A helium liquefaction system using a back heat type refrigerator cold end direct current as a liquefied working medium

Abstract

The application discloses a helium liquefaction system using a cold end direct current of a regenerative refrigerator as a liquefied working medium, comprising a regenerative refrigerator module, a liquefaction cavity, a liquefied helium module and a refrigerator air supplement module; a regenerator cold end heat exchanger in the regenerative refrigerator module is arranged in the liquefaction cavity, and the lower end of the regenerator cold end heat exchanger is provided with an opening which is connected with a cold end direct current pipeline provided with a cold end direct current control valve; the cold end direct current pipeline leads out the low-temperature high-pressure working medium of the regenerator cold end heat exchanger and discharges it near the regenerator cold end heat exchanger; the liquefied helium module is communicated with the liquefaction cavity through a liquefied gas pipeline; and the refrigerator air supplement module is connected with the low-pressure cavity side of a compression device of the regenerative refrigerator module through an air supplement pipeline. The application makes full use of the inter-stage surplus cold quantity of the regenerative low-temperature refrigerator and also utilizes the advantage of high deep low-temperature phase change refrigeration efficiency of the J-T refrigerator, and has high heat exchange efficiency and comprehensive liquefaction efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of low-temperature refrigeration, and particularly relates to a helium liquefaction system using a regenerative refrigerator cold end direct current as a liquefied working medium. BACKGROUND

[0002] The regenerative refrigerator such as a GM refrigerator and a pulse tube refrigerator is widely applied to current domestic and foreign small-sized hydrogen and helium liquefaction and recondensation systems due to its simple structure, reliable operation, low vibration, excellent refrigeration performance in the liquid helium temperature zone and the like.

[0003] A regenerative refrigerator high-efficiency liquefaction system using a direct current is disclosed in Chinese patent document CN213040803U, which comprises a regenerative refrigeration module and a liquefaction module. The regenerative refrigeration module comprises a regenerative refrigerator unit and a direct current external circulation unit; the regenerative refrigerator unit comprises, in sequence, a compression device, a regenerator hot end heat exchanger, a regenerator, a regenerator cold end heat exchanger, an expansion mechanism cold end heat exchanger, an expansion mechanism, and an expansion mechanism hot end heat exchanger.

[0004] With the progress of industrialization, the refrigeration performance of the regenerative refrigerator has been greatly improved in the past few decades, promoting the development of helium liquefaction. At the same time, by utilizing the excess cold quantity of the regenerator wall surface of the refrigerator, the helium gas can be gradually pre-cooled before reaching the condenser, thereby reducing the consumption of the helium gas sensible heat on the cold end refrigeration quantity. However, the sensible heat contained in the cooling from the ambient temperature to the helium liquefaction temperature still requires a large amount of refrigeration quantity, which means that a single refrigerator needs to provide a large amount of excess cold quantity from the regenerator and the first cold end temperature range to absorb the sensible heat, otherwise the high-grade cold quantity near the cold end will be consumed to absorb the sensible heat, resulting in a reduction of the liquefaction rate, which puts higher performance requirements on the current low-temperature refrigerator.

[0005] Due to the above reasons, the helium liquefaction rate of a single refrigerator still has a large room for improvement. Taking a pulse tube refrigerator with a refrigeration capacity of 1W@4.2K as an example, the theoretical liquefaction rate is 33L / day, while the actual BOG recondensation is only 18L / day, and the room temperature liquefaction is even less, only 10-12L / day, which is only 30%-60% of the ideal liquefaction amount, and the energy consumption is as high as 11-19kW·h / L.

[0006] The low single-machine liquefaction amount leads to the need for multiple refrigerators to jointly operate to meet the required hydrogen and helium liquefaction amount in many occasions, which increases the liquefaction cost and energy consumption and increases the system complexity.

[0007] Therefore, fully utilizing the existing cold capacity of the refrigerator to further improve the liquefaction capacity of single helium is the main direction of the development of current small helium liquefier. For this purpose, on the one hand, the sensible heat of the gas to be liquefied is absorbed by the surplus cold capacity of the regenerator, and on the other hand, the membrane condensation heat exchange process of helium liquefaction at the condenser is strengthened.

[0008] The current helium liquefaction system adopts non-contact heat exchange, that is, pre-cooling on the outer side of the regenerator pipe wall through the coil heat exchanger, natural convection heat exchange or annular fin heat exchanger. Therefore, the low liquefaction rate is mainly due to the large heat transfer loss of the indirect pre-cooling mode. SUMMARY

[0009] In order to overcome the technical defects existing in the pre-cooling process of the traditional small helium liquefier, the present application provides a helium liquefaction system using the cold end direct current of the regenerative refrigerator as the liquefied working medium. The system fully utilizes the inter-stage surplus cold capacity of the regenerative refrigerator and also utilizes the high phase change refrigeration efficiency of the J-T refrigerator at deep low temperature, so that the system has high heat exchange efficiency and comprehensive liquefaction efficiency.

[0010] A helium liquefaction system using the cold end direct current of the regenerative refrigerator as the liquefied working medium, comprising a regenerative refrigerator module, a liquefaction cavity, a liquefied helium gas module and a refrigerator gas supplementing module.

[0011] The regenerator cold end heat exchanger in the regenerative refrigerator module is arranged in the liquefaction cavity, and the lower end of the regenerator cold end heat exchanger is provided with an opening connected with a cold end direct current pipeline provided with a cold end direct current control valve. The cold end direct current pipeline leads out the low-temperature high-pressure working medium of the regenerator cold end heat exchanger and discharges it near the regenerator cold end heat exchanger. The bottom of the liquefaction cavity is provided with a liquid helium outlet.

[0012] The liquefied helium gas module comprises a liquefied gas cylinder, a liquefied gas control valve and a liquefied gas mass flowmeter connected in sequence. The liquefied gas mass flowmeter is communicated with the liquefaction cavity through a liquefied gas pipeline.

[0013] The refrigerator gas supplementing module comprises a gas supplementing cylinder, a gas supplementing control valve and a gas supplementing mass flowmeter connected in sequence. The gas supplementing mass flowmeter is connected with the low-pressure cavity side of the compression device of the regenerative refrigerator module through a gas supplementing pipeline.

[0014] The high-pressure normal-temperature helium working medium in the liquefied gas cylinder enters the liquefaction cavity first, is pre-cooled with the regenerative refrigerator, is mixed with the low-temperature low-pressure helium gas discharged by the cold-end direct-current pipeline under the condition of being lower than the critical pressure of helium, is further cooled, enters the vicinity of the cold-end heat exchanger of the regenerator of the regenerative refrigerator module, is further cooled, and is liquefied; the high-temperature high-pressure helium in the gas supplement cylinder enters the low-pressure cavity side of the compression device to supplement the helium working medium of the regenerative refrigerator; the high-pressure low-temperature helium is throttled to the cold-end direct-current control valve under the condition of being lower than the critical pressure of helium, is partially liquefied, is mixed with the low-pressure low-temperature helium of the liquefied helium module after being throttled into the gas phase, is liquefied, and is mixed with the throttled liquid phase; finally, the liquid helium is led out by the liquid helium outlet, and the helium liquefaction is completed.

[0015] Further, the regenerative refrigerator module comprises, in sequence, a compression device, a compressor transmission pipe, a regenerator hot-end heat exchanger, a regenerator, a regenerator cold-end heat exchanger, a regenerator and expansion mechanism transmission pipe, an expansion mechanism cold-end heat exchanger, an expansion mechanism, and an expansion mechanism hot-end heat exchanger.

[0016] Among them, the regenerator, the regenerator cold-end heat exchanger, the regenerator and expansion mechanism transmission pipe, the expansion mechanism cold-end heat exchanger, and the expansion mechanism are arranged inside the liquefaction cavity, and the rest are arranged outside the liquefaction cavity.

[0017] Further, the cold-end direct-current pipeline leads out the low-temperature high-pressure working medium of the regenerator cold-end heat exchanger, and leads to the vicinity of the regenerator cold-end heat exchanger, the regenerator and expansion mechanism transmission pipe, and the expansion mechanism cold-end heat exchanger.

[0018] Further, the cold-end direct-current pipeline is installed at the lower end opening of the regenerator cold-end heat exchanger by welding.

[0019] Alternatively, the structure of the regenerative refrigerator module is coaxial type, U type or straight line type.

[0020] Alternatively, the regenerative refrigerator module is a GM refrigerator, a GM type pulse tube refrigerator, a Stirling refrigerator, a Stirling type pulse tube refrigerator or a VM refrigerator.

[0021] Alternatively, the regenerative refrigerator module is a single-stage, two-stage or multi-stage coupled structure; wherein the two-stage or multi-stage coupled structure is a thermal coupling structure or a gas coupling structure.

[0022] Preferably, the regenerative refrigerator module adopts a 4K refrigerator matched with the liquid helium temperature zone.

[0023] Alternatively, in the regenerative refrigerator module, the compression device is a linear compressor or a GM compressor with a valve, and the corresponding low-pressure cavity sides of the two are a linear compressor back pressure cavity and a GM compressor low-pressure tank, respectively.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention has a simple and reliable structure. The process of drawing DC from the cold end of the regenerative refrigerator and replenishing gas from the back pressure chamber of the compressor does not require special structural requirements for other components of the refrigerator. Using the helium working fluid inside the refrigerator as part of the source of liquefied helium can further cool the helium to be liquefied outside the refrigerator, thus optimizing the problem of low pre-cooling heat exchange efficiency and improving the liquefaction performance of the system. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a helium liquefaction system that uses a regenerative refrigeration unit with a cold end DC current as the liquefied chemical medium, according to the present invention.

[0027] In the diagram: 1-Compression device; 2-Compressor transmission pipe; 3-Hot end heat exchanger of the regenerator; 4-Regenerator; 5-Cold end heat exchanger of the regenerator; 6-Transmission pipe between the regenerator and the expansion mechanism; 7-Cold end heat exchanger of the expansion mechanism; 8-Expansion mechanism; 9-Hot end heat exchanger of the expansion mechanism; 10-Cold end DC control valve; 11-Cold end DC pipeline; 12-Liquid helium outlet; 13-Liquefied chamber; 14-Liquefied gas pipeline; 15-Liquefied gas mass flow meter; 16-Liquefied gas control valve; 17-Liquefied gas cylinder; 18-Make-up gas pipeline; 19-Make-up gas mass flow meter; 20-Make-up gas control valve; 21-Make-up gas cylinder. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0029] like Figure 1 As shown, a helium liquefaction system using a regenerative refrigeration unit's cold-end DC as the liquefied chemical medium includes a regenerative refrigeration unit module, a cold-end DC module, a liquefaction chamber module, a liquefied helium module, and a refrigeration unit gas replenishment module; each module is interconnected to form a helium liquefaction system.

[0030] The regenerative refrigeration module includes a compressor unit 1, a compressor transmission pipe 2, a regenerator hot end heat exchanger 3, a regenerator 4, a regenerator cold end heat exchanger 5, a regenerator and expansion mechanism transmission pipe 6, an expansion mechanism cold end heat exchanger 7, an expansion mechanism 8, and an expansion mechanism hot end heat exchanger 9, connected in sequence.

[0031] The cold end direct current module comprises a cold end direct current control valve 10 and a cold end direct current pipeline 11; the liquefaction cavity module comprises a liquefaction cavity 13 and a liquid helium outlet 12; the liquefied helium gas module comprises a liquefied gas pipeline 14, a liquefied gas mass flow meter 15, a liquefied gas control valve 16 and a liquefied gas cylinder 17 connected in sequence; the refrigeration machine air supplementing module comprises an air supplementing pipeline 18, an air supplementing mass flow meter 19, an air supplementing control valve 20 and an air supplementing cylinder 21 connected in sequence.

[0032] The compression device 1 is connected with a regenerator hot end heat exchanger 3, a regenerator 4 and a regenerator cold end heat exchanger 5 in sequence through a compressor transmission pipeline 2; the regenerator cold end heat exchanger 5 is connected with an expansion mechanism cold end heat exchanger 7, an expansion mechanism 8 and an expansion mechanism hot end heat exchanger 9 in sequence through a regenerator and expansion mechanism transmission pipeline 6. The regenerator cold end heat exchanger 5 is provided with an opening at the lower end, and the opening is connected with the cold end direct current control valve 10 and the cold end direct current pipeline 11; the cold end direct current pipeline 11 is arranged close to the regenerator cold end heat exchanger 5, the regenerator and expansion mechanism transmission pipeline 6 and the expansion mechanism cold end heat exchanger 7.

[0033] The liquefaction cavity 13 comprises the regenerator 4, the regenerator cold end heat exchanger 5, the regenerator and expansion mechanism transmission pipeline 6, the expansion mechanism cold end heat exchanger 7, the expansion mechanism 8, the cold end direct current control valve 10 and the cold end direct current pipeline 11 inside, and is provided with the liquid helium outlet 12 at the bottom. The liquefaction cavity 13 is connected with the liquefied gas mass flow meter 15, the liquefied gas control valve 16 and the liquefied gas cylinder 17 in sequence through the liquefied gas pipeline 14 above; the air supplementing pipeline 18, the air supplementing mass flow meter 19, the air supplementing control valve 20 and the air supplementing cylinder 21 are connected in sequence, and the air supplementing pipeline 18 is connected with the low pressure side opening of the compression device 1.

[0034] When the system is running, the helium working substance is alternately flowed in the regenerative refrigerator module, and the regenerative refrigeration cycle is carried out. After the cycle is stable, the cold end direct current module leads out the low temperature and high pressure helium in the regenerator cold end heat exchanger 5, the high pressure and low temperature helium is further cooled through the cold end direct current control valve 10, and then is led to the vicinity of the regenerator cold end heat exchanger 5, the regenerator and expansion mechanism transmission pipeline 6 and the expansion mechanism cold end heat exchanger 7 of the regenerative refrigerator module. At the same time, the high pressure and normal temperature helium working substance in the liquefied gas cylinder 17 is led into the liquefaction cavity 13 through the liquefied gas control valve 16, is pre-cooled with the regenerative refrigerator, is mixed with the low temperature and low pressure helium of the cold end direct current module, and is further cooled. The mixed helium is led to the vicinity of the regenerator cold end heat exchanger 5, the regenerator and expansion mechanism transmission pipeline 6 and the expansion mechanism cold end heat exchanger 7, is further cooled and liquefied, and finally the liquid helium is led out through the liquid helium outlet 12, and the helium liquefaction is completed. At this time, the air supplementing control valve 20 is opened, the high temperature and high pressure helium of the air supplementing cylinder 21 is led into the low pressure cavity side of the compression device 1 of the regenerative refrigerator module, and the helium working substance is supplemented for the regenerative refrigerator.

[0035] The existing pre-cooling mode of the gas to be liquefied through a coil heat exchanger, natural convection heat exchange or an annular fin heat exchanger outside the tube wall of a regenerator belongs to non-contact heat exchange, and has a relatively large heat exchange thermal resistance, certain heat transfer loss, and thus low liquefaction rate. In particular, for a traditional liquefaction system using a GM refrigerator, there is air gap heat exchange between the regenerator and the cylinder wall, further affecting the heat exchange rate. On the other hand, existing experiments and numerical studies show that the COP of the regenerative refrigerator module can be improved by introducing direct flow. Therefore, the system of the present application introduces low-temperature high-pressure helium working medium from the regenerative refrigerator module through a direct-flow pipeline and a control valve, generates a small direct flow at the cold end of the regenerator as a liquefied working medium, overcomes the technical defects existing in the pre-cooling process of the traditional small helium liquefier, and makes full use of the inter-stage surplus cold quantity of the regenerative refrigerator and the high-efficiency phase-change refrigeration of the J-T refrigerator.

[0036] Under the liquefaction condition, the direct flow introduced from the cold end of the refrigerator and the mass flow of the gas-liquid mixture generated by the adiabatic throttling to the atmospheric pressure have the following relationship:

[0037]

[0038] wherein, is the direct flow introduced from the cold end, h c is the specific enthalpy of the direct flow introduced from the cold end, is the mass flow of the liquid phase, h a is the specific enthalpy of the saturated liquid at the atmospheric pressure, is the mass flow of the gas phase, h b is the specific enthalpy of the saturated gas at the atmospheric pressure.

[0039] The direct flow introduced from the liquefied gas pipeline is pre-cooled to a certain temperature by the refrigerator, and is cooled again by mixing with the gas phase generated by throttling. The first law of thermodynamics is applied to the process to obtain the following relationship:

[0040]

[0041] wherein, is the direct flow introduced from the liquefied gas pipeline, h x is the specific enthalpy of the direct flow introduced from the liquefied gas pipeline after pre-cooling, h y is the specific enthalpy after mixing.

[0042] The mixed working medium is further cooled by the secondary cold head to absorb sensible heat and latent heat and liquefied, and finally mixed with the liquid phase obtained by throttling. Under the refrigeration condition, the relationship between the generated liquid phase flow and the refrigeration capacity is as follows:

[0043]

[0044] Wherein, Q0 is refrigeration capacity, L is phase change latent heat under atmospheric pressure.

[0045] The production of liquid or liquefaction rate is defined as

[0046]

[0047] Take a 1.5W@4.2K GM refrigerator as an example, the mass flow rate of the compressor used is 4g / s. Due to the problems of pipeline welding, material temperature gradient and other reasons, the direct current introduced from the liquefied gas pipeline can only reach about 8K after pre-cooling by the refrigerator. Assuming that the direct current of 4.2K and 1.6Mpa is introduced from the refrigerator, the direct current flow is 1% of the mass flow rate of the compressor, which is 40mg / s, and according to the existing literature, its influence on the performance of the refrigerator can be ignored. The direct current is throttled to an atmospheric pressure condition to generate a gas-liquid mixture at 4.21K, and the state point dryness is 0.33275, i.e. 26.69mg / s of liquid phase and 13.31mg / s of gas phase. The gas phase after throttling is mixed with the direct current introduced from the liquefied gas pipeline to further reduce the temperature and become an unsaturated gas at atmospheric pressure, and the temperature is 6.63K, which is further reduced on the basis of the original 8K, thereby improving the liquefaction performance of the system.

[0048] The mixed gas further absorbs sensible heat and latent heat at the cold end of the refrigerator to become saturated liquid at the corresponding pressure. According to the refrigeration capacity, the liquefaction rate of the direct current introduced from the liquefied gas pipeline is 27.45mg / s, and the total liquefaction rate is 0.05414g / s, i.e. 37.42L / day. The liquefaction rate of the existing small helium liquefaction system using GM refrigerator has been in a bottleneck of about 20L / day, which is much smaller than the liquefaction rate of the present application. Therefore, the present application can break through the original pre-cooling temperature and has great potential for liquefaction rate optimization.

[0049] The above-described embodiments have described the technical solutions and beneficial effects of the present application in detail. It should be understood that the above-described embodiments are only specific embodiments of the present application and are not used to limit the present application. Any modification, supplement and equivalent replacement made within the principle range of the present application shall be included in the protection range of the present application.

Claims

1. A helium liquefaction system using a regenerative refrigerator with a cold-end direct current as the liquefied chemical medium, characterized in that, Includes a regenerative refrigeration module, a liquefaction chamber (13), a liquefied helium module, and a refrigeration gas replenishment module; The cold end heat exchanger (5) of the regenerator in the regenerator refrigeration module is set in the liquefaction chamber (13). The lower end of the cold end heat exchanger (5) is provided with an opening, which is connected to the cold end DC pipeline (11) with a cold end DC control valve (10). The cold end DC pipeline (11) leads out the low temperature and high pressure working fluid of the cold end heat exchanger (5) and leads it to the vicinity of the cold end heat exchanger (5) for release. The bottom of the liquefaction chamber (13) is provided with a liquid helium outlet (12). The liquefied helium module includes a liquefied gas cylinder (17), a liquefied gas control valve (16), and a liquefied gas mass flow meter (15) connected in sequence. The liquefied gas mass flow meter (15) is connected to the liquefaction chamber (13) through a liquefied gas pipeline (14). The gas replenishment module of the refrigeration unit includes a gas replenishment cylinder (21), a gas replenishment control valve (20), and a gas replenishment mass flow meter (19) connected in sequence. The gas replenishment mass flow meter (19) is connected to the low-pressure chamber side of the compression device (1) of the regenerative refrigeration unit through a gas replenishment pipeline (18). The high-pressure, room-temperature helium working medium in the liquefied gas cylinder (17) first enters the liquefaction chamber (13), and after being pre-cooled by the regenerative refrigerator, it mixes with the low-temperature, low-pressure helium released by the throttling of the cold-end DC pipeline (11) under conditions below the critical helium pressure and is further cooled. Then, it enters the vicinity of the cold-end heat exchanger (5) of the regenerative refrigerator module and is further cooled and liquefied. The high-temperature, high-pressure helium in the replenishment gas cylinder (21) enters the low-pressure chamber side of the compression device (1) to replenish the helium working medium for the regenerative refrigerator. The high-pressure, low-temperature helium is throttled by the cold-end DC control valve (10) to a condition below the critical helium pressure and partially liquefied. The throttled gas phase mixes with the low-temperature, low-pressure helium in the liquefied helium module and is liquefied, and then mixed with the throttled liquid phase. Finally, the liquid helium is drawn out from the liquid helium outlet (12) to complete the helium liquefaction.

2. The helium liquefaction system according to claim 1, which uses a regenerative refrigeration unit's cold-end direct current as the liquefied chemical medium, is characterized in that... The regenerative refrigeration module includes a compressor device (1), a compressor transmission pipe (2), a regenerator hot end heat exchanger (3), a regenerator (4), a regenerator cold end heat exchanger (5), a regenerator and expansion mechanism transmission pipe (6), an expansion mechanism cold end heat exchanger (7), an expansion mechanism (8), and an expansion mechanism hot end heat exchanger (9) connected in sequence. Among them, the regenerator (4), the cold end heat exchanger of the regenerator (5), the regenerator and expansion mechanism transmission pipe (6), the cold end heat exchanger of the expansion mechanism (7), and the expansion mechanism (8) are arranged inside the liquefaction chamber (13), and the rest are arranged outside the liquefaction chamber (13).

3. The helium liquefaction system according to claim 2, which uses a regenerative refrigeration unit's cold-end direct current as the liquefied chemical medium, is characterized in that... The cold end DC pipeline (11) draws out the low temperature and high pressure working fluid of the cold end heat exchanger (5) of the regenerator and releases it near the cold end heat exchanger (5), the regenerator and expansion mechanism transmission pipe (6), and the cold end heat exchanger (7) of the expansion mechanism.

4. The helium liquefaction system according to claim 1, which uses a regenerative refrigeration unit's cold-end direct current as the liquefied chemical medium, is characterized in that... The cold end DC pipeline (11) is installed at the lower opening of the cold end heat exchanger (5) of the regenerator by welding.

5. The helium liquefaction system according to claim 1, which uses a regenerative refrigerator cold-end direct current as the liquefied chemical medium, is characterized in that... The regenerative refrigeration module has a coaxial, U-shaped, or linear structure.

6. The helium liquefaction system according to claim 1, which uses a regenerative refrigeration unit's cold-end direct current as the liquefied chemical medium, is characterized in that... The regenerative refrigeration module is a GM refrigeration unit, a Stirling refrigeration unit, or a VM refrigeration unit.

7. The helium liquefaction system according to claim 1, which uses a regenerative refrigeration unit's cold-end direct current as the liquefied chemical medium, is characterized in that... The regenerative refrigeration module is a single-stage, two-stage, or multi-stage coupled structure; wherein, the two-stage or multi-stage coupled structure is a thermal coupling structure or a gas coupling structure.

8. The helium liquefaction system according to claim 1, which uses a regenerative refrigeration unit's cold-end direct current as the liquefied chemical medium, is characterized in that... The regenerative refrigeration module uses a 4K refrigeration unit that is matched to the liquid helium temperature range.

9. The helium liquefaction system according to claim 1, which uses a regenerative refrigeration unit's cold-end direct current as the liquefied chemical medium, is characterized in that... In the regenerative refrigeration module, the compression device (1) is a linear compressor or a GM compressor with a valve, and the low-pressure chamber side of the two is the back pressure chamber of the linear compressor and the low-pressure tank of the GM compressor, respectively.

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