EP4286771A1

EP4286771A1 - Refrigeration system

Info

Publication number: EP4286771A1
Application number: EP23176358.2A
Authority: EP
Inventors: Wei Zhang
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2022-05-31
Filing date: 2023-05-31
Publication date: 2023-12-06
Also published as: CN117190518A; US20230384008A1

Abstract

The present invention relates to a refrigeration system (100). The refrigeration system comprises: a main flow path comprising a compressor (110), a condenser (120), a throttling device (130) and an evaporator (140), wherein the compressor (110) comprises at least a first compression stage and a second compression stage; and the refrigeration system (100) further comprises: an ejector (150) configured to eject low-pressure refrigerant from the evaporator (140) by means of high-pressure refrigerant from the condenser (220) and to mix them into medium-pressure gas-liquid two-phase refrigerant; and a separator (160) configured to separate the medium-pressure gas-liquid two-phase refrigerant from the ejector (150) into gas-phase refrigerant and liquid-phase refrigerant, to deliver the gas-phase refrigerant separated to a gas supply port (114) between a fluid outlet of the first compression stage and a fluid inlet of the second compression stage in the compressor (110), and to deliver the liquid-phase refrigerant separated to a motor housing (113) of the compressor for cooling a rotor and a stator in the motor housing (113) by flash evaporation. The refrigeration system (100) according to the present invention can improve the adaptability and universality for different operating conditions, and enhance the overall energy efficiency level of the system.

Description

The present invention relates to the field of refrigeration systems, and is applicable in particular to oil-lubricated refrigeration systems and oil-free refrigeration systems.
At present, the refrigeration systems used in the fields of industrial equipment manufacturing, heating and heat exchange requires increasingly high energy efficiency. In order to improve the energy efficiency of the units, economizers are usually configured in refrigeration systems to improve the energy efficiency coefficient thereof the refrigeration systems. In the existing refrigeration systems with economizers, the refrigerant system comprises a main flow path, the main flow path comprising a compressor 11, a condenser 12, a throttling device 13, an evaporator 14 and other components that are fluidly communicated, with refrigerant circulating through them. As shown in FIG 1, for an oil-free compressor, the refrigeration system 10 combines an economizer 15 with an expansion valve 16 to provide intermediate gas supply to the compressor 11 to improve cycle efficiency. As shown in FIG 2, for a compressor using oil-lubricated bearings, in addition to a compressor 21, a condenser 22, a throttling device 23, an evaporator 24, an economizer 25 and an expansion valve 26, an additional oil return system that includes one or more ejectors 27 and an oil tank 28 is required for the refrigeration system 20. The ejector 27, by means of high-pressure refrigerant gas from the outlet of the compressor 21, ejects oil-mixed refrigerant from the oil-rich layer zone of the refrigeration system, such as the evaporator 24, while the oil tank 28 receives the output fluid from the output port of the ejector 27 and delivers the filtered lubricant oil to the compressor bearing chamber through an oil pump so as to lubricate the compressor bearings.
However, the existing refrigeration systems, whether oil-lubricated or oil-free, still have disadvantages and shortcomings in terms of structure, energy efficiency and other aspects, which can be improved and optimized further.
The objective of at least preferred embodiments of the present invention is to solve or at least alleviate problems existing in the prior art.
According to a first aspect of the present invention, a refrigeration system is provided, comprising:

a main flow path comprising a compressor, a condenser, a throttling device and an evaporator, wherein the compressor comprises at least a first compression stage and a second compression stage; and
the refrigeration system further comprising:
- an ejector configured to eject low-pressure refrigerant from the evaporator by means of high-pressure refrigerant from the condenser and to mix them into medium-pressure gas-liquid two-phase refrigerant; and
- a separator configured to separate the medium-pressure gas-liquid two-phase refrigerant from the ejector into gas-phase refrigerant and liquid-phase refrigerant, to deliver the gas-phase refrigerant separated to a gas supply port between a fluid outlet of the first compression stage and a fluid inlet of the second compression stage in the compressor, and to deliver the liquid-phase refrigerant separated to a motor housing of the compressor for cooling a rotor and a stator in the motor housing by flash evaporation.

Optionally, a plurality of ejectors are provided and are arranged in parallel, wherein high-pressure fluid inlets of the plurality of ejectors are connected near the bottom of the condenser and fluid suction inlets of the plurality of ejectors are connected near the internal liquid level of the evaporator.
Optionally, the compressor is an oil-free two-stage centrifugal compressor.
Optionally, the compressor comprises an electromagnetic bearing, a gas bearing or a refrigerant-lubricated bearing.
According to a second aspect of the present invention, a refrigeration system is provided, comprising:

a main flow path comprising a compressor, a condenser, a throttling device and an evaporator,
wherein the compressor comprises at least a first compression stage and a second compression stage; and
the refrigeration system further comprising:
- an ejector configured to eject low-pressure refrigerant from an oil-rich layer of the evaporator by means of high-pressure refrigerant from the condenser and to mix them into medium-pressure gas-liquid two-phase refrigerant;
- a separator configured to separate the medium-pressure gas-liquid two-phase refrigerant from the ejector into gas-phase refrigerant and liquid-phase refrigerant, and to deliver the gas-phase refrigerant separated to a gas supply port between a fluid outlet of the first compression stage and a fluid inlet of the second compression stage in the compressor, and to deliver the liquid-phase refrigerant separated to a motor housing of the compressor for cooling a rotor and a stator in the motor housing by flash evaporation; and
- an oil tank arranged downstream of the separator for filtering oil from the liquid-phase refrigerant and delivering the oil to a compressor bearing chamber.

Optionally, an oil pump is provided in the oil tank for delivering oil in the oil tank to the compressor bearing chamber.
Optionally, a heater for heating up oil is provided in the oil tank.
Optionally, a plurality of ejectors are provided and are arranged in parallel, wherein high-pressure fluid inlets of the plurality of ejectors are connected near the bottom of the condenser and fluid suction inlets of the plurality of ejectors are connected near the internal liquid level of the evaporator.
Optionally, the oil tank is a container, wherein an inlet port of the oil tank is connected to a range from near the internal liquid level of the separator to the bottom of the separator.
Optionally, the compressor is an oil-lubricated two-stage centrifugal compressor.
It can be appreciated that the refrigeration system according to the present invention has a lot of advantages such as high universality and high energy efficiency. When an oil-free compressor is used in the system (i.e., without oil return), it not only simplifies the structure but also lowers the manufacturing cost. When an oil-lubricated compressor is used in the system (i.e., with oil return), it is only necessary to add the oil tank and the corresponding oil return pipeline. In addition, through double filtration by the separator and the oil tank, the oil concentration and oil temperature are controllable and the oil return is stable, thus ensuring the normal operation of oil-lubricated bearings.
With reference to the accompanying drawings, embodiments of the present invention will become easier to understand. Those skilled in the art would readily appreciate that these drawings are for the purpose of illustration, and are not intended to limit the protection scope of the present invention, as defined in the appended claims. In addition, in the figures, similar numerals are used to denote similar components, where:

FIG 1 shows a schematic diagram of an oil-free (i.e., without an oil return system) refrigeration system of the prior art;
FIG 2 shows a schematic diagram of an oil-lubricated (i.e., with an oil return system) refrigeration system of the prior art;
FIG 3 shows a schematic diagram of an oil-free refrigeration system; and
FIG 4 shows a schematic diagram of an oil-lubricated refrigeration system.

Orientation terms such as upper, lower, left, right, front, rear, front, back, top, bottom, upstream, downstream, etc., referred to or possibly referred to in this specification, are defined in relation to the structures shown in the drawings. They are relative concepts and may therefore vary accordingly according to their different locations and states of use. Therefore, these or other orientation terms should not be construed as restrictive terms.
Referring to FIG 3, a schematic diagram of an embodiment of a refrigeration system is shown. As can be clearly seen in FIG 3, the refrigeration system 100 comprises a main flow path. The main flow path comprises a compressor 110, a condenser 120, a throttling device 130, and an evaporator 140 that are fluidly communicated, with refrigerant circulating through them, wherein the compressor 110 comprises at least a first compression stage and a second compression stage. Although not shown, other components of a refrigeration system may also be included in the main flow path. The compressor 110 may be a high-speed direct-drive compressor in which the motor shaft is directly connected to the compressor impeller without a gearbox. In this kind of compressor, heat generation is much less than that of a conventional compressor with a gearbox because there is no gearbox. The compressor 110 may include, for example, a compressor inlet 111, a compressor outlet 112, a motor housing 113, and a gas supply port 114 between the fluid outlet of the first compression stage and the fluid inlet of the second compression stage. To eliminate the relatively complex oil line design, the compressor 110 can employ a two-stage centrifugal compressor without oil lubrication. Further, the compressor 110 includes an electromagnetic bearing, a gas bearing or a refrigerant-lubricated bearing for supporting the motor shaft that rotates at high speed. When the refrigeration system is operating, the throttling device 130 may be an expansion valve, such as a mechanical expansion valve or an electronic expansion valve.
In the refrigeration system as described above, the refrigeration system 100 further comprises an ejector 150 and a separator 160. The ejector 150 is configured to eject low-pressure refrigerant from the evaporator 140 by means of high-pressure refrigerant from the condenser 120 and to mix them into a medium-pressure gas-liquid two-phase refrigerant. The separator 160 is arranged downstream of the ejector 150 in the direction of refrigerant flow for separating the medium-pressure gas-liquid two-phase refrigerant from the ejector 150 into gas-phase refrigerant and liquid-phase refrigerant. On the one hand, the separator 160 delivers the gas-phase refrigerant separated to the gas supply port 114 between the fluid outlet of the first compression stage and the fluid inlet of the second compression stage in the compressor 110 through the flow path, such that the gas-phase refrigerant mixes with the output gas of the first compression stage and then enters the second compression stage for continued compression, thus saving part of the compression work. On the other hand, the separator 160 delivers the liquid-phase refrigerant separated to a port on the motor housing 113 of the compressor 110 through the flow path, where the liquid-phase refrigerant is flash evaporated immediately due to a pressure drop. It can be seen that the rotor and stator in the motor housing 113 are cooled by flash evaporation to reduce the temperature.
As shown in FIG 3, the ejector 150 includes a high-pressure fluid inlet 151, a fluid suction inlet 152, and a fluid outlet 153. The high-pressure fluid inlet 151 of the ejector 150 is connected near the bottom of the condenser 120 to receive high-pressure fluid. The fluid suction inlet 152 of the ejector 150 is connected near the internal liquid level of the evaporator 140 to receive low-pressure fluid. The fluid outlet 153 of the ejector 150 is connected to the separator 160 to separate the medium-pressure gas-liquid two-phase refrigerant mixed by the ejector 150 into gas-phase refrigerant and liquid-phase refrigerant. It should be noted that "high-pressure" and "low-pressure" appearing in the text are relative concepts. For example, it would be readily appreciated by those skilled in the art that, in the refrigeration system, the pressure of the refrigerant fluid in the condenser 120 is generally greater than that of the refrigerant fluid in the evaporator 140, so that the ejector 150 receives "high-pressure" refrigerant fluid from the condenser 120 and a "low-pressure" refrigerant fluid from the evaporator 140. It is because of the pressure difference between the fluid of the condenser and that of the evaporator that it is possible for the ejector to mix the two fluids into a medium-pressure fluid by sucking the low-pressure fluid using the high-pressure fluid.
Considering the different operating conditions and design requirements of oil-free refrigeration systems, in addition to the single ejector shown in FIG 3, a plurality of ejectors can also be arranged, such as two, three or more. The plurality of ejectors may be arranged in parallel and switched on and off electrically to control the flow of the gas-liquid two-phase refrigerant output, wherein the high-pressure fluid inlets of the plurality of ejectors are connected near the bottom of the condenser and the fluid suction inlets of the plurality of ejectors are connected near the internal liquid level of the evaporator. The plurality of ejectors may be of the same size. Alternatively, each ejector may have a different size to accommodate system requirements for gas supply and motor cooling under different operating conditions.
The embodiments of the oil-free refrigeration system according to the present invention eliminates components such as economizers and electronic expansion valves in the prior art, thereby simplifying the structure of the system and lowering the manufacturing cost of the system. In addition, the system utilizes the pressure difference between the condenser and the evaporator to produce a medium-pressure gas-liquid two-phase refrigerant, which is further separated by the separator into a gas-phase refrigerant for gas supply for the intermediate stage of the compressor and a liquid-phase refrigerant for cooling the compressor motor, thereby improving the overall energy efficiency of the system.
With continued reference to FIG 4, a schematic diagram of an embodiment of another refrigeration system is shown. As can be clearly seen in FIG 4, the refrigeration system 200 comprises a main flow path. The main flow path comprises a compressor 210, a condenser 220, a throttling device 230 and an evaporator 240 that are fluidly communicated, with refrigerant circulating through them, wherein the compressor 210 comprises at least a first compression stage and a second compression stage. Although not shown, other components of a refrigeration system may also be included in the main flow path. The compressor 210 may be a high-speed direct-drive compressor in which the motor shaft is directly connected to the compressor impeller without a gearbox. In this kind of compressor, heat generation is much less than that of a conventional compressor with a gearbox because there is no gearbox. The compressor 210 may include, for example, a compressor inlet 211, a compressor outlet 212, a motor housing 213, a gas supply port 214 between the fluid outlet of the first compression stage and the fluid inlet of the second compression stage, and a compressor bearing chamber 215. To lower the cost of the system, the compressor 210 can employ a two-stage centrifugal compressor with oil lubrication. When the refrigeration system is operating, the throttling device 230 may be an expansion valve, such as a mechanical expansion valve or an electronic expansion valve.
In the refrigeration system as described above, the refrigeration system also involves oil return, which is intended to direct the lubricant oil in the refrigeration system (usually in the circulating refrigerant) to the compressor bearing chamber 215 for lubricating the compressor bearings. When oil-lubricated bearings are used, the high-speed direct-drive compressor, though without the need to use traditional oil cooling devices, needs to maintain an appropriate oil temperature. Specifically, the refrigeration system 200 further comprises an ejector 250, a separator 260, and an oil tank 270. The ejector 250 is configured to eject oil-containing low-pressure refrigerant from the evaporator 240 by means of high-pressure refrigerant from the condenser 220 and to mix them into a medium-pressure gas-liquid two-phase refrigerant. The separator 260 is arranged downstream of the ejector 250 for separating the gas-liquid two-phase refrigerant from the ejector 250 into a gas-phase refrigerant and a liquid-phase refrigerant. On the one hand, the separator 260 delivers the gas-phase refrigerant separated to the gas supply port 214 between the fluid outlet of the first compression stage and the fluid inlet of the second compression stage in the compressor 210 through the flow path, such that the gas-phase refrigerant mixes with the output gas of the first compression stage and then enters the second compression stage for continued compression. On the other hand, the separator 260 delivers the liquid-phase refrigerant separated to a port on the motor housing 213 of the compressor 210 through the flow path, where the liquid-phase refrigerant is flash evaporated immediately due to a pressure drop. It can be seen that the rotor and stator in the motor housing 213 are cooled by flash evaporation to reduce the temperature. The oil tank 270 is a container arranged downstream of the separator 260 for filtering oil from the liquid-phase refrigerant and delivering the oil to the compressor bearing chamber 215 to lubricate the compressor bearings.
As shown in FIG 4, the ejector 250 includes a high-pressure fluid inlet 251, a fluid suction inlet 252, and a fluid outlet 253. The high-pressure fluid inlet 251 of the ejector 250 is connected near the bottom of the condenser 220 to receive high-pressure fluid. The fluid suction inlet 252 of the ejector 250 is connected near the internal liquid level of the evaporator 240 to receive low-pressure fluid. The fluid outlet 253 of the ejector 250 is connected to the separator 260 to separate the medium-pressure gas-liquid two-phase refrigerant mixed by the ejector 250 into gas-phase refrigerant and liquid-phase refrigerant.
Considering the different operating conditions and design requirements of the oil-lubricated refrigeration systems, in addition to the single ejector shown in FIG 4, a plurality of ejectors can also be arranged, such as two, three or more. The plurality of ejectors may be arranged in parallel and switched on and off electrically to control the flow of the gas-liquid two-phase refrigerant output, wherein the high-pressure fluid inlets of the plurality of ejectors are connected near the bottom of the condenser and the fluid suction inlets of the plurality of ejectors are connected near the internal liquid level of the evaporator. The plurality of ejectors may be of the same size. Alternatively, each ejector may have a different size to accommodate system requirements for gas supply and motor cooling under different operating conditions.
It is noteworthy that after the gas-liquid two-phase refrigerant from the ejector is subjected to a gas-liquid separation, an oil-rich liquid-phase refrigerant is formed in the separator 260, so the separator 260 preliminarily filters the oil contained in the gas-liquid two-phase refrigerant. In order to better recover the lubricant oil from the oil-rich liquid-phase refrigerant, the inlet port of the oil tank 270 is connected to the range from near the internal liquid level of the separator 260 to the bottom of the separator 260. After the oil-rich fluid is further filtered by the oil tank 270, the lubricant oil with a higher purity is delivered to the compressor bearings, e.g., to the compressor bearing chamber 215, for lubricating the compressor bearings. As a result, oil with a higher concentration and a more stable state, including its temperature and consistency, can be achieved through the two-stage filtrations by the separator and the oil tank.
An oil pump 272 may be provided in the oil tank 270 for delivering the fluid from the oil tank 270 to the compressor bearing chamber 215. Therefore, the oil pump 272 is capable of enabling the lubricant oil delivered to the compressor bearing chamber 215 to have an appropriate pressure.
The oil tank 270 may include a heater 271, which can be a resistance heater that can be inserted into the wall of the oil tank 270 or directly into the oil tank 270. The heater 271 is used to accelerate the evaporation of part of the liquid-phase refrigerant in the oil tank 270, so that the oil-containing refrigerant to be delivered to lubricate the compressor bearings can have a higher oil concentration. In addition, by reducing the content of the liquid-phase refrigerant, the risk of further lowering the oil temperature due to heat loss caused by refrigerant evaporation will be reduced, thereby ensuring the normal operation of the oil-lubricated bearings and extending service life thereof. Since the oil-lubricated refrigeration system employs a two-stage filtration method which can greatly improve the purity of the lubricant oil in the oil tank, the turn-on time and power of the heater 271 can be minimized as much as possible, and it is also feasible to remove the heater if necessary.
The embodiments of the oil-lubricated refrigeration system according to the present invention can ensure that the purity and temperature of the lubricant oil in the oil tank are more controllable, so that the impact due to fluctuations in the return oil state can be minimized. On the other hand, as for heating in the oil tank, the oil temperature can be regulated intelligently according to different load conditions, which is conducive to improving the efficiency of the entire refrigeration system. In addition, oil is filtered out of the refrigerant by means of the separator and the oil tank, thus ensuring the purity of the lubricant oil in the oil tank. Furthermore, with the reduction of refrigerant content in the oil tank, less heat will be carried away due to evaporation of the refrigerant, thus ensuring that the temperature and differential pressure of the lubricant oil are controllable, which enables the bearings to be effectively lubricated so as to prolong the service life of the compressor.
The specific embodiments of the present invention described above are merely for a clearer description of the principles of the present invention, in which individual components are clearly shown or described to make the principles of the present invention easier to understand. Various modifications or changes to the present invention may be easily made by those skilled in the art without departing from the scope of the present invention, as defined in the appended claims. It should therefore be understood that these modifications or changes shall be included within the scope of the patent protection of the present invention defined in the appended claims.

Claims

A refrigeration system (100; 200), comprising:
a main flow path comprising a compressor (110; 210), a condenser (120; 220), a throttling device (130; 230) and an evaporator (140; 240), wherein the compressor (110; 210) comprises at least a first compression stage and a second compression stage; and

the refrigeration system (100; 200) further comprises:
an ejector (150; 250) configured to eject low-pressure refrigerant from the evaporator (140; 240) by means of high-pressure refrigerant from the condenser (120; 220) and to mix them into medium-pressure gas-liquid two-phase refrigerant; and

a separator (160; 260) configured to separate the medium-pressure gas-liquid two-phase refrigerant from the ejector (150; 250) into gas-phase refrigerant and liquid-phase refrigerant, to deliver the separated gas-phase refrigerant to a gas supply port (114; 214) between a fluid outlet of the first compression stage and a fluid inlet of the second compression stage in the compressor (110; 210), and to deliver the separated liquid-phase refrigerant to a motor housing (113; 213) of the compressor (110; 210) for cooling a rotor and a stator in the motor housing (113; 213) by flash evaporation.
The refrigeration system (100; 200) according to claim 1, wherein a plurality of ejectors (150; 250) are provided and are arranged in parallel, wherein high-pressure fluid inlets (151; 251) of the plurality of ejectors (150; 250) are connected near a bottom of the condenser (120; 220) and fluid suction inlets (152; 252) of the plurality of ejectors (150; 250) are connected near an internal liquid level of the evaporator (140; 240).
The refrigeration system (100) according to claim 1 or 2, wherein the compressor (110) is an oil-free two-stage centrifugal compressor (110).
The refrigeration system (100) according to any preceding claim, wherein the compressor (110) comprises an electromagnetic bearing, a gas bearing or a refrigerant-lubricated bearing.
A refrigeration system (200) according to claim 1, wherein:
the ejector (250) is configured to eject low-pressure refrigerant from an oil-rich layer of the evaporator (240) by means of high-pressure refrigerant from the condenser (220) and to mix them into medium-pressure gas-liquid two-phase refrigerant;

the refrigeration system further comprising:
an oil tank (270) arranged downstream of the separator (260) for filtering oil from the liquid-phase refrigerant and delivering the oil to a compressor bearing chamber (215).
The refrigeration system (200) according to claim 5, wherein an oil pump (272) is provided in the oil tank (270) for delivering oil in the oil tank (270) to the compressor bearing chamber (215).
The refrigeration system (200) according to claim 5 or 6, wherein a heater (271) for heating up oil is provided in the oil tank (270).
The refrigeration system (200) according to any of claims 5-7, wherein a plurality of ejectors (250) are provided and are arranged in parallel, wherein high-pressure fluid inlets (251) of the plurality of ejectors (250) are connected near a bottom of the condenser (220) and fluid suction inlets (252) of the plurality of ejectors (250) are connected near an internal liquid level of the evaporator (240).
The refrigeration system (200) according to any of claims 5-8, wherein the oil tank (270) is a container, and an inlet port of the oil tank (270) is connected to a range from near an internal liquid level of the separator (260) to the bottom of the separator (260).
The refrigeration system (200) according to any of claims 5-9, wherein the compressor (210) is an oil-lubricated two-stage centrifugal compressor (210).