A cold and thermal energy storage system for generating electricity using supercritical CO2

Abstract

The application discloses a cold-heat energy storage system for power generation by using supercritical CO2, which comprises a heat pump subsystem, a cold energy storage unit, a heat energy storage unit and a power generation subsystem. The heat pump subsystem is arranged in a cascade mode and generates a mixture of dry ice and liquid phase at a CO2 triple point by driving of electric energy; the cold energy storage unit is connected to the low-temperature side of the heat pump subsystem and is used for storing the generated dry ice; the heat energy storage unit is connected to the high-temperature side of the heat pump subsystem and is used for storing the heat energy generated in the compression process; the power generation subsystem is in fluid communication with the downstream of the cold energy storage unit and the heat energy storage unit, uses the output CO2 and heat energy to heat the CO2 to a supercritical state, and expands to drive a generator to generate power; the system forms a circulating loop, and the fluid discharged from the power generation subsystem flows back to the heat pump subsystem; the technical scheme utilizes the CO2 triple point to realize cold-heat collaborative energy storage, greatly improves the energy storage density and efficiency, and finally realizes efficient and stable power generation of renewable energy.

Description

Technical Field

[0001] This invention relates to the field of large-scale energy storage technology, and more specifically, to a cold and hot energy storage system that utilizes supercritical CO2 to generate electricity. Background Technology

[0002] With the rapid development of renewable energy power generation technologies such as solar and wind power, their inherent intermittency and volatility pose a severe challenge to the stable operation of the power grid. To achieve peak shaving and valley filling and stable operation of the power grid, it is necessary to implement large-scale, high-efficiency energy storage systems to store surplus electricity and release it during peak demand periods. Therefore, developing economical and reliable large-scale energy storage technologies has become a key link in promoting energy structure transformation.

[0003] Currently, common large-scale energy storage methods mainly include pumped hydro storage and battery energy storage. While pumped hydro storage is technologically mature, it is heavily reliant on geographical conditions, has a long construction cycle, and requires huge investments. Battery energy storage, such as lithium-ion batteries, has high energy density and rapid response, but suffers from high costs, limited cycle life, and safety concerns, making it difficult to meet the demands of grid-scale, long-term energy storage. Furthermore, technologies such as compressed air energy storage generally suffer from limitations such as low system efficiency, insufficient energy density, or reliance on specific geological structures.

[0004] Against this backdrop, exploring efficient energy storage systems based on new principles and media is urgently needed. Energy storage technologies using carbon dioxide (CO2) as the working medium have attracted attention due to their wide availability, easily achievable critical parameters, and non-toxicity. However, existing liquid CO2 or supercritical CO2 energy storage systems typically only utilize their gas-liquid phase change or pressure energy, leaving significant room for improvement in energy density and system compactness. The market urgently needs a novel energy storage solution that can simultaneously achieve high energy density, high system efficiency, environmental friendliness, and a compact structure. Summary of the Invention

[0005] In view of the above-mentioned technical problems in related technologies, the present invention proposes a cold and heat energy storage system for generating electricity using supercritical CO2, which can overcome the above-mentioned shortcomings of the prior art.

[0006] To achieve the above-mentioned technical objectives, the technical solution of the present invention is implemented as follows:

[0007] A cold and heat energy storage system that utilizes supercritical CO2 to generate electricity;

[0008] This supercritical CO2 power generation and thermal energy storage system includes a heat pump subsystem, a cold energy storage unit, a thermal energy storage unit, and a power generation system.

[0009] The heat pump subsystem, which is arranged in a cascade configuration, is used to generate a mixture containing dry ice and a liquid phase near the triple point of CO2 using electrical energy.

[0010] The cold energy storage unit is connected to the low-temperature side of the heat pump subsystem and is used to store the dry ice produced by the heat pump subsystem.

[0011] The thermal energy storage unit is connected to the high-temperature side of the heat pump subsystem and is used to store the thermal energy generated by the heat pump subsystem.

[0012] The generator system has a fluid channel connected downstream of the cold energy storage unit and the thermal energy storage unit. It is used to heat the CO2 output from the cold energy storage unit and the thermal energy output from the thermal energy storage unit to a supercritical state and expand it to do work, thereby driving the generator to generate electricity.

[0013] The fluid discharged from the power generation system is returned to the heat pump subsystem, forming a cycle.

[0014] Furthermore, the heat pump subsystem includes a first-stage heat pump circuit and a second-stage heat pump circuit;

[0015] The first-stage heat pump circuit includes a first-stage CO2 compressor, a first-stage CO2 condenser, a first-stage expansion valve, and an evaporator connected in sequence via pipes; the second-stage heat pump circuit includes a second-stage CO2 compressor, a second-stage CO2 condenser, a receiving tank, and an expansion device for throttling to the triple point connected in sequence via pipes.

[0016] The evaporator of the first-stage heat pump circuit and the second-stage CO2 condenser of the second-stage heat pump circuit are thermally coupled through a refrigerant circuit.

[0017] Furthermore, the expansion device for throttling to the triple point is selected from an expansion valve or an ejector; the expansion device is configured to throttle liquid CO2 to the triple point state, forming a mixture of dry ice and gas phase and sending it into the cold energy storage unit.

[0018] Furthermore, the cold energy storage unit is a dry ice refrigerator that receives the mixture from the expansion device and has a gas phase outlet, which is connected to the inlet of the second-stage CO2 compressor via a regenerator.

[0019] Furthermore, the thermal energy storage unit includes a molten thermal storage tank, a thermal storage circuit, and a heating circulation circuit;

[0020] The thermal storage circuit includes a first circulation pump and a first heat exchanger, used to transport and store the heat energy released by the first-stage CO2 condenser in the molten thermal storage tank;

[0021] The heating circulation loop includes a second circulation pump and a second heat exchanger, used to extract thermal energy from the molten thermal storage tank during discharge and supply it to the power generation system.

[0022] Furthermore, the molten heat storage tank is filled with a chemical melt material.

[0023] Furthermore, a high-temperature heat exchanger is coupled and connected to the heating circulation loop for receiving thermal energy;

[0024] A superheated heat exchanger is located downstream of the coupled high-temperature heat exchanger;

[0025] A turbine unit comprising a high-pressure CO2 gas turbine and a low-pressure CO2 gas turbine, wherein the high-pressure CO2 gas turbine receives supercritical CO2 from the superheated heat exchanger and performs work to generate electricity;

[0026] A CO2 regenerative heat exchanger is used to exchange heat between the exhaust gas of the turbine unit and the CO2 fluid from the cold energy storage unit.

[0027] Furthermore, the electronic system also includes:

[0028] A coupled cryogenic heat exchanger is used for preliminary heating of CO2 from the regenerator;

[0029] The first gas compressor and the second gas compressor are arranged in the fluid passage for compressing the CO2 working fluid flowing to the turbine unit.

[0030] Furthermore, it also includes a battery array configured to store electrical energy during charging and provide auxiliary heating power to the system during discharging.

[0031] Furthermore, the electrical energy input comes from intermittent renewable energy sources, and the system is used to smooth the power output of renewable energy sources to achieve peak shaving and valley filling of the power grid.

[0032] The beneficial effects of this invention are as follows: By utilizing the mixture of dry ice and liquid phase generated near the triple point of carbon dioxide for cold energy storage, and simultaneously using a heat pump system to store the heat of compression as latent heat in chemical melts such as molten salts, bidirectional synergistic storage of cold and heat energy is achieved, thereby significantly improving the energy density and energy storage efficiency of the entire energy storage system and making the system structure more compact; furthermore, by using the stored heat energy to heat the dry ice to a high-temperature, high-pressure, supercritical state to drive turbine expansion and power generation during energy release, the intermittent renewable energy is efficiently, stably, and economically converted into dispatchable grid power, with a short investment payback period and significant application value. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the overall structure of a cold and heat energy storage system for generating electricity using supercritical CO2, according to an embodiment of the present invention.

[0035] In the diagram: 1-L, First-stage CO2 heat pump loop; 1-1, First-stage CO2 compressor; 1-2, First-stage CO2 condenser; 1-3, Evaporator; 1-4, First-stage expansion valve; 1-5, Pressure regulating valve; 1-6, Refrigerant pump; 2-L, Second-stage CO2 heat pump loop; 2-1, Second-stage CO2 compressor; 2-2, CO2 storage tank; 2-3, Second-stage CO2 condenser; 2-4, Receiving tank; 2-i, First expansion process section; 2-i-1, Second-stage expansion valve; 2-i-2, First pressure regulating valve; 2-i', Second expansion process section; 2-i'-1, Ejector; 2-i'-2, Second pressure regulating valve; 2-5, Dry ice refrigerator; 2-6, Regenerator; 2-7, Coupled low-temperature heat exchanger; 2-8, First gas compressor; 2-9, Coupled high-temperature heat exchanger; 2-10, Second gas compressor; 2-11, Superheated heat exchanger; 2-12, High... 2-13 Low-pressure CO2 gas turbine; 2-14 CO2 regenerative heat exchanger; 3-L, third circulation loop; 3-L1, heating circulation loop; 3-L2, heat storage loop; 3-1, molten heat storage tank; 3-2, first circulation pump; 3-3, first heat exchanger; 3-4, second heat exchanger; 3-5, connecting device; 3-6, second circulation pump; 3-7, electric heater; 3-8, battery array; D-1, first input power; D-2, second input power; D-3, third input power; D-4, fourth input power; E, system input; E-1, first input electrical energy; E-2, second input electrical energy; E-3, third input electrical energy; E-4, fourth input electrical energy; P, system output; P-1, first output electrical energy; P-2, second output electrical energy. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0037] It should be understood that in the description of the embodiments of the present invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of the present invention and for simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of the embodiments of the present invention, "several" means two or more, unless otherwise explicitly specified.

[0038] like Figure 1 As shown in the embodiment of the present invention, a cold and heat energy storage system for generating electricity using supercritical CO2 includes a heat pump subsystem, a cold energy storage unit, a heat energy storage unit, and a power generation system.

[0039] The heat pump subsystem, which is arranged in a cascade configuration, is used to generate a mixture containing dry ice and a liquid phase near the triple point of CO2 using electrical energy.

[0040] The cold energy storage unit is connected to the low-temperature side of the heat pump subsystem and is used to store the dry ice produced by the heat pump subsystem.

[0041] The thermal energy storage unit is connected to the high-temperature side of the heat pump subsystem and is used to store the thermal energy generated by the heat pump subsystem.

[0042] The generator system has a fluid channel connected downstream of the cold energy storage unit and the thermal energy storage unit. It is used to heat the CO2 output from the cold energy storage unit and the thermal energy output from the thermal energy storage unit to a supercritical state and expand it to do work, thereby driving the generator to generate electricity.

[0043] The fluid discharged from the power generation system is returned to the heat pump subsystem, forming a cycle.

[0044] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 according to the present invention, the heat pump subsystem includes a first-stage heat pump circuit 1-L and a second-stage heat pump circuit 2-L.

[0045] The first-stage heat pump circuit 1-L includes a first-stage CO2 compressor 1-1, a first-stage CO2 condenser 1-2, a first-stage expansion valve 1-4, and an evaporator 1-3 connected in sequence via pipes; the second-stage heat pump circuit 2-L includes a second-stage CO2 compressor 2-1, a second-stage CO2 condenser 2-3, a receiving tank 2-4, and an expansion device for throttling to the triple point connected in sequence via pipes;

[0046] The evaporator 1-3 of the first-stage heat pump circuit 1-L and the second-stage CO2 condenser 2-3 of the second-stage heat pump circuit 2-L are thermally coupled through a refrigerant circuit.

[0047] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 according to the present invention, the expansion device for throttling to the triple point is selected from expansion valve 2-i-1 or ejector 2-i'-1; the expansion device is configured to throttle liquid CO2 to the triple point state, forming a mixture of dry ice and gas phase and sending it into the cold energy storage unit.

[0048] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 according to the present invention, the cold energy storage unit is a dry ice refrigerator 2-5, which receives the mixture from the expansion device and is provided with a gas phase outlet. The gas phase outlet is connected to the inlet of the second-stage CO2 compressor 2-1 through a regenerator 2-6.

[0049] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 according to the present invention, the heat energy storage unit includes a molten heat storage tank 3-1, a heat storage circuit 3-L2 and a heating circulation circuit 3-L1;

[0050] The heat storage circuit 3-L2 includes a first circulation pump 3-2 and a first heat exchanger 3-3, which are used to transport and store the heat energy released by the first-stage CO2 condenser 1-2 in the molten heat storage tank 3-1;

[0051] The heating circulation loop 3-L1 includes a second circulation pump 3-6 and a second heat exchanger 3-4, which are used to extract thermal energy from the molten heat storage tank 3-1 during discharge and provide it to the power generation system.

[0052] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 as described in this invention, the molten heat storage tank 3-1 is filled with a chemical melt material.

[0053] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 according to the present invention, a high-temperature heat exchanger 2-9 is coupled and connected to the heating circulation loop 3-L1 for receiving thermal energy.

[0054] Superheated heat exchanger 2-11 is located downstream of the coupled high-temperature heat exchanger 2-9;

[0055] The turbine unit includes a high-pressure CO2 gas turbine 2-12 and a low-pressure CO2 gas turbine 2-13, wherein the high-pressure CO2 gas turbine 2-12 receives supercritical CO2 from the superheated heat exchanger 2-11 and generates electricity.

[0056] CO2 regenerative heat exchanger 2-14 is used for heat exchange between the exhaust gas of the turbine unit and the CO2 fluid from the cold energy storage unit.

[0057] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 as described in this invention, the power generation system further includes:

[0058] A low-temperature heat exchanger 2-7 is coupled in place, which is used to preheat CO2 from the regenerator 2-6;

[0059] The first gas compressor 2-8 and the second gas compressor 2-10 are arranged in the fluid passage for compressing the CO2 working fluid flowing to the turbine unit.

[0060] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 according to the present invention, the system further includes a battery array 3-8, which is configured to store electrical energy during the charging period and provide auxiliary heating power to the system during the discharging period.

[0061] According to a specific embodiment of the cold and heat energy storage system for generating electricity using supercritical CO2 according to the present invention, the electrical energy input comes from intermittent renewable energy, and the system is used to smooth the power output of renewable energy to achieve peak shaving and valley filling of the power grid.

[0062] To facilitate understanding of the above technical solutions of the present invention, the following detailed description of the above technical solutions of the present invention is provided through specific system structure and working principle.

[0063] In practical application, according to the supercritical CO2 power generation and thermal energy storage system of the present invention, during the charging period, electrical energy provided by renewable or economical energy sources is used to compress the compressor. A cascaded CO2 heat pump system generates dry ice with a liquid phase mixture at the triple point, which is then stored in a cold tank. In the cascaded arrangement of the heat pumps, while the dry ice is stored in the cold tank, thermal energy is also stored as thermal energy in the hot tank. The chemical melt in the hot tank melts and liquefies with the thermal energy, storing a large amount of thermal energy. The energy stored as cold in the form of dry ice is completed by the next stage of the heat pump, while the energy stored as heat in the form of melt is completed by the previous stage of the heat pump.

[0064] During unloading, the cold energy (mixed with the liquid phase) stored in the cold tank as dry ice is heated by the heat energy stored in the hot tank, simultaneously heating the CO2. This causes the dry ice to absorb a large amount of latent heat, reaching a high-temperature, high-pressure supercritical state. Auxiliary heating can be provided by electrical energy from a battery array (such as lithium-ion batteries) and can be adjusted during the charging cycle.

[0065] Supercritical CO2 gas eventually expands within the turbine (both high-pressure and low-pressure stages), generating electrical energy. The resulting electricity has significant economic value when utilized in the power grid. During emission, the emitted CO2 gas is simultaneously cooled by sublimated dry ice, thereby cooling the thermal storage tank and causing the molten melt to re-solidify.

[0066] Because this system utilizes dry ice cold storage and melt thermal cold storage, its structure is more compact compared to traditional liquid-gas storage systems. The compactness of existing systems is as small as 1 / 100th. The system is also highly efficient because it utilizes the highest potential area for carbon dioxide performance. When expressed as energy density, its efficiency exceeds 40 kWh / m³ compared to traditional liquid-gas energy level systems. This patent offers advantages such as a short investment payback period and economical operation, making it widely applicable in industries such as refrigeration and power generation.

[0067] Component details of a carbon dioxide dry ice battery:

[0068] The first-stage CO2 heat pump circulation loop 1-L consists of the following components:

[0069] The first-stage CO2 compressor 1-1 is used to circulate CO2 within the first-stage CO2 compressor 1-1, and is arranged in parallel to control the pressure and flow rate of CO2 to vary with the input power of the first input electrical energy E-1.

[0070] The first-stage CO2 condenser 1-2, under a certain pressure at the outlet of the first-stage CO2 compressor 1-1, transports the hot gas discharged from the first-stage CO2 compressor 1-1 (e.g., 100℃-120℃) to the liquid phase. The condensation heat (thermal energy) in the CO2 hot gas is exchanged and transferred to the heat storage circuit 3-L2. After being exchanged by the heat exchanger 3-1, it is stored as thermal energy in the hot water tank of the heat exchanger 3-1.

[0071] The low-pressure two-phase liquid-gas mixture in evaporator 1-3 exchanges cold energy with the second-stage CO2 condenser 2-3 and evaporates at a low temperature in evaporator 1-3. Between evaporator 1-3 and condenser 2-3, the refrigerant circuit circulates refrigerant to transfer cold energy through refrigerant pump 1-6.

[0072] The first-stage expansion valve 1-4 generates the given conditions for the evaporator 1-3 by adjusting the mass flow rate. With the assistance of the pressure regulating valve 1-5, the first-stage expansion valve 1-4 sends out various states in the flow channel for the temperature and pressure of the evaporator 1-3, automatically cooperating with the operation of the evaporator 1-3.

[0073] Pressure regulating valves 1-5 can automatically adjust the mass flow rate and pressure to achieve the set temperature of evaporator 1-3.

[0074] Refrigerant pump 1-6 circulates refrigerant between evaporator 1-3 and second-stage CO2 condenser 2-3, between evaporator 1-3 and second-stage CO2 condenser 2-3, and between first-stage expansion valve 1-4, and can be combined into a unit in a shell and tube tank.

[0075] The second-stage CO2 heat pump circulation loop 2-L includes the following components:

[0076] The second-stage CO2 compressor 2-1 and the CO2 in the second-stage CO2 compressor 2-1 are arranged in parallel to control the pressure and flow rate of CO2 as the input power and the first input electrical energy E-1 change.

[0077] CO2 storage tank 2-2 can be filled with fresh CO2 (gas or liquid phase) from the outside.

[0078] The first heat exchanger 3-3, at the same pressure as the outlet of the second-stage CO2 compressor 2-1, converts cold air (e.g., -20°C to -25°C discharged from the second-stage CO2 compressor 2-1) into a liquid state. The heat of condensation (thermal energy) in the cold CO2 gas is transferred to the circulating refrigerant driven by the refrigerant pump 1-6 to supply the cooling capacity required by the evaporator 1-3. The condensed liquid CO2 is then transferred to the receiving tank 2-4.

[0079] The first-stage expansion valve 1-4 receiving tank separates the liquid phase from the excess gas phase, with only the liquid phase CO2 circulating to the first expansion process section 2-i.

[0080] First expansion process segment 2-i:

[0081] The second-stage expansion valve 2-i-1 is used for throttling, causing liquid CO2 to become a liquid-gas mixture at the lowest pressure and temperature. In this technical solution, this throttling process results in the CO2 triple point, i.e., temperature = -56.6℃ ≈ -56℃, pressure = 0.518MPa ≈ -0.52 MPa, causing the expansion process to form a dry ice and gas mixture. The dry ice and mixed vapor are then pumped into the dry ice refrigeration tank 2-5. The second-stage expansion valve 2-i-1 and the first pressure regulating valve 2-i-2 work automatically and collaboratively by sensing various states in the flow channel.

[0082] The first pressure regulating valve 2-i-2 regulates the mass flow rate and pressure, so that it automatically sets the triple point state.

[0083] The second expansion process, segment 2-i':

[0084] Ejector 2-i'-1 operates by receiving the liquid phase from receiver 2-4 and the phase return from regenerator 2-6, producing the same function as the second-stage expansion valve 2-i-1. The second-stage CO2 heat pump loop 2-L system is relatively large, with a significant pressure drop during expansion, making ejector 2-i'-1 effective. Ejector 2-i'-1 provides a CO2 triple point state similar to that of the second-stage expansion valve 2-i-1.

[0085] The second pressure regulating valve 2-i'-2 regulates mass flow rate and pressure, and automatically sets the triple point state.

[0086] Dry ice refrigeration tank 2-5 receives a mixture of dry ice and liquid gas from either the first expansion process section 2-i or the second expansion process section 2-i', and CO2 is returned via regenerator 2-6, which then flushes the interior of the dry ice refrigeration tank 2-5. The flushing gas phases, at the same temperature at the triple point, separate at the top of the tank and circulate to the second-stage CO2 compressor 2-1. The shape, volume, and structural materials are all designed according to the refrigeration system.

[0087] The regenerator 2-6 performs heat exchange, ensuring that the temperature of the liquid CO2 discharged from the dry ice refrigerator 2-5 (-56℃) is the same as that of the CO2 regener heat exchanger 2-14. On the other hand, the remaining carbon dioxide is heated into a gaseous phase under the same three-phase pressure.

[0088] The low-temperature heat exchanger 2-7 is coupled to exchange the low-temperature gas heat from the regenerator 2-6 with the circulating medium heat from the superheated heat exchanger 2-11 in an independent third circulation loop 3-L.

[0089] The first gas compressor 2-8 compresses the CO2 gas in the coupled cryogenic heat exchanger 2-7 and sends it to the CO2 regenerative heat exchanger 2-14. The power input driving the first gas compressor 2-8 is the second input power D-2.

[0090] The high-temperature heat exchanger 2-9, i.e., the high-temperature gas heat from the receiving tank 2-4 and the low-temperature circulating medium heat from the molten heat storage tank 3-1 are exchanged through the second heat exchanger 3-4 and the second circulating pump 3-6 installed in the third circulating loop 3-L.

[0091] The second gas compressor 2-10 compresses the CO2 gas in the coupled high-temperature heat exchanger 2-9 and sends the gas to the superheated heat exchanger 2-11. The power input of the second gas compressor 2-10 is the first input power D-1.

[0092] The superheated heat exchanger 2-11 heats the CO2 gas coupled to the high-temperature heat exchanger 2-9 to the highest temperature of the second-stage CO2 heat pump loop 2-L, driving the high-pressure CO2 gas turbine 2-12. The return circulation medium reduces the heat dissipation of the coupled low-temperature heat exchanger 2-7 in an independent loop of the second-stage CO2 heat pump loop 2-L.

[0093] The high-pressure CO2 gas turbine 2-12 receives high-temperature gas from the superheated heat exchanger 2-11 and drives a generator attached to the shaft through a speed regulating gas box to generate the first output electrical energy P-1. The high-pressure CO2 gas turbine 2-12 performs the first stage of the expansion process, namely: the first expansion process segment 2-i.

[0094] The low-pressure CO2 gas turbine 2-13 receives the high-temperature exhaust gas from the high-pressure CO2 gas turbine 2-12 and performs a two-stage expansion process. The low-pressure CO2 gas turbine 2-13 drives a generator attached to the shaft through a speed regulating gearbox to generate a second output electrical energy P-2.

[0095] CO2 regenerative heat exchanger 2-14 is used for heat exchange between the exhaust gas from the low-pressure CO2 gas turbine 2-13 and the exhaust gas from the coupled low-temperature heat exchanger 2-7. The gas cooled by CO2 regenerative heat exchanger 2-14 is circulated to the regenerator 2-6, and the gas heated by CO2 regenerative heat exchanger 2-14 is circulated to the coupled high-temperature heat exchanger 2-9, shutting down the second-stage CO2 heat pump circulation loop 2-L.

[0096] The heating circulation loop 3-L1, which circulates and releases heat, consists of the following parts:

[0097] The molten heat storage tank 3-1 receives heat from the first-stage CO2 condenser 1-2 through the circulation loop of the heat storage circuit 3-L2 and the first heat exchanger 3-3.

[0098] The molten thermal storage tank 3-1 contains endothermic materials, such as chemical melt materials, which store a large amount of heat energy in a liquid state after melting from a solid state at a given (fixed) temperature. The molten material can also release heat energy, causing the liquid to solidify. Due to the absorption and release of latent heat, the solid-liquid thermal process in the tank structure can store a large amount of heat energy on a relatively small scale. During the liquid-phase heat release process, a connecting device 3-5 can be used to enhance heat transfer; the input to the connecting device 3-5 is the third input power D-3.

[0099] The first circulation pump 3-2 circulates the heat transfer medium (such as hot oil) from the first-stage CO2 condenser 1-2 to the first heat exchanger 3-3, circulating in the independent loop of the heat storage circuit 3-L2;

[0100] The first heat exchanger 3-3 releases heat energy to the heat-absorbing material contained in the molten heat storage tank 3-1.

[0101] The second heat exchanger 3-4 absorbs heat energy and releases the heat into the heating circulation loop 3-L1.

[0102] The connecting device 3-5 (e.g., connecting a fan) connects to the liquid state of the melt to enhance heat transfer between the first heat exchanger 3-3 and the second heat exchanger 3-4. The electrical input of the connecting device 3-5 is the fourth input power D-4.

[0103] The second circulation pump 3-6 in the heating circulation loop 3-L1 circulates the heat transfer medium from the second heat exchanger 3-4 to the coupled high-temperature heat exchanger 2-9. The electrical power input to the second circulation pump 3-6 is the third input power D-3.

[0104] Electric heater 3-7 heats the heat transfer medium in the coupled high-temperature heat exchanger 2-9 to its highest point, and then sends it to the superheated heat exchanger 2-11. Electricity is supplied by battery array 3-8, such as a lithium iron phosphate battery array.

[0105] Battery array 3-8 stores electrical energy through the fourth input power E-4.

[0106] The heat storage circuit 3-L2 includes a first heat exchanger 3-3, a first-stage CO2 condenser 1-2, and a first circulation pump. The heat storage circuit 3-L2 charges the heat energy of the first-stage CO2 heat pump circulation circuit 1-L into the molten heat storage tank 3-1.

[0107] Energy input and output:

[0108] Charging cycles (e.g., 10 hours) and discharging cycles (e.g., 5 hours)

[0109] The first input electrical energy E-1 and the second input electrical energy E-2 are respectively the compression work performed by the first-stage CO2 compressor 1-1 and the second-stage CO2 compressor 2-1 in operation.

[0110] In this technical solution, the first input electrical energy E-1 and the second input electrical energy E-2 are supplied by the surplus energy of natural resources such as solar energy, wind energy, and geothermal energy, or by discounted electricity supply during nighttime charging.

[0111] The third input electrical energy E-3 is used to drive the first circulation pump 3-2 during charging. The power source is the same as the first input electrical energy E-1 and the second input electrical energy E-2.

[0112] The fourth input energy E-4 is an auxiliary energy storage source of the same electrical energy as the first input energy E-1 and the second input energy E-2. The fourth input energy E-4 is used to boost the pressure of the circulating medium in the heating loop 3-L1.

[0113] The first output power P-1 and the second output power P-2 are the power outputs of the high-pressure CO2 gas turbine 2-12 and the low-pressure CO2 gas turbine 2-13, respectively, which are supplied to the outside at a higher output power during the discharge period.

[0114] The first input power D-1 and the second input power D-2 represent the power supplied to the first gas compressor 2-8 and the second gas compressor 2-10 during the discharge period, respectively. The input power of the first input power D-1 and the second input power D-2 can be partially provided by the first output power P-1 and the second output power P-2.

[0115] The third input power D-3 is the input power during the discharge period. The input power of the third input power D-3 can be provided by the first output power P-1 and the second output power P-2.

[0116] The fourth power input, D-4, is available during both charging and discharging. The power of the fourth power input, D-4, can be divided into two periods depending on the system operation, and is supplied by either the system input, E, or the system output, P.

[0117] In summary, by utilizing the above-mentioned technical solution of this invention, a mixture of dry ice and liquid phase generated near the triple point of carbon dioxide is used for cold energy storage. Simultaneously, a heat pump system is used to store the heat of compression as latent heat in chemical melts such as molten salts, achieving bidirectional synergistic storage of cold and thermal energy. This significantly improves the energy density and energy storage efficiency of the entire energy storage system, resulting in a more compact system structure. Furthermore, by using the stored thermal energy to heat the dry ice to a high-temperature, high-pressure, supercritical state during energy release to drive turbine expansion and power generation, the system efficiently, stably, and economically converts intermittent renewable energy into dispatchable grid power, with a short investment payback period and significant application value.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cold and heat energy storage system for generating electricity using supercritical CO2, characterized in that, It includes a heat pump subsystem, a cold energy storage unit, a thermal energy storage unit, and a power generation system. The heat pump subsystem, which is arranged in a cascade configuration, is used to generate a mixture containing dry ice and a liquid phase near the triple point of CO2 using electrical energy. The cold energy storage unit is connected to the low-temperature side of the heat pump subsystem and is used to store the dry ice produced by the heat pump subsystem. The thermal energy storage unit is connected to the high-temperature side of the heat pump subsystem and is used to store the thermal energy generated by the heat pump subsystem. The generator system has a fluid channel connected downstream of the cold energy storage unit and the thermal energy storage unit. It is used to heat the CO2 output from the cold energy storage unit and the thermal energy output from the thermal energy storage unit to a supercritical state and expand it to do work, thereby driving the generator to generate electricity. The fluid discharged from the power generation system is returned to the heat pump subsystem, forming a cycle; The thermal energy storage unit includes a molten thermal storage tank (3-1), a thermal storage circuit (3-L2), and a heating circulation circuit (3-L1). The thermal storage circuit (3-L2) includes a first circulation pump (3-2) and a first heat exchanger (3-3) for transporting and storing the thermal energy released by the first-stage CO2 condenser (1-2) in the molten thermal storage tank (3-1). The heating circulation circuit (3-L1) includes a second circulation pump (3-6) and a second heat exchanger (3-4) for extracting thermal energy from the molten thermal storage tank (3-1) during discharge and providing it to the power generation system. The molten heat storage tank (3-1) is filled with chemical melt material.

2. The cold and heat energy storage system for generating electricity using supercritical CO2 according to claim 1, characterized in that, The heat pump subsystem includes a first-stage heat pump circuit (1-L) and a second-stage heat pump circuit (2-L). The first-stage heat pump circuit (1-L) includes a first-stage CO2 compressor (1-1), a first-stage CO2 condenser (1-2), a first-stage expansion valve (1-4), and an evaporator (1-3) connected in sequence via pipes; the second-stage heat pump circuit (2-L) includes a second-stage CO2 compressor (2-1), a second-stage CO2 condenser (2-3), a receiving tank (2-4), and an expansion device for throttling to the triple point connected in sequence via pipes; The evaporator (1-3) of the first-stage heat pump circuit (1-L) and the second-stage CO2 condenser (2-3) of the second-stage heat pump circuit (2-L) are thermally coupled through a refrigerant circuit.

3. A cold and heat energy storage system for generating electricity using supercritical CO2 according to claim 2, characterized in that, The expansion device for throttling to the triple point is selected from an expansion valve (2-i-1) or an ejector (2-i'-1); the expansion device is configured to throttle liquid CO2 to the triple point state, forming a mixture of dry ice and gas phase and sending it into the cold energy storage unit.

4. A cold and heat energy storage system for generating electricity using supercritical CO2 according to claim 2, characterized in that, The cold energy storage unit is a dry ice refrigerator (2-5), which receives the mixture from the expansion device and has a gas phase outlet, which is connected to the inlet of the second-stage CO2 compressor (2-1) through a regenerator (2-6).

5. A cold and heat energy storage system for generating electricity using supercritical CO2 according to claim 1, characterized in that, It also includes a battery array (3-8) configured to store electrical energy during charging and provide auxiliary heating power to the system during discharging.

6. A cold and heat energy storage system for generating electricity using supercritical CO2 according to any one of claims 1-5, characterized in that, The electrical energy input comes from intermittent renewable energy sources, and the system is used to smooth the power output of renewable energy sources to achieve peak shaving and valley filling of the power grid.

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