A transcritical carbon dioxide deep-earth long-distance refrigeration cycle system and its control method

Abstract

This invention discloses a transcritical carbon dioxide deep underground long-distance refrigeration cycle system and its control method. This invention effectively utilizes the natural pressure potential energy at underground depths; the multi-functional coupling unit has dynamic flow and pressure adjustment capabilities, allowing the system to adjust the flow and pressure of the working fluid in real time, ensuring stable operation under different working conditions; by connecting the vertical shaft pipeline with the multi-functional coupling unit to form a circulation loop, it completes the refrigeration and heat recovery of carbon dioxide, overcoming the challenges of ultra-deep transportation; equipped with multiple gas-liquid separation devices and pressure regulating devices, it ensures stable operation of the working fluid during long-distance underground transportation, improving the system's reliability and service life; it can solve the problem of fluid and thermodynamic performance losses caused by ultra-deep transportation depths exceeding 600 meters and ultra-long transportation distances exceeding 4000 meters, which are difficult to overcome in ultra-deep underground transportation hubs, underground building spaces, or underground energy extraction.

Description

Technical Field

[0001] This invention relates to deep-earth long-distance refrigeration technology, specifically to a transcritical carbon dioxide deep-earth long-distance refrigeration cycle system and its control method. Background Technology

[0002] As development deepens, the high-temperature heat hazards in deep underground spaces become increasingly severe. For example, controlling humidity in underground environments is a global challenge, and the future maximum mining depth will, to some extent, depend on the level of heat hazard management in mines. In subway stations, ventilation and air conditioning systems account for approximately 70% of the total energy consumption of all electromechanical equipment. Theories and technologies related to high-temperature heat hazard management with low energy consumption, low pollution, and high thermodynamic performance have become one of the key technologies for deep underground space development.

[0003] Currently, there are two main types of underground space cooling technologies used worldwide: non-refrigeration cooling and refrigeration cooling. Non-refrigeration cooling is ineffective for high-temperature underground spaces and is no longer used alone. Underground space cooling and air conditioning systems typically use Freon-based refrigerants as their working fluid. Because the use of these refrigerants contributes to ozone layer depletion and the greenhouse effect, it has caused long-term and far-reaching negative environmental impacts. Therefore, phasing out these substances and replacing them with more environmentally friendly alternatives is a key action promoted by international environmental organizations globally.

[0004] Carbon dioxide has a global warming potential (GWP) of 1 and an ozone depletion potential (ODP) of 0. As a naturally occurring substance, its negative impact on climate change as a refrigerant is minimal. Furthermore, transcritical carbon dioxide systems exhibit high energy efficiency due to their superior thermodynamic properties, enabling refrigeration with relatively low energy input. Compared to traditional refrigerants, carbon dioxide systems operate at relatively lower pressures, reducing equipment wear and extending system lifespan. They also demonstrate high heat exchange efficiency in the transcritical range, particularly in the condenser and evaporator processes. Moreover, they maintain good refrigeration performance at high temperatures, making them an important future application direction for refrigeration technology.

[0005] In existing deep underground space cooling technologies, the extreme depth leads to severely excessive fluid pressure, making it impossible for underground unit equipment and pipelines to withstand the pressure. The extremely long transportation distance results in significant heat loss along the way, preventing the delivery of cooling capacity to the end of the underground space. Due to the extreme depth and long transportation distance, the transfer and action of the refrigerant are affected by pressure and heat loss, thus reducing the performance of the cooling system, increasing energy consumption, and increasing technical difficulty. Traditional deep-earth cooling systems often fail to fully utilize the heat transported from deep underground to the surface, leading to substantial heat dissipation and environmental pollution. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a transcritical carbon dioxide deep-earth long-distance refrigeration cycle system and its control method. This invention can supply heat to heat users and water treatment systems while simultaneously providing refrigeration, effectively recovering thermal energy. It has good economic potential, environmental potential, and thermodynamic performance, and can solve the defects of existing technologies, such as fluid dynamics and thermodynamic performance losses, energy waste, and environmental pollution caused by ultra-deep transport depths of over 600 meters and ultra-long transport distances of over 4000 meters.

[0007] One object of the present invention is to propose a transcritical carbon dioxide deep-earth long-distance refrigeration cycle system.

[0008] The transcritical carbon dioxide deep-earth long-distance refrigeration cycle system of the present invention includes: a surface unit located on the ground and an underground unit located underground; the surface unit includes a compressor, a subcooling tower, first and second gas-liquid separators, a regenerator and a throttling device; the underground unit includes a multi-functional coupler unit; the surface unit and the underground unit are connected by a vertical shaft pipeline;

[0009] The gaseous outlet of the second gas-liquid separator is connected to the low-pressure side of the compressor, and the high-pressure side of the compressor is connected to the inlet of the subcooling tower. The outlet of the subcooling tower is divided into two paths: one path connects to the downward inlet of the regenerator, and the other path connects to the downward outlet of the regenerator and is located before the throttling device. The upward outlet and upward inlet of the regenerator are connected internally through an upward pipe, and the downward inlet and downward outlet of the regenerator are connected internally through a downward pipe. The upward outlet is connected to the gas-liquid two-phase inlet of the second gas-liquid separator. The downward outlet of the regenerator is connected to the gas-liquid two-phase inlet of the first gas-liquid separator via a throttling device. The gaseous outlet of the first gas-liquid separator is connected to the gas-liquid two-phase inlet of the second gas-liquid separator. The liquid outlet of the second gas-liquid separator is connected to the gas-liquid two-phase inlet of the first gas-liquid separator. The liquid outlet of the first gas-liquid separator is connected to the downward inlet of the underground multi-functional coupler unit via a vertical shaft pipeline. The downward outlet of the multi-functional coupler unit is connected to the inlet of the underground terminal air cooler. The outlet of the terminal air cooler is connected to the upward inlet of the multi-functional coupler unit. The upward outlet of the multi-functional coupler unit is connected to the upward inlet of the regenerator.

[0010] In the refrigeration cycle system, high-temperature supercritical carbon dioxide on the high-pressure side of the compressor is cooled in stages using multiple devices to distribute the heat load; temperature gradient matching is achieved through multi-stage heat exchange, reducing the cooling process. Losses; tiered utilization of heat at different temperature ranges to improve heat recovery efficiency.

[0011] Furthermore, the present invention also includes an oil separator, which is installed between the high-pressure side of the compressor and the subcooling tower. After passing through the compressor, the supercritical carbon dioxide, which becomes high temperature and high pressure, passes through the oil separator to separate the lubricating oil in the compressor from the carbon dioxide, so as to avoid affecting the subsequent fluid flow and heat exchange process.

[0012] It also includes heat-using unit heat exchangers, located after the compressor and before the subcooling tower. After passing through the compressor, the supercritical carbon dioxide, which is converted into high-temperature, high-pressure carbon dioxide, transfers heat to the heat-using unit heat exchanger for further utilization. Heat-using unit heat exchangers are used by heat users such as manufacturing workshops, steam production, industrial applications, domestic heating, or water treatment units.

[0013] The oil separator outlet is divided into two paths: one path connects to the heat exchanger of the heat-using unit, and the other path connects to the inlet of the subcooling tower. The fluid ratio of the two paths is flexibly allocated according to the heat demand of the heat-using unit. If the heat demand of the heat-using unit is high, more flow is allocated to the heat-using unit; if the heat demand is low, the flow allocation is reduced.

[0014] This invention also includes a circulating pump, which is optionally installed on pipelines with insufficient fluid pressure to increase power when flow is obstructed; it also includes a filter device to remove impurities that appear in the working fluid after the refrigeration system has been in use for a period of time, generally installed in underground pipelines; it also includes a transformer, which is the power supply equipment for the underground circulating pump, solenoid valves, and control panels, generally installed in an underground equipment room; and it includes a surface carbon dioxide storage tank, which is installed on the ground surface. The outlet of the surface carbon dioxide storage tank is connected after the throttling device and located before the gas-liquid two-phase inlet of the first gas-liquid separator, to provide a buffer when the refrigeration load changes and to replenish the loss of the working fluid. A carbon dioxide-water heat exchange device is added after the multi-functional coupler unit in the underground chamber; and an additional cooling equipment chamber is set up in the underground space to house the underground secondary chilled water pump and filter equipment, while an electrical chamber is set up to house electrical equipment such as transformers and secondary water pump frequency converters.

[0015] The multi-functional coupler unit includes a pressure reducing module, a gas-liquid separation module, and an upward circulation pump. The surface unit is connected to the pressure reducing module via a vertical shaft pipeline, which depressurizes the liquid carbon dioxide from the ground and then transmits it to the terminal air cooler. After heat exchange with the terminal air cooler to complete the cooling process, the gaseous carbon dioxide is transmitted to the gas-liquid separation module to separate the incompletely vaporized liquid carbon dioxide. The separated liquid carbon dioxide flows back to the outlet of the pressure reducing module of the multi-functional coupler unit, and then the gaseous carbon dioxide in the gas-liquid separator is transmitted to the surface unit through the vertical shaft pipeline. An upward circulation pump is installed on the upward vertical shaft pipeline after the gas outlet of the gas-liquid separation module. The upward circulation pump provides the upward power for the liquid carbon dioxide to return to the surface and complete the circulation. By reducing the excessive pressure generated during the deep underground transport of the working medium, the system utilizes the pressure potential energy from the underground depths to convert it into kinetic energy, facilitating the smooth transport of the working medium to its target location within the underground transport channel. It features dynamic flow and pressure regulation, allowing the system to adjust the flow and pressure of the working medium in real time to ensure stable operation under various working conditions. In addition to regulating the flow and pressure of carbon dioxide, it also possesses gas-liquid separation capabilities, preventing bubbles generated during long-distance underground transport from mixing with the carbon dioxide, thus ensuring the stable operation of the entire system. The liquid working medium flows through the multi-functional coupler unit, which not only transports the liquid working medium underground but also overcomes the challenges of transporting working media in deep-earth environments.

[0016] The throttling device can be a fixed throttling device, an adjustable flow device, an electronic throttling device, an intelligent throttling device, a multi-hole plug throttling device, or a labyrinth throttling device.

[0017] Another objective of this invention is to propose a control method for a transcritical carbon dioxide deep-earth long-distance refrigeration cycle system.

[0018] The control method for the transcritical carbon dioxide deep-earth long-distance refrigeration cycle system of the present invention includes the following steps:

[0019] 1) Low-temperature, low-pressure carbon dioxide gas from the second gas-liquid separator enters the compressor and is compressed into high-temperature, high-pressure supercritical carbon dioxide. It is pressurized and heated in the compressor, resulting in higher temperature and pressure on the high-pressure side of the compressor.

[0020] 2) Carbon dioxide is transferred to the subcooling tower, where its temperature is reduced through heat exchange. The carbon dioxide temperature decreases, but it still remains in a supercritical state.

[0021] 3) After being cooled by the subcooling tower, the low-temperature, high-pressure supercritical carbon dioxide selects its path based on temperature: If the temperature is too high to meet the low-temperature requirement of the throttling device, it is transferred to the downflow inlet of the regenerator and then to the downflow pipe. In the downflow pipe of the regenerator, the low-temperature, high-pressure supercritical carbon dioxide exchanges heat with the carbon dioxide from the underground located in the upflow pipe, further reducing the temperature to meet the temperature requirement of the throttling device, and then flows from the downflow outlet to the throttling device; if the temperature is low enough to meet the low-temperature requirement of the throttling device, it is directly transferred to the downflow outlet of the regenerator and before the throttling device.

[0022] 4) The supercritical carbon dioxide suddenly expands through the throttling device, its temperature drops and it partially vaporizes, entering a low-temperature, low-pressure gas-liquid two-phase state.

[0023] 5) After passing through the throttling device, the gas-liquid two-phase carbon dioxide enters the first gas-liquid separator. The liquid carbon dioxide settles and is transported to the ground, while the gaseous carbon dioxide rises and is transported to the second gas-liquid separator, where the liquid and gaseous carbon dioxide are separated.

[0024] 6) Low-temperature and high-pressure liquid carbon dioxide is transported underground through vertical shaft pipelines. After being depressurized by the multi-functional coupler unit, the liquid carbon dioxide is directly transported to the terminal air cooler. The liquid carbon dioxide undergoes a liquid-gas phase change and becomes gaseous, absorbing heat from the air to complete the refrigeration.

[0025] 7) After the heat exchange is completed, the gaseous carbon dioxide is transported back to the surface via the multi-functional coupler unit through the upward inlet of the regenerator to the upward pipe; the gaseous carbon dioxide in the upward pipe of the regenerator exchanges heat with the low temperature and high pressure supercritical carbon dioxide in the downward pipe, cooling the carbon dioxide in the downward pipe and increasing the temperature of the gaseous carbon dioxide in the upward pipe.

[0026] 8) The gaseous carbon dioxide in the upper pipe of the regenerator is transferred to the second gas-liquid separator, and the gaseous carbon dioxide re-enters the compressor for compression to form supercritical carbon dioxide, thereby completing the combined cooling and heating supply.

[0027] The surface unit connects to the multi-functional coupler unit through vertical shaft pipelines to form a circulation loop, completing the cooling of carbon dioxide and heat recovery.

[0028] In step 1), the temperature on the high-pressure side of the compressor is 65–120°C and the pressure is 7.38–12 MPa.

[0029] In step 6), the carbon dioxide after being depressurized by the multi-functional coupler unit has a temperature of -20 to 15°C and a pressure of 2 to 6 MPa.

[0030] Advantages of this invention:

[0031] This invention employs multi-stage cooling of high-temperature supercritical carbon dioxide on the high-pressure side of the compressor, distributing the heat load to avoid the risk of single-point overheating and extending equipment life; temperature gradient matching is achieved through multi-stage heat exchange, reducing the cooling process... This invention effectively utilizes the natural pressure potential energy at underground depths, reducing dependence on external energy sources, while minimizing energy loss through a multi-functional coupler unit. The multi-functional coupler unit features dynamic flow and pressure regulation, allowing the system to adjust the flow and pressure of the working fluid in real time, ensuring stable operation under different working conditions. A circulation loop is formed by connecting the vertical shaft pipeline to the multi-functional coupler unit, completing carbon dioxide refrigeration and heat recovery, overcoming the challenges of ultra-deep transportation. Equipped with multiple gas-liquid separation devices and pressure regulating devices, the working fluid maintains stable operation during long-distance underground transportation, improving system reliability and service life. It can solve the fluid and thermodynamic performance losses caused by ultra-deep transportation depths exceeding 600 meters and ultra-long transportation distances exceeding 4000 meters, which are difficult to overcome in ultra-deep underground transportation hubs, underground building spaces, or underground energy extraction. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of an embodiment of the transcritical carbon dioxide deep-earth long-distance refrigeration cycle system of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 As shown, the transcritical carbon dioxide deep underground long-distance refrigeration cycle system of this embodiment includes: a surface unit located on the ground and an underground unit located underground; the surface unit includes a compressor, an oil separator, a heat exchanger for heat-using units, a subcooling tower, first and second gas-liquid separators, a regenerator, and a throttling device; the underground unit includes a multi-functional coupler unit and a terminal air cooler; the surface unit and the underground unit are connected by an ultra-deep vertical shaft pipeline;

[0035] The gaseous outlet on the side of the second gas-liquid separator is connected to the low-pressure side of the compressor, and the high-pressure side of the compressor is connected to the inlet of the oil separator. The outlet of the oil separator is divided into two paths: one path connects to the heat exchanger of the heat-using unit; the other path connects to the inlet of the subcooling tower. The outlet of the subcooling tower is divided into two paths: one path connects to the downward inlet of the regenerator, and the other path connects to the downward outlet of the regenerator and is located before the throttling device. The upward outlet and upward inlet of the regenerator are connected internally through an upward pipe, and the downward inlet and downward outlet of the regenerator are connected internally through a downward pipe. The upward pipe and the downward pipe are not connected. The upward outlet is connected to the gas-liquid two-phase system of the second gas-liquid separator. Inlet; the downward outlet of the regenerator is connected to the gas-liquid two-phase inlet of the first gas-liquid separator via a throttling device; the gaseous outlet on the side of the first gas-liquid separator is connected to the gas-liquid two-phase inlet of the second gas-liquid separator; the liquid outlet at the bottom of the second gas-liquid separator is connected to the gas-liquid two-phase inlet of the first gas-liquid separator; the liquid outlet at the bottom of the first gas-liquid separator is connected to the downward inlet of the underground multi-functional coupler unit via a vertical shaft pipeline; the downward outlet of the multi-functional coupler unit is connected to the inlet of the underground terminal air cooler; the outlet of the terminal air cooler is connected to the upward inlet of the multi-functional coupler unit; and the upward outlet of the multi-functional coupler unit is connected to the upward inlet of the regenerator.

[0036] Heat exchangers for heat users include manufacturing workshops, steam production, industrial applications, domestic heating, and water treatment units. Throttling devices utilize throttling valves.

[0037] It also includes circulating pumps, which are optional on pipelines with insufficient fluid pressure to increase power when flow is obstructed; it also includes filter equipment to remove impurities that appear in the working fluid after the refrigeration system has been in use for a period of time, and is generally located underground; it also includes transformers, which are the power supply equipment for the underground circulating pumps, solenoid valves, and control panels, and are generally located in the underground equipment room; and it includes a surface carbon dioxide storage tank, which is located on the ground surface. The outlet of the surface carbon dioxide storage tank is connected to the throttling device and is located before the gas-liquid two-phase inlet of the first gas-liquid separator, to provide a buffer when the refrigeration load changes and to replenish the loss of working fluid. A carbon dioxide-water heat exchange device is added after the multi-functional coupler unit in the underground chamber; and an additional cooling equipment chamber is set up in the underground space to house the underground secondary chilled water pumps and filter equipment, while an electrical chamber is set up to house electrical equipment such as transformers and secondary water pump frequency converters.

[0038] The multi-functional coupler unit includes modules for pressure reduction, gas-liquid separation, and kinetic energy conversion. By reducing excessive pressure generated during deep underground transport of the working fluid, it utilizes the pressure potential energy from the depth of the underground environment to convert it into kinetic energy, facilitating the smooth transport of the working fluid to its target location within the underground transport channel. It features dynamic flow and pressure regulation, allowing the system to adjust the flow and pressure of the working fluid in real time to ensure stable operation under various working conditions. In addition to regulating the flow and pressure of carbon dioxide, it also performs gas-liquid separation to prevent air bubbles generated during long-distance underground transport from mixing with the carbon dioxide, ensuring the stable operation of the entire system. The liquid working fluid flows through the multi-functional coupler unit, which not only transports the liquid working fluid to the underground chamber but also converts the pressure potential energy from the depth into kinetic energy, applying it to the surface process of liquid cooling water or gaseous carbon dioxide, overcoming the challenges of transporting the working fluid in deep underground environments.

[0039] The control method for the transcritical carbon dioxide deep-earth long-distance refrigeration cycle system in this embodiment includes the following steps:

[0040] 1) Low-temperature and low-pressure carbon dioxide gas enters the compressor and is compressed into high-temperature and high-pressure supercritical carbon dioxide. It is pressurized and heated in the compressor, resulting in high temperature and pressure on the high-pressure side of the compressor. The high-pressure and high-temperature supercritical carbon dioxide passes through an oil separator to separate the lubricating oil in the compressor from the carbon dioxide, thus avoiding affecting the subsequent fluid flow and heat exchange process.

[0041] 2) The high-temperature and high-pressure carbon dioxide from the oil separator is divided into two paths. One path is connected to the heat exchanger of the heat-using unit. The carbon dioxide enters the heat exchanger and transfers heat to the heat-using unit. The carbon dioxide loses heat and its temperature drops, but it is still in a high-pressure supercritical state and is then transferred to the subcooling tower. The other path of the high-temperature and high-pressure carbon dioxide from the oil separator is directly connected to the subcooling tower, where the temperature is further reduced through heat exchange. The carbon dioxide temperature drops to 30°C, but it still remains in a supercritical state.

[0042] 3) After being cooled by the subcooling tower, the low-temperature, high-pressure supercritical carbon dioxide selects its path based on temperature. If the temperature is too high to meet the low-temperature requirement of the throttling device, it is transferred to the downflow inlet of the regenerator and then to the downflow pipe. In the downflow pipe of the regenerator, the low-temperature, high-pressure supercritical carbon dioxide exchanges heat with the carbon dioxide from the underground located in the upflow pipe, further reducing the temperature to meet the temperature requirement of the throttling device, and then flows from the downflow outlet to the throttling device. If the temperature is low enough to meet the low-temperature requirement of the throttling device, it is directly transferred to the downflow outlet of the regenerator and before the throttling device.

[0043] 4) The supercritical carbon dioxide suddenly expands through the throttling device, its temperature drops and it partially vaporizes, entering a low-temperature, low-pressure gas-liquid two-phase state.

[0044] 5) After passing through the throttling device, the gas-liquid two-phase carbon dioxide enters the first gas-liquid separator. The liquid carbon dioxide settles through the separator and is transported to the ground, while the gaseous carbon dioxide rises and is transported to the first gas-liquid separator, where the liquid and gas carbon dioxide are separated.

[0045] 6) Low-temperature and high-pressure liquid carbon dioxide is transported underground through vertical shaft pipelines. After being depressurized by the multi-functional coupler unit, the liquid carbon dioxide is directly transported to the terminal air cooler. The liquid carbon dioxide undergoes a liquid-gas phase change and becomes gaseous, absorbing heat from the air to complete the refrigeration.

[0046] 7) After the heat exchange is completed, the gaseous carbon dioxide is transported back to the surface via the multi-functional coupler unit through the upward inlet of the regenerator to the upward pipe; the gaseous carbon dioxide in the upward pipe of the regenerator exchanges heat with the low temperature and high pressure supercritical carbon dioxide in the downward pipe, cooling the carbon dioxide in the downward pipe, and the temperature of the gaseous carbon dioxide in the upward pipe increases slightly.

[0047] 8) The gaseous carbon dioxide in the upper pipe of the regenerator is transferred from the upper outlet of the heat exchanger to the second gas-liquid separator. The gaseous carbon dioxide re-enters the compressor for compression to form supercritical carbon dioxide, and then is transported to the heat exchanger of the heat-using unit for heat transfer, thereby completing the combined cooling and heating supply.

[0048] The surface unit is connected to the underground multi-functional coupler unit through an ultra-deep vertical shaft pipeline to form a circulation loop, completing the refrigeration and heat recovery of carbon dioxide and the transportation of refrigerant.

[0049] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A transcritical carbon dioxide deep-earth long-distance refrigeration cycle system, characterized in that, The cooling cycle system includes: a surface unit located on the ground and an underground unit located underground; the surface unit includes a compressor, a subcooling tower, first and second gas-liquid separators, a regenerator, and a throttling device; the underground unit includes a multi-functional coupler unit; the surface unit and the underground unit are connected by a vertical shaft pipeline; The gaseous outlet of the second gas-liquid separator is connected to the low-pressure side of the compressor, and the high-pressure side of the compressor is connected to the inlet of the subcooling tower. The outlet of the subcooling tower is divided into two paths: one path connects to the downward inlet of the regenerator, and the other path connects to the downward outlet of the regenerator and is located before the throttling device. The upward outlet and upward inlet of the regenerator are connected internally through an upward pipe, and the downward inlet and downward outlet of the regenerator are connected internally through a downward pipe. The upward outlet is connected to the gas-liquid two-phase inlet of the second gas-liquid separator. The downward outlet of the regenerator is connected to the gas-liquid two-phase inlet of the first gas-liquid separator via a throttling device. The gaseous outlet of the first gas-liquid separator is connected to the gas-liquid two-phase inlet of the second gas-liquid separator. The liquid outlet of the second gas-liquid separator is connected to the gas-liquid two-phase inlet of the first gas-liquid separator. The liquid outlet of the first gas-liquid separator is connected to the downward inlet of the underground multi-functional coupler unit through a vertical shaft pipeline. The downward outlet of the multi-functional coupler unit is connected to the inlet of the underground terminal air cooler. The outlet of the terminal air cooler is connected to the upward inlet of the multi-functional coupler unit. The upward outlet of the multi-functional coupler unit is connected to the upward inlet of the regenerator. In the refrigeration cycle system, high-temperature supercritical carbon dioxide on the high-pressure side of the compressor is cooled in stages using multiple devices to distribute the heat load; temperature gradient matching is achieved through multi-stage heat exchange to reduce heat loss during the cooling process; and heat is utilized in stages at each temperature range to improve heat recovery efficiency. The multi-functional coupler unit includes a pressure reducing module, a gas-liquid separation module, and an upward circulation pump. The surface unit is connected to the pressure reducing module via a vertical shaft pipeline, which depressurizes the liquid carbon dioxide from the ground and then transmits it to the terminal air cooler. After heat exchange with the terminal air cooler to complete cooling, the gaseous carbon dioxide is transmitted to the gas-liquid separation module to separate the incompletely vaporized liquid carbon dioxide. The separated liquid carbon dioxide flows back to the outlet of the pressure reducing module of the multi-functional coupler unit, and then the gaseous carbon dioxide in the gas-liquid separator is transmitted to the surface unit through the vertical shaft pipeline. An upward circulation pump is installed on the upward vertical shaft pipeline after the gas outlet of the gas-liquid separation module. The upward circulation pump provides the upward power for the liquid carbon dioxide to return to the surface to complete the circulation.

2. The refrigeration cycle system as described in claim 1, characterized in that, It also includes an oil separator, which is located between the high-pressure side of the compressor and the subcooling tower.

3. The refrigeration cycle system as described in claim 1, characterized in that, It also includes a heat exchanger unit, which is located after the compressor and in front of the subcooling tower.

4. The refrigeration cycle system as described in claim 1, characterized in that, It also includes filter equipment, installed in underground pipes.

5. The refrigeration cycle system as described in claim 1, characterized in that, It also includes a carbon dioxide surface storage tank, which is installed on the ground and whose outlet is connected after the throttling device and before the gas-liquid two-phase inlet of the first gas-liquid separator.

6. The refrigeration cycle system as described in claim 1, characterized in that, The throttling device can be a fixed throttling device, an adjustable throttling device, an electronic throttling device, an intelligent throttling device, a multi-hole plug-type throttling device, or a labyrinth-type throttling device.

7. A control method for a transcritical deep-earth long-distance carbon dioxide refrigeration cycle system as described in claim 1, characterized in that, The control method includes the following steps: 1) Low-temperature, low-pressure carbon dioxide gas from the second gas-liquid separator enters the compressor and is compressed into high-temperature, high-pressure supercritical carbon dioxide. It is pressurized and heated in the compressor, resulting in higher temperature and pressure on the high-pressure side of the compressor. 2) Carbon dioxide is transferred to the subcooling tower, where its temperature is reduced through heat exchange. The carbon dioxide temperature decreases, but it still remains in a supercritical state. 3) After being cooled by the subcooling tower, the low-temperature, high-pressure supercritical carbon dioxide selects its path based on temperature: If the temperature is too high to meet the low-temperature requirement of the throttling device, it is transferred to the downflow inlet of the regenerator and then to the downflow pipe. In the downflow pipe of the regenerator, the low-temperature, high-pressure supercritical carbon dioxide exchanges heat with the carbon dioxide from the underground located in the upflow pipe, further reducing the temperature to meet the temperature requirement of the throttling device, and then flows from the downflow outlet to the throttling device; if the temperature is low enough to meet the low-temperature requirement of the throttling device, it is directly transferred to the downflow outlet of the regenerator and before the throttling device. 4) The supercritical carbon dioxide suddenly expands through the throttling device, its temperature drops and it partially vaporizes, entering a low-temperature, low-pressure gas-liquid two-phase state. 5) After passing through the throttling device, the gas-liquid two-phase carbon dioxide enters the first gas-liquid separator. The liquid carbon dioxide settles and is transported to the ground, while the gaseous carbon dioxide rises and is transported to the second gas-liquid separator, where the liquid and gaseous carbon dioxide are separated. 6) Low-temperature and high-pressure liquid carbon dioxide is transported underground through vertical shaft pipelines. After being depressurized by the multi-functional coupler unit, the liquid carbon dioxide is directly transported to the terminal air cooler. The liquid carbon dioxide undergoes a liquid-gas phase change to become gaseous, absorbs heat from the air, and completes the refrigeration. 7) After the heat exchange is completed, the gaseous carbon dioxide is transported back to the surface via the multi-functional coupler unit through the upward inlet of the regenerator to the upward pipe; the gaseous carbon dioxide in the upward pipe of the regenerator exchanges heat with the low temperature and high pressure supercritical carbon dioxide in the downward pipe, cooling the carbon dioxide in the downward pipe and increasing the temperature of the gaseous carbon dioxide in the upward pipe. 8) The gaseous carbon dioxide in the upper pipe of the regenerator is transferred to the second gas-liquid separator, and the gaseous carbon dioxide re-enters the compressor for compression to form supercritical carbon dioxide, thereby completing the combined cooling and heating supply. The surface unit connects to the multi-functional coupler unit through vertical shaft pipelines to form a circulation loop, completing the cooling of carbon dioxide and heat recovery.

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