Pressure stabilizing device and method for fluid storage tank

Abstract

The invention relates to storage and pressure control of gas-liquid two-phase fluid. Aiming at the problem of two-way fluctuation of the pressure of the fluid storage tank under the working conditions of liquid filling and liquid discharging, a closed-loop pressure stabilizing scheme with a pressure stabilizing storage tank as pressure buffer is provided: when the pressure of the fluid storage tank is overhigh, a compressor pressurizes a gas-phase fluid in the fluid storage tank and then feeds the gas-phase fluid into the pressure stabilizing storage tank; when the pressure is under-pressure, the gaseous fluid in the pressure stabilizing storage tank is reduced to the working pressure of the fluid storage tank through the first pressure reducing device and then is reinjected, and preferably, the reinjected gaseous fluid is nearly saturated through the pressure stabilizing heat exchanger coupled with an external cold source so as to reduce liquid phase consumption. Under the scene of high pressure difference, gaseous fluid in the pressure stabilizing storage tank can be reinjected through the path of the second pressure reducing device, the buffer tank and the expansion machine, and energy is recycled. The working pressure of the pressure-stabilizing storage tank is preferably two times or more than two times that of the fluid storage tank, hysteresis control and protection logic of the pressure upper limit threshold value and the pressure lower limit threshold value of the fluid storage tank is adopted, and the pressure-stabilizing storage tank is suitable for liquid air energy storage systems and the like and gives consideration to pressure stabilization, consumption reduction and energy recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to gas-liquid two-phase storage and pressure control technology, in particular to a pressure stabilizing device and method for a gas-liquid two-phase fluid storage tank, and a liquid air energy storage system using the device. BACKGROUND

[0002] In the storage and transportation of liquefied media (such as liquid air, liquefied natural gas, liquid oxygen / liquid nitrogen, etc.), the fluid storage tank is usually in a gas-liquid two-phase coexistence state. The change in gas volume fraction caused by liquid charging or discharging and heat transfer / flash evaporation will cause fluctuations in the tank pressure, which will affect the stable operation of the upstream and downstream equipment. For a liquid air energy storage system (LAES), the liquefaction and injection of liquid air during the charging phase is easy to cause the tank pressure to rise; and the extraction of liquid and the gasification for power generation during the discharging phase is easy to cause the tank pressure to decrease. If the tank pressure cannot be stabilized within the target range, it may cause the system efficiency to decrease, the system to frequently start and stop, and even the system to be interlocked and shut down. Therefore, an active pressure stabilizing scheme that can work under both types of working conditions is urgently needed. SUMMARY

[0003] The present application aims to provide a device and method for stabilizing the pressure of a fluid storage tank under both liquid charging and liquid discharging conditions; by introducing an independent pressure stabilizing tank and a hysteresis control strategy, and pre-cooling the compressed gas phase fluid to a near-saturated state when needed, the consumption of liquid inventory by the re-injected gas is reduced or avoided; in high pressure difference applications, the potential energy can be recovered by an expander for power generation, and the expander inlet pressure fluctuation is not more than plus or minus 20% with the help of a buffer tank, which improves the operation stability and economy.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a pressure stabilizing device for a gas-liquid two-phase coexisting fluid storage tank. The pressure stabilizing device for a gas-liquid two-phase coexisting fluid storage tank comprises a fluid storage tank and a pressure stabilizing device. The fluid is stored in the form of gas-liquid two-phase coexistence in the fluid storage tank.

[0005] The pressure stabilizing device is used to maintain the stability of the pressure in the fluid storage tank, comprising a compressor, a pressure stabilizing tank, a first pressure reducing device, and a pressure control instruction module. The working pressure control value of the pressure stabilizing tank is not less than 2 times of the working pressure control value of the fluid storage tank. Mainly considering the size of the tank, the larger the working pressure control value is, the smaller the pressure stabilizing tank is, but the more the compression heat is. When there is a cheap external cold source, the working pressure control value of the pressure stabilizing tank can be higher. When there is no external cold source or no cheap external cold source, a lower working pressure control value is preferred. The working pressure control value of the pressure stabilizing tank is preferably in the range of 2-20 times of the working pressure control value of the fluid storage tank. When the ratio of the working pressure control value of the pressure stabilizing tank to the working pressure control value of the fluid storage tank is low, the compression power is reduced. When the ratio of the working pressure control value of the pressure stabilizing tank to the working pressure control value of the fluid storage tank is high, the compression power is increased, but the tank can be compressed at low electricity price and discharged at high electricity price, so the overall efficiency RTE is reduced, but the economic benefit is improved.

[0006] The pressure control instruction module acquires the pressure in the fluid storage tank and sets a pressure upper limit threshold P_high and a pressure lower limit threshold P_low. When the pressure in the fluid storage tank is greater than or equal to the pressure upper limit threshold P_high, the pressure control instruction module issues an instruction to start the compressor. When the pressure in the fluid storage tank is less than or equal to the pressure lower limit threshold P_low, the pressure control instruction module issues an instruction to start the first pressure reducing device. The pressure upper limit threshold P_high and the pressure lower limit threshold P_low are determined according to the system time lag and the valve response to avoid frequent start and stop.

[0007] Optionally, the gas phase space of the fluid storage tank is connected to the compressor and the first pressure reducing device, respectively. The inlet of the compressor is in communication with the gas phase space of the fluid storage tank, for pressurizing and transferring part of the gas phase fluid in the fluid storage tank into the pressure stabilizing tank when the fluid storage tank is over-pressured. The inlet of the first pressure reducing device is in communication with the pressure stabilizing tank, and the outlet thereof is in communication with the gas phase space of the fluid storage tank, for reducing the pressure of the gas in the pressure stabilizing tank to the working pressure control value of the fluid storage tank and injecting it back into the fluid storage tank when the fluid storage tank is under-pressured.

[0008] The first pressure reducing device can be a pressure reducing valve or an expander. When there is a large pressure difference between the fluid storage tank and the pressure stabilizing tank, the first pressure reducing device is an expander. The first pressure reducing device further comprises a generator, and the expander drives the generator to generate electricity.

[0009] Optionally, the pressure stabilizing device further comprises a pressure stabilizing heat exchanger for reducing the temperature of the dumped or reinjected gaseous fluid to a temperature close to the saturation temperature of the gas-liquid two-phase in the fluid storage tank under both overpressure and underpressure conditions. The pressure stabilizing heat exchanger can be arranged in the inlet flow process before the pressurized gaseous fluid enters the pressure stabilizing storage tank, or in the outlet flow process after the pressurized gaseous fluid exits the pressure stabilizing storage tank, thereby reducing the evaporation amount of the liquid phase fluid caused by the gaseous fluid entering the fluid storage tank.

[0010] In the method, the pressure stabilizing heat exchanger is thermally coupled with an external cold source, which can be at least one of liquefied natural gas regasification cold energy, a refrigerator or an environmental cold source.

[0011] The first aspect of the present application further provides a method for pressure stabilization of a fluid storage tank with gas-liquid two-phase coexistence, including a liquid state fluid inputting into the fluid storage tank (liquid inputting condition) and a liquid state fluid outputting from the fluid storage tank (liquid outputting condition):

[0012] In the liquid inputting condition, when the pressure in the fluid storage tank reaches the upper pressure threshold P_high (for example, 0.3 MPa higher than the working pressure) set by the pressure control instruction module, the pressure control instruction module issues an instruction to start the compressor, and pressurizes part of the gaseous phase fluid in the fluid storage tank and injects it into the pressure stabilizing storage tank; when the pressure control instruction module monitors that the pressure in the fluid storage tank falls to the working pressure control value of the fluid storage tank, the pressure control instruction module issues an instruction to stop the compressor again, thereby maintaining the pressure stability in the fluid storage tank and controlling the temperature variation amount of the gaseous phase fluid at the pressure of the pressure stabilizing storage tank.

[0013] In the liquid outputting condition, when the pressure in the fluid storage tank reaches the lower pressure threshold P_low (for example, 0.3 MPa lower than the working pressure) set by the pressure control instruction module, the pressure control instruction module issues an instruction to start the first pressure reducing device, and reduces part of the high pressure gaseous phase fluid in the pressure stabilizing storage tank to the working pressure control value of the fluid storage tank and inputs it into the fluid storage tank. When the pressure control instruction module monitors that the pressure in the fluid storage tank rises to the working pressure control value of the fluid storage tank, the pressure control instruction module issues an instruction to stop the first pressure reducing device again, thereby maintaining the pressure stability in the fluid storage tank and controlling the temperature variation amount of the gaseous phase fluid at the working pressure of the fluid storage tank, thereby reducing the evaporation of the liquid phase fluid in the fluid storage tank caused by the reinjected gas.

[0014] Optionally, the method further comprises that the working pressure of the fluid storage tank is P_MLC=1.7 MPa, P_high=1.73 MPa, and P_low=1.67 MPa; and the working pressure of the pressure stabilizing storage tank is P_PSC=3.4 MPa.

[0015] In a second aspect, the present application provides another pressure stabilizing device for a gas-liquid two-phase coexisting fluid storage tank. The pressure stabilizing device for a gas-liquid two-phase coexisting fluid storage tank comprises a fluid storage tank and a pressure stabilizing device. The pressure stabilizing device is used to maintain the stability of the pressure in the fluid storage tank, and comprises a second pressure reducing device, a buffer tank and an expander.

[0016] Preferably, the second pressure reducing device and the buffer tank are located between the fluid storage tank and the expander. The gas phase space of the fluid storage tank is connected to the compressor and the expander, respectively.

[0017] The working pressure control value of the pressure stabilizing storage tank is not less than 2 times the working pressure control value of the fluid storage tank. The working pressure control value is greater, the pressure stabilizing storage tank is smaller, but the compression heat is more. When there is a cheap external cold source, the working pressure control value of the pressure stabilizing storage tank can be higher. When there is no external cold source or no cheap external cold source, a lower working pressure control value is preferred. The working pressure control value of the pressure stabilizing storage tank is preferably 2-20 times the working pressure control value of the fluid storage tank. When the ratio of the working pressure control value of the pressure stabilizing storage tank to the working pressure control value of the fluid storage tank is low, the compression power is reduced. When the ratio of the working pressure control value of the pressure stabilizing storage tank to the working pressure control value of the fluid storage tank is high, the compression power is increased, but the compression can be carried out at low valley electricity price and the discharge can be carried out at high peak electricity price, so the overall efficiency RTE is reduced, but the economic benefit is improved.

[0018] Preferably, the pressure stabilizing device further comprises a pressure control instruction module for acquiring the pressure value of the fluid storage tank and setting the upper pressure threshold P_high and the lower pressure threshold P_low, and issuing operation instructions to the compressor, the second pressure reducing device and the expander according to the collected pressure signal.

[0019] The pressure control instruction module controls the second pressure reducing device, so that the relative fluctuation of the inlet pressure of the expander when the expander is in a stable state does not exceed ±20% of the working pressure control value of the expander, thereby improving the expansion efficiency and mechanical life.

[0020] Preferably, the pressure stabilizing device further comprises a pressure stabilizing heat exchanger for reducing the temperature of the diverted or reinjected gas to close to the saturation temperature of the gas-liquid two-phase in the fluid storage tank under the two working conditions of overpressure and underpressure. The pressure stabilizing heat exchanger can be arranged in the inlet flow process before the pressurized gaseous fluid enters the pressure stabilizing storage tank, or arranged in the outlet flow process after the pressurized gaseous fluid exits the pressure stabilizing storage tank, thereby reducing the evaporation amount of the liquid phase fluid caused by the gaseous fluid entering the fluid storage tank.

[0021] The stable pressure heat exchanger is coupled with an external cold source, and the external cold source can be at least one of liquefied natural gas regasification cold energy, a refrigerating machine or an environmental cold source.

[0022] The second aspect of the application further provides another method for stabilizing the pressure of a fluid storage tank with gas-liquid two-phase coexistence, including a working condition of inputting liquid fluid into the fluid storage tank (liquid input working condition) and a working condition of outputting liquid fluid from the fluid storage tank (liquid output working condition):

[0023] In the liquid input working condition, when the pressure in the fluid storage tank reaches the upper pressure threshold P_high set by the pressure control instruction module (for example, 0.3 MPa higher than the working pressure), the pressure control instruction module issues an instruction to start the compressor, and the part of the gaseous fluid in the fluid storage tank is pressurized and injected into the stable pressure storage tank; when the pressure control instruction module monitors that the pressure in the fluid storage tank falls to the working pressure control value of the fluid storage tank, the pressure control instruction module issues an instruction to stop the compressor again, so as to maintain the pressure stability in the fluid storage tank and control the temperature variation of the gaseous fluid at the stable pressure storage tank pressure.

[0024] In the liquid output working condition, when the pressure in the fluid storage tank reaches the lower pressure threshold P_low set by the pressure control instruction module (for example, 0.3 MPa lower than the working pressure), the pressure control instruction module issues an instruction to start the second pressure reducing device. The gaseous fluid from the stable pressure storage tank flows into the buffer tank through the second pressure reducing device, and the gaseous fluid in the buffer tank is input into the fluid storage tank by being depressurized to the working pressure control value of the fluid storage tank through the expander. When the pressure control instruction module monitors that the pressure in the fluid storage tank rises to the working pressure control value of the fluid storage tank, the pressure control instruction module issues an instruction to stop the second pressure reducing device and the expander again, so as to maintain the pressure stability in the fluid storage tank and control the temperature variation of the gaseous fluid at the working pressure of the fluid storage tank, thereby reducing the evaporation of the liquid fluid in the fluid storage tank caused by the re-injection gas.

[0025] Optionally, the method further includes that the working pressure of the fluid storage tank is P_MLC=1.7 MPa, P_high=1.73 MPa, and P_low=1.67 MPa; the pressure between the second pressure reducing device and the buffer tank is maintained at about 6.8 MPa; the working pressure of the stable pressure storage tank is P_PSC=6.8~13.6 MPa; and the outlet pressure of the expander is P_E-S 出口 =1.7 MPa.

[0026] The third aspect of the present application provides a liquid air energy storage system, which comprises the pressure stabilizing device of the first aspect or the second aspect of the present application, and realizes pressure stabilization in the charging mode and the discharging mode of the liquid air energy storage system.

[0027] Preferably, the liquid air energy storage system further comprises a charging module and a discharging module.

[0028] The charging module comprises a charging compressor, a cryogenic expander, and is configured to inject liquid air into the fluid storage tank.

[0029] Preferably, the charging module further comprises a charging heat exchanger configured to cool the air flowing out of the charging compressor.

[0030] The discharging module comprises a cryogenic pump and a discharging expander, and is configured to output the liquid air in the fluid storage tank to generate power.

[0031] Preferably, the discharging module further comprises a discharging heat exchanger configured to heat the liquid air flowing out of the cryogenic pump.

[0032] In the charging mode of the liquid air energy storage system of the present application, the ambient air is pressurized by the charging compressor and then enters the charging heat exchanger to become high-pressure low-temperature air. The high-pressure low-temperature air further enters the cryogenic expander to be further cooled and depressurized, and then becomes liquid air flowing into the fluid storage tank for storage. In order to avoid the pressure in the fluid storage tank rising during the charging process, according to the embodiments of the second aspect and the third aspect of the present application, the gas-phase air in the fluid storage tank is cooled by the pressure stabilizing heat exchanger after being pressurized by the charging compressor, and then enters the pressure stabilizing storage tank to maintain the pressure in the fluid storage tank stable.

[0033] In the discharging mode of the liquid air energy storage system of the present application, the cryogenic pump extracts the liquid air in the fluid storage tank, which is heated by the discharging heat exchanger and then flows into the discharging expander to expand and generate power. In order to avoid the pressure in the fluid storage tank decreasing during the discharging process, according to the embodiments of the second aspect and the third aspect of the present application, the air in the pressure stabilizing storage tank enters the fluid storage tank after being depressurized and cooled, thereby maintaining the pressure in the fluid storage tank stable.

[0034] Optionally, the system parameters include that the working pressure control value of the fluid storage tank is 0.5-3.8 MPa, and the working pressure control value of the pressure stabilizing storage tank is 2-20 times of the working pressure control value of the fluid storage tank.

[0035] Compared with the prior art, the application has many advantages, including but not limited to: closed loop pressure stabilization in both liquid filling and liquid discharging working conditions; through near-saturation pre-cooling and hysteresis control, liquid phase consumption and start-stop frequency are significantly reduced; in the high pressure difference scene, gas potential energy can be recovered and electricity can be generated; after introducing the buffer tank and the second pressure reducing device, the stability of the expander inlet pressure is improved, and the system operation is safer and more efficient. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a structure and control flow diagram of a pressure stabilizing device for a fluid storage tank with gas-liquid two-phase coexistence provided by the application;

[0037] Figure 2 is a liquid inlet working condition flow diagram of a pressure stabilizing device for a fluid storage tank with gas-liquid two-phase coexistence provided by the application;

[0038] Figure 3 is a liquid outlet working condition flow diagram of a pressure stabilizing device for a fluid storage tank with gas-liquid two-phase coexistence provided by the application;

[0039] Figure 4 is another structure and control flow diagram of a pressure stabilizing device for a fluid storage tank with gas-liquid two-phase coexistence provided by the application;

[0040] Figure 5 is another liquid inlet working condition flow diagram of a pressure stabilizing device for a fluid storage tank with gas-liquid two-phase coexistence provided by the application;

[0041] Figure 6 is another liquid outlet working condition flow diagram of a pressure stabilizing device for a fluid storage tank with gas-liquid two-phase coexistence provided by the application;

[0042] Figure 7 is an integrated application diagram of the device in a liquid air energy storage system.

[0043] BRIEF DESCRIPTION OF DRAWINGS

[0044] 100 - MLC Main Liquid Container, 110 - PSC Pressure Stabilization Container, 120 - BC Buffer Container, 200 - C-S Compressor-Stabilization, 210 - C-C Compressor-Charging, 220 - HX-S Heat Exchanger-Stabilization, 221 - HX-C Heat Exchanger-Charging, 222 - HX-DC Heat Exchanger-Discharging, 230 - CP Cryogenic Pump, 240 - PRD1 Pressure Reducing Device 1, 241 - PRD2 Pressure Reducing Device 2, 250 - E-S Expander-Stabilization, 251 - E-DC Expander-Discharging, 252 - CE Cryogenic Expander, 260 - CV1 Check Valve 1, 261 - CV2 Check Valve 2, 300 - ECS External Cold Energy Source, 400 - PDM Pressure Directive Module, 500 - PSD Pressure Stabilization Device, 600 - CM Charge Module, 700 - DCM Discharge Module. DETAILED DESCRIPTION

[0045] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0046] The technical parameters and connotations of the present application include the controllable accuracy and fault tolerance range in the specific implementation of the technical parameters, and cannot be understood as an accurate limitation of the technical parameters.

[0047] In a first aspect, the present application provides a pressure stabilizing device and method for a fluid storage tank with gas-liquid two-phase coexistence, and a specific embodiment thereof is described with reference to Figures 1-3 The pressure stabilizing device for a fluid storage tank with gas-liquid two-phase coexistence includes a fluid storage tank (100-MLC) and a pressure stabilizing device (500-PSD). The fluid is stored in the form of gas-liquid two-phase coexistence in the fluid storage tank (100-MLC). The pressure stabilizing device (500-PSD) is used to maintain the stability of the pressure in the fluid storage tank (100-MLC), including a compressor (200-C-S), a pressure stabilizing tank (110-PSC), a first pressure reducing device (240-PRD1), and a pressure control instruction module (400-PDM). The gas phase space of the fluid storage tank (100-MLC) is connected to the compressor (200-C-S) and the first pressure reducing device (240-PRD1), respectively. The inlet of the compressor (200-C-S) is in communication with the gas phase space of the fluid storage tank (100-MLC), and is used to pressurize and transfer part of the gas phase fluid into the pressure stabilizing tank (110-PSC) when the fluid storage tank (100-MLC) is over-pressured. The pressure control instruction module (400-PDM) acquires the pressure in the fluid storage tank and sets an upper pressure threshold and a lower pressure threshold. When the pressure in the fluid storage tank (100-MLC) is greater than or equal to the upper pressure threshold P_high, the pressure control instruction module issues an instruction to start the compressor. When the pressure in the fluid storage tank is less than or equal to the lower pressure threshold P_low, the pressure control instruction module issues an instruction to start the first pressure reducing device. Wherein, the upper pressure threshold P_high and the lower pressure threshold P_low are determined according to the system time lag and valve response to avoid frequent start and stop.

[0048] The working pressure control value of the pressure stabilizing tank (110-PSC) is not less than 2 times of the working pressure control value of the fluid tank (100-MLC). Mainly considering the size of the tank, the larger the working pressure control value is, the smaller the pressure stabilizing tank (110-PSC) is, but the more the compression heat is. When there is a cheap external cold source, the working pressure control value of the pressure stabilizing tank (110-PSC) can be higher. When there is no external cold source or no cheap external cold source, a lower working pressure control value is preferred. The working pressure control value of the pressure stabilizing tank (110-PSC) is preferably in the range of 2-20 times of the working pressure control value of the fluid tank (100-MLC). When the ratio of the working pressure control value of the pressure stabilizing tank (110-PSC) to the working pressure control value of the fluid tank (100-MLC) is lower, the compression power is reduced. When the ratio of the working pressure control value of the pressure stabilizing tank (110-PSC) to the working pressure control value of the fluid tank (100-MLC) is higher, the compression power is increased, but the compression can be carried out at low valley electricity price and the discharge can be carried out at high peak electricity price, so the overall efficiency RTE is reduced, but the economic benefit is improved.

[0049] The first pressure reducing device (240-PRD1) is in communication with the pressure stabilizing tank (110-PSC) at the inlet and in communication with the gas phase space of the fluid tank (100-MLC) at the outlet, for reducing the pressure of the gas in the pressure stabilizing tank (110-PSC) to the working pressure control value of the fluid tank (100-MLC) and injecting it back into the fluid tank (100-MLC) when the pressure of the fluid tank (100-MLC) is low.

[0050] The first pressure reducing device (240-PRD1) can be a pressure reducing valve or an expander as needed. When the first pressure reducing device (240-PRD1) is an expander, the first pressure reducing device (240-PRD1) further comprises a generator, and the expander drives the generator to generate electricity.

[0051] Further, as shown in Figure 1 The pressure stabilizing device (500-PSD) further comprises a pressure stabilizing heat exchanger (220-HX-S) for reducing the temperature of the diverted or injected gas phase fluid to close to the saturation temperature of the gas-liquid two-phase in the fluid tank under both overpressure and low pressure conditions. The pressure stabilizing heat exchanger (220-HX-S) can be arranged in the inlet flow process before the pressurized gaseous fluid enters the pressure stabilizing tank (110-PSC), or arranged in the outlet flow process after the pressurized gaseous fluid exits the pressure stabilizing tank (110-PSC), so as to reduce the evaporation amount of the liquid phase fluid caused by the gaseous fluid input into the fluid tank (100-MLC).

[0052] The pressure-stabilizing heat exchanger (220-HX-S) is thermally coupled to an external cold source (300-ECS), which can be at least one of liquefied natural gas regasification cold energy, a refrigeration unit, or an environmental cold source.

[0053] Furthermore, such as Figure 2 As shown, in the operating condition (liquid inlet condition) where liquid fluid is input into the fluid storage tank (100-MLC), the volume of liquid fluid in the fluid storage tank (100-MLC) gradually increases, the volume of gaseous fluid gradually decreases, and the pressure in the fluid storage tank (100-MLC) increases. When the pressure in the fluid storage tank (100-MLC) reaches the upper pressure threshold P_high set by the pressure control command module (400-PDM) (e.g., 0.3 MPa higher than the working pressure), the pressure control command module (400-PDM) issues a command to start the compressor (200-CS), pressurizing part of the gaseous fluid in the fluid storage tank (100-MLC) and injecting it into the pressure stabilizing tank (110-PSC). When the pressure control command module (400-PDM) detects that the pressure in the fluid storage tank (100-MLC) has fallen back to the working pressure control value of the fluid storage tank (100-MLC), the pressure control command module (400-PDM) issues another command to shut down the compressor (200-CS), thereby maintaining the pressure stability in the fluid storage tank (100-MLC) and controlling the change in gaseous fluid temperature under the pressure of the pressure stabilizing tank (110-PSC).

[0054] Furthermore, such as Figure 3As shown, in the working condition of outputting liquid fluid from the fluid storage tank (100-MLC) (liquid output working condition), the volume of liquid fluid in the fluid storage tank (100-MLC) gradually decreases, the volume of gaseous fluid gradually increases, and the pressure in the fluid storage tank (100-MLC) decreases. When the pressure in the fluid storage tank (100-MLC) reaches the lower pressure threshold P_low (for example, 0.3 MPa lower than the working pressure) set by the pressure control instruction module (400-PDM), the pressure control instruction module (400-PDM) issues an instruction to open the first pressure reduction device (240-PRD1) to reduce the pressure of part of the high-pressure gaseous fluid in the pressure stabilizing tank (110-PSC) to the working pressure control value of the fluid storage tank (100-MLC) and then input into the fluid storage tank (100-MLC). When the pressure control instruction module (400-PDM) monitors that the pressure in the fluid storage tank (100-MLC) rises to the working pressure control value of the fluid storage tank (100-MLC), the pressure control instruction module (400-PDM) again issues an instruction to close the first pressure reduction device (240-PRD1), thereby maintaining the pressure in the fluid storage tank (100-MLC) stable and controlling the temperature variation of the gaseous fluid in the fluid storage tank (100-MLC) at the working pressure of the backfill gas, thereby reducing the evaporation of the liquid fluid in the fluid storage tank caused by the backfill gas.

[0055] Preferably, the representative parameters in the above implementation can be: the working pressure P_MLC of the fluid storage tank (100-MLC) is 1.7 MPa, P_high is 1.73 MPa, and P_low is 1.67 MPa; and the working pressure P_PSC of the pressure stabilizing tank (110-PSC) is 3.4 MPa.

[0056] In the second aspect, another pressure stabilizing device and method for a fluid storage tank with gas-liquid two-phase coexistence are provided, and a specific embodiment thereof is described with reference to Figures 4-6The pressure stabilizing device of the fluid storage tank with gas-liquid two-phase coexistence includes a fluid storage tank (100-MLC) and a pressure stabilizing device (500-PSD). The fluid is stored in the form of gas-liquid two-phase coexistence in the fluid storage tank (100-MLC). The pressure stabilizing device (500-PSD) is used to maintain the stability of the pressure in the fluid storage tank (100-MLC), including a second pressure reducing device (241-PRD2), a buffer tank (120-BC), and an expander (250-E-S). The second pressure reducing device (241-PRD2) and the buffer tank (120-BC) are located between the fluid storage tank (100-MLC) and the expander (250-E-S). The gas phase space of the fluid storage tank (100-MLC) is connected to the compressor (200-C-S) and the expander (250-E-S), respectively. The inlet of the compressor (200-C-S) is in communication with the gas phase space of the fluid storage tank (100-MLC), and is used to pressurize and discharge part of the gas phase fluid into the pressure stabilizing storage tank (110-PSC) when the fluid storage tank (100-MLC) is overpressured. The pressure control instruction module (400-PDM) acquires the pressure value of the fluid storage tank (100-MLC) and sets the upper pressure threshold P_high and the lower pressure threshold P_low. The pressure control instruction module (400-PDM) sends operation instructions to the compressor (200-C-S), the second pressure reducing device (241-PRD2), and the expander (250-E-S) according to the collected pressure signals.

[0057] The working pressure control value of the pressure stabilizing storage tank (110-PSC) is not less than 2 times the working pressure control value of the fluid storage tank (100-MLC). Mainly considering the size of the storage tank, the larger the working pressure control value, the smaller the pressure stabilizing storage tank (110-PSC), but the more the compression heat. When there is a cheap external cold source, the working pressure control value of the pressure stabilizing storage tank (110-PSC) can be higher. When there is no external cold source or no cheap external cold source, a lower working pressure control value is preferred. The working pressure control value of the pressure stabilizing storage tank (110-PSC) is preferably in the range of 2-20 times the working pressure control value of the fluid storage tank (100-MLC). When the ratio of the working pressure control value of the pressure stabilizing storage tank (110-PSC) to the working pressure control value of the fluid storage tank (100-MLC) is low, the compression power is reduced. When the ratio of the working pressure control value of the pressure stabilizing storage tank (110-PSC) to the working pressure control value of the fluid storage tank (100-MLC) is high, the compression power is increased, but the overall efficiency RTE is reduced, but the economic benefit is improved.

[0058] Further, as Figure 4As shown, the pressure stabilizing device (500-PSD) further comprises a pressure stabilizing heat exchanger (220-HX-S) for reducing the temperature of the dumped or reinjected gaseous fluid to a value close to the saturation temperature of the gas-liquid two-phase in the fluid storage tank (100-MLC) under both overpressure and underpressure conditions. The pressure stabilizing heat exchanger (220-HX-S) can be arranged in the inlet flow process before the pressurized gaseous fluid enters the pressure stabilizing storage tank (110-PSC), or in the outlet flow process after the pressurized gaseous fluid exits the pressure stabilizing storage tank (110-PSC), so as to reduce the evaporation amount of the liquid phase fluid caused by the gaseous fluid entering the fluid storage tank (100-MLC).

[0059] The pressure stabilizing heat exchanger (220-HX-S) is thermally coupled with an external cold source (300-ECS), which can be at least one of liquefied natural gas regasification cold energy, a refrigerator, or an environmental cold source.

[0060] Further, as shown, Figure 5 Under the condition of liquid fluid entering the fluid storage tank (100-MLC) (liquid inlet condition), the volume of the liquid fluid in the fluid storage tank (100-MLC) gradually increases, and the volume of the gaseous fluid gradually decreases, and the pressure in the fluid storage tank (100-MLC) increases. When the pressure in the fluid storage tank (100-MLC) reaches the upper pressure threshold P_high (for example, 0.3 MPa higher than the working pressure) set by the pressure control instruction module (400-PDM), the pressure control instruction module (400-PDM) issues an instruction to start the compressor (200-C-S) to pressurize and inject part of the gaseous fluid in the fluid storage tank (100-MLC) into the pressure stabilizing storage tank (110-PSC); when the pressure control instruction module (400-PDM) monitors that the pressure in the fluid storage tank (100-MLC) falls to the working pressure control value of the fluid storage tank (100-MLC), the pressure control instruction module (400-PDM) again issues an instruction to stop the compressor (200-C-S), so as to maintain the pressure in the fluid storage tank (100-MLC) stable and control the temperature variation amount of the gaseous fluid under the pressure of the pressure stabilizing storage tank (110-PSC).

[0061] Further, as shown, Figure 6As shown, in the working condition (liquid output condition) of outputting liquid fluid from the fluid storage tank (100-MLC), the volume of the liquid fluid in the fluid storage tank (100-MLC) gradually decreases, the volume of the gaseous fluid gradually increases, and the pressure in the fluid storage tank (100-MLC) decreases. When the pressure in the fluid storage tank (100-MLC) reaches the lower pressure threshold P_low (for example, 0.3 MPa lower than the working pressure) set by the pressure control instruction module (400-PDM), the pressure control instruction module (400-PDM) issues an instruction to open the second pressure reduction device (241-PRD2). The gaseous fluid from the pressure stabilizing tank (110-PSC) flows into the buffer tank (120-BC) through the second pressure reduction device (241-PRD2) after being reduced in pressure, and the gaseous fluid in the buffer tank (120-BC) is input into the fluid storage tank (100-MLC) after being reduced in pressure to the working pressure control value of the fluid storage tank (100-MLC) by the expander (250-E-S). When the pressure control instruction module (400-PDM) monitors that the pressure in the fluid storage tank (100-MLC) rises to the working pressure control value of the fluid storage tank (100-MLC), the pressure control instruction module (400-PDM) again issues an instruction to close the second pressure reduction device (241-PRD2) and the expander (250-E-S), so as to maintain the stability of the pressure in the fluid storage tank (100-MLC) and control the change amount of the gas phase fluid temperature of the reinjection gas at the working pressure of the fluid storage tank (100-MLC).

[0062] In the above implementation, the pressure control instruction module (400-PDM) controls the second pressure reduction device (241-PRD2) so that the relative fluctuation of the inlet pressure of the expander (250-E-S) when the expander (250-E-S) is in a stable state does not exceed ±20% of the working pressure control value in the expander (250-E-S), thereby improving the expansion efficiency and mechanical life.

[0063] Preferably, in the above implementation, the representative parameters can be: the working pressure P_MLC of the fluid storage tank (100-MLC) is 1.7 MPa, P_high is 1.73 MPa, and P_low is 1.67 MPa; the pressure between the second pressure reduction device (241-PRD2) and the buffer tank (120-BC) is maintained at about 6.8 MPa; the working pressure P_PSC of the pressure stabilizing tank (110-PSC) is 6.8-13.6 MPa; and the outlet pressure P_E-S of the expander (250-E-S) is 1.7 MPa. 出口

[0064] The above-mentioned pressure stabilizing method of the fluid storage tank with coexisting gas-liquid two phases provided by the application comprises the following steps: ​

[0065] S1: The pressure control command module (400-PDM) acquires the pressure value in the fluid storage tank (100-MLC) in real time under any working condition;

[0066] S2: When the pressure in the fluid storage tank (100-MLC) rises to the upper pressure threshold P_high, the pressure control command module (400-PDM) issues a command to start the compressor (200-C-S) to pressurize part of the gaseous fluid in the fluid storage tank (100-MLC) to the working pressure P_PSC control value of the pressure stabilizing tank (110-PSC) and then inject it into the pressure stabilizing tank (110-PSC).

[0067] S3: When the pressure in the fluid storage tank (100-MLC) falls to the working pressure P_MLC control value of the fluid storage tank (100-MLC), the pressure control command module (400-PDM) issues a command to stop the compressor (200-C-S).

[0068] S4: When the pressure in the fluid storage tank (100-MLC) decreases to the lower pressure threshold P_low, the pressure control command module (400-PDM) issues a command to start the first pressure reducing device (240-PRD1) to depressurize part of the pressurized gaseous fluid in the pressure stabilizing tank (110-PSC) to the working pressure P_MLC control value of the fluid storage tank (100-MLC) and then inject it into the fluid storage tank (100-MLC).

[0069] S5: When the pressure in the fluid storage tank (100-MLC) rises to the working pressure P_MLC control value of the fluid storage tank (100-MLC), the pressure control command module (400-PDM) issues a command to stop the first pressure reducing device (240-PRD1).

[0070] Preferably, when the first pressure reducing device (240-PRD1) is a pressure stabilizing expander (250-E-S), the S4 is preceded by a pressure reduction by the second pressure reducing device (241-PRD2) and pressure stabilization in the buffer tank (120-BC), so that the inlet pressure of the expander (250-E-S) has a steady-state fluctuation of ≤±20%, and the expander (250-E-S) simultaneously drives a generator to generate electricity.

[0071] In the above embodiment, the difference between the upper threshold value P_high and the lower threshold value P_low of the pressure in the fluid storage tank (100-MLC) is determined according to the system time lag and the valve response to avoid frequent start-stop and enter the protection logic when over-temperature / over-pressure / under-pressure occurs. The working pressure control value of the pressure stabilizing storage tank (110-PSC) is not less than twice the working pressure control value of the fluid storage tank (100-MLC).

[0072] In a third aspect, the present application provides a liquid air energy storage system, and a specific embodiment thereof is described with reference to Figure 7 In the embodiment, the fluid in the fluid storage tank (100-MLC) is liquid air, and the fluid storage tank (100-MLC) is a liquid air storage tank. The liquid air energy storage system comprises a charging module (600-CM), a discharging module (700-DCM), and the pressure stabilizing device (500-PSD) of the present application. The pressure stabilizing device (500-PSD) is used to maintain the stability of the pressure in the fluid storage tank (100-MLC) of the liquid air energy storage system under discharging and charging conditions. The liquid air inlet and outlet of the fluid storage tank (100-MLC) are respectively provided with a first one-way valve (260-CV1) and a second one-way valve (261-CV2) to prevent backflow of the fluid.

[0073] Further, the charging module (600-CM) is connected to the liquid air inlet end of the fluid storage tank (100-MLC) and comprises a charging compressor (210-C-C) and a cryogenic expander (252-CE) for injecting liquid air into the fluid storage tank (100-MLC). A charging heat exchanger (221-HX-C) is arranged between the charging compressor (210-C-C) and the cryogenic expander (252-CE) to cool the air flowing out of the charging compressor (210-C-C).

[0074] Further, the discharging module (700-DCM) is connected to the liquid air outlet end of the fluid storage tank (100-MLC) and comprises a cryogenic pump (230-CP) and a discharging expander (251-E-DC) for outputting the liquid air in the fluid storage tank (100-MLC) to generate electricity. A discharging heat exchanger (222-HX-DC) is arranged between the cryogenic pump (230-CP) and the discharging expander (251-E-DC) to warm the liquid air flowing out of the cryogenic pump (230-CP).

[0075] In the charging condition in the embodiment of the application, the ambient air enters the charging heat exchanger (221-HX-C) after being pressurized by the charging compressor (210-C-C) and is cooled to become high-pressure low-temperature air, and the high-pressure low-temperature air enters the low-temperature expander (252-CE) to be further cooled and depressurized to become liquid air and flows into the fluid storage tank (100-MLC) for storage.

[0076] In the charging process, to avoid the pressure rise in the fluid storage tank (100-MLC), according to the second and third aspects of the application, the gaseous air in the fluid storage tank (100-MLC) is cooled by the pressure stabilizing heat exchanger (220-HX-S) after being pressurized by the charging compressor (210-C-C) and enters the pressure stabilizing storage tank (110-PSC).

[0077] In the discharging condition in the embodiment of the application, the low-temperature pump (230-CP) pumps out the liquid air in the fluid storage tank (100-MLC), the liquid air is warmed by the discharging heat exchanger (222-HX-DC) and then flows into the discharging expander (251-E-DC) to expand and generate electricity.

[0078] In the discharging process, to avoid the pressure drop in the fluid storage tank (100-MLC), according to the second and third aspects of the application, the air in the pressure stabilizing storage tank (110-PSC) is cooled and depressurized and then enters the fluid storage tank (100-MLC).

[0079] Preferably, the representative parameters in the above embodiment can be as follows: the working pressure P_MLC of the fluid storage tank (100-MLC) is controlled to be in the range of 0.5-3.8 MPa; and the working pressure P_PSC of the pressure stabilizing storage tank (110-PSC) is controlled to be 2-20 times of the working pressure of the fluid storage tank (100-MLC).

[0080] In a specific embodiment of the application, the working pressure P_MLC of the fluid storage tank (100-MLC) is 1.7 MPa, and the temperature is -158.3℃; and the working pressure P_PSC of the pressure stabilizing storage tank (110-PSC) is 3.4 MPa.

[0081] Preferably, in the charging condition, the outlet temperature of the compressor (200-C-S) is -125.9℃, and the pressure of the gaseous fluid in the pressure stabilizing tank (110-PSC) is 3.4 MPa, and the temperature is -125.9℃. In the discharging condition, the compressed gaseous fluid in the pressure stabilizing tank (110-PSC) enters the fluid storage tank (100-MLC) after being depressurized, and the pressure of the gaseous fluid after being depressurized is 1.7 MPa, and the temperature is -142.0℃, so that part of the liquid fluid in the fluid storage tank (100-MLC) is vaporized, and the temperature is lowered to -158.3℃.

[0082] Preferably, in the charging condition, the outlet temperature of the compressor (200-C-S) is -125.9℃, and the pressure of the gaseous fluid in the pressure stabilizing tank (110-PSC) is 3.4 MPa, and the temperature is -125.9℃. In the discharging condition, the compressed gaseous fluid in the pressure stabilizing tank (110-PSC) enters the fluid storage tank (100-MLC) after being depressurized, and the pressure of the gaseous fluid after being depressurized is 1.7 MPa, and the temperature is -142.0℃, so that part of the liquid fluid in the fluid storage tank (100-MLC) is vaporized, and the temperature is lowered to -158.3℃.

[0083] In another specific embodiment of the present application, the working pressure of the fluid storage tank (100-MLC) is P_MLC=1.7 MPa, and the temperature is -158.3℃, and the working pressure of the pressure stabilizing tank (110-PSC) is P_PSC=17 MPa.

[0084] Preferably, in the charging condition, the outlet temperature of the compressor (200-C-S) is -22.6℃, and the pressure of the gaseous fluid in the pressure stabilizing tank (110-PSC) is 17 MPa, and the temperature is -22.7℃. In the discharging condition, the compressed gaseous fluid in the pressure stabilizing tank (110-PSC) enters the fluid storage tank (100-MLC) after being depressurized, and the pressure of the gaseous fluid after being depressurized is 1.7 MPa, and the temperature is -62.8℃, so that part of the liquid fluid in the fluid storage tank (100-MLC) is vaporized, and the temperature is lowered to -159℃.

[0085] Preferably, in the charging condition, the outlet temperature of the compressor (200-C-S) is -22.6℃, and the pressure of the gaseous fluid in the pressure stabilizing tank (110-PSC) is 16 MPa, and the temperature is -22.64℃. In the discharging condition, the compressed gaseous fluid in the pressure stabilizing tank (110-PSC) enters the fluid storage tank (100-MLC) after being depressurized, and the pressure of the gaseous fluid after being depressurized is 1.7 MPa, and the temperature is -158.3℃, so that part of the liquid fluid in the fluid storage tank (100-MLC) is vaporized, and the temperature is lowered to -159℃.

Claims

1. A pressure stabilizing device for a gas-liquid two-phase coexisting fluid storage tank, characterized by, The system comprises: a pressure stabilizing tank, whose working pressure control value is not less than twice of that of the fluid tank; a compressor, whose inlet is connected with the gas phase space of the fluid tank, for pressurizing and discharging part of the gas phase fluid into the pressure stabilizing tank when the fluid tank is over-pressured; a first pressure reducing device, whose inlet is connected with the pressure stabilizing tank and whose outlet is connected with the gas phase space of the fluid tank, for reducing the pressure of the gas phase fluid in the pressure stabilizing tank to the working pressure control value of the fluid tank and injecting it into the fluid tank when the fluid tank is under-pressured; a pressure control instruction module, for obtaining the pressure in the fluid tank and setting an upper pressure threshold and a lower pressure threshold, and for issuing an instruction to start the compressor when the pressure in the fluid tank is greater than or equal to the upper pressure threshold, and for issuing an instruction to start the first pressure reducing device when the pressure in the fluid tank is less than or equal to the lower pressure threshold; wherein the upper pressure threshold and the lower pressure threshold are determined according to the system time lag and the valve response to avoid frequent start and stop.

2. The voltage stabilizing device according to claim 1, wherein The system further comprises a pressure stabilizing heat exchanger, which is thermally coupled with an external cold source, for reducing the temperature of the discharged or injected gas phase fluid in the over-pressured or under-pressured condition; wherein in the injection condition, the pressure stabilizing heat exchanger reduces the temperature of the injected gas phase fluid to the saturation temperature close to the gas-liquid two-phase in the fluid tank, thereby reducing the evaporation of the liquid phase fluid in the fluid tank caused by the injected gas phase fluid.

3. The voltage stabilizing device according to claim 2, wherein The heat exchanger can be thermally coupled with an external cold source, which comprises at least one of liquefied natural gas regasification cold energy, a refrigeration machine or an environmental cold source.

4. The voltage stabilizing device according to claim 1, wherein The first pressure reducing device is a pressure reducing valve or an expander.

5. The voltage stabilizing device according to claim 4, wherein When the first pressure reducing device is an expander, the system further comprises a generator driven by the expander.

6. The voltage stabilizing device according to claim 5, wherein The system further comprises a second pressure reducing device and a buffer tank, which are arranged between the pressure stabilizing tank and the expander; wherein the gas phase fluid from the pressure stabilizing tank enters the buffer tank after being reduced in pressure by the second pressure reducing device, and the gas phase fluid in the buffer tank flows into the fluid tank after being reduced in pressure by the expander; and the pressure control instruction module controls the second pressure reducing device to make the relative fluctuation amplitude of the inlet pressure of the expander in steady state operation not exceed 20% of the working pressure control value of the inlet pressure of the expander.

7. The apparatus of claim 1, wherein, The working pressure control value of the pressure stabilizing tank is 2-20 times of that of the fluid tank.

8. A method for stabilizing a pressure of a fluid storage tank in which gas and liquid phases coexist, characterized by, The system comprises: S1 the pressure control instruction module obtains the pressure value in the fluid tank and sets an upper pressure threshold and a lower pressure threshold; S2 when the pressure in the fluid tank rises to the upper pressure threshold, the pressure control instruction module issues an instruction to start the compressor to pressurize part of the gas phase fluid in the fluid tank to the working pressure control value of the pressure stabilizing tank and input it into the pressure stabilizing tank; S3 when the pressure in the fluid tank falls to the working pressure control value of the fluid tank, the pressure control instruction module issues an instruction to stop the compressor; S4 When the pressure in the fluid tank decreases to the lower threshold value, the pressure control instruction module issues an instruction to open the first pressure reduction device to reduce the pressure of part of the pressurized gaseous fluid in the pressure stabilizing tank to the working pressure control value of the fluid tank; S5 When the pressure in the fluid tank rises to the working pressure control value, the pressure control instruction module issues an instruction to close the first pressure reduction device; S6 When the pressure control instruction module detects that the pressure has recovered to the working pressure control value, the pressure control instruction module issues an instruction to close the corresponding actuator. The upper threshold value and the lower threshold value are set according to the system time lag and valve response to form a hysteresis control, and the working pressure control value of the pressure stabilizing tank is not less than twice the working pressure control value of the fluid tank.

9. The method of claim 8, wherein, When the first pressure reduction device is a low-temperature expander, before the S4 step, the second pressure reduction device is used to reduce the pressure and stabilize the pressure in the buffer tank, so that the relative fluctuation amplitude of the inlet pressure of the expander during stable operation does not exceed plus or minus 20%.

10. The method of claim 8, wherein, The pressure upper threshold value and the pressure lower threshold value are determined according to the system time lag and valve response to avoid frequent start-stop; and when the temperature / pressure is too high / low, the protection logic is entered.

11. A liquid air energy storage system, characterized in that, The system includes the pressure stabilizing device of any one of claims 1-7; wherein the fluid is air, and the fluid tank is a liquid air tank.

12. A liquid air energy storage system according to claim 11, wherein, It also includes a pressure stabilizing heat exchanger. In the charging condition, the gaseous air is first cooled by the pressure stabilizing heat exchanger after being pressurized by the compressor, and then enters the pressure stabilizing tank, or In the discharging condition, the gas in the pressure stabilizing tank is first cooled by the pressure stabilizing heat exchanger, and then enters the liquid air tank.

13. The liquid air energy storage system of claim 11, wherein, The working pressure control value of the liquid air tank is specifically in the range of 0.5MPa to 3.8MPa; and the working pressure control value of the pressure stabilizing tank is in the range of 2-20 times the working pressure control value of the liquid air tank.

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