Offshore constant-pressure compressed carbon dioxide energy storage system and method coupled with ocean temperature difference

Abstract

The invention discloses an ocean temperature difference coupled offshore constant-pressure compressed carbon dioxide energy storage system and method, and relates to the technical field of compressed gas energy storage. The system comprises a working medium constant-pressure storage device, a carbon dioxide energy storage circulation loop, a carbon dioxide energy release circulation loop and a heat storage circulation loop. Gaseous carbon dioxide is condensed into a liquid state by utilizing deep sea low-temperature seawater in an energy storage stage, liquid carbon dioxide is evaporated into a gaseous state by utilizing shallow sea high-temperature seawater in an energy release stage, and gas-liquid conversion of carbon dioxide is realized by fully utilizing ocean new energy and ocean temperature difference; the flexible working medium constant-pressure storage device is used for storing low-pressure gaseous carbon dioxide and high-pressure liquid carbon dioxide, the constant pressure of the working medium constant-pressure storage device in the charging and discharging process can be guaranteed, and efficient and stable operation of the system is achieved. Efficient liquefaction and high-density storage of high-pressure carbon dioxide are achieved through the ocean temperature difference and seawater static pressure, the efficiency and energy density of the energy storage system are improved, and deep development of offshore resources is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermo-mechanical energy storage, and more particularly to an offshore constant-pressure compressed carbon dioxide energy storage system and method coupled with ocean thermal energy difference. Background Art

[0002] In order to achieve the goal of carbon neutrality, it is imperative to vigorously develop new energy sources such as solar energy and wind energy to replace traditional energy sources. Since new energy sources such as wind power and photovoltaic power are intermittent and volatile, directly connecting to the grid will impact the power grid. At the same time, it is difficult to synchronize the energy consumption on the user side with the renewable energy generation. Therefore, large-scale long-term storage of electric energy is of great significance for the construction of a new power system. With the development of photovoltaic and wind power, onshore photovoltaic and wind power are restricted by land resources, while the ocean accounts for 71% of the earth's surface area. Therefore, offshore wind power and offshore photovoltaic power have emerged. By making full use of ocean space and high-quality resources, they show broad development prospects. As offshore wind power and photovoltaic power develop towards large-scale and deep-water, the problem of new energy consumption becomes more intractable. There are limitations in transmitting deep-sea power generation to the nearby onshore grid through cables. Therefore, exploring the local consumption of offshore wind power and photovoltaic power has become increasingly important in the current context. In order to suppress the fluctuations of wind power and photovoltaic power, a certain capacity of energy storage needs to be configured. Therefore, it is urgent to develop an energy storage system for local consumption of deep-sea wind power and photovoltaic power.

[0003] Compressed gas energy storage, including compressed air energy storage and carbon dioxide energy storage, is a thermo-mechanical energy storage technology. Its principle is to use off-peak electric energy to drive a compressor to compress and store gas in a gas storage reservoir, converting electric energy into the internal energy of the gas; during peak electricity consumption periods, high-pressure gas is released, heated, and then drives a generator to generate electricity through an expander, realizing the release of electric energy. Due to its excellent thermodynamic properties and environmental friendliness, carbon dioxide has attracted increasing attention. Compared with air, carbon dioxide has higher density and thermal conductivity in the near-critical region, enabling more energy to be stored in a smaller volume. Therefore, compressed carbon dioxide energy storage systems have significant advantages in improving energy conversion efficiency and volumetric energy density. In addition, compressed carbon dioxide energy storage can sequester a large amount of carbon dioxide captured and enriched by carbon capture, and it is a typical carbon dioxide utilization technology. According to the storage state of the working fluid, compressed carbon dioxide energy storage can be divided into different types, such as high-pressure liquid storage / low-pressure gas storage, high-pressure liquid storage / low-pressure liquid storage, etc. Among them, the subcritical gas-liquid storage scheme of high-pressure liquid storage / low-pressure gas storage has become the current mainstream technology due to its high round-trip efficiency, low investment cost, and high technology maturity. Chinese invention patent with publication number CN112985144B proposes a compressed carbon dioxide energy storage device and method based on gas-liquid phase change, which uses a throttle valve and a water tank to realize the gas-liquid conversion of carbon dioxide, and uses a constant-volume liquid storage tank to store high-pressure liquid carbon dioxide. However, when the ambient temperature is high and insufficient to liquefy carbon dioxide near the critical point, an additional refrigerator is required to provide the cold energy required for liquefaction, resulting in a reduction in system efficiency and an increase in cost. For the storage of high-pressure carbon dioxide, when using a constant-volume storage tank, the volume of the storage tank cannot be fully utilized (the utilization rate is about 50%), or the storage pressure changes, resulting in the turbine and compressor operating under off-design conditions, causing a reduction in energy storage density and round-trip efficiency. Summary of the Invention

[0004] In order to overcome the disadvantages of difficult liquefaction and difficult constant storage of high-pressure carbon dioxide in the prior art, the purpose of the present invention is to provide an offshore constant-pressure compressed carbon dioxide energy storage system and method coupled with ocean thermal energy difference. During the energy storage stage, the system uses deep-sea low-temperature seawater to condense gaseous carbon dioxide into liquid, and during the energy release stage, it uses shallow-sea high-temperature seawater to evaporate liquid carbon dioxide into gas, making full use of marine new energy and ocean thermal energy difference to realize the gas-liquid conversion of carbon dioxide; a flexible working fluid constant-pressure storage device is used to store low-pressure gaseous and high-pressure liquid carbon dioxide, realizing a constant pressure during the charging and discharging processes of the working fluid constant-pressure storage device. By constructing the compressed carbon dioxide energy storage on-site at the offshore new energy power generation side, making full use of the special marine environment and marine energy, realizing the local utilization of resources and the deep coupling of the system, improving the efficiency and energy density of the energy storage system, and realizing the deep development of marine resources.

[0005] In order to achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] Marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean thermal difference, comprising: a working medium constant-pressure storage device, a carbon dioxide energy storage cycle loop, a carbon dioxide energy release cycle loop, and a heat storage cycle loop;

[0007] Working medium constant-pressure storage device: It includes a low-pressure gas storage bag 1 for storing low-pressure gaseous carbon dioxide at a constant pressure and a high-pressure liquid storage bag 10 for storing high-pressure liquid carbon dioxide at a constant pressure;

[0008] Carbon dioxide energy storage cycle loop: The outlet of the low-pressure gas storage bag 1 is connected to the inlet of the high-pressure liquid storage bag 10 through the carbon dioxide energy storage cycle loop. The power input shaft of the carbon dioxide energy storage cycle loop is connected to the power output shaft of the motor 2, and the electrical energy inlet of the motor 2 is connected to the electrical energy outlet of marine new energy power generation; Marine new energy power generation supplies power to the motor 2, and the compressor is driven by the motor 2 to compress low-pressure gaseous carbon dioxide to a high-pressure state, and then deep-sea low-temperature seawater is used to condense the high-pressure carbon dioxide into a liquid state and store it in the high-pressure liquid storage bag 10;

[0009] Carbon dioxide energy release cycle loop: The inlet of the low-pressure gas storage bag 1 is connected to the outlet of the high-pressure liquid storage bag 10 through the carbon dioxide energy release cycle loop. The power output shaft of the carbon dioxide energy release cycle loop is connected to the power input shaft of the generator 17, and the electrical energy outlet of the generator 17 is connected to the electrical energy inlet of the energy-consuming side; Shallow-sea high-temperature seawater is used to evaporate high-pressure liquid carbon dioxide into a gaseous state, and the high-pressure gaseous carbon dioxide is used to expand and do work, converting the generated mechanical energy into electrical energy and stably transporting it to the energy-consuming side. At the same time, the expanded low-pressure gaseous carbon dioxide is stored in the low-pressure gas storage bag 1;

[0010] Heat storage cycle loop: During the energy storage process, the carbon dioxide energy storage cycle loop is connected to the heat storage cycle loop through a cooler, and the stored low-temperature heat storage medium absorbs the compression heat generated during the carbon dioxide energy storage cycle loop process and is converted into a high-temperature heat storage medium for storage; During the energy release process, the carbon dioxide energy release cycle loop is connected to the heat storage cycle loop through a heater, and the stored high-temperature heat storage medium heats the gaseous carbon dioxide during the carbon dioxide energy release cycle loop process and is converted into a low-temperature heat storage medium for storage.

[0011] The outer shells of the low-pressure gas storage bag 1 and the high-pressure liquid storage bag 10 are both made of flexible materials; The low-pressure gas storage bag 1 floats on the sea surface, and the pressure inside it is constantly at atmospheric pressure; The high-pressure liquid storage bag 10 is arranged at a depth of 500 to 600 meters underwater, and the pressure inside it is constantly at 5 to 6 MPa.

[0012] The heat storage circulation loop includes: a cold water storage tank 7, a hot water storage tank 8, a first cooler 4, a second cooler 6, a first heater 13, and a second heater 15; the outlet of the cold water storage tank 7 is respectively connected to the inlets of the low-temperature sides of the first cooler 4 and the second cooler 6, and the outlets of the low-temperature sides of the first cooler 4 and the second cooler 6 are both connected to the inlet of the hot water storage tank 8; the outlet of the hot water storage tank 8 is respectively connected to the inlets of the high-temperature sides of the first heater 13 and the second heater 15, and the outlets of the high-temperature sides of the first heater 13 and the second heater 15 are both connected to the inlet of the cold water storage tank 7; the cold water storage tank 7 is used to store a low-temperature heat storage medium, and the hot water storage tank 8 is used to store a high-temperature heat storage medium.

[0013] The carbon dioxide energy storage circulation loop includes: a low-pressure compressor 3, a high-pressure compressor 5, and a condenser 9; the power input shafts of the low-pressure compressor 3 and the high-pressure compressor 5 are both connected to the power output shaft of the motor 2, the electrical energy inlet of the motor 2 is connected to the electrical energy outlet of the offshore new energy power generation, and the offshore new energy power generation supplies power to the motor 2 to drive the two compressors; the outlet of the low-pressure gas storage bag 1 is connected to the inlet of the low-pressure compressor 3, the outlet of the low-pressure compressor 3 is connected to the inlet of the high-temperature side of the first cooler 4, the outlet of the high-temperature side of the first cooler 4 is connected to the inlet of the high-pressure compressor 5, the outlet of the high-pressure compressor 5 is connected to the inlet of the high-temperature side of the second cooler 6, the outlet of the high-temperature side of the second cooler 6 is connected to the inlet of the high-temperature side of the condenser 9, and the outlet of the high-temperature side of the condenser 9 is connected to the inlet of the high-pressure liquid storage bag 10; the low-pressure gaseous carbon dioxide is compressed in two stages by the low-pressure compressor 3 and the high-pressure compressor 5 to a high-pressure state, the compression heat is stored in the heat storage circulation loop, and then it is condensed into a liquid by the deep-sea low-temperature seawater in the condenser 9, and the liquid carbon dioxide is transported to the high-pressure liquid storage bag 10 for constant-pressure storage.

[0014] The deep-sea low-temperature seawater used in the carbon dioxide energy storage circulation loop is transported to the inlet of the low-temperature side of the condenser 9 through a pipeline, and the temperature of the deep-sea low-temperature seawater is below 10°C.

[0015] The carbon dioxide energy release cycle loop: It includes a working fluid pump 11, an evaporator 12, a high-pressure turbine 14, a low-pressure turbine 16, and a radiator 18; the outlet of the high-pressure liquid storage bladder 10 is connected to the inlet of the working fluid pump 11, the outlet of the working fluid pump 11 is connected to the inlet of the low-temperature side of the evaporator 12, the outlet of the low-temperature side of the evaporator 12 is connected to the inlet of the low-temperature side of the first heater 13, the outlet of the low-temperature side of the first heater 13 is connected to the inlet of the high-pressure turbine 14, the outlet of the high-pressure turbine 14 is connected to the inlet of the low-temperature side of the second heater 15, the outlet of the low-temperature side of the second heater 15 is connected to the inlet of the low-pressure turbine 16, the outlet of the low-pressure turbine 16 is connected to the inlet of the radiator 18, and the outlet of the radiator 18 is connected to the inlet of the low-pressure gas storage bladder 1; the power output shafts of the high-pressure turbine 14 and the low-pressure turbine 16 are both connected to the power input shaft of the generator 17, and the electric energy outlet of the generator 17 is connected to the electric energy inlet of the energy-consuming side; the stored liquid carbon dioxide evaporates into a gas by absorbing the heat of the high-temperature seawater in the shallow sea through the evaporator 12, and after the temperature is increased through the first heater 13 and the second heater 15, the high-pressure carbon dioxide is expanded to a low-pressure state through the high-pressure turbine 14 and the low-pressure turbine 16. The low-pressure gaseous carbon dioxide is dissipated through the radiator 18 and then transported to the low-pressure gas storage bladder 1 for constant-pressure storage.

[0016] The high-temperature seawater in the shallow sea used in the carbon dioxide energy release cycle loop is transported to the inlet of the high-temperature side of the evaporator 12 through a pipeline, and the temperature of the high-temperature seawater in the shallow sea is above 25 °C.

[0017] The carbon dioxide energy release cycle loop further includes a preheater 19. The outlet of the low-temperature side of the evaporator 12 is connected to the inlet of the low-temperature side of the preheater 19, and the outlet of the low-temperature side of the preheater 19 is connected to the inlet of the low-temperature side of the first heater 13; the outlets of the high-temperature sides of the first heater 13 and the second heater 15 are both connected to the inlet of the high-temperature side of the preheater 19, and the outlet of the high-temperature side of the preheater 19 is connected to the inlet of the cold water storage tank 7; the low-temperature carbon dioxide flows through the evaporator 12, enters the preheater 19, exchanges heat with the low-temperature heat storage medium at the outlets of the first heater 13 and the second heater 15, is preheated and then enters the first heater 13 and the second heater 15 to absorb the heat stored in the heat storage medium.

[0018] The present invention also provides an operation method for a constant-pressure compressed carbon dioxide energy storage system coupled with ocean thermal difference, including an energy storage process and an energy release process:

[0019] During the energy storage process, the low-pressure gaseous carbon dioxide stored in the low-pressure gas storage bladder 1 is compressed in two stages to a high-pressure state. The heat energy generated by the compressed carbon dioxide is absorbed by the low-temperature heat storage medium in the cold water storage tank 7, and the low-temperature heat storage medium is transformed into a high-temperature heat storage medium and stored in the hot water storage tank 8. The low-temperature and high-pressure carbon dioxide after releasing heat exchanges heat with the deep-sea low-temperature seawater through the condenser 9, so that the low-temperature and high-pressure carbon dioxide is condensed into a liquid and stored in the high-pressure liquid storage bladder 10;

[0020] During the energy release process, the high-pressure liquid carbon dioxide stored in the high-pressure liquid storage bag 10 is transported by the working fluid pump 11 to the evaporator 12, where it absorbs the heat of the high-temperature seawater in the shallow sea and evaporates into a gas. Then it rises to the sea surface and further absorbs the thermal energy of the high-temperature heat storage medium in the hot water storage tank 8. Then it performs work and generates electricity through two-stage expansion. The low-pressure gaseous carbon dioxide after heat release is stored in the low-pressure gas storage bag 1, and the high-temperature heat storage medium after absorbing thermal energy is transformed into a low-temperature heat storage medium and stored in the cold water storage tank 7.

[0021] During the energy storage process, a part of the low-temperature heat storage medium flowing out of the cold water storage tank 7 exchanges heat through the first cooler 4 to absorb the compression heat of the carbon dioxide after the first compression; another part of the low-temperature heat storage medium flowing out of the cold water storage tank 7 exchanges heat through the second cooler 6 to absorb the compression heat of the carbon dioxide after the second compression; after absorbing heat, the temperatures of these two parts of the low-temperature heat storage medium increase, and after mixing, they flow into the hot water storage tank 8 for storage;

[0022] During the energy release process, a part of the high-temperature heat storage medium flowing out of the hot water storage tank 8 exchanges heat with the carbon dioxide flowing through the first heater 13 through the first heater 13; another part of the high-temperature heat storage medium flowing out of the hot water storage tank 8 exchanges heat with the carbon dioxide flowing through the second heater 15 through the second heater 15. After releasing heat, the temperatures of these two parts of the high-temperature heat storage medium decrease, and after mixing, they flow into the cold water storage tank 7 for storage.

[0023] Compared with the existing technologies, the beneficial effects of the present invention are as follows:

[0024] 1. The subcritical gas-liquid conversion compressed carbon dioxide energy storage system proposed by the present invention uses the deep-sea low-temperature seawater to condense and liquefy the gaseous carbon dioxide during the energy storage process, and uses the relatively high-temperature shallow-sea seawater to evaporate and gasify the liquid carbon dioxide during the energy release process, making full use of the ocean temperature difference resources, realizing efficient carbon dioxide gas-liquid phase conversion, and overcoming the drawback that the traditional compressed carbon dioxide energy storage system requires an additional refrigerator.

[0025] 2. The subcritical constant-pressure compressed carbon dioxide energy storage system proposed by the present invention uses the underwater hydrostatic pressure to provide a stable external pressure for the high-pressure liquid storage bag, realizes the constant pressure of the liquid storage bag, makes the pressures at the compressor outlet and the turbine inlet constant, does not require sliding pressure operation, the whole unit operates under stable conditions, and at the same time, the space of the high-pressure liquid storage bag can be fully utilized. Compared with the traditional compressed carbon dioxide energy storage system, the round-trip efficiency and operation stability are improved, and the volume of the liquid storage device and the investment cost are reduced.

[0026] 3. The energy storage system of floating subcritical compressed carbon dioxide in the sea proposed by the present invention uses the seawater temperature difference to reduce the maximum pressure of the entire system to the range of 5 to 6 MPa, improving the economy; uses the seawater buoyancy to make the low-pressure storage airbag float on the sea surface, without occupying the space of the offshore platform, improving the volume energy density; uses the low-temperature heat of the stored hot water to preheat the evaporated carbon dioxide in the preheater, improving the utilization rate of the stored heat, and making the system independent of other low-grade waste heat, becoming an independent energy storage system for deep-sea offshore wind power and photovoltaic power.

[0027] In summary, the present invention is aimed at the local consumption of new energy such as deep-sea offshore wind power and photovoltaic power, integrates the ocean temperature difference resources, and overcomes the technical defects of traditional compressed carbon dioxide energy storage. Utilizing the ocean temperature difference and seawater hydrostatic pressure, it realizes the efficient liquefaction and high-density storage of high-pressure carbon dioxide, improves the efficiency and energy density of the energy storage system, and provides a feasible technical path for the development and consumption of deep-sea offshore new energy. Brief Description of the Drawings

[0028] Figure 1 It is a schematic structural diagram of the offshore constant-pressure compressed carbon dioxide system coupled with ocean temperature difference in Embodiment 1.

[0029] Figure 2 It is a schematic structural diagram of the offshore constant-pressure compressed carbon dioxide system coupled with ocean temperature difference in Embodiment 2.

[0030] Figure 3 It is a schematic diagram of the typical change of seawater temperature with seawater depth.

[0031] Description of the reference numerals: 1 - low-pressure storage airbag, 2 - motor, 3 - low-pressure compressor, 4 - first cooler, 5 - high-pressure compressor, 6 - second cooler, 7 - cold water storage tank, 8 - hot water storage tank, 9 - condenser, 10 - high-pressure liquid storage bag, 11 - working fluid pump, 12 - evaporator, 13 - first heater, 14 - high-pressure turbine, 15 - second heater, 16 - low-pressure turbine, 17 - generator, 18 - radiator, 19 - preheater; 20 - offshore platform. Detailed Embodiment

[0032] To further understand and recognize the structural features and achieved effects of the present invention, the following will clearly and completely describe the present invention in conjunction with the example diagrams.

[0033] Embodiment 1

[0034] Refer to Figure 1 , the offshore constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference, which includes: a working fluid constant-pressure storage device, a carbon dioxide energy storage circulation loop, a carbon dioxide energy release circulation loop, and a heat storage circulation loop.

[0035] Working fluid constant-pressure storage device: It includes a low-pressure gas storage bag 1 and a high-pressure liquid storage bag 10, which are used for constant-pressure storage of low-pressure gaseous carbon dioxide and high-pressure liquid carbon dioxide. Among them, the low-pressure gas storage bag 1 is used for constant-pressure storage of low-pressure gaseous carbon dioxide, and the high-pressure liquid storage bag 10 is used for constant-pressure storage of high-pressure liquid carbon dioxide. The outer shell of the high-pressure liquid storage bag 10 is made of flexible material, so that its volume can change while maintaining the internal pressure unchanged. The high-pressure liquid storage bag 10 is arranged at a depth of about 500 to 600 meters underwater, and uses the hydrostatic pressure of seawater to maintain a constant high pressure of about 5 to 6 MPa. The outer shell of the low-pressure gas storage bag 1 is made of flexible material, so that its volume can change while maintaining the internal pressure unchanged. The internal pressure of the low-pressure gas storage bag 1 is normal pressure, and the atmospheric pressure is used to maintain a constant low pressure. At the same time, it floats on the sea surface by the buoyancy of seawater and does not occupy the space of the artificial floating platform.

[0036] Heat storage cycle loop: It includes a hot water storage tank 8, a cold water storage tank 7, a first cooler 4, a second cooler 6, a first heater 13, and a second heater 15. The outlet of the cold water storage tank 7 is respectively connected to the inlets of the low-temperature sides of the first cooler 4 and the second cooler 6, and the outlets of the low-temperature sides of the first cooler 4 and the second cooler 6 are both connected to the inlet of the hot water storage tank 8. The outlet of the hot water storage tank 8 is respectively connected to the inlets of the high-temperature sides of the first heater 13 and the second heater 15, and the outlets of the high-temperature sides of the first heater 13 and the second heater 15 are both connected to the inlet of the cold water storage tank 7. The cold water storage tank 7 is used to store low-temperature heat storage medium, and the hot water storage tank 8 is used to store high-temperature heat storage medium. During the energy storage process, the low-temperature heat storage medium in the cold water storage tank 7 absorbs the compression heat generated during the operation of the carbon dioxide energy storage cycle loop and is transformed into a high-temperature heat storage medium, which is stored in the hot water storage tank 8. During the energy release process, the high-temperature heat storage medium in the hot water storage tank 8 heats the gaseous carbon dioxide evaporated by the evaporator 12 and is transformed into a low-temperature heat storage medium, which is stored in the cold water storage tank 7. The heat storage medium in the heat storage cycle loop is pressurized water.

[0037] Carbon dioxide energy storage cycle loop: Using new energy such as offshore wind power to generate electricity, low-pressure gaseous carbon dioxide is compressed into a high-pressure state, and then deep-sea low-temperature seawater is used to condense the high-pressure gaseous carbon dioxide into a liquid state; it includes a low-pressure compressor 3, a high-pressure compressor 5, and a condenser 9. The power input shafts of the low-pressure compressor 3 and the high-pressure compressor 5 are both connected to the power output shaft of the motor 2. The electrical energy inlet of the motor 2 is connected to the electrical energy outlet of new energy such as offshore wind power. The new energy such as offshore wind power is transmitted into the motor 2 to supply power to the motor 2 to drive the two compressors. The outlet of the low-pressure gas storage bag 1 is connected to the inlet of the low-pressure compressor 3. The outlet of the low-pressure compressor 3 is connected to the high-temperature side inlet of the first cooler 4. The high-temperature side outlet of the first cooler 4 is connected to the inlet of the high-pressure compressor 5. The outlet of the high-pressure compressor 5 is connected to the high-temperature side inlet of the second cooler 6. The outlet of the second cooler 6 is connected to the high-temperature side inlet of the condenser 9. The high-temperature side outlet of the condenser 9 is connected to the inlet of the high-pressure liquid storage bag 10. The low-pressure gaseous carbon dioxide is compressed in two stages by the low-pressure compressor 3 and the high-pressure compressor 5 to a high-pressure state. After the compression heat generated is stored in the heat storage cycle loop, it is condensed into a liquid by the deep-sea low-temperature seawater through the condenser 9. The high-pressure liquid carbon dioxide is transported to the high-pressure liquid storage bag 10 for constant-pressure storage.

[0038] Carbon dioxide energy release cycle loop: Using shallow-sea high-temperature seawater to evaporate high-pressure liquid carbon dioxide into a gas state, and using the expansion work of high-pressure gaseous carbon dioxide to generate electricity, and converting the generated mechanical energy into electrical energy and stably outputting it to the energy-consuming side; it includes a working fluid pump 11, an evaporator 12, a high-pressure turbine 14, a low-pressure turbine 16, and a radiator 18. The outlet of the high-pressure liquid storage bag 10 is connected to the inlet of the working fluid pump 11. The outlet of the working fluid pump 11 is connected to the low-temperature side inlet of the evaporator 12. The low-temperature side outlet of the evaporator 12 is connected to the low-temperature side inlet of the first heater 13. The low-temperature side outlet of the first heater 13 is connected to the inlet of the high-pressure turbine 14. The outlet of the high-pressure turbine 14 is connected to the low-temperature side inlet of the second heater 15. The low-temperature side outlet of the second heater 15 is connected to the inlet of the low-pressure turbine 16. The outlet of the low-pressure turbine 16 is connected to the inlet of the radiator 18. The outlet of the radiator 18 is connected to the inlet of the low-pressure gas storage bag 1. The power output shafts of the high-pressure turbine 14 and the low-pressure turbine 16 are both connected to the power input shaft of the generator 17. The electrical energy outlet of the generator 17 is connected to the electrical energy inlet of the energy-consuming side. The stored high-pressure liquid carbon dioxide is evaporated into a gas state by absorbing the heat of the shallow-sea high-temperature seawater through the evaporator 12. After the temperature is raised by the first heater 13 and the second heater 15, the high-pressure gaseous carbon dioxide is expanded in two stages through the high-pressure turbine 14 and the low-pressure turbine 16 to a low-pressure state. The low-pressure gaseous carbon dioxide is further cooled by the radiator 18 and then transported to the low-pressure gas storage bag 1 for constant-pressure storage.

[0039] Marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean thermal energy difference, which utilizes the action of seawater hydrostatic pressure and seawater buoyancy to make high-pressure liquid carbon dioxide and low-pressure gaseous carbon dioxide be stored under constant pressure by a flexible working medium constant-pressure storage device; during the energy storage and energy release processes, seawater at different depths is coupled as a cold source and a heat source to achieve the gas-liquid conversion of carbon dioxide under subcritical conditions.

[0040] The cold source is deep-sea low-temperature seawater below 10°C, which is coupled into the energy storage process; specifically, low-temperature seawater located about 500 to 600 meters deep below the sea level is introduced into the low-temperature side of the condenser 9. The heat source is shallow-sea high-temperature seawater above 25°C, which is coupled into the energy release process; specifically, high-temperature seawater located at the shallow sea level is introduced into the high-temperature side of the evaporator 12. See Figure 3 , relying on the characteristic that seawater temperature changes with depth, as the seawater depth increases, the seawater temperature decreases; the high-temperature seawater in the shallow layer and the low-temperature seawater in the deep layer are synergistically utilized as the cold source and the heat source for the gas-liquid conversion process.

[0041] For the heat storage circulation loop, the low-pressure compressor 3 and the high-pressure compressor 5 in the carbon dioxide energy storage circulation loop, the high-pressure turbine 14, the low-pressure turbine 16 and the radiator 18 in the carbon dioxide energy release circulation loop, and the motor 2 and the generator 17 are all arranged on the offshore platform 20.

[0042] The present invention also provides an operation method for the marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean thermal energy difference, including an energy storage process and an energy release process;

[0043] During the energy storage process, the low-pressure gaseous carbon dioxide stored in the low-pressure gas storage bag 1 is compressed in two stages to increase the carbon dioxide pressure to a high-pressure state. The heat energy generated by compressing the carbon dioxide is absorbed by the low-temperature pressurized water in the cold water storage tank 7, and the low-temperature pressurized water is transformed into high-temperature pressurized water and stored in the hot water storage tank 8; while the low-temperature high-pressure carbon dioxide after releasing heat is sent into the deep sea through a pipeline to exchange heat with the deep-sea low-temperature seawater, so that the low-temperature high-pressure carbon dioxide is condensed into a liquid state, and then stored in the deep sea by using the flexible high-pressure liquid storage bag 10;

[0044] Specifically, a part of the low-temperature pressurized water flowing out of the cold water storage tank 7 exchanges heat through the first cooler 4 to absorb the heat of the carbon dioxide after the first compression; another part of the low-temperature pressurized water flowing out of the cold water storage tank 7 exchanges heat through the second cooler 6 to absorb the heat of the carbon dioxide after the second compression; after absorbing heat, the temperatures of the two parts of low-temperature pressurized water increase, and after mixing, they flow into the hot water storage tank 8 for storage;

[0045] During the energy release process, first, the high-temperature seawater in the shallow sea is sent underwater through a pipeline. The liquid carbon dioxide stored in the high-pressure liquid storage bladder 10 is transported by the working medium pump 11 to the evaporator 12, where it absorbs the heat of the high-temperature seawater in the shallow sea and evaporates into a gas. Then it rises above the sea level and further absorbs the thermal energy of the high-temperature pressurized water in the hot water storage tank 8. Then it performs work and generates electricity through two-stage expansion. The low-pressure gaseous carbon dioxide after heat release is stored in the low-pressure gas storage bladder 1, and the high-temperature pressurized water after absorbing thermal energy is transformed into low-temperature pressurized water and stored in the cold water storage tank 7;

[0046] Specifically, a part of the high-temperature pressurized water flowing out of the hot water storage tank 8 passes through the first heater 13, transferring heat to the carbon dioxide flowing through the first heater 13; another part of the high-temperature pressurized water flowing out of the hot water storage tank 8 passes through the second heater 15, transferring heat to the carbon dioxide flowing through the second heater 15. After heat release, the temperatures of these two parts of high-temperature pressurized water drop, and after mixing, they flow into the cold water storage tank 7 for storage.

[0047] Embodiment 2

[0048] As Figure 2 shown, in addition to including the system structure of Embodiment 1, the energy release process of the carbon dioxide energy release circulation loop of this embodiment further includes a preheater 19; the low-temperature side outlet of the evaporator 12 is connected to the low-temperature side inlet of the preheater 19, and the low-temperature side outlet of the preheater 19 is connected to the low-temperature side inlet of the first heater 13; the high-temperature side outlets of the first heater 13 and the second heater 15 are both connected to the high-temperature side inlet of the preheater 19, and the high-temperature side outlet of the preheater 19 is connected to the inlet of the cold water storage tank 7; the low-temperature carbon dioxide flows through the evaporator 12, enters the preheater 19, exchanges heat with the low-temperature heat storage medium at the outlets of the first heater 13 and the second heater 15, and after being preheated, enters the first heater 13 and the second heater 15 to absorb the stored heat. By using the low-temperature heat storage medium that has not been utilized in the heat storage circulation loop to preheat the low-temperature carbon dioxide coming out of the evaporator 12, the stored heat is fully utilized to make the heat exchange matching degree of the system higher, thereby improving the round-trip efficiency of the entire energy storage system.

Claims

1. An offshore constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference, characterized in that: include: Working fluid constant pressure storage device, carbon dioxide energy storage cycle loop, carbon dioxide energy release cycle loop and heat storage cycle loop; The working fluid constant pressure storage device comprises a low-pressure gas storage bag (1) for constant pressure storage of low-pressure gaseous carbon dioxide and a high-pressure liquid storage bag (10) for constant pressure storage of high-pressure liquid carbon dioxide; Carbon dioxide energy storage circulation loop: the outlet of the low-pressure gas storage bag (1) is connected to the inlet of the high-pressure liquid storage bag (10) through the carbon dioxide energy storage circulation loop, the power input shaft of the carbon dioxide energy storage circulation loop is connected to the power output shaft of the motor (2), and the power inlet of the motor (2) is connected to the power outlet of the offshore new energy power generation; the offshore new energy power generation supplies power to the motor (2), and the motor (2) drives the compressor to compress the low-pressure gaseous carbon dioxide into a high-pressure state, and then uses deep-sea low-temperature seawater to condense the high-pressure gaseous carbon dioxide into a liquid state and store it in the high-pressure liquid storage bag (10); Carbon dioxide energy release circulation loop: the inlet of the low-pressure air storage bag (1) is connected to the outlet of the high-pressure liquid storage bag (10) through the carbon dioxide energy release circulation loop, the power output shaft of the carbon dioxide energy release circulation loop is connected to the power input shaft of the generator (17), and the power outlet of the generator (17) is connected to the power inlet of the energy consumption side; high-temperature seawater in shallow sea is used to evaporate high-pressure liquid carbon dioxide into gaseous state, and the high-pressure gaseous carbon dioxide is used to expand and do work, so that the generated mechanical energy is converted into electric energy and stably transmitted to the energy consumption side, and at the same time, the expanded low-pressure gaseous carbon dioxide is stored in the low-pressure air storage bag (1); Heat storage cycle loop: During the energy storage process, the carbon dioxide energy storage cycle loop is connected to the heat storage cycle loop through a cooler, and the stored low-temperature heat storage medium absorbs the compression heat generated in the carbon dioxide energy storage cycle loop and is converted into a high-temperature heat storage medium for storage; during the energy release process, the carbon dioxide energy release cycle loop is connected to the heat storage cycle loop through a heater, and the stored high-temperature heat storage medium heats the gaseous carbon dioxide in the carbon dioxide energy release cycle loop and is converted into a low-temperature heat storage medium for storage.

2. The marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 1 is characterized in that: The shells of the low-pressure air storage bag (1) and the high-pressure liquid storage bag (10) are both made of flexible materials; the low-pressure air storage bag (1) floats on the sea surface, and its internal pressure is constant at normal pressure; the high-pressure liquid storage bag (10) is arranged at a depth of 500 to 600 meters under the sea, and its internal pressure is constant at 5 to 6 MPa.

3. The marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 1 is characterized in that: The heat storage circulation loop comprises: a cold water storage tank (7), a hot water storage tank (8), a first cooler (4), a second cooler (6), a first heater (13), and a second heater (15); the outlet of the cold water storage tank (7) is respectively connected to the low-temperature side inlets of the first cooler (4) and the second cooler (6), and the low-temperature side outlets of the first cooler (4) and the second cooler (6) are both connected to the inlet of the hot water storage tank (8); the outlet of the hot water storage tank (8) is respectively connected to the high-temperature side inlets of the first heater (13) and the second heater (15), and the high-temperature side outlets of the first heater (13) and the second heater (15) are both connected to the inlet of the cold water storage tank (7); the cold water storage tank (7) is used to store a low-temperature heat storage medium, and the hot water storage tank (8) is used to store a high-temperature heat storage medium.

4. The marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 3 is characterized in that: The carbon dioxide energy storage circulation loop comprises: a low-pressure compressor (3), a high-pressure compressor (5), and a condenser (9); the power input shafts of the low-pressure compressor (3) and the high-pressure compressor (5) are both connected to the power output shaft of the motor (2); the power inlet of the motor (2) is connected to the power outlet of the offshore new energy power generation; the offshore new energy power generation supplies power to the motor (2) to drive the two compressors; the outlet of the low-pressure air storage bag (1) is connected to the inlet of the low-pressure compressor (3); the outlet of the low-pressure compressor (3) is connected to the high-temperature side inlet of the first cooler (4); the high-temperature side of the first cooler (4) is connected to the high-temperature side of the first cooler (4). The outlet is connected to the inlet of the high-pressure compressor (5), the outlet of the high-pressure compressor (5) is connected to the inlet of the high-temperature side of the second cooler (6), the outlet of the high-temperature side of the second cooler (6) is connected to the inlet of the high-temperature side of the condenser (9), and the outlet of the high-temperature side of the condenser (9) is connected to the inlet of the high-pressure liquid storage capsule (10); the low-pressure gaseous carbon dioxide is compressed in two stages by the low-pressure compressor (3) and the high-pressure compressor (5) to a high-pressure state, and the compression heat is stored in the heat storage circulation loop, and then condensed into liquid by the deep-sea low-temperature seawater through the condenser (9), and the liquid carbon dioxide is transported to the high-pressure liquid storage capsule (10) for constant pressure storage.

5. The marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 4 is characterized in that: The deep sea low temperature seawater used in the carbon dioxide energy storage circulation loop is transported to the low temperature side inlet of the condenser (9) through a pipeline, and the temperature of the deep sea low temperature seawater is below 10°C.

6. The marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 3 is characterized in that: The carbon dioxide energy release circulation loop comprises a working fluid pump (11), an evaporator (12), a high-pressure turbine (14), a low-pressure turbine (16), and a radiator (18); the outlet of the high-pressure liquid storage bag (10) is connected to the inlet of the working fluid pump (11), the outlet of the working fluid pump (11) is connected to the low-temperature side inlet of the evaporator (12), the low-temperature side outlet of the evaporator (12) is connected to the low-temperature side inlet of the first heater (13), the low-temperature side outlet of the first heater (13) is connected to the inlet of the high-pressure turbine (14), the outlet of the high-pressure turbine (14) is connected to the low-temperature side inlet of the second heater (15), the low-temperature side outlet of the second heater (15) is connected to the inlet of the low-pressure turbine (16), and the outlet of the low-pressure turbine (16) is connected to the inlet of the low-temperature side of the second heater (15). The radiator (18) is connected to the inlet of the radiator (18), and the outlet of the radiator (18) is connected to the inlet of the low-pressure air storage bag (1); the power output shafts of the high-pressure turbine (14) and the low-pressure turbine (16) are both connected to the power input shaft of the generator (17), and the power outlet of the generator (17) is connected to the power inlet of the energy-consuming side; the stored liquid carbon dioxide absorbs the heat of the shallow sea high-temperature seawater through the evaporator (12) and evaporates into gaseous state, and after the temperature is increased by the first heater (13) and the second heater (15), the high-pressure carbon dioxide is expanded to a low-pressure state through the high-pressure turbine (14) and the low-pressure turbine (16), and the low-pressure gaseous carbon dioxide is transported to the low-pressure air storage bag (1) for constant pressure storage after the heat is dissipated by the radiator (18).

7. The marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 6 is characterized in that: The shallow sea high temperature seawater used in the carbon dioxide energy release circulation loop is transported to the high temperature side inlet of the evaporator (12) through a pipeline, and the temperature of the shallow sea high temperature seawater is above 25°C.

8. The marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 6 is characterized in that: The carbon dioxide energy release circulation loop also includes a preheater (19); the low temperature side outlet of the evaporator (12) is connected to the low temperature side inlet of the preheater (19); the low temperature side outlet of the preheater (19) is connected to the low temperature side inlet of the first heater (13); the high temperature side outlets of the first heater (13) and the second heater (15) are both connected to the high temperature side inlet of the preheater (19); the high temperature side outlet of the preheater (19) is connected to the inlet of the cold water storage tank (7); the low temperature carbon dioxide flows through the evaporator (12) and enters the preheater (19), exchanges heat with the low temperature heat storage medium at the outlets of the first heater (13) and the second heater (15), and then enters the first heater (13) and the second heater (15) to absorb the stored heat after being preheated.

9. An operation method of an offshore constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference, characterized in that: Including energy storage process and energy release process: During the energy storage process, the low-pressure gaseous carbon dioxide stored in the low-pressure gas storage bag (1) is compressed in two stages to a high-pressure state. After the heat energy generated by the compressed carbon dioxide is absorbed by the low-temperature heat storage medium in the cold water storage tank (7), the low-temperature heat storage medium is converted into a high-temperature heat storage medium and stored in the hot water storage tank (8). After the heat is released, the low-temperature and high-pressure carbon dioxide is exchanged with the deep-sea low-temperature seawater through the condenser (9), so that the low-temperature and high-pressure carbon dioxide is condensed into a liquid state and stored in the high-pressure liquid storage bag (10). During the energy release process, the high-pressure liquid carbon dioxide stored in the high-pressure liquid storage bag (10) is transported to the evaporator (12) by the working fluid pump (11) to absorb the heat of the shallow sea high-temperature seawater and evaporate into gas, then rise to the sea level, further absorb the heat energy of the high-temperature heat storage medium in the hot water storage tank (8), and then perform work and generate electricity through two-stage expansion, while the low-pressure gaseous carbon dioxide after heat release is stored in the low-pressure gas storage bag (1), and the high-temperature heat storage medium after absorbing the heat energy is converted into a low-temperature heat storage medium and stored in the cold water storage tank (7).

10. The method for operating the marine constant pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 9, characterized in that: During the energy storage process, a portion of the low-temperature heat storage medium flowing out of the cold water storage tank (7) is heat exchanged through the first cooler (4) to absorb the compression heat of the carbon dioxide after the first compression; Another portion of the low-temperature heat storage medium flowing out of the cold water storage tank (7) is heat exchanged through the second cooler (6) to absorb the compression heat of the carbon dioxide after the second compression; After absorbing heat, the temperatures of the two parts of low-temperature heat storage medium rise, and after mixing, they flow into the hot water storage tank (8) for storage; During the energy release process, a portion of the high-temperature heat storage medium flowing out of the hot water storage tank (8) exchanges heat with the carbon dioxide flowing through the first heater (13) through the first heater (13); another portion of the high-temperature heat storage medium flowing out of the hot water storage tank (8) exchanges heat with the carbon dioxide flowing through the second heater (15) through the second heater (15). After releasing heat, the temperatures of the two portions of high-temperature heat storage medium drop, and after mixing, they flow into the cold water storage tank (7) for storage.

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