HIGHLY-INTEGRATED DOUBLE-LAYER VACUUM HEAT INSULATION COLD BOX
STRUCTURE FOR LIQUID HYDROGEN FLOW MEASUREMENT
TECHNICAL FIELDThe present disclosure belongs to the technical field of hy- drogen energy, and particularly relates to a highly-integrated double-layer vacuum heat insulation cold box structure for liquid hydrogen flow measurement.
BACKGROUND ARTHydrogen energy is one of the cleanest energy, with a variety of sources, a wide range of application and other advantages. It plays an important role in the current energy system, and is an important medium to achieve conversion of electric power, fuel oil and other energy. Meanwhile, the hydrogen energy can further be used as a bridge to carry renewable and unstable wind and solar energy, making a contribution to global energy efficiency.
In different application scenes, hydrogen mainly exists in two states of high-pressure gaseous hydrogen and low-temperature liquid hydrogen. Compared with the high-pressure gaseous hydrogen, the liquid hydrogen has more obvious advantages in storage and long-distance transportation, and its development prospect is promising. The liquid hydrogen is fluid fuel with low temperature, low viscosity and high efficiency, however, its boiling point is extremely low, and it is prone to gasification accordingly, which puts forward higher requirements for heat insulation, safety and operation convenience of a device during measurement and transfer of the liquid hydrogen.
A hydrogen energy measurement technology is involved in the processes of preparation, storage, transportation and use of the hydrogen energy. A liquid hydrogen flow standard device is a key part of the whole trade handover link. For the standard device, a stable heat insulation system is the basis for ensuring the accu- racy of liquid hydrogen flow measurement.
Heat insulation measures of key components such as pipelines, flow meters and liquid hydrogen pumps of devices in the prior art are scattered, and the risk of heat leakage is high, which hardly meets the actual requirements of liquid hydrogen flow measurement, especially hardly solves the problem of liquid hydrogen gasifica- tion probably existing in a plurality of device nodes. Specific to the problem of how to ensure the stability of heat insulation per- formance of the standard device, that is, how to reduce the influ- ence of liquid hydrogen gasification on the accuracy of flow in the test process or actual trade handover process, it is urgent to design a set of heat insulation system with stable heat insulation performance and a function of conveniently disassembling and re- placing components, so as to ensure the accuracy of liquid hydro- gen flow verification and calibration, while taking the operabil- ity into account.
SUMMARYThe present disclosure provides a highly-integrated double- layer vacuum heat insulation cold box structure to solve the prob- lem of heat leakage involved during flow verification and calibra- tion of liquid hydrogen.
In order to achieve the above objective and ensure heat insu- lation stability of a liquid hydrogen flow standard device and disassembly convenience of key components, the technical solution of the present disclosure is as follows:
In one aspect, the present disclosure provides a highly- integrated double-layer vacuum heat insulation cold box structure for liquid hydrogen flow measurement, including a cold box, a low- temperature liquid hydrogen pump, a refrigerator, matched regulat- ing valves, a detected flow meter and a pipeline system.
The cold box is of a double-layer vacuum structure combining an outer barrel and an inner barrel, and a bottom of the outer barrel is connected with a base to form an outer vacuum layer; the inner barrel is arranged inside the outer barrel, which is an in- ner vacuum layer; flange connectors of the low-temperature liquid hydrogen pump, the refrigerator and the matched valves are formed in a top of the outer barrel; an installation connector corresponding to the outer barrel is preformed in a top of the inner barrel; and the low-temperature liquid hydrogen pump, the detected flow meter, the pipeline system and the refrigerator are integrated in- to the cold box.
In one embodiment, the pipeline system is arranged in the in- ner barrel in forms of coil pipes and vertical pipes, and the dou- ble-layer vacuum structure of the cold box is used for heat insu- lation treatment, so as to be used for circulating inflow and out- flow of gas and liquid.
Furthermore, part of the coil pipes in the pipeline system make contact with a wall surface of the inner barrel.
In one embodiment, the matched valves are directly inserted into vacuum heat insulation sleeves through the flange connectors for connection, and the matched valves are used for regulating flow in the pipeline system.
Furthermore, the matched regulating valves are used for regu- lating start and stop of liquid inflow, liquid reflux, gas inflow and gas exhaust and flow, so as to achieve verification of differ- ent flow points.
Furthermore, a gas source flange connector is further pre- formed in a top cover plate of the cold box, so as to achieve ex- haust of purge gas.
In one embodiment, a visual window is formed in a front face of the outer barrel, and a corresponding rectangular window is formed in the inner barrel.
In one embodiment, the refrigerator further supercools liquid hydrogen flowing through liquid phase pipelines in the pipeline system, the liquid hydrogen enters the detected flow meter after flowing through the low-temperature liquid hydrogen pump, and the detected flow meter is calibrated based on a mass method.
Furthermore, liquid inflow pipelines and liquid reflux pipe- lines independent of each other are arranged in the liquid phase pipelines, a self-circulating state of the liquid hydrogen is achieved at a verification stage, and therefore stability of the liquid hydrogen flowing through the detected flow meter is en- sured; and meanwhile, part of the liquid hydrogen returns into storage tanks through the liquid reflux pipelines during verifica- tion, thereby achieving precise regulation and control of flow.
In the other aspect, the present disclosure provides an ap-
plication of the double-layer vacuum heat insulation cold box structure in liquid hydrogen flow measurement.
The present disclosure has the following beneficial effects:
According to the double-layer vacuum heat insulation cold box structure provided in the present disclosure, inner and outer dou- ble-layer vacuum heat insulation treatment is performed on the cold box, such that external heat is insulated to the maximum de- gree, so as to reduce liquid hydrogen gasification during testing and ensure verification and calibration accuracy.
According to the double-layer vacuum heat insulation cold box structure provided in the present disclosure, the low-temperature liquid hydrogen pump, the refrigerator and the detected flow meter are arranged in the vacuum heat insulation layers in the cold box, and can directly work in the cold box during verification, thereby preventing heat exchange with an external environment during work; and pipelines in the cold box are designed into a structure com- bining the coil pipes and the straight pipes from common straight pipes, thereby saving more space and meanwhile insulating heat ex- change between the pipelines and the external environment to the maximum degree, so as to relieve liquid hydrogen gasification.
According to the double-layer vacuum heat insulation cold box structure provided in the present disclosure, a liquid inlet and a liquid reflux outlet are independently formed, the self- circulating state of the liquid hydrogen is achieved at the veri- fication stage, and therefore stability of the liquid hydrogen flowing through the detected flow meter is ensured; and meanwhile, part of the liquid hydrogen returns into the storage tanks through the liquid reflux outlet during verification, thereby achieving precise regulation and control of flow.
The double-layer vacuum heat insulation cold box structure provided in the present disclosure is simple and convenient to disassemble, the visual window of the cold box has the functions of observing and disassembling the detected flow meter at the same time, meanwhile, the problems with replacement of the flow meter in a sealed space, observation of operating states of devices, overhauls of the devices and the like are solved, and operating difficulty of detection staff is lowered on the basis of prevent-
ing liquid hydrogen gasification.
BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic diagram of an overall structure of an embodiment of the present disclosure; FIG. 2 is an overall princi- 5 ple schematic diagram of the present disclosure; FIG. 3 is a sche- matic diagram of a double-layer heat insulation cold box structure according to the present disclosure; FIG. 4 is a schematic diagram of a top structure of a double-layer heat insulation cold box ac- cording to the present disclosure; FIG. 5 is a schematic diagram of an overall section structure of a double-layer heat insulation cold box according to the present disclosure; and FIG. 6 is a schematic diagram of an internal structure of a double-layer heat insulation cold box according to the present disclosure.
DETAILED DESCRIPTION OF THE EMBODIMENTSIn order to make the objectives, technical solutions and ad- vantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure; and ap- parently, the described embodiments are merely part, rather than all of the embodiments of the present disclosure. All other embod- iments obtained by those ordinarily skilled in the art without in- volving inventive effort based on the embodiments in the present disclosure fall within the scope of protection of the present dis- closure.
An embodiment of the present disclosure provides a highly- integrated double-layer vacuum heat insulation cold box structure for liquid hydrogen flow measurement, including a cold box, a low- temperature liquid hydrogen pump, a refrigerator, matched regulat- ing valves, a detected flow meter and a pipeline system.
The cold box is of a double-layer vacuum structure combining an outer barrel and an inner barrel, and a bottom of the outer barrel is connected with a base to form an outer vacuum layer; and the inner barrel is arranged inside the outer barrel, which is an inner vacuum layer. First flange installation connectors of the low-temperature liquid hydrogen pump, the refrigerator and the matched valves are formed in a top of the outer barrel, a second installation connector corresponding to the outer barrel is pre- formed in a top of the inner barrel, the low-temperature liquid hydrogen pump, the detected flow meter, the pipeline system, the refrigerator and other key equipment are integrated into the cold box, part of coil pipes make contact with a wall surface of the inner barrel, a degree of supercooling of the cold box can further be improved at a purge precooling stage of a device, and radiant heat leakage of a system is solved to the maximum degree in coop- eration with the outer vacuum layer. An installation manner of in- ternal equipment is more reasonable since the inner vacuum layer is of a cylindrical structure, such that the problem of convective heat leakage generated during flow of liquid hydrogen is greatly relieved; and the refrigerator further supercools the liquid hy- drogen flowing through liquid phase pipelines, so as to compensate for heat exchange generated by equipment in an external environ- ment and the inner barrel at the same time, thereby ensuring heat insulation performance of the system to the maximum degree. Spe- cifically,
As shown in FIG. 1, FIG. 3, FIG. 4, FIG. 5 and FIG. 6, the double-layer heat insulation cold box 2 is of a double-layer structure combining the outer barrel 207-1 and the inner barrel 207-2, the bottom of the outer barrel is connected with a base 208 to form an outer shell, and the inner barrel is arranged inside the outer barrel, which is an inner shell. The low-temperature liquid hydrogen pump 221 and the refrigerator 218 are in flange connection with a top cover plate of the cold box through the first flange connectors preformed in the top of the outer barrel, thereby achieving a fixing effect to the maximum degree and en- hancing sealing performance at joints. The matched valves are di- rectly inserted into vacuum sleeves through the flange connectors preformed in the top cover plate of the cold box for connection to be used for regulating flow in pipelines. Due to the adoption of vacuum sleeve structures, internal and external heat exchange can further be reduced, and the valves can be convenient to disassem- ble and replace through flange structures.
A gas source flange connector is preformed in the top cover plate of the cold box, a vacuum heat insulation sleeve is fixed to the connector in a flange connection manner, the vacuum sleeves of the liquid phase pipelines and gas phase pipelines outside the cold box are connected with preset flange discs on the cover plate of the cold box through flanges, and such structure has good de- tachability and heat insulation functions. Specifically, a liquid hydrogen liquid inlet 201, a liquid hydrogen liquid outlet 202 and a liquid hydrogen reflux outlet 204 are formed in the top cover plate of the cold box, and both a gas port 203 of the double-layer heat insulation cold box and a purge gas source connector 205 are fixedly connected in a flange connection manner. Vacuum plug-in and plug-out connectors are preformed at the liquid hydrogen lig- uid inlet 201 and the liquid hydrogen reflux outlet 204 of the double-layer heat insulation cold box, such that the problem of frosting at the connectors during connection with a liquid hydro- gen storage tank 1 is avoided.
The inner barrel layer is separated from the outer barrel layer by certain spacing, the two shells are connected by screws in a way that they are fixed and hang one above the other, a sec- ond installation connector corresponding to the outer barrel is preformed in a top of the inner barrel layer, each part is direct- ly inserted into the inner barrel layer, and due to such manner, heat exchange generated by contact between the two shells or con- tact between the shells and the pipelines is avoided, maximizing the heat insulation function of the cold box.
A visual window 206 is formed in a front face of the outer shell, the round transparent window is connected with a preset flange of the outer shell through a flange structure, a corre- sponding rectangular window is formed in the inner barrel layer, and by means of the visual window, an operator can conveniently observe the equipment inside the cold box, thereby solving the problem that the detected flow meter is difficult to replace in a sealed space. The low-temperature liquid hydrogen pump and a main body of the refrigerator are arranged in the inner barrel layer of the cold box, the double-layer vacuum structure of the cold box is used for heat insulation treatment, and the liquid phase pipelines penetrate through a cold head of the refrigerator to further achieve superccoling treatment of the liquid hydrogen, thereby en-
suring a liquid phase state of fluid in the pipelines; the detect- ed flow meter 219 is arranged in the inner barrel layer and fixed- ly connected with upstream and downstream pipelines through flang- es, and by means of such connection manner, the flow meter can be more convenient to disassemble and replace on the basis of achiev- ing the fixing effect; and the pipeline system is arranged in the inner barrel layer in forms of coil pipes 220 and vertical pipes, the double-layer vacuum structure of the cold box is used for heat insulation treatment, so as to be used for circulating inflow and outflow of gas and liquid, and by means of such structure, the volume occupied by the pipeline system is further reduced, and heat insulation treatment and disassembly and skid mounting are better facilitated. Specifically,
A liquid outflow pipeline regulating valve 209 of the low- temperature liquid hydrogen pump is connected with the correspond- ing flange connector preformed in the top of the outer barrel 207- 1, which is used for regulating flow of the liquid hydrogen flow- ing into the detected flow meter 219 from a liquid outflow pipe- line of the low-temperature liquid hydrogen pump. A first liquid inflow pipeline regulating valve 210 is connected with the corre- sponding flange connector preformed in the top of the outer barrel 207-1, which is used for regulating flow of gas in the pipeline system in the cold box at a purge precooling stage. A first liquid outflow pipeline regulating valve 216 is connected with the corre- sponding flange connector preformed in the top of the outer barrel 207-1, which is used for regulating flow of the liquid hydrogen flowing into a liquid hydrogen storage tank 3 and flow of the liq- uid hydrogen flowing out of the liquid hydrogen storage tank 3 during liquid reflux. A second liquid outflow pipeline regulating valve 217 is connected with the corresponding flange connector preformed in the top of the outer barrel 207-1, which is used for regulating flow of the liquid hydrogen flowing out of the detected flow meter 219. A first gas pipeline regulating valve 213 and a second gas pipeline regulating valve 214 are connected with the corresponding flange connectors preformed in the top of the outer barrel 207-1, which are used for regulating exhaust gas flow dur- ing purge precooling. A first liquid reflux pipeline regulating valve 215 is connected with the corresponding flange connector preformed in the top of the outer barrel 207-1, which is used for regulating liquid reflux flow and start and stop of the self- circulating state of the device. A first liquid reflux outlet pipeline regulating valve 211 and a second liquid reflux outlet pipeline regulating valve 212 are connected with the corresponding flange connectors preformed in the top of the outer barrel 207-1, which are used for regulating flow of the liquid hydrogen flowing into the liquid hydrogen storage tank 1 from the liquid reflux pipeline. Safety valves 222-1, 222-2 and 222-3 are connected with the coil pipes 220 in a directly-inserted manner, so as to prevent pressure in the coil pipes from going beyond limits, ensuring safety of the heat insulation system in accidents such as failure.
Preferably, an outer vacuum heat insulation layer is formed between the inner shell and the outer shell of the cold box, which is used for heat insulation and cooling on the detected flow me- ter, the low-temperature liquid hydrogen pump, the refrigerator, the coils and the like in the cold box, so as to reduce heat ex- change with the external environment.
Preferably, the inner barrel is the inner vacuum heat insula- tion layer, which is used for reducing heat leakage of the system, so as to prevent liquid hydrogen gasification.
Preferably, the liquid phase port of the double-layer heat insulation cold box is used for outflow of the liquid hydrogen during verification and inflow of the liquid hydrogen during liq- uid reflux.
Preferably, the gas source flange connector has an exhaust function, achieving exhaust of purge gas through the gas port.
Preferably, the matched regulating valves can regulate and control start and stop of liquid inflow, liquid reflux, gas inflow and gas exhaust and flow, so as to achieve verification of differ- ent flow points.
As shown in FIG. 2, a working process of the device is as follows: the liquid hydrogen flow standard device needs to perform purge precooling work before verification.
The device is vacuumized by a vacuum pump 7, and the device is kept in a negative pressure state, thereby greatly reducing content of oxygen in the device and shortening purge time of heli- um.
When the purge precooling work is started, purge gas is pro- vided by a high-pressure helium source 4-1 and a high-pressure ni- trogen source 4-2 in a gas source 4 to purge the device section by section, ensuring that oxygen residues in dead corners of the sys- tem pipelines are completely purged away.
Firstly, the high-pressure nitrogen source 4-2 purges the liquid hydrogen storage tank 1 and part of the liquid phase pipe- lines through a gas phase port 104 of the liquid hydrogen storage tank, stable high-pressure nitrogen is introduced into the device, and the nitrogen is fully mixed with gas in the device; and the liquid outflow pipeline regulating valve 209 of the low- temperature liquid hydrogen pump, the first liquid inflow pipeline regulating valve 210, the second liquid reflux pipeline regulating valve 212, the second liquid outflow pipeline regulating valve 217, the first liquid reflux pipeline regulating valve 215 and the first gas pipeline regulating valve 213 are opened, the other valves are closed, the low-temperature liquid hydrogen pump 221 is switched off, and the high-pressure nitrogen purges part of the pipelines of the liquid hydrogen storage tank 1, and is exhausted through a dilution tank € and a special exhaust pipeline 8 via a purge gas source connector 205 of the double-layer heat insulation cold box and a gas source pipeline 401 which are connected through a flange.
Then, the high-pressure nitrogen source 4-2 purges the liquid reflux pipeline of the liquid hydrogen storage tank 1, the first liquid reflux pipeline regulating valve 211 and the first gas pipeline regulating valve 213 are opened, the other valves are closed, and high-pressure nitrogen purges the liquid reflux pipe- line of the liquid hydrogen storage tank 1, and is exhausted out of the dilution tank 6 and the special exhaust pipeline 8 via the purge gas source connector 205 of the double-layer heat insulation cold box and the gas source pipeline 401 which are connected through the flange.
Finally, the high-pressure nitrogen source 4-2 purges the liquid hydrogen storage tank 3, the first liquid inflow pipeline regulating valve 210, the second liquid outflow pipeline regulat- ing valve 217, the first liquid outflow pipeline regulating valve 216 and the second gas pipeline regulating valve 214 are opened, the other valves are closed, and high-pressure nitrogen purges a storage tank 2 through a liquid phase port 301 of the liquid hy- drogen storage tank, enters the coil pipes 220 through a gas phase port 302 of the liquid hydrogen storage tank, and is exhausted out of the dilution tank 6 and the special exhaust pipeline 8 via the purge gas source connector 205 of the double-layer heat insulation cold box and the gas source pipeline 401 which are connected through the flange. [0040] In order to further ensure that there is no impurity gas inside the device as a whole, the inert gas high-pressure helium source 4-1 is adopted for secondarily purging the device again according to the above nitrogen purge process.
After helium purge, the vacuum pump 7 is used for vacuumizing the device again.
Before detection of liquid hydrogen flow, the device is pre- cooled firstly to reach a liquid hydrogen temperature, so as to prevent gas-liquid two-phase flow generated during detection.
Since the device is precooled in a gradient manner, the situ- ation that the storage tanks and the pipelines react sharply due to too large temperature difference, such that the service life thereof is shortened can be effectively avoided.
Firstly, liquid hydrogen gasification precooling is per- formed, a small amount of liquid hydrogen is introduced into the liquid hydrogen storage tank 1 and the liquid hydrogen storage tank 3, the liquid hydrogen is rapidly gasified due to too large temperature difference between the liquid hydrogen and interiors of the storage tanks to obtain cold hydrogen, the cold hydrogen further purges the pipeline system to preliminarily precool the device, and the step of precooling purge of the cold hydrogen is kept consistent with the purge process of the high-pressure nitro- gen source 4-2. In view of safety, the exhausted cold hydrogen is heated by a heating pipe 5 firstly, then mixed with the nitrogen in the dilution tank 6, so as to reduce a concentration of the hy- drogen, and is exhausted through the special exhaust pipeline 8.
[0043] Then, the low-temperature liquid hydrogen pump 221 is used for driving the liquid hydrogen to operate in the device for sec- ondary precooling, and the refrigerator 218 further supercools the liquid hydrogen, so as to ensure a stable liquid phase of the lig- uid hydrogen. The specific process is as follows:
Firstly, the liquid outflow pipeline regulating valve 209 of the low-temperature liquid hydrogen pump, the first liquid inflow pipeline regulating valve 210, the second liquid reflux pipeline regulating valve 212 and the first liquid reflux pipeline regulat- ing valve 211 are opened, the other valves are closed, and regu- lating liquid phase pipelines are precooled. [0044] Secondly, the liquid outflow pipeline regulating valve 209 of the low- temperature liquid hydrogen pump, the first liquid inflow pipeline regulating valve 210, the second liquid outflow pipeline regulat- ing valve 217, the first liquid reflux pipeline regulating valve 215 and the first liquid reflux pipeline regulating valve 211 are opened, the other valves are closed, and the self-circulating liq- uid phase pipelines are precooled.
Thirdly, the liquid outflow pipeline regulating valve 209 of the low-temperature liquid hydrogen pump, the first liquid inflow pipeline regulating valve 210, the second liquid reflux pipeline regulating valve 217, the first liquid reflux pipeline regulating valve 215 and the first liquid outflow pipeline regulating valve 216 are opened, and a main test path is precooled. [0046] After all the pipelines are precooled, states of the valves are switched, the liquid outflow pipeline regulating valve 209 of the low-temperature liquid hydrogen pump, the first liquid inflow pipeline regulating valve 210, the second liquid reflux pipeline regulating valve 217, the first liquid reflux pipeline regulating valve 215, and the first liguid reflux pipeline regulating valve 211 are opened, and the other valves are closed, such that the liquid hydrogen is kept in a self-circulating flow state, overall coldness of the device is ensured to prepare for verification, that is, the liquid hydrogen flows out of the liquid hydrogen storage tank 1 and returns into the liquid hydrogen storage tank 1 after passing through bypass liquid phase pipelines.
After purge precooling, the liquid hydrogen flow standard de- vice gets into a flow meter verification stage, the first liquid inflow pipeline regulating valve 210, the second liquid reflux pipeline regulating valve 212, the first reflux pipeline regulat- ing valve 211 and the first liquid reflux pipeline regulating valve 215 are closed, and the liquid outflow pipeline regulating valve 209 of the low-temperature liquid hydrogen pump, the second liquid outflow pipeline regulating valve 217 and the first liquid outflow pipeline regulating valve 216 are opened. The liquid hy- drogen flows out of the liquid hydrogen storage tank 1, passes through the detected flow meter 219 inside the cold box through a liquid outlet 101 and the liquid inlet 201 of the double-layer heat insulation cold box matched with the low-temperature liquid hydrogen pump 221, and flows into the liquid hydrogen storage tank 3 in which part of the liquid hydrogen is already present through the liquid phase port 202 of the double-layer heat insulation cold box and the liquid phase port 301 of the liquid hydrogen storage tank, wherein high-precision weighing units 103 and 303 are put below the liquid hydrogen storage tank 1 and the liquid hydrogen storage tank 3 respectively, which are used for weighing and meas- uring mass of the liquid hydrogen in the storage tanks before and after verification.
After verification, the first liquid reflux pipeline regulat- ing valve 215 and the first liquid reflux pipeline regulating valve 211 are opened, the liquid hydrogen in the liquid hydrogen storage tank 3 passes through the liquid reflux pipelines inside the cold box through the liquid phase port 301 and the liquid phase port 202 of the double-layer heat insulation cold box, and flows into the liquid hydrogen storage tank 1 again through the liquid reflux outlet 204 of the double-layer heat insulation cold box and a liquid reflux inlet 102 of the liquid hydrogen storage tank.
In the whole verification process, it is ensured that the liquid hydrogen entering the detected flow meter 219 is a pure liquid phase through the double-layer heat insulation cold box 2 under the action of the outer and inner vacuum heat insulation layers, and it is ensured that the liquid hydrogen flowing in the liquid phase pipelines inside the cold box is also a pure liquid phase, thereby ensuring that there is no liquid hydrogen gasifica-
tion in the system due to heat exchange with the external environ- ment.
In conclusion, by the adoption of the present disclosure, liquid hydrogen gasification caused by heat leakage during opera- tion of the device can be effectively reduced, heat insulation performance of key components such as the pipelines, the detected flow meter and the low-temperature liquid hydrogen pump is better, the regulating valves, the low-temperature liquid hydrogen pump and the refrigerator are connected with the double-layer heat in- sulation cold box through the flange connectors, so as to be more convenient to disassemble and maintain, the heat insulation effect is better due to the double-vacuum-layer structure of the cold box, and liquid hydrogen gasification can be avoided to the maxi- mum degree.
The specific implementations of the present disclosure are described with the reference to the drawings above, however, these descriptions cannot be understood as limitations to the scope of the present disclosure. The scope of protection of the present disclosure is limited by the appended claims, and any modification made on the basis of the claims of the present disclosure falls within the scope of protection of the present disclosure.