A molten salt-conductive oil heat exchanger for a trough type molten salt-conductive oil photo-thermal unit and a method for injecting conductive oil and molten salt

Abstract

The application discloses a molten salt-conductive oil photo-thermal unit oil-salt heat exchanger conductive oil and molten salt injection method, adopts a tube-shell heat exchanger, and is provided with electric heat tracing, a flow sensor, a temperature sensor, a pressure sensor, a salt pump, a pipeline, a valve and other equipment, and through a nitrogen replacement-equipment preheating-conductive oil injection-discharge of oil side nitrogen-maintenance of conductive oil flow-all equipment heat tracing system and conductive oil temperature reaches heating to 285±5ºC-salt temperature and oil-salt heat exchanger temperature difference is within ±10ºC, salt injection-discharge of salt side nitrogen-reinjection and recovery of excess molten salt in a pipeline process method, the temperature, temperature change rate and flow of the conductive oil and molten salt injection system are adjusted, so that the medium is safely and effectively injected into the system. The method has the advantages of simple and reliable operation, low technical requirement difficulty, and safety guarantee of the molten salt-conductive oil photo-thermal unit oil-salt heat exchanger conductive oil and molten salt injection work.

Description

Technical Field

[0001] This invention relates to the field of parabolic trough solar thermal power generation technology, specifically to a method for injecting heat transfer oil and molten salt into an oil-salt heat exchanger of a parabolic trough molten salt-heat transfer oil solar thermal unit. Background Technology

[0002] As an important component of my country's development of new energy sources, solar thermal power generation units have the advantages of having their own large-capacity, low-cost energy storage system, enabling continuous and stable operation 24 hours a day, and being low-carbon, environmentally friendly, and pollution-free.

[0003] Oil-salt heat exchangers are an important component of trough-type molten salt-thermal oil solar thermal power units. The injection of thermal oil and molten salt is a crucial step in system commissioning, and the following technical challenges exist during the injection process:

[0004] 1) Heat transfer oil will solidify when the ambient temperature is below 12℃;

[0005] 2) Molten salt has a freezing point of 245℃, and there is a risk of solidification when the temperature is below 260℃;

[0006] 3) The heat exchange surfaces of oil-salt heat exchangers are relatively thin and densely arranged. Excessive temperature change rate of the injected medium or excessive temperature difference on both sides may cause damage to the heat exchange surfaces or affect their service life. Summary of the Invention

[0007] The purpose of this invention is to address the above-mentioned technical difficulties by providing a reliable and effective method for injecting heat transfer oil and molten salt into a trough-type molten salt-thermal oil solar thermal unit. This method utilizes electric heat tracing, flow sensors, temperature sensors, pressure sensors, salt pumps, pipelines, and valves within the oil-salt heat exchanger. A specific injection process is employed to regulate the temperature, temperature change rate, and flow rate of the heat transfer oil and molten salt injection system, thereby achieving a safe and effective injection system. This method is simple and reliable to operate, has low technical requirements, and ensures the safe operation of heat transfer oil and molten salt injection into the oil-salt heat exchanger of the trough-type molten salt-thermal oil solar thermal unit.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for injecting heat transfer oil and molten salt into an oil-salt heat exchanger of a trough-type molten salt-heat transfer oil solar thermal unit, characterized by comprising the following steps:

[0010] S1. The oil-salt heat exchanger used is a shell-and-tube heat exchanger. Molten salt is injected into the shell side, and heat transfer oil is injected into the tube side. The valves in the heat transfer oil and molten salt pipelines have the following operating conditions: the bottom discharge valves of the pipelines and equipment will be closed, the top exhaust valve of the oil-salt heat exchanger will be closed, and will be opened when the system medium is injected until all the gas in the system is discharged and then closed; before the medium is injected, at ambient temperature, the heat transfer oil and molten salt sides of the oil-salt heat exchanger and related pipelines will be purged with pure nitrogen.

[0011] S2. The oil-salt heat exchanger shell, valves and pipes are preheated by electric heat tracing, and the temperature is raised to 60±10ºC at a rate of 5ºC / 6 hours. The rate of temperature rise of the oil-salt heat exchanger shell, valves and pipes is monitored by heat sensors evenly distributed around the equipment.

[0012] S3. When the temperature of the shell, valves, and pipes of the oil-salt heat exchanger reaches 60±10ºC, the heat transfer oil injection should be carried out first. The preheated heat transfer oil should be injected into the heat exchanger at a temperature of 60±10ºC. The heat transfer oil is injected through the pre-reserved outlet of the heat transfer oil side inlet pipe of the oil-salt heat exchanger by a pneumatic diaphragm pump. During the injection, the manual valve of the pre-reserved outlet should be fully opened. Nitrogen should be discharged through the heat transfer oil exhaust pipe at the same time. The flow rate of the injected heat transfer oil should be gradually increased, while the temperature of the oil-salt heat exchanger should be monitored. The rate of temperature change on the heat transfer oil side of the oil-salt heat exchanger should be less than 5℃ / minute. If it approaches or exceeds this rate, the heat transfer oil injection flow rate should be reduced to ensure that the operating limits are met. Follow this process until the heat transfer oil injection is completed.

[0013] S4. After the heat transfer oil is injected, maintain the flow of the heat transfer oil at a pressure of 1.0-1.5 MPa and a flow rate not exceeding 15% of the design flow rate. While flowing, the heat transfer oil is heated by the mirror filter at a rate of 30-35ºC / 12 hours, gradually increasing the temperature to 285ºC±5ºC. During this process, the electric heat tracing is simultaneously heated, with a maximum difference of 15ºC between the electric heat tracing temperature and the heat transfer oil temperature. All components of the oil-salt heat exchanger system are uniformly heated.

[0014] S5. Once the temperature of the heat tracing system and heat transfer oil of all equipment reaches approximately 285±5ºC, maintain this temperature for at least 24 hours before proceeding with salt injection. The temperature difference between the salt and the oil-salt heat exchanger should be within ±10ºC. Molten salt is injected through the bypass valve at the outlet of the cold salt pump. The flow rate is controlled by the opening of the bypass valve at the outlet of the cold salt pump. The initial salt injection opening is 10%, gradually increasing to 60%.

[0015] S6. During molten salt injection, nitrogen gas on the salt side is simultaneously discharged through the molten salt venting pipe. The nitrogen gas and a small amount of molten salt are discharged to the salt discharge system through the venting and desalting pipe until the system is completely filled with molten salt. The temperature change can be detected by the temperature transmitter in the venting pipe to determine whether the molten salt is full. Then, molten salt is filled into the molten salt recirculation pipe of the oil-salt heat exchanger to the cold tank pipeline. After the system is filled with molten salt and pressurized, the shell-side salt pressure can be controlled to 0.5-0.8 MPa through the molten salt recirculation regulating valve on the molten salt recirculation pipe for circulation. Molten salt that remains in the venting and desalting pipe after filling is discharged to the salt discharge system.

[0016] Furthermore, in step S1, the nitrogen concentration must be greater than 95% to be considered as qualified for inert filling, and the pressure must be maintained at 1-3 bar.

[0017] Furthermore, the maximum flow rate of the heat transfer oil injected in step S3 shall not exceed 15% of the design flow rate.

[0018] Furthermore, in step S4, after the heat transfer oil is injected into the equipment, the heat transfer oil enters the system from the oil-salt heat exchanger in the opposite direction of the injection port to maintain the circulation of the heat transfer oil, and the flow rate of the heat transfer oil does not exceed 15% of the design flow rate.

[0019] Furthermore, the temperature of the molten salt on the shell side should be kept between 270ºC and 300ºC during and after the molten salt injection process to prevent condensation on the molten salt side, and each section of the equipment should be heated evenly.

[0020] Furthermore, in step S6, before the system is filled with molten salt and pressurized, the heat transfer oil on the pipe side must first be pressurized and flow.

[0021] Furthermore, the salt discharge system consists of a salt discharge tank, a salt discharge pump, and pipelines. Molten salt that remains in the drain and desalination pipeline is discharged to the salt discharge tank through the pipelines. The molten salt in the salt discharge tank can be transported back to the hot and cold salt tanks by the salt discharge pump.

[0022] This invention is simple and reliable to operate, has low technical requirements, is easy to implement, and is safe and reliable. It can ensure the safe operation of the heat transfer oil and molten salt injection in the oil-salt heat exchanger of the trough-type heat transfer oil-molten salt unit, and will not reduce the service life of the oil-salt heat exchanger due to a large temperature change rate. Attached Figure Description

[0023] Figure 1 Diagram of the heat transfer oil and molten salt injection system of the oil-salt heat exchanger in the trough-type molten salt-heat transfer oil solar thermal unit of the present invention;

[0024] In the diagram: 1. First oil-salt heat exchanger; 2. Second oil-salt heat exchanger; 3. Third oil-salt heat exchanger; 4. Fourth oil-salt heat exchanger; 5. Fifth oil-salt heat exchanger; 6. Sixth oil-salt heat exchanger; 7. Main pipeline for heat transfer oil; 8. Heat transfer oil exhaust pipeline; 9. Heat transfer oil drain pipeline; 10. Main pipeline for molten salt; 11. Molten salt exhaust pipeline; 12. Molten salt recirculation pipeline; 13. Drainage and desalination pipeline; 14. Reserved outlet for oil discharge; 15. Heat transfer oil exhaust valve; 16. Heat transfer oil drain valve; 17. Cold salt pump outlet bypass valve; 18. Molten salt recirculation regulating valve; 19. Molten salt exhaust valve; 20. Drainage and desalination valve; 21. Molten salt desalination valve; 22. Desalination tank; 23. Desalination pump; 24. Desalination pump valve. Detailed Implementation

[0025] The following is in conjunction with the appendix Figure 1 The present invention will be further described in conjunction with specific embodiments.

[0026] As attached Figure 1 As shown: The oil-salt heat exchanger system includes a first oil-salt heat exchanger 1, a second oil-salt heat exchanger 2, a third oil-salt heat exchanger 3, a fourth oil-salt heat exchanger 4, a fifth oil-salt heat exchanger 5, and a sixth oil-salt heat exchanger 6, and a main heat transfer oil pipeline 7 and a main molten salt pipeline 10 connected sequentially to the tube side and shell side of the first to sixth oil-salt heat exchangers, respectively. The oil-salt heat exchangers are tube-shell type heat exchangers. Molten salt is injected into the shell side, and heat transfer oil is injected into the tube side. The main heat transfer oil pipeline 7 is also equipped with a bypass pipeline, a heat transfer oil exhaust pipeline 8, and a heat transfer oil drain. The oil pipeline 9 and the molten salt main pipeline 10 are also equipped with bypass pipelines: a molten salt venting pipeline 11, a molten salt recirculation pipeline 12, and a desalination pipeline 13. Specifically, the bypass pipelines are configured as follows: the top of the heat transfer oil main pipeline 7 is connected to the heat transfer oil venting pipeline 8, and the bottom is connected to the heat transfer oil drain pipeline 9; the top of the molten salt main pipeline 10 is connected to the molten salt venting pipeline 11, and the bottom is connected to the molten salt recirculation pipeline 12; the desalination pipeline 13 connects the molten salt venting pipeline 11 and the molten salt recirculation pipeline 12 to the desalination system. The desalination system includes a desalination tank 22, a desalination pump 23, and a desalination pump valve 24, used to discharge excess molten salt to the desalination tank 22 and then transport it back to the hot and cold salt tanks via the desalination pump. Valves are installed on all the above-mentioned bypass pipelines. Specifically, a heat transfer oil vent valve 15 is installed on the heat transfer oil vent pipeline 8; a heat transfer oil drain valve 16 is installed on the heat transfer oil drain pipeline 9; a molten salt vent valve 19 is installed on the molten salt vent pipeline 11; a molten salt recirculation regulating valve 18 and a molten salt drain valve 21 are installed on the molten salt recirculation pipeline 12; and a drain valve 20 is installed on the drain and desalination pipeline 13. A drain port 14 is provided at the heat transfer oil side inlet of the main heat transfer oil pipeline 7, and a cold salt pump outlet bypass valve 17 is installed where the main molten salt pipeline 10 connects to the cold salt tank.

[0027] After the piping, valves, and auxiliary equipment of the oil-salt heat exchanger system, such as insulation, electric heat tracing, flow sensors, temperature sensors, pressure sensors, and cold tank salt pumps, are installed and commissioned, and the conditions for injecting heat transfer oil and molten salt are met, the heat transfer oil and molten salt will be injected according to the following process:

[0028] 1) Before the medium is injected, at ambient temperature, the heat transfer oil and molten salt side of the oil-salt heat exchanger and related pipelines are purged with pure nitrogen. The nitrogen concentration must be greater than 95% to be considered as qualified for purging. The pressure is maintained at 1-3 bar.

[0029] 2) The valves in the heat transfer oil and molten salt pipelines are ready for operation. The bottom drain valves of the pipelines and equipment are closed, and the top exhaust valve of the oil-salt heat exchanger is closed. It is opened when the system medium is injected and closed after all the gas in the system is discharged.

[0030] 3) Electric heat tracing is applied to the shell, valves, and pipes of the oil-salt heat exchanger for preheating, raising the temperature to 60±10ºC at a rate of 5ºC / 6 hours. The rate of temperature increase of the shell, valves, and pipes of the oil-salt heat exchanger is monitored by thermal sensors evenly distributed around the equipment.

[0031] 4) When the temperature of the shells, valves, and pipes of the first to sixth oil-salt heat exchangers reaches 60±10ºC, the heat transfer oil injection should be carried out first. The preheated heat transfer oil must be injected within a temperature range of 60±10ºC (maximum 70ºC). The heat transfer oil is transported to the site by a transport vehicle and injected through the oil drain port 14 at the heat transfer oil side inlet pipe of the sixth oil-salt heat exchanger 6 via a pneumatic diaphragm pump. During oil injection, the manual valve of the oil drain port 14 is fully opened, and nitrogen is simultaneously discharged through the heat transfer oil exhaust pipe 8 until the system is completely filled with heat transfer oil. The flow rate of the injected heat transfer oil should be gradually increased, while the temperature of the oil-salt heat exchanger is monitored. The rate of temperature change on the heat transfer oil side of the oil-salt heat exchanger must be less than 5℃ / minute. If it approaches or exceeds this rate, the heat transfer oil injection flow rate should be reduced to ensure that the operating limits are met. This process should be followed until the heat transfer oil injection is completed. The maximum flow rate of the heat transfer oil injected during this operation shall not exceed 15% of the design flow rate (150 kg / s). If any heat transfer oil leaks during the injection process, the injection operation must be stopped immediately, and the leaked heat transfer oil must be collected to prevent environmental pollution.

[0032] 5) Once the heat transfer oil is injected into the equipment, it enters the system from the first oil-salt heat exchanger 1, maintaining its circulation. The pressure is maintained at 1.0-1.5 MPa, and the flow rate does not exceed 15% of the design flow rate (150 kg / s). Simultaneously, the heat transfer oil is heated during the day by a mirror filter, with a temperature rise rate of 30-35°C / 12 hours, gradually increasing to approximately 285°C. During this process, electric heating is performed synchronously, with a maximum difference of 15°C between the electric heating temperature and the heat transfer oil temperature (at any point). All components of the oil-salt heat exchanger system are uniformly heated.

[0033] 6) When the temperature of the heat tracing system and heat transfer oil of all equipment reaches about 285±5ºC, maintain this temperature for more than 24 hours before salt injection can be carried out. The temperature difference between the salt and the oil-salt heat exchanger should be within ±10ºC. Molten salt is injected through the cold salt pump outlet bypass valve 17. The salt flow direction is from the sixth oil-salt heat exchanger 6. The flow rate is controlled by the opening of the cold salt pump outlet bypass valve 17. The initial salt injection opening is 10%, which is gradually increased to 60%.

[0034] 7) During molten salt injection, nitrogen gas is simultaneously discharged through the molten salt venting pipe 11. Nitrogen gas and a small amount of molten salt are discharged to the salt discharge system through the venting and desalination pipe 13 until the system is completely filled with molten salt (the temperature change detected by the venting temperature transmitter indicates whether the system is full). Then, molten salt is added to the molten salt recirculation pipe 12 of the oil-salt heat exchanger recirculation line to the cold tank. After the system is filled with molten salt and pressurized, the shell-side salt pressure can be controlled at 0.5-0.8 MPa via the molten salt recirculation regulating valve 18 for circulation (the heat transfer oil on the pipe side must be pressurized and flowed first). Molten salt remaining in the venting and desalination pipe 13 after filling is discharged to the salt discharge tank 22 of the salt discharge system. The molten salt in the salt discharge tank 22 can be transported back to the hot and cold salt tanks via the salt discharge pump 23. This completes the heat transfer oil and molten salt injection process.

[0035] 8) As a general measure, the temperature of the molten salt on the shell side should always be above 270ºC (maximum 300ºC) during the injection process to prevent condensation on the molten salt side, and each section of the equipment should be heated evenly.

[0036] This invention is simple and reliable to operate, has low technical requirements, is easy to implement, and is safe and reliable. It can ensure the safe operation of the heat transfer oil and molten salt injection in the oil-salt heat exchanger of the trough-type heat transfer oil-molten salt unit, and will not reduce the service life of the oil-salt heat exchanger due to a large temperature change rate.

[0037] This invention is based on the design specifications of oil-salt heat exchanger manufacturers, and the specific parameters provided by the manufacturers are as follows:

[0038] 1) Temperature rise rate of molten salt, heat transfer oil pipelines or valves <1℃ / hour; 2) Temperature rise rate of oil-salt heat exchangers and salt discharge systems <1℃ / hour; 3) Heat transfer oil injection temperature 60-65℃; 4) Temperature rise rate of electric heat tracing of molten salt, heat transfer oil pipelines or valves <12℃ / hour; 5) Temperature rise rate of oil-salt heat exchangers <3℃ / hour; 6) Temperature rise rate of salt discharge systems <12℃ / hour; 7) Molten salt injection temperature 285-300℃.

[0039] Because all electric heat tracing in the oil-salt heat exchanger is automatically controlled by a PLC, heating automatically stops when the temperature exceeds the set temperature by 5°C and automatically restarts when the temperature falls below the set temperature by 5°C. This makes it impossible to precisely control the temperature rise rate, failing to meet the manufacturer's requirement of 1°C / hour. Furthermore, the heated temperature cannot be maintained indefinitely. Therefore, this invention modifies the process by controlling the temperature rise rate at a set temperature of 5°C / 6 hours, and closely monitoring the actual temperature after setting the temperature. This invention fully utilizes on-site conditions without significantly extending the preheating time, safely and effectively completing the electric heat tracing preheating of the oil-salt heat exchanger.

[0040] Since the manufacturer specifies a heat transfer oil injection temperature of 60-65°C, and the heat transfer oil can only be heated at the port during transportation, it cannot be heated during transport and injection. Therefore, this invention modifies the heat transfer oil injection temperature to 60±10°C while ensuring injection safety.

[0041] During the heating process of the heat transfer oil, the manufacturer specifies that the temperature rise rate of the oil-salt heat exchanger should be less than 3°C / hour when heating the oil side. Considering that the mirror factory has just been put into use, the temperature of the heat transfer oil fluctuates greatly during heating, and the heat transfer oil cannot be heated at night, the present invention sets the temperature rise rate to 30-35°C / 12 hours during temperature control.

[0042] Before the salt injection process, in order to ensure that there are no low temperature points in all salt injection areas, after the temperature of the heat tracing system and heat transfer oil of all equipment reaches about 285±5ºC, this temperature is maintained for more than 24 hours. This operation is an optimization step added to this invention while meeting the basic requirements of the manufacturer.

[0043] In the manufacturer's specified operation of heat transfer oil and molten salt, the maximum salt injection flow rate is given to be no more than 5% of the design flow rate (80 kg / s). However, since the molten salt enters from the cold salt pump outlet bypass valve 17 and the flow meter is located at the outlet of the first oil-salt heat exchanger 1, it is impossible to monitor the salt injection flow rate in real time. This invention adopts flow control by controlling the opening of the cold salt pump outlet bypass valve, with the initial salt injection opening at 10% and gradually increasing to 60%. Through practice, it has been found that when the first to sixth oil-salt heat exchangers are full of salt and the flow meter displays the flow rate, this opening flow rate is (60 kg / s), which meets the manufacturer's salt injection flow rate limit.

Claims

1. A method for injecting heat transfer oil and molten salt into an oil-salt heat exchanger of a trough-type molten salt-heat transfer oil solar thermal unit, characterized in that: Includes the following steps: S1. The oil-salt heat exchanger used is a shell-and-tube heat exchanger. Molten salt is injected into the shell side, and heat transfer oil is injected into the tube side. The valves in the heat transfer oil and molten salt pipelines have the following operating conditions: the bottom discharge valves of the pipelines and equipment will be closed, the top exhaust valve of the oil-salt heat exchanger will be closed, and will be opened when the system medium is injected until all the gas in the system is discharged and then closed; before the medium is injected, at ambient temperature, the heat transfer oil and molten salt sides of the oil-salt heat exchanger and related pipelines will be purged with pure nitrogen. S2. The oil-salt heat exchanger shell, valves and pipes are preheated by electric heat tracing, and the temperature is raised to 60±10ºC at a rate of 5ºC / 6 hours. The rate of temperature rise of the oil-salt heat exchanger shell, valves and pipes is monitored by heat sensors evenly distributed around the equipment. S3. When the temperature of the shell, valves, and pipes of the oil-salt heat exchanger reaches 60±10ºC, the heat transfer oil injection should be carried out first. The preheated heat transfer oil should be injected into the heat exchanger at a temperature of 60±10ºC. The heat transfer oil is injected through the pre-reserved outlet of the heat transfer oil side inlet pipe of the oil-salt heat exchanger by a pneumatic diaphragm pump. During the injection, the manual valve of the pre-reserved outlet should be fully opened. Nitrogen should be discharged through the heat transfer oil exhaust pipe at the same time. The flow rate of the injected heat transfer oil should be gradually increased, while the temperature of the oil-salt heat exchanger should be monitored. The rate of temperature change on the heat transfer oil side of the oil-salt heat exchanger should be less than 5℃ / minute. If it approaches or exceeds this rate, the heat transfer oil injection flow rate should be reduced to ensure that the operating limits are met. Follow this process until the heat transfer oil injection is completed. S4. After the heat transfer oil is injected, maintain the flow of the heat transfer oil at a pressure of 1.0-1.5 MPa and a flow rate not exceeding 15% of the design flow rate. While flowing, the heat transfer oil is heated by the mirror filter at a rate of 30-35ºC / 12 hours, gradually increasing the temperature to 285ºC±5ºC. During this process, the electric heat tracing is simultaneously heated, with a maximum difference of 15ºC between the electric heat tracing temperature and the heat transfer oil temperature. All components of the oil-salt heat exchanger system are uniformly heated. S5. Once the temperature of the heat tracing system and heat transfer oil of all equipment reaches approximately 285±5ºC, maintain this temperature for at least 24 hours before proceeding with salt injection. The temperature difference between the salt and the oil-salt heat exchanger should be within ±10ºC. Molten salt is injected through the bypass valve at the outlet of the cold salt pump. The flow rate is controlled by the opening of the bypass valve at the outlet of the cold salt pump. The initial salt injection opening is 10%, gradually increasing to 60%. S6. During molten salt injection, nitrogen gas on the salt side is simultaneously discharged through the molten salt venting pipe. The nitrogen gas and a small amount of molten salt are discharged to the salt discharge system through the venting and desalting pipe until the system is completely filled with molten salt. The temperature change can be detected by the temperature transmitter in the venting pipe to determine whether the molten salt is full. Then, molten salt is filled into the molten salt recirculation pipe of the oil-salt heat exchanger to the cold tank pipeline. After the system is filled with molten salt and pressurized, the shell-side salt pressure can be controlled to 0.5-0.8 MPa through the molten salt recirculation regulating valve on the molten salt recirculation pipe for circulation. Molten salt that remains in the venting and desalting pipe after filling is discharged to the salt discharge system.

2. The method for injecting heat transfer oil and molten salt into a trough-type molten salt-heat transfer oil solar thermal unit according to claim 1, characterized in that: In step S1, the nitrogen concentration must be greater than 95% to be considered as qualified for inert filling, and the pressure should be maintained at 1-3 bar.

3. The method for injecting heat transfer oil and molten salt into a trough-type molten salt-heat transfer oil solar thermal unit according to claim 1, characterized in that: The maximum flow rate of the heat transfer oil injected in step S3 shall not exceed 15% of the design flow rate.

4. The method for injecting heat transfer oil and molten salt into a trough-type molten salt-heat transfer oil solar thermal unit according to claim 1, characterized in that: In step S4, after the heat transfer oil is injected into the equipment, the heat transfer oil enters the system from the oil-salt heat exchanger in the opposite direction of the injection port to maintain the circulation of the heat transfer oil. The flow rate of the heat transfer oil does not exceed 15% of the design flow rate.

5. The method for injecting heat transfer oil and molten salt into a trough-type molten salt-heat transfer oil solar thermal unit according to claim 1, characterized in that: During and after the molten salt injection process, the temperature of the molten salt on the shell side should always be maintained between 270ºC and 300ºC to prevent condensation on the molten salt side. Each section of the equipment should be heated evenly.

6. The method for injecting heat transfer oil and molten salt into a trough-type molten salt-heat transfer oil solar thermal unit according to claim 1, characterized in that: In step S6, before the system is filled with molten salt and pressurized, the heat transfer oil on the pipe side must first be pressurized and flow.

7. The method for injecting heat transfer oil and molten salt into a trough-type molten salt-heat transfer oil solar thermal unit according to claim 1, characterized in that: The salt discharge system consists of a salt discharge tank, a salt discharge pump, and pipelines. Molten salt that remains in the drain pipe is discharged to the salt discharge tank through the pipelines. The molten salt in the salt discharge tank can be transported back to the hot and cold salt tanks by the salt discharge pump.

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