Method for improving heat exchange efficiency of heater of desulfurization wastewater low-temperature flash evaporation concentration system

Abstract

The invention relates to the field of electric desulfurization, in particular to a method for improving the heat exchange efficiency of a heater of a desulfurization wastewater low-temperature flash evaporation concentration system, which comprises the following steps of: arranging exhaust systems at the upper and lower ends of shell sides of a second-effect heater and a third-effect heater of the low-temperature flash evaporation concentration system respectively, and connecting the exhaust systems with a secondary steam pipeline at an outlet of a third-effect separator; during operation, the tail end vacuum pump can exhaust non-condensed gas in the second-effect heater and the third-effect heater to the atmosphere, the mobility of steam in the heaters can be improved, and the heat exchange efficiency of the heaters can be improved. U-shaped water seals are arranged on condensation water pipelines at the bottoms of shell sides of the second-effect heater and the third-effect heater, the water level at the bottoms of the shell sides of the heaters is automatically controlled, steam is prevented from entering a condensation water system, the phenomenon of pipeline vibration is avoided, the heat exchange efficiency of the heaters is improved, the negative pressure stability of the system is improved, and the operation energy consumption of the desulfurization wastewater low-temperature flash evaporation concentration system is reduced.

Description

Technical Field

[0001] The present invention relates to the field of power desulfurization, and in particular to a method for improving the heat exchange efficiency of a heater in a low-temperature flash evaporation and concentration system for desulfurization wastewater. Background Art

[0002] The operation of the zero-discharge low-temperature flash concentration system for desulfurization wastewater from Taiyuan Iron & Steel's 2×300MW units is affected by the desulfurization process. Because the desulfurization wastewater contains a certain amount of non-condensable gases such as air, nitrogen, hydrogen, and carbon dioxide, the wastewater is heated and flash-separated in the first and second-effect separators. The secondary steam carries non-condensable gases, which enter the second and third-effect heaters. After long-term accumulation, steam flow within the heaters is obstructed, reducing heat transfer efficiency. To maintain the condensate level at the bottom of the shell side of the second and third-effect heaters, operators need to frequently adjust the condensate valve opening based on changes in wastewater treatment volume. Failure to adjust the valve opening in time can affect the heat transfer efficiency of the steam within the heaters and lead to unstable negative pressure operation. Consequently, the presence of non-condensable gases and frequent fluctuations in the shell side water level within the second and third-effect heaters can affect the heater's heat transfer efficiency, increase system energy consumption and operating costs, and cause system negative pressure fluctuations, resulting in elevated condensate temperatures and boiling in the terminal water tank.

[0003] The purpose of the present invention is to provide a process for improving the heat exchange efficiency of the heater of the low-temperature flash concentration system for desulfurization wastewater, aiming to improve the heat exchange efficiency of the heater of the low-temperature flash concentration system, prevent the condensate temperature from rising and boiling of the terminal water tank, improve the negative pressure stability of the system, and reduce the operating energy consumption of the low-temperature flash concentration system for desulfurization wastewater. Summary of the Invention

[0004] The purpose of the present invention is to address the above problems and provide a method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system of desulfurization wastewater.

[0005] The object of the present invention is achieved as follows: a method for improving the heat exchange efficiency of the heater of the low-temperature flash concentration system of desulfurized wastewater, the process flow is: the desulfurized wastewater is transported to the first-effect separator by a wastewater feeding pump, the first-effect forced circulation pump extracts the wastewater at the bottom of the first-effect separator to the first-effect heater, and after being heated by low-pressure raw steam, it is transported to the first-effect separator for instant flash evaporation, and the secondary steam after flash separation enters the second-effect heater as its heat source, the low-pressure raw steam condensate in the first-effect heater enters the first-stage condensate tank, and the second-effect forced circulation pump transports the wastewater at the bottom of the second-effect separator to the second-effect heater After heating in the reactor, it is transported to the second-effect separator for flash separation. The secondary steam after flash evaporation enters the triple-effect heater as its heat source. The triple-effect forced circulation pump draws the wastewater at the bottom of the triple-effect separator into the triple-effect heater for heating, and then transported to the triple-effect separator for flash separation. The secondary steam after flash evaporation enters the evaporative cooler and condenses into water, which is then merged with the condensate at the bottom of the second-effect heater and the triple-effect heater and enters the terminal condensate tank. The wastewater at the bottom of the three separators is connected through a balance pipe, and the liquid level and pressure of the three separators are automatically balanced by the negative pressure established by the terminal vacuum pump.

[0006] Exhaust systems are respectively arranged above and below the straight sections of the shells of the second-effect heater and the triple-effect heater, and the exhaust systems are connected to the secondary steam pipeline at the outlet of the triple-effect separator.

[0007] The exhaust system of the second-effect heater is specifically as follows: pipes are respectively set at the top and bottom of the shell of the second-effect heater, and a manual ball valve is installed. The upper and lower exhaust pipes are connected and then connected to the secondary steam pipe at the outlet of the three-effect separator.

[0008] The material of its exhaust pipe and valve is the same as that of the two-effect heater shell. The upper exhaust pipe is located 50 cm from the top of the heater shell, and the lower exhaust pipe is located 100 cm from the bottom of the heater shell. During operation, the upper and lower exhaust valves are fully open.

[0009] The connection method between the exhaust pipe and the heater and the secondary steam pipe at the outlet of the three-effect separator is full welding.

[0010] The exhaust system is the same for both two-effect and three-effect heaters.

[0011] A U-shaped water seal is set on the condensate pipe at the bottom of the two-effect heater and the condensate pipe at the bottom of the three-effect heater. The position of the U-shaped water seal does not require special restrictions and can be reasonably determined according to the on-site location.

[0012] The diameter of the U-shaped water seal at the bottom of the condensate pipe of the second and third effect heaters is the same as that of the connecting pipe.

[0013] The height of the U-shaped water seal of the condensate pipe at the bottom of the second and triple-effect heaters is 2-3 times the diameter of the connecting pipe, and the width of the U-shaped water seal is 1.5-2 times the diameter of the connecting pipe. The U-shaped water seal and its connecting pipe are connected with a 90° elbow, and the diameter of the elbow is the same as the diameter of the connected pipe.

[0014] The beneficial effects of the present invention are: 1. By arranging an exhaust system in the straight section of the second-effect heater and the triple-effect heater, the heat exchange efficiency of the heater is significantly improved, the steam consumption of the first-effect heater is reduced by 30%, the wastewater treatment capacity of the system is increased, the condensate temperature is stable, the terminal water tank does not boil, the system vacuum degree is improved, and the energy consumption cost is reduced.

[0015] 2. By installing a U-shaped water seal system at the bottom of the condensate outlet pipe of the second-effect heater and the third-effect heater, the water level in the heater is automatically controlled, eliminating the need to manually adjust the condensate valve opening, reducing the amount of operating operations and the difficulty of operation. In addition, the condensate delivery system has not experienced steam-water resonance, the steam heat exchange efficiency of the heater is improved, and the system vacuum is stable.

[0016] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below in conjunction with the accompanying drawings.

[0018] Figure 1 This is a flow chart of non-condensable gas exhaust and condensate U-type water seal for two-effect and three-effect heaters.

[0019] Figure 2 This is a detailed drawing of the U-shaped water seal for the condensate of the second-effect heater.

[0020] Figure 3 This is a detailed drawing of the U-shaped water seal for the condensate of the triple-effect heater.

[0021] Including: 1. First-effect heater, 2. Second-effect heater, 3. Third-effect heater, 4. First-effect separator, 5. Second-effect separator, 6. Third-effect separator, 7. Second-effect heater shell-side upper exhaust ball valve, 8. Second-effect heater shell-side lower exhaust ball valve, 9. Third-effect heater shell-side upper exhaust ball valve, 10. Third-effect heater shell-side lower exhaust ball valve, 11. Second-effect heater non-condensable gas exhaust pipe, 12. Third-effect heater non-condensable gas exhaust pipe, 13. Third-effect separator outlet secondary steam pipe, 15. Second-effect heater condensate manual ball valve, 14. Second-effect heater condensate U-shaped water seal, 16. Second-effect heater condensate U-shaped water seal, 17. Third-effect heater condensate manual ball valve, 18. Low-pressure raw steam, 19. Desulfurization wastewater, 20. Desulfurization waste liquid balance pipe, 21. First-effect forced circulation pump, 22. First-effect heater condensate, 23. Head-end condensate tank, 24. Head-end condensate pump, 25. To process water tank, 26. Second-effect forced circulation pump, 27. Third-effect forced circulation pump, 28. Evaporative cooler, 29. Terminal vacuum pump, 30. Connection to outdoor exhaust, 31. Gas-liquid separator, 32. Terminal condensate tank, 33. Terminal condensate pump. DETAILED DESCRIPTION

[0022] Low-temperature flash distillation and concentration technology is widely used in zero-discharge desulfurization wastewater systems due to its low heat source parameter requirements, high concentration ratio, no need for chemical pretreatment, high system heat transfer coefficient, excellent anti-scaling effect, high operational flexibility, and low operating costs. The zero-discharge desulfurization wastewater system for TISCO's 2×300MW units utilizes a low-temperature, three-effect flash distillation and concentration process. This process uses a vacuum pump to create a negative pressure environment. Based on the different boiling points of the desulfurization wastewater at different negative pressures, the system performs cascade flash distillation and concentration reduction within three heating and separation systems. The system's heat source is low-pressure live steam from the plant's pipeline network. The secondary steam after flash separation is cooled and recycled into the desulfurization process water tank, achieving advanced treatment and resource utilization of the desulfurization wastewater.

[0023] 1. Due to the influence of the desulfurization system process, the desulfurization wastewater contains a certain amount of non-condensable gases such as air, nitrogen, hydrogen, and carbon dioxide. After the wastewater is flash-separated in the first and second-effect separators, the secondary steam will carry the non-condensable gases into the second and third-effect heaters. Since the heaters are in a closed state, the non-condensable gases accumulate continuously during operation, which hinders the flow of steam in the heaters, reduces the heat exchange effect, reduces the wastewater treatment capacity, increases the raw steam consumption, and increases the operating costs. At the same time, if the concentration density of the heater wastewater is high, its water content is reduced, and less heat source is required. The excess steam will affect the temperature of the terminal condensate, which can easily cause the terminal water tank to boil and reduce the negative pressure of the entire low-temperature flash evaporation system.

[0024] 2. Because the condensate pipe at the bottom of the second- and third-effect heaters is connected to the terminal vacuum system via a straight pipe, the bottom condensate valve opening must be frequently adjusted during operation to control the condensate level within the heater based on changes in the condensate volume. Since the heaters lack a level gauge, operators must estimate the valve opening based on changes in wastewater treatment volume. Excessive or insufficient valve opening can cause instability in the heater's liquid level, impacting heat exchange efficiency and destabilizing the system's vacuum.

[0025] This method utilizes the negative pressure environment of the vacuum pump of the low-temperature flash evaporation system. By setting exhaust pipes at the upper and lower ends of the two-effect heater and the three-effect heater body respectively, and connecting the exhaust pipes to the terminal vacuum system through valves, the non-condensable gas is sucked into the vacuum pump and discharged into the atmosphere. The excess steam will be condensed in the evaporative cooler together with the steam at the outlet of the three-effect separator and then recycled to the terminal water production tank. On the one hand, it can improve the steam flowability in the heater and improve the heat exchange efficiency of the heater. On the other hand, the terminal water production tank will not boil. Utilizing the working principle of the U-shaped water seal, by setting a U-shaped water seal on the condensate outlet pipe at the bottom of the two-effect heater and the three-effect heater, the U-shaped water seal can effectively control the water level of the heater. On the one hand, it prevents steam from entering the terminal vacuum system along with the condensate and destroying the vacuum degree of the system. On the other hand, it can extend the heat exchange time of the steam in the heater, reduce the condensate temperature, and improve its heat exchange efficiency.

[0026] This method significantly improves heater heat exchange efficiency by installing a non-condensable gas exhaust system in the straight sections of the second-effect and third-effect heaters, reducing live steam consumption by 30%, increasing the system's wastewater treatment capacity, eliminating overboiling in the terminal water tank, improving system vacuum, and reducing energy costs. A U-shaped water seal system is installed in the condensate outlet pipes at the bottom of the second-effect and third-effect heaters to automatically control the water level in the heaters, eliminating the need for manual adjustment of the condensate valve opening and reducing operational workload and difficulty. Furthermore, steam-water resonance in the condensate delivery system is eliminated, improving heater steam heat exchange efficiency and maintaining a stable system vacuum.

[0027] A process for improving the heat exchange efficiency of the heater of the low-temperature flash concentration system of desulfurization wastewater, the process flow is as follows: the desulfurization wastewater is transported to the first-effect separator by the wastewater feed pump, the first-effect forced circulation pump draws the wastewater at the bottom of the first-effect separator to the first-effect heater for heating with low-pressure raw steam, and then transports it to the first-effect separator for instant flash evaporation, the secondary steam after flash separation enters the second-effect heater as its heat source, the low-pressure raw steam condensate in the first-effect heater enters the first-stage condensate tank, the second-effect forced circulation pump transports the wastewater at the bottom of the second-effect separator to the second-effect heater for heating, It is transported to the second-effect separator for flash separation. The secondary steam after flash evaporation enters the triple-effect heater as its heat source. The triple-effect forced circulation pump draws the wastewater at the bottom of the triple-effect separator into the triple-effect heater for heating, and then transported to the triple-effect separator for flash separation. The secondary steam after flash evaporation enters the evaporative cooler and condenses into water, which is then merged with the condensate at the bottom of the second-effect heater and the triple-effect heater and enters the terminal condensate tank. The wastewater at the bottom of the three separators is connected through a balance pipe, and the liquid level and pressure of the three separators are automatically balanced by the negative pressure established by the terminal vacuum pump.

[0028] Exhaust systems are respectively arranged above and below the straight sections of the shells of the second-effect heater and the triple-effect heater, and the exhaust systems are connected to the secondary steam pipeline at the outlet of the triple-effect separator.

[0029] The exhaust system of the second-effect heater is specifically as follows: DN25 pipes are respectively installed at the top and bottom of the shell of the second-effect heater, and a DN25 manual ball valve is installed. The upper and lower exhaust pipes are connected and then connected to the secondary steam pipe at the outlet of the three-effect separator.

[0030] The material of its exhaust pipe and valve is the same as that of the two-effect heater shell, both of which are 2205. The upper exhaust pipe is located 50 cm from the top of the heater shell, and the lower exhaust pipe is located 100 cm from the bottom of the heater shell. During operation, the upper and lower exhaust valves are fully open.

[0031] The connection method between the exhaust pipe and the heater and the secondary steam pipe at the outlet of the three-effect separator is full welding.

[0032] The exhaust system of a three-effect heater is the same as that of a two-effect heater. The exhaust system of a two-effect heater and a three-effect heater is the same. The same means that the process flow is the same, including the pipe material, pipe diameter, and valve configuration.

[0033] A U-shaped water seal is set on the condensate pipe at the bottom of the two-effect heater and the condensate pipe at the bottom of the three-effect heater. The position of the U-shaped water seal does not require special restrictions and can be reasonably determined according to the on-site location.

[0034] The diameter of the U-shaped water seal at the bottom of the condensate pipe of the second and triple-effect heaters is the same as that of its connecting pipe, that is, the diameter of the U-shaped water seal at the bottom of the second-effect heater is DN125, and the diameter of the U-shaped water seal at the bottom of the triple-effect heater is DN150, and the material of the two U-shaped water seals is the same, both 2205.

[0035] The height of the U-shaped water seal of the condensate pipe at the bottom of the second and triple-effect heaters is 3 times the diameter of the connecting pipe, and the width of the U-shaped water seal is 1.5 times the diameter of the connecting pipe. The U-shaped water seal and its connecting pipe are connected with a 90° elbow, and the diameter of the elbow is the same as the diameter of the connected pipe.

[0036] The technical solution of the present invention is as follows: a process for improving the heat exchange efficiency of heaters in a low-temperature flash concentration system for desulfurization wastewater, comprising an exhaust system and a U-shaped water seal system for two-effect and three-effect heaters.

[0037] The exhaust system of the two-effect and three-effect heaters is characterized in that the exhaust systems are respectively arranged at the upper and lower ends of the shell of the two-effect heater and the three-effect heater.

[0038] Preferably, the exhaust system technology and materials of the second-effect and third-effect heaters are the same.

[0039] The exhaust system of the two-effect heater includes an exhaust pipe and an exhaust valve. The diameter of the exhaust pipe is DN25, and the exhaust valve is a DN25 manual ball valve.

[0040] Preferably, the upper exhaust system is 50 cm away from the top of the two-effect heater shell, and the lower exhaust pipe is 100 cm away from the bottom. After the upper and lower exhaust system pipes are connected, they are connected to the secondary steam pipe at the outlet of the three-effect separator, and the full welding process is selected for the pipe connection.

[0041] The U-shaped water seal system for the condensate of the second-effect and triple-effect heaters is characterized in that U-shaped water seals are respectively set on the condensate pipe at the bottom of the shell side of the second-effect heater and the condensate pipe at the bottom of the shell side of the triple-effect heater, so as to control the water level at the bottom of the shell side of the heater and prevent uncondensed steam from entering the terminal water production tank.

[0042] Preferably, the diameter of the U-shaped water seal of the condensate water of the two-effect and three-effect heaters is the same as the diameter and material of their respective condensate water pipes, that is, the diameter of the U-shaped water seal of the condensate water at the bottom of the two-effect heater is DN125, and the diameter of the U-shaped water seal of the condensate water at the bottom of the three-effect heater is DN150, and the material of the two U-shaped water seals is the same, both are 2205 stainless steel.

[0043] Preferably, the height of the U-shaped water seal of the condensate pipe at the bottom of the two-effect and triple-effect heaters is 3 times the diameter of their respective connecting pipes, the width of the U-shaped water seal is 1.5 times the diameter of their respective connecting pipes, and the U-shaped water seal and its connecting pipe are connected with a 90° elbow, and the diameter of the elbow is the same as the diameter of the pipe to which it is connected.

[0044] The following is combined with Figure 1 and attached Figure 2 The present invention is described in further detail so that those skilled in the art can implement the invention with reference to the description.

[0045] The present invention provides a process for improving the heat exchange efficiency of heaters in a low-temperature flash distillation and concentration system for desulfurization wastewater, which comprises a three-stage heating and separation system for desulfurization wastewater, a vacuum negative pressure system, a non-condensable gas exhaust system for second- and third-effect heaters, and a U-shaped water seal system for condensate water of second- and third-effect heaters.

[0046] The three-stage heating and separation system for desulfurization wastewater mainly includes a first-effect heater (1), a first-effect separator (4), a second-effect heater (2), a second-effect separator (5), a third-effect heater (3), a third-effect separator (6), three forced circulation pumps and an evaporative cooler.

[0047] The three-stage heating and separation system for desulfurization wastewater has the following process flow: the desulfurization wastewater is conveyed to the first-effect separator via a wastewater feed pump, and then conveyed to the first-effect heater via a first-effect forced circulation pump for heating. The heat source of the first-effect heater is low-pressure live steam. After being heated, the wastewater is conveyed to the first-effect separator for flash evaporation and concentration. The secondary steam produced enters the second-effect heater as its heat source. The low-pressure live steam of the first-effect heater is condensed and then conveyed to the head end condensate tank. After passing through the head end condensate pump, it is recovered to the desulfurization process water tank. The wastewater at the bottom of the second-effect separator is conveyed to the second-effect heater via a second-effect forced circulation pump for heating. The heated wastewater is then conveyed to the second-effect separator for flash evaporation and concentration. The secondary steam at the outlet of the second-effect separator enters the third-effect heater as its heat source. The wastewater at the bottom of the third-effect separator is conveyed to the third-effect heater via a third-effect forced circulation pump for heating. The heated wastewater is then conveyed to the third-effect separator for flash evaporation and concentration. The secondary steam at the outlet of the third-effect separator is conveyed to the evaporative cooler for condensation. The condensate at the bottom of the shell of the second-effect heater and the third-effect heater and the secondary steam condensate of the third-effect separator are combined and sent to the terminal condensate tank, and then recovered to the desulfurization process water tank after passing through the terminal condensate pump.

[0048] The vacuum negative pressure system is mainly equipped with a terminal vacuum pump, which is used to provide a negative pressure environment for the three-effect low-temperature flash concentration system, reduce the boiling temperature of the desulfurization wastewater, complete the flash concentration of the heated wastewater in the three-stage separator, and maintain the liquid level balance between the three-stage separation systems.

[0049] The non-condensable gas exhaust system of the second and third effect heaters, wherein the non-condensable gas exhaust system of the second effect heater comprises: an exhaust ball valve (7) at the upper end of the shell side of the second effect heater, an exhaust ball valve (8) at the lower end of the shell side of the second effect heater, and a non-condensable gas exhaust pipe (11) of the second effect heater. The non-condensable gas exhaust system of the third effect heater comprises: an exhaust ball valve (9) at the upper end of the shell side of the third effect heater, an exhaust ball valve (10) at the lower end of the shell side of the third effect heater, and a non-condensable gas exhaust pipe (12) of the third effect heater. After the non-condensable gas exhaust pipe (11) of the second effect heater and the non-condensable gas exhaust pipe (12) of the third effect heater are merged, they are connected to the secondary steam pipe ⒀ at the outlet of the third effect separator. The pipe diameter of (11) and (12) is DN25, and the material is 2205. The size of the exhaust ball valve of (7) (8) (9) (10) is DN25. The installation positions of (7) and (9) are 50 cm away from the top of the heater shell, and the installation positions of (8) and (10) are 100 cm away from the bottom of the heater shell. The exhaust pipe and the secondary steam pipe of the three-effect separator are connected by full welding process. The manual ball valve and the pipe are connected by flange connection. In operation, the upper and lower exhaust ball valves of the two-effect and three-effect heaters are always open.

[0050] The main equipment of the second-effect and third-effect heater condensate U-shaped water seal system includes a second-effect heater condensate manual ball valve (15), a second-effect heater condensate U-shaped water seal ⒁, a third-effect heater condensate manual ball valve (17), a second-effect heater condensate U-shaped water seal (16) and connecting pipes. The valve size of (15) is DN125, the valve size of (17) is DN150, the diameter of the second-effect condensate pipe is DN125, and the diameter of the third-effect condensate pipe is DN150. After the second-effect and third-effect heater condensate valves are debugged to a fixed opening during operation, no adjustment is required during operation.

[0051] The U-shaped water seal system for the condensate of the second and third effect heaters is characterized in that the specifications of the U-shaped water seal (⒁) for the condensate of the second effect heater are as follows: the diameter of the U-shaped water seal is DN125, the material is 2205, the height of the U-shaped water seal is 3 times the diameter of the connecting pipe, and the width of the U-shaped water seal is 1.5 times the diameter of the connecting pipe. The specifications of the U-shaped water seal (16) for the condensate of the third effect heater are as follows: the diameter of the pipe is DN150, the material is 2205, the height of the U-shaped water seal is 3 times the diameter of the connecting pipe, and the width of the U-shaped water seal is 1.5 times the diameter of the connecting pipe. The U-shaped water seal and its connecting pipe are connected by a 90° elbow, and the diameter of the elbow is the same as the diameter of the connecting pipe.

[0052] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by any technician in this field within the scope of the present invention are included in the patent scope of the present invention.

Claims

1. A method for improving the heat exchange efficiency of a heater in a low-temperature flash concentration system for desulfurization wastewater, characterized by: The process flow is as follows: the desulfurization wastewater is transported to the first-effect separator by the wastewater feed pump, the first-effect forced circulation pump draws the wastewater at the bottom of the first-effect separator to the first-effect heater for heating with low-pressure raw steam, and then transports it to the first-effect separator for instant flash evaporation. The secondary steam after flash separation enters the second-effect heater as its heat source, and the low-pressure raw steam condensate in the first-effect heater enters the first-section condensate tank. The second-effect forced circulation pump transports the wastewater at the bottom of the second-effect separator to the second-effect heater for heating, and then transports it to the second-effect separator for flash separation. The secondary steam after flash evaporation enters the third-effect heater as its heat source. The third-effect forced circulation pump draws the wastewater at the bottom of the third-effect separator to the third-effect heater for heating, and then transports it to the third-effect separator for flash separation. The secondary steam after flash evaporation enters the evaporative cooler and condenses into water, and then merges with the condensate at the bottom of the second-effect heater and the third-effect heater and enters the terminal condensate tank. The wastewater at the bottom of the three separators is connected through a balance pipe, and the liquid level and pressure of the three separators are automatically maintained in balance by the negative pressure established by the terminal vacuum pump.

2. The method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system for desulfurization wastewater according to claim 1, characterized in that: Exhaust systems are respectively arranged above and below the straight sections of the shells of the second-effect heater and the triple-effect heater, and the exhaust systems are connected to the secondary steam pipeline at the outlet of the triple-effect separator.

3. The method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system for desulfurization wastewater according to claim 2, characterized in that: The exhaust system of the second-effect heater is specifically as follows: pipes are respectively set at the top and bottom of the shell of the second-effect heater, and a manual ball valve is installed. The upper and lower exhaust pipes are connected and then connected to the secondary steam pipe at the outlet of the three-effect separator.

4. The method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system for desulfurization wastewater according to claim 3, characterized in that: The material of its exhaust pipe and valve is the same as that of the two-effect heater shell. The upper exhaust pipe is located 50 cm from the top of the heater shell, and the lower exhaust pipe is located 100 cm from the bottom of the heater shell. During operation, the upper and lower exhaust valves are fully open.

5. The method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system for desulfurization wastewater according to claim 4, characterized in that: The connection method between the exhaust pipe and the heater and the secondary steam pipe at the outlet of the three-effect separator is full welding.

6. The method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system for desulfurization wastewater according to claim 2, characterized in that: The exhaust system is the same for both two-effect and three-effect heaters.

7. The method for improving the heat exchange efficiency of a heater in a low-temperature flash concentration system for desulfurization wastewater according to claim 1, characterized in that: A U-shaped water seal is set on the condensate pipe at the bottom of the two-effect heater and the condensate pipe at the bottom of the three-effect heater. The position of the U-shaped water seal does not require special restrictions and can be reasonably determined according to the on-site location.

8. The method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system for desulfurization wastewater according to claim 7, characterized in that: The diameter of the U-shaped water seal at the bottom of the condensate pipe of the second and third effect heaters is the same as that of the connecting pipe.

9. The method for improving the heat exchange efficiency of the heater in the low-temperature flash concentration system for desulfurization wastewater according to claim 8, characterized in that: The height of the U-shaped water seal of the condensate pipe at the bottom of the second and triple-effect heaters is 2-3 times the diameter of the connecting pipe, and the width of the U-shaped water seal is 1.5-2 times the diameter of the connecting pipe. The U-shaped water seal and its connecting pipe are connected with a 90° elbow, and the diameter of the elbow is the same as the diameter of the connected pipe.

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