A heat storage system for pumping large flow of high temperature molten salts

Abstract

This invention discloses a thermal energy storage system for pumping large-flow-rate high-temperature molten salt, relating to the fields of solar thermal power generation, nuclear power, and thermal power energy storage. It includes a main molten salt storage tank, a stabilizing tank, a horizontal storage tank, a main circulating molten salt pump, and a salt-reducing temperature-regulating pump. The main molten salt storage tank is connected to the stabilizing tank via multiple pipelines. The outlet of the stabilizing tank is directly connected to the suction inlet of the main circulating molten salt pump via a pipeline equipped with an isolation valve and an air cooler, stabilizing the pump suction flow and enabling large-flow-rate molten salt pumping. The arrangement of one or more pipelines between the main molten salt storage tank and the stabilizing tank reduces the height of unusable molten salt in the main molten salt storage tank, saving costs. An air cooler is installed after the stabilizing tank to ensure safe isolation during isolation valve maintenance. This invention addresses the need for pumping large-flow-rate high-temperature molten salt in solar thermal power plants or nuclear power plants of 350MW or above, while also adapting to the requirements of long-term, uninterrupted low-speed pump operation.

Description

Technical Field

[0001] This invention relates to the fields of solar thermal power generation, nuclear power, and thermal power energy storage technology, and in particular to a thermal storage system for pumping high-flow-rate high-temperature molten salt. Background Technology

[0002] The mainstream technologies for concentrated solar power (CSP) include tower, molten salt trough, and molten salt Fresnel systems, with units exceeding 350MW already in operation. Molten salt nuclear power units are also being planned, with installed capacities typically not less than 600MW. CSP units exceeding 350MW require a total molten salt volume of 4500m³ pumped from the central island to the SGS heat exchanger. 3 The conventional technical solution is to use a long-shaft molten salt pump installed on top of the main molten salt storage tank and suspended inside the tank to transport high-temperature molten salt; however, this has the following problems: First, the use of a long-shaft pump, with a single pump selected having a flow rate of 1250 m³ / h or more. 3 / h, minimum submersion depth 800-1000mm; the minimum shutdown liquid level requirement in the tank leads to the procurement cost of unusable molten salt reaching over 20 million yuan; secondly, there are many pumps, with long-shaft pumps reaching 18-20m in length, resulting in high cost and difficulties in hoisting and maintenance; thirdly, they are not suitable for low-frequency operation at 15-20Hz; fourthly, the potential maintenance risks of long-shaft pumps, such as vibration, are relatively high.

[0003] Chinese invention patent CN114087210B discloses a molten salt pump device with in-tank pressurization, currently used in some solar thermal power plants. Molten salt in the main molten salt storage tank flows into a horizontal storage tank by gravity. The molten salt level in the main molten salt storage tank is balanced by adjusting the pressure of compressed gas (compressed air or nitrogen) above the lower tank. This effectively solves the shortcomings of long-shaft pumps and potential safety hazards in operation and maintenance. Practical experience has proven that short-shaft pumps have excellent operating performance. However, since the molten salt in the lower tank is covered by compressed gas, the pump still draws in molten salt from the lower tank. Gas is easily drawn in during lower-level pumping. To ensure the pump does not draw in gas and to prevent eddy currents, the pumping flow rate is limited to 1250 m³ / h. 3 Within / h; the low-level tank is pressurized and requires multiple tank openings, placing higher demands on the low-level tank. Additionally, because multiple pumps are installed inside the tank simultaneously, the gas consumption is large.

[0004] For molten salt pumps in molten salt bath solar thermal power plants and nuclear power plants, they must be able to operate under low-frequency conditions for extended periods to prevent system freezing. The required delivery capacity of a single molten salt pump in a 600MW nuclear power plant is 4000-6000 m³ / h. 3 / h. For molten salt reactor nuclear power units, in addition to meeting the requirements of high-flow-rate delivery, the molten salt pumps must also be able to operate continuously at low frequencies for extended periods to ensure that the molten salt in the loop is always in a flowing state and to prevent safety risks caused by molten salt freezing and blockage in the loop. These requirements pose greater challenges to the reliability and operational flexibility of the molten salt pumping system.

[0005] Chinese invention patent CN103292485B discloses a molten salt thermal storage and heat exchange system for solar thermal power generation, including a molten salt thermal storage system and a molten salt heat exchange system. The molten salt thermal storage system comprises a cryogenic tank and a high-temperature tank. A cryogenic molten salt pump for regulating the flow rate of molten gas entering the solar heating system is installed at the bottom of the cryogenic tank, and a high-temperature molten salt pump for regulating the flow rate of molten salt entering the heat exchange system is installed at the bottom of the high-temperature tank. Both the cryogenic and high-temperature molten salt pumps are horizontally installed at the bottom of the tanks, and their installation position is below ground level. The molten salt heat exchange system equipment adopts a serpentine heat exchange tube structure. This design uses a horizontally installed molten salt pump, a pump structure that is currently not feasible to implement.

[0006] Chinese invention patent CN119062914A discloses a centralized molten salt pumping system and its operation method, including a high-temperature molten salt storage tank, a low-temperature molten salt storage tank, an intermediate molten salt storage tank, and a desalination tank. A first molten salt pump is installed on the intermediate molten salt storage tank. The outlet of the first molten salt pump is connected to the high-temperature molten salt storage tank and the low-temperature molten salt storage tank respectively via a first pipe and a second pipe. The high-temperature molten salt storage tank is connected to the intermediate molten salt storage tank via a third pipe, and the low-temperature molten salt storage tank is connected to the intermediate molten salt storage tank via a fourth pipe. The intermediate molten salt storage tank and the desalination tank are connected via a fifth pipe. A desalination pump is installed on the desalination tank, and the outlet of the desalination pump is connected to the high-temperature molten salt storage tank and the low-temperature molten salt storage tank respectively via a sixth pipe and a seventh pipe. In this design, the molten salt pump inlet is located inside the intermediate molten salt storage tank. The liquid level in the intermediate molten salt storage tank is adjusted by regulating the opening of the molten salt valve entering the intermediate storage tank to maintain a certain gas phase space within the tank, and the molten salt valve or pump is difficult to maintain.

[0007] Chinese invention patent CN121323375A discloses an integrated high-low level molten salt tank, comprising a vertical molten salt storage tank and a low-level molten salt storage tank connected as one unit. The low-level molten salt storage tank is located at the bottom of the vertical molten salt storage tank, and the top of the vertical molten salt storage tank has a molten salt inlet and a vent. A short-shaft pump is installed on the top of the low-level molten salt storage tank, and the outlet of the short-shaft pump is connected to a molten salt delivery pipeline. A connecting pipe is provided between the top of the vertical molten salt storage tank and the top of the low-level molten salt storage tank. In this design, the short-shaft pump is installed on the top of the integrated low-level storage tank. If the pump fails, because the low-level storage tank is integrated with the main storage tank and is filled with molten salt, it is impossible to repair or replace the pump without emptying the entire system; furthermore, there is no low-pressure tank around the pump, making it impossible to resolve pump seal leakage.

[0008] Therefore, finding a reliable solution to properly address the pumping requirements of large-flow molten salt, meet the requirements for long-term operation at low frequencies of 10-25Hz, and ensure the safety, reliability, and cost-effectiveness of the energy storage process system is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to provide a thermal storage system that pumps high-flow-rate, high-temperature molten salt, solving the problems of high failure rate, high maintenance difficulty, and high cost of unusable molten salt and high-level platforms in solar thermal power plants, which lead to high power plant construction costs and lack of advantages for large-scale power plant development.

[0010] To achieve the above technical objectives and meet the above technical requirements, the technical solution adopted by this invention is: a thermal storage system for pumping high-flow-rate high-temperature molten salt, comprising: The main molten salt storage tank is used to store the high-temperature molten salt of the pumping main circuit system; The inlet of the stabilizing tank is connected to the outlet of the main molten salt storage tank through one or more pipelines. Molten salt in the main molten salt storage tank flows into the stabilizing tank under its own gravity. A horizontal storage tank is an atmospheric pressure tank connected to the atmosphere. It is used to store molten salt discharged from the main circulation molten salt pump and the main circuit system, or molten salt used for starting and stopping the temperature regulating pump of the power plant. It is also used to collect the molten salt leaking from the sealing of the main circulation molten salt pump and to provide a heat tracing and insulation environment for the main circulation molten salt pump.

[0011] The main circulation molten salt pump is installed on the upper platform of the horizontal storage tank. The suction port of the main circulation molten salt pump is connected to the outlet of the stabilizing tank through the first pipeline. The pump sucks in no vortex and no gas, and is used to pump the molten salt from the stabilizing tank to the main loop system or the first recirculation loop system. A salt-absorbing temperature regulating pump is installed on the upper platform of the horizontal storage tank. Its suction port extends into the horizontal storage tank and is used to pump the molten salt in the horizontal storage tank to the pipeline of the main loop system or the second recirculation loop system.

[0012] Preferably, the first pipeline is equipped with a first air cooler and a first electric isolation valve. The molten salt in the main molten salt storage tank flows into the stabilizing tank through one or more pipelines under its own gravity, and then is pumped out through the first air cooler and the first electric isolation valve under the suction of the main circulating molten salt pump, and enters the main loop system or the first recirculation loop system.

[0013] Preferably, a second pipeline connects the flow stabilizer tank and the horizontal storage tank, and a second air cooler and an electric regulating valve are installed on the second pipeline to replenish the molten salt level in the horizontal storage tank.

[0014] The first and second air coolers are configured to: when maintenance is required on the electric isolation valve or electric regulating valve of the corresponding inlet pipeline, cool air is introduced to freeze the molten salt in the pipeline and form a blockage; after maintenance is completed, heated air is introduced to thaw the frozen molten salt and restore normal flow.

[0015] Preferably, a discharge pipe is provided between the first pipeline and the horizontal storage tank, and a second electric isolation valve is provided on the discharge pipe. Molten salt from the main circulating molten salt pump and the main circuit system pipeline is discharged to the horizontal storage tank by gravity through the second electric isolation valve and the discharge pipe.

[0016] Preferably, the multi-pipeline arrangement between the main molten salt storage tank and the flow stabilizing tank is such that the minimum unusable molten salt level in the main molten salt storage tank is reduced to 500 mm.

[0017] Preferably, the outlet of the main circulating molten salt pump is connected to the top of the main molten salt storage tank through a first recirculation pipeline and a third electric isolation valve to form a first recirculation loop, which is used for the commissioning of the main circulating molten salt pump.

[0018] Preferably, the outlet of the salt-reducing temperature regulating pump is connected to the top of the main molten salt storage tank through a second recirculation pipeline and a fourth electric isolation valve to form a second recirculation loop, which is used to send the molten salt in the horizontal storage tank back to the main molten salt storage tank when the salt-reducing temperature regulating pump is being debugged, when the molten salt level in the horizontal storage tank exceeds the standard, or when the system is shut down for salt removal.

[0019] Preferably, the main molten salt storage tank and the horizontal storage tank are also equipped with radar level gauges to detect the level of high-temperature molten salt in the main molten salt storage tank and the horizontal storage tank, and to control the start and stop of the pump.

[0020] Preferably, the main molten salt storage tank and the horizontal storage tank are equipped with electric heaters for heating the molten salt.

[0021] Optionally, the main circulating molten salt pump is a cold salt pump or a hot salt pump of a solar thermal / nuclear power plant, and the salt-repellent temperature control pump is a temperature control pump or a salt-repellent pump of a solar thermal / nuclear power plant.

[0022] Preferably, both the main circulating molten salt pump and the salt-reducing temperature regulating pump are short-shaft pumps.

[0023] Preferably, the drive motors of the main circulating molten salt pump and the salt-reducing temperature regulating pump are variable frequency motors, configured to operate continuously for a long time in a low frequency range of 10-25Hz.

[0024] Working Principle: In this system, high-temperature molten salt in the main molten salt storage tank flows into a flow stabilizing tank through multiple pipelines under its own gravity. The flow stabilizing tank rectifies and stabilizes the flow of the molten salt, which is then drawn in by the main circulating molten salt pump via the first pipeline and pumped to the heat exchanger of the main loop system. No gas is drawn in at the pump's suction inlet, ensuring stable high-flow-rate delivery. A horizontal storage tank serves as an auxiliary container, collecting leaked molten salt from the main circulating molten salt pump and providing it with a heated environment. When the liquid level exceeds the limit, it is pumped back to the main molten salt storage tank by a salt-repellent temperature-regulating pump. Both the main circulating molten salt pump and the salt-repellent temperature-regulating pump have recirculation loops for pump commissioning.

[0025] Compared with the traditional structure, the beneficial effects of the present invention are as follows: 1. This invention overcomes flow rate limitations, enabling high-flow-rate, high-temperature molten salt pumping. By incorporating a flow stabilizing tank, eddy currents are prevented; the main circulating molten salt pump's suction inlet is directly connected to the flow stabilizing tank pipeline, avoiding the risk of flow interruption or unstable pump outlet flow caused by gas intake and vortices; the impeller suction method of the main circulating molten salt pump is changed from submerged suction to a suction flow channel method free of eddies and impurity gas, achieving a total system flow rate of 4500 m³ / h. 3 / h or even 10000m 3 With a stable high flow rate of / h, it meets the needs of solar thermal power plants of 350MW and above and nuclear power plants of 600MW and above.

[0026] 2. This invention reduces the height of the molten salt dead zone, saving costs. By arranging multiple pipelines between the main molten salt storage tank and the flow stabilizing tank, the height of the unusable molten salt (dead zone) in the main molten salt storage tank is reduced to a minimum of 500mm, significantly reducing the amount of unusable molten salt and saving on molten salt procurement costs.

[0027] 3. An air cooler is installed after the flow stabilizer. If the isolation valve on the inlet pipeline needs maintenance, cooling air is introduced to freeze the molten salt at this location, forming a solid plug and achieving safe isolation. After the isolation valve is maintained, heated air can be introduced to thaw the molten salt, restore flow, and facilitate on-site operation.

[0028] 4. This invention uses a high-flow-rate main circulation molten salt pump, which reduces the number of pumps required for the unit, improves the operating efficiency of a single pump, simplifies operation and maintenance, reduces platform construction costs, and lowers the overall construction cost of the power plant system, thus providing favorable conditions for the development of large-scale power plants.

[0029] 5. This invention can adapt to low-frequency continuous operation. Both the main circulation molten salt pump and the salt-repellent temperature regulating pump are short-shaft pumps, installed on a concrete platform, which improves operational stability and reliability. The operating vibration value can be controlled within 1.5mm / s, significantly improving the long-term operational reliability of the pump set and ensuring the operational reliability of large-scale power plants. The short-shaft pump with variable frequency drive can operate continuously for a long time at a low frequency of 10-25Hz, preventing molten salt from freezing and blocking in the pipeline. It is particularly suitable for solar thermal power plants that start and stop daily and nuclear power plants that require continuous circulation.

[0030] 6. This invention achieves automatic recovery of seal leakage. The horizontal storage tank simultaneously serves as a leakage collection container for the main circulating molten salt pump and a heat-tracing and insulation environment. Molten salt leaking from the pump seal flows directly back to the horizontal storage tank and is periodically pumped back to the main tank via a salt-reducing temperature-regulating pump, avoiding safety risks and equipment freezing caused by molten salt leakage.

[0031] 7. This invention enables online maintenance of pumps. Through the isolation valve and discharge pipeline on the pump inlet side, the molten salt in the pump and pipeline can be discharged into a horizontal storage tank, realizing safe disassembly and online maintenance of the pump without emptying the main molten salt storage tank. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the present invention; In the diagram: 1. Main molten salt storage tank, 2. Horizontal storage tank, 3. Flow stabilizing tank, 4. Main circulating molten salt pump, 5. Salt-reducing and temperature-regulating pump, 6. Main loop system, 7. Radar level gauge; 11. First electric isolation valve; 12. Second electric isolation valve; 13. Third electric isolation valve; 14. Electric regulating valve; 15. Fourth electric isolation valve; 21. First air cooler; 22. Second air cooler; 31. First pipeline, 32. Second pipeline, 33. Discharge pipeline, 34. First recirculation pipeline, 35. Second recirculation pipeline. Detailed Implementation

[0033] The present invention will be further described below.

[0034] Example 1: A thermal storage system for pumping high-flow-rate high-temperature molten salt includes a main molten salt storage tank 1, a horizontal storage tank 2, a flow stabilizer tank 3, a main circulating molten salt pump 4, a salt-reducing and temperature-regulating pump 5, a first electric isolation valve 11, a second electric isolation valve 12, a third electric isolation valve 13, a fourth electric isolation valve 15, an electric regulating valve 14, a first air cooler 21, a second air cooler 22, and pipelines.

[0035] The main molten salt storage tank 1 is used to store high-temperature molten salt for the main pumping circuit system. Its bottom is connected to the flow stabilizing tank 3 through multiple pipes (arranged at different heights and radially). The molten salt in the main molten salt storage tank 1 flows into the flow stabilizing tank 3 under the action of gravity through multiple pipes. The arrangement of multiple pipes ensures that when the liquid level in the main molten salt storage tank 1 drops to 500mm, the lowest pipe can still draw in molten salt, thereby significantly reducing the amount of molten salt in the dead zone inside the tank.

[0036] The bottom outlet of the flow stabilizer tank 3 is connected to the suction port of the main circulating molten salt pump 4 via the first pipeline 31. A first air cooler 21 and a first electrically operated isolation valve 11 are sequentially installed on this first pipeline 31. The first electrically operated isolation valve 11 is a fully open / fully closed valve located on the pump inlet side.

[0037] The main circulating molten salt pump 4 is installed on a concrete platform above the horizontal storage tank 2, and the pump body is sealed to the horizontal storage tank 2 via a bellows pipe. The suction inlet of the main circulating molten salt pump 4 is connected to the outlet of the stabilizing tank 3 through the first pipeline 31, drawing in molten salt from the side. There is no gas space at the suction inlet. The distance from the lowest liquid level of the main molten salt storage tank to the pump impeller is more than 3 meters. The stabilizing tank rectifies the molten salt, and the length of the first pipeline ensures that the molten salt forms a stable flow before entering the pump suction inlet, avoiding the risk of flow interruption or unstable outlet flow caused by eddies and gas entrainment. The entire first pipeline 31 and the stabilizing tank 3 are filled with molten salt, and there is no gas phase interface, enabling the main circulating molten salt pump 4 to achieve high-flow pumping.

[0038] Horizontal storage tank 2 is an atmospheric pressure tank connected to the atmosphere or the top of the main molten salt storage tank 1. The installation height of the stabilizing tank 3 and horizontal storage tank 2 is lower than the bottom elevation of the main molten salt storage tank 1. Horizontal storage tank 2 has a small volume and capacity, used only to store molten salt forcibly discharged during the main circuit desalination process and to seal leaking molten salt from the main circulation molten salt pump 4, as well as to provide a heat-tracing and insulation environment for the pump. The pump body of the main circulation molten salt pump 4 extends into horizontal storage tank 2. The molten salt stored in horizontal storage tank 2 provides heat tracing and insulation to the pump body through thermal radiation and heat conduction, ensuring that the pump body temperature remains above the freezing point of the molten salt and preventing the molten salt inside the pump from freezing. Horizontal storage tank 2 is equipped with a radar level gauge 7 for controlling the start and stop of the desalination and temperature-regulating pump 5.

[0039] A discharge pipe 33 is connected to the inlet pipe of the main circulating molten salt pump 4. One end of the discharge pipe 33 is connected downstream of the second electric isolation valve 12, and the other end is directly connected to the horizontal storage tank 2. The discharge pipe 33 is equipped with the second electric isolation valve 12. When the main circulating molten salt pump 4 needs maintenance, the first electric isolation valve 11 is closed, and the second electric isolation valve 12 and the third electric isolation valve 13 are opened. The molten salt in the pump and pipeline is discharged into the horizontal storage tank 2 by its own weight. After that, the pump can be disassembled for maintenance.

[0040] A small-diameter second pipe 32 is also led out from the bottom of the flow stabilizing tank 3 and connected to the horizontal storage tank 2. The second pipe 32 is equipped with a second air cooler 22 and an electric regulating valve 14. The electric regulating valve 14 is used to replenish molten salt according to the liquid level signal of the horizontal storage tank 2 to maintain the liquid level of the horizontal storage tank 2 within a reasonable range.

[0041] The outlet pipeline of the main circulation molten salt pump 4 is divided into two paths: one path leads to the heat exchanger of the main loop system 6 (not shown in the figure), and the other path returns to the top of the main molten salt storage tank 1 through the third electric isolation valve 13 and the first recirculation pipeline 34. The first recirculation pipeline 34 is configured to send the molten salt at the pump outlet back to the main molten salt storage tank 1 during the commissioning of the main circulation molten salt pump 4.

[0042] The brine-cooling and temperature-regulating pump 5 is also installed on the upper platform of the horizontal storage tank 2, with its suction inlet extending below the liquid level inside the horizontal storage tank 2. The outlet pipeline of the brine-cooling and temperature-regulating pump 5 is divided into two paths: one path returns to the top of the main molten salt storage tank 1 through the fourth electric isolation valve 15 and the second recirculation pipeline 35; the other path connects to the pipeline of the main loop system 6 to realize high-temperature molten salt temperature regulation or tank filling. The second recirculation pipeline 35 is configured to: send the molten salt in the horizontal storage tank 2 back to the main molten salt storage tank 1 when the brine-cooling and temperature-regulating pump 5 is being commissioned, when the molten salt level in the horizontal storage tank 2 exceeds the standard, or when the system is shut down for brine cooling.

[0043] The salt-removing temperature regulating pump 5 has two operating functions: (1) Salt removal function - when the molten salt level in the horizontal storage tank 2 exceeds the standard (such as too much molten salt collected after salt removal from the main loop system 6 pipeline, or too much accumulation of leakage from the main circulation molten salt pump 4), the salt-removing temperature regulating pump 5 is started, the fourth electric isolation valve 15 is opened, and the molten salt in the horizontal storage tank 2 is pumped back to the main molten salt storage tank 1 through the second recirculation pipeline 35 until the liquid level in the horizontal storage tank 2 is within a reasonable range; (2) Temperature regulation function - when the solar thermal power generation is started, the salt-removing temperature regulating pump 5 is started first, and the low-temperature molten salt in the horizontal storage tank 2 is pumped to the main loop pipeline of the system for low-temperature preheating and salt mixing. The main circulation molten salt pump 4 is started and enters normal circulation, gradually increasing the operating temperature. After reaching the rated operating temperature, the salt-removing temperature regulating pump 5 is stopped. When the solar thermal power generation is shut down, the salt-removing temperature regulating pump is started, and the temperature is gradually reduced, and the power station is safely shut down.

[0044] Both the main circulating molten salt pump 4 and the salt-reducing temperature regulating pump 5 are driven by variable frequency motors, which can operate continuously for a long time at a frequency of 10-25Hz to prevent the molten salt from freezing in the pipeline.

[0045] In this embodiment, the main circulating molten salt pump 4, at a minimum liquid level of 500mm and rated speed, is designed to achieve a single-unit flow rate of up to 3000 m³ / h. 3 / h, the head meets the system requirements.

[0046] The first electric isolation valve 11, the second electric isolation valve 12, and the third electric isolation valve 13 and the fourth electric isolation valve 15 on the recirculation pipeline are all fully open and fully closed valves. The electric regulating valve 14 is only used for flow regulation of the small-diameter supplementary pipeline.

[0047] The salt-absorbing temperature regulating pump 5 has a small operating flow rate and short operating time, and the electric regulating valve 14 does not require frequent adjustment and has a long service life.

[0048] Air cooler working principle: When the first electric isolation valve 11 needs maintenance, first stop the main circulating molten salt pump 4, then introduce ambient temperature compressed air (or cold air) into the first air cooler 21 to cool the molten salt in that section of the pipeline below its freezing point, forming a solid plug that isolates the upstream molten salt. Open the second electric isolation valve 12 and the third electric isolation valve 13, and the molten salt in the pump and pipeline will be discharged into the horizontal storage tank 2 by its own weight. At this time, the first electric isolation valve 11 can be safely disassembled for maintenance. After maintenance, introduce hot air (temperature higher than the melting point of the molten salt) into the first air cooler 21 to melt the solid plug, restore the flow of the molten salt, and restart the system.

[0049] The core power equipment of this invention, the short-shaft molten salt pump, has been validated in a solar thermal power plant, exhibiting a minimum operating vibration of 0.3 mm / s and demonstrating excellent performance. Furthermore, due to the installation of an inlet-side isolation valve and discharge pipeline, the pump's maintenance time has been reduced from over 30 days in traditional solutions to less than 6 days.

[0050] Example 2: This example applies to molten salt reactor nuclear power plants with a capacity of 300MW or higher. The main circulation molten salt pumps (4 units) are designed to deliver a flow rate of 8000 m³ / s. 3 / h, using a variable frequency motor, with a long-term operating frequency range of 10-25Hz. Everything else is the same as in Example 1.

[0051] The present invention describes the operation method of a thermal storage system for pumping large-flow-rate high-temperature molten salt, taking concentrated solar power generation as an example: (I) Debugging preparation: Before starting the molten salt pump for commissioning, the main molten salt storage tank 1 contains high-temperature molten salt, and the liquid level is higher than the minimum shutdown liquid level. Open the electric regulating valve 14, and the horizontal storage tank 2 contains molten salt at a reasonable liquid level. The liquid level is monitored by the radar level gauge 7 to ensure that the suction port of the salt-reducing temperature regulating pump 5 is submerged below the liquid surface.

[0052] Open the first electric isolation valve 11, and the flow stabilizer tank 3, the main circulating molten salt pump 4, the first pipeline 31, etc. are filled with molten salt.

[0053] (II) Commissioning of main circulation molten salt pump and salt-removing temperature regulating pump Debugging of the main circulating molten salt pump: Set the starting frequency of the variable frequency motor, open the third electric isolation valve 13, and then start the main circulating molten salt pump 4; under the suction action of the main circulating molten salt pump 4, the molten salt enters the pump inlet through the first pipeline 31, the first air cooler 21, and the first electric isolation valve 11, and then is pumped out from the pump outlet; the molten salt returns to the top of the main molten salt storage tank 1 through the first recirculation pipeline 34, forming a loop for debugging.

[0054] Salt-absorbing temperature regulating pump commissioning: Open the fourth electric isolation valve 15, start the salt-absorbing temperature regulating pump 5, open the electric regulating valve 14 to a certain degree, maintain the molten salt level in the horizontal storage tank 2, and the pump directly draws the molten salt in the horizontal storage tank 2 back to the top of the main molten salt storage tank 1 through the second recirculation pipeline 35 to form a loop for commissioning.

[0055] (III) Operation of cold salt pumps for solar thermal power generation The cold salt pumping system for solar thermal power generation is arranged in the same way as this system. The main molten salt storage tank 1 is the cold salt tank for the power plant, and the main circulating molten salt pump 4 is the cold salt pump for the power plant. The horizontal storage tank 2 also stores cold salt; the main function of the salt-reducing and temperature-regulating pump 5 is to regulate the system temperature.

[0056] Open the inlet valve of the cold salt pump (i.e., the first electric isolation valve 11), close the second electric isolation valve 12 and the third electric isolation valve 13, set the starting frequency of the cold salt pump motor, and after the pump is started, the molten salt enters the absorber or collector of the main circuit system 6 to absorb heat, and then the high-temperature molten salt is stored in the power plant hot salt tank.

[0057] (iv) Operation of the thermosalinity pump for solar thermal power generation The hot salt pumping system of the solar thermal power plant is arranged in the same way as this system. The main molten salt storage tank 1 is the power plant's hot salt tank, and the main circulating molten salt pump 4 is the power plant's hot salt pump. The horizontal storage tank 2 also stores hot salt; the main function of the salt removal and temperature control pump 5 is to remove salt from the system.

[0058] First, close the fourth electric isolation valve 15, start the temperature regulating pump in the horizontal storage tank of the power plant's cold salt pump, and pump the cold salt from the horizontal storage tank to the pipeline before the evaporator for preheating or mixing; then set the starting frequency of the hot salt pump motor, start the hot salt pump, enter the normal cycle, gradually increase the frequency of the hot salt pump, gradually increase the system operating temperature, and after reaching the rated operating temperature, stop the temperature regulating pump 5; the hot salt pump will operate normally.

[0059] The solar thermal power plant was shut down, and the temperature control pump was restarted to gradually reduce the system temperature, resulting in a safe shutdown of the power plant.

[0060] (v) Low-frequency operation When the load on the thermal collector system or power plant decreases at night, the frequency of the variable frequency motor of the main circulation molten salt pump 4 can be reduced to 15-25Hz, and the pump runs at a low speed to keep the molten salt flowing slowly in the main circuit and prevent the molten salt from solidifying.

[0061] (vi) Shutdown and salt removal When the pump stops, the second electric isolation valve 12 and the third electric isolation valve 13 are opened, and the molten salt in the main system pipeline is discharged from the low position of the pipeline to the horizontal storage tank 2 by its own gravity. The salt-releasing and temperature-regulating pump 5 is started, and the fourth electric isolation valve 15 is opened to pump the molten salt in the horizontal storage tank 2 that exceeds the liquid level back into the main molten salt storage tank 1 through the second recirculation pipeline 35.

[0062] (vii) Isolation valve maintenance methods When the first electric isolation valve 11 needs maintenance, follow these steps: (1) Cooling air (or ambient temperature compressed air) is introduced into the first air cooler 21 to cool the molten salt in this section of the pipeline to below the freezing point, forming a solid plug to isolate the upstream molten salt from the downstream. (2) After confirming the formation of the embolism (judged by temperature detection), open the second electric isolation valve 12 and the third electric isolation valve 13 to drain the molten salt in the first pipeline 31; disassemble and repair the first electric isolation valve 11; (3) After the maintenance is completed, hot air (temperature higher than the melting point of molten salt) is introduced into the first air cooler 21 to melt the solid plug and restore the flow of molten salt.

[0063] Similarly, the maintenance of other electric isolation valves or electric regulating valves 14 can be carried out by referring to the above method, using the nearby air cooler (the second air cooler 22 corresponds to the electric regulating valve 14) for freeze-thaw operation.

[0064] The above embodiments of the present invention are merely examples to clearly illustrate the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A thermal storage system for pumping high-flow-rate high-temperature molten salt, characterized in that: include: The main molten salt storage tank (1) is used to store high-temperature molten salt pumped to the main circuit system (6); The inlet of the stabilizing tank (3) is connected to the bottom outlet of the main molten salt storage tank (1) through one or more pipelines; Horizontal storage tank (2) is used to store molten salt discharged from the main circulation molten salt pump (4) and the main circuit system (6) or molten salt used for power plant start-up, shutdown and temperature regulation; The main circulation molten salt pump (4) is installed on the upper platform of the horizontal storage tank (2). The suction port of the main circulation molten salt pump (4) is connected to the outlet of the stabilizing tank (3) through the first pipeline (31) to pump the molten salt from the stabilizing tank (3) to the main loop system (6) or the first recirculation loop system. A salt-cooling temperature regulating pump (5) is installed on the upper platform of the horizontal storage tank (2), with its suction port extending into the horizontal storage tank (2) to pump the molten salt in the horizontal storage tank (2) to the pipeline of the main loop system (6) or the second recirculation loop system.

2. The thermal storage system for pumping high-flow-rate high-temperature molten salt according to claim 1, characterized in that: The first pipeline (31) is equipped with a first air cooler (21) and a first electric isolation valve (11). The molten salt in the main molten salt storage tank (1) flows into the stabilizing tank (3) through one or more pipelines under its own gravity. Then, under the suction of the main circulating molten salt pump (4), it is pumped out through the first air cooler (21) and the first electric isolation valve (11) and enters the main loop system (6) or the first recirculation loop system.

3. The thermal storage system for pumping high-flow-rate high-temperature molten salt according to claim 1 or 2, characterized in that: The outlet of the main circulating molten salt pump (4) is connected to the top of the main molten salt storage tank (1) through the first recirculation pipeline (34) and the third electric isolation valve (13) to form the first recirculation loop for the commissioning of the main circulating molten salt pump (4).

4. The thermal storage system for pumping high-flow-rate high-temperature molten salt according to claim 1, characterized in that: The outlet of the salt-repellent temperature regulating pump (5) is connected to the top of the main molten salt storage tank (1) through the second recirculation pipeline (35) and the fourth electric isolation valve (15) to form a second recirculation loop, which is used to send the molten salt in the horizontal storage tank (2) back to the main molten salt storage tank (1) when the salt-repellent temperature regulating pump (5) is being debugged, or when the molten salt level in the horizontal storage tank (2) exceeds the standard, or when the system is shut down for salt removal.

5. The thermal storage system for pumping high-flow-rate high-temperature molten salt according to claim 1, characterized in that: A second pipeline (32) is connected between the flow stabilizer (3) and the horizontal storage tank (2). The second pipeline (32) is equipped with a second air cooler (22) and an electric regulating valve (14) to replenish the molten salt level of the horizontal storage tank (2).

6. The thermal storage system for pumping high-flow-rate high-temperature molten salt according to claim 1, characterized in that: A discharge pipe (33) is provided between the first pipeline (31) and the horizontal storage tank (2). A second electric isolation valve (12) is provided on the discharge pipe (33). Molten salt from the main circulating molten salt pump (4) and the main circuit system (6) is discharged to the horizontal storage tank (2) by gravity through the second electric isolation valve (12) and the discharge pipe.

7. The thermal storage system for pumping high-flow-rate high-temperature molten salt according to claim 1, characterized in that: The multi-pipeline arrangement between the main molten salt storage tank (1) and the flow stabilizing tank (3) reduces the minimum unusable molten salt level in the main molten salt storage tank (1) to 500 mm.

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