Refrigeration system and oil return control method thereof

Abstract

The present disclosure relates to a refrigeration system and an oil return control method thereof, wherein the refrigeration system comprises: a compressor (1); an evaporator (2), an outlet (2A) of the evaporator (2) being communicated with a suction port (1A) of the compressor (1) through a suction pipeline (10); an oil separator (3), an inlet (3A) of the oil separator (3) being communicated with an exhaust port (1B) of the compressor (1), an oil outlet (3B) of the oil separator (3) being communicated with the compressor (1) through a first oil return pipeline (20), and a pump (11) being arranged on the first oil return pipeline (20); and an automatic oil return device (4), an inlet (4A) of the automatic oil return device (4) being communicated with the evaporator (2) through a liquid taking pipeline (60) for taking liquid refrigerant in the evaporator (2), an oil outlet (4B) of the automatic oil return device (4) being communicated with the suction pipeline (10) through a second oil return pipeline (30), and a first on-off valve (18) being arranged on at least one of the liquid taking pipeline (60) and the second oil return pipeline (30).

Description

Technical Field

[0001] This disclosure relates to the field of refrigeration system technology, and in particular to a refrigeration system and its oil return control method. Background Technology

[0002] Existing large-scale cryogenic screw compressor units rely solely on suction oil return to replenish oil volume during operation. When the compressor frequency changes, the amount of oil returned also changes, resulting in varying degrees of poor oil return and a risk of oil shortage. When the oil circuit becomes blocked, the unit must be shut down for maintenance, which significantly impacts production efficiency. Summary of the Invention

[0003] Some embodiments of this disclosure propose a refrigeration system and its oil return control method, which can improve the oil return reliability of the compressor in the refrigeration system.

[0004] The first aspect of this disclosure provides a cooling system, comprising:

[0005] The compressor has an air intake port, an exhaust port, and an oil return port;

[0006] The evaporator's outlet is connected to the compressor's suction port via a suction pipe.

[0007] An oil separator has its inlet connected to the compressor's outlet, and its outlet connected to the compressor via a first return oil line, which is equipped with a pump.

[0008] An automatic oil return device is provided. The inlet of the automatic oil return device is connected to the evaporator through a liquid intake pipe to obtain liquid refrigerant from the evaporator. The outlet of the automatic oil return device is connected to the suction pipe through a second oil return pipe. At least one of the liquid intake pipe and the second oil return pipe is provided with a first on / off valve.

[0009] In some embodiments, at least two pumps are provided on the first return line, and the at least two pumps are connected in parallel.

[0010] In some embodiments, it also includes:

[0011] A coarse filter is installed on the first return line and upstream of the pump; and / or

[0012] The fine filter is located on the first return oil line and downstream of the pump.

[0013] In some embodiments, at least two fine filters are also included, which are connected in parallel on the first return line and located downstream of the pump.

[0014] In some embodiments, it also includes:

[0015] An oil cooler is installed in parallel with the first return oil pipeline. The oil inlet of the oil cooler is connected to the oil outlet of the oil separator, and the oil outlet of the oil cooler is connected to the first return oil pipeline located upstream of the pump.

[0016] The oil temperature control valve has a first interface, a second interface, and a third interface. The first interface is connected to the oil outlet of the oil separator and does not conduct when the oil temperature exceeds a preset high temperature threshold. The second interface is connected to the oil outlet of the oil cooler, and the third interface is connected to the pump.

[0017] In some embodiments, the oil separator is provided with a first electric heater, which is configured to be turned on when the oil temperature in the oil separator is lower than a first preset low temperature threshold.

[0018] In some embodiments, it also includes:

[0019] A pressure sensor, located on the first return line and between the pump and the compressor, is configured to detect the pump's outlet pressure; and

[0020] The first bypass oil circuit has its first end connected to the first return oil line located downstream of the pump, and its second end connected to the oil inlet of the oil separator. A constant pressure valve is provided on the first bypass oil circuit, and the constant pressure valve is configured to open when the detection value of the pressure sensor exceeds a preset pressure threshold.

[0021] In some embodiments, it also includes:

[0022] The second bypass oil circuit has its first end connected to the first return oil line located downstream of the pump, and its second end connected to the oil inlet of the oil separator. A second on / off valve is provided on the second bypass oil circuit.

[0023] In some embodiments, the automatic oil return device has an oil level switch at a preset height position, and the automatic oil return device is configured to obtain liquid refrigerant from the evaporator when the oil level is below the preset height position.

[0024] In some embodiments, the automatic return oiler is provided with a second electric heater, which is configured to turn on when the oil temperature in the automatic return oiler is lower than a second preset low temperature threshold.

[0025] In some embodiments, the compressor has an oil discharge port, which is connected to the oil inlet of the oil separator via an oil discharge pipeline. The oil discharge pipeline is equipped with an oil discharge shut-off check valve to ensure one-way flow of the oil discharge pipeline from the compressor to the oil separator.

[0026] In some embodiments, the compressor's oil storage area is provided with a dual oil level switch, which includes a first oil level switch and a second oil level switch. The first oil level switch is set at a first height position Hmin, and the second oil level switch is set at a second height position Hmax, where the second height position Hmax is higher than the first height position Hmin.

[0027] In some embodiments, the refrigeration system further includes:

[0028] An oil cooler, connected in parallel with the first return oil line, is configured to cool the oil returning from the oil separator to the compressor; and

[0029] The condenser's inlet is connected to the compressor's outlet via an oil separator, and the liquid refrigerant flowing out of the condenser's outlet is supplied to the oil cooler for cooling the oil.

[0030] In some embodiments, the refrigeration system further includes:

[0031] The siphon liquid receiver has its inlet connected to the outlet of the condenser, its outlet connected to the inlet of the oil cooler, its air inlet connected to the exhaust port of the oil cooler, and its return air inlet connected to the air inlet of the condenser.

[0032] In some embodiments, the refrigeration system further includes:

[0033] The liquid receiver has its inlet connected to the overflow outlet of the siphon liquid receiver, and its outlet connected to the inlet of the evaporator.

[0034] In some embodiments, the refrigeration system further includes:

[0035] The subcooler, located between the siphon receiver and the evaporator, is configured to subcool the liquid refrigerant in the main circulation loop.

[0036] A second aspect of this disclosure provides a control method for the refrigeration system described in the above embodiments, comprising:

[0037] Detect the oil level in the compressor's oil reservoir;

[0038] When the oil level is between the first height position Hmin and the second height position Hmax, the suction oil return operation is activated and the automatic oil return device stops operating.

[0039] When the oil level is below the first height position Hmin, the suction oil return operation is activated, the automatic oil return device is activated, and the pump is activated to operate through the first oil return line.

[0040] When the oil level is above the second height position Hmax, the suction and oil return operation is activated, the automatic oil return device stops operating, and the compressor discharges oil through the oil discharge port into the oil separator.

[0041] Among them, the second altitude position Hmax is higher than the first altitude position Hmin.

[0042] Based on the above technical solution, this disclosure has at least the following beneficial effects:

[0043] The refrigeration system of this embodiment features multiple oil return methods for the compressor, including suction oil return, forced oil return via a first oil return line and pump, and automatic oil return via an automatic oil return device. The appropriate method can be selected based on the compressor's actual operating status, eliminating reliance on a single suction oil return method. This ensures timely and reliable oil return, preventing oil shortages due to fluctuations in oil return volume when the compressor frequency changes. This extends the compressor's lifespan and significantly improves the reliability of the refrigeration system. Furthermore, even if one oil return line becomes blocked or malfunctions, other oil return lines can still be used for oil return without requiring shutdown for maintenance. Oil return faults can be addressed while the unit is running, improving production efficiency. Attached Figure Description

[0044] The accompanying drawings, which are included to provide a further understanding of this disclosure and form part of this application, illustrate exemplary embodiments of this disclosure and are used to explain this disclosure, but do not constitute an undue limitation of this disclosure. In the drawings:

[0045] Figure 1 This is a schematic diagram of the system structure of some embodiments of the refrigeration system disclosed herein;

[0046] Figure 2 for Figure 1 Enlarged view of point I in the image;

[0047] Figure 3 The flowcharts are for some embodiments of the oil return control method of the refrigeration system disclosed herein.

[0048] It should be understood that the dimensions of the various parts shown in the accompanying drawings are not drawn to actual scale. Furthermore, the same or similar reference numerals denote the same or similar components. Detailed Implementation

[0049] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. The descriptions of the exemplary embodiments are merely illustrative and are in no way intended to limit the present disclosure or its application or use. The present disclosure may be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided so that the present disclosure will be thorough and complete, and will fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless specifically stated otherwise, the relative arrangement of components and steps, the composition of materials, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0050] The terms "first," "second," and similar words used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Words such as "including" or "contains" mean that the element preceding the word encompasses the element listed after it, and do not exclude the possibility of encompassing other elements as well. Terms such as "above," "below," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, this relative positional relationship may also change accordingly.

[0051] In this disclosure, when a specific device is described as being located between a first device and a second device, an intermediary device may or may not be present between the specific device and the first or second device. When a specific device is described as being connected to other devices, the specific device may be directly connected to the other devices without an intermediary device, or it may be not directly connected to the other devices but have an intermediary device.

[0052] All terms used in this disclosure (including technical or scientific terms) have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, such as a dictionary, should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and not as having an idealized or highly formalized meaning, unless expressly defined herein.

[0053] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0054] Based on the embodiments disclosed above, in the absence of explicit denial or conflict, the technical features of one embodiment may be advantageously combined with one or more other embodiments.

[0055] This disclosure provides a refrigeration system, such as Figure 1 and Figure 2 As shown, in some embodiments, the refrigeration system includes:

[0056] Compressor 1 has an air intake port 1A, an exhaust port 1B, and an oil return port 1C;

[0057] Evaporator 2, the outlet 2A of evaporator 2 is connected to the suction port 1A of compressor 1 through suction pipe 10;

[0058] Oil separator 3, with its inlet 3A connected to the outlet 1B of compressor 1, and its outlet 3B connected to the return oil port 1C of compressor 1 via a first return oil pipeline 20, on which a pump 11 is installed; and

[0059] Automatic oil return device 4, the liquid inlet 4A of automatic oil return device 4 is connected to evaporator 2 through liquid intake pipe 60, used to obtain liquid refrigerant in evaporator 2, the oil outlet 4B of automatic oil return device 4 is connected to suction pipe 10 through second oil return pipe 30, and at least one of liquid intake pipe 60 and second oil return pipe 30 is provided with a first on / off valve 18.

[0060] The compressor can be a screw compressor, such as a low-temperature refrigeration screw chiller, or a centrifugal compressor. Large compressors are more prone to insufficient oil return supply problems, and the oil return system disclosed herein is more effective. It is also suitable for small and medium-sized compressors. The compressor is powered by a drive component 39, which can be an electric motor or motor, and is connected to the compressor via a coupling 22.

[0061] The connections of evaporator 2 in the refrigeration system are not fully shown. The outlet 2A of evaporator 2 is connected to the suction port 1A of compressor 1 via suction pipe 10. Suction pipe 10 is equipped with suction check valve 23, which only allows gaseous refrigerant to flow from evaporator 2 to compressor 1 and does not allow reverse flow. A first filter 19 may also be installed on suction pipe 10 to filter impurities in the gaseous refrigerant.

[0062] The liquid inlet 2B of the evaporator 2 is connected to the position marked "B" in the main circulation loop. The compressor 1, condenser 6 and evaporator 2 are located in the main circulation loop. After the gaseous refrigerant is discharged from the compressor 1, it enters the condenser 6 for condensation and heat exchange to form a low-temperature and high-pressure liquid refrigerant. After throttling and cooling, it forms a low-temperature and low-pressure liquid refrigerant. Then it enters the evaporator 2 for evaporation and heat exchange to form a low-temperature and low-pressure gaseous refrigerant, which enters the compressor 1. During the refrigerant circulation process, oil is also added to the compressor along with the gaseous refrigerant to achieve the suction and oil return operation. The driving force of the gaseous refrigerant is used to return a small amount of lubricating oil to the compressor 1.

[0063] The inlet 3A of the oil separator 3 is connected to the outlet 1B of the compressor 1. The high-temperature, high-pressure gas discharged from the compressor 1 enters the oil separator 3 for oil-gas separation. Under the driving force of the pump 11, the oil flowing from the outlet 3B of the oil separator 3 can enter the return oil port 1C of the compressor 1 through the first return oil pipeline 20, enabling forced oil return when there is insufficient oil in the compressor 1. The oil separator 3 separates the lubricating oil carried in the exhaust gas of the compressor 1, purifying the high-pressure refrigerant gas entering the condenser 6, reducing the adverse effects of the lubricating oil film on heat transfer, and lowering lubricating oil consumption. The pump 11 can supply lubricating oil to the compressor 1 before startup or during operation; the pressure difference across the pump 11 is determined by the required oil supply pressure of the compressor.

[0064] The inlet 4A of the automatic oil return device 4 is connected to the evaporator 2 at the position marked "A" to obtain liquid refrigerant from the evaporator 2. The outlet 4B of the automatic oil return device 4 is connected to the suction line 10 through the second oil return line 30, and the connection position can be located between the suction check valve 23 and the evaporator 2. At least one of the second oil return line 30 and the liquid collection line 60 is equipped with a first on / off valve 18, such as a solenoid valve, to control the on / off state of the automatic oil return. When on, the automatic oil return is realized; when off, the automatic oil return is cut off. To increase the automatic oil return volume, two or more second oil return lines 30 can also be provided. Optionally, a first filter 19 can also be provided on the second oil return line 30 to filter impurities in the oil.

[0065] The automatic oil return device 4 is used to remove the liquid refrigerant from the evaporator 2 at the user end, and return the lubricating oil mixed in it to the suction port 1A of the compressor 1. This controls the amount of oil melted in the refrigerant in the evaporator 2 and prevents too much oil melted from affecting heat exchange.

[0066] The refrigeration system of this embodiment is equipped with multiple oil return methods for compressor 1, including suction oil return, forced oil return through the first oil return line 20 and pump 11, and automatic oil return through automatic oil return device 4. The appropriate method can be selected based on the actual operating state of compressor 1, eliminating the need to rely solely on suction oil return. This ensures timely and reliable oil return, preventing oil shortages due to fluctuations in oil return volume when compressor frequency changes. This extends compressor lifespan and significantly improves the reliability of the refrigeration system. Furthermore, if a certain oil return line becomes blocked or malfunctions, other oil return lines can still be used for oil return without shutdown for maintenance. Oil return faults can be addressed while the unit is running, improving production efficiency.

[0067] In some embodiments, at least two pumps 11 are provided on the first return oil line 20, and the at least two pumps 11 are connected in parallel. The at least two pumps 11 can supply oil simultaneously or be partially put into use to ensure reliable oil supply to the first return oil line 20.

[0068] Optionally, only one pump 11 may be provided.

[0069] This embodiment connects at least two pumps 11 in parallel on the first return oil line 20. Some or all of the pumps 11 can be put into operation according to the return oil demand to provide sufficient driving pressure and ensure reliable oil supply. Even if a pump 11 fails, driving pressure can still be provided by other pumps 11, allowing the unit to continue operating normally and enabling maintenance without shutting down the plant.

[0070] In some embodiments, such as Figure 1 As shown, the refrigeration system also includes:

[0071] Coarse filter 12 is installed on the first return oil line 20 and upstream of pump 11; and / or

[0072] Fine filter 13 is installed on the first return oil line 20 and is located downstream of pump 11.

[0073] In this embodiment, by setting a coarse filter 12, the oil has already been filtered when it is separated in the oil separator 3. After entering the coarse filter 12, larger impurity particles in the lubricating oil can be removed. By setting a fine filter 13, smaller impurity particles in the lubricating oil can be removed. Finally, it is ensured that the lubricating oil entering the compressor is very clean, so as to ensure good lubrication of friction points such as compressor bearings, rotor, and shaft seal, normal operation, and reduced wear.

[0074] When both a coarse filter 12 and a fine filter 13 are installed, after the oil is separated in the oil separator 3, it first enters the coarse filter 12 to remove larger impurities from the lubricating oil, making the lubricating oil entering the fine filter 13 relatively clean. This reduces the burden on the fine filter 13, ensuring good lubrication of the oil pump and compressor, normal operation, and preventing wear. After leaving the pump 11, it passes through the fine filter 13 again to further remove smaller impurities from the lubricating oil. Finally, it ensures that the lubricating oil entering the compressor is very clean, ensuring good lubrication of friction points such as the compressor bearings, rotor, and shaft seals, normal operation, and reducing wear.

[0075] In some embodiments, the refrigeration system further includes at least two fine filters 13, which are connected in parallel on the first oil return line 20 and located downstream of the pump 11. The at least two fine filters 13 can filter simultaneously, or they can be manually adjusted so that some are in use and some are on standby, ensuring reliable filtration of the first oil return line 20.

[0076] This embodiment connects at least two fine filters 13 in parallel on the first return oil line 20. Some or all of the fine filters 13 can be put into use according to filtration requirements to ensure effective oil filtration. Even if some fine filters 13 fail, filtration can still be achieved through other fine filters 13, improving system reliability. Furthermore, faulty fine filters 13 can be replaced or repaired without shutting down the system.

[0077] Optionally, a coarse filter 12 and at least two fine filters 13 connected in parallel are installed on the first return oil line 20 to ensure the cleanliness of the oil and improve the reliability of system operation.

[0078] In some embodiments, such as Figure 1 As shown, the refrigeration system also includes:

[0079] Oil cooler 5 is connected in parallel with the first return oil pipeline 20. The oil inlet 5A of oil cooler 5 is connected to the oil outlet 3B of oil separator 3. The oil outlet 5B of oil cooler 5 is connected to the first return oil pipeline 20 upstream of pump 11.

[0080] The oil temperature control valve 37 has a first interface 37A, a second interface 37B and a third interface 37C. The first interface 37A is connected to the oil outlet 3B of the oil separator 3, and the first interface 37A does not conduct when the oil temperature exceeds the preset high temperature threshold. The second interface 37B is connected to the oil outlet 5B of the oil cooler 5, and the third interface 37C is connected to the pump 11.

[0081] Among them, the oil cooler 5 can be a fluorinated oil cooler, etc. The fluorinated oil cooler is a shell-and-tube heat exchanger, with oil on the shell side and refrigerant on the tube side. A temperature sensor can be installed on the first return oil line 20 to detect the oil temperature.

[0082] The oil temperature control valve 37 is used to control the oil temperature. It can automatically adjust the temperature of the fluid in the pipeline to maintain a stable temperature output, and is also known as a thermostatic valve. The thermostatic valve is equipped with a temperature sensor to detect the fluid temperature. When the temperature exceeds the set range, the controller will control the valve opening, thereby adjusting the fluid flow rate and opening temperature.

[0083] After the oil flows out of the oil separator 3, when the oil temperature is normal, it directly enters the coarse filter 12 through the oil temperature control valve 37 and is then sucked into the pump 11. When the oil flowing out of the oil separator 3 exceeds the preset high temperature threshold, the first interface 37A connecting the oil temperature control valve 37 and the oil separator 3 is not open, and the oil can only flow into the oil cooler 5. Liquid refrigerant formed by the condenser 6 can be introduced into the oil cooler 5. The liquid refrigerant absorbs the heat of the oil and evaporates into gaseous refrigerant. The oil loses heat and is cooled. The oil that reaches a suitable temperature flows through the second interface 37B, through the oil temperature control valve 37, into the coarse filter 12, and is then sucked into the pump 11. After the oil is discharged from the pump 11, it passes through the fine filter 13 and finally flows into the compressor 1.

[0084] If the refrigeration system of this embodiment detects that the oil temperature is too high during operation, the lubricating oil separated by the oil separator 3 first passes through the oil cooler 5 to reach the viscosity and temperature required by the compressor 1, and then is sprayed into the compressor 1 for circulation, to prevent high temperature oil return from accelerating the wear of the compressor 1, thereby improving the service life of the compressor 1.

[0085] In some embodiments, the oil separator 3 is provided with a first electric heater 36, which is configured to be turned on when the oil temperature in the oil separator 3 is lower than a first preset low temperature threshold.

[0086] This embodiment provides a first electric heater 36 inside the oil separator 3. If the oil temperature is detected to be too low before the compressor 1 starts or during operation, the first electric heater 36 can be activated to raise the oil temperature to a suitable range, preventing low-temperature oil return from causing an increase in the power consumption of the compressor 1.

[0087] In some embodiments, such as Figure 2 As shown, the refrigeration system also includes:

[0088] Pressure sensor 15, located on the first return oil line 20 and between pump 11 and compressor 1, is configured to detect the outlet pressure of pump 11; and

[0089] The first bypass oil passage 40 has its first end connected to the first return oil line 20 located downstream of the pump 11, and its second end connected to the oil inlet 3C of the oil separator 3. The first bypass oil passage 40 is equipped with a constant pressure valve 14, which is configured to open when the detection value of the pressure sensor 15 exceeds a preset pressure threshold.

[0090] The pressure sensor 15 can be configured as one or at least two. Figure 2A pressure sensor 15 is installed upstream and downstream of the fine filter 13. The pressure sensor 15 downstream of the fine filter 13, closer to the compressor 1, has a detection value that is closer to the actual pressure of the compressor 1. When controlling the operation of the constant pressure valve 14, this pressure sensor 15 can be used as the reference, while the detection value of the other pressure sensor 15 is used as an auxiliary detection. If the pressure sensor 15 near the compressor 1 fails, the detection value of the other pressure sensor 15 is used to control the operation of the constant pressure valve 14. This structure solves the problem of having a single detection element, which requires production to be stopped for repair once a component fails.

[0091] This embodiment monitors the oil pressure before it enters the compressor 1 using a pressure sensor 15, and controls the return oil pressure of the first return oil line 20 using a constant pressure valve 14 to ensure that oil is supplied at a suitable pressure. When the oil supply pressure of the pump 11 exceeds a preset pressure threshold, the constant pressure valve 14 opens, releasing pressure through the first bypass oil line 40, and some oil flows back to the oil separator 3 to prevent high-pressure oil supply from causing jet noise. When the oil supply pressure of the pump 11 does not exceed the preset pressure threshold, the pump 11 continues to work to increase the oil supply pressure, ensuring that oil is supplied at a suitable pressure and preventing insufficient oil supply due to low-pressure oil supply.

[0092] In some embodiments, such as Figure 1 As shown, the refrigeration system also includes: a second bypass oil passage 70, the first end of the second bypass oil passage 70 is connected to the first return oil line 20 located downstream of the pump 11, the second end of the second bypass oil passage 70 is connected to the oil inlet 3C of the oil separator 3, and a second on / off valve 17 is provided on the second bypass oil passage 70.

[0093] The second on / off valve 17 is configured to open when the pressure sensor 15 detects a value exceeding a preset pressure threshold and the constant pressure valve 14 malfunctions; when the constant pressure valve 14 is functioning normally, it preferentially releases pressure through the first bypass oil passage 40. For example, the second on / off valve 17 can be a solenoid valve, etc.

[0094] In this embodiment, a first bypass oil passage 40 and a second bypass oil passage 70 are simultaneously provided between the outlet of pump 11 and oil separator 3. When the oil supply pressure of pump 11 exceeds a preset pressure threshold, the priority constant pressure valve 14 opens to release pressure through the first bypass oil passage 40, allowing some oil to flow back to oil separator 3. This maintains a stable oil supply pressure for pump 11 and prevents high-pressure oil supply from causing jet noise. Moreover, if the constant pressure valve 14 malfunctions and cannot release pressure, the second on / off valve 17 can still connect the second bypass oil passage 70 for pressure release, serving as a backup pressure release function and improving the reliability and safety of the refrigeration system.

[0095] In some embodiments, the automatic oil return device 4 is equipped with an oil level switch 4' at a preset height position, and the automatic oil return device 4 is configured to obtain liquid refrigerant from the evaporator 2 when the oil level is lower than the preset height position.

[0096] The automatic oil return device 4 is used to remove liquid refrigerant from the evaporator 2, returning the lubricating oil mixed in with it to the compressor suction end. This controls the amount of oil melted in the refrigerant in the evaporator, preventing excessive oil from affecting heat exchange. For example, the oil level switch 4' can be a single-pole double-throw float-type liquid level switch. When the first on / off valve 18 is closed, if the oil level is below the preset height, the oil level switch 4' opens, automatically drawing liquid refrigerant from the evaporator 2; if the oil level reaches the preset height, the oil level switch 4' closes, preventing the drawing of liquid refrigerant from the evaporator 2. The automatic oil return device 4 can be set to operate on / off; if the amount of oil melted in the evaporator 2 is low, the automatic oil return device 4 can be turned off.

[0097] This embodiment, by setting an oil level switch 4' in the automatic oil return device 4, can automatically obtain liquid refrigerant from the evaporator 2 when the oil level is below a preset height, without the need for control intervention, reducing the difficulty of controlling the automatic oil return. It can also release the lubricating oil mixed in and return it to the suction port 1A of the compressor 1, controlling the amount of oil melted in the refrigerant in the evaporator 2, and avoiding too much oil melt, which would affect heat exchange.

[0098] In some embodiments, the automatic return oiler 4 is provided with a second electric heater, which is configured to be turned on when the oil temperature in the automatic return oiler 4 is lower than a second preset low temperature threshold.

[0099] Before initial use, a small amount of lubricating oil can be injected into the cylinder of the automatic oil return device 4 to ensure that the oil level is above the second electric heater.

[0100] This embodiment, by setting a second electric heater in the automatic oil return device 4, can heat the oil that is automatically returned before the compressor 1 is turned on or during operation, raising the oil temperature to a suitable range and preventing the power consumption of the compressor 1 from increasing due to low-temperature oil return.

[0101] In some embodiments, the compressor 1 has an oil discharge port 1D, which is connected to the oil inlet 3C of the oil separator 3 via an oil discharge pipeline 50. The oil discharge pipeline 50 is provided with an oil discharge shut-off check valve 16 for unidirectionally guiding the oil discharge pipeline 50 from the compressor 1 to the oil separator 3.

[0102] Among them, the oil discharge port 1D corresponds to the high oil level in the compressor 1. When the oil level is higher than the oil discharge port 1D, the oil flows out from the compressor 1 and flows into the oil separator 3 through the oil discharge stop check valve 16.

[0103] In this embodiment, the compressor 1 is equipped with an oil drain port 1D. When the internal oil level is higher than the drain port 1D, the oil can automatically flow out through the drain port 1D and enter the oil separator 3 through the oil drain line 50, which can prevent the compressor 1 from experiencing hydraulic compression problems due to excessively high oil levels. Moreover, the oil drain shut-off check valve 16 is unidirectional, which can prevent the oil in the oil separator 3 from flowing back into the compressor 1, thereby improving the safety of the compressor 1 during operation.

[0104] In some embodiments, such as Figure 1 and Figure 3 As shown, the oil storage area of ​​compressor 1 is equipped with a dual oil level switch 21. The dual oil level switch 21 includes a first oil level switch and a second oil level switch. The first oil level switch is set at a first height position Hmin, and the second oil level switch is set at a second height position Hmax. The second height position Hmax is higher than the first height position Hmin.

[0105] When the oil level is between the first height position Hmin and the second height position Hmax, the suction oil return operation is activated and the automatic oil return device 4 stops operating.

[0106] When the oil level is below the first height position Hmin, the suction return operation is activated, the automatic return oil device 4 operates, and the pump 11 operates to operate through the first return oil line 20; and / or

[0107] When the oil level is above the second height position Hmax, the suction and oil return operation is activated, the automatic oil return device 4 stops operating, and the compressor 1 discharges oil into the oil separator 3 through the oil discharge port 1D.

[0108] Hmin can be the lowest allowable oil level of the compressor, and Hmax can be the highest allowable oil level of the compressor. The oil level h in compressor 1 is detected in real time and compared with Hmin and Hmax. Based on the analysis and judgment results, the oil return combination is selected autonomously.

[0109] Conventional compressors determine whether to return oil based solely on external parameters. When compressor parameters change, the control of the oil return amount is delayed, resulting in untimely, insufficient, unreliable, or even insufficient oil return.

[0110] This embodiment utilizes a dual oil level switch 21 to detect the liquid level in compressor 1. Based on the actual liquid level, different combinations of oil return—suction oil return, automatic oil return, and forced oil return—are selected for more direct control. This ensures timely, reliable, and sufficient oil return, guaranteeing compressor 1 achieves optimal lubrication before startup or during operation. It also enables precise control of the oil return volume, extending service life and preventing excessive oil buildup and hydraulic compression in compressor 1. Furthermore, the dual oil level switch 21 offers higher reliability compared to a single oil level switch. In case of switch failure, no shutdown is required, ensuring smooth production. Moreover, the dual oil level switch 21 minimizes frequent operation when liquid level fluctuates due to compressor frequency changes, further extending its service life. When the oil level deviates from the low or high position, it can quickly activate, promptly returning or unloading oil.

[0111] When h < Hmin, select the combination of suction return oil operation, automatic return oil operation and forced return oil operation for oil return control. Open the first on / off valve 18 in the second return oil line 30 and the liquid intake line 60 to enable automatic return oil operation under the action of pressure difference (liquid column pressure in the automatic return oiler 4 and the pressure difference between exhaust and suction). Pump 11 can enable forced return oil operation. At this time, oil can be returned simultaneously through the three return oil methods so as to quickly replenish the compressor 1 with lubricating oil to the appropriate height range.

[0112] When Hmin≤h≤Hmax, the combination of suction oil return operation, automatic oil return operation stop, and forced oil return stop is selected for oil return control. Closing the first on / off valve 18 in the second oil return line 30 and / or liquid intake line 60 will stop the automatic oil return operation, and stopping the pump 11 will stop the forced oil return operation. At this time, the oil return needs of the compressor 1 can be met by using only the trace amount of lubricating oil contained in the suction.

[0113] When h > Hmax, the combination of suction return oil operation, automatic oil return operation stop, and automatic oil unloading is selected for oil return control. This is because even if the oil in compressor 1 exceeds the maximum allowable level, there will still be a small amount of suction return oil. Therefore, the excess oil is automatically allowed to enter the oil separator 3 through the oil unloading port 1D.

[0114] In some embodiments, such as Figure 1 As shown, the refrigeration system also includes:

[0115] Oil cooler 5, connected in parallel with the first oil return line 20, is configured to cool the oil returning from oil separator 3 to compressor 1; and

[0116] The condenser 6 has an air inlet 6A connected to the exhaust port 1B of the compressor 1 via an oil separator 3. The liquid refrigerant flowing out of the liquid outlet 6B of the condenser 6 is supplied to the oil cooler 5 for cooling the oil.

[0117] For example, the oil cooler 5 can be a fluorinated oil cooler, which is a shell-and-tube heat exchanger with oil on the shell side and refrigerant on the tube side.

[0118] For example, condenser 6 can be an evaporative condenser, which is a device that utilizes the heat absorbed by the high-temperature gaseous refrigerant inside the coil when the sprayed water outside the coil partially evaporates, thus gradually cooling the refrigerant inside the coil from a gaseous state to a liquid state. After the gaseous refrigerant is drawn into compressor 1, the compressed gas enters condenser 6 and condenses into a saturated liquid with a certain degree of subcooling. A portion of the liquid refrigerant flowing out of condenser 6 can be supplied to oil cooler 5 for heat exchange with the oil.

[0119] This embodiment utilizes the liquid refrigerant flowing out of the condenser 6 to cool the oil in the oil cooler 5, directly using the subcooled liquid refrigerant in the main circulation loop without increasing system complexity. Furthermore, if the lubricating oil separated by the oil separator 3 is too hot, it enters the oil cooler 5 and exchanges heat with the liquid refrigerant, cooling the oil to the viscosity and temperature required by the compressor 1 before being injected back into the compressor 1 for recycling. This prevents high-temperature oil return from accelerating compressor 1 wear, thereby extending the compressor 1's service life.

[0120] In some embodiments, the refrigeration system further includes: a siphon receiver 7, the inlet 7A of the siphon receiver 7 being connected to the outlet 6B of the condenser 6, the outlet 7B of the siphon receiver 7 being connected to the inlet 5C of the oil cooler 5, the air inlet 7C of the siphon receiver 7 being connected to the exhaust port 5D of the oil cooler 5, and the return air port 7D of the siphon receiver 7 being connected to the air inlet 6A of the condenser 6.

[0121] The siphon liquid receiver 7 operates on the principle of the siphon effect of liquids. When liquid is present inside the container, a pressure difference occurs, meaning the gas pressure at the top is lower than the vapor pressure at the liquid surface. At this point, the gas trapped between the liquid surface and the inner wall of the container is drawn out, creating a vacuum inside the container. Under these conditions, liquid can be siphoned to the inlet through the inlet at the top of the container and, under the influence of gravity, flows freely into the storage tank. When the liquid level reaches a certain point, the container reaches a new equilibrium, and the siphon effect at the inlet ceases.

[0122] The liquid inlet 7A and the return gas inlet 7D can be located at the top of the siphon liquid receiver 7, and the liquid outlet 7B and the gas inlet 7C can be located at the bottom of the siphon liquid receiver 7. The siphon liquid receiver 7 can be located above the oil cooler 5 so that the liquid refrigerant can smoothly enter the oil cooler 5 by utilizing gravity. The gaseous refrigerant generated after the liquid refrigerant exchanges heat with the oil enters the return gas pipe through the exhaust port 5D of the oil cooler 5, and then enters the exhaust pipe from the return gas inlet 7D of the siphon liquid receiver 7, and then condenses again in the condenser 6.

[0123] Optionally, Figure 1 The device has two parallel condensers 6. The gaseous refrigerant from the oil separator 3 is divided into two paths and enters the inlet 6A of the two condensers 6 respectively. The liquid refrigerant flowing out of the outlet 6B of the two condensers 6 converges and enters the siphon liquid receiver 7. Part of the liquid refrigerant enters the oil cooler 5 for heat exchange and forms gaseous refrigerant which returns to the siphon liquid receiver 7 and is then divided into two paths and enters the two condensers 6 again for condensation.

[0124] This embodiment, by setting up a siphon receiver 7, can store and transfer the liquid refrigerant formed by the condenser 6, and supply liquid to the oil cooler 5 using the siphon principle. It can both use the subcooled liquid refrigerant in the main circulation loop to cool the oil and meet the refrigerant flow requirements of the main circulation loop. The refrigerant can also achieve gas-liquid separation in the siphon receiver 7.

[0125] In some embodiments, the refrigeration system further includes: a liquid receiver 8, the liquid inlet 8A of which is connected to the overflow port 7E of the siphon liquid receiver 7, and the liquid outlet 8B of the liquid receiver 8 being connected to the liquid inlet 2B of the evaporator 2.

[0126] The receiver 8 serves to store and transfer liquid refrigerant. Most of the liquid refrigerant in the siphon receiver 7 enters the receiver 8, and after exiting, it passes through the second filter 26 to remove impurities or moisture, undergoes further subcooling, and is then supplied to the evaporator 2 at the refrigeration terminal. The refrigerant gas exiting the evaporator 2 is then drawn back into the compressor 1 to complete the refrigeration cycle. A small portion of the liquid refrigerant in the siphon receiver 7 enters the oil cooler 5. For example, the receiver 8 can be positioned vertically below the siphon receiver 7 to allow for smoother liquid flow into the receiver 8.

[0127] In this embodiment, a liquid receiver 8 is installed downstream of the siphon liquid receiver 7, which allows most of the liquid refrigerant in the siphon liquid receiver 7 to flow into the liquid receiver 8 for storage in a timely manner. This increases the amount of liquid refrigerant stored, which can meet the needs of the refrigeration system when the load fluctuates greatly and improve the unit performance. Moreover, since the liquid refrigerant also contains gas, it can undergo two gas-liquid separations after passing through the siphon liquid receiver 7 and entering the liquid receiver 8, thereby improving the gas-liquid separation effect and increasing the content of liquid refrigerant entering the evaporator 2.

[0128] Optionally, the siphon reservoir 7 and the reservoir 8 can be combined into one to form a reservoir device, which can be modified into a vertical type, with the upper part being the siphon reservoir and the lower part being the reservoir.

[0129] In some embodiments, the refrigeration system further includes a subcooler 9, disposed between the siphon receiver 7 and the evaporator 2, configured to subcool the liquid refrigerant in the main circulation loop.

[0130] For example, the subcooler 9 can be a shell-and-tube economizer to subcool the refrigerant in the main circulation loop. In an embodiment where a receiver 8 is provided, the subcooler 9 can be located between the receiver 8 and the evaporator 2.

[0131] This embodiment, by setting up a subcooler 9, can subcool the liquid refrigerant in the main circulation loop, thereby improving the economy and efficiency of the refrigeration cycle.

[0132] The following is based on Figure 1 Taking a refrigeration system as an example, let's illustrate its specific structure. The diagram shows two dashed boxes, representing the compressor module 100 and the condenser module 200. The compressor module 100 drives the refrigerant transfer, while the condenser module 200 performs condensation and heat exchange, transferring the exhaust heat from the compressor 1 to the atmosphere or cooling water. The main components of the refrigeration system include: compressor 1, evaporator 2, condenser 6, oil separator 3, automatic oil return device 4, oil cooler 5, siphon receiver 7, receiver 8, and subcooler 9.

[0133] The connection methods of these main components have been described in the foregoing embodiments; this section mainly describes components not mentioned above. The compressor 1 is equipped with a solenoid valve assembly 22 for changing the operating parameters of the compressor 1 and adjusting cooling capacity, etc. A branch pipe 80 can be provided between the outlet of the oil separator 3 and the suction pipe 10. The branch pipe 80 is equipped with a sight glass 31, a third solenoid valve 32, and a first filter 19. The content of liquid refrigerant in the gaseous refrigerant drawn from the oil separator 3 can be observed through the sight glass 31. Excessive liquid refrigerant will adversely affect the operation of the compressor 1.

[0134] Optionally, a second filter 26 can be installed between the subcooler 9 and the compressor 1. For example, this filter can be a straight-through filter or a filter with an inclined filter element, which can be directly pulled out for easy replacement without removal. A second filter 26 and a sight glass 31 can also be installed between the liquid receiver 8 and the subcooler 9. A safety valve 33 is installed between the oil separator 3 and the air inlet 6A of the condenser 6. A pressure sensor 15 and a temperature sensor 41 can be installed on the pipeline between the fine filter 13 and the compressor 1.

[0135] Optionally, the refrigeration system is equipped with multiple shut-off valves to facilitate component and pipeline maintenance. For example, a first shut-off valve 24 is installed on the second oil return line 30 and the branch line 80; a second shut-off valve 35 is installed on the line between the oil separator 3 and the air inlet 6A of the condenser 6; a third shut-off valve 34 is installed between the liquid outlet 6B of the condenser 6 and the siphon liquid receiver 7; a fourth shut-off valve 27 can be installed between the fine filter 13 and the compressor 1; in addition, a fourth shut-off valve 25 is used at multiple bends in the pipeline.

[0136] Figure 1 The working principle of the refrigeration system shown is as follows:

[0137] The refrigerant circulation path is as follows: Gaseous refrigerant from evaporator 2 is drawn into compressor 1. After compression, the gas enters condenser 6 and condenses into a saturated liquid with some subcooling. The subcooled liquid enters siphon receiver 7, supplying liquid to oil cooler 5. The resulting gaseous refrigerant, after heat exchange, enters the exhaust pipe through the return pipe and condenses again in condenser 6. Most of the liquid in siphon receiver 7 enters receiver 8, and then passes through a filter or dryer to remove impurities and moisture. After further subcooling in economizer 9, it is supplied to evaporator 2. The gaseous refrigerant evaporated from evaporator 2 is drawn back into compressor 1 to complete the refrigeration cycle.

[0138] The lubricating oil circulation in the refrigeration system includes three flow paths: suction oil return flow path, automatic oil return flow path, and forced oil return flow path. The lubricating oil is supplied to compressor 1 for lubrication, sealing, noise reduction, and removal of some of the compression heat. These will be explained separately below.

[0139] The oil return flow path is: Compressor 1—Oil Separator 3—Condenser 6—Siphon Receiver 7—Receiver 8—Subcooler 9—Evaporator 2—Compressor 1. Tiny oil droplets entrained in the refrigerant circulate along with the refrigerant. Each component operates according to the refrigerant circulation requirements, requiring no special control.

[0140] The flow path for automatic oil return operation is as follows: Evaporator 2 — First on / off valve 18 of liquid intake line 60 — Automatic oil return device 4 — First on / off valve 18 of second oil return line 30 — First filter 19 — First shut-off valve 24 of second oil return line 30 — Suction check valve 23 — Compressor 1. During automatic oil return operation, the first on / off valve 18 of liquid intake line 60 and second oil return line 30 is connected. The function of automatic oil return operation is to remove liquid refrigerant from evaporator 2, precipitate the lubricating oil mixed in it, and return it to the compressor suction end, controlling the amount of oil melted in the refrigerant in the evaporator to prevent excessive oil melt from affecting heat exchange.

[0141] The forced oil return flow path is: Compressor 1—Oil separator 3—Oil cooler 5—Oil temperature control valve 37—Coarse filter 12—Pump 11—Fine filter 13—Compressor 1. During forced oil return, the oil temperature control valve 37 is opened and closed according to the temperature. After the oil flows out of the oil separator 3, when the oil temperature is normal, it directly enters the coarse filter 12 through the oil temperature control valve 37 and is then sucked into the pump 11. When the oil temperature is high, the first interface 37A connecting the oil temperature control valve 37 and the oil separator 3 is not conductive, and the oil can only flow into the oil cooler 5. Inside the cooler 5, the liquid refrigerant from the siphon receiver 7 absorbs the heat from the oil and evaporates into gaseous refrigerant, cooling the oil as it loses heat. The oil that has reached the appropriate temperature passes through the oil temperature control valve 37, flows into the coarse filter 12, and is then sucked into the pump 11. After exiting the pump 11, it passes through the fine filter 13 and finally flows into the compressor 1.

[0142] The refrigeration system disclosed herein provides timely, sufficient, and reliable oil return, preventing oil shortage, avoiding liquid compression, and ensuring the compressor's service life. It also boasts high oil return reliability, employing three return methods: suction oil return, automatic oil return, and forced oil return, significantly improving system operational reliability. Furthermore, it enhances production efficiency by handling oil return faults during unit operation. Additionally, it delivers high-quality oil return, with precise control over oil temperature, pressure, and cleanliness, greatly enhancing the quality of the returned oil.

[0143] In some embodiments of the large cryogenic screw chiller system, the cooling capacity is 1800kW and the liquid outlet temperature of the shell-and-tube economizer is -18°C.

[0144] Secondly, this disclosure provides a method for controlling the oil return of a refrigeration system based on the above embodiments. In some embodiments, such as... Figure 3 As shown, the control method includes:

[0145] Detect the oil level in the oil storage area of ​​compressor 1;

[0146] When the oil level is between the first height position Hmin and the second height position Hmax, the suction oil return operation is activated and the automatic oil return device 4 stops operating.

[0147] When the oil level is below the first height position Hmin, the suction return operation is activated, the automatic return oil device 4 operates, and the pump 11 operates to operate through the first return oil line 20; and / or

[0148] When the oil level is higher than the second height position Hmax, the suction and oil return operation is activated, the automatic oil return device 4 stops operating, and the compressor 1 discharges oil into the oil separator 3 through the oil discharge port 1D.

[0149] Among them, the second altitude position Hmax is higher than the first altitude position Hmin.

[0150] For example, the oil storage area of ​​compressor 1 is equipped with a dual oil level switch 21 to detect the oil level position. The dual oil level switch 21 includes a first oil level switch and a second oil level switch. The first oil level switch is set at a first height position Hmin, and the second oil level switch is set at a second height position Hmax.

[0151] In this embodiment, after the unit is running, different oil return combinations can be selected from suction oil return, automatic oil return, and forced oil return according to the actual liquid level in the compressor 1. This allows for timely, reliable, and sufficient oil return, ensuring that the compressor 1 reaches a good lubrication state before startup or during operation. It also enables precise control of the oil return amount of the compressor 1, improves its service life, and prevents excessive oil in the compressor 1 from causing hydraulic compression.

[0152] When h < Hmin, the oil return operation is controlled by a combination of suction oil return operation, automatic oil return operation and forced oil return operation. Opening the first on / off valve 18 in the second oil return line 30 and the liquid intake line 60 will enable automatic oil return operation under the action of pressure difference (which includes the liquid column pressure in the automatic oil return device 4 and the pressure difference between exhaust and suction). Pump 11 will enable forced oil return operation. At this time, oil can be returned simultaneously through the three oil return methods to quickly replenish the compressor 1 with lubricating oil to the appropriate height range.

[0153] When Hmin≤h≤Hmax, the combination of suction oil return operation, automatic oil return operation stop, and forced oil return stop is selected for oil return control. Closing the first on / off valve 18 in the second oil return line 30 and / or liquid intake line 60 will stop the automatic oil return operation, and stopping the pump 11 will stop the forced oil return operation. At this time, the oil return needs of the compressor 1 can be met by using only the trace amount of lubricating oil contained in the suction.

[0154] When h > Hmax, the combination of suction return oil operation, automatic oil return operation stop, and automatic oil unloading is selected for oil return control. This is because even if the oil in compressor 1 exceeds the maximum allowable level, there will still be a small amount of suction return oil. Therefore, the excess oil is automatically allowed to enter the oil separator 3 through the oil unloading port 1D.

[0155] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure. The scope of this disclosure is defined by the appended claims.

Claims

1. A refrigeration system, characterized in that, include: The compressor (1) has an air intake (1A), an exhaust (1B) and an oil return (1C); Evaporator (2), the outlet (2A) of the evaporator (2) is connected to the suction port (1A) of the compressor (1) through suction pipe (10); An oil separator (3) is provided, wherein the inlet (3A) of the oil separator (3) is connected to the outlet (1B) of the compressor (1), and the outlet (3B) of the oil separator (3) is connected to the compressor (1) through a first oil return pipeline (20), and a pump (11) is provided on the first oil return pipeline (20); and An automatic oil return device (4) is provided. The inlet (4A) of the automatic oil return device (4) is connected to the evaporator (2) through a liquid intake pipe (60) to obtain liquid refrigerant in the evaporator (2). The outlet (4B) of the automatic oil return device (4) is connected to the suction pipe (10) through a second oil return pipe (30). At least one of the liquid intake pipe (60) and the second oil return pipe (30) is provided with a first on / off valve (18).

2. The refrigeration system as described in claim 1, characterized in that, At least two pumps (11) are provided on the first return oil line (20), and the at least two pumps (11) are connected in parallel.

3. The refrigeration system as described in claim 1, characterized in that, Also includes: A coarse filter (12) is provided on the first return oil line (20) and located upstream of the pump (11); and / or A fine filter (13) is provided on the first return oil line (20) and located downstream of the pump (11).

4. The refrigeration system as described in claim 1, characterized in that, It also includes at least two fine filters (13), which are connected in parallel on the first return oil line (20) and located downstream of the pump (11).

5. The refrigeration system as described in claim 1, characterized in that, Also includes: An oil cooler (5) is connected in parallel with the first return oil pipeline (20). The oil inlet (5A) of the oil cooler (5) is connected to the oil outlet (3B) of the oil separator (3). The oil outlet (5B) of the oil cooler (5) is connected to the first return oil pipeline (20) located upstream of the pump (11). The oil temperature control valve (37) has a first interface (37A), a second interface (37B) and a third interface (37C). The first interface (37A) is connected to the oil outlet (3B) of the oil separator (3), and the first interface (37A) does not conduct when the oil temperature exceeds a preset high temperature threshold. The second interface (37B) is connected to the oil outlet (5B) of the oil cooler (5), and the third interface (37C) is connected to the pump (11).

6. The refrigeration system as described in claim 1, characterized in that, The oil separator (3) is equipped with a first electric heater (36), which is configured to be turned on when the oil temperature in the oil separator (3) is lower than a first preset low temperature threshold.

7. The refrigeration system as described in claim 1, characterized in that, Also includes: A pressure sensor (15), located on the first return line (20) and between the pump (11) and the compressor (1), is configured to detect the outlet pressure of the pump (11); and A first bypass oil passage (40) is provided. The first end of the first bypass oil passage (40) is connected to the first return oil line (20) located downstream of the pump (11). The second end of the first bypass oil passage (40) is connected to the oil inlet (3C) of the oil separator (3). A constant pressure valve (14) is provided on the first bypass oil passage (40). The constant pressure valve (14) is configured to open when the detection value of the pressure sensor (15) exceeds a preset pressure threshold.

8. The refrigeration system as described in claim 7, characterized in that, Also includes: The second bypass oil passage (70) has a first end connected to the first return oil line (20) located downstream of the pump (11), and a second end connected to the oil inlet (3C) of the oil separator (3). The second bypass oil passage (70) is provided with a second on / off valve (17).

9. The refrigeration system as described in claim 1, characterized in that, The automatic oil return device (4) has an oil level switch (4') at a preset height position. The automatic oil return device (4) is configured to obtain liquid refrigerant from the evaporator (2) when the oil level is lower than the preset height position.

10. The refrigeration system as claimed in claim 1, characterized in that, The automatic return oiler (4) is equipped with a second electric heater, which is configured to be turned on when the oil temperature in the automatic return oiler (4) is lower than a second preset low temperature threshold.

11. The refrigeration system according to any one of claims 1 to 10, characterized in that, The compressor (1) has an oil discharge port (1D), which is connected to the oil inlet (3C) of the oil separator (3) via an oil discharge pipeline (50). The oil discharge pipeline (50) is equipped with an oil discharge stop check valve (16) for unidirectionally connecting the oil discharge pipeline (50) from the compressor (1) to the oil separator (3).

12. The refrigeration system according to any one of claims 1 to 10, characterized in that, The compressor (1) has a dual oil level switch (21) in its oil storage area. The dual oil level switch (21) includes a first oil level switch and a second oil level switch. The first oil level switch is set at a first height position Hmin, and the second oil level switch is set at a second height position Hmax. The second height position Hmax is higher than the first height position Hmin.

13. The refrigeration system according to any one of claims 1 to 10, characterized in that, Also includes: An oil cooler (5), connected in parallel with the first oil return line (20), is configured to cool the oil returning from the oil separator (3) to the compressor (1); and The condenser (6) has an air inlet (6A) that is connected to the exhaust port (1B) of the compressor (1) through the oil separator (3). The liquid refrigerant flowing out of the liquid outlet (6B) of the condenser (6) is supplied to the oil cooler (5) for cooling the oil.

14. The refrigeration system as described in claim 13, characterized in that, Also includes: The siphon reservoir (7) has its inlet (7A) connected to the outlet (6B) of the condenser (6), its outlet (7B) connected to the inlet (5C) of the oil cooler (5), its air inlet (7C) connected to the exhaust port (5D) of the oil cooler (5), and its return air port (7D) connected to the air inlet (6A) of the condenser (6).

15. The refrigeration system as described in claim 14, characterized in that, Also includes: The liquid reservoir (8) has an inlet (8A) connected to the overflow port (7E) of the siphon liquid reservoir (7) and an outlet (8B) connected to the inlet of the evaporator (2).

16. The refrigeration system as described in claim 14, characterized in that, Also includes: The subcooler (9), located between the siphon receiver (7) and the evaporator (2), is configured to subcool the liquid refrigerant in the main circulation loop.

17. A method for controlling oil return in a refrigeration system according to any one of claims 1 to 16, characterized in that, include: Detect the oil level in the oil storage area of ​​the compressor (1); When the oil level is between the first height position Hmin and the second height position Hmax, the automatic oil return device (4) stops operating. When the oil level is below the first height position Hmin, the suction oil return operation is activated, the automatic oil return device (4) is activated, and the pump (11) is activated to operate through the first oil return line (20). When the oil level is higher than the second height position Hmax, the suction oil return operation is activated, the automatic oil return device (4) stops operating, and the compressor (1) discharges oil into the oil separator (3) through the oil discharge port (1D). Wherein, the second height position Hmax is higher than the first height position Hmin.

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