A method for controlling the flow of flue gas from the outlet of a boiler coal mill

Abstract

This invention discloses a method for controlling the outlet flue gas flow of a boiler coal mill, comprising: Step 1, dividing the flue gas pipeline into zones; Step 2, detecting and calculating the flue gas concentration and flue gas velocity in each zone of the flue gas pipeline; Step 3, calculating the required reducing agent flow rate for each zone based on the calculated flue gas concentration and flue gas velocity values; Step 4, compensating for the required reducing agent flow rate for each zone based on the temperature inside the flue gas pipeline; Step 5, adjusting the sprayed reducing agent flow rate for each zone based on the compensated reducing agent flow rate; Step 6, calculating the total reducing agent flow rate based on the adjusted reducing agent flow rate for each zone, and adjusting the power of the power unit based on the total reducing agent flow rate. Dividing the flue gas pipeline into zones based on the ammonia injection grid and individually controlling the ammonia injection flow rate in each zone improves the precise control of the ammonia injection flow rate in the flue gas pipeline and reduces ammonia escape.

Description

Technical Field

[0001] This invention relates to the field of flue gas flow control technology, and more specifically to a method for controlling the flue gas flow at the outlet of a boiler coal mill. Background Technology

[0002] Nitrogen oxides (NOx) are one of the major air pollutants. When combined with hydrocarbons under strong light, they can cause photochemical pollution. NOx emitted into the atmosphere is a major cause of acid rain, which seriously harms the ecological environment.

[0003] In current SCR flue gas denitrification processes, the measurement of NH3 escape is crucial to operating costs, equipment safety, and secondary pollution. Excessive ammonia injection into the entire pipeline or even just a portion thereof can lead to NH3 escape. The escaped NH3 reacts with sulfates produced in the process flow within the flue gas duct downstream of the reactor, forming salt deposits that accumulate further downstream of the boiler. These deposits can corrode and contaminate the air preheater, resulting in significant maintenance costs and other problems.

[0004] Therefore, how to control the flow rate of ammonia water in pipelines and reduce ammonia escape is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method for controlling the flow rate of flue gas at the outlet of a boiler coal mill, which realizes the control of the ammonia injection flow rate in the flue gas pipeline for flue gas denitrification, reduces the occurrence of ammonia escape, reduces equipment maintenance costs, and improves economic efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] Preferably, the above-mentioned method for controlling the flue gas flow rate at the outlet of a boiler coal mill includes:

[0008] Step 1: Divide the flue gas duct into zones;

[0009] Step 2: Detect and calculate the flue gas concentration and flue gas velocity for each section of the flue gas duct;

[0010] Step 3: Calculate the required reducing agent flow rate for each zone based on the calculated flue gas concentration and flue gas velocity values ​​for each zone;

[0011] Step 4: Calculate the required reducing agent flow rate for each zone based on the temperature inside the flue gas duct.

[0012] Step 5: Adjust the spraying flow rate of the reducing agent in each zone according to the compensated reducing agent flow rate;

[0013] Step 6: Calculate the total reducing agent flow rate based on the adjusted reducing agent flow rate for each zone, and adjust the power of the power unit based on the total reducing agent flow rate.

[0014] In the control method described above, the flue gas duct is divided into zones according to the location of the ammonia injection grid, and ammonia injection for denitrification is carried out in the flue gas duct by a zoned ammonia injection method, which improves the control of the ammonia water flow rate for denitrification in the flue gas duct.

[0015] Preferably, the step of detecting and calculating the flue gas concentration and flue gas velocity in each section of the flue gas duct includes:

[0016] Step 1: Use a flue gas concentration sensor and a flue gas velocity sensor to monitor the flue gas concentration and flue gas velocity values ​​in the flue gas duct in real time;

[0017] Step two: Set the sampling time and calculate the effective concentration value within the sampling time period. The calculation formula is as follows:

[0018]

[0019] Where c is the effective concentration value of flue gas during the sampling period, and n is the number of samplings during the sampling period. i This represents the flue gas concentration value for each sample taken.

[0020] Step 3: Calculate the average flue gas velocity during the sampling time. The calculation formula is as follows:

[0021]

[0022] Where v is the average velocity of the flue gas, m is the number of samples taken within the sampling time, and v i This represents the flue gas velocity value for each sample taken.

[0023] In the method described above, the concentration and flow rate of the flue gas in the flue gas duct are detected by a sensor. It should be noted that the concentration and flow rate of the flue gas inside the duct are constantly changing. The sampling time is set, and the effective concentration value and average flow rate value within the sampling time are calculated, which improves the accuracy of the ammonia water flow rate calculation.

[0024] Preferably, in some embodiments, the required reducing agent flow rate for each zone is calculated based on the calculated flue gas concentration and flue gas velocity values ​​for each zone, including:

[0025] Step 1: Calculate the flue gas content per unit length volume of the flue gas duct section based on the effective flue gas concentration value and the average flue gas velocity. The calculation formula is as follows:

[0026] h = c * v *

[0027] Where h is the flue gas content per unit length of the flue gas duct section, and s is the cross-sectional area of ​​the flue gas duct section.

[0028] Step 2: Calculate the ammonia spray reduction dosage based on the flue gas content (h) per unit length volume of the flue gas duct section. The calculation formula is as follows:

[0029]

[0030] Where a is the total ammonia injection amount of the ammonia injection grid, b is the reaction ratio of flue gas and reducing agent, e is the number of nozzles of the ammonia injection grid in the flue gas duct section, and d is the length of the ammonia injection grid in the flue gas flow direction.

[0031] Preferably, in some embodiments, the step of calculating the required reducing agent flow rate for each zone based on the temperature within the flue gas duct includes:

[0032] Step 1: Use a temperature sensor to detect the temperature inside the flue gas duct in real time and calculate the difference between the current temperature and the set temperature range;

[0033] Step 2: Based on the difference between the actual temperature and the set temperature, compensate for the calculated total ammonia injection amount 'a' of the ammonia injection grid.

[0034] Preferably, in some embodiments, adjusting the power of the power unit based on the total flow rate of the reducing agent includes:

[0035] The power of the power unit is adjusted by the required total flow rate A of the reducing agent. A matrix of total flow rate of the reducing agent is preset, and A0(A1, A2, A3, A4) is set, where A1 is the first preset total flow rate of the reducing agent, A2 is the second preset total flow rate of the reducing agent, A3 is the third preset total flow rate of the reducing agent, and A4 is the fourth preset total flow rate of the reducing agent, and A1 < A2 < A3 < A4.

[0036] The power B of the power unit is adjusted to achieve the desired total flow rate of reducing agent. The power matrix B0 of the power unit is preset, and B0(B1, B2, B3, B4) is set, where B1 is the power of the first preset power unit, B2 is the power of the second preset power unit, B3 is the power of the third preset power unit, and B4 is the power of the fourth preset power unit, and B1 < B2 < B3 < B4.

[0037] Based on the relationship between the required total reducing agent flow rate A and various set values, determine the power unit's power B:

[0038] When A < A1, the power B1 of the first preset power device is selected as the power of the power device;

[0039] When A1≤A<A2, the power B2 of the second preset power device is selected as the power of the power device;

[0040] When A2≤A<A3, the power B3 of the third preset power device is selected as the power of the power device;

[0041] When A3≤A<A4, the power B4 of the fourth preset power device is selected as the power of the power device.

[0042] Preferably, in some embodiments, the step of compensating the calculated total ammonia injection amount 'a' of the ammonia injection grid based on the difference between the actual temperature and the set temperature includes:

[0043] The total ammonia injection amount a of the ammonia injection grid is compensated by the temperature difference C. The preset temperature difference matrix C0 is set as C0(C1, C2, C3, C4), where C1 is the first preset temperature difference, C2 is the second preset temperature difference, C3 is the third preset temperature difference, and C4 is the fourth preset temperature difference, and C1 < C2 < C3 < C4.

[0044] The compensation value D for compensating the total ammonia injection amount a of the ammonia injection grid is determined based on the temperature difference value C. The preset compensation value matrix D0 is set as D0(D1, D2, D3, D4), where D1 is the first preset compensation value, D2 is the second preset compensation value, D3 is the third preset compensation value, and D4 is the fourth preset compensation value, and D1 < D2 < D3 < D4.

[0045] Based on the relationship between the temperature difference C and the preset temperature differences, determine the compensation value D for the total ammonia injection amount a of the ammonia injection grid:

[0046] When C < C1, the first preset compensation value D1 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid.

[0047] When C1≤C<C2, the second preset compensation value D2 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid;

[0048] When C2≤C<C3, the third preset compensation value D3 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid.

[0049] When C3≤C<C4, the fourth preset compensation value D4 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid.

[0050] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0051] By dividing the flue gas duct into zones according to the ammonia injection grid, and controlling the ammonia injection flow rate separately in each zone, the ammonia injection flow rate in the flue gas duct can be carefully controlled, reducing the occurrence of ammonia escape and improving economic efficiency. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0053] Figure 1 The attached figure is a schematic diagram of the method flow of the present invention.

[0054] Figure 2 The attached figure is a schematic diagram of the apparatus for implementing the method of the present invention.

[0055] In the diagram, 1. Flue gas duct; 2. Ammonia water main pipe; 3. Ammonia water branch pipe; 4. Flue gas concentration sensor; 5. Flue gas velocity sensor; 6. Temperature sensor; 7. Second flow meter; 8. Electric regulating valve; 9. First flow meter; 10. Power unit; Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] This invention discloses a method for controlling the flow rate of flue gas at the outlet of a boiler coal mill, comprising:

[0058] Step 1: Divide the flue gas duct 1 into sections;

[0059] Step 2: Detect and calculate the flue gas concentration and flue gas velocity in each section of flue gas duct 1;

[0060] Step 3: Calculate the required reducing agent flow rate for each zone based on the calculated flue gas concentration and flue gas velocity values ​​for each zone;

[0061] Step 4: Based on the temperature inside flue gas duct 1, calculate the required reducing agent flow rate for each zone.

[0062] Step 5: Adjust the spraying flow rate of the reducing agent in each zone according to the compensated reducing agent flow rate;

[0063] Step 6: Calculate the total flow rate of the reducing agent based on the adjusted flow rate of the reducing agent in each zone, and adjust the power of the power unit 10 according to the total flow rate of the reducing agent.

[0064] The beneficial effects of the above embodiments are as follows: dividing the flue gas duct 1 into zones according to the ammonia injection grid and controlling the ammonia injection flow rate separately in each zone can improve the careful control of the ammonia injection flow rate in the flue gas duct 1, reduce the occurrence of ammonia escape, and improve economic efficiency.

[0065] like Figure 2 As shown, in one embodiment, an apparatus for applying the above method includes:

[0066] Flue gas duct 1, in which flue gas flows from top to bottom or from bottom to top;

[0067] The ammonia water main pipe 2 is connected to the power unit 10. A first flow meter 9 is installed at the outlet of the power unit 10.

[0068] Ammonia water branch pipe 3 is connected to ammonia water main pipe 2 and ammonia injection grid. A second flow meter 7 and an electric regulating valve 8 are installed on ammonia water branch pipe 3.

[0069] The flue gas concentration sensor 4 and the flue gas flow rate sensor 5 are installed in front of each group of ammonia injection grids, and the temperature sensor 6 is installed in the middle of the flue gas duct 1.

[0070] Among them, the power unit 10, the first flow meter 9, the second flow meter 7, the electric regulating valve 8, the flue gas concentration sensor 4, the flue gas velocity sensor 5, and the temperature sensor 6 are all connected to the controller. The controller receives data information and controls each device to complete the adjustment of the ammonia water flow rate in the zone.

[0071] Among them, the power unit 10 is preferably an ammonia metering pump, and the first flow meter 9, the second flow meter 7, the electric regulating valve 8, the flue gas concentration sensor 4, the flue gas velocity sensor 5, and the temperature sensor 6 are all existing technologies.

[0072] In one embodiment, the flue gas concentration and flue gas velocity are detected and calculated for each section of the flue gas duct 1, including:

[0073] Step 1: Use flue gas concentration sensor 4 and flue gas velocity sensor 5 to monitor the flue gas concentration and flue gas velocity values ​​in flue gas duct 1 in real time.

[0074] Step two: Set the sampling time and calculate the effective concentration value within the sampling time period. The calculation formula is as follows:

[0075]

[0076] Where c is the effective concentration value of flue gas during the sampling period, and n is the number of samplings during the sampling period. i This represents the flue gas concentration value for each sample taken.

[0077] Step 3: Calculate the average flue gas velocity during the sampling time. The calculation formula is as follows:

[0078]

[0079] Where v is the average velocity of the flue gas, m is the number of samples taken within the sampling time, and v i This represents the flue gas velocity value for each sample taken.

[0080] The beneficial effects of the above embodiments are as follows: the concentration and flow rate of the flue gas in the flue gas duct 1 are detected by using the flue gas concentration sensor 4 and the flue gas flow rate sensor 5. It should be noted that the concentration and flow rate of the flue gas inside the duct are constantly changing. The sampling time is set, and the effective concentration value and average flow rate value within the sampling time are calculated, which improves the accuracy of ammonia water flow rate calculation.

[0081] In one embodiment, the required reducing agent flow rate for each zone is calculated based on the calculated flue gas concentration and flue gas velocity values ​​for each zone, including:

[0082] Step 1: Calculate the flue gas content per unit length volume in section 1 of the flue gas duct based on the effective flue gas concentration and the average flue gas velocity. The calculation formula is as follows:

[0083] h = c * v *

[0084] Where h is the flue gas content per unit length of the flue gas duct section 1, and s is the cross-sectional area of ​​the flue gas duct section 1.

[0085] It should be noted that the cross-sectional area s of the partition is calculated by taking the approximate spraying range of each group of ammonia spraying grids as the boundary of the partition.

[0086] Step 2: Based on the flue gas content h per unit length volume of flue gas duct section 1, calculate the ammonia spray reduction dosage using the ammonia grid. The calculation formula is as follows:

[0087]

[0088] Where a is the total ammonia injection amount of the ammonia injection grid, b is the reaction ratio of flue gas and reducing agent, e is the number of nozzles of the ammonia injection grid in section 1 of the flue gas duct, and d is the length of the ammonia injection grid in the flue gas flow direction.

[0089] In this embodiment, the reducing agent is ammonia water, and the ratio of ammonia water to flue gas concentration is 1 mol of NOx requires 1 mol of ammonia water for reduction catalysis. In this embodiment, the nozzles of the ammonia injection grid are evenly distributed on the ammonia injection grid, the number of nozzles e is a fixed value, and the length d of the ammonia injection grid in the flue gas flow direction is the length of the effective range of the ammonia injection grid when ammonia is injected, which will fluctuate slightly depending on the pressure in the ammonia water branch pipe 3.

[0090] In one embodiment, the required reducing agent flow rate for each zone is calculated based on the temperature within the flue gas duct 1, including:

[0091] Step 1: Use temperature sensor 6 to detect the temperature inside flue gas duct 1 in real time and calculate the difference between the current temperature and the set temperature range.

[0092] Step 2: Based on the difference between the actual temperature and the set temperature, compensate for the calculated total ammonia injection amount 'a' of the ammonia injection grid.

[0093] It should be noted that the catalytic reaction efficiency of ammonia water is highest within the set temperature range of 850℃-1050℃. Both high and low temperatures will affect the catalytic efficiency of ammonia water. When there is a temperature difference between the temperature in flue gas duct 1 and the set temperature, the flow rate of ammonia water needs to be increased to prioritize the denitrification effect of flue gas.

[0094] In one embodiment, adjusting the power of the power unit 10 based on the total flow rate of the reducing agent includes:

[0095] The power of the power unit 10 is adjusted by the required total flow rate A of the reducing agent. A matrix of total flow rate of the reducing agent is preset, and A0(A1, A2, A3, A4) is set, where A1 is the first preset total flow rate of the reducing agent, A2 is the second preset total flow rate of the reducing agent, A3 is the third preset total flow rate of the reducing agent, and A4 is the fourth preset total flow rate of the reducing agent, and A1 < A2 < A3 < A4.

[0096] The power B of the power unit 10 is adjusted to achieve the desired total flow rate of the reducing agent. The power matrix B0 of the power unit 10 is preset, and B0(B1, B2, B3, B4) is set, where B1 is the power of the first preset power unit 10, B2 is the power of the second preset power unit 10, B3 is the power of the third preset power unit 10, and B4 is the power of the fourth preset power unit 10, and B1 < B2 < B3 < B4.

[0097] Based on the relationship between the required total flow rate of reducing agent A and various set values, determine the power B of the power unit 10:

[0098] When A < A1, the power B1 of the first preset power device 10 is selected as the power of the power device 10;

[0099] When A1≤A<A2, the power B2 of the second preset power device 10 is selected as the power of the power device 10;

[0100] When A2≤A<A3, the power B3 of the third preset power device 10 is selected as the power of the power device 10;

[0101] When A3≤A<A4, the power B4 of the fourth preset power device 10 is selected as the power of the power device 10.

[0102] It should be noted that the flow rate of the ammonia water header 2 is controlled by the power unit 10. Adjusting the power of the power unit 10 is used to adjust the flow rate of the ammonia water header 2.

[0103] In one embodiment, compensation is made to the calculated total ammonia injection quantity 'a' of the ammonia injection grid based on the difference between the actual temperature and the set temperature, including:

[0104] The total ammonia injection amount a of the ammonia injection grid is compensated by the temperature difference C. The preset temperature difference matrix C0 is set as C0(C1, C2, C3, C4), where C1 is the first preset temperature difference, C2 is the second preset temperature difference, C3 is the third preset temperature difference, and C4 is the fourth preset temperature difference, and C1 < C2 < C3 < C4.

[0105] The compensation value D for compensating the total ammonia injection amount a of the ammonia injection grid is determined based on the temperature difference value C. The preset compensation value matrix D0 is set as D0(D1, D2, D3, D4), where D1 is the first preset compensation value, D2 is the second preset compensation value, D3 is the third preset compensation value, and D4 is the fourth preset compensation value, and D1 < D2 < D3 < D4.

[0106] Based on the relationship between the temperature difference C and the preset temperature differences, determine the compensation value D for the total ammonia injection amount a of the ammonia injection grid:

[0107] When C < C1, the first preset compensation value D1 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid.

[0108] When C1≤C<C2, the second preset compensation value D2 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid;

[0109] When C2≤C<C3, the third preset compensation value D3 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid;

[0110] When C3≤C<C4, the fourth preset compensation value D4 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid.

[0111] It should be noted that the greater the temperature difference, the worse the efficiency of the reducing agent and NOx. Therefore, the denitrification rate should be the primary consideration, and the compensation value should be greater as the temperature difference increases.

[0112] This application is based on Figure 2The device shown operates as follows: During the sampling period, the flue gas concentration sensor 4 and flue gas velocity sensor 5 detect the flue gas concentration and flue gas velocity of the current zone. The data is transmitted to the controller, where the effective concentration value and average flow rate value are calculated. Based on the effective concentration value and average flow rate value, the flow rate value of the corresponding ammonia branch pipe 3 for the zone is calculated. Based on the flow rate value of each ammonia branch pipe 3, the flow rate value of the ammonia main pipe 2 is calculated. Based on the flow rate value of the ammonia main pipe 2, the power of the power unit 10 is adjusted. Then, the electric regulating valve 8 is adjusted, and the second flow meter 7 detects the flow rate of the ammonia branch pipe 3. The flow rate stops when the calculated flow rate is reached.

[0113] The controller periodically adjusts the ammonia injection flow rate according to the set sampling time.

[0114] The beneficial effects of the above process are as follows: after dividing the flue gas duct 1 into zones according to the ammonia injection grid, the flow rate of the reducing agent in each zone is adjusted according to the changes in flue gas, which reduces the occurrence of ammonia escape and reduces the occurrence of equipment corrosion.

[0115] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0116] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the flow rate of flue gas at the outlet of a boiler coal mill, characterized in that, include: Step 1: Divide the flue gas duct into zones; Step 2: Detect and calculate the flue gas concentration and flue gas velocity for each section of the flue gas duct; Step 3: Calculate the required reducing agent flow rate for each zone based on the calculated flue gas concentration and flue gas velocity values ​​for each zone; Step 4: Calculate the required reducing agent flow rate for each zone based on the temperature inside the flue gas duct. Step 5: Adjust the spraying flow rate of the reducing agent in each zone according to the compensated reducing agent flow rate; Step 6: Calculate the total reducing agent flow rate based on the adjusted reducing agent flow rate for each zone, and adjust the power of the power unit based on the total reducing agent flow rate. The adjustment of the power unit's power based on the total flow rate of the reducing agent includes: The power of the power unit is adjusted by the required total flow rate A of the reducing agent. A matrix of total flow rate of the reducing agent is preset, and A0 is set (A1, A2, A3, A4), where A1 is the first preset total flow rate of the reducing agent, A2 is the second preset total flow rate of the reducing agent, A3 is the third preset total flow rate of the reducing agent, and A4 is the fourth preset total flow rate of the reducing agent, and A1 < A2 < A3 < A4. The power B of the power unit is adjusted to achieve the desired total flow rate of reducing agent. The power matrix B0 of the power unit is preset, and B0 (B1, B2, B3, B4) is set, where B1 is the power of the first preset power unit, B2 is the power of the second preset power unit, B3 is the power of the third preset power unit, and B4 is the power of the fourth preset power unit, and B1 < B2 < B3 < B4. Based on the relationship between the required total reducing agent flow rate A and various set values, determine the power unit's power B: When A < A1, the power B1 of the first preset power device is selected as the power of the power device; When A1≤A<A2, the power B2 of the second preset power device is selected as the power of the power device; When A2≤A<A3, the power B3 of the third preset power device is selected as the power of the power device; When A3≤A<A4, the power B4 of the fourth preset power device is selected as the power of the power device; The calculated total ammonia injection quantity 'a' of the ammonia injection grid is compensated based on the difference between the actual temperature and the set temperature, including: The total ammonia injection amount a of the ammonia injection grid is compensated by the temperature difference C. The preset temperature difference matrix C0 is set as C0 (C1, C2, C3, C4), where C1 is the first preset temperature difference, C2 is the second preset temperature difference, C3 is the third preset temperature difference, C4 is the fourth preset temperature difference, and C1 < C2 < C3 < C4. The compensation value D for compensating the total ammonia injection amount a of the ammonia injection grid is determined based on the temperature difference value C. The preset compensation value matrix D0 is set as D0 (D1, D2, D3, D4), where D1 is the first preset compensation value, D2 is the second preset compensation value, D3 is the third preset compensation value, and D4 is the fourth preset compensation value, and D1 < D2 < D3 < D4. Based on the relationship between the temperature difference C and the preset temperature differences, determine the compensation value D for the total ammonia injection amount a of the ammonia injection grid: When C < C1, the first preset compensation value D1 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid. When C1≤C<C2, the second preset compensation value D2 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid; When C2≤C<C3, the third preset compensation value D3 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid. When C3≤C<C4, the fourth preset compensation value D4 is selected as the compensation value for the total ammonia injection amount a of the ammonia injection grid.

2. The method for controlling the flue gas flow rate at the outlet of a boiler coal mill according to claim 1, characterized in that, The process of detecting and calculating flue gas concentration and flue gas velocity in each section of the flue gas duct includes: Step 1: Use a flue gas concentration sensor and a flue gas velocity sensor to monitor the flue gas concentration and flue gas velocity values ​​in the flue gas duct in real time; Step two: Set the sampling time and calculate the effective concentration value within the sampling time period. The calculation formula is as follows: Where c is the effective concentration value of flue gas during the sampling period, and n is the number of samplings during the sampling period. i This represents the flue gas concentration value for each sample taken. Step 3: Calculate the average flue gas velocity during the sampling time. The calculation formula is as follows: Where v is the average velocity of the flue gas, m is the number of samples taken within the sampling time, and v i This represents the flue gas velocity value for each sample taken.

3. The method for controlling the flue gas flow rate at the outlet of a boiler coal mill according to claim 2, characterized in that, Based on the calculated flue gas concentration and flue gas velocity values ​​for each zone, the required reducing agent flow rate for each zone is calculated, including: Step 1: Calculate the flue gas content per unit length volume of the flue gas duct section based on the effective flue gas concentration value and the average flue gas velocity. The calculation formula is as follows: Where h is the flue gas content per unit length of the flue gas duct section, and s is the cross-sectional area of ​​the flue gas duct section. Step 2: Calculate the ammonia spray reduction dosage based on the flue gas content (h) per unit length volume of the flue gas duct section. The calculation formula is as follows: Where a is the total ammonia injection amount of the ammonia injection grid, b is the reaction ratio of flue gas and reducing agent, e is the number of nozzles of the ammonia injection grid in the flue gas duct section, and d is the length of the ammonia injection grid in the flue gas flow direction.

4. The method for controlling the flue gas flow rate at the outlet of a boiler coal mill according to claim 3, characterized in that, The calculation of the required reducing agent flow rate for each zone based on the temperature inside the flue gas duct includes: Step 1: Use a temperature sensor to detect the temperature inside the flue gas duct in real time and calculate the difference between the current temperature and the set temperature range; Step 2: Based on the difference between the actual temperature and the set temperature, compensate for the calculated total ammonia injection amount 'a' of the ammonia injection grid.

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