any of the preceding claims, wherein the O2 content of the exhaust gas entering the exhaust treatment system is greater than 4.0% by volume.

54. The method of any of the preceding claims, wherein step (d) comprises reducing the N2O content in the exhaust gas by (d1) decomposing N2O over an N2O decomposition catalyst; preferably, wherein the N2O decomposition catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including a 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 structure type.

55. The method of any of the preceding claims, wherein step (d) comprises reducing the NO content in the exhaust gas by (d2) chemically reducing the NO with a reducing agent over a NO reduction catalyst; preferably, wherein the NO reduction catalyst comprises a zeolitic material; preferably a zeolite loaded with a transition metal (including a 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 structure type.

56. The method of 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 method of any one of the preceding claims, wherein the reducing agent in step (d2) is NH3 in an amount of 0.5 to 2.0 parts by mole, preferably 0.8 to 1.8 parts by mole, based on the molar proportion of N2O to be chemically reduced.

58. The method according to any one of the preceding claims, wherein the reducing agent in step (d2) is a hydrocarbon or a mixture of several hydrocarbons, preferably in an amount of 0.2 to 1.0 parts by mole, more preferably 0.2 to 0.7 parts by mole, based on the molar proportion of NO to be decomposed.

59. The method of any one of the preceding claims, wherein the NO X The reduction catalyst comprises a zeolite material; preferably, a transition metal (including lanthanide) loaded zeolite, in particular an 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.

60. The method of 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 method of any one of the preceding claims, wherein the reducing agent in step (e) is NH3 in an amount based on the NO to be chemically reduced. X The molar ratio is 0.9 to 2.5 parts by mole, preferably 1.0 to 1.4 parts by mole, and preferably 1.0 to 1.2 parts by mole.

62. The process of 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 of any of the preceding claims, wherein the exhaust gas treatment system comprises a first catalyst bed and a spatially separated 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, a first device having a first control valve for metering NH 3 to the exhaust gas is preferably arranged upstream of the first catalyst bed; wherein a second device having a second control valve for metering NH 3 into the exhaust gas is arranged downstream of the first catalyst bed and upstream of the second catalyst bed, wherein the second device is used to meter additional NH 3 into the exhaust gas; wherein both the first catalyst bed and the second catalyst bed each comprise an iron-loaded zeolite catalyst; in (i) in the first catalyst bed (d1) reducing the N2O content in the exhaust gas by catalytic decomposition of N2O; and (e) By using NH3 to NO X Catalytic chemical reduction is performed to incompletely reduce NO in the exhaust gas X content, wherein at least some of the NH3 comes from incomplete combustion of NH3 in step (a) (NH3 slip); and (ii) in the second catalyst bed (d2) reducing the residual N2O content by catalytic chemical reduction of N2O with NH3; (d1 * ) optionally, reducing the residual N2O content by catalytic decomposition of N2O; and (e * ) by using NH3 to NO X Catalytic chemical reduction to reduce residual NO X content;.

64. The method of claim 63, wherein the catalytic decomposition of N2O in the first catalyst bed is caused by the presence of NO in the exhaust gas. X Catalytic promoter.

65. The method of claim 63 or 64, wherein NH3 is used to convert NO into X Incomplete chemical reduction of NO leads to a predetermined residual NO X content, the residual NO X The content is sufficient to promote the decomposition of N2O in the first catalyst bed.

66. A process as claimed in any one of claims 63 to 65, wherein additional NH3 is metered into the exhaust gas by the first means; preferably under feedback control; wherein NO X A specific value of the concentration is preferably defined as a target value (set point) and the NO concentration is measured upon leaving the first catalyst bed. X The actual concentration (actual value) of In the event that there is a difference between the set point and the actual value (control difference), the output of the first control valve is varied so as to minimize the difference.

67. The method of claim 66, wherein the amount of additional NH3 is selected so that upon leaving the first catalyst bed NO X The residual concentration is at most 1000 ppmv, preferably at most 500 ppmv, more preferably at most 100 ppmv.

68. The process of claim 66 or 67, wherein the amount of additional NH3 is selected so that upon leaving the first catalyst bed NO X The residual concentration is at least 10 ppmv, preferably at least 20 ppmv, more preferably at least 40 ppmv.

69. The process of any one of claims 63 to 68, wherein residual NO is decomposed in the second catalyst bed such that the residual concentration of NO upon exiting the second catalyst bed is 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 of any one of claims 63 to 69, wherein the residual NO X decomposed in the second catalyst bed so that NO X The residual concentration is 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 of any one of claims 63 to 70, wherein the additional NH3 is metered by the second device under feedforward control; wherein NO is preferably measured upon leaving the first catalyst bed. X taking into account the amount of exhaust gas entering the second catalyst bed to calculate the required amount of NH3; and the calculation result (manipulated variable) is used to change the output of the second control valve to measure the required amount of NH3.

72. The process of any one of claims 63 to 71, wherein upon entering the second catalyst bed, NH3 / (NO X The molar ratio of N2O) 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 of any one of claims 63 to 72, wherein upon entering the second catalyst bed NH3 / NO X The molar ratio 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 of any one of claims 63 to 73, wherein the molar ratio of NH3 / N2O upon entry into 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 method of any one of claims 63 to 74, wherein the additional NH3 is not metered with the second device under feedback control.

76. The process of any one of claims 63 to 75, wherein the amount of catalyst is selected such that the decomposition of N2O in the first catalyst bed is at least 50%, more preferably at least 70%, even more preferably at least 80%, based on the concentration of N2O upon entering the first catalyst bed.

77. The process of any one of claims 63 to 76, wherein the amount of catalyst and the amount of additional NH3 are selected so that upon leaving the first catalyst bed, NO X The molar ratio of N2O to N2O is at least 5, more preferably at least 10, even more preferably at least 20.

78. The process of any one of claims 63 to 77, wherein the space velocity of the first catalyst bed is between 5000 h / min and 5000 h / min. -1 Up to 100,000 hours -1 In the range of 10000h, more preferably 10000h -1 Up to 50,000 hours -1 , even more preferably 15000h -1 Up to 45000h -1 .

79. The process of any one of claims 63 to 78, wherein upon exiting the first catalyst bed, NO X The molar ratio of NH3 to N2O is at least 10, and the additional NH3 metered in via the second device is only combined with the incoming NO X The amount is related.

80. The process of 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 of 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 method of any one of claims 63 to 81, wherein, depending on the exothermicity of the chemical reactions carried out in the first catalyst bed and in the second catalyst bed, the inlet temperature of the exhaust gas entering the first catalyst bed is selected so that the temperature of the exhaust gas when leaving 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 of any one of claims 63 to 82, wherein the space velocity of the second catalyst bed is between 5000 h / min and 5000 h / min. -1 Up to 100,000 hours -1 In the range of 10000h, more preferably 10000h -1 Up to 50,000 hours -1 , even more preferably 15000h -1 Up to 45000h -1 .

84. The process of any one of claims 63 to 83, wherein the first catalyst bed V1 cat With the second catalyst bed V2 cat The catalyst volume ratio (V1 cat / V2 cat ) is in the range of 1 / 2 to 20 / 1, more preferably 1 / 2 to 10 / 1, even more preferably 1 / 1 to 4 / 1.

85. The method of any one of claims 63 to 84, wherein at least one, more than one, or all of the following conditions are met: - the pressure of the exhaust gas upon entering the first catalyst bed is at most 5 bar, preferably at most 4 bar, more preferably at most 1.3 bar, most preferably at most 1.2 bar, and in particular at most 1.1 bar; - the H2O content of the off-gas upon entering the first catalyst bed is at least 5% by volume, preferably at least 10% by volume, more preferably at least 15% by volume, most preferably at least 20% by volume, and in particular at least 25% by volume; - NO in the exhaust gas when entering the first catalyst bed X The content 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 of the exhaust gas upon entering 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 contains unburned NH3 residues from NH3 combustion when entering the first catalyst bed; - the N2O decomposition catalyst and / or the N2O reduction catalyst are in the form of a honeycomb; -NO X The reduction catalyst is in the form of a honeycomb; - the first catalyst bed comprises Fe zeolite; - the second catalyst bed comprises Fe zeolite; - the exhaust gas passes through a heat exchanger before entering the first catalyst bed and is heated therein; - NO when leaving the first catalyst bed X The content is at most 1000 ppmv, preferably at most 500 ppmv, more preferably at most 300 ppmv, most preferably at most 100 ppmv; but preferably at least 10 ppmv, more preferably at least 20 ppm, more preferably at least 40 ppmv, most preferably at least 100 ppmv, and especially at least 250 ppmv; - an NO2 content on leaving the first catalyst bed of 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; - no intermediate cooling of the exhaust gas between leaving the first catalyst bed and entering the second catalyst bed; -N2O:NO when entering the first catalyst bed X The molar ratio of is at most 0.5, more preferably at most 0.2, even more preferably at most 0.1; -N2O:NO when leaving the first catalyst bed X The molar ratio of is at most 0.20, more preferably at most 0.1, even more preferably at most 0.05; - NH3 feeding into the exhaust gas upstream of the first catalyst bed in the direction of flow of the exhaust gas is optional; if present, it is preferably fed relative to NO on entry into the first catalyst bed. X is substoichiometric in content; and / or - It is necessary to feed NH3 into the exhaust gas downstream of the first catalyst bed and upstream of the second catalyst bed in the direction of flow of the exhaust gas, and preferably relative to NO3 on entry into the second catalyst bed X The total content of N2O is superstoichiometric.

86. The method of any one of the preceding claims, wherein the N2O decomposition catalyst and / or the N2O reduction catalyst and the NO X The reduction catalyst is independently in the form of a monolithic catalyst element permeated by parallel channels, preferably in the form of a monolithic honeycomb.

87. The method of any preceding claim, wherein the exhaust gas exits the exhaust gas treatment system and has a residual NO 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 X content.

88. The method of any of the preceding claims, wherein the exhaust gas leaves the exhaust gas treatment system 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 of any of the preceding claims, wherein in step (f), the exhaust gas is cooled in the at least one heat exchanger 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, steam, combustion air, NH3 and combinations thereof.

90. The method of any of the preceding claims, wherein in step (f), 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.

91. The method of any of the preceding claims, wherein in step (f), 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.

92. The method of any preceding claim, wherein in step (f), 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, and 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 of any preceding claim, wherein in step (f), 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 gases, and 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 gases.

94. The method of any preceding claim, wherein in step (f), 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 gases, 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 gases, and a second exhaust gas / combustion air heat exchanger, which is arranged downstream of the first exhaust gas / H 2 O heat exchanger in the flow direction of the exhaust gases.

95. The method of any of the preceding claims, wherein the exhaust gas is cooled in step (f) in at least one exhaust gas / combustion gas heat exchanger, and the at least one exhaust gas / combustion gas heat exchanger 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 of any of the preceding claims, wherein the exhaust gas is cooled in step (f) in at least one exhaust gas / combustion gas heat exchanger, and the at least one exhaust gas / combustion gas heat exchanger 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 of any of the preceding claims, wherein the exhaust gas is cooled in at least one second exhaust gas / H2O heat exchanger in step (f), and the at least one second exhaust gas / H2O heat exchanger 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 of any one of the preceding claims, wherein in step (f) 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 gases, 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 gases, 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 gases, and An exhaust gas / combustion gas heat exchanger is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gases.

99. The method of any preceding claim, wherein in step (f), 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 gases, 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 gases, 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 gases, and a second exhaust gas / H 2 O heat exchanger, which is arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gases.

100. The method of any preceding claim, wherein in step (f), 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 gases, 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 gases, 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 gases, an exhaust gas / combustion gas heat exchanger arranged downstream of the second exhaust gas / combustion air heat exchanger in the flow direction of the exhaust gases, and a second exhaust gas / H 2 O heat exchanger, which is arranged downstream of the exhaust gas / combustion gas heat exchanger in the flow direction of the exhaust gases.

101. A device comprising (i) an NH3-operated combustion system, preferably comprising a combustion device for burning NH3 and an NH3 decomposition device for cracking NH3 into N2 and H2; and (ii) exhaust gas treatment system; in, The apparatus is configured to perform the method of any one of the preceding claims.

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