A refrigeration system with ammonia and CO2 cascade

Abstract

The application discloses a kind of ammonia and CO2 cascade refrigeration system, including high temperature ammonia loop, low temperature carbon dioxide loop, cascade condenser and control system.End evaporator heat absorption is controlled by control system, and low temperature low pressure carbon dioxide vapor is obtained;Based on the low temperature low pressure carbon dioxide vapor, carbon dioxide compressor is compressed to obtain medium temperature high pressure carbon dioxide superheated steam;Based on the medium temperature high pressure carbon dioxide superheated steam, cascade condenser performs heat exchange to obtain high pressure liquid carbon dioxide, and high temperature ammonia loop absorbs condensing heat to obtain low pressure ammonia vapor;Based on the low pressure ammonia vapor, ammonia compressor is compressed to exhaust heat, and energy transfer is completed.Control system acquires temperature and pressure signal, and deviation data is obtained by comparing target value;Based on the deviation data, control system generates instruction to adjust throttle valve and compressor, maintains system heat exchange balance, the present application shares compression pressure difference to reduce energy consumption, and ammonia leakage path is blocked by physical and logical double modules.

Description

Technical Field

[0001] This invention relates to the field of refrigeration technology, specifically to a refrigeration system consisting of ammonia and CO2 cascades. Background Technology

[0002] Refrigeration systems are fundamental equipment used in industrial production, cold chain processing, and cryogenic storage to maintain ultra-low temperature environments. In applications such as quick-freezing tunnels, cryogenic cold storage, and cryogenic test chambers, the system typically needs to provide a low-temperature cold source in the range of -25°C to -45°C to the end user to meet the physical process requirements of quick-freezing products or maintaining the temperature environment.

[0003] In existing conventional refrigeration applications, the industry generally uses single-stage refrigeration systems to achieve heat transfer. A single-stage refrigeration system relies on a compressor within the same independent refrigeration loop to directly compress the low-pressure refrigerant, after absorbing heat, to the condensing pressure. The refrigerant then releases heat to the environment in the condenser and finally returns to the evaporator after throttling and pressure reduction to complete the cycle. In practical engineering, to achieve the aforementioned ultra-low temperature refrigeration, ammonia or carbon dioxide working fluids are typically used to construct a single-stage direct cooling system.

[0004] However, existing single-stage refrigeration systems suffer from technical drawbacks when dealing with ultra-low temperature conditions, such as excessively high exhaust temperatures or high system energy consumption. When a single-stage ammonia refrigeration cycle is used to produce a low-temperature cold source, the large pressure difference between the evaporation and condensation pressures leads to an increase in the compressor's compression ratio. This high compression ratio further results in excessively high exhaust temperatures and difficulties in oil return. When a single-stage carbon dioxide direct cooling cycle is used, carbon dioxide operates in a transcritical state to dissipate the absorbed heat to the outdoor environment. In this transcritical state, the working fluid undergoes no condensation phase change, resulting in a large temperature difference for heat exchange and consequently, high overall system energy consumption. Existing technologies cannot simultaneously address both the excessively high compression ratio and high energy consumption issues within a single independent refrigeration loop. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a refrigeration system based on ammonia and CO2 cascade, which solves the physical limitations of existing single-stage ammonia refrigeration systems under ultra-low temperature conditions, such as high compression ratio, high exhaust temperature, and difficulty in oil return; and the problem that single-stage carbon dioxide direct cooling systems require transcritical cycles for environmental heat dissipation, resulting in high system energy consumption.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a refrigeration system for ammonia and carbon dioxide cascade, comprising a high-temperature ammonia loop, a low-temperature carbon dioxide loop, a cascade condenser, and a control system; the high-temperature ammonia loop includes an ammonia compressor, a water-cooled condenser or an air-cooled condenser, an ammonia throttling valve, and an ammonia-side channel of the cascade condenser connected in sequence via pipelines; the low-temperature carbon dioxide loop includes a carbon dioxide compressor, a carbon dioxide-side channel of the cascade condenser, a carbon dioxide throttling valve, and a terminal evaporator connected in sequence via pipelines; the ammonia-side channel of the cascade condenser is connected in series between the ammonia throttling valve and the ammonia compressor; the control system is electrically connected to the ammonia compressor, the ammonia throttling valve, the carbon dioxide compressor, and the carbon dioxide throttling valve, and is also electrically connected to pressure monitoring elements and temperature monitoring elements arranged on the high-temperature ammonia loop, the low-temperature carbon dioxide loop, and the cascade condenser; The control system is configured to execute the following cooling control logic: The terminal evaporator is controlled to operate, so that the low-temperature liquid carbon dioxide absorbs heat and evaporates completely in the terminal evaporator to obtain low-temperature, low-pressure carbon dioxide vapor. The carbon dioxide compressor is controlled to draw in and compress the low-temperature, low-pressure carbon dioxide vapor, and output medium-temperature, high-pressure superheated carbon dioxide vapor which is discharged into the cascade condenser. The cascade condenser is controlled to perform heat exchange, causing the medium-temperature, high-pressure superheated carbon dioxide vapor to release condensation heat in the carbon dioxide side channel and undergo cooling liquefaction to obtain high-pressure liquid carbon dioxide; and the low-temperature gas-liquid two-phase ammonia working fluid in the ammonia side channel absorbs the condensation heat and undergoes complete vaporization to obtain low-pressure ammonia vapor. The carbon dioxide throttling valve is controlled to perform a pressure reduction operation, so that the high-pressure liquid carbon dioxide flows back to the terminal evaporator after pressure reduction; The ammonia compressor is controlled to draw in and compress the low-pressure ammonia vapor, and output high-temperature and high-pressure superheated ammonia vapor. The high-temperature and high-pressure superheated ammonia vapor releases heat and condenses in the water-cooled condenser or air-cooled condenser to obtain high-pressure room-temperature ammonia liquid. The ammonia throttling valve is controlled to perform a pressure reduction operation, so that the high-pressure room-temperature ammonia liquid is depressurized to obtain the low-temperature gas-liquid two-phase ammonia working fluid, which then enters the ammonia side channel of the cascade condenser.

[0007] Preferably, the refrigeration system further includes a pressure monitoring element and a temperature monitoring element electrically connected to the control system; the operating temperature range of the high-temperature ammonia loop is limited to an evaporation temperature of -5°C to a condensation temperature of 35°C; the pressure monitoring element in the high-temperature ammonia loop is arranged in the suction and discharge pipes of the ammonia compressor, and the temperature monitoring element in the high-temperature ammonia loop is arranged on the liquid ammonia side of the cascade condenser and the drain side of the water-cooled or air-cooled condenser. Based on the received temperature signal, the control system monitors the evaporation temperature on the liquid ammonia side of the cascade condenser and the condensation temperature on the drain side of the water-cooled or air-cooled condenser; the control system compares the evaporation temperature with a preset target value of -5°C evaporation temperature, and compares the condensation temperature with a preset target value of 35°C condensation temperature; based on the temperature deviation value generated by the comparison, the control system generates an opening adjustment command and sends the opening adjustment command to the ammonia throttling valve, which adjusts the cross-sectional area of ​​the throttling channel according to the opening adjustment command, thereby changing the ammonia working fluid flow rate into the cascade condenser.

[0008] Preferably, the cryogenic carbon dioxide loop adopts a subcritical cascade cycle. Under normal refrigeration operation, the operating pressure of carbon dioxide is maintained below the critical pressure of 7.38 MPa. A pressure monitoring element collects pressure signals within the cryogenic carbon dioxide loop and sends them to the control system. Based on the received pressure signals, the control system monitors the actual operating pressure on the carbon dioxide condenser side and compares the actual operating pressure with a preset condensing pressure range of 3.9 MPa to 5.2 MPa. Based on the pressure deviation value generated by the comparison, the control system generates an opening adjustment command and sends it to the carbon dioxide throttling valve. The carbon dioxide throttling valve adjusts the cross-sectional area of ​​the throttling channel according to the opening adjustment command, controlling the pressure reduction of the high-pressure liquid carbon dioxide. The control system compares the actual operating pressure with the 7.38 MPa critical pressure safety threshold. When the actual operating pressure reaches or exceeds the 7.38 MPa critical pressure safety threshold, the control system sends a shutdown command to the carbon dioxide compressor, executing high-pressure safety protection control.

[0009] Preferably, the cascade condenser has physically isolated ammonia-side channels and carbon dioxide-side channels. A temperature monitoring element continuously collects the actual evaporation temperature in the ammonia-side channel and the actual condensation temperature in the carbon dioxide-side channel, and sends these temperatures to the control system. Based on the received actual condensation and evaporation temperatures, the control system performs a subtraction operation to obtain the actual heat transfer temperature difference. Based on this actual heat transfer temperature difference, the control system compares it with a preset target range of 5°C to 8°C. When the actual heat transfer temperature difference deviates from the preset target range, the control system generates a load matching adjustment command based on the temperature difference deviation data. Based on the generated load matching adjustment command, the control system sends the command to the ammonia compressor and the carbon dioxide compressor. The ammonia compressor and the carbon dioxide compressor adjust their respective load operating power according to the command to maintain the actual condensation temperature on the carbon dioxide side higher than the actual evaporation temperature on the ammonia side.

[0010] Preferably, the high-temperature ammonia loop and the low-temperature carbon dioxide loop are each provided with independent and closed fluid pipelines, and the cascade condenser serves as the physical isolation interface between the two fluid pipelines; the control system is configured with independent control logic modules for the high-temperature ammonia loop and the low-temperature carbon dioxide loop respectively; when the control system detects an abnormal condition in the high-temperature ammonia loop, the independent control logic module of the control system cuts off the operation of the high-temperature ammonia loop, disconnects the control command linkage propagation path between the two loops, and restricts the flow and circulation range of the ammonia working fluid to the high-temperature ammonia loop in the computer room environment.

[0011] This invention provides a refrigeration system based on ammonia and CO2 cascade. It offers the following advantages: 1. This invention employs a combined heat exchange architecture of a high-temperature ammonia loop and a low-temperature carbon dioxide loop via a cascade condenser. The carbon dioxide side absorbs heat from the goods in the workshop and releases condensation heat on one side of the cascade condenser, while the ammonia side absorbs condensation heat and discharges the heat to the outdoor condenser. By utilizing the two-stage loop to share the compression pressure difference, this invention overcomes the technical limitations of high exhaust temperature in single-stage ammonia refrigeration systems and high energy consumption in direct carbon dioxide cooling transcritical cycles. It achieves a cooling effect that reduces the workload of a single compressor while maintaining stable system operation and outputting a low-temperature cold source.

[0012] 2. This invention receives pressure and temperature signals collected by pressure and temperature monitoring elements through a control system, compares these signals with preset temperature target values ​​and pressure operating ranges, and sends adjustment commands to the throttle valve and compressor based on the deviation data generated by the comparison. This changes the cross-sectional area of ​​the throttle channel and the operating power of the compressor, maintains the heat transfer temperature difference of the cascade condenser, and controls the actual operating pressure on the carbon dioxide side to be lower than the critical pressure safety threshold. This achieves the effect of matching the load of the two-stage loop and ensuring the safety of the subcritical cascade cycle.

[0013] 3. This invention sets the high-temperature ammonia loop in the machine room environment and the low-temperature carbon dioxide loop in the low-temperature workshop environment, using a cascade condenser as the physical isolation interface for the two-way piping. Combined with the independent control logic module configured inside the control system, the operation is cut off in case of an abnormality, thus restricting the flow and circulation range of the ammonia working fluid to within the machine room. This disconnects the control command linkage propagation path between the two-stage loops from the physical path of the ammonia working fluid entering the workshop, achieving a dual safety isolation effect for the refrigeration system at both the physical layout of the piping and the logic level of system operation. Attached Figure Description

[0014] Figure 1 This is a system architecture diagram of the present invention. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] See attached document Figure 1 , Figure 1 This is a general architecture diagram of an ammonia and carbon dioxide cascade refrigeration system according to an embodiment of the present invention. The present invention provides an ammonia and carbon dioxide cascade refrigeration system, comprising: High-temperature ammonia loop, low-temperature carbon dioxide loop, cascade condenser, and control system.

[0017] Existing single-stage ammonia refrigeration systems suffer from physical limitations at -45°C, including high compression ratios, high exhaust temperatures, and difficulties in oil return. Single-stage direct carbon dioxide refrigeration systems require transcritical cycles for heat dissipation at 30°C, resulting in high energy consumption. This embodiment addresses these issues through a two-stage loop architecture that shares the compression pressure difference.

[0018] The high-temperature ammonia loop is located in the machine room environment. The low-temperature carbon dioxide loop is located in the low-temperature workshop environment. The cascade condenser is located between the high-temperature ammonia loop and the low-temperature carbon dioxide loop. The control system is electrically connected to the ammonia compressor, ammonia throttling valve, pressure monitoring element, and temperature monitoring element in the high-temperature ammonia loop, and to the carbon dioxide compressor, carbon dioxide throttling valve, pressure monitoring element, and temperature monitoring element in the low-temperature carbon dioxide loop, and is also electrically connected to the temperature monitoring element located on the cascade condenser. The overall workflow of the ammonia and carbon dioxide cascade refrigeration system includes the following steps: The terminal evaporator is controlled to operate, so that the low-temperature liquid carbon dioxide absorbs heat and evaporates completely in the terminal evaporator to obtain low-temperature, low-pressure carbon dioxide vapor. The carbon dioxide compressor is controlled to draw in and compress the low-temperature, low-pressure carbon dioxide vapor, and output medium-temperature, high-pressure superheated carbon dioxide vapor which is discharged into the cascade condenser. The cascade condenser is controlled to perform heat exchange, causing the medium-temperature, high-pressure superheated carbon dioxide vapor to release condensation heat in the carbon dioxide side channel and undergo cooling liquefaction to obtain high-pressure liquid carbon dioxide; and the low-temperature gas-liquid two-phase ammonia working fluid in the ammonia side channel absorbs the condensation heat and undergoes complete vaporization to obtain low-pressure ammonia vapor. The carbon dioxide throttling valve is controlled to perform a pressure reduction operation, so that the high-pressure liquid carbon dioxide flows back to the terminal evaporator after pressure reduction; The ammonia compressor is controlled to draw in and compress the low-pressure ammonia vapor, and output high-temperature, high-pressure superheated ammonia vapor. The high-temperature, high-pressure superheated ammonia vapor releases heat and condenses in the condenser to obtain high-pressure, room-temperature ammonia liquid. The condenser can be a water-cooled condenser or an air-cooled condenser. The ammonia throttling valve is controlled to perform a pressure reduction operation, so that the high-pressure room-temperature ammonia liquid is depressurized to obtain the low-temperature gas-liquid two-phase ammonia working fluid, which then enters the ammonia side channel of the cascade condenser.

[0019] The high-temperature ammonia loop is entirely housed within the computer room environment. The control system is electrically connected to the ammonia compressor, water-cooled or air-cooled condenser, ammonia throttling valve, pressure monitoring elements, and temperature monitoring elements.

[0020] In the high-temperature ammonia loop, during refrigerant circulation, the ammonia compressor draws in low-pressure ammonia vapor from the cascade condenser. The ammonia compressor then compresses this low-pressure ammonia vapor to obtain high-temperature, high-pressure superheated ammonia vapor.

[0021] Based on the high-temperature, high-pressure superheated ammonia vapor obtained above, the ammonia compressor discharges the high-temperature, high-pressure superheated ammonia vapor into a water-cooled condenser or an air-cooled condenser. The water-cooled condenser or air-cooled condenser uses cooling water or outdoor air to absorb the heat of the high-temperature, high-pressure superheated ammonia vapor, causing the high-temperature, high-pressure superheated ammonia vapor to condense and obtain high-pressure, room-temperature ammonia liquid.

[0022] Based on the high-pressure, room-temperature ammonia liquid obtained above, the high-pressure, room-temperature ammonia liquid enters the ammonia throttling valve. The control system controls the ammonia throttling valve to perform a pressure reduction operation. After the high-pressure, room-temperature ammonia liquid is throttled and depressurized by the ammonia throttling valve, a low-temperature gas-liquid two-phase ammonia working fluid is obtained.

[0023] Based on the aforementioned low-temperature gas-liquid two-phase ammonia working fluid, an ammonia throttling valve delivers the fluid to a cascade condenser. Inside the cascade condenser, the ammonia working fluid absorbs the condensation heat released from the carbon dioxide side, undergoing evaporation and vaporization to obtain low-pressure ammonia vapor. This low-pressure ammonia vapor is then returned to the ammonia compressor, completing the high-temperature ammonia loop.

[0024] The operating temperature range of the high-temperature ammonia loop is limited to evaporation temperature -5℃ to condensation temperature 35℃. To obtain system operating parameters, pressure monitoring elements are installed on the suction and discharge lines of the ammonia compressor. Temperature monitoring elements are installed on the liquid ammonia side of the cascade condenser and the drain side of the water-cooled or air-cooled condenser.

[0025] The pressure monitoring element and temperature monitoring element continuously collect pressure and temperature signals within the high-temperature ammonia loop and send these signals to the control system.

[0026] Based on the received temperature signals, the control system monitors the evaporation temperature on the liquid ammonia side of the cascade condenser and the condensation temperature on the drain side of the water-cooled or air-cooled condenser. The control system compares the evaporation temperature with a preset target value of -5°C and the condensation temperature with a preset target value of 35°C. Based on the temperature deviation, the control system generates an opening adjustment command and sends it to the ammonia throttling valve. The ammonia throttling valve adjusts the cross-sectional area of ​​the throttling channel according to the opening adjustment command, thereby changing the ammonia flow rate into the cascade condenser.

[0027] Based on the received pressure signal, the control system monitors the operating pressure limit of the ammonia compressor. Combining the pressure signal with the heat exchange requirements of the cascade condenser, the control system adjusts the load power of the ammonia compressor to maintain the high-temperature ammonia loop's heat discharge to the outside.

[0028] The cryogenic carbon dioxide loop is integrated within the cryogenic workshop environment. The control system is electrically connected to the carbon dioxide compressor, carbon dioxide throttling valve, pressure monitoring element, and temperature monitoring element. The terminal evaporator is a quick-freezing rack, radiator, or plate freezer.

[0029] In the cryogenic carbon dioxide loop, during refrigerant circulation, cryogenic liquid carbon dioxide enters the terminal evaporator. Within the terminal evaporator, the cryogenic liquid carbon dioxide absorbs heat from the workshop and evaporates, producing cryogenic, low-pressure carbon dioxide vapor. The evaporation temperature range of the terminal evaporator is limited to -25°C to -45°C.

[0030] Based on the low-temperature, low-pressure carbon dioxide vapor obtained above, a carbon dioxide compressor draws in this low-temperature, low-pressure carbon dioxide vapor. The carbon dioxide compressor performs a compression operation on the low-temperature, low-pressure carbon dioxide vapor to obtain medium-temperature, high-pressure superheated carbon dioxide vapor.

[0031] Based on the medium-temperature, high-pressure superheated carbon dioxide steam obtained above, the carbon dioxide compressor discharges the medium-temperature, high-pressure superheated carbon dioxide steam into a cascade condenser. Inside the cascade condenser, the medium-temperature, high-pressure superheated carbon dioxide steam releases condensation heat, cools and liquefies, and then yields high-pressure liquid carbon dioxide.

[0032] Based on the high-pressure liquid carbon dioxide obtained above, the high-pressure liquid carbon dioxide flows into a carbon dioxide reservoir for storage. After flowing out of the carbon dioxide reservoir, the high-pressure liquid carbon dioxide enters a carbon dioxide throttling valve. The control system controls the carbon dioxide throttling valve to perform a pressure reduction operation. The high-pressure liquid carbon dioxide is depressurized and cooled by the carbon dioxide throttling valve to obtain a low-temperature, low-pressure carbon dioxide gas-liquid mixture.

[0033] Based on the low-temperature, low-pressure carbon dioxide gas-liquid mixture obtained above, the low-temperature, low-pressure carbon dioxide gas-liquid mixture enters the terminal evaporator to complete the circulation of the low-temperature carbon dioxide loop.

[0034] The cryogenic carbon dioxide loop employs a subcritical cascade cycle. Under normal refrigeration operation, the operating pressure of the carbon dioxide is maintained below the critical pressure of 7.38 MPa.

[0035] To obtain system operating parameters, pressure monitoring elements are installed on the carbon dioxide condenser side piping and the carbon dioxide compressor exhaust side. Temperature monitoring elements are installed on the carbon dioxide side of the terminal evaporator and cascade condenser. The pressure and temperature monitoring elements continuously collect pressure and temperature signals within the cryogenic carbon dioxide loop and transmit these signals to the control system.

[0036] Based on the received pressure signals, the control system monitors the actual operating pressure on the carbon dioxide condensation side. The control system compares the actual operating pressure with the preset condensation pressure range of 3.9 MPa to 5.2 MPa, and also compares the actual operating pressure with the critical pressure safety threshold of 7.38 MPa.

[0037] Based on the pressure deviation value generated by the above comparison, the control system generates an opening adjustment command according to the actual operating pressure and the pressure deviation value in the range of 3.9MPa to 5.2MPa, and sends the opening adjustment command to the carbon dioxide throttle valve. The carbon dioxide throttle valve adjusts the cross-sectional area of ​​the throttling channel according to the opening adjustment command, controlling the pressure drop of high-pressure liquid carbon dioxide. When the actual operating pressure reaches or exceeds the critical pressure safety threshold of 7.38MPa, the control system sends a shutdown command to the carbon dioxide compressor to execute high-pressure safety protection control.

[0038] Based on the received temperature signal, the control system monitors the actual evaporation temperature of the terminal evaporator. Combining this actual evaporation temperature with the set target temperature for the cold storage, the control system adjusts the load power of the carbon dioxide compressor to maintain the refrigeration operation of the low-temperature carbon dioxide loop.

[0039] The cascade condenser is specifically a plate heat exchanger or a shell-and-tube heat exchanger. Internally, the cascade condenser has physically isolated ammonia-side and carbon dioxide-side channels. Temperature monitoring elements are respectively arranged in the ammonia-side and carbon dioxide-side channels of the cascade condenser. The control system is electrically connected to the temperature monitoring elements, the ammonia compressor in the high-temperature ammonia loop, and the carbon dioxide compressor in the low-temperature carbon dioxide loop.

[0040] When the cascade condenser performs two-stage loop coupled heat exchange, medium-temperature, high-pressure superheated carbon dioxide vapor enters the carbon dioxide side channel, while low-temperature, gas-liquid two-phase ammonia working fluid enters the ammonia side channel. The media on both sides flow in a counter-current state inside the cascade condenser.

[0041] Medium-temperature, high-pressure superheated carbon dioxide vapor condenses in the carbon dioxide-side channel, releasing condensation heat to obtain high-pressure liquid carbon dioxide. This condensation heat is transferred to the ammonia-side channel through the metal heat exchange walls inside the cascade condenser.

[0042] Based on the heat conducted to the ammonia-side channel, the low-temperature gas-liquid two-phase ammonia working fluid within the ammonia-side channel absorbs this heat. The low-temperature gas-liquid two-phase ammonia working fluid then undergoes complete evaporation, yielding low-pressure ammonia vapor. This heat transfer process achieves the transfer of heat from the low-temperature carbon dioxide loop to the high-temperature ammonia loop.

[0043] To maintain stable heat transfer conditions, the temperature monitoring element continuously collects the actual evaporation temperature in the ammonia-side channel and the actual condensation temperature in the carbon dioxide-side channel. The temperature monitoring element then transmits these actual evaporation and condensation temperatures to the control system.

[0044] Based on the received actual condensation temperature and actual evaporation temperature, the control system performs a subtraction operation between the actual condensation temperature and the actual evaporation temperature to obtain the actual heat transfer temperature difference.

[0045] Based on the actual heat transfer temperature difference obtained above, the control system compares the actual heat transfer temperature difference with the preset target range of 5°C to 8°C.

[0046] When the actual heat transfer temperature difference deviates from the preset target range of 5°C to 8°C, the control system generates a load matching adjustment command based on the temperature difference deviation data generated by the comparison.

[0047] Based on the generated load matching adjustment command, the control system sends the command to the ammonia compressor and the carbon dioxide compressor. The ammonia compressor and the carbon dioxide compressor adjust their respective operating power according to the command. This adjustment maintains the actual condensation temperature on the carbon dioxide side higher than the actual evaporation temperature on the ammonia side, ensuring the heat transfer temperature difference remains stable within the range of 5°C to 8°C.

[0048] As a specific application scenario of this invention, when the system is performing a -45℃ quick-freezing operation, the control system sends a refrigeration operation command to the low-temperature carbon dioxide loop: The terminal evaporator in the low-temperature carbon dioxide loop absorbs heat from the workshop, and the control system adjusts the evaporation temperature in the terminal evaporator to -48℃.

[0049] The carbon dioxide compressor draws in low-temperature, low-pressure carbon dioxide vapor from the terminal evaporator and compresses it into medium-temperature, high-pressure superheated carbon dioxide vapor. The control system then discharges this medium-temperature, high-pressure superheated carbon dioxide vapor into the carbon dioxide side channel of the cascade condenser.

[0050] Medium-temperature, high-pressure superheated carbon dioxide steam releases condensation heat in the carbon dioxide side channel, and the condensation temperature in the carbon dioxide side channel reaches 0℃.

[0051] Simultaneously, the control system adjusts the operating load of the ammonia compressor within the high-temperature ammonia loop. The low-temperature gas-liquid two-phase ammonia working fluid within the high-temperature ammonia loop absorbs the aforementioned condensation heat in the ammonia-side channel of the cascade condenser, and the evaporation temperature within the ammonia-side channel reaches -5°C.

[0052] The 0°C condensation temperature on the carbon dioxide side of the cascade condenser and the -5°C evaporation temperature on the ammonia side create an actual heat transfer temperature difference of 5°C. This 5°C actual heat transfer temperature difference satisfies the heat transfer requirements.

[0053] After absorbing heat, the ammonia working fluid is compressed into high-temperature, high-pressure superheated ammonia vapor by an ammonia compressor. A water-cooled or air-cooled condenser absorbs the heat from this high-temperature, high-pressure superheated ammonia vapor, reaching a condensation temperature of 30°C, thus completing the heat dissipation operation to the outdoor environment.

[0054] To ensure system safety, the high-temperature ammonia loop and the low-temperature carbon dioxide loop are each equipped with independent, enclosed fluid pipelines. The high-temperature ammonia loop is located within the computer room environment, while the low-temperature carbon dioxide loop is located within the low-temperature workshop environment. The cascade condenser serves as the physical isolation interface between the two fluid pipelines.

[0055] In conjunction with the aforementioned independent and closed fluid pipelines, the control system is equipped with separate control logic modules for the high-temperature ammonia loop and the low-temperature carbon dioxide loop. When the control system detects an abnormality in the high-temperature ammonia loop, the independent control logic module of the control system only cuts off the operation of the high-temperature ammonia loop, disconnecting the control command linkage propagation path between the two loops, thus achieving logical-level safety isolation.

[0056] The aforementioned physical isolation interface and independent control logic module strictly limit the flow and circulation of ammonia working fluid within the high-temperature ammonia loop of the computer room environment. When a pipeline ruptures in the low-temperature carbon dioxide loop within the low-temperature workshop environment, only carbon dioxide leaks into the low-temperature workshop environment. This arrangement and control mechanism effectively block the physical path for ammonia working fluid to enter the low-temperature workshop environment.

[0057] The selection of the underlying hardware control chip, the metal wall welding process of the heat exchanger, and the cable arrangement of the sensor can be conventionally matched according to the application requirements by those skilled in the art. The selection of the underlying hardware control chip, the metal wall welding process of the heat exchanger, and the cable arrangement of the sensor are well known technologies in this field and will not be described in detail here.

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A refrigeration system for ammonia and CO2 cascade, comprising a high-temperature ammonia loop, a low-temperature carbon dioxide loop, a cascade condenser, and a control system; wherein the high-temperature ammonia loop comprises an ammonia compressor, a water-cooled condenser or an air-cooled condenser, an ammonia throttling valve, and an ammonia-side channel of the cascade condenser connected in sequence by pipelines; The ammonia-side channel outlet of the cascade condenser is connected to the suction port of the ammonia compressor; the low-temperature carbon dioxide loop includes a carbon dioxide compressor, a carbon dioxide-side channel of the cascade condenser, a carbon dioxide throttling valve, and a terminal evaporator connected in sequence by pipelines; the ammonia-side channel of the cascade condenser is connected in series between the ammonia throttling valve and the ammonia compressor, characterized in that... The control system is electrically connected to the ammonia compressor, ammonia throttle valve, carbon dioxide compressor, and carbon dioxide throttle valve, respectively, and is also electrically connected to the pressure monitoring element and temperature monitoring element arranged on the high-temperature ammonia loop, the low-temperature carbon dioxide loop, and the cascade condenser. The control system is configured to execute the following cooling control logic: The terminal evaporator is controlled to operate, so that the low-temperature liquid carbon dioxide absorbs heat and evaporates completely in the terminal evaporator to obtain low-temperature, low-pressure carbon dioxide vapor. Based on the low-temperature, low-pressure carbon dioxide vapor, the carbon dioxide compressor is controlled to compress it to obtain medium-temperature, high-pressure superheated carbon dioxide vapor, which is then discharged into the cascade condenser. Based on the medium-temperature and high-pressure carbon dioxide superheated steam, the cascade condenser is controlled to perform heat exchange, so that the medium-temperature and high-pressure carbon dioxide superheated steam releases condensation heat in the carbon dioxide side channel and undergoes cooling and liquefaction to obtain high-pressure liquid carbon dioxide; and the low-temperature gas-liquid two-phase ammonia working fluid in the ammonia side channel absorbs the condensation heat and undergoes complete vaporization to obtain low-pressure ammonia steam. Based on the high-pressure liquid carbon dioxide, the carbon dioxide throttling valve is controlled to perform a pressure reduction operation, so that the high-pressure liquid carbon dioxide flows back to the terminal evaporator after pressure reduction; Based on the low-pressure ammonia vapor, the ammonia compressor is controlled to compress it to obtain high-temperature and high-pressure superheated ammonia vapor. The high-temperature and high-pressure superheated ammonia vapor releases heat and condenses in the water-cooled condenser or air-cooled condenser to obtain high-pressure room-temperature ammonia liquid. Based on the high-pressure, room-temperature ammonia liquid, the ammonia throttling valve is controlled to perform a pressure reduction operation, thereby obtaining the low-temperature gas-liquid two-phase ammonia working fluid and entering the ammonia-side channel of the cascade condenser.

2. The refrigeration system of ammonia and CO2 cascade according to claim 1, characterized in that, The refrigeration system also includes pressure monitoring elements and temperature monitoring elements electrically connected to the control system; the operating temperature range of the high-temperature ammonia loop is limited to evaporation temperature -5°C to condensation temperature 35°C. The pressure monitoring element in the high-temperature ammonia loop is arranged in the suction pipe and the discharge pipe of the ammonia compressor, and the temperature monitoring element in the high-temperature ammonia loop is arranged on the liquid ammonia side of the cascade condenser and the liquid discharge side of the water-cooled condenser or the air-cooled condenser. The pressure monitoring element and temperature monitoring element continuously collect pressure and temperature signals within the high-temperature ammonia loop and send the pressure and temperature signals to the control system.

3. The refrigeration system of ammonia and CO2 cascade according to claim 2, characterized in that, Based on the received temperature signal, the control system monitors the evaporation temperature of the liquid ammonia side of the cascade condenser and the condensation temperature of the drain side of the water-cooled condenser or air-cooled condenser. The control system compares the evaporation temperature with the preset target value of -5℃ evaporation temperature, and compares the condensation temperature with the preset target value of 35℃ condensation temperature; Based on the temperature deviation value generated by the comparison, the control system generates an opening adjustment command and sends the opening adjustment command to the ammonia throttling valve. The ammonia throttling valve adjusts the cross-sectional area of ​​the throttling channel according to the opening adjustment command, thereby changing the flow rate of ammonia entering the cascade condenser.

4. The refrigeration system of ammonia and CO2 cascade according to claim 1, characterized in that, The refrigeration system also includes a pressure monitoring element electrically connected to the control system; the low-temperature carbon dioxide loop adopts a subcritical cascade cycle, and under normal refrigeration operation, the operating pressure of carbon dioxide is maintained below the critical pressure of 7.38 MPa. The pressure monitoring element in the cryogenic carbon dioxide loop is arranged on the carbon dioxide condensation side pipeline and the carbon dioxide compressor exhaust side; the pressure monitoring element collects the pressure signal in the cryogenic carbon dioxide loop and sends it to the control system. Based on the received pressure signal, the control system monitors the actual operating pressure on the carbon dioxide condensation side and compares the actual operating pressure with the preset operating range of 3.9 MPa to 5.2 MPa condensation pressure. Based on the pressure deviation value generated by the comparison, the control system generates an opening adjustment command and sends the opening adjustment command to the carbon dioxide throttle valve. The carbon dioxide throttle valve adjusts the cross-sectional area of ​​the throttle channel according to the opening adjustment command to control the pressure reduction of the high-pressure liquid carbon dioxide.

5. The refrigeration system of ammonia and CO2 cascade according to claim 4, characterized in that, The control system compares the actual operating pressure with the critical pressure safety threshold of 7.38 MPa. When the actual operating pressure reaches or exceeds the critical pressure safety threshold of 7.38 MPa, the control system sends a shutdown command to the carbon dioxide compressor and executes high-pressure safety protection control.

6. The refrigeration system of ammonia and CO2 cascade according to claim 1, characterized in that, The cascade condenser has an ammonia-side channel and a carbon dioxide-side channel that are physically isolated from each other; the refrigeration system also includes temperature monitoring elements arranged in the ammonia-side channel and the carbon dioxide-side channel respectively. The temperature monitoring element continuously collects the actual evaporation temperature in the ammonia-side channel and the actual condensation temperature in the carbon dioxide-side channel, and sends the actual evaporation temperature and the actual condensation temperature to the control system. Based on the received actual condensation temperature and actual evaporation temperature, the control system performs a subtraction operation between the actual condensation temperature and the actual evaporation temperature to obtain the actual heat transfer temperature difference; Based on the obtained actual heat transfer temperature difference, the control system compares the actual heat transfer temperature difference with the preset target range of 5°C to 8°C heat transfer temperature difference. When the actual heat transfer temperature difference deviates from the preset target range of 5°C to 8°C, the control system generates a load matching adjustment command based on the temperature difference deviation data generated by the comparison. Based on the generated load matching adjustment command, the control system sends the load matching adjustment command to the ammonia compressor and the carbon dioxide compressor. The ammonia compressor and the carbon dioxide compressor adjust the corresponding load operating power according to the load matching adjustment command to maintain the actual condensation temperature on the carbon dioxide side higher than the actual evaporation temperature on the ammonia side.

7. The refrigeration system of ammonia and CO2 cascade according to claim 6, characterized in that, The cascade condenser is a plate heat exchanger or a shell-and-tube heat exchanger, and the ammonia-side channel and the carbon dioxide-side channel are arranged in a countercurrent heat exchange configuration inside the cascade condenser.

8. The refrigeration system of ammonia and CO2 cascade according to claim 1, characterized in that, The low-temperature carbon dioxide loop also includes a carbon dioxide reservoir, and the terminal evaporator is a quick-freezing rack, a radiator, or a plate quick-freezing machine. The evaporation temperature range of the terminal evaporator is limited to -25°C to -45°C. Based on the high-pressure liquid carbon dioxide obtained by the cascade condenser, the high-pressure liquid carbon dioxide flows into a carbon dioxide storage tank for storage, and after flowing out of the carbon dioxide storage tank, it enters a carbon dioxide throttling valve; the high-pressure liquid carbon dioxide is depressurized and cooled by the carbon dioxide throttling valve to obtain a low-temperature, low-pressure carbon dioxide gas-liquid mixture. Based on the obtained low-temperature, low-pressure carbon dioxide gas-liquid mixture, the low-temperature, low-pressure carbon dioxide gas-liquid mixture enters the terminal evaporator.

9. The refrigeration system of ammonia and CO2 cascade according to claim 1, characterized in that, The high-temperature ammonia loop and the low-temperature carbon dioxide loop are each provided with independent and closed fluid pipelines, and the cascade condenser serves as a physical isolation interface for the fluid pipelines on both sides. The high-temperature ammonia loop is located in the computer room environment; the low-temperature carbon dioxide loop is located in the low-temperature workshop environment.

10. A refrigeration system for ammonia and CO2 cascade as described in claim 9, characterized in that, The control system is equipped with independent control logic modules for the high-temperature ammonia loop and the low-temperature carbon dioxide loop, respectively. When the control system detects an abnormality in the high-temperature ammonia loop, the independent control logic module of the control system cuts off the operation of the high-temperature ammonia loop, disconnects the control command linkage propagation path between the two-stage loops, and restricts the flow and circulation range of the ammonia working fluid to the high-temperature ammonia loop in the computer room environment.

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