Reducing agent injection device

Abstract

Invention details;

Description

Reductant injection device

[0001] The present disclosure relates to a reductant injection device.

[0002] In a heat recovery steam generator (HRSG), exhaust gas discharged from a gas turbine or the like passes through a duct (flue) and exchanges heat between the exhaust gas and water or steam in heat transfer tubes, thereby generating steam. Inside the duct of the heat recovery steam generator, there are installed a plurality of heat exchangers each having a large number of heat transfer tubes through which water or steam flows, and a denitrification device that removes (denitrifies) nitrogen oxides (NOx) from the exhaust gas.

[0003] A denitration system, for example, injects a reducing agent (e.g., ammonia or urea water) that reduces nitrogen oxides into exhaust gas flowing through a duct from multiple injection nozzles. The denitration system then removes nitrogen oxides from the exhaust gas by passing the exhaust gas, into which the reducing agent has been injected, through a reactor (e.g., a denitration catalyst). Multiple injection nozzles for injecting the reducing agent are attached at predetermined intervals to a mother pipe installed in a flue through which the exhaust gas flows. A supply pipe is connected to the mother pipe via a header or the like, and the reducing agent is supplied to the mother pipe via the header and the supply pipe. To ensure uniform injection rates from each injection nozzle, it is desirable to maintain the temperature of the reducing agent within the mother pipe. Therefore, a header and a supply pipe may be installed within the flue, and the reducing agent supplied to the mother pipe may be sufficiently heated within the supply pipe (see, for example, Patent Document 1). Patent Document 1 describes an apparatus for supplying ammonia-diluted gas to a nozzle mother pipe that injects the ammonia-diluted gas into the exhaust gas via an ammonia supply pipe installed within an exhaust gas duct.

[0004] Japanese Patent Application Publication No. 6-134259

[0005] When an ammonia supply pipe or a header is disposed in a flue gas duct, the flow velocity of part of the exhaust gas flowing through the flue gas duct is slowed by the influence of the ammonia supply pipe. As a result, a region (wake) where the flow velocity is slower than other regions is generated downstream of the ammonia supply pipe. Therefore, when an ammonia supply pipe or the like is installed upstream of a main pipe as in Patent Document 1, part of the ammonia injected from an injection nozzle provided on the main pipe is injected into the wake. This may cause variations in the ammonia concentration in the exhaust gas flowing through the duct. If variations in the injected ammonia concentration occur, ammonia may not reach a reactor provided downstream of the main pipe uniformly, and nitrogen oxides in the exhaust gas may not be suitably removed in the reactor.

[0006] In the flue gas duct, downstream of the main pipe, Kármán vortices are generated, which have the effect of diffusing the ammonia injected from the injection nozzle. However, if an ammonia supply pipe or the like is installed downstream of the main pipe and near the main pipe, the development of the Kármán vortices is hindered by the ammonia supply pipe or the like. As a result, it becomes difficult for the Kármán vortices to develop downstream of the main pipe, and there is a possibility that the diffusion of ammonia is suppressed. The suppression of the diffusion of ammonia may cause variations in the ammonia concentration in the exhaust gas flowing through the duct. Therefore, there is a possibility that the ammonia may not reach the reactor uniformly, and the nitrogen oxides in the exhaust gas may not be suitably removed in the reactor.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a reducing agent injection device that can homogenize the concentration of a reducing agent in gas flowing through a duct.

[0008] In order to solve the above problems, the reducing agent injection device of the present disclosure employs the following means: A reducing agent injection device according to one aspect of the present disclosure is a reducing agent injection device that injects a reducing agent having an effect of reducing nitrogen oxides contained in a gas flowing through a duct, and includes a plurality of injection units that inject the reducing agent into the gas flowing through the duct, a plurality of mother pipes that are provided with the plurality of injection units and through which the reducing agent flows, and a supply unit that is provided within the duct downstream of the mother pipe in the gas flow and that supplies the reducing agent to the plurality of mother pipes, wherein the distance from the mother pipe to the supply unit is greater than three times the outer diameter of the mother pipe.

[0009] According to the present disclosure, the concentration of the reducing agent in the gas flowing through the duct can be made uniform.

[0010] Fig. 3 is a schematic configuration diagram showing a heat recovery boiler according to an embodiment of the present disclosure. Fig. 4 is a schematic configuration diagram showing a denitration device according to an embodiment of the present disclosure. Fig. 5 is a schematic horizontal cross-sectional view showing an ammonia injection unit according to an embodiment of the present disclosure. Fig. 6 is a cross-sectional view taken along the arrows IV-IV in Fig. 3. Fig. 7 is a diagram showing the distribution of ammonia in an ammonia injection unit according to an embodiment of the present disclosure. Fig. 8 is a diagram showing the distribution of ammonia in an ammonia injection unit according to a comparative example of the present disclosure.

[0011] A denitration device according to an embodiment of the present disclosure will be described below with reference to Figures 1 to 6. In the following description and drawings, the vertical direction is referred to as the Z-axis direction, the horizontal direction in which exhaust gas flows is referred to as the X-axis direction, and the direction perpendicular to the X-axis direction and the Z-axis direction is referred to as the Y-axis direction. The flow direction of exhaust gas is indicated by arrow E in Figures 2 to 6.

[0012] First, a heat recovery steam generator 2 according to this embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the heat recovery steam generator 2 according to this embodiment is a horizontal type in which exhaust gas flows in an X-axis direction (a predetermined direction). In this embodiment, the X-axis direction, which is the direction in which exhaust gas flows, is set to the horizontal direction.

[0013] The heat recovery boiler 2 according to this embodiment includes a duct 3 extending in the X-axis direction and through which exhaust gas flows, a denitration device 10 provided inside the duct 3 for removing nitrogen oxides (NOx) contained in the exhaust gas, and a first heat exchange section 4 and a second heat exchange section 5 provided inside the duct 3.

[0014] The first heat exchange unit 4 and the second heat exchange unit 5 have a plurality of heat transfer tubes (not shown) extending in a direction intersecting the flow direction of the exhaust gas. The first heat exchange unit 4 and the second heat exchange unit 5 recover heat from the exhaust gas by heat exchange between the exhaust gas and a heat medium (e.g., water or steam) flowing inside the heat transfer tubes. The first heat exchange unit 4 is provided upstream of the denitration device 10. The first heat exchange unit 4 may be, for example, a superheater that superheats the heat medium flowing inside the heat transfer tubes. The second heat exchange unit 5 is provided downstream of the denitration device 10. The second heat exchange unit 5 may be, for example, an evaporator that evaporates the heat medium flowing inside the heat transfer tubes.

[0015] The high-temperature combustion exhaust gas (exhaust gas) discharged from the combustion engine 1 is introduced into the duct 3 from the inlet thereof, passes through the first heat exchange section 4, the denitration device 10 and the second heat exchange section 5 in sequence, and is then discharged from the chimney 7 via the outlet of the duct 3.

[0016] Next, the denitration device 10 will be described in detail with reference to FIGS. 1 to 5 . The denitration device 10 supplies a reducing agent (ammonia, urea water, etc.) that has the effect of reducing nitrogen oxides to exhaust gas flowing through a duct 3, and promotes a reaction between the nitrogen oxides (NOx) in the exhaust gas to which the reducing agent has been supplied and the reducing agent through the catalytic action of a denitration catalyst 40, thereby removing and reducing the nitrogen oxides in the exhaust gas. In the following description, an example will be described in which ammonia gas is used as the reducing agent. Note that the reducing agent according to the present disclosure is not limited to ammonia gas. For example, the reducing agent may be liquid ammonia or a substance other than ammonia.

[0017] As shown in FIGS. 1 and 2 , the denitration device 10 includes an ammonia injection section (reducing agent injection device) 20, a mixer 30, a denitration catalyst 40, and an ammonia decomposition catalyst 50, which are arranged in this order from the upstream side of the exhaust gas flow in a duct 3.

[0018] The ammonia injection unit 20 injects ammonia gas into the exhaust gas flowing through the duct 3 by injecting the ammonia gas from a plurality of injection nozzles 21 along the X-axis direction into the duct 3. The ammonia injection unit 20 will be described in detail later.

[0019] The mixer 30 is disposed so as to cover substantially the entire cross section of the flow path of the duct 3. The ammonia gas injected from the ammonia injection unit 20 and the exhaust gas flow into the mixer 30. The mixer 30 forms a swirling flow that swirls around a central axis extending in the X-axis direction. The exhaust gas (more specifically, the exhaust gas into which ammonia has been injected) that has passed through the mixer 30 becomes one or more swirling flows and circulates in the space downstream of the mixer 30. In this way, the mixer 30 mixes the exhaust gas and ammonia flowing through the duct 3 by forming a swirling flow.

[0020] The denitration catalyst 40 is disposed so as to cover substantially the entire cross section of the flow path of the duct 3. The denitration catalyst 40 has, for example, a rectangular cylindrical frame (not shown) and a plurality of catalysts (not shown) disposed inside the rectangular frame. Examples of the catalyst shape include, but are not limited to, a honeycomb shape or a corrugated plate shape that allows exhaust gas to pass in the X-axis direction. The catalyst promotes a reduction reaction of NOx (nitrogen oxides) contained in the exhaust gas (combustion exhaust gas) passing through the catalyst, thereby removing at least a portion of the NOx. The catalyst component is, for example, based on titanium oxide.

[0021] The ammonia decomposition catalyst 50 is disposed so as to cover substantially the entire cross section of the flow path of the duct 3. The ammonia decomposition catalyst 50 removes ammonia from the exhaust gas by decomposing the ammonia contained in the exhaust gas. In this embodiment, the ammonia decomposition catalyst 50 is provided downstream of the denitration catalyst 40, so that ammonia in the exhaust gas that has not completely reacted in the denitration catalyst 40 can be decomposed by the ammonia decomposition catalyst 50.

[0022] Next, details of the ammonia injection section 20 will be described with reference to Figures 3 and 4. Figure 3 is a top view of the ammonia injection section 20. Figure 4 is a vertical cross-sectional view of the ammonia injection section 20. In detail, Figure 4 is a cross-sectional view taken along the line IV-IV in Figure 3.

[0023] As shown in Figures 3 and 4, the ammonia injection section 20 has a plurality of injection nozzles (injection sections) 21 that inject ammonia gas, a plurality of main pipes 22 that are provided with the injection nozzles 21 and extend in the Y-axis direction, and a supply section 27 that supplies ammonia gas to the main pipes 22.

[0024] The multiple injection nozzles 21 are arranged side by side at predetermined intervals along the extension direction of the mother pipe 22 (i.e., the Y-axis direction). The injection nozzles 21 are provided on the surface of the mother pipe 22 on the downstream side in the exhaust gas flow. The injection nozzles 21 may be holes formed on the side surface of the mother pipe 22. The injection nozzles 21 inject ammonia gas at a predetermined injection pressure. Specifically, the injection nozzles 21 inject ammonia gas toward the downstream side in the exhaust gas flow. The diameter of the injection hole of the injection nozzle 21 is, for example, 3 mm to 6 mm. The injection nozzle 21 injects ammonia gas in a conical shape. Note that the above-described diameter of the injection hole of the injection nozzle 21 and the injection pattern are merely examples and are not limited to these.

[0025] The header pipe 22 extends along the Y-axis direction. Ammonia gas flows through the header pipe 22. The header pipe 22 has a circular tubular shape. The header pipe 22 has an outer diameter d of a predetermined length. A connecting pipe 24 is connected to the header pipe 22. A plurality of header pipes 22 are provided. The plurality of header pipes 22 are arranged side by side at predetermined intervals along the Z-axis direction, as shown in FIG. 4 .

[0026] 3 and 4 , the supply unit 27 is provided in the duct 3 on the downstream side of the gas flow of the header pipes 22, and supplies the reducing agent to the plurality of header pipes 22. The supply unit 27 has a header 23 connected to the plurality of header pipes 22, a connecting pipe 24 connecting the header pipe 22 and the header 23, and a supply pipe 25 that supplies ammonia gas to the header 23 from the outside.

[0027] The header 23 is provided downstream of the header pipe 22 in the exhaust gas flow. As shown in Fig. 4, the header 23 extends along the Z-axis direction. A connecting pipe 24 is connected to the header 23. A plurality of header pipes 22 are connected to the header 23 via the connecting pipe 24. A plurality of headers 23 are provided. The plurality of headers 23 are arranged side by side at predetermined intervals along the Y-axis direction. Note that, for convenience of illustration, only one header 23 is shown in Figs. 3 and 4. One supply pipe 25 is connected to each header 23.

[0028] The distance D from the main pipe 22 to the header 23 is set to be longer than three times the outer diameter d of the main pipe 22. That is, the following equation (1) holds. Note that the distance D may be the shortest distance from the downstream end of the main pipe 22 to the central axis of the header 23.

[0029] D>3d...(1)

[0030] The connecting pipe 24 is provided downstream of the header pipe 22 in the flow of exhaust gas. The connecting pipe 24 extends along the X-axis direction. The connecting pipe 24 connects the header pipe 22 and the header 23. A plurality of connecting pipes 24 are provided. The plurality of connecting pipes 24 are arranged side by side at predetermined intervals along the Z-axis direction.

[0031] The supply pipes 25 are provided downstream of the headers 23. Ammonia gas flows through the supply pipes 25. The supply pipes 25 guide ammonia gas supplied from an ammonia gas supply unit (not shown) provided outside the duct 3 to the headers 23. The upstream ends of the supply pipes 25 are connected to the ammonia gas supply unit. The downstream ends of the supply pipes 25 are connected to the downstream surface of the headers 23. The downstream ends of the supply pipes 25 are connected to approximately the center of the headers 23 in the Z-axis direction. The overall length of each supply pipe 25 is set so that the ammonia gas flowing through the supply pipes 25 exchanges heat with the exhaust gas flowing outside the supply pipes 25, thereby raising the temperature of the ammonia gas to approximately the same temperature as the exhaust gas.

[0032] A plurality of supply pipes 25 are provided. For illustrative purposes, only one supply pipe 25 is shown in Figures 3 and 4. The entire lengths of the supply pipes 25 are approximately the same. Each of the supply pipes 25 is connected to a header 23. There is a one-to-one correspondence between the supply pipes 25 and the headers 23.

[0033] Next, the flow of ammonia gas in the ammonia injection section 20 according to this embodiment will be described. An ammonia gas supply unit provided outside the duct 3 introduces ammonia gas into the supply pipe 25. The ammonia gas introduced into the supply pipe 25 flows through the supply pipe 25. At this time, the ammonia gas exchanges heat with the exhaust gas flowing outside the supply pipe 25, thereby raising its temperature to approximately the same as that of the exhaust gas. The ammonia gas that has flowed through the supply pipe 25 is introduced into the header 23. The ammonia gas introduced into the header 23 flows through the header 23 and is distributed to each header pipe 22 via the connecting pipes 24. The ammonia gas introduced into the header 22 flows through the header 22 and is injected into the duct 3 from each injection nozzle. Note that the ammonia gas has been sufficiently heated in the supply pipe 25 and the header 23, so that there is almost no temperature change while flowing through the header 22.

[0034] According to this embodiment, the following advantageous effects are achieved. In this embodiment, the header 23 and the supply pipe 25 are provided downstream of the main pipe 22. That is, the main pipe 22 is provided upstream of the header 23 and the supply pipe 25. This prevents the ammonia gas injected into the duct 3 from the injection nozzle 21 provided on the main pipe 22 from being affected by the wake (low flow velocity region) generated downstream of the header 23. Therefore, the flow velocity of the injected ammonia gas is made uniform, and the concentration of ammonia gas relative to the exhaust gas flowing through the duct 3 can be made uniform. This makes it possible to uniformize the ammonia gas that reaches the mixing section provided downstream of the ammonia injection section 20 and the denitration catalyst 40. This makes it possible to suitably remove nitrogen oxides from the exhaust gas in the denitration catalyst 40.

[0035] In the duct 3, Kármán vortices are generated downstream of the header 22 by the exhaust gas that has passed near the header 22. The Kármán vortices have the effect of diffusing ammonia gas injected from the header 22 into the exhaust gas flowing through the duct 3. On the other hand, when the distance between the header 23 and the header 23 is 3d or less, the header 23 inhibits the development of the Kármán vortices, preventing stable formation of the Kármán vortices. As a result, the Kármán vortices may not be stably formed in the downstream region where the header 23 is provided. On the other hand, in a region separated from the header 22 by a distance longer than three times the outer diameter of the header 22, a stable Kármán vortex street (linked vortex shedding) is formed. The formation of the Kármán vortices promotes the diffusion of ammonia. In this embodiment, the distance from the header 23 to the header 23 is set to be longer than three times the outer diameter of the header 22. That is, the distance between the header 23 and the header 23 is set to be longer than three times the outer diameter of the header 22. This suppresses the obstruction of Karman vortices by the header, making it easier for Karman vortices to form. Therefore, it is possible to diffuse the ammonia gas injected from the header pipe 22 into the exhaust gas flowing through the duct 3. This makes it possible to homogenize the concentration of ammonia gas in the exhaust gas flowing through the duct 3. Therefore, it is possible to effectively remove nitrogen oxides from the exhaust gas in the denitration catalyst 40.

[0036] The effect of the Karman vortex on the uniformity of ammonia gas concentration will be described in detail with reference to Figures 5 and 6. In Figures 5 and 6, points with equivalent ammonia concentrations are connected by lines. Also, the darker the black line, the higher the ammonia concentration.

[0037] 5 shows a state in which the main pipe 22 and the header 23 are arranged at a distance 12 times the outer diameter d of the main pipe 22. That is, in FIG. 5, the header 23 and the main pipe 22 are arranged so that the following formula (2) is satisfied.

[0038] D=12d...(2)

[0039] 5, when the header 23 is spaced a sufficient distance from the main pipe 22, Karman vortices are generated over substantially the entire area in the extension direction (Y-axis direction) of the main pipe 22 on the downstream side of the main pipe 22. Therefore, the exhaust gas and ammonia gas are mixed by the Karman vortices over substantially the entire area in the Y-axis direction, and the ammonia concentration in the exhaust gas is suitably uniformed as shown in FIG.

[0040] 5, the generated Karman vortices decay approximately uniformly in the Y-axis direction. This suppresses variations in the concentration of ammonia gas in the exhaust gas in the Y-axis direction of the header pipe 22. Furthermore, since the exhaust gas and ammonia gas pass near the header 23 in a state of being mixed to some extent, variations in the concentration of ammonia gas in the exhaust gas caused by the header 23 are suppressed.

[0041] In this way, when the main pipe 22 and the header 23 are spaced apart by a sufficient distance, it is possible to make uniform the concentration of ammonia gas in the exhaust gas flowing through the duct 3. Therefore, it is possible to suitably remove nitrogen oxides in the exhaust gas in the denitration catalyst 40. In other words, it is possible to improve the denitration efficiency in the denitration catalyst 40.

[0042] 6, the distance between the main pipe 22 and the header 23 is set to 3d or less. That is, the header 23 and the main pipe 22 are arranged so that the following formula (3) is satisfied:

[0043] D≦3d (3)

[0044] As shown in Figure 6, when the mother pipe 22 and the header 23 are not spaced apart by a sufficient distance, a flow of ammonia gas expands in the Y-axis direction around the header 23, and the ammonia gas injected from the injection nozzle 21 is divided by the header 23 before it can be sufficiently mixed with the exhaust gas.

[0045] Furthermore, the header 23 inhibits the generation of Karman vortices. Therefore, Karman vortices are less likely to be generated downstream of the header 23, and the diffusion of ammonia is suppressed. Therefore, as shown in Fig. 6, in the region where Karman vortices are not generated, the exhaust gas and ammonia gas are not mixed appropriately. This causes variations in the ammonia concentration.

[0046] In this way, if the mother pipe 22 and the header 23 are not spaced apart by a sufficient distance, variations occur in the concentration of ammonia gas in the exhaust gas flowing through the duct 3. Therefore, there is a possibility that the denitration efficiency of the denitration catalyst 40 will decrease.

[0047] Furthermore, in this embodiment, the supply pipe 25 is provided downstream of the header 23. That is, the distance from the header pipe 22 to the supply pipe 25 is also set to be longer than three times the outer diameter d of the header pipe 22. As a result, the supply pipe 25 does not hinder the generation of Karman vortices. Therefore, by providing both the header 23 and the supply pipe 25 at a position farther away from the header pipe 22 than 3d, it is possible to more effectively generate Karman vortices. Therefore, it is possible to more effectively diffuse the ammonia gas injected from the header pipe 22 into the exhaust gas flowing through the duct 3. Therefore, it is possible to more effectively uniform the concentration of ammonia gas in the exhaust gas flowing through the duct 3.

[0048] The present disclosure is not limited to the above-described embodiments and may be modified as appropriate without departing from the spirit and scope of the present disclosure. For example, in the above-described embodiments, an example in which a denitration device is provided in a horizontal duct in which exhaust gas flows horizontally has been described, but the present disclosure is not limited thereto. For example, the denitration device may be provided in a vertical duct in which exhaust gas flows vertically.

[0049] 5 has been described as an example in which the header 23 and the main pipe 22 are spaced apart by a distance 12 times the outer diameter d of the main pipe 22, but the present disclosure is not limited to this. The main pipe 22 and the header 23 may be spaced apart by a distance at which Karman vortices naturally disappear (a distance longer than three times the outer diameter of the main pipe 22).

[0050] The reducing agent injection device described in the above-described embodiments can be understood, for example, as follows: A reducing agent injection device (20) according to a first aspect of the present disclosure is a reducing agent injection device (20) that injects a reducing agent having an effect of reducing nitrogen oxides contained in a gas flowing through a duct (3), the reducing agent injection device (20) comprising: a plurality of injection sections (21) that inject the reducing agent into the gas flowing through the duct; a plurality of mother pipes (22) that are provided with the plurality of injection sections and through which the reducing agent flows; and a supply section (27) that is provided within the duct downstream of the mother pipe in the gas flow and that supplies the reducing agent to the plurality of mother pipes, the distance from the mother pipe to the supply section being longer than three times the outer diameter of the mother pipe.

[0051] In the above configuration, the supply unit is provided downstream of the main pipe. That is, the main pipe is provided upstream of the supply unit. This prevents the reducing agent injected from the injection unit provided in the main pipe from being affected by the wake (low flow velocity region) that occurs downstream of the supply unit. Therefore, the concentration of the reducing agent in the gas flowing through the duct can be made uniform.

[0052] Within the duct, Kármán vortices are generated downstream of the main pipe by gas that has passed near the main pipe. The Kármán vortices have the effect of diffusing the reducing agent injected from the main pipe into the gas flowing through the duct. On the other hand, when the distance between the main pipe and the supply section is 3d or less, the development of the Kármán vortices is inhibited by the supply section, and the Kármán vortices are not stably formed. As a result, the Kármán vortices may not be stably formed in the downstream region of the supply section. On the other hand, in a region separated from the main pipe by a distance greater than three times the outer diameter of the main pipe, a stable Kármán vortex street (linked vortex shedding) is formed. The formation of the Kármán vortices promotes the diffusion of the reducing agent.

[0053] In the above configuration, the distance from the mother pipe to the supply section is set to be longer than three times the outer diameter of the mother pipe. That is, the distance between the mother pipe and the supply section is set to be longer than three times. This suppresses the obstruction of Karman vortices by the header, making it easier for Karman vortices to form. Therefore, the reducing agent injected from the mother pipe can be diffused into the gas flowing through the duct. Therefore, the concentration of the reducing agent in the gas flowing through the duct can be made uniform.

[0054] A reducing agent injection device according to a second aspect of the present disclosure is the above-mentioned first aspect, wherein the supply section includes a header to which a plurality of the mother pipes are connected and which supplies reducing agent to the plurality of mother pipes, and a supply pipe which guides reducing agent from outside the duct to the header, and the distance from the mother pipe to the header and the supply pipe is longer than three times the outer diameter of the mother pipe.

[0055] In the above configuration, the distance from the main pipe to the header and the supply pipe is set to be longer than three times the outer diameter of the main pipe. By locating both the header and the supply pipe at a distance from the main pipe that is longer than three times the outer diameter of the main pipe, it is possible to more effectively generate and maintain Karman vortices. Therefore, it is possible to more effectively diffuse the reducing agent injected from the main pipe into the gas flowing through the duct. Therefore, it is possible to more effectively uniformize the concentration of the reducing agent in the gas flowing through the duct.

[0056] REFERENCE SIGNS LIST 1: Combustion engine 2: Exhaust heat recovery boiler 3: Duct 4: First heat exchange section 5: Second heat exchange section 7: Chimney 10: Denitrification device 20: Ammonia injection section (reducing agent injection device) 21: Injection nozzle (injection section) 22: Main pipe 23: Header 24: Connecting pipe 25: Supply pipe 27: Supply section 30: Mixer 40: Denitrification catalyst 50: Ammonia decomposition catalyst

Claims

DEPCT691. A reducing agent injection device constructed to inject the reducing agent into the gas flowing through the air duct. The reducing agent effectively reduces nitrogen oxides present in the gas. The reducing agent injection device comprises: a number of injection units constructed to inject the reducing agent into the gas flowing through the air duct; a number of header pipes where the number of injection units is provided at each section of the header pipe and the reducing agent flows within the header pipe; and a delivery unit provided within the air duct and at the end of the gas flow in the header pipe, constructed to deliver the reducing agent to a number of header pipes where the distance from each section of the header pipe to the delivery unit is greater than three times the outer diameter of each section of the header pipe.The reducing agent injection device under Claim 1, where the delivery unit contains a header and delivery pipes, where a number of header pipes are connected to the header, where the header is constructed to deliver the reducing agent to a number of header pipes, and where the delivery pipes are constructed to bring the reducing agent from outside the duct to the header, and where the distance between each number of header pipes to the header and the delivery pipe is greater than three times the outer diameter of each number of header pipes;

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