Flue gas denitration subzone ammonia injection system and method based on urea direct injection pyrolysis

Abstract

The present application relates to flue gas denitration system technical field, specifically for flue gas denitration partition ammonia injection system and method based on urea direct injection pyrolysis. The system comprises urea direct injection module A, inlet denitration measuring device B and outlet denitration measuring device C; the urea direct injection module A comprises several spray guns and a metering distribution unit for controlling the spray guns respectively; the spray guns are uniformly arranged in the flue gas partition of the economizer outlet flue; the inlet denitration measuring device B and the outlet denitration measuring device C both comprise a control measuring component and several sampling probes; the sampling probes of the inlet denitration measuring device B are arranged in the denitration inlet flue cross section according to the grid method; the sampling probes of the outlet denitration measuring device C are arranged in the denitration outlet flue cross section according to the grid method; the data input end of the control measuring component is connected with each sampling probe, and the data output end is connected with the metering distribution unit. The present application is reasonable in design, representative in measurement value, and can effectively detect and reduce ammonia escape.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flue gas denitration system, in particular to a flue gas denitration zoned ammonia injection system and method based on urea direct injection pyrolysis. BACKGROUND

[0002] At present, the flue gas denitration SCR reducing agent of coal-fired unit is basically concentrated in liquid ammonia, which has simple process, low initial investment and operation cost, and stable system, but since liquid ammonia is a kind of toxic and dangerous chemical, the liquid ammonia storage of coal-fired power plant is large, which has formed a major hazard source and has high safety risk. In view of the safety risk of liquid ammonia, the SCR denitration technology of reducing agent prepared by urea is widely used, and the reducing agent preparation technology mainly includes urea pyrolysis, urea direct injection and urea hydrolysis. The urea pyrolysis usually adopts hot primary air plus electric heater or gas-gas heat exchanger to heat the urea solution, which has high operation cost, complex system and is easy to cause crystallization; the urea hydrolysis system uses low-quality steam (0.8-1.0, 160-200 degrees) to make the urea solution in the reactor hydrolyze to produce mixed gas containing ammonia gas, which has complex system, high requirement for heat tracing of the auxiliary pipeline, and is easy to cause pipeline crystallization blockage and valve corrosion. The above two ammonia preparation technologies need a large amount of heat source, which has high system operation and maintenance cost, and to some extent, restricts the engineering application of the technology. The urea direct injection pyrolysis technology sprays the urea solution into the flue, uses the high-temperature flue gas (300-600 degrees) to pyrolyze the urea solution to generate mixed gas containing ammonia gas for the downstream SCR reactor, which has simple system and convenient operation.

[0003] The traditional ammonia injection system adjusts the ammonia amount of each reactor mother pipe through the ammonia valve according to the size of the nitrogen oxide and ammonia escape of the single measuring point at the outlet of the reactor, and then adjusts the ammonia amount of each branch pipe through the manual valve connected to the mother pipe, so as to achieve uniform mixing of the flue gas and ammonia amount in the flue cross section. However, the change of load and the difference of combustion mode (coal type, mill combination mode, burnout air ratio, etc.) will cause the change of the nitrogen oxide concentration mode at the inlet of the reactor, and usually only the ammonia amount of the manual valve of each branch pipe can be adjusted regularly (ammonia injection leveling experiment), so as to make the nitrogen oxide and ammonia escape in the flue cross section at the outlet of the reactor uniform. The traditional single point and multi-point sampling measurement at the outlet of the reactor cannot represent the average concentration and concentration distribution of the whole flue cross section, and the feedback of the measurement value to the ammonia valve will cause the mismatch of the nitrogen oxide concentration and ammonia amount in the reactor, and the large difference of the local denitration efficiency, so as to cause large local ammonia escape, which is not conducive to the normal operation of the downstream equipment. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a flue gas denitration zoned ammonia injection system and method based on urea direct injection pyrolysis, which has simple structure, reasonable design, representative measurement value, can effectively detect and reduce ammonia escape, and realizes stable denitration of coal-fired unit.

[0005] The present application is realized by the following technical solutions:

[0006] The flue gas denitration partition ammonia injection system based on urea direct injection pyrolysis comprises a urea direct injection module A, an inlet denitration measuring device B and an outlet denitration measuring device C.

[0007] The urea direct injection module A comprises a plurality of spray guns and a metering and distribution unit for controlling the spray guns respectively; the spray guns are uniformly arranged in the flue gas partition of the economizer outlet flue.

[0008] The inlet denitration measuring device B and the outlet denitration measuring device C each comprise a control measuring component and a plurality of sampling probes.

[0009] The sampling probes of the inlet denitration measuring device B are arranged in the denitration inlet flue cross section according to the grid method; the sampling probes of the outlet denitration measuring device C are arranged in the denitration outlet flue cross section according to the grid method.

[0010] The data input end of the control measuring component is connected to each sampling probe, and the data output end is connected to the metering and distribution unit.

[0011] Further, the metering and distribution unit comprises a urea solution metering module and a urea solution distribution module, a desalted water metering module and a desalted water distribution module, and a compressed air metering module and a compressed air distribution module.

[0012] The input end of the urea solution metering module is connected to a urea solution supply device through a urea solution main pipe, and the output end is connected to the input end of the urea solution distribution module; the output end of the urea solution distribution module is connected to each spray gun respectively.

[0013] The input end of the desalted water metering module is connected to a desalted water supply device through a desalted water main pipe, and the output end is connected to the input end of the desalted water distribution module; the output end of the desalted water distribution module is connected to each spray gun respectively.

[0014] The input end of the compressed air metering module is connected to a compressed air supply device through a compressed air main pipe, and the output end is connected to the input end of the compressed air distribution module; the output end of the compressed air distribution module is connected to each spray gun respectively.

[0015] Further, the metering and distribution unit further comprises a mixer and a mixed liquid flowmeter; the mixer is arranged at the output end of the urea solution distribution module and the desalted water distribution module respectively; the mixed liquid flowmeter is arranged on the pipeline connecting the mixer and each spray gun.

[0016] Further, the control measuring component comprises a high-temperature heat tracing pipe, a dilute sulfuric acid absorption liquid pool group, an analysis and measurement system and a plurality of sampling tubes.

[0017] The high-temperature heat tracing pipe is a tee pipe, one end of the main pipe is connected with a dilute sulfuric acid absorption liquid pool, the other end is connected with a sampling pipe through a joint converter, and the branch pipe is connected with an analysis and measurement system.

[0018] The plurality of sampling pipes are connected with sampling probes arranged according to a grid method one by one.

[0019] Further, the analysis and measurement system comprises a flue gas pretreatment device and a flue gas analysis device connected in sequence on the branch pipe of the high-temperature heat tracing pipe, and a signal processing module and a wireless transmission device connected with an upper computer; the flue gas analysis device comprises an oxygen measuring instrument and a nitric oxide measuring instrument, which are connected in sequence with the signal processing module and the wireless transmission device through control cables.

[0020] Further, a measurement manual valve is arranged on the pipe section connected with the analysis and measurement system of the high-temperature heat tracing pipe.

[0021] Further, a high-temperature filter and a sampling manual valve are arranged in sequence on the sampling pipe along the gas flow direction; a high-temperature air pump is arranged at the connection between the sampling pipe and the high-temperature heat tracing pipe.

[0022] Further, the dilute sulfuric acid absorption liquid pool group comprises a first dilute sulfuric acid absorption liquid pool and a second dilute sulfuric acid absorption liquid pool arranged in an ice water tank; a dilute sulfuric acid solution manual valve and a flow meter are arranged in sequence on the inlet pipe section of the first dilute sulfuric acid absorption liquid pool; a wastewater pool is connected to the outlet pipe section of the second dilute sulfuric acid absorption liquid pool.

[0023] The flue gas denitration partition ammonia injection method based on urea direct injection pyrolysis comprises,

[0024] Step one, arranging a urea direct injection module A in the flue gas denitration outlet flue according to the CFD numerical simulation results. x The concentration field and the velocity field are simulated by a CFD numerical simulation software to obtain simulation results, and then the flue gas economizer outlet flue is divided into a plurality of flue gas partition zones according to the simulation results;

[0025] Step two, arranging a urea direct injection module A in the flue gas denitration outlet flue according to the CFD numerical simulation results, one by one, to form a urea direct injection system partition zone; meanwhile, sampling probes are arranged uniformly at the flue gas denitration inlet flue and the flue gas denitration outlet flue, and the distribution of NO / O2 and NH3 at different cross sections of the flue gas denitration outlet flue and the flue gas denitration inlet flue is obtained through the arranged sampling probes and corresponding control measurement components.

[0026] Step three, according to the obtained NO / O2 and NH3 distribution, the concentration, flow and compressed air pressure parameters of the mixed solution of each lance in each urea direct injection system partition are adjusted by the metering control unit, and the ammonia injection denitration of the flue gas in the flue is completed.

[0027] Further, the number of flue gas sampling points arranged at different cross sections is determined according to the number and position of the lances in each urea direct injection system partition; the sampling probes are uniformly arranged in the cross sections of the denitration inlet flue and the denitration outlet flue according to the grid method, and at least three sampling probes are uniformly arranged in the same width direction in each partition of the inlet and outlet flues.

[0028] Compared with the prior art, the present application has the following beneficial technical effects:

[0029] The system of the present application adopts the mode of arranging urea direct injection modules at the economizer outlet flue and arranging outlet and inlet denitration measuring devices at the cross sections of the denitration inlet and outlet flues, distributing each lance of the urea direct injection module in the economizer outlet flue according to the corresponding flue partition position, and arranging each sampling probe at the cross sections of the denitration inlet and outlet flues according to the grid method; through the control measuring components connected with the metering and distribution units of each sampling probe and lance, the NO / O2 and NH3 distribution of the entire flue cross section at the denitration inlet and outlet can be measured synchronously and quickly, the denitration inlet ammonia nitrogen molar ratio and the NO / O2 and NH3 distribution at the denitration inlet and outlet under the conditions of low, medium and high loads of the unit and different mill groups can be reflected in real time, problems and defects existing in the denitration system device can be quickly diagnosed, solutions can be proposed according to the on-site collected data and the operation mode of each system, the measured values are representative, and ammonia escape can be effectively detected and reduced; at the same time, through the test of the NO / O2 and NH3 distribution at the denitration inlet and outlet under the low, medium and high loads of the coal-fired unit, the reasonable operation parameters of the urea direct injection pyrolysis under each load operation condition can be found out, ammonia production under the economy and coordination of the urea direct injection pyrolysis system can be realized, and stable denitration of the coal-fired unit can be realized.

[0030] Further, the system of the present application uses urea solution metering modules and distribution modules, desalted water metering modules and distribution modules, and compressed air metering modules and distribution modules to separately adjust and control different substances, so that the flue cross section flue gas and ammonia amount reaction concentration can be matched according to the actual demand, and the excessive nitrogen oxides and excessive ammonia escape can be effectively avoided.

[0031] Further, the system of the present application uses a mixer to uniformly mix the urea solution and the desalted water before entering the lances, effectively improves the treatment efficiency, and reasonably allocates the urea solution concentration; at the same time, a mixed liquid flowmeter is arranged on the pipeline to improve the dosage accuracy.

[0032] Further, the system of the present application can realize sampling at different flue cross sections by connecting the sampling tubes of different lengths with the sampling probes one by one, thereby ensuring the accuracy and integrity of the whole system.

[0033] Further, the system of the present application can realize sampling at different flue cross sections by connecting the sampling tubes of different lengths with the sampling probes one by one, thereby ensuring the accuracy and integrity of the whole system.

[0034] Further, the system of the present application can realize sampling at different flue cross sections by connecting the sampling tubes of different lengths with the sampling probes one by one, thereby ensuring the accuracy and integrity of the whole system.

[0035] Further, the system of the present application can realize sampling at different flue cross sections by connecting the sampling tubes of different lengths with the sampling probes one by one, thereby ensuring the accuracy and integrity of the whole system.

[0036] Further, the system of the present application can realize sampling at different flue cross sections by connecting the sampling tubes of different lengths with the sampling probes one by one, thereby ensuring the accuracy and integrity of the whole system. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The figure is a schematic diagram of the connection of the lance and the metering and distribution unit described in the embodiment of the present application.

[0038] Figure 2 The figure is a schematic diagram of the partition of the urea direct injection system described in the embodiment of the present application.

[0039] Figure 3 The figure is a schematic diagram of the installation and arrangement position of the system of the present application.

[0040] Figure 4 The figure is a schematic diagram of the structure of the inlet denitration measuring device and the outlet denitration measuring device described in the embodiment of the present application.

[0041] In the figure: A-urea direct injection module, B-inlet denitration measuring device, C-outlet denitration measuring device, 1-sampling tube manual valve, 2-high temperature air pump, 3-high temperature heat tracing tube, 4-dilute sulfuric acid solution manual valve, 5-flow meter, 6-first dilute sulfuric acid absorption liquid, 7-second dilute sulfuric acid absorption liquid, 8-waste water pool, 9-ice water tank, 10-manual valve, 11-flue gas pretreatment, 12-flue gas analysis device, 13-oxygen measuring instrument, 14-nitric oxide measuring instrument, 15-control cable, 16-signal processing module, 17-wireless transmission device, 18-upper computer, 19-sampling probe, 20-high temperature filter, 21-sampling tube, 22-lance, 23-denitration inlet flue, 24-denitration outlet flue, 25-urea solution metering module, 26-urea solution distribution module, 27-desalinated water metering module, 28-desalinated water distribution module, 29-compressed air metering module, 30-compressed air distribution module, 31-mixer, 32-mixed liquid flow meter, 33-SCR reactor. DETAILED DESCRIPTION

[0042] The application will be further described in detail below in connection with specific examples, which are intended to explain but not limit the application.

[0043] The application is based on a flue gas denitration partition ammonia injection system for urea direct injection pyrolysis, as shown in Figure 3 and Figure 4 which comprises a urea direct injection module A composed of several spray guns 22 and metering and distribution units for controlling the spray guns 22 respectively, an inlet denitration measuring device B and an outlet denitration measuring device C composed of control measuring components and several sampling probes 19.

[0044] As shown in Figure 1 , the metering and distribution unit comprises a urea solution metering module 25, a urea solution distribution module 26, a desalted water metering module 27, a desalted water distribution module 28, a compressed air metering module 29, a compressed air distribution module 30, a mixer 31 and a mixed liquid flow meter 32; the metering and distribution unit is used to control the spray guns 22, as shown in Figure 2 , the spray guns 22 are arranged in the economizer outlet flue according to the CFD numerical simulation results of the flue partition position.

[0045] Among them, the input end of the urea solution metering module 25, the desalted water metering module 27 and the compressed air metering module 29 is connected to the urea solution supply device, the desalted water supply device and the compressed air supply device through the urea solution main pipe, the desalted water main pipe and the compressed air main pipe respectively, and the output end is connected to the input end of the urea solution distribution module 26, the desalted water distribution module 28 and the compressed air distribution module 30 respectively; the output end of the urea solution distribution module 26 and the desalted water distribution module 28 is connected to each spray gun 22 through the mixer 31, and a flow meter 32 is arranged on the connecting pipeline respectively; the output end of the compressed air distribution module 30 is directly connected to each spray gun 22.

[0046] As shown in Figure 4 , the data input end of the control measuring component is connected to each sampling probe 19, and the data output end is connected to the metering and distribution unit; the control measuring component comprises a high-temperature heat tracing pipe 3, a dilute sulfuric acid absorption liquid pool group, an analysis and measurement system, and several sampling pipes 21 connected to the high-temperature heat tracing pipe 3; the high-temperature heat tracing pipe 3 is a three-way pipe, one end of the main pipe is connected to the dilute sulfuric acid absorption liquid pool, the other end is connected to the sampling pipe 21, and the branch pipe is connected to the analysis and measurement system; the lengths of the several sampling pipes 21 are different, and they are connected to the sampling probes 19 one by one respectively.

[0047] The analysis measurement system comprises a flue gas pretreatment 11 and a flue gas analysis device 12 connected in sequence on the branch pipe of the high-temperature heat tracing pipe 3, and a signal processing module 16 and a wireless transmission device 17 connected with the upper computer 18; the flue gas analysis device 12 comprises an oxygen measuring instrument 13 and a nitric oxide measuring instrument 14, which are connected in sequence with the signal processing module 16 and the wireless transmission device 17 through a control cable 15.

[0048] The sampling pipe 21 is provided with a high-temperature filter 20 and a sampling manual valve 1 in sequence along the gas flow direction; and the sampling pipe 21 is provided with a high-temperature air pump 2 at the connection position with the high-temperature heat tracing pipe 3.

[0049] The first dilute sulfuric acid absorption liquid pool 6 and the second dilute sulfuric acid absorption liquid pool 7 are arranged in the ice water tank 9; the inlet pipe section of the first dilute sulfuric acid absorption liquid pool 6 is provided with a dilute sulfuric acid solution manual valve 4 and a flow meter 5 in sequence; and the outlet pipe section of the second dilute sulfuric acid absorption liquid pool 7 is connected with a waste water pool 8.

[0050] The measurement manual valve 10 is arranged on the pipe section connected with the high-temperature heat tracing pipe 3.

[0051] As shown in Figure 3 The sampling probes 19 are arranged in the cross sections of the denitration inlet flue 23 and the denitration outlet flue 24 in a grid method.

[0052] The system of the present application simulates the NO x The urea solution and the desalted water are mixed to form urea of a certain concentration, and then the urea is mixed with compressed air of a certain pressure in the mixer 31 and is atomized into the flue through the nozzle of the spray gun 22; the sampling probe 19, the high-temperature filter 20 and the sampling pipe 21 are connected to the inlet end of the main pipe of the high-temperature heat tracing pipe 3 through a joint converter, the inlet end of the main pipe of the high-temperature heat tracing pipe 3 is connected with the inlet of the high-temperature air pump 2, the flue gas enters the inlet of the flue gas pretreatment 11 connected with the branch pipe outlet end of the high-temperature heat tracing pipe 3 through the sampling pipe 21, the outlet of the flue gas pretreatment 11 is connected with the flue gas analysis device 12, the flue gas analysis device 12 transmits the measurement data to the signal processing module 16 through a control cable, and then the data is input into the upper computer 18 through the wireless transmission device 17 for summary analysis; the outlet end of the main pipe of the high-temperature heat tracing pipe 3 is connected with the dilute sulfuric acid solution manual valve 4 and the flow meter 5, the flue gas is fully absorbed in the first dilute sulfuric acid solution pool 6 and the second dilute sulfuric acid solution pool 7 in sequence, then a small amount of absorption liquid is taken, the ammonia gas sensitive electrode is placed in the absorption liquid to measure the corresponding data, and the sampling time and the flow are transmitted to the upper computer 18 through the wireless transmission device 17.

[0053] In this embodiment, the flue gas duct at the outlet of the economizer is divided into four zones, as shown in Figure 2 Three spray guns 22 are arranged in the same width direction to form a group of ammonia injection systems, two groups of ammonia injection systems are arranged in each zone, and eight groups of ammonia injection systems are arranged in the flue gas duct 4 at the outlet of the economizer.

[0054] In one group of urea ammonia injection systems, a urea solution main pipe connected to a urea solution supply device passes through a urea solution metering module 25 and enters a urea solution distribution module 26, from which three urea branch pipes enter a mixer 31; similarly, a demineralized water main pipe connected to a demineralized water supply device passes through a demineralized water metering module 27 and enters a demineralized water distribution module 28, from which three demineralized water branch pipes enter the mixer 31, in which the urea solution and the demineralized water are mixed to form a mixed solution of a certain concentration, which then enters a flow meter 32, is adjusted and sent into each spray gun 22, and is injected into the flue gas through the spray gun 22; another inlet of the spray gun 22 is connected to a compressed air distribution module 30, a compressed air metering module 29 and a compressed air supply device through a compressed air main pipe, and the compressed air pressure is adjusted so that the atomization effect of the mixed solution in the spray gun 22 is optimal. The urea mixed solution injected into the flue gas is decomposed into mixed gases such as ammonia gas by high-temperature flue gas, and enters the denitration inlet flue gas duct 23 after passing through the guide plate, the zone mixer and the static mixer, and then enters the denitration outlet flue gas duct 24 after passing through the SCR reactor;

[0055] In the outlet denitration measurement device C and the inlet denitration measurement device B, each sampling probe 19 is arranged in the denitration outlet flue gas duct 24 and the denitration inlet flue gas duct 23 according to the grid method, a high-temperature filter 20 is arranged in the sampling pipe 21, and the number of sampling points at each cross section is determined according to the number and position of the zone spray guns 22. The flue gas passing through the high-temperature filter 20 is connected to the outside soft connection high-temperature heat tracing pipe 3 through the sampling pipe manual valve 1 of the sampling pipe 21, the high-temperature heat tracing pipe 3 is connected to the inlet of the high-temperature air pump 2, and the outlet is connected to the dilute sulfuric acid solution manual valve 4 and the flow meter 5;

[0056] The flue gas enters the first dilute sulfuric acid absorption liquid pool 6 and the second dilute sulfuric acid absorption liquid pool 7 in turn, and the two absorption liquid pools fully absorb the amount of ammonia in the flue gas, and the remaining tail gas is discharged into the wastewater pool 8; then the ammonia gas sensitive electrode is placed in the absorption liquid to obtain the ammonium ion, and the amount of ammonia at this point is obtained according to the time and flow rate; the high-temperature heat tracing pipe 3 is connected to the sampling pipe 21, the outlet of which is connected to the inlet of the flue gas pretreatment 11, the outlet of the flue gas pretreatment 11 is connected to the inlet of the flue gas analyzer 12, the flue gas analyzer 12 is distributed with an oxygen measuring instrument 13 and a nitric oxide measuring instrument 14, and the concentrations of O2 and NO in the flue gas are measured in turn, the measuring signals are transmitted to the signal processing module 16 through the control cable 15, and then the data of the signal processing module 16 are uploaded to the upper computer 18 through the wireless transmission device 17;

[0057] The distribution of NO / O2 and NH3 at the cross section of the denitration outlet flue 24 and the denitration inlet flue 23 is displayed through the host computer 18 system, and then the concentration, flow and compressed air pressure of the mixed solution of each urea direct injection system partition spray gun 22 are adjusted, so that the ammonia production under the economy and coordination of the urea direct injection pyrolysis system is achieved, and the flue gas denitration of the coal-fired unit is stabilized.

[0058] Based on the above system, the application also provides a flue gas denitration partition ammonia injection method based on urea direct injection pyrolysis, comprising,

[0059] Step one, the NO x The concentration field and the velocity field are simulated and calculated by the CFD numerical simulation software to obtain simulation results, and then the economizer outlet flue is divided into several flue partitions according to the simulation results;

[0060] Step two, in the economizer outlet flue, the spray guns 22 of the urea direct injection module A are arranged in the flue partitions by using the CFD numerical simulation results, and the urea direct injection system partitions are formed one by one; meanwhile, the sampling probes 19 are evenly arranged at the denitration inlet flue 23 and the denitration outlet flue 24, respectively, and the distribution of NO / O2 and NH3 at different cross sections of the denitration outlet flue 24 and the denitration inlet flue 23 is obtained through the arranged sampling probes 19 and the corresponding control measurement components;

[0061] Step three, according to the obtained distribution of NO / O2 and NH3, the concentration, flow and compressed air pressure parameters of each spray gun 22 in each direct injection system partition are adjusted through the metering control unit, and the partition ammonia injection denitration of the flue gas in the flue is completed.

[0062] The number of the arranged flue gas sampling points at different cross sections is determined according to the number and position of the spray guns 22 in each urea direct injection system partition; the sampling probes 19 are evenly arranged in the cross sections of the denitration inlet flue 23 and the denitration outlet flue 24 according to the grid method, and at least three sampling probes 19 are evenly arranged in the same width direction of each flue partition of the inlet and outlet.

[0063] The application overcomes the technical problems of the existing coal-fired unit denitration technology, adjusts the parameters of each spray gun in each flue area according to the amount of nitrogen oxides and ammonia at the inlet of each urea direct injection system partition and the size of nitrogen oxide and ammonia escape at the outlet of each partition, so that the uniform mixing of the flue gas and ammonia in each partition at the inlet is achieved, the ammonia production under the economy and coordination of the urea direct injection pyrolysis system at the inlet of each partition of the reactor is realized, and the uniform distribution of nitrogen oxides in the outlet flue of the reactor is realized. Meanwhile, the performance of the existing catalyst can be detected according to the parameters such as the denitration efficiency and the size of ammonia escape of each partition.

Claims

1. Flue gas denitrification zoned ammonia injection system based on urea direct injection pyrolysis, characterized by: It includes urea direct injection module A, inlet denitration measuring device B and outlet denitration measuring device C; The urea direct injection module A comprises a plurality of spray guns (22) and a metering and dispensing unit for controlling the spray guns (22) respectively; the spray guns (22) are evenly arranged in the flue partition of the economizer outlet flue; The inlet denitration measuring device B and the outlet denitration measuring device C both include a control and measurement component and a plurality of sampling probes (19); The sampling probes (19) of the inlet denitration measuring device B are arranged in a cross section of the denitration inlet flue (23) according to a grid method; the sampling probes (19) of the outlet denitration measuring device C are arranged in a cross section of the denitration outlet flue (24) according to a grid method; The data input end of the control and measurement component is connected to each sampling probe (19) respectively, and the data output end is connected to the metering and dispensing unit; The metering and distributing unit comprises a urea solution metering module (25) and a urea solution distributing module (26), a desalted water metering module (27) and a desalted water distributing module (28), a compressed air metering module (29) and a compressed air distributing module (30); The input end of the urea solution metering module (25) is connected to the urea solution supply device through the urea solution main pipe, and the output end is connected to the input end of the urea solution distribution module (26); the output end of the urea solution distribution module (26) is respectively connected to each spray gun (22); The input end of the desalted water metering module (27) is connected to the desalted water supply device via the desalted water jellyfish pipe, and the output end is connected to the input end of the desalted water distribution module (28); the output end of the desalted water distribution module (28) is respectively connected to each spray gun (22); The input end of the compressed air metering module (29) is connected to the compressed air supply device through the compressed air main pipe, and the output end is connected to the input end of the compressed air distribution module (30); the output end of the compressed air distribution module (30) is respectively connected to each spray gun (22); The metering and dispensing unit further comprises a mixer (31) and a mixed liquid flow meter (32); the mixer (31) is respectively arranged at the output ends of the urea solution dispensing module (26) and the desalted water dispensing module (28); the mixed liquid flow meter (32) is respectively arranged on the pipeline connecting the mixer (31) and each spray gun (22); the urea mixed solution sprayed into the flue is heated by the high-temperature flue gas and decomposed into a mixed gas containing ammonia; The other inlet of the spray gun (22) is connected to the compressed air distribution module (30), the compressed air metering module (29) and the compressed air supply device through the compressed air main pipe, and the compressed air pressure is adjusted to achieve the best atomization effect of the mixed solution in the spray gun (22); The control and measurement components include a high-temperature heating pipe (3), a dilute sulfuric acid absorption liquid pool group, an analysis and measurement system, and a plurality of sampling tubes (21); The high-temperature heating pipe (3) is a three-way pipe, one end of the main pipe is connected to the dilute sulfuric acid absorption liquid pool, the other end is connected to the sampling pipe (21) through a joint converter, and the branch pipe is connected to the analysis and measurement system; The plurality of sampling tubes (21) are connected in a one-to-one correspondence with the sampling probes (19) arranged according to the grid method; The analysis and measurement system comprises a flue gas pretreatment device (11) and a flue gas analysis device (12) connected in sequence to a branch pipe of a high-temperature heating pipe (3), and a signal processing module (16) and a wireless transmission device (17) connected to a host computer (18); the flue gas analysis device (12) comprises an oxygen meter (13) and a nitric oxide meter (14), which are connected in sequence to the signal processing module (16) and the wireless transmission device (17) via a control cable (15); A measuring manual valve (10) is provided on the pipe section connecting the analysis and measurement system and the high-temperature heating pipe (3); A high-temperature filter (20) and a sampling manual valve (1) are sequentially provided on the sampling tube (21) along the gas flow direction; a high-temperature vacuum pump (2) is provided at the connection between the sampling tube (21) and the high-temperature heating tube (3); The dilute sulfuric acid absorption liquid pool group comprises a first dilute sulfuric acid absorption liquid pool (6) and a second dilute sulfuric acid absorption liquid pool (7) arranged in an ice water tank (9); a dilute sulfuric acid solution manual valve (4) and a flow meter (5) are sequentially arranged on the inlet pipe section of the first dilute sulfuric acid absorption liquid pool (6); and the outlet pipe section of the second dilute sulfuric acid absorption liquid pool (7) is connected to a wastewater pool (8).

2. A flue gas denitrification and ammonia injection method based on urea direct injection pyrolysis, characterized in that: The system according to claim 1, comprising: Step 1: Remove NO from the denitrification outlet flue (24) x The concentration field and velocity field are simulated and calculated by CFD numerical simulation software, and then the economizer outlet flue is divided into several flue zones according to the simulation results; Step 2: In the economizer outlet flue, the spray guns (22) of the urea direct injection module A are arranged in the corresponding flue partitions according to the CFD numerical simulation results, and the urea direct injection system partitions are formed one by one; at the same time, sampling probes (19) are evenly arranged at the denitrification inlet flue (23) and the denitrification outlet flue (24), and the distribution of NO / O2 and NH3 at different cross sections of the denitrification outlet flue (24) and the denitrification inlet flue (23) are obtained through the arranged sampling probes (19) and their corresponding control and measurement components; Step 3: According to the obtained NO / O2 and NH3 distribution, the concentration, flow rate and pressure parameters of the mixed solution of each spray gun (22) in each urea direct injection system partition are adjusted by the metering control unit to complete the ammonia spraying denitrification of the flue gas in the flue; The number of flue gas sampling points arranged at different cross sections is determined according to the number and position of the spray guns (22) in each urea direct injection system partition; the sampling probes (19) are evenly arranged in the cross sections of the denitrification inlet flue (23) and the denitrification outlet flue (24) according to the grid method, and at least three sampling probes (19) are evenly arranged in the same width direction in each inlet and outlet flue partition.

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