SCR (Selective Catalytic Reduction) denitration system for cement kiln flue gas

Abstract

The utility model discloses an SCR (Selective Catalytic Reduction) denitration system for cement kiln flue gas. The SCR denitration system comprises an ammonia water storage tank, an ammonia water metering and distributing device, a cement kiln tail preheater, a reactor, a bypass pipeline device, an ash return device, a waste heat utilization device and a compressed air supply device, the ammonia water storage tank is connected with the ammonia water metering and distributing device through an ammonia water distributing pipe; the ammonia water metering and distributing device is connected with a cement kiln tail preheater through a pipeline; the reducing agent spraying direction at the outlet end of the ammonia water metering and distributing device is opposite to the flue gas output direction at the outlet end of the cement kiln tail preheater; one side end of the reactor is connected with a compressed air supply device; the bottom end of the reactor is respectively connected with the ash return device and the waste heat utilization device; and the cement kiln tail preheater, the reactor and the waste heat utilization device are respectively connected with the bypass pipeline device. According to the SCR denitration system for the cement kiln flue gas, the SNCR-SCR combined denitration technology is used, and the denitration efficiency is more than 90%.

Description

Technical Field

[0001] The utility model relates to the technical field of flue gas denitration, in particular to an SCR denitration system for cement kiln flue gas. Background Art

[0002] Denitrification technologies in the cement industry mainly include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), as well as some other auxiliary technologies. These technologies aim to reduce nitrogen oxides (NO x )emission.

[0003] Although most of the current technologies using low-nitrogen combustion + SNCR or low-nitrogen combustion + SCR can basically meet environmental emission requirements, in some cement plants, due to the kiln's own design and operating conditions and coal type restrictions, SNCR or SCR alone cannot meet the emission requirements.

[0004] SNCR-SCR combined denitrification technology refers to the simultaneous use of SNCR denitrification technology and SCR denitrification technology in the flue gas denitrification of the kiln. The reducing agent is directly sprayed into the furnace of the kiln to carry out the SNCR denitrification reaction first. After the flue gas after SNCR denitrification is cooled by the kiln heating surface and reaches the suitable temperature range for SCR denitrification, it is introduced into the SCR denitrification reactor to further remove NO. x .

[0005] In terms of the order of reaction, SCR denitrification is located after SNCR denitrification, and the SNCR denitrification technology itself has a large amount of reducing agent leakage, which can provide reducing agent for the SCR denitrification of downstream flue gas. Therefore, the SNCR-SCR combined denitrification technology is feasible, and theoretically, this technology can improve the overall denitrification efficiency while also reducing the amount of ammonia leakage when only SNCR denitrification is used. SNCR-SCR combined denitrification technology is generally used in the flue gas denitrification of circulating fluidized bed kilns, and its denitrification efficiency can reach more than 80%, but in actual application, it will be affected by factors such as the structure of the kiln itself and whether an SCR ammonia injection device is installed. The SNCR-SCR denitrification process is mostly used for efficiency improvement when an existing SNCR denitrification device is unable to meet the new emission standards. An SCR denitrification device is added to the existing SNCR device to achieve NO x Under the premise of ensuring higher denitrification efficiency, it is also necessary to carry out corresponding transformation based on the current status of the kiln. Utility Model Content

[0006] In view of this, the utility model proposes an SCR denitrification system for cement kiln flue gas, a new SCR denitrification system outside the furnace is newly built, the newly added SCR denitrification system is integrated with the original SNCR denitrification system, and the SNCR-SCR combined denitrification of flue gas is optimized to reduce NO in kiln flue gas. x The upgraded denitrification system can realize the independent operation of SNCR device and SCR device, as well as the coordinated operation of SNCR device and SCR device.

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

[0008] A cement kiln flue gas SCR denitrification system comprises an ammonia water storage tank, an ammonia water metering and distribution device, a cement kiln tail preheater, a reactor, a bypass piping device, an ash return device, a waste heat utilization device, and a compressed air supply device; the ammonia water storage tank is connected to the ammonia water metering and distribution device via an ammonia water distribution pipe; the ammonia water metering and distribution device is connected to the cement kiln tail preheater via a pipeline; the reducing agent spraying direction of the ammonia water metering and distribution device outlet is opposite to the flue gas output direction of the cement kiln tail preheater outlet;

[0009] One side end of the reactor is connected to the compressed air supply device; the bottom end of the reactor is connected to the ash return device and the waste heat utilization device respectively;

[0010] The bypass device includes a first bypass pipe, a second bypass pipe, a third bypass pipe and a fourth bypass pipe; one end of the first bypass pipe is connected to the outlet end of the cement kiln tail preheater, and the other end is connected to the fourth bypass pipe; one end of the second bypass pipe is connected to the top end of the reactor, and the other end is connected to the first bypass pipe; one end of the third bypass pipe is connected to the bottom end of the reactor, and the other end is connected to the fourth bypass pipe; the fourth bypass pipe is connected to the waste heat utilization device; the first bypass pipe, the second bypass pipe, the third bypass pipe and the fourth bypass pipe are respectively provided with a baffle door.

[0011] Furthermore, the ammonia water metering and dispensing device includes a compressed air pipe and a plurality of spray guns;

[0012] The inlet end of each spray gun is connected to the compressed air pipe and the ammonia distribution pipe respectively;

[0013] A delivery pump is provided on the ammonia water distribution pipe.

[0014] Furthermore, the cement kiln tail preheater includes a rotary kiln, a kiln tail smoke chamber, a decomposition furnace, a C1-level cyclone, a C2-level cyclone, a C3-level cyclone, a C4-level cyclone, and a C5-level cyclone;

[0015] The C1-level cyclone, C2-level cyclone, C3-level cyclone, C4-level cyclone, and C5-level cyclone are arranged alternately from top to bottom;

[0016] The rotary kiln is connected to the kiln tail smoke chamber;

[0017] The bottom end of the decomposition furnace is provided with a denitrification chamber; the upper end of the kiln tail smoke chamber is connected to the denitrification chamber;

[0018] The top of the decomposition furnace is connected to the ascending flue of the C5-level cyclone;

[0019] The top of the C5-level cyclone is connected to the ascending flue of the C4-level cyclone;

[0020] The top of the C4-level cyclone is connected to the ascending flue of the C3-level cyclone;

[0021] The top of the C3-level cyclone is connected to the ascending flue of the C2-level cyclone;

[0022] The top of the C2-level cyclone is connected to the ascending flue of the C1-level cyclone;

[0023] The top end of the C1-level cyclone is arranged opposite to the outlet ends of a plurality of spray guns through a pipeline.

[0024] Furthermore, the compressed air supply device includes a compressed air supply assembly, a first air storage tank and a second air storage tank;

[0025] The compressed air supply assembly is connected to the first air storage tank and the second air storage tank through pipelines respectively.

[0026] Furthermore, the compressed air supply assembly includes a screw air compressor, a third air storage tank, a pre-filter, a cold dryer and a post-filter;

[0027] The screw air compressor is connected to the third air storage tank;

[0028] The third gas storage tank is connected to the cold dryer through a pipeline; the pre-filter is provided on the pipeline between the third gas storage tank and the cold dryer;

[0029] The cold dryer is connected to the first gas storage tank and the second gas storage tank through pipelines respectively; a post-filter is provided on the pipeline between the cold dryer and the first gas storage tank and the second gas storage tank.

[0030] Furthermore, the reactor includes a reactor body, a catalyst module, a dust cleaning module and an air-to-air heat exchanger;

[0031] A catalyst module is provided inside the reactor body;

[0032] A dust cleaning module is provided inside the reactor body;

[0033] An air-to-air heat exchanger is provided inside the reactor body; the air-to-air heat exchanger is located below the catalyst module and the dust cleaning module.

[0034] Furthermore, a rectifying grid is provided at the upper end of the interior of the reactor body;

[0035] The catalyst module is a plurality of denitration catalyst beds; the interior of the reactor body is provided with a plurality of denitration catalyst beds from top to bottom; and the plurality of denitration catalyst beds are located below the rectifying grid.

[0036] Furthermore, the soot cleaning module includes a plurality of sonic soot blowers and a plurality of rake soot blowers;

[0037] A sonic soot blower and a rake soot blower are provided above each denitration catalyst bed;

[0038] The inlet ends of the plurality of sonic soot blowers are respectively connected to the first gas storage tank through pipelines; the outlet ends of the sonic soot blowers are located inside the reactor body;

[0039] The inlet end of the gas-to-gas heat exchanger is connected to the second gas storage tank through a pipeline; the outlet end of the gas-to-gas heat exchanger is connected to the inlet ends of several rake soot blowers through pipelines; the outlet ends of the rake soot blowers are located inside the reactor body.

[0040] Furthermore, the waste heat utilization device includes a waste heat boiler and a high-temperature fan;

[0041] The inlet end of the waste heat boiler is connected to the fourth bypass pipe; the outlet end of the waste heat boiler is connected to the inlet end of the high-temperature fan;

[0042] The inlet end of the high-temperature fan is connected to the fourth bypass pipeline; the outlet of the high-temperature fan is connected to subsequent process equipment.

[0043] Furthermore, the ash return device includes an ash return pipe, a rotary feeder and an embedded scraper conveyor;

[0044] The bottom end of the reactor body is connected to the ash return pipe;

[0045] The ash return pipe is equipped with a manual gate valve and a rotary feeder;

[0046] The outlet end of the ash return pipe is connected to the buried scraper conveyor.

[0047] Compared with the existing technology, the beneficial effects of the present invention are as follows: the present invention provides an SCR denitrification system for cement kiln flue gas, which builds a new SCR denitrification system on the basis of the original SNCR system, and adopts 20% ammonia solution as the denitrification reducing agent. By integrating and optimizing the newly added SCR denitrification system with the original SNCR denitrification system, the flue gas SNCR-SCR combined denitrification is realized, and the kiln flue gas NO is reduced. x The denitrification efficiency is over 90%; the upgraded denitrification system can realize the independent operation of SNCR device and SCR device, as well as the coordinated operation of SNCR device and SCR device. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic structural diagram of an SCR denitrification system for cement kiln flue gas provided in an embodiment of the present invention;

[0049] Figure 2 for Figure 1 A magnified view of part A in FIG;

[0050] Figure 3 for Figure 1 Enlarged view of part B in .

[0051] Figure 1: Ammonia storage tank; 2: Compressed air pipe; 3: Spray gun; 4: Delivery pump; 5: Ammonia distribution pipe; 6: Rotary kiln; 7: Kiln tail smoke chamber; 8: Decomposition furnace; 9: C1-class cyclone; 10: C2-class cyclone; 11: C3-class cyclone; 12: C4-class cyclone; 13: C5-class cyclone; 14: Denitrification chamber; 15: First bypass pipe; 16: Second bypass pipe; 17: Third bypass pipe; 18: Fourth bypass pipe; 19: Baffle door; 20: Metal expansion joint ; 21. Screw air compressor; 22. Third air storage tank; 23. Pre-filter; 24. Cold dryer; 25. Post-filter; 26. First air storage tank; 27. Second air storage tank; 28. Reactor body; 29. ​​Rectifier grid; 30. DeNOx catalyst bed; 31. Sonic soot blower; 32. Rake soot blower; 33. Waste heat boiler; 34. High-temperature fan; 35. Ash return pipe; 36. Rotary feeder; 37. Buried scraper conveyor; 38. Air-to-air heat exchanger; 39. Manual plug valve. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0053] In the description of this utility model, unless otherwise specified, "plurality" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this utility model and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific direction, be constructed, or operate in a specific direction, and therefore should not be construed as limiting this utility model. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0054] In the description of this utility model, it should be noted that, unless otherwise specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on the specific circumstances.

[0055] Example:

[0056] like Figure 1-3 As shown, an SCR denitrification system for cement kiln flue gas includes an ammonia water storage tank 1, an ammonia water metering and distribution device, a cement kiln tail preheater, a reactor, a bypass pipeline device, an ash return device, a waste heat utilization device and a compressed air supply device.

[0057] The ammonia water storage tank 1 is connected to the ammonia water metering and distributing device through the ammonia water distribution pipe 5 .

[0058] The ammonia water metering and distributing device comprises a compressed air pipe 2 and a plurality of spray guns 3; the inlet end of each spray gun 3 is connected to the compressed air pipe 2 and the ammonia water distribution pipe 5 respectively; the ammonia water distribution pipe 5 is provided with a delivery pump 4.

[0059] The function of the ammonia water storage tank 1 is to store and supply 20% concentration ammonia water for denitrification.

[0060] The motor of the delivery pump 4 is a variable frequency motor. The flow rate can be changed by adjusting the frequency. The speed of the pump is related to the chimney NO. x The emission volume corresponds to the actual emission volume, achieving "more discharge, more spraying, less discharge, less spraying".

[0061] The 20% ammonia solution from the ammonia distribution pipe 5 enters the ammonia metering and distribution device and is then delivered to the spray gun 3. Under the pressure of the delivery pump 4, the ammonia solution passes through the spray gun 3 and is atomized by the compressed air. It is then sprayed into the SCR front flue (i.e., the outlet pipe of the cement kiln tail preheater. The ammonia solution and flue gas mix for more than 5 seconds) and mixes with NO in the flue gas.x Oxidation-reduction reaction occurs, generating nitrogen and removing NO x , thereby achieving the purpose of denitrification.

[0062] Spray gun 3 is a key component of the atomization system. The nozzle's key components undergo special surface treatment, resulting in superior wear, corrosion, and high-temperature resistance. It atomizes ammonia into fine droplets with an average particle size of tens of microns, providing a wide diffusion angle and coverage. A C1 cyclone evenly mixes the atomized ammonia with the kiln exhaust gas before entering the SCR reactor, enhancing denitrification efficiency.

[0063] The cement kiln tail preheater includes a rotary kiln 6, a kiln tail smoke chamber 7, a decomposition furnace 8, a C1-level cyclone 9, a C2-level cyclone 10, a C3-level cyclone 11, a C4-level cyclone 12, and a C5-level cyclone 13.

[0064] The C1-level cyclone 9, C2-level cyclone 10, C3-level cyclone 11, C4-level cyclone 12, and C5-level cyclone 13 are arranged alternately from top to bottom. The rotary kiln 6 is connected to the kiln tail flue gas chamber 7. The bottom end of the decomposition furnace 8 is provided with a denitrification chamber 14. The top end of the kiln tail flue gas chamber 7 is connected to the denitrification chamber 14.

[0065] The top of the decomposition furnace 8 is connected to the ascending flue of the C5-level cyclone 13; the top of the C5-level cyclone 13 is connected to the ascending flue of the C4-level cyclone 12; the top of the C4-level cyclone 12 is connected to the ascending flue of the C3-level cyclone 11; the top of the C3-level cyclone 11 is connected to the ascending flue of the C2-level cyclone 10; the top of the C2-level cyclone 10 is connected to the ascending flue of the C1-level cyclone 9; and the top of the C1-level cyclone 9 is arranged opposite the outlet ends of several spray guns 3 via a pipe. That is, the reductant spraying direction of the outlet end of the ammonia metering and distribution device is opposite to the flue gas output direction of the outlet end of the cement kiln preheater. The reductant is a 20% by mass ammonia solution, which is obtained from the existing ammonia storage system.

[0066] An ammonia spray gun 3 is added at the C1 flue gas inlet as a supplementary ammonia spray system.

[0067] The bypass device includes a first bypass pipe 15, a second bypass pipe 16, a third bypass pipe 17, and a fourth bypass pipe 18. One end of the first bypass pipe 15 is connected to the outlet of the cement kiln preheater, and the other end is connected to the fourth bypass pipe 18. One end of the second bypass pipe 16 is connected to the top of the reactor, and the other end is connected to the first bypass pipe 15. One end of the third bypass pipe 17 is connected to the bottom of the reactor, and the other end is connected to the fourth bypass pipe 18. The fourth bypass pipe 18 is connected to the waste heat utilization device. Baffle doors 19 are respectively provided on the first bypass pipe 15, the second bypass pipe 16, the third bypass pipe 17, and the fourth bypass pipe 18. Metal expansion joints 20 are respectively provided on the second bypass pipe 16 and the third bypass pipe 17.

[0068] In order to prevent the condensation of water in the flue gas and the rapid rise in flue gas temperature from damaging the catalyst, the flue gas is passed through the first bypass pipe 15. After the catalyst is heated to above the acid dew point by the soot-blowing compressed air, the damper door 19 on the first bypass pipe 15 is opened. During the kiln startup phase, due to the low flue gas temperature in the decomposition furnace 8 and the kiln, basically no NO is generated. x If a certain concentration of NO is generated after reaching a certain temperature x , and emission requirements can also be met through the SNCR system.

[0069] The compressed air supply device includes a compressed air supply assembly, a first air storage tank 26 and a second air storage tank 27 .

[0070] The compressed air supply assembly includes a screw compressor 21, a third air tank 22, a pre-filter 23, a cold dryer 24, and a post-filter 25. The screw compressor 21 is connected to the third air tank 22; the third air tank 22 is connected to the cold dryer 24 via a pipeline. The pre-filter 23 is installed on the pipeline between the third air tank 22 and the cold dryer 24. The cold dryer 24 is connected to the first air tank 26 and the second air tank 27 via pipelines, respectively. The post-filter 25 is installed on the pipeline between the cold dryer 24 and the first and second air tanks 26 and 27.

[0071] This compressed air supply assembly provides compressed air for the dust cleaning module and is equipped with a heating system (a heating pipe can be provided in the third air storage tank 22), and is only used in the kiln startup phase.

[0072] The reactor includes a reactor body 28, a rectifying grid 29, a catalyst module, a dust cleaning module and an air-to-air heat exchanger 38; the air-to-air heat exchanger 38 is located below the rectifying grid 29, the catalyst module and the dust cleaning module.

[0073] A rectifier grid 29 is installed at the upper end of the reactor body 28 to evenly distribute the flue gas within the reactor. The catalyst module comprises several denitration catalyst beds 30 ; these beds are arranged from top to bottom within the reactor body 28 , each located below the rectifier grid 29 .

[0074] During the startup phase of the SCR system, compressed air is heated to 128°C by an electric heater and then supplied to the SCR reactor rake-type dust collector for purging. During normal operation of the SCR system, the electric heater is turned off, and the compressed air is passed through the bypass pipe to the ash hopper and heated to 200°C-250°C by the pipe heat exchanger before being supplied to the dust collector module for purging.

[0075] The soot cleaning module includes several sonic soot blowers 31 and several rake soot blowers 32. A sonic soot blower 31 and a rake soot blower 32 are located above each denitration catalyst bed 30. The inlet ends of the several sonic soot blowers 31 are connected to the first gas storage tank 26 via pipes; the outlet ends of the sonic soot blowers 31 are located inside the reactor body 28. The inlet end of the gas-to-gas heat exchanger 38 is connected to the second gas storage tank 27 via pipes; the outlet end of the gas-to-gas heat exchanger 38 is connected to the inlet ends of the several rake soot blowers 32 via pipes; the outlet ends of the rake soot blowers 32 are located inside the reactor body 28.

[0076] The sonic sootblower 31 uses acoustic vibrations to disperse particles and break surface tension, loosening and removing fine dust particles. The rake sootblower 32 uses compressed air to forcibly clean dust, specifically large or difficult-to-dislodge particles. The combined technologies of the sonic sootblower 31 and the rake sootblower 32 complement each other, enhancing the dust removal efficiency of the dust removal system, maintaining stable operation, and improving filtration efficiency.

[0077] Flue gas enters the reactor from the top and flows vertically downward through the reactor. A flue gas rectifier grid 29 is installed at the inlet to guide and optimize flue gas distribution. A denitrification catalyst bed 30 is installed in the vertical section of the reactor. An ash return hopper is located at the outlet. The denitrification catalyst is housed in modular assemblies for easy handling, installation, and replacement. Soot blowers are installed between the catalyst layers to remove dust and SCR reaction byproducts deposited on the catalyst, thereby reducing reactor pressure drop.

[0078] The reactor is connected to the bypass device. During the startup phase, the kiln-drying flue gas is required to go through the first bypass pipe 15 and cannot directly enter the reactor to prevent excessive temperature rise, excessive moisture in the flue gas, and acidic components from having a great impact on the service life of the catalyst. At the same time, a heater is used to heat the ash cleaning compressed air, and then the reactor system is heated. Only when the temperature of the reactor system reaches above the acid dew point temperature can the kiln tail flue gas pass through the second bypass pipe 16 and enter the reactor. In addition, when an abnormal operating condition occurs or the reactor needs to be shut down, etc., the second bypass pipe 16, the third bypass pipe 17 and the fourth bypass pipe 18 can also be closed, and the first bypass pipe 15 can be opened to protect the reactor.

[0079] The waste heat utilization device includes a waste heat boiler 33 and a high-temperature fan 34. The inlet of the waste heat boiler 33 is connected to the fourth bypass pipe 18; the outlet of the waste heat boiler 33 is connected to the inlet of the high-temperature fan 34; the inlet of the high-temperature fan 34 is connected to the fourth bypass pipe 18; and the outlet of the high-temperature fan 34 is connected to subsequent process equipment.

[0080] The ash return device includes an ash return pipe 35, a rotary feeder 36, and an embedded scraper conveyor 37. The bottom end of the reactor body 28 is connected to the ash return pipe 35; a manual gate valve 39 and a rotary feeder 36 are installed on the ash return pipe 35; the outlet end of the ash return pipe 35 is connected to the embedded scraper conveyor 37.

[0081] The settled material recovered from the bottom of the reactor is recovered and reused by the recovery device, and the waste heat recovered from the bottom of the reactor is recovered and reused by the waste heat utilization device.

[0082] Working principle:

[0083] The first reaction stage is a five-stage cyclone cone, using the SNCR method, which is a high-temperature stage with a temperature of 800℃-900℃. An ammonia spray gun 3 is installed at the outlet pipe of the C1-stage cyclone 9 to spray ammonia into the cyclone to react with the flue gas NO x Reaction occurs, initially removing NO x , change NO x Concentration from 800mg / m 3 Reduce to 450 mg / m 3 the following;

[0084] The second reaction stage is in the reactor, using the SCR denitrification process, which is a low-temperature stage with a temperature of 300℃~450℃. The unreacted reducing agent in the SNCR stage also enters the reactor and reacts with NO on the catalyst surface together with the ammonia supplied in the reactor. x A secondary reduction reaction occurs to further remove the remaining NO x , change NO x Concentration from 450mg / m 3 Reduced to about 50mg / m3 the following.

[0085] The denitrification efficiency of the SNCR-SCR combined denitrification technology is over 90%.

[0086] The above are only preferred specific implementation methods of the present invention, but the protection scope of the present invention is not limited to them. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solution and utility model concept of the present invention within the technical scope disclosed by the present invention, and they should be covered by the protection scope of the present invention.

Claims

1. A SCR denitrification system for cement kiln flue gas, comprising an ammonia water storage tank (1), an ammonia water metering and distributing device, a cement kiln tail preheater, a reactor, a bypass piping device, an ash return device, a waste heat utilization device and a compressed air supply device; characterized in that: The ammonia water storage tank (1) is connected to the ammonia water metering and distributing device via an ammonia water distributing pipe (5); the ammonia water metering and distributing device is connected to the cement kiln tail preheater via a pipeline; the reducing agent spraying direction of the outlet end of the ammonia water metering and distributing device is opposite to the flue gas output direction of the outlet end of the cement kiln tail preheater; One side end of the reactor is connected to the compressed air supply device; the bottom end of the reactor is connected to the ash return device and the waste heat utilization device respectively; The bypass device comprises a first bypass pipe (15), a second bypass pipe (16), a third bypass pipe (17) and a fourth bypass pipe (18); one end of the first bypass pipe (15) is connected to the outlet end of the cement kiln tail preheater, and the other end is connected to the fourth bypass pipe (18); one end of the second bypass pipe (16) is connected to the top end of the reactor, and the other end is connected to the first bypass pipe (15); one end of the third bypass pipe (17) is connected to the bottom end of the reactor, and the other end is connected to the fourth bypass pipe (18); the fourth bypass pipe (18) is connected to the waste heat utilization device; and baffle doors (19) are respectively provided on the first bypass pipe (15), the second bypass pipe (16), the third bypass pipe (17) and the fourth bypass pipe (18).

2. The SCR denitrification system for cement kiln flue gas according to claim 1, characterized in that: The ammonia water metering and distributing device comprises a compressed air pipe (2) and a plurality of spray guns (3); The inlet end of each spray gun (3) is connected to the compressed air pipe (2) and the ammonia water distribution pipe (5) respectively; A delivery pump (4) is provided on the ammonia water distribution pipe (5).

3. The SCR denitrification system for cement kiln flue gas according to claim 1, characterized in that: The cement kiln tail preheater comprises a rotary kiln (6), a kiln tail smoke chamber (7), a decomposition furnace (8), a C1-level cyclone (9), a C2-level cyclone (10), a C3-level cyclone (11), a C4-level cyclone (12), and a C5-level cyclone (13); The C1-level cyclone (9), C2-level cyclone (10), C3-level cyclone (11), C4-level cyclone (12), and C5-level cyclone (13) are arranged alternately from top to bottom; The rotary kiln (6) is connected to the kiln tail smoke chamber (7); The bottom end of the decomposition furnace (8) is provided with a denitration chamber (14); the upper end of the kiln tail smoke chamber (7) is connected to the denitration chamber (14); The top of the decomposition furnace (8) is connected to the ascending flue of the C5-level cyclone (13); The top end of the C5-level cyclone (13) is connected to the ascending flue of the C4-level cyclone (12); The top end of the C4-level cyclone (12) is connected to the ascending flue of the C3-level cyclone (11); The top end of the C3-level cyclone (11) is connected to the ascending flue of the C2-level cyclone (10); The top end of the C2-level cyclone (10) is connected to the ascending flue of the C1-level cyclone (9); The top end of the C1-level cyclone (9) is arranged opposite to the outlet ends of a plurality of spray guns (3) through a pipeline.

4. The SCR denitrification system for cement kiln flue gas according to claim 1, characterized in that: The compressed air supply device comprises a compressed air supply assembly, a first air storage tank (26) and a second air storage tank (27); The compressed air supply assembly is connected to the first air storage tank (26) and the second air storage tank (27) respectively through pipelines.

5. The SCR denitrification system for cement kiln flue gas according to claim 4, characterized in that: The compressed air supply assembly includes a screw air compressor (21), a third air storage tank (22), a pre-filter (23), a cold dryer (24) and a post-filter (25); The screw air compressor (21) is connected to the third air storage tank (22); The third gas storage tank (22) is connected to the cold dryer (24) via a pipeline; the pre-filter (23) is provided on the pipeline between the third gas storage tank (22) and the cold dryer (24); The cold dryer (24) is connected to the first gas storage tank (26) and the second gas storage tank (27) through pipelines respectively; a post-filter (25) is provided on the pipeline between the cold dryer (24) and the first gas storage tank (26) and the second gas storage tank (27).

6. The SCR denitrification system for cement kiln flue gas according to claim 4, characterized in that: The reactor comprises a reactor body (28), a catalyst module, a dust cleaning module and an air-to-air heat exchanger (38); A catalyst module is provided inside the reactor body (28); A dust cleaning module is provided inside the reactor body (28); An air-to-air heat exchanger (38) is provided inside the reactor body (28); the air-to-air heat exchanger (38) is located below the catalyst module and the dust cleaning module.

7. The SCR denitrification system for cement kiln flue gas according to claim 6, characterized in that: A rectifying grid (29) is provided at the upper inner end of the reactor body (28); The catalyst module comprises a plurality of denitration catalyst beds (30); the interior of the reactor body (28) is provided with a plurality of denitration catalyst beds (30) from top to bottom; and the plurality of denitration catalyst beds (30) are located below the rectifying grid (29).

8. The SCR denitrification system for cement kiln flue gas according to claim 7, characterized in that: The soot cleaning module includes a plurality of sonic soot blowers (31) and a plurality of rake soot blowers (32); A sonic soot blower (31) and a rake soot blower (32) are provided above each denitration catalyst bed (30); The inlet ends of the plurality of sonic soot blowers (31) are respectively connected to the first gas storage tank (26) through pipelines; the outlet ends of the sonic soot blowers (31) are located inside the reactor body (28); The inlet end of the gas-to-gas heat exchanger (38) is connected to the second gas storage tank (27) through a pipeline; the outlet end of the gas-to-gas heat exchanger (38) is connected to the inlet ends of several rake soot blowers (32) through pipelines; the outlet end of the rake soot blower (32) is located inside the reactor body (28).

9. The SCR denitrification system for cement kiln flue gas according to claim 1, characterized in that: The waste heat utilization device includes a waste heat boiler (33) and a high-temperature fan (34); The inlet end of the waste heat boiler (33) is connected to the fourth bypass pipe (18); the outlet end of the waste heat boiler (33) is connected to the inlet end of the high-temperature fan (34); The inlet end of the high-temperature fan (34) is connected to the fourth bypass pipeline (18); the outlet of the high-temperature fan (34) is connected to subsequent process equipment.

10. The SCR denitrification system for cement kiln flue gas according to claim 8, characterized in that: The ash return device comprises an ash return pipe (35), a rotary feeder (36) and a scraper conveyor (37); The bottom end of the reactor body (28) is connected to the ash return pipe (35); The ash return pipe (35) is equipped with a manual gate valve (39) and a rotary feeder (36); The outlet end of the ash return pipe (35) is connected to the buried scraper conveyor (37).

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