Automatic white smoke removal system of periodic blowdown flash tank for realizing two-stage waste heat utilization

Abstract

The utility model discloses an automatic white water removal system of a periodic blowdown flash tank for realizing two-stage waste heat utilization, the top of the periodic blowdown flash tank is communicated with a hot water tank through a second steam exhaust pipe so as to realize that flash steam enters the hot water tank, the top of the hot water tank is communicated with a desuperheater, and the desuperheater is communicated with a demineralized water pipeline; the flash steam and the demineralized water are subjected to heat exchange in the desuperheater, non-condensed gas is emptied through the top of the desuperheater, and mixed liquid enters the hot water tank; the hot water tank is communicated with the heat exchanger through a second drainage branch pipe, the periodic blowdown flash tank is communicated with the heat exchanger through a high-temperature drainage pipe, and the heat exchanger is communicated with the blowdown cooling well through a low-temperature drainage pipe and communicated to the deaerator through a hot water drainage pipe; after mixed liquid discharged by the hot water tank and high-temperature drain water discharged by the periodic drainage flash tank exchange heat in the heat exchanger, the cooled drain water enters the drainage cooling well, and the heated mixed liquid is fed into the deaerator through the hot water pump, so that hot water recovery is realized. The device has the advantages of safety, reliability, high heat energy utilization rate, high automation degree and the like.

Description

Technical Field

[0001] The utility model belongs to the technical field of boiler sewage discharge and heat recovery treatment, and in particular relates to an automatic whitening system for a fixed-discharge expansion tank for realizing two-stage waste heat utilization. Background Art

[0002] The waste heat boiler of the garbage incineration power plant is equipped with a fixed-discharge expansion tank to receive water from the boiler water level gauge, water wall header drain, emergency drum drain, superheater and desuperheater drain, water supply pipeline drain, steam soot blowing drain, boiler room high-pressure drain, steam engine room high-pressure drain, low-pressure drain, continuous expansion tank water side drain, and deaerator drain. Generally, after the expansion tank is expanded, part of the steam or drain enters the fixed-discharge expansion tank becomes saturated drain and is discharged to the sewage cooling well, while the other part flashes into saturated steam after expansion and is discharged from the furnace top through the exhaust pipe at the top of the fixed-discharge expansion tank. The discharge of steam not only causes the loss of working fluid and heat energy, but also the white mist generated at the exhaust port will condense and pollute the exhaust pipe and boiler roof, which will bring a bad impression to the image of the power plant. The saturated water discharged from the bottom of the fixed-discharge expansion tank to the sewage cooling well also has a large heat energy loss.

[0003] At present, the mainstream fixed-row expansion tank desalination device uses fixed-row expansion tank to spray water for cooling to reduce the emission of saturated steam into the air, which mainly has the following shortcomings:

[0004] (1) The high-temperature and high-pressure drain water from the boiler water-cooled wall blowdown, continuous blowdown, and steam soot blowing heating pipe has a temperature of about 260°C. It enters the fixed discharge expansion tank for expansion and pressure reduction, and is cooled by industrial water spray at the top of the expansion tank. However, a certain amount of flash steam is still discharged into the atmosphere, and the exhaust steam de-whitening effect is limited. At the same time, there is still about 100°C of drain water at the bottom of the expansion tank that is discharged to the blowdown cooling well, resulting in the loss of steam-water working fluid and heat energy.

[0005] (2) Putting a large amount of industrial water into the fixed discharge expansion tank for water spraying and cooling will cause the water level of the sewage cooling well to rise. It is necessary to frequently start the sewage cooling water pump to lower the water level of the sewage cooling well, resulting in increased power consumption.

[0006] (3) The quality of industrial water used for cooling is relatively poor, with high hardness and conductivity. In addition, the collection of various drainage water and sewage leads to serious scaling and compaction inside the expansion tank, which can easily cause blockage of the steam outlet and drain outlet of the fixed-discharge expansion tank, posing a major safety hazard to the boiler drainage system.

[0007] (4) The degree of automation is low. The existing fixed-discharge expansion tank has no temperature measurement point, and the white steam removal method is relatively extensive. That is, the exhaust of steam from the exhaust pipe of the fixed-discharge expansion tank on the roof of the boiler can only be observed through the video monitoring arranged on the chimney; when white steam is found to be discharged, the supervisor opens the cooling water solenoid valve of the fixed-discharge expansion tank and injects cooling water into the fixed-discharge expansion tank to cool down and remove the white steam until the white steam disappears. This process cannot be automatically and accurately controlled.

[0008] In summary, the existing dewhitening technology has obvious shortcomings: the dewhitening effect is poor, the heat loss of steam and water is large, the thermal energy utilization rate is low, the fixed-discharge expansion vessel body and the discharge pipe are prone to scaling and clogging, and the safety risk is relatively large. Utility Model Content

[0009] The technical problem to be solved by the utility model is to overcome the deficiencies of the prior art and provide an automatic de-whitening system for fixed row expansion vessels which has a compact structure, is safe and reliable, has a high heat recovery rate, and a high degree of automation to realize two-stage waste heat utilization.

[0010] In order to solve the above technical problems, the utility model adopts the following technical solutions:

[0011] An automatic desalination system for a fixed-discharge expansion tank for realizing two-stage waste heat utilization, comprising: a fixed-discharge expansion tank, a hot water tank, a desuperheater, a heat exchanger and a sewage cooling well; the top of the fixed-discharge expansion tank is connected to the hot water tank through a second exhaust pipe to realize the flash steam generated in the fixed-discharge expansion tank to enter the hot water tank, the top of the hot water tank is connected to the desuperheater, the desuperheater is connected to a desalted water pipeline to realize the heat exchange between the flash steam and the desalted water in the desuperheater, the non-condensable gas escaping after the heat exchange is emptied through the top of the desuperheater, and the mixed liquid after the heat exchange enters the hot water tank; The bottom of the hot water tank is connected to the heat exchanger through the second drainage branch pipe, the bottom of the fixed-discharge expansion tank is connected to the heat exchanger through the high-temperature drain pipe, the heat exchanger is connected to the sewage cooling well through the low-temperature drain pipe, and the heat exchanger is connected to the deaerator through the hot water discharge pipe and the hot water pump; when the mixed liquid discharged from the hot water tank and the high-temperature drain discharged from the fixed-discharge expansion tank are heat exchanged in the heat exchanger, the drain after heat exchange and cooling enters the sewage cooling well through the low-temperature drain pipe, and the mixed liquid after heat exchange and heating is pressurized and sent to the deaerator through the hot water discharge pipe and the hot water pump to realize hot water recovery.

[0012] As a further improvement of the utility model, a temperature sensor is provided in the hot water tank to monitor the temperature in the hot water tank in real time.

[0013] As a further improvement of the utility model, two parallel spray branches are provided on the desalted water pipeline, both of which are connected to the desuperheater, and one of the spray branches is provided with a first pneumatic valve, and the other spray branch is provided with a second pneumatic valve, and the first pneumatic valve and the second pneumatic valve are interlocked with the temperature sensor to achieve temperature regulation of the mixed liquid in the hot water tank.

[0014] As a further improvement of the utility model, a liquid level sensor is provided in the hot water tank to monitor the liquid level in the hot water tank in real time.

[0015] As a further improvement of the utility model, the hot water discharge pipe is provided with two parallel branches, both of which are connected to the deaerator, and one of the branches is provided with a first hot water pump and a one-way valve, and the other branch is provided with a second hot water pump and a one-way valve, and the first hot water pump and the second hot water pump are interlocked to achieve liquid level regulation of the mixed liquid in the hot water tank.

[0016] As a further improvement of the utility model, a first electric valve and a one-way valve are provided on the second steam exhaust pipe to adjust the amount of flash steam entering the hot water tank.

[0017] As a further improvement of the utility model, the high-temperature drain pipe is provided with an inverted U-shaped pipe section to ensure the drain liquid level of the fixed-row expansion tank and prevent the gas in the fixed-row expansion tank from being discharged through the low-temperature drain pipe due to emptying.

[0018] As a further improvement of the utility model, the upper part of the fixed-discharge expansion vessel and the top of the hot water tank are both provided with safety valves for emergency pressure relief.

[0019] As a further improvement of the utility model, a first steam exhaust pipe with a first control valve is provided on the top of the fixed-discharge expansion tank, the first steam exhaust pipe is connected to the furnace top for emptying, and the hot water tank is connected to the sewage cooling well through a first drainage branch pipe with a third control valve. When the hot water tank is under maintenance, the steam in the fixed-discharge expansion tank is emptied through the first steam exhaust pipe, and the mixed liquid in the hot water tank is emptied through the first drainage branch pipe.

[0020] As a further improvement of the utility model, a fourth control valve is provided on the inlet pipe of the fixed-row expansion tank, and a drainage groove is provided at the bottom of the fixed-row expansion tank. When the fixed-row expansion tank is under maintenance, the fourth control valve is closed and the drain in the fixed-row expansion tank is discharged into the drainage groove.

[0021] Compared with the prior art, the advantages of the utility model are:

[0022] The utility model realizes the automatic desalination system of the fixed-row expansion tank for realizing two-stage waste heat utilization, by connecting the top of the fixed-row expansion tank with the hot water tank, realizing that the flash steam generated in the fixed-row expansion tank enters the hot water tank, the top of the hot water tank is connected with the desuperheater, the desuperheater is connected with the desalted water pipeline, the desalted water is sprayed in the desuperheater, that is, the flash steam and the desalted water are heat exchanged in the desuperheater, the non-condensable gas escaping after the heat exchange is emptied through the top of the desuperheater, the mixed liquid after the heat exchange enters the hot water tank, realizing the production of the fixed-row expansion tank The heat of flash steam is recovered, eliminating the phenomenon of white steam coming out of the exhaust pipe leading from the fixed-discharge expansion tank to the roof of the boiler room; at the same time, the bottom of the hot water tank is connected to the heat exchanger, and the bottom of the fixed-discharge expansion tank is also connected to the heat exchanger, and the heat exchangers are respectively connected to the sewage cooling well and the deaerator; when the mixed liquid discharged from the hot water tank and the high-temperature drain discharged from the fixed-discharge expansion tank are heat-exchanged in the heat exchanger, the drain after heat exchange cooling enters the sewage cooling well, and the mixed liquid after heat exchange heating is pressurized and sent to the deaerator through the hot water discharge pipe and the hot water pump to realize hot water recovery. The utility model can not only eliminate the exhaust steam at the top of the fixed-discharge expansion tank (referred to as "whitening"), but also realize the two-stage waste heat utilization of the exhaust steam and drainage heat energy of the fixed-discharge expansion tank, and has the advantages of environmental protection, energy saving, automatic, low cost and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structural principle of the automatic de-whitening system of the fixed-row expansion vessel for realizing two-stage waste heat utilization in the utility model.

[0024] Legend: 1. Fixed-discharge expansion tank; 2. Safety valve; 3. First control valve; 4. First exhaust pipe; 5. Second exhaust pipe; 6. First electric valve; 7. Hot water tank; 8. Temperature sensor; 9. Second electric valve; 10. Desuperheater; 11. First pneumatic valve; 12. Second pneumatic valve; 13. Liquid level sensor; 14. Third pneumatic valve; 15. Desalted water pipeline; 16. First drainage branch pipe; 17. Second drainage branch pipe; 18. Second control valve; 19. Third control valve; 20. Drain trough; 21. High-temperature drain pipe; 22. Heat exchanger; 23. Low-temperature drain pipe; 24. Sewage cooling well; 25. Hot water discharge pipe; 26. First hot water pump; 27. Second hot water pump; 28. One-way valve; 29. ​​Fourth control valve. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0026] Example

[0027] like Figure 1As shown, the automatic de-whitening system of the fixed-row expansion tank for realizing two-stage waste heat utilization of the utility model comprises: a fixed-row expansion tank 1, a hot water tank 7, a desuperheater 10, a heat exchanger 22 and a sewage cooling well 24. The design pressure of the fixed-row expansion tank 1 is 0.6MPa, and the enthalpy value of the saturated steam flashed after the high-temperature drainage water on the furnace side enters reaches 2756.54KJ / kg, which has a high waste heat utilization value. The top of the fixed-row expansion tank 1 is connected to the hot water tank 7 through the second exhaust pipe 5, so that the flash steam generated in the fixed-row expansion tank 1 can enter the hot water tank 7. The top of the hot water tank 7 is connected to the desuperheater 10, and the top of the desuperheater 10 is connected to the furnace top through a pipeline with a second electric valve 9 to be emptied. The desuperheater 10 is connected to the desalted water pipeline 15 to realize heat exchange between the flash steam and the desalted water in the desuperheater 10, and the non-condensable gas escaping after the heat exchange is emptied through the top of the desuperheater 10, and the mixed liquid after the heat exchange enters the hot water tank 7. The bottom of the hot water tank 7 is connected to the heat exchanger 22 through the second drainage branch pipe 17 with the second control valve 18, the bottom of the fixed-discharge expansion tank 1 is connected to the heat exchanger 22 through the high-temperature drain pipe 21, the heat exchanger 22 is connected to the sewage cooling well 24 through the low-temperature drain pipe 23, and the heat exchanger 22 is connected to the deaerator through the hot water discharge pipe 25 and the hot water pump. After the mixed liquid discharged from the hot water tank 7 and the high-temperature drain discharged from the fixed-discharge expansion tank 1 are heat exchanged in the heat exchanger 22, the drain after heat exchange cooling enters the sewage cooling well 24 through the low-temperature drain pipe 23, and the mixed liquid after heat exchange heating is pressurized and sent to the deaerator through the hot water discharge pipe 25 and the hot water pump to realize hot water recovery, and the flash steam of the fixed-discharge expansion tank 1 and the two-stage waste heat of the drain are both utilized. Specifically, the heat exchanger 22 can adopt a plate heat exchanger, which has the characteristics of simple structure and high heat exchange efficiency.

[0028] In this embodiment, by connecting the top of the fixed-displacement expansion tank 1 with the hot water tank 7, the flash steam generated in the fixed-displacement expansion tank 1 enters the hot water tank 7, the top of the hot water tank 7 is connected to the desuperheater 10, the desuperheater 10 is connected to the desalted water pipeline 15, and the desalted water is sprayed in the desuperheater 10, that is, the flash steam and the desalted water are heat exchanged in the desuperheater 10, the non-condensable gas escaping after the heat exchange is discharged through the top of the desuperheater 10, and the mixed liquid after the heat exchange enters the hot water tank 7, so that the heat of the flash steam generated by the fixed-displacement expansion tank 1 is recovered, and the phenomenon of white steam emitting from the exhaust pipe outlet connected from the fixed-displacement expansion tank 1 to the roof of the boiler room is eliminated. At the same time, the bottom of the hot water tank 7 is connected to the heat exchanger 22, and the bottom of the fixed-discharge expansion tank 1 is also connected to the heat exchanger 22, and the heat exchanger 22 is respectively connected to the sewage cooling well 24 and the deaerator; when the mixed liquid discharged from the hot water tank 7 and the high-temperature drain water discharged from the fixed-discharge expansion tank 1 are heat exchanged in the heat exchanger 22, the drain water after heat exchange cooling enters the sewage cooling well 24, and the mixed liquid after heat exchange heating is pressurized and sent to the deaerator through the hot water discharge pipe 25 and the hot water pump to realize hot water recovery. The utility model can not only eliminate the exhaust steam at the top of the fixed-discharge expansion tank 1 (referred to as "de-whitening"), but also realize the two-stage waste heat utilization of the exhaust steam and drainage heat energy of the fixed-discharge expansion tank 1, and has the advantages of environmental protection, energy saving, automatic, low cost and high efficiency.

[0029] In this embodiment, a temperature sensor 8 connected to a remote controller is provided in the hot water tank 7 to monitor the temperature in the hot water tank 7 in real time. Further, a third pneumatic valve 14 is provided on the desalted water pipeline 15, and two parallel spray branches are provided on the desalted water pipeline 15, both of which are connected to the desuperheater 10, and a first pneumatic valve 11 is provided on one of the spray branches, and a second pneumatic valve 12 is provided on the other spray branch, and the first pneumatic valve 11 and the second pneumatic valve 12 are interlocked with the temperature sensor 8 to realize automatic temperature adjustment of the mixed liquid in the hot water tank 7.

[0030] When the temperature in the hot water tank 7 is higher than the set value of 60°C, the first pneumatic valve 11 is interlocked to open; when the flash steam volume is large and the temperature in the hot water tank 7 is higher than 75°C, the second pneumatic valve 12 is further interlocked to open, and when the temperature in the hot water tank 7 is lower than the set value of 60°C, the corresponding water spray pneumatic valve is interlocked to close. By setting two layers of spraying in the desuperheater 10, which are controlled by the corresponding water spray pneumatic valves, a large water spray cooling amount is provided, which fully guarantees the de-whitening effect. The temperature in the hot water tank 7 and the desuperheater 10 is maintained at 60°C, and the corresponding saturated water enthalpy is 251.5KJ / kg, which can still be heat exchanged with the hotter hydrophobic water with an enthalpy of 670KJ / kg discharged from the bottom of the fixed-discharge expansion tank 1 through the heat exchanger 22.

[0031] In this embodiment, a liquid level sensor 13 connected to a remote controller is provided in the hot water tank 7 to monitor the liquid level in the hot water tank 7 in real time. Furthermore, two parallel branches are provided on the hot water discharge pipe 25, both branches are connected to the deaerator, and a first hot water pump 26 and a one-way valve 28 are provided on one branch, and a second hot water pump 27 and a one-way valve 28 are provided on the other branch. The first hot water pump 26 and the second hot water pump 27 are interlocked to realize automatic adjustment of the liquid level of the mixed liquid in the hot water tank 7.

[0032] When the liquid level in the hot water tank 7 is higher than 400 mm, the first hot water pump 26 is started by interlocking, and when the liquid level in the hot water tank 7 is higher than 500 mm, the second hot water pump 27 is further started by interlocking to ensure that the liquid level is within a reasonable range.

[0033] In this embodiment, the second exhaust pipe 5 is provided with a first electric valve 6 and a one-way valve 28 for adjusting the amount of flash steam entering the hot water tank 7 and for blocking steam from entering the hot water tank 7 when the hot water tank 7 is being repaired.

[0034] In this embodiment, an inverted U-shaped pipe section is provided in the high-temperature drain pipe 21 to ensure a certain drain liquid level in the fixed-discharge expansion vessel 1, thereby preventing the steam inside the fixed-discharge expansion vessel 1 from being discharged into the sewage cooling well 24 through the drain pipe at the bottom due to emptying.

[0035] In this embodiment, the upper part of the fixed-discharge expansion tank 1 and the top of the hot water tank 7 are both provided with a safety valve 2 for emergency pressure relief. When the pressure in the fixed-discharge expansion tank 1 and the hot water tank 7 exceeds 0.6Mpa, the safety valve 2 is opened to relieve the pressure to ensure the safety of the fixed-discharge expansion tank 1 and the hot water tank 7.

[0036] In this embodiment, a first exhaust pipe 4 with a first control valve 3 is provided on the top of the fixed-discharge expansion tank 1. The first exhaust pipe 4 is connected to the furnace top for emptying. The hot water tank 7 is connected to the sewage cooling well through a first drainage branch pipe 16 with a third control valve 19. When the hot water tank 7 is overhauled, the first electric valve 6, the second electric valve 9 and the third pneumatic valve 14 are closed, the first control valve 3 is opened, and the steam in the fixed-discharge expansion tank 1 is emptied through the first exhaust pipe 4; the second control valve 18 is closed, the third control valve 19 is opened, and the mixed liquid in the hot water tank 7 is emptied through the first drainage branch pipe 16.

[0037] Furthermore, a fourth control valve 29 is provided on the inlet pipe of the fixed-discharge expansion tank 1, and a drainage groove 20 is provided at the bottom of the fixed-discharge expansion tank 1. When the fixed-discharge expansion tank 1 is under maintenance, the fourth control valve 29 is closed to cut off external steam and drain, the first control valve 3 is opened to connect the fixed-discharge expansion tank 1 to the atmosphere, the valve between the drainage groove 20 and the fixed-discharge expansion tank 1 is opened, and the drain in the fixed-discharge expansion tank 1 is discharged into the drainage groove 20; at the same time, the first electric valve 6 and the second electric valve 9 are closed to prevent the water in the hot water tank 7 from returning to the fixed-discharge expansion tank 1.

[0038] In this embodiment, the first control valve 3, the second control valve 18, the third control valve 19 and the fourth control valve 29 can all be conventional manual stop valves.

[0039] In this embodiment, a better de-whitening effect is achieved for the boiler fixed discharge system, the thermal energy utilization efficiency is improved, and the safety risks caused by scaling and blockage inside the fixed discharge expansion vessel and its discharge pipeline are reduced.

[0040] Although the utility model is disclosed as above with preferred embodiments, it is not intended to limit the utility model. Any technician familiar with the art can use the above disclosed methods and technical contents to make many possible changes and modifications to the technical solution of the utility model without departing from the spirit and technical solution of the utility model, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the utility model without departing from the content of the technical solution of the utility model still falls within the scope of protection of the technical solution.

Claims

1. An automatic de-whitening system for fixed row expansion tanks to achieve two-stage waste heat utilization, characterized in that: include: A fixed-discharge expansion tank (1), a hot water tank (7), a desuperheater (10), a heat exchanger (22) and a sewage cooling well (24); the top of the fixed-discharge expansion tank (1) is connected to the hot water tank (7) through a second exhaust pipe (5) to enable flash steam generated in the fixed-discharge expansion tank (1) to enter the hot water tank (7); the top of the hot water tank (7) is connected to the desuperheater (10); the desuperheater (10) is connected to a desalted water pipeline (15) to enable flash steam and desalted water to exchange heat in the desuperheater (10); the non-condensable gas escaping after heat exchange is discharged through the top of the desuperheater (10); and the mixed liquid after heat exchange enters the hot water tank (7); the bottom of the hot water tank (7) is connected to a second exhaust pipe (5) to enable flash steam generated in the fixed-discharge expansion tank (1) to enter the hot water tank (7); the top of the hot water tank (7) is connected to the desuperheater (10); the desuperheater (10) is connected to a desalted water pipeline (15) to enable flash steam and desalted water to exchange heat in the desuperheater (10); the non-condensable gas escaping after heat exchange is discharged through the top of the desuperheater (10); and the mixed liquid after heat exchange enters the hot water tank (7); The branch pipe (17) is connected to the heat exchanger (22), the bottom of the fixed-discharge expansion tank (1) is connected to the heat exchanger (22) through a high-temperature drain pipe (21), the heat exchanger (22) is connected to a sewage cooling well (24) through a low-temperature drain pipe (23), and the heat exchanger (22) is connected to a deaerator through a hot water discharge pipe (25) and a hot water pump; when the mixed liquid discharged from the hot water tank (7) and the high-temperature drain discharged from the fixed-discharge expansion tank (1) are heat exchanged in the heat exchanger (22), the drain after heat exchange cooling enters the sewage cooling well (24) through the low-temperature drain pipe (23), and the mixed liquid after heat exchange heating is pressurized and sent to the deaerator through the hot water discharge pipe (25) and the hot water pump to realize hot water recovery.

2. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to claim 1 is characterized in that: The hot water tank (7) is provided with a temperature sensor (8) for real-time monitoring of the temperature in the hot water tank (7).

3. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to claim 2 is characterized in that: The desalted water pipeline (15) is provided with two parallel spray branches, both of which are connected to the desuperheater (10), and one of the spray branches is provided with a first pneumatic valve (11), and the other spray branch is provided with a second pneumatic valve (12), and the first pneumatic valve (11) and the second pneumatic valve (12) are interlocked with a temperature sensor (8) to achieve temperature regulation of the mixed liquid in the hot water tank (7).

4. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to claim 2 is characterized in that: A liquid level sensor (13) is provided in the hot water tank (7) to monitor the liquid level in the hot water tank (7) in real time.

5. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to claim 4 is characterized in that: The hot water discharge pipe (25) is provided with two parallel branches, both of which are connected to the deaerator, and one of the branches is provided with a first hot water pump (26) and a one-way valve (28), and the other branch is provided with a second hot water pump (27) and a one-way valve (28). The first hot water pump (26) and the second hot water pump (27) are interlocked to achieve liquid level adjustment of the mixed liquid in the hot water tank (7).

6. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to any one of claims 1 to 5, characterized in that: The second steam exhaust pipe (5) is provided with a first electric valve (6) and a one-way valve (28) for adjusting the amount of flash steam entering the hot water tank (7).

7. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to any one of claims 1 to 5, characterized in that: The high-temperature drain pipe (21) is provided with a pipe section of an inverted U-shaped structure, so as to ensure the drain liquid level of the fixed-discharge expansion vessel (1) and prevent the gas in the fixed-discharge expansion vessel (1) from being discharged through the low-temperature drain pipe (23) due to emptying.

8. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to any one of claims 1 to 5, characterized in that: The upper part of the fixed-discharge expansion tank (1) and the top of the hot water tank (7) are both provided with safety valves (2) for emergency pressure relief.

9. The automatic de-whitening system for fixed-row expansion vessels for realizing two-stage waste heat utilization according to any one of claims 1 to 5, characterized in that: A first steam exhaust pipe (4) with a first control valve (3) is provided on the top of the fixed-discharge expansion tank (1), and the first steam exhaust pipe (4) is connected to the furnace top for discharge; the hot water tank (7) is connected to the sewage cooling well (24) through a first drainage branch pipe (16) with a third control valve (19); when the hot water tank (7) is under maintenance, the steam in the fixed-discharge expansion tank (1) is discharged through the first steam exhaust pipe (4); and the mixed liquid in the hot water tank (7) is discharged through the first drainage branch pipe (16).

10. The automatic de-whitening system for fixed-row expansion vessels realizing two-stage waste heat utilization according to claim 9, characterized in that: A fourth control valve (29) is provided on the inlet pipe of the fixed-displacement expansion tank (1), and a drainage groove (20) is provided at the bottom of the fixed-displacement expansion tank (1). When the fixed-displacement expansion tank (1) is under maintenance, the fourth control valve (29) is closed, and the drain in the fixed-displacement expansion tank (1) is discharged into the drainage groove (20).

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