Method and apparatus for reducing the concentration of nitrogen oxides in a flue gas stream

Abstract

Method for reducing the concentration of nitrogen oxides (10) of a flue gas stream (12) of a combustion reaction (18) by selective catalytic reduction, SCR, comprising the following process steps: a) Providing a liquid catalyst precursor (14), b) Producing a catalyst (16) from the catalyst precursor (14), wherein the produced catalyst (16) comprises nanoparticles, c) Feeding the produced catalyst (16) into the flue gas stream (12), d) Adding ammonia (22), NH3 or an ammonia precursor to the flue gas stream (12) as a reducing agent (22) and e) Reducing the concentration of nitrogen oxides (10) in the flue gas stream (12) by means of a first SCR using the catalyst (16) and the reducing agent (22) in the flue gas stream (12), wherein the liquid catalyst precursor (14) comprises a metal dissolved in a flammable solvent, wherein the metal is selected from the group comprising iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni) and copper (Cu), or wherein the liquid catalyst precursor (14) is iron pentacarbonyl (Fe(CO)5), and wherein process step b) comprises supplying the catalyst precursor (14) to a support combustion reaction (20) located in the flue gas stream (12).

Description

[0001] The invention relates to a method for reducing the concentration of nitrogen oxides in a flue gas stream from a combustion reaction. The invention further relates to a device for carrying out the above method.

[0002] In a combustion reaction, such as that which takes place in a biomass plant or a waste incineration plant, combustion products are produced as flue gases during the material conversion process. The nitrogen oxides contained in the flue gas are harmful to humans and the environment, which is why the concentration of nitrogen oxides in the flue gas is reduced during flue gas denitrification using so-called primary or secondary measures.

[0003] While primary measures aim to prevent nitrogen oxides from forming in the first place through optimized combustion processes, secondary measures focus on reducing the concentration of nitrogen oxides already formed in the flue gas. One possibility is the reduction of the nitrogen oxides to elemental nitrogen, for example, by spraying ammonia. Reductive processes are further divided into selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR), depending on whether the reaction is mediated by a catalyst or not.

[0004] In SCR (Selective Catalytic Reduction) systems, V₂O₅ / MoO₃ / TiO₂ metal catalysts are predominantly used for the denitrification of flue gas. These catalysts consist of a support material (monolith) and a catalytic coating. As high-temperature catalysts, they are used in industrial plants at temperatures of 280 °C to 380 °C because they are relatively insensitive to the dust contained in the flue gas. To achieve the temperatures required for efficient denitrification in this process, a reduced energy recovery from combustion waste heat must be accepted. Furthermore, these catalysts can be poisoned by gaseous trace contaminants (e.g., sulfur compounds) and thus lose their catalytic effect. Additionally, the given flow geometry limits the residence time of the flue gas at the catalyst, as the catalyst is stationary within the monolith's coating.

[0005] EP 1 378 560 A2 describes an aqueous additive containing a metal compound for improving the operation of combustion exhaust aftertreatment systems. The additive is introduced into the combustion chamber as part of an emulsion with the fuel, or alternatively, it is fed into the exhaust or emission path as an aqueous stream, either in the emulsion or on its own. The metal compound traps combustion byproducts to protect and improve the efficiency of the aftertreatment system.

[0006] Based on this, the object of the invention is to provide a method and a device for carrying out the method which overcomes the aforementioned disadvantages of the prior art and has a high efficiency in reducing the concentration of nitrogen oxides in the flue gas stream.

[0007] This problem is solved by the subject matter of the independent patent claims. Preferred further developments are found in the dependent claims.

[0008] According to the invention, a method for reducing the concentration of nitrogen oxides in a flue gas stream of a combustion reaction by selective catalytic reduction (SCR) is provided, comprising the following process steps: a) Providing a liquid catalyst precursor, b) Production of a catalyst from the catalyst precursor, wherein the produced catalyst comprises nanoparticles, c) Feeding the manufactured catalyst into the flue gas stream, d) Adding ammonia, NH3, or an ammonia precursor to the flue gas stream as a reducing agent, and e) Reducing the concentration of nitrogen oxides in the flue gas stream by means of a first SCR using the catalyst and the reducing agent in the flue gas stream, wherein the liquid catalyst precursor comprises a metal dissolved in a flammable solvent, wherein the metal is selected from the group comprising iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni) and copper (Cu) or wherein the liquid catalyst precursor is iron pentacarbonyl (Fe(CO)5), and wherein process step b) comprises feeding the catalyst precursor to a propagation combustion reaction located in the flue gas stream.

[0009] The basic idea of ​​the process according to the invention is that the catalyst is produced essentially directly at or near the place of use, or insignificantly before the time of use, in the sense of an online synthesis. This spatial and temporal connection between the production of the catalyst and its use can be implemented in the process as follows: In an alternative approach not covered by the claim, the catalyst precursor is fed into the combustion reaction from which the flue gas stream originates. The combustion reaction thus simultaneously serves to produce the catalyst. Consequently, the catalyst is produced essentially within the flue gas stream from the combustion reaction, i.e., essentially at the location where the catalyst is also used. This has the particular advantage that by feeding the catalyst precursor into the combustion reaction, the produced catalyst is simultaneously introduced into the flue gas stream. Therefore, in this case, no separate action is required for process step c).

[0010] According to the invention, the catalyst precursor is fed to a propagation combustion reaction for the production of the catalyst. The propagation combustion reaction can, for example, be a gas burner flame. Furthermore, the propagation combustion reaction is located within the flue gas stream, so that by feeding the catalyst precursor to the propagation combustion reaction, the produced catalyst is simultaneously introduced into the flue gas stream. In this preferred case, no separate action is required for process step c). Alternatively, the propagation combustion reaction can also be located in close proximity to the flue gas stream, for example, essentially directly upstream of the flue gas stream. In this case, the produced catalyst is introduced into the flue gas stream essentially immediately following the propagation combustion reaction.

[0011] The catalyst in the process according to the invention can exhibit very high catalytic activity. This high catalytic activity is due, on the one hand, to the fact that the catalyst comprises nanoparticles and thus has a very large surface area. Furthermore, the production of the catalyst, which takes place essentially directly before and at the point of use, means that the surface of the catalyst has been exposed to virtually no or only minimal influences that could have led to a reduction in catalytic activity.

[0012] Furthermore, the process according to the invention results in a long contact time between the reactants of the first SCR and the catalyst in process step e). In process step e), the catalyst is located in the flue gas stream, meaning that the nanoparticles move along with the nitrogen oxides and the reducing agent in the flue gas stream. Thus, the contact time between the nitrogen oxides, the reducing agent, and the catalyst is much longer than if the catalyst were stationary. The first SCR therefore takes place in the entrained flow, which can contribute to a particularly intensive and rapid mass and / or heat exchange during the SCR.

[0013] The high catalytic activity of the catalyst, as well as the long contact time between the reactants of the first SCR and the catalyst, can lead to a very high efficiency of the process. This allows the process to be used effectively even at low flue gas temperatures in the range of T ≤ 200 °C.

[0014] The method according to the invention is therefore particularly suitable for the denitrification of flue gas streams from waste incineration plants, biogas plants, biomass combustion plants, combustion plants, industrial plants, coal and / or gas turbine power plants.

[0015] During a combustion reaction, combustion products are produced as a result of the material conversion process, with the gaseous combustion products generally being referred to as exhaust gases. Depending on the type of combustion process, various other substances may be contained in the exhaust gas, for example, solids such as soot, dust particles and / or fly ash, or liquid components such as water, oil vapors and / or acid vapors.

[0016] Within the scope of the invention, flue gas is understood to be the mixture of gaseous combustion products (exhaust gas) and solids produced during the combustion of fuels. Furthermore, the flue gas may also include liquid components. For example, flue gas can consist of a mixture of the gases nitrogen (N2), carbon dioxide (CO2), sulfur dioxide (SO2), nitric oxide (NO), and the solid particles fly ash and soot.

[0017] Nitrogen oxides is a collective term for numerous gaseous oxides of nitrogen that can be present in flue gas. Examples of nitrogen oxides include NO, NO₂, N₂O₃, and N₂O₄. Because nitrogen oxides can have adverse effects on humans and the environment, their concentration in flue gas is reduced through flue gas denitrification.

[0018] In the selective catalytic reduction (SCR) of nitrogen oxides, the nitrogen oxides are selectively reduced at the catalyst using a reducing agent. The products of the reaction are water (H₂O) and nitrogen (N₂). Undesired side reactions, such as the oxidation of sulfur dioxide to sulfur trioxide, are largely suppressed.

[0019] Ammonia (NH3) or an ammonia precursor is typically used as the reducing agent in SCR. Within the scope of the invention, ammonia precursors are understood to be chemical compounds that decompose to ammonia in the flue gas stream. For example, urea ((NH2)2CO), ammonium sulfate ((NH4)2SO4), and / or cyanuric acid (C3H3N3O3) can be used as ammonia precursors.

[0020] The catalyst produced in process step b) comprises nanoparticles. For the purposes of this invention, nanoparticles are defined as particles in the size range of 5 nm to 50 nm. The nanoparticles can exhibit a broad or narrow distribution of different sizes. Furthermore, the catalyst may consist of composite nanoparticles, i.e., particles composed of several components, at least one of which is nanoscale.

[0021] According to a preferred embodiment of the invention, the method additionally comprises the following process steps: f) Separation of the catalyst from the flue gas stream by means of a surface filter, and g) Reducing the concentration of nitrogen oxides in the flue gas stream by means of a second SCR using the catalyst on the surface filter and the reducing agent in the flue gas stream.

[0022] These additional process steps offer several advantages. By separating the catalyst in process step f), its release into the environment is prevented. This makes the process environmentally friendly. The catalyst deposited in the surface filter and / or filter cake also exhibits high catalytic activity. Therefore, in process step g), a second SCR further reduces the nitrogen oxide concentration in the flue gas stream. This makes the process particularly effective at denitrification of the flue gas stream.

[0023] Preferably, process step f) also includes the separation of solids from the flue gas stream using the surface filter. The solids contained in the flue gas stream, particularly dust and soot, are thus retained in the surface filter, resulting in the cleaning of the flue gas stream. The solids from the flue gas stream preferably precipitate together with the catalyst on the surface of the filter medium or on the surface of the filter cake that forms thereon. To separate even the smallest particles and to prevent irreversible clogging of the surface filter, a thin (approx. 1 mm) layer of a filter aid (e.g., hydrated lime powder) is applied to the surface filter. Furthermore, if hydrated lime is used as a filter aid, acidic pollutants from the raw gas can also be bound. This step is essentially equivalent to the dedusting of the flue gas.The combined denitrification and dust removal of the flue gas stream results in a particularly cost-effective process.

[0024] In principle, any type of surface filter, also called a fabric filter, can be used. However, a bag filter is preferred. A bag filter is a filter in which the filter medium is formed into a tube. Bag filters have become established as separators in numerous industrial processes, such as gas purification and dust collection, so that the use of a bag filter makes it particularly easy to implement process steps f) and g) into existing processes.

[0025] By combining denitrification and dust removal, and through its easy integration into existing systems, this process is particularly suitable for use in combustion plants fueled by biogenic residues and waste materials with a thermal output of up to 5 MW. Existing reduction processes for individual pollutants used in power plants are not always economically viable for decentralized biomass plants. Combining denitrification and dust removal in a single compact module reduces investment and operating costs, thus enabling cost-effective use in small and medium-sized plants.

[0026] According to a preferred further development of the process, process steps a) to g) are carried out continuously. Continuous execution of the process steps results in the process running essentially without interruption. A continuous process has the advantage over a discontinuous process (batch process) of being more economical, since the downtimes typical of batch processes for cleaning and refilling are eliminated. Thus, the continuous execution of process steps a) to g) results in high productivity due to reduced downtime.

[0027] In principle, various catalysts can be used for the SCR of nitrogen oxides, for example the metal oxides V₂O₅, MoO₃ and / or TiO₂. However, according to a preferred embodiment of the invention, process step b) involves the production of a metal oxide M x Oy The group M comprises metals from the group {iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu)}. These metals have the advantage of being relatively inexpensive, making the process very economical. Due to the freshly produced metal oxides and their relatively short lifespan, catalyst poisoning is not a significant factor in the process. Therefore, the process exhibits a very high efficiency.

[0028] In connection with the production of the catalyst, process step a) includes the provision of a liquid catalyst precursor. Liquids are very easy to dose and transport and therefore offer advantages over solids in terms of handling. This makes the process particularly easy to implement. Possible liquid catalyst precursors include, for example, acetylacetonates, naphthenates, and / or propionates of the metals M, where M = {iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu)}, dissolved in a solvent. Preferably, the liquid catalyst precursor is flammable. A flammable solvent such as xylene or ethanol is used. Alternatively, iron pentacarbonyl (Fe(CO)₅), which is a liquid under standard conditions and is also flammable, is used as the catalyst precursor.

[0029] With regard to the simplified handling of the liquid catalyst precursor, a preferred embodiment of the invention provides that in process step b) the supply of the catalyst precursor to the support combustion reaction comprises enriching a carrier gas stream with vapor of the catalyst precursor or atomizing the catalyst precursor in a carrier gas stream.

[0030] In the first variant, the liquid catalyst precursor is supplied to the propagation combustion reaction by enriching a carrier gas stream with the catalyst precursor vapor. For example, in a bubbler system, the carrier gas stream can be passed through the liquid, preferably temperature-controlled, catalyst precursor, after which a mixture of introduced carrier gas and vaporized catalyst precursor exits the bubbler system. An inert gas, such as argon and / or nitrogen, can be used as the carrier gas. Alternatively or additionally, hydrogen, air, a flammable gas, and / or a gas mixture can also be used as the carrier gas.

[0031] In the second variant, the liquid catalyst precursor is introduced into the auxiliary combustion reaction by atomizing it in the carrier gas stream. The carrier gas stream then contains minute droplets of the liquid catalyst precursor. An atomizing nozzle can be used for this purpose. An inert gas can also be used as the carrier gas, or alternatively or additionally, air, a flammable gas, and / or a gas mixture.

[0032] In this respect, a preferred embodiment of the invention provides that the production of the catalyst in process step b) comprises flame synthesis and / or a pyrolysis process. Flame synthesis is an established process in which gaseous or liquid starting materials (catalyst precursors) are converted into nanoparticles. Compared to wet synthesis of the nanoparticles, this type of production has the advantage of being a continuous process with a significantly shorter process chain. For example, the steps of solid-liquid separation, purification, and drying of the produced nanoparticles are eliminated. Furthermore, flame synthesis and / or the pyrolysis process is more environmentally friendly, as no wastewater requiring treatment is generated. In particular, the auxiliary combustion reaction is used to produce the catalyst.By atomizing the catalyst precursor, even catalyst precursors that are difficult to vaporize can be used in flame synthesis and / or pyrolysis processes, since a flammable gas can be used as the carrier gas stream. Furthermore, flame synthesis and / or pyrolysis processes result in particularly pure nanoparticles, giving the produced catalyst a particularly high activity.

[0033] In a preferred embodiment of the invention, it is provided that process step e) comprises a reduction of the concentration of nitrogen oxides in the flue gas stream by means of a first SCR using the catalyst and the reducing agent in the flue gas stream at a flue gas stream temperature of T ≤ 200 °C.

[0034] In this context, according to a preferred embodiment of the invention, it is also provided that process step g) comprises a reduction of the concentration of nitrogen oxides in the flue gas stream by means of a second SCR by means of the catalyst on the surface filter and by means of the reducing agent in the flue gas stream at a flue gas stream temperature of T ≤ 200 °C.

[0035] The flue gas stream for the first and / or second SCR stage therefore has a temperature of T ≤ 200 °C. This low temperature has the advantage that, if the combustion waste heat is recovered upstream of the denitrification stage, a large amount of heat is available for thermal utilization. The process is thus very cost-effective and economical. Furthermore, this makes the process very flexible, as an efficient reduction of the nitrogen oxide concentration in the flue gas can also be carried out after dust removal, for example. The temperature reduction of the flue gas stream necessary for operating the dust removal system does not need to be compensated for by reheating the flue gas stream, as is the case with conventional processes. The low temperature thus leads to a particularly flexible, economical, and environmentally friendly process, as costs and energy for reheating the flue gas stream are saved.

[0036] Furthermore, according to the invention, a device is provided for carrying out the above method, comprising a discharge pipeline for conveying a flue gas stream from a combustion reaction, a catalyst precursor supply system for supplying a liquid catalyst precursor to a supplementary combustion reaction, and a catalyst production system for producing the catalyst from the liquid catalyst precursor, wherein the catalyst production system includes the supplementary combustion reaction. The device according to the invention thus comprises a discharge pipeline through which the flue gas stream is conveyed. The discharge pipeline can, for example, be a chimney or flue of an industrial plant. Furthermore, the device comprises the catalyst precursor supply system by means of which the catalyst precursor can be supplied to the supplementary combustion reaction.The catalyst precursor supply system includes, for example, a bubbler system to enrich a carrier gas stream with vapor of the catalyst precursor. Furthermore, the device includes the catalyst production system, which comprises the auxiliary combustion reaction by which the catalyst is produced from the catalyst precursor.

[0037] The invention is explained below by way of example with reference to the drawings and a preferred embodiment.

[0038] The drawing shows Fig. 1 a flowchart showing the steps of the method for reducing the concentration of nitrogen oxides in a flue gas stream according to a preferred embodiment of the invention, Fig. 2 a process flow diagram of the procedure from Fig. 1 and a device for carrying out the method, according to a preferred embodiment of the invention, wherein a first variant of the implementation of method step b) is shown, and Fig. 3 a process flow diagram of the procedure from Fig. 1 and a device for carrying out the method, according to a preferred embodiment of the invention, wherein a second variant of the implementation of method step b) is shown.

[0039] Fig. Figure 1 shows a flow diagram with the process steps a) to g) of the process for reducing the concentration of nitrogen oxides 10 of a flue gas stream 12, according to a preferred embodiment of the invention.

[0040] In process step a), a catalyst precursor 14 is provided, which in the preferred embodiment is a liquid catalyst precursor 14. Possible liquid catalyst precursors 14 include, for example, acetylacetonates, naphthenates, and / or propionates of the metals iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), or copper (Cu) dissolved in a flammable solvent such as xylene or ethanol. Alternatively, iron pentacarbonyl (Fe(CO)5), which exists as a liquid under standard conditions, can be used as the catalyst precursor 14.

[0041] In process step b), a catalyst 16 is produced from the catalyst precursor 14 by flame synthesis. The synthesized catalyst 16 comprises nanoparticles, wherein, in process step b), a metal oxide M is added, depending on the chosen catalyst precursor 14. x O yfrom the group M = {iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu)}. The production of catalyst 16 is achieved by feeding the catalyst precursor 14 into a propagation combustion reaction 20, for example, a gas burner flame. In the process flow diagrams in the Fig. 2 and Fig. Two variants are shown (bubbler system variant and spray flame variant).

[0042] In the directly subsequent process step c), the produced catalyst 16 is fed into the flue gas stream 12.

[0043] In process step d) a reducing agent 22 is added to the flue gas stream 12; in the preferred embodiment here, this is ammonia.

[0044] In principle, process step d) can also be carried out before or during process steps a) to c). However, all four process steps a) to d) must have been carried out before process step e), the reduction of the concentration of nitrogen oxides 10 in the flue gas stream 12 by a first SCR using the catalyst 16 and the reducing agent 22 in the flue gas stream 12, takes place. The catalyst 16 is located in the flue gas stream 12 during process step e), meaning that the nanoparticles move along with the nitrogen oxides 10 and the reducing agent 22 in the flue gas stream 12.

[0045] In the further process step f), the catalyst 16 is separated together with the solids 24 of the flue gas stream 12 by means of a surface filter 26.

[0046] The catalyst 16 deposited in the surface filter 26 and / or filter cake continues to exhibit high catalytic activity, so that in the further process step g) the concentration of nitrogen oxides 10 in the flue gas stream 12 is further reduced by a second SCR.

[0047] In the preferred embodiment, process steps a) to g) are carried out continuously, so that the process is a continuous process. Furthermore, in the preferred embodiment, the flue gas stream 12 has a temperature of T ≤ 200 °C. The reduction of the concentration of nitrogen oxides 10 in the flue gas stream 12 in process steps e) and g) therefore takes place at a temperature of T ≤ 200 °C.

[0048] Fig. Figure 2 shows a process flow diagram of the method and a device 44 for carrying out the method, according to a preferred embodiment of the invention, wherein a first implementation variant – the bubbler system variant – of process step b) is shown. In the process flow diagram, a biomass combustion plant 18 is shown as the combustion reaction 18, the flue gas stream 12 of which is fed to a discharge pipe 30 via a first fan 28. Ammonia 22 is continuously supplied to this discharge pipe 30 and thus to the flue gas stream 12 as a reducing agent 22, which mixes with the flue gas stream 12 (process step d)).

[0049] In Fig. Figure 2 further shows that the device 44 according to the invention for carrying out the process comprises a catalyst precursor supply system 46 and a catalyst production system 48. The catalyst precursor 14 is supplied to the catalyst production system 48 by means of the catalyst precursor supply system 46. In the embodiment shown here, the catalyst production system 48 comprises the auxiliary combustion reaction 20, by which the catalyst 16 is produced from the catalyst precursor 14 by flame synthesis.

[0050] In a bubbler system 32, which is part of the catalyst precursor supply system 46, the catalyst precursor 14 is provided (process step a)). In process step b), the catalyst 16 is produced from this catalyst precursor 14. The catalyst precursor 14, here iron pentacarbonyl (Fe(CO)5) 14, is present as a liquid in the bubbler system 32. A carrier gas stream 34, here an air stream, is passed through the liquid iron pentacarbonyl 14 via the bubbler system 32, thereby enriching the carrier gas stream 34 with vapor of the catalyst precursor 14. The degree to which the carrier gas 34 is enriched with vapor of the catalyst precursor 14 can be controlled by adjusting the temperature of the liquid iron pentacarbonyl 14 and the flow rate of the carrier gas stream 34. The enriched carrier gas 34 and thus the catalyst precursor 14 is transported to the support combustion reaction 20 via a feed line 36.Essentially, where the supply pipe 36 meets the discharge pipe 30, the auxiliary combustion reaction 20 is located, in this case a propane gas flame 20. In the auxiliary combustion reaction 20, the flame synthesis of the catalyst 16 takes place, whereby the corresponding metal oxides, in this embodiment iron oxides, Fe. x O y, in nanoparticle form. The catalyst precursor 14 is added radially or axially to the propane flame 20, thereby synthesizing nanoscale catalyst particles online. The produced catalyst 16 is fed to the flue gas stream 12 via the carrier gas stream 34 and / or the suction of the flue gas stream 12 (process step c)), where it mixes with the nitrogen oxide 10 and the reducing agent 22. The first SCR then takes place in the discharge pipe 30, in the sense of an entrained flow reaction (process step e)), whereby the concentration of the nitrogen oxides 10 in the flue gas stream 12 is reduced.

[0051] Fig. Figure 3 shows the second variant of the implementation of process step b), namely the spray flame variant. Also in Fig. Figure 3 shows a biomass combustion process 18, the flue gas stream of which is fed to the discharge pipe 30 via the first fan 28. Ammonia 22 is continuously supplied to this discharge pipe 30 as a reducing agent 22, which mixes with the flue gas stream 12 (process step d)).

[0052] In the spray flame variant, the liquid catalyst precursor 14 is supplied to the auxiliary combustion reaction 20 by atomizing it in the carrier gas stream 34. For this purpose, the catalyst precursor 14, in this embodiment ferrous acetylacetonate dissolved in xylene, is supplied to a nozzle 40 by means of a pump 38. The carrier gas stream 34 then contains minute droplets of the liquid catalyst precursor 14. This aerosol stream of carrier gas 34 and liquid droplets of the catalyst precursor 14 is transported to the auxiliary combustion reaction 20 via the supply line 36. Essentially, the auxiliary combustion reaction 20 is located where the supply pipe 36 meets the discharge pipe 30. In principle, the aerosol stream consisting of carrier gas 34 and liquid catalyst precursor 14 can burn independently after ignition by the auxiliary combustion reaction 20.However, it is shown here that the flame of the support combustion reaction 20 surrounds the aerosol stream and thus combusts. The flame synthesis of the catalyst 16 takes place in the flame, producing iron oxides, Fe. x O y , in nanoparticle form. The produced catalyst 16 is fed into the flue gas stream 12 via the carrier gas stream 34 and / or the suction of the flue gas stream 12 (process step c)), where it mixes with the nitrogen oxides 10 and the reducing agent 22. The first SCR then takes place in the discharge pipe 30, in the sense of an entrained flow reaction (process step e)), whereby the concentration of the nitrogen oxides 10 is reduced.

[0053] Fig. 2 and Fig.Figure 3 shows that a surface filter 26, in this case a bag filter 26, is located in the region of the rear end of the discharge pipe 30. This filter removes the solids 24 from the flue gas stream 12 together with the catalyst 16. The solids 24 from the flue gas stream 12, along with the catalyst 16, are deposited on the surface of the filter medium or on the surface of the filter cake that forms on it. Here, the concentration of nitrogen oxides 10 in the flue gas stream 12 is also reduced by the second SCR (process step g)). To compensate for the pressure drop during filtration and to maintain good filter performance, a second fan 42 is located downstream of the bag filter 26. This fan conveys the denitrified and dust-free flue gas stream 12, which is generally referred to as the exhaust air stream after dust removal. Reference symbol list 10 Nitrogen oxides 12 Flue gas flow 14 Catalyst precursors, iron pentacarbonyl, iron acetylacetonate in xylene 16 Catalyst 18 Combustion reaction, biomass combustion 20 Support combustion reaction, propane flame 22 Reducing agent, ammonia 24 solids in the flue gas stream 26 surface filters, bag filters 28 first fan 30 Drainage pipe 32 Bubbler System 34 Carrier gas flow 36 Supply pipe 38 Pump 40 nozzle 42 second fan 44 Device 46 Catalyst precursor feeding system 48 Catalyst manufacturing system

Claims

[1] Method for reducing the concentration of nitrogen oxides (10) of a flue gas stream (12) of a combustion reaction (18) by selective catalytic reduction, SCR, comprising the following process steps: a) Providing a liquid catalyst precursor (14), b) Producing a catalyst (16) from the catalyst precursor (14), wherein the produced catalyst (16) comprises nanoparticles, c) Feeding the produced catalyst (16) into the flue gas stream (12), d) Adding ammonia (22), NH3 or an ammonia precursor to the flue gas stream (12) as a reducing agent (22) and e) Reducing the concentration of nitrogen oxides (10) in the flue gas stream (12) by means of a first SCR using the catalyst (16) and the reducing agent (22) in the flue gas stream (12), wherein the liquid catalyst precursor (14) comprises a metal dissolved in a flammable solvent, wherein the metal is selected from the group comprising iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni) and copper (Cu), or wherein the liquid catalyst precursor (14) is iron pentacarbonyl (Fe(CO)5), and wherein process step b) comprises supplying the catalyst precursor (14) to a support combustion reaction (20) located in the flue gas stream (12). [2] Method according to claim 1 characterized by , that the procedure additionally includes the following procedural steps: f) Separation of the catalyst (16) from the flue gas stream (12) by means of a surface filter (26), and g) Reducing the concentration of nitrogen oxides (10) in the flue gas stream (12) by means of a second SCR using the catalyst (16) on the surface filter (26) and using the reducing agent (22) in the flue gas stream (12). [3] Method according to claim 2 characterized by that the process steps a) to g) are carried out continuously. [4] Method according to any of the preceding claims characterized by , that process step b) is the production of a metal oxide M x O y from the group M = {Iron (Fe), Manganese (Mn), Cobalt (Co), Nickel (Ni), Copper (Cu)}. [5] Method according to claim 4 characterized by , that in process step b) the supply of the catalyst precursor (14) to the support combustion reaction (20) includes enriching a carrier gas stream (34) with vapor of the catalyst precursor (14) or atomizing the catalyst precursor (14) in a carrier gas stream (34). [6] Method according to any of the preceding claims characterized by , that the production of the catalyst (16) in process step b) includes a flame synthesis and / or a pyrolysis process. [7] Method according to any of the preceding claims characterized by, that process step e) comprises a reduction of the concentration of nitrogen oxides (10) in the flue gas stream (12) by means of a first SCR using the catalyst (16) and the reducing agent (22) in the flue gas stream (12) at a flue gas stream temperature (12) of T ≤ 200 °C. [8] Method according to claim 2 characterized by , that process step g) comprises a reduction of the concentration of nitrogen oxides (10) in the flue gas stream (12) by means of a second SCR by means of the catalyst (16) on the surface filter (26) and by means of the reducing agent (22) in the flue gas stream (12) at a temperature of the flue gas stream (12) of T < 200 °C. [9] Device (44) configured for carrying out the method according to any one of claims 1 to 8, comprising a discharge pipeline (30) for passing a flue gas stream (12) through a combustion reaction (18), a catalyst precursor supply system (46) for supplying a liquid catalyst precursor (14) to a support combustion reaction (20), and a catalyst production system (48) for producing the catalyst (16) from the liquid catalyst precursor (14), wherein the catalyst production system (48) comprises the support combustion reaction (20) located in the flue gas stream (12).

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