SCR (Selective Catalytic Reduction) denitration auxiliary system and coal-fired device energy-saving and flue gas comprehensive utilization system

Abstract

The utility model discloses an SCR (Selective Catalytic Reduction) denitration auxiliary system and a coal-fired device energy-saving and flue gas comprehensive utilization system, and the SCR denitration auxiliary system comprises a bypass device arranged on a pipeline between a flue gas outlet of a coal-fired device and a flue gas inlet of the SCR denitration device; the bypass device comprises a bypass flue inlet close to a flue gas outlet of the coal-fired device and a bypass flue outlet close to a flue gas inlet of the SCR denitration device, the bypass flue inlet and the bypass flue outlet are connected through a bypass flue, and the bypass flue is provided with a fan and is connected with a dosing end of a denitration agent dosing system. The technical problems of pipe blockage, inner wall corrosion and heat efficiency reduction caused by spraying of the SNCR denitration agent in a coal burning device in the related technology can be solved.

Description

Technical Field

[0001] The utility model relates to the technical field of coal-fired flue gas treatment, in particular to an SCR denitration auxiliary system and a coal-fired device energy-saving and flue gas comprehensive utilization system. Background Art

[0002] SCR denitrification is the mainstream of flue gas denitrification in today's industrial industry. It uses solid catalytic materials for denitrification. When the denitrification efficiency is 85%, it is generally designed to be arranged on the second floor with three layers. When the denitrification efficiency is above 90%, it is generally designed to be arranged on the second floor with three layers. At present, the production of catalysts is very mature, the cost has been reduced by half compared with the initial stage, and the denitrification is relatively stable. The disadvantage is that its reaction temperature is 360℃±20℃, which is relatively harsh. At the same time, the service life of the catalyst is 3-5 years. If the flue gas composition is complex, the service life of the general catalyst is 2-3 years.

[0003] Generally, the SCR denitration process requires the installation of SNCR denitration in the front. SNCR denitration is to install a spray system of liquid denitration agents such as urea or ammonia in the combustion chamber of the coal-fired device, such as the furnace of the boiler, before the flue gas enters the SCR catalyst, and spray urea or ammonia into the flue gas generated by coal combustion to decompose nitrogen oxides into water and nitrogen. However, this structure has the following disadvantages:

[0004] Firstly, long-term spraying of urea or ammonia water can easily cause blockage of the spray system pipes, resulting in the inability to decompose nitrogen oxides or a reduction in the decomposition effect.

[0005] Secondly, the sprayed urea and ammonia water may not have time to vaporize and directly spray onto the inner wall of the coal-fired device, such as the water-cooled wall tube of the coal-fired boiler, causing corrosion.

[0006] Furthermore, the sprayed urea or ammonia water will also lower the temperature in the combustion chamber, such as the furnace, so that the thermal efficiency is reduced.

[0007] In view of this, the present utility model is proposed. Utility Model Content

[0008] The purpose of the utility model is to overcome the above-mentioned technical deficiencies and provide an SCR denitrification auxiliary system and a coal-fired device energy-saving and flue gas comprehensive utilization system to solve the technical problems of pipe blockage, inner wall corrosion and reduced thermal efficiency caused by spraying SNCR denitrification agent in the coal-fired device in the related technology.

[0009] In order to achieve the above technical purpose, the utility model adopts the following technical solutions:

[0010] According to one aspect of the utility model, an SCR denitrification auxiliary system is provided, comprising a bypass device arranged on a pipeline between the flue gas outlet of a coal-fired device and the flue gas inlet of an SCR denitrification device; the bypass device comprises a bypass flue inlet close to the flue gas outlet of the coal-fired device, and a bypass flue outlet close to the flue gas inlet of the SCR denitrification device, the bypass flue inlet and the bypass flue outlet are connected via a bypass flue, and the bypass flue is provided with a fan and connected to the dosing end of a denitrification agent dosing system.

[0011] Optionally, the dosing end is an injection system.

[0012] Optionally, the bypass flue includes a bypass air inlet duct arranged on the upwind side of the fan, and a bypass air outlet duct arranged on the downwind side of the fan; the denitrification agent dosing system is arranged in the bypass air outlet duct.

[0013] Optionally, it also includes an air inlet buffer bin arranged at the end of the bypass air inlet duct, and an air outlet buffer bin arranged at the head end of the bypass air outlet duct; two branches extend from the downstream end of the bypass air inlet duct, one of which leads to the air inlet of the fan, and the other branch leads to the air inlet buffer bin; two branches extend from the upstream end of the bypass air outlet duct, one of which leads to the air outlet of the fan, and the other branch leads to the air outlet buffer bin.

[0014] Optionally, the bottoms of the air inlet end buffer bin and the air outlet end buffer bin are both provided with openable and closable sewage outlets.

[0015] Optionally, the bypass gas outlet flue is further provided with an atomizing mixing device downstream of the denitrification agent dosing system.

[0016] According to another aspect of the utility model, a coal-fired device energy-saving and flue gas comprehensive utilization system is provided, comprising a coal-fired device and an induced draft system, wherein the flue gas outlet of the coal-fired device is connected to an SCR denitration system via a pipeline, and the pipeline is provided with an SCR denitration auxiliary system according to any one of claims 1 to 6;

[0017] The flue gas outlet of the SCR denitration system is connected in sequence to an air preheater, a bag filter, an energy-saving dust removal unit, a denitration device and a desulfurization device;

[0018] The energy-saving dust removal unit includes a first dust removal device, a second dust removal device, and a third dust removal device, which are arranged in sequence from the flue gas inlet to the flue gas outlet. The first dust removal device is a mechanical dust removal device; the second-stage dust removal device also includes a heat exchanger that uses the return water of the coal-fired device as a heat exchange medium, and the third dust removal device also includes a heat exchanger that uses flue gas as a heat exchange medium to heat outdoor cold air;

[0019] The induced air system includes an air inlet end and an air supply end, the air inlet end is connected to at least one or more spaces among an outdoor space, an indoor space and an internal space of an energy-saving dust removal unit, and the air supply end is connected to the coal burning device.

[0020] Optionally, the induced draft system includes an outdoor wind system, which includes an outdoor wind duct. The outdoor wind duct is introduced into the end of the energy-saving dust removal unit to perform a first heat exchange with the flue gas at the end of the energy-saving dust removal unit. The outdoor wind duct is further led out from the energy-saving dust removal unit and connected to the air preheater. The air preheater includes a heat exchange pipeline, the outside of which is the flue gas output by the coal-fired boiler, and the inside of the heat exchange pipeline is connected to the outdoor wind duct to perform a second heat exchange on the outdoor air from the outdoor wind duct. The air preheater is connected to the coal-fired device to send the outdoor air after the second heat exchange back to the coal-fired device.

[0021] Optionally, the induced draft system also includes a secondary air system, which includes a secondary air fan. The air inlet end of the secondary air fan is connected to the flue gas output end of the energy-saving dust removal unit through a pipeline to introduce flue gas therefrom. The air inlet end of the secondary air fan is also connected to the indoor space, and the air supply end of the secondary air fan is connected to the coal burning device.

[0022] Optionally, a cyclone device is provided in the desulfurization device.

[0023] The utility model provides an SCR denitrification auxiliary system and a coal-fired device energy-saving and flue gas comprehensive utilization system, wherein the SCR denitrification auxiliary system includes a bypass device arranged on a pipeline between the flue gas outlet of the coal-fired device and the flue gas inlet of the SCR denitrification device, and a fan is arranged in the bypass flue and connected to the dosing end of the denitrification agent dosing system, so that the injection of the SNCR denitrification agent can be completed in the bypass device instead of in the combustion chamber of the coal-fired device, thereby avoiding corrosion of the inner wall and reducing the thermal efficiency of the combustion chamber. At the same time, the bypass device is mainly flue gas, and the particulate impurities are less than those inside the coal-fired device, so it is not easy to cause pipe blockage in the injection system. The technical problems of pipe blockage, inner wall corrosion and reduced thermal efficiency caused by spraying the denitrification agent in the combustion chamber of the coal-fired device in the related art can be solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic structural diagram of an SCR denitration auxiliary system is provided for an embodiment of the utility model;

[0025] Figure 2 The present invention provides a schematic structural diagram of a coal-fired device energy-saving and flue gas comprehensive utilization system.

[0026] In the figure:

[0027] 1- bypass flue inlet; 2- bypass flue outlet; 3- bypass flue; 4- fan; 5- denitrification agent dosing system; 6- atomization mixing device; 7- coal-fired device; 8- pre-dust collector; 9- SCR denitrification auxiliary system; 10- SCR denitrification system; 11- air preheater; 12- bag filter; 13- energy-saving dust removal unit; 131- first dust removal device; 132- second dust removal device; 133- third dust removal device; 14- Denitration device; 15-desulfurization device; 16-induced draft fan; 17-first flue gas analyzer; 18-denitrification dosing tank; 19-outdoor air duct; 20-fresh air fan; 21-secondary air fan; 22-coal-fired device exhaust flue; 23-chimney; 24-second flue gas analyzer; 25-cyclone device; 31-bypass air inlet duct; 32-bypass air outlet duct; 33-air inlet end buffer bin; 34-air outlet end buffer bin; 35-drainage outlet. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0029] Embodiment 1

[0030] According to an embodiment of the utility model, a SCR denitration auxiliary system is provided, combining Figure 1 The SCR denitration auxiliary system includes a pipe arranged between the smoke outlet of the coal-fired device and the smoke inlet of the SCR denitration device, that is, a bypass device on the smoke exhaust duct 22 of the coal-fired device, so that the injection of the denitration agent is completed in the bypass device, and does not need to be completed in the coal-fired device. In the following embodiments, the coal-fired device of the utility model is introduced as a coal-fired boiler, such as a layer-fired boiler. However, it should be understood that the embodiments of the utility model can be extended to any type of coal-fired device.

[0031] As an example, the bypass device includes a bypass flue inlet 1 near the flue gas outlet of the coal-fired device, and a bypass flue outlet 2 near the flue gas inlet of the SCR denitrification device. The bypass flue inlet 1 and the bypass flue outlet 2 are connected by a bypass flue 3. The bypass flue 3 is provided with a fan 4 and connected to the dosing end of the denitrification agent dosing system 5. In the spray embodiment, the dosing end is a spray system, such as a spray head, a spray head, etc., which has a better vaporization effect of the liquid denitrification agent. In this way, after the flue gas is output from the coal-fired device, at least a part of it will enter the bypass flue 3 along the bypass flue inlet 1 under the action of the fan 4 of the bypass device, and then react with the denitrification agent of the denitrification agent dosing system 5 to decompose the nitrogen oxides. There is no need to set up a denitrification agent spray system in the coal-fired device to avoid corrosion of the inner wall (such as the water-cooled wall of the coal-fired boiler) and reduce the thermal efficiency of the coal-fired boiler. At the same time, the bypass device is mainly flue gas, and the particulate impurities are less than those in the boiler furnace. Therefore, it is not easy to cause blockage of the injection system. Even if the pipe is blocked or corroded, since the bypass device and its dosing system are externally connected to the flue gas pipe, it is convenient to replace and repair, and the cost is also lower.

[0032] In addition, in order to enhance corrosion resistance, the bypass flue 3 may be made of stainless steel, and in order to further improve thermal efficiency, the outer wall of the bypass flue 3 may be covered with thermal insulation materials.

[0033] As an example, the bypass flue 3 includes an air inlet flue 31 arranged on the upwind side of the fan, and a bypass air outlet flue 32 arranged on the downwind side of the fan; the denitrification agent dosing system 5 is arranged in the bypass air outlet flue 32. On the basis, the bypass device also includes an air inlet end buffer bin 33 arranged at the end of the bypass air inlet flue 31, and an air outlet end buffer bin 34 arranged at the head end of the bypass air outlet flue 32; two branches extend from the downstream end of the bypass air inlet flue 31, one of which leads to the air inlet of the fan, and the other branch leads to the air inlet end buffer bin 33; two branches extend from the upstream end of the bypass air outlet flue 32, one of which leads to the air outlet of the fan, and the other branch leads to the air outlet end buffer bin 34. During operation, a portion of the unreacted liquid denitrification agent will be stored at the bottom of the air outlet end buffer bin 34, or will flow back to the bottom of the air inlet end buffer bin 33 under the action of the circulating wind of the fan. The buffer bin 33 at the air inlet end and the buffer bin 34 at the air outlet end can temporarily store this part of the unreacted liquid denitrification agent, and fully react with the next round of flue gas after entering the bypass device, thereby improving the utilization rate of the denitrification agent.

[0034] Furthermore, the bottoms of the air inlet buffer bin 33 and the air outlet buffer bin 34 are both provided with openable and closable sewage outlets 35 , through which decomposed products after the denitration reaction in the bypass device, excess denitration agent, impurities, etc. are discharged.

[0035] The bypass exhaust flue 32 is also provided with an atomizing mixing device 6 downstream of the denitrification agent dosing system 5. For example, a pipe with a small opening on the upwind side and a large opening on the downwind side can be used as the atomizing mixing device 6, which can further enhance the atomizing mixing effect of the flue gas and the denitrification agent by means of the Venturi principle.

[0036] After denitrification by the bypass device, the flue gas enters the SCR denitrification system again, which can make the denitrification more complete, improve the denitrification efficiency of the SCR denitrification system, improve the operating stability of the SCR denitrification system, and reduce ammonia escape.

[0037] Embodiment 2

[0038] The present embodiment provides a coal-fired device energy-saving and flue gas comprehensive utilization system, which is characterized in that it includes a coal-fired device 7 and an induced draft system, and the flue gas outlet of the coal-fired device 7 is connected to the SCR denitrification system 10 through a pipeline, and a pre-dust collector 8 and the SCR denitrification auxiliary system 9 of the first embodiment are provided on the pipeline.

[0039] As for the pre-dust collector 8, since the SCR denitration catalyst tower is arranged at the flue gas temperature of 360℃±20℃ at the tail end of the boiler, there is generally no dust removal device before the flue gas enters the catalyst. The denitration catalyst works under the flushing of high-ash flue gas, and the catalyst is easily blocked and worn by dust. In order to reduce the wear and blockage of the catalyst, the present embodiment adds a pre-dust collector 8 in front of the catalyst to precipitate larger dust particles in advance, thereby extending the service life of the catalyst.

[0040] For the SCR denitration auxiliary system 9, the general SCR denitration process is to spray urea or ammonia water into the flue gas before the flue gas enters the catalyst to decompose nitrogen oxides into water and nitrogen. In order to improve the stability of denitration, this embodiment uses the bypass device of the SCR denitration auxiliary system 9 before the flue gas enters the catalyst, and uses the high-temperature flue gas to heat and vaporize the ammonia water, and then returns it to the flue gas to enter the catalyst. This can further promote the stability of the denitration reaction and improve the denitration efficiency.

[0041] The flue gas outlet of the SCR denitration system 10 is sequentially connected to an air preheater 11, a bag filter 12, an energy-saving dust removal unit 13, a denitration device 14 and a desulfurization device 15. Among them, an induced draft fan 16 and a first flue gas analyzer 17 can also be provided at the front end of the denitration device 14. The denitration device 14 is connected to a denitration dosing tank 18 to further denitrate the flue gas, thereby achieving a more thorough denitration effect.

[0042] For the air preheater 11, since the SCR denitrification technology requires a catalyst reaction temperature of 360℃±20℃, the smoke temperature after denitrification is >340℃. In order for the subsequent bag filter 12 to work normally, the air preheater 11 must be used to reduce the smoke temperature to below 200℃.

[0043] For the bag filter 12, as an example, the dust-containing gas enters the middle and lower boxes from the air inlet of the dust collector, and in the process of entering the upper box through the filter bag, the dust and gas are separated due to various effects of the filter bag, and the dust is adsorbed on the filter bag, while the gas passes through the filter bag and enters the upper box through the venturi tube and is discharged from the air outlet. In the process of dust-containing gas passing through the filter bag for purification, as time increases, more and more dust accumulates on the filter bag, so that the resistance of the filter bag gradually increases, and the amount of gas passing through the filter bag gradually decreases. In order to make the dust collector work normally, the resistance must be controlled within a limited range (generally 120 to 150 mm water column). In this way, when the resistance rises to the limited range, the controller will issue a command to trigger each control valve in sequence, open the pulse valve, and the compressed air in the air bag will be sprayed from each hole of the injection pipe through the venturi tube into each corresponding filter bag. The filter bag expands rapidly under the instantaneous reverse action of the air flow, so that the dust accumulated on the surface of the filter bag falls off, the filter bag is regenerated, and the cleaned dust falls into the ash hopper and is discharged from the body through the ash discharge system. Since the dust accumulated on the filter bags is removed regularly, the purified gas passes normally, ensuring the normal operation of the dust collector.

[0044] The energy-saving dust removal unit 13 includes a first dust removal device 131, a second dust removal device 132, and a third dust removal device 133, which are sequentially arranged from the flue gas inlet to the flue gas outlet. The first dust removal device 131 is a mechanical dust removal device, such as a cyclone dust removal device, which plays a first-level dust removal effect; the second-level dust removal device 132 also includes a heat exchanger using the return water of the coal-fired device as a heat exchange medium, and the third dust removal device 133 also includes a heat exchanger using the flue gas as a heat exchange medium to heat the outdoor cold air. The second dust removal device 132 can be provided with a heat exchange pipeline with boiler return water, that is, a heat exchanger flue gas and water heat exchanger, and the flue gas and the heat exchange pipeline collide and settle, which plays a second-level dust removal effect. The third dust removal device 132 is arranged at the rear end of the second dust removal device 132, specifically an outdoor cold air and flue gas heat exchanger, which is referred to as an external air heating flue gas heat exchange device in this embodiment, which is used to heat the boiler combustion air and reduce the flue gas temperature, and further plays a third-level dust removal effect.

[0045] In this embodiment, the water inlet end of the flue gas and water heat exchanger is the boiler return water. After heat exchange, the boiler return water temperature increases and can be introduced into the boiler water supply for circulation.

[0046] Furthermore, the induced air system includes an air inlet end and an air supply end, the air inlet end is connected to at least one or more spaces among the outdoor space, the indoor space and the internal space of the energy-saving dust removal unit, and the air supply end is connected to the coal burning device.

[0047] As an example, the induced draft system includes an outdoor wind system, which includes an outdoor wind duct 19. The outdoor wind duct 19 is introduced into the end of the energy-saving dust removal unit 13 to perform a first heat exchange with the flue gas at the end of the energy-saving dust removal unit 13. The outdoor wind duct 19 is further led out from the energy-saving dust removal unit and connected to the air preheater 11 through the fresh air fan 20. The air preheater 11 includes a heat exchange pipeline, the outside of the heat exchange pipeline is the flue gas output by the coal-fired boiler, and the inside of the heat exchange pipeline is connected to the outdoor wind duct 19 to perform a second heat exchange on the outdoor air from the outdoor wind duct 19. The air preheater 11 is connected to the coal-fired device 7 to send the outdoor air after the second heat exchange back to the coal-fired device 7.

[0048] The outdoor air is introduced into the external air heating flue gas heat exchange device at the tail end of the energy-saving dust removal unit 13 through the outdoor air duct 19, and after heat exchange with the flue gas therein, it is led out of the energy-saving dust removal unit 13, and further connected to the air preheater 11 through the pipeline and the fresh air fan 20, wherein, as described above, the air preheater 11 is arranged between the flue gas inlet of the energy-saving dust removal unit 13 and the flue gas outlet of the coal-fired device 7, and the outdoor air is introduced into the tail end of the energy-saving dust removal unit 13 for heat exchange, and the outdoor air temperature is increased. For example, the outdoor sub-zero temperature air can be heated to a temperature above zero, such as from 30 degrees below zero to 30 degrees Celsius above zero. Then, the outdoor air that has undergone the first heat exchange is further introduced into the air preheater 11 through the pipeline, and is heated with the high-temperature flue gas just discharged from the boiler. For example, the temperature of the outdoor air can be further heated to 120 degrees Celsius. Furthermore, the gas outlet of the air preheater 11 is also connected to the air inlet of the coal-burning device 7, so that the heated outdoor air is introduced into the coal-burning device 7 to assist combustion and improve the coal combustion efficiency.

[0049] As described above, in some embodiments, the outdoor air temperature is relatively low, for example, it can reach minus 30 degrees Celsius. If the air is directly introduced into the coal-fired device 7 without passing through the external air heating flue gas heat exchange device and the air preheater 11 of the energy-saving dust removal unit 13 designed in this embodiment, the fuel efficiency will be greatly reduced. Therefore, this embodiment can especially improve the combustion efficiency of the coal-fired device in a low-temperature outdoor environment.

[0050] The induced draft system also includes a secondary air system, which includes a secondary air fan 21. The air inlet end of the secondary air fan 21 is connected to the flue gas output end of the energy-saving dust removal unit 13 through a pipeline to introduce flue gas therefrom. The air inlet end of the secondary air fan 21 is also connected to the indoor space, and the air supply end of the secondary air fan is connected to the coal burning device 7.

[0051] In one embodiment, a portion of the flue gas is drawn out from the end of the energy-saving dust removal unit 13, that is, in the form of flue gas recirculation, the flue gas outlet is connected to the fan through a pipeline (this embodiment is referred to as a flue gas secondary circulation and indoor air mixing fan, that is, a secondary air fan 21, and the output wind is referred to as secondary air for short), and the fan also introduces indoor air to mix with the drawn flue gas, and finally passes into the furnace of the coal-fired boiler, further improving the combustion efficiency of coal and reducing the generation of nitrogen oxides. In some embodiments, a separate wind chamber can be set in the coal-fired boiler, corresponding to the tail of the grate, for introducing secondary air, burning the small part of the coal that has not been burned at the tail of the grate, and further optimizing the burnout efficiency.

[0052] The specific structure and function of the energy-saving dust removal unit and the induced draft system can also refer to the contents of the inventor's Chinese patent document CN117190226A. For example, in some embodiments, the main functions of the energy-saving dust removal unit include:

[0053] 1) As the flue gas flows, when the flue gas enters the cyclone dust removal device at the front end of the energy-saving dust removal unit and then expands the flow area, the particles in the flue gas are physically settled and dusted. In addition, the electrostatic effect of the dust and the energy-saving fin tube are used to further remove the dust.

[0054] 2) Heat is exchanged between the heating return water and the flue gas, reducing the flue gas temperature of about 150°C to about 90°C. After the heating return water is heated, it directly enters the heating pipe to mix with water for heating.

[0055] 3) After the flue gas passes through the heating return water flue gas heat exchanger, it enters the outdoor air heat exchanger to heat the combustion-supporting fresh air to about 70°C, and then the fresh air at about 70°C is sent to the air heat exchanger through the blower, and then the flue gas flow is heated to about 120°C, and then sent to the combustion-supporting air chamber of the coal-fired boiler to increase the initial temperature of the coal, thereby improving the combustion efficiency.

[0056] 4) The hot water after heat exchange in the heat exchange device of the energy-saving dust removal unit directly participates in the system circulation and does not return to the boiler for circulation.

[0057] As an example, the desulfurization device 15 is also provided with a cyclone device 25, which plays the role of flue gas desulfurization and further improves the flue gas treatment effect. Furthermore, the top of the desulfurization device 15 discharges the purified flue gas through the chimney 23, and the chimney 23 can also be connected to the second flue gas analyzer 24.

[0058] In some embodiments, the arch of the boiler may also be modified. The modified structure may refer to the contents of the inventor's Chinese patent document CN117190226A, which will not be described in detail here.

[0059] The above are only preferred implementations of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. An SCR denitration auxiliary system, characterized in that: It includes a bypass device arranged on a pipeline between the smoke outlet of a coal-fired device and the smoke inlet of an SCR denitrification device; the bypass device includes a bypass flue inlet close to the smoke outlet of the coal-fired device, and a bypass flue outlet close to the smoke inlet of the SCR denitrification device, the bypass flue inlet and the bypass flue outlet are connected via a bypass flue, and the bypass flue is provided with a fan and connected to the dosing end of a denitrification agent dosing system.

2. The SCR denitration auxiliary system according to claim 1, characterized in that: The dosing end is an injection system.

3. The SCR denitration auxiliary system according to claim 1, characterized in that: The bypass flue comprises a bypass air inlet flue arranged on the upwind side of the fan, and a bypass air outlet flue arranged on the downwind side of the fan; the denitrification agent dosing system is arranged in the bypass air outlet flue.

4. The SCR denitration auxiliary system according to claim 3, characterized in that: It also includes an air inlet end buffer bin arranged at the end of the bypass air inlet duct, and an air outlet end buffer bin arranged at the head end of the bypass air outlet duct; two branches extend from the downstream end of the bypass air inlet duct, one of which leads to the air inlet of the fan, and the other branch leads to the air inlet end buffer bin; two branches extend from the upstream end of the bypass air outlet duct, one of which leads to the air outlet of the fan, and the other branch leads to the air outlet buffer bin.

5. The SCR denitration auxiliary system according to claim 4, characterized in that: The bottoms of the air inlet buffer bin and the air outlet buffer bin are both provided with openable and closable sewage outlets.

6. The SCR denitration auxiliary system according to claim 3, characterized in that: The bypass gas outlet flue is also provided with an atomizing mixing device downstream of the denitrification agent dosing system.

7. Energy saving and comprehensive utilization system of flue gas for coal-fired devices, characterized in that: It comprises a coal-burning device and an induced draft system, wherein the flue gas outlet of the coal-burning device is connected to an SCR denitration system through a pipeline, and the pipeline is provided with a pre-dust collector and the SCR denitration auxiliary system according to any one of claims 1 to 6; The flue gas outlet of the SCR denitration system is connected in sequence to an air preheater, a bag filter, an energy-saving dust removal unit, a denitration device and a desulfurization device; The energy-saving dust removal unit includes a first dust removal device, a second dust removal device, and a third dust removal device, which are arranged in sequence from the flue gas inlet to the flue gas outlet. The first dust removal device is a mechanical dust removal device; the second dust removal device also includes a heat exchanger that uses the return water of the coal-fired device as a heat exchange medium, and the third dust removal device also includes a heat exchanger that uses flue gas as a heat exchange medium to heat outdoor cold air; The induced air system includes an air inlet end and an air supply end, the air inlet end is connected to at least one or more spaces among an outdoor space, an indoor space and an internal space of an energy-saving dust removal unit, and the air supply end is connected to the coal burning device.

8. The energy-saving and flue gas comprehensive utilization system for coal-fired devices according to claim 7 is characterized in that: The induced draft system includes an outdoor wind system, which includes an outdoor wind duct. The outdoor wind duct is introduced into the end of the energy-saving dust removal unit to perform a first heat exchange with the flue gas at the end of the energy-saving dust removal unit. The outdoor wind duct is further led out from the energy-saving dust removal unit and connected to the air preheater. The air preheater includes a heat exchange pipeline, the outside of which is the flue gas output by the coal-fired boiler, and the inside of the heat exchange pipeline is connected to the outdoor wind duct to perform a second heat exchange on the outdoor air from the outdoor wind duct. The air preheater is connected to the coal-fired device to send the outdoor air after the second heat exchange back to the coal-fired device.

9. The energy-saving and flue gas comprehensive utilization system for coal-fired devices according to claim 7, characterized in that: The induced draft system also includes a secondary air system, which includes a secondary air fan. The air inlet end of the secondary air fan is connected to the smoke output end of the energy-saving dust removal unit through a pipeline to introduce smoke therefrom. The air inlet end of the secondary air fan is also connected to the indoor space, and the air supply end of the secondary air fan is connected to the coal-burning device.

10. The energy-saving and flue gas comprehensive utilization system for coal-fired devices according to claim 7, characterized in that: The desulfurization device is provided with a cyclone device.

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