Closed fused salt energy storage system

Abstract

A closed fused salt energy storage system comprises a high-temperature fused salt tank, a low-temperature fused salt tank and a nitrogen storage buffer tank, the high-temperature fused salt tank is connected with an outlet of a high-temperature fused salt conveying pipeline, and a high-temperature fused salt conveying pump is connected to the high-temperature fused salt conveying pipeline in series. The high-temperature fused salt conveying pipeline is connected with an inlet of a heat release loop of a heat exchange unit for generating steam or hot water, an outlet of the heat release loop of the heat exchange unit is connected with an inlet of a low-temperature fused salt return pipeline, and an outlet of the low-temperature fused salt return pipeline is connected with a low-temperature fused salt tank; the low-temperature fused salt tank is connected with an outlet of the low-temperature fused salt conveying pipeline, the low-temperature fused salt conveying pipeline is connected with the low-temperature fused salt conveying pump and the fused salt heating device in series, and an outlet of the low-temperature fused salt conveying pipeline is connected with the high-temperature fused salt tank. The invention aims to provide an economical, energy-saving and environment-friendly closed molten salt energy storage system which is extremely low in nitrogen consumption, greatly reduces energy waste, greatly reduces NOx emission and greatly reduces environmental pollution.

Description

Technical Field

[0001] The present invention relates to a closed molten salt energy storage system. Background Art

[0002] A molten salt energy storage system generally includes a storage unit (high-temperature molten salt tank, low-temperature molten salt tank), a conveying unit (high-temperature molten salt pump, low-temperature molten salt pump), a heating unit (molten salt electric heater, molten salt steam heater, molten salt heat transfer oil heater, etc.), a heat release unit (preheater, evaporator, superheater) and a nitrogen sealing unit. By storing electrical energy or heat energy during low valley periods or peak shaving periods in molten salt, heat is released during peak periods or non-peak shaving periods to generate steam (hot water) for power generation or heating.

[0003] As the molten salt heating and heat release processes proceed, the molten salt needs to be transferred between the high-temperature molten salt tank and the low-temperature molten salt tank. Since molten salt is prone to decomposition in an oxygen atmosphere at high temperatures, nitrogen is generally injected into the heat storage system for nitrogen sealing to prevent direct contact between oxygen and the molten salt.

[0004] In the prior art, both the high-temperature molten salt tank and the low-temperature molten salt tank are independently nitrogen sealed, that is, the nitrogen discharged when the molten salt enters the high-temperature molten salt tank and the low-temperature molten salt tank is directly discharged. In this way, a large amount of nitrogen needs to be consumed as the molten salt enters and leaves the high-temperature molten salt tank or the low-temperature molten salt tank, and then a large amount of nitrogen needs to be replenished. Since the discharged nitrogen contains a large amount of heat energy, directly discharging the high-temperature nitrogen will cause waste of energy, and the exhaust pipe is directly connected to the atmosphere, resulting in a large heat dissipation loss. At the same time, the discharged nitrogen contains a certain amount of NOx, and the emission of NOx into the environment will cause air pollution. Summary of the Invention

[0005] The purpose of the present invention is to provide an economical, energy-saving and environmentally friendly closed molten salt energy storage system with extremely low nitrogen consumption, greatly reduced energy waste, significantly reduced NOx emissions, and greatly reduced environmental pollution.

[0006] The closed molten salt energy storage system of the present invention includes a high-temperature molten salt tank, a low-temperature molten salt tank and a nitrogen storage buffer tank. The high-temperature molten salt tank is connected to the outlet of the high-temperature molten salt conveying pipeline. A high-temperature molten salt pump is connected in series on the high-temperature molten salt conveying pipeline. The high-temperature molten salt conveying pipeline is connected to the inlet of the heat release loop of the heat exchange unit for generating steam or hot water. The outlet of the heat release loop of the heat exchange unit is connected to the inlet of the low-temperature molten salt return pipeline. The outlet of the low-temperature molten salt return pipeline is connected to the low-temperature molten salt tank;

[0007] The low-temperature molten salt tank is connected to the outlet of the low-temperature molten salt conveying pipeline. A low-temperature molten salt pump and a molten salt heating device are connected in series on the low-temperature molten salt conveying pipeline. The outlet of the low-temperature molten salt conveying pipeline is connected to the high-temperature molten salt tank;

[0008] The top of the high-temperature molten salt tank is connected to the nitrogen storage buffer tank through a high-temperature nitrogen connecting pipe, and the top of the low-temperature molten salt tank is connected to the nitrogen storage buffer tank through a low-temperature nitrogen connecting pipe. The nitrogen storage buffer tank is connected to the outlet of the nitrogen delivery pipe.

[0009] Preferably, a check valve and a nitrogen heating device for heating nitrogen are connected in series on the nitrogen delivery pipe, and the inlet of the nitrogen delivery pipe is connected to the nitrogen storage tank of the nitrogen production device.

[0010] Preferably, the heat exchange unit is one, two or any combination of three of a preheater, an evaporator or a superheater. The molten salt heating device is a molten salt electric heater, a molten salt steam heater or a molten salt heat transfer oil heater. The nitrogen heating device is an electric heating device.

[0011] Preferably, the inlet of the nitrogen delivery pipe is connected to the nitrogen storage tank through a nitrogen storage tank expansion joint, the high-temperature nitrogen connecting pipe is connected to the high-temperature molten salt tank through a high-temperature nitrogen expansion joint, and the low-temperature nitrogen connecting pipe is connected to the low-temperature molten salt tank through a low-temperature nitrogen expansion joint.

[0012] Preferably, the outer surfaces of the high-temperature nitrogen connecting pipe, the low-temperature nitrogen connecting pipe and the nitrogen delivery pipe are respectively wrapped with heat insulation layers.

[0013] Preferably, a high-temperature molten salt tank rupture disk for pressure relief when the safety pressure is exceeded is provided at the top of the high-temperature molten salt tank, a low-temperature molten salt tank rupture disk for pressure relief when the safety pressure is exceeded is provided at the top of the low-temperature molten salt tank, and an overpressure check exhaust valve for pressure relief when the safety pressure is exceeded is provided at the top of the nitrogen storage buffer tank.

[0014] When the closed molten salt energy storage system of the present invention is in operation, nitrogen can be injected into the entire system through the nitrogen delivery pipe, that is, to fill nitrogen in the nitrogen storage buffer tank, high-temperature nitrogen connecting pipe, low-temperature nitrogen connecting pipe, high-temperature molten salt tank, low-temperature molten salt tank, high-temperature molten salt delivery pipeline, low-temperature molten salt return pipeline and nitrogen delivery pipe. Then, the molten salt is melted and filled into the low-temperature molten salt tank. Due to the occupancy of the molten salt entering the low-temperature molten salt tank, a certain amount of nitrogen is discharged into the nitrogen storage buffer tank and the high-temperature molten salt tank through the low-temperature nitrogen connecting pipe. If the pressure in the nitrogen storage buffer tank exceeds the set pressure value, the excess nitrogen will be discharged through two overpressure one-way exhaust valves; when energy storage is required, the molten salt is transported from the low-temperature molten salt tank to the molten salt heating device under the action of the low-temperature molten salt delivery pump. After being heated by the molten salt heating device, the molten salt is then transported to the high-temperature molten salt tank for storage. At the same time, the nitrogen in the high-temperature molten salt tank has its pressure increased due to the occupancy of the molten salt and is transferred to the nitrogen storage buffer tank and the low-temperature molten salt tank by relying on the pressure; when discharging energy, the molten salt is transported from the high-temperature molten salt tank to the heat exchange unit under the action of the high-temperature molten salt delivery pump, and the heat is transferred to the heat-conducting medium at the heat exchange unit through the heat exchange unit. The molten salt then enters the low-temperature molten salt tank for storage after heat exchange. At the same time, the nitrogen in the low-temperature molten salt tank has its pressure increased due to the occupancy of the molten salt, and the nitrogen in the low-temperature molten salt tank is transferred to the nitrogen storage buffer tank and the high-temperature molten salt tank by relying on the pressure. Therefore, the nitrogen consumption of the closed molten salt energy storage system of the present invention is extremely small, which can greatly save the usage amount of nitrogen. At the same time, since the amount of nitrogen discharged and supplemented in the system is extremely small, the heat carried out due to the discharge of nitrogen is also greatly reduced. Moreover, heat-insulating layers are provided on the pipelines of the nitrogen sealing unit, which greatly reduces the waste of energy. Since the amount of gas to be discharged is extremely small, the discharged NOx pollutants are also greatly reduced, greatly reducing the pollution to the environment.

[0015] Other details and features of the closed molten salt energy storage system of the present invention can be clearly understood by reading the embodiments described in detail below in conjunction with the drawings. Brief Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of the closed molten salt energy storage system of the present invention. Detailed Embodiments

[0017] As Figure 1 shown, the closed molten salt energy storage system of the present invention includes a high-temperature molten salt tank 1, a low-temperature molten salt tank 2 and a nitrogen storage buffer tank 3. The high-temperature molten salt tank 1 is connected to the outlet of the high-temperature molten salt delivery pipeline 4. A high-temperature molten salt delivery pump 5 is connected in series on the high-temperature molten salt delivery pipeline 4. The high-temperature molten salt delivery pipeline 4 is connected to the inlet of the heat release loop of the heat exchange unit 6 for generating steam or hot water. The outlet of the heat release loop of the heat exchange unit 6 is connected to the inlet of the low-temperature molten salt return pipeline 7. The outlet of the low-temperature molten salt return pipeline 7 is connected to the low-temperature molten salt tank 2;

[0018] The low-temperature molten salt tank 2 is connected to the outlet of the low-temperature molten salt conveying pipeline 8. A low-temperature molten salt pump 9 and a molten salt heating device 10 are connected in series on the low-temperature molten salt conveying pipeline 8, and the outlet of the low-temperature molten salt conveying pipeline 8 is connected to the high-temperature molten salt tank 1;

[0019] The top of the high-temperature molten salt tank 1 is connected to the nitrogen storage buffer tank 3 through a high-temperature nitrogen connecting pipe 11. The top of the low-temperature molten salt tank 2 is connected to the nitrogen storage buffer tank 3 through a low-temperature nitrogen connecting pipe 12. The nitrogen storage buffer tank 3 is connected to the outlet of the nitrogen delivery pipe 13.

[0020] As a further improvement of the present invention, a check valve 14 and a nitrogen heating device 15 for heating nitrogen are connected in series on the above-mentioned nitrogen delivery pipe 13, and the inlet of the nitrogen delivery pipe 13 is connected to the nitrogen storage tank 23 of the nitrogen production device 16. A check valve 14 is connected in series on the nitrogen delivery pipe 13, which can prevent the gas in the nitrogen storage buffer tank 3 from flowing back into the nitrogen storage tank 23 of the nitrogen production device 16.

[0021] As a further improvement of the present invention, the above-mentioned heat exchange unit 6 is any one, two or three of a preheater, an evaporator and a superheater in any combination. The molten salt heating device 10 is a molten salt electric heater, a molten salt steam heater or a molten salt heat transfer oil heater, and the nitrogen heating device 15 is an electric heating device. The nitrogen heating device 15 is used to heat the nitrogen supplemented into the nitrogen storage buffer tank 3 to a suitable temperature, thereby reducing the adverse effects on the molten salt system caused by the low temperature of nitrogen.

[0022] As a further improvement of the present invention, the inlet of the above-mentioned nitrogen delivery pipe 13 is connected to the nitrogen storage tank 23 through a nitrogen storage tank expansion joint 17, the high-temperature nitrogen connecting pipe 11 is connected to the high-temperature molten salt tank 1 through a high-temperature nitrogen expansion joint 18, and the low-temperature nitrogen connecting pipe 12 is connected to the low-temperature molten salt tank 2 through a low-temperature nitrogen expansion joint 19. The expansion joint can prevent the pipeline deformation caused by the thermal expansion and contraction of the pipeline from damaging the relevant pipelines.

[0023] As a further improvement of the present invention, the outer surfaces of the above-mentioned high-temperature nitrogen connecting pipe 11, low-temperature nitrogen connecting pipe 12 and nitrogen delivery pipe 13 are respectively wrapped with heat insulation layers. The outer surfaces of the high-temperature nitrogen connecting pipe 11, low-temperature nitrogen connecting pipe 12 and nitrogen delivery pipe 13 are respectively wrapped with heat insulation layers, which can reduce heat loss.

[0024] As a further improvement of the present invention, a high-temperature molten salt tank rupture disk 20 for pressure relief when the safety pressure is exceeded is provided at the top of the high-temperature molten salt tank 1, a low-temperature molten salt tank rupture disk 21 for pressure relief when the safety pressure is exceeded is provided at the top of the low-temperature molten salt tank 2, and an overpressure one-way exhaust valve 22 for pressure relief when the safety pressure is exceeded is provided at the top of the nitrogen storage buffer tank 3.

[0025] When the closed molten salt energy storage system of the present invention is initially operated, nitrogen needs to be injected into the entire system through the nitrogen delivery pipe 13, that is, the nitrogen storage buffer tank 3, the high-temperature nitrogen connecting pipe 11, the low-temperature nitrogen connecting pipe 12, the high-temperature molten salt tank 1, the low-temperature molten salt tank 2, the high-temperature molten salt delivery pipeline 4, the low-temperature molten salt return pipeline 7, and the nitrogen delivery pipe 13 should all be filled with nitrogen. Then, the molten salt is melted and filled into the low-temperature molten salt tank 2. Due to the occupation of space by the molten salt in the low-temperature molten salt tank 2, a certain amount of nitrogen is discharged into the nitrogen storage buffer tank 3 and the high-temperature molten salt tank 1 through the low-temperature nitrogen connecting pipe 12. If the pressure in the nitrogen storage buffer tank 3 exceeds the set pressure value, the excess nitrogen will be discharged through two overpressure one-way exhaust valves 22.

[0026] When energy storage is required, the molten salt is transported from the low-temperature molten salt tank 2 to the molten salt heating device 10 under the action of the low-temperature molten salt delivery pump 9. After being heated by the molten salt heating device 10, the molten salt is then transported to the high-temperature molten salt tank 1 for storage. At the same time, the nitrogen in the high-temperature molten salt tank 1 has its pressure increased due to the occupation of space by the molten salt and is transferred to the nitrogen storage buffer tank 3 and the low-temperature molten salt tank 2 depending on the pressure.

[0027] When discharging energy, the molten salt is transported from the high-temperature molten salt tank 1 to the heat exchange unit 6 under the action of the high-temperature molten salt delivery pump 5. The heat is transferred to the heat transfer medium - steam and water at the heat exchange unit 6 through the heat exchange unit 6, and the molten salt enters the low-temperature molten salt tank 2 for storage after heat exchange. At the same time, the nitrogen in the low-temperature molten salt tank 2 has its pressure increased due to the occupation of space by the molten salt, and the nitrogen in the low-temperature molten salt tank 2 is transferred to the nitrogen storage buffer tank 3 and the high-temperature molten salt tank 1 depending on the pressure.

[0028] Under ideal conditions, under the condition that the system has good sealing performance and no leakage occurs, the entire energy storage and energy discharge process does not require the replenishment and discharge of nitrogen, and the entire system reaches a balanced state.

[0029] In actual situations, the nitrogen consumed after the system operates normally is mainly due to the nitrogen consumption caused by the poor sealing of the system. This will reduce the nitrogen consumption to less than 5% of the original amount, greatly saving the use of nitrogen; at the same time, since the amount of nitrogen discharged and replenished by the system is extremely small, the heat carried out due to the discharge of nitrogen is also greatly reduced, and heat insulation layers are provided on the pipelines of the nitrogen sealing unit, which greatly reduces the waste of energy. Since the amount of gas to be discharged is extremely small, the discharged NOx pollutants are also greatly reduced, greatly reducing the pollution to the environment.

[0030] Therefore, the nitrogen consumption of the closed molten salt energy storage system of the present invention is extremely small, which can greatly save the usage of nitrogen. At the same time, since the amount of nitrogen discharged and replenished by the system is extremely small, the heat carried out due to the discharge of nitrogen is also greatly reduced. Moreover, heat insulation layers are provided on the pipelines of the nitrogen sealing unit, which greatly reduces the waste of energy. Since the amount of gas to be discharged is extremely small, the discharged NOx pollutants are also greatly reduced, greatly reducing the pollution to the environment.

Claims

1. Closed molten salt energy storage system, Characterized in that: It includes a high-temperature molten salt tank (1), a low-temperature molten salt tank (2) and a nitrogen storage buffer tank (3). The high-temperature molten salt tank (1) is connected to the outlet of the high-temperature molten salt delivery pipeline (4). A high-temperature molten salt delivery pump (5) is connected in series on the high-temperature molten salt delivery pipeline (4). The high-temperature molten salt delivery pipeline (4) is connected to the inlet of the heat release loop of a heat exchange unit (6) for generating steam or hot water. The outlet of the heat release loop of the heat exchange unit (6) is connected to the inlet of the low-temperature molten salt return pipeline (7). The outlet of the low-temperature molten salt return pipeline (7) is connected to the low-temperature molten salt tank (2); The low-temperature molten salt tank (2) is connected to the outlet of the low-temperature molten salt delivery pipeline (8). A low-temperature molten salt delivery pump (9) and a molten salt heating device (10) are connected in series on the low-temperature molten salt delivery pipeline (8). The outlet of the low-temperature molten salt delivery pipeline (8) is connected to the high-temperature molten salt tank (1); The top of the high-temperature molten salt tank (1) is connected to the nitrogen storage buffer tank (3) through a high-temperature nitrogen connecting pipe (11). The top of the low-temperature molten salt tank (2) is connected to the nitrogen storage buffer tank (3) through a low-temperature nitrogen connecting pipe (12). The nitrogen storage buffer tank (3) is connected to the outlet of a nitrogen delivery pipe (13).

2. The closed molten salt energy storage system according to claim 1, Characterized in that: A check valve (14) and a nitrogen heating device (15) for heating nitrogen are connected in series on the nitrogen delivery pipe (13). The inlet of the nitrogen delivery pipe (13) is connected to the nitrogen storage tank (23) of a nitrogen generation device (16).

3. The closed molten salt energy storage system according to claim 2, Characterized in that: The heat exchange unit (6) is one or any combination of two or three of a preheater, an evaporator or a superheater. The molten salt heating device (10) is a molten salt electric heater, a molten salt steam heater or a molten salt heat transfer oil heater. The nitrogen heating device (15) is an electric heating device.

4. The closed molten salt energy storage system according to claim 3, Characterized in that: The inlet of the nitrogen delivery pipe (13) is connected to the nitrogen storage tank (23) through a nitrogen storage tank expansion joint (17). The high-temperature nitrogen connecting pipe (11) is connected to the high-temperature molten salt tank (1) through a high-temperature nitrogen expansion joint (18). The low-temperature nitrogen connecting pipe (12) is connected to the low-temperature molten salt tank (2) through a low-temperature nitrogen expansion joint (19).

5. The closed molten salt energy storage system according to claim 4, Characterized in that: Heat insulation layers are respectively wrapped on the outer surfaces of the high-temperature nitrogen connecting pipe (11), the low-temperature nitrogen connecting pipe (12) and the nitrogen delivery pipe (13).

6. The closed molten salt energy storage system according to any one of claims 1 to 5, Characterized in that: A high-temperature molten salt tank rupture disc (20) for relieving pressure when the safety pressure is exceeded is provided at the top of the high-temperature molten salt tank (1). A low-temperature molten salt tank rupture disc (21) for relieving pressure when the safety pressure is exceeded is provided at the top of the low-temperature molten salt tank (2). An overpressure check valve (22) for relieving pressure when the safety pressure is exceeded is provided at the top of the nitrogen storage buffer tank (3).

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