A crude helium purification and liquefaction circulation system and method based on cryogenic distillation

Abstract

The present invention relates to a crude helium purification and liquefaction circulation system and method based on cryogenic distillation, and relates to the fields of cryogenic refrigeration technology and chemical separation technology. The present invention comprises a crude helium liquefaction unit, a pure helium circulation liquefaction unit, and a cold supply unit. The crude helium liquefaction unit comprises a crude helium pipeline, a 77K cryogenic adsorber, a multi-stage turbine expander, a multi-stage heat exchanger, a gas-liquid separator, a 20K adsorber, a throttle valve, and a liquid helium tank, for liquefying and purifying crude helium; the pure helium circulation liquefaction unit comprises a pure helium pipeline, a multi-stage turbine expander, a reflux compressor, a throttle valve, etc., for liquefying the refluxed pure helium; and the heat exchange unit comprises a liquid nitrogen pipeline, a reflux pipeline, a multi-stage heat exchanger, etc., for providing cold supply. The present invention adopts a technical solution of crude helium purification and liquefaction + pure helium reflux liquefaction, which can purify and liquefy crude helium extracted from natural gas through cryogenic condensation. It has low energy consumption, flexible operating temperature, high recovery rate, and can directly process crude helium from cryogenic distillation.

Description

Technical Field

[0001] The present invention relates to the technical fields of low-temperature refrigeration and chemical separation, and in particular to a system and method for purifying and liquefying crude helium based on low-temperature distillation. Background Art

[0002] Liquid helium, due to its unique properties, is crucial in aerospace, cryogenic superconductors, semiconductors, healthcare, and other fields. With the development of various high-tech industries, the demand for helium is increasing. Because it is non-renewable, it is a crucial strategic resource. Helium is primarily extracted from natural gas fields.

[0003] Because crude helium from natural gas undergoes cryogenic distillation, containing nitrogen and trace amounts of neon and hydrogen, these impurities may solidify at low temperatures during the liquefaction process. Nitrogen can be removed by subjecting the crude helium to adsorption at around 77K, or by cooling it and then performing gas-liquid separation. Hydrogen and neon are difficult to remove at low temperatures, and since neon is a rare and inert gas, it requires adsorption at 20K using an adsorbent to purify the helium and subsequently liquefy it.

[0004] Currently, large-scale helium liquefaction plants are optimized based on the Collins cycle. However, when the Collins cycle system converts gas into liquid and then reduces the pressure to send it into the liquid helium tank for storage, the pressure before the throttle valve is too high, and the system pressure reduction will generate more gas phase; and generally only the low-temperature gas phase helium of natural gas is used for the final liquefaction. Before the helium liquefaction process, the low-temperature gas phase helium of natural gas must be purified by various methods; at the same time, most of the current liquefaction plants are based on pure helium at room temperature for liquefaction, or the crude helium is first purified at low temperature and then liquefied. It is impossible to simultaneously purify and liquefy the raw gas, and the pretreatment is complicated, which will result in a low helium liquefaction rate. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a crude helium purification and liquefaction circulation system and method based on cryogenic distillation, which can directly purify and liquefy high-concentration crude helium with a high liquefaction rate and low energy loss.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The first object of the present invention is to provide a crude helium purification and liquefaction circulation system based on cryogenic distillation, comprising a crude helium liquefaction unit, a pure helium circulation liquefaction unit and a refrigeration supply unit;

[0008] The crude helium liquefaction unit comprises a first pipeline, the first pipeline connecting the raw gas inlet and the liquid helium throttle valve inlet, a multi-stage crude helium purification device and a multi-stage heat exchange device connected in series between the raw gas inlet and the liquid helium throttle valve, the outlet of the last-stage gas purification device connected to a third mixer, and the outlet of the third mixer connected to the next-stage heat exchanger; a fourth expander is connected before the liquid helium throttle valve, and the end of the first pipeline is connected to the liquid helium tank inlet;

[0009] The pure helium circulation liquefaction unit comprises a pure helium pipeline, which passes through at least one stage of the multi-stage heat exchange device; the end of the pure helium pipeline is connected to the third mixer and merged into the first pipeline;

[0010] The cold supply unit includes a cold supply pipeline, which is reversely connected to the multi-stage heat exchange device on the first pipeline, and a local cold supply loop is provided on at least one stage of the heat exchange device; a splitter is provided at the front end of the first pipeline inlet and / or the pure helium pipeline inlet of the at least one stage of the heat exchange device, and the splitter outlet is connected to the expander through the cold supply pipeline, the expander outlet is connected to the cold supply pipeline inlet of the heat exchange device, and the cold supply pipeline outlet of the heat exchange device is connected to the cold supply pipeline, thereby forming the local cold supply loop;

[0011] The end of the cooling pipeline is connected to the beginning of the pure helium pipeline through the first-stage heat exchanger in the multi-stage heat exchange device, and the gas phase outlet of the liquid helium tank is connected to the cooling circuit;

[0012] Preferably, the last stage of the multi-stage heat exchange device is a sixth heat exchanger, and a local cooling circuit is provided on the sixth heat exchanger;

[0013] The front end of the first pipeline inlet of the sixth heat exchanger is connected to the third splitter, and the split outlet of the third splitter is connected to the cold pipeline inlet of the sixth heat exchanger through the cold pipeline; a third expander and a mixer are connected in series between the third splitter and the sixth heat exchanger, and the gas phase outlet of the liquid helium tank is connected to the first mixer inlet;

[0014] The inlet of the third splitter is connected to the outlet of the third mixer, and the outlet of the cold pipeline of the sixth heat exchanger is connected to the cold pipeline.

[0015] Preferably, the sixth heat exchanger is provided on the first pipeline between the fourth expander and the liquid helium throttle valve.

[0016] Preferably, the multi-stage heat exchanger includes a fifth heat exchanger, and the fifth heat exchanger is arranged on the first pipeline between the third mixer outlet and the third splitter.

[0017] Preferably, the multi-stage heat exchange device includes a fourth heat exchanger, and the first pipeline, pure helium pipeline and cold pipeline pass through the fourth heat exchanger; the cold pipeline inlet of the fourth heat exchanger is connected to the outlet of the second mixer, and the cold pipeline is connected to the inlet of the second mixer.

[0018] Further preferably, a first local cooling circuit is provided on the fourth heat exchanger;

[0019] The first pipeline inlet of the fourth heat exchanger is connected to a second splitter, and the splitting outlet of the second splitter is connected to the inlet of the second mixer; a second expander and a second 20K adsorber are connected in series between the second splitter and the second mixer;

[0020] The first pipeline outlet of the fourth heat exchanger is connected to the first 20K adsorber.

[0021] More preferably, the fourth heat exchanger is provided with a second local cooling circuit;

[0022] The pure helium pipeline inlet of the fourth heat exchanger is connected to another second splitter, and the splitting outlet of the other second splitter is connected to the inlet of the second mixer; another second expander is connected in series between the other second splitter and the second mixer.

[0023] Preferably, the multi-stage heat exchange device includes a third heat exchanger, and a local cooling circuit is provided on the third heat exchanger;

[0024] The front end of the pure helium pipeline inlet of the third heat exchanger is connected to the first splitter, the split outlet of the first splitter is connected to the inlet of the fourth mixer, and the outlet of the fourth mixer is connected to the inlet of the cold pipeline of the third heat exchanger; a first expander is connected in series between the first splitter and the inlet of the fourth mixer;

[0025] The cooling pipeline is connected to the inlet of the fourth mixer, and a gas-liquid separator is provided at the front end of the first pipeline inlet of the third heat exchanger.

[0026] Preferably, a pure helium pre-cooling heat exchanger is connected to the pure helium pipeline at the front end of the first-stage heat exchanger, and the pure helium pre-cooling heat exchanger is connected in parallel with a liquid nitrogen pipeline, and the liquid nitrogen pipeline is connected to a liquid nitrogen valve.

[0027] A second object of the present invention is to provide a crude helium purification and liquefaction circulation method based on cryogenic distillation, the crude helium purification and liquefaction circulation system based on cryogenic distillation comprising:

[0028] After the raw gas enters the first pipeline, it passes through a multi-stage crude helium purification device and a multi-stage heat exchange device in sequence to achieve purification and initial cooling of the raw gas, turning it into pure helium in gas-liquid two-phase;

[0029] Pure helium in both gas and liquid phases enters the liquid helium tank, where the helium gas merges with the cooling pipeline through the gas phase outlet of the liquid helium tank. The cooling pipeline passes through the multi-stage heat exchange device on the first pipeline. The flow direction of the stream in the cooling pipeline is opposite to that of the raw gas in the first pipeline. The purified raw gas is split by the splitter in the first pipeline, and the cooling energy is obtained by the expander and then merged into the cooling pipeline.

[0030] The end of the cooling pipeline enters the pure helium pipeline after heat exchange in the first-stage heat exchange device. The pure helium pipeline passes through some heat exchange devices on the first pipeline and merges with the first pipeline after the raw gas in the first pipeline is purified. It enters the next-stage heat exchange device and finally enters the liquid helium tank. The pure helium pipeline is split by the splitter and also obtains cooling energy through the expander and then enters the cooling pipeline.

[0031] The cooling pipeline is fed from the first pipeline and the liquid helium pipeline into the expansion mechanism to refrigerate the cooling capacity, and cools the parallel first pipeline and / or pure helium pipeline in the heat exchanger.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The crude helium purification and liquefaction cycle system based on cryogenic distillation provided by the present invention can introduce the crude helium gas phase generated from the boil-off gas of natural gas or liquefied natural gas after cryogenic condensation into a crude helium liquefaction unit. The crude helium vapor phase is directly processed using a multi-stage crude helium purification unit and a multi-stage heat exchanger, eliminating the need for purification and subsequent liquefaction of the crude helium. This achieves simultaneous helium purification and liquefaction within the same system. Furthermore, by providing a refrigeration circuit with an expander in series with the heat exchanger, the present invention provides additional refrigeration to the heat exchanger, reducing the heat exchanger's exergy losses and maximizing refrigeration utilization. The parallel use of the Collins cycle and the Brayton cycle, which have a higher liquefaction capacity, fully utilizes refrigeration and reduces compressor cycle power consumption. This improves the efficiency of gaseous helium liquefaction compared to a pure Brayton cycle helium liquefaction system. Furthermore, by using an expander to reduce pressure and temperature before the liquid helium throttle valve, the present invention improves the helium liquefaction rate and reduces energy losses. This application focuses on liquefying high-concentration crude helium from natural gas through cryogenic distillation. This high-concentration crude helium is at a low temperature and high pressure, saving some refrigeration capacity. Furthermore, an expander is positioned before the final heat exchanger, enabling the final heat exchanger and the expander to work synergistically, increasing the liquefaction rate of gaseous pure helium and reducing energy losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a process flow chart of the system equipment of Example 1 of the present invention;

[0035] Figure 2 This is a process flow chart of the system equipment of Example 2 of the present invention;

[0036] Figure 3 This is a process flow chart of the system equipment of Example 3 of the present invention;

[0037] Figure 4 This is a process flow chart of the system equipment of Example 4 of the present invention;

[0038] Figure 5This is a process flow chart of the system equipment of Example 5 of the present invention;

[0039] Among them: helium reflux compressor EX0, cold box including (77K adsorber P1, pure helium pre-cooling heat exchanger E-1, second heat exchanger E-2, third heat exchanger E-3, fourth heat exchanger E-4, fifth heat exchanger E-5, sixth heat exchanger E-6, heat exchanger Ea, heat exchanger Eb, first expander EX-1, second expander EX2-1, second expander EX2-2, third expander EX-3, fourth expander EX-4, three-way splitter Sa , first diverter S-1, second diverter S2-1, second diverter S2-2, third diverter S-3, and multiple mixers: three-way mixer Ma, first M-1, second mixer M-2, third mixer M-3, fourth mixer M-4, low-pressure pipeline, high-pressure pipeline, liquid nitrogen pipeline, liquid nitrogen valve V0, liquid helium throttle valve V1, first 20K adsorber P3-1, second 20K adsorber P3-2, gas-liquid separator P2), liquid helium tank C1. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] The present invention provides a crude helium purification and liquefaction circulation system based on cryogenic distillation, comprising a crude helium liquefaction unit, a pure helium circulation liquefaction unit and a cold supply unit;

[0043] The crude helium liquefaction unit comprises a first pipeline, which connects the feed gas inlet and the inlet of the liquid helium throttle valve V1. A multi-stage crude helium purification device and a multi-stage heat exchange device are connected in series between the feed gas inlet and the liquid helium throttle valve V1. The outlet of the last-stage gas purification device is connected to the third mixer M-3, and the outlet of the third mixer M-3 is connected to the next-stage heat exchanger. A fourth expander EX-4 is connected before the liquid helium throttle valve V1. The end of the first pipeline is connected to the inlet of the liquid helium tank C1.

[0044] The pure helium circulation liquefaction unit has a pure helium pipeline, which passes through at least one stage of the multi-stage heat exchange device; the end of the pure helium pipeline is connected to the third mixer M-3 and merged into the first pipeline;

[0045] The cooling supply unit comprises a cooling pipeline, which is reversely connected to the multi-stage heat exchange device on the first pipeline, and a local cooling loop is provided on at least one stage of the heat exchange device; a flow divider is provided at the front end of the first pipeline inlet and / or the pure helium pipeline inlet of the at least one stage of the heat exchange device, the flow diversion outlet of the flow divider is connected to the expander through the cooling pipeline, the expander outlet is connected to the cooling pipeline inlet of the heat exchange device, and the cooling pipeline outlet of the heat exchange device is connected to the return pipeline, thereby forming a local cooling loop;

[0046] The end of the cold pipeline is connected to the beginning of the pure helium pipeline through the first-stage heat exchanger in the multi-stage heat exchanger, and the gas phase outlet of the liquid helium tank C1 is connected to the cold circuit.

[0047] In an embodiment of the present invention, a multi-stage gas purification device generally includes three types, firstly a 77K adsorber P1 arranged at the crude helium inlet of the first pipeline, followed by a gas-liquid separator P2 after cooling through at least one stage of heat exchanger, and a first 20K adsorber P3-1 and a second 20K adsorber P3-2 connected when the raw gas in the first pipeline is cooled to below 20K.

[0048] Waste gas removal pipelines are provided on each level of gas purification equipment of the present invention. Nitrogen can be removed by subjecting the crude helium to adsorption treatment at about 77K, or by gas-liquid separation after cooling. Hydrogen and neon are difficult to remove using low temperatures, and neon is a rare inert gas, so it needs to be adsorbed using an adsorbent at 20K to purify the helium and then liquefy it. In the system designed by the present invention, the mainstream of the crude helium liquefaction unit passes through the 77K low-temperature adsorber P1, flows through each heat exchanger to cool down in sequence, and after the heat exchanger cools down, a gas-liquid separator P2 will be used to remove some impurities. When the temperature drops below 20K, it will pass through the 20K low-temperature adsorber to remove some hydrogen and neon that are difficult to remove at low temperatures to extremely low levels. After removal, it will be merged into the helium reflux stream.

[0049] In the present invention, the first-stage multi-stage heat exchange device is the second heat exchanger E-2, and the last-stage multi-stage heat exchange device is the sixth heat exchanger E-6.

[0050] In some embodiments of the present invention, a local cooling circuit is provided on the sixth heat exchanger E-6: the front end of the first pipeline inlet of the sixth heat exchanger E-6 is connected to the third diverter S-3, and the diversion outlet of the third diverter S-3 is connected to the cooling pipeline inlet of the sixth heat exchanger E-6 through the cooling pipeline; the third expander EX-3 and the first mixer M-1 are connected in series between the third diverter S-3 and the sixth heat exchanger E-6, and the gas phase outlet of the liquid helium tank C1 is connected to the inlet of the first mixer M-1; the inlet of the third diverter S-3 is connected to the third mixer M-3, and the cooling pipeline outlet of the sixth heat exchanger E-6 is connected to the cooling pipeline.

[0051] In the above embodiment of the present invention, the first pipeline between the third splitter S-3 and the sixth heat exchanger E-6 is connected in series with the fourth expander EX-4.

[0052] In the above embodiment of the present invention, the multi-stage heat exchanger may further include a fifth heat exchanger E-5, which is disposed on the first pipeline between the outlet of the third mixer M-3 and the third splitter S-3.

[0053] In some embodiments of the present invention, the multi-stage heat exchange device includes a fourth heat exchanger E-4, and the first pipeline, the pure helium pipeline and the cold pipeline pass through the fourth heat exchanger E-4; the cold pipeline inlet of the fourth heat exchanger E-4 is connected to the outlet of the second mixer M-2, and the cold pipeline is connected to the inlet of the second mixer M-2.

[0054] In this embodiment, a first local cooling circuit can be set on the fourth heat exchanger E-4: the first pipeline inlet of the fourth heat exchanger E-4 is connected to the second splitter S2-1, and the splitter outlet of the second splitter S2-1 is connected to the inlet of the second mixer M-2; the expander EX2-1 and the second 20K adsorber P3-2 are connected in series between the second splitter S2-1 and the second mixer M-2; the first pipeline outlet of the fourth heat exchanger E-4 is connected to the first 20K adsorber P3-1.

[0055] In addition, the fourth heat exchanger E-4 can also be provided with a second local cooling circuit, or only a second local cooling circuit can be provided. In this case: the pure helium pipeline inlet of the fourth heat exchanger E-4 is connected to the second splitter S2-2, and the splitter outlet of the second splitter S2-2 is connected to the inlet of the second mixer M-2; the second expander EX2-2 is connected in series between the second splitter S2-2 and the second mixer M-2.

[0056] In an embodiment of the present invention, the multi-stage heat exchange device may further include a third heat exchanger E-3. A local cooling circuit is provided on the third heat exchanger E-3. In this case, the front end of the pure helium pipeline inlet of the third heat exchanger E-3 is connected to the first splitter S-1, the split outlet of the first splitter S-1 is connected to the inlet of the fourth mixer M-4, and the outlet of the fourth mixer M-4 is connected to the cooling pipeline inlet of the third heat exchanger E-3; a first expander EX-1 is connected in series between the first splitter S-1 and the inlet of the fourth mixer M-4.

[0057] The cooling pipeline is connected to the inlet of the fourth mixer M-4, and a gas-liquid separator P2 is provided at the front end of the first pipeline inlet of the third heat exchanger E-3.

[0058] The pure helium pipeline at the front end of the second heat exchanger E-2 is connected to the pure helium precooling heat exchanger E-1, and the pure helium precooling heat exchanger E-1 is connected in parallel with a liquid nitrogen pipeline.

[0059] The mainstream of the pure helium liquefaction unit is compressed by the reflux compressor EX0 and pre-cooled with liquid nitrogen by the pure helium pre-cooling heat exchanger E-1. It is cooled in sequence by each heat exchanger and expanded to a preferred pre-throttling pressure before the sixth heat exchanger E-6. After cooling by the sixth heat exchanger E-6, it is throttled by the liquid helium throttle valve V1 and enters the liquid helium tank C1 for storage.

[0060] The crude helium purification and liquefaction circulation system uses crude helium with a high helium content after low-temperature condensation as the raw gas. It is suitable for crude helium after low-temperature condensation of natural gas or liquefied natural gas boil-off gas.

[0061] In the system proposed by the present invention, except for the circulating compressor EX0 and the liquid helium tank C1, other devices are integrated in a vacuum cold box under high vacuum multi-layer insulation.

[0062] Flow sensors are arranged at the inlet of each turbine expander, the inlet of the helium circulation compressor, the inlet of the liquid nitrogen and the inlet of the crude helium to facilitate the adjustment of the cooling capacity required by each heat exchanger and the energy consumption of the helium circulation compressor.

[0063] Temperature and pressure sensors are arranged at the inlet and outlet of each heat exchanger and the outlet of the expander to timely adjust the cooling capacity required by each heat exchanger.

[0064] The crude helium and pure helium streams are processed to similar states in each heat exchanger, which facilitates the temperature matching between the heat exchangers, facilitates the establishment of the heat exchanger, and prevents large temperature changes after mixing.

[0065] The present invention proposes a crude helium purification and liquefaction circulation method based on the above system, comprising:

[0066] After the first pipeline of the raw gas, it passes through the multi-stage crude helium purification device and the multi-stage heat exchange device in sequence to achieve the purification and initial cooling of the raw gas, and becomes pure helium in gas-liquid two-phase;

[0067] Pure helium in both gas and liquid phases enters the liquid helium tank, where the helium passes through the gas phase outlet of the liquid helium tank and merges with the refrigeration pipeline. The refrigeration pipeline passes through the multi-stage heat exchange device on the first pipeline. The flow direction of the stream in the refrigeration pipeline is opposite to that of the raw gas in the first pipeline. The raw gas purified by the multi-stage crude helium purification device is split by the splitter in the first pipeline, and the refrigeration is obtained by the expander and merged into the refrigeration pipeline.

[0068] The end of the cooling pipeline enters the pure helium pipeline after heat exchange in the first-stage heat exchange device. The pure helium pipeline passes through some heat exchange devices on the first pipeline and merges with the first pipeline after the raw gas in the first pipeline is purified. It enters the next-stage heat exchange device and finally enters the liquid helium tank. The pure helium pipeline is split by the splitter and also obtains cooling energy through the expander and then enters the cooling pipeline.

[0069] The cooling pipeline is fed from the first pipeline and the liquid helium pipeline into the expansion mechanism to refrigerate the cooling capacity, and cools the parallel first pipeline and / or pure helium pipeline in the heat exchanger.

[0070] The cooling capacity of the crude helium liquefaction of the present invention is provided by the gaseous reflux of the helium turbine expander and the liquid helium tank, and the helium is gradually cooled by the low-temperature heat exchanger, and finally the helium is liquefied by throttling, that is:

[0071] Crude helium liquefaction is divided into three units, integrated into a single cold box. These units contain three pipelines: crude helium, pure helium, and reflux. The crude helium is purified by a cryogenic adsorption process at 20K before being fed into the pure helium or reflux pipelines. To maximize the helium liquefaction rate and reduce reflux energy consumption, the pipeline pressure is set to an optimal value before throttling. Furthermore, to avoid wasting cooling capacity in the heat exchanger, split flow is utilized to provide cooling capacity.

[0072] The following is a detailed description with reference to the embodiments and accompanying drawings:

[0073] Example 1

[0074] See attached Figure 1 , which is a crude helium purification and liquefaction circulation system based on cryogenic distillation provided in this embodiment, including a crude helium liquefaction unit, a pure helium circulation liquefaction unit and a cold capacity providing unit;

[0075] The crude helium liquefaction unit has a first pipeline, which is connected in sequence to the 77K cryogenic adsorber P1, the second heat exchanger E-2, the gas-liquid separator P2, the three-way second splitter S2-1, the second heat exchanger E-2, the first 20K cryogenic adsorber P3-1, the three-way third mixer M-3, the fifth heat exchanger E-5, the three-way third splitter S-3, the turbine fourth expander EX-4, the heat exchanger E-6, the liquid helium throttle valve V1 and the liquid helium tank C1.

[0076] In the pure helium circulation liquefaction unit, the pure helium pipeline feed is the cold stream outlet of the second heat exchanger E-2 after circulation. It then passes through the reflux compressor, the pure helium precooling heat exchanger E-1, the second heat exchanger E-2, the fourth heat exchanger E-4, and finally merges into the first pipeline through the three-way third mixer M-3. A liquid nitrogen pipeline is connected in parallel to the pure helium precooling heat exchanger E-1.

[0077] The cooling supply unit has a cooling pipeline, which is sequentially connected to the sixth heat exchanger E-6, the fifth heat exchanger E-5, the second three-way mixer M-2, the fourth heat exchanger E-4, and the second heat exchanger E-2. After passing through the second heat exchanger E-2, the cold flow stream enters the pure helium pipeline as the outlet stream. The local cooling loop is arranged between the sixth heat exchanger E-6 and the fourth heat exchanger E-4: the local cooling loop of the sixth heat exchanger E-6 is connected by the gas phase of the liquid helium tank and the third three-way splitter S-3. A branch flow is cooled by the third turbine expander EX-3 and then mixed in the first three-way mixer M-1, enters the cooling pipeline and passes into the sixth heat exchanger E-6; the local cooling circuit of the fourth heat exchanger E-4 is connected to the cooling pipeline outlet of the fifth heat exchanger E-5 and the second three-way splitter S2-1. A branch flow is cooled by the second turbine expander EX2-1 and then purified by the second 20K adsorber P3-2. After that, it is mixed in the second three-way mixer M-2 and passes into the fourth heat exchanger E-4.

[0078] The temperature of the low-temperature adsorber is below 20K.

[0079] The crude helium stream passes through the third heat exchanger E-3 and is pressure-reduced to a low pressure temperature below 20K.

[0080] The crude helium stream needs to be reduced to below 20K after passing through the fourth heat exchanger E-4.

[0081] All heat exchangers, mixers, splitters, gas-liquid separators P2, cryogenic adsorbers, turbine expanders and throttle valves in the system are fixed in a vacuum cold box, which uses high vacuum multi-layer insulation.

[0082] Temperature sensors, pressure sensors and flow meters are installed at the inlets and outlets of each device.

[0083] The turbine expander outlet temperature is slightly lower than the helium reflux temperature.

[0084] This embodiment provides a crude helium purification and liquefaction circulation system based on cryogenic distillation. Specifically, during operation:

[0085] When the mainstream of the crude helium liquefaction unit passes through the 77K low-temperature adsorber P1, a large amount of nitrogen components are removed, and it flows through each stage of heat exchangers to be cooled in sequence. When the temperature is cooled in each stage of heat exchangers, some impurities are removed by the gas-liquid separator P2. When the temperature drops below 20K, some hydrogen and neon that are difficult to remove by low temperature are removed to extremely low content when passing through the 20K low-temperature adsorber P3-2 and the low-temperature adsorber P3-1, and then merged into the helium reflux stream of the first pipeline.

[0086] The mainstream of the pure helium liquefaction unit is compressed by the reflux compressor EX0 and pre-cooled by liquid nitrogen in the liquid helium heat exchanger E-1. It is cooled in sequence through each heat exchanger and merged into the first pipeline. It is expanded to a preferred pre-throttling pressure by the turbine fourth expander EX-4 before the sixth heat exchanger E-6. It is cooled by the sixth heat exchanger E-6 and throttled by the liquid helium throttle valve V1 before entering the liquid helium tank for storage.

[0087] The cooling capacity providing unit is provided by the cooling capacity provided by the gas phase of the liquid helium tank and the cooling capacity provided by the crude helium liquefaction unit and the pure helium liquefaction unit to the turbine fourth expander EX-4, the turbine second expander EX2-1 and the turbine third expander EX-3.

[0088] The crude helium liquefaction system provided in this embodiment uses crude helium with a high helium content after cryogenic condensation as the raw gas, and is suitable for crude helium obtained by cryogenic condensation of natural gas or liquefied natural gas boil-off gas.

[0089] Example 2

[0090] See attached Figure 2 , which is a crude helium purification and liquefaction circulation system based on cryogenic distillation provided in this embodiment, including a crude helium liquefaction unit, a pure helium circulation liquefaction unit and a cold capacity providing unit;

[0091] The crude helium liquefaction unit has a first pipeline. The crude helium enters the first pipeline from the helium extraction tower in the gas phase and passes through the 77K low-temperature adsorber P1, the second heat exchanger E-2, the gas-liquid separator P2, the fourth heat exchanger E-4, the first 20K adsorber P3-1, the three-way third mixer M-3, the three-way third splitter S-3, the turbine fourth expander EX-4, the sixth heat exchanger E-6, the liquid helium throttle valve V1 and the liquid helium tank C1.

[0092] In the pure helium circulation liquefaction unit, the pure helium pipeline feed is the cold stream outlet of the second heat exchanger E-2 after circulation. It then passes through the reflux compressor EX0, the pure helium precooling heat exchanger E-1, the second heat exchanger E-2, the second three-way splitter S2-2, the fourth heat exchanger E-4, and finally merges into the first pipeline through the third three-way mixer M-3. A liquid nitrogen pipeline is connected in parallel to the pure helium precooling heat exchanger E-1.

[0093] The cooling supply unit comprises a cooling pipeline, which sequentially connects the sixth heat exchanger E-6, the second three-way mixer M-2, the fourth heat exchanger E-4, and the second heat exchanger E-2. After passing through the second heat exchanger E-2, the cooling pipeline enters the pure helium pipeline as a cold stream outlet stream. Partial cooling circuits are arranged between the sixth heat exchanger E-6 and the fourth heat exchanger E-4: the local cooling circuit of the sixth heat exchanger E-6 is composed of the gas phase of the liquid helium tank and a branch of the third three-way splitter S-3, which is refrigerated by the third turbine expander EX-3 and then mixed in the first three-way mixer M-1. The liquid flows into the cooling pipeline and is passed into the sixth heat exchanger E-6. The local cooling circuit of the fourth heat exchanger E-4 is composed of the cooling pipeline of the sixth heat exchanger E-6 and a branch of the second three-way splitter S2-2. The liquid flows through the second turbine expander EX2-2 and is refrigerated and then mixed in the second three-way mixer M-2 and is passed into the fourth heat exchanger E-4.

[0094] The temperature of the low-temperature adsorber is below 20 K. The crude helium stream is reduced to a low pressure temperature below 20 K after passing through the second heat exchanger E-2. The crude helium stream is also required to be reduced to below 20 K after passing through the fourth heat exchanger E-4.

[0095] All heat exchangers, mixers, splitters, gas-liquid separators P2, cryogenic adsorbers, turbine expanders and throttle valves in the system are fixed in a vacuum cold box, which uses high vacuum multi-layer insulation.

[0096] Temperature sensors, pressure sensors and flow meters are installed at the inlets and outlets of each device.

[0097] The turbine expander outlet temperature is slightly lower than the helium reflux temperature.

[0098] This embodiment provides a crude helium purification and liquefaction circulation system based on cryogenic distillation. Specifically, during operation:

[0099] When the mainstream of the crude helium liquefaction unit passes through the 77K low-temperature adsorber P1, a large amount of nitrogen components are removed, and then it flows through each stage of heat exchangers to be cooled in sequence. When the temperature of each stage of heat exchanger is cooled, some impurities are removed by the gas-liquid separator P2. When the temperature drops below 20K, some hydrogen and neon that are difficult to remove by low temperature are removed to extremely low content when passing through the second 20K low-temperature adsorber P3-2 and the first low-temperature adsorber P3-1, and then it is merged into the helium reflux stream of the first pipeline.

[0100] The mainstream of the pure helium liquefaction unit is compressed by the reflux compressor EX0 and pre-cooled by liquid nitrogen in the pure helium pre-cooling heat exchanger E-1. It is cooled in sequence through each heat exchanger and merged into the first pipeline. It is expanded to a preferred pre-throttling pressure by the turbine fourth expander EX-4 before the sixth heat exchanger E-6, cooled by the sixth heat exchanger E-6, and throttled by the liquid helium throttle valve before entering the liquid helium tank for storage.

[0101] The cooling capacity providing unit is provided by the cooling capacity provided by the gas phase of the liquid helium tank and the cooling capacity provided by the crude helium liquefaction unit and the pure helium liquefaction unit to the turbine fourth expander EX-4, the turbine second expander EX2-2, and the turbine third expander EX-3.

[0102] The crude helium liquefaction system provided in this embodiment uses crude helium with a high helium content after cryogenic condensation as the raw gas, and is suitable for crude helium obtained by cryogenic condensation of natural gas or liquefied natural gas boil-off gas.

[0103] Example 3

[0104] See attached Figure 3 , which is a crude helium purification and liquefaction circulation system based on cryogenic distillation provided in this embodiment, including a crude helium liquefaction unit, a pure helium circulation liquefaction unit and a cold capacity providing unit;

[0105] The crude helium liquefaction unit has a first pipeline. The crude helium enters the first pipeline from the helium extraction tower in the gas phase and passes through the 77K low-temperature adsorber P1, the second heat exchanger E-2, the gas-liquid separator P2, the third heat exchanger E-3, the three-way second splitter S2-2, the fourth heat exchanger E-4, the three-way third mixer M-3, the fifth heat exchanger E-5, the turbine fourth expander EX-4, the sixth heat exchanger E-6, the liquid helium throttle valve V1 and the liquid helium tank C1.

[0106] In the pure helium circulation liquefaction unit, the pure helium pipeline feed is the cold stream outlet of the second heat exchanger E-2 after circulation. It then passes through the reflux compressor, the pure helium pre-cooling heat exchanger E-1, the second heat exchanger E-2, the third heat exchanger E-3, the second splitter S2-2, the fourth heat exchanger E-4, and finally merges into the first pipeline through the third three-way mixer M-3. A liquid nitrogen pipeline is connected in parallel to the pure helium pre-cooling heat exchanger E-1.

[0107] The cold supply unit has a cold supply pipeline, which is connected in sequence to the sixth heat exchanger E-6, the fifth heat exchanger E-5, the four-way second mixer M-2, the fourth heat exchanger E-4, the third heat exchanger E-3 and the second heat exchanger E-2, and enters the pure helium pipeline as a cold flow outlet stream after passing through the second heat exchanger E-2; wherein the local cold supply circuit is arranged on the fourth heat exchanger E-4: 1) a branch from the three-way second splitter S2-1 is refrigerated by the turbine second expander EX2-1, and then purified by the second 20K adsorber P3-2, and then mixed in the four-way second mixer M-2 and passed into the fourth heat exchanger E-4; a branch from the three-way second splitter S2-2 is refrigerated by the turbine second expander EX2-2, and then mixed in the four-way second mixer M-2 and passed into the fourth heat exchanger E-4.

[0108] The temperature of the low-temperature adsorber is below 20K.

[0109] The crude helium stream passes through the third heat exchanger E-3 and is pressure-reduced to a low pressure temperature of less than 20 K. The crude helium stream passes through the fourth heat exchanger E-4 and is pressure-reduced to less than 20 K.

[0110] The heat exchanger, mixer, splitter, gas-liquid separator P2, low-temperature adsorber, turbine expander and throttle valve are all fixed in the vacuum cold box, which adopts high vacuum multi-layer insulation.

[0111] Temperature sensors, pressure sensors and flow meters are installed at the inlets and outlets of each device.

[0112] The expander outlet temperature is slightly lower than the helium reflux temperature.

[0113] The crude helium purification and liquefaction circulation system based on cryogenic distillation provided in this embodiment specifically operates as follows:

[0114] When the mainstream of the crude helium liquefaction unit passes through the 77K low-temperature adsorber P1, a large amount of nitrogen components are removed, and then it flows through each stage of heat exchangers to be cooled in sequence. When the temperature of each stage of heat exchanger is cooled, some impurities are removed by the gas-liquid separator P2. When the temperature drops below 20K, some hydrogen and neon that are difficult to remove by low temperature are removed to extremely low content when passing through the second 20K low-temperature adsorber P3-2 and the first 20K adsorber P3-1, and then it is merged into the helium reflux stream of the first pipeline.

[0115] The mainstream of the pure helium liquefaction unit is compressed by the reflux compressor and pre-cooled by liquid nitrogen in the pure helium pre-cooling heat exchanger E-1. It is cooled in sequence through each heat exchanger and merged into the first pipeline. It is expanded to a preferred pre-throttling pressure by the turbine fourth expander EX-4 before the sixth heat exchanger E-6. It is cooled by the sixth heat exchanger E-6 and throttled by the liquid helium throttle valve before entering the liquid helium tank for storage.

[0116] The cooling capacity providing unit is provided by the cooling capacity provided by the gas phase of the liquid helium tank and the cooling capacity provided by the crude helium liquefaction unit and the pure helium liquefaction unit to the turbine fourth expander EX-4, the turbine second expander EX2-1 and the turbine second expander EX2-2.

[0117] Example 4

[0118] See attached Figure 4This embodiment provides a crude helium liquefaction system based on cryogenic distillation, comprising a crude helium liquefaction unit, a pure helium circulation liquefaction unit, and a cooling capacity supply unit (heat exchange unit). The system includes a helium reflux compressor EX0, a cold box (77K adsorber P1, pure helium pre-cooling heat exchanger E-1, second heat exchanger E-2, third heat exchanger E-3, fourth heat exchanger E-4, fifth heat exchanger E-5, sixth heat exchanger E-6, first expander EX-1, second expander EX2-1, second expander EX2-2, third expander EX-3, fourth expander EX-4, multiple flow dividers and mixers, low-pressure and high-pressure pipelines, liquid nitrogen pipelines, liquid nitrogen valve V0, liquid helium throttle valve V1, first 20K adsorber P3-1, second 20K adsorber P3-2, gas-liquid separator P2), and a liquid helium tank C1.

[0119] The so-called crude helium liquefaction unit, the crude helium feed gas inlet pipeline is connected to the 77K low-temperature adsorber P1, and then passes through the second heat exchanger E-2, the gas-liquid separator P2, the third heat exchanger E-3, the three-way second splitter S2-1, the fourth heat exchanger E-4, the first 20K adsorber P3-1, the three-way third mixer M-3, the fifth heat exchanger E-5, the three-way third splitter S-3, the fourth expander EX-4, the sixth heat exchanger E-6, the liquid helium throttle valve V1, and the liquid helium tank C1.

[0120] The pure helium circulation liquefaction unit is fed with the cold stream outlet stream of the second heat exchanger E-2 after circulation, and passes through the circulation compressor EX0, the pure helium pre-cooling heat exchanger E-1, the second heat exchanger E-2, the three-way first splitter S-1, the third heat exchanger E-3, the three-way second splitter S2-2, the fourth heat exchanger E-4, the three-way third mixer M-3, the fifth heat exchanger E-5, the three-way third splitter S-3, the fourth expander EX-4, the sixth heat exchanger E-6, the liquid helium throttle valve V1, and the liquid helium tank C1.

[0121] In the cooling unit, the liquid helium tank gas phase is combined with a split from the third three-way splitter S-3, cooled by the third expander EX-3, and then mixed in the first three-way mixer M-1. The gas then flows through the sixth heat exchanger E-6, the fifth heat exchanger E-5, and the split from the second three-way splitter S2-1. It is then cooled by the second expander EX2-1 and the second 20K adsorber P3-2. The split is then combined with a split from the second three-way splitter S2-2, cooled by the second expander EX2-2, and then mixed in the second four-way mixer M-2. The gas then enters the fourth heat exchanger E-4. The split is then combined with a split from the first three-way splitter S-1, cooled by the first expander EX-1, and then mixed in the fourth three-way mixer M-4. The gas then enters the third heat exchanger E-3 and the second heat exchanger E-2. Liquid nitrogen is used to provide cooling for the pure helium pre-cooling heat exchanger E-1.

[0122] The temperature of the low-temperature adsorber is below 20K.

[0123] The crude helium stream passes through the third heat exchanger E-3 and is pressure-reduced to a low pressure temperature of less than 20 K. The crude helium stream passes through the fourth heat exchanger E-4 and is pressure-reduced to less than 20 K.

[0124] The heat exchanger, mixer, splitter, gas-liquid separator P2, low-temperature adsorber, turbine expander and throttle valve are all fixed in the vacuum cold box, which adopts high vacuum multi-layer insulation.

[0125] Temperature sensors, pressure sensors and flow meters are installed at the inlets and outlets of each device.

[0126] The expander outlet temperature is slightly lower than the helium reflux temperature.

[0127] The helium liquefier process device provided in this embodiment operates as follows:

[0128] When the mainstream of the crude helium liquefaction unit passes through the 77K low-temperature adsorber P1, a large amount of nitrogen components are removed, and it flows through each heat exchanger to be cooled in sequence. When the temperature is reduced in the heat exchanger, a gas-liquid separator P2 will remove some impurities. When the temperature drops below 20K, it will pass through the 20K low-temperature adsorber to remove some hydrogen and neon that are difficult to remove at low temperatures to extremely low levels, and then merge into the helium reflux stream.

[0129] The mainstream of the pure helium liquefaction unit is compressed by the reflux compressor EX0 and pre-cooled with liquid nitrogen by the pure helium pre-cooling heat exchanger E-1. It is cooled in sequence by each heat exchanger and expanded to a preferred pre-throttling pressure before the sixth heat exchanger E-6. It is cooled by the sixth heat exchanger E-6 and throttled by the liquid helium throttle valve before entering the liquid helium tank for storage.

[0130] The cooling capacity providing unit (heat exchange unit) is provided by the cooling capacity provided by the gas phase of the liquid helium tank and the cooling capacity provided by the crude helium liquefaction unit and the pure helium liquefaction unit which are diverted to the turbine expander flow stream.

[0131] The crude helium liquefaction system provided in this embodiment uses crude helium with a high helium content after cryogenic condensation as the raw gas, and is suitable for crude helium obtained by cryogenic condensation of natural gas or liquefied natural gas boil-off gas.

[0132] The crude helium liquefaction process provided in this embodiment is described in detail below using crude helium after cryogenic distillation as the raw gas:

[0133] The feed gas pressure is 1.3 MPa, the temperature is -198.8°C, and the processing capacity is 9.058 kmol / h. The main components of the feed gas are hydrogen (1.73%), nitrogen (9.83%), helium (88.4%), neon (0.04%) and others (0.04%).

[0134] The mainstream of the raw gas crude helium passes through the second heat exchanger E-2 and the third heat exchanger E-3 to be cooled to -238.8℃, and after gas-liquid separation, crude helium with a helium content of 98.08% is obtained. It is then cooled to -253.4℃ through the fourth heat exchanger E-4, and hydrogen and neon are removed to below 3ppm in a 20K low-temperature adsorber to obtain pure helium and merge with the circulating pure helium.

[0135] The reflux helium is pressurized to 1300 kPa by the circulation compressor EX0 and cooled to -195°C through the liquid nitrogen pipeline of the pure helium pre-cooling heat exchanger E-1. The mainstream undergoes the same steps as the crude helium and merges (the temperature is treated to the same level). After merging, it is cooled by the fifth heat exchanger E-5, depressurized by the fourth expander EX-4, cooled by the sixth heat exchanger E-6, and passed through the liquid helium throttle valve V1 to obtain liquid helium.

[0136] The system and method of this embodiment make it easier to achieve a lower pre-throttling temperature for pure helium in the gas phase. Generally, to achieve the same temperature in the Collins cycle, the temperature of the produced liquid helium decreases, reducing the post-throttling gas phase and resulting in insufficient cooling capacity. In this embodiment, the system can directly process the crude helium gas phase generated after cryogenic condensation of natural gas or from liquefied natural gas boil-off, integrating the crude helium and reflux helium into a single cold box. Additional cooling capacity is provided at the fourth heat exchanger E-4, reducing the flow rate required by the final-stage expander EX-4, thereby minimizing heat exchanger exergy losses and maximizing cooling capacity utilization. The final-stage heat exchanger uses the third expander EX-3 to provide a stream of cooling capacity, so that it is not solely affected by the amount of flashed cryogenic helium. An expander is used before the sixth heat exchanger E-6 to reduce pressure and temperature, thereby increasing the helium liquefaction rate and minimizing energy losses.

[0137] Example 5

[0138] See attached Figure 5 This embodiment provides a crude helium purification and liquefaction circulation system based on cryogenic distillation, comprising a crude helium liquefaction unit, a pure helium circulation liquefaction unit, and a refrigeration supply unit. This system, based on Example 4, adds a set of reverse Brayton refrigeration stages, consisting of a heat exchanger Ea, a heat exchanger Eb, and an expander EX-a. The arrangement of the reverse Brayton refrigeration stages reduces the inlet and outlet temperature difference of the heat exchanger itself, facilitating construction. The specific system structure is as follows:

[0139] The crude helium liquefaction unit has a first pipeline. The crude helium enters the first pipeline from the helium extraction tower in the gas phase and passes through the 77K low-temperature adsorber P1, the second heat exchanger E-2, the gas-liquid separator P2, the third heat exchanger E-3, the heat exchanger Ea, the three-way splitter Ea, the heat exchanger Eb, the three-way second splitter S2-1, the fourth heat exchanger E-4, the first 20K adsorber P3-1, the three-way third mixer M-3, the fifth heat exchanger E-5, the three-way third splitter S-3, the turbine fourth expander EX-4, the sixth heat exchanger E-6, the liquid helium throttle valve V1 and the liquid helium tank C1.

[0140] In the pure helium circulation liquefaction unit, the pure helium pipeline feed is the cold stream outlet stream of the post-circulation heat exchanger E-2. It then passes through the reflux compressor EX0, the pure helium pre-cooling heat exchanger E-1, the second heat exchanger E-2, the first three-way splitter S-1, the third heat exchanger E-3, the heat exchanger Ea, the three-way splitter Sa, the heat exchanger Eb, the second three-way splitter S2-2, the fourth heat exchanger E-4, the third three-way mixer M-3, and finally merges into the first pipeline through the third three-way mixer M-3. A liquid nitrogen pipeline is connected in parallel to the pure helium pre-cooling heat exchanger E-1.

[0141] The cold supply unit has a cold supply pipeline, which is sequentially connected to the three-way first mixer M-1, the sixth heat exchanger E-6, the fifth heat exchanger E-5, the four-way second mixer M-2, the fourth heat exchanger E-4, the three-way mixer Ma, the heat exchanger Eb, the heat exchanger Ea, the three-way fourth mixer M-4, the third heat exchanger E-3 and the second heat exchanger E-2, and enters the pure helium pipeline as a cold flow outlet stream after passing through the second heat exchanger E-2;

[0142] The local cooling circuit is arranged at:

[0143] On the sixth heat exchanger E-6, the arrangement is the same as in Example 4;

[0144] On the fourth heat exchanger E-4, the arrangement is the same as in Example 4;

[0145] On the third heat exchanger E-3, the arrangement is the same as in Example 4;

[0146] In the reverse Brayton refrigeration stage, the liquid helium pipeline passes through the heat exchanger Ea, and a cold flow is diverted by the three-way splitter Sa to enter the expander EX-a, and then enters the three-way mixer Ma and re-merges into the cold flow pipeline to enter the heat exchanger Eb.

[0147] The crude helium purification and liquefaction circulation system based on cryogenic distillation provided in this embodiment specifically operates as follows:

[0148] When the mainstream of the crude helium liquefaction unit passes through the 77K low-temperature adsorber P1, a large amount of nitrogen components are removed, and then it flows through each stage of heat exchangers to be cooled in sequence. When the temperature of each stage of heat exchangers is cooled, some impurities are removed by the gas-liquid separator P2. When the temperature drops below 20K, some hydrogen and neon that are difficult to remove by low temperature are removed to extremely low content when passing through the first 20K adsorber P3-1 and the second 20K adsorber P3-2, and then it is merged into the helium reflux stream of the first pipeline.

[0149] The mainstream of the pure helium liquefaction unit is compressed by the reflux compressor and pre-cooled with liquid nitrogen in the pure helium pre-cooling heat exchanger E-1. It is cooled in sequence through each heat exchanger and merged into the first pipeline. It is expanded to a preferred pre-throttling pressure by the turbine fourth expander EX-4 before the sixth heat exchanger E-6. It is cooled by the sixth heat exchanger E-6 and throttled by the liquid helium throttle valve V1 before entering the liquid helium tank C1 for storage.

[0150] The cooling capacity providing unit is provided by the cooling capacity provided by the gas phase of the liquid helium tank and the crude helium liquefaction unit and the pure helium liquefaction unit, which are diverted to the turbine fourth expander EX-4, the turbine third expander EX-3, the turbine second expander EX2-1, the turbine second expander EX2-2, the turbine first expander EX-1, and the expander EX-a stream.

[0151] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A crude helium purification and liquefaction circulation system based on cryogenic distillation, characterized in that: It includes a crude helium liquefaction unit, a pure helium circulation liquefaction unit and a cold supply unit; The crude helium liquefaction unit comprises a first pipeline, the first pipeline connecting the raw gas inlet and the inlet of the liquid helium throttle valve (V1), a multi-stage crude helium purification device and a multi-stage heat exchange device connected in series between the raw gas inlet and the liquid helium throttle valve (V1), the outlet of the last-stage gas purification device connected to the third mixer (M-3), and the outlet of the third mixer (M-3) connected to the next-stage heat exchanger; the fourth expander (EX-4) is connected before the liquid helium throttle valve (V1), and the end of the first pipeline is connected to the inlet of the liquid helium tank (C1); The pure helium circulation liquefaction unit comprises a pure helium pipeline, which passes through at least one stage of the multi-stage heat exchange device; the end of the pure helium pipeline is connected to the third mixer (M-3) and merged into the first pipeline; The cold supply unit includes a cold supply pipeline, which is reversely connected to the multi-stage heat exchange device on the first pipeline, and a local cold supply loop is provided on at least one stage of the heat exchange device; a splitter is provided at the front end of the first pipeline inlet and / or the pure helium pipeline inlet of the at least one stage of the heat exchange device, and the splitter outlet is connected to the expander through the cold supply pipeline, the expander outlet is connected to the cold supply pipeline inlet of the heat exchange device, and the cold supply pipeline outlet of the heat exchange device is connected to the cold supply pipeline, thereby forming the local cold supply loop; The end of the cooling pipeline is connected to the beginning of the pure helium pipeline through the first-stage heat exchanger in the multi-stage heat exchange device, and the gas phase outlet of the liquid helium tank (C1) is connected to the cooling circuit; The last stage of the multi-stage heat exchange device is the sixth heat exchanger (E-6), and the sixth heat exchanger (E-6) is provided with a local cooling circuit; The front end of the first pipeline inlet of the sixth heat exchanger (E-6) is connected to the third splitter (S-3), and the split outlet of the third splitter (S-3) is connected to the cold pipeline inlet of the sixth heat exchanger (E-6) through the cold pipeline; the third expander (EX-3) and the first mixer (M-1) are connected in series between the third splitter (S-3) and the sixth heat exchanger (E-6), and the gas phase outlet of the liquid helium tank (C1) is connected to the inlet of the first mixer (M-1); the inlet of the third splitter (S-3) is connected to the outlet of the third mixer (M-3), and the cold pipeline outlet of the sixth heat exchanger (E-6) is connected to the cold pipeline.

2. The crude helium purification and liquefaction circulation system based on cryogenic distillation according to claim 1, characterized in that: The sixth heat exchanger (E-6) is provided on the first pipeline between the fourth expander (EX-4) and the liquid helium throttle valve (V1).

3. The crude helium purification and liquefaction circulation system based on cryogenic distillation according to claim 1, characterized in that: The multi-stage heat exchange device includes a fifth heat exchanger (E-5), which is connected in series on the first pipeline between the third mixer (M-3) and the third splitter (S-3).

4. The crude helium purification and liquefaction circulation system based on cryogenic distillation according to claim 1, characterized in that: The multi-stage heat exchange device includes a fourth heat exchanger (E-4), and the first pipeline, the pure helium pipeline and the cold pipeline pass through the fourth heat exchanger (E-4); the cold pipeline inlet of the fourth heat exchanger (E-4) is connected to the outlet of the second mixer (M-2), and the cold pipeline is connected to the inlet of the second mixer (M-2).

5. The crude helium purification and liquefaction circulation system based on cryogenic distillation according to claim 4, characterized in that: The fourth heat exchanger (E-4) is provided with a first local cooling circuit; The first pipeline inlet of the fourth heat exchanger (E-4) is connected to the second splitter (S2-1), and the split outlet of the second splitter (S2-1) is connected to the inlet of the second mixer (M-2); the second expander (EX2-1) and the second 20K adsorber (P3-2) are connected in series between the second splitter (S2-1) and the second mixer (M-2); The first pipeline outlet of the fourth heat exchanger (E-4) is connected to the first 20K adsorber (P3-1).

6. The crude helium purification and liquefaction circulation system based on cryogenic distillation according to claim 4 or 5, characterized in that: The fourth heat exchanger (E-4) is provided with a second local cooling circuit; The pure helium pipeline inlet of the fourth heat exchanger (E-4) is connected to the second splitter (S2-2), and the splitter outlet of the splitter (S2-2) is connected to the inlet of the second mixer (M-2); a second series expander (EX2-2) is connected between the second splitter (S2-2) and the second mixer (M-2).

7. The crude helium purification and liquefaction circulation system based on cryogenic distillation according to claim 1, characterized in that: The multi-stage heat exchange device includes a third heat exchanger (E-3), and a local cooling circuit is provided on the third heat exchanger (E-3); The front end of the pure helium pipeline inlet of the third heat exchanger (E-3) is connected to the first splitter (S-1), the split outlet of the first splitter (S-1) is connected to the inlet of the fourth mixer (M-4), and the outlet of the fourth mixer (M-4) is connected to the cold capacity pipeline inlet of the third heat exchanger (E-3); a first expander (EX-1) is connected in series between the first splitter (S-1) and the inlet of the fourth mixer (M-4); The cooling pipeline is connected to the inlet of the fourth mixer (M-4), and a gas-liquid separator (P2) is provided at the front end of the first pipeline inlet of the third heat exchanger (E-3).

8. The crude helium purification and liquefaction circulation system based on cryogenic distillation according to claim 1, characterized in that: A pure helium precooling heat exchanger (E-1) is connected to the pure helium pipeline at the front end of the first-stage heat exchanger. The pure helium precooling heat exchanger (E-1) is connected in parallel with a liquid nitrogen pipeline, and the liquid nitrogen pipeline is connected to a liquid nitrogen valve (V0).

9. A crude helium purification and liquefaction circulation method based on cryogenic distillation, based on the crude helium purification and liquefaction circulation system based on cryogenic distillation according to any one of claims 1 to 8, characterized in that: include: After the raw gas enters the first pipeline, it passes through a multi-stage crude helium purification device and a multi-stage heat exchange device in sequence to achieve purification and initial cooling of the raw gas, turning it into pure helium in gas-liquid two-phase; Pure helium in both gas and liquid phases enters the liquid helium tank, where the helium gas merges with the cooling pipeline through the gas phase outlet of the liquid helium tank. The cooling pipeline passes through the multi-stage heat exchange device on the first pipeline. The flow direction of the stream in the cooling pipeline is opposite to that of the raw gas in the first pipeline. The purified raw gas is split by the splitter in the first pipeline, and the cooling energy is obtained by the expander and then merged into the cooling pipeline. The end of the cooling pipeline enters the pure helium pipeline after heat exchange in the first-stage heat exchange device. The pure helium pipeline passes through some heat exchange devices on the first pipeline and merges with the first pipeline after the raw gas in the first pipeline is purified. It enters the next-stage heat exchange device and finally enters the liquid helium tank. The pure helium pipeline is split by the splitter and also obtains cooling energy through the expander and then enters the cooling pipeline. The cooling pipeline is fed from the first pipeline and the liquid helium pipeline into the expansion mechanism to refrigerate the cooling capacity, and cools the parallel first pipeline and / or pure helium pipeline in the heat exchanger.

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