Injection supercooling CO2 refrigerating and heating system and application

Abstract

The invention provides an injection supercooling CO2 refrigerating and heating system and application, and the injection supercooling CO2 refrigerating and heating system comprises a high-temperature stage ejector; an outlet of the high-temperature-stage ejector sequentially communicates with the refrigerant side of the cooling evaporator, an inlet of the compressor, the heating medium side of the gas cooler and a main flow inlet of the high-temperature-stage ejector. According to the injection supercooling CO2 heating and refrigerating system, the suction pressure of the compressor can be improved, the exhaust pressure of the compressor can be reduced, the pressure ratio of the CO2 compressor is reduced, the isentropic efficiency is improved, and the service life of the compressor is prolonged. And three-stage heat exchange is carried out on air and the refrigerant, the heat exchange temperature difference is reduced, and energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of refrigeration and heating, and heat pump technology, and in particular relates to an induced supercooled CO2 heating and refrigeration system and its application. Background Art

[0002] Vapor compression refrigeration systems are widely used in both residential and commercial refrigeration, accounting for a significant portion of society's energy consumption. The refrigeration industry's significant contribution to global warming and ozone depletion has become an increasingly prominent issue. Properly selecting refrigeration system cycle structures and environmentally friendly refrigerants can significantly contribute to energy conservation and emission reduction. Natural working fluids, such as carbon dioxide, can serve as alternative refrigerants.

[0003] CO2 refrigeration technology is more efficient, energy-efficient, and environmentally friendly than traditional technologies. Due to its excellent properties, CO2 is hailed as the most promising permanent replacement for CFCs, HCFCs, and HFCs. Therefore, green CO2 refrigeration technology holds broad prospects for development. However, under typical refrigeration conditions, CO2 refrigeration systems must operate in a supercritical cycle due to the low critical temperature of CO2. Furthermore, significant expansion losses result in lower coefficients of performance (COP) than conventional cycles using CFCs and HCFCs. In recent years, ejectors have garnered significant attention for their distinctive features, including no moving parts, low cost, simple structure, minimal maintenance requirements, and significant potential for performance improvement. Therefore, using ejectors as expansion devices in transcritical CO2 cycles is a promising approach to improving cycle performance.

[0004] In conventional refrigeration systems, the throttled gas-liquid two-phase fluid enters the evaporator directly, or passes through a gas-liquid separator to throttle the gaseous working fluid before entering the compressor for further compression. The gaseous working fluid does not participate in the evaporation heat absorption and does not contribute to the refrigeration process. This traditional treatment method results in a deterioration of the heat exchanger's heat transfer efficiency or an increase in compressor power consumption. The present invention provides a feasible solution to these problems. Summary of the Invention

[0005] In view of this, the present invention aims to propose an induced subcooled CO2 refrigeration and heating system to overcome the defects of the prior art, which can reduce the compressor exhaust pressure, increase the compressor inlet gas pressure, reduce the CO2 compressor pressure ratio, improve the isentropic efficiency, and extend the compressor service life.

[0006] To achieve the above object, the technical solution created by the present invention is implemented as follows: An ejector subcooled CO2 refrigeration and heating system includes a high-temperature ejector and a medium-temperature ejector; The outlet of the high-temperature ejector is connected in sequence to the inlet of the refrigerant side of the cooling evaporator, the refrigerant side of the cooling evaporator is connected to the inlet of the compressor and the inlet of the heat medium side of the gas cooler, and the outlet of the gas cooler is connected to the mainstream inlet of the high-temperature ejector and the inlet of the heat medium side of the cooling evaporator.

[0007] The heat medium side outlet of the cooling evaporator is divided into three paths. The first path is connected in sequence to the high-temperature expansion valve, the refrigerant side inlet of the high-temperature evaporator, the mainstream inlet of the medium-temperature ejector and the secondary flow inlet of the high-temperature ejector; the second path is connected in sequence to the medium-temperature expansion valve, the refrigerant side inlet of the medium-temperature evaporator, the mainstream inlet of the low-temperature ejector and the secondary flow inlet of the medium-temperature ejector; the third path is connected in sequence to the low-temperature expansion valve, the refrigerant side inlet of the low-temperature evaporator and the secondary flow inlet of the low-temperature ejector.

[0008] Furthermore, the above-mentioned supercooled CO2 refrigeration and heating system is characterized in that: a high-temperature CO2 ejector is installed between the CO2 gas cooler and the cooling evaporator; a medium-temperature CO2 ejector is installed between the high-temperature CO2 evaporator and the high-temperature CO2 ejector; and a low-temperature CO2 ejector is installed between the medium-temperature CO2 evaporator and the medium-temperature CO2 ejector.

[0009] Furthermore, the above-mentioned ejector subcooled CO2 refrigeration and heating system is characterized in that a cooling evaporator is installed between the high-temperature ejector and the compressor.

[0010] Furthermore, the induced subcooled CO2 refrigeration and heating system is characterized in that a fan is installed below the low-temperature stage evaporator.

[0011] Furthermore, the above-mentioned subcooled CO2 refrigeration and heating system is characterized in that the cooling evaporator is a double-tube heat exchanger or a plate heat exchanger; the gas cooler is a double-tube heat exchanger or a plate heat exchanger; and the high-temperature C evaporator, the medium-temperature evaporator, and the low-temperature CO2 evaporator all use finned tube heat exchangers.

[0012] Furthermore, the subcooled CO2 ejector cooling and heating system is characterized by: the high-temperature evaporator has an operating temperature range of 0-20°C and a pressure range of 3.5-5.7 MPa; the medium-temperature evaporator has an operating temperature range of -5-10°C and a pressure range of 3.0-4.5 MPa; and the low-temperature evaporator has an operating temperature range of -10-5°C and a pressure range of 2.6-4.0 MPa. The gas cooler outlet has a temperature range of 50-80°C and a pressure range of 7.7-8.9 MPa. The secondary flow suction temperature of the high-temperature ejector has a range of 0-15°C and a pressure range of 3.5-5.1 MPa, while the exhaust temperature range is 10-25°C and a pressure range of 4.5-6.4 MPa. The compressor suction pressure range is 4.5-6.4 MPa, and the exhaust pressure range is 7.5-12 MPa.

[0013] Preferably, the temperature of the high-temperature evaporator is 20°C and the pressure is 5.7MPa; the temperature of the medium-temperature evaporator is 0°C and the pressure is 3.5MPa; the temperature of the low-temperature compressor is -10°C and the pressure is 2.6MPa; the temperature of the gas cooler outlet is 50°C and the pressure is 7.7MPa; the secondary flow suction temperature of the high-temperature ejector is 15°C and the pressure is 5.1MPa; the exhaust temperature is 25°C and the pressure is 6.4MPa; the suction pressure of the compressor is 6.4MPa and the exhaust pressure is 10MPa.

[0014] Furthermore, the induced subcooled CO2 refrigeration and heating system is characterized in that the refrigerant used is CO2.

[0015] The invention also relates to the application of the above-mentioned ejection pressurized subcooled transcritical CO2 dual-temperature system in the fields of refrigeration, heating and heat pumps.

[0016] Compared with the prior art, the induced subcooled CO2 refrigeration and heating system created by the present invention has the following advantages: (1) By arranging three ejectors in series, the high-temperature ejector ejects the low-temperature, low-pressure gas from the medium-temperature ejector, lowering the temperature of the gas cooler outlet to a pressure intermediate between the two temperatures. This avoids the use of an expansion valve, reduces losses during the throttling process, and increases the compressor suction pressure. In addition, the ejection of the medium-temperature and low-temperature ejectors recovers, to a certain extent, the expansion work lost during the throttling process of the expansion valve.

[0017] (2) By setting up a subcooler to cool the CO2 at the outlet of the gas cooler, the evaporation process of the conventional refrigerant and the temperature drop process of the supercritical CO2 fluid form a good temperature match, narrowing the heat transfer temperature difference, reducing the irreversible heat exchange loss and irreversible throttling loss, and improving the overall energy efficiency of the system.

[0018] (3) By setting up low-temperature and medium-temperature ejectors, the pressures of the two streams of CO2 gas from the first and second paths at the outlet of the heat medium side of the cooling evaporator are respectively ejected to the intermediate pressure of the medium-temperature CO2 ejector and the outlet of the high-temperature evaporator, and the intermediate pressure of the outlet of the low-temperature evaporator and the outlet of the medium-temperature evaporator, which can eliminate the configuration of expansion valve throttling and pressure reduction or compressor power equipment pressure increase. Under the premise of greatly reducing throttling loss and not introducing power configuration, the saturated gas that does not participate in refrigeration is ejected to the inlet of the compressor. The ejector has no moving parts, the equipment volume is small, and the suction volume of the compressor is reduced, reducing the volume and cost of the compressor. The outlet pressure of the CO2 ejector is mixed to the intermediate pressure, which increases the suction pressure of the compressor, reduces the compression ratio of the compressor, and improves the efficiency of the compressor.

[0019] (4) By setting up three evaporators, the air flows continuously through the high-temperature, medium-temperature and low-temperature evaporators for heat exchange, achieving step-by-step subcooling and forming a better temperature match between the air and the refrigerant.

[0020] (5) By setting two ejectors in series, three evaporation temperatures are constructed, which can be suitable for low-temperature preservation and freezing and refrigeration applications, and can produce medium-temperature hot water for domestic use. A set of equipment can realize both cooling and heating functions, which improves the utilization rate of the equipment and saves the space occupied by the equipment. It can be used for low-temperature preservation and air-conditioning cooling and heating in large shopping malls and supermarkets, and can also be used in application fields such as slaughterhouses and food processing plants that require both refrigeration and preservation and medium-temperature hot water. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a simple structural diagram of the induced subcooled CO2 refrigeration and heating system created by the present invention.

[0022] Figure 2 This is a temperature entropy diagram of the induced supercooled CO2 refrigeration and heating system created by the present invention.

[0023] Reference numerals: 1- Compressor; 2- Gas cooler; 3- High-temperature ejector; 4- Cooling evaporator; 5- High-temperature expansion valve; 6- High-temperature evaporator; 7- Medium-temperature ejector; 8- Medium-temperature expansion valve; 9- Medium-temperature evaporator; 10- Low-temperature ejector; 11- Low-temperature expansion valve; 12- Low-temperature evaporator; 13- Fan. DETAILED DESCRIPTION

[0024] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods described, unless otherwise specified, are conventional methods.

[0025] The present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0026] like Figure 1 As shown, a subcooled CO2 ejection refrigeration and heating system includes 1- compressor; 2- gas cooler; 3- high temperature stage ejector; 4- cooling evaporator; 5- high temperature stage expansion valve; 6- high temperature stage evaporator; 7- medium temperature stage ejector; 8- medium temperature stage expansion valve; 9- medium temperature stage evaporator; 10- low temperature stage ejector; 11- low temperature stage expansion valve; 12- low temperature stage evaporator; 13- fan. Specifically: The outlet of the high-temperature CO2 ejector (3) is connected in sequence to the inlet of the refrigerant side of the cooling evaporator (4), one outlet of the refrigerant side of the cooling evaporator (4) is connected to the inlet of the compressor (1) and the inlet of the heat medium side of the CO2 gas cooler (2), and the outlet of the CO2 gas cooler (2) is connected to the mainstream inlet of the CO2 ejector (3) and the inlet of the heat medium side of the cooling evaporator (4).

[0027] The heat medium side outlet of the cooling evaporator (4) is divided into three paths, the first path is connected in sequence to the high-temperature expansion valve (5), the heat medium side inlet of the high-temperature CO2 evaporator (6), the mainstream inlet of the medium-temperature CO2 ejector (7) and the secondary flow inlet of the high-temperature CO2 ejector (3); the second path is connected in sequence to the medium-temperature expansion valve (8), the heat medium side inlet of the medium-temperature CO2 evaporator (9), the mainstream inlet of the low-temperature CO2 ejector and the secondary flow inlet of the medium-temperature CO2 ejector (7); the third path is connected in sequence to the low-temperature expansion valve (11), the heat medium side inlet of the low-temperature CO2 evaporator (12) and the secondary flow inlet of the low-temperature CO2 ejector (10).

[0028] The CO2 gas at the outlet of the gas cooler (2) is divided into two streams of CO2 gas by the cooling evaporator (4). The CO2 gas at the outlet of the heat medium side is divided into three small streams and enters the high-temperature expansion valve (5), the medium-temperature expansion valve (8) and the low-temperature expansion valve (11), and then enters the evaporator for evaporation respectively. By reducing the amount of CO2 gas entering the evaporator, the volume of the evaporator can be reduced. For example, when used in supermarket fresh-keeping cabinets and refrigerators, the equipment can be made more compact and the space utilization rate of the refrigeration equipment can be improved. The pressure of the CO2 gas discharged from the cooling evaporator is increased by the medium-temperature CO2 ejector (7) and the low-temperature CO2 ejector (10). Compared with the traditional throttling and then compression process, the throttling process is omitted, thereby reducing the throttling irreversible loss of this part of the gas. In addition, compared with the throttling and then compression process, the evaporator suction pressure is increased and the compression ratio is reduced in the ejection process. The CO2 fluid passing through the gas cooler outlet is ejected to an intermediate pressure in the CO2 ejector, eliminating the need for a throttle valve to reduce pressure, significantly reducing throttling losses and eliminating the need for power equipment. The ejector has no moving parts, resulting in a compact device. The cooling evaporator reduces the amount of air entering the compressor, lowering the compressor's intake volume and reducing the size and cost of the compressor.

[0029] In addition, the cooling evaporator (4) can realize the cooling of CO2 at the outlet of the gas cooler (2), and the CO2 evaporation process forms a good temperature match with the supercritical CO2 fluid temperature drop process, narrowing the heat transfer temperature difference, reducing the irreversible heat exchange loss and irreversible throttling loss, and improving the overall energy efficiency of the system.

[0030] As an optional embodiment of the present invention, in order to increase the pressure of the CO2 gas entering the compressor (1), the outlet gas of the low-temperature stage evaporator (12) is ejected by the low-temperature stage ejector (10). The outlet gas of the low-temperature stage ejector (10) is ejected by the medium-temperature stage ejector (7), and the series ejection is used to increase the pressure of the secondary flow ejected by the high-temperature stage ejector (3).

[0031] As an optional embodiment of the present invention, in order to increase the CO2 gas pressure at the inlet of the compressor (1), a high-temperature ejector (3) is installed between the gas cooler (2) and the cooling evaporator (4); a medium-temperature ejector (7) is installed between the high-temperature evaporator (6) and the high-temperature ejector (3); and a low-temperature ejector (10) is installed between the medium-temperature evaporator (9) and the medium-temperature ejector (7).

[0032] As an optional embodiment of the present invention, a fan (13) is installed below the low-temperature stage evaporator (12). As an optional embodiment of the present invention, the cooling evaporator (4) is a shell-and-tube heat exchanger or a plate heat exchanger; the gas cooler (2) is a shell-and-tube heat exchanger or a plate heat exchanger. The high-temperature evaporator (6), the medium-temperature evaporator (9), and the low-temperature evaporator (12) all use finned tube heat exchangers. A more preferred embodiment is that the cooling evaporator (4) is a shell-and-tube heat exchanger. The gas cooler (2) is a shell-and-tube heat exchanger.

[0033] As an optional embodiment of the present invention, in order to reduce losses, a cooling evaporator is installed between the gas cooler (2) and the compressor (1) to achieve supercooling of the CO2 gas at the outlet of the gas cooler.

[0034] As an optional embodiment of the present invention, the operating temperature range of the high-temperature evaporator is 0-20°C, and the pressure range is 3.5-5.7 MPa; the operating temperature range of the medium-temperature evaporator is -5-10°C, and the pressure range is 3.0-4.5 MPa; the operating temperature of the low-temperature evaporator is -10-5°C, and the pressure range is 2.6-4.0 MPa. The temperature range of the gas cooler outlet is 50-80°C, and the pressure range is 7.7-8.9 MPa; the secondary flow suction temperature of the high-temperature ejector is 0-15°C, and the pressure range is 3.5-5.1 MPa; the exhaust temperature range is 10-25°C, and the pressure range is 4.5-6.4 MPa; the compressor suction pressure range is 4.5-6.4 MPa, and the exhaust pressure range is 7.5-12 MPa.

[0035] The present invention creates the described induced subcooled CO2 system. When used, a relatively preferred process condition is: the temperature of the high-temperature evaporator is 20°C and the pressure is 5.7MPa; the temperature of the medium-temperature evaporator is 0°C and the pressure is 3.5MPa; the temperature of the low-temperature compressor is -10°C and the pressure is 2.6MPa; the temperature of the gas cooler outlet is 50°C and the pressure is 7.7MPa; the secondary flow suction temperature of the high-temperature ejector is 15°C and the pressure is 5.1MPa; the exhaust temperature is 25°C and the pressure is 6.4MPa; the suction pressure of the compressor is 6.4MPa and the exhaust pressure is 10MPa.

[0036] The method of using the supercooled CO2 refrigeration and heating system created by the present invention to perform refrigeration, heating and heat exchange is as follows: Figure 1 As shown, the following steps are included: Step 1: The high-temperature and high-pressure CO2 gas at the outlet of the compressor (1) enters the gas cooler (2) for heat exchange and releases heat. The medium-temperature and medium-pressure CO2 gas at the outlet of the gas cooler (2) is divided into two paths. One path directly enters the heat medium side of the cooling evaporator (4) for heat exchange and cooling. The low-temperature and low-pressure CO2 gas after heat exchange and cooling is divided into three small streams: the first stream enters the low-temperature expansion valve (11) for throttling, and then enters the low-temperature evaporator (12) for heat exchange and releases cold; the second stream enters the medium-temperature expansion valve (8) for throttling, and then enters the medium-temperature evaporator (9) for heat exchange and releases cold. The saturated low-temperature and low-pressure CO2 gas at the outlet is superheated as the mainstream to be ejected into the low-temperature evaporator The low-temperature, low-pressure CO2 gas at the outlet of the ejector (12) is continuously drawn into the suction chamber of the ejector and mixed with the low-pressure mainstream in the mixing chamber. The mixed fluid enters the diffusion chamber, the fluid velocity decreases, and the pressure increases to between the mainstream and the secondary fluid; the third stream enters the high-temperature expansion valve (5) for throttling, and then enters the high-temperature evaporator (6) for convection heat exchange to release cold energy. The saturated medium-temperature, medium-pressure gas at the outlet is superheated as the mainstream to eject the low-temperature, low-pressure gas at the outlet of the medium-temperature CO2 ejector (10). It is continuously drawn into the suction chamber of the ejector and mixed with the low-pressure mainstream in the mixing chamber. The mixed fluid enters the diffusion chamber, the fluid velocity decreases, and the pressure increases to between the mainstream and the secondary fluid.

[0037] Step 2: The other stream from the outlet of the gas cooler (3) enters the CO2 ejector (3) as the main stream, undergoes isentropic expansion at the nozzle, increases the flow rate, and reduces the pressure, ejecting the medium-temperature, medium-pressure CO2 gas from the medium-temperature CO2 ejector (7). The medium-temperature, medium-pressure CO2 gas from the outlet of the CO2 ejector (3) enters the refrigerant side of the cooling evaporator (4) for heat exchange and evaporation. The evaporated medium-temperature, medium-pressure CO2 gas enters the suction port of the compressor (1) for compression, becoming high-temperature, high-pressure CO2 gas.

[0038] The induced supercooled CO2 refrigeration and heating system created by the present invention is provided with a compressor with a small pressure ratio, which is suitable for low-temperature preservation and freezing and refrigeration applications, and can produce medium-temperature hot water for daily use. Through a set of equipment, both cooling and heating functions can be realized, which improves the utilization rate of the equipment and saves the space occupied by the equipment. It can be applied to low-temperature preservation and air-conditioning refrigeration and heating in large shopping malls and supermarkets, and can also be used in application fields such as slaughterhouses and food processing plants that require both refrigeration and preservation and medium-temperature hot water.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An induced subcooled CO2 refrigeration and heating system, characterized by: High temperature stage ejector (3) and medium temperature stage ejector (7); The outlet of the high-temperature ejector (3) is sequentially connected to the inlet of the refrigerant side of the cooling evaporator (4), the refrigerant side of the cooling evaporator (4) is connected to the inlet of the compressor (1) and the inlet of the heat medium side of the gas cooler (2), and the outlet of the gas cooler (2) is respectively connected to the mainstream inlet of the high-temperature ejector (3) and the inlet of the heat medium side of the cooling evaporator (4); The heat medium side outlet of the cooling evaporator (4) is divided into three paths, the first path is connected in sequence to the high-temperature expansion valve (5), the refrigerant side inlet of the high-temperature evaporator (6), the mainstream inlet of the medium-temperature ejector (7) and the secondary flow inlet of the high-temperature ejector (3); the second path is connected in sequence to the medium-temperature expansion valve (8), the refrigerant side inlet of the medium-temperature evaporator (9), the mainstream inlet of the low-temperature ejector and the secondary flow inlet of the medium-temperature ejector (7); the third path is connected in sequence to the low-temperature expansion valve (11), the refrigerant side inlet of the low-temperature evaporator (12) and the secondary flow inlet of the low-temperature ejector (10).

2. The induced subcooled CO2 refrigeration and heating system according to claim 1, characterized in that: A high-temperature ejector (3) is installed between the gas cooler (2) and the cooling evaporator (4); a medium-temperature ejector (7) is installed between the high-temperature evaporator (6) and the high-temperature ejector (3); and a low-temperature ejector (10) is installed between the medium-temperature evaporator (9) and the medium-temperature ejector (7).

3. The induced subcooled CO2 refrigeration and heating system according to claim 1, characterized in that: A cooling evaporator (4) is installed between the high-temperature ejector (3) and the compressor (1).

4. The induced subcooled CO2 refrigeration cycle system according to claim 1, characterized in that: A fan (13) is installed below the low-temperature stage evaporator (12).

5. The induced subcooled CO2 refrigeration and heating system according to claim 1, characterized in that: The cooling evaporator (4) adopts a shell-and-tube heat exchanger or a plate heat exchanger; the gas cooler (2) is a shell-and-tube heat exchanger or a plate heat exchanger; the high-temperature evaporator (6), the medium-temperature evaporator (9) and the low-temperature evaporator (12) all adopt finned tube heat exchangers.

6. The transcritical two-stage subcooled CO2 injection system according to claim 1, characterized in that: The operating temperature range of the high-temperature evaporator (6) is 0~20°C, and the pressure range is 3.5~5.7MPa; the operating temperature range of the medium-temperature evaporator (9) is -5~10°C, and the pressure range is 3.0~4.5MPa; the operating temperature range of the low-temperature evaporator (12) is -10~5°C, and the pressure range is 2.6~4.0MPa; the temperature range of the outlet of the gas cooler (2) is 50~80°C, and the pressure range is 7.7~8.9MPa; the secondary flow suction temperature range of the high-temperature CO2 ejector (3) is 0~15°C, the pressure range is 3.5~5.1MPa, the exhaust temperature range is 10~25°C, and the pressure range is 4.5~6.4MPa; the suction pressure range of the compressor (1) is 4.5~6.4MPa, and the exhaust pressure range is 7.5~12MPa.

7. The induced subcooled CO2 refrigeration and heating system according to any one of claims 1 to 6, characterized in that: The refrigerant used is CO2.

8. Application of the ejection, pressurization, subcooled, transcritical CO2 dual-temperature system according to any one of claims 1 to 7 in the fields of refrigeration, heating, and heat pumps.

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