A low-temperature distillation system and process using a small-scale refrigerator

Abstract

This invention discloses a low-temperature distillation system and process using a small-scale refrigerator, comprising: a fan inlet connected to a filter, and a fan outlet sequentially connected to a water-cooled heat exchanger, a dryer, and a buffer tank; a pre-cooling-purification module including two heat exchangers and equipped with a dry compressed gas inlet, a cold purified gas outlet, a column bottom waste liquid inlet, and a waste gas outlet; the dry compressed gas inlet is connected to the buffer tank; a single-stage distillation column has a feed inlet and a waste liquid outlet at the column bottom, respectively connected to the cold purified gas outlet and the column bottom waste liquid inlet; a high-purity gas outlet and a reflux outlet are located at the top of the column; the inlet of the small-scale refrigerator is connected to the high-purity gas outlet, and the liquid outlet is positioned above the top of the single-stage distillation column, with a T-connector connected after the liquid outlet, one end connected to the reflux outlet at the top of the single-stage distillation column, and the other end connected to the system product outlet. This invention solves the problems of low product extraction rate and large irreversible heat loss in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature distillation and air separation, and in particular relates to a low-temperature distillation system and process using a small-scale refrigeration unit. Background Technology

[0002] Cryogenic liquefied gases are frequently used in aerospace, biomedicine, semiconductors, energy extraction, and animal husbandry. As the distributed supply system of the gas market continues to expand, the liquefied gases used by users are mainly produced centrally by large air separation companies and then distributed and transported via cryogenic tank trucks or cryogenic Dewar flasks. During long-distance transportation, the loss rate of liquefied gas is very high. This will significantly increase the operating costs of cryogenic liquefiers for applications with long-term but low-volume usage, or in remote areas with poor transportation conditions.

[0003] Taking liquid nitrogen, the most widely used cryogenic liquefied gas, as an example, current small-scale liquefaction equipment typically uses pressure swing adsorption (PSA) or membrane separation technology to purify nitrogen from the air, and then uses a regenerative refrigeration unit to liquefy the nitrogen.

[0004] For example, Chinese patent document CN112142017A discloses a nitrogen preparation device based on pressure swing adsorption separation technology; Chinese patent document CN107739024A discloses a process for preparing nitrogen by membrane separation composite method.

[0005] However, when the nitrogen purity requirement is above 99.5%, the nitrogen extraction rate of PSA technology is less than 20%, and that of membrane separation technology is even lower. Both of these nitrogen extraction rates are far lower than those of cryogenic distillation. In addition, both PSA and membrane separation technologies produce room temperature nitrogen. When this nitrogen is directly liquefied in a refrigerator, the temperature difference between the gas and the refrigerator's cold head is large, resulting in significant irreversible heat exchange losses. In contrast, cryogenic distillation produces low-temperature nitrogen at the top of the distillation column. When this nitrogen is liquefied in a refrigerator, the irreversible heat exchange losses are smaller, and the refrigerator's liquefaction efficiency is higher.

[0006] Therefore, a low-temperature distillation system using a small refrigeration unit is proposed, which features low operating pressure, compact structure, easy skid-mounting, and high safety and reliability. Summary of the Invention

[0007] This invention provides a low-temperature distillation system and process using a small-scale refrigerator, which can solve the problems of low product extraction rate and large irreversible heat loss of the refrigerator when using PSA technology and membrane separation technology in existing small-scale liquefaction equipment. It has the advantages of low operating pressure, compact structure, easy skid-mounting, and safety and reliability.

[0008] A low-temperature distillation system employing a small-scale refrigerator includes: a filter, a fan, a water-cooled heat exchanger, a dryer, a buffer tank, a pre-cooling-purification module, a single-stage distillation column, and a small-scale refrigerator;

[0009] The air inlet of the fan is connected to a filter, and the air outlet of the fan is sequentially connected to a water-cooled heat exchanger, a dryer, and a buffer tank.

[0010] The precooling-purification module includes a first heat exchanger and a second heat exchanger, and is equipped with a dry compressed gas inlet pipe, a cold purified gas outlet pipe, a tower bottom waste liquid inlet pipe and a system waste gas discharge pipe; wherein, the buffer storage tank is connected to the dry compressed gas inlet pipe, and a first flow regulating valve is connected in the middle.

[0011] The single-stage distillation column is loaded with high-efficiency random packing. It has an inlet and a waste liquid outlet at the bottom of the column, which are respectively connected to the cold purified gas outlet pipe and the waste liquid outlet pipe of the precooling-purification module. A second flow regulating valve is connected between the waste liquid outlet pipe and the waste liquid inlet pipe. It has a high-purity gas outlet and a reflux port at the top of the column, which are respectively connected to the high-purity gas outlet pipe and the reflux liquid pipe at the top of the single-stage distillation column.

[0012] The air inlet of the small refrigerator is connected to the high-purity gas outlet pipe at the top of the single-stage distillation column; the liquid outlet of the small refrigerator is positioned higher than the top of the single-stage distillation column, and an eleven-way tee is connected after the liquid outlet. One end is connected to the reflux port at the top of the single-stage distillation column through the reflux liquid pipe, and the other end is connected to the system product pipe through the third flow regulating valve.

[0013] Furthermore, the precooling-purification module also includes ten solenoid valves and ten three-way valves, namely solenoid valves No. 1, No. 2, No. 3, No. 4, No. 5, No. 6, No. 7, No. 8, No. 9, and No. 10; and three-way valves No. 1, No. 2, No. 3, No. 4, No. 5, No. 6, No. 7, No. 8, No. 9, and No. 10; each three-way valve has three interfaces: A, B, and C.

[0014] The dry compressed gas inlet pipe is connected to port A of the No. 1 tee, and the corresponding ports B and C are connected to the No. 1 solenoid valve and the No. 2 solenoid valve, respectively, and then connected to the port A of the corresponding No. 2 tee and the No. 9 tee; the ports B of the No. 2 tee and the No. 9 tee are connected to the hot runner inlets of the first heat exchanger and the second heat exchanger, respectively; the port C of the No. 2 tee is sequentially connected to the No. 10 solenoid valve, the No. 10 tee, the No. 9 solenoid valve, and the port C of the No. 9 tee; the port C of the No. 10 tee is connected to the exhaust gas discharge pipe.

[0015] The hot runner outlets of the first and second heat exchangers are connected to port A of the No. 3 tee and the No. 8 tee, respectively. Port B of the No. 3 tee and the No. 8 tee are connected to the No. 3 solenoid valve and the No. 4 solenoid valve, respectively. After the valves, they are connected to ports A and B of the No. 4 tee, respectively. Port C of the No. 4 tee is connected to the cold purified gas outlet pipe.

[0016] The waste liquid inlet pipe of the tower bottom is connected to port A of the No. 5 tee. Ports B and C of the No. 5 tee are connected to solenoid valves No. 5 and No. 6, respectively. After the solenoid valves, ports A of the No. 6 tee and No. 7 tee are connected. Ports B of the No. 6 tee and No. 7 tee are connected to the cold flow channel inlets of the first heat exchanger and the second heat exchanger, respectively. Solenoid valve No. 8 is connected between ports C of the No. 3 tee and the No. 6 tee, and solenoid valve No. 7 is connected between ports C of the No. 7 tee and the No. 8 tee. The cold flow channel outlets of the first heat exchanger and the second heat exchanger are connected by pipes.

[0017] Furthermore, the operation process of the pre-cooling-purification module is as follows:

[0018] The first heat exchanger and the second heat exchanger are in the pre-cooling-purification working state and the reheating purging state respectively during operation, and a single heat exchanger switches between these two states.

[0019] Solenoid valves 1, 3, 5, 7, and 9 are open, while the remaining solenoid valves are closed. At this time, the first heat exchanger is in pre-cooling-purification mode, and the second heat exchanger is in reheating and purging mode. Dry compressed gas, as a hot fluid, enters this module through the first flow regulating valve, and then enters the hot flow channel of the first heat exchanger via the 1-way valve, 1 solenoid valve, and 2-way valve for pre-cooling-purification. Here, substances with higher freezing points will gradually precipitate and accumulate in the heat exchanger channel. The remaining pre-cooled gas passes through the 3-way valve, 3 solenoid valve, and 4-way valve. The cold fluid flows out of this module via the No. 5 tee, the No. 5 solenoid valve, and the No. 6 tee into the module and is heated in the cold flow channel of the first heat exchanger. After being reheated, it flows to the cold flow channel of the second heat exchanger, indirectly heating the solid material frozen in the hot flow channel of the second heat exchanger to thaw the solid blockage. The fluid after heat exchange flows in reverse into the hot flow channel of the second heat exchanger via the No. 7 tee, the No. 7 solenoid valve, and the No. 8 tee to purge the thawed gaseous material. Finally, it flows out of the system as system exhaust gas via the No. 9 tee, the No. 9 solenoid valve, and the No. 10 tee.

[0020] When the substances to be removed precipitate for a certain period of time, causing blockage in the first heat exchanger channel, the operating state of the heat exchanger is switched. At this time, solenoid valves No. 2, No. 4, No. 6, No. 8, and No. 10 are opened, while the remaining solenoid valves are closed. The first heat exchanger is in the reheating and purging state, and the second heat exchanger is in the precooling-purification state. Dry compressed gas, as a hot fluid, enters this module through the first flow regulating valve, and then enters the hot flow channel of the second heat exchanger through the No. 1 three-way valve, the No. 2 solenoid valve, and the No. 9 three-way valve for precooling-purification. Here, substances with higher freezing points will gradually precipitate and accumulate in the heat exchanger channel. After pre-cooling, the gas flows out of the module through the No. 8 three-way valve, the No. 4 solenoid valve, and the No. 4 three-way valve. The cold fluid enters the module and then enters the cold flow channel of the second heat exchanger through the No. 5 three-way valve, the No. 6 solenoid valve, and the No. 7 three-way valve to be heated. After reheating, it flows to the cold flow channel of the first heat exchanger to indirectly heat the solid material frozen in the hot flow channel of the first heat exchanger, thereby thawing the solid blockage. The fluid after heat exchange flows back into the hot flow channel of the first heat exchanger through the No. 6 three-way valve, the No. 8 solenoid valve, and the No. 3 three-way valve to purge the thawed gaseous material. Finally, it flows out of the system as system exhaust gas through the No. 2 three-way valve, the No. 10 solenoid valve, and the No. 10 three-way valve.

[0021] The cold runner and hot runner mentioned above are defined by the temperature of the fluid flowing in the pipe when the heat exchanger is in the pre-cooling-purification working state.

[0022] Furthermore, the fan is a blower equipped with a frequency converter. The dryer uses hygroscopic materials such as silica gel and activated alumina.

[0023] Furthermore, the high-efficiency random packing is Dixon packing, Canon packing, or Finsk packing.

[0024] Furthermore, the small refrigerator is a Stirling refrigerator, a GM refrigerator, a Stirling-type pulse tube refrigerator, or a GM-type pulse tube refrigerator.

[0025] Furthermore, the precooling-purification module and the single-stage distillation column both adopt high-vacuum multi-layer insulation technology and are installed in a vacuum-insulated cold box; the inlet and outlet of each pipeline and the wall of the cold box adopt a heat insulation structure.

[0026] Furthermore, the single-stage distillation column is composed of detachable column sections with connecting joints, and gas purity detection ports are arranged along the column height.

[0027] A low-temperature distillation process using a small-scale refrigerator, employing the aforementioned low-temperature distillation system using a small-scale refrigerator, includes the following steps:

[0028] After large particulate impurities are removed by the filter, the raw gas is pressurized and introduced into the air by the action of the blower; the resulting compressed gas is pre-cooled to room temperature by the water-cooled heat exchanger and then enters the dryer for dehydration and enters the buffer storage tank for temporary storage.

[0029] The dry compressed gas in the buffer tank enters the precooling-purification module as a hot fluid after the flow rate is regulated by the first flow regulating valve. The waste liquid in the bottom of the single-stage distillation column also enters the precooling-purification module as a cold fluid after the flow rate is controlled by the second flow regulating valve. The two exchange heat in the same heat exchanger, which is in the precooling-purification working state. The hot fluid needs to ensure that the temperature after cooling is lower than the precipitation temperature of the substance to be removed in order to achieve the purpose of purification. The cold fluid is reheated to above 0°C and then goes to another heat exchanger in the precooling-purification module to indirectly reheat and thaw the blockage. Finally, it flows to the frozen area to purge it out of the system.

[0030] The cold purified gas enters the single-stage distillation column, where it undergoes full heat and mass transfer with the reflux liquid from the top of the column on the surface of the high-efficiency random packing, realizing the distillation process within the column. The high-purity gas obtained from the purification at the top of the column is directly fed to the cold head of the small refrigerator for further cooling and condensation. The low-temperature liquid obtained from the outlet of the refrigerator is divided into two streams. Relying on the gravity of the liquid itself, one stream is returned to the column as the reflux liquid of the single-stage distillation column, and the other stream is produced as the system product.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention uses a blower instead of a traditional air compressor to maintain the operating pressure of the entire system at a level slightly higher than atmospheric pressure, which greatly reduces the energy consumption of the air intake equipment. In addition, the low air intake pressure results in a less significant increase in gas temperature, which reduces the power consumption of the compressed gas cooling equipment. In fact, this equipment can be omitted when the ambient temperature is not high.

[0033] 2. This invention designs a pre-cooling-purification module based on freeze-drying, utilizing the system's own flow stream to fully recover system cooling capacity while maintaining a compact size. Employing low-temperature distillation technology instead of room-temperature adsorption, the system achieves higher product extraction rates. Simultaneously, the high-purity gas obtained through distillation is in a low-temperature saturated state, resulting in a small temperature difference for heat exchange with the refrigerator's cold head, minimizing irreversible losses and increasing the refrigerator's liquefaction efficiency.

[0034] 3. This invention leverages the superior performance of existing small-scale chillers, ensuring the chiller outlet is higher than the top of the column in the layout. Recirculation is achieved by gravity, eliminating the need for additional pumps and other equipment, thus reducing system construction costs and process equipment energy consumption. Using a small-scale cryogenic chiller instead of an expander to provide cooling for the liquefaction system results in lower equipment noise, wider applicability, and facilitates equipment miniaturization. The distillation column employs a detachable, removable section design, facilitating the filling of the column packing and the disassembly and relocation of the system. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a low-temperature distillation system using a small refrigerator according to the present invention;

[0036] Figure 2 This is a schematic diagram of the pre-cooling-purification module in this invention. Detailed Implementation

[0037] 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.

[0038] like Figure 1 As shown, a low-temperature distillation process using a small-scale refrigerator includes a filter F101, a fan C101, a water-cooled heat exchanger H101, a dryer D101, a buffer tank G101, a pre-cooling-purification module YL-CH101, a single-stage distillation column T101, a small-scale refrigerator CR101, and a high-efficiency random packing CF101.

[0039] Taking a small-scale cryogenic distillation nitrogen production system using a high-capacity Stirling refrigerator as an example, the raw material air enters the filter F101 through pipe 101. Large particulate impurities in the raw material air are discharged from the system through pipe 103. The purified gas is then compressed and introduced into the system by the blower C101 through pipe 102. The compressed air from the blower outlet is cooled to room temperature by the water-cooled heat exchanger H101 through pipe 104. The cooling water is circulated between pipes 201 and 202 and the chiller unit. Due to the low operating pressure, the gas temperature rise is not significant. Under suitable ambient temperature conditions, this area can also be replaced by natural cooling of the air through finned tubes. The compressed air cooled to room temperature enters the dryer D101 through pipe 105, where the moisture is removed by the internal hygroscopic material, becoming dry compressed air. It then enters the buffer storage tank G101 through pipe 106 for temporary storage. Dry compressed air, after passing through pipeline 107, has its flow rate regulated by the first flow regulating valve V101. It then enters the pre-cooling-purification module YL-CH101 via the dry compressed gas inlet pipeline 108. Within this module, the dry compressed air is pre-cooled to below the CO2 precipitation temperature by the oxygen-rich liquid air discharged from the column bottom. This achieves full recovery of the cold energy from the column bottom waste liquid while freezing the CO2 in the feed gas, resulting in dry and pure compressed air. This air leaves the module via the cold purified gas outlet pipeline 109 and enters the single-stage distillation column T101. The cold purified gas flows upward within the single-stage distillation column T101, where it undergoes thorough heat and mass transfer with the liquid nitrogen refluxed from the top of the column on the surface of the high-efficiency random packing CF101. Along the column height, the purity of the light nitrogen component gradually increases, achieving a nitrogen purity greater than 99.5% at the top of the column, thus completing the distillation process.

[0040] High-purity nitrogen gas enters the cold head of the small refrigeration unit CR101 directly through the high-purity gas outlet pipe 110 at the top of the column, where it is cooled and liquefied. The resulting liquid nitrogen is divided into two streams by the No. 11 tee M111 after passing through pipe 111 at the outlet of the refrigeration unit. One stream flows back through the reflux liquid pipe 112, relying on gravity due to the position of the refrigeration unit outlet above the top of the column. The other stream flows through pipe 113, and the flow rate is regulated by the third flow regulating valve V103 before being discharged as liquid nitrogen product through the product pipe 114. The oxygen-enriched liquid air from the bottom of the distillation column flows into the precooling-purification module YL-CH101 through the bottom waste liquid outlet pipe 115, the second flow regulating valve V102, and the bottom waste liquid inlet pipe 116. In the heat exchanger within the module, it serves as a cold source and purge gas, and is ultimately discharged as system waste gas.

[0041] like Figure 2 The diagram shows the structure of the precooling-purification module, including a first heat exchanger H102, a second heat exchanger H103, ten three-way valves, and ten solenoid valves. During operation, the two heat exchangers alternate between precooling-purification and reheating / purging states. In the following description, cold and hot flow channels are defined by the fluid temperature flowing through them when the heat exchangers are in the precooling-purification state; any solenoid valves not mentioned are in the closed state.

[0042] When the first heat exchanger H102 is in pre-cooling-purification operation and the second heat exchanger H103 is in reheating and purging operation: Dry compressed air, after flow control, enters this module through the dry compressed gas inlet pipe 108, passes through the No. 1 tee M101, pipe 301, No. 1 solenoid valve KV01, pipe 302, No. 2 tee M102, and pipe 303, and enters the hot runner of the first heat exchanger H102 for pre-cooling. The pre-cooled gas then flows out of the module through pipe 304, No. 3 tee M103, pipe 305, No. 3 solenoid valve KV03, pipe 306, and No. 4 tee M104, and goes to the single-stage distillation column T101 through the cold purified gas outlet pipe 109. The oxygen-enriched liquid air from the bottom of the single-stage distillation column T101 enters this module through the bottom waste liquid inlet pipe 116, passes through the No. 5 tee M105, pipe 401, and No. 5 solenoid valve KV05. Pipes 402, M106 (6-way tee), and 403 enter the cold flow channel of the first heat exchanger H102 and are heated. The reheated oxygen-enriched air flows through pipe 404 to the cold flow channel of the second heat exchanger H103, indirectly heating the CO2 frozen in the hot flow channel of the second heat exchanger H103 to thaw the solid CO2. The oxygen-enriched air after heat exchange flows in the opposite direction into the hot flow channel of the second heat exchanger H103 through pipes 405, M107 (7-way tee), 406, KV07 (7-way solenoid valve), 407, M108 (8-way tee), and 310 to purge the thawed CO2. Finally, the oxygen-enriched air carrying CO2 flows out of the system as system exhaust gas through pipes 309, M109 (9-way tee), 408, KV09 (9-way solenoid valve), 409, M110 (10-way tee), and system exhaust gas discharge pipe 410.

[0043] After a certain interval, CO2 blockage occurs in the flow channel of the first heat exchanger H102. The solenoid valve is switched to change the heat exchanger state, placing the first heat exchanger H102 in the reheating and purging state, and the second heat exchanger H103 in the pre-cooling and purification state. At this time, dry compressed air, after flow control, enters the module through the dry compressed gas inlet pipe 108, passes through the first three-way valve M101, pipe 307, the second solenoid valve KV02, and pipe 30... 8. Gas is pre-cooled in the hot runner of the second heat exchanger H103 via No. 9 tee M109 and pipe 309. After pre-cooling, the gas flows out of the module via pipe 310, No. 8 tee M108, pipe 311, No. 4 solenoid valve KV04, pipe 312, and No. 4 tee M104, and goes to the single-stage distillation column T101 via the cold purified gas outlet pipe 109. The oxygen-enriched liquid air from the bottom of the single-stage distillation column T101 enters the module via the bottom waste liquid inlet pipe 116, and then... The oxygen-enriched air, connected to T-joint M105 (No. 5), pipe 411, solenoid valve KV06 (No. 6), pipe 412, T-joint M107 (No. 7), and pipe 405, enters the cold flow channel of the second heat exchanger H103 and is heated. The reheated oxygen-enriched air then flows through pipe 404 to the cold flow channel of the first heat exchanger H102, indirectly heating the CO2 frozen in the hot flow channel of the first heat exchanger H102, thus thawing the solid CO2. The oxygen-enriched air then flows through pipe 403, T-joint M105, and solenoid valve KV06 (No. 6), pipe 412, and solenoid valve M107 (No. 7), pipe 405. Pipe 413, No. 8 solenoid valve KV08, pipe 414, No. 3 tee M103, and pipe 304 flow in reverse into the hot runner of the first heat exchanger H102 to purge the thawed CO2. Finally, the oxygen-enriched air carrying CO2 flows out of the system as system exhaust gas through pipe 303, No. 2 tee M102, pipe 415, No. 10 solenoid valve KV10, pipe 416, No. 10 tee M110, and system exhaust gas discharge pipe 410.

[0044] According to the above system flow, the raw material air is compressed to an absolute pressure of 0.16 MPa by the blower C101, and the inlet flow rate is adjusted to 16.9–17.7 kg / h. After precooling by the precooling-purification module YL-CH101, the temperature range of the raw material gas is -179.8℃ to -189.2℃, which can achieve efficient atmospheric pressure distillation. Finally, a liquid nitrogen yield of approximately 10.38 L / h can be achieved, and the system's specific power consumption can be as low as 1.11 kW·h / L. LN2 .

[0045] This invention uses a blower as the air intake device for the entire distillation system. Compared with traditional high-pressure-ratio compressors, the air intake energy consumption is significantly reduced. At the same time, the temperature rise of the feed gas after intake is not significant, which can reduce the energy consumption of the chiller unit. In cases where the ambient temperature is low, this equipment can be eliminated. A pre-cooling-purification module is used to efficiently recover and utilize the cold energy of the waste liquid in the distillation column bottom. CO2 is removed while pre-cooling the feed gas to achieve purification. The chiller is directly connected to the top of the distillation column, and the reflux liquid is sent directly back to the top of the column by gravity, further reducing system costs and energy consumption. A small chiller is used to provide cooling for the entire distillation system, which can reduce equipment noise and avoid the problem of low recovery rate of expansion work in small systems. The use of high-efficiency random packing for distillation and purification, combined with the structure of the column section quick-connection, facilitates equipment miniaturization and disassembly and transportation.

[0046] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cryogenic rectification system employing a small refrigeration machine, characterized by, The application relates to a high-purity gas production system. The air inlet of the fan (C101) is connected with the filter (F101), the air outlet of the fan (C101) is sequentially connected with the water-cooled heat exchanger (H101), the dryer (D101) and the buffer storage tank (G101), the pre-cooling-purification module (YL-CH101) comprises a first heat exchanger (H102) and a second heat exchanger (H103), and is provided with a dry compressed gas inlet pipeline (108), a cold-state purified gas outlet pipeline (109), a tower kettle waste liquid inlet pipeline (116) and a system waste gas discharge pipeline (410); the buffer storage tank (G101) is connected with the dry compressed gas inlet pipeline (108) and is connected with the first flow regulating valve (V101) in the middle. The single-stage rectifying tower (T101) is loaded with high-efficiency scattered pile (CF101), is provided with a feeding port and a waste liquid outlet at the tower kettle position, the feeding port is connected with the cold-state purified gas outlet pipeline (109) of the pre-cooling-purification module (YL-CH101), the waste liquid outlet is connected with the tower kettle waste liquid outlet pipeline (115) of the pre-cooling-purification module (YL-CH101), the tower kettle waste liquid outlet pipeline (115) and the tower kettle waste liquid inlet pipeline (116) are connected with the second flow regulating valve (V102) in the middle, is provided with a high-purity gas outlet and a reflux port at the top position, the high-purity gas outlet is connected with the high-purity gas outlet pipeline (110) at the top of the single-stage rectifying tower (T101), the reflux port is connected with the reflux liquid pipeline (112) at the top of the single-stage rectifying tower (T101). The air inlet of the small-sized refrigerating machine (CR101) is connected with the high-purity gas outlet pipeline (110) at the top of the single-stage rectifying tower (T101), the liquid outlet of the small-sized refrigerating machine (CR101) is arranged at a position higher than the top of the single-stage rectifying tower (T101), is connected with the eleventh three-way joint (M111) after the liquid outlet, one end of the eleventh three-way joint (M111) is connected with the reflux port at the top of the single-stage rectifying tower (T101) through the reflux liquid pipeline (112), and the other end of the eleventh three-way joint (M111) is connected with the system product pipeline (114) through the third flow regulating valve (V103). ​ ​ 2. The cryogenic rectification system employing a small- scale refrigerator according to claim 1, characterized by, The pre-cooling-purification module (YL-CH101) further comprises ten electromagnetic valves and ten three-way valves, namely, a first electromagnetic valve (KV01), a second electromagnetic valve (KV02), a third electromagnetic valve (KV03), a fourth electromagnetic valve (KV04), a fifth electromagnetic valve (KV05), a sixth electromagnetic valve (KV06), a seventh electromagnetic valve (KV07), an eighth electromagnetic valve (KV08), a ninth electromagnetic valve (KV09), and a tenth electromagnetic valve (KV10); a first three-way valve (M101), a second three-way valve (M102), a third three-way valve (M103), a fourth three-way valve (M104), a fifth three-way valve (M105), a sixth three-way valve (M106), a seventh three-way valve (M107), an eighth three-way valve (M108), a ninth three-way valve (M109), and a tenth three-way valve (M110); each three-way valve is provided with A, B, and C three interfaces; The dry compressed gas inlet pipeline (108) is connected to the A port of the first three-way valve (M101), the B port of the first three-way valve (M101) is connected to the first electromagnetic valve (KV01) and then connected to the A port of the second three-way valve (M102), and the C port of the first three-way valve (M101) is connected to the second electromagnetic valve (KV02) and then connected to the A port of the ninth three-way valve (M109); the B port of the second three-way valve (M102) is connected to the hot flow channel inlet of the first heat exchanger (H102), and the B port of the ninth three-way valve (M109) is connected to the hot flow channel inlet of the second heat exchanger (H103); the C port of the second three-way valve (M102) is sequentially connected to the tenth electromagnetic valve (KV10), the tenth three-way valve (M110), the ninth electromagnetic valve (KV09), and the C port of the ninth three-way valve (M109); and the C port of the tenth three-way valve (M110) is connected to the system waste gas discharge pipeline (410); The hot flow channel outlet of the first heat exchanger (H102) is connected to the A port of the third three-way valve (M103), the hot flow channel outlet of the second heat exchanger (H103) is connected to the A port of the eighth three-way valve (M108), the B port of the third three-way valve (M103) is connected to the third electromagnetic valve (KV03) and then connected to the A port of the fourth three-way valve (M104), the B port of the eighth three-way valve (M108) is connected to the fourth electromagnetic valve (KV04) and then connected to the B port of the fourth three-way valve (M104), and the C port of the fourth three-way valve (M104) is connected to the cold-state purified gas outlet pipeline (109); The tower kettle waste liquid inlet pipeline (116) is connected to the A port of the No. 5 tee (M105), the B port of the No. 5 tee (M105) is connected to the No. 5 electromagnetic valve (KV05) and then connected to the A port of the No. 6 tee (M106), the C port of the No. 5 tee (M105) is connected to the No. 6 electromagnetic valve (KV06) and then connected to the A port of the No. 7 tee (M107), the B port of the No. 6 tee (M106) is connected to the cold flow channel inlet of the first heat exchanger (H102), and the B port of the No. 7 tee (M107) is connected to the cold flow channel inlet of the second heat exchanger (H103); the C ports of the No. 3 tee (M103) and the No. 6 tee (M106) are connected by the No. 8 electromagnetic valve (KV08), and the C ports of the No. 7 tee (M107) and the No. 8 tee (M108) are connected by the No. 7 electromagnetic valve (KV07); the cold flow channel outlets of the first heat exchanger (H102) and the second heat exchanger (H103) are communicated by the pipeline (404).

3. The cryogenic rectification system employing a small- scale refrigerator of claim 2, wherein The working process of the precooling-purification module (YL-CH101) is as follows: The first heat exchanger (H102) and the second heat exchanger (H103) are respectively in a precooling-purification working state and a rewarming purge state during operation, and a single heat exchanger switches between the two states; The No. 1 electromagnetic valve (KV01), the No. 3 electromagnetic valve (KV03), the No. 5 electromagnetic valve (KV05), the No. 7 electromagnetic valve (KV07) and the No. 9 electromagnetic valve (KV09) are opened, and the remaining electromagnetic valves are closed, at this time, the first heat exchanger (H102) is in a precooling-purification working state, and the second heat exchanger (H103) is in a rewarming purge state; dry compressed gas as a hot fluid enters the module through the first flow regulating valve (V101), enters the first heat exchanger (H102) hot flow channel through the No. 1 tee (M101), the No. 1 electromagnetic valve (KV01) and the No. 2 tee (M102), is pre-cooled and purified, and the remaining pre-cooled gas flows out of the module through the No. 3 tee (M103), the No. 3 electromagnetic valve (KV03) and the No. 4 tee (M104); the cold fluid enters the module, enters the first heat exchanger (H102) cold flow channel through the No. 5 tee (M105), the No. 5 electromagnetic valve (KV05) and the No. 6 tee (M106), is heated, flows to the second heat exchanger (H103) cold flow channel after rewarming, indirectly heats the solid-state substances frozen in the hot flow channel of the second heat exchanger (H103), realizes thawing of the solid-state blockage, and the heat-exchanged fluid reversely flows into the hot flow channel of the second heat exchanger (H103) through the No. 7 tee (M107), the No. 7 electromagnetic valve (KV07) and the No. 8 tee (M108), and performs purge on the gaseous substances after thawing, and finally, as system waste gas, flows out of the system through the No. 9 tee (M109), the No. 9 electromagnetic valve (KV09) and the No. 10 tee (M110); When the first heat exchanger (H102) channel is blocked by the precipitated material for a certain period of time, the working state of the heat exchanger is switched, at this time, the second solenoid valve (KV02), the fourth solenoid valve (KV04), the sixth solenoid valve (KV06), the eighth solenoid valve (KV08), and the tenth solenoid valve (KV10) are opened, and the remaining solenoid valves are closed, the first heat exchanger (H102) is in a re-warming and purging state, and the second heat exchanger (H103) is in a pre-cooling and purification working state; dry compressed gas enters the module as a hot fluid through the first flow regulating valve (V101), enters the second heat exchanger (H103) through the first three-way valve (M101), the second solenoid valve (KV02), and the ninth three-way valve (M109), and is pre-cooled and purified, at this point, the material to be removed with a higher freezing point will gradually precipitate and accumulate in the heat exchanger channel, after pre-cooling, the gas flows out of the module through the eighth three-way valve (M108), the fourth solenoid valve (KV04), and the fourth three-way valve (M104); after the cold fluid enters the module, it enters the second heat exchanger (H103) through the fifth three-way valve (M105), the sixth solenoid valve (KV06), and the seventh three-way valve (M107), is heated, flows to the cold flow channel of the first heat exchanger (H102) after re-warming, indirectly heats the solid material frozen in the hot flow channel of the first heat exchanger (H102), and realizes thawing of the solid blockage; after heat exchange, the fluid flows into the hot flow channel of the first heat exchanger (H102) through the sixth three-way valve (M106), the eighth solenoid valve (KV08), and the third three-way valve (M103), and purges the gaseous material after thawing, and finally, as system waste gas, flows out of the system through the second three-way valve (M102), the tenth solenoid valve (KV10), and the tenth three-way valve (M110); The temperature of the fluid in the pipeline is defined when the heat exchanger is in a pre-cooling and purification working state.

4. The cryogenic rectification system employing a small- scale refrigerator of claim 1, wherein The fan (C101) is a blower equipped with a frequency converter.

5. The cryogenic rectification system employing a small- scale refrigerator of claim 1, wherein, The high-efficiency random packing (CF101) is a Dixon packing, a Cannon packing, or a Finke packing.

6. The cryogenic rectification system employing a small- scale refrigerator of claim 1, wherein, The small-sized refrigerator (CR101) is a Stirling refrigerator, a G-M refrigerator, a Stirling pulse tube refrigerator, or a G-M pulse tube refrigerator.

7. The cryogenic rectification system employing a small- scale refrigerator of claim 1, wherein, The pre-cooling and purification module (YL-CH101) and the single-stage rectification tower (T101) both adopt high-vacuum multi-layer insulation technology and are arranged in a vacuum insulation cold box; the inlet and outlet of each pipeline are insulated from the wall surface of the cold box.

8. The cryogenic rectification system employing a small- scale refrigerator of claim 1, wherein, The single-stage rectification tower (T101) is composed of detachable tower segment joints, and a gas purity detection port is arranged along the tower height.

9. A cryogenic rectification process employing a small scale refrigerator, characterized in that, The low-temperature rectification system using a small-sized refrigerator according to any one of claims 1-8 comprises the following processes: The raw gas after removing large-particle impurities through the filter (F101) is pressurized by the fan (C101); the obtained compressed gas is pre-cooled to room temperature by the water-cooled heat exchanger (H101), then dehydrated in the dryer (D101), and temporarily stored in the buffer storage tank (G101); Dry compressed gas in buffer tank (G101) enters pre-cooling-purification module (YL-CH101) as hot fluid through first flow regulating valve (V101) to regulate flow, waste liquid in single-stage rectification tower (T101) tank also enters pre-cooling-purification module (YL-CH101) as cold fluid through second flow regulating valve (V102) to control flow, heat transfer occurs between the two in the same heat exchanger, the heat exchanger is in pre-cooling-purification working state, and the hot fluid needs to ensure that the temperature after cooling is lower than the precipitation temperature of the substance to be removed, so as to achieve the purpose of purification, the cold fluid is then reheated to above 0℃, and then goes to another heat exchanger in pre-cooling-purification module (YL-CH101) to indirectly thaw the frozen block, and finally flows to the frozen part to blow it out of the system; Cold purified gas enters single-stage rectification tower (T101), fully exchanges heat and mass with reflux liquid at the top of the tower on the surface of high-efficiency random packing (CF101), and realizes the rectification process in the tower; the high-purity gas obtained by purification at the top of the tower is directly connected to the cold head of a small chiller (CR101) for further cooling and condensation; the low-temperature liquid obtained from the outlet of the chiller is divided into two streams, relying on the gravity of the liquid, one stream returns to the tower as reflux liquid through reflux liquid pipeline (112), and the other stream is the product output of the system.

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