Cascade refrigeration system with two-stage pre-cooling of low-temperature refrigeration cycle and control method

Abstract

This invention provides a cascade refrigeration system and control method with two-stage precooling in a low-temperature refrigeration cycle, comprising: a first precooler, a second precooler, a condenser-evaporator, a low-temperature refrigeration cycle, and a high-temperature refrigeration cycle. The second precooler has a cooling side and an evaporation side, and the condenser-evaporator has a condensation side and an evaporation side. The low-temperature refrigeration cycle is located on the cooling side of the second precooler and the condensation side of the condenser-evaporator. The high-temperature refrigeration cycle uses a high-temperature compressor and is located on the evaporation side of the condenser-evaporator and the evaporation side of the second precooler. The first precooler is located between the low-temperature compressor and the second precooler. The high-temperature superheated gas discharged from the low-temperature compressor sequentially enters the first precooler, the second precooler, and the condenser-evaporator, gradually reducing the enthalpy of the superheated gas as it cools and condenses. The refrigerant in the evaporation side of the second precooler is drawn in at a higher evaporation pressure and does not undergo a complete compression process from low pressure to high pressure as in the condenser-evaporator. The high-temperature compressor consumes less power, resulting in higher refrigeration efficiency of the cascade refrigeration system.

Description

Technical Field

[0001] This invention relates to the field of refrigeration technology, and in particular to a cascade refrigeration system and control method with two-stage precooling in a low-temperature refrigeration cycle. Background Technology

[0002] Cascade refrigeration systems solve problems such as low energy efficiency and high compressor discharge temperature in single-stage vapor compression refrigeration systems under large temperature difference conditions, and are widely used in applications requiring lower storage temperatures, such as deep-sea seafood, vaccines, and blood.

[0003] A cascade refrigeration system consists of two separate refrigerant cycles: a high-temperature refrigeration cycle and a low-temperature refrigeration cycle. These cycles are thermally coupled using a condenser-evaporator. The system is characterized by heat transfer at each stage, with the refrigerants circulating independently. In the low-temperature refrigeration cycle, the refrigerant absorbs heat from a low-temperature heat source in the evaporator and transfers this heat to the high-temperature refrigeration cycle via the condenser-evaporator. The high-temperature refrigeration cycle then carries the heat away to the outdoor environment. During the heat transfer process between the high and low-temperature refrigeration cycles, the condenser-evaporator acts as both the evaporator for the high-temperature cycle and the condenser for the low-temperature cycle. In the low-temperature refrigeration cycle, the refrigerant undergoes both cooling and condensation processes within the condenser-evaporator. For refrigerants with a high adiabatic index used in the low-temperature cycle, such as R744 and R717, the superheat of the refrigerant discharge from the low-temperature compressor is often high, resulting in a longer cooling process within the condenser-evaporator. However, because this heat is at a relatively high temperature, it can be cooled by a normal-temperature fluid medium without consuming the cooling capacity required by the compressor in the high-temperature refrigeration cycle's condenser-evaporator. Based on this, the existing technology involves setting up a pre-cooler at the exhaust outlet of the cryogenic compressor, with room temperature water as the cooling medium. This reduces the refrigerant superheat at the inlet of the condenser-evaporator, thereby reducing the refrigeration load of the high-temperature refrigeration cycle, reducing the power consumption of the high-temperature compressor, and improving the refrigeration efficiency of the entire cascade refrigeration system.

[0004] Figure 1 The figure shows the theoretical temperature-entropy diagram of a cascade refrigeration system using R290 / R744 as refrigerant, where the ambient temperature is 36℃, the evaporation temperature is -40℃, and the discharge temperature of the cryogenic compressor is 70.4℃.

[0005] In practical engineering, water-cooled precoolers have limited effectiveness in precooling the overheated compressor exhaust in low-temperature loops; their effect is limited by the temperature of the precooling water (e.g., ...). Figure 1 At ambient temperatures, the refrigerant temperature decreases after passing through the water-cooled precooler, and some heat is directly carried away by the water. Figure 1 Of the total cooling heat, approximately 5.86% is generated between 70.4℃ and 36℃, but a significant portion of the cooling heat occurs at higher temperatures between the pre-cooling water temperature and the high-temperature refrigeration cycle evaporation temperature. Figure 1Of the heat generated, approximately 16.69% is cooling heat between 36°C and -8.6°C, and this heat has a high degree of superheat, still accounting for a significant portion of the cooling load in the high-temperature refrigeration cycle. The refrigeration system cannot efficiently transfer this portion of heat to the environment. Summary of the Invention

[0006] This invention provides a cascade refrigeration system and control method with two-stage precooling in a low-temperature refrigeration cycle, which solves the problem in the prior art that a large amount of high-temperature cooling heat in the exhaust of the low-temperature compressor cannot be efficiently transferred to the outdoor environment, resulting in high power consumption of the high-temperature compressor and low efficiency of the cascade refrigeration system.

[0007] This invention provides a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle, comprising: a first precooler; a second precooler having a cooling side and an evaporation side; a condenser-evaporator having a condensation side and an evaporation side; a low-temperature refrigeration cycle including an evaporator, a low-temperature compressor, and a first throttling device, wherein the low-temperature refrigeration cycle is located on the cooling side of the second precooler and on the condensation side of the condenser-evaporator, the outlet of the evaporator is connected to the suction port of the low-temperature compressor, and the exhaust port of the low-temperature compressor is sequentially connected to the cooling side of the second precooler, the condensation side of the condenser-evaporator, the first throttling device, and the inlet of the evaporator; the inlet of the first precooler is connected to the exhaust port of the low-temperature compressor, and the outlet of the first precooler is connected to the cooling side of the second precooler; and a high-temperature refrigeration cycle located on the evaporation side of the condenser-evaporator and also on the evaporation side of the second precooler.

[0008] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided. The high-temperature refrigeration cycle includes a high-temperature compressor, a condenser, and a second throttling device. The high-temperature compressor has a first suction port and a discharge port. The outlet of the evaporation side of the condenser-evaporator is connected to the first suction port. The discharge port is connected in sequence to the condenser, the second throttling device, and the inlet of the evaporation side of the condenser-evaporator.

[0009] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided. The high-temperature refrigeration cycle further includes a subcooler, which is disposed between the condenser and the second throttling device. The subcooler has a cooling side, the inlet of the cooling side of the subcooler is connected to the outlet of the condenser, and the outlet of the cooling side of the subcooler is connected to the inlet of the second throttling device.

[0010] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided. The high-temperature refrigeration cycle further includes a third throttling device. The high-temperature compressor also has a second suction port. The outlet of the evaporator side of the second precooler is connected to the second suction port. The exhaust port of the high-temperature compressor is sequentially connected to the condenser, the third throttling device, and the inlet of the evaporator side of the second precooler.

[0011] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided, wherein the subcooler further has an evaporation side, the inlet of the evaporation side of the subcooler is connected to the outlet of the third throttling device, and the outlet of the evaporation side of the subcooler is connected to the inlet of the evaporation side of the second precooler.

[0012] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided. The high-temperature refrigeration cycle further includes a first control valve and a second control valve. The first control valve is located between the third throttling device and the evaporator side of the subcooler, and the second control valve is located between the third throttling device and the evaporator side of the second precooler.

[0013] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided, wherein the first precooler and the condenser are an integrated heat exchanger.

[0014] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided. The integrated heat exchanger has a first heat exchange tube and a second heat exchange tube that are independent of each other. The inlet of the first heat exchange tube is connected to the exhaust port of the low-temperature compressor, and the outlet of the first heat exchange tube is connected to the inlet of the cooling side of the second precooler. The inlet of the second heat exchange tube is connected to the exhaust port of the high-temperature compressor, and the outlet of the second heat exchange tube is connected to the inlet of the third throttling device and the cooling side of the subcooler, respectively.

[0015] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided, wherein the second precooler is one of a plate heat exchanger, a shell-and-tube heat exchanger, a plate-and-shell heat exchanger, and a coaxial heat exchanger.

[0016] According to the present invention, a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle is provided, wherein the high-temperature compressor is one of a scroll compressor with an intermediate gas inlet, a screw compressor with an intermediate gas inlet, a single-unit two-stage compressor, and a single-unit multi-cylinder compressor.

[0017] The present invention also provides a control method for a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle, based on the cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle as described above, comprising: acquiring an outdoor ambient temperature; when the outdoor ambient temperature is greater than or equal to a preset ambient temperature, controlling a first control valve to open and a second control valve to close; when the outdoor ambient temperature is less than the preset ambient temperature, controlling the second control valve to open and the first control valve to close.

[0018] The present invention provides a cascade refrigeration system and control method with two-stage precooling in a low-temperature refrigeration cycle. The low-temperature refrigeration cycle is completed by placing the low-temperature refrigeration cycle on the cooling side of the second precooler and on the condensing side of the condenser-evaporator. A high-temperature refrigeration cycle is placed on the evaporating side of the condenser-evaporator and on the evaporating side of the second precooler, transferring some of the heat discharged in the low-temperature refrigeration cycle to the environment. A first precooler is placed between the low-temperature compressor exhaust and the second precooler to initially cool the low-temperature compressor exhaust, transferring the portion of cooling heat above ambient temperature to the environment. A high-temperature refrigeration cycle is placed on the evaporating side of the second precooler to further cool the low-temperature compressor exhaust, transferring the remaining high-temperature cooling heat to the environment. Finally, a high-temperature refrigeration cycle is placed on the evaporating side of the condenser-evaporator to transfer the lower-temperature cooling heat and condensation heat to the environment. The present invention gradually reduces the enthalpy of the refrigerant in the low-temperature refrigeration cycle according to the low-temperature compressor exhaust temperature gradient, efficiently transferring heat from the low-temperature refrigeration cycle to the environment. The refrigerant in the evaporator side of the second precooler is drawn in at a higher evaporation pressure and does not undergo a complete compression process from low pressure to high pressure like in a condenser evaporator. The high-temperature compressor consumes less power, and the cascade refrigeration system has higher refrigeration efficiency. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 The theoretical R290 / R744 cascade refrigeration system is illustrated with a temperature-entropy diagram of the two-stage precoolable temperature range;

[0021] Figure 2 This is one of the schematic diagrams of the cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle provided by the present invention;

[0022] Figure 3 This is the second schematic diagram of the cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle provided by the present invention;

[0023] Figure 4 This is a schematic diagram of the integrated heat exchanger provided by the present invention;

[0024] Figure 5 This is a schematic flowchart of the control method for a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle provided by the present invention.

[0025] Figure label:

[0026] 1: Evaporator; 2: Low-temperature compressor; 3: Second precooler; 31: Cooling side of the second precooler; 32: Evaporation side of the second precooler; 4: Condensing evaporator; 41: Condensing side of the condensing evaporator; 42: Evaporation side of the condensing evaporator; 5: First throttling device; 6: High-temperature compressor; 61: First suction port; 62: Second suction port; 63: Exhaust port; 7: Condenser; 8: Second throttling device; 9: Subcooler; 91: Cooling side of the subcooler; 92: Evaporation side of the subcooler; 10: Third throttling device; 11: First precooler; 12: First control valve; 13: Second control valve; 14: Integrated heat exchanger; 141: First heat exchange tube; 142: Second heat exchange tube. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "high pressure," "medium pressure," "low pressure," "high temperature," and "low temperature" should be interpreted broadly. For example, in a high-temperature refrigeration cycle, "high pressure," "medium pressure," and "low pressure" refer to relative comparative values ​​within the same high-temperature refrigerant loop. The pressure between the first suction port of the high-temperature compressor and the outlet of the second throttling device is low pressure; the pressure between the second suction port of the high-temperature compressor and the outlet of the third throttling device is medium pressure; and the pressure between the discharge port of the high-temperature compressor and the inlets of the second and third throttling devices is high pressure. In a high-temperature refrigeration cycle, the main refrigerant refers to the refrigerant flowing from the condenser outlet to the first suction port of the high-temperature compressor, and the auxiliary refrigerant refers to the refrigerant flowing from the condenser outlet to the second suction port of the high-temperature compressor. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0030] The following is combined Figures 2 to 5 This invention describes a cascade refrigeration system and control method with two-stage precooling in a low-temperature refrigeration cycle.

[0031] refer to Figure 2 The cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle provided by the present invention includes: a first precooler 11, a second precooler 3, a condenser-evaporator 4, a low-temperature refrigeration cycle, and a high-temperature refrigeration cycle. The second precooler 3 has a cooling side and an evaporation side; the condenser-evaporator 4 has a condensation side and an evaporation side; the low-temperature refrigeration cycle includes an evaporator 1, a low-temperature compressor 2, and a first throttling device 5. The low-temperature refrigeration cycle is located on the cooling side 31 of the second precooler and on the condensation side 41 of the condenser-evaporator. The outlet of the evaporator 1 is connected to the suction port of the low-temperature compressor 2, and the exhaust port of the low-temperature compressor 2 is connected sequentially to the cooling side 31 of the second precooler, the condensation side 41 of the condenser-evaporator, the first throttling device 5, and the inlet of the evaporator 1; the inlet of the first precooler 11 is connected to the exhaust port of the low-temperature compressor 2, and the outlet of the first precooler 11 is connected to the cooling side 31 of the second precooler; the high-temperature refrigeration cycle is located on the evaporation side 42 of the condenser-evaporator and on the evaporation side 32 of the second precooler.

[0032] The second precooler 3 has a cooling side and an evaporation side. The cooling side 31 of the second precooler is used to cool the high-temperature superheated gas of the cryogenic compressor 2, and the evaporation side 32 of the second precooler is used to evaporate and absorb heat from the cooling side. The condenser-evaporator 4 has a condensing side and an evaporation side. The condensing side 41 of the condenser-evaporator is used to cool and condense the refrigerant gas discharged from the cryogenic compressor 2, and the evaporation side 42 of the condenser-evaporator is used to evaporate and absorb heat from the condensing side.

[0033] Evaporator 1, low-temperature compressor 2, cooling side 31 of the second precooler, condensing side 41 of the condensing evaporator, and first throttling device 5 are connected in sequence to form a low-temperature refrigeration cycle; specifically, refer to Figure 2The outlet of evaporator 1 is connected to the suction port of cryogenic compressor 2. The low-temperature, low-pressure refrigerant gas in evaporator 1 is drawn into cryogenic compressor 2, compressed, and pressurized into high-temperature, high-pressure superheated gas. The exhaust port of cryogenic compressor 2 is connected to the inlet of the first precooler 11. The high-temperature superheated gas enters the first precooler 11 for preliminary cooling, becoming a gas with a certain degree of precooling. The outlet of the first precooler 11 is connected to the cooling side 31 of the second precooler. The superheated gas enters the second precooler 3 for further cooling, becoming a gas with a lower temperature and greater degree of precooling. The cooling side 31 of the second precooler is connected to the condenser-evaporator. The condenser side 41 is connected, and the superheated gas enters the condenser side 41 of the condenser evaporator for cooling and condensation, becoming a high-pressure saturated liquid; the condenser side 41 of the condenser evaporator is connected to the inlet of the first throttling device 5, and the saturated liquid is throttled and depressurized by the first throttling device 5 to become a low-temperature gas-liquid mixture; the outlet of the first throttling device 5 is connected to the inlet of the evaporator 1, and the low-temperature gas-liquid mixture enters the evaporator 1, where the liquid part of the gas-liquid mixture absorbs heat and evaporates in the evaporator 1 to become saturated gas, producing a refrigeration phenomenon; the saturated gas and the gas in the gas-liquid mixture are drawn into the low-temperature compressor 2 to start the next low-temperature refrigeration cycle.

[0034] The cascade refrigeration system with two-stage precooling of the low-temperature refrigeration cycle provided in this embodiment also includes a high-temperature refrigeration cycle. The high-temperature refrigeration cycle is located on the evaporation side 42 of the condenser-evaporator and is also located on the evaporation side 32 of the second precooler. The higher-temperature cooling heat discharged in the low-temperature refrigeration cycle is transferred to the environment through the second precooler 3, and the lower-temperature cooling condensation heat discharged in the low-temperature refrigeration cycle is transferred to the environment through the condenser-evaporator 4.

[0035] In this embodiment, a first precooler 11 is provided between the second precooler 3 and the cryogenic compressor 2. The first precooler 11 initially reduces the temperature of the refrigerant gas discharged from the cryogenic compressor 2, making it a gas with a certain degree of precooling, thus carrying away the high-temperature cooling heat in the cryogenic refrigerant cycle. A second precooler 3 is provided between the first precooler 11 and the condenser-evaporator 4, further reducing the temperature of the refrigerant gas discharged from the cryogenic compressor, making it a gas with an even lower temperature and a greater degree of precooling, thus carrying away the higher-temperature cooling heat in the cryogenic refrigerant cycle. The two precooling processes reduce the enthalpy of the refrigerant entering the condenser-evaporator 41 by lowering the refrigerant gas temperature, reducing the refrigerant cooling load in the high-temperature refrigeration cycle, reducing power consumption, and thus improving the refrigeration efficiency of the cascade refrigeration system.

[0036] This embodiment completes the low-temperature refrigeration cycle by placing the low-temperature refrigeration cycle on the cooling side of the second precooler and on the condensing side of the condenser-evaporator. A high-temperature refrigeration cycle is placed on the evaporating side of the condenser-evaporator and on the evaporating side of the second precooler, transferring some of the heat discharged in the low-temperature refrigeration cycle to the environment. A first precooler is placed between the low-temperature compressor exhaust and the second precooler to initially cool the low-temperature compressor exhaust, transferring the portion of cooling heat with a temperature higher than ambient temperature to the environment. A high-temperature refrigeration cycle is placed on the evaporating side of the second precooler to further cool the low-temperature compressor exhaust, transferring the remaining high-temperature cooling heat to the environment. Finally, a high-temperature refrigeration cycle is placed on the evaporating side of the condenser-evaporator to transfer the lower-temperature cooling heat and condensation heat to the environment. This invention gradually reduces the enthalpy of the refrigerant in the low-temperature refrigeration cycle according to the low-temperature compressor exhaust temperature gradient, efficiently transferring heat from the low-temperature refrigeration cycle to the environment. The refrigerant in the evaporating side of the second precooler is drawn in at a higher evaporation pressure, without undergoing the complete compression process from low pressure to high pressure as in the condenser-evaporator. This results in lower power consumption of the high-temperature compressor and higher refrigeration efficiency of the cascade refrigeration system.

[0037] This embodiment sets up a first precooler 11 and a second precooler 3 between the condenser evaporator 4 and the low-temperature compressor 2. The high-temperature heat discharged in the low-temperature cycle is transferred to the environment through the first precooler 11 and the second precooler 3 in the high-temperature refrigeration cycle, thereby reducing the refrigerant refrigeration load, reducing the power consumption in the high-temperature refrigeration cycle, and thus improving the refrigeration efficiency of the refrigeration system.

[0038] Based on the above embodiments, the high-temperature refrigeration cycle includes a high-temperature compressor 6, a condenser 7, and a second throttling device 8. The high-temperature compressor 6 has a first suction port 61 and a discharge port 63. The outlet of the evaporation side 42 of the condenser evaporator is connected to the first suction port 61, and the discharge port 63 is connected in sequence to the condenser 7, the second throttling device 8, and the inlet of the evaporation side 42 of the condenser evaporator.

[0039] Based on the above embodiments, the high-temperature refrigeration cycle also includes a third throttling device 10, the high-temperature compressor 6 also has a second suction port 62, the outlet of the evaporation side 32 of the second precooler is connected to the second suction port 62, and the exhaust port 63 of the high-temperature compressor is connected in sequence to the condenser 7, the third throttling device 10 and the inlet of the evaporation side 32 of the second precooler.

[0040] Based on the above embodiments, the high-temperature refrigeration cycle also includes a subcooler 9, which is disposed between the condenser 7 and the second throttling device 8. The subcooler 9 has a cooling side and an evaporating side. The inlet of the cooling side 91 of the subcooler is connected to the outlet of the condenser 7, the outlet of the cooling side 91 of the subcooler is connected to the inlet of the second throttling device 8, the inlet of the evaporating side 92 of the subcooler is connected to the outlet of the third throttling device 10, and the outlet of the evaporating side 92 of the subcooler is connected to the inlet of the evaporating side 32 of the second precooler.

[0041] The high-temperature compressor 6, condenser 7, third throttling device 10, subcooler 9, evaporator side 42 of the condenser-evaporator, evaporator side 32 of the second precooler, and second throttling device 8 are connected in sequence to form a high-temperature refrigeration cycle; specifically, refer to Figure 2 The outlet of the evaporator side 42 of the condenser is connected to the first suction port 61 of the high-temperature compressor 6. The low-temperature, low-pressure refrigerant gas on the evaporator side 42 of the condenser is drawn into the high-temperature compressor 6 and undergoes a first-stage compression and pressurization to become a medium-pressure superheated gas. The outlet of the evaporator side 92 of the subcooler is connected to the inlet of the evaporator side 32 of the second precooler. The outlet of the evaporator side 32 of the second precooler is connected to the second suction port 62 of the high-temperature compressor. The medium-temperature, medium-pressure refrigerant gas on the evaporator side 32 of the second precooler is drawn into the high-temperature compressor 6 and mixed with the superheated gas drawn into the first suction port 61 and compressed to medium pressure. The high-temperature compressor 6 performs a second-stage compression and pressurization to compress the medium-pressure gas mixture into a high-temperature, high-pressure superheated gas. The exhaust port 63 of the high-temperature compressor is connected to the inlet of the condenser 7. The high-temperature, high-pressure superheated gas dissipates heat to the environment and is condensed into a high-pressure saturated liquid.

[0042] The outlet of condenser 7 is connected in sequence to the inlet of the cooling side 91 of the subcooler and the inlet of the third throttling device 10. A portion of the high-temperature, high-pressure saturated liquid enters the cooling side 91 of the subcooler, and a small portion of the high-temperature, high-pressure saturated liquid is throttled and depressurized by the third throttling device 10 to become a medium-pressure, medium-temperature gas-liquid mixture. The third throttling device 10 is connected to the inlet of the evaporation side 92 of the subcooler. A portion of the liquid in the medium-pressure, medium-temperature gas-liquid mixture evaporates in the evaporation side 92 of the subcooler, absorbing the subcooling heat from the cooling side 91 of the subcooler, thus transforming the high-temperature, high-pressure saturated liquid entering from the cooling side 91 of the subcooler into a medium-temperature, high-pressure liquid with a lower temperature and a certain degree of subcooling. The outlet of the evaporation side 92 of the subcooler is connected to the inlet of the evaporation side 32 of the second precooler. The liquid that has not been completely evaporated in the medium-pressure, medium-temperature gas-liquid mixture enters the evaporation side 32 of the second precooler to continue evaporating, absorbing the subcooling heat from the low-temperature refrigeration cycle in the cooling side 31 of the second precooler, thus transforming the gas in the low-temperature refrigeration cycle into a gas with a lower temperature and a greater degree of precooling, forming a medium-pressure saturated gas.

[0043] Furthermore, the outlet of the cooling side 91 of the subcooler is connected to the inlet of the second throttling device 8. The medium-temperature high-pressure liquid is throttled and depressurized by the second throttling device 8 to become a low-pressure low-temperature gas-liquid mixture. The outlet of the second throttling device 8 is connected to the inlet of the evaporation side 42 of the condenser. The liquid part of the medium-temperature gas-liquid mixture evaporates on the evaporation side 42 of the condenser and absorbs the condensation heat in the low-temperature refrigeration cycle, so that the gas in the low-temperature refrigeration cycle on the condensation side 41 of the condenser is cooled and condensed to form a low-pressure saturated gas. The outlet of the evaporation side 42 of the condenser is connected to the first suction port 61 of the high-temperature compressor, and the outlet of the evaporation side 32 of the second precooler is connected to the second suction port 62 of the high-temperature compressor. The low-pressure saturated gas mixes with the gas in the low-pressure low-temperature gas-liquid mixture, and the medium-pressure saturated gas mixes with the gas in the medium-pressure medium-temperature gas-liquid mixture. They are then drawn into the first suction port 61 and the second suction port 62 of the high-temperature compressor to start the next high-temperature refrigeration cycle.

[0044] Based on the above embodiments, the first precooler 11 and the condenser 7 are integrated heat exchangers 14, that is, the first precooler 11 in the low temperature cycle and the condenser 7 in the high temperature refrigeration cycle share a heat exchanger, which can exchange heat with the outdoor environment simultaneously in different refrigeration cycles.

[0045] Furthermore, the integrated heat exchanger 14 has a first heat exchange tube 141 and a second heat exchange tube 142 that are independent of each other. The inlet of the first heat exchange tube 141 is connected to the exhaust port of the cryogenic compressor 2, and the outlet of the first heat exchange tube 141 is connected to the inlet of the cooling side 31 of the second precooler. The inlet of the second heat exchange tube 142 is connected to the exhaust port 63, and the outlet of the second heat exchange tube 142 is connected to the inlet of the third throttling device 10 and the cooling side 91 of the subcooler, respectively.

[0046] refer to Figure 4 In this embodiment, the first precooler 11 and the condenser 7 in the high-temperature refrigeration cycle are integrated heat exchangers 14. The integrated heat exchanger 14 has a first heat exchange tube 141 and a second heat exchange tube 142 that are independent of each other. Each heat exchange tube has an inlet and an outlet.

[0047] refer to Figure 3The outlet of evaporator 1 is connected to the suction port of cryogenic compressor 2. The low-temperature, low-pressure refrigerant gas in evaporator 1 is drawn into cryogenic compressor 2, compressed, and pressurized into high-temperature, high-pressure superheated gas. The exhaust port of cryogenic compressor 2 is connected to the inlet of the first heat exchange tube 141. The high-temperature, high-pressure superheated gas enters the first heat exchange tube 141 for preliminary cooling, becoming gas with a certain degree of pre-cooling. The outlet of the first heat exchange tube 141 is connected to the cooling side 31 of the second precooler. The superheated gas enters the second precooler 3 for further cooling, becoming gas with an even lower temperature and greater degree of pre-cooling. The cooling side 31 of the second precooler is connected to... The condenser side 41 of the condenser-evaporator is connected, and the superheated gas enters the condenser side 41 of the condenser-evaporator for cooling and condensation, becoming a high-pressure saturated liquid; the condenser side 41 of the condenser-evaporator is connected to the inlet of the first throttling device 5, and the saturated liquid is throttled and depressurized by the first throttling device 5 to become a low-temperature, low-pressure gas-liquid mixture; the outlet of the first throttling device 5 is connected to the inlet of the evaporator 1, and the low-temperature gas-liquid mixture enters the evaporator 1, where the liquid part of the low-temperature gas-liquid mixture evaporates and absorbs heat to become saturated gas, producing a refrigeration phenomenon. The saturated gas and the gas of the low-temperature gas-liquid mixture are drawn into the low-temperature compressor 2 to start the next low-temperature refrigeration cycle.

[0048] The high-temperature compressor 6, condenser 7, third throttling device 10, second heat exchange tube 142, evaporator side 42 of the condenser-evaporator, evaporator side 32 of the second precooler, and second throttling device 8 are connected in sequence to form a high-temperature refrigeration cycle; specifically, refer to Figure 3 The outlet of the evaporator side 42 of the condenser is connected to the first suction port 61 of the high-temperature compressor 6. The low-temperature, low-pressure refrigerant gas from the evaporator side 42 of the condenser is drawn into the high-temperature compressor 6 and undergoes a first-stage compression and pressurization to become a medium-pressure superheated gas. The outlet of the evaporator side 92 of the subcooler is connected to the inlet of the evaporator side 42 of the condenser. The outlet of the evaporator side 32 of the second precooler is connected to the second suction port 62 of the high-temperature compressor. The medium-temperature, medium-pressure refrigerant gas from the evaporator side 32 of the second precooler is drawn into the high-temperature compressor 6 and mixed with the superheated gas drawn into the first suction port 61 and compressed to medium pressure. The high-temperature compressor 6 performs a second-stage compression and pressurization to compress the medium-pressure gas mixture into a high-temperature, high-pressure superheated gas. The exhaust port 63 of the high-temperature compressor is connected to the inlet of the second heat exchange tube 142 of the integrated heat exchanger. The high-temperature, high-pressure superheated gas dissipates heat to the environment and is condensed into a high-pressure saturated liquid.

[0049] The outlet of the second heat exchange tube 142 is connected to the inlet of the cooling side 91 of the subcooler and the inlet of the third throttling device 10. A portion of the high-temperature, high-pressure saturated liquid enters the cooling side 91 of the subcooler, and a small portion of the high-temperature, high-pressure saturated liquid is throttled and depressurized by the third throttling device 10 to become a medium-pressure, medium-temperature gas-liquid mixture. The third throttling device 10 is connected to the inlet of the evaporation side 92 of the subcooler. A portion of the liquid in the medium-pressure, medium-temperature gas-liquid mixture evaporates in the evaporation side 92 of the subcooler, absorbing the subcooling heat from the cooling side 91 of the subcooler, thus transforming the high-temperature, high-pressure saturated liquid entering from the cooling side 91 of the subcooler into a medium-temperature, high-pressure liquid with a lower temperature and a certain degree of subcooling. The outlet of the evaporation side 92 of the subcooler is connected to the inlet of the evaporation side 32 of the second precooler. The liquid that has not been completely evaporated in the medium-pressure, medium-temperature gas-liquid mixture enters the evaporation side 32 of the second precooler to continue evaporating, absorbing the subcooling heat from the low-temperature refrigeration cycle in the cooling side 31 of the second precooler, thus transforming the gas in the low-temperature refrigeration cycle into a gas with a lower temperature and a greater degree of precooling, forming a medium-pressure saturated gas.

[0050] The cooling side outlet 91 of the subcooler is connected to the inlet of the second throttling device 8. The medium-temperature high-pressure liquid is throttled and depressurized by the second throttling device 8 to become a low-pressure low-temperature gas-liquid mixture. The outlet of the second throttling device 8 is connected to the inlet of the evaporation side 42 of the condenser-evaporator. The liquid part of the medium-temperature gas-liquid mixture evaporates on the evaporation side 42 of the condenser-evaporator, absorbing the condensation heat in the low-temperature refrigeration cycle, which cools and condenses the gas in the low-temperature refrigeration cycle on the condensation side 41 of the condenser-evaporator, forming a low-pressure saturated gas. The evaporation side outlet 42 of the condenser-evaporator is connected to the first suction port 61 of the high-temperature compressor, and the evaporation side outlet 32 ​​of the second precooler is connected to the second suction port 62 of the high-temperature compressor. The low-pressure saturated gas mixes with the gas in the low-pressure low-temperature gas-liquid mixture, and the medium-pressure saturated gas mixes with the gas in the medium-pressure medium-temperature gas-liquid mixture. They are then drawn into the first suction port 61 and the second suction port of the high-temperature compressor to start the next high-temperature refrigeration cycle.

[0051] Based on the above embodiments, the high-temperature refrigeration cycle further includes a first control valve 12 and a second control valve 13. The first control valve 12 is located between the third throttling device 10 and the evaporator side 92 of the subcooler, and the second control valve 13 is located between the third throttling device 10 and the evaporator side 32 of the second precooler.

[0052] The first control valve 12 is located between the outlet of the third throttling device 10 and the inlet of the evaporation side 92 of the subcooler, and is used to control the connection between the third throttling device 10 and the evaporation side 92 of the subcooler; the second control valve 13 is located between the outlet of the third throttling device 10 and the inlet of the evaporation side 32 of the second precooler, and is used to control the connection between the third throttling device 10 and the evaporation side 32 of the second precooler.

[0053] Specifically, the outlet of the third throttling device 10 is connected to the evaporator side 92 of the subcooler via a first pipeline, and the first control valve 12 is located on the first pipeline; the outlet of the third throttling device 10 is connected to the inlet of the evaporator side 32 of the second precooler via a second pipeline, and the second control valve 13 is located on the second pipeline; when the outdoor ambient temperature is greater than or equal to the preset ambient temperature, the outdoor ambient temperature is high, and the compressor discharge temperature is high, so the first control valve 12 is opened and the second control valve 13 is closed, so that the gas-liquid mixture throttled and depressurized by the third throttling device 10 enters the evaporator side 92 of the subcooler and the evaporator side 32 of the second precooler in sequence to evaporate and absorb heat. At this time, the liquid before the second throttling device 8 is a medium-temperature, high-pressure liquid with a certain degree of subcooling, the refrigerant unit cooling capacity in the evaporator side 42 of the condenser evaporator is large, the refrigerant intake at the second suction port of the high-temperature compressor 6 is large, and the refrigerant temperature at the discharge port is low, thereby ensuring that the discharge temperature of the high-temperature compressor operates within a safe range.

[0054] When the outdoor ambient temperature is lower than the preset ambient temperature, the first control valve 12 is closed and the second control valve 13 is opened, allowing the gas-liquid mixture, which has been throttled and depressurized by the third throttling device 10, to directly enter the evaporator side 32 of the second precooler for evaporation and absorption of heat from the low-temperature refrigeration cycle. At this time, the subcooler 9 does not consume the refrigeration capacity of the high-temperature refrigeration loop, and the high-pressure, high-temperature liquid flowing from the condenser 7 or the second heat exchange tube 142 of the integrated heat exchanger flows more towards the second throttling device, resulting in a larger refrigerant flow rate on the evaporator side 42 of the condenser-evaporator.

[0055] This embodiment controls the opening and closing of the first control valve 12 and the second control valve 13 based on the relationship between the outdoor ambient temperature and the preset ambient temperature. This controls whether the evaporator side 92 of the subcooler 9 is activated, preventing the compressor from being damaged due to excessively high discharge temperature under harsh operating conditions, while improving the system's cooling efficiency under normal operating conditions. The specific value of the preset ambient temperature is related to the type of refrigerant used in the high-temperature refrigeration cycle and the low-temperature refrigeration cycle, the size of equipment such as the compressor heat exchanger, and the actual operating conditions of the system, and is determined accordingly.

[0056] Compared with the prior art, the cascade refrigeration system of the two-stage precooling of the low-temperature refrigeration cycle of the present invention places the low-temperature refrigeration cycle on the cooling side of the second precooler and on the condensing side of the condenser-evaporator to complete the low-temperature refrigeration cycle; by placing the high-temperature refrigeration cycle on the evaporating side of the condenser-evaporator and on the evaporating side of the second precooler, part of the heat discharged in the low-temperature refrigeration cycle is transferred to the environment; by placing the first precooler between the low-temperature compressor exhaust and the second precooler, the low-temperature compressor exhaust is initially cooled, and part of the cooling heat with a temperature higher than the ambient temperature is transferred to the environment; by placing the refrigerant of the high-temperature refrigeration cycle auxiliary circuit on the evaporating side of the second precooler, the low-temperature compressor exhaust is cooled again, and part of the cooling heat with a still high temperature is transferred to the environment; by placing the refrigerant of the high-temperature refrigeration cycle main circuit on the evaporating side of the condenser-evaporator, the cooling heat and condensation heat with a lower temperature are transferred to the environment.

[0057] This invention relates to a two-stage pre-cooling cascade refrigeration system for a high-temperature compressor. This system gradually reduces the enthalpy of the refrigerant during the low-temperature refrigeration cycle by following the discharge temperature gradient of the low-temperature compressor. This efficiently transfers heat from the low-temperature refrigeration cycle to the environment, reducing the refrigerant load on the main circuit of the high-temperature compressor. While still satisfying the cooling and condensation requirements of the low-temperature refrigeration cycle, the refrigerant gas in the evaporator side of the second pre-cooler, which performs the pre-cooling function, is drawn in through the second suction port of the high-temperature compressor. Unlike the refrigerant drawn in through the first suction port, which undergoes a complete compression process from low pressure to high pressure, this system only experiences a partial compression process from intermediate pressure to discharge pressure. This reduces the power consumption of the high-temperature compressor, thereby improving the refrigeration efficiency of the refrigeration system.

[0058] The cascade refrigeration system of the low-temperature refrigeration cycle with two-stage precooling utilizes the refrigerant under the high-temperature compressor's injection pressure in the high-temperature refrigeration cycle as the cold source for the second precooler, without setting up a separate mechanical precooling loop, making the system simpler and more compact.

[0059] The first precooler 11 of the cascade refrigeration system with two-stage precooling in the low-temperature refrigeration cycle of the present invention can use an air-cooled heat exchanger, without the need for a water-cooled heat exchanger. It can achieve a certain degree of precooling without relying on low-temperature cooling water and without consuming water resources.

[0060] Based on the above embodiments, the condenser-evaporator 4 is one of a plate heat exchanger, a shell-and-tube heat exchanger, a plate-and-shell heat exchanger, and a coaxial heat exchanger.

[0061] In this embodiment, the second precooler 3 is one of a plate heat exchanger, a shell-and-tube heat exchanger, a plate-and-shell heat exchanger, and a coaxial heat exchanger.

[0062] The high-temperature compressor in this embodiment is one of the following: a scroll compressor with an intermediate air inlet, a screw compressor with an intermediate air inlet, a single-unit two-stage compressor, and a single-unit multi-cylinder compressor.

[0063] In this embodiment, the cryogenic compressor 2 is any one of a scroll compressor, a rotary compressor, a screw compressor, and a piston compressor. In this embodiment, the high-temperature compressor 6 is any one of a scroll compressor with an intermediate gas inlet, a screw compressor with an intermediate gas inlet, or a single-unit multi-cylinder rotary compressor.

[0064] In this embodiment, the first throttling device 5 is one of an electronic expansion valve, a thermal expansion valve, a capillary tube, and an orifice plate throttling device. In this embodiment, the second throttling device 8 is one of an electronic expansion valve, a thermal expansion valve, a capillary tube, and an orifice plate throttling device. In this embodiment, the third throttling device 10 is one of an electronic expansion valve, a thermal expansion valve, a capillary tube, and an orifice plate throttling device. In this embodiment, the first throttling device 5, the second throttling device 8, and the third throttling device 10 can be the same or different.

[0065] In this embodiment, the pre-cooling degree refers to the temperature reduction of the refrigerant gas discharged from the cryogenic compressor during the cooling process, with the refrigerant temperature at the discharge port of the cryogenic compressor as the comparison value.

[0066] This embodiment also provides a control method for a cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle. Based on the cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle in any of the above embodiments, the method includes: step 100, acquiring the outdoor ambient temperature; step 200, when the outdoor ambient temperature is greater than or equal to a preset ambient temperature, controlling the first control valve to open and the second control valve to close; step 300, when the outdoor ambient temperature is less than the preset ambient temperature, controlling the second control valve to open and the first control valve to close.

[0067] refer to Figure 5 Step 100: Obtain the outdoor ambient temperature through a temperature monitoring device; Step 200: When the outdoor ambient temperature is greater than or equal to a preset ambient temperature, the outdoor ambient temperature is high, and the compressor discharge temperature is high. Control the first control valve to open and the second control valve to close, so that the gas-liquid mixture, throttled and depressurized by the third throttling device, sequentially enters the evaporator side of the subcooler and the evaporator side of the second precooler for evaporation and heat absorption. At this time, the liquid before the second throttling device is a medium-temperature, high-pressure liquid with a certain degree of subcooling. The refrigerant unit cooling capacity in the evaporator side of the condenser-evaporator is large, the refrigerant intake at the second suction port of the high-temperature compressor is large, and the refrigerant temperature at the discharge port is low, thereby ensuring that the discharge temperature of the high-temperature compressor operates within a safe range.

[0068] Step 300: When the outdoor ambient temperature is lower than the preset ambient temperature, the first control valve is closed and the second control valve is opened, allowing the gas-liquid mixture, which has been throttled and depressurized by the third throttling device, to directly enter the evaporator side of the second precooler to evaporate and absorb heat from the low-temperature refrigeration cycle. At this time, the subcooler does not consume the refrigeration capacity of the high-temperature refrigeration loop, and the high-pressure, high-temperature liquid flowing from the second heat exchange tube of the condenser or integrated heat exchanger flows more towards the second throttling device, resulting in a larger refrigerant flow rate on the evaporator side of the condenser-evaporator.

[0069] This embodiment controls the opening and closing of the first and second control valves based on the relationship between the outdoor ambient temperature and the preset ambient temperature. This controls whether the evaporator side of the subcooler is activated, preventing damage to the compressor discharge temperature due to excessively high temperatures under harsh operating conditions, while simultaneously improving the system's cooling efficiency under normal operating conditions. The specific value of the preset ambient temperature is determined based on the type of refrigerant used in the high-temperature and low-temperature refrigeration cycles, the dimensions of equipment such as the compressor and heat exchanger, and the actual operating conditions of the system.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle, characterized in that, include: First precooler; The second precooler has a cooling side and an evaporation side; A condensing evaporator having a condensing side and an evaporating side; A low-temperature refrigeration cycle includes an evaporator, a low-temperature compressor, and a first throttling device. The low-temperature refrigeration cycle is located on the cooling side of the second precooler and on the condensing side of the condenser-evaporator. The outlet of the evaporator is connected to the suction port of the low-temperature compressor. The exhaust port of the low-temperature compressor is connected in sequence to the cooling side of the second precooler, the condensing side of the condenser-evaporator, the first throttling device, and the inlet of the evaporator. The inlet of the first precooler is connected to the exhaust port of the cryogenic compressor, and the outlet of the first precooler is connected to the cooling side of the second precooler; A high-temperature refrigeration cycle is provided on the evaporation side of the condenser-evaporator and also on the evaporation side of the second precooler; The high-temperature refrigeration cycle includes a high-temperature compressor, a condenser, and a second throttling device. The high-temperature compressor has a first suction port and a discharge port. The outlet on the evaporation side of the condenser-evaporator is connected to the first suction port. The discharge port is connected in sequence to the condenser, the second throttling device, and the inlet on the evaporation side of the condenser-evaporator. The high-temperature refrigeration cycle further includes a subcooler, which is located between the condenser and the second throttling device. The subcooler has a cooling side, the inlet of which is connected to the outlet of the condenser, and the outlet of which is connected to the inlet of the second throttling device. The high-temperature refrigeration cycle also includes a third throttling device. The high-temperature compressor also has a second suction port. The outlet of the evaporation side of the second precooler is connected to the second suction port. The exhaust port of the high-temperature compressor is sequentially connected to the condenser, the third throttling device, and the inlet of the evaporation side of the second precooler. The subcooler also has an evaporation side, the inlet of which is connected to the outlet of the third throttling device, and the outlet of which is connected to the inlet of the evaporation side of the second precooler. The high-temperature refrigeration cycle also includes a first control valve and a second control valve. The first control valve is located between the third throttling device and the evaporator side of the subcooler, and the second control valve is located between the third throttling device and the evaporator side of the second precooler.

2. The cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle according to claim 1, characterized in that, The first precooler and the condenser are an integrated heat exchanger.

3. The cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle according to claim 2, characterized in that, The integrated heat exchanger has a first heat exchange tube and a second heat exchange tube that are independent of each other. The inlet of the first heat exchange tube is connected to the exhaust port of the low-temperature compressor, and the outlet of the first heat exchange tube is connected to the inlet of the cooling side of the second precooler. The inlet of the second heat exchange tube is connected to the exhaust port of the high-temperature compressor, and the outlet of the second heat exchange tube is connected to the inlet of the third throttling device and the cooling side of the subcooler, respectively.

4. The cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle according to claim 1, characterized in that, The second precooler is one of a plate heat exchanger, a shell and tube heat exchanger, a plate and shell heat exchanger, and a coaxial heat exchanger.

5. The cascade refrigeration system with two-stage precooling in a low-temperature refrigeration cycle according to claim 1, characterized in that, The high-temperature compressor is one of the following: a scroll compressor with an intermediate air inlet, a screw compressor with an intermediate air inlet, a single-unit two-stage compressor, and a single-unit multi-cylinder compressor.

6. A control method for a cascade refrigeration system with two-stage precooling in a cryogenic refrigeration cycle, based on the cascade refrigeration system with two-stage precooling in a cryogenic refrigeration cycle as described in any one of claims 1 to 5, characterized in that, include: Obtain the outdoor ambient temperature; When the outdoor ambient temperature is greater than or equal to the preset ambient temperature, the first control valve is opened and the second control valve is closed. When the outdoor ambient temperature is lower than the preset ambient temperature, the second control valve is opened and the first control valve is closed.

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