Carbon dioxide energy storage system with cooperation of seabed liquid storage and high-temperature heat storage and operation method of carbon dioxide energy storage system

Abstract

The invention discloses a seabed liquid storage and high-temperature heat storage synergetic carbon dioxide energy storage system and an operation method thereof, an energy conversion and heat storage subsystem is arranged on a coast, a single-stage compression and expansion structure is adopted, water and fused salt are combined to carry out cascade heat storage, and high-temperature storage and release of heat energy are realized; the floating type flexible air storage bag is arranged on the offshore sea surface, the flexible liquid storage bag is moored to the seabed, the carbon dioxide gas-liquid phase change is driven through the temperature difference between the seabed cold seawater and the sea surface hot seawater, and constant-pressure liquid storage is achieved; carbon dioxide is liquefied and compressed through seabed cold seawater to improve the density so as to weaken buoyancy, and reliable ballasting of the seabed storage device is achieved. Meanwhile, the condensation pressure of carbon dioxide is reduced through the deep-sea low-temperature environment, the exhaust temperature of the compressor is reduced in combination with the pressure gradient of carbon dioxide in the vertical direction, and the reliability of the high-pressure-ratio compressor and low-melting-point fused salt is improved. According to the carbon dioxide energy storage system, seabed constant-pressure liquid storage and high-temperature fused salt heat storage are cooperatively utilized, and the back-and-forth efficiency of the system can be remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermo-mechanical energy storage, in particular to a carbon dioxide energy storage system cooperating with seabed liquid storage and high-temperature heat storage and a method for operating the same. BACKGROUND

[0002] In recent years, with the rapid development of offshore wind power and photovoltaic, coastal areas have gradually become important regions for large-scale development of new energy. However, offshore new energy has intermittency and volatility, which poses a challenge to the stability of the power grid. Large-scale long-time energy storage technology plays an increasingly important role in balancing energy supply and demand and improving the stability of the power grid, providing a solution for power balancing and peak shaving. Among various new long-time energy storage technology paths, compressed carbon dioxide energy storage has become an important branch of thermo-mechanical energy storage due to its long system life, low cost per kilowatt-hour, environmental friendliness, and independence from scarce materials. Among them, compressed carbon dioxide energy storage technology based on gaseous and liquid storage has been implemented in engineering applications in inland, desert, and other scenarios, attracting more and more attention and is expected to become a potential solution for efficient energy storage technology in coastal areas.

[0003] The compressed carbon dioxide energy storage system realizes energy storage and release through the processes of compression, heat storage, heat release, and expansion, and realizes electricity storage by simultaneously storing pressure energy and heat energy, involving core links such as compression heat storage, working fluid liquefaction, and heat recovery. Therefore, the key to improving the system efficiency lies in avoiding meaningless loss of pressure energy and reducing irreversible dissipation of heat . In order to avoid the system operating at variable pressure and reducing efficiency due to pressure change during the charging and discharging process of storing high-pressure carbon dioxide in a pressure vessel, the Chinese invention patent application with publication number CN120062847A proposes a marine constant-pressure compressed carbon dioxide energy storage system and method coupled with ocean temperature difference, which realizes the gas-liquid conversion of carbon dioxide by using deep cold seawater and shallow warm seawater and stores constant-pressure carbon dioxide by using seawater static pressure. However, this scheme uses two-stage compression and low-temperature heat storage, which reduces the energy quality in the process of converting electrical energy into thermal energy, limiting the round-trip efficiency of the system. The scheme uses a floating offshore platform to carry the energy storage system, which needs to rely on an additional offshore platform, resulting in high investment cost. Wang Ding et al. (Performance analysis of a new gas-liquid phase change compressed carbon dioxide energy storage system [J]. Power Engineering, 2024.) propose a compressed carbon dioxide energy storage system based on single-stage compression, which realizes high-temperature heat storage by using molten salt heat storage. However, due to the lack of effective heat management during the heat storage and release processes, the compressor inlet temperature cannot be restored to a high temperature level, hindering the system performance. Moreover, using an environmental cold source to liquefy carbon dioxide results in high high-pressure, which makes the compressor discharge temperature too high, affecting the normal operation of the compressor and easily leading to high-temperature decomposition of low-melting-point molten salt heat storage. SUMMARY

[0004] In order to overcome the low efficiency of the two-stage compression system and the poor reliability of the single-stage compression system in the prior art, the purpose of the present application is to provide a carbon dioxide energy storage system cooperating with submarine liquid storage and high-temperature heat storage and an operation method thereof, wherein the energy conversion and heat storage subsystem is arranged on the coast, a single-stage compression and expansion structure is adopted, cascade heat storage is combined with water and molten salt, high-temperature heat storage and release are realized, the gas storage device adopts a floating flexible gas bag and is arranged on the sea surface, the liquid storage device adopts a flexible liquid bag and is moored on the seabed, the temperature difference between the cold seawater on the seabed and the hot seawater on the sea surface is utilized to drive the carbon dioxide gas-liquid phase change, and constant-pressure liquid storage is realized, the carbon dioxide two-way transportation pipeline is utilized to connect the coast energy conversion and heat storage subsystem and the submarine gas-liquid phase change and liquid storage subsystem, the pipeline laying is reduced, and the cost is reduced, the density of the carbon dioxide is significantly increased by the submarine cold seawater to weaken the buoyancy, the reliable ballast of the submarine storage device is realized, the carbon dioxide condensing pressure is reduced by the deep sea environment, the pressure gradient of the carbon dioxide in the vertical direction is combined, the exhaust temperature of the compressor is effectively reduced, and the reliability of the high-pressure ratio compressor and the low-melting-point molten salt is improved. The carbon dioxide energy storage system provided by the present application cooperates with the submarine constant-pressure liquid storage and the high-temperature molten salt heat storage, the round-trip efficiency of the system can be significantly improved, and an efficient energy storage solution is provided for the coastal areas, island areas and the like.

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

[0006] The carbon dioxide energy storage system cooperating with submarine liquid storage and high-temperature heat storage comprises a coast energy conversion and heat storage subsystem, a carbon dioxide two-way transportation pipeline, a submarine gas-liquid phase change and liquid storage subsystem, and a near-sea sea surface floating gas bag 1 for storing low-pressure gaseous carbon dioxide.

[0007] The coast energy conversion and heat storage subsystem comprises a compressor 3, a first heat storage heat exchanger 4, a second heat storage heat exchanger 5, a low-temperature water storage tank 6, a high-temperature water storage tank 7, a low-temperature molten salt storage tank 8, a high-temperature molten salt storage tank 9, a third heat storage heat exchanger 19, a fourth heat storage heat exchanger 20, and a turbine 21; during energy storage, the outlet of the gas bag 1 is sequentially connected with the compressor 3, the high-temperature side of the first heat storage heat exchanger 4 and the high-temperature side of the second heat storage heat exchanger 5; the outlet of the low-temperature water storage tank 6 is connected with the inlet of the high-temperature water storage tank 7 through the low-temperature side of the second heat storage heat exchanger 5; the outlet of the low-temperature molten salt storage tank 8 is connected with the inlet of the high-temperature molten salt storage tank 9 through the low-temperature side of the first heat storage heat exchanger 4; during energy release, the carbon dioxide outlet of the submarine gas-liquid phase change and liquid storage subsystem is sequentially connected with the low-temperature side of the third heat storage heat exchanger 19 and the low-temperature side of the fourth heat storage heat exchanger 20 through the carbon dioxide two-way transportation pipeline, and the low-temperature side outlet of the fourth heat storage heat exchanger 20 is connected with the inlet of the turbine 21; the outlet of the high-temperature water storage tank 7 is connected with the inlet of the low-temperature water storage tank 6 through the high-temperature side of the third heat storage heat exchanger 19; and the outlet of the high-temperature molten salt storage tank 9 is connected with the inlet of the low-temperature molten salt storage tank 8 through the high-temperature side of the fourth heat storage heat exchanger 20.

[0008] The submarine gas-liquid phase change and liquid storage subsystem comprises a condenser 13, a first seawater pump 14, a liquid storage bag 15, a working medium pump 16, an evaporator 17, and a second seawater pump 18; during energy storage, the high-temperature side outlet of the second heat storage heat exchanger 5 is connected with the high-temperature side inlet of the condenser 13 through a carbon dioxide bidirectional transportation pipeline, and the high-temperature side outlet of the condenser 13 is connected with the inlet of the liquid storage bag 15; the low-temperature side inlet of the condenser 13 is connected with the submarine pipeline through the first seawater pump 14; during energy release, the outlet of the liquid storage bag 15 is connected with the low-temperature side inlet of the evaporator 17 through the working medium pump 16, and the low-temperature side outlet of the evaporator 17 is connected with the low-temperature side inlet of the third heat storage heat exchanger 19 through the carbon dioxide bidirectional transportation pipeline; the high-temperature side inlet of the evaporator 17 is connected with the sea surface pipeline through the second seawater pump 18.

[0009] The compressor 3 is connected with the motor 2 through a shaft coupling, and the power inlet of the motor 2 is connected with the power outlet of the offshore wind power generation device; the turbine 21 is connected with the generator 22 through a shaft coupling, and the power outlet of the generator 22 is connected with the power inlet of the power grid or user.

[0010] The submarine energy conversion and heat storage subsystem further comprises a regenerator 23, the low-temperature side outlet of the evaporator 17 is connected with the low-temperature side inlet of the regenerator 23 through the carbon dioxide bidirectional transportation pipeline, and the low-temperature side outlet of the regenerator 23 is connected with the low-temperature side inlet of the third heat storage heat exchanger 19; the outlet of the turbine 21 is connected with the inlet of the gas storage bag 1 through the high-temperature side of the regenerator 23.

[0011] The heat storage temperatures of the high-temperature water storage tank 7 and the low-temperature molten salt storage tank 8 are close, and are between 150℃ and 300℃.

[0012] The carbon dioxide bidirectional transportation pipeline comprises a first switching valve 10, a carbon dioxide pipeline 11, and a second switching valve 12; the carbon dioxide pipeline 11 is divided into a heat preservation section pipeline and a non-heat preservation section pipeline, and the heat preservation section pipeline is a section of pipeline whose surrounding seawater temperature is lower than a set carbon dioxide evaporation temperature.

[0013] The liquid storage bag 15 is arranged on the seabed and is used for constant-pressure storage of high-pressure liquid carbon dioxide.

[0014] The submarine pipeline is arranged at a depth on the seabed which is deeper than the depth of the liquid storage bag 15 on the seabed.

[0015] The coastal energy conversion and heat storage subsystem further comprises an intermediate water storage tank 24 and an intermediate molten salt tank 25; the intermediate water storage tank 24 is connected with the intermediate outlet of the low-temperature side of the second heat storage heat exchanger 5, and the outlet of the intermediate water storage tank 24 is connected with the intermediate inlet of the high-temperature side of the third heat storage heat exchanger 19; the intermediate molten salt tank 25 is located between the intermediate pipeline of the low-temperature side of the first heat storage heat exchanger 4 and the intermediate pipeline of the high-temperature side of the fourth heat storage heat exchanger 20, and the flow direction of the molten salt in the intermediate molten salt tank 25 needs to be determined according to the selected type of molten salt.

[0016] The application further provides an operation method of the seabed liquid storage and high-temperature heat storage coordinated carbon dioxide energy storage system, comprising:

[0017] During energy storage, the low-pressure gaseous carbon dioxide in the gas bag 1 is compressed by the compressor 3 in a single stage, and the compression heat generated is recovered by the molten salt heat storage and the pressurized water heat storage in turn; and the carbon dioxide is cooled and then transported to the condenser 13 through the carbon dioxide bidirectional transportation pipeline, is completely condensed into liquid by the seabed cold seawater, and is then stored in the liquid storage bag 15 at a constant pressure.

[0018] During energy release, the liquid carbon dioxide stored in the liquid storage bag 15 is pressurized by the working medium pump 16 and then transported to the evaporator 17, is evaporated into gas by the surface hot seawater, is transported to the regenerator 23 through the carbon dioxide bidirectional transportation pipeline to absorb the waste gas waste heat at the outlet of the turbine 21, and then the high-pressure carbon dioxide preheated is heated to a high-temperature state by the pressurized water heat storage and the molten salt heat storage in turn, enters the turbine 21 to expand and do work to generate electricity; the carbon dioxide at the outlet of the turbine 21 is cooled after being reheated by the regenerator 23, and is then stored in the gas bag 1.

[0019] During energy storage, the molten salt heat storage recovers the heat of the high-temperature carbon dioxide at the outlet of the compressor 3 by using the low-temperature molten salt in the low-temperature molten salt storage tank 8, the temperature of the low-temperature molten salt is increased, becomes high-temperature molten salt and is stored in the high-temperature molten salt storage tank 9; the pressurized water heat storage further recovers the heat of the carbon dioxide at the outlet of the first heat storage heat exchanger 4 by using the low-temperature pressurized water in the low-temperature water storage tank 6, the temperature of the low-temperature pressurized water is increased, becomes high-temperature pressurized water and is stored in the high-temperature water storage tank 7.

[0020] During energy release, the pressurized water heat storage releases heat to the carbon dioxide at the low-temperature side outlet of the regenerator 23 by using the high-temperature pressurized water in the high-temperature water storage tank 7, the temperature of the high-temperature pressurized water is decreased, becomes low-temperature pressurized water and is stored in the low-temperature water storage tank 6; the molten salt heat storage further heats the carbon dioxide at the outlet of the third heat storage heat exchanger 19 by using the high-temperature molten salt in the high-temperature molten salt storage tank 9, the temperature of the high-temperature molten salt is decreased, becomes low-temperature molten salt and is stored in the low-temperature molten salt storage tank 8.

[0021] Compared with the prior art, the application has the beneficial effects that:

[0022] 1. The seabed liquid storage and high-temperature heat storage collaborative carbon dioxide energy storage system can make full use of the geographical conditions of the coast (such as coastal areas or islands), place the energy conversion and heat storage subsystem on the coast, and does not need to build an offshore platform; the atmospheric pressure gas bag is floated on the sea surface, and does not occupy land space; the cold seawater is used to liquefy and compress carbon dioxide, the density of the carbon dioxide is significantly increased, the buoyancy is greatly reduced, the liquid storage bag is moored to the seabed, the reliable ballast of constant pressure liquid storage can be realized, and the investment cost of the long-distance carbon dioxide pipeline is reduced.

[0023] 2. The seabed liquid storage and high-temperature heat storage collaborative carbon dioxide energy storage system can fully play the performance advantages of high-pressure single-stage compression and expansion under the condition that the compressor device and the low-melting-point molten salt heat storage medium can reliably operate. The carbon dioxide can be condensed at a lower temperature (pressure) by using the cold seawater on the seabed, and the pressure gradient of the carbon dioxide in the vertical direction can further reduce the outlet pressure and temperature of the compressor, so that the reliable operation range of the compressor and the molten salt heat storage due to the excessively high temperature is avoided.

[0024] 3. The seabed liquid storage and high-temperature heat storage collaborative carbon dioxide energy storage system adopts high-temperature and low-temperature two-stage heat storage of pressurized water and molten salt, different temperatures of heat are stored in stages, the efficiency loss caused by the storage of low-temperature heat by the high-temperature medium is avoided, and the energy utilization rate of the system is higher. The regenerator is arranged to increase the self-regenerative process, the waste heat of the turbine outlet is used to preheat the low-temperature carbon dioxide, the heat recovery rate of the system is improved, and the additional radiator is avoided.

[0025] 4. The intermediate storage tank is used to adjust the flow rates of the pressurized water and the molten salt respectively, so that the heat exchange matching between the carbon dioxide and the heat storage medium in the heat storage and release process is improved, the heat management level is improved, the turbine inlet temperature is improved, and the round-trip efficiency of the system is improved.

[0026] In summary, the carbon dioxide energy storage system cooperatively uses the seabed constant-pressure liquid storage and the high-temperature molten salt heat storage, can significantly improve the round-trip efficiency of the system, and provides an efficient energy storage solution for the nearshore, island and other regions. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a structure schematic view of the seabed liquid storage and high-temperature heat storage collaborative carbon dioxide energy storage system of embodiment 1.

[0028] Figure 2 It is a structure schematic view of the seabed liquid storage and high-temperature heat storage collaborative carbon dioxide energy storage system of embodiment 2.

[0029] Explanation of reference signs: 1 - gas storage bag, 2 - electric motor, 3 - compressor, 4 - first heat storage heat exchanger, 5 - second heat storage heat exchanger, 6 - low-temperature water storage tank, 7 - high-temperature water storage tank, 8 - low-temperature molten salt tank, 9 - high-temperature molten salt tank, 10 - first switching valve, 11 - carbon dioxide pipeline, 12 - second switching valve, 13 - condenser, 14 - first seawater pump, 15 - liquid storage bag, 16 - working medium pump, 17 - evaporator, 18 - second seawater pump, 19 - third heat storage heat exchanger, 20 - fourth heat storage heat exchanger, 21 - turbine, 22 - generator, 23 - regenerator, 24 - intermediate water storage tank, 25 - intermediate molten salt tank. DETAILED DESCRIPTION

[0030] To further understand and appreciate the structural features and effects of the present application, the following will combine the examples to clearly and completely describe the present application.

[0031] Example 1

[0032] Reference Figure 1 , the seabed liquid storage and high-temperature heat storage cooperative carbon dioxide energy storage system, the system comprises: a coastal energy conversion and heat storage subsystem, a seabed gas-liquid phase change and liquid storage subsystem, a near-shore sea surface floating gas storage bag 1, and a carbon dioxide bidirectional transportation pipeline.

[0033] The near-shore sea surface floating gas storage bag 1 is used for storing low-pressure gaseous carbon dioxide; the gas storage bag 1 is a multi-layer composite film structure, the inner layer is made of a flexible polymer material resistant to carbon dioxide permeation, the volume of the gas storage bag 1 can change, atmospheric pressure is used to maintain a constant pressure, and the inside of the gas storage bag 1 is always at normal pressure; the gas storage bag 1 floats on the near-shore sea surface by using the buoyancy of seawater, does not occupy land space, and the bottom is directly in contact with seawater, which can be cooled to the environmental temperature by seawater.

[0034] The coastal energy conversion and heat storage subsystem uses offshore wind power to drive a compressor with a high pressure ratio to compress low-pressure gaseous carbon dioxide into a high-temperature and high-pressure state, and then uses a double heat storage loop of pressurized water and molten salt to store and release heat; high-pressure gaseous carbon dioxide is expanded to do work to generate electricity, and the generated mechanical energy is converted into electrical energy which is stably output to the power grid or users; the carbon dioxide waste heat at the outlet of the turbine with a high pressure ratio is used to preheat the low-temperature carbon dioxide in the gas storage bag 1, increasing the internal heat recovery of the system; the subsystem specifically comprises an electric motor 2, a compressor 3, a first heat storage heat exchanger 4, a second heat storage heat exchanger 5, a low-temperature water storage tank 6, a high-temperature water storage tank 7, a low-temperature molten salt storage tank 8, a high-temperature molten salt storage tank 9, a third heat storage heat exchanger 19, a fourth heat storage heat exchanger 20, a turbine 21, a generator 22, and a regenerator 23.

[0035] The energy storage process, the motor 2 is connected with the compressor 3 through the shaft coupling, the power import of the motor 2 is connected with the power export of the offshore wind power generation device; the outlet of the gas bag 1 is connected with the import of the compressor 3, the outlet of the compressor 3 is connected with the high-temperature side import of the first heat storage heat exchanger 4, the high-temperature side outlet of the first heat storage heat exchanger 4 is connected with the high-temperature side import of the second heat storage heat exchanger 5, the high-temperature side outlet of the second heat storage heat exchanger 5 is connected with the carbon dioxide import of the submarine gas-liquid phase change and liquid storage subsystem through the carbon dioxide two-way transport pipeline; the outlet of the low-temperature water storage tank 6 is connected with the low-temperature side import of the second heat storage heat exchanger 5, the low-temperature side outlet of the second heat storage heat exchanger 5 is connected with the import of the high-temperature water storage tank 7; the outlet of the low-temperature molten salt storage tank 8 is connected with the low-temperature side import of the first heat storage heat exchanger 4, the low-temperature side outlet of the first heat storage heat exchanger 4 is connected with the import of the high-temperature molten salt storage tank 9. The offshore wind power generation device is used to supply power to the motor 2 to drive the compressor 3, and the low-pressure gaseous carbon dioxide in the gas bag 1 is compressed; the low-temperature molten salt in the low-temperature molten salt storage tank 8 recovers the heat of the high-temperature carbon dioxide at the outlet of the compressor 3, the temperature of the low-temperature molten salt is increased to become high-temperature molten salt, and is stored in the high-temperature molten salt storage tank 9; the low-temperature pressurized water in the low-temperature water storage tank 6 further recovers the heat of the carbon dioxide at the outlet of the first heat storage heat exchanger 4, the temperature of the low-temperature water is increased to become high-temperature pressurized water, and is stored in the high-temperature water storage tank 7.

[0036] The energy releasing process, the generator 22 is connected with the turbine 21 through the shaft coupling, the power outlet of the generator 22 is connected with the power inlet of the power grid or the user; the carbon dioxide outlet of the submarine gas-liquid phase change and liquid storage subsystem is connected with the low-temperature side inlet of the regenerator 23 through the carbon dioxide bidirectional transportation pipeline, the low-temperature side outlet of the regenerator 23 is connected with the low-temperature side inlet of the third heat storage heat exchanger 19, the low-temperature side outlet of the third heat storage heat exchanger 19 is connected with the low-temperature side inlet of the fourth heat storage heat exchanger 20, the low-temperature side outlet of the fourth heat storage heat exchanger 20 is connected with the inlet of the turbine 21, the outlet of the turbine 21 is connected with the high-temperature side inlet of the regenerator 23, and the high-temperature side outlet of the regenerator 23 is connected with the inlet of the gas storage bag 1; the outlet of the high-temperature water storage tank 7 is connected with the high-temperature side inlet of the third heat storage heat exchanger 19, and the high-temperature side outlet of the third heat storage heat exchanger 19 is connected with the inlet of the low-temperature water storage tank 6; the outlet of the high-temperature molten salt storage tank 9 is connected with the high-temperature side inlet of the fourth heat storage heat exchanger 20, and the high-temperature side outlet of the fourth heat storage heat exchanger 20 is connected with the inlet of the low-temperature molten salt storage tank 8. The low-temperature gaseous carbon dioxide from the submarine gas-liquid phase change and liquid storage subsystem is firstly preheated in the regenerator 23, then sequentially enters the third heat storage heat exchanger 19 and the fourth heat storage heat exchanger 20 to further increase the temperature, and then enters the turbine 21 to expand and do work, and the pressure is reduced; after the high-temperature pressurized water in the high-temperature water storage tank 7 releases heat to the carbon dioxide at the low-temperature side outlet of the regenerator 23, the temperature of the high-temperature pressurized water is reduced to become low-temperature pressurized water and is stored in the low-temperature water storage tank 6; the high-temperature molten salt in the high-temperature molten salt storage tank 9 further heats the carbon dioxide at the outlet of the third heat storage heat exchanger 19, the temperature of the high-temperature molten salt is reduced to become low-temperature molten salt and is stored in the low-temperature molten salt storage tank 8. The low-pressure gaseous carbon dioxide at the outlet of the turbine 21 enters the regenerator 23 to exchange heat, improve the internal heat recovery of the system, and reduce the temperature after entering the gas storage bag 1, and meanwhile, the additional radiator is avoided.

[0037] The heat storage temperatures of the high-temperature water storage tank 7 and the low-temperature molten salt storage tank 8 are close, between 150℃ and 300℃; the molten salt can adopt solar salt or low-melting-point ternary molten salt, and the ternary molten salt is preferably Hitec molten salt.

[0038] The carbon dioxide bidirectional transportation pipeline is used for bidirectional transportation of high-pressure gaseous carbon dioxide between the seabed and the coast, and comprises a first reversing valve 10, a carbon dioxide pipeline 11 and a second reversing valve 12. The carbon dioxide pipeline 11 is divided into a heat preservation section pipeline and a non-heat preservation section pipeline. The pipeline part with a surrounding seawater temperature lower than a set carbon dioxide evaporation temperature (15-23℃) is heat preserved by using conventional heat preservation materials (such as polyurethane foam or polyethylene foam). In the embodiment, the pipeline part below about 230 meters from the sea level is the heat preservation section pipeline. In the energy storage process, the carbon dioxide from the coast energy conversion and heat storage subsystem enters the carbon dioxide pipeline 11 through the first reversing valve 10, is cooled by seawater in the non-heat preservation section pipeline for transportation to the seabed, and then enters the seabed gas-liquid phase change and liquid storage subsystem through the second reversing valve 12. In the energy release process, the carbon dioxide from the seabed gas-liquid phase change and liquid storage subsystem enters the carbon dioxide pipeline 11 through the second reversing valve 12, is heated by seawater in the non-heat preservation section pipeline for transportation to the coast, and then enters the coast energy conversion and heat storage subsystem through the first reversing valve 10.

[0039] The seabed gas-liquid phase change and liquid storage subsystem utilizes hot seawater on the sea surface and cold seawater on the seabed to realize phase change of carbon dioxide between the gaseous state and the liquid state, and utilizes seawater static pressure and a flexible material liquid storage bag to realize constant pressure storage of liquid carbon dioxide. The subsystem specifically comprises a condenser 13, a first seawater pump 14, a liquid storage bag 15, a working medium pump 16, an evaporator 17 and a second seawater pump 18.

[0040] In the energy storage process, the high-temperature side outlet of the second heat storage heat exchanger 5 is connected with the high-temperature side inlet of the condenser 13 through the carbon dioxide bidirectional transportation pipeline, the high-temperature side outlet of the condenser 13 is connected with the inlet of the liquid storage bag 15, the low-temperature side of the condenser 13 is connected with the seabed pipeline through the first seawater pump 14, and the high-pressure carbon dioxide from the high-temperature side of the second heat storage heat exchanger 5 enters the condenser 13 through the carbon dioxide bidirectional transportation pipeline, is condensed into liquid by cold seawater on the seabed, and is then stored in the liquid storage bag 15 at constant pressure.

[0041] In the energy release process, the outlet of the liquid storage bag 15 is connected with the low-temperature side inlet of the evaporator 17 through the working medium pump 16, the low-temperature side outlet of the evaporator 17 is connected with the low-temperature side inlet of the regenerator 23 through the carbon dioxide bidirectional transportation pipeline, the high-temperature side inlet of the evaporator 17 is connected with the sea surface pipeline through the second seawater pump 18, and the liquid carbon dioxide in the liquid storage bag 15 enters the evaporator 17 through the working medium pump 16, is evaporated into gas by hot seawater transported through the second seawater pump 18, and then enters the regenerator 23 through the carbon dioxide bidirectional transportation pipeline and is preheated. The liquid storage bag 15 is used for constant pressure storage of high-pressure liquid carbon dioxide, the shell of the liquid storage bag 15 is made of multiple layers of flexible materials, the volume of the liquid storage bag 15 can be changed to maintain constant internal pressure, the liquid storage bag 15 is moored on the seabed about 450-500 meters deep, and the internal pressure of about 4.5-5.5 MPa is maintained by using seawater static pressure.

[0042] The sea surface hot seawater temperature is between 25 DEG C and 30 DEG C; the seabed cold seawater temperature is below 10 DEG C, and the low-temperature side of the condenser 13 extracts seawater deeper than the position of the storage bag 15 through the first seawater pump 14.

[0043] The seabed liquid storage and high-temperature heat storage collaborative carbon dioxide energy storage system utilizes seabed cold seawater to condense carbon dioxide, realizes lower condensing temperature than in a land environment, and reduces the high-pressure pressure of the system; meanwhile, the pressure difference of carbon dioxide in the vertical direction is utilized to further reduce the outlet pressure of the compressor 3, thereby reducing the compressor exhaust temperature when a single-stage compression is adopted, which can be less than 450 DEG C, so that the compressor is in a feasible temperature range, and low-melting-point molten salt is also helpful to be adopted to avoid high-temperature decomposition. Meanwhile, the carbon dioxide energy storage system utilizes seabed cold seawater to realize liquid storage of high-pressure carbon dioxide, increases the density of carbon dioxide through liquefaction, reduces the density difference with seawater, thereby weakening the buoyancy effect, and improving the reliability of the storage bag 15 in seabed mooring.

[0044] The application further provides a running method of the seabed liquid storage and high-temperature heat storage collaborative carbon dioxide energy storage system, including an energy storage process and an energy release process.

[0045] In the energy storage process, the low-pressure gaseous carbon dioxide stored in the gas bag 1 is compressed by using a single-stage high-pressure compressor 3, so that the generated heat is more high-temperature, and the generated high-temperature heat energy is recycled by using molten salt heat storage and pressurized water heat storage in turn; and the carbon dioxide is cooled and then transported to the condenser 13 through the carbon dioxide bidirectional transportation pipeline, in the transportation process, the carbon dioxide is cooled by seawater and the temperature is reduced, the pressure is further increased with the increase of the depth, and the carbon dioxide is completely condensed into liquid at the seabed by cold seawater, and then is stored in the storage bag 15 at constant pressure.

[0046] The molten salt heat storage recovers the heat of high-temperature carbon dioxide at the outlet of the compressor 3 by using low-temperature molten salt in the low-temperature molten salt storage tank 8, the low-temperature molten salt is increased in temperature and becomes high-temperature molten salt and is stored in the high-temperature molten salt storage tank 9; the pressurized water heat storage further recovers the heat of carbon dioxide at the outlet of the first heat storage heat exchanger 4 by using low-temperature pressurized water in the low-temperature water storage tank 6, the low-temperature pressurized water is increased in temperature and becomes high-temperature pressurized water and is stored in the high-temperature water storage tank 7.

[0047] During the energy release process, hot seawater from the sea surface is first piped into the evaporator 17 on the seabed. Liquid carbon dioxide stored in the storage bag 15 is pressurized by the working fluid pump 16 and transported to the evaporator 17 to be evaporated into gas. Then, it is transported to the coast through a bidirectional carbon dioxide transport pipeline. During the transport process, the pressure of carbon dioxide decreases as the depth decreases. It is preheated by seawater in the pipeline near the sea surface and then enters the regenerator 23 to absorb the waste heat of the exhaust gas from the turbine 21 outlet. Then, pressurized water heat storage and molten salt heat storage are used in sequence to heat the preheated high-pressure carbon dioxide to a high temperature state. It then enters the turbine 21 to expand and do work to generate electricity. The carbon dioxide at the turbine 21 outlet is cooled after reheating and enters the floating gas storage bag 1 near the sea surface for storage. During storage, it is cooled to room temperature by seawater and air.

[0048] The pressurized water thermal storage utilizes the high-temperature pressurized water in the high-temperature storage tank 7 to release heat to the carbon dioxide at the low-temperature side outlet of the regenerator 23. The temperature of the high-temperature pressurized water then decreases, becoming low-temperature pressurized water, which is then stored in the low-temperature storage tank 6. The molten salt thermal storage utilizes the high-temperature molten salt in the high-temperature molten salt storage tank 9 to further heat the carbon dioxide at the outlet of the third thermal storage heat exchanger 19. The temperature of the high-temperature molten salt then decreases, becoming low-temperature molten salt, which is then stored in the low-temperature molten salt storage tank 8.

[0049] Example 2

[0050] like Figure 2 As shown, in addition to the system structure of Embodiment 1, the thermal storage device of the coastal energy conversion and thermal storage subsystem also includes an intermediate water tank 24 and an intermediate molten salt tank 25; by adjusting the structure of the thermal storage heat exchanger, the thermal storage medium side (pressurized water and molten salt) has an intermediate inlet or outlet.

[0051] For the pressurized water thermal storage loop, the inlet of the intermediate water tank 24 is connected to the intermediate outlet on the low-temperature side of the second thermal storage heat exchanger 5, and the outlet of the intermediate water tank 24 is connected to the intermediate inlet on the high-temperature side of the third thermal storage heat exchanger 20. During the energy storage process, the pressurized water in the low-temperature water tank 6 enters the second thermal storage heat exchanger 5 and is heated. When heated to the intermediate temperature, a portion of the pressurized water flows out from the intermediate outlet and enters the intermediate water tank 24 for storage, while the remaining pressurized water is further heated to a higher temperature and then enters the high-temperature water tank 7 for storage. During the energy release process, the pressurized water in the high-temperature water tank 7 is cooled by carbon dioxide to the same temperature as the intermediate water tank 24. After the two are mixed, they are further cooled by carbon dioxide and then enter the low-temperature water tank 6 for storage.

[0052] For the molten salt heat storage loop, the principle of setting the intermediate molten salt tank 25 is the same as that of the pressurized water heat storage loop, except that the flow direction of the molten salt in the intermediate molten salt tank 25 needs to be determined according to the selected molten salt type. Since the specific heat of carbon dioxide increases slightly in the high temperature zone, when the specific heat of the molten salt decreases with the increase of temperature, if the flow is not changed, it will cause the temperature mismatch of the heat exchange process. In this embodiment, when a typical low melting point ternary salt Hitec is used, the flow direction of the molten salt in the intermediate molten salt tank 25 is given, that is, in the energy storage process, part of the molten salt enters the low temperature side of the first heat storage heat exchanger 4 from the intermediate molten salt tank 25; in the energy release process, part of the molten salt is extracted from the high temperature side of the fourth heat storage heat exchanger 20 into the intermediate molten salt tank 25; by increasing the flow of Hitec salt in the high temperature zone to balance the decrease of its specific heat.

[0053] Since the specific heat capacity of carbon dioxide, pressurized water and molten salt changes with temperature in different trends, large temperature difference heat exchange will cause obvious heat exchange matching problems, which is not conducive to the efficient heat recovery of the system; the present application increases an intermediate heat storage tank in the pressurized water heat storage loop and the molten salt heat storage loop respectively, which can split the flow of water and molten salt in the energy storage and energy release processes; by controlling the temperature and flow of the heat storage medium (water and molten salt) at the split point, the change of the specific heat capacity of carbon dioxide and the heat storage medium with temperature is balanced, the temperature curve of the heat storage and heat release process is adjusted, the heat exchange temperature matching is improved, the heat management level is improved, thereby further increasing the inlet temperature of the turbine 21 and improving the round trip efficiency of the whole system.

Claims

1. A carbon dioxide energy storage system in cooperation with a high-temperature thermal storage and a seabed liquid storage, characterized in that, It comprises: a coastal energy conversion and heat storage subsystem, a carbon dioxide bidirectional transportation pipeline, a submarine gas-liquid phase change and liquid storage subsystem, and a near-shore floating gas storage bag (1) for storing low-pressure gaseous carbon dioxide; the coastal energy conversion and heat storage subsystem comprises a compressor (3), a first heat storage heat exchanger (4), a second heat storage heat exchanger (5), a low-temperature water storage tank (6), a high-temperature water storage tank (7), a low-temperature molten salt storage tank (8), a high-temperature molten salt storage tank (9), a third heat storage heat exchanger (19), a fourth heat storage heat exchanger (20), and a turbine (21); during energy storage, the outlet of the gas storage bag (1) is sequentially connected to the compressor (3), the high-temperature side of the first heat storage heat exchanger (4), and the high-temperature side of the second heat storage heat exchanger (5); the outlet of the low-temperature water storage tank (6) is connected to the inlet of the high-temperature water storage tank (7) through the low-temperature side of the second heat storage heat exchanger (5); the outlet of the low-temperature molten salt storage tank (8) is connected to the inlet of the high-temperature molten salt storage tank (9) through the low-temperature side of the first heat storage heat exchanger (4); during energy release, the carbon dioxide outlet of the submarine gas-liquid phase change and liquid storage subsystem is sequentially connected to the low-temperature side of the third heat storage heat exchanger (19) and the low-temperature side of the fourth heat storage heat exchanger (20) through the carbon dioxide bidirectional transportation pipeline, and the outlet of the low-temperature side of the fourth heat storage heat exchanger (20) is connected to the inlet of the turbine (21); the outlet of the high-temperature water storage tank (7) is connected to the inlet of the low-temperature water storage tank (6) through the high-temperature side of the third heat storage heat exchanger (19); the outlet of the high-temperature molten salt storage tank (9) is connected to the inlet of the low-temperature molten salt storage tank (8) through the high-temperature side of the fourth heat storage heat exchanger (20); the submarine gas-liquid phase change and liquid storage subsystem comprises a condenser (13), a first seawater pump (14), a liquid storage bag (15), a working medium pump (16), an evaporator (17), and a second seawater pump (18); during energy storage, the high-temperature side outlet of the second heat storage heat exchanger (5) is connected to the high-temperature side inlet of the condenser (13) through the carbon dioxide bidirectional transportation pipeline, and the high-temperature side outlet of the condenser (13) is connected to the inlet of the liquid storage bag (15); the low-temperature side inlet of the condenser (13) is connected to the submarine pipeline through the first seawater pump (14); during energy release, the outlet of the liquid storage bag (15) is connected to the low-temperature side inlet of the evaporator (17) through the working medium pump (16), and the low-temperature side outlet of the evaporator (17) is connected to the low-temperature side inlet of the third heat storage heat exchanger (19) through the carbon dioxide bidirectional transportation pipeline; the high-temperature side inlet of the evaporator (17) is connected to the surface pipeline through the second seawater pump (18).

2. The seabed liquid storage and high temperature thermal storage coordinated carbon dioxide energy storage system according to claim 1, characterized in that: The compressor (3) is connected to the motor (2) through a shaft coupling, and the power inlet of the motor (2) is connected to the power outlet of the offshore wind power generation device; the turbine (21) is connected to the generator (22) through a shaft coupling, and the power outlet of the generator (22) is connected to the power inlet of the power grid or user.

3. The seabed liquid storage and high temperature thermal storage coordinated carbon dioxide energy storage system according to claim 1, characterized in that: The coastal energy conversion and heat storage subsystem further comprises a regenerator (23), the low-temperature side outlet of the evaporator (17) is connected with the low-temperature side inlet of the regenerator (23) through a carbon dioxide bidirectional transportation pipeline, the low-temperature side outlet of the regenerator (23) is connected with the low-temperature side inlet of the third heat storage heat exchanger (19), and the outlet of the turbine (21) is connected with the inlet of the gas bag (1) through the high-temperature side of the regenerator (23).

4. The seabed liquid storage and high temperature thermal storage coordinated carbon dioxide energy storage system according to claim 1, characterized in that: The heat storage temperature of the high-temperature water storage tank (7) is close to that of the low-temperature molten salt storage tank (8), and is between 150 DEG C and 300 DEG C.

5. The seabed liquid storage and high temperature thermal storage integrated carbon dioxide energy storage system in accordance with claim 1, wherein: The carbon dioxide bidirectional transportation pipeline comprises a first reversing valve (10), a carbon dioxide pipeline (11) and a second reversing valve (12), the carbon dioxide pipeline (11) is divided into a heat preservation section pipeline and a non-heat preservation section pipeline, and the heat preservation section pipeline is a section pipeline with a surrounding seawater temperature lower than a set carbon dioxide evaporation temperature.

6. The seabed liquid storage and high temperature thermal storage integrated carbon dioxide energy storage system in accordance with claim 1, wherein: The liquid storage bag (15) is arranged on the seabed and is used for storing high-pressure liquid carbon dioxide at a constant pressure.

7. The seabed liquid storage and high temperature thermal storage integrated carbon dioxide energy storage system in accordance with claim 1, wherein: The seabed pipeline has a depth deeper than that of the liquid storage bag (15) on the seabed.

8. The seabed fluid storage and high temperature thermal storage integrated carbon dioxide storage system of claim 1, wherein: The coastal energy conversion and heat storage subsystem further comprises an intermediate water storage tank (24) and an intermediate molten salt tank (25), the inlet of the intermediate water storage tank (24) is connected with an intermediate outlet of the low-temperature side of the second heat storage heat exchanger (5), the outlet of the intermediate water storage tank (24) is connected with an intermediate inlet of the high-temperature side of the third heat storage heat exchanger (19), and the intermediate molten salt tank (25) is arranged between an intermediate pipeline of the low-temperature side of the first heat storage heat exchanger (4) and an intermediate pipeline of the high-temperature side of the fourth heat storage heat exchanger (20), and the flow direction of the molten salt in the intermediate molten salt tank (25) needs to be determined according to the selected type of the molten salt.

9. The operation method of the seabed liquid storage and high-temperature heat storage coordinated carbon dioxide energy storage system according to claims 1-8, characterized in that, The energy storage process comprises the following steps: During energy storage, low-pressure gaseous carbon dioxide in the gas bag (1) is compressed by a single-stage compressor (3), the compression heat generated is recovered by molten salt heat storage and pressurized water heat storage in sequence, the carbon dioxide is cooled and then delivered to a condenser (13) through a carbon dioxide bidirectional transportation pipeline, is completely condensed into liquid by cold seawater on the seabed, and is stored in a liquid storage bag (15) at a constant pressure; During energy release, liquid carbon dioxide stored in the liquid storage bag (15) is pressurized by a working medium pump (16), is evaporated into gas by hot seawater on the sea surface in an evaporator (17), is delivered to a regenerator (23) through the carbon dioxide bidirectional transportation pipeline to absorb waste heat of exhaust gas from the outlet of a turbine (21), is then heated to a high-temperature state by pressurized water heat storage and molten salt heat storage in sequence, and is expanded to generate power in the turbine (21); the carbon dioxide from the outlet of the turbine (21) is cooled by the regenerator (23) and is then stored in the gas bag (1).

10. The method according to claim 9, wherein During energy storage, the molten salt heat storage uses the heat of high-temperature carbon dioxide at the outlet of the low-temperature molten salt recovery compressor (3) in the low-temperature molten salt storage tank (8) to increase the temperature of the low-temperature molten salt, so that the low-temperature molten salt becomes high-temperature molten salt and is stored in the high-temperature molten salt storage tank (9); the pressurized water heat storage uses the low-temperature pressurized water in the low-temperature water storage tank (6) to further recover the heat of carbon dioxide at the outlet of the first heat storage heat exchanger (4), so that the temperature of the low-temperature pressurized water is increased, the low-temperature pressurized water becomes high-temperature pressurized water, and the high-temperature pressurized water is stored in the high-temperature water storage tank (7); During energy release, the pressurized water heat storage uses the high-temperature pressurized water in the high-temperature water storage tank (7) to release heat to carbon dioxide at the low-temperature side outlet of the regenerator (23), so that the temperature of the high-temperature pressurized water is decreased, the high-temperature pressurized water becomes low-temperature pressurized water, and the low-temperature pressurized water is stored in the low-temperature water storage tank (6); the molten salt heat storage uses the high-temperature molten salt in the high-temperature molten salt storage tank (9) to further heat carbon dioxide at the outlet of the third heat storage heat exchanger (19), so that the temperature of the high-temperature molten salt is decreased, the high-temperature molten salt becomes low-temperature molten salt, and the low-temperature molten salt is stored in the low-temperature molten salt storage tank (8).

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