Precise ammonia spraying system and method for SCR (Selective Catalytic Reduction) denitration device of power station boiler

Abstract

The invention discloses a power station boiler SCR denitration device precise ammonia spraying system and method, and the system comprises a plurality of ammonia spraying grid nozzles, an automatic adjusting valve, a flue gas sampling pipe, a nitrogen oxide concentration sensor and a DCS system, the ammonia spraying grid nozzles are installed in an inlet flue of the SCR denitration device and are located in front of a reactor; each ammonia spraying grid nozzle is connected with an ammonia gas mother pipe through an automatic regulating valve, each automatic regulating valve is connected with a DCS system, a plurality of flue gas sampling pipes are installed in an outlet flue of an SCR denitration device and located behind a reactor, the flue gas sampling pipes are connected with a nitrogen oxide concentration sensor through a first vacuum pump, and the nitrogen oxide concentration sensor is connected with the DCS system through a second vacuum pump. The nitrogen oxide concentration sensor is used for circularly detecting the flue gas collected by the flue gas sampling pipe in sequence, and is connected with the DCS system. According to the invention, the requirement of flue gas emission of the power station boiler on NOx concentration can be met, the ammonia escape rate can be reduced to the minimum, the generation amount of ammonium hydrogen sulfate is reduced, and the influence on safe and economical operation of the boiler due to blockage of the air preheater is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia injection systems for SCR denitration devices, and in particular to a precise ammonia injection system and method for a power station boiler SCR denitration device. Background Art

[0002] With the rapid development of economy, people's demand for electricity is increasing. Although traditional thermal power generation can meet the demand of electricity market in time, the NOx, SO2 and dust emitted by thermal power generation flue gas have caused serious pollution to the environment, and the normalization of haze weather has affected people's health.

[0003] In order to control NOx emissions from power plant boilers, low-nitrogen burners and SCR denitrification devices are used in all boilers. The SCR denitrification device uses ammonia to react with NOx in flue gas in a reactor containing a catalyst to generate N2 and H2O, which can control the NOx concentration at 50mg / Nm 3 , meeting environmental protection requirements.

[0004] However, in order to control the NOx concentration in the power plant boiler flue gas below 50mg / Nm 3 , often excessive ammonia is sprayed into the flue gas, and the excess ammonia will react with SO3 in the flue gas to generate NH4HSO4. In the temperature range of 150-220℃, ammonium bisulfate is a highly viscous liquid substance, which is easily deposited on the surface of the air preheater heat exchange element after the SCR denitrification device, adheres to the fly ash particles in the flue gas, reduces the gap between the corrugated plates of the air preheater heat exchange element, increases the resistance of the air preheater, and even partially blocks it, resulting in insufficient output of the induced draft fan, and gradually causes the boiler to burn in the absence of oxygen; at the same time, it will also affect the heat exchange effect of the air preheater, reduce the temperature of the hot primary air and secondary air, and affect the ignition and combustion of coal powder in the furnace. Therefore, how to control the ammonia spraying amount of the SCR denitrification device, not only to control the NOx concentration at the outlet of the SCR denitrification device to meet environmental protection requirements, but also to avoid excessive injection of ammonia and SO3 in the flue gas to generate ammonium bisulfate, block the air preheater, and affect the safe and economical operation of the boiler.

[0005] In order to control the ammonia escape rate at the outlet of the SCR denitrification device, a precise ammonia injection system came into being. By dividing the outlet of the SCR denitrification device into multiple areas and installing multiple sensors, the NOx concentration in multiple areas of the outlet of the SCR denitrification device is measured. At the same time, in front of the manual door of the ammonia injection grid at the inlet of the SCR denitrification device, the ammonia injection mother pipe is divided into multiple pipe sections, and an automatic regulating valve is installed at the inlet of each pipe section. According to the NOx concentration in the corresponding area of ​​the outlet of the SCR denitrification device, the opening of the automatic regulating valve after the ammonia injection mother pipe at the inlet of the SCR denitrification device is adjusted to control the NOx concentration at the outlet of the SCR denitrification device, and finally control the NOx concentration at the outlet of the SCR denitrification device, which can control both the NOx emission at the outlet of the SCR denitrification device and the ammonia escape rate at the outlet of the SCR denitrification device. After the ammonia injection grid at the inlet of the SCR denitrification device is leveled, the precise ammonia injection system can meet the requirements. However, the precise ammonia injection system has defects. If the ammonia injection grid of the SCR denitrification device is not leveled, or the SCR denitrification device needs to be leveled after running for a period of time, otherwise, it will cause large fluctuations in NOx at the outlet of the SCR denitrification device or large fluctuations in NOx concentration at the chimney inlet. The main reason is that the number of NOx sensors installed at the outlet of the SCR denitrification device is insufficient, and the measured NOx concentration cannot fully represent the change in NOx concentration at the outlet of the SCR denitrification device. If enough NOx sensors are installed, the cost is high. Summary of the invention

[0006] The purpose of the present invention is to provide a precise ammonia injection system for a power station boiler SCR denitration device, which can accurately level and control the nitrogen oxide concentration at the outlet of the SCR denitration device, reduce the ammonia escape rate of the SCR denitration device, avoid the increase of air preheater resistance caused by excessive denitration ammonia gas resulting in the generation of ammonium bisulfate in boiler auxiliary equipment such as air preheaters, and solve the above-mentioned problems existing in the prior art.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The invention discloses a precise ammonia injection system for a power plant boiler SCR denitration device, comprising an ammonia injection grid nozzle, an automatic regulating valve, a flue gas sampling tube, a first vacuum pump, a nitrogen oxide concentration sensor and a DCS system, wherein a plurality of the ammonia injection grid nozzles are installed in the inlet flue of the SCR denitration device and are located in front of the reactor, each of the ammonia injection grid nozzles is connected to the ammonia main pipe through the automatic regulating valve, each of the automatic regulating valves is connected to the DCS system, a plurality of the flue gas sampling tubes are installed in the outlet flue of the SCR denitration device and are located after the reactor, and the flue gas sampling tubes are connected to the automatic regulating valves one by one. Correspondingly, the flue gas sampling tube is connected to the nitrogen oxide concentration sensor through the first vacuum pump, the nitrogen oxide concentration sensor performs cyclic detection on the flue gas collected by several flue gas sampling tubes in turn, the nitrogen oxide concentration sensor is connected to the DCS system, the DCS system receives the NOx concentration data measured by the nitrogen oxide concentration sensor, and adjusts the opening of the corresponding automatic regulating valve according to the NOx concentration data of the flue at the outlet of the SCR denitrification device sampled by the flue gas sampling tube, so as to adjust the ammonia injection amount of the corresponding ammonia injection grid nozzle, thereby achieving precise ammonia injection.

[0009] Furthermore, each outlet of the flue gas sampling tube is installed with a back-purge device and a filter, the outlet of the filter is connected to a 3-position 2-way solenoid valve to form a flue gas sampling pipeline, the first outlet of the 3-position 2-way solenoid valve is connected to the air inlet of the second vacuum pump, the air outlet of the second vacuum pump is connected to the SCR outlet flue, the second outlet of the 3-position 2-way solenoid valve is connected to the air inlet of the first vacuum pump, and the air outlet of the first vacuum pump is connected to the nitrogen oxide concentration sensor.

[0010] Furthermore, the NOx concentration data detected by the nitrogen oxide concentration sensor is transmitted to the DCS system after digital-to-analog conversion. The DCS system compares the average value of NOx concentration detection collected by all flue gas sampling tubes with the flue gas NOx concentration value collected by each flue gas sampling tube in turn, and issues an instruction to the automatic regulating valve corresponding to the flue gas sampling tube with excessive concentration installed in the inlet flue of the SCR denitrification device, so as to adjust the opening of the automatic regulating valve.

[0011] Furthermore, 36 automatic regulating valves are provided, and 36 flue gas sampling tubes are provided correspondingly, and each automatic regulating valve controls 4 ammonia injection grid nozzles.

[0012] The present invention also provides a method for accurately spraying ammonia in a power station boiler SCR denitration device, which uses the accurate ammonia spraying system for the power station boiler SCR denitration device, and comprises the following steps:

[0013] S1. Install the precise ammonia injection system for the SCR denitration device of the power station boiler;

[0014] S2, start the first vacuum pump, and energize the 3-position 2-way solenoid valve at the outlet of each flue gas sampling tube in turn. At this time, the first outlet of the 3-position 2-way solenoid valve is closed, and the filtered flue gas enters the first vacuum pump from the second outlet of the 3-position 2-way solenoid valve, and then enters the nitrogen oxide concentration sensor; when the 3-position 2-way solenoid valve is not energized, the flue gas goes out from the first outlet of the 3-position 2-way solenoid valve, mixes with the flue gas coming out of other flue gas sampling pipelines, and is sent to the outlet flue of the SCR denitration device through the second vacuum pump;

[0015] S3. The corresponding flue gas sampling tubes collect the flue gas from the outlet of the SCR denitration device in turn, and transmit the flue gas to the nitrogen oxide concentration sensor. The nitrogen oxide concentration sensor detects the NOx concentration in turn, and sends the NOx concentration detection data to the DCS system;

[0016] S4. The DCS system compares the average value of NOx concentration collected by all flue gas sampling tubes with the flue gas NOx concentration value collected by each flue gas sampling tube in sequence. If the deviation between the NOx concentration value of the flue gas at the outlet of the SCR denitration device collected by one or several flue gas sampling tubes and the average value of NOx concentration detection exceeds the threshold, the DCS system issues an instruction to the automatic regulating valve corresponding to the flue gas sampling tube with excessive concentration installed in the inlet flue of the SCR denitration device to adjust the opening of the automatic regulating valve, and the automatic regulating valve controls the ammonia spraying amount of the corresponding ammonia spraying grid nozzle;

[0017] S5. Until the flue gas NOx concentration value collected by the flue gas sampling tube at the outlet of the SCR denitrification device corresponding to the automatic regulating valve does not exceed the threshold value compared with the NOx concentration detection average value, the precise ammonia injection control is completed.

[0018] Furthermore, after step S1, a NOx concentration value of the flue gas at the outlet of the SCR denitrification device is set in the DCS system as the NOx concentration target control value, and the NOx concentration detection average value is compared with the NOx concentration target control value. If the NOx concentration detection average value differs from the NOx concentration target control value by more than 20%, the operator manually controls the main valve on the ammonia main pipe for adjustment.

[0019] Furthermore, in step S4, the threshold is 15%.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are:

[0021] The precise ammonia injection system and method of the power station boiler SCR denitrification device of the present invention can not only meet the NOx concentration requirements of the power station boiler flue gas emission, but also reduce the ammonia escape rate to a minimum, reduce the amount of ammonium bisulfate generated, and avoid affecting the safe and economical operation of the boiler due to blockage of the air preheater. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a schematic diagram of the overall structure of the precise ammonia injection system of the SCR denitration device of a power station boiler of the present invention;

[0024] Figure 2 It is a structural schematic diagram of a flue gas sampling tube in the precise ammonia injection system of the SCR denitration device of a power station boiler of the present invention;

[0025] Figure 3 It is a schematic diagram of the structure of the use principle of the precise ammonia injection system of the power station boiler SCR denitration device of the present invention.

[0026] Explanation of the accompanying drawings: 1. Ammonia spray grid nozzle; 2. Automatic regulating valve; 3. Flue gas sampling tube; 4. First vacuum pump; 5. Nitrogen oxide concentration sensor; 6. DCS system; 7. Back-purge device; 8. Filter; 9. 3-position 2-way solenoid valve; 10. Second vacuum pump. DETAILED DESCRIPTION

[0027] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0028] In the description of the present invention, it should be understood that the terms "length", "width", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0029] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] The technical solutions provided by various embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0031] Example 1

[0032] like Figures 1 to 3 As shown, the precise ammonia injection system of the power plant boiler SCR denitration device of this embodiment 1 includes an ammonia injection grid nozzle 1, an automatic regulating valve 2, a flue gas sampling tube 3, a nitrogen oxide concentration sensor 5, and a DCS system 6. The ammonia injection grid nozzle 1 is installed in the inlet flue of the SCR denitration device and is located in front of the reactor. The ammonia injection grid nozzle 1 is connected to the ammonia main pipe. An automatic regulating valve 2 is arranged between the ammonia injection grid nozzle 1 and the ammonia main pipe. The automatic regulating valve 2 is connected to the DCS system 6 to control the opening of the corresponding automatic regulating valve 2 according to the instruction of the DCS system 6, so as to adjust the ammonia injection amount of the ammonia injection grid nozzle 1 controlled by it.

[0033] Among them, the flue gas sampling tube 3 is installed in the outlet flue of the SCR denitrification device and is located after the reactor. The flue gas sampling tube 3 corresponds to the automatic regulating valve 2 one by one, and is used to collect the NOx concentration of the ammonia spraying grid nozzle 1 controlled by the automatic regulating valve 2 at the relative position of the flue inlet flow field; the nitrogen oxide concentration sensor 5 is connected to the flue gas sampling tube 3 to circulate the flue gas collected by the flue gas sampling tube 3 for detection; the DCS system 6 is connected to the nitrogen oxide concentration sensor 5, and receives the NOx concentration data measured by the nitrogen oxide concentration sensor 5; the DCS system 6 adjusts the opening of the automatic regulating valve 2 according to the NOx concentration data of the SCR denitrification device outlet flue sampled by the flue gas sampling tube 3 to achieve precise ammonia injection.

[0034] In this embodiment, a first vacuum pump 4 is further installed between the flue gas sampling tube 3 and the nitrogen oxide concentration sensor 5, and the first vacuum pump 4 is used to transmit the flue gas collected by the flue gas sampling tube 3 to the nitrogen oxide concentration sensor 5. The nitrogen oxide sensor should have the ability to quickly measure the nitrogen oxide concentration and be able to work normally and stably for a long time.

[0035] like Figure 2 As shown, a back-purge device 7 and a filter 8 are installed at the outlet of the flue gas sampling tube 3 to prevent dust from entering the measuring sensor and to prevent the sampling tube from being blocked.

[0036] In addition, the outlet of the filter 8 is connected to the 3-position 2-way solenoid valve 9 to form a sampling pipeline, the first outlet of the 3-position 2-way solenoid valve 9 is connected to the air inlet of the second vacuum pump 10, the air outlet of the second vacuum pump 10 is connected to the outlet flue of the SCR denitration device, the second outlet of the 3-position 2-way solenoid valve 9 is connected to the air inlet of the first vacuum pump 4, the air outlet of the first vacuum pump 4 is connected to the nitrogen oxide concentration sensor 5, and the flue gas enters the inlet of the 3-position 2-way solenoid valve 9. When the 3-position 2-way solenoid valve 9 is not energized, the flue gas goes out from the first outlet of the 3-position 2-way solenoid valve 9, mixes with the flue gas coming out of other sampling pipelines, and is sent to the outlet flue of the SCR denitration device through the second vacuum pump 10; when the 3-position 2-way solenoid valve 9 is energized, the first outlet of the 3-position 2-way solenoid valve 9 is closed, and the filtered flue gas comes out from the second outlet of the 3-position 2-way solenoid valve 9, enters the first vacuum pump 4, and then enters the nitrogen oxide concentration sensor 5. The capacity of the first vacuum pump 4 and the second vacuum pump 10 should be sufficient, and the pressure should ensure that the flue gas can be quickly extracted. The second vacuum pump 10 is mainly used to extract non-measured flue gas to ensure that the non-extraction sampling tube and its pipeline are unobstructed and not blocked; the first vacuum pump 4 is mainly used to extract and measure the flue gas in the measuring flue gas channel. It should be ensured that the first vacuum pump does not leak, operates normally and stably for a long time, and can deliver the extracted flue gas to the nitrogen oxide sensor within 2 seconds.

[0037] Specifically, the NOx concentration data detected by the nitrogen oxide concentration sensor 5 is transmitted to the DCS system 6 after digital-to-analog conversion.

[0038] Preferably, 36 automatic regulating valves 2 are provided, and 36 flue gas sampling tubes 3 are also provided accordingly, and each automatic regulating valve 2 controls 4 ammonia injection grid nozzles 1 .

[0039] Example 2

[0040] The precise ammonia injection method of the power station boiler SCR denitration device of this embodiment 2 is implemented by using the precise ammonia injection system of the power station boiler SCR denitration device, and includes the following steps:

[0041] S1. Install the precise ammonia injection system of the SCR denitration device of the power station boiler;

[0042] S2, the first vacuum pump 4 is started, and the 3-position 2-way solenoid valve 9 at the outlet of each flue gas sampling tube 3 is energized in turn. At this time, the first outlet of the 3-position 2-way solenoid valve 9 is closed, and the filtered flue gas enters the first vacuum pump 4 from the second outlet of the 3-position 2-way solenoid valve 9, and then enters the nitrogen oxide concentration sensor 5; when the 3-position 2-way solenoid valve 9 is not energized, the flue gas goes out from the first outlet of the 3-position 2-way solenoid valve 9, mixes with the flue gas coming out of other flue gas sampling pipelines, and is sent to the outlet flue of the SCR denitration device through the second vacuum pump 10;

[0043] S3, the corresponding flue gas sampling tubes 3 collect the flue gas from the outlet of the SCR denitration device in turn, and transmit the flue gas to the nitrogen oxide concentration sensor 5, respectively perform NOx concentration detection in turn, and send the NOx concentration detection data to the DCS system 6;

[0044] S4, DCS system 6 compares the average value of NOx concentration detected by all flue gas sampling tubes 3 with the NOx concentration value of flue gas collected by each flue gas sampling tube 3 in sequence; if the deviation between the NOx concentration value of the flue gas at the outlet of the SCR denitration device collected by one or several flue gas sampling tubes 3 and the average value of NOx concentration detected exceeds the threshold value, the automatic regulating valve 2 corresponding to the flue gas sampling tube 3 with excessive concentration installed at the inlet of the SCR denitration device is commanded through DCS6 to adjust the opening of the automatic regulating valve 2, and the automatic regulating valve 2 controls the corresponding ammonia spraying grid nozzle 1 to spray ammonia;

[0045] S5, until the flue gas NOx concentration value collected by the flue gas sampling tube 3 at the outlet of the SCR denitration device corresponding to the automatic regulating valve 2 does not exceed the threshold value compared with the NOx concentration detection average value, and the precise ammonia injection control is completed.

[0046] Specifically, after the precise ammonia injection system is installed, a NOx concentration value of the flue gas at the outlet of the SCR denitrification device is set in the DCS system 6 as the NOx concentration target control value, and the NOx concentration detection average value is compared with the NOx concentration target control value. If the NOx concentration detection average value differs too much from the NOx concentration target control value (more than 20%), the operator manually controls the main valve on the ammonia main pipe for adjustment.

[0047] Among them, the threshold is 15%.

[0048] In this embodiment, as many flue gas sampling tubes as there are automatic regulating valves at the inlet of the SCR denitrification device, the flue gas sampling tubes are installed at the outlet of the SCR denitrification device, and the NOx concentration corresponding to the automatic regulating valve at the outlet of the SCR denitrification device can be controlled by adjusting the automatic regulating valve at the inlet of the SCR denitrification device. The nitrogen oxide sensor measures the NOx concentration of the flue gas sampling tube within 10 seconds, and sends the data to the DCS system after digital-to-analog conversion; in the second 10 seconds, the next solenoid valve is energized to measure the NOx concentration of the flue gas extracted by the next flue gas sampling tube, and so on, and repeats after 6 minutes, and so on.

[0049] In the DCS system, an SCR denitrification device outlet NOx concentration is artificially set. The average value of the SCR denitrification device outlet NOx concentration measured by the nitrogen oxide sensor is the control value of the SCR denitrification device outlet NOx concentration, and the deviation does not exceed 15%. If the deviation of the SCR denitrification device outlet NOx concentration measured by one or several flue gas sampling tubes exceeds 15%, the DCS system can be used to give an instruction to the automatic regulating valve of the ammonia grid at the inlet of the SCR denitrification device to adjust the opening of the ammonia grid regulating valve until the SCR denitrification device outlet concentration corresponding to the ammonia grid nozzle controlled by the automatic regulating valve deviates from the SCR denitrification device outlet NOx concentration average value by less than 15%.

[0050] Specifically, after the NOx concentration of each area at the outlet of the SCR denitrification device is sent to the DCS system, the average value is calculated, which is the NOx concentration at the outlet of the SCR on this side. If the NOx concentration of the flue gas extracted from one or more flue gas sampling tubes deviates from the average value by more than a certain value (15%), the DCS system can automatically send instructions to the corresponding ammonia spraying grid automatic regulating valve to adjust the valve opening to control the NOx concentration deviation measured by each flue gas sampling tube to be within 15%. The NOx concentration control value on this side is set at the outlet of the SCR denitrification device. The operating conditions of the SCR denitrification device can be manually controlled according to the boiler combustion conditions, or the NOx concentration control value set at the SCR outlet can be closed. The precise ammonia spraying system of the SCR denitrification device is automatically adjusted to ensure the normal operation of the SCR denitrification device, reduce the amount of ammonia sprayed and the ammonia escape rate, and avoid the air preheater from increasing resistance or blocking due to ammonium bisulfate.

[0051] The present invention measures the nitrogen oxide value of the ammonia injection nozzle control area controlled by each automatic regulating valve, and compares it with the nitrogen oxide setting value at the outlet of the SCR denitration device. The DCS sends instructions to the corresponding ammonia injection automatic regulating valve to adjust the ammonia injection amount. Under different loads, the nitrogen oxide concentration at the inlet of the SCR denitration device is different. The original ammonia injection master regulating valve can automatically adjust the valve opening of the ammonia injection automatic regulating valve according to the outlet setting value of the SCR denitration device, ultimately achieving the best effect of precise ammonia injection, reducing the ammonia injection amount and the ammonia escape rate, extending the service life of the SCR denitration device equipment, air preheater and other power station boiler equipment, and ensuring the safe and economical operation of the unit.

[0052] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A precise ammonia injection system for a power station boiler SCR denitration device, characterized in that: The invention comprises an ammonia spraying grid nozzle (1), an automatic regulating valve (2), a flue gas sampling tube (3), a first vacuum pump (4), a nitrogen oxide concentration sensor (5) and a DCS system (6), wherein a plurality of the ammonia spraying grid nozzles (1) are installed in the inlet flue of the SCR denitration device and are located in front of the reactor, each of the ammonia spraying grid nozzles (1) is connected to the ammonia main pipe through the automatic regulating valve (2), each of the automatic regulating valves (2) is connected to the DCS system (6), a plurality of the flue gas sampling tubes (3) are installed in the outlet flue of the SCR denitration device and are located after the reactor, the flue gas sampling tubes (3) and the automatic regulating valves (2) are arranged in a one-to-one correspondence, and the flue gas The sampling tube (3) is connected to the nitrogen oxide concentration sensor (5) through the first vacuum pump (4). The nitrogen oxide concentration sensor (5) performs cyclic detection on the flue gas collected by the plurality of flue gas sampling tubes (3) in turn. The nitrogen oxide concentration sensor (5) is connected to the DCS system (6). The DCS system (6) receives the NOx concentration data measured by the nitrogen oxide concentration sensor (5), and adjusts the opening of the corresponding automatic regulating valve (2) according to the NOx concentration data of the flue gas outlet of the SCR denitration device sampled by the flue gas sampling tube (3), so as to adjust the ammonia injection amount of the corresponding ammonia injection grid nozzle (1), thereby achieving accurate ammonia injection.

2. According to claim 1, a precise ammonia injection system for a power station boiler SCR denitration device is characterized in that: The outlet of each flue gas sampling tube (3) is installed with a back-purge device (7) and a filter (8); the outlet of the filter (8) is connected to a 3-position 2-way solenoid valve (9) to form a flue gas sampling pipeline; the first outlet of the 3-position 2-way solenoid valve (9) is connected to the air inlet of the second vacuum pump (10); the air outlet of the second vacuum pump (10) is connected to the SCR outlet flue; the second outlet of the 3-position 2-way solenoid valve (9) is connected to the air inlet of the first vacuum pump (4); and the air outlet of the first vacuum pump (4) is connected to the nitrogen oxide concentration sensor (5).

3. According to claim 1, a precise ammonia injection system for a power station boiler SCR denitration device is characterized in that: The NOx concentration data detected by the nitrogen oxide concentration sensor (5) is transmitted to the DCS system (6) after digital-to-analog conversion. The DCS system (6) compares the average value of the NOx concentration detected by all the flue gas sampling tubes (3) with the flue gas NOx concentration values ​​collected by each flue gas sampling tube (3) in sequence, and issues an instruction to the automatic regulating valve (2) corresponding to the flue gas sampling tube (3) with excessive concentration installed in the inlet flue of the SCR denitration device, so as to adjust the opening of the automatic regulating valve (2).

4. A precise ammonia injection system for a power station boiler SCR denitration device according to any one of claims 1 to 3, characterized in that: The automatic regulating valves (2) are provided in 36 numbers, and the flue gas sampling tubes (3) are provided in 36 numbers accordingly. Each automatic regulating valve (2) controls four ammonia spraying grid nozzles (1).

5. A precise ammonia injection method for a power station boiler SCR denitration device, characterized in that: The precise ammonia injection system for the SCR denitration device of a power station boiler according to any one of claims 1 to 4 comprises the following steps: S1. Install the precise ammonia injection system for the SCR denitration device of the power station boiler; S2, start the first vacuum pump (4), and energize the 3-position 2-way solenoid valve (9) at the outlet of each flue gas sampling tube (3) in turn. At this time, the first outlet of the 3-position 2-way solenoid valve (9) is closed, and the filtered flue gas enters the first vacuum pump (4) from the second outlet of the 3-position 2-way solenoid valve (9), and then enters the nitrogen oxide concentration sensor (5); when the 3-position 2-way solenoid valve (9) is not energized, the flue gas goes out from the first outlet of the 3-position 2-way solenoid valve (9), mixes with the flue gas coming out of other flue gas sampling pipelines, and is sent to the outlet flue of the SCR denitration device through the second vacuum pump (10); S3, the corresponding flue gas sampling tubes (3) respectively collect the flue gas at the outlet of the SCR denitration device in sequence, and transmit the flue gas to the nitrogen oxide concentration sensor (5), the nitrogen oxide concentration sensor (5) respectively performs NOx concentration detection in sequence, and sends the NOx concentration detection data to the DCS system (6); S4, the DCS system (6) compares the average value of the NOx concentration detected by all the flue gas sampling tubes (3) with the flue gas NOx concentration value collected by each flue gas sampling tube (3) in sequence. If the deviation between the NOx concentration value of the flue gas at the outlet of the SCR denitration device collected by one or several flue gas sampling tubes (3) and the average value of the NOx concentration detected exceeds a threshold value, the DCS system (6) issues an instruction to the automatic regulating valve (2) corresponding to the flue gas sampling tube (3) with the concentration exceeding the limit installed in the flue gas inlet of the SCR denitration device, and adjusts the opening of the automatic regulating valve (2), so that the automatic regulating valve (2) controls the ammonia spraying amount of the corresponding ammonia spraying grid nozzle (1); S5, until the flue gas NOx concentration value collected by the flue gas sampling tube (3) at the outlet of the SCR denitration device corresponding to the automatic regulating valve (2) does not exceed the threshold value compared with the average value of the NOx concentration detection, that is, the precise ammonia injection control is completed.

6. A precise ammonia injection method for a power station boiler SCR denitration device according to claim 5, characterized in that: After step S1, a NOx concentration value of the flue gas at the outlet of the SCR denitration device is set in the DCS system (6) as a NOx concentration target control value, and the NOx concentration detection average value is compared with the NOx concentration target control value. If the NOx concentration detection average value differs from the NOx concentration target control value by more than 20%, the operator manually controls the main valve on the ammonia main pipe for adjustment.

7. The precise ammonia injection method for a power station boiler SCR denitration device according to claim 5, characterized in that: In step S4, the threshold is 15%.

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