A cold-state inspection and status diagnosis and evaluation method for the ammonia injection grid of a denitration system

Abstract

The present invention relates to a method for cold-state inspection and status diagnosis and evaluation of an ammonia injection grid in a denitration system. The present invention conducts a systematic diagnosis and evaluation of the overall ammonia injection grid through the appearance inspection of the ammonia injection grid and pipelines, the wind speed test of the grid nozzles, the verification of the purging system, and the characteristic test of the manual valves of the ammonia injection branch pipes, clarifies the status of the ammonia injection grid, guides the maintenance, and lays a foundation for the hot-state ammonia injection adjustment. Starting from the key points of the equipment, the present invention summarizes a scientific and systematic evaluation method and criteria, with small workload and high efficiency. It can systematically inspect, diagnose and evaluate the status of the ammonia injection grid during the cold-state maintenance of power station boilers.

Description

Technical Field

[0001] The present invention relates to the field of SCR flue gas denitrification treatment for coal-fired boilers, and particularly to a method for cold-state inspection and condition diagnosis and evaluation of an ammonia injection grid in a denitrification system. Background Art

[0002] The SCR flue gas denitrification technology is the most widely used, mature and reliable denitrification technology for current coal-fired boilers. Among them, the SCR denitrification ammonia injection mixing system (AIG) is the key affecting the operation performance of SCR denitrification. At present, SCR generally adopts a multi-branch multi-nozzle AIG ammonia injection grid with horizontal and vertical adjustability. During the operation of SCR denitrification, the ammonia-air mixed gas passes through each branch pipeline of the AIG and is sprayed into the SCR inlet flue through the nozzles on each branch pipeline to be fully mixed with the flue gas. The nozzles are evenly arranged on the flue cross-section, so as to ensure the uniformity of the NH3 / NOx molar ratio distribution in the SCR inlet flue, and improve the safe and economic operation of the SCR denitrification device. Therefore, the state of the ammonia injection grid directly affects the operation efficiency of the entire denitrification system.

[0003] During the operation of SCR denitrification, problems such as blockage of AIG nozzles, wear of ammonia injection branch pipelines, and aging of manual regulating valve characteristics often occur. Once the above problems occur during operation, it will seriously damage the uniformity of ammonia injection mixing in the SCR inlet flue, easily cause local under-ammonia injection and local over-ammonia injection in the cross-section, and further cause excessive local ammonia slip concentration at the outlet of the SCR reactor and a decline in SCR denitrification performance, and further cause blockage of the ABS of the air preheater of the unit, thus seriously affecting the safe, stable and economic operation of the SCR denitrification device and the safe and stable operation of the unit.

[0004] At present, there is no set of scientific evaluation and diagnosis methods for the SCR ammonia injection grid system. The operation and maintenance personnel of the denitrification system can only maintain the denitrification system through personal experience. And it is impossible to conduct an internal inspection and evaluation of the ammonia injection grid system during the hot-state operation. Therefore, there is an urgent need for a clear method for cold-state inspection and condition diagnosis and evaluation of the SCR ammonia injection grid to guide relevant personnel to maintain the equipment, ensure the equipment operates in the optimal state, and at the same time be able to understand the equipment state and provide guidance for hot-state operation. Summary of the Invention

[0005] In view of the above situation, in order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for cold-state inspection and condition diagnosis and evaluation of an ammonia injection grid in a denitrification system, which can comprehensively evaluate the state of the ammonia injection grid under cold-state conditions, including the equipment appearance state and system characteristics of the ammonia injection grid system, and can quickly and specifically find out and handle equipment defects.

[0006] The technical solution solved by the present invention is:

[0007] A cold-state inspection and status diagnosis and evaluation method for the ammonia injection grid of a denitration system, comprising the following steps:

[0008] S1. Appearance inspection of the ammonia injection grid nozzles:

[0009] Under cold state, observe from directly above the nozzles of the ammonia injection grid. If there is no ash accumulation in the nozzles, it is determined that the nozzles are not blocked, and proceed to step S2;

[0010] If there is ash accumulation in the nozzles, purge the nozzles with compressed air at a wind speed of 4 - 6 m / s:

[0011] If the ash is blown out, it is determined that the nozzles are not blocked, and proceed to step S2;

[0012] If the ash cannot be blown out, it is determined that the nozzles are blocked. Perform backflushing of the blocked ammonia injection grid with high-pressure and large-flow compressed air, or disconnect the pipeline to remove the ash blockage until the blockage is removed and then proceed to step S2;

[0013] S2. Wear inspection of the ammonia injection grid spray pipes:

[0014] Measure the wall thickness of the ammonia injection grid spray pipes and compare it with the wall thickness at the time of factory shipment:

[0015] If the wall thickness of the ammonia injection grid spray pipes is less than half of the wall thickness at the time of factory shipment, it is determined that the wear of the ammonia injection grid spray pipes exceeds the standard, and replace the pipes at the corresponding positions. After replacement, proceed to step S3;

[0016] If the wall thickness of the ammonia injection grid spray pipes is greater than or equal to half of the wall thickness at the time of factory shipment, it is determined that the wear of the ammonia injection grid spray pipes does not exceed the standard, and proceed to step S3;

[0017] S3. Wind speed test of the ammonia injection grid nozzles:

[0018] Start the dilution air system, open the manual valves corresponding to each group of ammonia injection grid nozzles fully or set them to the operating habitual opening degree, measure the wind speed of each ammonia injection grid nozzle one by one in the flue with a portable anemometer, and record the wind speed of each group of nozzles;

[0019] The operating habitual opening degree is the opening degree in the hot state before the denitration system is set to the cold state;

[0020] Calculate the relative deviation of the wind speed of each group through the following formula:

[0021]

[0022] Where: δ is the relative deviation of the wind speed;

[0023] x i is the measured value of the wind speed corresponding to each nozzle;

[0024] is the arithmetic mean of multiple wind speed measurement values;

[0025] Thus, the uniformity of each group of ammonia injection grids is obtained. For nozzles with a relative deviation δ < -15%, it is determined that the nozzle is blocked; and the smaller the δ value, the lower the wind speed and the more serious the blockage degree. Based on this, its uniformity is evaluated;

[0026] S4. Purge system effect test:

[0027] If no blocked nozzles are found in step S3, directly proceed to step S5;

[0028] For the nozzles determined to be blocked, introduce compressed air through the purge system for purging;

[0029] During purging, first close the manual valves of the ammonia injection branch pipes and purge each group of ammonia injection grids one by one;

[0030] After purging is completed, repeat step S3 to evaluate the purging effect:

[0031] If the blow-through rate exceeds 85%, it is determined that the purging effect is good;

[0032] Blow-through rate = number of unblocked nozzles / number of blocked nozzles × 100%;

[0033] For nozzles that cannot be unblocked, mechanically dredge them or replace the pipelines to solve the blockage problems of all nozzles of the ammonia injection grids;

[0034] S5. Manual valve characteristic test of ammonia injection branch pipes:

[0035] Conduct valve characteristic tests on the manual valves corresponding to the nozzles of each group of ammonia injection grids respectively:

[0036] Measure the orifice plate pressure difference and the corresponding measured nozzle wind speed with an electronic differential pressure gauge at different valve openings. Use the valve opening as the abscissa and the average wind speed and dynamic pressure of the ammonia injection grid nozzles as the ordinate to draw the valve characteristic curve;

[0037] In the drawn valve characteristic curve, according to the two sets of data of the pressure difference and the measured nozzle wind speed obtained at different valve openings, through the linear regression fitting curve of the least squares method, calculate the coefficient of determination R 2 :

[0038] If R 2 ≥ 0.8, it is determined that the valve characteristic is good, and the cold state inspection and status diagnosis evaluation of the ammonia injection grid of the denitration system are completed;

[0039] If R 2<0.8, the valve is judged to have poor characteristics, indicating that the valve core has lost its regulating characteristics due to blockage or damage, and the valve needs to be decoupled for maintenance or replaced, and the process re-enters step S5 until R is satisfied. 2 ≥0.8.

[0040] Preferably, the openings of different valves in the valve characteristic test of step S5 are arranged at equal intervals of 0-100%, and the opening intervals are 10%, 12.5%, 20% or 25%.

[0041] Preferably, after obtaining the pressure difference at different valve openings and the corresponding measured nozzle wind speed in step S5, the flow orifice coefficient k is obtained according to the following formula:

[0042]

[0043] Where: ω——wind speed, m / s;

[0044] k——flow orifice coefficient;

[0045] ΔP——measured dynamic pressure value, Pa;

[0046] ρ——primary air density, kg / m 3 .

[0047] Therefore, by measuring the dynamic pressure value of the flow orifice during hot operation and substituting it into the above formula, the average wind speed of the ammonia injection grid nozzle in the flue under hot state can be calculated to guide the optimization adjustment of hot ammonia injection.

[0048] Preferably, after the valve characteristic curve is obtained in step S5, in the valve characteristic curve, the area with a slope greater than the average slope of the entire curve is defined as the valve regulation sensitive area, and the area with a slope less than the average slope of the entire curve is defined as the valve regulation insensitive area; thereby, the regulating characteristics of the valve can be understood as a basis for hot state adjustment, thereby guiding that during hot state operation, the ammonia injection amount of the valve is adjusted to change more in the valve regulation sensitive area, and change less in the ammonia injection amount in the insensitive area.

[0049] When the ammonia injection grid is running hot, the uniformity of the nozzle wind speed is the key factor to ensure that the flue gas and ammonia in the SCR inlet flue are fully mixed, thereby ensuring the NH3 / NO x The uniformity of molar ratio distribution. Therefore, it is necessary to measure the wind speed of all nozzles in the cold state and establish the physical relationship between wind speed and valve to guide the adjustment of hot operation, because in hot operation, the flue gas temperature in the flue is 300-420℃, and the wind speed of the nozzle cannot be measured. Therefore, according to the valve characteristic curve obtained in the cold test, it is possible to determine the opening degree of the valve in hot operation. This is of great significance for the optimization and adjustment of hot ammonia injection.

[0050] The ammonia injection grid system is complex and involves a wide range of aspects. The workload of cold-state inspection to find system defects is extremely large. Therefore, there is an urgent need for a method to quickly locate defects and problems. Through valve characteristic tests, faulty valves can be quickly detected without removing the valves, saving a large amount of time and workload.

[0051] Currently, there is no complete set of evaluation methods for the SCR ammonia injection grid status system in the industry, nor are there standards for equipment condition-based maintenance. It is relatively vague in the industry as to what state the equipment should be repaired or replaced, and there is no very clear standard. Starting from the key points of the equipment, the present invention summarizes a scientific and systematic evaluation method and standard, with a small workload and high efficiency. It can systematically inspect and diagnose the status of the ammonia injection grid during the cold-state maintenance of power plant boilers. Through the visual inspection of the ammonia injection grid and pipelines, the air velocity test at the grid nozzles, the verification of the purge system, and the characteristic tests of the manual valves on the ammonia injection branches, a systematic diagnosis and evaluation of the entire ammonia injection grid are carried out to clarify the status of the ammonia injection grid, guide the maintenance, and lay a foundation for the hot-state ammonia injection adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a schematic diagram of the ammonia injection grid system of the present invention.

[0053] Figure 2 It is a schematic diagram of the compressed air pipeline of the ammonia injection grid of the present invention.

[0054] Figure 3 It is the valve characteristic curve graph of the original working condition of the application example of the present invention.

[0055] Figure 4 It is a schematic diagram of the physical object of the original working condition valve disconnection of the application example of the present invention.

[0056] Figure 5 It is the valve characteristic curve graph after valve clogging removal of the application example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0057] The following further details the specific embodiments of the present invention in conjunction with the accompanying drawings and embodiments.

[0058] As Figures 1 - 5 shown, a cold-state inspection and status diagnosis and evaluation method for the ammonia injection grid of a denitration system of a valve includes the following steps:

[0059] S1. Visual inspection of the ammonia injection grid nozzles:

[0060] The appearance state of the equipment is the basis for its function realization. Therefore, it is first necessary to inspect the appearance state of the equipment. Under cold conditions, observe from directly above the nozzles of the ammonia injection grid. If there is no ash accumulation in the nozzles, it is determined that the nozzles are not blocked, and step S2 is entered;

[0061] If there is ash accumulation in the nozzle, purge the nozzle with compressed air at a wind speed of 4-6 m / s:

[0062] If the ash is blown out, it is determined that the nozzle is not blocked, and proceed to step S2;

[0063] If the ash cannot be blown out, it is determined that the nozzle is blocked. Conduct a reverse purge of the blocked ammonia injection grid with high-pressure and large-flow compressed air, or disconnect the pipeline to remove the ash blockage until the blockage is cleared and then proceed to step S2;

[0064] S2. Inspection of wear of the ammonia injection grid and pipeline:

[0065] Measure the wall thickness of the ammonia injection grid and pipeline and compare it with the wall thickness at the time of factory shipment:

[0066] If the wall thickness of the ammonia injection grid and pipeline is less than half of the wall thickness at the time of factory shipment, it is determined that the wear of the ammonia injection grid and pipeline exceeds the standard, and replace the pipeline at the corresponding position. After replacement, proceed to step S3;

[0067] If the wall thickness of the ammonia injection grid and pipeline is greater than or equal to half of the wall thickness at the time of factory shipment, it is determined that the wear of the ammonia injection grid and pipeline does not exceed the standard, and proceed to step S3;

[0068] After a large amount of time testing, if during cold-state inspection, the wall thickness reduction of the ammonia injection grid pipeline due to wear exceeds 1 / 2 of the original wall thickness, if not treated, after one year of hot-state operation, the thinned area will wear through, resulting in ammonia leakage.

[0069] S3. Wind speed test of the ammonia injection grid nozzle:

[0070] Start the dilution air system, open the manual valve corresponding to each ammonia injection grid nozzle to its full open position or the opening degree of the operating habit, and measure the wind speed of each ammonia injection grid nozzle in the flue one by one with a portable anemometer, and record the wind speed of each group of nozzles;

[0071] The opening degree of the operating habit is the opening degree in the hot-state condition before the denitration system is set to the cold state;

[0072] Calculate the relative deviation of the wind speed of each group through the following formula:

[0073]

[0074] where: δ is the relative deviation of the wind speed;

[0075] x i is the measured wind speed value corresponding to each nozzle;

[0076] is the arithmetic mean of multiple wind speed measurement values;

[0077] Thus, the uniformity of each ammonia injection grid is obtained. For the nozzles with a relative deviation δ < -15%, it is determined that the nozzles are blocked; and the smaller the δ value, the lower the wind speed, and the more serious the blockage degree. Based on this, its uniformity is evaluated;

[0078] The following are the actual application data:

[0079]

[0080]

[0081] S4. Purge system effect test:

[0082] If no blocked nozzles are found in step S3, directly proceed to step S5;

[0083] For the nozzles determined to be blocked, introduce compressed air through the purge system for purging;

[0084] During purging, first close the manual valves of the ammonia injection branch pipes and purge each ammonia injection grid one by one;

[0085] After purging, repeat step S3 to evaluate the purging effect:

[0086] If the blow-through rate exceeds 85%, it is determined that the purging effect is good;

[0087] Blow-through rate = number of blow-through nozzles / number of blocked nozzles × 100%;

[0088] For the nozzles that cannot be blown through, arrange maintenance personnel to mechanically dredge them or replace the pipelines to solve the blockage problems of all nozzles of the ammonia injection grids;

[0089] S5. Manual valve characteristic test of ammonia injection branch pipes:

[0090] Conduct valve characteristic tests on the manual valves corresponding to the nozzles of each ammonia injection grid respectively:

[0091] Measure the orifice plate pressure difference and the corresponding measured nozzle wind speed with an electronic differential pressure gauge at different valve openings. Take the valve opening as the abscissa and the average wind speed and dynamic pressure of the ammonia injection grid nozzles as the ordinate to draw the valve characteristic curve;

[0092] The different valve openings are set at equal intervals of 0 - 100%, and the opening intervals are 10%, 12.5%, 20% or 25%.

[0093] In the drawn valve characteristic curve, according to the two sets of data of the pressure difference and the measured nozzle wind speed obtained at different valve openings, through the linear regression fitting curve of the least squares method, calculate the determination coefficient R 2 :

[0094] If R 2If it is ≥0.8, it is determined that the valve characteristic is good, and the cold inspection and status diagnosis evaluation of the ammonia injection grid in the denitration system are completed;

[0095] If R 2 <0.8, it is determined that the valve characteristic is poor, indicating that the regulating characteristic is lost due to the valve core being blocked or damaged. The valve needs to be disconnected for maintenance or the valve needs to be replaced, and then re-enter step S5 until R 2 ≥0.8.

[0096] Taking a certain on-site test as an example, when conducting the valve characteristic test, at different valve openings, the data of the dynamic pressure of the flow orifice plate of the ammonia injection grid in the corresponding group and the average wind speed at the nozzle are as follows:

[0097] Relationship between valve opening and nozzle wind speed (original working condition)

[0098] Valve opening (%) Dynamic pressure (Pa) Average wind speed (m / s) 0 0 0 12.5 0 0 25 1250 15.73 37.5 600 9.70 50 3000 23.24 62.5 2700 20.55 75 500 8.54 87.5 1200 13.17 100 1200 13.98

[0099] The corresponding valve characteristic curve is as Figure 3 shown. From the valve characteristic curve, R 2 = 0.2694, which is less than 0.8. It is determined that the valve characteristic is poor, indicating that the regulating characteristic is lost due to the valve core being blocked or damaged. The valve needs to be disconnected for maintenance or the valve needs to be replaced. Therefore, the valve is disconnected for inspection and it is found that this valve has been blocked, as Figure 4 shown.

[0100] After cleaning the valve blockage problem, the valve characteristic test is carried out again, and the data are as follows:

[0101] Relationship between valve opening and nozzle wind speed

[0102] Valve opening (%) Dynamic pressure (Pa) Average wind speed (m / s) 0 0 0 12.5 0 0 25 150 5.45 37.5 600 9.70 50 2200 19.90 62.5 2700 20.55 75 3300 21.95 87.5 3900 23.75 100 4100 25.85

[0103] The corresponding valve characteristic curve is as Figure 5 shown. After the valve blockage problem is solved, R 2 = 0.9254 in the valve characteristic curve, which is greater than 0.8, indicating that the valve characteristic is good, thus proving that the reliability of this determination basis is relatively strong;

[0104] In addition, the adjustment of the valve in the 25% - 50% opening range is linearly steep, indicating that the adjustment in this range is relatively sensitive and can be used as a basis during hot commissioning.

[0105] In addition, the applicant has also done a large number of applications and all have achieved the expected technical effects. The data are as follows:

[0106]

[0107]

[0108] After obtaining the pressure difference and the corresponding measured nozzle wind speed at different valve openings in step S5, the flow orifice coefficient k is obtained according to the following formula:

[0109]

[0110] where: ω——wind speed, m / s;

[0111] k——flow orifice coefficient;

[0112] ΔP——measured dynamic pressure value, Pa;

[0113] ρ——primary air density, kg / m 3 .

[0114] Therefore, by measuring the dynamic pressure value of the flow orifice during hot-state operation and substituting it into the above formula, the average wind speed of the ammonia injection grille nozzles in the flue duct under hot state can be calculated, which is used to guide the optimization and adjustment of ammonia injection under hot state.

[0115] After obtaining the valve characteristic curve in step S5, in the valve characteristic curve, the area with a slope greater than the average slope of the whole curve is defined as the valve adjustment sensitive area, and the area with a slope less than the average slope of the whole curve is defined as the valve adjustment non-sensitive area; thus, the adjustment characteristics of the valve can be understood, which can be used as the basis for hot-state adjustment, so as to guide that when operating under hot state, the change of ammonia injection amount by adjusting the valve in the sensitive area is large, and the change of ammonia injection amount in the non-sensitive area is small.

[0116] Compared with the prior art, the present invention provides a cold-state inspection and status diagnosis and evaluation method for the SCR ammonia injection grille of the denitration system, which can systematically inspect, diagnose and evaluate the status of the ammonia injection grille during the cold-state overhaul of the power plant boiler. Through the appearance inspection of the ammonia injection grille and pipeline, the wind speed test of the grille nozzles, the verification of the purging system, and the manual valve characteristic test of the ammonia injection branch pipes, the whole ammonia injection grille is systematically diagnosed and evaluated, the status of the ammonia injection grille is clarified, the overhaul is guided, and a foundation is laid for the hot-state ammonia injection adjustment. It is convenient to use and has good effects. It is a set of SCR ammonia injection grille cold-state inspection and status diagnosis and evaluation methods with strong practicability, high efficiency and high accuracy, which can guide relevant personnel to maintain the equipment, ensure the equipment to operate in the optimal state, and at the same time can understand the equipment status and provide guidance for the hot-state operation, having good social and economic benefits.

Claims

1. A cold-state inspection and status diagnosis and evaluation method for an ammonia injection grid in a denitration system, characterized in that, It includes the following steps: S1. Visual inspection of the nozzles of the ammonia injection grid: Under cold conditions, observe from directly above the nozzles of the ammonia injection grid. If there is no ash accumulation in the nozzles, it is determined that the nozzles are not blocked, and proceed to step S2; If there is ash accumulation in the nozzles, purge the nozzles with compressed air at a wind speed of 4 - 6 m / s: If the ash is blown out, it is determined that the nozzles are not blocked, and proceed to step S2; If the ash cannot be blown out, it is determined that the nozzles are blocked. Use high-pressure and large-flow compressed air to backflush and clear the blocked ammonia injection grid, or disconnect the pipeline to remove the ash blockage until the blockage is cleared and then proceed to step S2; S2. Inspection of the wear of the pipelines of the ammonia injection grid nozzles: Measure the wall thickness of the pipelines of the ammonia injection grid nozzles and compare it with the wall thickness at the time of factory shipment: If the wall thickness of the pipelines of the ammonia injection grid nozzles is less than half of the wall thickness at the time of factory shipment, it is determined that the wear of the pipelines of the ammonia injection grid nozzles exceeds the standard, and replace the pipelines at the corresponding positions. After replacement, proceed to step S3; If the wall thickness of the pipelines of the ammonia injection grid nozzles is greater than or equal to half of the wall thickness at the time of factory shipment, it is determined that the wear of the pipelines of the ammonia injection grid nozzles does not exceed the standard, and proceed to step S3; S3. Wind speed test of the nozzles of the ammonia injection grid: Start the dilution air system, open the manual valves corresponding to each group of nozzles of the ammonia injection grid to their full open position or the operating habitual opening degree, and use a portable anemometer to measure the wind speed of each nozzle of the ammonia injection grid one by one in the flue, and record the wind speed of each group of nozzles; Calculate the relative deviation of the wind speed of each group through the following formula: Where: δ is the relative deviation of the wind speed; x i The measured wind speed value corresponding to each nozzle is the arithmetic mean of multiple wind speed measurement values; Thus, the uniformity of each group of ammonia injection grids is obtained. For nozzles with a relative deviation δ < -15%, it is determined that the nozzles are blocked; and the smaller the δ value, the lower the wind speed, and the more serious the blockage degree. Based on this, evaluate its uniformity; S4. Test of the effect of the purge system: If no blocked nozzles are found in step S3, directly proceed to step S5; For the nozzles determined to be blocked, introduce compressed air through the purge system for purging; During purging, first close the manual valves of the ammonia injection branch pipes and purge each group of ammonia injection grids one by one; After purging, repeat step S3 to evaluate the purging effect: If the blow-through rate exceeds 85%, it is determined that the purging effect is good; Blow-through rate = number of blow-through nozzles / number of blocked nozzles × 100%; For nozzles that cannot be blown through, mechanically dredge them or replace the pipelines to solve the blockage problem of all nozzles of the ammonia injection grid; S5. Characteristic test of the manual valves of the ammonia injection branch pipes: Conduct characteristic tests on the manual valves corresponding to each group of nozzles of the ammonia injection grid respectively: Measure the orifice pressure difference and the corresponding measured nozzle wind speed with an electronic differential pressure gauge at different valve opening degrees. Use the valve opening degree as the abscissa, and the average wind speed and dynamic pressure of the nozzles of the ammonia injection grid as the ordinate to draw the valve characteristic curve; In the drawn valve characteristic curve, according to the two sets of data of the pressure difference obtained at different valve openings and the measured nozzle wind speed, a linear regression fitting curve is obtained by the least squares method, and the coefficient of determination R is calculated 2 : If R 2 ≥ 0.8, it is determined that the valve characteristics are good, and the cold-state inspection and status diagnosis and evaluation of the ammonia injection grid in the denitration system are completed; If R 2 < 0.8, it is determined that the valve characteristic is poor, indicating that the regulating characteristic is lost due to the spool blockage or spool damage. It is necessary to disconnect the valve for maintenance or replace the valve, and then re-enter step S5 until R 2 ≥ 0.8 is satisfied.

2. The method for cold state inspection and status diagnosis and evaluation of the ammonia injection grid in the denitration system according to claim 1, characterized in that The different valve opening degrees in the valve characteristic test in step S5 are set at equal intervals from 0 - 100%, and the opening degree intervals are 10%, 12.5%, 20% or 25%.

3. The method for cold state inspection and status diagnosis evaluation of the ammonia injection grid in the denitration system according to claim 1, wherein, After obtaining the pressure difference and the corresponding measured nozzle wind speed at different valve opening degrees in step S5, according to the following formula, obtain the flow orifice coefficient k: Where: ω - wind speed, m / s; k - flow orifice coefficient; ΔP - measured dynamic pressure value, Pa; ρ——primary air density, kg / m 3； Therefore, by measuring the dynamic pressure value of the orifice plate during hot-state operation and substituting it into the above formula, the average wind speed at the ammonia injection grille nozzles in the flue duct under hot state can be calculated, which is used to guide the optimization and adjustment of ammonia injection during hot state.

4. The method for cold-state inspection and status diagnosis and evaluation of the ammonia injection grid in the denitration system according to claim 1, characterized in that, After obtaining the valve characteristic curve in step S5, in the valve characteristic curve, the region with a slope greater than the average slope of the entire curve is defined as the valve adjustment sensitive region, and the region with a slope less than the average slope of the entire curve is defined as the valve adjustment non-sensitive region; thus, the adjustment characteristics of the valve can be understood, serving as the basis for hot-state adjustment, and guiding that during hot-state operation, the change in ammonia injection amount by adjusting the valve is relatively large in the valve adjustment sensitive region and relatively small in the non-sensitive region.

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