SCR flue gas denitration device suitable for severe change in NOX distribution at inlet

Abstract

An SCR flue gas denitration device suitable for severe change in NOx distribution at an inlet. The device comprises: an economizer outlet flue (1), an economizer ash hopper (3) being arranged at the bottom of the economizer outlet flue; a coarse ash pre-removal device (2); an SCR inlet horizontal flue (5); a flared flue (6) which is horizontally arranged; an SCR ascending flue (11) comprising a vertical section and an outlet section; an SCR reactor (14); an SCR catalyst layer (15); and an SCR outlet flue (16), wherein a communication port in one side of the bottom of the economizer outlet flue (1) is in communication with an inlet of the SCR inlet horizontal flue (5), the SCR inlet horizontal flue (5) is in communication with a feeding port of the SCR ascending flue (11) via the flared flue (6), the vertical section of the SCR ascending flue (11) is arranged from bottom to top, the outlet section is arranged at the upper portion of the SCR ascending flue, an outlet of the outlet section is arranged to be interfaced with an inlet of the SCR reactor (14), the SCR catalyst layer (15) is arranged below the SCR reactor (14), and the SCR outlet flue (16) is arranged at the bottom of the SCR catalyst layer (15).

Description

An SCR flue gas denitrification device suitable for severely changing inlet NOx distribution

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the Patent Office of China on July 17, 2023, with application number 202310871615.0 and invention name “A SCR flue gas denitrification device suitable for severe changes in imported NOx distribution”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of SCR flue gas denitrification, and in particular to an SCR flue gas denitrification device suitable for severely changing inlet NOx distribution. Background Art

[0004] With the rapid development of renewable energy sources such as wind and photovoltaic power, traditional coal-fired power generation units are shifting from primary power sources to load-regulated power sources, and are also co-managing the disposal of solid waste such as municipal sludge. While coal-fired power generation units are shouldering greater social responsibilities, their loads and feed fuels are significantly deviating from their design values. Changes in unit load, mill configuration, feed fuel, and combustion adjustments can significantly alter the NOx concentration distribution at the SCR inlet, reducing the uniformity of the NH3 / NOx molar ratio distribution at the catalyst inlet and increasing ammonia slip at the denitrification outlet.

[0005] To address the issue of poor and variable NOx distribution at the SCR inlet, two technical approaches have been proposed in China: one is to improve NOx distribution uniformity through a static mixer, and the other is to adapt to changes in NOx distribution through a zoned automatic ammonia injection control system.

[0006] Using technical route 1, Chinese patent document CN106823796A discloses a static mixer with one to three rows of circular or star-shaped discs, each with a diameter of 1 to 1.5 meters, arranged in a horizontal flue 10 to 15 meters in front of the AIG to premix the flue gas before ammonia injection. Chinese patent document CN106731827B discloses a large-scale self-mixing device for flue gas upstream of the AIG. Chinese patent document CN210752111U discloses a full-load adaptive SCR ammonia injection system, including an ammonia injection device, a large-scale self-mixing device for flue gas, and a rectifier.

[0007] Adopting technical route 2, Chinese patent document CN106000087A discloses an SCR ultra-low emission control system based on zoned mixing regulation, comprising an SCR inlet flue, a plurality of inlet flue baffles, a plurality of outlet flue baffles, an SCR outlet flue, a DCS control system, an ammonia input pipeline, and an SCR reactor. Each inlet flue baffle is located within the outlet of the SCR inlet flue, and each inlet flue baffle divides the outlet of the SCR inlet flue into a plurality of inlet flue gas channels. Each outlet flue baffle is located within the inlet of the SCR outlet flue, and each outlet flue baffle divides the inlet of the SCR outlet flue into a plurality of outlet flue gas channels. An ammonia injection grid is provided in each inlet flue gas channel, and an ammonia input pipeline is respectively connected to the inlet of each ammonia injection grid, wherein a regulating valve is provided at the inlet of each ammonia injection grid. One inlet flue gas channel corresponds to one outlet flue gas channel.

[0008] Chinese patent document CN106823796A proposes a solution of arranging 1 to 3 rows of circular or star-shaped disc static mixers with a diameter of 1 to 1.5 m in a horizontal flue 10 to 15 m in front of the AIG to premix the flue gas before ammonia injection, thereby improving the NOx concentration and flue gas velocity distribution uniformity at the AIG inlet and enhancing the AIG's adaptability to variable operating conditions.

[0009] The SCR inlet flue is typically rectangular, with a width typically exceeding 9 meters and a depth approximately one-quarter of the depth. Circular or star-shaped static mixers, with diameters of only 1 to 1.5 meters, cannot achieve sufficient mixing of flue gases across the entire width. Therefore, while this technical solution can improve the uniformity of NOx distribution in localized flue gas, it cannot effectively reduce NOx distribution deviation across the width.

[0010] The triangular flue gas large-scale self-mixing device used in Chinese patent documents CN106731827B and CN210752111U has a mixing effect on NOx concentration deviations within a rectangular flue, as shown in Figure 2. This device is superior to the technical solution in Chinese patent document CN106823796A. However, due to its large size, the triangular flue gas large-scale self-mixing device's applicability is significantly limited by on-site installation space.

[0011] The SCR ultra-low emission control system based on zoned mixing regulation proposed in Chinese patent document CN106000087A reduces the flue width of each zoned channel by dividing the inlet and outlet flues into multiple channels. Furthermore, a static mixer, an ammonia injection grid, an ammonia delivery and flow control system, and an outlet NOx concentration detector are installed in each channel to match the local ammonia injection amount with the NOx distribution. This solution essentially utilizes the mature technology of the existing dual-channel SCR reactor to further increase the number of flue zones, thereby improving the flexibility of regulating the regional ammonia injection amount and adaptability to operating conditions. The technology is theoretically feasible, but the system is complex and the implementation cost is high. The actual effect is heavily dependent on the accuracy and timeliness of the measurement of the NOx concentration distribution in the SCR outlet cross section. Its practicality is poor when the unit is frequently and flexibly operated for peak shaving.

[0012] Summary of the Invention

[0013] To address these issues, this application provides an SCR flue gas denitrification system suitable for applications with severely variable inlet NOx distribution. This system reduces the relative standard deviation (CV) of NOx distribution at the SCR inlet flue by up to 93%. The NOx distribution pattern at the top catalyst inlet cross section is more uniform under different operating conditions, significantly reducing the impact of unit load and mill combination on the uniformity of the NH3 / NO molar ratio distribution at the catalyst inlet. Pre-removal of coarse ash effectively reduces wear on the SCR inlet flue and catalyst, ensuring the reliability and stability of the denitrification system.

[0014] An SCR flue gas denitrification device suitable for severely changing inlet NOx distribution, characterized in that it comprises:

[0015] The economizer outlet flue has a connecting port on one side of its bottom and an economizer ash hopper is provided at its bottom;

[0016] Coarse ash pre-removal device;

[0017] SCR inlet horizontal flue;

[0018] The expanded flue is arranged horizontally;

[0019] The SCR ascending flue includes a vertical section and an outlet section;

[0020] SCR reactor;

[0021] SCR catalyst layer;

[0022] and SCR outlet flue;

[0023] A connecting port on one side of the bottom of the economizer outlet flue is connected to the inlet of the SCR inlet horizontal flue, and the SCR inlet horizontal flue is connected to the inlet of the SCR ascending flue through a flared flue. The vertical sections of the SCR ascending flue are arranged from bottom to top, and an outlet section is provided on the upper part. The outlet of the outlet section is connected to the inlet of the SCR reactor. An SCR catalyst layer is provided below the SCR reactor, and an SCR outlet flue is provided at the bottom of the SCR catalyst layer.

[0024] The optional features are:

[0025] The inlet cavity of the vertical section of the SCR ascending flue is evenly arranged with a number of ascending flue inlet arc guide plates, and the outlet cavity of the vertical section of the SCR ascending flue is evenly arranged with a number of ascending flue outlet arc guide plates to reduce the phenomenon of flue gas and fly ash deviation caused by the flow in the bend; the number of the ascending flue inlet arc guide plates and the ascending flue outlet arc guide plates is 2 to 5;

[0026] An AIG flue gas large-scale mixer and an ammonia injection grid are installed in the area below the vertical section of the SCR ascending flue. Under the action of the large-scale flue gas mixer, the flue gas forms a circular flow and local vortex covering the entire flue cross section, which helps to enhance the uniform mixing of NH3 and flue gas at the AIG outlet, while reducing the flow velocity distribution deviation in the width direction of the flue upstream of the AIG. In addition, due to the installation of the AIG flue gas large-scale mixer, the number of nozzles of the ammonia injection grid can be greatly reduced, the gas flow rate of each nozzle is greatly increased, and the blockage risk is significantly reduced;

[0027] The AIG flue gas large-scale mixer is installed upstream or downstream of the ammonia injection grid;

[0028] An inwardly angled corner is provided on the rear wall of the economizer outlet flue, and a coarse ash pre-removal device is provided at a position corresponding to the lower end of the angle. The angle guides the flue gas into the inlet of the coarse ash pre-removal device, and an economizer ash hopper is provided below the bottom of the coarse ash pre-removal device.

[0029] A front flue gas large-scale mixer is provided in the SCR inlet horizontal flue, which is used to obtain a strong circulation across the entire flue cross-section, thereby achieving sufficient mixing of the flue gas across the entire cross-section. The front flue gas large-scale mixer is arranged in front of the flared flue, and the flue gas quickly fills the entire outward-expanding flue under the action of the strong circulation, thereby avoiding the occurrence of a low flow velocity area in the flared flue.

[0030] A rectifying grid is provided at the connection position between the outlet section and the SCR reactor.

[0031] The above technical solution, which utilizes efficient coarse ash removal and extensive flue gas self-mixing, reduces the relative standard deviation (CV) of NOx distribution at the SCR inlet flue by 93%. This results in a more uniform NOx distribution pattern across the top catalyst inlet cross-section under different operating conditions, significantly reducing the impact of unit load and mill combination on the uniformity of the NH3 / NO molar ratio distribution at the catalyst inlet. Pre-removal of coarse ash effectively reduces wear on the SCR inlet flue and catalyst, ensuring the operational reliability of the denitrification system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic diagram of the main structure of the present application;

[0033] FIG2 is a schematic diagram of the three-dimensional structure of the present application;

[0034] FIG3 is a schematic diagram of the downstream flue gas flow line in which a front flue gas large-scale mixer is provided in this application;

[0035] FIG4 is a schematic diagram of the downstream flue gas flow line of the AIG flue gas large-scale mixer set in this application;

[0036] FIG5 is a graph showing the inlet NO concentration distribution of the first simulated operating condition;

[0037] FIG6 is a concentration distribution diagram of the SCR inlet flue gas after adopting the specific embodiment of the present application under the first working condition;

[0038] FIG7 is a graph showing the inlet NO concentration distribution of the second simulated operating condition;

[0039] FIG8 is a concentration distribution diagram of the SCR inlet flue gas after adopting the specific embodiment of the present application under the second working condition;

[0040] Figure 9 is a schematic diagram of the velocity distribution of the SCR inlet flue after adopting this method;

[0041] The names of the corresponding serial numbers in the figure are as follows: 1. Economizer outlet flue; 2. Coarse ash pre-removal device; 3. Economizer ash hopper; 4. Front flue gas large-scale mixer; 5. SCR inlet horizontal flue; 6. Expanded flue; 7. Denitrification ash hopper; 8. Upstream flue inlet arc guide plate; 9. AIG flue gas large-scale mixer; 10. Ammonia injection grid; 11. SCR upstream flue; 12. Upstream flue outlet arc guide plate; 13. Rectifier grid; 14. SCR reactor; 15. SCR catalyst layer; 16. SCR outlet flue. DETAILED DESCRIPTION

[0042] An SCR flue gas denitrification device suitable for severely variable inlet NOx distribution, as shown in Figures 1 to 4, includes an economizer outlet flue 1, a coarse ash pre-removal device 3, an SCR inlet horizontal flue 5, a flared flue 6, an SCR ascending flue 11, an SCR reactor 14, an SCR catalyst layer 15, and an SCR outlet flue 16;

[0043] A communication port is opened on one side of the bottom of the economizer outlet flue 1, and an economizer ash hopper 3 is provided at the bottom thereof;

[0044] The SCR ascending flue 11 includes a vertical section and an outlet section;

[0045] The connecting port on one side of the bottom of the economizer outlet flue 1 is connected to the inlet of the SCR inlet horizontal flue 5, and the SCR inlet horizontal flue 5 is connected to the inlet of the SCR ascending flue 11 through the expanded flue 6. The vertical sections of the SCR ascending flue 11 are arranged from bottom to top, and an outlet section is provided on the upper part thereof. The outlet section is arranged to connect with the inlet cross-section of the SCR reactor 14. An SCR catalyst layer 15 is provided below the SCR reactor 14, and an SCR outlet flue 16 is provided at the bottom of the SCR catalyst layer 15.

[0046] In a specific implementation, a plurality of ascending flue inlet arc guide plates 8 are evenly arranged on the inlet cavity of the vertical section of the SCR ascending flue 11, and a plurality of ascending flue outlet arc guide plates 12 are evenly arranged on the outlet cavity of the vertical section of the SCR ascending flue 11 to reduce the phenomenon of flue gas and fly ash deviation caused by the flow in the bend; the number of the ascending flue inlet arc guide plates 8 and the ascending flue outlet arc guide plates 12 is 2 to 5;

[0047] An AIG flue gas large-scale mixer 9 and an ammonia injection grid 10 are provided in the lower area of ​​the vertical section of the SCR ascending flue 11. The AIG flue gas large-scale mixer 9 can be installed upstream or downstream of the ammonia injection grid 10.

[0048] An inwardly angled corner is provided on the rear wall of the economizer outlet flue 1. A coarse ash pre-removal device 2 is provided at the position corresponding to the lower end of the angle. The angle guides the flue gas into the inlet of the coarse ash pre-removal device 2. An economizer ash hopper 3 is provided below the bottom of the coarse ash pre-removal device 2.

[0049] A front flue gas large-scale mixer 4 is provided in the SCR inlet horizontal flue 5. The front flue gas large-scale mixer 4 is used to obtain a strong circulation across the entire flue cross-section, achieving sufficient mixing of the flue gas across the entire cross-section. The front flue gas large-scale mixer 4 is arranged in front of the flared flue 6. Under the action of the strong circulation, the flue gas quickly fills the entire flared flue, thereby avoiding the occurrence of a low flow velocity area in the flared flue 6.

[0050] A rectifying grid 13 is provided at the connection position between the outlet section and the SCR reactor 14 .

[0051] During specific implementation, the SCR ascending flue 11 is connected to the SCR inlet horizontal flue 5, and a set of arc guide plates 8 at the ascending flue inlet are provided at the connecting bend to reduce the deviation of flue gas and fly ash caused by the flow in the bend; at the front end of the SCR ascending flue 11, an AIG flue gas large-scale mixer 9 and an ammonia spraying grid 10 are arranged; under the action of the flue gas large-scale mixer 9, the flue gas forms a circular flow and local vortex diagram 5 covering the entire flue cross section, which helps to enhance the uniform mixing of NH3 and flue gas at the AIG outlet, while reducing the flow velocity distribution deviation in the width direction of the flue in the upstream section of the AIG. Due to the provision of the AIG flue gas large-scale mixer 9, the number of nozzles of the ammonia spraying grid 10 can be greatly reduced, the airflow of a single nozzle can be greatly increased, and the risk of blockage can be significantly reduced. It should be pointed out that the AIG flue gas large-scale mixer 9 can be installed upstream of the ammonia spraying grid 10 or downstream of the ammonia spraying grid 10.

[0052] At the top bend of the SCR ascending flue 11, a set of arc deflectors 12 are installed at the ascending flue outlet to reduce the deviation of flue gas and fly ash caused by the bend. The arc deflectors 8 and 12 are usually arranged in a set of 2 to 5 pieces.

[0053] Flue gas from the ascending flue 11 passes through a rectifier grid 13 and then flows vertically downward into the SCR reactor 14. Three to four layers of catalyst 15 are arranged within the SCR reactor 14. Under the action of the catalyst, the reducing agent NH3 gas reacts with NOx in the flue gas to produce pollution-free N2 and H2O. Unreacted NOx and NH3 gas flow with the flue gas into the SCR outlet flue 16.

[0054] The rear wall of the economizer outlet flue 1 is provided with an inwardly-pointing angle, the end of which is directly above the economizer ash hopper 3 .

[0055] The coarse ash pre-removal device 2 is arranged in the area behind the economizer outlet flue 1 and is in contact with the corner rear wall to avoid flue gas short circuit.

[0056] The economizer ash hopper 3 adopts a deep ash hopper, and the angle between the side wall and the horizontal direction is greater than 50 degrees.

[0057] The large-scale flue gas mixer 4 in front of the expanded flue adopts a 2LXV large-scale flue gas mixer to obtain a strong circulation across the entire flue cross section as shown in Figures 6 and 8.

[0058] Optionally, the AIG flue gas large-scale mixer 9 adopts a 4LXV type flue gas large-scale mixer to obtain the circular flow and local vortex covering the entire flue cross section as shown in Figures 6 and 8.

[0059] The distance between the AIG flue gas large-scale mixer 9 and the ammonia injection grid 10 is 1 to 3 meters.

[0060] In the SCR inlet flue, no other guide plates are provided except the arc guide plates 8 and 12 at the inlet and outlet of the ascending flue.

[0061] In specific implementation, an SCR flue gas denitrification device suitable for severely variable inlet NOx distribution was used to optimize the flow field design of the SCR denitrification device for a 600MW coal-fired power generation unit. Along the flue gas flow path, a 2LXV-type flue gas large-scale mixer was placed in the front section of the expanded horizontal flue at the SCR inlet, two arc guide plates were placed in the turning area of ​​the ascending flue inlet, a 4LXV-type AIG flue gas large-scale mixer was placed downstream of the ammonia injection grid, and two arc guide plates were placed in the turning area of ​​the ascending flue outlet.

[0062] Under two harsh conditions where the NO concentration in the economizer outlet flue cross-section is high on one side and low on the other side, high in the middle and low on both sides, and the average standard deviation CV value of the distribution is as high as 20.5%, a numerical simulation method is used to calculate and analyze the adaptability of the SCR flue gas denitrification device proposed in this application to the harsh working conditions where the inlet NOx distribution is poorly uniform and the distribution pattern is changeable.

[0063] The first working condition is shown in Figure 5; the second working condition is shown in Figure 7;

[0064] The simulation results show that the SCR denitrification device design proposed in this application has excellent adaptability to harsh operating conditions. For the two distributions of NO concentration, high on one side and low on the other side, and high in the middle and low on both sides, the NO concentration distribution CV of the 500mm section upstream of the top catalyst is reduced to below 1.5%. The NO concentration distribution of the SCR inlet section shown in Figures 6 and 8 intuitively shows the changes in NO distribution along the process.

[0065] Under the simulated working conditions, the velocity distribution of the SCR inlet section is shown in Figure 9. The velocity distribution CV upstream of the ammonia injection grid is 19.8%, and the velocity distribution CV of the 500mm section upstream of the top catalyst is 13.5%.

[0066] Table 1 shows the flow field statistics for a section 500 mm upstream of the top catalyst. The CV of the NH₃ / NO distribution in Case 1 reached 4.8% for uniform ammonia injection. After adjusting the flow rate in the ammonia injection grid branch pipe based on the upstream velocity distribution, the CV of the NH₃ / NO distribution reached 1.1% and 1.2% for two inlet NO distributions.

[0067] Table 1 Flow field statistics of the 500 mm section upstream of the top catalyst

[0068] This case illustrates that the SCR flue gas denitrification device proposed in this application, which is suitable for thermal power plants with severely variable inlet NOx distribution, can reduce the relative standard deviation CV value of the NO distribution in the upstream section of the top catalyst by 93% under extremely harsh operating conditions, and the NH3 / NO molar ratio distribution CV = 1.1~1.2%, which is close to completely uniform. All performance indicators of the flow field of the SCR denitrification device are significantly better than conventional design requirements.

[0069] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above, and that the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present application is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0070] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. An SCR flue gas denitrification device suitable for severe changes in inlet NOx distribution, characterized in that: It includes: The economizer outlet flue has a connecting port on one side of its bottom, and an economizer ash hopper is arranged at its bottom; Coarse ash pre-removal device; SCR inlet horizontal flue; The expanded flue is arranged horizontally; The SCR ascending flue includes a vertical section and an outlet section; SCR reactor; SCR catalyst layer; and SCR outlet flue; A connecting port on one side of the bottom of the economizer outlet flue is connected to the inlet of the SCR inlet horizontal flue, and the SCR inlet horizontal flue is connected to the inlet of the SCR ascending flue through a flared flue. The vertical sections of the SCR ascending flue are arranged from bottom to top, and an outlet section is provided on the upper part thereof, and the outlet of the outlet section is connected to the inlet of the SCR reactor. An SCR catalyst layer is provided below the SCR reactor, and an SCR outlet flue is provided at the bottom of the SCR catalyst layer.

2. The SCR flue gas denitrification device suitable for severe changes in inlet NOx distribution as claimed in claim 1, characterized in that: The inlet cavity of the vertical section of the SCR ascending flue is evenly arranged with a number of ascending flue inlet arc guide plates, and the outlet cavity of the vertical section of the SCR ascending flue is evenly arranged with a number of ascending flue outlet arc guide plates to reduce the smoke and fly ash deviation caused by the flow in the curve; the number of the ascending flue inlet arc guide plates and the ascending flue outlet arc guide plates is 2 to 5.

3. The SCR flue gas denitrification device suitable for severe changes in inlet NOx distribution as claimed in claim 2, characterized in that: AIG flue gas large-scale mixer and ammonia injection grid are arranged in the lower area of ​​the vertical section of the SCR ascending flue. Under the action of the flue gas large-scale mixer, the flue gas forms a circulation and local vortex covering the entire flue cross section.

4. The SCR flue gas denitrification device suitable for severe changes in inlet NOx distribution as claimed in claim 3, characterized in that: The AIG flue gas large-scale mixer is installed upstream or downstream of the ammonia injection grid.

5. The SCR flue gas denitrification device suitable for severe changes in inlet NOx distribution as claimed in claim 1, characterized in that: An inward angle is arranged on the rear wall of the economizer outlet flue, and a coarse ash pre-removal device is arranged at a position corresponding to the lower end of the angle. The angle guides the flue gas into the inlet of the coarse ash pre-removal device, and an economizer ash hopper is arranged below the bottom of the coarse ash pre-removal device.

6. The SCR flue gas denitrification device suitable for severe changes in inlet NOx distribution as claimed in claim 1, characterized in that: A front flue gas large-range mixer is arranged in the SCR inlet horizontal flue, and the front flue gas large-range mixer is used to obtain a strong circulation across the entire flue cross section to achieve full mixing of the flue gas in the entire cross section.

7. The SCR flue gas denitrification device suitable for severe changes in inlet NOx distribution as claimed in claim 1, characterized in that: A rectifying grid is arranged at the connection position between the outlet section and the SCR reactor.

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