Denitrification unit

Abstract

This denitration device (10) is provided with: an ammonia injection unit (11) for injecting ammonia into an exhaust gas flowing through a duct (3); a mixer (12) which is provided on the downstream side of the ammonia injection unit (11) and mixes the exhaust gas with ammonia; and a denitration catalyst (13) which is provide on the downstream side of the mixer (12), applies resistance to the flow of a mixed fluid that is a mixture of the exhaust gas and ammonia, and is provided over the entire area of a flow path cross-sectional surface of the duct (3). The ammonia injection unit (11) has an ammonia piping (11a) and an injection nozzle (11b) provided in the ammonia piping (11a) and capable of injecting ammonia into the duct (3). The distance A between the ammonia injection unit (11) and the mixer (12) is 10 times to 30 times inclusive larger than the outer diameter d of the ammonia piping (11a). The distance B between the mixer (12) and the denitration catalyst (13) is longer than the distance A between the ammonia injection unit (11) and the mixer (12).

Description

Technical Field

[0001] This disclosure relates to a denitration device.

Background Art

[0002] An exhaust heat recovery boiler (HRSG) generates steam by passing exhaust gas discharged from a gas turbine or the like through a duct and exchanging heat between the exhaust gas and water or steam in a heat transfer tube. Inside the duct of the exhaust heat recovery boiler, a plurality of heat exchangers having a large number of heat transfer tubes through which water or steam flows, a denitration device for removing (denitrifying) nitrogen oxides (NOx) in the exhaust gas, and the like are installed.

[0003] The denitration device injects a reducing agent (e.g., ammonia or aqueous urea) having the effect of reducing nitrogen oxides from an injection nozzle into the exhaust gas flowing through the duct, and the exhaust gas into which the reducing agent is injected passes through a reaction device (e.g., a denitration catalyst) to remove the nitrogen oxides in the exhaust gas. In such a denitration device, in order to mix the exhaust gas and the reducing agent and make the concentration of the reducing agent in the exhaust gas uniform, a mixing device for mixing the exhaust gas and the reducing agent may be installed downstream of the injection nozzle and upstream of the reaction device (e.g., Patent Document 1). Patent Document 1 describes a denitration device in which a mixing device having a plurality of triangular plates is provided upstream of the reaction device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the denitrification apparatus described in Patent Document 1, exhaust gas to which a reducing agent has been injected passes through a mixing device, generating a gas vortex downstream of the mixing device, which mixes the exhaust gas and the reducing agent. The fluid, which is a mixture of exhaust gas and the reducing agent, is denitrified by passing through a reaction device located downstream of the mixing device. When the gas vortices generated in the mixing device are not sufficiently attenuated, the mixed fluid of exhaust gas and reducing agent flowing through the duct after passing through the mixing device exhibits variations in flow velocity at various points in the cross-sectional area of ​​the flow path. When this mixed fluid flows into the reactor under these conditions, variations occur in the amount of mixed fluid flowing into the reactor at different points. Variations in the amount of mixed fluid flowing into the reactor could potentially reduce the denitrification efficiency of the reactor.

[0006] Furthermore, if the concentration of the reducing agent is not uniform when the exhaust gas containing the reducing agent flows into the mixing device, it may not be possible to properly mix the exhaust gas and the reducing agent in the mixing device. If the exhaust gas and the reducing agent cannot be properly mixed, the reaction may not occur. Device There was a possibility that the denitrification efficiency would be reduced.

[0007] This disclosure has been made in view of these circumstances and aims to provide a denitrification apparatus that can improve denitrification efficiency. [Means for solving the problem]

[0008] To solve the above problems, the denitrification apparatus of this disclosure employs the following means. A denitrification apparatus according to one aspect of the present disclosure is a denitrification apparatus installed in a duct through which exhaust gas flows in a predetermined direction, comprising: an injection section for injecting a reducing agent having the effect of reducing nitrogen oxides contained in the exhaust gas into the exhaust gas flowing in the duct; a mixing section provided downstream of the injection section for mixing the exhaust gas flowing in the duct with the reducing agent by forming a vortex centered on a central axis extending in the predetermined direction; and a resistance section provided downstream of the mixing section for providing resistance to the flow of the mixed fluid of the exhaust gas and the reducing agent, and extending over the entire cross-sectional area of ​​the flow path of the duct, wherein the injection section comprises a reducing agent pipe extending in an intersecting direction which is a direction intersecting the predetermined direction and through which the reducing agent flows, and a nozzle provided on the side of the reducing agent pipe for injecting the reducing agent into the duct, and the distance from the injection section to the mixing section is 10 times or more the outer diameter of the reducing agent pipe, 20 The distance from the mixing section to the resistance section is less than or equal to the ratio, and the distance from the injection section to the mixing section is longer than the distance from the injection section to the mixing section. The mixing section has a plurality of cells that determine the size of the vortex formed, and the distance from the mixing section to the resistance section is longer than five times the length of the intersecting direction, which is the direction that intersects the predetermined direction of the cells. . [Effects of the Invention]

[0009] According to this disclosure, denitrification efficiency can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing a waste heat recovery boiler according to an embodiment of the present disclosure. [Figure 2] This is a schematic diagram showing a denitrification apparatus according to an embodiment of the present disclosure. [Figure 3] This is a schematic perspective view showing a cell of a mixer according to an embodiment of the present disclosure. [Figure 4] This is a schematic side view showing a mixer according to an embodiment of the present disclosure. [Figure 5] This is a schematic front view showing a mixer according to an embodiment of the present disclosure. [Figure 6] This graph shows the relationship between ammonia concentration and the distance from the ammonia injection point to the mixer. [Figure 7]This graph shows the relationship between the standard deviation of the fluid mixture velocity and the distance from the mixer to the denitrification catalyst. [Figure 8] This is a schematic diagram showing a denitrification apparatus according to a modified embodiment of the present disclosure. [Modes for carrying out the invention]

[0011] Hereinafter, a denitrification apparatus according to the embodiment of this disclosure will be described with reference to Figures 1 to 8. In the following description and drawings, the vertical direction will be referred to as the Z-axis direction, the horizontal direction in which exhaust gas flows will be referred to as the X-axis direction, and the direction perpendicular to the X-axis direction and the Z-axis direction will be referred to as the Y-axis direction. Also, in Figures 2, 3, 5, and 8, the direction of exhaust gas flow is indicated by arrow E.

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

[0013] The waste heat recovery boiler 2 according to this embodiment includes a duct 3 extending in the X-axis direction through which exhaust gas flows, a denitrification device 10 provided inside the duct 3 to remove 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 section 4 and the second heat exchange section 5 have a plurality of heat transfer tubes (not shown) extending vertically (in the Z-axis direction) so as to intersect with the exhaust gas flow direction. The first heat exchange section 4 and the second heat exchange section 5 recover heat from the exhaust gas by heat exchange between the exhaust gas and a heat transfer medium (e.g., water or steam) circulating inside the heat transfer tubes. The first heat exchanger 4 is provided upstream of the denitration device 10. The first heat exchanger 4 may be, for example, a superheater that superheats a heat medium flowing inside a heat transfer tube. The second heat exchanger 5 is provided downstream of the denitration device 10. The second heat exchanger 5 may be, for example, an evaporator that evaporates a heat medium flowing inside a heat transfer tube.

[0015] The high-temperature combustion exhaust gas (exhaust gas) discharged from the combustion engine 1 is introduced into the duct 3 from the inlet of the duct 3, passes through the first heat exchanger 4, the denitration device 10, and the second heat exchanger 5 in sequence, and then is discharged from the chimney 7 through 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 having an action of reducing nitrogen oxides such as ammonia and aqueous urea to the exhaust gas flowing in the duct 3, and promotes the reaction between the nitrogen oxides (NOx) in the exhaust gas supplied with the reducing agent and the reducing agent by the catalytic action of the denitration catalyst 13, thereby removing and reducing the nitrogen oxides in the exhaust gas. In the following description, an example using ammonia gas as the reducing agent will be described. Note that the reducing agent according to the present disclosure is not limited to ammonia gas. For example, it may be liquid ammonia, or it may be other than ammonia.

[0017] As shown in FIGS. 1 and 2, the denitration device 10 includes an ammonia injection part (injection part) 11, a mixer 12, a denitration catalyst (resistance part) 13, and an ammonia decomposition catalyst 14, which are arranged in order from the upstream side of the exhaust gas flow in the duct 3.

[0018] The ammonia injection part 11 has an ammonia pipe (reducing agent pipe) 11a extending in the Z-axis direction and a plurality of injection nozzles (nozzles) 11b provided on the side surface of the ammonia pipe 11a. The ammonia injection part 11 injects ammonia gas along the X-axis direction into the duct 3 from the plurality of injection nozzles 11b, thereby injecting ammonia into the exhaust gas flowing in the duct 3. The ammonia pipe 11a is cylindrical. Ammonia flows through the ammonia pipe 11a. The outer diameter d of the ammonia pipe 11a is set to a predetermined length. Multiple injection nozzles 11b are arranged at predetermined intervals along the extending direction (i.e., the Z-axis direction) of the ammonia pipe 11a. The injection nozzles 11b may be round holes formed in the side surface of the ammonia pipe 11a. Ammonia gas is injected from the injection nozzles 11b at a predetermined injection pressure. The diameter of the injection holes of the injection nozzles 11b is, for example, 3 mm to 6 mm. The injection nozzles 11b inject the ammonia gas in a conical shape. Note that the diameter of the injection holes and the injection pattern of the injection nozzles 11b described above are examples and are not limited thereto.

[0019] The denitrification catalyst 13 is arranged to cover substantially the entire cross-section of the flow path of the duct 3. The denitrification catalyst 13 includes, for example, a rectangular cylindrical rectangular frame (not shown) and a plurality of catalysts (not shown) provided inside the rectangular frame. Examples of catalyst shapes include honeycomb shapes and corrugated shapes that allow exhaust gas to pass in the X-axis direction, but are not limited to these. The catalyst promotes the reduction reaction of NOx (nitrogen oxides) contained in the exhaust gas (combustion gas) passing through it, thereby removing at least a portion of the NOx. The catalyst components are, for example, based on titanium dioxide.

[0020] The ammonia decomposition catalyst 14 is positioned to cover almost the entire cross-section of the flow path of the duct 3. The ammonia decomposition catalyst 14 removes ammonia from the exhaust gas by decomposing the ammonia contained in the exhaust gas. In this embodiment, since the ammonia decomposition catalyst 14 is provided downstream of the denitrification catalyst 13, any ammonia in the exhaust gas that did not react completely with the denitrification catalyst 13 can be decomposed by the ammonia decomposition catalyst 14.

[0021] The mixer 12 is positioned to cover substantially the entire cross-section of the flow path of the duct 3. As shown in Figures 3 and 4, the mixer 12 has multiple mixing sections 12A that form a swirling flow S that revolves around a central axis extending in the X-axis direction. The mixing section 12A also has multiple cells 12a (four in this embodiment as an example). That is, the mixing section 12A forms a single swirling flow (vortex) S by combining multiple cells 12a. The swirling flow S is formed substantially at the center of the mixing section 12A. The exhaust gas (specifically, the exhaust gas to which ammonia has been injected) that has passed through the mixer 12 flows in the space downstream of the mixer 12 as multiple swirling flows S. In this way, the mixer 12 mixes the exhaust gas flowing through the duct with ammonia by forming swirling flows S.

[0022] As shown in Figure 4, the multiple mixing units 12A are arranged in a row in the Z-axis direction (two as an example in this embodiment) and in the Y-axis direction (two as an example in this embodiment). Furthermore, as shown in Figure 5, the multiple mixing units 12A are also arranged in a row in the X-axis direction (two as an example in this embodiment). In other words, the mixing units 12A are arranged in two stages in the X-axis direction. Note that the number of mixing units 12A is just an example and is not limited to the number in this embodiment. The mixing section 12A has multiple cells 12a arranged in a row (two in this embodiment, for example) in the Z-axis direction (first intersection direction) and the Y-axis direction (second intersection direction). The cells 12a have a regular shape.

[0023] Furthermore, as shown in Figure 4, multiple cells 12a are arranged in a row in the Z-axis direction (two as an example in this embodiment) and in the Y-axis direction (two as an example in this embodiment) relative to one mixing section 12A. Adjacent cells 12a in the Z-axis and Y-axis directions are arranged so that their orientations are rotated 90 degrees around a central axis extending in the X-axis direction. As shown in Figure 2, the length of cell 12a in the Z-axis direction is length D. The length of cell 12a in the X-axis direction is length L. The size of cell 12a affects the size of the vortex formed downstream of the mixer 12. In other words, cell 12a determines the size of the vortex formed.

[0024] As shown in Figure 3, cell 12a has four triangular and plate-like plate portions 18. The four plate portions 18 are identical in shape. The four plate portions 18 consist of two upstream plate portions 18a positioned upstream of the center point in the X-axis direction of cell 12a, and two downstream plate portions 18b positioned downstream of the center point.

[0025] The two upstream plates 18a are arranged to form two opposing faces of a hypothetical square pyramid whose vertices are located on the downstream side. The two upstream plates 18a are arranged so that their vertices, located furthest downstream, are in contact with each other. The two downstream side plates 18b are arranged to form two opposing faces of a hypothetical square pyramid with its vertices located on the upstream side. The two downstream side plates 18b are arranged so that their vertices, located on the upstream side, are in contact with each other.

[0026] The vertex located at the downstream end of the upstream plate portion 18a and the vertex located at the upstream end of the downstream plate portion 18b are in contact. Furthermore, the upstream plate portion 18a and the downstream plate portion 18b are positioned such that their orientations are rotated 90 degrees around a central axis extending in the X-axis direction.

[0027] The structure of the mixer 12 is not limited to the structure described above. The mixer 12 can be any structure in which a regular shape is arranged in a sequence of multiple planar or curved surfaces that generate a swirling flow. Furthermore, the shape of the plate portion 18 is not limited to a triangular shape; for example, it may be trapezoidal. In the case of a trapezoidal shape, the upstream plate portion 18a is positioned so that its short side (the shorter side of a pair of parallel sides) is located downstream, and the downstream plate portion 18b is positioned so that its short side is located upstream. In addition, the short sides (the shorter side of a pair of parallel sides) of the two upstream plate portions 18a and the short sides of the two downstream plate portions 18b are connected to form a square. That is, there is a square-shaped plate portion that connects all the short sides of the four plate portions 18.

[0028] Next, the arrangement of each part of the denitrification apparatus 10 will be described. As shown in Figure 2, the distance B from the mixer 12 to the denitrification catalyst 13 is longer than the distance A from the ammonia injection unit 11 to the mixer 12. Distance B is the distance from the downstream end of the mixer 12 to the upstream end of the denitrification catalyst 13. Distance A is the distance from the downstream end of the ammonia injection unit 11 to the upstream end of the mixer 12.

[0029] Furthermore, the distance A from the ammonia injection section 11 (specifically, the downstream end of the ammonia pipe 11a) to the mixer 12 is set to be at least 10 times the outer diameter d of the ammonia pipe 11a, and no more than 30 times its length. That is, the following equation (1) holds true.

[0030] 10d ≤ A ≤ 30d ···(1)

[0031] Furthermore, the distance B from the mixer 12 to the denitrification catalyst 13 is longer than five times the length D of cell 12a in the Z-axis direction. That is, equation (2) below holds true. Note that in this embodiment, the length of cell 12a in the Y-axis direction and the length of cell 12a in the Z-axis direction are the same, so the length of cell 12a in the Y-axis direction may be taken as length D.

[0032] B / D>5···(2)

[0033] This embodiment provides the following effects and advantages. The fluid that passes through the mixer 12 (a mixed fluid of exhaust gas and ammonia) forms a swirling flow in the space downstream of the mixer 12. Therefore, the exhaust gas and reducing agent are mixed more effectively in the space from the mixer 12 to the denitrification catalyst 13, where the swirling flow is formed, than in the space from the ammonia injection unit 11 to the mixer 12. In this embodiment, the distance B from the mixer 12 to the denitrification catalyst 13 is longer than the distance A from the ammonia injection unit 11 to the mixer 12. This allows for a longer space from the mixer 12 to the denitrification catalyst 13, enabling more effective mixing of the exhaust gas and ammonia. Consequently, the denitrification reaction occurs more effectively in the denitrification catalyst 13, improving the denitrification efficiency.

[0034] The effect of improving denitrification efficiency will be explained in detail using the graph in Figure 6. The vertical axis of Figure 6 shows the standard deviation of ammonia concentration at a distance of 60d (60 times the length d of the outer diameter of the ammonia pipe 11a) from the ammonia injection section 11, and the horizontal axis of Figure 6 shows the distance A from the ammonia injection section 11 to the mixer 12 as the length based on the outer diameter d of the ammonia pipe 11a. Figure 6 also shows the case where the distance B from the mixer 12 to the denitrification catalyst 13 is 30d. In Figure 6, when distance A is less than 30d, the standard deviation of ammonia concentration decreases as the value of distance A decreases. In other words, the smaller the value of distance A, the smaller the variation in ammonia concentration, indicating that mixing is progressing. In particular, it can be seen that the standard deviation decreases sharply in the range of distance A from 30d to 20d. As can be seen from the graph in Figure 6, the distance B from the mixer 12 to the denitrification catalyst 13 is longer than the distance A from the ammonia injection unit 11 to the mixer 12, which allows for suitable mixing of exhaust gas and ammonia.

[0035] When a swirling flow is present, variations in flow velocity occur at various points in the cross-sectional area of ​​the flow path within the duct. Therefore, if the mixed fluid flows into the denitrification catalyst 13 before the swirling flow has sufficiently attenuated, there is a possibility that the denitrification efficiency will be reduced. On the other hand, in this embodiment, the distance B from the mixer 12 to the denitrification catalyst 13 is five times longer than the length D in the Z-axis direction of the cell 12a. This allows the distance B from the mixer 12 to the denitrification catalyst 13 to be increased, so that the mixed fluid reaches the denitrification catalyst 13 in a state where the swirling flow has been sufficiently attenuated (a state where the swirling force has been sufficiently weakened). Therefore, the mixed fluid can be introduced into the denitrification catalyst 13 in a state where variations in flow velocity at each position in the cross-sectional area of ​​the flow path of the duct 3 are suppressed. Thus, a mixed fluid in a homogenized state can be supplied to the denitrification catalyst 13. As a result, the denitrification reaction occurs suitably in the denitrification catalyst 13, and the denitrification efficiency can be improved.

[0036] The effect of improving denitrification efficiency will be explained in detail using the graph in Figure 7. The vertical axis of Figure 7 shows the standard deviation of the fluid velocity of the mixed fluid, and the horizontal axis of Figure 7 shows the B / D value. In Figure 7, when B / D is less than 5, the smaller the B / D value, the larger the standard deviation of the fluid velocity of the mixed fluid. On the other hand, when B / D is greater than 5, the standard deviation of the fluid velocity of the mixed fluid is about the same as when there is no mixer 12. From this, it can be concluded that when B / D is greater than 5, the swirling flow formed by the mixer 12 is attenuated to the same extent as when there is no mixer 12. As can be seen from the graph in Figure 7, by making the distance B five times the length D of cell 12a, the swirling flow can be sufficiently attenuated, and a homogenized mixed fluid can be supplied to the denitrification catalyst 13.

[0037] Furthermore, in this embodiment, the distance A from the ammonia injection unit 11 to the mixer 12 is set to 10 times or more the outer diameter d of the ammonia pipe 11a. As a result, the ammonia injected from the injection nozzle 11b flows into the mixer 12 in a suitably diffused state, allowing the exhaust gas and ammonia to be suitably mixed in the mixer 12. Therefore, the denitrification efficiency can be improved. Also, in this embodiment, the distance A from the ammonia injection unit 11 to the mixer 12 is set to 30 times or less the outer diameter d of the ammonia pipe 11a. As a result, the total length of the duct 3 can be shortened. Therefore, the denitrification device 10 can be miniaturized. Thus, in this embodiment, the mixing performance in the mixer 12 can be improved, and the denitrification device 10 can be miniaturized.

[0038] [Example 1] Next, a modified example of this embodiment will be described with reference to Figure 8. In the above embodiment, an example was described in which no large resistor is provided between the mixer 12 and the denitrification catalyst 13, but the disclosure is not limited thereto. For example, as shown in Figure 8, a high-pressure heat exchange section (heat exchanger) 21, which acts as a resistor, may be provided between the mixer 12 and the denitrification catalyst 13. In this modified example, the denitrification catalyst 13 is provided downstream of the high-pressure heat exchange section 21. The high-pressure heat exchange section 21, like the first heat exchange section 4 and the second heat exchange section 5, has heat transfer tubes (not shown) through which a heat transfer medium flows, and exchanges heat between the heat transfer medium flowing inside the heat transfer tubes and the exhaust gas flowing outside the heat transfer tubes. In this structure, the distance between the mixer 12 and the high-pressure heat exchange section 21 is length B. That is, the distance from the mixer 12 to the high-pressure heat exchange section 21 (distance B) is set to be longer than five times the length D in the Z-axis direction of the cell 12a of the mixer 12.

[0039] Thus, in this embodiment, distance B may be the distance between the mixer 12 and the resistor (for example, the denitrification catalyst 13 or the high-pressure heat exchange unit 21) located downstream of the mixer 12 and furthest upstream. The resistor is an object that is arranged to cover substantially the entire flow path area of ​​the duct 3 and provides resistance to the exhaust gas (specifically, the exhaust gas to which ammonia has been injected) flowing through the duct 3. Specifically, the resistor is an object that greatly attenuates the swirling flow generated in the mixer 12. In addition to the denitrification catalyst 13 and the high-pressure heat exchange unit 21 described in the above embodiment, the resistor may also be an ammonia decomposition catalyst that decomposes ammonia or a CO decomposition catalyst that decomposes carbon monoxide.

[0040] According to this modified version, the following effects are produced. In this embodiment, since the mixed fluid flows into the high-pressure heat exchange section 21 with suppressed variations, variations in the flow velocity of the mixed fluid can be sufficiently suppressed even downstream of the high-pressure heat exchange section 21. Therefore, a homogenized mixed fluid can also flow into the denitrification catalyst 13 located downstream of the high-pressure heat exchange section 21. Consequently, the denitrification reaction occurs favorably in the denitrification catalyst 13, thereby improving the denitrification efficiency.

[0041] This disclosure is not limited to the embodiments described above, and can be modified as appropriate without departing from its essence.

[0042] For example, in the above embodiment, an example was described in which two mixing units 12A (cells 12a) are provided in the X-axis direction (two stages), but the disclosure is not limited thereto. For example, three or more mixing units 12A (cells 12a) may be provided in the X-axis direction (three or more stages), or only one mixing unit 12A (cells 12a) may be provided in the X-axis direction (one stage).

[0043] Furthermore, although the above embodiment describes an example in which a denitrification device is installed in a horizontal duct in which exhaust gas flows horizontally, this disclosure is not limited to this. For example, the denitrification device may be installed in a vertical duct in which exhaust gas flows vertically.

[0044] The denitrification apparatus described in the above-described embodiment can be understood, for example, as follows. A denitrification apparatus according to a first aspect of the present disclosure is a denitrification apparatus (10) provided in a duct (3) through which exhaust gas flows in a predetermined direction (X-axis direction), comprising: an injection section (11) for injecting a reducing agent having the effect of reducing nitrogen oxides contained in the exhaust gas into the exhaust gas flowing in the duct; a mixing section (12) provided downstream of the injection section for mixing the exhaust gas flowing in the duct with the reducing agent by forming a vortex about a central axis extending in the predetermined direction; and a mixing section provided downstream of the mixing section for the mixed fluid of the exhaust gas and the reducing agent. The injection section comprises resistance sections (13, 21) that provide resistance to the flow and are provided over the entire cross-sectional area of ​​the flow path of the duct, and the injection section comprises a reducing agent pipe that extends in a direction intersecting the predetermined direction and through which the reducing agent flows, and a nozzle provided on the side of the reducing agent pipe that injects the reducing agent into the duct, the distance (A) from the injection section to the mixing section is 10 times or more and 30 times or less the outer diameter (d) of the reducing agent pipe, and the distance (B) from the mixing section to the resistance section is longer than the distance (A) from the injection section to the mixing section.

[0045] The fluid that passes through the mixing section forms a vortex in the space downstream of the mixing section. Therefore, the exhaust gas and reducing agent are mixed more effectively in the space from the mixing section to the resistance section where the vortex is formed than in the space from the injection section to the mixing section. In the above configuration, the distance from the mixing section to the resistance section is longer than the distance from the injection section to the mixing section. This allows for a longer distance from the mixing section to the resistance section, enabling optimal mixing of the exhaust gas and reducing agent. Consequently, the denitrification reaction occurs optimally in the denitrification catalyst, improving the denitrification efficiency. Furthermore, since the gas flows into the resistance section with reduced variation, the variation in the flow velocity of the mixed fluid can be sufficiently suppressed even downstream of the resistance section. Therefore, even if, for example, the resistance section is a heat exchanger and a denitrification catalyst is provided downstream of the heat exchanger, the variation in the flow velocity of the mixed fluid can be sufficiently suppressed downstream of the heat exchanger, resulting in a homogenized mixed fluid flowing into the denitrification catalyst. Consequently, the denitrification reaction occurs favorably in the denitrification catalyst, improving the denitrification efficiency. Furthermore, in the above configuration, the distance from the injection section to the mixing section is set to 10 times or more the outer diameter of the reducing agent piping. This allows the reducing agent sprayed from the nozzle to flow into the mixing section in a suitably diffused state, enabling suitable mixing of the exhaust gas and reducing agent in the mixer. Therefore, the denitrification efficiency can be improved. Also, in the above configuration, the distance from the injection section to the mixing section is set to 30 times or less the outer diameter of the reducing agent piping. This allows the total length of the duct to be shortened. Therefore, the denitrification device can be miniaturized. Thus, the above configuration can improve the mixing performance in the mixing section and miniaturize the denitrification device.

[0046] Furthermore, in the denitrification apparatus according to the second aspect of the present disclosure, in the first aspect, the mixing section has a plurality of cells (12a) that determine the size of the vortices formed, and the distance (B) from the mixing section to the resistance section is longer than five times the length (D) of the intersecting direction, which is the direction that intersects the predetermined direction of the cells.

[0047] In the above configuration, the distance from the mixing section to the resistance section is greater than five times the length of the cells in the intersecting direction. This allows for a longer distance from the mixing section to the resistance section, so that the mixed fluid reaches the resistance section with the vortices formed in the mixing section sufficiently attenuated. Therefore, the mixed fluid can be introduced into the resistance section with reduced variation in flow velocity at each position in the flow channel cross-section. Thus, for example, if the resistance section is a denitrification catalyst, the mixed fluid will flow into the denitrification catalyst in a homogenized state, allowing the denitrification reaction to occur favorably in the denitrification catalyst, thereby improving the denitrification efficiency.

[0048] Furthermore, in the third aspect of the present disclosure, the denitrification apparatus, in the first or second aspect, has a denitrification catalyst (13) through which the mixed fluid passes to remove nitrogen oxides contained in the exhaust gas.

[0049] In the above configuration, the mixed fluid can be introduced into the denitrification catalyst while suppressing variations in flow velocity at each position in the flow channel cross-section. Therefore, a homogenized mixed fluid enters the denitrification catalyst, allowing the denitrification reaction to occur favorably in the catalyst, thus improving the denitrification efficiency.

[0050] Furthermore, the denitrification apparatus according to the fourth aspect of the present disclosure comprises, in the first or second aspect, a denitrification catalyst (13) arranged downstream of the resistance section and removing nitrogen oxides contained in the exhaust gas by which the mixed fluid passes, and the resistance section comprises a heat exchanger (21) that exchanges heat between the water or steam flowing through the heat exchanger tube and the exhaust gas flowing through the duct.

[0051] In the above configuration, variations in the flow velocity of the mixed fluid can be sufficiently suppressed even downstream of the resistance section (heat exchanger), allowing a homogenized mixed fluid to flow into the denitrification catalyst. Therefore, the denitrification reaction occurs favorably in the denitrification catalyst, improving the denitrification efficiency. [Explanation of symbols]

[0052] 1: Combustion engine 2: Waste heat recovery boiler 3: Duct 4: 1st heat exchange section 5:Second heat exchange section 7: Chimney 10: Denitration equipment 11: Ammonia injection section 11a: Ammonia piping 11b: Spray nozzle 12: Mixer 12A: Mixing section 12a: Cell 13:Denitrification catalyst 14: Ammonia decomposition catalyst 18: Board part 18a:Upstream side plate part 18b: Downstream side plate part 21: High-pressure heat exchange section

Claims

1. A denitrification device installed in a duct through which exhaust gas flows in a predetermined direction, An injection unit for injecting a reducing agent having the effect of reducing nitrogen oxides contained in the exhaust gas flowing through the duct, A mixing unit is provided downstream of the injection unit and mixes the exhaust gas flowing through the duct with the reducing agent by forming a vortex centered on a central axis extending in the predetermined direction, A resistance section is provided downstream of the mixing section, which provides resistance to the flow of the mixed fluid in which the exhaust gas and the reducing agent are mixed, and is provided over the entire cross-sectional area of ​​the flow path of the duct, The injection section comprises a reducing agent pipe extending in an intersecting direction, which is a direction intersecting the predetermined direction, through which the reducing agent flows, and a nozzle provided on the side of the reducing agent pipe for injecting the reducing agent into the duct. The distance from the injection section to the mixing section is 10 times or more the outer diameter of the reducing agent piping, and 20 times or less. The distance from the mixing section to the resistance section is longer than the distance from the injection section to the mixing section. The mixing section has a plurality of cells that determine the size of the vortex formed, A denitrification apparatus in which the distance from the mixing section to the resistance section is longer than five times the length of the intersecting direction, which is the direction that intersects the predetermined direction of the cell.

2. The denitrification apparatus according to claim 1, wherein the resistive portion has a denitrification catalyst that removes nitrogen oxides contained in the exhaust gas by passing the mixed fluid through it.

3. A denitrification catalyst is provided, which is located downstream of the resistance section and removes nitrogen oxides contained in the exhaust gas by passing the mixed fluid through it. The denitrification apparatus according to claim 1, wherein the resistive section comprises a heat transfer tube through which water or steam flows, and a heat exchanger that exchanges heat between the water or steam flowing through the heat transfer tube and the exhaust gas flowing through the duct.

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