A double-tank nitrogen sealing system suitable for molten salt heat storage

Abstract

This invention discloses a dual-tank nitrogen sealing system suitable for molten salt thermal storage, comprising a nitrogen generator, nitrogen storage tanks, a cryogenic tank, and a high-temperature tank. The nitrogen generator is connected to a main valve, and a nitrogen analyzer and an exhaust pipe are installed between the nitrogen generator and the main valve. An exhaust valve is installed on the exhaust pipe. The inlet of each nitrogen storage tank is connected to the outlet of the main valve through its own inlet shut-off valve. The outlet of each nitrogen storage tank is connected to the inlet of a self-operated nitrogen sealing valve through its own exhaust shut-off valve. The outlet of the self-operated nitrogen sealing valve is connected to the middle of a connecting pipe via an electric quick-closing valve and a connecting pipe. The two ends of the connecting pipe are respectively connected to the gas phase zones of the cryogenic tank and the high-temperature tank. Both the cryogenic tank and the high-temperature tank are equipped with pressure transmitters and primary breather valves. The pressure transmitters are connected to the controllers of the electric quick-closing valves. The pressure taps of the self-operated nitrogen sealing valves are connected to the gas phase zones of both the cryogenic tank and the high-temperature tank. This invention can reduce nitrogen consumption, prevent nitrogen sealing valve failure under high-temperature conditions, and achieve multi-stage pressure protection for the storage tanks, ensuring long-term stable and safe operation of the storage tanks.

Description

Technical Field

[0001] This invention relates to a dual-tank nitrogen sealing system, and more particularly to a dual-tank nitrogen sealing system suitable for molten salt thermal storage. Background Technology

[0002] Nitrogen blanketing systems are widely used in industries such as petroleum, chemical, environmental protection, water treatment, and pharmaceuticals. By injecting nitrogen into storage tanks and displacing the air inside, nitrogen blanketing reduces the contact between materials and oxygen, thereby lowering the risk of oxidation. It also inhibits material volatilization, maintains pressure balance, improves safety, and protects the tank structure.

[0003] With the widespread application of molten salt thermal energy storage, the molten salt in the molten salt storage tank operates at a high temperature for a long time. When air is present in the molten salt tank, the molten salt will be oxidized and lost. Moreover, 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 water content of the molten salt, which in turn reduces the specific heat capacity of the molten salt and reduces its thermal energy storage capacity. At the same time, the water combined with the molten salt will become crystal water. When crystal water mixes with molten salt during circulation, it will cause stress corrosion on the steel of the storage tank. Therefore, molten salt tanks need to be equipped with a nitrogen sealing system. Currently, molten salt thermal storage projects generally adopt a dual-tank design with a low-temperature tank and a high-temperature tank. Conventional nitrogen sealing systems introduce nitrogen into both the low-temperature and high-temperature tanks through self-operated nitrogen sealing valves. However, because the molten salt in the two tanks circulates alternately during the thermal storage process, the gas phase volume and pressure of the two molten salt tanks change significantly, resulting in a large nitrogen consumption. Furthermore, the self-operated nitrogen sealing valves use rubber ring seals, which soften when the temperature exceeds 120°C, causing valve leakage. This allows nitrogen to continuously enter the storage tanks, leading to pressure imbalance and making it impossible to guarantee the efficient and stable operation of the nitrogen sealing system under high-temperature conditions. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned shortcomings of the prior art by providing a dual-tank nitrogen sealing system suitable for molten salt thermal storage. This system can reduce nitrogen consumption, prevent nitrogen sealing valve failure under high-temperature conditions, and provide multi-stage pressure protection for the storage tank, ensuring long-term stable and safe operation of the storage tank.

[0005] To achieve the above objectives, the present invention provides a dual-tank nitrogen sealing system suitable for molten salt thermal storage, comprising a nitrogen generator, one or more nitrogen storage tanks, a cryogenic tank, and a high-temperature tank. The nitrogen generator is connected to a main valve via a pipeline. A nitrogen analyzer and an exhaust pipe are installed on the pipeline between the nitrogen generator and the main valve. An exhaust valve is installed on the exhaust pipe. The inlet end of each nitrogen storage tank is connected to the outlet of the main valve via its own inlet shut-off valve. The system is characterized in that the outlet end of each nitrogen storage tank is connected to the inlet of a self-operated nitrogen sealing valve via its own exhaust shut-off valve. The outlet of the self-operated nitrogen sealing valve is connected to a connecting pipe via an electric quick-closing valve. The middle of the connecting pipe is connected, and the two ends of the connecting pipe are respectively connected to the gas phase zone of the cryogenic tank and the high-temperature tank. The electric quick-closing valve and the self-operated nitrogen sealing valve are arranged far apart, and the downstream electric quick-closing valve is arranged close to the high- and low-temperature tanks, while the self-operated nitrogen sealing valve is far away from the high- and low-temperature tanks. The room-temperature nitrogen gas sealed between the electric quick-closing valve and the self-operated nitrogen sealing valve plays a heat insulation role and provides heat insulation protection for the self-operated nitrogen sealing valve. Both the cryogenic tank and the high-temperature tank are equipped with pressure transmitters and first-stage breather valves connected to their gas phase zones. The pressure transmitters are all connected to the controllers of the electric quick-closing valves. The pressure taps of the self-operated nitrogen sealing valves are connected to the gas phase zones of both the cryogenic tank and the high-temperature tank.

[0006] In this invention, nitrogen is drawn from a nitrogen generator and monitored in real time by a nitrogen analyzer. Unqualified nitrogen is discharged through a discharge pipe, while qualified nitrogen enters a nitrogen storage tank for later use. The gas phase pressures of the cryogenic and high-temperature tanks are kept equal through a connecting pipe. During normal operation, the gas phase pressure is maintained within a preset range, and under this condition, the self-operated nitrogen sealing valve and the electric quick-closing valve are closed. When the gas phase pressure in both tanks falls below the lower limit, the self-operated nitrogen sealing valve automatically opens after sensing the gas phase pressure in the storage tank through the pressure tapping pipe, and the electric quick-closing valve also opens after receiving a signal from the storage tank pressure transmitter. High-pressure nitrogen enters both tanks through the connecting pipe. When the pressure inside the tank rises to the upper limit, the self-operated nitrogen sealing valve and the electric quick-closing valve close. When the molten salt thermal storage system is working, the low-temperature molten salt in the low-temperature tank is heated by the thermal storage heat exchanger and then enters the high-temperature tank. The high-temperature molten salt in the high-temperature tank is cooled by the heat release heat exchanger and then enters the low-temperature tank. This invention uses a connecting pipe to balance the pressure changes in the high and low temperature tanks caused by the flow of molten salt during operation. However, since the volume of molten salt changes at different temperatures, and the temperature change caused by the flow of molten salt also leads to volume changes, only a small amount of nitrogen needs to be added, which can reduce nitrogen consumption and achieve a high degree of automation. Furthermore, the downstream electric quick-closing valve is located close to the high and low temperature tanks, while the nitrogen sealing valve is located far away from the high and low temperature tanks. The room-temperature nitrogen sealed between the two valves can play a role in heat insulation and provide heat insulation protection for the nitrogen sealing valve, preventing leakage caused by the softening of its rubber sealing ring. This can prevent the nitrogen sealing valve from failing under high-temperature conditions. In addition, the first-stage breather valve can prevent pressure imbalance between the low-temperature tank and the high-temperature tank, providing pressure protection for the tank and ensuring the long-term stable and safe operation of the tank.

[0007] As a further improvement of the present invention, 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; when an electric valve is closed, the corresponding molten salt tank can be inspected and repaired.

[0008] As a further improvement of the present invention, a safety valve is provided on the connecting pipe between the two electric valves; this can prevent overpressure and ensure the safety of the entire system.

[0009] As a further improvement of the present invention, both the low-temperature tank and the high-temperature tank are equipped with a secondary breather valve connected to their gas phase zone. The set pressure of the secondary breather valve is greater than that of the primary breather valve. When overpressure occurs in the two tanks, the breather valves of the primary and secondary breather valves open one after the other, thereby realizing multi-stage pressure protection for the storage tank and further ensuring the long-term stable and safe operation of the storage tank.

[0010] As a further improvement of the present invention, a gas pipe is connected to the pipeline between the main valve and each inlet shut-off valve. The gas pipe is connected to the nitrogen manifold through the shut-off valve, and the nitrogen manifold is connected to the spare nitrogen tank. When the nitrogen generating equipment is under maintenance, nitrogen can be supplied through the nitrogen manifold to ensure the long-term stable and safe operation of the storage tank.

[0011] As a further improvement of the present invention, a pressure gauge, a flow meter and an online dew point meter are installed on the pipeline between the nitrogen generator and the main valve; these can detect the pressure, flow rate and water vapor content of the output nitrogen, thus preventing damage to the equipment.

[0012] In summary, this invention can reduce nitrogen consumption, prevent nitrogen sealing valve failure under high-temperature conditions, and achieve multi-stage pressure protection for storage tanks, ensuring long-term stable and safe operation of the storage tanks. Attached Figure Description

[0013] Figure 1 This is a structural diagram of an embodiment of the present invention. Detailed Implementation

[0014] The invention will be further described below with reference to the accompanying drawings.

[0015] like Figure 1As shown, this embodiment of a dual-tank nitrogen sealing system suitable for molten salt thermal storage includes a nitrogen generator 1, two nitrogen storage tanks 2 and 3, a cryogenic tank 4, and a high-temperature tank 5. The nitrogen generator 1 is connected to a main valve 6 via a pipeline. A pressure gauge 7, a flow meter 8, an online dew point meter 9, a nitrogen analyzer 10, and a discharge pipe 11 are installed on the pipeline between the nitrogen generator 1 and the main valve 6. A discharge valve 12 is installed on the discharge pipe 11. The two nitrogen storage tanks 2 and 3 are connected in parallel. The inlet and outlet of the two nitrogen storage tanks 2 and 3 are connected in parallel. Each of the two nitrogen storage tanks 2 and 3 has its own inlet shut-off valve 13 connected to the outlet of the main valve 6. A gas pipe 14 is connected between the main valve 6 and the two inlet shut-off valves 13. The gas pipe 14 is connected to the nitrogen manifold 16 via a shut-off valve 15. The nitrogen manifold 16 is connected to a spare nitrogen tank (not shown) or a nitrogen generator. The outlets of the two nitrogen storage tanks 2 and 3 are each connected to the inlet of a self-operated nitrogen sealing valve 18 via their respective exhaust shut-off valves 17. The outlet of the self-operated nitrogen sealing valve 18 is connected to an electrically operated quick-closing valve 19. The connecting pipe 20 is connected to the middle of the connecting pipe 21. The two ends of the connecting pipe 21 are connected to the gas phase zones of the cryogenic tank 4 and the high-temperature tank 5, respectively. The electric quick-closing valve 19 and the self-operated nitrogen sealing valve 18 are arranged far apart, with the downstream electric quick-closing valve 19 close to the high- and low-temperature tanks, and the self-operated nitrogen sealing valve 18 far away from the high- and low-temperature tanks. The room-temperature nitrogen gas sealed between the electric quick-closing valve 19 and the self-operated nitrogen sealing valve 18 can play a heat insulation role and provide heat insulation protection for the self-operated nitrogen sealing valve; cryogenic tank 4 and high-temperature tank Each of the five tanks is equipped with a pressure transmitter 22, a primary breather valve 23, and a secondary breather valve 24 connected to its respective gas phase zone. Electric valves 25 are installed on the connecting pipe between the connecting pipe 20 and the cryogenic tank 4, and on the connecting pipe between the connecting pipe 20 and the high-temperature tank 5. A safety valve 26 is installed on the connecting pipe 21 between the two electric valves 25. Both pressure transmitters 22 are connected to the controller of the electric quick-closing valve 19. The pressure tap of the self-operated nitrogen sealing valve 18 is connected to the gas phase zones of both the cryogenic tank 4 and the high-temperature tank 5.

[0016] In this embodiment, the preset normal operating gas phase pressure of the cryogenic tank 4 and the high-temperature tank 5 is between 300Pa and 600Pa. The set pressure of the exhalation valve of the first-stage breathing valve 23 is set to 1.35KPa, the set pressure of the exhalation valve of the second-stage breathing valve 24 is set to 1.8KPa, and the set pressure of the inhalation valve of the first-stage breathing valve 23 and the second-stage breathing valve 24 is set to -0.25KPa. The pressure setting value of the safety valve 26 is 4KPa.

[0017] During operation, nitrogen is drawn from nitrogen generator 1 and monitored in real time by nitrogen analyzer 10. Unqualified nitrogen is discharged through discharge pipe 11 and discharge valve 12, while qualified nitrogen enters two nitrogen storage tanks 2 and 3 for standby. Pressure gauge 7, flow meter 8, and online dew point meter 9 ensure that the pressure, flow rate, and humidity of the output nitrogen meet the requirements. The nitrogen pressure is higher than the normal operating upper limit pressure of the gas phase of cryogenic tank 4 and high-temperature tank 5 by 600 Pa. The gas phase pressure of cryogenic tank 4 and high-temperature tank 5 is kept equal through connecting pipe 21. During normal operation, the gas phase pressure is maintained between 300 Pa and 600 Pa. Under this condition, the self-operated nitrogen sealing valve 18 and the electric quick-closing valve 19 are in the closed state.

[0018] When the gas phase pressure of cryogenic tank 4 and high-temperature tank is below 300 Pa, the self-operated nitrogen sealing valve 18 automatically opens after sensing the gas phase pressure inside the tank through the pressure tapping 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, replenishing the tanks with nitrogen, and the pressure in cryogenic tank 4 and high-temperature tank 5 increases. When the pressure inside the tank reaches 600 Pa, the self-operated nitrogen sealing valve 18 and the electric quick-closing valve 19 automatically close. If molten salt leakage occurs in cryogenic tank 4 and high-temperature tank 5 at this time, the internal pressure will continue to decrease. When it reaches the set pressure of the suction valve of the first-stage breather valve 23 and the second-stage breather valve 24, the suction valves of the two-stage breather valves will open, and air will enter the tank, which can prevent the tank from collapsing and ensure the safety of the tank.

[0019] When the pressure inside cryogenic tank 4 and high-temperature tank 5 exceeds 600 Pa and continues to rise to the activation pressure of the first-stage breather valve 23 (1.147 kPa), the breather valve 23 begins to leak, releasing pressure. If the pressure continues to rise to the fully open pressure of the first-stage breather valve 23 (1.485 kPa), the breather valve 23 fully opens, further releasing pressure. If the gas phase pressure inside the tank continues to rise to the activation pressure of the second-stage breather valve 24 (1.53 kPa), the breather valve 24 begins to leak, releasing pressure. If the pressure inside the tank continues to rise to the fully open pressure of the second-stage breather valve 24 (1.98 kPa), the breather valve 24 fully opens, releasing tank pressure and achieving multi-stage pressure protection for the tank. At this time, all four breather valves are open. When the pressure of the entire system rises to 4 kPa, safety valve 26 opens to ensure the safety of the entire system and ensure the long-term stable and safe operation of the tank.

[0020] When the molten salt thermal storage system is working, the low-temperature molten salt in the low-temperature tank 4 is heated by the thermal storage heat exchanger and then enters the high-temperature tank 5. The high-temperature molten salt in the high-temperature tank 5 is cooled by the heat release heat exchanger and then enters the low-temperature tank 4. This invention uses the connecting pipe 21 to balance the pressure changes caused by the flow of molten salt between the high- and low-temperature tanks during operation. However, since the volume of molten salt changes at different temperatures, and the temperature change caused by the flow of molten salt also leads to volume changes, only a small amount of nitrogen needs to be added, which can reduce nitrogen consumption and achieve a high degree of automation. To avoid nitrogen seal valve... Due to the high temperature of molten salt, the electric quick-closing valve 19 and the self-operated nitrogen sealing valve 18 are arranged far apart. The downstream electric quick-closing valve 19 is arranged close to the high and low temperature tanks, while the self-operated nitrogen sealing valve 18 is far away from the high and low temperature tanks. The room temperature nitrogen gas sealed between the two valves can play a role in heat insulation and provide heat insulation protection for the self-operated nitrogen sealing valve, preventing leakage caused by the softening of its rubber sealing ring. It can prevent the nitrogen sealing valve from failing under high temperature conditions. In addition, the two-stage breather 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 tank.

[0021] Two nitrogen storage tanks 2 and 3 are connected in parallel. When one nitrogen storage tank is under maintenance, its inlet shut-off valve 13 and exhaust shut-off valve 17 can be closed. When the nitrogen generator 1 is under maintenance, nitrogen can be supplied through the nitrogen manifold 16 to ensure the long-term stable and safe operation of the storage tank. When an electric valve 25 is closed, the corresponding cryogenic tank 4 or high-temperature tank 5 can be under maintenance.

[0022] This invention is not limited to the above embodiments. For example, the number of nitrogen storage tanks can be set to more or one, and the electric valve 25 can also be replaced by other valves, such as gate valves or other manual valves.

[0023] The above embodiments have been used to illustrate the invention, but it should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the invention to the scope of the described embodiments.

Claims

1. A dual-tank nitrogen sealing system suitable for molten salt thermal storage, comprising a nitrogen generator, one or more nitrogen storage tanks, a cryogenic tank, and a high-temperature tank; the nitrogen generator is connected to a main valve via pipelines; a nitrogen analyzer and an exhaust pipe are installed on the pipeline between the nitrogen generator and the main valve; an exhaust valve is installed on the exhaust pipe; and the inlet end of each nitrogen storage tank is connected to the outlet of the main valve via its own inlet shut-off valve; characterized in that: Each nitrogen storage tank's outlet is connected to the inlet of a self-operated nitrogen sealing valve via its own exhaust shut-off valve. The outlet of the self-operated nitrogen sealing valve is connected to the middle of a connecting pipe via an electric quick-closing valve. The two ends of the connecting pipe are connected to the gas phase zones of the cryogenic tank and the high-temperature tank, respectively. The electric quick-closing valve and the self-operated nitrogen sealing valve are arranged far apart, with the downstream electric quick-closing valve located close to the cryogenic and high-temperature tanks, while the self-operated nitrogen sealing valve is located far away from the cryogenic and high-temperature tanks. The room-temperature nitrogen gas sealed between the electric quick-closing valve and the self-operated nitrogen sealing valve provides thermal insulation and protects the self-operated nitrogen sealing valve. Both the cryogenic and high-temperature tanks are equipped with pressure transmitters and primary breather valves connected to their gas phase zones. The pressure transmitters are connected to the controllers of the electric quick-closing valves, and the pressure taps of the self-operated nitrogen sealing valves are connected to the gas phase zones of both the cryogenic and high-temperature tanks.

2. The dual-tank nitrogen sealing system for molten salt thermal storage as described in claim 1, characterized in that: Electric valves are installed on the connecting pipe between the connecting pipe and the cryogenic tank, and on the connecting pipe between the connecting pipe and the high-temperature tank.

3. A dual-tank nitrogen sealing system for molten salt thermal storage as described in claim 2, characterized in that: A safety valve is installed on the connecting pipe between the two electric valves.

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

5. A dual-tank nitrogen sealing system suitable for molten salt thermal storage as described in claim 4, characterized in that: Gas pipes are connected to the pipelines between the main valve and each inlet shut-off valve. The gas pipes are connected to the nitrogen manifold through the shut-off valves. The nitrogen manifold is connected to the spare nitrogen tank.

6. A dual-tank nitrogen sealing system suitable for molten salt thermal storage as described in claim 4, characterized in that: A pressure gauge, flow meter, and online dew point meter are installed on the pipeline between the nitrogen generator and the main valve.

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