Heat storage type gas storage device applied to compressed supercritical carbon dioxide energy storage system

Abstract

The invention discloses a heat storage type gas storage device applied to a compressed supercritical carbon dioxide energy storage system, which comprises a gas storage container, a carbon dioxide working medium and a heat storage module, the storage pressure of the carbon dioxide working medium is greater than 7.38 MPa, the heat storage module is in direct contact with the carbon dioxide working medium, and the heat storage module stores heat by sensible heat or phase change latent heat. The carbon dioxide working medium is in a liquid-like or two-phase-like region high-density state during high-pressure storage in the device, the heat storage module transfers heat to carbon dioxide in the energy release process, the temperature and pressure reduction rate of the carbon dioxide is reduced, and the carbon dioxide working medium is in a gas-like or two-phase-like region low-density state during low-pressure storage after energy release. In the energy storage process, carbon dioxide stores heat in a heat storage module, and the temperature and pressure rising rate of a carbon dioxide working medium is slowed down. The device has the advantages that the heat storage module can improve the change rate of the temperature and pressure of carbon dioxide, the storage / release amount of a carbon dioxide working medium is increased, and finally the energy storage density and the operation efficiency of the compressed supercritical carbon dioxide energy storage system can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of compressed carbon dioxide energy storage, and in particular, the present invention relates to a heat storage type gas storage device applied to a compressed supercritical carbon dioxide energy storage system. Technical Background

[0002] In today's power industry, the effective storage of electric energy is still a problem that needs to be solved urgently. People are in urgent need of an energy storage technology that is both economical and environmentally friendly. To this end, researchers have developed a variety of energy storage technologies, including but not limited to pumped storage, compressed gas energy storage, electrochemical energy storage, flywheel energy storage, etc. Compressed carbon dioxide energy storage (CCES) technology in compressed gas energy storage technology is currently a research hotspot, which has higher energy density, longer operating life and more compact system design.

[0003] The CCES system stores energy when electricity demand is low, uses excess electricity to drive the compressor to compress carbon dioxide, and stores energy in the form of high-pressure gas; it releases energy when electricity demand peaks, releases high-pressure carbon dioxide to drive the turbine generator set to generate electricity, and completes the conversion between electricity and gas potential energy. The CCES system is mainly composed of key components such as compressors, high-pressure gas storage tanks, low-pressure gas storage tanks, turbines and generators. The capacity of the gas storage tank, the pressure and temperature changes of the working fluid in the tank determine the system energy storage density and cycle efficiency. The CCES system often uses steel tanks to store gas. The constant volume energy release of this gas storage tank will cause the pressure and temperature in the tank to drop rapidly due to the expansion of carbon dioxide, the working fluid release amount is low, and the unit operation characteristics are poor; the energy storage process is the opposite. The constant volume energy storage of the gas storage tank will cause the pressure and temperature in the tank to rise rapidly due to the conversion of carbon dioxide compression work into heat energy, and the working fluid storage amount is reduced, which ultimately leads to a decrease in the energy storage density and cycle efficiency of the CCES system. Therefore, it is urgent to develop a new gas storage device for carbon dioxide energy storage system to slow down the temperature and pressure changes of the working fluid in the tank during the CCES energy storage and release process.

[0004] According to the physical properties of supercritical carbon dioxide (sCO2): the physical properties of sCO2 will diverge at the critical point. After leaving the critical point, the thermal properties of supercritical carbon dioxide still have a certain degree of divergence, and the farther away from the critical point, the weaker the divergence. Under a given pressure, there is a maximum value of isobaric specific heat capacity. The temperature at which the isobaric specific heat capacity reaches the maximum value is called the quasi-critical temperature T. pc , which is called the quasi-critical point. When the temperature of sCO2 is higher than the quasi-critical point, the density is small, while when the temperature is lower than the critical point, the density is large. pc The working fluid near the quasi-two-phase state is called the quasi-gas state (lower density), and the working fluid with a temperature higher than the quasi-two-phase state is called the quasi-liquid state (higher density). The boundary temperature between the quasi-gas state and the quasi-two-phase state is T + The boundary temperature between the two-phase state and the liquid state is T- Based on the above characteristics, the present invention proposes a heat storage type gas storage device applied to a supercritical carbon dioxide energy storage system. Summary of the invention

[0005] The purpose of the present invention is to provide a thermal storage gas storage device to address the problem of low working fluid utilization rate caused by rapid changes in temperature and pressure in a high-pressure gas storage device during the energy storage / release process of a compressed supercritical carbon dioxide energy storage system, which can slow down the changes in working fluid temperature and pressure in the gas storage device, thereby improving the energy storage density and system efficiency of the energy storage system and reducing construction costs.

[0006] A heat storage type gas storage device applied to a compressed supercritical carbon dioxide energy storage system comprises a gas storage container, a carbon dioxide working medium and a heat storage module, wherein the heat storage module is located in the gas storage container and is in direct contact with the carbon dioxide working medium for heat exchange; the storage pressure of the carbon dioxide working medium is greater than 7.38 MPa, and when energy storage is completed, the working medium stored at high pressure is in a liquid-like or two-phase-like region, and when energy release is completed, the working medium stored at low pressure is in a gas-like or two-phase-like region.

[0007] The temperature at which the high-pressure storage of carbon dioxide working fluid energy storage ends is lower than T + , T + is the boundary between the supercritical fluid two-phase region and the gas-like region, T + The calculation method is

[0008]

[0009] Among them, h 0,pc Indicates T pc Reference value of time enthalpy, T pc The temperature corresponding to the extreme value of the specific heat of carbon dioxide at constant pressure, c p,pc represents the maximum specific heat at constant pressure, γ is the adiabatic coefficient, and R is the gas constant;

[0010] The temperature of the carbon dioxide working fluid at the end of low-pressure storage is higher than T - , T - is the boundary between the supercritical fluid two-phase region and the liquid region, T - The calculation method is

[0011]

[0012] Among them, h 0,L Indicates the reference value of liquid state enthalpy, c p,L Specific heat of liquid at constant pressure.

[0013] In a preferred embodiment of the present invention, the working fluid exists in a liquid-like form when energy storage is completed, that is, the working fluid temperature is lower than T - ; At the end of energy release, the working fluid exists in a gas-like form, that is, the working fluid temperature is higher than T+ .

[0014] In the present invention, the gas storage container may be in the form of a gas storage tank, an underground cave, a salt cave or other natural or artificial space.

[0015] In a preferred embodiment of the present invention, the gas storage tank may be made of steel, aluminum alloy, organic material or other materials suitable for high-pressure gas storage.

[0016] In a preferred embodiment of the present invention, the gas storage tank is in a cylindrical, spherical, hemispherical or other geometric shapes. Preferably, the gas storage tank is a steel cylindrical gas storage tank.

[0017] The heat storage method of the heat storage module in the present invention can be sensible heat storage, phase change heat storage or a combination of the two. Preferably, the heat storage method is phase change heat storage, and the heat storage density is large.

[0018] In the present invention, the material of the heat storage module can be one or more of metal, ceramic or phase change material. When the heat storage material is a metal material and a ceramic material, preferably, these material structures should have a high specific surface area, be able to withstand high pressure and low airflow resistance. Preferably, the material structure of the metal material and the ceramic material is one or a combination of foam, granular, honeycomb, finned tube, and fiber.

[0019] Preferably, the metal material can be one or more of copper, aluminum, nickel, iron-chromium-aluminum alloy, and the material structure has a high specific surface area, such as foam metal, granular metal, honeycomb metal or metal fiber felt. Preferably, the metal material needs to have high specific heat and high density, such as copper; and the preferred material structure is foam metal, and its porosity can be from 70% to 98%.

[0020] Preferably, the ceramic material can be one or more of silicon nitride, silicon carbide, aluminum oxide, calcium silicate, lithium aluminum silicate or magnesium oxide stabilized zirconia, and the structure has the characteristics of high specific surface area, ability to withstand high pressure, low thermal expansion coefficient and low airflow resistance, such as foam ceramic, granular ceramic, honeycomb ceramic or finned ceramic tube structure.

[0021] In the present invention, when the heat storage material of the storage tank is a phase change material, the phase change temperature of the phase change material is T corresponding to the storage temperature of the high pressure state of the working fluid at the end of energy storage and the pressure of the gas storage device at the end of energy release. - Preferably, the phase change temperature is between the storage temperature of the working fluid in the high pressure state and the T corresponding to the pressure of the gas storage device at the end of energy release. + between.

[0022] Preferably, the phase change material is sodium acetate trihydrate (CH3COONa·3H2O), paraffin, hydrated sodium sulfate (Na2S·H2O), hydrated urea (CO(NH2)2·H2O), NaNO3-KNO2-NaNO2-LiNO3 quaternary molten salt and other materials whose phase change temperature meets the requirements, or a combination of the above materials.

[0023] In the present invention, when the phase change thermal storage material is incompatible with supercritical carbon dioxide, the phase change material is wrapped by a packaging material to form a phase change thermal storage unit. Preferably, the packaging material is a material with high thermal conductivity and corrosion resistance, and does not react with supercritical carbon dioxide and the phase change material. Preferably, it can be a metal or a polymer material.

[0024] Preferably, the packaging structure of the phase change heat storage unit is a straight tube type, a spiral tube type, a fin plate type, a shell and tube type or a phase change capsule type; the tube bundle arrangement is a straight row, a staggered arrangement, a spiral arrangement, etc.; the fin type is a straight fin, a corrugated fin, a serrated fin, a spiral fin, a folded fin or a rib fin, etc.

[0025] In the present invention, when energy storage ends, the carbon dioxide working fluid is stored at a relatively high density, and during the energy release process, as the pressure gradually decreases, the temperature of the carbon dioxide working fluid decreases, and the heat storage material can transfer heat to the carbon dioxide working fluid, thereby reducing the rate of change of its temperature and pressure, increasing the expansion capacity of the carbon dioxide working fluid, and thereby increasing the release amount of the carbon dioxide working fluid. Finally, when the energy release ends, the carbon dioxide is stored in a gas-like or two-phase-like low-density state. During the energy storage process, as the pressure in the gas storage device gradually increases, the compression work is converted into thermal energy, the temperature of the carbon dioxide working fluid increases, and the carbon dioxide working fluid transfers heat to the heat storage material, reducing the rate of increase of its temperature and pressure, and increasing the storage amount of the carbon dioxide working fluid. Finally, when the energy storage ends, the carbon dioxide working fluid is stored in a liquid-like or two-phase-like high-density state.

[0026] In the existing compressed carbon dioxide energy storage system, the gas storage device generally uses a fixed volume gas tank with a hollow interior. During the energy storage and release process, the temperature and pressure of the carbon dioxide working fluid change rapidly, the system operation characteristics are poor, and the energy storage density of the system is low. In order to improve the operating characteristics of the system, a throttle valve is often installed at the outlet of the gas storage container to keep the pressure at the turbine inlet and the compressor outlet constant, but this will introduce a large pressure loss and reduce the operating efficiency of the system. Therefore, it is necessary to develop a gas storage device to reduce the temperature and pressure change rate of the storage tank during the CCES energy storage and release process, and improve the operating efficiency of the CCES.

[0027] Beneficial technical effects of the present invention: The specific advantages of the present invention are as follows: When energy storage is completed, the temperature of the high-pressure carbon dioxide in the gas storage device is lower than the T under the current pressure. +, the density of the working fluid is relatively large, and more carbon dioxide can be stored at the same pressure and volume, increasing the energy storage density of the system; secondly, due to the decrease in temperature during the energy storage process and working fluid storage, the gas storage device can reduce the temperature difference with the outside world, reduce the investment in insulation materials outside the gas storage device, and thus reduce the investment cost; finally, due to the decrease in the rate of change of temperature and pressure during the gas storage process, the compressor outlet pressure can be maintained relatively constant, improving the operating characteristics of the unit. After the energy release is completed, the temperature of the high-pressure carbon dioxide in the gas storage device is higher than the T under the current pressure. - , the density of the working fluid is smaller, and the remaining carbon dioxide in the gas storage device is less under the same pressure and volume, so that the compressed carbon dioxide energy storage system can utilize more high-pressure carbon dioxide in the energy release process, increasing the energy output of the system and improving the energy storage density; secondly, the reduced pressure drop rate can effectively improve the turbine's work capacity, thereby improving the system's energy utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of an embodiment of a heat storage type gas storage device for a compressed supercritical carbon dioxide energy storage system according to the present invention;

[0029] Figure 2 This is the curve of 15Mpa supercritical carbon dioxide density changing with temperature;

[0030] Figure 3 A comparison diagram of pressure and temperature changes during energy storage / release in an embodiment of the present invention and a conventional storage tank;

[0031] Figure 4 A comparison diagram of the temperature variation over time during the energy storage / release process of the embodiment of the present invention and the traditional storage tank;

[0032] Figure 5 It is a comparison chart of the pressure change over time during the energy storage / release process of the embodiment of the present invention and the traditional storage tank. Specific implementation methods

[0034] The specific implementation method of the present invention is further described in detail below in conjunction with the examples and drawings. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0035] The heat storage type gas storage device applied to the compressed supercritical carbon dioxide energy storage system of the present invention comprises a gas storage container 1, a carbon dioxide working medium and a heat storage module 2, such as Figure 1 As shown. Among them, the pressure of carbon dioxide working fluid at the end of high-pressure storage is 15MPa, and the working fluid temperature is 61.05℃. According to the physical properties of carbon dioxide at 15MPa, T + is 181.34℃, T - is 35.03℃, the working fluid is in the quasi-two-phase region, tending towards the quasi-liquid region, such as Figure 2As shown in the figure, the pressure of carbon dioxide working fluid at low pressure storage after energy release is 10MPa, and the working fluid temperature is 47℃. According to the physical properties of carbon dioxide at 10MPa, T + is 69.27℃, T - It is 33.64℃, and the working fluid is in the quasi-two-phase region, tending towards the quasi-gas region.

[0036] The gas storage container in this embodiment is a gas storage tank, made of stainless steel, cylindrical in shape, with an internal volume of 1000m 3 The working fluid pressure range of carbon dioxide is 10MPa-15MPa, and the outlet flow rate of the energy storage process and the energy release process is maintained at 5kg / s.

[0037] In the thermal storage type gas storage system in the embodiment of the present invention, the thermal storage module is located in the storage tank body, and is in direct contact with the carbon dioxide working medium for heat exchange. The thermal storage module is sensible heat storage. The thermal storage module is composed of foamed metal copper with a porosity of 70%, which is evenly distributed at the bottom of the storage tank and has a specific heat of 390J / (kg·℃), wherein the actual copper volume accounts for 20% of the volume of the gas tank. The low-pressure storage temperature of 10Mpa supercritical carbon dioxide is 47℃, and the temperature of the thermal storage module is the same as the temperature of the carbon dioxide working medium.

[0038] like Figure 3 As shown, when electricity consumption is low, the motor drives the compressor to compress carbon dioxide for energy storage, and the compressed supercritical carbon dioxide is stored in the gas storage tank of the present invention. The compression work in the storage tank is converted into heat energy, and the working fluid temperature gradually increases from 47°C. In this process, part of the heat of the carbon dioxide working fluid is stored in the foam metal copper heat storage module. Compared with the traditional gas storage tank without heat storage module, the working fluid temperature rise rate is reduced, and the pressure rise rate is also reduced. Figure 4 and Figure 5 As shown. At the end of the energy storage process, the temperature of supercritical carbon dioxide rises to 61.05℃, which is in the quasi-two-phase region and tends to be in the quasi-liquid region, and the working fluid storage mass is 119.14t. In contrast, for the traditional gas storage tank without thermal storage module, at the same initial temperature and initial pressure, the energy storage end temperature is 67.99℃, and the working fluid mass stored in the energy storage stage is only 80.06t.

[0039] During peak hours of electricity consumption, the compressed carbon dioxide energy storage system releases energy, and supercritical carbon dioxide is discharged from the gas storage container to drive the turbine to generate electricity. During this energy release process, the pressure of the gas tank drops from 15MPa to 10MPa. As the pressure potential energy is converted into expansion work, the temperature drops from 61.05°C. During this process, the foamed copper heat storage module releases heat to the supercritical carbon dioxide working fluid. Compared with traditional gas tanks without heat storage modules, the working fluid temperature drop rate is reduced, and the pressure drop rate is also reduced (such as Figure 4 and Figure 5As shown), the energy release process is prolonged, the energy release time is increased, the turbine power generation is increased, and the energy storage density is improved. At the end of the energy release process, the temperature of supercritical carbon dioxide drops to 47°C, which is in a quasi-two-phase region and tends to be in a quasi-gas region, with a released mass of 119.14t. In contrast, for a gas tank without a thermal storage module, within the same pressure range, the initial release temperature is 67.99°C, the end release temperature is 47°C, and the released mass is 80.06t. The thermal storage module significantly improves the energy storage density of the energy storage system.

[0040] This embodiment is only a preferred specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A heat storage type gas storage device applied to a compressed supercritical carbon dioxide energy storage system, characterized in that: It comprises a gas storage container, a carbon dioxide working medium and a heat storage module, wherein the heat storage module is located in the gas storage container and is in direct contact with the carbon dioxide working medium for heat exchange; the storage pressure of the carbon dioxide working medium is greater than 7.38MPa, and the working medium stored at high pressure is in a liquid-like or two-phase region at the end of energy storage, and the working medium stored at low pressure is in a gas-like or two-phase region at the end of energy release.

2. A heat storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 1, characterized in that: The temperature at which the high-pressure storage of carbon dioxide working fluid energy storage ends is lower than T + , T + is the boundary between the supercritical fluid two-phase region and the gas-like region, T + The calculation method is Among them, h 0,pc Indicates T pc Reference value of time enthalpy, T pc The temperature corresponding to the extreme value of the specific heat of carbon dioxide at constant pressure, c p,pc represents the maximum specific heat at constant pressure, γ is the adiabatic coefficient, and R is the gas constant; The temperature of the carbon dioxide working fluid at the end of low-pressure storage after energy release is higher than T - , T - is the boundary between the supercritical fluid two-phase region and the liquid region, T - The calculation method is Among them, h 0,L Indicates the reference value of liquid state enthalpy, c p,L Specific heat of liquid at constant pressure.

3. A heat storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 1, characterized in that: The heat storage module stores heat in a sensible heat storage manner, a phase change heat storage manner or a combination of the two.

4. A thermal storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claims 1 and 3, characterized in that: The heat storage module is made of one or more of metal, ceramic or phase change material.

5. A heat storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 4, characterized in that: The material structure of the metal material and the ceramic material has a high specific surface area, can withstand high pressure and has low air flow resistance.

6. A heat storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 5, characterized in that: The material structure of the metal material and the ceramic material is one or a combination of foam, granular, honeycomb, finned tube, and fiber.

7. A heat storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 4, characterized in that: The phase change temperature of the phase change material is T corresponding to the storage temperature of the high pressure state of the working fluid at the end of energy storage and the pressure of the gas storage device at the end of energy release. - between.

8. A heat storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 4 or 6, characterized in that: The phase change material is sodium acetate trihydrate, paraffin, hydrated sodium sulfate, hydrated urea, NaNO3-KNO2-NaNO2-LiNO3 quaternary molten salt or a combination of the above materials.

9. A heat storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 4, characterized in that: When the phase change material is incompatible with supercritical carbon dioxide, the phase change material is wrapped by a packaging material to form a phase change heat storage unit. The packaging material is a material with high thermal conductivity and corrosion resistance, which does not react with supercritical carbon dioxide and the phase change material, and is a metal or polymer material.

10. A thermal storage type gas storage device for use in a compressed supercritical carbon dioxide energy storage system according to claim 1, characterized in that: At the end of energy storage, the carbon dioxide working fluid is stored at a higher density. During the energy release process, as the pressure gradually decreases, the temperature of the carbon dioxide working fluid decreases, and the thermal storage material can transfer heat to the carbon dioxide working fluid, thereby reducing the rate of change of its temperature and pressure, increasing the expansion capacity of the carbon dioxide working fluid, and thereby increasing the release amount of the carbon dioxide working fluid. Finally, at the end of energy release, the carbon dioxide is stored in a gas-like or two-phase low-density state. During the energy storage process, as the pressure in the gas storage device gradually increases, the compression work is converted into thermal energy, the temperature of the carbon dioxide working fluid increases, and the carbon dioxide working fluid transfers heat to the thermal storage material, reducing the rate of increase of its temperature and pressure, thereby increasing the storage amount of the carbon dioxide working fluid. Finally, at the end of energy storage, the carbon dioxide working fluid is stored in a liquid-like or two-phase high-density state.

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