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

Abstract

The application discloses a marine constant-pressure compression carbon dioxide energy storage system and method coupled with ocean temperature difference, 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; in the energy storage stage, the low-temperature deep sea water is used to condense gaseous carbon dioxide into liquid carbon dioxide; in the energy release stage, the high-temperature shallow sea water is used to evaporate liquid carbon dioxide into gaseous carbon dioxide; the ocean new energy and the ocean temperature difference are fully utilized to realize the gas-liquid conversion of carbon dioxide; the flexible working medium constant-pressure storage device is used to store 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 is ensured, and the efficient and stable operation of the system is realized; the ocean temperature difference and the seawater static pressure are used to realize the efficient liquefaction and high-density storage of high-pressure carbon dioxide, the efficiency and the energy density of the energy storage system are improved, and the deep development of marine resources is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermo-mechanical energy storage, in particular to an offshore constant-pressure carbon dioxide compression energy storage system and method coupled with ocean temperature difference. BACKGROUND

[0002] Due to the intermittency and volatility of new energy such as wind power and photovoltaic, direct grid connection will impact the power grid. At the same time, the user side energy consumption and renewable energy generation are difficult to synchronize, so large-scale long-time storage of electric energy is of great significance to the construction of new power systems. With the development of photovoltaic and wind power, land-based photovoltaic and wind power are limited by land resources, and the ocean accounts for 71% of the earth's surface. Therefore, offshore wind power and photovoltaic have emerged as the times require, and have shown broad prospects for development by taking full advantage of ocean space and high-quality resources. With the development of offshore wind power and photovoltaic towards large-scale and deep water, the problem of new energy consumption is more difficult. There are limitations in transmitting deep-sea power generation to the nearby onshore power grid through cables, so exploring the on-site consumption of offshore wind power and photovoltaic has become increasingly important under the current background. In order to smooth the fluctuations of wind power and photovoltaic, a certain capacity of energy storage needs to be configured, so it is urgent to develop an energy storage system for on-site consumption of deep-sea wind power and photovoltaic.

[0003] Compressed gas energy storage, including compressed air and carbon dioxide energy storage, is a kind of thermo-mechanical energy storage technology. Its principle is to use off-peak electricity to drive the compressor to compress and store the gas in the gas storage, and to convert the electrical energy into the internal energy of the gas; during the peak electricity consumption period, the high-pressure gas is released, heated and then expanded through the expander to drive the generator to generate electricity, realizing the release of electrical energy. Carbon dioxide is increasingly concerned due to its excellent thermodynamic performance and environmental friendliness. Compared with air, carbon dioxide has higher density and thermal conductivity in the near-critical region, and can store more energy in a smaller volume. Therefore, compressed carbon dioxide energy storage system has significant advantages in improving energy conversion efficiency and volume energy density. In addition, compressed carbon dioxide energy storage can store a large amount of carbon capture and enrichment of carbon dioxide, and is a typical carbon dioxide utilization technology. According to the storage state of the working medium, 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 the characteristics of high round-trip efficiency, low investment cost and high technical maturity, and has become the current mainstream technology. The 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 pool 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 relatively high and insufficient to liquefy carbon dioxide near the critical point, an additional chiller is needed to provide the required cold energy for liquefaction, resulting in a decrease in system efficiency and an increase in cost. For high-pressure carbon dioxide storage, when using a constant-volume storage tank, the volume of the storage tank cannot be fully utilized (utilization rate of about 50%) or the storage pressure changes cause the turbine and compressor to operate under non-design conditions, resulting in a decrease in energy storage density and round-trip efficiency. SUMMARY

[0004] In order to overcome the shortcomings of the prior art that high-pressure carbon dioxide is difficult to liquefy and difficult to store constantly, the purpose of the present application is to provide an offshore constant-pressure compressed carbon dioxide energy storage system and method coupled with ocean temperature difference, which uses deep-sea low-temperature seawater to condense gaseous carbon dioxide into liquid during the energy storage stage, and uses shallow-sea high-temperature seawater to evaporate liquid carbon dioxide into gas during the energy release stage, thereby fully utilizing ocean new energy and ocean temperature difference to realize the gas-liquid conversion of carbon dioxide; a flexible working medium constant-pressure storage device is used to store low-pressure gaseous and high-pressure liquid carbon dioxide, thereby realizing constant pressure of the working medium constant-pressure storage device during the charging and discharging processes. By constructing the compressed carbon dioxide energy storage on the offshore new energy power generation side, the special environment and ocean energy of the sea are fully utilized, the on-site utilization of resources and the deep coupling of the system are realized, the efficiency and energy density of the energy storage system are improved, and the deep development of offshore resources is realized.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] The offshore constant-pressure compression carbon dioxide energy storage system coupled with ocean temperature difference comprises a working medium constant-pressure storage device, a carbon dioxide energy storage cycle, a carbon dioxide energy release cycle and a heat storage cycle;

[0007] The working medium 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.

[0008] The carbon dioxide energy storage cycle: 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, the power input shaft of the carbon dioxide energy storage cycle is connected to the power output shaft of the electric motor 2, and the electric energy inlet of the electric motor 2 is connected to the electric energy outlet of the offshore new energy power generation; the offshore new energy power generation supplies power to the electric motor 2, the low-pressure gaseous carbon dioxide is compressed to a high-pressure state by the compressor driven by the electric motor 2, and then the high-pressure carbon dioxide is condensed into a liquid state by deep-sea low-temperature seawater and stored in the high-pressure liquid storage bag 10.

[0009] The carbon dioxide energy release cycle: 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, the power output shaft of the carbon dioxide energy release cycle is 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 consumption side; the high-pressure liquid carbon dioxide is evaporated into a gaseous state by shallow-sea high-temperature seawater, the gaseous carbon dioxide is expanded to do work, the generated mechanical energy is converted into electric energy and stably transmitted to the energy consumption side, and the expanded low-pressure gaseous carbon dioxide is stored in the low-pressure gas storage bag 1.

[0010] The heat storage cycle: in the energy storage process, the carbon dioxide energy storage cycle is connected to the heat storage cycle through a cooler, the stored low-temperature heat storage medium absorbs the compression heat generated in the carbon dioxide energy storage cycle process and is converted into a high-temperature heat storage medium for storage; in the energy release process, the carbon dioxide energy release cycle is connected to the heat storage cycle through a heater, the stored high-temperature heat storage medium heats the gaseous carbon dioxide in the carbon dioxide energy release cycle 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 made of flexible materials; the low-pressure gas storage bag 1 floats on the sea level and its internal pressure is constant at atmospheric pressure; the high-pressure liquid storage bag 10 is arranged at a depth of 500 to 600 meters below the sea level and its internal pressure is constant at 5 to 6 megapascals.

[0012] 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 connected to the low-temperature side inlet of the first cooler 4 and the second cooler 6 respectively, the low-temperature side outlet of the first cooler 4 and the second cooler 6 is connected to the inlet of the hot water storage tank 8; the outlet of the hot water storage tank 8 is connected to the high-temperature side inlet of the first heater 13 and the second heater 15 respectively, and the high-temperature side outlet of the first heater 13 and the second heater 15 is connected to the inlet of the cold water storage tank 7; the cold water storage tank 7 is used for storing low-temperature heat storage medium, and the hot water storage tank 8 is used for storing high-temperature heat storage medium.

[0013] 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 connected to the power output shaft of the electric motor 2, the electric energy inlet of the electric motor 2 is connected to the electric energy outlet of the offshore new energy power generation, and the offshore new energy power generation supplies power to the electric motor 2 to drive the two compressors; the outlet of the low-pressure gas 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 high-temperature side outlet of the second cooler 6 is connected to the high-temperature side inlet of the condenser 9, and 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 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 state by 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 low-temperature side inlet of the condenser 9 through a pipeline, and the temperature of the deep-sea low-temperature seawater is below 10℃.

[0015] The carbon dioxide energy release cycle loop comprises a working medium 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 with the inlet of the working medium pump 11, the outlet of the working medium pump 11 is connected with the low-temperature side inlet of the evaporator 12, the low-temperature side outlet of the evaporator 12 is connected with the low-temperature side inlet of the first heater 13, the low-temperature side outlet of the first heater 13 is connected with the inlet of the high-pressure turbine 14, the outlet of the high-pressure turbine 14 is connected with the low-temperature side inlet of the second heater 15, the low-temperature side outlet of the second heater 15 is connected with the inlet of the low-pressure turbine 16, the outlet of the low-pressure turbine 16 is connected with the inlet of the radiator 18, and the outlet of the radiator 18 is connected with 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 connected with the power input shaft of the generator 17, and the electric energy outlet of the generator 17 is connected with the electric energy inlet of the energy utilization side; the stored liquid carbon dioxide absorbs the heat of the shallow high-temperature seawater through the evaporator 12 to be evaporated into a gaseous state, the temperature of the gaseous carbon dioxide is raised 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, and the low-pressure gaseous carbon dioxide is stored in the low-pressure gas storage bag 1 after heat dissipation through the radiator 18.

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

[0017] The carbon dioxide energy release cycle loop further comprises a preheater 19, the low-temperature side outlet of the evaporator 12 is connected with the low-temperature side inlet of the preheater 19, and the low-temperature side outlet of the preheater 19 is connected with 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 connected with the high-temperature side inlet of the preheater 19, and the high-temperature side outlet of the preheater 19 is connected with 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.

[0018] The application further provides a running method of the offshore constant-pressure compression carbon dioxide energy storage system coupled with ocean temperature difference, which comprises an energy storage process and an energy release process.

[0019] In the energy storage process, the low-pressure gaseous carbon dioxide stored in the low-pressure gas storage bag 1 is compressed to a high-pressure state through two-stage compression, 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 high-temperature heat storage medium and stored in the hot water storage tank 8, and the low-temperature high-pressure carbon dioxide after heat release exchanges heat with deep low-temperature seawater through the condenser 9, so that the low-temperature high-pressure carbon dioxide is condensed into liquid and stored in the high-pressure liquid storage bag 10.

[0020] In the energy releasing process, the high-pressure liquid carbon dioxide stored in the high-pressure storage bag 10 is transported to the evaporator 12 by the working fluid pump 11 to absorb the heat of the shallow sea water, and then evaporated into gas state, and then rises to the sea level to further absorb the heat energy of the high-temperature heat storage medium in the hot water storage tank 8, and then does work to generate electricity through two-stage expansion, and the low-pressure gaseous carbon dioxide after heat release is stored in the low-pressure gas bag 1, and the high-temperature heat storage medium after absorbing heat is changed into low-temperature heat storage medium and stored in the cold water storage tank 7.

[0021] In 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 compressed for the first time, and 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 compressed for the second time, and the temperature of the two parts of the low-temperature heat storage medium after heat absorption is increased, and then mixed and flowed into the hot water storage tank 8 for storage.

[0022] In the energy releasing 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, and 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, and the temperature of the two parts of the high-temperature heat storage medium after heat release is decreased, and then mixed and flowed into the cold water storage tank 7 for storage.

[0023] Compared with the prior art, the beneficial effects of the present application are that:

[0024] 1. The subcritical gas-liquid mutual conversion compression carbon dioxide energy storage system provided by the present application utilizes the deep sea low-temperature seawater to condense and liquefy the gaseous carbon dioxide in the energy storage process, and utilizes the relatively high-temperature shallow sea water to evaporate and gasify the liquid carbon dioxide in the energy releasing process, fully utilizes the ocean temperature difference resources, realizes efficient carbon dioxide gas-liquid phase state conversion, and overcomes the shortcomings of the traditional compression carbon dioxide energy storage system that needs an additional refrigerating machine.

[0025] 2. The subcritical constant-pressure compression carbon dioxide energy storage system provided by the present application utilizes the underwater hydrostatic pressure to provide stable external pressure for the high-pressure storage bag, realizes constant pressure of the storage bag, makes the compressor outlet and the turbine inlet pressure constant, does not need to run at sliding pressure, and the whole unit runs in stable working condition, and meanwhile the high-pressure storage bag space can be fully utilized. Compared with the traditional compression carbon dioxide energy storage system, the round-trip efficiency and the running stability are improved, and the volume and the investment cost of the storage device are reduced.

[0026] 3、The offshore floating subcritical compression carbon dioxide energy storage system provided by the application reduces the maximum pressure of the whole system to the range of 5 to 6 MPa by using the seawater temperature difference, improves the economy, makes the low-pressure gas storage bag float on the sea surface by using the seawater buoyancy, does not occupy the space of the offshore platform, and improves the volume energy density; the low-temperature heat of the heat storage water is used to preheat the evaporated carbon dioxide in the preheater, improves the utilization rate of heat storage, makes the system not dependent on other low-grade waste heat, and becomes an independent energy storage system for deep-sea offshore wind power and photovoltaic.

[0027] In summary, the application faces the in-situ consumption of deep-sea offshore wind power and photovoltaic and the like new energy, integrates the marine temperature difference resources, and overcomes the technical defects of the traditional compressed carbon dioxide energy storage. The marine temperature difference and seawater static pressure are used to realize the efficient liquefaction and high-density storage of high-pressure carbon dioxide, improve the efficiency and energy density of the energy storage system, and provide a feasible technical path for the development and consumption of deep-sea offshore new energy. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a structure schematic view of the offshore constant-pressure compression carbon dioxide system coupled with the marine temperature difference of the embodiment 1.

[0029] Figure 2 It is a structure schematic view of the offshore constant-pressure compression carbon dioxide system coupled with the marine temperature difference of the embodiment 2.

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

[0031] Mark explanation: 1-low pressure gas storage bag, 2-electric 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 medium 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 DESCRIPTION

[0032] In order to further understand and recognize the structural characteristics and effects achieved by the application, the following will combine the example to clearly and completely describe the application.

[0033] Embodiment 1

[0034] Reference Figure 1 , the offshore constant-pressure compression carbon dioxide energy storage system coupled with the marine temperature difference, the system comprises: 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.

[0035] The working medium constant pressure storage device 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; wherein 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 shell of the high-pressure liquid storage bag 10 is made of flexible material, so that the volume can change while maintaining the internal pressure unchanged; the high-pressure liquid storage bag 10 is arranged at a depth of about 500-600 meters below the sea level, and uses the static pressure of seawater to maintain a constant high pressure of about 5-6 MPa; the shell of the low-pressure gas storage bag 1 is made of flexible material, so that the volume can change while maintaining the internal pressure unchanged; the inside of the low-pressure gas storage bag 1 is at atmospheric pressure, which uses atmospheric pressure to maintain a constant low pressure, and at the same time uses the buoyancy of seawater to float on the sea level, without occupying the space of the artificial floating platform.

[0036] The heat storage cycle circuit 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 connected with the low-temperature side inlet of the first cooler 4 and the second cooler 6 respectively, and the low-temperature side outlets of the first cooler 4 and the second cooler 6 are connected with the inlet of the hot water storage tank 8; the outlet of the hot water storage tank 8 is connected with the high-temperature side inlet of the first heater 13 and the second heater 15 respectively, and the high-temperature side outlets of the first heater 13 and the second heater 15 are connected with the inlet of the cold water storage tank 7; the cold water storage tank 7 is used for storing low-temperature heat storage medium, and the hot water storage tank 8 is used for storing high-temperature heat storage medium. In the energy storage process, the low-temperature heat storage medium in the cold water storage tank 7 absorbs the compression heat generated in the carbon dioxide energy storage cycle process, and is converted into high-temperature heat storage medium and stored in the hot water storage tank 8; in 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 converted into low-temperature heat storage medium and stored in the cold water storage tank 7; the heat storage medium in the heat storage cycle circuit is pressurized water.

[0037] The carbon dioxide energy storage cycle loop: using offshore wind power and other new energy power generation to compress low-pressure gaseous carbon dioxide into high-pressure state, and then using deep sea low-temperature seawater to condense high-pressure gaseous carbon dioxide into liquid state; including low-pressure compressor 3, high-pressure compressor 5, condenser 9; the power input shafts of the low-pressure compressor 3 and the high-pressure compressor 5 are connected with the power output shaft of the motor 2, the electric energy inlet of the motor 2 is connected with the electric energy outlet of the offshore wind power and other new energy power generation, the offshore wind power and other new energy power generation is transported into the motor 2 to supply power to the motor 2 to drive the two compressors; the outlet of the low-pressure gas bag 1 is connected with the inlet of the low-pressure compressor 3, the outlet of the low-pressure compressor 3 is connected with the high-temperature side inlet of the first cooler 4, the high-temperature side outlet of the first cooler 4 is connected with the inlet of the high-pressure compressor 5, the outlet of the high-pressure compressor 5 is connected with the high-temperature side inlet of the second cooler 6, the outlet of the second cooler 6 is connected with the high-temperature side inlet of the condenser 9, and the high-temperature side outlet of the condenser 9 is connected with the inlet of the high-pressure liquid storage bag 10. The low-pressure gaseous carbon dioxide is compressed by the low-pressure compressor 3 and the high-pressure compressor 5 to high-pressure state, and the compression heat generated is stored in the heat storage cycle loop, and then condensed into liquid state by the deep sea low-temperature seawater through the condenser 9, and the high-pressure liquid carbon dioxide is transported into the high-pressure liquid storage bag 10 for constant pressure storage.

[0038] The carbon dioxide energy release cycle loop: using shallow sea high-temperature seawater to evaporate high-pressure liquid carbon dioxide into gaseous state, using high-pressure gaseous carbon dioxide expansion to generate power, and converting the generated mechanical energy into electric energy to stably output to the energy consumption side; including working fluid pump 11, evaporator 12, high-pressure turbine 14, low-pressure turbine 16, heat radiator 18; the outlet of the high-pressure liquid storage bag 10 is connected with the inlet of the working fluid pump 11, the outlet of the working fluid pump 11 is connected with the low-temperature side inlet of the evaporator 12, the low-temperature side outlet of the evaporator 12 is connected with the low-temperature side inlet of the first heater 13, the low-temperature side outlet of the first heater 13 is connected with the inlet of the high-pressure turbine 14, the outlet of the high-pressure turbine 14 is connected with the low-temperature side inlet of the second heater 15, the low-temperature side outlet of the second heater 15 is connected with the inlet of the low-pressure turbine 16, the outlet of the low-pressure turbine 16 is connected with the inlet of the heat radiator 18, and the outlet of the heat radiator 18 is connected with the inlet of the low-pressure gas bag 1; the power output shafts of the high-pressure turbine 14 and the low-pressure turbine 16 are connected with the power input shaft of the generator 17, and the electric energy outlet of the generator 17 is connected with the electric energy inlet of the energy consumption side; the stored high-pressure liquid carbon dioxide absorbs the heat of the shallow sea high-temperature seawater through the evaporator 12 to evaporate into gaseous state, and then the temperature is raised through the first heater 13 and the second heater 15, and then the high-pressure gaseous carbon dioxide is expanded through the high-pressure turbine 14 and the low-pressure turbine 16 to low-pressure state, and then the low-pressure gaseous carbon dioxide is further cooled through the heat radiator 18, and then transported into the low-pressure gas bag 1 for constant pressure storage.

[0039] The offshore constant-pressure compression carbon dioxide energy storage system coupled with ocean temperature difference uses the action of seawater static pressure and seawater buoyancy to store high-pressure liquid carbon dioxide and low-pressure gaseous carbon dioxide in a constant-pressure storage device; in the energy storage and release process, seawater at different depths is coupled as a cold source and a heat source to realize the gas-liquid conversion of carbon dioxide under subcritical state.

[0040] The cold source is deep-sea low-temperature seawater below 10 DEG C, which is coupled to the energy storage process; specifically, the low-temperature seawater at a depth of about 500 to 600 meters below sea level is introduced into the low-temperature side of the condenser 9. The heat source is shallow-sea high-temperature seawater above 25 DEG C, which is coupled to the energy release process; specifically, the high-temperature seawater at the shallow sea level is introduced into the high-temperature side of the evaporator 12. Referring to Figure 3 , by virtue of the characteristics that the temperature of seawater decreases with the increase of the depth, the high-temperature seawater at the shallow layer and the low-temperature seawater at the deep layer are cooperatively utilized as the cold source and the heat source of the gas-liquid conversion process.

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

[0042] The application also provides a running method of the offshore constant-pressure compression carbon dioxide energy storage system coupled with ocean temperature difference, which comprises an energy storage process and an energy release process.

[0043] In the energy storage process, the low-pressure gaseous carbon dioxide stored in the low-pressure gas bag 1 is compressed by two stages to increase the pressure of the carbon dioxide to a high-pressure state, and the heat energy generated by the compressed carbon dioxide is absorbed by the low-temperature pressurized water in the cold water storage tank 7, and then the low-temperature pressurized water is converted into high-temperature pressurized water and stored in the hot water storage tank 8; and the low-temperature high-pressure carbon dioxide after heat release 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 liquid, and then stored in the flexible high-pressure liquid storage bag 10 in the deep sea.

[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 compressed for the first time; 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 compressed for the second time; after absorbing heat, the two streams of low-temperature pressurized water are mixed and then flow into the hot water storage tank 8 for storage;

[0045] In the energy releasing process, the high-temperature seawater from the shallow sea is first sent to the underwater through the pipeline, the 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 high-temperature seawater and then evaporate into a gaseous state, and then rises to the sea level to further absorb the heat energy of the high-temperature pressurized water in the hot water storage tank 8, and then performs work to generate electricity through two-stage expansion, and the low-pressure gaseous carbon dioxide after heat release is stored in the low-pressure gas storage bag 1, and the high-temperature pressurized water after absorbing heat is converted 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 to transfer 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 to transfer heat to the carbon dioxide flowing through the second heater 15, and the temperature of the two parts of the high-temperature pressurized water after heat release is reduced, and then mixed and flows into the cold water storage tank 7 for storage.

[0047] Embodiment 2

[0048] As shown in Figure 2 In addition to the system structure of embodiment 1, the energy releasing process of the carbon dioxide energy releasing cycle loop of the present embodiment further includes a preheater 19; the low-temperature side outlet of the evaporator 12 is connected with the low-temperature side inlet of the preheater 19, the low-temperature side outlet of the preheater 19 is connected with 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 with the high-temperature side inlet of the preheater 19, and the high-temperature side outlet of the preheater 19 is connected with 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 stored heat. By using the low-temperature heat storage medium in the heat storage cycle loop which is not utilized to preheat the low-temperature carbon dioxide from the evaporator 12, the stored heat is fully utilized to make the heat exchange matching degree of the system higher, and thus the round-trip efficiency of the entire energy storage system is improved.

Claims

1. A marine 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; Working fluid constant pressure storage device: includes a low pressure gas storage bladder (1) for constant pressure storage of low pressure gaseous carbon dioxide and a high pressure liquid storage bladder (10) for constant pressure storage of high pressure liquid carbon dioxide. Carbon dioxide energy storage loop: The outlet of the low-pressure gas storage bladder (1) is connected to the inlet of the high-pressure liquid storage bladder (10) through the carbon dioxide energy storage loop. The power input shaft of the carbon dioxide energy storage loop is 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). The motor (2) drives the compressor to compress the low-pressure gaseous carbon dioxide to a high-pressure state. Then, the high-pressure gaseous carbon dioxide is condensed into liquid by deep-sea low-temperature seawater and stored in the high-pressure liquid storage bladder (10). Carbon dioxide energy release circulation 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 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). The power outlet of the generator (17) is connected to the power inlet of the energy user side. The high-pressure liquid carbon dioxide is evaporated into gaseous state by using high-temperature seawater in shallow sea. The high-pressure gaseous carbon dioxide is expanded to do work, and the generated mechanical energy is converted into electrical energy and stably delivered to the energy user side. At the same time, the expanded low-pressure gaseous carbon dioxide is stored in the low-pressure gas storage bag (1). Thermal storage loop: During energy storage, the carbon dioxide energy storage loop is connected to the thermal storage loop via a cooler. The stored low-temperature thermal storage medium absorbs the compression heat generated during the carbon dioxide energy storage loop process and transforms into a high-temperature thermal storage medium for storage. During energy release, the carbon dioxide energy release loop is connected to the thermal storage loop via a heater. The stored high-temperature thermal storage medium heats the gaseous carbon dioxide during the carbon dioxide energy release loop process and transforms into a low-temperature thermal storage medium for storage. The thermal storage loop includes: a cold water storage tank (7), a hot water storage tank (8), a first cooler (4), a second cooler (6), and a third cooler (7). A heater (13) and a second heater (15); the outlet of the cold water storage tank (7) is connected to the low-temperature side inlet of the first cooler (4) and the second cooler (6), respectively, 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 connected to the high-temperature side inlet of the first heater (13) and the second heater (15), respectively, 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 low-temperature heat storage medium, and the hot water storage tank (8) is used to store high-temperature heat storage medium.

2. The marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 1, characterized in that: The shells of the low-pressure air reservoir (1) and the high-pressure liquid reservoir (10) are both made of flexible materials; the low-pressure air reservoir (1) floats on the sea surface and its internal pressure is constant at atmospheric pressure; the high-pressure liquid reservoir (10) is set at a depth of 500 to 600 meters below sea level 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, characterized in that, The carbon dioxide energy storage cycle includes: a low-pressure compressor (3), a high-pressure compressor (5), and a condenser (9); the power input shafts of both the low-pressure compressor (3) and the high-pressure compressor (5) are 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, 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 bladder (1) is connected to the inlet of the low-pressure compressor (3), and the outlet of the low-pressure compressor (3) is connected to the high-temperature side inlet of the first cooler (4), and the high-temperature side of the first cooler (4) is connected to the inlet 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 high-temperature side inlet of the second cooler (6), the high-temperature side outlet of the second cooler (6) is connected to the high-temperature side inlet of the condenser (9), and the high-temperature side outlet of the condenser (9) is connected to the inlet of the high-pressure liquid storage bladder (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 is stored in the heat storage circulation loop, it is condensed into liquid by the deep-sea low-temperature seawater through the condenser (9). The liquid carbon dioxide is transported to the high-pressure liquid storage bladder (10) for constant pressure storage.

4. The marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 3, characterized in that: The deep-sea low-temperature seawater used in the carbon dioxide energy storage cycle 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.

5. The marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 1, characterized in that, The carbon dioxide energy release cycle 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 reservoir (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 low-temperature side inlet of the second heater (15). The radiator (18) is connected to the inlet, and the radiator (18) outlet 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). The power outlet of the generator (17) is connected to the power inlet of the energy user. The stored liquid carbon dioxide absorbs heat from the high-temperature seawater in the shallow sea through the evaporator (12) and evaporates into a gaseous state. After the temperature is raised 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). After the low-pressure gaseous carbon dioxide is cooled by the radiator (18), it is transported to the low-pressure gas storage bladder (1) for constant pressure storage.

6. The marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 5, characterized in that: The shallow seawater with high temperature used in the carbon dioxide energy release cycle is transported to the high temperature side inlet of the evaporator (12) through a pipeline, and the temperature of the shallow seawater with high temperature is above 25°C.

7. The marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 5, characterized in that, The carbon dioxide energy release 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), 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), and 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, it enters the first heater (13) and the second heater (15) to absorb the stored heat.

8. An operation method for a marine constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference, employing the marine constant-pressure compressed carbon dioxide energy storage system as described in any one of claims 1-7, characterized in that, Including energy storage and energy release processes: During the energy storage process, the low-pressure gaseous carbon dioxide stored in the low-pressure gas storage bladder (1) undergoes two-stage compression to a high-pressure state. The heat energy generated by the compression of 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 high-pressure carbon dioxide after heat release exchanges heat with the low-temperature seawater in the deep sea through the condenser (9), causing the low-temperature high-pressure carbon dioxide to condense into a liquid state and be stored in the high-pressure liquid storage bladder (10). During the energy release process, the high-pressure liquid carbon dioxide stored in the high-pressure liquid storage bladder (10) is transported to the evaporator (12) by the working fluid pump (11) to absorb the heat of the high-temperature seawater in the shallow sea and evaporate into gas. Then it rises to the sea surface and further absorbs the heat energy of the high-temperature heat storage medium in the hot water storage tank (8). Then it 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). The high-temperature heat storage medium after absorbing heat energy is transformed into a low-temperature heat storage medium and stored in the cold water storage tank (7).

9. The operation method of the offshore constant-pressure compressed carbon dioxide energy storage system coupled with ocean temperature difference according to claim 8, characterized in that: During the energy storage process, a portion of the low-temperature heat storage medium flowing out from the cold water storage tank (7) exchanges heat through the first cooler (4) and absorbs the heat of compression of carbon dioxide after the first compression. Another portion of the low-temperature heat storage medium flowing out from the cold water storage tank (7) exchanges heat through the second cooler (6) and absorbs the heat of compression of carbon dioxide after being compressed for the second time. After absorbing heat, the temperature of the two low-temperature heat storage media rises, 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 the heat is released, the temperature of the two portions of high-temperature heat storage medium decreases, and after mixing, they flow into the cold water storage tank (7) for storage.

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