A cold energy recovery system and method based on a low-temperature storage tank refrigeration system

Abstract

The application provides a cold energy recovery system and method based on a low-temperature storage tank refrigeration system. The system and method mainly relate to the reverse cycle application of the refrigeration system in the low-temperature storage tank system. The system and method comprise a motor / generator, a refrigerator / engine, a low-temperature storage tank, a power device, a power transmission line, a pipeline, a low-temperature valve and a circulating pump. In the non-working or low-load working state of the power device, the motor drives the refrigerator to work, provides cold energy for the low-temperature storage tank and reduces the heat leakage of the stored low-temperature working medium. In the high-load working state of the power device, the engine converts the cold energy of the low-temperature working medium into mechanical energy to drive the generator to generate electric energy. The application realizes the recycling of the cold energy in the low-temperature working medium by using the reverse process of the refrigeration device in the low-temperature storage system without functional interference, reduces the energy consumption of the preheating of the low-temperature working medium and simplifies the device for the preheating of the low-temperature working medium.

Description

Technical Field

[0001] This invention relates to the field of cold energy recovery, and more particularly to a cold energy recovery system and method for cryogenic working fluid in a cryogenic storage tank. Background Technology

[0002] In recent years, with the rapid development of technologies in aerospace, energy, information, and other related fields, cryogenic technology has also developed rapidly and been widely applied, showing enormous development potential. Cryogenicity refers to the temperature range below 120K. Cryogenic working fluids with boiling points within this temperature range, such as liquid hydrogen, liquid oxygen, and liquid methane, have become ideal choices for spacecraft propellants due to their excellent performance. Liquid nitrogen and liquid helium have important applications in many areas, including satellite launches, spacecraft on-orbit operation, missile industry, and cryogenic and superconducting research. During long-term, large-capacity storage, these cryogenic working fluids are stored at temperatures far below ambient temperatures. Heat transfer between the hot and cold ends causes the cryogenic working fluid to evaporate within the storage tank. The resulting cryogenic gases accumulate inside the tank, leading to a gradual increase in pressure and temperature, which can severely damage the tank.

[0003] Most existing cryogenic working fluid storage technologies combine active refrigeration with passive thermal protection. In a cryogenic storage tank system, active refrigeration technology couples the refrigeration unit's heat exchanger to the cryogenic tank. Through heat exchange, external heat leakage that cannot be completely isolated by passive thermal protection is removed, thereby cooling the cryogenic working fluid and condensing and reliquefying the cryogenic gas. This allows for control over the evaporation rate of the cryogenic working fluid, ultimately enabling long-term storage.

[0004] On the other hand, cryogenic working fluids require preheating before entering power devices such as fuel cells. Current preheating methods primarily involve electric heating, which uses electrical energy to heat the cryogenic working fluid to its operating temperature before it enters the power device. In engineering, the heat exchanged between a system operating below ambient temperature and its surroundings is called cooling capacity Q0, and the maximum useful work performed by the system when absorbing heat is called cooling capacity. Use E x,Q0 Indicated. Relatively speaking, heat. E refers to the maximum useful work that a system with a temperature higher than the ambient temperature can do by transferring heat Q to its surroundings. x,Q express. Figure 1 The figure shows the heat. and cooling capacity In general, regarding the relationship with temperature, when the system temperature T is greater than the ambient temperature T0, as T→∞, E... x,Q →Q, E x,Q The ratio of E to Q is always less than 1, meaning that heat cannot be 100% converted into useful work; when the system temperature T is less than the ambient temperature T0, as T→0, E... x,Q0 →∞,E x,Q0The absolute value of the ratio to Q0 can be greater than 1, i.e., the cooling capacity. In quantity, it can be greater than the heat itself. This indicates that the amount of cold energy... It is even more valuable, especially in cryogenic systems where it can yield significant useful work. However, directly preheating the cryogenic working fluid with electricity not only consumes a large amount of electrical energy but also results in a huge waste of the abundant and abundant cold energy in the cryogenic working fluid.

[0005] Most refrigeration systems used in cryogenic storage tank systems, such as pulse tube refrigeration systems and Stirling refrigeration systems, share the same key components as similar thermodynamic systems. This means that by reversing the operation of the same refrigeration system, the system can achieve thermodynamic conversion, thus possessing both refrigeration and thermodynamic conversion functions. Under the premise of ensuring no functional interference, the reverse circulation of the refrigeration system enables the recovery and utilization of cold energy from the cryogenic working fluid, while simultaneously reducing the energy consumption required for preheating the cryogenic working fluid and simplifying the preheating device. Summary of the Invention

[0006] To fully utilize the cold energy in the cryogenic working fluid, and considering the energy loss from electric heating preheating, this invention aims to provide a cold energy recovery system and method based on a cryogenic storage tank refrigeration system. Specifically, based on the actual storage and usage of the cryogenic working fluid in the cryogenic storage tank refrigeration system, this invention changes the traditional design concept of electric heating preheating of the working fluid. Without causing functional interference, it achieves both cooling and preheating of the cryogenic working fluid within the same refrigeration system through reverse circulation of the refrigeration system used for cooling the working fluid. This invention efficiently recovers the abundant and substantial cold energy in the cryogenic working fluid, realizing its power generation function while reducing the energy consumption required to heat the working fluid, thus improving the overall energy efficiency of the cryogenic storage tank refrigeration system.

[0007] The technical solution of the present invention is as follows:

[0008] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, comprising: an electric motor / generator, a refrigeration unit / engine, a cryogenic storage tank, a power unit, a power transmission line, pipelines, a cryogenic valve, and a circulating pump, etc., characterized in that the electric motor / generator has a dual-function mode of electric motor and generator, and the refrigeration unit / engine has a dual-function mode of refrigeration conversion and thermodynamic conversion.

[0009] When the power unit is not in operation or under low load, the electric motor consumes electrical energy to drive the refrigeration unit to provide cooling capacity to the cryogenic storage tank and reduce or eliminate heat leakage of the stored cryogenic working fluid; the electric motor / generator operates in electric motor mode, and the refrigeration unit / engine operates in refrigeration unit mode.

[0010] When the power unit is under high load, the cryogenic working fluid is output from the cryogenic storage tank, and the engine converts the cold energy of the cryogenic working fluid into mechanical energy to drive the generator to generate electrical energy; the motor / generator operates in generator mode, and the refrigeration unit / engine operates in engine mode.

[0011] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the refrigeration unit / engine is a pulse tube refrigeration unit when operating in refrigeration mode and a thermoacoustic engine when operating in cold energy recovery mode.

[0012] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the refrigeration unit / engine is a Stirling refrigeration unit when operating in refrigeration mode and a Stirling engine when operating in cold energy recovery mode.

[0013] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the refrigeration unit / engine is a single-stage, two-stage, three-stage, or four-stage unit.

[0014] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the motor / generator is a linear compressor, a permanent magnet synchronous motor, a three-phase asynchronous motor, or a series-wound DC motor.

[0015] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the cryogenic storage tank is a liquid hydrogen storage tank, a liquefied natural gas storage tank, a liquid methane storage tank, a liquid oxygen storage tank, a liquid nitrogen storage tank, or a liquid helium storage tank.

[0016] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the power unit is a fuel cell, a piston internal combustion engine, or a gas turbine.

[0017] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the fuel cell is a proton exchange membrane fuel cell, a solid oxide fuel cell, an alkaline fuel cell, a phosphoric acid fuel cell, or a molten carbonate fuel cell.

[0018] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the piston internal combustion engine is a reciprocating piston internal combustion engine or a rotary piston engine.

[0019] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the power transmission line is a system-compatible wire, the pipeline is a system-compatible seamless steel pipe, the cryogenic valve is a system-compatible cryogenic pressure reducing valve, cryogenic shut-off valve, and cryogenic three-way valve, and the circulating pump is a system-compatible circulating pump with cryogenic working fluid transport function.

[0020] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the working fluid inside the refrigeration unit / engine is a usable gas such as helium, nitrogen, or air.

[0021] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, characterized in that the external fluid at the cold end of the refrigeration unit / engine is a cryogenic working fluid, and the external fluid at the hot end of the refrigeration unit / engine is a usable fluid such as air, pure water, or ethylene glycol.

[0022] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, which realizes the reverse circulation application of the refrigeration system in principle. Figure 2 This is a schematic diagram of the refrigeration cycle and its reverse cycle application principle, where T1 > T2, q1 and q2 represent the heat transferred, and w0 represents the useful work input to or output to the system.

[0023] Most refrigeration systems used in cryogenic storage tank systems, such as pulse tube refrigeration systems and Stirling refrigeration systems, utilize a thermodynamic cycle of "compression-heat release-expansion-heat absorption." The refrigeration engine consumes useful work to pump heat from the cold end to the hot end, thus producing a cooling effect at the cold end. In contrast, for a similar type of engine, when the temperature gradient of the regenerator reaches its critical value, gas particles undergo a thermodynamic cycle of "compression-heat absorption-expansion-heat release" in the regenerator. The engine outputs useful work, achieving the conversion of thermal energy into mechanical energy.

[0024] Based on their working principles, it can be seen that the working principle of an engine can be considered a "reverse cycle" of a refrigeration engine. Combined with the similarities in their structural composition and key components, this makes the implementation of reverse cycle applications in refrigeration systems possible. When operating as an engine, i.e., performing a reverse cycle function, the heat input to the hot-end heat exchanger is transferred to the low-temperature working fluid passing through the cold-end heat exchanger, and the cooling capacity of the low-temperature working fluid... The mechanical energy is output as useful work, and then the mechanical energy is converted into electrical energy by a generator, thus realizing the recovery of cold energy in the low-temperature working fluid.

[0025] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system, such as... Figure 3 As shown, solid arrows indicate the refrigeration conversion function when the refrigeration unit / engine functions as a refrigeration unit, while dashed arrows indicate the thermodynamic conversion function when the refrigeration unit / engine functions as an engine. When the power unit is not operating or under low load, and it is necessary to reduce heat leakage of the cryogenic working fluid in the storage tank, the electric motor consumes electrical energy to drive the refrigeration unit, providing cooling to the cryogenic storage tank and reducing heat leakage of the stored cryogenic working fluid. When the power unit is operating under high load, the cryogenic working fluid is output from the cryogenic storage tank, and the engine converts the cold energy of the cryogenic working fluid into mechanical energy, driving the generator to produce electrical energy.

[0026] The cold energy recovery system and method based on a cryogenic storage tank refrigeration system of the present invention have the following advantages:

[0027] The present invention relates to a cold energy recovery system and method based on a cryogenic storage tank refrigeration system. This system utilizes a refrigeration system that is not used under high-load operating conditions of the power unit. By applying a reverse circulation method to the refrigeration system, it efficiently recovers the abundant and substantial cold energy from the cryogenic working fluid, thus avoiding the loss of cold energy in the cryogenic working fluid. This invention addresses the significant waste associated with preheating the cryogenic working fluid. By utilizing the reverse process of the cryogenic storage system's own refrigeration device, without causing functional interference, the invention achieves the recovery and utilization of the cryogenic working fluid's cold energy. Simultaneously, it reduces the energy consumption required for preheating the cryogenic working fluid and simplifies the preheating device. Attached Figure Description

[0028] To more clearly illustrate the purpose, basic principles, technical solutions, and advantages of this invention, the accompanying drawings used in the prior art description will be briefly introduced below. The following drawings are incorporated herein as part of this invention and are used to provide a further understanding of the invention. Those skilled in the art will be able to obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0029] Figure 1 For heat and cooling capacity A diagram illustrating the relationship between temperature and other parameters;

[0030] Figure 2 A schematic diagram illustrating the principle of a refrigeration cycle and its reverse cycle application;

[0031] Figure 3 This is a schematic diagram of the dual-function mode of the refrigeration unit / engine.

[0032] Figure 4 This is a schematic diagram of a cold energy recovery system based on a cryogenic storage tank refrigeration system provided in Embodiment 1 of the present invention;

[0033] Figure 5 This is a schematic diagram of a cold energy recovery system based on a cryogenic storage tank refrigeration system provided in Embodiment 2 of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are merely illustrative and not intended to limit the invention. In addition to the following detailed description, the present invention may have other implementations. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] The structure of this embodiment is as follows: Figure 4 As shown, it includes a liquid hydrogen storage tank 1, a hydrogen high-pressure buffer tank 2, a liquid oxygen storage tank 3, an oxygen high-pressure buffer tank 4, a proton exchange membrane fuel cell 5, a lithium battery 6, a linear compressor 7, a two-stage pulse tube refrigerator / thermoacoustic engine 8, as well as power transmission lines, pipelines, cryogenic valves, and a circulation pump 9. The two-stage pulse tube refrigerator / thermoacoustic engine 8 is arranged in a U-shape, and both stages of the phasing structure are inertial tube-gas reservoir type structures with bidirectional air intake. The solid arrows in the figure represent the process by which the two-stage pulse tube refrigerator 8 reduces heat leakage from the liquid hydrogen in the liquid hydrogen storage tank 1 and the liquid oxygen in the liquid oxygen storage tank 3 in this embodiment. The dashed arrows represent the process by which the thermoacoustic engine 8 recovers and utilizes the cold energy of the cryogenic hydrogen and cryogenic oxygen before they are used in the proton exchange membrane fuel cell 5.

[0037] When the proton exchange membrane fuel cell 5 is not in operation or under low load, the linear compressor 7 is driven by the lithium battery 6. The linear compressor 7 operates in electric motor mode, providing the necessary pressure wave for cooling, which in turn drives the secondary pulse tube refrigerator / thermoacoustic engine 8. The secondary pulse tube refrigerator / thermoacoustic engine 8 operates in refrigerator mode, performing its refrigeration conversion function. Based on the acoustic cooling effect, the pulse tube refrigerator pumps heat from the cold end to the hot end of the cryogenic hydrogen and oxygen. The first-stage cold-end heat exchanger of the secondary pulse tube refrigerator 8 is coupled to the cryogenic gas-cooled screen of the liquid oxygen storage tank 3. Through heat exchange, external heat leakage from the liquid oxygen storage tank 3 is removed, achieving cooling of the liquid oxygen and condensation and reliquefaction of the cryogenic oxygen. This allows for control of the liquid oxygen evaporation rate, ultimately enabling long-term storage of liquid oxygen. The second-stage cold-end heat exchanger of the two-stage pulse tube refrigerator 8 is coupled to the low-temperature gas-cooled screen of the liquid hydrogen storage tank 1. Through heat exchange, the external heat leakage of the liquid hydrogen storage tank 1 is removed, thereby achieving cooling of liquid hydrogen and condensation and reliquefaction of low-temperature hydrogen. This allows for control of the amount of liquid hydrogen evaporation and ultimately enables long-term storage of liquid hydrogen.

[0038] Under high-load operation of the proton exchange membrane fuel cell 5, the cryogenic hydrogen output from the liquid hydrogen storage tank 1 enters the hydrogen high-pressure buffer tank 2. When the hydrogen high-pressure buffer tank 2 is full of cryogenic hydrogen, the output cryogenic hydrogen passes through the secondary pulse tube refrigerator / thermoacoustic engine 8. The cryogenic oxygen output from the liquid oxygen storage tank 3 enters the oxygen high-pressure buffer tank 4. When the oxygen high-pressure buffer tank 4 is full of cryogenic oxygen, the output cryogenic oxygen passes through the secondary pulse tube refrigerator / thermoacoustic engine 8. The secondary pulse tube refrigerator / thermoacoustic engine 8 operates in engine mode at this time, performing the thermodynamic conversion function of the thermoacoustic engine. Based on the thermoacoustic effect, the heat from the hot end of the thermoacoustic engine is transferred to the cold end, preheating the cryogenic hydrogen and cryogenic oxygen entering the proton exchange membrane fuel cell 5 to the operating temperature. The secondary thermoacoustic engine 8 generates sound waves, which, as a form of mechanical energy, drive the linear compressor 7 to generate electrical energy. The linear compressor 7 operates in generator mode at this time, and the generated electrical energy is input into the lithium battery 6 for storage. Meanwhile, low-temperature hydrogen and low-temperature oxygen are heated to the operating temperature and then enter the proton exchange membrane fuel cell 5 to react, where chemical energy is directly converted into electrical energy, which is then input into the lithium battery 6 for storage.

[0039] Example 2

[0040] The structure of this embodiment is as follows: Figure 5 As shown, it includes a liquid methane storage tank 10, a high-pressure methane buffer tank 11, a reciprocating piston internal combustion engine 12, a lithium battery 13, a permanent magnet synchronous motor 14, a first-stage Stirling refrigerator / engine 15, and power transmission lines, pipelines, cryogenic valves, and a circulation pump 16, etc. The solid arrows in the figure indicate the process by which the first-stage Stirling refrigerator 15 reduces heat leakage from the liquid methane in the liquid methane storage tank 10 in this embodiment, while the dashed arrows indicate the process by which the first-stage Stirling engine 15 recovers and utilizes the cold energy of the cryogenic methane before it enters the reciprocating piston internal combustion engine 12.

[0041] When the reciprocating piston internal combustion engine 12 is not in operation or under low load, the lithium battery 13 drives the permanent magnet synchronous motor 14, which operates in electric motor mode. The permanent magnet synchronous motor 14 drives the first-stage Stirling refrigerator / engine 15, which operates in refrigerator mode, performing its refrigeration conversion function. The Stirling refrigerator is based on the reverse Stirling cycle, a thermodynamic cycle consisting of "isothermal expansion – isochoric heat absorption – isothermal compression – isochoric heat release," pumping heat from the cold end to the hot end of the low-temperature methane. The cold-end heat exchanger of the first-stage Stirling refrigerator 15 is coupled to the low-temperature gas-cooled screen of the liquid methane storage tank 10. Through heat exchange, external heat leakage from the liquid methane storage tank 10 is removed, achieving cooling of the liquid methane and condensation and reliquefaction of the low-temperature methane. This allows for control of the liquid methane evaporation rate, ultimately enabling long-term storage of liquid methane.

[0042] Under high-load operation of the reciprocating piston internal combustion engine 12, the cryogenic methane output from the liquid methane storage tank 10 enters the high-pressure methane buffer tank 11. When the high-pressure methane buffer tank 11 is full of cryogenic methane, the output cryogenic methane passes through the first-stage Stirling refrigerator / engine 15. The first-stage Stirling refrigerator / engine 15 operates in engine mode, utilizing the thermodynamic conversion function of the Stirling engine. Based on the Stirling cycle's "isothermal compression—constant-volume heat absorption—isothermal expansion—constant-volume heat release," heat from the hot end of the Stirling engine is transferred to the cold end, preheating the cryogenic methane entering the reciprocating piston internal combustion engine 12 to its operating temperature. Through the crankshaft-connecting rod mechanism connected to the first-stage Stirling engine 15, the reciprocating motion of the piston in the first-stage Stirling engine 15 is converted into the rotational motion of the crankshaft. That is, the force acting on the piston is converted into the torque output by the crankshaft, driving the permanent magnet synchronous motor 14 to generate electrical energy. The permanent magnet synchronous motor 14 operates in generator mode at this time, and the generated electrical energy is stored in the lithium battery 13. Meanwhile, after the low-temperature methane is heated to the working temperature, it enters the reciprocating piston internal combustion engine 12 and mixes with air. It burns in the cylinder of the reciprocating piston internal combustion engine 12, and the heat energy released causes high-temperature and high-pressure gas to be generated in the cylinder. The gas expands and pushes the piston to do work. Then, through the crankshaft connecting rod mechanism of the reciprocating piston internal combustion engine 12, the mechanical work is output to drive the driven machinery to work.

Claims

1. A cold energy recovery system based on a cryogenic storage tank refrigeration system, comprising: An electric motor / generator, a refrigeration unit / engine, a cryogenic storage tank, a power unit, and power transmission lines, pipelines, cryogenic valves, and circulating pumps connecting the aforementioned electric motor / generator, refrigeration unit / engine, cryogenic storage tank, and power unit, characterized in that the electric motor / generator has a dual-function mode of electric motor and generator, and the refrigeration unit / engine has a dual-function mode of refrigeration conversion and thermodynamic conversion; When the power unit is not working or is operating under low load, the electric motor consumes electrical energy to drive the refrigeration unit to provide cooling capacity to the cryogenic storage tank and reduce or eliminate heat leakage of the stored cryogenic working fluid; the electric motor / generator operates in electric motor mode, and the refrigeration unit / engine operates in refrigeration unit mode. When the power unit is under high load, the cryogenic working fluid is output from the cryogenic storage tank, and the engine converts the cold energy of the cryogenic working fluid into mechanical energy to drive the generator to generate electrical energy; the motor / generator operates in generator mode, and the refrigeration unit / engine operates in engine mode.

2. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 1, characterized in that, The refrigeration unit / engine operates as a pulse tube refrigeration unit in refrigeration mode and as a thermoacoustic engine in cold energy recovery mode.

3. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 1, characterized in that, The refrigeration unit / engine is a Stirling refrigeration unit when operating in refrigeration mode and a Stirling engine when operating in cold energy recovery mode.

4. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 2 or 3, characterized in that, The refrigeration unit / engine is of one, two, three, or four stages.

5. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 1, characterized in that, The motor / generator is a linear compressor, a permanent magnet synchronous motor, a three-phase asynchronous motor, or a series-wound DC motor.

6. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 1, characterized in that, The cryogenic storage tanks are liquid hydrogen storage tanks, liquefied natural gas storage tanks, liquid methane storage tanks, liquid oxygen storage tanks, liquid nitrogen storage tanks, and liquid helium storage tanks.

7. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 1, characterized in that, The power unit is a fuel cell, a piston internal combustion engine, or a gas turbine.

8. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 7, characterized in that, The fuel cell is a proton exchange membrane fuel cell, a solid oxide fuel cell, an alkaline fuel cell, a phosphoric acid fuel cell, or a molten carbonate fuel cell.

9. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 7, characterized in that, The piston-type internal combustion engine is a reciprocating piston internal combustion engine or a rotary piston engine.

10. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 1, characterized in that, The transmission line is a system-compatible wire, the pipeline is a system-compatible seamless steel pipe, the cryogenic valve is a system-compatible cryogenic pressure reducing valve, cryogenic shut-off valve, or cryogenic three-way valve, and the circulating pump is a system-compatible circulating pump with cryogenic working fluid conveying function.

11. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to claim 1, characterized in that, The working fluid inside the refrigeration unit / engine is helium, nitrogen, or air.

12. The cold energy recovery system based on a cryogenic storage tank refrigeration system according to any one of claims 1-3, characterized in that, The external fluid at the cold end of the refrigeration unit / engine is a low-temperature working fluid, and the external fluid at the hot end of the refrigeration unit / engine is air, pure water, or ethylene glycol.

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