Compressed gas energy storage system based on difluoromethane

Abstract

The utility model discloses a compressed gas energy storage system based on difluoromethane, which comprises a reservoir, a pump / water turbine, a gas-water mixing container and a generator / motor, the reservoir is connected with a water inlet and a water outlet of the gas-water mixing container through the pump / water turbine, the generator / motor is connected with the pump / water turbine, and the gas-water mixing container is filled with water and difluoromethane. Difluoromethane gas with a phase change function is selected as an energy storage medium, water is adopted as a working medium, and the requirement of a large-scale pressure container for the energy storage medium is remarkably reduced by achieving mutual decoupling of the energy storage medium and the working medium; the difluoromethane gas with the phase change function is adopted as an energy storage medium, in the compression and power generation process, the pressure in the closed container can be stably maintained near the critical pressure, the problem that the pressure fluctuates greatly in the energy storage and power generation process is effectively solved, core equipment for energy conversion is a pump / water turbine, and the energy conversion efficiency is improved. And high-efficiency operation can be kept in a high-pressure system and a low-pressure system.

Description

Technical Field

[0001] The utility model belongs to the technical field of energy storage, and particularly relates to a compressed gas energy storage system based on difluoromethane. Background Technique

[0002] With the adjustment of the energy structure transformation, a large amount of new energy has been continuously incorporated into the power grid. According to statistics, as of the end of December 2023, the cumulative installed power generation capacity in the country was approximately 2.919 billion kilowatts. Among them, the installed solar power generation capacity was approximately 609 million kilowatts, the installed wind power capacity was approximately 441 million kilowatts, and the installed hydropower capacity was approximately 421 million kilowatts. The proportion of new energy installed capacity has reached 35.97%, and the proportion of renewable energy installed capacity has reached 50.39%. In some local areas or provinces, a new type of power system dominated by new energy has emerged. For example, at the end of 2023, the total installed power in Qinghai Province was 54.9708 million kilowatts, and the installed clean energy capacity was 51.0794 million kilowatts, accounting for 93% of the total installed capacity, becoming a provincial power grid dominated by new energy; at the end of 2023, the installed new energy power generation capacity in the Northwest Power Grid had reached 210 million kilowatts, accounting for more than 50%, becoming a regional power grid dominated by new energy. It can be predicted that similar situations will continue to increase, and power systems dominated by new energy will become a common phenomenon in various regions and provinces. Due to the volatility, randomness, and uncertainty of new energy, it has brought serious challenges to the safe and stable operation of the power system. The trend of the gradually expanding peak-valley difference of the power grid has further worsened this problem, and the demand for flexible regulation resources in the power system has increased significantly. The power system urgently needs advanced large-scale energy storage technologies to solve the problem of renewable energy access, so as to improve the efficiency, safety, and economy of conventional power systems and regional energy systems.

[0003] As the proportion of new energy increases, the on-grid electricity of renewable energy will be divided into two parts: guaranteed acquisition electricity, market transaction electricity, and surplus electricity that has not reached a transaction. Grid enterprises no longer need to fully purchase the on-grid power of renewable energy grid-connected power generation projects within their jurisdiction. This requires new energy power generation enterprises to actively seek new consumption methods and improve the utilization methods of surplus electricity that has not reached a transaction. Energy storage technology, as one of the important technical measures to solve this problem, plays an important role in increasing the interests of new energy power generation enterprises and reducing surplus electricity that has not reached a transaction. The integration of new energy and energy storage plays a major role in suppressing the output of new energy, improving the consumption of new energy, reducing the deviation of power generation plans, and enhancing the safety and stability of the power grid. This combination can achieve the effective utilization and dispatching control of new energy, and improve the reliability and stability of the power grid. Pumped storage and compressed gas energy storage can be flexibly configured according to the specific power system requirements and environmental conditions. Pumped storage power stations can be built as the main energy storage facilities, and at the same time, compressed gas energy storage systems can be configured to cope with short-term power fluctuations.

[0004] Compressed air energy storage has the advantages of large capacity, long life, cleanliness, safety and reliability, and good economy. In existing non-supplementary combustion compressed air energy storage systems, both the working medium and the energy storage medium are air. However, it highly depends on large-scale high-pressure gas storage containers and has a low energy storage density. In current engineering practices, large-scale salt caverns and pipeline steels are often used as gas storage containers, resulting in a long construction period for the system, a large floor area for the system, and the pressure of the containers seriously affecting the system cycle efficiency. Although liquefied air energy storage utilizes the phase change characteristics of air and has a high energy storage density, the system structure is complex and the insulation structure requirements are stringent (the air liquefaction temperature is -196 degrees Celsius), and the system power conversion efficiency is low. In hydraulic compressed air energy storage, the working medium is water and the energy storage medium is air, and the energy storage density is higher than that of non-supplementary combustion compressed air energy storage. However, during the energy storage and power generation processes, the air pressure in the closed container varies significantly, presenting great technical challenges in maintaining stable power output. Affected by the large pressure variation, the system operation efficiency is significantly reduced, and the volume ratio of air is relatively large, resulting in a large volume of pressure vessels required for the system during long-term large-scale energy storage applications, and the system economy urgently needs to be improved. Summary of the Invention

[0005] To solve the above problems, the present invention provides a compressed gas energy storage system based on difluoromethane, which improves the energy storage density, overcomes the drawback that the energy storage medium and the working medium in a non-supplementary combustion compressed air energy storage system cannot be separated, solves the problems of strong dependence of compressed air energy storage on large-scale pressure vessels and the pressure seriously affecting the system cycle efficiency, and eliminates the problem of complex system structure in liquefied air energy storage.

[0006] To achieve the above object, the technical solution adopted by the present invention is: A compressed gas energy storage system based on difluoromethane, comprising a reservoir, a pump / turbine, a gas-water mixing container, and a generator / motor. The reservoir is connected to the water inlet and outlet of the gas-water mixing container through the pump / turbine, the generator / motor is connected to the pump / turbine, and the gas-water mixing container is filled with water and difluoromethane.

[0007] Further, a valve is provided on the pipeline between the pump / turbine and the gas-water mixing container.

[0008] Further, the pump / turbine adopts independent devices, with a water pump and a turbine respectively provided. The reservoir is connected to the water inlet of the gas-water mixing container through the water pump; the water outlet of the gas-water mixing container is connected to the water inlet of the turbine, and the water outlet of the turbine is connected to the reservoir.

[0009] Further, a spray head is provided in the gas-water mixing container, and the spray head is connected to the water extraction port of the gas-water mixing container or an external water source through a pressure pump.

[0010] Further, the power output end of the generator / motor is connected to the power grid.

[0011] Furthermore, a pressure sensor and a temperature sensor are provided on the gas-water mixing container.

[0012] Furthermore, the gas-water mixing container is connected to the evaporator of the refrigeration system.

[0013] Furthermore, the gas-water mixing container is connected to the outlet of the geothermal system.

[0014] Furthermore, a heat insulation layer is provided on the outer side of the gas-water mixing container.

[0015] Furthermore, a plurality of gas-water mixing containers are arranged in parallel.

[0016] Compared with the prior art, the present utility model has at least the following beneficial effects: The present utility model provides an innovative compressed gas energy storage system based on difluoromethane. Among them, the energy storage medium is difluoromethane gas with a phase change function, and the working medium is water. By realizing the decoupling of the energy storage medium and the working medium, the demand for the energy storage medium in large-scale pressure vessels is significantly reduced; the energy storage medium is difluoromethane gas with a phase change function. During the compression and power generation processes, the pressure in the closed container can be stably maintained near the critical pressure, effectively solving the problem of large pressure fluctuations during the energy storage and power generation processes; the working medium of this system is water, and the core equipment for energy conversion is the pump / turbine. It not only has the characteristics of high-efficiency operation and long service life, but also can maintain high efficiency in both high- and low-pressure systems, thus overcoming the serious impact of pressure on the system cycle efficiency; by using difluoromethane as the energy storage medium in this system, its highest temperature is higher than room temperature, and the highest pressure is at a medium level. At the same time, the working medium and the energy storage medium are in direct contact with each other, thus simplifying the system structure, reducing the heat insulation requirements, and solving the complex structure and harsh heat insulation problems faced by traditional air energy storage systems; during the energy storage and power generation processes, the pump / turbine of this system operates under stable head conditions and does not rely on power electronic conversion devices. This not only simplifies the system control strategy and control device, but also ensures that the system can output power efficiently and stably; at room temperature, 1 cubic meter of the energy storage medium in this system can expand to 10 to 30 cubic meters of gaseous energy storage medium after gasification, greatly reducing the volume of the energy storage medium. This characteristic not only avoids the dependence on power electronic rectifier and inverter equipment at the generator outlet, but also significantly reduces the overall cost of the system, providing a new solution for the technical economy of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of Embodiment 1 of the present utility model.

[0018] Figure 2 It is a schematic diagram of Embodiment 2 of the present utility model.

[0019] In the attached drawings, 1 - water storage tank, 2 - pump / water turbine, 3 - gas - water mixing container, 4 - generator / motor, 5 - power grid, 6 - valve, 7 - water pump, 8 - water turbine. Detailed implementation mode

[0020] In order to enable those skilled in the art to better understand the solution of the present utility model, the following will clearly and completely describe the technical solutions in the embodiments of the present utility model with reference to the attached drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, not all of the embodiments, and are not intended to limit the scope of the disclosure of the present utility model. In addition, in the following description, the descriptions of well - known structures and technologies are omitted to avoid unnecessarily confusing the concepts disclosed in the present utility model. Based on the embodiments in the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present utility model.

[0021] The structural schematic diagrams according to the disclosed embodiments of the present utility model are shown in the attached drawings. These figures are not drawn to scale. For the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are only exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0022] Compressed - gas energy storage compresses gas into high - pressure gas or liquid and stores it in a gas storage tank or a gas - water co - storage tank, and releases the gas to drive a turbine / generator set to generate electricity when needed; pumped - storage energy storage and compressed - gas energy storage can be used complementarily. Pumped - storage energy storage is suitable for energy transfer between peak and trough power loads, while compressed - gas energy storage is used for short - term energy balance and rapid response.

[0023] The compression ratio of difluoromethane is higher than that of air, and difluoromethane is insoluble in water. The present utility model intends to use a water pump to inject water into the gas - water mixing container to compress difluoromethane and absorb the heat generated during the compression process; the expansion process of difluoromethane can be achieved through an expansion valve or a throttle valve. Difluoromethane is mature in industrial use, with stable production and easy availability, and can be used in large quantities.

[0024] Example 1, refer to Figure 1, A compressed gas energy storage system based on difluoromethane, comprising a water storage tank 1, a gas-water mixing container 3, valves, a pump / turbine 2, pipelines, a generator / motor 4 and a power grid 5; the water storage tank 1 is used to store water so as to release or recover it through the pump / turbine 2 when needed; when the pump / turbine 2 operates as a pump, water is pumped from the water storage tank 1 to the gas-water mixing container 3; when the pump / turbine 2 operates as a turbine, electricity is generated by utilizing the water flow. When the power demand is low or the energy price is low, the generator / motor 4 operates as a motor to drive the pump / turbine 2 to pump water from the water storage tank 1 to the gas-water mixing container 3; when the power demand is high or the energy price is high, the water flow flows back from the gas-water mixing container 3 to the water storage tank 1 through the pump / turbine 2, driving the pump / turbine 2 to operate as a turbine, and then driving the generator / motor 4 to generate electricity; when the pressure in the gas-water mixing container 3 decreases, the liquid difluoromethane expands and transforms into a gas to continue to press out the water, and the water continuously enters the turbine. It is also possible to spray water mist on the upper part of the gas-water mixing container 3 while the water flows out of the gas-water mixing container 3 to heat the liquid difluoromethane and make it expand and do work.

[0025] The gas-water mixing container 3 is connected to the valves through pipelines, the valves are connected to the pump / turbine 2 through pipelines, the pump / turbine 2 is connected to the water storage tank 1 through pipelines, the pump / turbine 2 is connected to the generator / motor 4 through a shaft system, and the generator / motor 4 is connected to the power grid 5 through electrical wiring; in the system of the present utility model, the energy storage medium and the work medium are separated from each other, the energy storage medium adopts difluoromethane, and the work medium is water. And the power generation efficiency of the turbine is generally not less than 91%. The energy storage medium of the present utility model has the characteristics of phase change, the density of the energy storage medium is less than that of the work medium, and the energy storage medium is not easily soluble in the work medium. Therefore, difluoromethane can also be replaced by a medium with similar physical and chemical properties.

[0026] During the power generation process of the system, difluoromethane is transformed from a liquid state to a gaseous state, realizing the basic stability of the pressure in the steam-water mixing container; during the energy storage process of the system, difluoromethane is transformed from a gaseous state to a liquid state.

[0027] During the energy storage / power generation process, the temperature of the difluoromethane gas is not higher than 78 °C, and during the energy storage / power generation process, the pressure of the difluoromethane is not higher than 5.8 MPa; compared with the compressed air energy storage system, the pressure-bearing requirement of the gas-water mixing container 3 used in this application is lower than that of the high-pressure air tank, and reducing the volume of the gas-water mixing container 3 can reduce the equipment manufacturing cost to a certain extent.

[0028] During the energy storage process, the generator / motor 4 operates in the motor mode, and the pump / turbine 2 operates in the pump condition. The system absorbs electrical energy from the power grid, drives the motor to drive the pump to pump the water in the reservoir 1 into the gas-water mixing container 3, and the difluoromethane gas is compressed and liquefied. During the power generation process, the generator / motor 4 operates in the generator mode, and the pump / turbine 2 operates in the turbine condition. The difluoromethane expands from a liquid to a gas, and the system releases electrical energy to the power grid 5.

[0029] In the gas-water mixing container 3 of this embodiment, a pressure sensor and a temperature sensor are both provided to monitor the pressure and temperature in the gas-water mixing container 3 in real time, and the operating conditions of the system are adjusted according to the real-time pressure and temperature parameters.

[0030] In this embodiment, a heat insulation layer is provided outside the gas-water mixing container 3 to improve the stability of the gas-water mixing container 3 during operation, and multiple gas-water mixing containers 3 can be designed according to actual needs. When multiple gas-water mixing containers 3 operate alternately, it is beneficial to realize the continuity of power generation by doing work; when multiple gas-water mixing containers 3 operate simultaneously, the output power of the system can be increased, and those of ordinary skill in the art are capable of setting pumps and turbines with power matching according to the number and operating conditions of multiple gas-water mixing containers 3.

[0031] Embodiment 2, refer to Figure 2 , based on Embodiment 1, includes a reservoir 1, a gas-water mixing container 3, a valve 6, a water pump 7, a water turbine 8, pipelines, a generator / motor 4 and a power grid 5; different from Embodiment 1, the present utility model uses an independent water pump 7 and a water turbine 8 to replace the pump / turbine 2. The water pump 7 and the water turbine 8 operate independently. The reservoir 1 is connected to the gas-water mixing container 3 through the water pump 7 and the valve 6, and the gas-water mixing container 3 is connected to the reservoir through the valve 6 and the water turbine 8.

[0032] During the energy storage process, a large amount of heat will be generated during the compression of difluoromethane (CH2F2). If this heat is not removed in time, it will cause the temperature of the container to rise, affecting the compression efficiency and the physical properties of difluoromethane. To control the temperature inside the container, a water circulation system is set up. The system includes a circulation water pump, a spray head and a recovery device. The circulation water pump pumps the water in the container to the spray head, and the spray head sprays the water into the container in the form of a mist or fine water droplets to exchange heat with the heat generated by the compressed difluoromethane. Inside the gas-water mixing container 3, the water is sprayed out from the spray head by the circulation water pump to absorb the heat generated by the compressed difluoromethane and maintain the temperature stability of the gas-water mixing container. By maintaining the temperature stability inside the container, it can be ensured that difluoromethane maintains a high efficiency during the compression process. The stable temperature is beneficial to increase the compression ratio, so that more difluoromethane gas can be compressed into a smaller volume.

[0033] During the energy storage process, the generator / motor 4 operates in the motor mode. The system absorbs electrical energy from the power grid, drives the motor to drive the water pump 7 to pump the water in the reservoir 1 into the gas-water mixing container 3, and the difluoromethane gas is compressed and liquefied. During the power generation process, the generator / motor 4 operates in the generator mode. Difluoromethane expands from a liquid to a gas, and the difluoromethane presses the water into the water turbine 8. The water turbine 8 drives the generator to generate electricity, and the system releases electrical energy to the power grid 5.

[0034] In the gas-water mixing container 3 of this embodiment, a pressure sensor and a temperature sensor are both provided to monitor the pressure and temperature in the gas-water mixing container 3 in real time, and adjust the system operating conditions according to the real-time pressure and temperature parameters.

[0035] In the energy storage process and the power generation process of the present utility model, the electricity of the water pump and the circulation pump can come from the power grid power supply or the electrical energy of distributed new energy. The distributed new energy is a wind farm, a photovoltaic power station or a solar thermal power station.

[0036] An insulating layer is provided outside the gas-water mixing container 3 to improve the stability of the gas-water mixing container 3 during operation, and multiple gas-water mixing containers 3 can be designed according to actual needs. When multiple gas-water mixing containers 3 operate alternately, it is beneficial to realize the continuity of power generation by doing work; when multiple gas-water mixing containers 3 operate simultaneously, the output power of the system can be increased. Those of ordinary skill in the art are capable of setting water pumps and water turbines with power matching according to the number and operating conditions of multiple gas-water mixing containers 3.

[0037] Based on the system described in this application, difluoromethane operates in a closed environment, does not contact the external air, and performs cyclic compression and expansion work, which is beneficial to the safety of difluoromethane during the operation of the entire system. The gas-water mixing container 3 can be made of stainless steel. The present utility model uses difluoromethane and water. Difluoromethane is used as the energy storage medium, and water is used as the work medium. Difluoromethane is insoluble in water. During the compression and expansion process, it is beneficial to store and release a higher energy density. At the same time, water has a large specific heat capacity and can cool it down during the compression process of difluoromethane, realizing near-isothermal compression, further improving the energy storage density, and giving full play to the advantages of difluoromethane as an energy storage medium to a greater extent.

[0038] A spray head is provided in the gas-water mixing container 3. The spray head is connected to the water intake of the gas-water mixing container 3 through a pipeline, or the spray head is connected to an external water source, and the water source is preferably a low-temperature water source. During the process of pumping and storing energy to compress difluoromethane, the water in the gas-water mixing container 3 can also be pressurized and then sprayed back into the gas-water mixing container 3 to cool the difluoromethane, achieving isothermal compression, avoiding energy loss caused by temperature rise, thereby improving the efficiency and stability of the compressor. External water can also be pumped and sprayed into the gas-water mixing container 3. If a better cooling effect is to be achieved, it is preferably to use an external water source with a temperature lower than the water temperature in the gas-water mixing container 3.

[0039] Example 3, as an optional example, when the regional geothermal energy of the system is rich, the system can also be coupled with the geothermal system. A heat exchanger is provided outside the gas-water mixing container 3. The heat-carrying medium of the geothermal energy exchanges heat with the liquid difluoromethane in the heat exchanger, and the geothermal energy is used to heat and expand the liquid difluoromethane in the gas-water mixing container 3, improving the expansion efficiency of difluoromethane and the thermal efficiency and response speed of the system.

[0040] Example 4, in another possible working condition, the system of the present invention is coupled with a refrigeration system. The liquid difluoromethane outlet of the gas-water mixing container 3 is connected to the evaporator of the refrigeration system, which can release cold energy to the refrigeration system and absorb its heat, reasonably utilize cold energy and heat energy, and improve the efficiency and response speed of the system described in this application.

[0041] In summary, the compressed gas energy storage system of difluoromethane with heat compensation provided by the present utility model can achieve energy storage and power generation through the compression and expansion of inert gas during the power generation process, enabling energy storage-power generation without topographic elevation difference and allowing for flexible layout; the energy storage medium of the present utility model innovatively selects a medium with a phase change function, and the working medium is water, which helps to significantly reduce the dependence of the energy storage system on large pressure vessels; during the compression and power generation processes, the present utility model can ensure that the pressure in the closed container is maintained near the critical pressure, thus effectively avoiding large fluctuations in pressure during the energy storage and power generation processes; the phase change function medium of the present utility model can be flexibly selected, either a medium with a relatively low saturation pressure or other types of media can be used, greatly increasing the applicability and flexibility of the system; the energy storage and expansion processes of the present utility model are both close to isobaric processes, and both the pump and the water turbine can operate at their highest efficiency points, enabling a high cycle efficiency of the system; the present utility model simplifies the system structure, solves the problems of complex structure and demanding heat preservation requirements in traditional liquid compressed air energy storage systems, making the system more concise and efficient; during the energy storage and power generation processes, both the pump / water turbine can operate under stable head conditions without relying on power electronic conversion devices, which not only helps to simplify the system control strategy and control devices but also enables the system to operate with high efficiency and stability; the present utility model significantly reduces the volume of the energy storage medium and avoids the dependence of the generator outlet on power electronic rectifier and inverter equipment, thereby greatly reducing the overall cost of the system and achieving a double optimization of the technical economy of the energy storage system.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present utility model and not to limit them. Although the present utility model has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present utility model, and any modification or equivalent replacement that does not depart from the spirit and scope of the present utility model should be covered by the protection scope of the claims of the present utility model.

Claims

1. A compressed gas energy storage system based on difluoromethane, characterized in that: The invention comprises a water reservoir (1), a pump / water turbine (2), an air-water mixing container (3) and a generator / motor (4); the water reservoir (1) is connected to a water inlet and a water outlet of the air-water mixing container (3) via the pump / water turbine (2); the generator / motor (4) is connected to the pump / water turbine (2); and the air-water mixing container (3) is filled with water and difluoromethane.

2. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: A valve (6) is arranged on the pipeline between the pump / turbine (2) and the air-water mixing container (3).

3. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: The pump / turbine (2) is an independent device, and a water pump (7) and a water turbine (8) are respectively provided. The water reservoir (1) is connected to the water inlet of the air-water mixing container (3) through the water pump; the water outlet of the air-water mixing container (3) is connected to the water inlet of the water turbine, and the water outlet of the water turbine is connected to the water reservoir (1).

4. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: A spray head is arranged in the air-water mixing container (3), and the spray head is connected to the water suction port of the air-water mixing container (3) or an external water source via a pressure pump.

5. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: The power output end of the generator / motor (4) is connected to the power grid (5).

6. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: The gas-water mixing container (3) is provided with a pressure sensor and a temperature sensor.

7. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: The air-water mixing container (3) is connected to an evaporator of a refrigeration system.

8. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: The gas-water mixing container (3) is connected to the outlet of the geothermal system.

9. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: A heat insulating layer is arranged outside the gas-water mixing container (3).

10. The compressed gas energy storage system based on difluoromethane according to claim 1, characterized in that: A plurality of gas-water mixing containers (3) are arranged in parallel.

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