Transcritical carbon dioxide underground heat exchange deep ground long-distance refrigerating system and control method

Abstract

The invention discloses a transcritical carbon dioxide underground heat exchange deep ground long-distance refrigerating system and a control method. Natural pressure potential energy of underground depth is effectively utilized, dependence on external energy is reduced, and meanwhile energy loss is reduced to the maximum extent through the multifunctional coupler unit; a vertical shaft pipeline is connected with a multifunctional coupler unit to form a circulation loop, refrigeration and heat recovery of carbon dioxide are completed, and challenges caused by ultra-large deep transportation are overcome; the underground direct connection scheme of the phase change heat exchanger is adopted, a vertical section, hundreds of meters away from the ground surface to the underground, of a cold carrying working medium is omitted, liquid carbon dioxide absorbs heat from a cold carrying working medium loop of a tail end air cooler in the underground carbon dioxide phase change heat exchanger through isothermal liquid-gas phase change, and the cooling capacity is reserved through a high latent heat value; low-dissipation energy transfer is realized; the carbon dioxide phase change heat exchanger is located at the depth consistent with the cooling demand load center, the low-temperature secondary refrigerant conveying distance is shortened, and pipeline cold losses are greatly reduced.

Description

Technical Field

[0001] The present invention relates to a deep underground long-distance refrigeration technology, and in particular to a transcritical carbon dioxide underground heat exchange deep underground long-distance refrigeration system and a control method thereof. Background Art

[0002] As development continues to deepen, high-temperature heat damage in deep underground spaces is becoming increasingly serious. For example, controlling underground humidity is a global challenge, and the future maximum mining depth will, in part, depend on the level of heat damage management. Of all the energy consumed by electromechanical equipment in subway stations, ventilation and air conditioning systems account for approximately 70% of the total. Theories and technologies for high-temperature heat damage management with low energy consumption, low pollution, and high thermodynamic performance have become 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 solely. Underground space cooling and air conditioning systems generally use Freon-based refrigerants as working fluids. However, their use has long-term and far-reaching negative environmental impacts, such as ozone depletion and the greenhouse effect. Therefore, the global phase-out of these substances and their replacement with more environmentally friendly alternatives is a key initiative promoted by international environmental organizations.

[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. Transcritical carbon dioxide systems, however, offer a high energy efficiency ratio. Due to their superior thermodynamic properties, they can complete the refrigeration process with relatively low energy input. Compared to traditional refrigerants, carbon dioxide systems operate at a relatively low pressure, which reduces equipment wear and improves system life. They also exhibit high heat exchange efficiency in the transcritical region, particularly during the heat exchange between the condenser and evaporator. They can maintain good cooling performance even in high-temperature environments, making them a key application area for future refrigeration technology.

[0005] Existing deep underground cooling technologies suffer from extreme depths, resulting in excessive fluid pressure, making underground equipment and pipelines unable to withstand the pressure. The extremely long transport distances result in significant heat losses along the way, preventing the cold from reaching the end of the underground space. Due to the extreme depths and lengthy cold transport distances, the transmission and function of the refrigerant are affected by pressure and heat loss, which reduces cooling system performance, increases energy consumption, and increases technical difficulty. Traditional deep underground cooling systems often fail to fully utilize the heat transported from the deep underground to the surface, resulting in significant heat dissipation and environmental pollution. Summary of the Invention

[0006] In response to the above problems existing in the existing technology, the present invention proposes a transcritical carbon dioxide underground heat exchange deep long-distance refrigeration system and its control method. The present invention can provide heat to heat users and water treatment systems while cooling, effectively recovering thermal energy, and has good economic potential, environmental potential and thermodynamic performance. It is used to solve the defects of the existing technology that are difficult to overcome, such as the loss of fluid dynamics and thermodynamic properties, energy waste and environmental pollution caused by ultra-deep transportation depths of more than 600 meters and ultra-long transportation distances of more than 4000 meters.

[0007] One object of the present invention is to provide a transcritical carbon dioxide underground heat exchange deep underground long-distance refrigeration system.

[0008] The transcritical carbon dioxide underground heat exchange deep-ground long-distance refrigeration system of the present invention comprises: a surface unit located on the ground and an underground unit located underground; the surface unit comprises a compressor, a subcooling cooling tower, first and second gas-liquid separators, a regenerator, and a throttling device; the underground unit comprises a multifunctional coupler unit and a carbon dioxide phase-change heat exchanger; the surface unit and the underground unit are connected via an ultra-deep vertical shaft pipeline;

[0009] The gaseous outlet of the second gas-liquid separator is connected to the low-pressure side of the compressor, the high-pressure side of the compressor is connected to the inlet of the subcooling cooling tower, and the outlet of the subcooling cooling tower is divided into two paths, one is connected to the downward inlet of the regenerator, and the other is connected to the back of the downward outlet of the regenerator and is located before the throttling device; the upward outlet and the upward inlet of the regenerator are connected internally through an upward pipe, and the downward inlet and the downward outlet of the regenerator are connected internally through a downward pipe, and 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 through the 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;

[0010] The liquid outlet of the first gas-liquid separator is connected to the downward inlet of the multifunctional coupler unit located underground via a vertical shaft pipeline. The downward outlet of the multifunctional coupler unit is connected to the refrigerant inlet of the carbon dioxide phase-change heat exchanger via a pipeline. The refrigerant inlet and the refrigerant outlet of the carbon dioxide phase-change heat exchanger are connected via a refrigerant connecting pipe. The refrigerant outlet of the carbon dioxide phase-change heat exchanger is connected to the upward inlet of the multifunctional coupler unit via a pipeline. The upward outlet of the multifunctional coupler unit is connected to the upward inlet of the regenerator via a vertical shaft pipeline. The refrigerant connecting pipe of the carbon dioxide phase-change heat exchanger is connected to various instruments of the surface unit via pipelines to form a refrigerant circulation system. Carbon dioxide is used as the refrigerant in the refrigerant circulation system.

[0011] The cooling medium outlet of the carbon dioxide phase change heat exchanger is connected to the inlet of the terminal air cooler, and the outlet of the terminal air cooler is connected to the cooling medium inlet of the carbon dioxide phase change heat exchanger. The cooling medium inlet and the cooling medium outlet are connected through a cooling medium connecting pipe. The cooling medium connecting pipe located underground is connected to the terminal air cooler to form a cooling medium circuit. A liquid cooling medium that does not undergo phase change circulates in the cooling medium circuit; the cooling medium connecting pipe and the refrigeration medium connecting pipe are not connected.

[0012] The refrigerant is carbon dioxide; the cooling medium is liquid water, salt solution or organic solvent that always remains liquid without phase change within the working temperature range.

[0013] Furthermore, the present invention also includes an oil separator, which is arranged between the high-pressure side of the compressor and the supercooling cooling tower. After passing through the compressor, the supercritical carbon dioxide becomes high-temperature and high-pressure carbon dioxide and 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.

[0014] The heat exchanger is located after the compressor and before the subcooling tower. After passing through the compressor, the supercritical carbon dioxide is converted into high-temperature, high-pressure supercritical carbon dioxide, which transfers heat to the heat exchanger for further utilization. Heat users include manufacturing workshops, steam generation, industrial applications, domestic heating, or water treatment units.

[0015] The outlet of the oil separator is divided into two routes, one is connected to the heat exchanger of the heat-using unit, and the other is connected to the inlet of the subcooling cooling tower. The fluid ratio of the two routes is flexibly allocated according to the changes in the heat demand of the heat-using unit. If the heat demand of the heat-using unit is high, more flow will be allocated to the heat-using unit. If the heat demand is low, the flow allocation will be reduced.

[0016] The present invention also includes a circulating pump, which is optionally installed on pipelines with insufficient fluid pressure to increase power when flow is obstructed; a filter device, which is used to remove impurities from the working fluid after the refrigeration system has been used for a period of time and is generally installed in underground pipelines; a transformer, which is an electrical auxiliary equipment for the underground circulating pump, solenoid valve, and control panel, and is generally installed in an underground equipment room; and a surface carbon dioxide liquid storage tank, which is installed on the ground and has an outlet connected to the back of the throttling device and before the gas-liquid two-phase inlet of the first gas-liquid separator to provide a buffer when the refrigeration load condition changes and to replenish the loss of the working fluid. A set of carbon dioxide-water heat exchange devices is added after the multifunctional coupler unit in the underground chamber; and an additional cooling equipment chamber is set in the underground space to accommodate the underground secondary chilled water pump and filter equipment, and an electrical chamber is set to accommodate electrical equipment such as the transformer and the secondary water pump inverter.

[0017] The multifunctional 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 of the multifunctional coupler unit through an extra-deep vertical shaft pipeline, and the liquid refrigerant from the ground is decompressed and transmitted to the carbon dioxide phase change heat exchanger; after completing the refrigeration through heat exchange with the carbon dioxide phase change heat exchanger, the liquid refrigerant is transmitted to the gas-liquid separation module, and the bubbles mixed in during the transportation process are separated. If the separated bubbles are harmless to the air quality, they are directly discharged into the air; if they are harmful to the air, they are collected in special containers or discharged after harmless treatment; then the liquid refrigerant in the gas-liquid separation module is transmitted to the surface unit through the extra-deep vertical shaft pipe; an upward circulation pump is set on the upward vertical shaft pipe behind the gas outlet of the gas-liquid separation module, and the upward circulation pump provides upward power for the refrigerant to return to the surface to complete the cycle. By reducing the excessive pressure generated by the refrigerant during deep underground transportation, the pressure potential energy brought by the depth underground is utilized and converted into kinetic energy, helping the refrigerant to be smoothly transported to the target location in the underground transportation channel. With the function of dynamically adjusting flow and pressure, the system can adjust the flow and pressure of the refrigerant in real time to ensure stable operation under different working conditions. It not only has the function of regulating the flow and pressure of the flowing refrigerant, but also has the function of gas-liquid separation to prevent bubbles generated during long-distance underground transportation from mixing with the refrigerant, ensuring the stable operation of the entire system. The refrigerant flows through the multifunctional coupler unit, which is responsible for not only transporting the refrigerant underground, but also overcoming the transportation difficulties of the refrigerant in deep underground scenarios.

[0018] The throttling device adopts a fixed throttling device, an adjustable flow device, an electronic throttling device, an intelligent throttling device, a porous plug throttling device or a labyrinth throttling device.

[0019] Another object of the present invention is to provide a control method for a transcritical carbon dioxide underground heat exchange deep underground long-distance refrigeration system.

[0020] The control method of the transcritical carbon dioxide underground heat exchange deep underground long-distance refrigeration system of the present invention comprises the following steps:

[0021] 1) The 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, and the temperature and pressure on the high-pressure side of the compressor are higher.

[0022] 2) The carbon dioxide is transferred to a supercooling tower, where the temperature is lowered through heat exchange. The temperature of the carbon dioxide decreases, but it still remains in a supercritical state.

[0023] 3) After cooling in the supercooling tower, the low-temperature, high-pressure supercritical carbon dioxide is routed based on its temperature. If the temperature is too high to meet the low temperature requirement of the throttling device, it is transferred to the downstream inlet of the regenerator and then to the downstream pipeline. In the downstream pipeline of the regenerator, the low-temperature, high-pressure supercritical carbon dioxide undergoes heat exchange with the carbon dioxide from underground in the upward pipeline, further reducing its temperature to meet the temperature requirement of the throttling device, and then flows from the downstream 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 downstream outlet of the regenerator and before the throttling device.

[0024] 4) The supercritical carbon dioxide suddenly expands after passing through the throttling device, the temperature drops and it partially vaporizes, entering a low-temperature and low-pressure gas-liquid two-phase state;

[0025] 5) After passing through the throttling device, the gaseous and liquid carbon dioxide enters the first gas-liquid separator. The gaseous carbon dioxide rises and is transferred to the second gas-liquid separator. The liquid and gaseous carbon dioxide are separated. The low-temperature and low-pressure liquid carbon dioxide is separated and settled and then transported underground through the vertical shaft pipeline.

[0026] 6) After being depressurized by the multifunctional coupler unit, the liquid carbon dioxide is transferred to the refrigerant connecting pipe of the underground carbon dioxide phase-change heat exchanger. The liquid carbon dioxide in the refrigerant connecting pipe exchanges heat with the refrigerant in the refrigerant connecting pipe, cooling the refrigerant in the refrigerant connecting pipe and heating the carbon dioxide in the refrigerant connecting pipe.

[0027] 7) After the heated carbon dioxide in the refrigerant connecting pipe passes through a multifunctional coupler unit for gas-liquid separation to remove incompletely vaporized liquid carbon dioxide, the gaseous carbon dioxide is transported upward through a vertical shaft pipeline to the upward inlet of a regenerator located on the surface and to the upward pipeline. The gaseous carbon dioxide in the upward pipeline of the regenerator exchanges heat with the low-temperature, high-pressure supercritical carbon dioxide in the downward pipeline, cooling the carbon dioxide in the downward pipeline and increasing its temperature in the upward pipeline.

[0028] 8) The gaseous carbon dioxide in the upward pipeline of the regenerator is transmitted 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 supply of cooling and heating;

[0029] 9) The liquid refrigerant in the refrigerant connecting pipe of the cooled carbon dioxide phase-change heat exchanger is transported to the terminal air cooler through a pipeline; the liquid refrigerant exchanges heat with the air, absorbing heat from the air, completing the cooling process;

[0030] 10) After the heat exchange is completed, the cooling medium is transported back to the cooling medium connecting pipe of the underground carbon dioxide phase change heat exchanger, and the cooling medium in the cooling medium connecting pipe exchanges heat with the carbon dioxide in the refrigeration medium connecting pipe;

[0031] The carbon dioxide phase change heat exchanger completes the heat exchange between the refrigerant and the cooling medium. The phase change process maintains a stable low-temperature heat exchange interface, avoids end difference loss in sensible heat exchange, and significantly improves heat transfer efficiency. In addition, the carbon dioxide phase change heat exchanger is located underground, and liquid carbon dioxide with low latent heat loss is directly transported underground. The underground carbon dioxide phase change heat exchanger absorbs heat from the cooling medium of the terminal air cooler through isothermal liquid-to-gas phase change, maximizing the use of the high latent heat value of the cooling medium to retain cooling capacity and achieve low-dissipation energy transfer.

[0032] Wherein, in step 1), the temperature of the high-pressure side of the compressor is 65-120° C., and the pressure is 7.38-12 MPa.

[0033] In step 6), the lower limit of the temperature of the cooling medium flowing out of the cooling medium outlet of the carbon dioxide phase-change heat exchanger is the freezing point of the selected cooling medium, and the upper limit is 15°C.

[0034] The liquid supply to the CO2 phase-change heat exchanger is controlled by a throttling device to match the heat load of the terminal air cooler; the flow is adjusted in conjunction with the compressor to stabilize the exhaust pressure, and the cooling capacity of the CO2 phase-change heat exchanger located on the surface is used to jointly adjust the CO2 saturation pressure.

[0035] In step 9), the temperature of the cooling medium at the inlet of the terminal air cooler is less than 20°C.

[0036] Advantages of the present invention:

[0037] The present invention effectively utilizes the natural pressure potential energy at depth underground, reduces dependence on external energy sources, and at the same time minimizes energy loss through a multifunctional coupler unit. The multifunctional coupler unit has the function of dynamically adjusting flow and pressure, and the system can adjust the flow and pressure of the working fluid in real time to ensure stable operation under different working conditions. By connecting the vertical shaft pipeline with the multifunctional coupler unit to form a circulation loop, carbon dioxide refrigeration and heat recovery are completed, overcoming the challenges brought by ultra-deep transportation. The pressure reduction module equipped with multiple sets of gas-liquid separation devices and multifunctional coupler units enables the working fluid to maintain stable operation during long-distance underground transportation, thereby improving the reliability and service life of the system. It can solve the problems of fluid mechanics and thermodynamic performance loss caused by ultra-deep transportation depths of more than 600 meters and ultra-long transportation distances of more than 4,000 meters, which are difficult to overcome in ultra-deep underground transportation hubs, underground building spaces, or underground energy mining. By adjusting the carbon dioxide saturation pressure, the phase change temperature in the carbon dioxide phase change heat exchanger can flexibly match the selected cooling working fluid circuit requirements, which is particularly suitable for deep underground heat flux density scenarios. In addition, most refrigerants are toxic or asphyxiating to the human body. The installation space for pipelines in ultra-deep underground spaces is narrow and the pipeline arrangement is complex. Once a leak occurs, it will cause serious consequences including but not limited to respiratory poisoning and frostbite of limbs. The present invention arranges the carbon dioxide phase change radiator underground and uses a low-hazard or harmless refrigerant to transport cold to the terminal air cooler. The refrigerant is responsible for reaching the required depth of the cooling part, and the transportation in the underground horizontal tunnel is completed by the refrigerant circuit, which minimizes the dissipation of cold while ensuring a low leakage risk. Moreover, since the rock mass itself is an excellent natural insulator, the installation of the carbon dioxide phase change heat exchanger in the underground space does not require an additional insulation layer. Compared with placing the carbon dioxide phase change heat exchanger on the surface, which consumes a lot of energy to resist environmental heat intrusion, it is more conducive to reducing operating energy consumption.

[0038] The present invention adopts an underground direct connection scheme of the phase change heat exchanger, which can eliminate the vertical section of the refrigerant from the surface to hundreds of meters underground. In the vertical section, the latent heat loss of liquid carbon dioxide is much smaller than the sensible heat loss of the refrigerant. The liquid carbon dioxide absorbs heat from the refrigerant circuit of the terminal air cooler through isothermal liquid-to-gas phase change in the underground carbon dioxide phase change heat exchanger, making the maximum use of its high latent heat value to retain cooling capacity and realize low-dissipation energy transfer; the carbon dioxide phase change heat exchanger is arranged at a depth close to or consistent with the cooling demand load center, which can shorten the transportation distance of the low-temperature refrigerant, eliminate the need for long-distance refrigerant downhole pipelines, and greatly reduce pipeline cooling losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of an embodiment of the transcritical carbon dioxide underground heat exchange deep underground long-distance refrigeration system of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0041] like Figure 1 As shown, the transcritical carbon dioxide underground heat exchange deep long-distance refrigeration 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, an oil separator, a heat exchanger of a heat-using unit, a subcooling cooling tower, first and second gas-liquid separators, a regenerator, a throttling device, and a carbon dioxide phase-change heat exchanger; the underground unit includes a multifunctional coupler unit and a terminal air cooler; the surface unit and the underground unit are connected by an ultra-deep vertical shaft pipeline;

[0042] 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 is connected to the heat exchanger of the heat consumption unit; the other path is connected to the inlet of the subcooling cooling tower, and the outlet of the subcooling cooling tower is divided into two paths, one path is connected to the downward inlet of the regenerator, and the other path is connected to the back of the downward outlet of the regenerator and is located before the throttling device; the upward outlet and the upward inlet of the regenerator are connected through an upward pipe, and the downward inlet and the downward outlet of the regenerator are connected through a downward pipe, and the upward pipe and the downward pipe are not connected, and 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 through the 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;

[0043] The liquid outlet at the bottom of the first gas-liquid separator is connected to the downward inlet of the multifunctional coupler unit located underground via a vertical shaft pipeline. The downward outlet of the multifunctional coupler unit is connected to the refrigerant inlet of the carbon dioxide phase-change heat exchanger via a pipeline. The refrigerant inlet and the refrigerant outlet of the carbon dioxide phase-change heat exchanger are connected via a refrigerant connecting pipe. The refrigerant outlet of the carbon dioxide phase-change heat exchanger is connected to the upward inlet of the multifunctional coupler unit via a pipeline. The upward outlet of the multifunctional coupler unit is connected to the upward inlet of the regenerator via a vertical shaft pipeline. The refrigerant connecting pipe of the carbon dioxide phase-change heat exchanger is connected to various instruments of the surface unit via pipelines to form a refrigerant circulation system. Carbon dioxide is used as the refrigerant in the refrigerant circulation system.

[0044] The cooling medium outlet of the carbon dioxide phase change heat exchanger is connected to the inlet of the terminal air cooler, and the outlet of the terminal air cooler is connected to the cooling medium inlet of the carbon dioxide phase change heat exchanger. The cooling medium inlet and the cooling medium outlet are connected through a cooling medium connecting pipe. The cooling medium connecting pipe located underground is connected to the terminal air cooler to form a cooling medium circuit. A liquid cooling medium that does not undergo phase change circulates in the cooling medium circuit; the cooling medium connecting pipe and the refrigeration medium connecting pipe are not connected to each other.

[0045] The control method of the transcritical carbon dioxide underground heat exchange deep underground long-distance refrigeration system of this embodiment includes the following steps:

[0046] 1) The 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, and the temperature and pressure on the high-pressure side of the compressor are higher.

[0047] 2) The carbon dioxide is transferred to a supercooling tower, where it is further cooled by heat exchange. The temperature of the carbon dioxide is reduced to 30°C, but it still remains in a supercritical state.

[0048] 3) After cooling in the supercooling tower, the low-temperature, high-pressure supercritical carbon dioxide is routed based on its temperature. If the temperature is too high to meet the low temperature requirement of the throttling device, it is transferred to the downstream inlet of the regenerator and then to the downstream pipeline. In the downstream pipeline of the regenerator, the low-temperature, high-pressure supercritical carbon dioxide undergoes heat exchange with the carbon dioxide from underground in the upward pipeline, further reducing its temperature to meet the temperature requirement of the throttling device, and then flows from the downstream 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 downstream outlet of the regenerator and before the throttling device.

[0049] 4) The supercritical carbon dioxide suddenly expands after passing through the throttling device, the temperature drops and it partially vaporizes, entering a low-temperature and low-pressure gas-liquid two-phase state;

[0050] 5) After passing through the throttling device, the gaseous and liquid carbon dioxide enters the first gas-liquid separator. The gaseous carbon dioxide rises and is transmitted to the second gas-liquid separator. The liquid and gaseous carbon dioxide are separated. The liquid carbon dioxide is separated and settled and transmitted underground.

[0051] 6) Liquid carbon dioxide is transported to the refrigerant connecting pipe of the carbon dioxide phase-change heat exchanger through the multifunctional coupler unit. The liquid carbon dioxide in the refrigerant connecting pipe exchanges heat with the refrigerant in the refrigerant connecting pipe. The refrigerant in the refrigerant connecting pipe is cooled, and the carbon dioxide in the refrigerant connecting pipe is heated.

[0052] 7) After the heated carbon dioxide in the refrigerant connecting pipe passes through a multifunctional coupler unit for gas-liquid separation to remove incompletely vaporized liquid carbon dioxide, the gaseous carbon dioxide is transported upward through a vertical shaft pipeline to the upward inlet of a regenerator located on the surface and to the upward pipeline. The gaseous carbon dioxide in the upward pipeline of the regenerator exchanges heat with the low-temperature, high-pressure supercritical carbon dioxide in the downward pipeline, cooling the carbon dioxide in the downward pipeline and increasing its temperature in the upward pipeline.

[0053] 8) The gaseous carbon dioxide in the upward pipe of the regenerator is transmitted from the upward outlet of the regenerator to the second gas-liquid separator. The gaseous carbon dioxide re-enters the compressor for compression to form supercritical carbon dioxide, thereby completing the combined supply of heat and cold.

[0054] 9) The liquid refrigerant in the refrigerant connecting pipe of the cooled carbon dioxide phase-change heat exchanger is transported to the terminal air cooler through a horizontal (or nearly horizontal) pipeline. The liquid refrigerant exchanges heat with the air, absorbing heat from the air, thus completing the cooling process.

[0055] 10) After the heat exchange is completed, the cooling medium is transported back to the cooling medium connecting pipe of the underground carbon dioxide phase change heat exchanger via a horizontal (or nearly horizontal) pipeline. The cooling medium in the cooling medium connecting pipe exchanges heat with the carbon dioxide in the refrigeration medium connecting pipe.

[0056] The carbon dioxide phase change heat exchanger completes the heat exchange between the refrigerant on the surface and the cooling medium. The liquid carbon dioxide absorbs the heat of the underground cooling medium through isothermal liquid-to-gas phase change in the carbon dioxide phase change heat exchanger, and uses its high latent heat value to achieve efficient energy transfer. The phase change process maintains a stable low-temperature heat exchange interface, avoids end difference loss in sensible heat exchange, and significantly improves heat transfer efficiency. The carbon dioxide phase change radiator located on the surface can use the atmosphere or auxiliary cooling system to accurately control the heat exchange boundary conditions to prevent the influence of geothermal gradient, which makes it impossible to accurately control the CO2 evaporation temperature when it deviates from the design value. The surface unit and the underground unit are connected through an ultra-deep vertical shaft pipeline to complete the transportation of the cooling medium.

[0057] In this embodiment, water is used as the cooling medium.

[0058] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate 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 contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A transcritical carbon dioxide underground heat exchange deep long-distance refrigeration system, characterized in that: The refrigeration system includes: a surface unit located on the ground and an underground unit located underground; the surface unit includes a compressor, a subcooling cooling tower, first and second gas-liquid separators, a regenerator, and a throttling device; the underground unit includes a multifunctional coupler unit and a carbon dioxide phase-change heat exchanger; the surface unit and the underground unit are connected through an extra-deep vertical shaft pipeline; The gaseous outlet of the second gas-liquid separator is connected to the low-pressure side of the compressor, the high-pressure side of the compressor is connected to the inlet of the subcooling cooling tower, and the outlet of the subcooling cooling tower is divided into two paths, one is connected to the downward inlet of the regenerator, and the other is connected to the back of the downward outlet of the regenerator and is located before the throttling device; the upward outlet and the upward inlet of the regenerator are connected internally through an upward pipe, and the downward inlet and the downward outlet of the regenerator are connected internally through a downward pipe, and 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 through the 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 multifunctional coupler unit located underground via a vertical shaft pipeline. The downward outlet of the multifunctional coupler unit is connected to the refrigerant inlet of the carbon dioxide phase-change heat exchanger via a pipeline. The refrigerant inlet and the refrigerant outlet of the carbon dioxide phase-change heat exchanger are connected via a refrigerant connecting pipe. The refrigerant outlet of the carbon dioxide phase-change heat exchanger is connected to the upward inlet of the multifunctional coupler unit via a pipeline. The upward outlet of the multifunctional coupler unit is connected to the upward inlet of the regenerator via a vertical shaft pipeline. The refrigerant connecting pipe of the carbon dioxide phase-change heat exchanger is connected to various instruments of the surface unit via pipelines to form a refrigerant circulation system. Carbon dioxide is used as the refrigerant in the refrigerant circulation system. The cooling medium outlet of the carbon dioxide phase change heat exchanger is connected to the inlet of the terminal air cooler, and the outlet of the terminal air cooler is connected to the cooling medium inlet of the carbon dioxide phase change heat exchanger. The cooling medium inlet and the cooling medium outlet are connected through a cooling medium connecting pipe. The cooling medium connecting pipe located underground is connected to the terminal air cooler to form a cooling medium circuit. A liquid cooling medium that does not undergo phase change circulates in the cooling medium circuit; the cooling medium connecting pipe and the refrigeration medium connecting pipe are not connected.

2. The refrigeration system according to claim 1, wherein: The cooling medium is a liquid medium, which always remains in liquid state without phase change within the working temperature range.

3. The refrigeration system according to claim 1, wherein: It also includes an oil separator, which is arranged between the high-pressure side of the compressor and the supercooling cooling tower. After passing through the compressor, the supercritical carbon dioxide becomes high-temperature and high-pressure carbon dioxide and passes through the oil separator to separate the lubricating oil in the compressor from the carbon dioxide to avoid affecting the subsequent fluid flow and heat exchange process.

4. The refrigeration system according to claim 1, wherein: It also includes a heat-using unit heat exchanger, which is arranged after the compressor and in front of the supercooling cooling tower. After passing through the compressor, it becomes high-temperature and high-pressure supercritical carbon dioxide, which transfers heat to the heat-using unit heat exchanger for further utilization of heat.

5. The refrigeration system according to claim 1, wherein: It also includes a carbon dioxide surface liquid storage tank, which is set on the ground. The outlet of the carbon dioxide surface liquid storage tank is connected to the back of the throttling device and before the gas-liquid two-phase inlet of the first gas-liquid separator, so as to provide a buffer when the refrigeration load conditions change and to make up for the loss of the working fluid.

6. The refrigeration system according to claim 1, wherein: The multifunctional 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 of the multifunctional coupler unit through an extra-deep vertical shaft pipeline, and the liquid refrigerant from the ground is decompressed and then transmitted to the carbon dioxide phase change heat exchanger; after completing the refrigeration through heat exchange with the carbon dioxide phase change heat exchanger, the liquid refrigerant is transmitted to the gas-liquid separation module, and the bubbles mixed in during the transportation process are separated. If the separated bubbles are harmless to the air quality, they are directly discharged into the air; if they are harmful to the air, they are collected in a special container or discharged after being harmlessly treated; then the liquid refrigerant in the gas-liquid separation module is transmitted to the surface unit through the extra-deep vertical shaft pipe; an upward circulation pump is set on the upward vertical shaft pipe behind the gas outlet of the gas-liquid separation module, and the upward circulation pump provides upward power for the refrigerant to return to the surface to complete the cycle.

7. The refrigeration system according to claim 1, wherein: The throttling device is a fixed throttling device, an adjustable flow device, an electronic throttling device, an intelligent throttling device, a porous plug throttling device or a labyrinth throttling device.

8. A control method for a transcritical carbon dioxide underground heat exchange deep long-distance refrigeration system according to claim 1, characterized in that: The control method comprises the following steps: 1) The 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, and the temperature and pressure on the high-pressure side of the compressor are higher. 2) The carbon dioxide is transferred to a supercooling tower, where the temperature is lowered through heat exchange. The temperature of the carbon dioxide decreases, but it still remains in a supercritical state. 3) After cooling in the supercooling tower, the low-temperature, high-pressure supercritical carbon dioxide is routed based on its temperature. If the temperature is too high to meet the low temperature requirement of the throttling device, it is transferred to the downstream inlet of the regenerator and then to the downstream pipeline. In the downstream pipeline of the regenerator, the low-temperature, high-pressure supercritical carbon dioxide undergoes heat exchange with the carbon dioxide from underground in the upward pipeline, further reducing its temperature to meet the temperature requirement of the throttling device, and then flows from the downstream 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 downstream outlet of the regenerator and before the throttling device. 4) The supercritical carbon dioxide suddenly expands after passing through the throttling device, the temperature drops and it partially vaporizes, entering a low-temperature and low-pressure gas-liquid two-phase state; 5) After passing through the throttling device, the gaseous and liquid carbon dioxide enters the first gas-liquid separator. The gaseous carbon dioxide rises and is transferred to the second gas-liquid separator. The liquid and gaseous carbon dioxide are separated. The low-temperature and low-pressure liquid carbon dioxide is separated and settled and then transported underground through the vertical shaft pipeline. 6) After being depressurized by the multifunctional coupler unit, the liquid carbon dioxide is transferred to the refrigerant connecting pipe of the underground carbon dioxide phase-change heat exchanger. The liquid carbon dioxide in the refrigerant connecting pipe exchanges heat with the refrigerant in the refrigerant connecting pipe, cooling the refrigerant in the refrigerant connecting pipe and heating the carbon dioxide in the refrigerant connecting pipe. 7) After the heated carbon dioxide in the refrigerant connecting pipe passes through a multifunctional coupler unit for gas-liquid separation to remove incompletely vaporized liquid carbon dioxide, the gaseous carbon dioxide is transported upward through a vertical shaft pipeline to the upward inlet of a regenerator located on the surface and to the upward pipeline. The gaseous carbon dioxide in the upward pipeline of the regenerator exchanges heat with the low-temperature, high-pressure supercritical carbon dioxide in the downward pipeline, cooling the carbon dioxide in the downward pipeline and increasing its temperature in the upward pipeline. 8) The gaseous carbon dioxide in the upward pipeline of the regenerator is transmitted 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 supply of cooling and heating; 9) The liquid refrigerant in the refrigerant connecting pipe of the cooled carbon dioxide phase-change heat exchanger is transported to the terminal air cooler through a pipeline; the liquid refrigerant exchanges heat with the air, absorbing heat from the air, completing the cooling process; 10) After the heat exchange is completed, the cooling medium is transported back to the cooling medium connecting pipe of the underground carbon dioxide phase change heat exchanger, and the cooling medium in the cooling medium connecting pipe exchanges heat with the carbon dioxide in the refrigeration medium connecting pipe; The carbon dioxide phase change heat exchanger completes the heat exchange between the refrigerant and the cooling medium. The phase change process maintains a stable low-temperature heat exchange interface, avoids end difference loss in sensible heat exchange, and significantly improves heat transfer efficiency. In addition, the carbon dioxide phase change heat exchanger is located underground, and liquid carbon dioxide with low latent heat loss is directly transported underground. The underground carbon dioxide phase change heat exchanger absorbs heat from the cooling medium of the terminal air cooler through isothermal liquid-to-gas phase change, maximizing the use of the high latent heat value of the cooling medium to retain cooling capacity and achieve low-dissipation energy transfer.

9. The control method according to claim 8, wherein: The liquid supply to the CO2 phase-change heat exchanger is controlled by a throttling device to match the heat load of the terminal air cooler; the flow is adjusted in conjunction with the compressor to stabilize the exhaust pressure, and the cooling capacity of the CO2 phase-change heat exchanger located on the surface is used to jointly adjust the CO2 saturation pressure.

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