Carbon dioxide energy storage and geothermal heat supplement system based on coaxial sleeve and operation method

Abstract

This invention discloses a carbon dioxide energy storage and geothermal heat replenishment system and its operation method based on a coaxial sleeve. The system includes a carbon dioxide compressor unit, a carbon dioxide expander unit, a modified coaxial sleeve buried pipe, a heat pump system, a throttling cold storage device, and a liquid storage tank. By modifying the existing coaxial sleeve and utilizing its original properties, the space inside the pipe is used to store liquid carbon dioxide, reducing the use of the liquid storage tank and ground space, and improving the system's economy and safety. The high-temperature source water stored in the annular pipe space enables the replenishment of geothermal energy and the sustainable utilization of geothermal energy during non-heating periods. The modified spiral flow channel also solves the problem of varying heat replenishment demand at different depths during geothermal replenishment. During energy release, the medium-temperature source water stored in the annular pipe space that has completed heat replenishment is extracted and used as a heat source for the heat pump system to utilize the waste heat of the source water, achieving cascade utilization of thermal energy.

Description

Technical Field

[0001] This invention belongs to the field of physical energy storage technology, specifically relating to a carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve and its operation method. Background Technology

[0002] With the rapid growth of total installed capacity of new energy sources, addressing the instability and intermittency of power generation has become a major challenge for the large-scale utilization of new energy. Energy storage is one of the main solutions, and by 2025, my country's installed capacity of new energy storage will reach over 30 million kW. Among new energy storage technologies, electrochemical energy storage and compressed air energy storage are the most mature. However, electrochemical energy storage facilities have not yet formed a universally accepted safety solution, posing safety hazards such as fire and explosion. In comparison, compressed air energy storage is safer and has advantages such as large storage capacity, long discharge time, long service life, and wide applicability of heat, cold, and electricity. In recent years, with increased understanding and research into compressed air energy storage technology, several large-scale compressed air energy storage power plants have been built.

[0003] Compressed air energy storage facilities come in various forms, including high-pressure gas tanks, cryogenic storage tanks, abandoned mine shafts, newly built caverns, and salt caverns. While converting caverns for gas storage offers advantages such as large capacity and low cost, resources are limited and geographical constraints apply. Utilizing man-made gas tanks eliminates geographical limitations, but as energy storage systems increase in scale and demand higher airtightness and pressure resistance from high-pressure tanks, costs become prohibitively high, resulting in low economic viability. To overcome the heavy reliance on large storage spaces, compressed air energy storage systems have developed new technologies based on liquid air. Liquid air energy storage systems offer advantages such as high energy density and no geographical limitations; however, air has a very low critical temperature, requiring excellent insulation to ensure its stability. Furthermore, cryogenic air can cause many common materials to become brittle or even fracture under stress, posing potential hazards to liquid air energy storage systems. Compared to air, carbon dioxide, as a working medium, has the advantage of a high critical temperature and is easily liquefied. In addition, liquid carbon dioxide energy storage systems offer better safety and flexibility, showing broad application prospects.

[0004] Geothermal energy is the thermal energy stored within the Earth's interior. It includes heat energy generated from the decay of radioactive elements deep within the Earth, as well as heat energy from the Earth's interior and solar radiation in the shallow layers. It is a renewable energy source with enormous development potential, widely utilized due to its abundant total amount, high energy density, wide distribution, green and low-carbon nature, strong applicability, and good stability. However, after years of geothermal energy development and utilization, geothermal resource parameters in many areas have declined significantly. Because geothermal energy recovers slowly under natural conditions, artificial heating is necessary to alleviate geothermal energy depletion, protect geothermal resources, and guide the future path towards sustainable development. This is generally achieved through hot water reinjection technology, which is the reverse process of geothermal energy extraction.

[0005] The development of medium-deep geothermal energy mainly utilizes buried pipe heat exchangers, which are primarily divided into coaxial sleeve type and U-tube type. The coaxial sleeve type involves burying a slender coaxial sleeve underground, using water as the flowing heat exchange medium within the pipe for heat extraction. This heat extraction method, also known as sleeve heat exchange, relies on heat conduction to exchange heat with the ground, thus developing geothermal energy in a "heat extraction without water extraction" manner. It does not consume or pollute groundwater and has no potential geological hazards. Geothermal heating typically occurs in winter. During the long non-heating season, the coaxial sleeve is essentially idle. This invention modifies the coaxial sleeve to replace the storage tank required for liquid carbon dioxide energy storage systems, reducing equipment costs. Furthermore, it utilizes the heat generated from compressing carbon dioxide by a carbon dioxide compressor unit to supplement the geothermal energy, achieving sustainable utilization of geothermal energy. Summary of the Invention

[0006] To address the problems in the existing technology, the present invention aims to provide a carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve and its operation method. During the non-heating period of geothermal energy, the idle coaxial sleeve is modified to not only meet the needs of the liquid carbon dioxide energy storage system for working fluid storage space, but also to use the compression heat generated by the energy storage system during the energy storage stage to uniformly replenish the ground, protect geothermal resources, and realize the sustainable utilization of geothermal energy.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve, comprising a carbon dioxide compressor unit, a carbon dioxide expander unit, a coaxial sleeve, a heat pump system, a throttling cold storage device, and a storage tank; the coaxial sleeve includes an inner tube and an outer tube arranged coaxially, the inner side of the inner tube is an inner tube pipe space, and an annular pipe space is formed between the outer tube and the inner tube, and an isolation plate with the same outer diameter as the inner tube is provided at the bottom of the channel opening of the inner tube of the coaxial sleeve; the carbon dioxide compressor unit includes at least two stages of compressors, and a water cooler is provided at the outlet of each stage of compressor, the cold medium of the water cooler... All outlets are connected to the inner pipe space, and the outlet of the hot medium of the highest-level water cooler is connected to the annular pipe space; the carbon dioxide expander unit includes at least two expanders, and a condenser is installed at the inlet of each expander. The condenser is installed in the heat pump system to cool the working medium of the heat pump system. The condenser at the inlet of the first-stage expander is connected to the outlet of the inner pipe space, and the outlet of the annular pipe space is connected to the heat source inlet of the heat pump system. The outlet of the carbon dioxide expander unit is connected in sequence to the throttling cold storage device and the liquid storage tank. The outlet of the throttling cold storage device is also connected to the inlet of the carbon dioxide compressor unit; the coaxial sleeve is a buried pipe, and multiple ones are installed.

[0008] The carbon dioxide compressor unit includes a low-pressure compressor and a high-pressure compressor. A first water cooler is installed at the outlet of the low-pressure compressor, and a second water cooler is installed at the outlet of the high-pressure compressor. The hot side of the first water cooler is connected to both the low-pressure compressor and the high-pressure compressor, and the cold side of the first water cooler is connected to a water source and an annular pipe space. A first water pump is installed between the water source outlet and the first water cooler. The hot side of the second water cooler is connected to both the high-pressure compressor and the inner pipe space. The inlet of the low-pressure compressor is connected to the outlet of the throttling cold storage device. A second water pump is installed at the outlet of the annular pipe space.

[0009] The heat pump system includes an evaporator, a compressor, a second condenser, a first condenser, and an expansion valve. The hot-side inlet of the evaporator serves as the heat source inlet of the heat pump system, the hot-side outlet of the evaporator is connected to a water source, the cold-side inlet and outlet of the evaporator are connected to the compressor and the expansion valve, the outlet of the compressor is connected to the hot-side inlets of the second condenser and the first condenser, respectively, and the hot-side outlets of the second condenser and the first condenser are both connected to the inlet of the expansion valve.

[0010] The carbon dioxide expander unit includes a high-pressure expander and a low-pressure expander arranged along the medium flow direction. The cold side of the first condenser is connected to the outlet of the inner pipe space and the inlet of the high-pressure expander, respectively. The cold side of the second condenser is connected to the high-pressure expander and the low-pressure expander, respectively. The low-pressure expander is connected to the inlet of the throttling cold storage device. The high-pressure expander and the low-pressure expander are connected to the generator.

[0011] The throttling cold storage device includes a cold storage unit and a throttling valve. The outlet of the cold storage unit is connected to a liquid storage tank, the outlet of the liquid storage tank is connected to the throttling valve, and the outlet of the throttling valve is connected in sequence to the cold storage unit and the compressor unit inlet.

[0012] The inner tube is made of heat-insulating material, and the outer tube is made of heat-conducting material; the isolation plate is made of heat-insulating material and has a cavity inside it, which is filled with inert gas.

[0013] The entire inner tube is welded with spiral fins, the width of which is equal to the width of the annular pipe space, dividing the entire annular pipe space into spirally descending flow channels. Taking the inner spiral line of the spiral fins as the reference, the inner spiral line at the ground end is the starting end. As the inner spiral line extends downward, its pitch decreases by 10-20m per turn. In the annular pipe space, the pitch of the spiral fins decreases with the increase of the underground depth.

[0014] Based on the operation method of the carbon dioxide energy storage and geothermal heat replenishment system described in this invention, during the energy storage stage, liquid carbon dioxide is released from the storage tank and enters the throttling cold storage device. After being heated by throttling, the gaseous carbon dioxide enters the carbon dioxide compressor unit for stage compression. At the same time, the source water is used as the cooling medium of the water cooler to cool the high-temperature carbon dioxide after the compressor stage. After being cooled by the water cooler, the liquid carbon dioxide flowing out from the hot side outlet of the water cooler enters the inner pipe space and is stored in the inner pipe space in liquid form. The source water on the cold side of the water cooler is heated by the high-temperature carbon dioxide, collected and passed into the annular pipe space for storage. The heat of the high-temperature water is transferred from the annular pipe space to the surrounding area outside the coaxial sleeve.

[0015] During the energy release phase, the high-temperature source water stored in the annular pipe space and having completed geothermal replenishment is transformed into medium-temperature source water. This medium-temperature source water is then introduced into the heat source inlet of the heat pump system from the annular pipe space, serving as a heat source to provide heat to the system. The heat pump system then begins operation. After completing the heating process, the low-temperature source water is reintroduced into the source water. Simultaneously, liquid carbon dioxide is introduced from the outlet of the inner pipe space into the cold side inlet of the first condenser and heated into high-temperature, high-pressure gaseous carbon dioxide. This gaseous carbon dioxide enters the expander unit to perform work, and the expander unit operates, driving the generator to generate electricity. The carbon dioxide exhaust gas flowing out of the expander unit continues to flow into the throttling cold storage device and is condensed into liquid carbon dioxide, which is then stored in the storage tank.

[0016] The carbon dioxide compressor unit includes a low-pressure compressor and a high-pressure compressor. A first water cooler is installed at the outlet of the low-pressure compressor, and a second water cooler is installed at the outlet of the high-pressure compressor. The hot side of the first water cooler is connected to both the low-pressure compressor and the high-pressure compressor, and the cold side of the first water cooler is connected to a water source and an annular pipe space. A first water pump is installed between the water source outlet and the first water cooler. The hot side of the second water cooler is connected to both the high-pressure compressor and the inner pipe space. The inlet of the low-pressure compressor is connected to the outlet of the throttling cold storage device. A second water pump is installed at the outlet of the annular pipe space.

[0017] The first water pump drives the source water as the cooling medium for the first and second water coolers to cool the high-temperature carbon dioxide after the compressor stage. After being cooled by the second water cooler, the liquid carbon dioxide flowing out from the hot side outlet of the second water cooler enters the inner pipe space. The source water on the cold side of the first and second water coolers is heated by the high-temperature carbon dioxide, and then collected and passed into the annular pipe space for storage.

[0018] The heat pump system includes an evaporator, a compressor, a second condenser, a first condenser, and an expansion valve. The hot-side inlet of the evaporator serves as the heat source inlet of the heat pump system, the hot-side outlet of the evaporator is connected to a water source, the cold-side inlet and outlet of the evaporator are connected to the compressor and the expansion valve, the outlet of the compressor is connected to the hot-side inlets of the second condenser and the first condenser respectively, and the hot-side outlets of the second condenser and the first condenser are both connected to the inlet of the expansion valve. The carbon dioxide expander unit includes a high-pressure expander and a low-pressure expander arranged along the medium flow direction. The cold side of the first condenser is connected to the outlet of the inner pipe space and the inlet of the high-pressure expander respectively, the cold side of the second condenser is connected to the high-pressure expander and the low-pressure expander respectively, the low-pressure expander is connected to the inlet of the throttling cold storage device, and the high-pressure expander and the low-pressure expander are connected to a generator.

[0019] Driven by the second water pump, medium-temperature source water is introduced into the hot-side inlet of the evaporator through the annular pipe space outlet. After heating is completed, low-temperature source water is reintroduced into the water source. At the same time, liquid carbon dioxide is introduced into the cold-side inlet of the first condenser of the heat pump system through the inner pipe space outlet and is heated into gaseous high-temperature and high-pressure gaseous carbon dioxide. The gaseous carbon dioxide enters the high-pressure expander and expands to do work, becoming exhaust gas. The exhaust gas is heated by the working fluid on the hot side of the second condenser of the heat pump and then introduced into the low-pressure expander to continue expanding and doing work. The two-stage expanders operate and drive the generator to generate electricity. The carbon dioxide exhaust gas flowing out of the low-pressure expander outlet continues to enter the throttling cold storage device and is condensed into liquid carbon dioxide, which is then stored in the liquid storage tank.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a coaxial sleeve geothermal heat exchange structure in which two pipes with different diameters are nested together along their coincident axes, and the bottom of the outer pipe is sealed. Circulating water flows from the ground into the annular pipe formed by the inner and outer pipes. Due to the temperature difference between the water and the underground soil, geothermal heat is conducted into the pipe. The outer pipe uses a high thermal conductivity. The circulating water that completes geothermal heat collection at the bottom of the coaxial sleeve flows upward from the inner pipe to complete heat extraction. The inner pipe is made of insulating material to prevent the high-temperature circulating water in the inner pipe from transferring heat to the medium- and low-temperature circulating water in the annular pipe. This is achieved through the coaxial... An isolation plate with the same size as the outer diameter of the inner tube is installed at the bottom of the channel opening of the inner tube. The isolation plate is made of heat-insulating material and has a cavity filled with inert gas inside to enhance its heat insulation performance. The inner tube forms a heat-insulated and independent space. Liquid carbon dioxide is introduced into the inner tube space for storage, which reduces the use of storage tanks and ground space and improves economy. The modified inner tube space has good heat insulation performance, which prevents the stored liquid carbon dioxide from absorbing heat and vaporizing during energy storage. In addition, the carbon dioxide is stored underground, which has strong stability and can be quickly remedied even if a gas leak occurs.

[0021] Furthermore, based on the basic principle of heat extraction from coaxial tube heat exchangers, the outer tube material is made of a material with high thermal conductivity. Therefore, the high-temperature source water stored in the annular pipe space can quickly transfer heat to the surrounding area of ​​the coaxial tube, realizing the supplementation of geothermal energy and sustainable utilization of geothermal energy during non-heating periods, alleviating geothermal energy decay and protecting geothermal resources. In addition to driving the circulation of water, the first water pump also increases the water saturation temperature by pressurizing to ensure that the source water does not vaporize when heated.

[0022] Furthermore, spiral fins with a width equal to the difference in diameter between the inner and outer pipes are welded onto the entire inner pipe, dividing the entire annular pipe space into flow channels that spiral downwards around the inner pipe. Taking the inner spiral line of the spiral fins as the reference, and the inner spiral line at the ground end as the starting point, as the number of coils of the inner spiral increases, its pitch decreases by 10-20m per coil, depending on the inlet water flow rate of the annular pipe space. The larger the water flow rate, the smaller the pitch reduction needs to be. In the annular pipe space, because the pitch of the spiral fins decreases with the increase of underground depth, the spiral flow trend of high-temperature water from top to bottom in the spiral flow channel becomes slower, that is, the high-temperature water stays in the annular space deeper than the ground for a longer time. Since the ground temperature is positively correlated with the underground depth, the greater the depth, the greater the temperature difference for heat extraction and the higher the heat extraction, allowing more heat energy to be replenished from the deeper underground layers that have lost more heat.

[0023] Furthermore, during energy release, a second water pump is driven to extract the medium-temperature source water stored in the annular pipe space that has undergone geothermal replenishment. This water is then used as a heat source for the heat pump system, utilizing the waste heat of the source water to achieve cascaded utilization of thermal energy. Taking advantage of the heat pump system's high cycle efficiency and strong heat collection capacity, and using the medium-temperature source water that has completed geothermal replenishment as a heat source, the heat collected by the heat pump is used to heat the carbon dioxide at the outlet of the inner pipe space and the outlet of the high-pressure expander during energy release. This carbon dioxide is transformed into high-temperature, high-pressure gaseous carbon dioxide, which then sequentially enters the high-pressure expander and the low-pressure expander to perform work and drive the generator to generate electricity. Attached Figure Description

[0024] Figure 1 This is a diagram of a carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve according to the present invention.

[0025] Figure 2 This is a cross-sectional schematic diagram of an isolation plate structure according to the present invention.

[0026] Figure 3 This is a schematic diagram of a spiral fin of the present invention.

[0027] Figure 4 This is a schematic diagram of a coaxial sleeve inner tube for welding spiral fins according to the present invention.

[0028] Figure 5 This is a schematic diagram of a modified coaxial sleeve structure according to the present invention.

[0029] Figure 6 This is a schematic diagram of the upper cross-section of a modified coaxial sleeve structure according to the present invention.

[0030] Figure 7 This is a schematic diagram of the bottom cross-section of a modified coaxial sleeve structure according to the present invention.

[0031] In the attached diagram, 1-low-pressure compressor, 2-high-pressure compressor, 3-water source, 4-first water pump, 5-first water cooler, 6-second water cooler, 7-coaxial sleeve, 8-second water pump, 9-first condenser, 10-second condenser, 11-expansion valve, 12-evaporator, 13-compressor, 14-high-pressure expander, 15-low-pressure expander, 16-cold accumulator, 17-liquid storage tank, 18-throttle valve, 19-annular pipe space, 20-inner pipe space, 21-spiral fin, 22-isolation plate. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings:

[0033] Please see Figure 1The present invention provides a carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve, comprising a carbon dioxide compressor unit, a carbon dioxide expander unit, a coaxial sleeve 7, a circulating water system, a heat pump system, a throttling cold storage device, and a liquid storage tank; the circulating water system includes a water source 3, a first water pump 4, a second water pump 8, and a first water cooler 5 and a second water cooler 6 connected in parallel; the heat pump system includes a compressor 13, an evaporator 12, an expansion valve 11, and a first condenser 9 and a second condenser 10 connected in parallel; the carbon dioxide compressor unit is divided into two stages: a low-pressure compressor 1 and a high-pressure compressor 2, and the outlet of each stage compressor is connected to the water cooler of the circulating water system to cool the carbon dioxide to reduce the power consumption of the compressor unit; the cooling medium of the water cooler is water from a natural water source or a reservoir, and driven by the first water pump 4, water from the water source 3 enters from the cold side of the first water cooler 5 and the second water cooler 6 and absorbs the heat of compression from the carbon dioxide on the hot side;

[0034] The coaxial sleeve includes an inner pipe space 20 and an outer pipe arranged coaxially. An annular pipe space 19 is formed between the outer pipe and the outer wall of the inner pipe space 20. An isolation plate 22 with the same size as the outer diameter of the inner pipe is installed at the bottom opening of the inner pipe. (Refer to...) Figure 2 and Figure 7 The carbon dioxide compressor unit includes at least two stages of compressors. Each stage of compressor has a water cooler at its outlet. The cold medium outlet of each water cooler is connected to the inner pipe space 20. The hot medium outlet of the highest stage water cooler is connected to the annular pipe space 19. The carbon dioxide expander unit includes at least two stages of expanders. Each stage of expander has a condenser at its inlet. The condenser is installed in the heat pump system to cool the working fluid of the heat pump system. The condenser at the inlet of the first stage expander is connected to the outlet of the inner pipe space 20. The outlet of the annular pipe space 19 is connected to the heat source inlet of the heat pump system. The outlet of the carbon dioxide expander unit is connected in sequence to the throttling cold storage device and the liquid storage tank 17. The outlet of the throttling cold storage device is also connected to the inlet of the carbon dioxide compressor unit. The coaxial sleeve 7 is a buried pipe and multiple of them are installed.

[0035] refer to Figure 1 and Figure 2The underground pipes used in the renovation employ coaxial sleeves, commonly used in medium-deep geothermal heat extraction projects. The coaxial sleeve and its basic principle involve fitting two pipes of different diameters together along their coincident axes. Through a geothermal heat exchanger connected at the bottom of the pipes, during the heating phase, cold water flows from top to bottom through the annular pipe space, absorbing geothermal energy and becoming hot water, which then flows out from bottom to top through the inner pipe, thus extracting geothermal energy. To facilitate geothermal energy absorption, the outer pipe is made of a material with high thermal conductivity, while the inner pipe is made of a material with low thermal conductivity to facilitate the insulation of the medium within the inner pipe. During the non-heat extraction phase of the medium-deep geothermal system, the inner pipe of the coaxial sleeve... An isolation plate 22 with the same size as the outer diameter of the inner tube is installed at the bottom channel opening, so that two independent spaces are formed inside the coaxial sleeve: the inner tube pipe space 20 and the annular pipe space 19 formed by the inner and outer tubes. The isolation plate 22 is made of heat-insulating material and has a cavity inside it. Rare gases such as helium or argon are filled into the cavity to increase the heat exchange thermal resistance and enhance its heat insulation performance. The existing coaxial sleeve is based on the basic principle of heat extraction of the sleeve heat exchanger: its inner tube material is made of a material with low thermal conductivity. Therefore, the inner tube forms a basically heat-insulated and independent space by adding the isolation plate 22, which provides conditions for the storage of liquid carbon dioxide.

[0036] The carbon dioxide compressor unit includes a low-pressure compressor 1 and a high-pressure compressor 2. A first water cooler 5 is installed at the outlet of the low-pressure compressor 1, and a second water cooler 6 is installed at the outlet of the high-pressure compressor 2. The hot side of the first water cooler 5 is connected to both the low-pressure compressor 1 and the high-pressure compressor 2, respectively. The cold side of the first water cooler 5 is connected to a water source 3 and an annular pipe space 19, respectively. A first water pump 4 is installed between the outlet of the water source 3 and the first water cooler 5. The hot side of the second water cooler 6 is connected to the high-pressure compressor 2 and the inner pipe space 20, respectively. The inlet of the low-pressure compressor 1 is connected to the outlet of a throttling cold storage device. A second water pump 8 is installed at the outlet of the annular pipe space 19. The heat pump system includes an evaporator 12, a compressor 13, a second condenser 10, a first condenser 9, and an expansion valve 11. The hot side inlet of the evaporator 12 serves as... The heat source inlet of the heat pump system is connected to the water source 3 via the hot side outlet of the evaporator 12. The cold side inlet and outlet of the evaporator are connected to the compressor 13 and the expansion valve 11. The outlet of the compressor 13 is connected to the hot side inlet of the second condenser 10 and the first condenser 9, respectively. The hot side outlets of the second condenser 10 and the first condenser 9 are both connected to the inlet of the expansion valve 11. The carbon dioxide expander unit includes a high-pressure expander 14 and a low-pressure expander 15 arranged along the medium flow direction. The cold side of the first condenser 9 is connected to the outlet of the inner pipe space 20 and the inlet of the high-pressure expander 14, respectively. The cold side of the second condenser 10 is connected to the high-pressure expander 14 and the low-pressure expander 15, respectively. The low-pressure expander 15 is connected to the inlet of the throttling cold storage device. The high-pressure expander 14 and the low-pressure expander 15 are connected to the generator.

[0037] The throttling cold storage device includes a cold storage 16 and a throttling valve 18. The outlet of the cold storage 16 is connected to a liquid storage tank 17. The outlet of the liquid storage tank 17 is connected to the throttling valve 18. The outlet of the throttling valve 18 is connected in sequence to the cold storage 16 and the compressor unit inlet.

[0038] refer to Figure 1 The high-temperature, high-pressure gaseous carbon dioxide from the outlet of the high-pressure compressor 2 is cooled by the water source of the second water cooler 6 and becomes liquid carbon dioxide. The hot side outlet of the second water cooler 6 is connected to the inlet of the inner pipe space, allowing the liquid carbon dioxide to be introduced into the inner pipe space 20 for storage. This reduces the use of storage tanks and ground space, improving economic efficiency. The modified inner pipe space has good thermal insulation performance, preventing the stored liquid carbon dioxide from absorbing heat and vaporizing during energy storage. Moreover, the carbon dioxide is stored underground, which has good stability, and even if a gas leak occurs, it can be quickly remedied.

[0039] refer to Figure 1 Water source water flows out from the cold side outlet of the first water cooler 5 and the second water cooler 6. Due to the heat of compression from absorbing high-temperature carbon dioxide, it forms high-temperature water source water. After collection, it is introduced into the annular pipe space 19 and stored in the annular pipe space. Based on the basic principle of heat extraction of the shell and tube heat exchanger, its outer tube material is made of a material with high thermal conductivity. Therefore, the high-temperature water stored in the annular pipe space can quickly transfer heat to the coaxial shell 7 and outward, realizing the supplementation of geothermal energy during non-heating periods and realizing the sustainable use of geothermal energy. In addition to driving the circulation of water, the first water pump 4 also increases the water saturation temperature by pressurizing to ensure that the water source water does not vaporize when heated.

[0040] refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 The entire inner pipe is welded with spiral fins. The width of the spiral fins 21 should be equal to the width of the annular pipe space. Therefore, the entire annular pipe space 19 is divided into spiral descending channels. Taking the inner spiral line of the spiral fins as the reference, the inner spiral line at the ground end is the starting end. As the number of inner spiral coils increases, the pitch decreases by 10-20m per coil, depending on the inlet water flow rate of the annular pipe space. The larger the water flow rate, the smaller the pitch reduction needs to be. In the annular pipe space, since the pitch of the spiral fins decreases with the increase of the underground depth, the spiral flow trend of high-temperature water from top to bottom in the spiral channel becomes slower. That is, the high-temperature water stays in the annular space deeper than the ground for a longer time. Since the ground temperature is positively correlated with the underground depth, the greater the depth, the greater the temperature difference for heat extraction and the higher the heat extraction. Therefore, this modification can allow more heat energy to be replenished from the deeper underground layers that have more heat loss.

[0041] refer to Figure 1The outlet of the annular pipe space 19 is connected to the inlet of the second water pump 8, the outlet of the second water pump 8 is connected to the hot side inlet of the evaporator 12 of the heat pump system, and the hot side outlet of the evaporator 12 is connected to the water source 3. When releasing energy, the medium-temperature water source stored in the annular pipe space 19 that has completed geothermal supplementation is extracted by driving the second water pump and used as the heat source of the heat pump system to utilize the waste heat of the water source and realize the cascade utilization of thermal energy.

[0042] refer to Figure 1 The outlet of the inner pipe space 20 is connected to the cold side inlet of the first condenser 9 of the heat pump system, and the outlet of the high-pressure expander 14 is connected to the cold side inlet of the second condenser 10. Taking advantage of the high efficiency and strong heat collection capacity of the heat pump system, and using the medium-temperature water for geothermal supplementation as the heat source, the heat collected by the heat pump is used to heat the carbon dioxide at the outlet of the inner pipe space 20 and the outlet of the high-pressure expander 14 when releasing energy, so that it becomes high-temperature and high-pressure gaseous carbon dioxide, which enters the high-pressure expander 14 and the low-pressure expander 15 in sequence to do work and drive the generator to generate electricity.

[0043] refer to Figure 1 During the energy storage phase, liquid carbon dioxide is released from the storage tank 17, enters the throttling valve 18, and releases cold energy using the throttling cooling effect principle. The cold energy is then stored in the cold storage tank 16. Specifically, the throttled low-temperature carbon dioxide is introduced into the cold storage tank 16, and the cold energy is stored in the cold storage working medium of the cold storage tank through heat exchange between the low-temperature carbon dioxide and the working medium of the cold storage tank. After being heated by throttling, the gaseous carbon dioxide enters the carbon dioxide compression unit for staged compression. Simultaneously, the water from the water source 3 driven by the first water pump 4 is used as the cooling medium of the water cooler to cool the high-temperature carbon dioxide after the compressor stage. After being cooled by the second water cooler 6, the liquid carbon dioxide flowing out from the hot side outlet of the second water cooler 6 enters through the inlet of the inner pipe space 20 and is stored in the inner pipe space 20 in liquid form. The water source water on the cold side of the first water cooler 5 and the second water cooler 6 is heated by the high-temperature carbon dioxide, collected, and passed into the annular pipe space 19 for storage. The heat from the high-temperature water source water is transferred from the annular pipe space 19 to the surrounding area of ​​the coaxial sleeve 7, replenishing the geothermal energy lost during the heating season. Since a large number of coaxial sleeve groups are often used in buried pipe geothermal heat extraction projects to expand the heat extraction scale, the working fluid storage space of the energy storage system is sufficient. The number of buried pipes used and modified can be flexibly adjusted according to variables such as energy storage time, carbon dioxide flow rate, and water source flow rate.

[0044] During the energy release phase, the high-temperature source water stored in the annular pipe space 19 and completed geothermal heat replenishment is transformed into medium-temperature source water. Driven by the second water pump 8, it is introduced from the outlet of the annular pipe space 19 into the hot-side inlet of the evaporator 12 of the heat pump system and serves as a heat source to provide heat to the heat pump system. The heat pump system starts working, and the low-temperature source water after completing the heating is reintroduced into the water source 3. At the same time, liquid carbon dioxide is introduced from the outlet of the inner pipe space 20 into the cold-side inlet of the first condenser 9 of the heat pump system and is heated into gaseous high-temperature and high-pressure gaseous carbon dioxide. The gaseous carbon dioxide enters the high-pressure expander 14 to expand and do work, becoming exhaust gas. The exhaust gas is heated by the working fluid on the hot side of the second condenser 10 of the heat pump and then introduced into the low-pressure expander 15 to continue expanding and doing work. The two-stage expanders operate and drive the generator to generate electricity. The carbon dioxide exhaust gas flowing out from the outlet of the low-pressure expander 15 continues to enter the cold storage 16 and is condensed into liquid carbon dioxide, which is then stored in the liquid storage tank 17.

Claims

1. A carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve, characterized in that, The system includes a carbon dioxide compressor unit, a carbon dioxide expander unit, a coaxial sleeve (7), a heat pump system, a throttling cold storage device, and a liquid storage tank (17). The coaxial sleeve includes an inner tube and an outer tube arranged coaxially. The inner side of the inner tube is an inner tube pipe space (20), and an annular pipe space (19) is formed between the outer tube and the inner tube. An isolation plate (22) with the same outer diameter as the inner tube is installed at the bottom of the channel of the inner tube of the coaxial sleeve. The carbon dioxide compressor unit includes at least two stages of compressors. A water cooler is installed at the outlet of each stage of compressor. The cold medium outlet of the water cooler is connected to the inner tube pipe space (20). The hot medium outlet of the highest stage water cooler is connected to the annular pipe space (19). The carbon dioxide expander unit includes at least two stages of expanders. A condenser is installed at the inlet of each stage of expander. The condenser is installed in the heat pump system to cool the working fluid of the heat pump system. The condenser at the inlet of the first stage expander is connected to the outlet of the inner tube pipe space (20). The outlet of the annular pipe space (19) is connected to the heat source inlet of the heat pump system. The outlet of the carbon dioxide expander unit is connected to the throttling cold storage device and the liquid storage tank (17) in sequence. The outlet of the throttling cold storage device is also connected to the inlet of the carbon dioxide compressor unit. The coaxial sleeve (7) is a buried pipe and is provided with multiple units. The inner pipe is made of heat-insulating material and the outer pipe is made of heat-conducting material. The isolation plate (22) is made of heat-insulating material and has a cavity inside it. The cavity is filled with inert gas. The entire inner pipe is welded with spiral fins (21). The width of the spiral fins (21) is equal to the width of the annular pipe space, dividing the entire annular pipe space (19) into spiral descending channels. Taking the inner spiral line of the spiral fins (21) as the reference, the inner spiral line at the ground end is the starting end. As the inner spiral line extends downward, its pitch decreases by 10-20m per turn. In the annular pipe space, the pitch of the spiral fins decreases with the increase of the underground depth.

2. The carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve according to claim 1, characterized in that, The carbon dioxide compressor unit includes a low-pressure compressor (1) and a high-pressure compressor (2). The outlet of the low-pressure compressor (1) is equipped with a first water cooler (5), and the outlet of the high-pressure compressor (2) is equipped with a second water cooler (6). The hot side of the first water cooler (5) is connected to the low-pressure compressor (1) and the high-pressure compressor (2) respectively. The cold side of the first water cooler (5) is connected to a water source (3) and an annular pipe space (19) respectively. A first water pump (4) is installed between the outlet of the water source (3) and the first water cooler (5). The hot side of the second water cooler (6) is connected to the high-pressure compressor (2) and the inner pipe space (20) respectively. The inlet of the low-pressure compressor (1) is connected to the outlet of the throttling cold storage device. A second water pump (8) is installed at the outlet of the annular pipe space (19).

3. The carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve according to claim 1, characterized in that, The heat pump system includes an evaporator (12), a compressor (13), a second condenser (10), a first condenser (9), and an expansion valve (11). The hot side inlet of the evaporator (12) serves as the heat source inlet of the heat pump system. The hot side outlet of the evaporator (12) is connected to a water source (3). The cold side inlet and outlet of the evaporator are connected to the compressor (13) and the expansion valve (11). The outlet of the compressor (13) is connected to the hot side inlets of the second condenser (10) and the first condenser (9), respectively. The hot side outlets of the second condenser (10) and the first condenser (9) are both connected to the inlet of the expansion valve (11).

4. The carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve according to claim 3, characterized in that, The carbon dioxide expander unit includes a high-pressure expander (14) and a low-pressure expander (15) arranged along the medium flow direction. The cold side of the first condenser (9) is connected to the outlet of the inner pipe space (20) and the inlet of the high-pressure expander (14), respectively. The cold side of the second condenser (10) is connected to the high-pressure expander (14) and the low-pressure expander (15), respectively. The low-pressure expander (15) is connected to the inlet of the throttling cold storage device. The high-pressure expander (14) and the low-pressure expander (15) are connected to the generator.

5. The carbon dioxide energy storage and geothermal heat replenishment system based on a coaxial sleeve according to claim 1, characterized in that, The throttling cold storage device includes a cold storage unit (16) and a throttling valve (18). The outlet of the cold storage unit (16) is connected to the liquid storage tank (17). The outlet of the liquid storage tank (17) is connected to the throttling valve (18). The outlet of the throttling valve (18) is connected to the cold storage unit (16) and the compressor unit inlet in sequence.

6. An operation method for the carbon dioxide energy storage and geothermal heat replenishment system according to any one of claims 1-5, characterized in that, During the energy storage stage, liquid carbon dioxide is released from the storage tank (17) and enters the throttling cold storage device. After being heated by throttling, the gaseous carbon dioxide enters the carbon dioxide compressor unit for step-by-step compression. At the same time, the water source (3) is used as the cooling medium of the water cooler to cool the high-temperature carbon dioxide after the compressor stage. After being cooled by the water cooler, the liquid carbon dioxide flowing out from the hot side outlet of the water cooler enters the inner pipe space (20) and is stored in the inner pipe space (20) in liquid form. After the water source water on the cold side of the water cooler is heated by the high-temperature carbon dioxide, it is collected and passed into the annular pipe space (19) for storage. The heat of the high-temperature water is transferred from the annular pipe space (19) to the surrounding area of ​​the coaxial sleeve (7). During the energy release phase, the high-temperature water source stored in the annular pipe space (19) and completed geothermal heat replenishment is transformed into medium-temperature water source. It is then introduced into the heat source inlet of the heat pump system from the annular pipe space (19) and used as a heat source to provide heat to the heat pump system. The heat pump system starts to work, and the low-temperature water source after completing the heating is reintroduced into the water source (3). At the same time, liquid carbon dioxide is introduced from the outlet of the inner pipe space (20) into the cold side inlet of the first condenser (9) and heated into gaseous high-temperature and high-pressure gaseous carbon dioxide. The gaseous carbon dioxide enters the expander unit to do work. The expander unit operates and drives the generator to generate electricity. The carbon dioxide exhaust gas flowing out from the outlet of the expander unit continues to be introduced into the throttling cold storage device and condensed into liquid carbon dioxide, which is then stored in the liquid storage tank (17).

7. The operating method according to claim 6, characterized in that, The first water pump (4) drives the water source (3) as the cooling medium of the first water cooler (5) and the second water cooler (6) to cool the high-temperature carbon dioxide after the compressor stage. After being cooled by the second water cooler, the liquid carbon dioxide flowing out from the hot side outlet of the second water cooler enters the inner pipe space (20). The water source water on the cold side of the first water cooler (5) and the second water cooler (6) is heated by the high-temperature carbon dioxide, and then collected and passed into the annular pipe space (19) for storage.

8. The operating method according to claim 6, characterized in that, Driven by the second water pump (8), the medium-temperature source water is fed into the hot side inlet of the evaporator (12) through the outlet of the annular pipe space (19). The low-temperature source water after heating is fed back into the source water. At the same time, liquid carbon dioxide is fed into the cold side inlet of the first condenser (9) of the heat pump system through the outlet of the inner pipe space (20) and heated into gaseous high-temperature and high-pressure gaseous carbon dioxide. The gaseous carbon dioxide enters the high-pressure expander (14) to expand and do work, becoming exhaust gas. After being heated by the working fluid on the hot side of the second condenser (10) of the heat pump, the exhaust gas is fed into the low-pressure expander (15) to continue to expand and do work. The two-stage expanders operate and drive the generator to generate electricity. The carbon dioxide exhaust gas flowing out from the outlet of the low-pressure expander (15) continues to be fed into the throttling cold storage device and condensed into liquid carbon dioxide, which is then stored in the liquid storage tank (17).

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