Systems and methods for efficient SCR at high NO2 to NOx ratios

Abstract

NO x High NO2 to NO ratio with NO2 content of 50 mol% or more x The present invention provides a system for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from an off-gas, even if the off-gas is in an oxidation state, the system comprising: an ammonia source; means for introducing the ammonia into a catalyst article having SCR functionality; a catalyst article having both oxidation and SCR functionality, the catalyst article including a catalyst substrate and a catalyst composition comprising at least one platinum group metal and / or at least one platinum group metal oxide, at least one oxide of titanium, and at least one oxide of vanadium, wherein a washcoat of the catalyst composition is located within and / or on a wall of the catalyst substrate; and a means for introducing the ammonia into a catalyst article having SCR functionality, the catalyst article including a catalyst substrate and a catalyst composition comprising at least one platinum group metal and / or at least one platinum group metal oxide, at least one oxide of titanium, and at least one oxide of vanadium, the washcoat of the catalyst composition being located within and / or on a wall of the catalyst substrate; and a means for introducing the ammonia into a catalyst article having SCR functionality, the catalyst article including a catalyst substrate and a washcoat of the catalyst composition being located within and / or on a wall of the catalyst substrate; and a means for introducing the ammonia into a catalyst article having SCR functionality, the catalyst article having both oxidation and SCR functionality, the catalyst substrate and a washcoat of the catalyst composition being located between an outlet end of the catalyst article and the stack or between the outlet end of the catalyst article and the stack. x and / or ammonia slip; at least one carbon monoxide source; and means for introducing carbon monoxide into the catalyst article. Optionally, an SCR catalyst article can be located downstream or upstream of the catalyst article having both oxidation and SCR functions. NO between the outlet end of the catalyst article and the stack or at the stack. x The present invention further provides a method for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from an off-gas that incorporates carbon monoxide to maintain the amount of carbon monoxide and / or ammonia slip at a predetermined value. The method utilizes the system provided above. These systems and methods can be used to purify exhaust gases.

Description

[Technical Field]

[0001] The present invention is based on the NO2 vs. NO x The present invention relates to a system for oxidizing volatile organic compounds and carbon monoxide to carbon dioxide and water, even at high ratios, and a system for reducing nitrogen oxides to nitrogen and water. Additionally, the present invention provides a method for removing volatile organic compounds and nitrogen oxides from off-gas. The present system and method for removing volatile organic compounds and nitrogen oxides from off-gas is particularly useful for cleaning exhaust gases emitted during the combustion of fossil fuels, such as from gas turbines used to generate electricity and from nitric acid plants. [Background technology]

[0002] Problems that the invention aims to solve Modern power plant exhaust gas cleaning systems typically include oxidation catalysts to remove volatile organic compounds (VOCs) and carbon monoxide (CO), as well as nitrogen oxides (NO x ) is equipped with a reduction catalyst for selective catalytic reduction (SCR). NO from combustion turbine exhaust gas x The removal of NO, VOCs, and CO has traditionally been achieved using two different catalyst compositions. Catalysts for oxidizing CO and VOCs are typically NOx and VOCs. x The ammonia is injected between the two catalyst layers. Hereinafter, the terms "exhaust gas" and "exhaust gas" will be used synonymously.

[0003] Selective catalytic reduction (SCR) involves the catalytic reaction of nitrogen oxides NO and NO2 with ammonia to form elemental nitrogen and water according to the following reaction scheme: [ka]

[0004] Reactions 1 and 2 are the main reactions, and each NO xFor each mole of NO, one mole of ammonia is consumed. Reactions 3 and 4 x The majority of this occurs with the gas present as NO2. A catalyst is used to drive the reaction at temperatures between 150 and 480°C (300 and 900°F). The most common type of SCR catalyst is based on vanadium pentoxide (V2O5) as the active compound on a titanium dioxide (TiO2) support system. Reaction 1 is known as the "standard SCR reaction," reaction 2 is known as the "fast SCR reaction," and reactions 3 and 4 are known as the "NO2 SCR reactions."

[0005] However, the proportion of NO2 in the off-gas is x If the ratio exceeds 50%, the reaction rate of the SCR will decrease significantly. This has a significant impact on exhaust gas purification, especially in gas turbines used for power generation. For example, the ratio of NO2 to NO2 during start-up is x The molar ratio can exceed 90%, which significantly reduces the performance of existing vanadium-based SCR catalyst technology in common use. This problem also arises in the production of nitric acid, where NO in the off-gas is released. x This can also occur when the water contains high levels of NO2.

[0006] The prior art describes catalytic devices that combine a catalyst for the oxidation of carbon monoxide and volatile organic compounds with a catalyst for the selective catalytic reduction of nitrogen oxides.

[0007] WO 2014 / 063738 A1 discloses a method for purifying sulfur dioxide-containing off-gas by selectively oxidizing carbon monoxide and volatile organic compounds in the off-gas with reduced sulfur trioxide production, the method comprising contacting the off-gas with an oxidation catalyst comprising palladium and vanadium oxide supported on a carrier. If the off-gas also contains nitrogen oxides, the off-gas is contacted with a catalyst effective for selective reduction before or after contacting with the vanadium oxide and palladium-containing oxidation catalyst.

[0008] WO 2014 / 124830(A1) describes harmful carbon monoxide, organic volatile compounds and NO x exhaust gas containing carbon monoxide and NO x The present invention discloses a method and catalyst for contacting a layered catalyst for the simultaneous removal of NH3 and NH4, wherein a first layer of the layered catalyst comprises an oxidation catalyst and a lower layer comprises an ammonia SCR catalyst (NH3-SCR catalyst).

[0009] WO 2017 / 220473 A1 discloses a method for preparing a monolithic catalyst for reducing nitrogen oxides, volatile organic compounds, and carbon monoxide in off-gases. The catalyst comprises at least one platinum group metal, vanadium oxide, titania, and optionally tungsten oxide. The problem solved by this method is to avoid the formation of platinum group metal concentration gradients along the entire axial and vertical length of the substrate. This gradient formation is particularly problematic when the substrate is pre-loaded with vanadium oxide and then impregnated with platinum group metals. Because platinum group metals strongly and rapidly adsorb to vanadium oxide in the catalyst substrate, it is necessary to impregnate the catalyst substrate with excess palladium and / or platinum to minimize loading in the center of the substrate. Because catalytic activity in SCR reactions and CO and VOC oxidation depends on the platinum group metal concentration on the catalytically active surface of the coated substrate, the thickness of the washcoat layer and concentration gradients along the channels of the substrate monolith are disadvantageous.

[0010] MS Li, ​​K Seshan, and L Lefferts: "Influence of NO on the Reduction of NO with CO over Pt / SiO in the Presence of O," Chin J Chem 2007, 25, 435-438, investigated the reduction of NO with CO over a 0.1% Pt / SiO catalyst in the presence of NO and excess oxygen, a model mixture of exhaust gas. Related reaction mechanisms, such as the oxidation of CO and NO, were discussed. A narrow temperature window (180-190°C) was found for the reduction of NO with CO. At temperatures below the lower limit of the window, reduction was difficult. At temperatures above the upper limit of the window, direct oxidation of CO by O occurred, preventing effective reduction of NO with CO. The presence of NO suppressed the activation of O by NO on Pt, shifting the window to higher temperatures, thereby enabling the reduction of NO with CO in exhaust gas.

[0011] VA Ostapyuk, MG Martsenyuk-Kukharuk, and YI Pyatnitskii: "Reaction between NO2 and CO on a palladium catalyst," Kinet Catal 1991, 32, 189-190, investigated the reaction of CO with NO2 at atmospheric pressure over a 0.5 wt.% Pd on SiO2 catalyst in a flow reactor with a reaction mixture flow rate of 0.05 L / min. NO2 was prepared by first mixing NO / helium and O2 streams of a given composition and then passing the mixture through a cooled vessel. The reaction of CO with NO2 proceeded rapidly even at room temperature, with virtually complete conversion achieved at approximately 100 °C. Furthermore, it was shown that the reaction of CO with NO2 to produce CO2 and NO occurs at temperatures significantly lower than the reactions of CO with O2 and CO with NO. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] International Publication No. 2014 / 063738(A1) [Patent Document 2] International Publication No. 2014 / 124830(A1) [Patent Document 3] International Publication No. 2017 / 220473(A1) [Non-patent literature]

[0013] [Non-Patent Document 1] Chin J Chem 2007,25,pp.435-438 [Non-patent document 2] Kinet Catal 1991,32,pp.189-190 Summary of the Invention [Problem to be solved by the invention]

[0014] However, none of the prior art documents known to date have shown that the proportion of NO2 in the off-gas is greater than the total NO x The present invention does not address or solve the problem of reduced SCR reaction rates when the NO2 to NO2 ratio exceeds 50 mole percent. x It is an object of the present invention to provide a system for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from off-gas, even at high ratios.It is a further object of the present invention to provide a method for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from off-gas. [Means for solving the problem]

[0015] technical solution The objectives of providing a system for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from off-gas are to: a) an ammonia source; b) means for introducing ammonia into the catalytic article having SCR functionality; c) A catalytic article having both oxidation and SCR functions, A catalyst substrate; a catalyst composition comprising at least one platinum group metal and / or at least one platinum group metal oxide, at least one oxide of titanium, and at least one oxide of vanadium; a catalytic article comprising: d) NO between the outlet end of the catalyst article and the stack or at the stack x a means for measuring the amount of and / or ammonia slip; e) at least one carbon monoxide source; f) means for introducing carbon monoxide into the catalytic article; are resolved by the system, including

[0016] The system and method for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from off-gas according to the present invention surprisingly provides a high ratio of NO to NO x It has been found that even at high ratios, nitrogen oxides can be removed from the off-gas. x When the amount of NO2 in the x The system and method according to the present invention is x Even when the amount of NO2 in the x It can be used to remove

[0017] Below is NO2 vs. NO x A system for removing volatile organic compounds, carbon monoxide and nitrogen oxides from off-gas, even at high ratios, and a method for removing volatile organic compounds, carbon monoxide and nitrogen oxides from off-gas are described, and the invention includes all of the embodiments shown below, both individually and in combination with each other. [Brief explanation of the drawings]

[0018] [Figure 1] ΔNOx [%] values ​​versus NH3 / NOx [ppm / ppm] for various NO2 contents are shown. [Figure 2]The NO / NOx [%] values ​​versus NH3 / NOx [ppm / ppm] values ​​are shown for various NO2 contents. [Figure 3] ΔNOx [%] vs. NH3 / NOx for measurements 2a), 2b), and 2c). [Figure 4] ΔNOx [%] vs. NH3 / NOx for measurements 2a), 2b), and 2d). [Figure 5] A comparison of ΔNOx vs. NH3 / NOx is shown for Comparative Example 1 and Example 1 at 0% and 100% NO2, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0019] A "catalyst" or "catalyst composition" is a substance or mixture of substances capable of converting one or more components of exhaust gas into one or more other components. Examples of such catalysts include, for example, oxidation catalysts or oxidation catalyst compositions capable of converting volatile organic compounds and carbon monoxide into carbon dioxide. Other examples of such catalysts include, for example, selective catalytic reduction catalysts (SCR catalysts) or SCR catalyst compositions capable of converting nitrogen oxides into nitrogen and water. In the context of the present invention, a catalyst article having SCR functionality is a catalyst article comprising an SCR catalyst or an SCR catalyst composition.

[0020] A "catalyst substrate" is a support onto which a catalyst or catalyst composition is deposited to form the final catalyst. Thus, a catalyst substrate is a carrier for a catalyst or catalyst composition.

[0021] A "catalytic article" includes a catalytic substrate and a catalyst or catalyst composition deposited on the catalytic substrate. The catalytic article according to the present invention is a "dual-function catalyst" (DFC) because it has both oxidation and reduction functions; the DFC can oxidize volatile organic compounds and carbon monoxide to carbon dioxide and water. In addition, the DFC can reduce nitrogen oxides to nitrogen and water in the presence of ammonia. This means that the DFC also has an SCR reduction function.

[0022] The terms "exhaust gas," "flood gas," or "off-gas," as used in the context of the present invention, refer to gases emitted as a result of the combustion of a fuel, such as natural gas, gasoline, petroleum, biodiesel blends, diesel fuel, fuel oil, or coal.

[0023] "Uncleaned" or "raw" exhaust gas, flue gas, or off-gas is gas as defined above that has not yet passed through an exhaust gas cleaning system.

[0024] "Upstream" and "downstream" are terms that refer to the normal flow direction of off-gases in the exhaust line. "An object, article, or device 1 located upstream of an object, article, or device 2" means that object 1 is positioned near the source of the off-gases, i.e., near the motor or gas turbine. In this case, object 2 is located "downstream" of object 1, i.e., object 2 is farther from the source of the off-gases than object 1. The flow direction is from the source of the off-gases toward the stack or exhaust line.

[0025] The "inlet end" of the catalyst article is the end that faces the combustion source, and the "outlet end" is the end that faces the stack.

[0026] The reaction of reducing nitrogen oxides to nitrogen and water is well known as the SCR reaction, and it is also known that the SCR reaction requires ammonia. Accordingly, the system according to the present invention also includes an ammonia source and a means for introducing ammonia.

[0027] The ammonia source can be ammonia itself or an ammonia precursor capable of releasing ammonia. The ammonia source is preferably selected from aqueous ammonia, anhydrous ammonia, aqueous urea, aqueous ammonium formate, and ammonium carbamate, and mixtures thereof, more preferably anhydrous ammonia or aqueous urea. Anhydrous ammonia (NH3) can be used as either a gas or a liquid. Suitable ammonia precursors include, for example, urea, ammonium carbamate, and ammonium formate, preferably urea. The precursor hydrolyzes to ammonia when heated. For example, aqueous urea hydrolyzes at temperatures above 130°C, thereby releasing ammonia. Because off-gases from power plants and nitric acid plants exceed 130°C during operation, aqueous urea hydrolyzes easily when introduced into the SCR catalyst in such plants. Furthermore, aqueous ammonia can be effectively decomposed when injected as fine particles into a gas stream at a temperature of at least 350°C.

[0028] Anhydrous ammonia, aqueous ammonia, or ammonia precursor is stored in a container and added to the off-gas stream as needed and introduced to the inlet side of the catalyst article. Storage containers and means for introducing anhydrous ammonia, aqueous ammonia, or ammonia precursor to the inlet side of the SCR catalyst are well known in the art and can be applied to the present invention without departing from the scope of the claims. In the context of the present invention, the term "means for introducing ammonia" encompasses means for introducing ammonia itself as well as means for introducing an ammonia precursor. Preferably, the container contains anhydrous ammonia or an aqueous urea solution. The preferred means for introducing aqueous ammonia or aqueous ammonia precursor is via an injector located upstream, i.e., on the inlet side, of the catalyst article.

[0029] In a preferred embodiment of the present invention, the means for introducing ammonia into the off-gas is a means for introducing anhydrous ammonia.

[0030] The catalytic substrate is selected from a flow-through substrate, a wall-flow substrate, and a corrugated substrate. The wall-flow substrate and the flow-through substrate may be composed of an inert material such as silicon carbide, aluminum titanate, cordierite, a metal, or a metal alloy. The inert material may, for example, be extruded itself and then coated with at least one washcoat containing the catalytic composition. Alternatively, the inert material for the wall-flow substrate or the flow-through substrate may be mixed with the catalytic material or its precursor to form a paste, and the mixture may be extruded to obtain the catalytic article defined above in one step. Furthermore, the substrate may be selected from a ceramic candle filter, a bag filter, or a catalytic pellet.

[0031] Such support substrates are well known to those skilled in the art and are commercially available. In a preferred embodiment, the catalyst substrate is a corrugated substrate monolith. The corrugated substrate monolith is a high silica content glass paper or E-glass fiber paper, coated with at least one washcoat.

[0032] Methods for preparing washcoats, applying them onto catalyst substrates, and manufacturing extruded catalyst articles are well known to those skilled in the art and may be applied in the context of the present invention without departing from the scope of the claims.

[0033] The catalyst or catalyst composition is located within and / or on the walls of the catalytic substrate. Preferably, the catalyst or catalyst composition is located within the walls of the catalytic substrate.

[0034] The catalyst or catalyst composition of the catalyst article having both oxidation and SCR functions comprises at least one platinum group metal and / or at least one platinum group metal oxide, at least one oxide of titanium, and at least one oxide of vanadium.

[0035] The at least one platinum group metal and / or at least one platinum group metal oxide is selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, and their oxides. When two or more platinum group metals are present, the platinum group metals and / or their oxides can be used as physical mixtures, alloys, or mixtures of physical mixtures and alloys. For example, when platinum and palladium are selected, they can be present as a) physical mixtures, b) alloys of platinum and palladium, where neither pure platinum nor pure palladium is present, or c) the platinum and palladium alloys mentioned in b), as well as pure platinum and / or pure palladium. When oxides of two or more platinum group metals are present, they can be present as a) mixtures of oxides of the same metal in various oxidation states, b) mixtures of oxides of one or more different metals in various oxidation states, c) oxides of alloys, or d) combinations of mixtures of oxides of one or more metals in various oxidation states and oxides of different metals. Furthermore, the platinum group metals and platinum group metal oxides described above can coexist.

[0036] Preferably, the at least one platinum group metal is selected from palladium, platinum, iridium, and mixtures, alloys, oxides, and mixtures of alloys, oxides, and physical mixtures. Even more preferably, the at least one platinum group metal is palladium and / or palladium (II) oxide, PdO.

[0037] In a preferred embodiment, the catalyst substrate is a corrugated substrate, and the catalyst or catalyst composition is located within and / or on the walls of the catalyst substrate, as described above. In this embodiment, the total weight of the catalyst article is the sum of the amounts of at least one platinum group metal and / or at least one platinum group metal oxide, at least one titanium oxide, at least one vanadium oxide, and the catalyst substrate. The amounts of at least one platinum group metal and / or at least one platinum group metal oxide, at least one titanium oxide, and at least one vanadium oxide in this embodiment are shown below.

[0038] The at least one platinum group metal and / or platinum group metal oxide is present in the catalyst article in an amount of 50 to 10,000 ppmw, preferably 200 to 3,000 ppmw, and even more preferably 400 to 1,500 ppmw, calculated as pure precious metal, based on the total weight of the catalyst article. The unit "ppmw" stands for "parts per million by weight." Preferably, the at least one platinum group metal is palladium.

[0039] The at least one oxide of titanium in the catalyst article is present in an amount of 60-90 wt. %, preferably 65-85 wt. %, and more preferably 70-80 wt. %, calculated as TiO2, based on the total weight of the catalyst article. In one embodiment, the at least one oxide of titanium is titanium dioxide (TiO2). Suitable titanium dioxides contain at least 95 wt. %, preferably at least 98 wt. %, and even more preferably at least 99.5 wt. % anatase. The remainder of the TiO2, adding up to 100 wt. %, is represented by rutile and / or brookite, preferably rutile. The at least one oxide of titanium functions as a support for the washcoat.

[0040] The at least one oxide of vanadium is present in an amount of 0.1 to 17 wt. %, preferably 0.6 to 5 wt. %, and more preferably 1.8 to 3.6 wt. %, calculated as VO, based on the total weight of the catalyst article. In one embodiment, the at least one oxide of vanadium is vanadium pentoxide (VO).

[0041] In one embodiment, the first washcoat further comprises at least one oxide of tungsten. The at least one oxide of tungsten is present in an amount of 0.001 to 10 wt. %, preferably 2 to 7 wt. %, more preferably 2.5 to 6 wt. %, and most preferably 2.7 to 3.3 wt. %, calculated as WO, based on the total weight of the catalyst substrate. In one embodiment, the at least one oxide of tungsten is tungsten trioxide (WO). In this embodiment, the total weight of the catalyst article is the sum of the amounts of the at least one platinum group metal and / or at least one platinum group metal oxide, the at least one oxide of titanium, the at least one oxide of vanadium, the at least one oxide of tungsten, and the catalyst substrate.

[0042] To control the efficiency of the off-gas cleaning, NO is introduced into the off-gas cleaning system between the outlet end of the catalyst article and the stack or into the stack. x In all embodiments of the present invention, the amount of NO and / or ammonia slip can be measured. x The amount of and / or ammonia slip is preferably measured at the stack.

[0043] NO x The amount of each of NO can be determined, for example, by chemiluminescence detection (CLD), Fourier transform infrared spectroscopy (FTIR), or infrared spectroscopy (IR). x These means for determining the amount of are well known to those skilled in the art and may be applied to the present invention without departing from the scope of the claims.

[0044] As stated above NO x Instead of measuring the amount of NO between the outlet end of the catalyst article and the stack or at the stack, it is also possible to measure ammonia slip (NH3 slip) in the off-gas cleaning system. The ammonia emitted at the stack of the off-gas cleaning system is known as "ammonia slip". Ammonia slip is usually measured by FTIR. The ammonia slip measurement is based on the amount of NO between the outlet end of the catalyst article and the stack or at the stack. xThis can be done in addition to, or as an alternative to, measuring the amount.

[0045] Optionally, the amount of CO emitted between the outlet end of the catalyst article and the stack or at the stack can be measured. This measurement can be used to measure the amount of NO emitted between the outlet end of the catalyst article and the stack or at the stack. x This can be done in addition to measuring the amount of CO and / or NH3 slip. A suitable means for measuring CO is, for example, a non-dispersive infrared analyzer (NDIR). Means and methods for measuring CO are known to those skilled in the art and can be applied in the context of the present invention without departing from the scope of the claims. x As described above for measuring the amount of CO and / or ammonia slip, CO measurements are also preferably made in the stack.

[0046] In one embodiment of the present invention, the DFC is the only catalytic article with SCR functionality in a system for removing volatile organic compounds, carbon monoxide, and nitrogen oxides. In this embodiment, the means for introducing ammonia is located immediately upstream of the catalytic article and is configured to introduce NO x The means for measuring the amount of CO and / or ammonia slip, and optionally also the means for measuring the emitted CO, are located between the outlet end of the DFC and the stack or in the stack, preferably in the stack.

[0047] In another embodiment of the present invention, an SCR catalyst article is present upstream of the DFC. In contrast to the DFC, the SCR catalyst article only has a selective catalytic reduction function, but does not have an oxidation function. When the SCR catalyst article is present upstream of the DFC, the means for introducing ammonia is located immediately upstream of the SCR catalyst article. This means that the SCR catalyst article is located between the means for introducing ammonia according to b) and the DFC according to c), as defined above. In this embodiment, NO x Means for measuring the amount of CO and / or ammonia slip, and optionally also means for measuring the emitted CO, are located between the outlet end of the DFC and the stack or in the stack, preferably in the stack.

[0048] In yet another embodiment of the present invention, there is an SCR catalyst article downstream of the DFC. When there is an SCR catalyst article downstream of the DFC, the means for introducing ammonia is located immediately upstream of the SCR catalyst article. In this embodiment, the means for introducing ammonia according to b) is located either upstream of the DFC or between the DFC and the SCR catalyst article. In this embodiment, NO x The means for measuring the amount of and / or ammonia slip, and also optionally the means for measuring the released CO, are located between the outlet end of the SCR catalyst article and the stack or in the stack, preferably in the stack.

[0049] "NO x The term "the means for measuring the amount of SCR catalyst and / or ammonia slip, and also optionally the means for measuring the released CO, are located between the outlet end of the catalyst article and the stack" means that these measuring means are located downstream of the catalyst article having the SCR catalytic function, which is located closest to the stack.

[0050] The catalyst component with SCR catalytic function located closest to the stack is the DFC, and NO x When the means for measuring the amount of and / or ammonia slip, and optionally also the means for measuring released CO, are located between the outlet end of the SCR catalyst article and the stack, the measuring means are located downstream of the DFC and upstream of the stack. This arrangement applies both to embodiments in which the DFC is the only catalyst article having SCR catalytic function, and to embodiments in which the SCR catalyst article is located upstream of the DFC, as described above.

[0051] However, if the SCR catalyst assembly is located downstream of the DFC, NO xIn the case where the means for measuring the amount of and / or ammonia slip, and also optionally the means for measuring the emitted CO, are located between the outlet end of the SCR catalyst article and the stack, the term "located between the outlet end of the SCR catalyst article and the stack" refers to an SCR catalyst article that has only a selective catalytic reduction function, but does not have an oxidation function.

[0052] SCR catalyst articles are known to those skilled in the art and can be used in the context of the present invention without departing from the scope of the claims. SCR catalyst articles known in the art may include a zeolite or a metal oxide, or a mixture of a zeolite and a metal oxide, as the SCR catalyst or catalyst composition.

[0053] Suitable zeolites are, for example, small-pore aluminosilicate zeolites selected from ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, BIK, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, ESV, ETL, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON, and mixtures and intergrowths thereof. Preferably, the zeolite is selected from AEI, AFT, AFX, CHA, DDR, ERI, ESV, ETL, KFI, LEV, UFI, and mixtures and intergrowths thereof, and even more preferably, the zeolite is selected from AEI, CHA, AFX. The small pore zeolite further comprises 0.1 to 10 wt. % of a transition metal, calculated as the respective transition metal oxide, based on the total weight of the zeolite. Preferably, the transition metal is selected from Fe, Cu, and mixtures thereof, and more preferably, the transition metal is copper. The zeolite further comprises at least one alkali metal and / or alkaline earth metal, calculated as the respective metal, in a concentration of up to 2 wt. % based on the total weight of the zeolite. The alkali metal and alkaline earth metal are selected from lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, and mixtures thereof. Preferably, the alkali metal and / or alkaline earth metal is selected from sodium, potassium, and mixtures thereof.

[0054] Suitable metal oxides that can be used in the SCR catalyst composition are, for example, mixtures of titania and vanadia oxides, as described above for DFC, which may optionally further contain other oxides such as tungsten oxide, antimony oxide, niobium oxide, molybdenum oxide, cerium oxide, lanthanum oxide, and mixtures thereof.

[0055] As used herein, NO xThe term "oxides of nitrogen", also referred to as NO, refers to the total amount of nitric oxide (NO) and nitrogen dioxide (NO) present in the exhaust gas or off-gas, regardless of the relative amounts of NO and NO, respectively, in the exhaust gas or off-gas.

[0056] Exhaust or off-gas NO2 vs. NO x The ratio can be calculated by the following formula:

number

[0057] In the context of the present invention, "high" NO2 vs. NO x The ratio is given when x[NO2] is greater than 50 mol%.

[0058] As mentioned above, the proportion of NO2 in the off-gas is x Above 50 mole % of the SCR catalyst, the reaction rate of the SCR catalyst decreases significantly, with a greater decrease at 60% and an even greater decrease at 70%, 80%, or 90%, causing a significant decrease in the performance of the vanadium-based SCR catalyst.

[0059] Especially during gas turbine start-up, i.e., at low loads or load changes, the NO2 vs. NO x The ratio is high and the incomplete combustion process also produces significant amounts of carbon monoxide, which is known to reduce nitrogen dioxide according to the following equation: [ka]

[0060] Surprisingly, high NO2 vs. NO x It was found that a high CO concentration increases the reaction rate of SCR in DFCs, because NO2 is reduced to NO, and the ratio of NO2 to NO x This is explained by the fact that the ratio is below 50 mol % which is optimal for the SCR reaction.

[0061] A catalytic article according to the present invention that is active in the oxidation of volatile organic compounds and carbon monoxide to carbon dioxide and water and is also active in the reduction of nitrogen oxides to nitrogen and water, reduces NO to NO x Feeding carbon monoxide to keep the ratio below 90 mole %, preferably below 80 mole %, below 70 mole %, below 60 mole %, and even more preferably below 50 mole %, provides consistently high activity.

[0062] The at least one carbon monoxide source may originate from unpurified exhaust gas emitted by a power plant, such as a gas turbine, because unpurified exhaust gas contains carbon monoxide and / or volatile organic compounds (VOCs). VOCs may emit carbon monoxide. Alternatively or additionally, hydrocarbons, VOCs, and / or CO may be added to the exhaust gas from an external source. By "external source" is meant, for example, injecting natural gas or fuel that emits CO upon incomplete combustion into the catalyst article, or adding CO gas that does not originate from the unpurified exhaust gas emitted by the power plant. Thus, the at least one carbon monoxide source is selected from unpurified exhaust gas, natural gas, fuel, carbon monoxide gas that does not originate from unpurified exhaust gas, volatile organic compounds, and mixtures thereof. The carbon monoxide is introduced into the catalyst article at the inlet side.

[0063] If the source of carbon monoxide is unpurified exhaust gases emitted by the power plant or VOCs present in the power plant, then the power plant itself is the means for introducing carbon monoxide.

[0064] In the case of an "external source" of CO, the means for introducing carbon monoxide is an injector, atomizer, or nozzle.

[0065] The objectives of providing a method for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from an off-gas are to: a) introducing ammonia into the off-gas; b) introducing the off-gas into a catalytic article having both an oxidizing function and a reducing function, the catalytic article having: A catalyst substrate; a catalyst composition comprising at least one platinum group metal and / or at least one platinum group metal oxide, at least one oxide of titanium, and at least one oxide of vanadium; a step comprising: c) NO between the outlet end of the catalyst article and the stack or at the stack x measuring the amount of and / or ammonia slip; d) introducing carbon monoxide into the catalyst article to measure the NO in the stack measured in step c); x and / or ammonia slip, e) After the introduction of carbon monoxide, NO is introduced between the outlet end of the catalyst article and the stack or at the stack. x measuring the amount of and / or ammonia slip; The problem is solved by a method including:

[0066] The source of ammonia and the means for introducing the ammonia are as described above.

[0067] In one embodiment, the ammonia source injected in step a) of the method according to the invention is selected from aqueous ammonia, anhydrous ammonia, aqueous urea, aqueous ammonium formate, and ammonium carbamate. Preferably, the ammonia source is selected from anhydrous ammonia or aqueous urea. The precursor is hydrolyzed to ammonia upon heating as described above.

[0068] The container for storing ammonia or an ammonia precursor and the means for introducing ammonia are as described above.

[0069] In a preferred embodiment of the process according to the invention, the ammonia introduced into the off-gas according to step a) is anhydrous ammonia.

[0070] In step b) of the method according to the invention, the off-gas is introduced into the catalyst article as described above.

[0071] As noted above, in one embodiment of the present invention, the DFC is the only catalytic article with SCR functionality in a system for removing volatile organic compounds, carbon monoxide, and nitrogen oxides. In this embodiment, ammonia is introduced immediately upstream of the catalytic article, and NO x The means for measuring the amount of CO and / or ammonia slip, and also optionally the means for measuring the emitted CO, are located between the outlet end of the DOC and the stack or in the stack, preferably in the stack.

[0072] In another embodiment of the present invention, an SCR catalyst article is present upstream of the DFC. In contrast to the DFC, the SCR catalyst article only has a selective catalytic reduction function, but not an oxidation function. When the SCR catalyst article is present upstream of the DFC, ammonia is introduced immediately upstream of the SCR catalyst article. This means that the SCR catalyst article is located between the means for introducing ammonia and the DFC defined above. In this embodiment, NO x A means for measuring the amount of CO and / or ammonia slip, and optionally also a means for measuring the emitted CO, is located between the outlet end of the DOC and the stack or in the stack, preferably in the stack.

[0073] In yet another embodiment of the present invention, there is an SCR catalyst article downstream of the DFC. When there is an SCR catalyst article downstream of the DFC, ammonia is introduced immediately upstream of the SCR catalyst article. In this embodiment, the means for introducing ammonia according to b) is located either upstream of the DFC or between the DFC and the SCR catalyst article. In this embodiment, NO x The means for measuring the amount of and / or ammonia slip, and also optionally the means for measuring the released CO, are located between the outlet end of the SCR catalyst article and the stack or in the stack, preferably in the stack.

[0074] In one embodiment, the catalyst substrate is selected from a flow-through substrate, a wall-flow substrate, and a corrugated substrate. Further, the substrate can be selected from a ceramic candle filter, a bag filter, or a catalyst pellet. Preferably, the catalyst substrate is a corrugated substrate. The catalyst or catalyst composition and their loadings are the same as those described above.

[0075] NO x The methods and means for measuring the amount of and / or ammonia slip have been described above and can be applied in steps c) and e) of the method according to the invention.

[0076] Optionally, it is also possible to measure the amount of CO emitted between the outlet end of the catalyst article and the stack or at the stack. Means and methods for measuring CO have been described above. These can be applied in steps c) and e) of the method according to the invention. The measurement of CO is carried out by measuring the amount of NO between the outlet end of the catalyst article and the stack or at the stack. x This can be done in addition to measuring the amount of NH3 and / or NH3 slip.

[0077] NO xMeasuring the amount of CO released and / or ammonia slip, and also optionally measuring the amount of CO released "between the outlet end of the catalyst article and the stack" has the same meaning as defined above for system embodiments in which the DFC is either the only catalyst article having SCR catalytic function, or an additional SCR catalyst article is located either upstream or downstream of the DFC.

[0078] The carbon monoxide source and the means for introducing it are as described above and can be applied in step d) of the method according to the invention. Carbon monoxide is introduced between the outlet end of the catalyst article and the stack, or at the stack, to reduce the NO 2 measured in step c). x and / or ammonia slip reducing amounts are introduced into the catalyst article.

[0079] For selective catalytic reduction, the standard SCR reaction and the fast SCR reaction, defined as Reactions 1 and 2 above, are preferred. Both require a stoichiometric amount of NH3 relative to the amount of NO (Reaction 1) or the sum of the amounts of NO and NO2, respectively. On the other hand, the NO2 SCR reaction requires a greater than stoichiometric amount of NH3 relative to the amount of NO2 (see Reaction 3). Of these three, the standard SCR reaction is the fastest, followed by the fast SCR reaction, and the NO2 SCR reaction is the slowest.

[0080] During off-gas purification, ammonia is introduced into the catalyst article having the SCR function. x and / or ammonia is typically measured between the outlet end of the catalyst article and the stack or at the stack. The ammonia that does not react and is released at the stack is called "ammonia slip."

[0081] Off-gas NO x The amount of ammonia introduced into the SCR catalyst article can be adjusted to optimize conversion. x If the amount of NO2 in xMore ammonia can be introduced to convert NO to N and H O. However, if too much ammonia is introduced and / or if the rather slow NO SCR reaction dominates, some of the ammonia may leave the exhaust cleaning system in an unmodified form, leading to increased ammonia slip. If the NO SCR reaction dominates, x Ammonia slip can increase because the NO2SCR reaction cannot react with the NO2SCR reaction quickly enough. This is because the primary NO2SCR reaction is then too slow to convert all the ammonia and NO2 to N2 and HO before it reaches the stack. In this case, the NO2SCR reaction in the stack x The amount of ammonia and ammonia slip increases, and introducing more ammonia into the exhaust cleaning system cannot alleviate this problem because the slow NO2 SCR reaction dominates.

[0082] The method according to the present invention provides a remedy for this problem.

[0083] NO x The amount of NO and / or ammonia slip is measured between the outlet end of the catalyst article and the stack or at the stack. If at least one of these amounts is too high, carbon monoxide is introduced into the exhaust cleaning system. This reduces some of the NO to NO, so that the standard SCR reaction and / or the fast SCR reaction dominates, reducing ammonia slip and NO in the stack. x The emissions are reduced, which can be measured according to step e) of the method according to the invention.

[0084] ammonia slip and / or NO between the outlet end of the catalyst article and the stack or at the stack according to steps c) and e) of the method according to the invention x The discharge measurement can be continuous or at intervals.

[0085] Ammonia slip and NO between the outlet end of the catalyst article and the stack or at the stack x The emission thresholds depend on the respective exhaust cleaning system and also on regulations.

[0086] In one embodiment, NH3 slip is maintained at a value of 30 ppm, 29 ppm, 28 ppm, 27 ppm, 26 ppm, 25 ppm, 24 ppm, 23 ppm, 22 ppm, 21 ppm, 19 ppm, 18 ppm, 17 ppm, 16 ppm, 15 ppm, 14 ppm, 13 ppm, 12 ppm, 11 ppm, 10 ppm, 9 ppm, 8 ppm, 7 ppm, 6 ppm, 5 ppm, 4 ppm, 3 ppm, 2 ppm, 1 ppm, 0.5 ppm, or 0.1 ppm or less.

[0087] NH3 slip and / or NO between the outlet end of the catalyst article and the stack or at the stack. x Keeping the amount of CO below a threshold is achieved by injecting carbon monoxide, as explained above.

[0088] The injection is between the outlet end of the catalyst article and the stack or at the stack. x The injection of carbon monoxide can be carried out continuously or at intervals, provided that the amount of NO and / or ammonia slip is kept below a threshold value. x This can be done at intervals by injecting carbon monoxide only when the amount of carbon monoxide rises above a certain threshold, which may be, for example, as mentioned above, a value of 2.5 ppm or more, preferably 2.0 ppm or less, and even more preferably 1.8 ppm or less.

[0089] Alternatively, spaced injections of carbon monoxide may be performed at predetermined time intervals and / or between the outlet end of the catalyst article and the stack or at the stack to separate NO 2 from the exhaust. x This can also be done to keep the amount of CO below 30 ppm as mentioned above. Thus, the following options are available for injecting CO at intervals: 1. NO emitted between the outlet end of the catalyst article and the stack or at the stack xinjecting CO to maintain the amount of CO in the air at or below 300 ppm, 250 ppm, 200 ppm, 150 ppm, 100 ppm, 50 ppm, 25 ppm, 24 ppm, 23 ppm, 22 ppm, 21 ppm, 19 ppm, 18 ppm, 17 ppm, 16 ppm, 15 ppm, 14 ppm, 13 ppm, 12 ppm, 11 ppm, 10 ppm, 9 ppm, 8 ppm, 7 ppm, 6 ppm, 5 ppm, 4 ppm, 3 ppm, 2 ppm, 1 ppm, 0.5 ppm, or 0.1 ppm; or 2. Injecting CO to maintain NH3 slip at or below 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 16, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, or 0.1 ppm; 3. Injecting CO at predetermined time intervals.

[0090] Option 1 or Option 2 is a NOx gas exhausted between the outlet end of the catalyst article and the stack or at the stack. x This is particularly applicable when the amount of NH3 and / or the time interval during which the NH3 slip falls below a certain threshold is not yet known by prior empirical data, the threshold being freely selectable between 30 ppm and / or 20 ppm NH3 slip, as described above.

[0091] Similarly, option 3 is NH3 slip and / or NO x This is particularly applicable when the time interval during which the amount of NO rises above a certain threshold is already known by prior empirical data, the threshold being, as mentioned above, 20 to 1 ppm NH3 slip or 30 to 1 ppm NO x It is possible to freely select from

[0092] Within the scope of the present invention, NO 2 emitted between the outlet end of the catalyst article and the stack or at the stack x It is possible to measure either only the amount of NO or only the NH slip, or to measure both. Preferably, the NH slip is determined by measuring the amount of NO x It is measured in combination with or alone as the amount of

[0093] When CO is injected at intervals, the amount of CO injected is 0 ppm during periods when no injection occurs and greater than 0 ppm when an injection occurs.

[0094] Preferred ranges for the amount of CO applied are given above and these ranges apply both to continuous CO injection and to CO injections spaced apart during the injection period.

[0095] Optionally, the method according to the invention comprises measuring the amount of carbon monoxide present in the catalyst article and / or the amount of carbon monoxide introduced into the catalyst article. Preferably, the amount of carbon monoxide is measured by NDIR (Non-Dispersive Infrared). Those skilled in the art know methods for measuring carbon monoxide and can apply this knowledge without departing from the scope of the claims.

[0096] Systems and methods for removing volatile organic compounds and nitrogen oxides from off-gases are particularly useful for cleaning exhaust gases emitted by gas turbines used to generate electricity and by nitric acid plants.

[0097] The catalytic article disclosed above has both the oxidation function of volatile organic compounds and the reduction function for removing nitrogen oxides. Because of its dual function, such catalysts are also called dual-function catalysts (DFCs). DFCs can partially or completely replace conventional SCR catalysts in, for example, power plants and nitric acid plants.

[0098] In summary, the catalytic article, i.e., dual function catalyst (DFC), of the present invention can partially or completely replace conventional SCR catalysts found in, for example, power plants and nitric acid plants. When partially replacing an SCR, the DFC can be located upstream or downstream of the conventional SCR catalyst. When the DFC is located upstream of a conventional SCR catalyst, the DFC can provide a NO to NO ratio, provided that carbon monoxide is also present. xOn the other hand, when a conventional SCR catalyst is installed upstream of a DFC, the conventional SCR catalyst reduces NO x In this case, a downstream DFC can reduce NO to NO in the presence of carbon monoxide. x The ratio decreases. [Example]

[0099] Embodiment Comparative example 1.NH3 / NO x NO of standard SCR catalyst article as a function of ratio x Removal efficiency The SCR reaction rate of a standard SCR catalyst was tested to determine whether the proportion of NO2 in the off-gas was greater than the total NO x The conditions were investigated when the mol% of V2O5 was varied between 0 and 100%. The reference catalyst was a vanadia-titania-tungsten catalyst article containing 3 wt% V2O5, 3 wt% WO3, 70-80 wt% TiO2, and approximately 15 wt% silica-alumina binder on a corrugated substrate. The catalyst contained no precious metals or precious metal oxides.

[0100] Measurement conditions: 35 ppmvd NO x , ppmvd stands for "parts per million per volume, dry basis." 10% dry O2 temperature: Measurements were taken at 0, 25, 50, 75, and 100% NO2 at 560°F (=293.3°C), and 0% NO2 at 700°F (=371.1°C). 5% H2O 35 Nm / Hr A v

[0101] [Table 1]

[0102] The results are shown in Figure 1.

[0103] [Table 2]

[0104] The results are shown in Figure 2.

[0105] Embodiment 1: NH3 / NO x NO of the DFC according to the present invention depending on the ratio x Removal efficiency The SCR kinetics of a DFC according to the present invention was tested. The DFC contained 400 ppm Pd, 4 wt. % V2O5, 3 wt. % WO3, 78 wt. % TiO2, and the remainder binder (SiO2 / Al2O3) on a corrugated substrate.

[0106] Measurement conditions: 35 ppmvd NO x 10% dry O2 temperature: Measurements were taken at 700°F (371.1°C) for 0% and 100% NO2. 5% H2O 35 Nm / Hr A v

[0107] The measurements were carried out under the following conditions: a) 0% NO2, b) 100% NO2 c) 100% NO2 repeat d) 100% NO2 and 400 ppm CO

[0108] [Table 3]

[0109] The results for 2a), 2b), and 2c), and 2a), 2b), and 2d) are shown in Figures 3 and 4, respectively.

[0110] ΔNO in measurement 2d) x The negative value of is due to the production of NO across the catalyst while CO is present.

[0111] ΔNO at 0% and 100% NO for Comparative Example 1 and Example 1, respectively x NH3 / NO x A comparison is shown in Figure 5.

Claims

1. 1. A system for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from an off-gas, comprising: a) a source of ammonia; b) means for introducing ammonia into the catalytic article having SCR functionality; c) A catalytic article (DFC) having both oxidation and SCR functions, A catalyst substrate; a catalyst composition comprising at least one platinum group metal and / or at least one platinum group metal oxide, at least one oxide of titanium, and at least one oxide of vanadium; a catalytic article comprising: d) NO between the outlet end of the catalyst article and the stack or at the stack ｘ means for measuring the amount of and / or ammonia slip; e) at least one carbon monoxide source; f) means for introducing carbon monoxide into said catalytic article; Including, NO in the off-gas ２ is more than 50 mol % of the nitrogen oxides, The catalyst substrate is a corrugated substrate, the catalyst composition comprising 50 to 10,000 ppmw (parts per million by weight) of at least one platinum group metal, which is palladium, calculated as pure precious metal, based on the total weight of the catalyst article; and TiO ２ 60 to 90 wt. % of at least one oxide of titanium which is titanium dioxide, calculated as: ２ O ５ 0.1 to 17 wt. % of at least one oxide of vanadium, which is vanadium pentoxide, calculated as: ３ and 2 to 7 weight percent of at least one oxide of tungsten, calculated as:

2. 10. The system of claim 1, wherein the ammonia source is selected from anhydrous ammonia, aqueous ammonia, or an ammonium precursor selected from aqueous urea, aqueous ammonium formate, and aqueous ammonium carbamate, and mixtures thereof.

3. 3. The system of claim 1 or 2, wherein the means for introducing ammonia or an aqueous ammonia precursor into the off-gas is means for introducing anhydrous ammonia.

4. 4. The system of claim 1, wherein the catalytic article having both oxidation and SCR functionality is the only catalytic article having SCR functionality, and the means for introducing ammonia is located immediately upstream of the catalytic article.

5. 4. The system of claim 1, wherein an SCR catalyst article is present upstream of the catalyst article having both oxidation and SCR functions, the SCR catalyst article having only selective catalytic reduction function but not oxidation function, and the means for introducing ammonia is located immediately upstream of the SCR catalyst article.

6. 4. The system according to claim 1, wherein an SCR catalyst article is present downstream of the catalyst article having both oxidation and SCR functions, the SCR catalyst article having only selective catalytic reduction function but not oxidation function, and the means for introducing ammonia according to b) is located either upstream of the DFC or between the DFC and the SCR catalyst article.

7. 7. The system of any one of claims 1 to 6, wherein the at least one carbon monoxide source is selected from unpurified exhaust gas emitted from a power plant and / or hydrocarbons and / or carbon monoxide from an external source.

8. The system of any one of claims 1 to 7, wherein the system further comprises means for measuring the amount of CO emitted between the outlet end of the catalyst article and the stack or at the stack.

9. 1. A method for removing volatile organic compounds, carbon monoxide, and nitrogen oxides from an off-gas, comprising: a) introducing ammonia into the off-gas; b) introducing the off-gas into a catalytic article having both an oxidizing function and a reducing function, the catalyst article comprising: A catalyst substrate; a catalyst composition comprising at least one platinum group metal and / or at least one platinum group metal oxide, at least one oxide of titanium, and at least one oxide of vanadium; including, steps, c) between the outlet end of the catalyst article and the stack or the stack, ｘ and / or ammonia slip; d) introducing carbon monoxide into the catalyst article to measure the NO in the stack measured in step c); ｘ and / or ammonia slip; e) after the introduction of carbon monoxide, between the outlet end of the catalyst article and the stack or the stack, ｘ and / or ammonia slip, NO in the off-gas ２ is more than 50 mol % of the nitrogen oxides, The catalyst substrate is a corrugated substrate, the catalyst composition comprising 50 to 10,000 ppmw (parts per million by weight) of at least one platinum group metal, which is palladium, calculated as pure precious metal, based on the total weight of the catalyst article; and TiO ２ 60 to 90 wt. % of at least one oxide of titanium which is titanium dioxide, calculated as: ２ O ５ 0.1 to 17 wt. % of at least one oxide of vanadium, which is vanadium pentoxide, calculated as: ３ and 2 to 7 weight percent of at least one oxide of tungsten, calculated as:

10. 10. The method of claim 9, wherein the ammonia source is selected from anhydrous ammonia, aqueous ammonia, or an ammonium precursor selected from aqueous urea, aqueous ammonium formate, and aqueous ammonium carbamate, and mixtures thereof.

11. 11. The method of claim 9 or 10, wherein steps c) and e) further comprise measuring the amount of CO emitted between the outlet end of the catalyst article and the stack or at the stack.

12. 12. The method of any one of claims 9 to 11, wherein the catalytic article having both oxidation and SCR functionality is the only catalytic article having SCR functionality, and the means for introducing ammonia is located immediately upstream of the catalytic article.

13. 12. The method according to any one of claims 9 to 11, wherein an SCR catalyst article is present upstream of the catalyst article having both oxidation and SCR functions, the SCR catalyst article having only selective catalytic reduction function but not oxidation function, and the means for introducing ammonia is located immediately upstream of the SCR catalyst article.

14. 12. The method according to any one of claims 9 to 11, wherein an SCR catalyst article is present downstream of the catalyst article having both oxidation and SCR functions, the SCR catalyst article having only selective catalytic reduction function but not oxidation function, and the means for introducing ammonia according to b) is located either upstream of the DFC or between the DFC and the SCR catalyst article.

15. Use of a system according to any one of claims 1 to 8 for cleaning exhaust gases emitted by a gas turbine or a nitric acid plant.

16. Use of the method according to any one of claims 9 to 14 for cleaning exhaust gases emitted by gas turbines or nitric acid plants.

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