A freeze protection system and control method for molten salt heat exchangers and piping

Abstract

The application discloses a kind of freeze-proof system and control method for molten salt heat exchange equipment and pipeline, by setting up reverse warm pipeline on existing steam circulation pipeline, and sequentially setting up liquid storage unit, circulating pump, molten salt heat exchange unit and steam energy storage unit on reverse warm pipeline, circulating liquid in liquid storage unit enters molten salt heat exchange unit under the action of circulating pump, and forms heat tracing steam with molten salt heat exchange that is introduced from outside molten salt storage tank, and is stored to steam energy storage unit. When needing heat tracing, steam in steam energy storage unit is led out to existing steam circulation pipeline, and the heat exchange capacity of steam molten salt heat exchange equipment itself is used to heat trace molten salt, so as to maintain molten salt above condensation temperature. Only residual thermal energy in external molten salt storage tank is consumed, and operation is stable and reliable, solve the problem of large energy consumption and low reliability of existing electric heat tracing system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solar thermal power generation, and particularly relates to a freeze-proof system for molten salt heat exchange equipment and pipelines and a control method. BACKGROUND

[0002] In a solar thermal power generation project, molten salt (binary salt) is used as a heat storage medium, and the working temperature is above the solidification temperature of the molten salt. To prevent the liquid molten salt working medium from solidifying during transportation and storage, a commonly used method is to lay an electric heat tracing between the outer surface of the molten salt pipeline and the heat preservation layer, and to heat the molten salt heat exchange equipment through the electric heat tracing to offset the heat loss of the molten salt heat exchange equipment from the outside, so as to ensure that the temperature of the molten salt in the heat exchange equipment is above the solidification temperature.

[0003] The electric heat tracing system can be automatically adjusted through temperature monitoring, but has the disadvantages of high power consumption and high failure rate, resulting in a decrease in the overall efficiency of the system and an increase in the forced shutdown maintenance time. Therefore, a more reliable freeze-proof system is urgently needed in the field of molten salt heat storage and exchange of solar thermal power generation.

[0004] The main disadvantages of electric heat tracing for molten salt heat exchange equipment are as follows: 1. The molten salt working medium temperature is in a repeated cycle of heating and cooling with the start and stop of the unit, and thermal expansion and contraction can easily cause damage to the insulation layer; 2. Frequent operation of electrical components can reduce reliability, and the on-site maintenance workload is large; and 3. Unreasonable arrangement of electric heat tracing can cause local metal overheating and accelerate the creep rate of the metal. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a freeze-proof system for molten salt heat exchange equipment and pipelines and a control method, so as to solve the problems of high energy consumption and low reliability of the existing electric heat tracing system.

[0006] To solve the above problems, the technical scheme of the present application is as follows:

[0007] The freeze-proof system for molten salt heat exchange equipment and pipelines of the present application is used to provide a reverse warm steam to a steam circulation pipeline of an external solar power generation system, and comprises:

[0008] A reverse warm pipeline, a steam output end of the reverse warm pipeline is communicated with the steam circulation pipeline and is located upstream of a first steam molten salt heat exchange equipment in a medium flow direction on the steam circulation pipeline; and a backwater end of the reverse warm pipeline is communicated with the steam circulation pipeline and is located downstream of a last steam molten salt heat exchange equipment in the medium flow direction on the steam circulation pipeline;

[0009] Wherein, a liquid storage unit, a circulating pump, a molten salt heat exchange unit and a steam energy storage unit are sequentially arranged on the reverse warm pipeline; a temperature regulating pump is arranged at a molten salt input end of the molten salt heat exchange unit, and the molten salt input end is communicated with a molten salt storage tank of the external solar power generation system.

[0010] The control unit is connected with the temperature regulating pump and the circulating pump, and is used for controlling the temperature regulating pump and the circulating pump.

[0011] The anti-freezing system for the molten salt heat exchange equipment and pipeline of the application, the return water pipeline, the water delivery pipeline, the steam input pipeline and the steam output pipeline are included in the reverse warm pipeline;

[0012] The input end of the return water pipeline is communicated with the steam circulation pipeline and is located downstream of the steam molten salt heat exchange equipment at the end of the medium flow direction on the steam circulation pipeline; the output end of the return water pipeline is communicated with the input end of the liquid storage unit;

[0013] The two ends of the water delivery pipeline are respectively communicated with the output end of the liquid storage unit and the water working medium input end of the molten salt heat exchange unit;

[0014] The two ends of the steam input pipeline are respectively communicated with the steam output end of the molten salt heat exchange unit and the steam input end of the steam storage unit;

[0015] The input end of the steam output pipeline is communicated with the steam output end of the steam storage unit; the output end of the steam output pipeline is communicated with the steam circulation pipeline and is located upstream of the first steam molten salt heat exchange equipment at the beginning of the medium flow direction on the steam circulation pipeline.

[0016] The anti-freezing system for the molten salt heat exchange equipment and pipeline of the application, the steam circulation pipeline includes a superheater branch and a reheater branch which are independent of each other;

[0017] The return water pipeline is a first return water pipeline and a second return water pipeline; the two ends of the first return water pipeline are respectively communicated with the output end of the superheater branch and the input end of the liquid storage unit; the two ends of the second return water pipeline are respectively communicated with the output end of the reheater branch and the input end of the liquid storage unit;

[0018] The first return water pipeline and the second return water pipeline are respectively provided with a first return water valve and a second return water valve.

[0019] The anti-freezing system for the molten salt heat exchange equipment and pipeline of the application, the steam input end and the steam output end of the steam storage unit are a steam connection port located on the steam storage unit;

[0020] The steam input pipeline includes a first steam section and a second steam section which are connected in sequence; the leading end of the first steam section is communicated with the steam output end of the molten salt heat exchange unit; the trailing end of the second steam section is communicated with the steam connection port;

[0021] The steam output pipeline includes a second steam section and a third steam section; the first end of the third steam section is connected to the first end of the second steam section, and the last end of the third steam section is connected to the steam circulation pipeline and is located upstream of the first steam molten salt heat exchanger in the medium flow direction of the steam circulation pipeline.

[0022] The first steam section is equipped with a first steam valve, and the second steam section is equipped with a second steam valve.

[0023] The present invention provides an antifreeze system for molten salt heat exchange equipment and pipelines, wherein the steam output pipeline further includes a first steam branch and a second steam branch; the two ends of the first steam branch are respectively connected to the tail end of the third steam section and the input end of the superheater branch; the two ends of the second steam branch are respectively connected to the tail end of the third steam section and the input end of the reheater branch.

[0024] The first steam branch is equipped with a superheated steam valve, and the second steam branch is equipped with a reheated steam valve.

[0025] The present invention provides an antifreeze system for molten salt heat exchange equipment and pipelines, wherein a superheater, a steam drum, an evaporator and a preheater are sequentially arranged on the superheater branch.

[0026] The present invention provides an antifreeze system for molten salt heat exchange equipment and pipelines, wherein the molten salt heat exchange unit includes an auxiliary heat exchanger, a first molten salt pipeline, and a second molten salt pipeline;

[0027] The input end of the first molten salt pipeline is connected to the molten salt storage tank, the output end of the first molten salt pipeline is connected to the molten salt inlet of the auxiliary heat exchanger, and the temperature regulating pump is provided on the first molten salt pipeline;

[0028] The input end of the second molten salt pipeline is connected to the molten salt outlet of the auxiliary heat exchanger, and the output end of the second molten salt pipeline is connected to the corresponding molten salt storage tank.

[0029] The antifreeze system for molten salt heat exchange equipment and pipelines of the present invention further includes a third molten salt pipeline;

[0030] A first molten salt valve is provided on the first molten salt pipeline, and the first molten salt valve is located downstream of the temperature regulating pump;

[0031] The input end of the third molten salt pipeline is connected to the first molten salt pipeline and is located between the temperature regulating pump and the first molten salt valve; the output end of the third molten salt pipeline is connected to the salt inlet header of the external solar power generation system.

[0032] The antifreeze system for molten salt heat exchange equipment and pipelines of the present invention further includes a drainage pipe;

[0033] The inlet of the condensate drain pipe is connected to the bottom of the steam energy storage unit, the outlet of the condensate drain pipe is connected to the inlet of the liquid storage unit, and a condensate drain valve is provided on the condensate drain pipe.

[0034] The present invention provides an antifreeze system for molten salt heat exchange equipment and pipelines, wherein the liquid storage unit is equipped with a level gauge and a first thermometer, and the steam energy storage unit is equipped with a pressure gauge, and the level gauge, the first thermometer and the pressure gauge are all signal connected to the control unit.

[0035] The antifreeze system for molten salt heat exchange equipment and pipelines of the present invention further includes a second thermometer for detecting the temperature of the molten salt side outlet of the end steam molten salt heat exchange equipment;

[0036] The control unit is configured to activate the temperature regulating pump when the temperature detected by the second thermometer is lower than a preset temperature, thereby driving the molten salt in the molten salt storage tank of the external solar power generation system to replace the original molten salt in the system.

[0037] One control method of the present invention, applied to the antifreeze system for molten salt heat exchange equipment and pipelines as described in any one of the above claims, is as follows:

[0038] When the external solar power generation system reduces its load: the temperature regulating pump and the circulation pump start, and the steam energy storage unit stores energy to the preset energy storage pressure;

[0039] When the external solar power generation system is shut down: monitor the temperature of the molten salt outlet of the end steam molten salt heat exchanger. If it is lower than the preset temperature, open the reverse heating pipeline to heat the steam molten salt heat exchanger and pipeline on the steam circulation pipeline.

[0040] When the pressure of the steam storage unit is lower than the preset value, the circulation pump and temperature control pump are turned on to maintain the pressure of the steam storage unit above the preset value.

[0041] When the liquid level in the storage unit is higher than the preset maximum liquid level, the circulation pump and temperature control pump are turned on to bring the liquid level in the storage unit between the preset maximum liquid level and the preset minimum liquid level.

[0042] Because the present invention adopts the above technical solution, it has the following advantages and positive effects compared with the prior art:

[0043] One embodiment of the present invention involves setting up a reverse heating pipeline on an existing steam circulation pipeline, and sequentially installing a liquid storage unit, a circulation pump, a molten salt heat exchange unit, and a steam energy storage unit on the reverse heating pipeline. The circulating liquid in the liquid storage unit enters the molten salt heat exchange unit under the action of the circulation pump, exchanging heat with the molten salt introduced from the external molten salt storage tank to form tracing steam, which is then stored in the steam energy storage unit. When the solar power generation system is shut down, parameters of devices such as a level gauge, a first thermometer, a pressure gauge, and a second thermometer can be monitored. When heat tracing is required, the tracing steam in the steam energy storage unit is led out to the existing steam circulation pipeline. The steam-molten salt heat exchange equipment on the steam circulation pipeline receives the tracing steam and uses its own heat exchange capacity to heat the molten salt, thereby maintaining the molten salt above the condensation temperature. The only energy consumed is the residual heat energy in the external molten salt storage tank; no electricity is required. The system is stable and reliable, with a low failure rate and a design life similar to that of pressure pipelines and containers, solving the problems of high energy consumption and low reliability in existing electric heat tracing systems. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the antifreeze system for molten salt heat exchange equipment and pipelines according to the present invention.

[0045] Explanation of reference numerals in the attached drawings: 1: Liquid storage unit; 2: Circulation pump; 3: Auxiliary heat exchanger; 4: Steam storage unit; 5: Liquid level gauge; 6: First thermometer; 7: Temperature regulating pump; 8: Pressure gauge; 9: Second thermometer; 10: First return water pipe; 11: Second return water pipe; 12: Water supply pipeline; 13: First steam section; 14: Second steam section; 15: Third steam section; 16: First steam branch; 17: Second steam branch; 18: First return water valve; 19: Second return water valve; 20: First steam valve; 21: Second steam valve; 22: Superheated steam valve; 23: Reheated steam valve; 24: First molten salt pipeline; 25: Second molten salt pipeline; 26: Third molten salt pipeline; 27: First molten salt valve; 28: Second molten salt valve; 29: Molten salt storage tank; 30: Salt inlet header; 31: Superheater; 32: Steam drum; 33: Evaporator; 34: Preheater; 35: Reheater; 36: Reheater steam inlet isolation valve; 37: Reheater steam outlet isolation valve. Detailed Implementation

[0046] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides an anti-freezing system and control method for molten salt heat exchangers and pipelines according to the present invention. The advantages and features of the present invention will become clearer from the following description and claims.

[0047] See Figure 1In one embodiment, an antifreeze system for molten salt heat exchange equipment and piping is provided for providing back-warming steam to an external solar power generation system through a steam circulation pipeline. The antifreeze system may include a back-warming pipeline, a second thermometer 9, and a control unit.

[0048] The steam output end of the reverse heating pipe is connected to the steam circulation pipe and is located upstream of the first steam molten salt heat exchanger in the direction of medium flow (i.e., the direction of water flow) in the steam circulation pipe. The return end of the reverse heating pipe is connected to the steam circulation pipe and is located downstream of the last steam molten salt heat exchanger in the direction of medium flow (i.e., the direction of water flow) in the steam circulation pipe.

[0049] The heating pipeline is equipped with a liquid storage unit 1, a circulation pump 2, a molten salt heat exchange unit, and a steam storage unit 4 in sequence. The liquid storage unit 1 is equipped with a level gauge 5 and a first thermometer 6. The molten salt input end of the molten salt heat exchange unit is equipped with a temperature regulating pump 7, and the molten salt input end is connected to the molten salt storage tank 29 of the external solar power generation system. The steam storage unit 4 is equipped with a pressure gauge 8.

[0050] The second thermometer 9 measures the molten salt outlet temperature of the preheater 34 of the external solar power generation system.

[0051] The control unit is configured to be connected to the level gauge 5, the first thermometer 6, the pressure gauge 8, the second thermometer 9, the temperature regulating pump 7, and the circulation pump 2 respectively, and is used to control the temperature regulating pump 7 and the circulation pump 2 according to the parameters of the level gauge 5, the first thermometer 6, the pressure gauge 8, and the second thermometer 9.

[0052] In this embodiment, a reverse heating pipeline is installed on the existing steam circulation pipeline. A liquid storage unit 1, a circulation pump 2, a molten salt heat exchange unit, and a steam energy storage unit 4 are sequentially installed on the reverse heating pipeline. The circulating liquid in the liquid storage unit 1 enters the molten salt heat exchange unit under the action of the circulation pump 2, where it exchanges heat with the molten salt introduced from the external molten salt storage tank 29 to form tracing steam, which is then stored in the steam energy storage unit 4. When the solar power generation system is shut down, the parameters of devices such as the level gauge 5, the first thermometer 6, the pressure gauge 8, and the second thermometer 9 can be monitored. When heat tracing is required, the tracing steam in the steam energy storage unit 4 is led out to the existing steam circulation pipeline. The steam-molten salt heat exchange equipment on the steam circulation pipeline receives the tracing steam and uses its own heat exchange capacity to heat the molten salt, thereby maintaining the molten salt above the condensation temperature. The system consumes only the residual heat energy in the external molten salt storage tank 29, requires no electricity, and operates stably and reliably with a low failure rate. Its design life is the same as that of pressure pipelines and containers, solving the problems of high energy consumption and low reliability of existing electric heat tracing systems.

[0053] The following description, using water as the circulating fluid, further illustrates the specific structure of the antifreeze system for molten salt heat exchange equipment and pipelines in this embodiment:

[0054] In this embodiment, the aforementioned heating pipeline may specifically include a return water pipeline, a water supply pipeline 12, a steam input pipeline, and a steam output pipeline.

[0055] The inlet of the return water pipeline is connected to the steam circulation pipeline and is located downstream of the steam molten salt heat exchanger at the end of the medium flow direction on the steam circulation pipeline. The outlet of the return water pipeline is connected to the inlet of the liquid storage unit 1.

[0056] The two ends of the water supply pipeline 12 are respectively connected to the output end of the liquid storage unit 1 and the liquid input end of the molten salt heat exchange unit. The circulation pump 2 is installed on the water supply pipeline 12 and is used to pump water into the molten salt heat exchange unit for heat exchange.

[0057] The two ends of the steam input pipeline are connected to the steam output end of the molten salt heat exchange unit and the steam input end of the steam energy storage unit 4, respectively. The input end of the steam output pipeline is connected to the steam output end of the steam energy storage unit 4. The output end of the steam output pipeline is connected to the steam circulation pipeline and is located upstream of the first steam molten salt heat exchanger in the direction of medium flow in the steam circulation pipeline.

[0058] Furthermore, many existing steam circulation pipelines are not just a single loop; most have branches within a larger circulation framework to improve efficiency. For example, steam circulation pipelines may include independent superheater branches and reheater branches.

[0059] In this case, the return water pipeline can be divided into a first return water pipe 10 and a second return water pipe 11. The two ends of the first return water pipe 10 are respectively connected to the output end of the reheater branch and the input end of the liquid storage unit 1, and the two ends of the second return water pipe 11 are respectively connected to the output end of the reheater branch and the input end of the liquid storage unit 1.

[0060] The first return water pipe 10 and the second return water pipe 11 are respectively equipped with a first return water valve 18 and a second return water valve 19. The opening and closing of the two return water valves can realize the connection and disconnection of different pipelines.

[0061] Similarly, the steam input and steam output lines can also be adjusted. The steam input and steam output ends of the steam energy storage unit 4 can be set as a steam connection port located on the steam energy storage unit 4.

[0062] The steam input pipeline includes a first steam section 13 and a second steam section 14 connected in sequence. The first end of the first steam section 13 is connected to the steam output end of the molten salt heat exchange unit, and the tail end of the second steam section 14 is connected to the steam connection port.

[0063] The steam output pipeline may include the aforementioned second steam section 14, third steam section 15, first steam branch 16, and second steam branch 17. The first end of the third steam section 15 is connected to the first end of the second steam section 14. The two ends of the first steam branch 16 are connected to the tail end of the third steam section 15 and the input end of the superheater branch, respectively. The two ends of the second steam branch 17 are connected to the tail end of the third steam section 15 and the input end of the reheater branch, respectively.

[0064] The first steam section 13 is equipped with a first steam valve 20, the second steam section 14 is equipped with a second steam valve 21, the first steam branch 16 is equipped with a superheated steam valve 22, and the second steam branch 17 is equipped with a reheated steam valve 23. The second steam valve 21 can be a switching valve.

[0065] When steam needs to be stored, open the first steam valve 20 and the second steam valve 21, and close the superheated steam valve 22 and the reheated steam valve 23; when the generated steam needs to be directly used for heat tracing, open the first steam valve 20 and the superheated steam valve 22 and / or the reheated steam valve 23, and close the second steam valve 21; when only steam needs to be drawn out, open the second steam valve 21 and the superheated steam valve 22 and / or the reheated steam valve 23, and close the first steam valve 20.

[0066] Specifically, a superheater 31, a steam drum 32, an evaporator 33, and a preheater 34 can be sequentially installed on the superheater branch. Among them, the aforementioned second thermometer 9 is installed at the molten salt outlet of the preheater 34 to detect the molten salt temperature at the molten salt outlet.

[0067] In this embodiment, the molten salt heat exchange unit may include an auxiliary heat exchanger 3, a first molten salt pipeline 24, and a second molten salt pipeline 25.

[0068] The inlet of the first molten salt pipeline 24 is connected to the molten salt storage tank 29 (which may specifically be a cold salt storage tank), and the outlet of the first molten salt pipeline 24 is connected to the molten salt inlet of the auxiliary heat exchanger 3. A temperature regulating pump 7 is installed on the first molten salt pipeline 24. The inlet of the second molten salt pipeline 25 is connected to the molten salt outlet of the auxiliary heat exchanger 3, and the outlet of the second molten salt pipeline 25 is connected to the corresponding molten salt storage tank 29.

[0069] Furthermore, the antifreeze system may also include a third molten salt pipeline 26. A first molten salt valve 27 is provided on the first molten salt pipeline 24, and the first molten salt valve 27 is located downstream of the temperature regulating pump 7. The first molten salt valve 27 can be used to regulate the flow rate of molten salt.

[0070] The input end of the third molten salt pipeline 26 is connected to the first molten salt pipeline 24 and is located between the temperature regulating pump 7 and the first molten salt valve 27. The output end of the third molten salt pipeline 26 is connected to the salt inlet header 30 of the external solar power generation system. A second molten salt valve 28 can be installed on the third molten salt pipeline 26.

[0071] When the temperature at the second thermometer 9 is detected to be lower than the preset value, the temperature regulating pump 7 can be started and the second molten salt valve 28 can be opened, so that molten salt can be slowly pushed through the main circuit of the molten salt system to prevent freezing.

[0072] In this embodiment, the antifreeze system may further include a drain pipe. The inlet of the drain pipe is connected to the bottom of the steam storage unit 4, the outlet of the drain pipe is connected to the inlet of the liquid storage unit 1, and a drain valve is provided on the drain pipe.

[0073] In summary, this embodiment utilizes two methods—steam back-heating and maintaining continuous flow of molten salt—to make molten salt antifreeze more energy-efficient and reliable.

[0074] The main factors that cause molten salt to solidify are: (1) large heat dissipation from the outer surface of the equipment during shutdown and electric heat tracing failure. (2) low feedwater temperature during unit startup, which causes molten salt in the shell side of the preheater 34 to solidify.

[0075] The basic working process of the anti-condensation system is as follows: Saturated steam in the steam accumulator flows through the superheater 31 / reheater 35, steam drum 32, evaporator 33, and preheater 34 in stages by means of pressure difference. The condensate that has completed heat exchange is connected to the liquid storage unit 1 and pumped into the auxiliary heat exchanger 3 by the circulation pump 2. Part of the generated steam enters the steam storage unit 4 for storage, and part of the steam continuously supplies steam to the steam molten salt heat exchange equipment in the steam circulation pipeline.

[0076] The antifreeze system serves the following purposes: 1. To continuously heat the tubes, plates, shell, and internal molten salt of the heat exchanger equipment in a shutdown state, ensuring that the outer surface temperature of the heat exchanger is not lower than the solidification temperature of the molten salt. Simultaneously, by activating the temperature-regulating pump 7 (interlocking the molten salt outlet pipe wall temperature of the preheater 34), the flow rate of the cold molten salt is controlled via a regulating valve, propelling the molten salt to flow slowly through the heat exchange equipment and pipelines. This sends the molten salt, which is close to its solidification temperature, back to the cold salt tank, replacing it with molten salt at a higher temperature. 2. To preheat the tubes, plates, shell, and internal molten salt of the heat exchanger equipment before startup, ensuring that the outer surface temperature of the heat exchanger is not lower than the solidification temperature of the molten salt before proceeding with boiler water filling, steam drum 32 startup of the circulating heating equipment, and salt filling of the equipment and pipelines, thus shortening the startup time.

[0077] The operating pressure of the steam storage unit 4 can be set to 5 MPa. During operation, the pressure of the tracing steam from the inlet of the superheater 31 to the outlet of the preheater 34 is always maintained above the saturated steam pressure, which is the saturation temperature of the molten salt solidification temperature. The stored effective heat supply can meet the needs of the heat exchange equipment to maintain the surface temperature during a single warm-state start-up and shutdown, and can also meet the preheating steam requirements for a single cold-state start-up of the steam generation system.

[0078] This embodiment utilizes the principle that the working fluid temperature remains constant in saturated steam, steam-water two-phase mixtures, and saturated water states, combined with the large heat transfer characteristic of phase change, to achieve a novel heat tracing system through the cyclic storage and release of energy. Its main advantages are as follows: 1. Stable and reliable operation, low failure rate, and a design life similar to pressure pipelines and containers; 2. This embodiment shares some temperature and pressure measurement points with the power generation steam generation system, simplifying the control system; 3. The steam energy storage unit 4 has pressure stabilization and energy storage effects, serving as both a heat tracing steam source and a heating and process steam supply, offering highly flexible operation and reducing the temperature fluctuation range of the heat exchange equipment; 4. The heat exchange equipment can be preheated before unit startup, which is more flexible than starting a circulating electric heater and shortens startup time.

[0079] Example 2

[0080] This embodiment provides a control method applied to the antifreeze system for molten salt heat exchange equipment and pipelines in Embodiment 1 above, as follows:

[0081] When the external solar power generation system reduces its load: the temperature regulating pump 7 and the circulation pump 2 start to preheat and replenish the steam storage unit 4, and the steam storage unit 4 stores energy to the preset storage pressure (6MPa in this embodiment). At the same time as the system stops, the second steam valve 21 is closed.

[0082] When the external solar power generation system is shut down: when the second thermometer 9 is below 260℃ or the steam-water remote thermometer is below 250℃, the second steam valve 21 is opened. The steam in the steam storage unit 4 is divided into two paths. One path enters the superheater 31, steam drum 32, evaporator 33, and preheater 34. It achieves reverse heating through the main steam pipeline, riser pipe, downcomer pipe, and water supply pipeline. The water supply inlet isolation valve of the preheater 34 is shut down and closed at the same time. The first return water pipe 10 is led out between the isolation valve and the preheater 34 and connected to the liquid storage unit 1. The first return water valve 18 is opened.

[0083] Another path enters the reheater 35 through the second steam branch 17. The reheater steam inlet isolation valve 36 and the reheater steam outlet isolation valve 37 are closed when the machine stops. A second return water pipe 11 is provided before the reheater steam inlet isolation valve 36. The second return water valve 19 is opened, and the return water enters the liquid storage unit 1.

[0084] Monitor the steam drum 32 and pressure gauge 8. When the pressure gauge 8 reading is below 3.5 MPa and the level gauge 5 shows that the liquid level in the storage unit 1 is at the normal level, start the circulation pump 2 and temperature control pump 7 to stabilize the level gauge 5 and control the pressure of the steam drum 32 and pressure gauge 8 to above 3.5 MPa. At the same time, monitor the temperature of the medium in the storage unit 1 to above 250℃.

[0085] When the molten salt outlet temperature at the second thermometer 9 is lower than the preset temperature, such as 260°C, the temperature regulating pump 7 and the second molten salt valve 28 are started to slowly advance the molten salt through the main circuit of the molten salt system of the solar power generation system (i.e., the salt inlet header 30) to prevent the molten salt in the molten salt system of the solar power generation system from freezing. The superheater branch and the reheater branch are both part of the molten salt system of the solar power generation system.

[0086] By monitoring the liquid level gauge 5, when the liquid level is high, the interlocking circulation pump 2 and temperature regulating pump 7 are started. At the same time, the first steam valve 20 and the second steam valve 21 are interlocked and regulated by the remote pressure transmitted by the pressure gauge 8. When the liquid level of the storage unit 1 returns to below the low liquid level, the steam energy storage process ends, the circulation pump 2 and the first steam valve 20 are closed, and the second steam valve 21 is operated to change the steam flow to the direction of the steam energy storage unit 4 towards the superheater 31 and the reheater 35.

[0087] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they shall still fall within the protection scope of the present invention.

Claims

1. An antifreeze system for molten salt heat exchange equipment and pipelines, characterized in that, Steam circulation piping used to supply warm steam to an external solar power generation system includes: The reverse heating pipe has its steam output end connected to the steam circulation pipe and located upstream of the first steam molten salt heat exchanger in the direction of medium flow in the steam circulation pipe; the return water end of the reverse heating pipe is connected to the steam circulation pipe and located downstream of the last steam molten salt heat exchanger in the direction of medium flow in the steam circulation pipe. The inverted heating pipeline is sequentially equipped with a liquid storage unit, a circulation pump, a molten salt heat exchange unit, and a steam energy storage unit; the molten salt input end of the molten salt heat exchange unit is equipped with a temperature regulating pump, and the molten salt input end is connected to the molten salt storage tank of an external solar power generation system. The control unit is signal-connected to the temperature regulating pump and the circulation pump, and is used to control the temperature regulating pump and the circulation pump; The heating system includes a return water pipe, a supply water pipe, a steam input pipe, and a steam output pipe; The inlet of the return water pipeline is connected to the steam circulation pipeline and is located downstream of the steam molten salt heat exchanger at the end of the medium flow direction on the steam circulation pipeline; the outlet of the return water pipeline is connected to the inlet of the liquid storage unit. The two ends of the water pipeline are respectively connected to the output end of the liquid storage unit and the water working fluid input end of the molten salt heat exchange unit; The two ends of the steam input pipeline are respectively connected to the steam output end of the molten salt heat exchange unit and the steam input end of the steam energy storage unit; The input end of the steam output pipeline is connected to the steam output end of the steam energy storage unit; the output end of the steam output pipeline is connected to the steam circulation pipeline and is located upstream of the first steam molten salt heat exchanger in the medium flow direction of the steam circulation pipeline.

2. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 1, characterized in that, The steam circulation pipeline includes independent superheater branches and reheater branches; The return water pipeline is a first return water pipeline and a second return water pipeline; the two ends of the first return water pipeline are respectively connected to the output end of the superheater branch and the input end of the liquid storage unit, and the two ends of the second return water pipeline are respectively connected to the output end of the reheater branch and the input end of the liquid storage unit. The first return water pipe and the second return water pipe are respectively equipped with a first return water valve and a second return water valve.

3. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 1 or 2, characterized in that, The steam input end and steam output end of the steam energy storage unit are a steam connection port located on the steam energy storage unit; The steam input pipeline includes a first steam section and a second steam section connected in sequence. The first end of the first steam section is connected to the steam output end of the molten salt heat exchange unit, and the tail end of the second steam section is connected to the steam connection port. The steam output pipeline includes a third steam section; the first end of the third steam section is connected to the first end of the second steam section, and the last end of the third steam section is connected to the steam circulation pipeline and is located upstream of the first steam molten salt heat exchanger in the direction of medium flow on the steam circulation pipeline. The first steam section is equipped with a first steam valve, and the second steam section is equipped with a second steam valve.

4. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 3, characterized in that, The steam output pipeline also includes a first steam branch and a second steam branch; the two ends of the first steam branch are respectively connected to the tail end of the third steam section and the input end of the superheater branch; the two ends of the second steam branch are respectively connected to the tail end of the third steam section and the input end of the reheater branch. The first steam branch is equipped with a superheated steam valve, and the second steam branch is equipped with a reheated steam valve.

5. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 2, characterized in that, The superheater branch is provided with a superheater, a steam drum, an evaporator and a preheater in sequence.

6. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 1, characterized in that, The molten salt heat exchange unit includes an auxiliary heat exchanger, a first molten salt pipeline, and a second molten salt pipeline; The input end of the first molten salt pipeline is connected to the molten salt storage tank, the output end of the first molten salt pipeline is connected to the molten salt inlet of the auxiliary heat exchanger, and the temperature regulating pump is provided on the first molten salt pipeline; The input end of the second molten salt pipeline is connected to the molten salt outlet of the auxiliary heat exchanger, and the output end of the second molten salt pipeline is connected to the corresponding molten salt storage tank.

7. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 6, characterized in that, It also includes a third molten salt pipeline; A first molten salt valve is provided on the first molten salt pipeline, and the first molten salt valve is located downstream of the temperature regulating pump; The input end of the third molten salt pipeline is connected to the first molten salt pipeline and is located between the temperature regulating pump and the first molten salt valve; the output end of the third molten salt pipeline is connected to the salt inlet header of the external solar power generation system.

8. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 1, characterized in that, It also includes a drainage pipe; The inlet of the condensate drain pipe is connected to the bottom of the steam energy storage unit, the outlet of the condensate drain pipe is connected to the inlet of the liquid storage unit, and a condensate drain valve is provided on the condensate drain pipe.

9. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 1, characterized in that, The liquid storage unit is equipped with a level gauge and a first thermometer, and the steam energy storage unit is equipped with a pressure gauge. The level gauge, the first thermometer, and the pressure gauge are all connected to the control unit via signal connection.

10. The antifreeze system for molten salt heat exchange equipment and pipelines as described in claim 1, characterized in that, It also includes a second thermometer for detecting the temperature of the molten salt side outlet of the end steam-molten salt heat exchanger; The control unit is configured to activate the temperature regulating pump when the temperature detected by the second thermometer is lower than a preset temperature, thereby driving the molten salt in the molten salt storage tank of the external solar power generation system to replace the original molten salt in the system.

11. A control method, characterized in that, The antifreeze system for molten salt heat exchangers and pipelines as described in any one of claims 1 to 10 is as follows: When the external solar power generation system reduces its load: the temperature regulating pump and the circulation pump start, and the steam energy storage unit stores energy to the preset energy storage pressure; When the external solar power generation system is shut down: monitor the temperature of the molten salt outlet of the end steam molten salt heat exchanger. If it is lower than the preset temperature, open the reverse heating pipeline to heat the steam molten salt heat exchanger and pipeline on the steam circulation pipeline. When the pressure of the steam energy storage unit is lower than the preset value, the circulation pump and the temperature control pump are turned on to keep the pressure of the steam energy storage unit above the preset value; when the liquid level of the liquid storage unit is higher than the preset maximum liquid level, the circulation pump and the temperature control pump are turned on to keep the liquid level of the liquid storage unit between the preset maximum liquid level and the preset minimum liquid level.

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