De-nitrification ammonia injection control method and system based on accurate measurement of ammonia escape

Abstract

The application discloses a denitration ammonia injection control method and system based on accurate ammonia escape measurement, comprising the following steps: dividing the SCR inlet flue into ammonia injection control subareas, and dividing the SCR outlet flue into the same number of sampling subareas; setting a judgment condition, if the judgment condition is met, determining whether to perform ammonia injection adjustment according to the SCR outlet ammonia escape concentration deviation or the NOx concentration deviation, otherwise, performing a purging operation or raising the flue gas temperature on the sampling subarea and the catalyst. The application firstly divides the SCR inlet flue and the SCR outlet flue into subareas, calculates the SCR outlet ammonia escape concentration by testing the inlet and outlet NOx concentrations of each subarea catalyst module, and then determines whether to perform ammonia injection adjustment according to whether the SCR outlet ammonia escape concentration deviation or the NOx concentration deviation exceeds a limited value, so that the ammonia escape deviation is 20% to 30%, the outlet NOx concentration deviation is 30% to 40%, and the problem that ammonia escape measurement is inaccurate and cannot participate in ammonia injection control is solved.

Description

Technical Field

[0001] This invention belongs to the field of denitrification ammonia injection technology, specifically relating to a denitrification ammonia injection control method and system based on accurate measurement of ammonia slip. Background Technology

[0002] Improving the uniformity of the ammonia-nitrogen molar ratio distribution at the catalyst inlet cross section and eliminating local high ammonia escape values ​​are key to improving the operating level of the denitrification unit and avoiding ammonium bisulfate blockage problems in downstream equipment.

[0003] Because the amount of ammonia slip at the denitrification outlet is in the ppm level, and is limited by conditions such as ash in the flue gas and equipment vibration, it is difficult to detect ammonia slip online in real time. According to statistics, more than 90% of NH3-CEMS instruments in China have distortion problems. Therefore, it is almost impossible to obtain an accurate cross-sectional ammonia slip distribution by using NH3-CEMS instruments.

[0004] For the reasons mentioned above, domestically, the uniformity of NOx concentration distribution at the denitrification outlet is currently used as a criterion for adjusting ammonia injection. It is assumed that when the NOx concentration distribution is uniform, the ammonia-nitrogen molar ratio can also achieve a certain degree of uniformity. This method is only suitable for units with relatively good inlet NOx distribution uniformity or where overall denitrification efficiency requirements are not high. When the inlet NOx concentration distribution deviates significantly or the denitrification efficiency requirement is high, the denitrification efficiency in local areas will be significantly higher, resulting in a higher corresponding ammonia slip concentration. Meanwhile, the catalyst capacity in low-efficiency areas is not fully utilized. In reality, there will inevitably be deviations in the inlet NOx concentration distribution of denitrification. Therefore, uniform ammonia slip distribution and uniform outlet NOx concentration distribution are inherently contradictory. Using only the uniformity of NOx concentration distribution as a single indicator cannot achieve the fundamental goal of optimizing ammonia injection. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the purpose of this invention is to provide a denitrification ammonia injection control method and system based on accurate measurement of ammonia slip.

[0006] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0007] The denitrification ammonia injection control method based on accurate ammonia slip measurement includes the following steps:

[0008] 1) Connect the ammonia supply main pipe to the SCR inlet flue, measure the NOx concentration and flue gas velocity of the SCR inlet flue, and divide it into several ammonia injection control zones according to the NOx content. The NOx content deviation within the same ammonia injection control zone should be within the set range.

[0009] 2) Based on the number of ammonia injection control zones, divide the SCR outlet flue into the same number of sampling zones and calculate the ammonia slip concentration in each sampling zone.

[0010] 3) Set the judgment conditions. If the judgment conditions are met, proceed to step 4); otherwise, proceed to step 5.

[0011] 4) Test the NOx concentration at the inlet and outlet of the catalyst in each sampling zone, calculate the ammonia slip concentration at the SCR outlet, and determine whether to adjust the ammonia injection based on whether the deviation of the ammonia slip concentration or the NOx concentration at the SCR outlet exceeds the limit.

[0012] 5) Purge the sampling area and catalyst or increase the flue gas temperature.

[0013] Furthermore, in step 1), the NOx content deviation within the same ammonia injection control zone is within 10%; each ammonia injection control zone is controlled by a pneumatic regulating valve, and several branch pipes of each ammonia injection control zone extend into different depths of the SCR inlet flue. Each branch pipe is equipped with a manual regulating valve to facilitate fine adjustment under hot conditions.

[0014] Furthermore, in step 2), each sampling branch pipe in each sampling zone is equipped with a pneumatic switch valve, and each sampling branch pipe merges into the sample gas main pipe. The sample gas main pipe is connected to the outlet of the air preheater through the fly ash separation channel and the flue gas test channel, respectively. The flue gas test channel is equipped with a catalyst, a flue gas temperature detection module and a flue gas pressure detection module. The ammonia escaping in the flue gas undergoes a denitrification reaction on the catalyst surface. The ammonia escape concentration in each sampling zone is accurately obtained by testing the NOx concentration at the catalyst inlet and outlet.

[0015] Furthermore, the diameter of the sample gas main pipe is D1, the diameter of the fly ash separation channel is D2, and the diameter of the flue gas testing channel is D3, where D1>D3>D2. A flue gas deflector and a fly ash interceptor are installed at the inlet of the fly ash separation channel.

[0016] Furthermore, the angle α between the flue gas deflector and the horizontal axis of the sample gas header is 15° to 30°, the height l1 of the flue gas deflector is ≥ 1 / 3 × D1 / sinα, and the distance from the outer edge of the flue gas deflector to the central axis of the fly ash separation channel is between 1 / 2 × D1 and 2D1.

[0017] Furthermore, the angle β between the fly ash interception baffle and the horizontal axis is 20° to 30°, the height l2 of the fly ash interception baffle is ≥ 1 / 3 × D1 / sinβ, and the distance between the top edge of the fly ash interception baffle and the wall of the fly ash separation channel is ≥ 1 / 3 × D2.

[0018] Furthermore, in step 3), the determination condition is:

[0019] 1) Stable load;

[0020] 2) The catalyst was not continuously operated below 270℃ for more than 5 hours;

[0021] 3) Flue gas differential pressure Δp increases by <20%;

[0022] 4) Smoke temperature > 250℃;

[0023] Meeting any one of these criteria is sufficient to satisfy the judgment condition.

[0024] Furthermore, in step 4), if the ammonia slip concentration deviation at the SCR outlet exceeds 30% or the NOx concentration deviation exceeds 40%, the corresponding SCR inlet ammonia injection grille valve is adjusted to control the ammonia slip concentration deviation between 20% and 30% and the NOx concentration deviation between 30% and 40%, while ensuring that NOx emissions meet standards; during unit load changes, the ammonia injection grille valve is not adjusted.

[0025] Furthermore, in step 5), if the judgment condition is not met, the steps of purging the sampling area and catalyst or increasing the flue gas temperature include:

[0026] When the flue gas temperature is below 250℃, the pipeline may become blocked, affecting the extraction volume. In this case, the pipeline is backflushed by purging each sampling branch in the sampling zone with compressed air. During backflushing, the pneumatic valve on the main sample gas pipe is closed, the valve of one of the sampling branch pipes is opened, and the valves of the remaining sampling branch pipes are closed. The purging is carried out sequentially, and the purging time for each pipeline is >20s.

[0027] When the flue gas differential pressure Δp rises by more than 20%, the catalyst purging pipeline is opened, and compressed air is used to purge the catalyst ash accumulation in the flue gas test channel until the flue gas differential pressure returns to normal; the low-temperature operation time is controlled to avoid catalyst blockage caused by ammonium bisulfate.

[0028] When the flue gas temperature is below 270℃ and the cumulative operating time exceeds 5 hours, all sampling branches are opened simultaneously to increase the flue gas extraction volume, raise the flue gas temperature to above 300℃ and run continuously for 2 hours, and then the single sampling branch inspection mode is restored.

[0029] This invention also discloses a denitrification ammonia injection control system based on accurate measurement of ammonia slip, comprising:

[0030] Ammonia supply main pipe;

[0031] The SCR inlet flue is connected to the ammonia supply main pipe and is divided into several ammonia injection control zones according to the NOx content. The NOx content deviation within the same ammonia injection control zone is within the set range. Each ammonia injection control zone is controlled by a pneumatic regulating valve. Several branch pipes of each ammonia injection control zone extend into the SCR inlet flue at different depths. Each branch pipe is equipped with a manual regulating valve for easy fine adjustment under hot conditions.

[0032] Sample gas header;

[0033] The SCR outlet flue is connected to the sample gas main pipe. It is divided into the same number of sampling zones according to the number of ammonia injection control zones. Each sampling zone has a pneumatic switch valve installed on each sampling branch pipe. All sampling branch pipes converge into the sample gas main pipe. The sample gas main pipe is connected to the air preheater outlet through the fly ash separation channel and the flue gas test channel. The flue gas test channel is equipped with catalyst, flue gas temperature detection module and flue gas pressure detection module.

[0034] The condition determination module has the following determination conditions: 1) stable load; 2) catalyst has not been running continuously below 270℃ for more than 5 hours; 3) flue gas differential pressure Δp increases by less than 20%; 4) flue gas temperature is greater than 250℃; if all conditions are met, the determination conditions are considered met.

[0035] The data analysis module is used to determine whether to adjust ammonia injection based on whether the deviation of SCR outlet ammonia slip concentration or NOx concentration exceeds the limit value.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention discloses a method and system for controlling ammonia injection in denitrification based on accurate ammonia slip measurement. First, the SCR inlet flue and SCR outlet flue are divided into zones. The ammonia slip concentration at the SCR outlet is calculated by testing the easily measurable NOx concentrations at the catalyst inlet and outlet of each zone. Then, whether ammonia injection adjustment is needed is determined based on whether the deviation of the SCR outlet ammonia slip concentration or the NOx concentration deviation exceeds the limit value. This achieves an ammonia slip deviation between 20% and 30% and an SCR outlet NOx concentration deviation between 30% and 40%, solving the key problem that inaccurate ammonia slip measurement prevents its participation in ammonia injection control. Attached Figure Description

[0038] Figure 1 This is a structural schematic diagram of step 1) of the present invention;

[0039] Figure 2 This is a schematic diagram of the structure of step 2) of the present invention;

[0040] Figure 3 This is a flowchart of the present invention. Detailed Implementation

[0041] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0042] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0043] like Figure 1-3 As shown, the denitrification ammonia injection control method based on accurate ammonia slip measurement includes the following steps:

[0044] 1) Ammonia injection control zone division

[0045] Under typical high, medium, and low loads, the NOx concentration and flue gas velocity of SCR inlet flue 1 were measured. Based on the NOx content, the flue was divided into n ammonia injection control zones, with the NOx content deviation within the same zone within 10%. Therefore, the area of ​​each zone may differ, which differs from the conventional uniform zoning scheme, making this invention more targeted.

[0046] Each ammonia injection control zone is controlled by a pneumatic regulating valve 2. Each ammonia injection control zone is further divided into several branch pipes 3 that extend into the SCR inlet flue 1 at different depths. Each branch pipe 3 is equipped with a manual regulating valve 4 for easy fine adjustment under hot conditions.

[0047] 2) Accurate measurement by zone

[0048] Based on the number of ammonia injection control zones, the SCR outlet flue 5 is divided into n sampling zones. Each sampling branch pipe 6 in the sampling zone is equipped with a pneumatic switch valve 7. Each sampling branch pipe 6 merges into the sample gas header pipe 8 (diameter D1). As the sample gas header pipe 8 moves downward, it is divided into a fly ash separation channel 9 (diameter D2) and a flue gas testing channel 10 (diameter D3). Finally, they are connected to the outlet of the air preheater 11. The differential pressure between the denitrification outlet and the air preheater outlet is used to achieve rapid extraction of flue gas, enabling patrol testing and overall testing. The pipe diameter relationship is D1>D3>D2.

[0049] A flue gas deflector baffle 12 and a fly ash interceptor baffle 13 are installed at the inlet of the fly ash separation channel 9. The angle α between the flue gas deflector baffle 12 and the horizontal axis of the sample gas header 8 is 15°–30°, the height l1 of the flue gas deflector baffle 12 is ≥1 / 3×D1 / sinα, and the distance from the outer edge of the flue gas deflector baffle 12 to the central axis of the fly ash separation channel 9 is between 1 / 2×D1 and 2D1. The angle β between the fly ash interceptor baffle 13 and the horizontal axis is 20°–30°, the height l2 of the fly ash interceptor baffle 13 is ≥1 / 3×D1 / sinβ, and the distance from the top edge of the fly ash interceptor baffle 13 to the wall of the fly ash separation channel 9 is ≥1 / 3×D2. By setting up the fly ash separation channel 9 and utilizing the flue gas deflector baffle 12 and the fly ash interceptor baffle 13, fly ash can be effectively separated, ensuring the cleanliness of the flue gas in the test channel.

[0050] A catalyst unit 101 is arranged in the flue gas test channel 10. The ammonia that escapes in the flue gas will continue to undergo denitrification reaction on the surface of the catalyst unit 101. The ammonia escape concentration in each sampling zone can be accurately obtained by testing the NOx concentration at the inlet and outlet of the catalyst unit 101.

[0051] The flue gas test channel 10 is also equipped with a flue gas temperature detection module 102 and a flue gas pressure detection module 103, which are placed at the catalyst inlet and outlet respectively, and are used for temperature detection and flue gas pressure detection respectively.

[0052] 3) Compressed air purging

[0053] When the flue gas temperature is below 250℃, the pipeline may become blocked, affecting the extraction volume. The pipeline is backflushed by purging each sampling branch pipe 6 with compressed air. During backflushing, the pneumatic valve on the main pipe 8 is closed, the valve of one of the sampling branch pipes 6 is opened, and the valves of the remaining sampling branch pipes 6 are closed. The purging is carried out in sequence, and the purging time for each pipeline is >20s.

[0054] 4) Catalyst protection control

[0055] The flue gas temperature detection module 102 and the flue gas pressure detection module 103 monitor the inlet and outlet flue gas pressure of the catalyst respectively. When the flue gas differential pressure Δp rises by more than 20%, the catalyst purging pipeline is opened, and compressed air is used to purge the ash accumulated in the catalyst unit 101 until the differential pressure returns to normal.

[0056] On the other hand, the low-temperature operation time is controlled to avoid the catalyst of catalyst unit 101 from being blocked by ammonium bisulfate: when the flue gas temperature is below 270°C and the cumulative operation time exceeds 5 hours, all sampling branches 6 are opened at the same time to increase the flue gas extraction volume, raise the flue gas temperature to above 300°C and run continuously for 2 hours, and then the single sampling branch inspection mode is restored.

[0057] 5) Zoned inspection

[0058] Under normal circumstances, the zone measurement adopts the patrol measurement mode, that is, the valve of each sampling branch pipe 6 is opened sequentially, and the opening time is 40 seconds each time. The NOx concentration at the inlet and outlet of the catalyst unit 101 is tested online in real time, thereby obtaining the cross-sectional flue gas component concentration distribution.

[0059] 6) Calculation of ammonia slip concentration

[0060] After initial commissioning, data was collected manually and the catalyst potential was calculated using the following formula:

[0061]

[0062]

[0063]

[0064] In the formula, P is the catalyst potential; MR is the ammonia-nitrogen molar ratio; and η is the average denitrification efficiency under this load. The concentration of ammonia slip at the catalyst outlet is μL / L; NO x,in NO x,out The NOx concentrations at the catalyst inlet and outlet are in mg / m³. 3 .

[0065] During continuous operation, the catalyst potential can be considered constant. The SCR outlet ammonia slip concentration can be calculated based on the actual measured NOx concentration in each zone, using the following formula:

[0066]

[0067] In the formula, The value represents ammonia escape at the SCR outlet, in μL / L.

[0068] 7) Ammonia injection control

[0069] Under stable load, the NOx and ammonia slip concentrations at the SCR outlet are tested and calculated. The average of three tests is taken as the values ​​for each zone. If the calculated ammonia slip concentration deviation at the SCR outlet exceeds 30% or the NOx concentration deviation at the SCR outlet (i.e., the inlet of catalyst unit 101) exceeds 40%, the corresponding inlet ammonia injection grille damper is adjusted to control the ammonia slip deviation between 20% and 30% and the NOx concentration deviation at the SCR outlet between 30% and 40%, while ensuring that NOx emissions meet standards. During unit load changes, the ammonia injection grille damper is not adjusted.

[0070] This invention also discloses a denitrification ammonia injection control system based on accurate measurement of ammonia slip, comprising:

[0071] The SCR inlet flue 1 is connected to the ammonia supply main pipe 801. It is divided into several ammonia injection control zones according to the NOx concentration. The NOx concentration deviation within the same ammonia injection control zone is within the set range. Each ammonia injection control zone is controlled by a pneumatic regulating valve 2. Each ammonia injection control zone is further divided into several branch pipes 3 that extend into the SCR inlet flue 1 at different depths. Each branch pipe 3 is equipped with a manual regulating valve 4 for easy fine adjustment under hot conditions.

[0072] Sample gas header 8;

[0073] The SCR outlet flue 5 is connected to the sample gas main pipe 8. It is divided into several sampling zones according to the number of ammonia injection control zones. Each sampling zone is equipped with a pneumatic switch valve 7 on the sampling branch pipe 6. All sampling branch pipes 6 converge into the sample gas main pipe 8. The sample gas main pipe 8 is connected to the outlet of the air preheater 11 through the fly ash separation channel 9 and the flue gas test channel 10 respectively. The flue gas test channel 10 is equipped with a catalyst, a flue gas temperature detection module 102 and a flue gas pressure detection module 103.

[0074] The condition judgment module has the following judgment conditions: 1) stable load; 2) catalyst has not been running continuously below 270℃ for more than 5 hours; 3) flue gas differential pressure Δp increases by <20%; 4) flue gas temperature >250℃; if all conditions are met, the judgment condition is considered to be met.

[0075] The data analysis module is used to determine whether to adjust ammonia injection based on whether the deviation of SCR outlet ammonia slip concentration or NOx concentration exceeds the limit value.

[0076] Example 1

[0077] The denitrification ammonia injection control method based on accurate ammonia slip measurement includes the following steps:

[0078] 1) Ammonia injection control zone division

[0079] The SCR inlet rectangular flue is divided according to the equal area method. Measurement points are arranged at the center of each grid to test NOx concentration and flue gas velocity. In this embodiment, 9 holes (A1, A2, A3, A4, A5, A6, A7, A8, A9) are arranged along the width of the flue, and each hole has 3 points (P1, P2, P3 along the depth direction).

[0080] NOx concentration measured in SCR inlet flue using grid method (unit: mg / m³) 3 As shown in Table 1 below:

[0081] Table 1

[0082] A1 A2 A3 A4 A5 A6 A7 A8 A9 P1 508 532 565 571 625 614 617 566 503 P2 519 552 568 584 637 613 610 574 508 P3 525 563 573 584 614 613 607 576 496

[0083] The measured flue gas velocity at the SCR inlet (unit: m / s) using the grid method is shown in Table 2 below:

[0084] Table 2

[0085] A1 A2 A3 A4 A5 A6 A7 A8 A9 P1 10.1 12.9 13.1 13.0 13.5 14.3 13.2 12.1 10.5 P2 10.9 12.0 12.5 13.4 13.3 15.5 14.3 12.9 9.8 P3 9.5 12.6 12.9 13.5 13.8 15.2 14.1 11.8 10

[0086] The NOx content (in g / s) is calculated based on the following formula, combined with the grid flow area, concentration, and flow velocity data, as shown in Table 3:

[0087] Table 3

[0088] A1 A2 A3 A4 A5 A6 A7 A8 A9 P1 5.1 6.9 7.4 7.4 8.4 8.8 8.1 6.8 5.3 P2 5.7 6.6 7.1 7.8 8.5 9.5 8.7 7.4 5.0 P3 5.0 7.1 7.4 7.9 8.5 9.3 8.6 6.8 5.0

[0089] F i =A i ×v i ×C i / 1000

[0090] In the formula: F i Indicates the NOx content of each grid cell, unit: g / s; A i This represents the flow area of ​​each grid cell, in meters. 2 ;v i This indicates the flue gas velocity in each grid, in m / s; C i This indicates the NOx concentration in each grid cell, in mg / m³. 3 ;

[0091] Based on the differences in NOx content, the SCR inlet flue is divided into 6 ammonia injection control zones (F1, F2, F3, F4, F5, F6), as shown in Table 4:

[0092] Table 4

[0093]

[0094] 2) The SCR outlet flue is also divided into 6 sampling and monitoring zones (T1, T2, T3, T4, T5, T6), as shown in Table 5:

[0095] Table 5

[0096]

[0097] 3) Set judgment conditions. When each judgment condition is met, measure the NOx concentration in each zone and calculate the SCR outlet ammonia slip concentration in each zone based on the catalyst potential. The data is shown in Table 6 below:

[0098] Table 6

[0099]

[0100]

[0101] At this point, the relative standard deviation of ammonia slip distribution exceeds 30%, and the relative standard deviation of NOx concentration distribution exceeds 40%, requiring adjustment of the ammonia injection control zone valves.

[0102] First, the ammonia injection control zone valve at the SCR inlet is automatically adjusted several times. At this point, the relative standard deviation of ammonia escape distribution is <30%, and the relative standard deviation of NOx concentration distribution is <40%, as shown in Table 7. Then, the adjustment is stopped and the next round of detection and judgment process begins.

[0103] Table 7

[0104]

[0105] In this embodiment, after adjusting the ammonia injection, the ammonia slip concentration distribution deviation decreased from 44.0% to 22.3%, the local ammonia slip peak concentration decreased from 5.1 μL / L to 3.5 μL / L, and the NOx concentration distribution deviation decreased from 42.5% to 24.6%. This invention accurately monitors and obtains the ammonia slip concentration in different zones and incorporates this indicator into the ammonia injection control system, truly achieving precise control of ammonia slip while also ensuring the uniformity of NOx concentration distribution, thus possessing significant potential for widespread application.

[0106] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0107] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A denitrification ammonia injection control method based on accurate ammonia slip measurement, characterized in that, Includes the following steps: 1) Connect the ammonia supply main pipe to the SCR inlet flue, measure the NOx concentration and flue gas velocity of the SCR inlet flue, and divide it into several ammonia injection control zones according to the NOx content. The NOx content deviation within the same ammonia injection control zone should be within the set range. 2) Based on the number of ammonia injection control zones, divide the SCR outlet flue into the same number of sampling zones and calculate the ammonia slip concentration in each sampling zone. 3) Set the judgment conditions. If the judgment conditions are met, proceed to step 4; otherwise, proceed to step 5. 4) Test the NOx concentration at the inlet and outlet of the catalyst in each sampling zone, calculate the ammonia slip concentration at the SCR outlet, and determine whether to adjust the ammonia injection based on whether the deviation of the ammonia slip concentration or the NOx concentration at the SCR outlet exceeds the limit. 5) Purge the sampling area and catalyst or increase the flue gas temperature; In step 2), each sampling branch pipe in each sampling zone is equipped with a pneumatic switch valve. The sampling branch pipes converge into the sample gas main pipe. The sample gas main pipe is connected to the outlet of the air preheater through the fly ash separation channel and the flue gas test channel. The flue gas test channel is equipped with a catalyst, a flue gas temperature detection module and a flue gas pressure detection module. The ammonia that escapes in the flue gas undergoes a denitrification reaction on the catalyst surface. The ammonia escape concentration in each sampling zone is accurately obtained by testing the NOx concentration at the catalyst inlet and outlet. In step 3), the determination condition is: 1) Stable load; 2) The catalyst was not continuously operated below 270℃ for more than 5 hours; 3) Flue gas differential pressure Δp increases by <20%; 4) Smoke temperature > 250℃; Meeting any one of the criteria is sufficient to satisfy the judgment condition. The diameter of the sample gas header is D1, the diameter of the fly ash separation channel is D2, and the diameter of the flue gas testing channel is D3, where D1>D3>D2. A flue gas deflector and a fly ash interceptor are installed at the inlet of the fly ash separation channel. The angle α between the flue gas deflector and the horizontal axis of the sample gas header is 15°~30°, the height l1 of the flue gas deflector is ≥1 / 3×D1 / sinα, and the distance from the outer edge of the flue gas deflector to the central axis of the fly ash separation channel is between 1 / 2×D1~2D1. The angle β between the fly ash interception baffle and the horizontal axis is 20°~30°, the height l2 of the fly ash interception baffle is ≥1 / 3×D1 / sinβ, and the distance between the top edge of the fly ash interception baffle and the wall of the fly ash separation channel is ≥1 / 3×D2.

2. The denitrification ammonia injection control method based on accurate ammonia slip measurement according to claim 1, characterized in that, In step 1), the NOx content deviation within the same ammonia injection control zone is within 10%; each ammonia injection control zone is controlled by a pneumatic regulating valve, and several branch pipes of each ammonia injection control zone extend into the SCR inlet flue at different depths. Each branch pipe is equipped with a manual regulating valve to facilitate fine adjustment under hot conditions.

3. The denitrification ammonia injection control method based on accurate ammonia slip measurement according to claim 1, characterized in that, In step 4), if the ammonia slip concentration deviation at the SCR outlet exceeds 30% or the NOx concentration deviation exceeds 40%, the corresponding SCR inlet ammonia injection grille valve will be adjusted to control the ammonia slip concentration deviation between 20% and 30% and the NOx concentration deviation between 30% and 40%, while ensuring that NOx emissions meet standards. During unit load changes, the ammonia injection grille valve will not be adjusted.

4. The denitrification ammonia injection control method based on accurate ammonia slip measurement according to claim 1, characterized in that, In step 5), if the judgment condition is not met, the steps to purge the sampling area and catalyst or increase the flue gas temperature include: When the flue gas temperature is below 250℃, the pipeline may become blocked, affecting the extraction volume. In this case, the pipeline is backflushed by purging each sampling branch in the sampling zone with compressed air. During backflushing, the pneumatic valve on the main sample gas pipe is closed, the valve of one of the sampling branch pipes is opened, and the valves of the remaining sampling branch pipes are closed. The purging is carried out sequentially, and the purging time for each pipeline is >20s. When the flue gas differential pressure Δp rises by more than 20%, the catalyst purging pipeline is opened, and compressed air is used to purge the catalyst ash accumulation in the flue gas test channel until the flue gas differential pressure returns to normal; the low-temperature operation time is controlled to avoid catalyst blockage caused by ammonium bisulfate. When the flue gas temperature is below 270℃ and the cumulative operating time exceeds 5 hours, all sampling branches are opened simultaneously to increase the flue gas extraction volume, raise the flue gas temperature to above 300℃ and run continuously for 2 hours, and then the single sampling branch inspection mode is restored.

5. A denitrification ammonia injection control system based on accurate measurement of ammonia slip, characterized in that, Control is performed using the denitrification ammonia injection control method based on accurate ammonia slip measurement as described in any one of claims 1-4, including: Ammonia supply main pipe; The SCR inlet flue is connected to the ammonia supply main pipe and is divided into several ammonia injection control zones according to the NOx content. The NOx content deviation within the same ammonia injection control zone is within the set range. Each ammonia injection control zone is controlled by a pneumatic regulating valve. Several branch pipes of each ammonia injection control zone extend into the SCR inlet flue at different depths. Each branch pipe is equipped with a manual regulating valve for easy fine adjustment under hot conditions. Sample gas header; The SCR outlet flue is connected to the sample gas main pipe. It is divided into the same number of sampling zones according to the number of ammonia injection control zones. Each sampling zone has a pneumatic switch valve installed on each sampling branch pipe. All sampling branch pipes converge into the sample gas main pipe. The sample gas main pipe is connected to the air preheater outlet through the fly ash separation channel and the flue gas test channel. The flue gas test channel is equipped with catalyst, flue gas temperature detection module and flue gas pressure detection module. The condition determination module defines the determination conditions as follows: 1) stable load; 2) catalyst not continuously operating below 270℃ for more than 5 hours; 3) flue gas differential pressure Δp increases by less than 20%; 4) flue gas temperature > 250℃. Meeting all conditions is considered to satisfy the determination criteria. The data analysis module is used to determine whether to adjust ammonia injection based on whether the deviation of SCR outlet ammonia slip concentration or NOx concentration exceeds the limit value.

Images