Denitration device

Abstract

The purpose of the present invention is to improve denitration efficiency. A denitration device (10) comprises: an ammonia injection part (11) that is provided inside a duct (3) through which exhaust gas circulates, and that injects ammonia into the exhaust gas circulating inside the duct (3); a denitration catalyst (13) that is provided on a downstream side of the ammonia injection part (11) inside the duct (3); and a rectification part (20) that is provided on an upstream side of the ammonia injection part (11) inside the duct (3) and spaced a predetermined distance from the ammonia injection part (11) and that rectifies the exhaust gas circulating inside the duct (3).

Description

Denitration equipment

[0001] The present disclosure relates to a denitration device.

[0002] In a heat recovery steam generator (HRSG), exhaust gas discharged from a gas turbine or the like passes through a duct, and heat exchange occurs between the exhaust gas and water or steam in heat transfer tubes, generating steam. Inside the duct of the heat recovery steam generator, multiple heat exchangers having multiple heat transfer tubes through which water or steam flows, and a denitration device that removes (denitrifies) nitrogen oxides (NOx) from the exhaust gas are installed.

[0003] A denitration device, for example, injects a reducing agent (e.g., ammonia or urea water) that has the effect of reducing nitrogen oxides into exhaust gas flowing through a duct from an injection nozzle, and removes nitrogen oxides from the exhaust gas by passing the exhaust gas into which the reducing agent has been injected through a reaction device (e.g., a denitration catalyst). For example, a denitration device described in Patent Document 1 is known as such a denitration device.

[0004] Japanese Patent Application Publication No. 9-75673

[0005] In order to improve the efficiency of nitrogen oxide removal (hereinafter referred to as "denitrification efficiency") in a reactor, it is effective to make the molar ratio of nitrogen oxides to reducing agent uniform across the cross section of the duct. However, due to various factors, variations in the flow rate of exhaust gas may occur across the entire cross section of the duct in a denitrification device. If reducing agent is injected into the exhaust gas in this state, variations in the concentration of reducing agent will occur across the entire cross section of the flow path. If exhaust gas flows into the reactor while variations in the concentration of reducing agent occur, variations will occur in the amount of reducing agent flowing in depending on the position in the reactor. Variations in the amount of reducing agent flowing into the reactor could reduce the denitrification efficiency of the reactor.

[0006] In addition, in order to mix the exhaust gas and the reducing agent and homogenize the concentration of the reducing agent in the exhaust gas across the cross section of the flow path, a mixer that mixes the exhaust gas and the reducing agent may be installed downstream of the injection nozzle and upstream of the reactor. However, a mixer is generally configured by combining multiple cells that mix the exhaust gas. Therefore, if the variation in the flow rate of the exhaust gas extends across the entire cross section of the flow path of the duct, the variation in the concentration of the reducing agent exceeds the range that a single cell can mix, and the mixer may not be able to appropriately homogenize the concentration of the reducing agent. Therefore, even in a configuration with a mixer, the denitration efficiency of the reactor may be reduced.

[0007] The present disclosure has been made in view of the above circumstances, and has an object to provide a denitration device that can improve denitration efficiency.

[0008] In order to solve the above problems, the denitration device of the present disclosure employs the following means: A denitration device according to one embodiment of the present disclosure includes an injection part that is provided in a duct through which exhaust gas flows and that injects a reducing agent into the exhaust gas flowing through the duct, a denitration catalyst that is provided in the duct and downstream of the injection part, and a rectification part that is provided in the duct and upstream of the injection part at a predetermined distance from the injection part and that rectifies the exhaust gas flowing through the duct.

[0009] According to the present disclosure, denitration efficiency can be improved.

[0010] Fig. 1 is a schematic configuration diagram showing a heat recovery boiler according to an embodiment of the present disclosure. Fig. 2 is a schematic configuration diagram showing a denitration device according to an embodiment of the present disclosure. Fig. 3 is a schematic side view showing a perforated plate according to an embodiment of the present disclosure. Fig. 4 is a schematic side view showing a mixer according to an embodiment of the present disclosure. Fig. 5 is a schematic perspective view showing cells of a mixer according to an embodiment of the present disclosure. Fig. 6 is a graph showing the relationship between variation in flow velocity of exhaust gas and distance D1 in a denitration device according to an embodiment 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. In Figures 2 and 5, the flow direction of exhaust gas is indicated by arrow E.

[0012] First, with reference to FIG. 1 , a heat recovery steam generator 2 according to this embodiment will be described. As shown in FIG. 1 , the heat recovery steam generator 2 according to this embodiment is a horizontal heat recovery steam generator 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. Note that, although this embodiment describes an example in which a denitration device is provided in a horizontal duct in which exhaust gas flows horizontally, 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.

[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 (resistance section) 4 and a second heat exchange section 5 provided inside the duct 3.

[0014] The first heat exchange unit 4 has a plurality of heat transfer tubes 4a (see FIG. 2 ) extending in the vertical direction (Z-axis direction) so as to intersect with the flow direction of the exhaust gas. The length (height H) of the heat transfer tubes 4a in the Z-axis direction is 5 m or more and 30 m or less (see FIG. 2 ). The first heat exchange unit 4 recovers 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 4a. 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 4a.

[0015] The second heat exchange unit 5 has a plurality of heat transfer tubes (not shown) extending in a vertical direction (Z-axis direction) so as to intersect with the flow direction of the exhaust gas. The second heat exchange unit 5 recovers 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 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.

[0016] 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.

[0017] Next, the denitration device 10 will be described in detail with reference to FIGS. 1 to 6 . The denitration device 10 supplies a reducing agent, such as ammonia or urea water, that has the ability to reduce nitrogen oxides to the exhaust gas flowing through the duct 3, and promotes the 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 the denitration catalyst 13, 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.

[0018] As shown in FIGS. 1 and 2 , the denitration device 10 includes a flow straightening section 20, an ammonia injection section (injection section) 11, a mixer 12, a denitration catalyst 13, and an ammonia decomposition catalyst 14, which are arranged in this order from the upstream side of the exhaust gas flow in the duct 3.

[0019] The flow straightening section 20 has a flow straightening grid (not shown) and a perforated plate 21 (not shown in FIG. 3 ). The flow straightening grid is disposed upstream of the perforated plate 21. The flow straightening grid is a lattice-shaped member disposed so as to cover substantially the entire cross section of the flow path of the duct 3.

[0020] The perforated plate 21 is attached to the downstream portion of the straightening grid. As shown in Fig. 3, the perforated plate 21 is arranged so as to cover substantially the entire flow path cross section of the duct 3. The perforated plate 21 is a metal plate-shaped member. As shown in Fig. 3, the perforated plate 21 has a plurality of through holes 21a penetrating in the X-axis direction. The plurality of through holes 21a are arranged side by side at predetermined intervals along the Z-axis direction and the Y-axis direction. The diameter d of the through holes 21a is set to a length that allows the exhaust gas to be straightened.

[0021] As shown in FIG. 2 , the ammonia injection unit 11 has an ammonia pipe 11a extending in the Z-axis direction and a plurality of injection nozzles (not shown) provided on the side of the ammonia pipe 11a. The ammonia injection unit 11 injects ammonia gas from the plurality of injection nozzles into the duct 3 along the X-axis direction, thereby injecting ammonia into the exhaust gas flowing through the duct 3. The ammonia pipe 11a is a cylindrical member. Ammonia flows through the ammonia pipe 11a. The plurality of injection nozzles are arranged side by side at predetermined intervals along the extension direction of the ammonia pipe 11a (i.e., the Z-axis direction). Ammonia gas is injected from each injection nozzle at a predetermined injection pressure. Each injection nozzle injects the ammonia gas in a conical shape.

[0022] The denitration catalyst 13 is disposed so as to cover substantially the entire cross section of the flow path of the duct 3. The denitration catalyst 13 has, for example, a rectangular cylindrical frame (not shown) and a plurality of catalysts (not shown) provided 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 gas) passing through the catalyst, thereby removing at least a portion of the NOx. The catalyst component is, for example, based on titanium oxide.

[0023] The ammonia decomposition catalyst 14 is disposed so as to cover substantially 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, the ammonia decomposition catalyst 14 is provided downstream of the denitration catalyst 13, so that any ammonia in the exhaust gas that does not completely react in the denitration catalyst 13 can be decomposed by the ammonia decomposition catalyst 14.

[0024] The mixer 12 is disposed so as to cover substantially the entire cross section of the flow path of the duct 3. As shown in FIG. 4 , the mixer 12 includes a plurality of mixing sections 12A that form a swirling flow S swirling around a central axis extending in the X-axis direction. Each mixing section 12A has a plurality of cells 12a (four cells in this embodiment, for example). That is, the mixing section 12A forms a single swirling flow (vortex) S by combining the plurality of cells 12a. The swirling flow S is formed substantially at the center of the mixing section 12A. The exhaust gas (more specifically, the exhaust gas into which ammonia has been injected) that has passed through the mixer 12 becomes a plurality of swirling flows S and circulates in the space downstream of the mixer 12. In this way, the mixer 12 mixes the exhaust gas and ammonia flowing through the duct by forming the swirling flow S.

[0025] 4, the plurality of mixing sections 12A are arranged side by side in the Z-axis direction (two, for example, in this embodiment), and in the Y-axis direction (two, for example, in this embodiment). Note that the number of mixing sections 12A is just an example and is not limited to the number in this embodiment.

[0026] The mixing section 12A has a plurality of cells 12a (two in this embodiment, for example) arranged in the Z-axis direction and the Y-axis direction. The cells 12a have a regular shape. Adjacent cells 12a in the Z-axis direction and the Y-axis direction are arranged so that their orientations are rotated 90 degrees around a central axis extending in the X-axis direction.

[0027] 5, the cell 12a has four triangular plate-like plates 18. The four plates 18 have the same shape. The four plates 18 include two upstream plates 18a located upstream of the center point of the cell 12a in the X-axis direction, and two downstream plates 18b located downstream of the center point.

[0028] The two upstream plate portions 18a are arranged so that they form two opposing faces of an imaginary quadrangular pyramid whose apex is located on the downstream side. The two upstream plate portions 18a are arranged so that their most downstream apexes contact each other. The two downstream plate portions 18b are arranged so that they form two opposing faces of an imaginary quadrangular pyramid whose apex is located on the upstream side. The two downstream plate portions 18b are arranged so that their most upstream apexes contact each other.

[0029] The upstream plate 18a has a most downstream vertex that is in contact with the downstream plate 18b, and the upstream plate 18a and the downstream plate 18b have a most upstream vertex that is in contact with each other. The upstream plate 18a and the downstream plate 18b are arranged so that their orientations are rotated by 90 degrees around a central axis that extends in the X-axis direction.

[0030] The structure of the mixer 12 is not limited to the above-described structure, and may be any structure in which regular shapes that generate a swirling flow by combining a plurality of flat or curved surfaces are arranged side by side.

[0031] Next, the arrangement of each device in the denitration device 10 will be described. As shown in Fig. 2, the distance D1 from the downstream end of the first heat exchanger 4 to the upstream end of the flow straightener 20 is set to 140 mm or more. Preferably, the distance D1 from the first heat exchanger 4 to the flow straightener 20 is set to 530 mm or more.

[0032] A distance D2 from the downstream end of the flow straightening section 20 to the upstream end of the ammonia injection section 11 is set to a length that is 11 times or more the diameter d of the through-hole 21 a formed in the porous plate 21 of the flow straightening section 20. That is, the following formula (1) is established.

[0033] D2 ≧ 11d (1)

[0034] According to this embodiment, the following advantageous effects are achieved. In this embodiment, the flow straightening unit 20 is provided upstream of the ammonia injection unit 11 at a predetermined distance from the ammonia injection unit 11. As a result, the flow straightening unit 20 straightens the exhaust gas upstream of the ammonia injection unit 11, making it possible to homogenize the flow velocity distribution of the exhaust gas in the cross section of the duct 3. Therefore, the ammonia injection unit 11 injects ammonia into the exhaust gas whose flow velocity has been homogenized. This makes it possible to suppress variations in ammonia concentration caused by variations in flow velocity at various positions in the cross section of the flow path. Therefore, the exhaust gas flows into the denitration catalyst 13 in a state in which variations in ammonia concentration are suppressed, and the denitration reaction occurs favorably in the denitration catalyst 13, thereby improving denitration efficiency.

[0035] Generally, the flow straightening unit 20 (e.g., a grid or a perforated plate 21) acts to equalize the flow velocity of the gas upstream of the flow straightening unit 20 so as to equalize the pressure loss in the cross section of the flow path of the gas passing through the flow straightening unit 20. In this case, if a first heat exchange unit 4 is provided in the gas flow upstream of the flow straightening unit 20, the first heat exchange unit 4 may hinder the equalization of the flow velocity of the exhaust gas. In particular, if the heat transfer tubes 4a of the first heat exchange unit 4 extend in the Z-axis direction, the variation in the flow velocity in the Z-axis direction tends to increase.

[0036] On the other hand, in this embodiment, the flow rectifier 20 is provided at a predetermined distance (specifically, 140 mm or more) from the first heat exchanger 4. This allows a sufficient distance D1 between the flow rectifier 20 and the first heat exchanger 4, thereby reducing the influence of the first heat exchanger 4 on the exhaust gas flow rectification (uniformization of the flow velocity in the exhaust gas flow direction at the flow cross section) effect of the flow rectifier 20. Therefore, the flow rectifier 20 can uniformize the flow velocity distribution of the exhaust gas at the flow cross section of the duct 3. This improves the denitration efficiency. In particular, when the longitudinal length H of the heat transfer tube 4a of the first heat exchanger 4 is 5 m or more and 30 m or less, the flow rectifier 20 can more suitably uniformize the flow velocity distribution of the exhaust gas at the flow cross section of the duct 3.

[0037] The effect of improving the denitration efficiency will be described in detail using the graph in Fig. 6. The vertical axis of Fig. 6 represents the variation in the flow velocity of the exhaust gas in the ammonia injection section 11 (AIG) (specifically, the root mean square (RMS)), and the horizontal axis represents the value of the distance D1 from the first heat exchange section 4 to the rectification section 20.

[0038] In Figure 6, the greater the distance D1, the smaller the variation in the flow velocity of the exhaust gas. It can be seen that the variation in the flow velocity of the exhaust gas is particularly small when the distance D1 is 140 mm or greater. Therefore, from the graph in Figure 6, it can be seen that setting the distance D1 to 140 mm or greater suppresses the variation in the flow velocity of the exhaust gas. In Figure 6, when the distance D1 is 530 mm or less, the slope is steeper than when the distance D1 is greater than 530 mm. Therefore, it can be seen that the variation can be more effectively suppressed up to a distance D1 of 530 mm. Therefore, it can be seen that setting the distance D1 to 530 mm or greater more effectively suppresses the variation in the flow velocity of the exhaust gas. Note that in Figure 6, a distance D1 of 0 indicates the case where the flow straightening unit 20 is not provided. In this case, the variation in the flow velocity is greatest. Therefore, it can be seen that the flow straightening unit 20 has a variation suppression effect.

[0039] In this embodiment, the flow straightening unit 20 has a lattice portion. This allows the flow of exhaust gas passing through the lattice portion to be straightened. Therefore, the lattice portion can homogenize the flow velocity distribution of the exhaust gas in the flow path cross section of the duct 3. This can improve the denitration efficiency.

[0040] In this embodiment, the flow straightening unit 20 has a perforated plate 21. This allows the flow of exhaust gas passing through the perforated plate 21 to be straightened. Therefore, the perforated plate 21 can uniformize the flow velocity distribution of the exhaust gas in the flow path cross section of the duct 3. This allows the denitration efficiency to be improved.

[0041] In this embodiment, the distance D2 from the porous plate 21 to the ammonia injection section 11 is longer than 11 times the diameter d of the through-holes 21a. A jet flows in the exhaust gas as it passes through the through-holes 21a of the porous plate 21. However, in this embodiment, the distance D2 from the porous plate 21 to the ammonia injection section 11 can be increased, so that the exhaust gas reaches the ammonia injection section 11 with the jet flow sufficiently attenuated. That is, the exhaust gas reaches the ammonia injection section 11 with the flow velocity variation suppressed at each position on the flow path cross section. This allows ammonia to be injected into the exhaust gas with the variation suppressed. Therefore, the variation in ammonia concentration caused by the variation in flow velocity at each position on the flow path cross section can be suppressed. Therefore, the exhaust gas flows into the denitration catalyst 13 with the variation in ammonia concentration suppressed, and the denitration reaction occurs favorably in the denitration catalyst 13, thereby improving the denitration efficiency.

[0042] The present disclosure is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit and scope of the present disclosure. For example, in the above-described embodiments, an example was described in which the distance from the first heat exchange section 4 to the perforated plate 21 was 140 mm or more (preferably 530 mm or more), but the present disclosure is not limited thereto. The distance from a structure (hereinafter referred to as an "upstream structure") provided upstream of the perforated plate 21 and affecting the flow of exhaust gas in the duct 3 to the perforated plate 21 may be 140 mm or more (preferably 530 mm or more). The upstream structure may be, for example, a structure having an elongated member extending in the Y-axis direction or the Z-axis direction. An example of the upstream structure is a reinforcing member (such as a strut or a brace) that reinforces the duct 3 from the inside. When there are multiple upstream structures, the distance from the upstream structure closest to the perforated plate 21 to the perforated plate 21 may be 140 mm or more (preferably 530 mm or more).

[0043] The denitration device according to the above-described embodiment can be understood as follows, for example: A denitration device according to a first aspect of the present disclosure includes an injection section (11) provided in a duct (3) through which exhaust gas flows and configured to inject a reducing agent into the exhaust gas flowing through the duct, a denitration catalyst (13) provided in the duct downstream of the injection section, and a rectification section (20) provided in the duct upstream of the injection section at a predetermined distance from the injection section and configured to rectify the exhaust gas flowing through the duct.

[0044] In the above configuration, a rectifying section is provided upstream of the injection section at a predetermined distance from the injection section. This rectifies the exhaust gas upstream of the injection section, making it possible to uniformize the flow velocity distribution of the exhaust gas across the cross section of the duct. Therefore, the injection section injects the reducing agent into the exhaust gas with a uniform flow velocity. This makes it possible to suppress variations in the reducing agent concentration due to variations in the flow velocity at various positions across the cross section of the flow path. Therefore, the exhaust gas flows into the denitration catalyst with suppressed variations in the reducing agent concentration, and the denitration reaction occurs favorably in the denitration catalyst, thereby improving the denitration efficiency.

[0045] The denitration device according to a second aspect of the present disclosure is the same as that of the first aspect, and further comprises a resistance section (4) that is provided within the duct and upstream of the rectification section and that provides resistance to the flow of exhaust gas, and the rectification section is provided at a position that is 140 mm or more away from the resistance section.

[0046] Generally, a flow straightening section (e.g., a grid or a perforated plate) acts to equalize the flow velocity of gas upstream of the flow straightening section so that the pressure loss of the gas passing through the flow straightening section is uniform across the cross section of the flow path. In this case, if a gas flow resistance section is provided upstream of the flow straightening section, the resistance section may hinder the uniformity of the flow velocity of the exhaust gas. In the above configuration, the flow straightening section is located at a distance of 140 mm or more from the resistance section. This allows for a sufficient distance between the flow straightening section and the resistance section, thereby reducing the influence of the resistance section on the flow straightening function of the exhaust gas (uniformity of the flow velocity in the exhaust gas flow direction across the cross section of the flow path). Therefore, the flow straightening section can uniformize the flow velocity distribution of the exhaust gas across the cross section of the duct. This improves denitration efficiency. It is more preferable that the flow straightening section be located at a distance of 530 mm or more from the resistance section.

[0047] A denitration device according to a third aspect of the present disclosure is the denitration device of the first or second aspect, wherein the rectifying section has a lattice-shaped lattice section.

[0048] In the above configuration, the flow of exhaust gas passing through the lattice portion can be rectified. This makes it possible to make the flow velocity distribution of the exhaust gas uniform in the cross section of the duct flow path at the lattice portion, thereby improving the denitration efficiency.

[0049] A denitration device according to a fourth aspect of the present disclosure is the denitration device of any one of the first to third aspects, wherein the flow straightening section includes a porous plate (21) having a plurality of through holes (21a).

[0050] In the above configuration, the flow of the exhaust gas passing through the perforated plate can be rectified, thereby making the flow velocity distribution of the exhaust gas uniform in the cross section of the flow path of the duct at the perforated plate, thereby improving the denitration efficiency.

[0051] A denitration device according to a fifth aspect of the present disclosure is the above-mentioned fourth aspect, wherein a distance from the porous plate to the injection portion is longer than 11 times the length of the diameter of the through-hole.

[0052] In the above configuration, the distance from the perforated plate to the injection portion is longer than 11 times the diameter of the through-hole. A jet is generated in the exhaust gas when it passes through the through-holes in the perforated plate. In the above configuration, the distance from the perforated plate to the injection portion can be increased, allowing the exhaust gas to reach the injection portion with the jet sufficiently attenuated. That is, the exhaust gas reaches the injection portion with the flow velocity variation at each position in the flow path cross section suppressed. This allows the reducing agent to be injected into the exhaust gas with the variation suppressed. Therefore, the variation in the reducing agent concentration caused by the variation in the flow velocity at each position in the flow path cross section can be suppressed. Therefore, the exhaust gas flows into the denitration catalyst with the variation in the reducing agent concentration suppressed, and the denitration reaction occurs favorably in the denitration catalyst, thereby improving the denitration efficiency.

[0053] REFERENCE SIGNS LIST 1: Combustion engine 2: Exhaust heat recovery boiler 3: Duct 4: First heat exchange section (resistance section) 4a: Heat transfer tube 5: Second heat exchange section 7: Chimney 10: Denitration device 11: Ammonia injection section (injection section) 11a: Ammonia piping 12: Mixer 12A: Mixing section 12a: Cell 13: Denitration catalyst 14: Ammonia decomposition catalyst 18: Plate section 18a: Upstream plate section 18b: Downstream plate section 20: Flow straightening section 21: Perforated plate 21a: Through-hole

Claims

1. A denitration device comprising: an injection section provided in a duct through which exhaust gas flows, for injecting a reducing agent into the exhaust gas flowing through the duct; a denitration catalyst provided in the duct downstream of the injection section; and a straightening section provided in the duct upstream of the injection section a predetermined distance away from the injection section, for straightening the exhaust gas flowing through the duct.

2. A denitration device as described in claim 1, further comprising a resistance section provided within the duct and upstream of the straightening section for providing resistance to the flow of exhaust gas, the straightening section being provided at a position 140 mm or more away from the resistance section.

3. The denitration device according to claim 1, wherein the flow straightening section has a lattice-shaped lattice section.

4. The denitration device according to claim 1, wherein the flow straightening section comprises a porous plate having a plurality of through holes.

5. A denitration device according to claim 4, wherein the distance from said porous plate to said injection portion is longer than 11 times the diameter of said through-hole.

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