A low-temperature oil-free centrifugal compressor placed in an adiabatic environment

Abstract

The application discloses a low-temperature oil-free centrifugal compressor placed in an adiabatic environment, comprising an adiabatic cold box, a centrifugal compressor unit, connecting pipelines and a vacuum pump. The centrifugal compressor is placed in the adiabatic cold box and comprises a motor, an impeller, a volute and a bearing. The impeller and the motor at two ends of the centrifugal compressor are placed in different chambers of the adiabatic cold box. The centrifugal compressor can adopt the same rotor structure at two ends. The motor does not need to be cooled. The centrifugal compressor is provided with a motor heat preservation loop. The bearing adopts a gas bearing or a gas-magnetic hybrid bearing, and the gas bearing type is full dynamic pressure, dynamic-static pressure or full static pressure. The low-temperature oil-free centrifugal compressor placed in the adiabatic environment can greatly reduce the power consumption and cold leakage loss of the compressor. The compressor with the same structure at two sides does not need to consider the axial force. Through the measures of setting different adiabatic chambers and heat preservation loops, the compressor can operate at an import temperature of -268 to -20 DEG C. The low-temperature centrifugal compressor is purely oil-free, and the system volume and weight are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of centrifugal compressor technology for cryogenic applications, and specifically designs a cryogenic oil-free centrifugal compressor placed in an adiabatic environment. Background Technology

[0002] Centrifugal compressors play a crucial role in the liquefaction of gases such as helium, air, nitrogen, neon, and hydrogen. Gas liquefaction typically involves cooling the gas to very low temperatures to transform it from a gaseous to a liquid state. During gas liquefaction, the centrifugal compressor provides the necessary pressure and energy for the refrigeration cycle by compressing the working gas to high pressure. The high-pressure gas releases heat during expansion, thus achieving cooling. Centrifugal compressors have a high energy efficiency ratio, providing large flow rates and high pressures, which helps reduce energy consumption during the working gas liquefaction process, improves overall energy efficiency, and meets the needs of large-scale production.

[0003] Conventional compressors require heating the gas to room temperature before compression. The compressed gas is then filtered to remove oil before being cooled and expanded. The system requires devices such as air temperature controllers and regenerators, which greatly increases the system cost and floor space. At the same time, the process of heating and then cooling causes significant energy loss.

[0004] Meanwhile, conventional compressors, due to their use of oil bearings, cannot operate at low ambient temperatures, resulting in high power consumption when operating at normal temperatures. Since the compressor's compression work is closely related to the inlet temperature of its working fluid, an effective way to reduce power consumption is to lower the compressor's inlet temperature. When centrifugal compressors operate in extremely low-temperature environments, the inlet temperature is extremely low, requiring the compressor to minimize heat exchange with the external environment while ensuring the compressor motor can operate normally. Therefore, this places higher demands on the compressor's structure and rotor support method. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this invention proposes a low-temperature oil-free centrifugal compressor placed in an adiabatic environment. This centrifugal compressor can operate at an inlet temperature of -268°C. Due to the presence of an adiabatic cold box and multiple chambers inside the cold box, the compressor's cold leakage is greatly reduced. At the same time, various compressors with different structural forms can meet the different needs of industrial production.

[0006] To achieve the above objectives, the present invention provides a low-temperature oil-free centrifugal compressor placed in an adiabatic environment, comprising:

[0007] The centrifugal compressor unit is placed in an insulated cold box and can operate within the inlet temperature range of -268℃ to -20℃.

[0008] The insulated cold box has multiple chambers inside;

[0009] A centrifugal compressor includes a motor, impeller, volute, and air bearing;

[0010] When a centrifugal compressor with identical structures on both sides is used, the impellers at both ends of the centrifugal compressor are the same, and the motor rotor structure is the same and symmetrically distributed. There is no need to consider axial force. At this time, the compressor does not need to be equipped with a thrust plate, and the structure is more simplified. In this case, the thrust surface is a vertical plane on the rotor main shaft that is perpendicular to the main shaft or an inclined plane that forms a certain angle with the rotor main shaft. When an inclined plane is used as the thrust surface, the thrust surface area can be increased without increasing the outer diameter of the rotor main shaft, and the rotor operation is more stable.

[0011] Centrifugal compressor motors do not require cooling when operating at low temperatures. The motor includes a stator, rotor, and end covers. The motor housing has an air inlet and an air outlet. The motor rotor is supported by air bearings.

[0012] The impellers at both ends of the centrifugal compressor and the motor in the middle are located in different chambers within the insulated cold box;

[0013] The centrifugal compressor casing is divided into a primary casing and a secondary casing. The secondary casing has an additional air passage that connects to the inside of the centrifugal compressor motor, forming a motor insulation circuit. The insulation circuit is equipped with a temperature sensor to determine the motor temperature. The direction and volume of the air passage are controlled by an electric opening regulating valve.

[0014] The centrifugal compressor is supported by gas bearings and uses a self-lubricating working fluid. The gas bearings are divided into radial bearings and thrust bearings. The bearing type can be fully dynamic, dynamic-static combined, or fully static.

[0015] Furthermore, the cryogenic centrifugal compressor can operate at an inlet temperature of -268°C, greatly reducing compressor power consumption. The working gas can be helium, air, nitrogen, neon, or hydrogen.

[0016] Furthermore, since the compressor's variable compression work is directly proportional to the intake air temperature, the expression is as follows:

[0017]

[0018] Where W is the multi-gauge compression work, m is the polytropic index, R is a constant, is the inlet temperature, and p2 / p1 is the compressor pressure ratio. When the centrifugal compressor operates at an extremely low inlet temperature, some of the cooling capacity needs to maintain the low-temperature environment. When the compression ratio remains constant, and the compressor inlet temperature is -200℃, the compressor compression work is approximately 25% of that at an inlet temperature of 20℃, which greatly reduces the compressor power consumption and saves system energy.

[0019] Furthermore, when the centrifugal compressor adopts the same structure on both sides, the compressor can be supported by only radial bearings or by radial bearings plus thrust bearings. When thrust bearings are provided, the thrust bearings are parallel to the thrust surface.

[0020] Furthermore, the impellers at both ends and the motor in the middle, located in different chambers of the insulated cold box, can be in the same vacuum environment, or in different vacuum environments, or in an environment wrapped with insulating material or perlite.

[0021] Furthermore, the cryogenic centrifugal compressor does not require motor cooling during low-temperature operation. The motor temperature is monitored by a temperature sensor installed in the insulation circuit. When the motor temperature is low, a higher-temperature gas from the secondary volute outlet is used via an electrically operated regulating valve to heat the primary and secondary compressor motors, ensuring normal motor operation. If the gas from the secondary volute outlet is insufficient to fully meet the motor's insulation needs, a separate gas storage tank can be used for auxiliary insulation of the motor casing, ensuring normal motor operation.

[0022] Furthermore, the centrifugal compressor unit can have 1-12 stages, and interstage cooling can be further provided between each stage of the compressor.

[0023] Furthermore, the centrifugal compressor unit can be composed of 1-8 centrifugal compressors with identical structures on both sides connected in parallel or 1-8 multi-stage centrifugal compressors connected in series.

[0024] Furthermore, the gas bearing is divided into radial bearing and thrust bearing. The radial bearing can be of dynamic or static type, and the thrust bearing can also be of dynamic or static type.

[0025] Furthermore, the connecting pipe is flexible to avoid the stress caused by thermal expansion and contraction.

[0026] Furthermore, the motor end is provided with a heat insulation plate, the heat insulation plate material is polytetrafluoroethylene or epoxy resin, and the compressor terminal is led out from the motor stator, through the compressor housing and the heat insulation chamber where the motor is located, and led out to the heat insulation cold box.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects:

[0028] Placing the cryogenic centrifugal compressor within an insulated cold box, with the impellers and motors at both ends housed in different chambers within the box, reduces power consumption and cold leakage during cryogenic operation. Using a centrifugal compressor with identical structures at both ends eliminates the influence of axial forces; a single two-stage centrifugal compressor results in a more compact system; and multiple two-stage compressors connected in series achieve a higher compression ratio. The insulated cold box and insulation circuit allow for motor temperature monitoring and gas flow regulation, ensuring proper motor insulation during cryogenic operation and guaranteeing normal motor performance. The different chambers within the insulated cold box enable various insulation methods and avoid large-volume vacuum extraction, reducing energy consumption. A combined mechanical and molecular pump vacuum structure achieves a higher vacuum level, further reducing cold leakage. The use of air-bearing supports enables oil-free operation of the entire system, reducing friction losses and extending service life. Attached Figure Description

[0029] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0030] Figure 1 This is a schematic diagram of a structure using two centrifugal compressors with identical structures on both sides connected in parallel;

[0031] Figure 2 This is a schematic diagram of a single two-stage centrifugal compressor.

[0032] Figure 3 This is a schematic diagram of a structure using two two-stage centrifugal compressors connected in series;

[0033] Figure 4 This is a schematic diagram of a single-stage centrifugal compressor.

[0034] Figure 5 A schematic diagram of the rotor structure and bearing arrangement of a centrifugal compressor with identical structures on both sides. Figure 1 ;

[0035] Figure 6 A schematic diagram of the rotor structure and bearing arrangement of a centrifugal compressor with identical structures on both sides. Figure 2 ;

[0036] Figure 7 A schematic diagram of the rotor structure and bearing arrangement of a centrifugal compressor with identical structures on both sides. Figure 3 ;

[0037] Figure 8 A schematic diagram of the rotor structure and bearing arrangement of a centrifugal compressor with identical structures on both sides. Figure 3 ;

[0038] Figure 9 A schematic diagram of the rotor structure and bearing arrangement of a two-stage centrifugal compressor;

[0039] Among them, 1-insulated cold box, 11-first insulated chamber, 12-second insulated chamber, 13-third insulated chamber, 14-fourth insulated chamber, 15-fifth insulated chamber, 16-sixth insulated chamber, 2-first-stage centrifugal compressor, 211-first-stage compressor stator, 212-first-stage compressor rotor, 213-first-stage compressor cover plate, 214-motor housing insulation material, 22-first-stage compressor impeller, 231-first-stage compressor radial bearing, 232-first-stage compressor thrust bearing, 233-first-stage compressor thrust plate, 24-first-stage compressor volute, 25-first-stage compressor terminal, 3-second-stage compressor, 311-second-stage compressor stator, 34-second-stage compressor... Compressor volute, 341-Second stage compressor volute opening, 35-Second stage compressor terminal, 4-Vacuum pump, 41-Mechanical pump, 42-Molecular pump, 51~55-Gas receiver, 6-Two-stage compressor 1, 611-Two-stage compressor stator, 612-Two-stage compressor rotor, 621-Two-stage compressor first-stage impeller, 622-Two-stage compressor second-stage impeller, 631-Two-stage compressor radial bearing, 632-Two-stage compressor thrust bearing, 641-Two-stage compressor first-stage volute, 642-Two-stage compressor second-stage volute, 65-Two-stage compressor terminal, 7-Two-stage compressor 2, 8-Two-stage compressor 3, 91-Temperature sensor, 92-Electric opening regulating valve. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] Example 1:

[0043] Appendix Figure 1 The attached diagram shows a structure consisting of two identical centrifugal compressors, a first-stage centrifugal compressor 2 and a second-stage centrifugal compressor 3, connected in parallel. Figure 1The structure shown completes the assembly and welding of the primary centrifugal compressor 2 and the secondary centrifugal compressor 3. The two centrifugal compressors are then placed in an insulated cold box 1 in parallel. The impellers at both ends of the primary compressor 2 are located in the first insulated chamber 11, and the motor of the primary compressor 2 is located in the second insulated chamber 12. During compressor operation, when the compressor inlet temperature is extremely low, the impellers and motor can be insulated separately by drawing different vacuum levels from the first and second insulated chambers 11 and 12. Since we want a low impeller operating temperature but not a very low motor temperature, the vacuum level in the second insulated chamber 12 can be lower than that in the first insulated chamber 11. When the centrifugal compressor inlet temperature is not extremely low, the insulated chambers do not need to be evacuated, and the impellers and motor can be encased in insulating material or perlite.

[0044] When two centrifugal compressors with identical structures on both sides are connected in parallel and operated, the working gas enters the flow channel of the first-stage compressor 1 from the inlet of the first-stage compressor volute 24, flows through the first-stage compressor impeller 22, and flows into the pipeline from the outlet of the first-stage compressor volute 24. Then, the working gas enters the flow channel of the second-stage compressor 2 from the inlet of the second-stage compressor volute 34, flows through the second-stage compressor impeller 32, and is discharged from the outlet of the second-stage compressor volute 34. After the outlet airflows of the two centrifugal compressors are combined, they are discharged from the insulated cold box 1, thus completing the compression process of the working gas.

[0045] As attached Figure 1 During the operation of the centrifugal compressor shown, since the structures on both sides of the compressor are identical, the influence of axial force can be disregarded, as illustrated in the attached diagram. Figure 5 ~Appendix Figure 8 The diagram shown illustrates the rotor structure and bearings of a centrifugal compressor with identical structures on both sides. (See attached diagram.) Figure 5 As shown, the centrifugal compressor does not require a thrust bearing; the thrust surface is an inclined surface on the rotor. Only a radial bearing 231 is needed to support the rotor's high-speed operation. This structural design can increase the thrust area without increasing the outer diameter of the main shaft, thus improving the rotor's operational stability. (See attached diagram.) Figure 6 As shown, the inclined surface on the rotor is used as the thrust surface, and a thrust bearing 232 is also provided. The thrust bearing 232 is parallel to the thrust surface of the rotor. The thrust bearing 232 and the radial bearing 231 jointly support the high-speed rotation of the rotor; as shown in the attached figure. Figure 7 As shown, the vertical surface on the rotor is used as the thrust surface, eliminating the need for a separate thrust plate. The thrust bearing 232 is located on both sides of the thrust surface, supporting the rotor's operation; as shown in the attached diagram. Figure 8 As shown, the rotor is provided with two additional thrust plates 233. The thrust plates 233 are interference-fitted with the rotor main shaft 212, and the thrust bearings 232 are located on both sides of the thrust plates.

[0046] During the operation of the centrifugal compressor, the primary compressor rotor 212, supported by a gas bearing, drives the primary compressor impeller 22 to rotate. Since both sides of the primary compressor 2 use impellers 22 with the same structure, the influence of axial force on the compressor's operation is essentially negligible. The primary compressor end cover 213 has a labyrinth seal structure to prevent gas leakage. The primary compressor end cover 213 is welded to the primary compressor housing 211 to prevent cold leakage. A heat insulation plate, made of polytetrafluoroethylene or epoxy resin, is provided at the end of the compressor motor to prevent cold leakage. The operation of the secondary compressor 3 is similar to that of the primary compressor 2, and therefore will not be described in detail.

[0047] As attached Figure 1 The insulated cold box and pipelines shown are welded together to prevent gas leakage. During operation, the centrifugal compressor experiences extremely low inlet temperatures, especially during helium liquefaction, where the inlet temperature can reach -268°C. Therefore, it is necessary to consider whether the motor can operate normally at such low temperatures. This invention incorporates a thermal insulation circuit, which includes a temperature sensor 91 and an electrically operated regulating valve 92. The temperature sensor 91 monitors the motor temperature, and the multiple electrically operated regulating valves adjust the direction and amount of gas flow. Since the pressure and temperature rise during compression, the outlet temperature of the secondary compressor volute 34 is relatively high. Higher-temperature working gas can be introduced into the motors of the primary compressor 2 and the secondary compressor 3 through the secondary compressor volute opening 341 to insulate the motors. If the airflow from the secondary volute is insufficient to completely insulate the compressor motors, based on feedback from the temperature sensor, the airflow in the gas storage tank 51 can heat the stator of the primary centrifugal compressor 2, and the airflow in the gas storage tank 52 can heat the stator of the secondary centrifugal compressor 3, thereby assisting in motor insulation.

[0048] By setting up an insulated cold box, configuring each chamber within the cold box, and implementing a motor insulation circuit, the compressor's cold leakage is reduced, ensuring normal motor operation. This allows the compressor to operate normally at an inlet temperature of -268℃.

[0049] Example 2:

[0050] Appendix Figure 2 This is a schematic diagram of a single two-stage centrifugal compressor. The two-stage centrifugal compressor 6 has advantages such as compact structure and small size. When used as shown in the attached diagram... Figure 2When the single two-stage compressor shown is in operation, the assembly and welding of the whole machine is completed first according to the structural diagram of the two-stage centrifugal compressor 6. Then the whole machine is placed in an insulated cold box. The first stage of the two-stage centrifugal compressor is located in the fifth insulated chamber 15, the motor is located in the sixth insulated chamber 16, and the second stage of the two-stage centrifugal compressor is located in the sixth insulated chamber 16. As described in Example 1, the two insulated chambers are vacuumed, filled with perlite or wrapped with insulation material, and then the two-stage centrifugal compressor 6 starts to work.

[0051] The working gas enters the compressor from the inlet of the first-stage volute 641 of the two-stage compressor, flows through the first-stage impeller 621 of the two-stage compressor, enters the second-stage volute 642 of the two-stage centrifugal compressor through the intermediate connecting pipe, flows through the second-stage impeller 622 of the two-stage compressor, and is discharged from the outlet of the second-stage volute 642 of the two-stage centrifugal compressor. Then it flows out of the insulated cold box through the pipeline for the next step of operation.

[0052] Appendix Figure 2 The rotor structure and bearing structure of the single two-stage centrifugal compressor shown are attached. Figure 9 As shown, the first-stage impeller 621 and the second-stage impeller 622 are fixed at both ends of the motor rotor 612. Due to the differences in the structure on both sides, it is necessary to consider the influence of axial force on the normal operation of the compressor. A thrust plate is set on the first-stage side of the rotor, and two thrust bearings are located on both sides of the thrust plate set on the first-stage side. The thrust bearings and the radial bearings jointly support the high-speed rotation of the rotor.

[0053] Similarly, to ensure the normal operation of the centrifugal compressor, the motor needs to be kept warm, and the motor temperature is monitored by a temperature sensor. An opening is provided at the outlet of the secondary volute, connecting to the inside of the centrifugal compressor motor. The motor is kept warm by a higher-temperature airflow from the outlet. If this airflow is insufficient for complete insulation, the compressor stator 611 is heated through an air tank 53, allowing the compressor to operate normally even in low-temperature environments.

[0054] Example 3:

[0055] Appendix Figure 3 This is a schematic diagram of a structure using two two-stage centrifugal compressors connected in series. When a higher airflow pressure is required, an additional... Figure 3 The diagram shows two two-stage centrifugal compressors connected in series. When using the method shown in the attached diagram... Figure 3 When the two two-stage compressors shown are connected in series and are in operation, first follow the steps outlined in the attached diagram. Figure 3 The structural schematic diagram shown completes the assembly and welding of the entire machine. After that, the entire machine is placed in an insulated cold box. After completing the vacuum extraction, perlite filling or insulation material wrapping of the insulated chamber as described in Example 1, the two-stage centrifugal compressors 7 and 8 begin to work.

[0056] The working process of a single centrifugal compressor is as described in Example 2. When two compressors are connected in series, the outlet airflow of the two-stage centrifugal compressor 7 is discharged into the inlet of the two-stage centrifugal compressor 8 through the connecting pipe, and is compressed again in the flow channel of the two-stage centrifugal compressor 8. Finally, it is discharged from the outlet of the two-stage centrifugal compressor 8, and then flows out of the insulated cold box through the pipe to carry out the next step of the work, thus completing the compression process of the two centrifugal compressors connected in series.

[0057] Similarly, to ensure the normal operation of the two two-stage centrifugal compressors connected in series, motor insulation is required, and the motor temperature is monitored by temperature sensors. Openings are provided at the outlet of the second-stage volute of both two-stage centrifugal compressors 7 and 8, connecting to the interior of the compressor motor. The motor is insulated by a higher-temperature airflow from the outlet. If this airflow is insufficient for complete insulation, the stator of the motor in two-stage centrifugal compressor 7 is heated through an air tank 54, and the stator of the motor in two-stage centrifugal compressor 8 is heated through an air tank 55, allowing the compressors to operate normally even in low-temperature environments.

[0058] Example 4:

[0059] Appendix Figure 4 The diagram shows a single-stage cryogenic centrifugal compressor. Airflow enters through the compressor casing, passes through the impeller, and exits through the insulated cold chamber. In this single-stage centrifugal compressor structure, the impeller and motor are located in different chambers. Depending on the operating environment and requirements, the two chambers can be set to the same or different vacuum levels, or they can be wrapped with insulation material to reduce cold leakage. An insulation circuit is also included to ensure the compressor operates normally at lower ambient temperatures.

Claims

1. A low-temperature oil-free centrifugal compressor placed in an insulated environment, comprising an insulated cold box, a centrifugal compressor unit, connecting pipes, and a vacuum pump, characterized in that: The centrifugal compressor unit is placed in an insulated cold box and can operate within the inlet temperature range of -268℃ to -20℃. The insulated cold box has multiple chambers inside; A centrifugal compressor includes a motor, impeller, volute, and bearings; A centrifugal compressor with identical structures on both sides is used. The centrifugal compressor uses the same impeller at both ends and the motor rotor has the same structure and is symmetrically distributed. There is no need to consider axial force. In this case, the compressor does not have a separate thrust plate. The thrust surface is a vertical plane on the rotor main shaft that is perpendicular to the main shaft or an inclined plane that forms a certain angle with the rotor main shaft. Centrifugal compressor motors do not require cooling when operating at low temperatures. The motor includes a stator, rotor, and end covers. The motor housing has an air inlet and an air outlet. The motor rotor is supported by a gas bearing or a gas-magnetic hybrid bearing. The impellers at both ends of the centrifugal compressor and the motor in the middle are located in different chambers within the insulated cold box; The centrifugal compressor casing is divided into a primary casing and a secondary casing. An air passage is provided in the secondary casing, which is connected to the inside of the centrifugal compressor motor to form a motor insulation circuit. A temperature sensor is provided on the insulation circuit to determine the motor temperature. The direction and volume of the air passage are controlled by an electric opening regulating valve. When a centrifugal compressor is supported by a gas bearing, it uses a self-lubricating working fluid. Gas bearings are divided into radial bearings and thrust bearings, and the bearing types are all dynamic pressure type, dynamic-static pressure combination type or all static pressure type. The motor temperature is monitored by a temperature sensor installed on the insulation circuit. When the motor temperature is low, the higher temperature gas from the outlet of the secondary volute is used to heat the primary and secondary compressor motors through an electric opening regulating valve to ensure the normal operation of the motor. If the gas from the outlet of the secondary volute cannot fully meet the motor insulation function, the motor casing is supplemented with heat preservation through an air tank to ensure the normal operation of the motor. The impellers at both ends and the motor in the middle of different chambers of the insulated cold box are located in the same vacuum environment, or in different vacuum environments, or in an environment wrapped by insulation material.

2. The low-temperature oil-free centrifugal compressor placed in an adiabatic environment as described in claim 1, characterized in that, It can operate at an inlet temperature of -268℃, and the working gas is helium, air, nitrogen, neon or hydrogen.

3. The low-temperature oil-free centrifugal compressor placed in an adiabatic environment as described in claim 1, characterized in that, When the centrifugal compressor uses the same structure on both sides, it is supported only by radial bearings or by radial bearings plus thrust bearings. When thrust bearings are installed, the thrust bearings are parallel to the thrust surface.

4. The low-temperature oil-free centrifugal compressor placed in an adiabatic environment as described in claim 1, characterized in that, The centrifugal compressor unit has 1-12 stages, with interstage cooling between each stage of the compressor.

5. The low-temperature oil-free centrifugal compressor placed in an adiabatic environment as described in claim 1, characterized in that, The centrifugal compressor unit consists of 1-8 centrifugal compressors with identical structures on both sides connected in parallel or 1-8 multi-stage centrifugal compressors connected in series.

6. The low-temperature oil-free centrifugal compressor placed in an adiabatic environment as described in claim 1, characterized in that, The connecting pipe is flexible, avoiding the stress caused by thermal expansion and contraction.

7. The low-temperature oil-free centrifugal compressor placed in an adiabatic environment as described in claim 1, characterized in that, The motor end is provided with a heat insulation plate, the heat insulation plate material is polytetrafluoroethylene or epoxy resin, and the compressor terminal is led out from the motor stator, through the compressor housing and the heat insulation chamber where the motor is located, and led out to the heat insulation cold box.

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