Double-storage-tank nitrogen sealing system suitable for fused salt heat storage

Abstract

The invention discloses a double-storage-tank nitrogen sealing system suitable for fused salt heat storage, which comprises a nitrogen making device, a nitrogen storage tank, a low-temperature tank and a high-temperature tank, the nitrogen making device is connected with a main valve, a nitrogen analyzer and a discharge pipe are arranged between the nitrogen making device and the main valve, a discharge valve is arranged on the discharge pipe, and the nitrogen storage tank is connected with the low-temperature tank. The inlet end of each nitrogen storage tank is connected with the outlet of the main valve through a respective gas inlet stop valve; the outlet end of each nitrogen storage tank is connected with an inlet of a self-operated nitrogen-sealed valve through a corresponding exhaust stop valve, an outlet of the self-operated nitrogen-sealed valve is connected with the middle of a communicating pipe through an electric quick-closing valve and a connecting pipe, and the two ends of the communicating pipe are connected with the gas phase area of the low-temperature tank and the gas phase area of the high-temperature tank respectively. The low-temperature tank and the high-temperature tank are each provided with a pressure transmitter and a first-stage breather valve, the pressure transmitters are connected with a controller of the electric quick-closing valve, and a pressure guide pipe of the self-operated nitrogen-sealed valve is connected with the gas phase area of the low-temperature tank and the gas phase area of the high-temperature tank. The nitrogen consumption can be reduced, failure of the nitrogen-sealed valve under the high-temperature working condition can be prevented, multi-stage pressure protection of the storage tank is achieved, and long-term stable and safe operation of the storage tank is guaranteed.

Description

Technical Field

[0001] The invention relates to a double storage tank nitrogen sealing system, in particular to a double storage tank nitrogen sealing system suitable for molten salt heat storage. Background Art

[0002] Nitrogen sealing system is widely used in petroleum, chemical, environmental protection, water treatment and pharmaceutical industries. Nitrogen sealing system injects nitrogen into the storage tank to expel the air in the tank, reduce the contact between the material and oxygen, thereby reducing the risk of material oxidation. At the same time, it can inhibit the volatilization of materials, maintain pressure balance, improve safety and protect the tank structure.

[0003] With the widespread application of molten salt heat storage, the molten salt in the molten salt storage tank is kept in a high temperature state for a long time. When there is air in the molten salt tank, the molten salt will be lost due to oxidation. When there is a large amount of air inside the molten salt storage tank, the moisture in the air will be absorbed by the molten salt, resulting in an increase in the moisture content of the molten salt, thereby reducing the specific heat capacity of the molten salt and reducing the heat storage capacity of the molten salt. At the same time, the water combined with the molten salt will become crystallization water. The mixture of crystallization water and molten salt will cause stress corrosion to the tank steel during the circulation process. Therefore, a nitrogen sealing system is required for the molten salt tank. At present, molten salt heat storage projects generally adopt a dual tank design of low-temperature tank and high-temperature tank. Conventional nitrogen sealing systems introduce nitrogen into the low-temperature tank and the high-temperature tank through a self-operated nitrogen sealing valve. Since the molten salt in the two tanks will circulate alternately during the heat storage process, the gas phase volume and pressure of the two molten salt tanks vary greatly, resulting in a large amount of nitrogen consumption. In addition, the self-operated nitrogen sealing valve is sealed with a rubber ring. When the temperature is higher than 120°C, the rubber will soften and cause valve leakage. Nitrogen will continuously enter the storage tank, causing the tank pressure to be unbalanced, and the efficient and stable operation of the nitrogen sealing system under high temperature conditions cannot be guaranteed. Summary of the invention

[0004] The purpose of the present invention is to provide a double storage tank nitrogen sealing system suitable for molten salt heat storage in view of the above-mentioned deficiencies in the prior art, which can reduce the nitrogen consumption, prevent the failure of the nitrogen sealing valve under high temperature conditions, and realize multi-level pressure protection for the storage tank, thereby ensuring the long-term stable and safe operation of the storage tank.

[0005] In order to achieve the above object, the present invention provides a double-tank nitrogen sealing system suitable for molten salt heat storage, comprising a nitrogen making device, more than one nitrogen storage tank, a low-temperature tank and a high-temperature tank, the nitrogen making device is connected to the main valve through a pipeline, a nitrogen analyzer and a discharge pipe are arranged on the pipeline between the nitrogen making device and the main valve, a discharge valve is arranged on the discharge pipe, and the inlet end of each nitrogen storage tank is connected to the outlet of the main valve through its own air intake stop valve; it is characterized in that: the outlet end of each nitrogen storage tank is connected to the inlet of the self-operated nitrogen sealing valve through its own exhaust stop valve, the outlet of the self-operated nitrogen sealing valve is connected to the middle part of the connecting pipe through an electric fast closing valve and a connecting pipe, the two ends of the connecting pipe are respectively connected to the gas phase regions of the low-temperature tank and the high-temperature tank, the low-temperature tank and the high-temperature tank are both provided with a pressure transmitter and a primary breathing valve connected to their gas phase regions, the pressure transmitters are connected to the controller of the electric fast closing valve, and the pressure-inducing pipe of the self-operated nitrogen sealing valve is connected to the gas phase regions of the low-temperature tank and the high-temperature tank.

[0006] The nitrogen of the present invention is drawn out from the nitrogen making equipment, and is monitored in real time by the nitrogen analyzer. Unqualified nitrogen is discharged through the discharge pipe, and qualified nitrogen enters the nitrogen storage tank for standby. The gas phase pressure of the low-temperature tank and the high-temperature tank is kept equal through the connecting pipe, and the gas phase pressure is maintained in a preset range during normal operation. Under this working condition, the self-operated nitrogen sealing valve and the electric quick-closing valve are in a closed state. When the gas phase pressure of the two tanks is lower than the lower limit, the self-operated nitrogen sealing valve automatically opens after sensing the gas phase pressure of the storage tank through the pressure-inducing pipe, and the electric quick-closing valve also opens after receiving the signal of the storage tank pressure transmitter, and the high-pressure nitrogen enters the two tanks through the connecting pipe. When the pressure in the tank rises to reach the upper limit, the self-operated nitrogen sealing valve and the electric quick-closing valve are closed. When the molten salt heat storage system is working, the low-temperature molten salt in the low-temperature tank will enter the high-temperature tank after being heated by the heat storage heat exchanger, and the high-temperature molten salt in the high-temperature tank will enter the low-temperature tank after being cooled by the heat release heat exchanger. The present invention balances the air pressure changes caused by the flow of molten salt in the high and low-temperature storage tanks during operation through a connecting pipe. However, since the volume of the molten salt changes at different temperatures, the temperature change caused by the flow of the molten salt also causes the volume change. Therefore, only a small amount of nitrogen needs to be supplemented, which can reduce the nitrogen consumption and has a high degree of automation. The downstream electric fast-closing valve is arranged close to the high and low-temperature storage tanks, and the nitrogen sealing valve is far away from the high and low-temperature storage tanks. The room-temperature nitrogen sealed between the two valves can play a heat-insulating role and provide heat-insulating protection for the nitrogen sealing valve to prevent leakage caused by softening of its rubber sealing ring, and prevent failure of the nitrogen sealing valve under high-temperature conditions. In addition, the first-level breathing valve can prevent pressure imbalance between the low-temperature tank and the high-temperature tank, provide pressure protection for the storage tank, and ensure long-term stable and safe operation of the storage tank. As a further improvement of the present invention, an electric valve is provided on the connecting pipe between the connecting pipe and the low temperature tank and on the connecting pipe between the connecting pipe and the high temperature tank; when one electric valve is closed, the corresponding molten salt tank can be inspected and repaired; As a further improvement of the present invention, a safety valve is provided on the connecting pipe between the two electric valves to avoid overpressure and ensure the safety of the entire system; As a further improvement of the present invention, the low-temperature tank and the high-temperature tank are both provided with a secondary breathing valve connected to their gas phase regions, and the set pressure of the secondary breathing valve is greater than the set pressure of the primary breathing valve; when overpressure occurs in the two tanks, the primary breathing valve and the secondary breathing valve are opened first and then, to achieve multi-level pressure protection for the storage tanks, further ensuring the long-term stable and safe operation of the storage tanks; As a further improvement of the present invention, an air pipe is connected to the pipeline between the main valve and each air inlet stop valve, the air pipe is connected to the nitrogen bus through the stop valve, and the nitrogen bus is connected to the spare nitrogen tank; when the nitrogen making equipment is overhauled, nitrogen can be supplied through the nitrogen bus to ensure long-term stable and safe operation of the storage tank; As a further improvement of the present invention, a barometer, a flowmeter and an online dew point meter are provided on the pipeline between the nitrogen generator and the main valve; the pressure, flow rate and water vapor content of the output nitrogen can be detected to avoid damage to the equipment; In summary, the present invention can reduce the amount of nitrogen used, prevent the nitrogen sealing valve from failing under high temperature conditions, and achieve multi-level pressure protection for the storage tank, thereby ensuring the long-term stable and safe operation of the storage tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 4 is a structural diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0008] The present invention will be further described below in conjunction with the accompanying drawings.

[0009] like Figure 1As shown, a double-tank nitrogen sealing system suitable for molten salt heat storage in this embodiment includes a nitrogen making device 1, two nitrogen storage tanks 2 and 3, a low-temperature tank 4 and a high-temperature tank 5. The nitrogen making device 1 is connected to a main valve 6 through a pipeline. A barometer 7, a flow meter 8, an online dew point meter 9, a nitrogen analyzer 10 and a discharge pipe 11 are arranged on the pipeline between the nitrogen making device 1 and the main valve 6. A discharge valve 12 is arranged on the discharge pipe 11. The two nitrogen storage tanks 2 and 3 are arranged in parallel. The inlet ends of the two nitrogen storage tanks 2 and 3 are connected to the outlet of the main valve 6 through their own air intake stop valves 13. An air pipe 14 is connected to the pipeline between the main valve 6 and the two air intake stop valves 13. The air pipe 14 is connected to a nitrogen bus 16 through a stop valve 15. The nitrogen bus 16 is connected to a spare nitrogen tank (not shown) or a nitrogen making machine; the two nitrogen storage tanks 2, The outlet ends of the self-operated nitrogen sealing valve 18 are connected to the inlet of the self-operated nitrogen sealing valve 18 through their respective exhaust stop valves 17; the outlet of the self-operated nitrogen sealing valve 18 is connected to the middle part of the connecting pipe 21 through the electric fast closing valve 19 and the connecting pipe 20, and the two ends of the connecting pipe 21 are respectively connected to the gas phase areas of the low temperature tank 4 and the high temperature tank 5. The low temperature tank 4 and the high temperature tank 5 are provided with a pressure transmitter 22, a first-level breathing valve 23 and a second-level breathing valve 24 connected to their respective gas phase areas. The connecting pipe between the connecting pipe 20 and the low temperature tank 4 and the connecting pipe between the connecting pipe 20 and the high temperature tank 5 are provided with an electric valve 25, and the connecting pipe 21 between the two electric valves 25 is provided with a safety valve 26. The two pressure transmitters 22 are connected to the controller of the electric fast closing valve 19, and the pressure-inducing pipe of the self-operated nitrogen sealing valve 18 is connected to the gas phase areas of the low temperature tank 4 and the high temperature tank 5.

[0010] In this embodiment, the preset normal operating gas phase pressure of the low-temperature tank 4 and the high-temperature tank 5 is between 300Pa-600Pa, the exhalation valve set pressure of the first-level breathing valve 23 is set to 1.35KPa, the exhalation valve set pressure of the second-level breathing valve 24 is set to 1.8KPa, and the suction valve set pressure of the first-level breathing valve 24 and the second-level breathing valve 24 is set to -0.25KPa; the pressure setting value of the safety valve 26 is 4KPa.

[0011] During operation, nitrogen is drawn out from the nitrogen production equipment 1 and monitored in real time by the nitrogen analyzer 10. Unqualified nitrogen is discharged through the discharge pipe 11 and the discharge valve 12, and qualified nitrogen enters the two nitrogen storage tanks 2 and 3 for standby. The barometer 7, the flow meter 8, and the online dew point meter 9 can ensure that the pressure, flow rate, and humidity of the output nitrogen meet the requirements. The nitrogen pressure is higher than the normal operating gas phase upper limit pressure of 600Pa of the low temperature tank 4 and the high temperature tank 5; the gas phase pressure of the low temperature tank 4 and the high temperature tank 5 is kept equal through the connecting pipe 21. During normal operation, the gas phase pressure is maintained between 300Pa-600Pa. Under this working condition, the self-operated nitrogen sealing valve 18 and the electric quick closing valve 19 are in a closed state; When the gas phase pressure of the low temperature tank 4 and the high temperature tank is lower than 300Pa, the self-operated nitrogen sealing valve 18 automatically opens after sensing the gas phase pressure in the tank through the pressure-inducing pipe, and the electric quick-closing valve 19 also opens after receiving the signal from the pressure transmitter 22. High-pressure nitrogen enters the two tanks through the connecting pipe 21 to replenish nitrogen in the tanks. The pressure in the low temperature tank 4 and the high temperature tank 5 increases. When the pressure in the tank rises to 600Pa, the self-operated nitrogen sealing valve 18 and the electric quick-closing valve 19 automatically close. If molten salt leaks from the low temperature tank 4 and the high temperature tank 5 at this time, the internal pressure continues to decrease and reaches the suction valve set pressure of the first-stage breathing valve 24 and the second-stage breathing valve 24. The suction valves of the two-stage breathing valves open and air enters the tank, which can prevent the tank from being deflated and ensure the safety of the tank. When the pressure in the low temperature tank 4 and the high temperature tank 5 is higher than 600Pa, and continues to rise to the call valve starting pressure of the first breathing valve 23 of 1.147KPa, the call valve of the first breathing valve 23 begins to leak and release the pressure. If the pressure continues to rise to the call valve fully open pressure of the first breathing valve 23 of 1.485KPa, the call valve of the first breathing valve 23 is fully opened to further release the pressure. If the gas phase pressure in the tank continues to rise to the call valve starting pressure of the second breathing valve 24 of 1.53KPa, the call valve of the second breathing valve 24 begins to leak and release the pressure. If the pressure in the tank continues to rise to the call valve fully open pressure of the second breathing valve 24 of 1.98KPa, the call valve of the second breathing valve 24 is fully opened to release the tank pressure and realize multi-level pressure protection of the tank. At this time, all four breathing valves are opened. When the pressure of the entire system rises to 4KPa, the safety valve 26 is opened to ensure the safety of the entire system and ensure the long-term stable and safe operation of the tank.

[0012] When the molten salt heat storage system is working, the low-temperature molten salt in the low-temperature tank 4 will enter the high-temperature tank 5 after being heated by the heat storage heat exchanger, and the high-temperature molten salt in the high-temperature tank 5 will enter the low-temperature tank 4 after being cooled by the heat release heat exchanger. The present invention uses a connecting pipe 21 to balance the pressure changes in the high and low-temperature storage tanks caused by the flow of molten salt during operation. However, since the volume of the molten salt changes at different temperatures, the temperature change caused by the flow of the molten salt also causes the volume change. Therefore, only a small amount of nitrogen needs to be added, which can reduce the nitrogen consumption and has a high degree of automation. In order to avoid The nitrogen sealing valve 18 is affected by the high temperature of the molten salt. The electric quick-closing valve 19 and the nitrogen sealing valve 18 are arranged far apart, and the downstream electric quick-closing valve 19 is arranged close to the high and low temperature storage tanks. The nitrogen sealing valve 18 is far away from the high and low temperature storage tanks. The room temperature nitrogen sealed between the two valves can play a heat insulation role and provide heat insulation protection for the nitrogen sealing valve to prevent leakage caused by softening of its rubber sealing ring, and prevent failure of the nitrogen sealing valve under high temperature conditions. In addition, the two-stage breathing valves 23 and 24 can prevent pressure imbalance between the low temperature tank and the high temperature tank, and provide pressure protection for the storage tanks. Two parallel nitrogen storage tanks 2 and 3, when one nitrogen storage tank is overhauled, it can be achieved by closing 11 its intake stop valve 13 and exhaust stop valve 17; when the nitrogen production equipment 1 is overhauled, nitrogen can be provided through the nitrogen bus 16 to ensure the long-term stable and safe operation of the storage tank; when an electric valve 25 is closed, the corresponding low-temperature tank 4 or high-temperature tank 5 can be overhauled; The present invention is not limited to the above-mentioned embodiments, for example, the number of nitrogen storage tanks may be set to more or one, and the electric valve 25 may be replaced by other valves, such as a gate valve or other manual valves; The above embodiments have been described, but it should be understood that the above embodiments are only for the purpose of example and description, and are not intended to limit the present invention to the scope of the described embodiments.

Claims

1. A double-tank nitrogen sealing system suitable for molten salt heat storage, comprising a nitrogen generator, one or more nitrogen storage tanks, a low-temperature tank and a high-temperature tank, wherein the nitrogen generator is connected to a main valve through a pipeline, a nitrogen analyzer and a discharge pipe are arranged on the pipeline between the nitrogen generator and the main valve, a discharge valve is arranged on the discharge pipe, and the inlet end of each nitrogen storage tank is connected to the outlet of the main valve through its own air inlet stop valve; characterized in that: The outlet end of each nitrogen storage tank is connected to the inlet of the self-operated nitrogen sealing valve through its own exhaust stop valve. The outlet of the self-operated nitrogen sealing valve is connected to the middle part of the connecting pipe through an electric quick-closing valve and a connecting pipe. The two ends of the connecting pipe are respectively connected to the gas phase areas of the low-temperature tank and the high-temperature tank. The low-temperature tank and the high-temperature tank are both provided with a pressure transmitter and a first-level breathing valve connected to their gas phase areas. The pressure transmitters are connected to the controller of the electric quick-closing valve. The pressure-inducing pipe of the self-operated nitrogen sealing valve is connected to the gas phase areas of the low-temperature tank and the high-temperature tank.

2. A double-tank nitrogen sealing system suitable for molten salt heat storage as claimed in claim 1, characterized in that: Electric valves are provided on the connecting pipe between the connecting pipe and the low-temperature tank and on the connecting pipe between the connecting pipe and the high-temperature tank.

3. A double-tank nitrogen sealing system suitable for molten salt heat storage as claimed in claim 2, characterized in that: A safety valve is arranged on the connecting pipe between the two electric valves.

4. A double-tank nitrogen sealing system suitable for molten salt heat storage as described in any one of claims 1 to 3, characterized in that: The low-temperature tank and the high-temperature tank are both provided with a secondary breathing valve connected to their gas phase regions, and the set pressure of the secondary breathing valve is greater than the set pressure of the primary breathing valve.

5. A double-tank nitrogen sealing system suitable for molten salt heat storage as claimed in claim 4, characterized in that: An air pipe is connected to the pipeline between the main valve and each air inlet stop valve. The air pipe is connected to the nitrogen bus through the stop valve, and the nitrogen bus is connected to the spare nitrogen tank.

6. A double-tank nitrogen sealing system suitable for molten salt heat storage as claimed in claim 4, characterized in that: A barometer, flow meter and online dew point meter are installed on the pipeline between the nitrogen making equipment and the main valve.

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