A cooling method and system of carbon dioxide closed cycle

Abstract

The application provides a closed carbon dioxide circulation cooling method and system, which comprises the following steps: S1, storing the working medium containing liquid carbon dioxide captured by a power plant CCUS device; S2, heat exchanging the working medium containing liquid carbon dioxide after drying and filtering to obtain a carbon dioxide gas-liquid mixture which is partially or completely vaporized; and S3, carrying out gas-liquid separation on the obtained carbon dioxide gas-liquid mixture, circulating the separated liquid carbon dioxide to a carbon dioxide adiabatic storage tank, and returning the gaseous carbon dioxide to storage after being compressed to a supercritical state by a compressor, then being cooled and adiabatically expanded. The system comprises a carbon dioxide supply unit, a carbon dioxide adiabatic storage tank, a drying and filtering unit, an evaporation heat exchange unit, a gas-liquid separation unit, a compressor and a gas cooling unit. The cooling method realizes the resource utilization of the carbon dioxide of the power plant and the cascade recovery of heat, and applies the transcritical CO2 closed transcritical circulation framework to the direct cooling of a large permanent magnet synchronous motor of a coal preparation plant.

Description

Technical Field

[0001] This invention relates to the technical field of low-carbon and energy-saving technologies, specifically to a cooling method and system for a closed-loop carbon dioxide cycle. Background Technology

[0002] High-power, large-scale permanent magnet synchronous motors, due to their high efficiency and energy saving characteristics, have been widely adopted in modern coal preparation plants, undertaking the driving tasks of key processes such as raw coal conveying, media circulation, and ventilation separation. These motors operate continuously at full load for 24 hours a day. During operation, the stator windings and rotor permanent magnets continuously generate a large amount of heat. Among them, the neodymium iron boron permanent magnets built into the rotor are extremely sensitive to temperature. Local overheating is the primary cause of permanent magnet motor failure and is the core problem restricting the safe and long-term operation of permanent magnet motors in coal preparation scenarios.

[0003] Currently, coal preparation plants mainly use air cooling or water cooling for high-power, large permanent magnet synchronous motors. Air cooling uses forced ventilation to dissipate heat, but its cooling efficiency is greatly affected by ambient temperature, and its effectiveness drops sharply in hot seasons. It also suffers from problems such as dust blockage and high noise. Water cooling involves installing water jackets or water-cooled pipelines on the equipment casing and using circulating water to remove heat. However, circulating water in coal preparation plants suffers from three major problems: scaling, corrosion, and leakage. It requires regular maintenance, and frequent shutdowns for repairs significantly reduce production efficiency. Furthermore, both methods only provide cooling from outside the equipment and cannot effectively control the temperature of the permanent magnets, which can easily lead to uneven temperature rise of the permanent magnets and poor cooling effect, potentially causing irreversible demagnetization.

[0004] On the other hand, with the advancement of dual carbon targets, the CCUS (carbon capture, utilization and storage) technology of coal-fired power plants is becoming increasingly mature. The high-purity liquid carbon dioxide captured needs to find a way to consume it on a large scale. Using the carbon dioxide captured by CCUS as a cooling medium for cooling large permanent magnet synchronous motors in coal preparation plants can not only realize the resource utilization of carbon, but also solve the industry pain points of existing cooling methods such as difficulty in cooling, high risk of demagnetization, and high operation and maintenance costs of traditional cooling methods.

[0005] While some other industries utilize carbon dioxide for industrial cooling, their technical solutions differ fundamentally from this one. For instance, the metallurgical industry uses liquid CO2 to cool quenching media, but this involves high-pressure air delivery and multiple tank switching, cooling an external medium rather than the equipment itself. In industries like sludge and chemicals, liquid CO2 is injected into sludge reactors as a reaction or cooling medium, typically for single-use or simple recycling. Neither of these solutions employs a closed-loop circulation architecture or integrates internal motor flow channels for targeted cooling. Neither can meet the core requirement of full-range stator and rotor cooling for permanent magnet motors in coal preparation plants. Currently, there is no integrated cooling solution for large permanent magnet synchronous motors in coal preparation plants that incorporates CCUS working fluid supply, closed-loop transcritical CO2 circulation, stator jacket heat exchange, rotor microchannel direct cooling, and waste heat recovery. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to realize the resource utilization of carbon dioxide and the cascade recovery of heat in power plants. It applies a transcritical CO2 closed-loop transcritical cycle architecture to the direct cooling of large permanent magnet synchronous motors in coal preparation plants and makes adaptive designs for the operating conditions of coal preparation plants.

[0007] To achieve the objectives of this invention, the following technical solution is adopted: The present invention provides a closed-loop carbon dioxide cooling method in a first aspect, comprising the following steps: S1. The working fluid containing liquid carbon dioxide captured by the power plant's CCUS unit is transported to a carbon dioxide insulated storage tank for storage. S2. The working fluid containing liquid carbon dioxide is dried and filtered before heat exchange to obtain a partially or completely vaporized carbon dioxide gas-liquid mixture; S3. The resulting carbon dioxide gas-liquid mixture is subjected to gas-liquid separation. The separated liquid carbon dioxide is recycled to the carbon dioxide adiabatic storage tank. The gaseous carbon dioxide is compressed to a supercritical state by a compressor, and then cooled and adiabatic expanded before being returned to the carbon dioxide adiabatic storage tank for storage.

[0008] In some embodiments, in S1, the working fluid containing liquid carbon dioxide has a carbon dioxide purity of ≥99.9%, a temperature of -20℃ to -15℃, and a pressure of 2 to 3 MPa.

[0009] In some embodiments, in S2, the working fluid containing liquid carbon dioxide is dried under conditions where the dew point temperature is below -40°C; Preferably, the dried and filtered liquid carbon dioxide enters the evaporative heat exchanger at a flow rate of 0.4~0.8 m / s to absorb heat from the motor for heat exchange. More preferably, the temperature of the carbon dioxide after heat exchange is 0~5℃ and the pressure is 2.6~2.7 MPa.

[0010] In some embodiments, in S3, the gaseous carbon dioxide is compressed to a supercritical state with a pressure of 8~12 MPa and a temperature of 80~120°C. Preferably, the flow rate of gaseous carbon dioxide at the inlet of the compressor is 3~5 m / s.

[0011] In some implementations, supercritical carbon dioxide is cooled to a subcritical state of 27-28°C and 9.0-9.2 MPa, and then adiabatically expanded to -8-0°C and 2.0-2.7 MPa.

[0012] In a second aspect, the present invention provides a system for the above-described cooling method, comprising: Carbon dioxide supply unit: Used to supply the system with a working fluid containing liquid carbon dioxide; Carbon dioxide insulated storage tank: used to receive and store the working fluid containing liquid carbon dioxide supplied by the carbon dioxide supply unit; Drying and filtration unit: used to adsorb moisture from the working fluid and filter solid particles; Evaporation heat exchange unit: used for heat exchange of the liquid carbon dioxide filtered out by the drying and filtration unit; Gas-liquid separation unit: used to separate the heat-exchanged material into gas and liquid phases, and the separated liquid carbon dioxide is recycled back into the carbon dioxide insulated storage tank; Compressor: Used to compress the separated gaseous carbon dioxide to a supercritical state; Gas cooling unit: used to cool supercritical carbon dioxide and then circulate it back into the carbon dioxide adiabatic storage tank.

[0013] In some embodiments, the evaporative heat exchange unit includes a housing, a motor, and an evaporative heat exchanger; The motor is located inside the housing and includes a stator and a rotor that are sleeved and connected together. The stator has a hollow cylindrical inner cavity, and the rotor is rotatably sleeved in the cylindrical inner cavity and cooperates with the stator. A heat exchange channel is provided inside the rotor. The evaporative heat exchanger includes a jacketed evaporator disposed outside the shell and heat exchange tubes disposed in the heat exchange channel. The heat exchange tubes are arranged axially along the heat exchange channel. The inlet of the jacketed evaporator is connected to the outlet of the carbon dioxide insulated storage tank to deliver a cooling medium into the jacketed evaporator. The outlet of the jacketed evaporator is connected to the inlet of the heat exchange tubes to provide directional cooling to the rotor. The outlet of the heat exchange tubes is connected to the gas-liquid separation unit.

[0014] In some embodiments, the carbon dioxide supply unit includes an insulated storage tank and a filter; The insulated storage tank is equipped with a liquid level sensor and an automatic replenishment mechanism to monitor and replenish the liquid carbon dioxide level.

[0015] In some embodiments, a circulation pump is provided between the drying and filtration unit and the evaporation heat exchange unit to drive the liquid carbon dioxide in the drying and filtration unit to circulate in the cooling system.

[0016] In some embodiments, a throttling valve is installed on the pipeline between the gas cooling unit and the carbon dioxide insulated storage tank; Preferably, a heat recovery unit is also provided between the compressor and the gas cooling unit to recover the heat from the supercritical carbon dioxide generated by the compressor.

[0017] The technical solution provided by this invention has the following beneficial effects: The carbon dioxide closed-loop cooling method provided by this invention uses high-purity liquid carbon dioxide captured by the power plant's CCUS as a dedicated closed-loop cooling medium for motors, constructing a complete closed loop for carbon resource utilization. The entire cooling method operates in a completely closed system with extremely low working medium loss, requiring only a small amount of carbon dioxide replenishment throughout the year, eliminating the need for continuous refueling of consumables. Simultaneously, it utilizes the carbon media produced by the power plant's CCUS, aligning with the coal industry's dual-carbon green transformation policy, and possessing both environmental protection and resource utilization value.

[0018] The cooling system provided by this invention adopts an integrated heat exchange structure with a stator jacketed evaporator connected in series with heat exchange tubes in the rotor cavity. Liquid carbon dioxide flows sequentially through the outer wall of the motor housing and the interior of the rotor permanent magnet, simultaneously carrying away heat from the stator windings and rotor hot spots. This completely solves the inherent defects of traditional water cooling and air cooling, which can only cool the motor housing and have heat dissipation blind spots in the rotor. It significantly reduces the risk of irreversible high-temperature demagnetization of NdFeB permanent magnets from the root, extending the service life of high-power permanent magnet synchronous motors. It completely avoids the problems of pipe scaling, corrosion, and leakage that exist in traditional water cooling, eliminating the need for periodic shutdowns for acid washing and pipe dredging, greatly reducing equipment downtime for maintenance and improving the continuous production efficiency of coal preparation plants. Attached Figure Description

[0019] Figure 1 The figure shows one embodiment of the closed-loop carbon dioxide circulation system provided by the present invention; Figure 2 As shown Figure 1 Cross-sectional view of the evaporative heat exchange unit; Figure 3 As shown Figure 2 Schematic diagram of the structure of the jacketed evaporator in the middle shell; The components include: 1. Carbon dioxide insulated storage tank; 2. Drying and filtration unit; 3. Circulating pump; 4. Evaporation heat exchange unit; 5. Gas-liquid separation unit; 6. Compressor; 7. Gas cooling unit; 8. Throttling valve; 9. Shell; 10. Stator; 11. Rotor; 12. Jacketed evaporator; and 13. Heat exchange tube. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0022] This invention provides a closed-loop carbon dioxide cooling method, comprising the following steps: S1. The working fluid containing liquid carbon dioxide captured by the power plant's CCUS unit is transported to a carbon dioxide insulated storage tank for storage. S2. The working fluid containing liquid carbon dioxide is dried and filtered before heat exchange to obtain a partially or completely vaporized carbon dioxide gas-liquid mixture; S3. The resulting carbon dioxide gas-liquid mixture is subjected to gas-liquid separation. The separated liquid carbon dioxide is recycled to the carbon dioxide adiabatic storage tank. The gaseous carbon dioxide is compressed to a supercritical state by a compressor, and then cooled and adiabatic expanded before being returned to the carbon dioxide adiabatic storage tank for storage.

[0023] In this invention, the CCUS device refers to a carbon capture, utilization and storage device.

[0024] In some embodiments, in S1 of the cooling method provided by the present invention, the purity of carbon dioxide in the working fluid containing liquid carbon dioxide is ≥99.9%, the temperature is -20℃ to -15℃, for example -18℃ or -16℃, and the pressure is 2 to 3 MPa, for example 2.5 MPa or 2.6 MPa.

[0025] In some embodiments, in step S2 of the cooling method provided by the present invention, the working fluid containing liquid carbon dioxide is dried under conditions where the dew point temperature is below -40°C. Preferably, the dried and filtered liquid carbon dioxide enters the evaporative heat exchanger at a flow rate of 0.4~0.8 m / s to absorb heat from the motor for heat exchange. More preferably, the temperature of the carbon dioxide after heat exchange is 0~5℃ and the pressure is 2.6~2.7 MPa.

[0026] In some embodiments, in step S3 of the cooling method provided by the present invention, the gaseous carbon dioxide is compressed to a supercritical state with a pressure of 8~12 MPa and a temperature of 80~120°C. Preferably, the flow rate of gaseous carbon dioxide at the inlet of the compressor is 3~5 m / s, for example, 4.0 m / s or 4.5 m / s.

[0027] In some embodiments, supercritical carbon dioxide is cooled to a subcritical state of 27-28°C and 9.0-9.2 MPa, and then adiabatically expanded to -8-0°C, for example -3°C or -5°C, and a pressure of 2.0-2.7 MPa, for example 2.2 MPa or 2.5 MPa.

[0028] The present invention also provides a system employing the above method, such as Figure 1 As shown, it includes: Carbon dioxide supply unit: Used to supply the system with a working fluid containing liquid carbon dioxide; Carbon dioxide insulated storage tank 1: Used to receive and store the working fluid containing liquid carbon dioxide supplied by the carbon dioxide supply unit; Drying and filtration unit 2: used to adsorb moisture in the working fluid and filter solid particles; Evaporation heat exchange unit 4: used for heat exchange of the liquid carbon dioxide filtered out by the drying and filtration unit 2; Gas-liquid separation unit 5: used to separate the heat-exchanged material into gas and liquid, and the separated liquid carbon dioxide is recycled back into the carbon dioxide insulated storage tank 1; Compressor 6: Used to compress the separated gaseous carbon dioxide to a supercritical state; Gas cooling unit 7: used to cool supercritical carbon dioxide and then circulate it back into the carbon dioxide adiabatic storage tank 1.

[0029] In some implementations, such as Figure 2 As shown, the evaporative heat exchange unit 4 includes a housing 9, a motor, and an evaporative heat exchanger; The motor is located inside the housing 9. The motor includes a stator 10 and a rotor 11 that are sleeved and connected. The stator 10 has a hollow cylindrical inner cavity. The rotor 11 is rotatably sleeved in the cylindrical inner cavity and cooperates with the stator 10. The rotor 11 has a heat exchange channel inside. The evaporative heat exchanger includes a jacketed evaporator 12 disposed outside the shell 9 (e.g., Figure 3(as shown) and heat exchange tube 13 arranged in the heat exchange channel. The heat exchange tube 13 is arranged along the axial direction of the heat exchange pipeline. The inlet of the jacketed evaporator 12 is connected to the outlet of the carbon dioxide insulated storage tank 1 to deliver cooling medium into the jacketed evaporator 12. The outlet of the jacketed evaporator 12 is connected to the inlet of the heat exchange tube 13 to directionally cool the rotor 11. The outlet of the heat exchange tube 13 is connected to the gas-liquid separation unit 5.

[0030] During the heat exchange process, liquid carbon dioxide flows sequentially through the heat exchange channels of the motor housing 9 and the permanent magnet rotor 11, simultaneously carrying away the heat from the stator winding 10 and the hot spots of the rotor 11. This completely solves the inherent defects of traditional water cooling and air cooling, which can only cool the motor housing and have heat dissipation blind spots in the rotor. It significantly reduces the risk of irreversible high-temperature demagnetization of NdFeB permanent magnets from the root, extending the service life of high-power permanent magnet synchronous motors. It completely avoids the problems of pipe scaling, corrosion, and leakage that exist in traditional water cooling, eliminating the need for periodic shutdowns for acid washing and pipe dredging, greatly reducing equipment downtime for maintenance and improving the continuous production efficiency of coal preparation plants.

[0031] In some embodiments, the carbon dioxide supply unit includes an insulated storage tank and a filter; wherein the insulated storage tank is equipped with a level sensor and an automatic replenishment mechanism to realize the level monitoring and replenishment of liquid carbon dioxide.

[0032] In some embodiments, a circulation pump 3 is provided between the drying and filtration unit 2 and the evaporation heat exchange unit 4 to drive the liquid carbon dioxide in the drying and filtration unit 2 to circulate in the cooling system.

[0033] In some embodiments, a throttling valve 8 is installed on the pipeline between the gas cooling unit 7 and the carbon dioxide insulated storage tank 1; Preferably, a heat recovery unit is also provided between the compressor 6 and the gas cooling unit 7 to recover the heat from the supercritical carbon dioxide produced by the compressor 6. Specifically, a heat recovery unit with a bypass valve is provided between the compressor 6 and the gas cooling unit 7, and the supercritical / subcritical operating conditions within the same cycle are adaptively switched by opening and closing the bypass. In winter, the bypass is closed, and the high-temperature waste heat from the supercritical carbon dioxide is recovered, which can be used for heating in the plant workshop and preheating raw coal for antifreeze purposes, with the recovered heat replacing boiler energy consumption; in summer, the bypass is opened, and the working fluid is directly fed into the gas cooling unit 7 for full-load heat dissipation, taking into account both the cooling needs throughout the year and the cascade recovery of waste heat, significantly reducing the overall energy consumption of the system.

[0034] The present invention will be further illustrated below with specific examples, but it should not be construed as the present invention being limited to these examples.

[0035] Where specific experimental steps or conditions are not specified in the embodiments, the corresponding conventional experimental steps or conditions in this technical field can be followed.

[0036] A 5m3 The insulated storage tank is used to store liquid carbon dioxide from the power plant's CCUS (Combustion Control System). The tank is filled with approximately 3 tons of working fluid containing liquid carbon dioxide (purity ≥99.9%, temperature -18℃, pressure 2.5 MPa). During operation, a circulating pump dries the liquid carbon dioxide in the insulated storage tank at approximately -18℃ and 2.5 MPa under a dew point of -40℃, filtering out solid particles with a diameter ≥10μm. The filtered liquid carbon dioxide is then fed into the evaporative heat exchanger at a flow rate of 0.4~0.8 m / s. The liquid carbon dioxide flows sequentially through the outer wall of the motor casing and the interior of the rotor permanent magnet, simultaneously carrying away heat from the stator windings and rotor hot spots. After heat exchange, the temperature of the carbon dioxide rises to approximately 5℃, and the pressure to approximately 2.7 MPa.

[0037] The carbon dioxide gas-liquid mixture, after evaporation and heat exchange, enters the gas-liquid separator. Since it has been completely vaporized, no liquid returns from the separator, and the pure gaseous carbon dioxide enters the compressor. The working fluid velocity at the compressor inlet is approximately 3~5 m / s. The compressor compresses the gaseous carbon dioxide to a supercritical state with a pressure of 9.5 MPa and a temperature of 95℃.

[0038] High-temperature and high-pressure supercritical carbon dioxide enters the gas cooler, where it is cooled by forced ventilation and heat dissipation by a fan to a subcritical state of high-pressure liquid carbon dioxide at 28°C and 9.2 MPa. The liquid carbon dioxide undergoes adiabatic expansion and pressure reduction through an electronic throttle valve to 2.7 MPa and -8°C, forming a gas-liquid two-phase mixture before returning to the storage tank, completing one cycle.

[0039] During the above operation, the stator temperature in the motor dropped to around 67°C, and the temperature of the rotor permanent magnet in the motor dropped from 98°C to around 73°C, effectively avoiding the risk of demagnetization. The closed-loop system results in extremely low working fluid loss, requiring only about 15 kg of carbon dioxide to be replenished annually, with almost no operating consumption, significantly reducing power consumption and greatly reducing the workload of equipment maintenance.

Claims

1. A closed-loop carbon dioxide cooling method, characterized in that, Includes the following steps: S1. The working fluid containing liquid carbon dioxide captured by the power plant's CCUS unit is transported to a carbon dioxide insulated storage tank for storage. S2. The working fluid containing liquid carbon dioxide is dried and filtered before heat exchange to obtain a partially or completely vaporized carbon dioxide gas-liquid mixture; S3. The resulting carbon dioxide gas-liquid mixture is subjected to gas-liquid separation. The separated liquid carbon dioxide is recycled to the carbon dioxide adiabatic storage tank. The gaseous carbon dioxide is compressed to a supercritical state by a compressor, and then cooled and adiabatic expanded before being returned to the carbon dioxide adiabatic storage tank for storage.

2. The cooling method according to claim 1, characterized in that, In S1, the working medium containing liquid carbon dioxide has a carbon dioxide purity of ≥99.9%, a temperature of -20℃ to -15℃, and a pressure of 2 to 3 MPa.

3. The cooling method according to claim 2, characterized in that, In S2, the working fluid containing liquid carbon dioxide is dried under conditions where the dew point temperature is below -40°C; Preferably, the dried and filtered liquid carbon dioxide enters the evaporative heat exchanger at a flow rate of 0.4~0.8 m / s to absorb heat from the motor for heat exchange. More preferably, the temperature of the carbon dioxide after heat exchange is 0~5℃ and the pressure is 2.6~2.7 MPa.

4. The cooling method according to claim 3, characterized in that, In S3, the gaseous carbon dioxide is compressed to reach a supercritical state with a pressure of 8~12 MPa and a temperature of 80~120℃. Preferably, the flow rate of gaseous carbon dioxide at the inlet of the compressor is 3~5 m / s.

5. The cooling method according to any one of claims 1 to 4, characterized in that, Supercritical carbon dioxide is cooled to a subcritical state of 27~28℃ and 9.0~9.2 MPa, and then adiabatically expanded to -8~0℃ and 2.0~2.7 MPa.

6. A system employing the cooling method according to any one of claims 1 to 5, characterized in that, The system includes: Carbon dioxide supply unit: Used to supply the system with a working fluid containing liquid carbon dioxide; Carbon dioxide insulated storage tank: used to receive and store the working fluid containing liquid carbon dioxide supplied by the carbon dioxide supply unit; Drying and filtration unit: used to adsorb moisture from the working fluid and filter solid particles; Evaporation heat exchange unit: used for heat exchange of the liquid carbon dioxide filtered out by the drying and filtration unit; Gas-liquid separation unit: used to separate the heat-exchanged material into gas and liquid phases, and the separated liquid carbon dioxide is recycled back into the carbon dioxide insulated storage tank; Compressor: Used to compress the separated gaseous carbon dioxide to a supercritical state; Gas cooling unit: used to cool supercritical carbon dioxide and then circulate it back into the carbon dioxide adiabatic storage tank.

7. The system according to claim 6, characterized in that, The evaporative heat exchange unit includes a shell, a motor, and an evaporative heat exchanger; The motor is located inside the housing and includes a stator and a rotor that are sleeved and connected together. The stator has a hollow cylindrical inner cavity, and the rotor is rotatably sleeved in the cylindrical inner cavity and cooperates with the stator. A heat exchange channel is provided inside the rotor. The evaporative heat exchanger includes a jacketed evaporator disposed outside the shell and heat exchange tubes disposed in the heat exchange channel. The heat exchange tubes are arranged axially along the heat exchange channel. The inlet of the jacketed evaporator is connected to the outlet of the carbon dioxide insulated storage tank to deliver a cooling medium into the jacketed evaporator. The outlet of the jacketed evaporator is connected to the inlet of the heat exchange tubes to provide directional cooling to the rotor. The outlet of the heat exchange tubes is connected to the gas-liquid separation unit.

8. The system according to claim 7, characterized in that, The carbon dioxide supply unit includes an insulated storage tank and a filter; The insulated storage tank is equipped with a liquid level sensor and an automatic replenishment mechanism to monitor and replenish the liquid carbon dioxide level.

9. The cooling system according to any one of claims 6 to 8, characterized in that, A circulation pump is provided between the drying and filtration unit and the evaporation heat exchange unit to drive the liquid carbon dioxide in the drying and filtration unit to circulate in the cooling system.

10. The cooling system according to claim 9, characterized in that, A throttling valve is installed on the pipeline between the gas cooling unit and the carbon dioxide insulated storage tank. Preferably, a heat recovery unit is also provided between the compressor and the gas cooling unit to recover the heat from the supercritical carbon dioxide generated by the compressor.

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