An antifreeze water cooling system and method for an offshore flexible DC transmission converter station

Abstract

The present invention relates to an antifreeze water cooling system and method for an offshore flexible direct current transmission converter station, comprising: a seawater circulation module is connected to a freshwater circulation module through a first heat exchanger; the freshwater circulation module is connected to a valve cooling circulation module through a second heat exchanger; in the seawater circulation module, seawater flows into the first converter through a seawater pump, flows into the sea after heat exchange, and a drain hole is arranged on the pipeline between the seawater pump and the first heat exchanger; the freshwater circulation module comprises a circulation pipeline connecting the first heat exchanger and the second heat exchanger, and a bypass valve connected in parallel with the first heat exchanger is arranged beside the first heat exchanger; the valve cooling circulation module comprises a converter valve assembly and a three-way valve connected to the output end of the second heat exchanger, the converter valve assembly is connected to one end of the three-way valve, the other end of the three-way valve is connected to the input end of the second heat exchanger, and the third end of the three-way valve is connected to the pipeline between the converter valve assembly and the output end of the second heat exchanger. The reliability of the operation of the water cooling system and the cooled components is improved.

Description

Technical Field

[0001] The invention relates to an antifreeze water cooling system and method for an offshore flexible direct current transmission converter station, belongs to the field of direct current transmission, and particularly relates to water cooling equipment for an offshore flexible direct current transmission converter station. Background Art

[0002] With the increasing power consumption of offshore operations and the deep development of the ocean, power transmission from land to offshore platforms can no longer meet the needs of offshore operations, so offshore power transmission converter stations have emerged. Flexible DC transmission is widely used in offshore power transmission converter stations because it can realize the self-closing and opening of the converter valve, has no requirements for the short-circuit capacity of the receiving power grid, has no commutation failure problem, and has flexible control.

[0003] At present, from a global perspective, offshore flexible DC transmission converter stations are mainly concentrated in the North Sea region of Europe, where the temperature in winter is generally below zero degrees Celsius, which leads to freezing of pipes in the cooling system of offshore flexible DC transmission converter stations, as well as low cooling water temperature, and condensation may occur on the surface of the pipes, thus posing a major safety hazard to the operation of the converter station. From the actual situation in my country, offshore flexible DC transmission converter stations also have the problem of ambient temperature dropping below zero in winter. Therefore, the water cooling system must not only consider the maximum heat dissipation capacity of the heat dissipation equipment under the highest temperature conditions, but also ensure that the water cooling system and pipes do not freeze or condense under low temperature and low load, causing damage to the equipment or affecting the normal operation of the system. Summary of the invention

[0004] In view of the above problems, the object of the present invention is to provide an antifreeze water cooling system and method for an offshore flexible DC transmission converter station, which can prevent the freezing of external pipes of the water cooling system and improve the reliability of the operation of the water cooling system and the cooled components.

[0005] In order to achieve the above-mentioned purpose, the present invention proposes the following technical scheme: an antifreeze water cooling system for an offshore flexible DC transmission converter station, comprising: a seawater circulation module, a fresh water circulation module, a valve cooling circulation module, a first heat exchanger and a second heat exchanger; the seawater circulation module is connected to the fresh water circulation module through the first heat exchanger; the fresh water circulation module is connected to the valve cooling circulation module through the second heat exchanger; seawater in the seawater circulation module flows into the first converter through a seawater pump, flows into the sea after heat exchange, and a drain hole is arranged on the pipeline between the seawater pump and the first heat exchanger The fresh water circulation module includes a circulation pipeline connecting the first heat exchanger and the second heat exchanger, and a bypass valve connected in parallel with the first heat exchanger is arranged beside the first heat exchanger; the valve cooling circulation module includes a converter valve assembly and a three-way valve connected to the output end of the second heat exchanger, the converter valve assembly is connected to one end of the three-way valve, the other end of the three-way valve is connected to the input end of the second heat exchanger, and the third end of the three-way valve is connected to the pipeline between the converter valve assembly and the output end of the second heat exchanger; the temperature of the cooling water in the water cooling system is controlled by adjusting the opening of the drain hole, the bypass valve and the three-way valve.

[0006] Furthermore, the seawater circulation module also includes a seawater filter for filtering impurities in the seawater, and the seawater filter is arranged between the drain hole and the input end of the first heat exchanger.

[0007] Furthermore, the valve cooling circulation module also includes a degassing tank, which is arranged between the converter valve assembly and the three-way valve. A heater is arranged in the degassing tank to heat the cooling water in the pipeline.

[0008] Furthermore, a filter is provided on the pipeline between the flow conversion valve assembly and the output end of the second heat exchanger, and the third end of the three-way valve is connected to the input end of the filter.

[0009] Furthermore, there are two three-way valves, which are connected in parallel, and there are two filters, which are connected in parallel.

[0010] Furthermore, a heating and insulation layer is laid on the pipeline between the converter valve assembly and the output end of the second heat exchanger.

[0011] Furthermore, the heating and insulation layer includes a conductive busbar, a conductive polymer, an insulating layer, a shielding layer and a protective outer sheath. The conductive busbar is the innermost layer, and its outer layer is coated with a conductive polymer. An insulating layer is coated on the outer layer of the conductive polymer. A shielding layer is coated outside the insulating layer, and a protective outer sheath is arranged outside the shielding layer.

[0012] The present invention also discloses an antifreeze water cooling method for an offshore flexible direct current transmission converter station, which adopts any of the above-mentioned antifreeze water cooling systems for an offshore flexible direct current transmission converter station, comprising: if the seawater temperature is lower than a set value, stopping the running seawater pumps one by one, and testing the cooling water temperature in the valve, if it remains stable, the seawater pumps will no longer be stopped, and the stopped seawater pumps will be restored after the seawater temperature returns to normal; if only the last seawater pump is left running, but the cooling water temperature in the valve is still lower than the set value, opening the bypass valve to adjust the flow of the fresh water circulation module through the first radiator; if the bypass valves are all opened, but the cooling water temperature in the valve is still lower than the set value, adjusting the three-way valve to adjust the water temperature in the pipeline; if the three-way valves are all closed, and the cooling water temperature in the valve is still lower than the set value, starting the heater to heat the cooling water in the pipeline; if the heater has reached the maximum power, and the cooling water temperature in the valve is still lower than the set value, starting the heating and insulation layer laid on the pipeline to ensure that the circulating water temperature in the valve is higher than the condensation temperature.

[0013] Furthermore, when the converter valve stops operating, all seawater pumps stop operating, the drain holes are automatically activated, and the seawater in all pipes is drained; the fresh water circulation module remains in operation, and the bypass valve is closed; the valve cooling circulation module remains in operation, and the three-way valve, heater and heating insulation layer are adjusted to make the circulating water temperature in the valve higher than the condensation temperature.

[0014] Furthermore, the control method of the three-way valve is as follows: when the cooling water inlet valve temperature is in the high temperature section, the three-way valve is in a fully open state to ensure that all cooling water passes through the second heat exchanger; when the cooling water inlet valve temperature is in the medium temperature section, the valve opening of the three-way valve is controlled by the PLC, and the flow ratio of the fresh water circulation module and the valve cold circulation module is adjusted by controlling the valve opening of the three-way valve to keep the cooling water inlet valve temperature between 20°C and 25°C; when the cooling water inlet valve temperature is in the low temperature section, the three-way valve is in a closed state.

[0015] Due to the adoption of the above technical scheme, the present invention has the following advantages: the scheme in the present invention can effectively prevent the freezing of the external pipes of the water cooling system; it can control the medium of the three-circulation water cooling system to operate in the optimal temperature range, and can improve the reliability of the operation of the water cooling system and the cooled components. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of an antifreeze water cooling system for an offshore flexible DC transmission converter station in one embodiment of the present invention;

[0017] Figure 2 is a schematic structural diagram of a valve internal circulation module in one embodiment of the present invention;

[0018] Figure 3 It is a schematic structural diagram of a heat tracing and thermal insulation layer in one embodiment of the present invention.

[0019] Reference numerals:

[0020] 1-seawater circulation module; 2-fresh water circulation module; 3-valve cooling circulation module; 4-seawater pump; 5-drain hole; 6-bypass valve; 7-first water pump; 8-filter; 9-converter valve assembly; 10-degassing tank; 11-second water pump; 12-three-way valve; 13-heater; 14-heating insulation layer; 141-conductive busbar; 142-conductive polymer; 143-insulating layer; 144-shielding layer; 145-protective outer sheath. DETAILED DESCRIPTION

[0021] In order to make those skilled in the art better understand the technical direction of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the provision of specific embodiments is only for a better understanding of the present invention, and they should not be understood as limitations of the present invention. In the description of the present invention, it should be understood that the terms used are only for the purpose of description and cannot be understood as indicating or suggesting relative importance.

[0022] In order to overcome the technical problems in the prior art that the pipes of the water cooling system of the offshore flexible DC transmission converter station are easy to freeze, and the cooling water temperature is low, and condensation may occur on the pipe surface, an antifreeze water cooling system and method for the offshore flexible DC transmission converter station is proposed, which adjusts the temperature of the cooling water in the entire water cooling system by setting a drain hole in the seawater circulation module, setting a bypass valve in the fresh water circulation module, and setting a three-way valve, a heater 13 and a heating insulation layer 14 in the valve circulation module, so that it can work within the optimal temperature, prevent the freezing of the pipes caused by too low temperature, or the condensation on the pipe surface, and effectively improve the reliability of the operation of the water cooling system and the cooled components. The technical solution of the present invention is described in detail below through embodiments in conjunction with the accompanying drawings.

[0023] Embodiment 1

[0024] Figure 1 : is a schematic diagram of the structure of the antifreeze water cooling system of the offshore flexible DC transmission converter station in this embodiment. Figure 1 As shown, the antifreeze water cooling system of the offshore flexible DC transmission converter station includes: a seawater circulation module 1, a freshwater circulation module 2, a valve cooling circulation module 3, a first heat exchanger and a second heat exchanger; the seawater circulation module 1 is connected to the freshwater circulation module 2 through the first heat exchanger; the freshwater circulation module 2 is connected to the valve cooling circulation module 3 through the second heat exchanger. In this embodiment, the first heat exchanger and the second heat exchanger are both plate heat exchangers, but other types of heat exchangers can also be selected as needed, and are not limited to this.

[0025] Among them, the seawater in the seawater circulation module 1 flows into the seawater circulation pipeline through the seawater pump 4, and passes through the seawater filter to filter impurities in the seawater to avoid pipeline blockage. The seawater enters the first converter, and after the conversion in the first converter, it absorbs the heat generated by the valve group and flows back to the sea from the pipeline at the output end of the first converter. A drain hole 5 is set on the pipeline between the seawater pump 4 and the first heat exchanger. When the converter valve stops working, the seawater pump 4 stops working, and the drain hole 5 is automatically activated to drain the seawater in all pipelines to increase the cooling water temperature in the water cooling system. The drain hole 5 may be blocked by sediment, and the aperture of the drain hole 5 can be increased, or a filter can be set at the position of the drain hole 5.

[0026] In this embodiment, there are multiple seawater pumps 4, which are configured in N+1 redundancy, i.e., N+1 seawater pumps 4, of which N seawater pumps 4 are put into use and 1 seawater pump 4 is in standby. When it is detected that the ambient temperature is too cold, the cooling water temperature in the water cooling system is detected. If the cooling water temperature is too low, the number of seawater pumps 4 in operation is reduced, the flow rate of the seawater circulation system flowing through the first heat exchanger is reduced, the heat dissipation of the system is reduced, and the cooling water circulation temperature is increased until the cooling water temperature no longer decreases.

[0027] The fresh water circulation module 2 includes a circulation pipeline connecting the first heat exchanger and the second heat exchanger. A bypass valve 6 connected in parallel with the first heat exchanger is arranged beside the first heat exchanger, which is used to adjust the flow of the fresh water circulation module 2 through the first radiator when all seawater pumps 4 have stopped operating but the temperature of the cooling water in the valve continues to decrease, thereby reducing the heat dissipation of the system and increasing the temperature of the fresh water circulation. A first water pump 7 is arranged on the pipeline between the first heat exchanger and the second heat exchanger to provide power for the flow of cooling water.

[0028] Figure 2 Schematic diagram of the structure of the valve internal circulation module in this embodiment. Figure 2 As shown, the valve cooling cycle module 3 includes a filter 8, a converter valve assembly 9, a degassing tank 10, a second water pump 11 and a three-way valve 12 connected to the output end of the second heat exchanger. The cooling water enters the filter 8, the converter valve assembly 9, the degassing tank 10 and the second water pump 11 in sequence through the output end of the second converter valve, and enters the input end of the second converter valve through the three-way valve 12 to form a circulation loop. The converter valve assembly 9 is connected to one end of the three-way valve 12, and the other end of the three-way valve 12 is connected to the input end of the second heat exchanger. The third end of the three-way valve 12 is connected to the pipeline between the converter valve assembly 9 and the output end of the second heat exchanger. The control method of the three-way valve 12 is: when the cooling water inlet valve temperature is in the medium temperature section, the flow rate of the cooling medium flowing through the outdoor heat exchanger is changed by opening / closing the electric three-way valve 12, thereby changing the heat dissipation of the system, and finally stabilizing the cooling water inlet valve temperature within the working temperature range of the electric three-way valve 12.

[0029] When the cooling water inlet valve temperature is higher than 25℃, the three-way valve 12 is fully open to ensure that all cooling water passes through the second heat exchanger; when the cooling water inlet valve temperature is between 20℃ and 25℃, the valve opening of the three-way valve 12 is controlled by the PLC, and the flow ratio of the fresh water circulation module and the valve cold circulation module is adjusted by controlling the valve opening of the three-way valve 12 to keep the cooling water inlet valve temperature between 20℃ and 25℃; when the cooling water inlet valve temperature is lower than 20℃, the three-way valve 12 is in a closed state. The opening and closing of the three-way valve 12 is determined by the PLC controller to find the set temperature working range, and it uses a pulse signal for opening and closing. When the three-way valve 12 fails, an alarm signal is issued and the spare three-way valve 12 is started.

[0030] A heater 13 is provided in the degassing tank 10 to heat the cooling water in the pipeline. When the cooling water temperature drops to the start setting value of the heater 13 or approaches the dew point, the heater 13 is started to prevent the cooling water inlet valve temperature from being too low, causing damage to the pipelines and cooled devices along the way and condensation.

[0031] A heat tracing and heat-insulating layer 14 is laid on the pipeline between the converter valve assembly 9 and the output end of the second heat exchanger, especially on the pipeline between the filter 8 and the converter valve assembly 9. The heat tracing and heat-insulating layer 14 can be electrically heated by the control system when the ambient temperature is low. Preferably, a self-limiting temperature electric heating belt is used. The structure is as follows: Figure 3 As shown, it includes two parallel conductive busbars 141, conductive polymer 142, insulating layer 143, shielding layer 144 and protective outer sheath 145. The conductive busbar 141 is the innermost layer, and its outer layer is coated with conductive polymer 142. The outer layer of conductive polymer 142 is coated with insulating layer 143. The shielding layer 144 is coated outside the insulating layer 143. The protective outer sheath 145 is arranged outside the shielding layer 144. The conductive polymer 142 has a very high positive temperature coefficient characteristic, that is, PTC characteristic, which can automatically adjust the output power and automatically limit the heating temperature as the temperature of the heated system changes. It allows multiple cross-overlaps without the worry of high temperature hot spots and burning. The self-limiting temperature heating cable has the following advantages: the self-limiting temperature electric heating cable has automatic output power, will not burn due to excessive heating temperature, can start quickly at low temperature, and has uniform temperature. Each part can automatically adjust according to the temperature change of the heated part; it is easy to install, simple to maintain, and can provide all-day service, with high automation level, low operation and maintenance costs, no pollution, and long service life.

[0032] The filter 8, the second water pump 11 and the three-way valve 12 are each provided with two groups, which are connected in parallel, one group is put into use and the other group is standby, so that when one group of equipment fails, the system can still operate normally.

[0033] Embodiment 2

[0034] Based on the same inventive concept, this embodiment discloses an antifreeze water cooling method for an offshore flexible DC transmission converter station, using any of the above-mentioned antifreeze water cooling systems for an offshore flexible DC transmission converter station, including:

[0035] During normal operation, if the seawater temperature is lower than the set value, the running seawater pumps 4 are stopped one by one, and the cooling water temperature in the valve is tested. If it remains stable, the seawater pumps 4 are no longer stopped. When the seawater temperature returns to normal, the stopped seawater pumps 4 are resumed.

[0036] If only the last seawater pump 4 is running, but the cooling water temperature in the valve is still lower than the set value, the bypass valve 6 is opened to adjust the flow of the fresh water circulation module 2 through the first radiator;

[0037] If the bypass valve 6 is fully opened so that half of the cooling water does not pass through the first heat exchanger, but the cooling water temperature in the valve is still lower than the set value, the three-way valve 12 is adjusted to adjust the water temperature in the pipeline;

[0038] If the three-way valve 12 is completely closed and the cooling water temperature in the valve is still lower than the set value, the heater 13 is turned on to heat the cooling water in the pipeline;

[0039] If the heater 13 has reached the maximum power and the cooling water temperature in the valve is still lower than the set value, the heating and insulation layer 14 laid on the pipeline is started to ensure that the circulating water temperature in the valve is higher than the condensation temperature.

[0040] When the converter valve stops operating, all seawater pumps 4 stop operating, the drain hole 5 is automatically activated, and all seawater in the pipeline is drained to prevent the low-temperature seawater from freezing the pipeline; the fresh water circulation module 2 remains in operation, and the bypass valve 6 is closed; the valve cooling circulation module 3 remains in operation, and the three-way valve 12, heater 13 and heating insulation layer 14 are adjusted to make the circulating water temperature in the valve higher than the condensation temperature. The method of adjusting the three-way valve 12, heater 13 and heating insulation layer 14 is the same as that in normal operation, and will not be repeated here.

[0041] The control method of the three-way valve 12 is as follows: when the cooling water inlet valve temperature is in the high temperature section, the three-way valve 12 is in a fully open state to ensure that all cooling water passes through the second heat exchanger; when the cooling water inlet valve temperature is in the medium temperature section, the valve opening of the three-way valve 12 is controlled by the PLC, and the flow ratio of the fresh water circulation module and the valve cold circulation module is adjusted by controlling the valve opening of the three-way valve 12 to keep the cooling water inlet valve temperature between 20°C and 25°C; when the cooling water inlet valve temperature is in the low temperature section, the three-way valve 12 is in a closed state.

[0042] Among them, the high temperature section refers to the situation that is higher than or close to room temperature. In this embodiment, above 25°C is selected as the high temperature section. The specific temperature of the room temperature can be adjusted according to the ambient temperature and season, but is not limited to this; the medium temperature section refers to the transition temperature section between the high temperature section and the low temperature section. In this embodiment, it is preferably 20°C-25°C. The low temperature section refers to the temperature section where there is a risk of freezing and condensation. In this embodiment, it is preferably below 20°C.

[0043] When the inlet valve temperature drops to the start setting value of the heater 13 or approaches the dew point, the heater 13 is started to prevent the cooling water inlet valve temperature from being too low to cause damage to the pipelines and cooled devices along the way and condensation.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention should be included in the protection scope of the claims of the present invention. The above content is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. An antifreeze water cooling system for an offshore flexible DC transmission converter station, characterized in that: include: A seawater circulation module, a fresh water circulation module, a valve cooling circulation module, a first heat exchanger and a second heat exchanger; The seawater circulation module is connected to the fresh water circulation module through the first heat exchanger; the fresh water circulation module is connected to the valve cooling circulation module through the second heat exchanger; The seawater circulation module comprises a seawater pump, through which seawater flows into the first heat exchanger and then flows into the sea after heat exchange, and a drain hole is arranged on the pipeline between the seawater pump and the first heat exchanger; The fresh water circulation module comprises a circulation pipeline connecting the first heat exchanger and the second heat exchanger, and a bypass valve connected in parallel with the first heat exchanger is arranged beside the first heat exchanger; The valve cooling cycle module comprises a converter valve assembly and a three-way valve connected to the output end of the second heat exchanger, the converter valve assembly is connected to one end of the three-way valve, the other end of the three-way valve is connected to the input end of the second heat exchanger, and the third end of the three-way valve is connected to the pipeline between the converter valve assembly and the output end of the second heat exchanger; Controlling the temperature of cooling water in the water cooling system by adjusting the opening of the drain hole, the bypass valve and the three-way valve; There are at least two seawater pumps in operation. If the seawater temperature is lower than the set value, stop the running seawater pumps one by one and test the cooling water temperature in the valve. If it remains stable, stop stopping the seawater pumps. When the seawater temperature returns to normal, resume the stopped seawater pumps. The control method of the three-way valve is: When the cooling water inlet valve temperature is in the high temperature range, the three-way valve is fully opened to ensure that all cooling water passes through the second heat exchanger; When the cooling water inlet valve temperature is in the medium temperature range, the valve opening of the three-way valve is controlled by the PLC. By controlling the valve opening of the three-way valve, the cooling water inlet valve temperature is kept between 20℃ and 25℃. When the cooling water inlet valve temperature is in the low temperature range, the three-way valve is in the closed state.

2. The antifreeze water cooling system for the offshore flexible DC transmission converter station according to claim 1, characterized in that: The seawater circulation module further includes a seawater filter for filtering impurities in the seawater, and the seawater filter is arranged between the drain hole and the input end of the first heat exchanger.

3. The antifreeze water cooling system for the offshore flexible DC transmission converter station according to claim 1 or 2, characterized in that: The valve cooling circulation module also includes a degassing tank, which is arranged between the converter valve assembly and the three-way valve. A heater is arranged in the degassing tank to heat the cooling water in the pipeline.

4. The antifreeze water cooling system for the offshore flexible DC transmission converter station according to claim 1 or 2, characterized in that: A filter is also provided on the pipeline between the flow conversion valve assembly and the output end of the second heat exchanger, and the third end of the three-way valve is connected to the input end of the filter.

5. The antifreeze water cooling system for the offshore flexible DC transmission converter station according to claim 4, characterized in that: There are two three-way valves, which are connected in parallel; there are also two filters, which are connected in parallel.

6. The antifreeze water cooling system for the offshore flexible DC transmission converter station according to claim 1 or 2, characterized in that: A heat tracing and insulation layer is laid on the pipeline between the output ends of the converter valve assembly and the second heat exchanger.

7. The antifreeze water cooling system for the offshore flexible DC transmission converter station according to claim 6, characterized in that: The heating and insulation layer includes a conductive busbar, a conductive polymer, an insulating layer, a shielding layer and a protective outer sheath. The conductive busbar is the innermost layer, and the outer layer thereof is coated with a conductive polymer. The outer layer of the conductive polymer is coated with an insulating layer, and the shielding layer is coated outside the insulating layer. A protective outer sheath is arranged outside the shielding layer.

8. A method for antifreeze water cooling of an offshore flexible DC transmission converter station, characterized in that: The antifreeze water cooling system for an offshore flexible DC transmission converter station as claimed in any one of claims 1 to 7 comprises: There are at least two seawater pumps in operation. If the seawater temperature is lower than the set value, stop the running seawater pumps one by one and test the cooling water temperature in the valve. If it remains stable, stop stopping the seawater pumps. When the seawater temperature returns to normal, resume the stopped seawater pumps. If only the last seawater pump is left running, but the cooling water temperature in the valve is still lower than the set value, the bypass valve is opened to adjust the flow of the fresh water circulation module through the first radiator; If the bypass valves are fully opened, but the cooling water temperature in the valve is still lower than the set value, the three-way valve is adjusted to adjust the temperature of the cooling water in the circulation module in the valve; If the three-way valves are all closed and the cooling water temperature in the valve is still lower than the set value, the heater is turned on to heat the cooling water in the pipeline; If the heater has reached the maximum power, the cooling water temperature in the valve is still lower than the set value, start the heating insulation layer laid on the pipeline to ensure that the temperature of the cooling water in the circulation module in the valve is higher than the condensation temperature.

9. The antifreeze water cooling method for an offshore flexible DC transmission converter station according to claim 8, characterized in that: When the converter valve stops operating, All seawater pumps are stopped, and the drain holes are automatically activated to drain the seawater in the seawater circulation module; The fresh water circulation module remains in operation and the bypass valve is closed; The valve cooling circulation module keeps running, and adjusts the three-way valve, heater and heating insulation layer to make the circulating water temperature in the valve higher than the condensation temperature.

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