Ejector enhanced transcritical carbon dioxide refrigeration system and method of operation

Abstract

The application discloses a kind of ejector synergistic transcritical carbon dioxide refrigeration system and working method, the system includes low pressure stage compressor, high pressure stage compressor, gas cooler, ejector, two expansion valves, two T-tubes, high temperature stage evaporator, low temperature stage evaporator and two regenerators;Cleverly use the shortcoming of T-tube gas-liquid separation effect is not good in the system of the application and convert it into an advantage;Use the saturated or two-phase refrigerant at the outlet of low temperature stage evaporator and the liquid-rich refrigerant from two T-tubes to carry out cascade heat recovery, respectively condense the liquid-rich refrigerant into supercooled liquid refrigerant, which is beneficial to reduce the dryness of the refrigerant before entering the high temperature stage evaporator and low temperature stage evaporator, and improve the refrigeration performance of the system;At the same time, cascade heat recovery can reduce the irreversible loss of heat transfer process and improve the heat transfer efficiency.In addition, the outlet of high temperature stage evaporator is gas-liquid two-phase refrigerant, which is beneficial to improve the heat transfer efficiency of the refrigerant in high temperature stage evaporator.

Description

Technical Field

[0001] This invention belongs to the field of refrigeration and cryogenic technology, specifically relating to a transcritical carbon dioxide refrigeration system with ejector enhancement and its working method. Background Technology

[0002] Statistics show that commercial refrigeration equipment accounts for approximately 25%-60% of supermarket electricity consumption. Currently, most supermarket refrigeration equipment uses R404A as the refrigerant, but it has a high GWP (Gross Power Potential) of 3922. With the introduction and implementation of the Montreal Protocol, its Kigali Amendment, and the Paris Agreement, the replacement of low-GWP refrigerants is progressing steadily. Carbon dioxide has advantages such as zero ODP (Oxygen Depletion), low GWP, non-toxicity, non-flammability, and high heat transfer coefficient. Therefore, carbon dioxide as an alternative refrigerant is an important direction for future refrigeration technology research.

[0003] In commercial refrigeration, two-stage compression transcritical CO2 systems, including single or dual evaporators, have received widespread attention in practical applications. However, traditional two-stage compression transcritical CO2 systems suffer from low refrigeration efficiency due to high throttling losses in the system. One effective solution to reduce throttling losses is to use an ejector as an expansion device. Using an ejector instead of a capillary tube or throttling valve has great potential to improve the performance of the refrigeration system. Therefore, ejector expansion systems are receiving increasing attention.

[0004] As a novel expansion mechanism, the injector, when applied to a transcritical CO2 system, can effectively recover the expansion work of the system, reduce throttling losses, and decrease compressor power consumption, thereby significantly improving the overall system efficiency. However, existing injectors still have considerable room for improvement in terms of configuration and performance enhancement in transcritical CO2 systems. Summary of the Invention

[0005] To address the shortcomings and deficiencies in the existing technology, the present invention aims to provide an ejector-enhanced transcritical carbon dioxide refrigeration system and its operating method. This system incorporates an ejector, two T-tubes, and two regenerators within a traditional transcritical two-stage carbon dioxide compression refrigeration system. The ejector recovers some of the expansion work, improving system efficiency. Compared to existing gas-liquid separators, although the gas-liquid separation effect of the T-tubes is not high, their structure is simple and low-cost. Furthermore, the present invention cleverly utilizes the disadvantage of the poor gas-liquid separation effect of the T-tubes, transforming it into an advantage. Firstly, the saturated or two-phase carbon dioxide refrigerant at the outlet of the low-temperature evaporator and the liquid-phase carbon dioxide refrigerant outlets in the two T-tubes form a stepped regeneration system. This fully condenses and subcools the liquid-phase carbon dioxide refrigerant in the T-tubes, reducing the dryness of the refrigerant before it enters the evaporator and improving the system's refrigeration performance. Secondly, the gas-phase carbon dioxide refrigerant in the T-tubes effectively reduces the suction superheat of the high-pressure stage compressor, decreasing its power consumption and further improving system performance. Furthermore, the outlet of the high-temperature stage evaporator in this invention is in a gas-liquid two-phase state, which is beneficial to improving the heat transfer efficiency of the refrigerant and reducing the flow pressure drop, thus significantly improving the efficiency and performance of the refrigeration system.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A transcritical carbon dioxide refrigeration system with ejector enhancement includes a high-pressure stage compressor 102. The outlet of the high-pressure stage compressor 102 is connected to the inlet of a gas cooler 103. The outlet of the gas cooler 103 is connected to the primary flow inlet of an ejector 104. The outlet of the ejector 104 is connected to the inlet of a first T-tube 105. The outlet of the first T-tube 105, rich in liquid-phase carbon dioxide refrigerant, passes through a second regenerator 112 and is then connected to the inlet of a first expansion valve 106. The outlet of the first expansion valve 106 is connected to the inlet of a high-temperature stage evaporator 107. The outlet of the high-temperature stage evaporator 107 is connected to the inlet of a second T-tube 108. The second T-tube 108 is rich in liquid-phase carbon dioxide refrigerant. The outlet containing gaseous carbon dioxide refrigerant is connected to the secondary flow inlet of ejector 104; the outlet of the second T-tube 108, rich in liquid carbon dioxide refrigerant, is connected to the inlet of the second expansion valve 109 after passing through the first regenerator 111. The outlet of the second expansion valve 109 is connected to the inlet of the low-temperature evaporator 110. The outlet of the low-temperature evaporator 110 is connected to the first regenerator 111 and the second regenerator 112 in sequence, and then to the inlet of the low-pressure compressor 101. The outlet of the low-pressure compressor 101 is connected to the outlet of the first T-tube 105, rich in gaseous carbon dioxide refrigerant, and then to the inlet of the high-pressure compressor 102, forming the entire circulation system.

[0008] The outlet of the high-temperature stage evaporator 107 is a two-phase gas-liquid carbon dioxide refrigerant. The two-phase flow is beneficial to improving the heat transfer efficiency of the carbon dioxide refrigerant in the high-temperature stage evaporator 107, which has a significant effect on improving the heat transfer efficiency and performance of the refrigeration system. The outlet of the low-temperature stage evaporator 110 is connected to the first regenerator 111 and the second regenerator 112 in sequence. The saturated or two-phase carbon dioxide refrigerant at the outlet of the low-temperature stage evaporator 110 is used to perform stepped reheating with the carbon dioxide refrigerant rich in liquid phase at the outlets of the second T-tube 108 and the first T-tube 105. On the one hand, the liquid-rich refrigerant in the second T-tube 108 and the first T-tube 105 is condensed into subcooled liquid carbon dioxide refrigerant, which helps to reduce the dryness of the refrigerant before entering the high-temperature stage evaporator 107 and the low-temperature stage evaporator 110, thereby improving the refrigeration performance of the system. On the other hand, stepped reheating can reduce irreversible losses in the heat transfer process and improve heat transfer efficiency.

[0009] The operation method of the transcritical carbon dioxide refrigeration system with enhanced ejector efficiency is as follows: High-temperature, high-pressure, transcritical, superheated gaseous carbon dioxide refrigerant, compressed by the high-pressure stage compressor 102, enters the gas cooler 103. After being cooled in the gas cooler 103, the transcritical, high-pressure, room-temperature gaseous carbon dioxide refrigerant serves as the working fluid of the ejector 104. It enters the nozzle of the first ejector 104, expands in the nozzle, and becomes a low-pressure, high-speed fluid, which then entrains the fluid from the outlet of the second T-tube 108, which is rich in gaseous carbon dioxide refrigerant. The two fluids are fully mixed in the mixing section of the ejector 104, and then decelerated and pressurized in the diffuser section of the ejector 104 to become a gas-liquid two-phase mixed refrigerant before exiting the ejector 104. The pressurized gas-liquid two-phase mixed refrigerant enters the first T-tube 105, where the fluid from the outlet of the first T-tube 105, rich in liquid carbon dioxide refrigerant, enters the second regenerator 112 and condenses into subcooled liquid carbon dioxide. The refrigerant, after being cooled by enthalpy throttling at the first expansion valve 106, enters the high-temperature evaporator 107 for endothermic evaporation. The gas-liquid two-phase carbon dioxide refrigerant from the outlet of the high-temperature evaporator 107 enters the second T-tube 108, where the fluid from the outlet of the second T-tube 108, rich in liquid refrigerant, enters the first regenerator 111 and condenses into subcooled liquid carbon dioxide refrigerant. After being cooled by enthalpy throttling at the second expansion valve 109, it enters the low-temperature evaporator 110 for endothermic evaporation. The refrigerant from the outlet of the low-temperature evaporator 110 passes through the first regenerator 111 and the second regenerator 112 in sequence for heat exchange, becoming superheated gaseous carbon dioxide refrigerant. It then enters the low-pressure compressor 101 for compression and is discharged from the low-pressure compressor 101. It mixes with the fluid from the outlet of the first T-tube 105, rich in gaseous refrigerant, and then enters the suction port of the high-pressure compressor 102, completing the refrigeration cycle of the entire system.

[0010] Compared to existing transcritical two-stage carbon dioxide refrigeration systems, this invention proposes an ejector-enhanced transcritical carbon dioxide refrigeration system. This system incorporates one ejector, two T-tubes, and two regenerators within the traditional transcritical two-stage carbon dioxide refrigeration system. The ejector recovers some of the expansion work, improving system efficiency. While the T-tubes have lower gas-liquid separation efficiency compared to existing gas-liquid separators, their simple structure and low cost are cleverly utilized and transformed into advantages. Firstly, the saturated or two-phase carbon dioxide refrigerant at the outlet of the low-temperature evaporator forms a stepped regeneration system with the liquid-rich carbon dioxide refrigerant outlets in the two T-tubes, improving heat transfer efficiency and reducing heat loss. The liquid-rich carbon dioxide refrigerant in the T-tubes is fully condensed and subcooled, reducing the refrigerant's dryness before entering the evaporator and improving system refrigeration performance. Secondly, the gas-rich carbon dioxide refrigerant in the T-tubes effectively reduces the suction superheat of the high-pressure compressor, decreasing its power consumption and further enhancing system performance. Furthermore, the application of a regenerator can prevent liquid carryover in the low-pressure stage compressor's intake, ensuring stable operation of the low-pressure stage compressor and further improving system performance. In this invention, the high-temperature stage evaporator outlet is in a gas-liquid two-phase state, which is beneficial for improving refrigerant heat transfer efficiency and reducing flow pressure drop, significantly improving the efficiency and performance of the refrigeration system. This technology will play a positive role in improving the performance and promoting energy conservation of carbon dioxide refrigeration systems, bringing better economic and environmental benefits. In summary, the system of this invention is an economical, effective, and feasible innovative solution that can effectively improve the performance of transcritical carbon dioxide refrigeration systems and promote the development of transcritical carbon dioxide refrigeration technology. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the refrigeration system of the present invention.

[0012] Figure 2 This is a cyclic pressure-enthalpy diagram (Ph diagram) of the working process of the refrigeration system of the present invention. Detailed Implementation

[0013] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0014] By rationally configuring the system, ejectors, regenerators, and T-tubes are simultaneously installed in the transcritical carbon dioxide refrigeration system. The ejectors are used to recover part of the expansion work, thereby improving the system performance.

[0015] like Figure 1As shown, this invention relates to a transcritical carbon dioxide refrigeration system with ejector enhancement, comprising a high-pressure stage compressor 102, the outlet of which is connected to the inlet of a gas cooler 103, the outlet of which is connected to the primary flow inlet of an ejector 104, the outlet of which is connected to the inlet of a first T-tube 105, the outlet of which is rich in liquid refrigerant and then connected to the inlet of a first expansion valve 106 after passing through a second regenerator 112, the outlet of which is connected to the inlet of a high-temperature stage evaporator 107, and the outlet of which is connected to the inlet of a second T-tube 108. The outlet of the refrigerant rich in gaseous carbon dioxide is connected to the secondary flow inlet of the ejector 104; the outlet of the second T-tube 108 rich in liquid carbon dioxide refrigerant is connected to the inlet of the second expansion valve 109 after passing through the first regenerator 111, and the outlet of the second expansion valve 109 is connected to the inlet of the low-temperature evaporator 110. The outlet of the low-temperature evaporator 110 is connected to the first regenerator 111 and the second regenerator 112 in sequence, and then to the inlet of the low-pressure compressor 101. The outlet of the low-pressure compressor 101 is connected to the outlet of the first T-tube 105 rich in gaseous carbon dioxide refrigerant, and then to the inlet of the high-pressure compressor 102, forming the entire circulation system.

[0016] like Figure 2The figure shows the pressure-enthalpy diagram (also known as the Ph diagram) of the transcritical carbon dioxide refrigeration system with ejector enhancement according to the present invention. The refrigeration system operates as follows: the high-temperature transcritical superheated gaseous carbon dioxide refrigerant (point 4 in the figure), compressed by the high-pressure stage compressor 102, enters the gas cooler 103. The cooled transcritical high-pressure room-temperature gaseous carbon dioxide refrigerant (point 5 in the figure) then enters the nozzle of the first ejector 104 (point 5' in the figure) as the working fluid. After expanding in the nozzle of the ejector 104, it... The fluid is converted into a low-pressure, high-speed fluid, which then entrains the fluid from the outlet of the second T-tube 108, which is rich in gaseous carbon dioxide refrigerant (point 9v in the figure). The two fluids are fully mixed in the mixing section of the ejector 104, and then decelerated and pressurized in the diffuser section of the ejector 104 to become a gas-liquid two-phase mixed refrigerant (point 6' in the figure) before being discharged from the ejector 104. The pressurized gas-liquid two-phase mixed refrigerant (point 6 in the figure) enters the first T-tube 105, and the fluid from the outlet of the first T-tube 105, which is rich in liquid refrigerant (point 6l in the figure), enters the second regenerator 112 and condenses into subcooled liquid carbon dioxide refrigerant. The refrigerant (at point 7 in the diagram) is then cooled by isenthalpic throttling at the first expansion valve 106 (at point 8 in the diagram) and enters the high-temperature evaporator 107 for endothermic evaporation. The gas-liquid two-phase refrigerant at the outlet of the high-temperature evaporator 107 (at point 9 in the diagram) enters the second T-tube 108. The fluid at the outlet of the second T-tube 108, which is rich in liquid refrigerant (at point 91 in the diagram), enters the first regenerator 111 and condenses into subcooled liquid carbon dioxide refrigerant (at point 10 in the diagram). Then, after being cooled by isenthalpic throttling at the second expansion valve 109 (at point 11 in the diagram), it enters the low-temperature evaporator 110. The refrigeration process involves heat absorption and evaporation. The refrigerant from the outlet of the low-temperature evaporator 110 (point 12 in the figure) passes through the first regenerator 111 (point 13 in the figure) and the second regenerator 112 in sequence for heat exchange, and then becomes superheated gaseous carbon dioxide refrigerant (point 1 in the figure). It enters the low-pressure compressor 101 for compression and is discharged from the low-pressure compressor 101. It mixes with the fluid from the outlet of the first T-tube 105, which is rich in gaseous carbon dioxide refrigerant (point 6v in the figure), and then enters the suction port of the high-pressure compressor 102 (point 3 in the figure), completing the refrigeration cycle of the entire system.

[0017] Compared to existing transcritical two-stage carbon dioxide refrigeration systems, this invention proposes an ejector-enhanced transcritical carbon dioxide refrigeration system. This system incorporates one ejector, two T-tubes, and two regenerators within the traditional transcritical two-stage carbon dioxide refrigeration system. The ejector recovers some of the expansion work, improving system efficiency. While the T-tubes have lower gas-liquid separation efficiency compared to existing gas-liquid separators, their simple structure and low cost are cleverly utilized and transformed into advantages. Firstly, the saturated or two-phase carbon dioxide refrigerant at the outlet of the low-temperature evaporator forms a stepped regeneration system with the liquid-rich carbon dioxide refrigerant outlets of the two T-tubes. This fully condenses and subcools the liquid-rich carbon dioxide refrigerant in the T-tubes, reducing the dryness of the refrigerant before it enters the evaporator and improving the system's refrigeration performance. Secondly, the gas-rich carbon dioxide refrigerant in the T-tubes effectively reduces the suction superheat of the high-pressure compressor, decreasing its power consumption and further improving system performance. Furthermore, the outlet of the high-temperature stage evaporator in this invention is in a gas-liquid two-phase state, which is beneficial to improving the heat transfer efficiency of the refrigerant and reducing the flow pressure drop, thus significantly improving the efficiency and performance of the refrigeration system.

Claims

1. A transcritical carbon dioxide refrigeration system with ejector enhancement, characterized in that: The ejector-enhanced transcritical carbon dioxide refrigeration system includes a high-pressure stage compressor (102), the outlet of which is connected to the inlet of a gas cooler (103), the outlet of which is connected to the primary flow inlet of an ejector (104), the outlet of which is connected to the inlet of a first T-tube (105), the outlet of which is rich in liquid carbon dioxide refrigerant and passes through a second regenerator (112) before being connected to the inlet of a first expansion valve (106), the outlet of which is connected to the inlet of a high-temperature stage evaporator (107), the outlet of which is connected to the inlet of a second T-tube (108), and the second T-tube (109) is connected to the inlet of a second T-tube (100). 8) The outlet of the refrigerant rich in gaseous carbon dioxide is connected to the secondary inlet of the ejector (104); the outlet of the second T-tube (108) rich in liquid refrigerant is connected to the inlet of the second expansion valve (109) after passing through the first regenerator (111), the outlet of the second expansion valve (109) is connected to the inlet of the low-temperature evaporator (110), the outlet of the low-temperature evaporator (110) is connected to the first regenerator (111) and the second regenerator (112) in sequence, and then connected to the inlet of the low-pressure compressor (101). The outlet of the low-pressure compressor (101) is connected to the outlet of the first T-tube (105) rich in gaseous refrigerant, and then connected to the inlet of the high-pressure compressor (102) to form the entire cycle system.

2. The transcritical carbon dioxide refrigeration system with ejector enhancement according to claim 1, characterized in that: The outlet of the high-temperature stage evaporator (107) is a gas-liquid two-phase carbon dioxide refrigerant. The gas-liquid two-phase flow is beneficial to improving the heat transfer efficiency of the carbon dioxide refrigerant in the high-temperature stage evaporator (107), which has a significant effect on improving the heat transfer efficiency and performance of the refrigeration system. The outlet of the low-temperature stage evaporator (110) is connected to the first regenerator (111) and the second regenerator (112) in sequence. The saturated or two-phase carbon dioxide refrigerant at the outlet of the low-temperature stage evaporator (110) is used to perform stepped reheating with the refrigerant rich in liquid phase at the outlet of the second T-tube (108) and the first T-tube (105). On the one hand, the liquid-rich carbon dioxide refrigerant in the second T-tube (108) and the first T-tube (105) is condensed into subcooled liquid carbon dioxide refrigerant, which is beneficial to reducing the dryness of the refrigerant before entering the high-temperature stage evaporator (107) and the low-temperature stage evaporator (110) and improving the refrigeration performance of the system. On the other hand, stepped reheating reduces the irreversible loss in the heat transfer process and improves the heat transfer efficiency.

3. The operating method of the injector-enhanced transcritical carbon dioxide refrigeration system according to claim 1 or 2, characterized in that: The high-temperature transcritical high-pressure superheated gaseous carbon dioxide refrigerant, compressed by the high-pressure compressor (102), enters the gas cooler (103). After being cooled in the gas cooler (103), the transcritical high-pressure room-temperature gaseous carbon dioxide refrigerant becomes the working fluid of the ejector (104). It enters the nozzle of the first ejector (104), expands in the nozzle, and becomes a low-pressure, high-speed fluid. This fluid then ejects the fluid from the outlet of the second T-tube (108) rich in gaseous carbon dioxide refrigerant. The two fluids are fully mixed in the mixing section of the ejector (104) and then decelerate and pressurize in the diffuser section of the ejector (104) to become a gas-liquid two-phase mixed carbon dioxide refrigerant before exiting the ejector (104). The pressurized gas-liquid two-phase mixed carbon dioxide refrigerant enters the first T-tube (105), where the fluid from the outlet of the first T-tube (105) rich in liquid carbon dioxide refrigerant enters the second regenerator (112) and condenses into subcooled liquid carbon dioxide refrigerant. Then, it exits through the first expansion valve (…). 106) After being cooled by throttling with moderate enthalpy, the refrigerant enters the high-temperature evaporator (107) for endothermic evaporation. The gas-liquid two-phase carbon dioxide refrigerant at the outlet of the high-temperature evaporator (107) enters the second T-tube (108), where the fluid at the outlet of the second T-tube (108) rich in liquid carbon dioxide refrigerant enters the first regenerator (111) and condenses into subcooled liquid refrigerant. Then, after being cooled by throttling with moderate enthalpy in the second expansion valve (109), it enters the low-temperature evaporator (110) for endothermic evaporation. The refrigeration process: The refrigerant from the outlet of the low-temperature stage evaporator (110) passes through the first regenerator (111) and the second regenerator (112) in sequence for heat exchange and becomes superheated gaseous carbon dioxide refrigerant. It enters the low-pressure stage compressor (101) for compression and is discharged from the low-pressure stage compressor (101). It mixes with the fluid from the outlet of the first T-tube (105) which is rich in gaseous carbon dioxide refrigerant and then enters the suction port of the high-pressure stage compressor (102) to complete the refrigeration cycle of the entire system.

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