System and control method for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment

Abstract

The present invention relates to the field of air preheating of boiler systems, and discloses a system for preventing ammonium bisulfate deposition in air preheaters and tail waste heat utilization equipment and a control method thereof, wherein the system comprises an air preheater, and a flue gas heat exchanger is arranged in the flue after the air preheater, and the flue gas heat exchanger is composed of at least two or more parallel heat exchange modules, each heat exchange module corresponds to a flue gas channel and a liquid phase working medium channel, and each heat exchange module is isolated from each other and can independently control the flue gas-working medium heat exchange, and the flue gas channel is also provided with a heated flue gas inlet, and the working medium of the flue gas heat exchanger is provided with a working medium constant pressure system and a working medium heating device. The present invention can reduce the smoke and wind resistance of the system, reduce the power consumption of the blower and the primary blower, reduce the loss caused by the air preheater shutdown cleaning, reduce the exhaust temperature of the boiler, and completely solve the problem of ammonium bisulfate blockage in the air preheater and the tail waste heat utilization equipment, and is suitable for the new design or modification of the boiler preheating system.

Description

Technical Field

[0001] The invention relates to air preheating of a boiler, in particular to a system capable of preventing ammonium bisulfate deposition from occurring in an air preheater and a tail waste heat utilization device. Background Art

[0002] In large-scale units used for power generation, coal-fired boilers usually use tubular preheaters or rotary preheaters as air preheating devices. Smaller power units use tubular preheaters, while large power units use rotary preheaters. As national environmental protection policies become increasingly stringent, NO in coal-fired boiler flue gas is X The emission concentration is getting lower and lower. The SCR technology under the ultra-low emission demand causes the excess sprayed ammonia to react with SO3 in the flue gas to form ammonium bisulfate. The ammonium bisulfate adheres to the heat exchange elements at the cold end of the rotary air preheater or the tube wall of the tubular preheater, resulting in: (1) decreased heat exchange efficiency, increased exhaust temperature, decreased hot air temperature, etc.; (2) increased resistance on the flue gas side, increased induced draft fan speed, and increased power consumption.

[0003] At present, the problem of ammonium bisulfate blockage and corrosion in the rotary air preheater is very serious. The conventional solution of power plants is to add a low-temperature economizer in the flue after the air preheater to recover the flue gas waste heat. The recovered flue gas waste heat is used in the heater to heat the cold air at the inlet of the air preheater, thereby increasing the wind temperature entering the preheater and increasing the comprehensive temperature of the cold end of the preheater to prevent corrosion and blockage of the preheater.

[0004] However, after adding low-temperature economizers and heaters, the blockage and corrosion of the air preheater were alleviated, and the risk of ammonium bisulfate blockage was transferred to the low-temperature economizer, while the outlet flue gas temperature of the low-temperature economizer is generally low, usually around 90°C. According to relevant research, ammonium bisulfate is solid in an environment of 90°C. On-site sampling found that the ammonium bisulfate scale resembled the tile-like "streaky pork" shape, which was difficult to remove during unit operation.

[0005] In actual operation, the effective solution to the blockage of ammonium bisulfate is mainly to increase the outlet flue gas temperature of the preheater, but this affects the comprehensive utilization of flue gas waste heat. Therefore, the blockage of ammonium bisulfate in subsequent waste heat utilization equipment such as air preheater or low-temperature economizer has become one of the biggest hidden dangers affecting boiler efficiency and safe operation. The technology to solve the blockage of ammonium bisulfate in the preheater and tail waste heat utilization equipment of coal-fired units has become a very urgent need.

[0006] In order to reduce the risk of cold-end corrosion and ammonium bisulfate blockage in rotary preheaters, a variety of solutions are mentioned in the prior art. For example, the Chinese invention patent application with publication number CN107191963A, "A rotary air preheater and a method for preventing ammonium bisulfate blockage in the rotary air preheater", the Chinese invention patent application with publication number CN107642793A, "A system and method for preventing ammonium bisulfate from blocking the air preheater after SCR denitration modification", and the Chinese invention patent application with publication number CN106765288A, "A hierarchical heat exchange system for a rotary air preheater of a power station boiler", etc.

[0007] The above technologies are all based on increasing the flue gas temperature at the outlet of the rotary air preheater to prevent the condensation of ammonium bisulfate and avoid the cleaning and maintenance of the complex rotary air preheater. They only increase the inlet wind temperature of the rotary preheater and slow down the cold end corrosion of the rotary preheater. However, they cannot completely eliminate the blockage and deposition of ammonium bisulfate in the rotary preheater. In terms of how to comprehensively utilize the existing equipment of the boiler and its waste heat, etc., they have not been carefully considered and are not complete, and there is a need for improvement. Summary of the invention

[0008] In order to completely solve the problem of ammonium bisulfate blockage in the rotary preheater and the tail waste heat utilization equipment, the technical problem to be solved by the present invention is to provide a system and a control method for preventing the deposition of ammonium bisulfate in the air preheater and the tail waste heat utilization equipment. The concept of the present invention is: (1) a flue gas heat exchanger is set in the flue after the air preheater to recover the flue gas waste heat and use it to heat the cold air at the inlet of the air preheater, thereby increasing the temperature of the cold end of the air preheater and transferring the risk of ammonium bisulfate blockage to the flue gas heat exchanger downstream of the air preheater; (2) the local metal wall temperature of the flue gas heat exchanger is intermittently increased to above 232°C, so that the solid ammonium bisulfate that has been attached to the surface of this part of the flue gas heat exchanger is volatilized, thereby completely eliminating the deposition of ammonium bisulfate in the air preheater and the tail waste heat utilization equipment.

[0009] The technical solution adopted by the present invention to solve its technical problems is: a system for preventing ammonium bisulfate deposition in an air preheater and a tail waste heat utilization device, including an air preheater, wherein the tail waste heat utilization device is a flue gas heat exchanger arranged in the flue after the air preheater, and the flue gas heat exchanger is composed of at least two or more parallel heat exchange modules, each heat exchange module corresponds to a liquid phase working medium channel and a flue gas channel branched off from the flue, the heat exchange modules are isolated from each other and can independently control the flue gas-working medium heat exchange in a single heat exchange module, each flue gas channel is also respectively provided with a heated flue gas inlet, and a working medium constant pressure system and a working medium heating device are configured for the working medium of the flue gas heat exchanger, the system also includes an air duct and a heater, the inlet of the air duct is connected to the outlet of the blower, and the outlet of the air duct is connected to the air inlet of the air preheater via the heater.

[0010] This technical solution arranges a flue gas heat exchanger in the flue after the air preheater as a tail waste heat utilization device. In the boiler system, the high-temperature flue gas coming out of the air preheater absorbs the flue gas waste heat through the flue gas heat exchanger and then enters the dust collector. The recovered flue gas waste heat is then sent to the heater for heating the cold air at the air preheater inlet after heat exchange with the liquid working medium, which greatly increases the comprehensive temperature of the cold end of the air preheater and reduces the risk of ammonium bisulfate blockage and corrosion at the cold end of the air preheater. The risk of ammonium bisulfate blockage is transferred to the flue gas heat exchanger, and then the working medium heating device and the high-temperature flue gas input from the heated flue gas inlet are used to heat the tube wall of the flue gas heat exchanger where ammonium bisulfate is deposited to volatilize the ammonium bisulfate, thereby preventing the entire air preheater system from being blocked by ammonium bisulfate and continuously ensuring the smooth operation of the boiler system.

[0011] To ensure the normal operation of the above system, the working fluid constant pressure system includes a working fluid pipeline, which is used to connect the flue gas heat exchanger, the heater, the booster pump, the constant pressure tank and the working fluid heating device: the outlet of the constant pressure tank is connected in series with the heater and the booster pump in turn, the outlet of the booster pump and the inlet of the constant pressure tank are connected in parallel with the liquid phase working fluid channels of each heat exchange module, the outlet of the booster pump and the working fluid inlet of the flue gas heat exchanger are connected in parallel with the working fluid heating device by the working fluid pipeline, and the working fluid pipeline is also provided with a shut-off valve to block the working fluid from entering the heat exchange module. The booster pump can provide power for the system and overcome the operating resistance of the liquid phase working fluid system; the shut-off valve is closed when it is necessary to heat up the pipe wall of the heat exchange module, blocking the working fluid from circulating into the heat exchange module and exchanging heat with the flue gas. At this time, the working fluid trapped in the heat exchange module is circulated and heated by the parallel working fluid heating device to ensure the heating effect.

[0012] A recirculation pipe is connected in parallel between the working fluid inlet and the working fluid outlet of the heater, and a regulating valve is connected in series in the recirculation pipe, the opening of which can be adjusted as needed to adjust the ratio of the partial flow of the liquid working fluid for direct circulation heating to the partial flow used for heat exchange in the heater, thereby adjusting the inlet wind temperature of the air preheater, etc.

[0013] A safety valve is provided on the working medium pipeline at the outlet of the flue gas heat exchanger, which can be closed in the event of an accident or abnormal working condition to protect the system.

[0014] Taking into account the cost, safety and ease of use, it is recommended that the liquid phase working fluid is water, the working fluid heating device is a steam heating device, and the heat source of the working fluid heating device can also be water, electricity, etc. other than steam. Shut-off valves are set on the inlet and outlet working fluid pipelines of the working fluid heating device. Different pipelines correspond to different heat exchange modules. When the system is in operation and the wall temperature of the heat exchanger module needs to be increased, the corresponding shut-off valve is opened and the working fluid heating device is put into use, otherwise it is closed.

[0015] The inlet and outlet of the liquid working medium of each heat exchange module are provided with a header, which can be connected to the corresponding shut-off valve for easy independent control.

[0016] A flue partition is provided in the flue to divide the inlet flue into corresponding flue gas channels corresponding to the heat exchange modules. Relevant baffles are independently provided on each flue gas channel, and corresponding heating flue gas baffles are also provided corresponding to each heating flue gas inlet. Each baffle can be remotely and independently controlled, so that each heat exchange module can be remotely and independently controlled.

[0017] The heating flue gas inlet is connected to the flue gas inlet or hot air outlet of the air preheater, and the inlet flue gas or outlet hot air of the air preheater can be selected as one of the heat sources for heating the tube wall of the corresponding heat exchange module according to needs. The air preheater can be a rotary air preheater or a tubular air preheater.

[0018] According to specific parameters, the heat exchange tubes of the heat exchange module can adopt different tube types, such as plain tubes, H-shaped fin tubes, spiral fin tubes, etc.

[0019] Furthermore, to facilitate automatic control, the present invention also provides a control method for a system for preventing the deposition of ammonium bisulfate in an air preheater and a tail waste heat utilization device. For the aforementioned system for preventing the deposition of ammonium bisulfate in an air preheater and a tail waste heat utilization device, a pressure detection device is further provided between the flue gas inlet and outlet of the flue gas heat exchanger, and a temperature detection device is arranged in the low-temperature section of each heat exchange module. When the inlet and outlet differential pressure detected by the pressure detection device exceeds the set value, the working fluid heating device is controlled to be in use, and the corresponding heating flue gas dampers of each heat exchange module are controlled to be in an open state one by one until the temperature detection device feedback temperature reaches above 232°C and is maintained for a set time. This step is repeated until it is detected that the inlet and outlet differential pressure of the flue gas heat exchanger returns to the set value. At this time, the working fluid heating device is controlled to be in an inactive state, and each heating flue gas damper is controlled to be in a closed state.

[0020] A pressure detection device may also be provided between the flue gas inlet and outlet of each heat exchange module of the flue gas heat exchanger, and a temperature detection device may be arranged in the low-temperature section of each heat exchange module. When a pressure detection device detects that the differential pressure at the inlet and outlet of the heat exchange module exceeds the set value, the working fluid heating device is controlled to be in use, and the corresponding heated flue gas damper is controlled to be in an open state until the feedback temperature of the temperature detection device reaches above 232°C and is maintained until the pressure detection device detects that the differential pressure at the inlet and outlet of the flue gas heat exchanger returns to the set value. At this time, the working fluid heating device is controlled to be in an inactive state, and each heated flue gas damper is controlled to be in a closed state.

[0021] The pressure detection device can be a differential pressure transmitter or a pressure transmitter, which monitors the resistance on the flue gas side of the tubular preheater online. If the flue gas resistance is detected to exceed the set value, it means that the tubular preheater is ash-deposited or blocked by ammonium bisulfate.

[0022] The flue gas heat exchanger can also be equipped with a soot blower. When the flue gas resistance is monitored to exceed the set value, the soot blower is put into operation for a period of time. If the flue gas resistance still exceeds the set value, the working fluid heating device is put into use and high-temperature flue gas is introduced to volatilize the deposited ammonium bisulfate.

[0023] The beneficial effects of the present invention are as follows: the present invention can reduce the smoke and wind resistance of the system, reduce the power consumption of the blower and the primary blower, reduce the loss caused by the air preheater shutdown cleaning, recover the flue gas waste heat to the boiler, reduce the boiler exhaust temperature, and completely solve the problem of ammonium bisulfate blockage in the air preheater and the tail waste heat utilization equipment. The present invention is suitable for the new design or modification of the boiler preheating system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the system composition principle of the present invention.

[0025] Figure 2 It is a schematic diagram of the arrangement of the flue gas heat exchanger in the present invention.

[0026] Figure 3 It is a schematic structural diagram of an embodiment of the present invention.

[0027] Markings in the figure are: 1-flue duct (inlet section); 2-flue gas heat exchanger; 3-flue duct (outlet section); 4-air duct (inlet section); 5-air heater; 6-air duct (outlet section); 7-working fluid pipeline; 8-boosting pump; 9-shut-off valve; 10-regulating valve; 11-recirculation pipeline, 12-heat exchange module, 13-differential pressure transmitter, 14-hot air (smoke) pipeline, 15-flue duct partition plate, 16-smoke damper, 17-header, 18-thermocouple, 19-constant pressure tank, 20-working fluid heating device, 21-safety valve, 22-heating flue gas inlet, 23-heating flue gas damper, 24-smoke channel, 25-main control valve. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0029] Example:

[0030] like Figure 1 , Figure 2 and Figure 3 As shown, a 300MW coal-fired boiler unit is taken as an example for explanation.

[0031] The unit is transformed by applying the present invention.

[0032] Before the renovation, the rotary air preheater was severely clogged, with a flue gas side resistance of about 3000Pa, much higher than the original design value. In addition, the exhaust gas temperature of the air preheater was relatively high, reaching up to 160°C in summer (based on 40°C inlet air).

[0033] The specific transformation plan is as follows.

[0034] A flue gas heat exchanger 2 is arranged in the flue after the air preheater, and a flue (inlet section) 1 is arranged before the flue gas heat exchanger 2, and a flue (outlet section) 3 is arranged after the flue gas heat exchanger 2. The flue gas heat exchanger 2 is divided into four heat exchange modules 12, and a wall temperature thermocouple 18 is arranged at the low temperature section of each heat exchange module 12. The flue (inlet section) 1 is divided into four mutually isolated flue gas channels 24 by three mutually parallel partition plates 15, and each flue gas channel 24 is respectively arranged with a flue gas baffle 16 to control whether the flue gas in the flue is introduced into the flue gas channel 24. Each heat exchange module 12 is located in one of the flue gas channels 24, and the flue gas inlets and outlets of the four heat exchange modules 12 are independently provided with differential pressure transmitters 13. The liquid phase working medium of the flue gas heat exchanger 2 is water, and the heat medium water inlet and outlet are provided with headers 17, and the flue gas heat exchanger 2 is controlled by the configured main control valve 25. The master control is adjusted, and a working fluid heating device 20 is arranged before the heat medium water inlet. The working fluid heating device 20 is used to heat the heat medium water. The heat source can be steam, water, electricity, etc. The working fluid heating device 20 can independently heat the heat medium water flowing to the four heat exchange modules 12, that is, independent pipelines and control valves are arranged at the outlets of the working fluid heating device 20 to be connected with the working fluid inlets of the corresponding heat exchange modules 12, and independent pipelines and control valves are arranged before the inlet of the working fluid heating device 20 to be connected with the outlet of the booster pump 8. The outlet of the booster pump 8 is connected to the working fluid inlet of the corresponding heat exchange module 12 through another pipeline with a shut-off valve 9, and the inlet of the booster pump 8 is connected to the outlet of the constant pressure tank 19 through the recirculation pipeline 11 and the heater 5. The constant pressure tank 19 ensures that when the wall temperature of the heat exchanger is increased, the working fluid pressure of the heat medium water remains constant and ensures that the heat medium water does not vaporize. A regulating valve 10 is connected in series in the recirculation pipe 11. The heater 5 is arranged in the air duct, with its hot end close to the air duct (inlet section) 4 and its cold end close to the air duct (outlet section) 6, which is used to heat the cold air sent from the blower or primary blower, and the heated hot air is sent to the cold end of the air preheater. The pipes connected between the heater 5, the constant pressure tank 19, the flue gas heat exchanger 2 and the working medium heating device are collectively referred to as the working medium pipe 7. A safety valve 21 is provided on the pipe at the outlet of the flue gas heat exchanger 2. The heat source of the working medium heating device 20 comes from auxiliary steam. In addition, each flue gas channel 24 can introduce hot air from the outlet of the air preheater through the hot air (smoke) pipe 14 and the heated flue gas inlet 22. The hot air can be blocked by closing the heated flue gas damper 23. The introduced hot air (smoke) can also come from any flue gas or air with a temperature ≥250°C.

[0035] like Figure 3 As shown, the hot air (smoke) duct 14 can be led to the vicinity of the flue gas heat exchanger 2 through a main duct, and then separately introduced into each flue gas channel 24. The hot air (smoke) duct 14 can also be separately introduced into the flue gas channel 24 corresponding to each heat exchange module 12.

[0036] Here's how it works.

[0037] When a differential pressure transmitter 13 detects that the inlet and outlet differential pressure of the flue where the corresponding heat exchange module 12 is located exceeds the set value, the soot blower is first opened for purging. After purging for a period of time, if the inlet and outlet differential pressure still exceeds the set value, the flue gas damper 16 of the corresponding flue gas channel 24 is closed, the corresponding heating flue gas damper 23 is opened, and the control valve on the working medium pipeline connected to the working medium heating device 20 and the heat exchange module 12 is opened to heat the metal pipe wall of the heat exchanger. When the thermocouple 18 detects that the temperature has reached above 232°C, the ammonium bisulfate attached to the outside of the pipe wall begins to volatilize and maintains this state for a period of time, the flue gas side resistance of the heat exchanger module is reduced. When the differential pressure transmitter 13 detects that the inlet and outlet differential pressure of the flue gas heat exchanger is lower than the set value, the corresponding heating flue gas damper 23 can be closed, the control valve on the working medium pipeline connected to the working medium heating device 20 and the heat exchange module 12 is closed, and the flue gas damper 16 of the corresponding flue gas channel 24 is opened, and the heat exchange module 12 returns to a normal heat exchange state.

[0038] After the transformation, the recovered flue gas waste heat was used to heat the air preheater inlet cold air. The average air temperature at the air preheater inlet increased from 25°C to 100°C, the air preheater exhaust temperature increased to 191°C, the comprehensive temperature of the air preheater cold end increased significantly, the ammonium bisulfate blockage and cold end corrosion of the rotary air preheater were fundamentally alleviated, the operating resistance of the rotary air preheater was greatly reduced, and the resistance on the flue gas side and air side was reduced to 1500-2000 Pa. In addition, the exhaust temperature of the boiler was reduced from 150°C before the transformation (based on 25°C inlet air) to 131°C, the exhaust temperature was reduced by about 19°C, and the boiler efficiency was increased by about 0.95%.

[0039] Under long-term operation conditions, the resistance of the rotary air preheater and flue gas heat exchanger does not increase. When the wall temperature of a module heat exchanger is increased, the comprehensive flue gas temperature at the flue gas heat exchanger outlet will rise to about 160°C for a short time, which basically does not affect the normal operation of the subsequent dust collector.

[0040] Based on this embodiment, the system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment and the control method thereof of the present invention can be modified to a certain extent. For example, the flue gas heat exchanger can be provided with a differential pressure transmitter to monitor the differential pressure before and after the heat exchanger, and pressure transmitters can also be provided on the flue before and after the heat exchanger, respectively. The differential pressure transmitter (pressure transmitter) can be provided on the flue mother pipe before and after the flue of the flue gas heat exchanger, and the differential pressure transmitter (pressure transmitter) can also be provided on the flue before and after each module.

[0041] In addition, the heat exchange area of ​​the air preheater can be increased to raise the inlet air temperature to a higher temperature.

Claims

1. A system for preventing ammonium bisulfate deposition in an air preheater and a tail waste heat utilization device, including an air preheater, characterized by: The tail waste heat utilization equipment is a flue gas heat exchanger arranged in the flue after the air preheater. The flue gas heat exchanger is composed of at least two parallel heat exchange modules, each heat exchange module corresponds to a liquid phase working medium channel and a flue gas channel branched off from the flue, the heat exchange modules are isolated from each other and can independently control the flue gas-working medium heat exchange in a single heat exchange module, each flue gas channel is also respectively provided with a heated flue gas inlet, and a working medium constant pressure system and a working medium heating device are configured for the working medium of the flue gas heat exchanger, the system also includes an air duct and a heater, the inlet of the air duct is connected to the outlet of the blower, and the outlet of the air duct is connected to the air inlet of the air preheater via the heater.

2. The system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment as claimed in claim 1 is characterized by: The working fluid constant pressure system includes a working fluid pipeline, which is used to connect the flue gas heat exchanger, the heater, the booster pump, the constant pressure tank and the working fluid heating device: the outlet of the constant pressure tank is connected in series with the heater and the booster pump in sequence, the liquid phase working fluid channels of each heat exchange module are connected in parallel between the outlet of the booster pump and the inlet of the constant pressure tank, the working fluid heating device is connected in parallel between the outlet of the booster pump and the working fluid inlet of the flue gas heat exchanger via a working fluid pipeline, and a shut-off valve is also provided on the working fluid pipeline to block the working fluid from entering the heat exchange module.

3. The system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment as claimed in claim 2, characterized in that: A recirculation pipeline is connected in parallel between the working medium inlet and the working medium outlet of the air heater, and a regulating valve is connected in series in the recirculation pipeline.

4. The system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment as claimed in claim 2, characterized in that: A safety valve is provided on the working medium pipeline at the outlet of the flue gas heat exchanger.

5. The system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment as claimed in claim 2, characterized in that: The liquid phase working medium is water, and the working medium heating device is a steam heating device.

6. The system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment as claimed in claim 1, 2, 3, 4 or 5, characterized in that: The inlet and outlet of the liquid working medium of each heat exchange module are both provided with a header.

7. The system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment as claimed in claim 1, 2, 3, 4 or 5, characterized in that: The flue is provided with a flue partition plate to divide the inlet flue into corresponding flue gas channels corresponding to the heat exchange modules. Each flue gas channel is independently provided with a relevant baffle, and a corresponding heating flue gas baffle is also provided corresponding to each heating flue gas inlet. Each baffle can be remotely and independently controlled.

8. The system for preventing ammonium bisulfate deposition in air preheater and tail waste heat utilization equipment as claimed in claim 1, 2, 3, 4 or 5, characterized in that: The heated flue gas inlet is connected to the flue gas inlet or hot air outlet of the air preheater, and the air preheater is a rotary air preheater or a tubular air preheater.

9. A control method for a system for preventing ammonium bisulfate deposition in an air preheater and a tail waste heat utilization device, comprising the system for preventing ammonium bisulfate deposition in an air preheater and a tail waste heat utilization device according to claim 7, characterized in that: A pressure detection device is provided between the flue gas inlet and outlet of the flue gas heat exchanger, and a temperature detection device is arranged in the low-temperature section of each heat exchange module. When the inlet and outlet differential pressure detected by the pressure detection device exceeds the set value, the working fluid heating device is controlled to be in use, and the corresponding heating flue gas dampers of each heat exchange module are controlled to be in an open state one by one until the temperature detection device feedback temperature reaches above 232°C and maintains the set time. This step is repeated until it is detected that the inlet and outlet differential pressure of the flue gas heat exchanger returns to the set value. At this time, the working fluid heating device is controlled to be in an inactive state, and each heating flue gas damper is controlled to be in a closed state.

10. A control method for a system for preventing ammonium bisulfate deposition in an air preheater and a tail waste heat utilization device, comprising the system for preventing ammonium bisulfate deposition in an air preheater and a tail waste heat utilization device according to claim 7, characterized in that: A pressure detection device is provided between the flue gas inlet and outlet of each heat exchange module of the flue gas heat exchanger, and a temperature detection device is arranged in the low-temperature section of each heat exchange module. When a pressure detection device detects that the differential pressure at the inlet and outlet of the heat exchange module exceeds the set value, the working fluid heating device is controlled to be in use, and the corresponding heated flue gas damper is controlled to be in an open state until the feedback temperature of the temperature detection device reaches above 232°C and is maintained until the pressure detection device detects that the differential pressure at the inlet and outlet of the flue gas heat exchanger returns to the set value. At this time, the working fluid heating device is controlled to be in a disabled state, and each heated flue gas damper is controlled to be in a closed state.

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