Cold and hot energy storage system for generating power by using supercritical CO2

Abstract

The invention discloses a cold and heat energy storage system utilizing supercritical CO2 to generate power. The cold and heat energy storage system comprises a heat pump subsystem, a cold energy storage unit, a heat energy storage unit and a power generation subsystem. The heat pump subsystems are arranged in a stepped mode, and a mixture of dry ice and a liquid phase is generated at a CO2 three-phase point through electric energy driving. The cold energy storage unit is connected to the low-temperature side of the heat pump subsystem and used for storing generated dry ice. The heat energy storage unit is connected to the high-temperature side of the heat pump subsystem and used for storing heat energy generated in the compression process. The power generation subsystem is in fluid communication with the downstream of the cold energy and heat energy storage unit, heats the cold energy and heat energy storage unit to a supercritical state by using the output CO2 and heat energy, and expands to drive a power generator to generate power; the system forms a circulation loop, and fluid discharged by the power generation subsystem flows back to the heat pump subsystem; according to the technical scheme, the carbon dioxide three-phase point is used for achieving cold and heat collaborative energy storage, the energy storage density and efficiency are greatly improved, and finally efficient and stable power generation of renewable energy sources is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of large-scale energy storage, in particular to a cold-heat energy storage system for generating electricity by using supercritical CO2. BACKGROUND

[0002] With the rapid development of renewable energy generation technologies such as solar and wind energy, their inherent intermittency and volatility pose a serious challenge to the stable operation of the power grid. In order to achieve peak load shifting and smooth operation of the power grid, a large-scale and high-efficiency energy storage system must be developed to store excess electricity and release it during peak demand. Therefore, developing an economic and reliable large-scale energy storage technology has become a key link in promoting the transformation of energy structure.

[0003] At present, common large-scale energy storage methods mainly include pumped storage and battery storage. Although pumped storage is mature, it is heavily dependent on geographical conditions, has a long construction period and huge investment. Battery storage, such as lithium-ion batteries, has high energy density and rapid response, but has problems such as high cost, limited cycle life and safety, which makes it difficult to meet the demand for large-scale, long-term energy storage at the grid level. In addition, technologies such as compressed air energy storage generally have low system efficiency, insufficient energy density, or rely on specific geological structures, etc.

[0004] Under this background, it is urgent to explore high-efficiency energy storage systems based on new principles and new media. Carbon dioxide (CO2) based energy storage technology has attracted attention due to its wide availability, easy-to-reach critical parameters, and non-toxicity. However, existing liquid CO2 or supercritical CO2 energy storage systems usually only utilize its gas-liquid phase change or pressure energy, and there is still a lot of room for improvement in energy storage density and system compactness. The market urgently needs a new energy storage solution that can achieve high energy density, high system efficiency, environmental friendliness, and compact structure. SUMMARY

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

[0006] To achieve the above technical purpose, the technical solution of the present application is as follows: A cold-heat energy storage system for generating electricity by using supercritical CO2; The cold-heat energy storage system for generating electricity by using supercritical CO2 comprises a heat pump subsystem, a cold energy storage unit, a hot energy storage unit, and an electricity generation subsystem, The heat pump subsystem is arranged in a cascade manner and is used to generate a mixture containing dry ice and liquid phase near the triple point of CO2 by using electric energy; the cold energy storage unit, connected to the low temperature side of the heat pump subsystem, for storing the dry ice generated by the heat pump subsystem; the heat energy storage unit, connected to the high temperature side of the heat pump subsystem, for storing the heat energy generated by the heat pump subsystem; the power generation subsystem, fluidly connected downstream of the cold energy storage unit and the heat energy storage unit, for heating the CO2 outputted from the cold energy storage unit to a supercritical state and expanding to do work, driving the generator to generate electricity, using the heat energy outputted from the heat energy storage unit; wherein the fluid discharged from the power generation subsystem is returned to the heat pump subsystem, forming a cycle.

[0007] Further, the heat pump subsystem comprises a first stage heat pump circuit and a second stage heat pump circuit; the first stage heat pump circuit comprises a first stage CO2 compressor, a first stage CO2 condenser, a first stage expansion valve and an evaporator connected in sequence by pipes; the second stage heat pump circuit comprises a second stage CO2 compressor, a second stage CO2 condenser, a receiving tank and an expansion device for throttling to a triple point; the evaporator of the first stage heat pump circuit is thermally coupled to the second stage CO2 condenser of the second stage heat pump circuit through a refrigerant circuit.

[0008] Further, the expansion device for throttling to a triple point is selected from an expansion valve or an ejector; the expansion device is configured to throttle the liquid CO2 to a triple point state, forming a mixture of dry ice and gas phase and feeding into the cold energy storage unit.

[0009] Further, the cold energy storage unit is a dry ice refrigeration tank, which receives the mixture from the expansion device and is provided with a gas phase outlet connected to the inlet of the second stage CO2 compressor through a regenerator.

[0010] Further, the heat energy storage unit comprises a molten heat storage tank, a heat storage circuit and a heating circulation circuit; the heat storage circuit comprises a first circulating pump and a first heat exchanger, for transporting and storing the heat energy released by the first stage CO2 condenser in the molten heat storage tank; the heating circulation circuit comprises a second circulating pump and a second heat exchanger, for extracting heat energy from the molten heat storage tank and providing it to the power generation subsystem during discharge.

[0011] Further, the molten heat storage tank is filled with a chemical melt material.

[0012] Further, a high temperature heat exchanger is coupled to the heating circulation circuit for receiving heat energy; a superheating heat exchanger arranged downstream of the coupling high-temperature heat exchanger; a turbine unit comprising a high-pressure CO2 gas turbine and a low-pressure CO2 gas turbine, the high-pressure CO2 gas turbine receiving supercritical CO2 from the superheating heat exchanger and generating power by work; a CO2 regenerative heat exchanger for exchanging heat between exhaust gas of the turbine unit and CO2 fluid from the cold energy storage unit.

[0013] Further, the power generation sub-system further comprises: a coupling low-temperature heat exchanger for initially heating CO2 from the regenerator; a first gas compressor and a second gas compressor arranged on the fluid passage for compressing CO2 working fluid flowing to the turbine unit.

[0014] Further, a battery array is further included, which is configured to store electrical energy during charging period and provide auxiliary heating power for the system during discharging period.

[0015] Further, the electrical energy input is from intermittent renewable energy, and the system is used for smoothing the power output of renewable energy and realizing peak shaving of power grid.

[0016] The present application has the following beneficial effects: by using dry ice and liquid mixture near the triple point of carbon dioxide to store cold energy, and simultaneously using heat pump system to store compression heat in the form of latent heat in chemical melt such as molten salt, the bidirectional collaborative storage of cold energy and heat energy is realized, so that the energy density and energy storage efficiency of the whole energy storage system are greatly improved, and the system structure is more compact; then by using the stored heat energy to heat the dry ice to a high-temperature high-pressure supercritical state to drive the turbine to expand and generate power during energy release, the intermittent renewable energy is efficiently, stably and economically converted into dispatchable power grid power, the investment recovery period is short, and the application value is significant. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described in the following only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 is a whole structure schematic diagram of a cold and heat energy storage system using supercritical CO2 power generation according to the present application; In the figure: 1-L, first stage CO2 heat pump circulation 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 circulation loop; 2-1, second stage CO2 compressor; 2-2, CO2 gas 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 cold storage tank; 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 pressure CO2 gas turbine; 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 electric energy; E-2, second input electric energy; E-3, third input electric energy; E-4, fourth input electric energy; P, system output; P-1, first output electric energy; P-2, second output electric energy. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0020] It should be understood that, in the description of the embodiments of the present application, the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the present application. In addition, the terms "first", "second" are only for description purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "several" is two or more, unless otherwise explicitly specified.

[0021] As Figure 1 shown, a cold and heat energy storage system for generating electricity by using supercritical CO2 according to an embodiment of the present application 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 manner and is used to generate a mixture containing dry ice and liquid phase near the triple point of CO2 by using electric 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 generated by the heat pump subsystem; The heat energy storage unit is connected to the high-temperature side of the heat pump subsystem and is used to store the heat energy generated by the heat pump subsystem; The power generation subsystem is connected to the downstream of the cold energy storage unit and the heat energy storage unit in a fluid channel and is used to heat CO2 to a supercritical state and expand to do work by using the CO2 output by the cold energy storage unit and the heat energy output by the heat energy storage unit, so as to drive the generator to generate electricity; Wherein, the fluid discharged by the power generation subsystem flows back to the heat pump subsystem to form a cycle.

[0022] In a specific embodiment, the heat pump subsystem according to the cold and heat energy storage system for generating electricity by using supercritical CO2 comprises 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 comprises 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 by pipes; the second-stage heat pump circuit 2-L comprises 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 a triple point; The evaporator 1-3 of the first-stage heat pump circuit 1-L is thermally coupled with the second-stage CO2 condenser 2-3 of the second-stage heat pump circuit 2-L through a refrigerant circuit.

[0023] In a specific embodiment of the cold and heat energy storage system for power generation using supercritical CO2 according to the present application, the expansion device for throttling to a 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 a triple point state to form a mixture of dry ice and gas phase and send the mixture into the cold energy storage unit.

[0024] In a specific embodiment of the cold and heat energy storage system for power generation using supercritical CO2 according to the present application, the cold energy storage unit is a dry ice cold storage tank 2-5 which receives the mixture from the expansion device and is provided with a gas phase outlet connected with the inlet of the second-stage CO2 compressor 2-1 through a regenerator 2-6.

[0025] In a specific embodiment of the cold and heat energy storage system for power generation using supercritical CO2 according to the present application, the heat energy storage unit comprises a molten heat storage tank 3-1, a heat storage circuit 3-L2 and a heating circulation circuit 3-L1. The heat storage circuit 3-L2 comprises a first circulating pump 3-2 and a first heat exchanger 3-3 for transporting and storing the heat energy released by the first-stage CO2 condenser 1-2 in the molten heat storage tank 3-1. The heating circulation circuit 3-L1 comprises a second circulating pump 3-6 and a second heat exchanger 3-4 for extracting heat energy from the molten heat storage tank 3-1 and providing the heat energy to the power generation system during discharge.

[0026] In a specific embodiment of the cold and heat energy storage system for power generation using supercritical CO2 according to the present application, the molten heat storage tank 3-1 is filled with a chemical melt material.

[0027] In a specific embodiment of the cold and heat energy storage system for power generation using supercritical CO2 according to the present application, a high-temperature coupled heat exchanger 2-9 is connected with the heating circulation circuit 3-L1 for receiving heat energy. A superheated heat exchanger 2-11 is arranged downstream of the high-temperature coupled heat exchanger 2-9. a turbine set comprising a high pressure CO2 gas turbine 2-12 receiving supercritical CO2 from the superheating heat exchanger 2-11 and doing work to generate electricity, and a low pressure CO2 gas turbine 2-13 receiving supercritical CO2 from the superheating heat exchanger 2-11 and doing work to generate electricity; a CO2 regenerative heat exchanger 2-14 for exchanging heat between exhaust gas of the turbine set and CO2 fluid from the cold energy storage unit.

[0028] According to the cold and heat energy storage system for supercritical CO2 power generation, in a specific embodiment, the power generation system further comprises: a coupling low temperature heat exchanger 2-7 for initially heating CO2 from the regenerator 2-6; a first gas compressor 2-8 and a second gas compressor 2-10 arranged on a fluid passage for compressing CO2 working fluid flowing to the turbine set.

[0029] According to the cold and heat energy storage system for supercritical CO2 power generation, in a specific embodiment, further comprising a battery array 3-8 configured to store electrical energy during charging period and provide auxiliary heating power for the system during discharging period.

[0030] According to the cold and heat energy storage system for supercritical CO2 power generation, in a specific embodiment, the electrical energy input is from intermittent renewable energy, and the system is used to smooth the power output of renewable energy and realize peak shaving of power grid.

[0031] In order to facilitate the understanding of the above technical solutions of the present application, the above technical solutions of the present application are described in detail below through specific system structure and action principle.

[0032] In specific use, according to the cold and heat energy storage system for supercritical CO2 power generation, during charging period, the compressor is compressed by electrical energy provided by renewable energy or economic energy, and a CO2 heat pump system arranged in stages generates dry ice with liquid mixture at triple point and stores it in a cold tank. In the stage arrangement of the heat pump, while the dry ice is stored in the cold tank, the heat energy is also stored in the hot tank as heat energy, and the chemical melt in the hot tank is liquefied by heat energy, storing a large amount of heat energy. The energy stored in the form of dry ice is completed by the next stage of heat pump, and the energy stored in the form of melt is completed by the previous stage of heat pump.

[0033] At the time of discharge, the cold energy stored in the cold tank in the form of dry ice (mixed with liquid phase) is heated by the heat energy stored in the hot tank, while heating the CO2, so that the dry ice absorbs a large amount of latent heat to reach a high-temperature and high-pressure supercritical state. Auxiliary heating can be provided by the electrical energy provided by the battery array (such as lithium-ion battery) during the charging period.

[0034] The supercritical CO2 gas is finally expanded in the turbine (both high and low pressure stages) to generate electrical energy output. The generated electrical energy is utilized in the power grid with great economic value. During the discharge period, the discharged CO2 gas is cooled simultaneously with the sublimated dry ice, thereby cooling the hot storage tank and re-solidifying the melted melt.

[0035] Due to the adoption of the dry ice cold store and the melt hot cold store, the system structure is compact compared with the traditional liquid gas storage system. The compactness ratio of the existing system of the patent is as small as 1 / 100. The system also has very high efficiency because the current system adopts the highest potential area of carbon dioxide performance. When expressed in energy density, the efficiency is as high as 40 kwh / m3 or more compared with the traditional liquid gas energy level system. The patent has the advantages of short investment recovery period and economical operation, and has wide practical application value in the refrigeration, power generation and other industries.

[0036] Element details of the carbon dioxide dry ice battery: The first stage CO2 heat pump circulation loop 1-L is composed of the following elements: The first stage CO2 compressor 1-1 is used to circulate CO2 in the first stage CO2 compressor 1-1, and is arranged in parallel to control the pressure and flow of CO2 to change with the input power of the first input electrical energy E-1.

[0037] The first stage CO2 condenser 1-2 delivers the hot gas (for example, 100℃-120℃) discharged by the first stage CO2 compressor 1-1 to the liquid phase at a certain pressure, and the condensation heat (thermal energy) in the CO2 hot gas is exchanged and transferred to the heat storage loop 3-L2 through the heat exchanger 3-1, and is stored in the form of thermal energy in the heat storage water tank of the heat exchanger 3-1 after exchange.

[0038] The low-pressure two-phase liquid gas mixture in the evaporator 1-3 is evaporated at low temperature by exchanging cold energy with the second stage CO2 condenser 2-3. Between the evaporator 1-3 and the condenser 2-3, the refrigerant loop circulates the refrigerant to transfer cold energy.

[0039] The first stage expansion valve 1-4 generates a given condition of the evaporator 1-3 by adjusting the mass flow, and in the assistance of the pressure regulating valve 1-5, the first stage expansion valve 1-4 sends out various states in the flow passage for the temperature and pressure of the evaporator 1-3, and automatically cooperates with the evaporator 1-3 to work.

[0040] Pressure regulating valve 1-5, automatically regulating mass flow and pressure to reach the set temperature of evaporator 1-3.

[0041] Refrigerant pump 1-6 pumps the circulating refrigerant between evaporator 1-3 and second stage CO2 condenser 2-3, evaporator 1-3 and second stage CO2 condenser 2-3, first stage expansion valve 1-4, and can be combined into one unit in the shell tank.

[0042] Second stage CO2 heat pump cycle loop 2-L, including the following elements: Second stage CO2 compressor 2-1, CO2 in second stage CO2 compressor 2-1, arranged in parallel to control the pressure and flow of CO2 with the change of input power first input electric energy E-1.

[0043] CO2 storage tank 2-2, which can be externally charged with fresh CO2 (gaseous or liquid phase).

[0044] First heat exchanger 3-3, at the same pressure as the outlet of second stage CO2 compressor 2-1, converts cold air (e.g. -20℃-25℃ discharged from second stage CO2 compressor 2-1) into liquid. The condensation heat (thermal energy) in the CO2 cold gas is transferred to the circulating refrigerant driven by refrigerant pump 1-6, which is used to supply the required cold quantity for evaporator 1-3. The condensed liquid CO2 is then transferred to receiving tank 2-4.

[0045] First stage expansion valve 1-4 receiving tank separates the liquid phase from the excess gas phase, and only the liquid CO2 circulates to first expansion process section 2-i.

[0046] First expansion process section 2-i part: Second stage expansion valve 2-i-1, used for throttling to make liquid CO2 into a liquid-gas mixture at the lowest pressure and temperature state. In this technical solution, this throttling process causes the CO2 triple point, i.e. temperature = -56.6℃≈-56℃, pressure = 0.518MPa≈-0.52 MPa, so that a mixture of dry ice and gas phase is formed after the expansion process. Dry ice and mixed steam are flushed into dry ice cold storage tank 2-5. Second stage expansion valve 2-i-1 and first pressure regulating valve 2-i-2 work automatically in coordination through various states in the sensing flow channel.

[0047] First pressure regulating valve 2-i-2, regulating mass flow and pressure to automatically set the triple point state.

[0048] Second expansion process section 2-i' part: Ejector 2-i'-1, which is operated by the liquid phase of the receiving tank 2-4 and the return phase of the regenerator 2-6, produces the same function as the second stage expansion valve 2-i-1. The second stage CO2 heat pump cycle loop 2-L is large in system scale, and the pressure drop in the expansion process is large, so the ejector 2-i'-1 is effective. The ejector 2-i'-1 gives a CO2 triple point state similar to that of the second stage expansion valve 2-i-1.

[0049] Second pressure regulating valve 2-i'-2, which adjusts the mass flow and pressure, automatically sets the triple point state.

[0050] Dry ice refrigeration tank 2-5, which receives dry ice and liquid gas mixture from the first expansion process section 2-i or the second expansion process section 2-i', and CO2 returned through the regenerator 2-6, and is flushed inside the dry ice refrigeration tank 2-5. The flushing gas phase at the same temperature at the triple point is separated at the top of the tank and circulated to the second stage CO2 compressor 2-1. The shape, volume, and structural material are designed according to the refrigeration system.

[0051] Regenerator 2-6, which performs cold and heat exchange, makes the temperature of the liquid CO2 discharged from the dry ice refrigeration tank 2-5 (-56°C) the same as that of the CO2 regenerative heat exchanger 2-14. On the other hand, the remaining carbon dioxide is heated to a gas phase at the same triple pressure.

[0052] Coupling low-temperature heat exchanger 2-7, which exchanges the low-temperature gas heat of the regenerator 2-6 with the circulating medium heat of the superheating heat exchanger 2-11 in a separate third cycle loop 3-L.

[0053] First gas compressor 2-8, which compresses the CO2 gas in the coupling low-temperature heat exchanger 2-7 and sends it to the CO2 regenerative heat exchanger 2-14. The power input to drive the first gas compressor 2-8 is the second input power D-2.

[0054] Coupling high-temperature heat exchanger 2-9, which receives the high-temperature gas heat of the receiving tank 2-4 and the low-temperature circulating medium heat of the molten heat storage tank 3-1 through the second heat exchanger 3-4 and the second circulating pump 3-6 installed in the third cycle loop 3-L.

[0055] Second gas compressor 2-10, which compresses the CO2 gas in the coupling high-temperature heat exchanger 2-9 and sends the gas to the superheating heat exchanger 2-11. The power input to drive the second gas compressor 2-10 is the first input power D-1.

[0056] The superheating heat exchanger 2-11 heats the CO2 gas coupled with the high-temperature heat exchanger 2-9 to the highest temperature of the second-stage CO2 heat pump circulation loop 2-L, and drives the high-pressure CO2 gas turbine 2-12. The backflow circulation medium reduces the exhaust heat coupled with the low-temperature heat exchanger 2-7 in an independent circulation loop of one second-stage CO2 heat pump circulation loop 2-L.

[0057] The high-pressure CO2 gas turbine 2-12 receives the high-temperature gas of the superheating heat exchanger 2-11, and drives the generator attached to the rotating shaft through the speed regulation gas tank to generate the first output electric energy P-1. The high-pressure CO2 gas turbine 2-12 performs the first stage of the expansion process, i.e., the first expansion process section 2-i.

[0058] The low-pressure CO2 gas turbine 2-13 receives the high-temperature exhaust gas discharged by the high-pressure CO2 gas turbine 2-12, and performs the second-stage expansion process. The low-pressure CO2 gas turbine 2-13 drives the generator attached to the rotating shaft through the speed regulation gear tank to generate the second output electric energy P-2.

[0059] The CO2 regenerative heat exchanger 2-14 is used for heat exchange between the exhaust gas of the low-pressure CO2 gas turbine 2-13 and the exhaust gas coupled with the low-temperature heat exchanger 2-7. The cooled gas of the CO2 regenerative heat exchanger 2-14 is circulated to the regenerator 2-6, and the heated gas of the CO2 regenerative heat exchanger 2-14 is circulated to the coupled high-temperature heat exchanger 2-9, and the second-stage CO2 heat pump circulation loop 2-L is closed.

[0060] The heating circulation loop 3-L1 heats the circulation exothermicity, which consists of the following parts: The molten heat storage tank 3-1 receives the heat of 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.

[0061] The molten heat storage tank 3-1 contains heat-absorbing materials, such as chemical melt materials, which can store a large amount of heat (thermal) thermal energy in a liquid state after melting at a given (fixed) temperature. The molten material can also release heat energy (heat) to solidify the thermal energy in a liquid state. Due to the absorption and release of latent heat, the solid-liquid heat process in the structure of the storage tank can store a large amount of thermal energy in a small scale. In the liquid phase exothermic process, the heat transfer can be enhanced by using the connecting device 3-5, and the input connecting device 3-5 is the third input electric power D-3.

[0062] The first circulation pump 3-2 circulates the heat delivery medium (such as hot oil) from the first-stage CO2 condenser 1-2 to the first heat exchanger 3-3 in the independent loop of the heat storage circuit 3-L2; The first heat exchanger 3-3 releases heat energy to the heat-absorbing materials contained in the molten heat storage tank 3-1.

[0063] The second heat exchanger 3-4 absorbs heat (thermal) energy and releases heat to the heating circulation loop 3-L1.

[0064] The connecting device 3-5 (such as connecting fan) connects the liquid of the melt to enhance the heat transfer of the first heat exchanger 3-3 and the second heat exchanger 3-4. The electric input of the connecting device 3-5 is the fourth input power D-4.

[0065] 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 electric power input of the second circulation pump 3-6 is the third input power D-3.

[0066] The electric heater 3-7 heats the heat transfer medium in the coupled high-temperature heat exchanger 2-9 to the highest point and then sends it to the superheating heat exchanger 2-11. The electric power is supplied by the battery array 3-8, such as lithium-iron battery array.

[0067] The battery array 3-8 stores electric energy through the fourth input electric energy E-4.

[0068] The heat storage loop 3-L2 includes the first heat exchanger 3-3, the first-stage CO2 condenser 1-2, and the first circulation pump, and the heat storage loop 3-L2 charges the heat energy of the first-stage CO2 heat pump circulation loop 1-L into the molten heat storage tank 3-1.

[0069] Energy input and output: Charging period (for example, 10 hours) and discharging period (for example, 5 hours) The first input electric energy E-1 and the second input electric energy E-2 are respectively for the compression work done by the first-stage CO2 compressor 1-1 and the second-stage CO2 compressor 2-1 in operation.

[0070] In the present technical solution, the first input electric energy E-1 and the second input electric energy E-2 are supplied by the excess energy of natural resources such as solar energy, wind energy, and geothermal energy, or discounted electricity supply during night charging.

[0071] The third input electric energy E-3 is used to drive the first circulation pump 3-2 during charging. The electric energy source is the same as the first input electric energy E-1 and the second input electric energy E-2.

[0072] The fourth input electric energy E-4 is the auxiliary power storage of the same electric energy source as the first input electric energy E-1 and the second input electric energy E-2. The fourth input electric energy E-4 is used to boost the circulating medium in the heating circulation loop 3-L1.

[0073] The first output electric energy P-1 and the second output electric energy P-2 are powers output by the high-pressure CO2 gas turbine 2-12 and the low-pressure CO2 gas turbine 2-13 during system operation, and are supplied to the outside at a high output power during discharging.

[0074] The first input electric power D-1 and the second input electric power D-2 represent electric powers of the first gas compressor 2-8 and the second gas compressor 2-10 during discharging. The input powers of the first input electric power D-1 and the second input electric power D-2 can be partially provided by the first output electric energy P-1 and the second output electric energy P-2.

[0075] The third input electric power D-3 is an input power during discharging, and the input power of the third input electric power D-3 can be partially provided by the first output electric energy P-1 and the second output electric energy P-2.

[0076] The fourth input electric power D-4 is present during both charging and discharging. The power of the fourth input electric power D-4 can be divided into two periods according to system operation, and is supplied by the system input E or the system output P.

[0077] In summary, by means of the above technical solutions of the present application, through the use of dry ice and liquid mixture generated by carbon dioxide near the triple point for cold energy storage, and the use of heat pump system to store compressed heat in the form of latent heat in the chemical melt such as molten salt, the bidirectional collaborative storage of cold energy and heat energy is realized, so that the energy density and energy storage efficiency of the entire energy storage system are greatly improved, and the system structure is more compact. Further, by using the stored heat energy to heat the dry ice to a high-temperature and high-pressure supercritical state to drive the turbine to expand and generate electricity during energy release, the intermittent renewable energy is efficiently, stably and economically converted into dispatchable grid power, the investment recovery period is short, and the application value is significant.

[0078] The above only describes the preferred embodiments of the present application and should not be used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A cold heat energy storage system for power generation using supercritical CO2, characterized by, The system 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 manner and is driven by electric energy to generate a mixture containing dry ice and liquid phase near the triple point of CO2; 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 generated by the heat pump subsystem; The heat energy storage unit is connected to the high-temperature side of the heat pump subsystem and is used to store the heat energy generated by the heat pump subsystem; The power generation subsystem is connected downstream of the cold energy storage unit and the heat energy storage unit and is used to heat CO2 to a supercritical state and expand to do work to drive a generator to generate electricity by using the CO2 output by the cold energy storage unit and the heat energy output by the heat energy storage unit; The fluid discharged by the power generation subsystem is returned to the heat pump subsystem to form a cycle.

2. The cold and heat storage system using supercritical CO2 for power generation according to claim 1, wherein The heat pump subsystem comprises 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) comprises a first-stage CO2 compressor (1-1), a first-stage CO2 condenser (1-2), an evaporator (1-3) and a first-stage expansion valve (1-4) connected in sequence by pipelines; the second-stage heat pump circuit (2-L) comprises 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; The evaporator (1-3) of the first-stage heat pump circuit (1-L) is thermally coupled to the second-stage CO2 condenser (2-3) of the second-stage heat pump circuit (2-L) through a refrigerant circuit.

3. The cold and heat storage system using supercritical CO2 for power generation according to claim 2, wherein 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 to form a mixture of dry ice and gas phase and send the mixture into the cold energy storage unit.

4. The cold and heat storage system using supercritical CO2 for power generation according to claim 2, wherein The cold energy storage unit is a dry ice refrigeration tank (2-5) which receives the mixture from the expansion device and is provided with a gas phase outlet connected to the inlet of the second-stage CO2 compressor (2-1) through a regenerator (2-6).

5. The cold and heat storage system using supercritical CO2 for power generation according to claim 2, wherein The heat energy storage unit comprises a molten heat storage tank (3-1), a heat storage circuit (3-L2) and a heating circulation circuit (3-L1); The heat storage circuit (3-L2) comprises a first circulating pump (3-2) and a first heat exchanger (3-3) for transporting and storing the heat energy released by the first-stage CO2 condenser (1-2) in the molten heat storage tank (3-1); The heating circulation circuit (3-L1) comprises a second circulating pump (3-6) and a second heat exchanger (3-4) for extracting heat energy from the molten heat storage tank (3-1) and providing the heat energy to the power generation subsystem during discharge.

6. The cold and heat storage system using supercritical CO2 for power generation according to claim 5, wherein The molten heat storage tank (3-1) is filled with a chemical melt material.

7. The cold and heat storage system using supercritical CO2 for power generation according to claim 1, wherein A high-temperature heat exchanger (2-9) is coupled to the heating circulation circuit (3-L1) and is used to receive heat energy; a superheating heat exchanger (2-11) disposed downstream of the coupling high-temperature heat exchanger (2-9); a turbine unit comprising a high-pressure CO2 gas turbine (2-12) and a low-pressure CO2 gas turbine (2-13), the high-pressure CO2 gas turbine (2-12) receiving supercritical CO2 from the superheating heat exchanger (2-11) and generating power by work; a CO2 regenerative heat exchanger (2-14) for exchanging heat between exhaust gas of the turbine unit and CO2 fluid from the cold energy storage unit.

8. The cold and heat storage system using supercritical CO2 for power generation according to claim 7, wherein The power generation subsystem further comprises: a coupling low-temperature heat exchanger (2-7) for preliminary heating of CO2 from the regenerator (2-6); a first gas compressor (2-8) and a second gas compressor (2-10) disposed in a fluid passage for compressing CO2 working fluid flowing to the turbine unit.

9. The cold and heat storage system using supercritical CO2 for power generation according to claim 1, wherein, a battery array (3-8) configured to store electrical energy during a charging period and to provide auxiliary heating power for the system during a discharging period.

10. A cold and heat storage system using supercritical CO2 power generation according to any one of claims 1 to 9, characterized by, The electrical energy input is from intermittent renewable energy sources, and the system is used to smooth the power output of renewable energy sources and to realize peak shaving of the power grid.

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