CN219199534U - Oilless cascade refrigeration system - Google Patents

Abstract

The utility model relates to an oilless cascade refrigeration system, which comprises a low-temperature-level refrigeration loop and a high-temperature-level refrigeration loop, wherein the low-temperature-level refrigeration loop comprises a first centrifugal compressor, a condensation evaporator, a first expansion valve and a first evaporator which are sequentially connected to form a loop; the high-temperature-stage refrigeration loop comprises a second centrifugal compressor, a condenser, a second expansion valve and the condensation evaporator which are sequentially connected to form a loop, and the low-temperature-stage refrigeration loop and the high-temperature-stage refrigeration loop exchange heat through the condensation evaporator; each of the first centrifugal compressor and the second centrifugal compressor includes a housing, a main shaft rotatably disposed within the housing, and a bearing for supporting the main shaft, the bearing being an air suspension bearing. The oil-free cascade refrigeration system solves the problems of oil return problem and high cost investment caused by an oil way system in the related technology, saves the cost of the oil way system and improves the reliability of the system operation.

Description

Oilless cascade refrigeration system

Technical Field

The utility model relates to the technical field of low-temperature refrigeration, in particular to an oilless cascade refrigeration system.

Background

Compared with the traditional single-stage refrigeration system, the cascade refrigeration system can divide a larger total temperature difference into two or more sections, selects proper refrigerant circulation according to the temperature area of each section, and then stacks the sections, can realize lower refrigeration temperature under the premise of normal working pressure and pressure ratio, and can provide more refrigeration working temperature areas, so that the cascade refrigeration system is widely applied to the low-temperature refrigeration industry.

At present, a cascade refrigeration system mostly adopts a piston compressor or a screw compressor, and the inside of the compressor has larger friction and mechanical loss, and lubricating oil is needed to lubricate the compressor, so that the whole system needs a separate oil circuit circulation system, and oil cooling is needed when the oil temperature is too high, otherwise, serious abrasion is caused by carbonization of the lubricating oil, so that separate oil coolers, oil separators and other devices are needed, and the difficulty of management and control and the cost of oil circuit maintenance are increased. If the pipelines of the refrigeration cycle are too long, the oil return is difficult due to too large height difference, and the compressor is insufficiently lubricated and is worn, so that the initial investment of the existing cascade refrigeration system on the market occupies a certain cost on the oil circulation system; in addition, in the circulation process of the refrigerating system, lubricating oil can circulate in the whole system along with the refrigerant, and an oil film is formed on the surface of a heat exchange tube of the heat exchanger, so that the heat exchange efficiency of the heat exchanger is reduced, and the energy efficiency of the whole refrigerating system is affected.

Disclosure of Invention

The present utility model aims to solve at least one of the technical problems in the related art to some extent. Therefore, the embodiment of the utility model provides an oilless cascade refrigeration system, which solves the problems of oil return problem and high cost investment caused by an oil way system in the cascade refrigeration system in the related art, saves the cost of the oil way system and improves the reliability of system operation.

The oilless cascade refrigeration system of the embodiment of the utility model comprises a low-temperature-level refrigeration loop and a high-temperature-level refrigeration loop, wherein,

the low-temperature-stage refrigeration loop comprises a first centrifugal compressor, a condensation evaporator, a first expansion valve and a first evaporator which are sequentially connected to form the loop, wherein the condensation evaporator is provided with a first heat release channel and a first heat absorption channel, the first heat release channel is provided with a first heat release inlet and a first heat release outlet, the first heat release inlet is communicated with an exhaust port of the first centrifugal compressor, the first heat release outlet is communicated with an inlet of the first expansion valve, and the first heat absorption channel is provided with a first heat absorption inlet and a first heat absorption outlet;

the high-temperature-stage refrigeration loop comprises a second centrifugal compressor, a condenser, a second expansion valve and the condensation evaporator which are sequentially connected to form a loop, wherein the first heat absorption inlet is communicated with the outlet of the second expansion valve, and the first heat absorption outlet is communicated with the air suction port of the second centrifugal compressor;

Each of the first centrifugal compressor and the second centrifugal compressor includes a housing, a main shaft rotatably disposed within a chamber of the housing, and a bearing for supporting the main shaft, the bearing being an air suspension bearing.

According to the oilless cascade refrigeration system provided by the embodiment of the utility model, the first centrifugal compressor and the second centrifugal compressor are adopted, so that the bearings of the first centrifugal compressor and the second centrifugal compressor do not need to be lubricated, the problems of oil return problem and high cost investment caused by an oil way system of the oilless cascade refrigeration system in the related art are solved, the cost of the oil way system is saved, the investment cost is low, and meanwhile, the running reliability of the system is improved.

In some embodiments, the first centrifugal compressor further comprises a first primary compressor, a first secondary compressor, a first intermediate line, and a first drive motor, each of the first primary compressor and the first secondary compressor being disposed on the main shaft of the first centrifugal compressor, the first intermediate line communicating an outlet of the first primary compressor with an inlet of the first secondary compressor, the first drive motor comprising a first stator disposed within a chamber of the housing of the first centrifugal compressor and a first rotor disposed on the main shaft of the first centrifugal compressor, the first rotor cooperating with the first stator, the first drive motor driving the main shaft of the first centrifugal compressor to rotate to drive the first primary compressor and the first secondary compressor to operate synchronously;

The second centrifugal compressor further comprises a second primary compressor, a second secondary compressor, a second intermediate pipeline and a second driving motor, each of the second primary compressor and the second secondary compressor is arranged on the main shaft of the second centrifugal compressor, the second driving motor comprises a second stator and a second rotor, the second stator is arranged in the shell of the second centrifugal compressor, the second rotor is arranged on the main shaft of the second centrifugal compressor, the second rotor is matched with the second stator, and the second driving motor drives the main shaft of the second centrifugal compressor to rotate so as to drive the second primary compressor and the second secondary compressor to synchronously operate.

In some embodiments, the low temperature stage refrigeration circuit further comprises a first plate heat exchanger having a second heat absorption channel having a second heat absorption inlet and a second heat absorption outlet, and a second heat release channel having a second heat release inlet and a second heat release outlet, the first heat release outlet being in communication with the inlet of the third expansion valve, the outlet of the third expansion valve being in communication with the second heat absorption inlet, the second heat absorption outlet being in communication with the first intermediate conduit, the first heat release outlet also being in communication with the second heat release inlet, the second heat release outlet being in communication with the inlet of the first expansion valve;

The high-temperature-stage refrigeration loop further comprises a second plate heat exchanger and a fourth expansion valve, the second plate heat exchanger is provided with a third heat absorption channel and a third heat release channel, the third heat absorption channel is provided with a third heat absorption inlet and a third heat absorption outlet, the third heat release channel is provided with a third heat release inlet and a third heat release outlet, the outlet of the condenser is communicated with the inlet of the fourth expansion valve, the outlet of the fourth expansion valve is communicated with the third heat absorption inlet, the third heat absorption outlet is communicated with the second intermediate pipeline, the outlet of the condenser is also communicated with the third heat release inlet, and the third heat release outlet is communicated with the inlet of the second expansion valve.

In some embodiments, the low temperature stage refrigeration circuit further comprises a first regulator valve having an inlet in communication with the second heat absorption outlet and an outlet in communication with the first intermediate line; and/or the number of the groups of groups,

the high-temperature-stage refrigeration loop further comprises a second regulating valve, wherein an inlet of the second regulating valve is communicated with the third heat absorption outlet, and an outlet of the second regulating valve is communicated with the second intermediate pipeline.

In some embodiments, the high temperature stage refrigeration circuit further comprises a fifth expansion valve and a second evaporator, the third heat rejection outlet further communicating with an inlet of the fifth expansion valve, an outlet of the fifth expansion valve communicating with an inlet of the second evaporator, an outlet of the second evaporator communicating with an inlet of the second stage compressor.

In some embodiments, a first flow channel and a first exhaust pipe are provided on the housing of the first centrifugal compressor, the first flow channel being matched with the first stator, each of an outlet of the first flow channel and an inlet of the first exhaust pipe being in communication with a chamber of the housing of the first centrifugal compressor; the low-temperature-stage refrigeration loop further comprises a sixth expansion valve, the second heat release outlet of the first plate heat exchanger is also communicated with an inlet of the sixth expansion valve, an outlet of the sixth expansion valve is communicated with an inlet of the first circulation groove, and an outlet of the first exhaust pipe is communicated with an inlet of the first primary compressor;

a second circulation groove and a second exhaust pipe are arranged on the shell of the second centrifugal compressor, the second circulation groove is matched with the second stator, and each of the outlet of the second circulation groove and the inlet of the second exhaust pipe is communicated with a cavity of the shell of the second centrifugal compressor; the high-temperature-stage refrigeration loop further comprises a seventh expansion valve, the third heat release outlet of the second plate heat exchanger is further communicated with an inlet of the seventh expansion valve, an outlet of the seventh expansion valve is communicated with an inlet of the second circulating groove, and an outlet of the second exhaust pipe is communicated with an inlet of the second stage compressor.

In some embodiments, the low temperature stage refrigeration circuit further comprises a first gas-liquid separator having a first inlet in communication with the outlet of the first bleed line, a second inlet in communication with the outlet of the first evaporator, and a first outlet in communication with the inlet of the first primary compressor;

the high temperature stage refrigeration circuit further includes a second vapor-liquid separator having a third inlet communicating with the outlet of the second exhaust pipe, a fourth inlet communicating with each of the outlet of the second evaporator and the first heat absorption outlet of the condensing evaporator, and a second outlet communicating with the inlet of the second stage compressor.

In some embodiments, the low temperature stage refrigeration circuit further comprises a third regulator valve having an inlet in communication with the first outlet of the first gas-liquid separator and an outlet in communication with the inlet of the first primary compressor.

In some embodiments, the high temperature stage refrigeration circuit further comprises a fourth regulator valve having an inlet in communication with the second outlet of the second gas-liquid separator and an outlet in communication with the inlet of the second stage compressor.

In some embodiments, the low-temperature-stage refrigeration circuit further comprises a first communication pipe, one end of the first communication pipe is communicated with the outlet of the first secondary compressor, the other end of the first communication pipe is communicated with the inlet of the first primary compressor, and a first electromagnetic valve is arranged on the first communication pipe;

the high-temperature-stage refrigeration loop further comprises a second communicating pipe, one end of the second communicating pipe is communicated with the outlet of the second secondary compressor, the other end of the second communicating pipe is communicated with the inlet of the second primary compressor, and a second electromagnetic valve is arranged on the second communicating pipe.

Drawings

FIG. 1 is a schematic diagram of an oilless cascade refrigeration system of an embodiment of the utility model;

FIG. 2 is a schematic diagram of a low temperature stage refrigeration circuit according to an embodiment of the present utility model;

fig. 3 is a schematic diagram of a high temperature stage refrigeration circuit according to an embodiment of the present utility model.

Reference numerals:

an oilless cascade refrigeration system 100;

a low-temperature-stage refrigeration circuit 1;

the first centrifugal compressor 11, the first primary compressor 111, the first secondary compressor 112, the first intermediate line 113, the first driving motor 114, the first communication line 115, the first solenoid valve 116, the first exhaust pipe 118, the condensation evaporator 12, the first heat release inlet 121, the first heat release outlet 122, the first heat absorption inlet 123, the first heat absorption outlet 124, the first evaporator 13, the first gas-liquid separator 14, the first plate heat exchanger 15, the second heat absorption inlet 151, the second heat absorption outlet 152, the second heat release inlet 153, the second heat release outlet 154, the third expansion valve 16, the first regulating valve 17, the third regulating valve 18, the first expansion valve 19, the sixth expansion valve 110;

A high-temperature-stage refrigeration circuit 2;

the second centrifugal compressor 21, the second primary compressor 211, the second secondary compressor 212, the second intermediate line 213, the second driving motor 214, the second communication pipe 215, the second solenoid valve 216, the second exhaust pipe 218, the condenser 22, the second evaporator 23, the second gas-liquid separator 24, the second plate heat exchanger 25, the third heat absorption inlet 251, and the third heat absorption outlet 252, the third heat release inlet 253, the third heat release outlet 254, the fourth expansion valve 26, the second regulating valve 27, the fourth regulating valve 28, the second expansion valve 29, the fifth expansion valve 231, the seventh expansion valve 210.

Detailed Description

Reference will now be made in detail to embodiments of the present utility model, examples of which are illustrated in the accompanying drawings. The embodiments described below by referring to the drawings are illustrative and intended to explain the present utility model and should not be construed as limiting the utility model.

As shown in fig. 1 to 3, the oilless cascade refrigeration system 100 of the embodiment of the present utility model includes a low-temperature-stage refrigeration circuit 1 and a high-temperature-stage refrigeration circuit 2.

The low-temperature-stage refrigeration circuit 1 comprises a first centrifugal compressor 11, a condensation evaporator 12, a first expansion valve 19 and a first evaporator 13 which are sequentially connected to form a circuit, wherein the condensation evaporator 12 is provided with a first heat release channel and a first heat absorption channel, the first heat release channel is provided with a first heat release inlet 121 and a first heat release outlet 122, the first heat release inlet 121 is communicated with an exhaust port of the first centrifugal compressor 11, the first heat release outlet 122 is communicated with an inlet of the first expansion valve 19, and the first heat absorption channel is provided with a first heat absorption inlet 123 and a first heat absorption outlet 124.

The high-temperature-stage refrigeration circuit 2 comprises a second centrifugal compressor 21, a condenser 22, a second expansion valve 29 and a condensation evaporator 12 which are sequentially connected to form a circuit, wherein a first heat absorption inlet 123 is communicated with an outlet of the second expansion valve 29, and a first heat absorption outlet 124 is communicated with an air suction port of the second centrifugal compressor 21.

Each of the first centrifugal compressor 11 and the second centrifugal compressor 21 includes a housing, a main shaft rotatably provided in a chamber of the housing, and a bearing for supporting the main shaft, the bearing being an air suspension bearing.

The refrigeration process of the oilless cascade refrigeration system 100 of the embodiment of the utility model is as follows:

high temperature stage refrigeration circuit 2: the second centrifugal compressor 21 compresses the gaseous refrigerant to discharge the high-temperature and high-pressure gaseous refrigerant, the high-temperature and high-pressure gaseous refrigerant is condensed by the condenser 22 to form a high-temperature and high-pressure liquid refrigerant, the high-temperature and high-pressure liquid refrigerant is throttled by the second expansion valve 29 to form a low-temperature and low-pressure gas-liquid mixed state refrigerant, the low-temperature and low-pressure gas-liquid mixed state refrigerant enters the first heat absorption channel of the condensation evaporator 12 to exchange heat with the refrigerant in the first heat release channel of the low-temperature stage refrigeration circuit 1 to condense the high-temperature and high-pressure gaseous refrigerant in the low-temperature stage refrigeration circuit 1, the refrigerant in the first heat absorption channel absorbs heat and evaporates to form a low-temperature and low-pressure gaseous refrigerant, and the low-temperature and low-pressure gaseous refrigerant is absorbed into the second centrifugal compressor 21.

Low temperature stage refrigeration circuit 1: the first centrifugal compressor 11 compresses the gaseous refrigerant to discharge the high-temperature high-pressure gaseous refrigerant, and the high-temperature high-pressure gaseous refrigerant exchanges heat and cools with the low-temperature low-pressure gas-liquid mixed refrigerant in the first heat absorption channel of the high-temperature stage refrigeration loop 2 through the first heat release channel of the condensation evaporator 12 to form a high-temperature high-pressure liquid refrigerant. In other words, the first heat release passage and the first heat absorption passage of the condensation evaporator 12 cooperate with each other to exchange heat. The high-temperature high-pressure liquid refrigerant is throttled by the first expansion valve 19 to form a low-temperature low-pressure gas-liquid mixed state refrigerant, the low-temperature low-pressure gas-liquid mixed state refrigerant enters the first evaporator 13 to exchange heat with the environment to reduce the environment temperature, the low-temperature low-pressure gas-liquid mixed state refrigerant absorbs heat and evaporates in the first evaporator 13 to form a low-temperature low-pressure gas-state refrigerant, and then the low-temperature low-pressure gas-state refrigerant is sucked into the first centrifugal compressor 11.

The oilless cascade refrigeration system 100 of the embodiment of the present utility model employs the first centrifugal compressor 11 and the second centrifugal compressor 12 to compress refrigerant to perform work, and each of the first centrifugal compressor 11 and the second centrifugal compressor 21 includes a housing, a main shaft rotatably provided in a chamber of the housing, and a bearing for supporting the main shaft, the bearing being an air suspension bearing, the air suspension bearing requiring no lubricating oil. Compared with the prior art that a piston compressor or a screw compressor is adopted to compress and apply work to the refrigerant, the first centrifugal compressor 11 and the second centrifugal compressor 12 of the oilless cascade refrigeration system 100 of the embodiment of the utility model do not need to use lubricating oil, thereby saving the cost of an oil way system for lubrication, eliminating the possibility of compressor abrasion caused by the oil return problem of the oil way system and improving the operation reliability of the oilless cascade refrigeration system 100.

The low-temperature-stage refrigeration circuit 1 of the oilless cascade refrigeration system 100 of the embodiment of the utility model can use R507 refrigerant, and the high-temperature-stage refrigeration circuit 2 can use R134a refrigerant. In the related art, ammonia/carbon dioxide or two-stage ammonia is adopted as the refrigerant of the oilless cascade refrigeration system, however, the ammonia refrigerant is toxic and inflammable, and high pressure equipment and pipelines are needed for the carbon dioxide system, so compared with the related art, the oilless cascade refrigeration system 100 of the embodiment of the utility model is safer and more reliable, has low cost investment, and can achieve the system performance similar to that of the cascade refrigeration system adopting the two modes.

By adopting the first centrifugal compressor 11 and the second centrifugal compressor 12, the bearings of the oilless cascade refrigeration system 100 provided by the embodiment of the utility model do not need to be lubricated, so that the problems of oil return and high cost investment caused by an oil way system in the oilless cascade refrigeration system in the related art are solved, the cost of the oil way system is saved, the investment cost is low, and the running reliability of the system is improved.

In order to make the solution of the present application easier to understand, a detailed description will be given by taking fig. 1 to 3 as an example.

The oilless cascade refrigeration system 100 of the embodiment of the utility model includes a low-temperature-stage refrigeration circuit 1 and a high-temperature-stage refrigeration circuit 2.

The low-temperature-stage refrigeration circuit 1 comprises a first centrifugal compressor 11, a condensation evaporator 12, a first plate heat exchanger 15, a first evaporator 13, a first cooling line, a first gas-liquid separator 14 and a third expansion valve 16, a first regulating valve 17, a third regulating valve 18, a first expansion valve 19, a sixth expansion valve 110, a first communication pipe 115 and a first solenoid valve 116. The high-temperature-stage refrigeration circuit 2 includes a second centrifugal compressor 21, a condenser 22, a fourth expansion valve 26, a second plate heat exchanger 25, a second evaporator 23, a second cooling line, a condensation evaporator 12, a second gas-liquid separator 24, and a second regulating valve 26, a second regulating valve 27, a fourth regulating valve 28, a second expansion valve 29, a fifth expansion valve 231, a seventh expansion valve 210, a second communication pipe 215, and a second solenoid valve 116. The low-temperature-stage refrigeration circuit 1 and the high-temperature-stage refrigeration circuit 2 exchange heat by the condensation evaporator 12.

The first centrifugal compressor 11 comprises a housing, a main shaft rotatably arranged in a chamber of the housing and a bearing for supporting the main shaft, the bearing being an air suspension bearing.

The first centrifugal compressor 11 further includes a first primary compressor 111, a first secondary compressor 112, a first intermediate line 113, and a first drive motor 114, each of the first primary compressor 111 and the first secondary compressor 112 being provided on the main shaft of the first centrifugal compressor 11. The first primary compressor 111 is located at one end of the housing of the first centrifugal compressor 11 and the first secondary compressor 112 is located at the other end of the housing of the first centrifugal compressor 11.

The first intermediate line 113 communicates between the outlet of the first primary compressor 111 and the inlet of the first secondary compressor 112. That is, the outlet of the first primary compressor 111 and the inlet of the first secondary compressor 112 are communicated through the first intermediate pipe 113. The inlet of the first primary compressor 111 constitutes the suction port of the first centrifugal compressor 11 and the outlet of the first secondary compressor 112 constitutes the discharge port of the first centrifugal compressor 11. The first driving motor 114 includes a first stator and a first rotor, the first stator is disposed in a chamber of the housing of the first centrifugal compressor 11, the first rotor is disposed on the main shaft of the first centrifugal compressor 11, the first rotor is matched with the first stator, and the first driving motor 114 drives the main shaft of the first centrifugal compressor 11 to rotate so as to drive the first primary compressor 111 and the first secondary compressor 112 to operate synchronously.

The first driving motor 114 is a permanent magnet motor formed by the first rotor and the first stator, the first centrifugal compressor 11 is driven by the permanent magnet motor, and the permanent magnet motor directly drives the main shaft to rotate so as to drive the first primary compressor 111 and the first secondary compressor 112 to apply work to realize the refrigerant compression process.

The first centrifugal compressor 11 forms a two-stage centrifugal compression by the first one-stage compressor 111 and the first two-stage compressor 112, and in the case of satisfying the compression ratio of the oil-free cascade refrigeration system 100, the compression ratio of single compression is reduced compared with that of single-stage centrifugal compressors, that is, the compression ratio of the first one-stage compressor 111 and the compression ratio of the first two-stage compressor 112 are reduced, so that the requirements on the specification and the material of the first centrifugal compressor 11 are reduced, and the manufacturing cost of the first centrifugal compressor 11 is reduced.

The bearing of the first centrifugal compressor 11 is an air suspension bearing, and the support for the main shaft can be provided by means of air. Specifically, the casing of the first centrifugal compressor 11 is provided with a first hole, and the gaseous refrigerant flowing to the casing of the first centrifugal compressor 11 from the first primary compressor 111 and the first secondary compressor 112 flows through the gas suspension bearing and is discharged through the first hole. For example, a single-machine two-stage centrifugal compressor is disclosed in patent publication No. CN 152330U.

Specifically, the number of bearings of the first centrifugal compressor 11 is four, two of which are radial bearings, and the other two are thrust bearings, and the radial bearings and the thrust bearings employ dynamic foil gas bearings.

The condensing evaporator 12 has a first heat release passage having a first heat release inlet 121 and a first heat release outlet 122, and a first heat absorption passage having a first heat absorption inlet 123 and a first heat absorption outlet 124.

The first heat release inlet 121 communicates with the outlet of the first secondary compressor 112 of the first centrifugal compressor 11, and the first heat release outlet 122 communicates with the inlet of the first evaporator 13. The high-temperature and high-pressure gaseous refrigerant discharged from the first-stage compressor 112 is condensed in the first heat release passage of the condensing evaporator 12 to form a high-temperature and high-pressure liquid refrigerant.

The first plate heat exchanger 15 has a second heat absorption channel with a second heat absorption inlet 151 and a second heat absorption outlet 152, and the second heat release channel with a second heat release inlet 153 and a second heat release outlet 154, the first heat release outlet 122 being in communication with the inlet of the third expansion valve 16, the outlet of the third expansion valve 16 being in communication with the second heat absorption inlet 151, the second heat absorption outlet 152 being in communication with the first intermediate line 113, the first heat release outlet 122 also being in communication with the second heat release inlet 153, the second heat release outlet 154 being in communication with the inlet of the first expansion valve 19, the outlet of the first expansion valve 19 being in communication with the inlet of the first evaporator 13.

The high-temperature and high-pressure liquid refrigerant discharged from the first heat release outlet 122 is divided into a first main path and a first branch path, the first main path enters the second heat release channel through the second heat release inlet 153, and the first branch path enters the second heat absorption channel through the third expansion valve 16 and the second heat absorption inlet 151. In the first plate heat exchanger 15, the high-temperature and high-pressure liquid refrigerant from the first main path exchanges heat with the low-temperature and low-pressure gas-liquid mixed refrigerant from the first branch path, which is throttled by the third expansion valve 16, to form a high-temperature and high-pressure liquid refrigerant, and the high-temperature and high-pressure liquid refrigerant flows out of the second heat release outlet 154, and the low-temperature and low-pressure gas-liquid mixed refrigerant from the first branch path exchanges heat to form a low-temperature and low-pressure gas refrigerant and flows out of the second heat absorption outlet 152.

The low-temperature low-pressure gaseous refrigerant discharged from the second heat absorption outlet 152 flows to the first intermediate line 113, and is mixed with the gaseous refrigerant discharged from the outlet of the first primary compressor 111 to the inlet of the first secondary compressor 112, thereby supplementing the first secondary compressor 112 with air. The temperature of the mixed gaseous refrigerant is lower than that of the gaseous refrigerant without air supplement, that is, the temperature of the high-temperature high-pressure gaseous refrigerant discharged by the first secondary compressor 112 after air supplement is lower than that before air supplement, so that the work of the first centrifugal compressor 11 is reduced, the power consumption of the first centrifugal compressor 11 is reduced, the running cost of the oil-free cascade refrigeration system 100 is further reduced, and the system is more economical and energy-saving.

The arrangement of the first plate heat exchanger 15 provides cold for the low-temperature-stage refrigeration circuit 1, reduces the temperature of the liquid refrigerant flowing out of the second heat release outlet 154, and improves the refrigerating capacity of the low-temperature-stage refrigeration circuit 1, thereby further improving the energy efficiency of the oilless cascade refrigeration system 100. On the other hand, the first stage compressor 112 is provided with gaseous refrigerant for greater economy.

Specifically, the third expansion valve 16 is an electronic expansion valve.

The inlet of the first regulating valve 17 communicates with the second heat absorbing outlet 152 of the first plate heat exchanger 15, and the outlet of the first regulating valve 17 communicates with the first intermediate line 113. The first regulating valve 17 is arranged to facilitate regulating the flow of refrigerant to supplement the first secondary compressor 112 so that the first centrifugal compressor 11 achieves optimal performance under different load conditions by controlling and regulating the opening of the first regulating valve 17 by its load percentage when the first centrifugal compressor 11 is in operation.

Specifically, the first regulating valve 17 is an electric regulating valve.

The second heat release outlet 154 is communicated with the inlet of the first expansion valve 19, the outlet of the first expansion valve 19 is communicated with the inlet of the first evaporator 13, and the outlet of the first evaporator 13 is communicated with the inlet of the first gas-liquid separator 14. A part of the high-temperature and high-pressure liquid refrigerant flowing out of the second heat release outlet 154 is throttled by the first expansion valve 19 to form a low-temperature and low-pressure gas-liquid mixed state refrigerant, and then flows to the first evaporator 13, and exchanges heat with the environment in the first evaporator 13 so as to achieve the purpose of refrigerating the environment. The low-temperature low-pressure gas-liquid mixed state refrigerant is formed into a low-pressure low-temperature gaseous refrigerant after endothermic evaporation in the first evaporator 13, and is then discharged from the outlet of the first evaporator 13 at the suction pressure of the first centrifugal compressor 11.

Specifically, the first expansion valve 19 is an electronic expansion valve.

In some embodiments, the housing of the first centrifugal compressor 11 is provided with a first flow channel and a first exhaust duct 118, the first flow channel being matched to the first stator, each of the outlet of the first flow channel and the inlet of the first exhaust duct 118 being in communication with the chamber of the housing of the first centrifugal compressor 11, that is, the first flow channel being in communication with the chamber of the housing of the first centrifugal compressor 11 and the first exhaust duct 118.

Specifically, the first exhaust pipe 118 is provided on the first hole of the housing of the first centrifugal compressor 11.

The second heat release outlet 154 of the first plate heat exchanger 15 is also connected to the inlet of the sixth expansion valve 110, the outlet of the sixth expansion valve 110 is connected to the inlet of the first flow channel, and the outlet of the first exhaust pipe 118 is connected to the inlet of the first primary compressor 111.

The other part of the high-temperature and high-pressure liquid refrigerant flowing out of the second heat release outlet 154 is throttled by the sixth expansion valve 110 to form a low-temperature and low-pressure gas-liquid mixed state refrigerant flowing to the first flow channel, the first driving motor 114 is cooled in the first flow channel, the low-temperature and low-pressure gas-state refrigerant is formed to flow into the cavity of the shell of the first centrifugal compressor 11 from the first flow channel, and then discharged from the outlet of the first exhaust pipe 118.

Specifically, the sixth expansion valve 110 is an electronic expansion valve.

The first gas-liquid separator 14 has a first inlet 141, a second inlet 142, and a first outlet 143, the first inlet 141 communicating with the outlet of the first discharge pipe 118, the second inlet 142 communicating with the outlet of the first evaporator 13, and the first outlet 143 communicating with the inlet of the first primary compressor 111. The low-temperature low-pressure gaseous refrigerant discharged from the outlet of the first exhaust pipe 118 and the outlet of the first evaporator 13 enters the first gas-liquid separator 14, the first gas-liquid separator 14 separates the liquid refrigerant entrained in the gaseous refrigerant, the separated gaseous refrigerant is sucked by the first primary compressor 111, the separated liquid refrigerant is temporarily stored in the first gas-liquid separator 14 to be naturally evaporated to form the gaseous refrigerant, and then is sucked by the first primary compressor 111.

During normal operation of the first centrifugal compressor 11, the refrigerant discharged from the outlet of the first discharge pipe 118 and the outlet of the first evaporator 13 is a gaseous refrigerant, and is not mixed with a liquid refrigerant. However, when the power of the first centrifugal compressor 11 or the oil-free cascade refrigeration system 100 is adjusted, the condition fluctuation is large, that is, the required cooling capacity is small, and the liquid supply amount of the first evaporator 13 is large, the gaseous refrigerant discharged from the outlet of the first evaporator 13 may have a liquid carrying condition.

An inlet of the third regulating valve 18 communicates with the first outlet 143 of the first gas-liquid separator 14, and an outlet of the third regulating valve 18 communicates with an inlet of the first primary compressor 111. The third regulating valve 18 is used to regulate the flow rate of the gaseous refrigerant entering the first primary compressor 111 so as to reduce the flow rate of the gaseous refrigerant entering the first primary compressor 111 when the power of the oilless cascade refrigeration system 100 needs to be regulated and the rotation speed of the main shaft of the first centrifugal compressor 11 cannot be reduced, thereby improving the performance of the system while ensuring the operational reliability of the first centrifugal compressor 11.

Specifically, the third regulating valve 18 is an electric regulating valve.

One end of the first communication pipe 115 is communicated with the outlet of the first secondary compressor 112, the other end of the first communication pipe 115 is communicated with the inlet of the first primary compressor 111, and a first electromagnetic valve 116 is arranged on the first communication pipe 115.

The first solenoid valve 116 is normally closed when the first centrifugal compressor 11 is in operation and is opened only before the first centrifugal compressor 11 is shut down to communicate the outlet of the first secondary compressor 112 with the inlet of the first primary compressor 111 to prevent the backflow of gas from the first secondary compressor 112 to the first primary compressor 111 via the first intermediate line 113 during the shut down to cause the surge of the first centrifugal compressor 11 and thereby cause axial force changes and damage to the thrust bearings.

The second centrifugal compressor 21 comprises a housing, a main shaft rotatably arranged in a chamber of the housing and a bearing for supporting the main shaft, the bearing being an air suspension bearing.

The second centrifugal compressor 21 further includes a second primary compressor 211, a second secondary compressor 212, a second intermediate line 213, and a second drive motor 214, each of the second primary compressor 211 and the second secondary compressor 212 being provided on the main shaft of the second centrifugal compressor 21. The second stage compressor 211 is located at one end of the housing of the second centrifugal compressor 21, and the second stage compressor 212 is located at the other end of the housing of the second centrifugal compressor 21.

The second intermediate line 213 communicates between the outlet of the second stage compressor 211 and the inlet of the second stage compressor 212. That is, the outlet of the second stage compressor 211 and the inlet of the second stage compressor 212 are communicated through the second intermediate pipe 213. The inlet of the second stage compressor 211 constitutes the suction port of the second centrifugal compressor 21, and the outlet of the second stage compressor 212 constitutes the discharge port of the second centrifugal compressor 21. The second driving motor 214 includes a second stator and a second rotor, the second stator is disposed in a cavity of the housing of the second centrifugal compressor 21, the second rotor is disposed on the main shaft of the second centrifugal compressor 21, the second rotor is matched with the second stator, and the second driving motor 214 drives the main shaft of the second centrifugal compressor 21 to rotate so as to drive the second primary compressor 211 and the second secondary compressor 212 to operate synchronously.

The second drive motor 214 is a permanent magnet motor formed of a second rotor and a second stator. The second centrifugal compressor 21 is driven by a permanent magnet motor, and the permanent magnet motor directly drives the main shaft to rotate so as to drive the second primary compressor 211 and the second secondary compressor 212 to do work to realize the refrigerant compression process.

The second centrifugal compressor 21 is formed by the second primary compressor 211 and the second secondary compressor 212 to form a two-stage centrifugal compression, and compared with a single-stage centrifugal compressor, the compression ratio of the single-stage compression is reduced under the condition of meeting the compression ratio of the oil-free cascade refrigeration system 100, that is, the compression ratio of the second primary compressor 211 and the compression ratio of the second secondary compressor 212 are reduced, so that the requirements on the specification and the material of the second centrifugal compressor 21 are reduced, and the manufacturing cost of the second centrifugal compressor 21 is reduced.

Alternatively, the bearings of the second centrifugal compressor 21 are air suspension bearings, by means of which support for the main shaft is provided. Specifically, the casing of the second centrifugal compressor 21 is provided with a second hole, and the gaseous refrigerant flowing to the casing of the second centrifugal compressor 21 from the second primary compressor 211 and the second secondary compressor 212 flows through the gas suspension bearing and is discharged through the second hole. For example, a single-machine two-stage centrifugal compressor is disclosed in patent publication No. CN 152330U.

Specifically, the number of bearings of the second centrifugal compressor 21 is four, two of which are radial bearings, and the other two are thrust bearings, and the radial bearings and the thrust bearings employ dynamic foil gas bearings.

The outlet of the second-stage compressor 212 is connected to the inlet of the condenser 22, and the condenser 22 condenses the high-temperature and high-pressure gaseous refrigerant discharged from the second-stage compressor 212 and then discharges the high-temperature and high-pressure liquid refrigerant.

The second plate heat exchanger 25 has a third heat absorption channel with a third heat absorption inlet 251 and a third heat absorption outlet 252, and a third heat release channel with a third heat release inlet 253 and a third heat release outlet 254, the outlet of the condenser 22 being connected to the inlet of the fourth expansion valve 26, the outlet of the fourth expansion valve 26 being connected to the third heat absorption inlet 251, the third heat absorption outlet 252 being connected to the second intermediate line 213, the outlet of the condenser 22 also being connected to the third heat release inlet 253, the third heat release outlet 254 being connected to the first heat absorption inlet 123 of the condensing evaporator 12.

The high-temperature and high-pressure liquid refrigerant discharged from the condenser 22 is divided into a second main path and a second branch path, the second main path enters the third heat release passage through the third heat release inlet 253, and the second branch path enters the third heat absorption passage through the third heat absorption inlet 151. In the second plate heat exchanger 25, the high-temperature and high-pressure liquid refrigerant from the second main path exchanges heat with the low-temperature and low-pressure gas-liquid mixed refrigerant from the second branch path, which is throttled by the fourth expansion valve 26, and is supercooled, so that the high-temperature and high-pressure liquid refrigerant flows out of the third heat release outlet 254, and the low-temperature and low-pressure gas-liquid mixed refrigerant from the second branch path exchanges heat so that the low-temperature and low-pressure gas refrigerant flows out of the third heat absorption outlet 252.

The low-temperature low-pressure gaseous refrigerant discharged from the third heat absorption outlet 252 flows to the second intermediate pipe 213, is mixed with the gaseous refrigerant discharged from the outlet of the second-stage compressor 211 to the inlet of the second-stage compressor 212, and supplements the second-stage compressor 212 with air. The temperature of the mixed gaseous refrigerant is lower than before air supplement, that is, the temperature of the high-temperature high-pressure gaseous refrigerant discharged by the second secondary compressor 212 after air supplement is lower than before air supplement, so that the work of the second centrifugal compressor 21 is reduced, the power consumption of the second centrifugal compressor 21 is reduced, the running cost of the oil-free cascade refrigeration system 100 is further reduced, and the oil-free cascade refrigeration system is more economical and energy-saving.

The second plate heat exchanger 25 provides cold for the high-temperature-stage refrigeration circuit 2, reduces the temperature of the liquid refrigerant flowing out of the third heat release outlet 254, and improves the refrigerating capacity of the high-temperature-stage refrigeration circuit 2, thereby further improving the energy efficiency of the oilless cascade refrigeration system 100. On the other hand, the second stage compressor 212 is provided with gaseous refrigerant for greater economy.

Specifically, the fourth expansion valve 26 is an electronic expansion valve.

The inlet of the second regulating valve 27 communicates with the third heat absorbing outlet 252 of the second plate heat exchanger 25 and the outlet of the second regulating valve 27 communicates with the second intermediate conduit 213. The second regulating valve 27 is arranged to facilitate the regulation of the flow rate of the air supplied to the second secondary compressor 212, so that the second centrifugal compressor 21 achieves optimal performance under different load conditions by controlling and regulating the opening of the second regulating valve 27 according to the load percentage when the second centrifugal compressor 21 is operated.

Specifically, the second regulating valve 27 is an electric regulating valve.

The third heat release outlet 254 is connected to the inlet of the second expansion valve 29, the outlet of the second expansion valve 29 is connected to the first heat absorption inlet 123, and the first heat absorption outlet 124 is connected to the second gas-liquid separator 24. A part of the high-temperature and high-pressure liquid refrigerant flowing out of the third heat release outlet 254 is throttled by the second expansion valve 29 to form a low-temperature and low-pressure gas-liquid mixed refrigerant, which flows to the first heat absorption channel of the condensation evaporator 12, exchanges heat with the high-temperature and high-pressure gas refrigerant in the first heat release channel in the first heat absorption channel to condense the high-temperature and high-pressure gas refrigerant in the low-temperature stage refrigeration circuit 1, and then the low-temperature and low-pressure gas-liquid mixed refrigerant is evaporated to form a low-temperature and low-pressure gas refrigerant, and flows to the second gas-liquid separator 24 under the suction pressure of the second centrifugal compressor 21.

Specifically, the second expansion valve 29 is an electronic expansion valve.

The third heat release outlet 254 is also connected to the inlet of the fifth expansion valve 231, the outlet of the fifth expansion valve 231 is connected to the inlet of the second evaporator 23, and the outlet of the second evaporator 23 is connected to the inlet of the second stage compressor 211. A part of the high-temperature and high-pressure liquid refrigerant flowing out of the third heat release outlet 254 is throttled by the fifth expansion valve 231 to form a low-temperature and low-pressure gas-liquid mixed refrigerant, and the low-temperature and low-pressure gas-liquid mixed refrigerant flows to the second evaporator 23 and exchanges heat with the environment in the second evaporator 23 so as to achieve the purpose of refrigerating the environment. The low-temperature low-pressure gas-liquid mixed refrigerant absorbs heat and evaporates in the second evaporator 23 to form a low-temperature low-pressure gaseous refrigerant, which is then discharged from the outlet of the second evaporator 23 at the suction pressure of the second centrifugal compressor 21.

The arrangement of the second evaporator 23 increases the refrigerating end of the high-temperature-stage refrigerating system 2, further increases the refrigerating end of the oilless cascade refrigerating system 100, improves the medium-temperature refrigerating requirement of the oilless cascade refrigerating system 100, expands the temperature interval of the oilless cascade refrigerating system 100, and improves the utilization efficiency of the system.

Specifically, the fifth expansion valve 231 is an electronic expansion valve.

In some embodiments, the housing of the second centrifugal compressor 21 is provided with a second flow channel and a second exhaust duct 218, the second flow channel being matched to the second stator, each of the outlet of the second flow channel and the inlet of the second exhaust duct 218 being in communication with the chamber of the housing of the second centrifugal compressor 21, that is, the second flow channel being in communication with the chamber of the housing of the second centrifugal compressor 21 and the second exhaust duct 218.

Specifically, the second exhaust pipe 218 is provided on the second hole of the housing of the second centrifugal compressor 21.

The third heat release outlet 254 of the second plate heat exchanger 25 is also in communication with the inlet of the seventh expansion valve 210, the outlet of the seventh expansion valve 210 is in communication with the inlet of the second flow channel, and the outlet of the second bleed duct 218 is in communication with the inlet of the second stage compressor 222.

The other part of the high-temperature and high-pressure liquid refrigerant flowing out of the third heat release outlet 254 is throttled by the seventh expansion valve 210 to form a low-temperature and low-pressure gas-liquid mixed state refrigerant flowing to the second flow channel, cooling the second driving motor 214 in the second flow channel, and then forming a low-temperature and low-pressure gas-state refrigerant flowing from the first flow channel to the chamber of the housing of the second centrifugal compressor 21, and then being discharged from the outlet of the second exhaust pipe 218.

Specifically, the seventh expansion valve 210 is an electronic expansion valve.

The second gas-liquid separator 24 has a third inlet 241, a fourth inlet 242, and a second outlet 243, the third inlet 241 being in communication with the outlet of the second discharge pipe 218, each of the outlet of the second evaporator 23 and the first heat absorption outlet 124 of the condensing evaporator 12 being in communication with the fourth inlet 242, the second outlet 243 being in communication with the inlet of the second stage compressor 211. The gaseous refrigerant discharged from the outlet of the second discharge pipe 218, the outlet of the second evaporator 23 and the first heat absorbing outlet 124 of the condensing evaporator 12 enters the second gas-liquid separator 24, the second gas-liquid separator 24 separates the liquid refrigerant entrained in the gaseous refrigerant, the separated gaseous refrigerant is sucked by the second stage compressor 211, the separated liquid refrigerant is temporarily stored in the second gas-liquid separator 24 to be naturally evaporated to form the gaseous refrigerant, and then is sucked by the first stage compressor 111.

During normal operation of the second centrifugal compressor 21, the refrigerant discharged from the outlet of the second discharge pipe 218, the outlet of the second evaporator 23, and the first heat absorption outlet 124 of the condensation evaporator 12 is gaseous refrigerant, and is not mixed with liquid refrigerant. However, when the power of the second centrifugal compressor 21 or the oilless cascade refrigeration system 100 is adjusted, the condition fluctuation is large, that is, the required cooling capacity is small, and the liquid supply amount of the second evaporator 23 is large, the gaseous refrigerant discharged from the outlet of the second evaporator 13 may be brought into a liquid-carrying condition.

An inlet of the fourth regulating valve 28 communicates with the second outlet 243 of the second gas-liquid separator 24, and an outlet of the fourth regulating valve 28 communicates with an inlet of the second stage compressor 211. The fourth regulating valve 28 is used to regulate the flow rate of the gaseous refrigerant entering the second stage compressor 211 so as to reduce the flow rate of the gaseous refrigerant entering the second stage compressor 211 when the power of the oilless cascade refrigeration system 100 needs to be regulated while the rotation speed of the main shaft of the second centrifugal compressor 21 cannot be reduced, thereby improving the performance of the system while ensuring the operational reliability of the second centrifugal compressor 21.

Specifically, the fourth regulator valve 28 is an electric regulator valve.

One end of the second communicating pipe 215 is communicated with the outlet of the second secondary compressor 212, the other end of the second communicating pipe 215 is communicated with the inlet of the second primary compressor 211, and a second electromagnetic valve 216 is arranged on the second communicating pipe 215.

The second solenoid valve 216 is kept normally closed when the second centrifugal compressor 21 is operated, and is opened only before the second centrifugal compressor 21 is stopped to communicate the outlet of the second secondary compressor 212 with the inlet of the second primary compressor 211, so as to prevent the gas from flowing back from the second secondary compressor 212 to the second primary compressor 211 through the second intermediate pipeline 213 during the stopping process to cause the surge of the second centrifugal compressor 21, thereby causing the axial force to change and damaging the thrust bearing.

When the oilless cascade refrigeration system 100 of the embodiment of the utility model is operated, the minimum operation evaporation temperature reaches minus 30 ℃, and the second evaporator 23 can meet the refrigeration requirement that the refrigeration space temperature is operated at 0-8 ℃. Compared with an oil-free cascade refrigeration system adopting ammonia/carbon dioxide and an oil-free cascade refrigeration system adopting two-stage ammonia, the oil-free cascade refrigeration system 100 provided by the embodiment of the utility model has the advantages of equivalent energy efficiency, low equipment cost of a compressor and low overall cost.

In the description of the present utility model, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present utility model and simplifying the description, and do not indicate or imply that the device or element being referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present utility model.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present utility model, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.

In the present utility model, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; may be mechanically connected, may be electrically connected or may be in communication with each other; either directly or indirectly, through intermediaries, or both, may be in communication with each other or in interaction with each other, unless expressly defined otherwise. The specific meaning of the above terms in the present utility model can be understood by those of ordinary skill in the art according to the specific circumstances.

In the present utility model, unless expressly stated or limited otherwise, a first feature "up" or "down" a second feature may be the first and second features in direct contact, or the first and second features in indirect contact via an intervening medium. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.

For purposes of this disclosure, the terms "one embodiment," "some embodiments," "example," "a particular example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the utility model. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

While embodiments of the present utility model have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the utility model, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the utility model.

Claims (10)

1. An oilless cascade refrigeration system is characterized by comprising a low-temperature-level refrigeration loop (1) and a high-temperature-level refrigeration loop (2), wherein,

The low-temperature-stage refrigeration loop (1) comprises a first centrifugal compressor (11), a condensation evaporator (12), a first expansion valve (19) and a first evaporator (13) which are sequentially connected to form a loop, wherein the condensation evaporator (12) is provided with a first heat release channel and a first heat absorption channel, the first heat release channel is provided with a first heat release inlet (121) and a first heat release outlet (122), the first heat release inlet (121) is communicated with an exhaust port of the first centrifugal compressor (11), the first heat release outlet (122) is communicated with an inlet of the first expansion valve (19), and the first heat absorption channel is provided with a first heat absorption inlet (123) and a first heat absorption outlet (124);

the high-temperature-stage refrigeration loop (2) comprises a second centrifugal compressor (21), a condenser (22), a second expansion valve (29) and the condensation evaporator (12) which are sequentially connected to form a loop, wherein the first heat absorption inlet (123) is communicated with the outlet of the second expansion valve (29), and the first heat absorption outlet (124) is communicated with an air suction port of the second centrifugal compressor (21);

each of the first centrifugal compressor (11) and the second centrifugal compressor (21) includes a housing, a main shaft rotatably provided in a chamber of the housing, and a bearing for supporting the main shaft, the bearing being an air suspension bearing.

2. An oil-free cascade refrigeration system as recited in claim 1, wherein,

the first centrifugal compressor (11) further comprises a first primary compressor (111), a first secondary compressor (112), a first intermediate pipeline (113) and a first driving motor (114), each of the first primary compressor (111) and the first secondary compressor (112) is arranged on the main shaft of the first centrifugal compressor (11), the first intermediate pipeline (113) is communicated with the outlet of the first primary compressor (111) and the inlet of the first secondary compressor (112), the first driving motor (114) comprises a first stator and a first rotor, the first stator is arranged in the cavity of the shell of the first centrifugal compressor (11), the first rotor is arranged on the main shaft of the first centrifugal compressor (11), the first rotor is matched with the first stator, and the first driving motor (114) drives the main shaft of the first centrifugal compressor (11) to rotate so as to drive the first primary compressor (111) and the first secondary compressor (112) to operate synchronously;

the second centrifugal compressor (21) further comprises a second primary compressor (211), a second secondary compressor (212), a second intermediate pipeline (213) and a second driving motor (214), each of the second primary compressor (211) and the second secondary compressor (212) is arranged on the main shaft of the second centrifugal compressor (21), the second driving motor (214) comprises a second stator and a second rotor, the second stator is arranged in the shell of the second centrifugal compressor (21), the second rotor is arranged on the main shaft of the second centrifugal compressor (21), the second rotor is matched with the second stator, and the second driving motor (214) drives the main shaft of the second centrifugal compressor (21) to rotate so as to drive the second primary compressor (211) and the second secondary compressor (212) to synchronously operate.

3. An oil-free cascade refrigeration system as recited in claim 2, wherein,

the low-temperature-stage refrigeration circuit (1) further comprises a first plate heat exchanger (15) and a third expansion valve (16), the first plate heat exchanger (15) is provided with a second heat absorption channel and a second heat release channel, the second heat absorption channel is provided with a second heat absorption inlet (151) and a second heat absorption outlet (152), the second heat release channel is provided with a second heat release inlet (153) and a second heat release outlet (154), the first heat release outlet (122) is communicated with the inlet of the third expansion valve (16), the outlet of the third expansion valve (16) is communicated with the second heat absorption inlet (151), the second heat release outlet (152) is communicated with the first intermediate pipeline (113), the first heat release outlet (122) is also communicated with the second heat release inlet (153), and the second heat release outlet (154) is communicated with the inlet of the first expansion valve (19);

the high-temperature-stage refrigeration circuit (2) further comprises a second plate heat exchanger (25) and a fourth expansion valve (26), the second plate heat exchanger (25) is provided with a third heat absorption channel and a third heat release channel, the third heat absorption channel is provided with a third heat absorption inlet (251) and a third heat absorption outlet (252), the third heat release channel is provided with a third heat release inlet (253) and a third heat release outlet (254), the outlet of the condenser (22) is communicated with the inlet of the fourth expansion valve (26), the outlet of the fourth expansion valve (26) is communicated with the third heat absorption inlet (251), the third heat absorption outlet (252) is communicated with the second intermediate pipeline (213), the outlet of the condenser (22) is also communicated with the third heat release inlet (253), and the third heat release outlet (254) is communicated with the inlet of the second expansion valve (29).

4. An oil-free cascade refrigeration system as recited in claim 3, wherein,

the low-temperature-stage refrigeration circuit (1) further comprises a first regulating valve (17), wherein the inlet of the first regulating valve (17) is communicated with the second heat absorption outlet (152), and the outlet of the first regulating valve (17) is communicated with the first intermediate pipeline (113); and/or the number of the groups of groups,

the high-temperature-stage refrigeration circuit (2) further comprises a second regulating valve (27), wherein the inlet of the second regulating valve (27) is communicated with the third heat absorption outlet (252), and the outlet of the second regulating valve (27) is communicated with the second intermediate pipeline (213).

5. An oil-free cascade refrigeration system as claimed in claim 3, characterized in that the high-temperature-stage refrigeration circuit (2) further comprises a fifth expansion valve (231) and a second evaporator (23), the third heat release outlet (254) being further in communication with the inlet of the fifth expansion valve (231), the outlet of the fifth expansion valve (231) being in communication with the inlet of the second evaporator (23), the outlet of the second evaporator (23) being in communication with the inlet of the second stage compressor (211).

6. An oil-free cascade refrigeration system as recited in claim 5, wherein,

a first circulation groove and a first exhaust pipe (118) are arranged on the shell of the first centrifugal compressor (11), the first circulation groove is matched with the first stator, and each of the outlet of the first circulation groove and the inlet of the first exhaust pipe (118) is communicated with a cavity of the shell of the first centrifugal compressor (11); the low-temperature-stage refrigeration circuit (1) further comprises a sixth expansion valve (110), the second heat release outlet (154) of the first plate heat exchanger (15) is also communicated with the inlet of the sixth expansion valve (110), the outlet of the sixth expansion valve (110) is communicated with the inlet of the first circulation tank, and the outlet of the first exhaust pipe (118) is communicated with the inlet of the first primary compressor (111);

A second circulation groove and a second exhaust pipe (218) are arranged on the shell of the second centrifugal compressor (21), the second circulation groove is matched with the second stator, and each of the outlet of the second circulation groove and the inlet of the second exhaust pipe (218) is communicated with a cavity of the shell of the second centrifugal compressor (21); the high-temperature-stage refrigeration circuit (2) further comprises a seventh expansion valve (210), the third heat release outlet (254) of the second plate heat exchanger (25) is also communicated with the inlet of the seventh expansion valve (210), the outlet of the seventh expansion valve (210) is communicated with the inlet of the second circulation tank, and the outlet of the second exhaust pipe (218) is communicated with the inlet of the second stage compressor (211).

7. An oil-free cascade refrigeration system as recited in claim 6, wherein,

the low-temperature-stage refrigeration circuit (1) further comprises a first gas-liquid separator (14), wherein the first gas-liquid separator (14) is provided with a first inlet (141), a second inlet (142) and a first outlet (143), the first inlet (141) is communicated with the outlet of the first exhaust pipe (118), the second inlet (142) is communicated with the outlet of the first evaporator (13), and the first outlet (143) is communicated with the inlet of the first primary compressor (111);

The high temperature stage refrigeration circuit (2) further comprises a second gas-liquid separator (24), the second gas-liquid separator (24) has a third inlet (241), a fourth inlet (242) and a second outlet (243), the third inlet (241) is communicated with the outlet of the second exhaust pipe (218), the outlet of the second evaporator (23) and each of the first heat absorption outlets (124) of the condensing evaporator (12) are communicated with the fourth inlet (242), and the second outlet (243) is communicated with the inlet of the second stage compressor (211).

8. An oil-free cascade refrigeration system as recited in claim 7, wherein,

the low-temperature-stage refrigeration circuit (1) further comprises a third regulating valve (18), wherein the inlet of the third regulating valve (18) is communicated with the first outlet (143) of the first gas-liquid separator (14), and the outlet of the third regulating valve (18) is communicated with the inlet of the first primary compressor (111).

9. An oil-free cascade refrigeration system as claimed in claim 7, characterized in that the high-temperature-stage refrigeration circuit (2) further comprises a fourth regulating valve (28), an inlet of the fourth regulating valve (28) being in communication with the second outlet (243) of the second gas-liquid separator (24), an outlet of the fourth regulating valve (28) being in communication with an inlet of the second stage compressor (211).

10. An oil-free cascade refrigeration system as recited in claim 2, wherein,

the low-temperature-stage refrigeration circuit (1) further comprises a first communication pipe (115), one end of the first communication pipe (115) is communicated with the outlet of the first secondary compressor (112), the other end of the first communication pipe (115) is communicated with the inlet of the first primary compressor (111), and a first electromagnetic valve (116) is arranged on the first communication pipe (115);

the high-temperature-stage refrigeration circuit (2) further comprises a second communicating pipe (215), one end of the second communicating pipe (215) is communicated with the outlet of the second secondary compressor (212), the other end of the second communicating pipe (215) is communicated with the inlet of the second primary compressor (211), and a second electromagnetic valve (216) is arranged on the second communicating pipe (215).

Images