Carbon dioxide storage system based on underground space and construction method thereof

Abstract

The application discloses a carbon dioxide energy storage system based on underground space and a construction method thereof. The energy storage system comprises a low-pressure gas storage, a high-pressure liquid storage and a carbon supplement system. The low-pressure gas storage is located in a shallow underground cavern, and the internal pressure of gaseous carbon dioxide in the gas storage is balanced by using natural or abandoned underground space stress, so that the gas storage space is greatly reduced. The high-pressure liquid storage is located in an abandoned underground space or a newly-excavated cavity at a certain buried depth, and high-pressure liquid carbon dioxide meeting a liquefaction pressure is stored, so that the storage space is further reduced in a liquid phase form. The carbon supplement system is located on the ground. The carbon supplement system is used for initial gas charging and gas supplement of a closed circulation system of the high-pressure and low-pressure storages. The application belongs to an industrial-grade compressed gas energy storage system, can recycle and utilize large-scale underground carbon dioxide as an energy storage medium, effectively solves the problems of resource recycling post-processing and limited underground space, and realizes energy saving and emission reduction.

Description

Technical Field

[0001] This invention belongs to the field of underground space energy storage technology, specifically relating to a carbon dioxide energy storage system based on underground space and its construction method. Background Technology

[0002] New energy power generation has ushered in a leapfrog development, and its installed capacity in the power system is also increasing. However, this has also brought about problems such as difficulties in the absorption of new energy, reduced rotational inertia, and increased risks to safe power supply.

[0003] Energy storage, as a flexible regulatory resource, can ensure the absorption of new energy sources, improve the flexibility of the power system, and support the safe and stable operation of new power systems. It is expected to experience explosive growth in the future. In the field of energy storage, pumped hydro storage has always been the core technology; however, considering its large investment, long construction period, and difficulty in site selection, compressed gas storage serves as a complementary technology and is considered one of the new energy storage technologies with the greatest development potential.

[0004] Currently, compressed gas energy storage primarily uses two media: air and carbon dioxide. Compressed carbon dioxide energy storage systems are based on traditional compressed gas energy storage technology, and the use of carbon dioxide as the working medium in compressed gas energy storage systems is still in the early stages of development. Compressed air energy storage systems have advantages over compressed carbon dioxide energy storage systems in that the technology is relatively mature and the selection of process systems is wider. Compressed carbon dioxide energy storage systems have advantages over compressed air energy storage systems in that the boundary conditions for controlling critical temperature and pressure are less stringent than those for air. Air requires -146.9℃ at normal pressure to liquefy, and carbon dioxide has a higher energy density, resulting in a smaller storage structure volume for power plants of the same scale, thus saving more space.

[0005] The low-pressure gas storage chambers of the aforementioned compressed carbon dioxide energy storage systems are all located on the ground, such as existing ground-based gas storage structures (e.g., CN 113280252A, Control and Installation Methods for Gas Storage Tanks, Energy Storage Devices, and Gas Storage Storage Facilities). The pressure within the gas chamber of the ground-based low-pressure side carbon dioxide gas storage tank is typically maintained at atmospheric pressure (0.1 MPa). Furthermore, ground-based low-pressure side gas storage tanks occupy a huge area, making large-scale deployment difficult. They also exhibit poor stability under wind, rain, and snow loads, and are susceptible to large outdoor temperature variations. Simultaneously, ground-based high-pressure side liquid storage tanks have high storage pressure, high cost, low safety, and are subject to large outdoor temperature variations and complex insulation and temperature control.

[0006] Furthermore, in existing compressed carbon dioxide energy storage systems, to maintain the liquid or supercritical state of the carbon dioxide working fluid within the storage chamber, the system requires specially manufactured insulating materials and monitoring equipment to ensure that the temperature and pressure within the storage chamber remain at the design operating conditions. In addition, some existing energy storage systems (such as CN 112985145 A, an energy storage device and method based on carbon dioxide gas-liquid phase change) are experimental-grade gas-liquid conversion systems and do not incorporate practical engineering applications, thus failing to achieve industrial-grade development and utilization. Summary of the Invention

[0007] In view of this, the present invention provides a carbon dioxide energy storage system based on underground space and its construction method. Based on existing underground carbon dioxide storage technology, it can recycle carbon dioxide stored on a large scale underground as an energy storage medium, effectively solving the difficulties of post-recycling processing of resources and limited underground space resources, thereby achieving energy conservation and emission reduction.

[0008] This invention is achieved through the following technical solution:

[0009] A compressed carbon dioxide energy storage system based on an underground gas storage facility includes: a low-pressure gas storage facility, a high-pressure liquid storage facility, and a carbon replenishment system;

[0010] The low-pressure gas storage facility is located in a shallow underground cavern, utilizing natural underground space, abandoned underground space, or artificially excavated space. A flexible air-bag membrane is installed inside the low-pressure gas storage facility. The flexible air-bag membrane is fixed to the inner wall of the low-pressure gas storage facility by anchoring components and a supporting mesh chain. The flexible air-bag membranes are connected to form a closed gas-containing cavity, and a sandwich cavity is formed between the inner wall of the low-pressure gas storage facility and the outer wall of the flexible air-bag membrane. The gas-containing cavity stores low-pressure gaseous carbon dioxide released by the expanding turbine, and the storage environment pressure is maintained at 0.1-1 MPa.

[0011] High-pressure liquid storage tanks utilize underground vertical abandoned spaces or newly excavated vertical caves to store ambient-temperature high-pressure liquid carbon dioxide released by compressors at temperatures below 25°C. The storage environment pressure is maintained at 6MPa. The burial depth of high-pressure liquid storage tanks is greater than that of low-pressure gas storage tanks, with a burial depth greater than 100m.

[0012] The carbon replenishment system is located on the ground. The carbon replenishment system stores and replenishes gas in the gas chamber of the low-pressure gas storage tank through the low-pressure side inflation pipeline until it exceeds 0.1 MPa. The flexible air bladder membrane expands and adheres to the inner wall of the low-pressure gas storage tank. The carbon replenishment system inflates the inner cavity of the high-pressure liquid storage tank through the high-pressure side inflation pipeline.

[0013] The carbon replenishment system is equipped with a carbon replenishment interface, and both the low-pressure side inflation pipeline and the high-pressure side inflation pipeline are connected to the carbon replenishment system through the carbon replenishment interface.

[0014] The low-pressure side inflation pipeline is equipped with a low-pressure side pressure valve, and the high-pressure side inflation pipeline is equipped with a high-pressure side pressure valve; a pressure gauge is installed at the carbon replenishment interface; based on the expansion rate and adhesion of the flexible air bladder membrane of the low-pressure gas storage tank and the liquid volume and pressure in the high-pressure liquid storage tank, the replenishment rate and pressure of carbon dioxide into the low-pressure gas storage tank and the high-pressure liquid storage tank are controlled by the low-pressure side pressure valve and the high-pressure side pressure valve, respectively.

[0015] The carbon replenishment system is also equipped with a carbon dioxide leakage monitoring device to ensure that the daily carbon dioxide leakage rate in the low-pressure gas storage facility meets the design requirements.

[0016] Furthermore, the compressed carbon dioxide energy storage system also includes: a compressor, an expander, a heat storage tank, and a pumping device;

[0017] The compressor, expander, heat storage tank, and pump are all located on the ground. The gas chamber of the low-pressure gas storage tank is connected to the input end of the compressor through a low-pressure side outlet pipe, and the output end of the compressor is connected to the inner cavity of the high-pressure liquid storage tank through a high-pressure side return pipe. The high-pressure side outlet pipe of the high-pressure liquid storage tank is connected to the input end of the expander, and the output end of the expander is connected to the gas chamber of the low-pressure gas storage tank through a low-pressure side return pipe. The heat storage tank is installed on the high-pressure side outlet pipe and the high-pressure side return pipe of the high-pressure liquid storage tank and is connected to them respectively. The pump is installed on the high-pressure side outlet pipe.

[0018] During energy storage, the compressor inlet is at constant pressure, with an inlet pressure of 0.1 MPa. When the storage pressure in the gas chamber of the low-pressure gas storage tank is 1 MPa, a pressure relief valve is installed on the low-pressure side outlet pipe before introducing low-pressure gaseous carbon dioxide into the compressor. By adjusting the valve, the stored low-pressure gaseous carbon dioxide is slowly reduced from 1 MPa to 0.1 MPa, so that the pressure entering the compressor remains constant at atmospheric pressure. Similarly, during the energy release process, a check valve is installed on the low-pressure side return gas pipe. Since the low-pressure gaseous carbon dioxide output by the expander is 0.1 MPa higher than atmospheric pressure, the check valve gradually and smoothly introduces the low-pressure gaseous carbon dioxide (0.1 MPa higher than atmospheric pressure) into the gas chamber of the low-pressure gas storage tank until the pressure in the gas chamber of the low-pressure gas storage tank changes back from atmospheric pressure of 0.1 MPa to 1 MPa.

[0019] The high-pressure storage tank maintains a constant pressure of 6 MPa. Gaseous carbon dioxide is introduced into the high-pressure storage tank through a carbon replenishment system to maintain the pressure of the high-pressure storage cavern. At this time, a small amount of gaseous carbon dioxide liquefies into liquid under the constant 6 MPa condition in the underground high-pressure storage tank. The high-pressure liquid carbon dioxide in the high-pressure storage tank is pumped into the high-pressure side outlet pipe through a pumping device. At the same time, the carbon dioxide filling rate is controlled by a pressure gauge and a high-pressure side pressure valve. When the high-pressure storage tank is pumped out and the pressure inside the high-pressure storage tank is lower than the liquefaction pressure, some of the liquid carbon dioxide vaporizes into high-pressure gaseous carbon dioxide to achieve a thermal equilibrium state inside the tank.

[0020] Furthermore, the compressed carbon dioxide energy storage system also includes construction traffic tunnels;

[0021] The construction traffic tunnel is used for the passage of construction workers and the transportation of construction machinery during the construction period. It consists of two tunnel sections, namely the first tunnel section and the second tunnel section. Both tunnel sections are connected to the low-pressure gas storage facility. The first tunnel section is located in front of the low-pressure gas storage facility, and the second tunnel section is located behind the low-pressure gas storage facility and is connected to the high-pressure liquid storage facility.

[0022] The cross-section of the construction traffic tunnel adopts the shape of a city gate; an entry valve is installed at the entrance of the first tunnel section, and pressure-bearing valves are installed at the exit of the first tunnel section and at both ends of the second tunnel section to seal the construction traffic tunnel; the rock wall of the construction traffic tunnel is lined with reinforced concrete.

[0023] The inner wall of the low-pressure gas storage is a surrounding rock structure. The reinforced concrete lining of the construction access roadway and the surrounding rock structure of the low-pressure gas storage are both low-pressure side linings. The low-pressure side lining is supported by shotcrete and anchor according to the surrounding rock conditions. The outermost side of the low-pressure side lining is the low-pressure side surrounding rock.

[0024] Furthermore, when the low-pressure gas storage facility uses an existing underground large cavity space as the low-pressure cavern, the inner wall surface of the low-pressure cavern needs to be polished smooth, trimmed to remove sharp edges and supported, and the low-pressure cavern needs to meet three conditions: stability, no external water pressure, and no sharp corners.

[0025] Furthermore, the high-pressure liquid storage tank consists of a three-layer structure, from the inside out: a high-pressure side sealing layer, a high-pressure side lining, and a high-pressure side surrounding rock. The high-pressure side lining is made of concrete, and its thickness is greater than that of the low-pressure side lining. The stress and temperature fields of the high-pressure side sealing layer are transmitted to the high-pressure side surrounding rock through the high-pressure side lining. The high-pressure liquid storage tank adopts a hollow cylindrical structure with an open top. The top opening of the high-pressure liquid storage tank is sealed with a concrete plug, and the temperature control standard for the air intake of the high-pressure liquid storage tank is the local natural ground temperature.

[0026] Furthermore, the carbon replenishment system may employ a carbon capture device or a carbon dioxide tank;

[0027] When a carbon capture device is used, the carbon capture device can directly obtain high-pressure gaseous carbon dioxide. The outlet of the carbon capture device is directly connected to the carbon replenishment interface. The carbon capture device can be directly connected to the low-pressure gas storage tank through the low-pressure side gas filling pipeline and directly connected to the high-pressure liquid storage tank through the high-pressure side gas filling pipeline to replenish the low-pressure gas storage tank and the high-pressure liquid storage tank respectively.

[0028] When using a carbon dioxide liquid tank, the liquid carbon dioxide in the tank needs to be vaporized to obtain high-pressure gaseous carbon dioxide. The outlet of the commercial carbon dioxide liquid tank is connected to a liquid carbon dioxide vaporizer through a ground filling pipeline. The liquid carbon dioxide vaporizer is used to vaporize the liquid carbon dioxide into high-pressure gaseous carbon dioxide and discharge it. The outlet of the liquid carbon dioxide vaporizer is connected to the carbon replenishment interface.

[0029] Furthermore, the carbon replenishment system stores and replenishes gas in the gas-bearing cavity of the low-pressure gas storage tank through a low-pressure side inflation pipeline. The interface between the low-pressure side inflation pipeline and the gas-bearing cavity is pre-embedded at the bottom of the low-pressure gas storage tank. The gas-bearing cavity is inflated by the carbon replenishment system until the flexible gasbag membrane expands and completely adheres to the smooth inner wall surface of the low-pressure gas storage tank, and the pressure reaches atmospheric pressure of 0.1 MPa. The inflation rate is controlled by a low-pressure side pressure valve. At the same time, the carbon replenishment system inflates the inner cavity of the high-pressure liquid storage tank through a high-pressure side inflation pipeline. When the liquid level in the high-pressure liquid storage tank drops, high-pressure gaseous carbon dioxide is injected into the high-pressure liquid storage tank through the carbon replenishment system to maintain the pressure of the high-pressure storage tank. The inflation rate is controlled by a high-pressure side pressure valve.

[0030] Furthermore, the compressed carbon dioxide energy storage system also includes a drainage system;

[0031] The drainage system includes: a water collection tank, a drainage ditch, drainage pipes, drainage manhole covers, and an intelligent drainage sensor.

[0032] The water collection pool is located below the entrance of the first section of the construction access roadway. The drainage ditch is located on both sides of the bottom of the construction access roadway and is connected to the water collection pool. The drainage ditch maintains a certain slope and eventually flows into the water collection pool. The drainage pipeline is laid along the periphery of the low-pressure gas storage tank to collect underground pressurized water and ensure that the flexible airbag membrane does not bear external water pressure. One end of the drainage pipeline is connected to the water collection pool, and the other end is connected to the surface pumping equipment. The intelligent drainage sensor is embedded in the water collection pool to monitor the water level in real time. When the water level in the pool reaches the maximum limit, the water in the water collection pool is discharged through the drainage pipeline and submersible pump. When the water level is higher than the set value, the drainage pipeline can be pre-embedded according to the terrain to drain the water from the mountain. The drainage well cover is used to cover the water collection pool and can be opened for maintenance.

[0033] Furthermore, the low-pressure gas storage tank is provided with a vent hole that communicates with the interlayer cavity. The vent hole is connected to an external ventilation device, which is used to fill and release air into the interlayer cavity, thereby controlling the carbon dioxide pressure in the low-pressure gas storage cavity.

[0034] Furthermore, the outer surface of the flexible airbag membrane is coated with a waterproof and corrosion-resistant coating.

[0035] Furthermore, the inner surfaces of the low-pressure gas storage facility and the construction access roadway are reinforced with wire mesh and sprayed concrete.

[0036] Furthermore, the high-pressure liquid storage tank adopts a horizontal tunnel-type storage method.

[0037] Furthermore, when the single low-pressure side gas storage space is smaller than the required space, multiple gas bags can be combined for gas storage or multiple underground caverns connected in series can be used.

[0038] Furthermore, the compressor in the ground plant can be a variable frequency compressor with a first-stage inlet and a fixed frequency compressor with a second-stage outlet, and the expander can be a fixed frequency expander with a first-stage inlet and a variable frequency expander with a second-stage outlet.

[0039] A method for constructing a compressed carbon dioxide energy storage system based on an underground gas storage chamber, wherein the compressed carbon dioxide energy storage system adopts the aforementioned compressed carbon dioxide energy storage system, and the specific steps of the method are as follows:

[0040] Step 1: After entering the site, the construction of the construction traffic tunnels shall be carried out first. After the tunnels are connected, the support lining and transportation system shall be arranged and installed in a timely manner. Based on the hydrogeological conditions of the underground space, advanced support design and sealing grouting measures shall be carried out.

[0041] Step 2: Based on the construction traffic tunnel, carry out a small-scale leveling project on the low-pressure gas storage tank, and manually or mechanically grind and repair the original outline of the low-pressure side cavern into the leveled outline of the cavern; then the stability of the cavern itself needs to be rechecked, and corresponding wire mesh and shotcrete support measures are carried out in weak locations.

[0042] Step 3: Assemble the flexible airbag membrane and the skeleton support chain, and fix them in the corresponding positions with anchoring devices. At the same time, according to the design, pre-embed monitoring chips for physical parameters of temperature and pressure in the surrounding rock wall of the low-pressure gas storage.

[0043] Step 4: After the low-pressure gas storage tank is completed, continue to excavate horizontally into the underground mountain through the construction access roadway, and then excavate downward to form a vertical shaft-type hollow cylindrical high-pressure liquid storage tank until the excavation meets the burial depth of the high-pressure liquid storage tank. Then, carry out the construction and arrangement of high-pressure side lining and high-pressure side steel plate in sequence. At the same time, physical parameter monitoring chips are pre-embedded in the surrounding rock wall of the high-pressure liquid storage tank.

[0044] Step 5: After all the storage tunnels have been excavated, all the pipe holes will be constructed, and the drainage system will be constructed at the same time. In the same way, water collection pools, drainage ditches, drainage well covers, drainage pipes and intelligent drainage sensor plates will be laid out.

[0045] Step 6: After the underground engineering construction is completed, the innermost side of the construction traffic tunnel and the upper part of the high-pressure liquid storage tank are sealed with plugs. At the same time, pressure-bearing valves are installed at both ends of the low-pressure side gas storage cavern, and an entry valve is installed at the cavern inlet.

[0046] Step 7: Connect the various pre-buried pipelines in the underground gas storage facility to the carbon replenishment system, compressor, expander, heat storage tank and pumping device, and construct the above-ground plant to house the compressor, expander, heat storage tank and pumping device.

[0047] Beneficial effects:

[0048] (1) Compared with the prior art, the present invention discloses a carbon dioxide energy storage system structure based on underground space; the energy storage system continuously converts carbon dioxide into physical gas and liquid phases by controlling power equipment, thereby storing electrical energy in underground space through carbon dioxide medium. The carbon dioxide energy storage system based on underground space typically uses two gas storage chambers, one low-pressure gas storage chamber to store low-pressure carbon dioxide released by the expansion turbine, and the other high-pressure liquid storage chamber to store high-pressure carbon dioxide released by the compressor, thereby forming a closed energy storage system; the design and construction process of the underground low-pressure gas storage chamber and high-pressure liquid storage chamber have great advantages over the surface gas storage structure, not only saving surface land resources and significantly reducing the cost of surface steel tank storage, but also allowing for flexible layout according to the type of cave structure, such as waste transformation of abandoned mines and natural caves, thereby making full use of underground space; the low-pressure gas storage chamber is equipped with a flexible airbag membrane to wrap gaseous carbon dioxide to prevent leakage, and utilizes The stress of the large cavity in the low-pressure side gas storage tank counteracts the carbon dioxide pressure inside the flexible gasbag membrane, increasing the gas pressure to 1 MPa and resulting in a 10-fold increase in density. Under the same installed capacity, the volume of the low-pressure side gas chamber is reduced by 10 times. The high-pressure liquid storage tank uses steel plates to prevent liquid carbon dioxide from seeping into the rock strata. The entire carbon dioxide system is a closed-loop system, isolating it from air, making the underground compressed carbon dioxide energy storage system more reliable and safe. Therefore, this invention belongs to the industrial-grade compressed gas energy storage system, placing the compressed carbon dioxide energy storage system's storage tank underground. Simultaneously, the large-scale carbon dioxide sealing storage tank is utilized as a compressed gas energy storage facility, thereby achieving energy conservation and emission reduction. Furthermore, placing the compressed air energy storage system's storage tank underground, due to the stable underground temperature and less influence from external temperatures, eliminates the need for storage tank insulation, further saving costs. At the same time, placing it underground ensures the system's safe and stable operation, with potential damage from accidents being far less than on the surface.

[0049] (2) When the low-pressure gas storage of the present invention uses the existing underground large cavity space as the low-pressure cavern, the inner wall surface of the low-pressure cavern needs to be repaired and supported, and the low-pressure cavern must meet the three conditions of stability, no external water pressure, and no sharp corners to prevent damage to the flexible airbag membrane in the low-pressure gas storage.

[0050] (3) The drainage system of the present invention can discharge groundwater outside the surrounding rock in a timely manner through a reasonably designed drainage pipeline, thus ensuring the normal operation of the energy storage system.

[0051] (4) When the single low-pressure side gas storage space of the present invention is smaller than the required space, multiple bags can be combined to store gas or multiple underground caverns connected in series can be used to meet the large-scale energy storage requirements.

[0052] (5) The compressor first stage inlet and the expander last stage outlet of the present invention are set to variable frequency and variable pressure, while the other stages are set to constant frequency and constant pressure. This is different from the conventional method of requiring constant pressure to enter the power equipment, which is a technical difficulty, in order to meet greater working conditions.

[0053] (6) This invention discloses a construction method for a carbon dioxide energy storage system based on underground space. This method, combined with practical engineering applications, achieves industrial-grade energy storage construction and further promotes the specific implementation process and construction method of compressed gas system in the field of underground space engineering. It has great practical significance for the implementation of this system.

[0054] In summary, the low-pressure gas storage tank of this invention is located in a shallow underground cavern, utilizing the natural or abandoned underground space stress to balance the internal pressure of gaseous carbon dioxide in the storage tank, significantly reducing the storage space. The high-pressure liquid storage tank is located in an abandoned underground space at a certain depth or in a newly excavated cavern, storing high-pressure liquid carbon dioxide that meets the liquefaction pressure, further reducing the storage space through the liquid phase. The carbon replenishment system is located on the ground. The carbon replenishment system is used to initially fill and replenish the closed-loop system of the high and low pressure storage tanks. Compared to conventional ground storage at 0.1 MPa, this invention can store up to 1 MPa using the surrounding rock stress, reducing the storage space by 10 times for the same installed capacity. Therefore, this invention belongs to an industrial-grade compressed gas energy storage system, which can recycle carbon dioxide stored on a large scale underground as an energy storage medium, effectively solving the difficulties of post-recycling processing of resources and limited underground space resources, thereby achieving energy conservation and emission reduction. Attached Figure Description

[0055] Figure 1 This is a three-dimensional schematic diagram of the overall compressed carbon dioxide energy storage system of the present invention;

[0056] Figure 2 This is a schematic diagram of the overall compressed carbon dioxide energy storage system of the present invention;

[0057] Figure 3 This is a schematic cross-sectional view of a typical traffic lane during the construction of the energy storage system of this invention;

[0058] Figure 4 This is a schematic diagram of the low-pressure gas storage tank of the compressed carbon dioxide energy storage system of the present invention;

[0059] Figure 5 This is a schematic diagram of the high-pressure gas storage tank of the compressed carbon dioxide energy storage system of the present invention;

[0060] Figure 6 This is a schematic diagram showing the gas-liquid pipeline relationship between the energy storage system and the carbon replenishment device of the present invention;

[0061] Figure 7 This is a schematic diagram of the horizontal tunnel-type storage of the high-pressure gas storage tank in the compressed carbon dioxide energy storage system of the present invention.

[0062] Figure 8 This is a schematic diagram showing the relationship between the multi-stage power equipment in the compressed carbon dioxide energy storage system of the present invention.

[0063] Among them, 1-Construction access tunnel, 2-Low-pressure gas storage, 3-Pre-buried pipeline system, 4-Surface plant, 5-High-pressure liquid storage, 6-Carbon replenishment system, 7-Drainage system, 101-Inlet valve, 102-Low-pressure side lining, 103-Low-pressure side surrounding rock, 201-Interlayer cavity, 202-Gas-containing cavity, 203-Original outline of the cavern, 204-Leveled outline of the cavern. 205-Flexible airbag membrane; 206-Skeleton support mesh chain; 207-Pressure-bearing valve; 301-Low-pressure side outlet pipe; 302-Low-pressure side return pipe; 303-High-pressure side liquid outlet pipe; 304-High-pressure side liquid return pipe; 305-Ventilation port; 401-Compressor; 4011-Variable frequency compressor; 4012-Fixed frequency compressor; 402-Expander; 4021-Variable frequency expander; 4022-Fixed frequency expander; 403-Low-pressure gaseous carbon dioxide; 404-High-pressure gaseous carbon dioxide; 405-High-pressure liquid carbon dioxide; 406-Heat storage tank; 407-Pressure relief valve. 408-Check valve, 409-Pump device, 501-High-pressure side sealing layer, 502-High-pressure side lining, 503-High-pressure side surrounding rock, 504-Plug, 601-Low-pressure side air filling pipeline, 602-High-pressure side air filling pipeline, 603-Carbon replenishment interface, 604-Low-pressure side pressure valve, 605-Pressure gauge, 606-Liquid carbon dioxide vaporizer, 607-Ground liquid filling pipeline, 608-Carbon dioxide liquid tank, 609-High-pressure side pressure valve, 701-Water collection tank, 702-Drainage pipeline, 703-Intelligent drainage sensor, 704-Drainage well cover, 705-Drainage ditch. Detailed Implementation

[0064] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0065] Example 1:

[0066] This embodiment provides a compressed carbon dioxide energy storage system based on an underground gas storage facility. See Appendix. Figure 1-2 It includes: 1. Construction traffic tunnel, 2. Low-pressure gas storage, 3. Pre-buried pipeline system, 4. Ground plant, 5. High-pressure liquid storage, 6. Carbon replenishment system, and 7. Drainage system.

[0067] The construction traffic tunnel 1, low-pressure gas storage 2 and high-pressure liquid storage 5 are all located underground. The low-pressure gas storage 2 is located in a shallow underground cavern and can be built using natural underground space, abandoned underground space or artificially excavated space. The high-pressure liquid storage 5 can utilize a relatively regular vertical abandoned space underground or be newly excavated vertical cavern, and the burial depth of the high-pressure liquid storage 5 is greater than that of the low-pressure gas storage 2.

[0068] The construction traffic tunnel 1 is used for the passage of construction workers and the transportation of construction machinery during the construction period. It consists of two tunnel sections, namely the first tunnel section and the second tunnel section. Both tunnel sections are connected to the low-pressure gas storage tank 2. The first tunnel section is located in front of the low-pressure gas storage tank 2, and the second tunnel section is located behind the low-pressure gas storage tank 2 and is connected to the high-pressure liquid storage tank 5.

[0069] The low-pressure gas storage facility 2 stores low-pressure gaseous carbon dioxide 403 released by the expansion turbine. The storage environment pressure is maintained at 0.1-1 MPa, which is considered low-pressure storage. When the existing underground large cavity space is used as the low-pressure cavern for the low-pressure gas storage facility 2, the inner wall surface of the low-pressure cavern needs to be ground until there are no sharp edges and supported. The low-pressure cavern should meet three conditions: stability, no external water pressure, and no sharp corners. The inner wall surface of the low-pressure gas storage facility 2 is the surrounding rock structure. Before grinding, the inner wall surface of the low-pressure gas storage facility 2 is the original outline 203 of the cavern. After grinding, the inner wall surface of the low-pressure gas storage facility 2 is the leveled outline 204 of the cavern.

[0070] The high-pressure liquid storage tank 5 stores ambient-temperature high-pressure liquid carbon dioxide 405 released by the compressor. The storage environment pressure is maintained at 6 MPa, and the underground storage environment temperature is kept constant at around 15°C. Low-pressure gaseous carbon dioxide 403 can be liquefied into high-pressure liquid carbon dioxide 405 when the pressure rises to 6 MPa. Compared with gaseous storage, high-pressure liquid carbon dioxide 405 has a higher working fluid density and smaller storage volume, which can store a large amount of energy in a very small storage tank space. Moreover, as long as the temperature is kept stable during the vaporization process, a stable pressure can be obtained. The burial depth of the high-pressure liquid storage tank 5 should be greater than 100m to meet the storage pressure requirements, so as not to cause ground uplift, thus forming a closed energy storage system.

[0071] The carbon replenishment system 6 is an external carbon dioxide supply device located on a flat ground. The carbon replenishment system 6 is connected to the low-pressure gas storage tank 2 through the low-pressure side gas filling pipeline 601, and is also connected to the high-pressure liquid storage tank 5 through the high-pressure side gas filling pipeline 602. The carbon replenishment system 6 is used to replenish the low-pressure gas storage tank 2 and the high-pressure liquid storage tank 5 with carbon source (i.e. carbon dioxide).

[0072] See appendix Figure 3 The cross-section of the construction access roadway 1 adopts the shape of a city gate. An entry valve 101 is provided at the entrance of the first section of the roadway. At the exit of the first section of the roadway (i.e., the intersection of the first section of the roadway and the low-pressure gas storage 2) and at both ends of the second section of the roadway, there are pressure valves 207 to seal the construction access roadway 1. The rock wall of the construction access roadway 1 is lined with reinforced concrete. The reinforced concrete lining of the construction access roadway 1 and the surrounding rock structure of the low-pressure gas storage 2 are both low-pressure side linings 102. The low-pressure side lining 102 needs to be supported by shotcrete and anchor according to the surrounding rock conditions. Sealing measures are not considered here. The outermost part of the low-pressure side lining 102 is the low-pressure side surrounding rock 103.

[0073] See appendix Figure 4 The low-pressure gas storage 2 is equipped with a flexible airbag membrane 205. The edge of the flexible airbag membrane 205 is fixed to the surrounding rock foundation structure of the low-pressure gas storage 2 by anchoring components and a skeleton support chain 206 provided on the outer surface of the flexible airbag membrane 205. There are fixed points on the ground. The flexible airbag membrane 205 forms a closed gas-containing cavity 202, and an interlayer cavity 201 is formed between the inner wall of the low-pressure gas storage 2 and the outer wall of the flexible airbag membrane 205.

[0074] When carbon dioxide is first filled into the gas chamber 202, the flexible gasbag membrane 205, after being stretched from a flat state to a certain extent, will abut against the skeleton support mesh chain 206. From an unpressurized state to the filling of 0.1 MPa of gaseous carbon dioxide, it then adheres tightly to the inner wall of the low-pressure gas storage tank 2. At this time, the volume of the interlayer cavity 201 is 0. Afterward, there is no relative displacement between the flexible gasbag membrane 205 and the inner wall of the low-pressure gas storage tank 2. Subsequently, the working operating pressure in the gas chamber 202 can be maintained at an internal pressure of 0.1-1 MPa. The skeleton support mesh chain 206 effectively shares the internal pressure on the flexible gasbag membrane 205, making the membrane less prone to tearing, and further distributing the force on the membrane to a large extent, thereby improving the membrane durability. The flexible gasbag membrane 205, which adheres tightly to the inner wall of the low-pressure gas storage tank 2, effectively increases the storage pressure of low-pressure gaseous carbon dioxide 403 through the rock mass stress, increases the gas density of the gas chamber 202, and thus reduces the storage volume.

[0075] When carbon dioxide is first stored in the gas chamber 202, the volume of the gas chamber 202 gradually increases, while the volume of the interlayer chamber 201 gradually decreases. During maintenance, when carbon dioxide is discharged from the gas chamber 202, the flexible air bladder membrane 205 gradually collapses downwards, causing the volume of the gas chamber 202 to gradually decrease and the volume of the interlayer chamber 201 to gradually increase. Under other operating conditions, the pressure inside the gas chamber 202 remains within a range of 0.1-1 MPa, which is greater than 1 atmosphere (0.1 MPa), and the flexible air bladder membrane 205 always remains completely in contact with the inner wall of the low-pressure gas storage tank 2. That is, the volume of the gas-containing cavity 202 is approximately the volume of the entire low-pressure gas storage tank 2, while the volume of the interlayer cavity 201 is approximately zero; at the same time, the structure of the entire flexible airbag membrane 205 is similar in shape to the cavern shape of the low-pressure gas storage tank 2, and the volume of the inflated flexible airbag membrane 205 is slightly larger than the cavern volume of the low-pressure gas storage tank 2 (to prevent the flexible airbag membrane 205 from bursting). The material of the flexible airbag membrane 205 is selected to be tear-resistant, tough, and heat-insulating; when the construction is completed, the pressure-bearing valves 207 at both ends of the construction access road 1 that can withstand high pressure should be sealed and closed;

[0076] See appendix Figure 5 The high-pressure liquid storage tank 5 consists of a three-layer structure, from the inside out: a high-pressure side sealing layer 501, a high-pressure side lining 502, and a high-pressure side surrounding rock 503. The innermost layer is a high-pressure side sealing layer 501, approximately 2 cm thick, which uses a dense steel lining to seal high-pressure liquid carbon dioxide 405 within the shaft or tunnel. The middle reinforced concrete high-pressure side lining 502 is 60 cm thick. Because the burial depth is greater than that of the low-pressure gas storage tank 2, the concrete lining should be 102 cm thicker than the low-pressure side lining. The stress and temperature fields experienced by the high-pressure side sealing layer 501 are sequentially transmitted to the high-pressure side surrounding rock 503 through the high-pressure side lining 502. The high-pressure liquid storage tank 5 adopts... The hollow cylindrical structure is the best choice for the shape of underground caverns for lined rock gas storage tanks because it has good stress characteristics and can ensure the overall stability of the structure. After the excavation of underground high-pressure liquid storage tank 5, attention should be paid to the deformation, stress and plastic zone changes of the surrounding rock. At the same time, appropriate cavern wall support measures should be taken according to the integrity of the surrounding rock, the degree of fissure development and the distribution of groundwater. After all construction stages of underground high-pressure liquid storage tank 5 are completed, the top of the shaft will be sealed with concrete plug 504 to form a closed pressure system and maintain the overall stability of the underground structure.

[0077] See appendix Figure 6 The carbon replenishment system 6 is equipped with a carbon replenishment interface 603. The low-pressure side gas filling pipeline 601 and the high-pressure side gas filling pipeline 602 are both connected to the carbon replenishment system 6 through the carbon replenishment interface 603. The carbon replenishment system 6 can be a carbon capture device or a commercial carbon dioxide liquid tank 608.

[0078] When a carbon capture device is used, the carbon capture device can directly obtain high-pressure gaseous carbon dioxide 404. The outlet of the carbon capture device is directly connected to the carbon replenishment interface 603. The carbon capture device can be directly connected to the low-pressure gas storage tank 2 through the low-pressure side gas filling pipeline 601 and directly connected to the high-pressure liquid storage tank 5 through the high-pressure side gas filling pipeline 602, respectively replenishing the low-pressure gas storage tank 2 and the high-pressure liquid storage tank 5 with gas.

[0079] This embodiment uses a commercial carbon dioxide liquid tank 608. When using a commercial carbon dioxide liquid tank 608, the liquid carbon dioxide in the carbon dioxide liquid tank 608 needs to be vaporized to obtain high-pressure gaseous carbon dioxide 404. The liquid outlet of the commercial carbon dioxide liquid tank 608 is connected to a liquid carbon dioxide vaporizer 606 through a ground filling pipeline 607. The liquid carbon dioxide vaporizer 606 is used to vaporize the liquid carbon dioxide into high-pressure gaseous carbon dioxide 404 and discharge it. The gas outlet of the liquid carbon dioxide vaporizer 606 is connected to a carbon replenishment interface 603.

[0080] The low-pressure side inflation pipeline 601 is equipped with a low-pressure side pressure valve 604, and the high-pressure side inflation pipeline 602 is equipped with a high-pressure side pressure valve 609; a pressure gauge 605 is installed at the carbon replenishment interface 603; based on the expansion rate and adhesion of the flexible air bladder membrane of the low-pressure gas storage tank 2 and the liquid volume and pressure in the high-pressure liquid storage tank 5, the replenishment rate and pressure of carbon dioxide into the low-pressure gas storage tank 2 and the high-pressure liquid storage tank 5 are controlled by the low-pressure side pressure valve 604 and the high-pressure side pressure valve 609, respectively; wherein, the carbon dioxide replenishment rate is usually set according to factors such as the system installed capacity, energy storage duration, pipe diameter, and pipeline arrangement, and is monitored in real time by the pressure gauge 605; specifically:

[0081] The carbon replenishment system 6 stores and replenishes gas in the gas-containing cavity 202 of the low-pressure gas storage tank 2 through the low-pressure side inflation pipeline 601. The interface end of the low-pressure side inflation pipeline 601 and the gas-containing cavity 202 is pre-embedded at the bottom of the low-pressure gas storage tank 2. The gas-containing cavity 202 is inflated by the carbon replenishment system 6 until the flexible air bladder membrane 205 expands and completely adheres to the smooth inner wall surface of the low-pressure gas storage tank 2, and the pressure reaches the atmospheric pressure of 0.1 MPa. The inflation rate is controlled by the low-pressure side pressure valve 604. Meanwhile, the carbon replenishment system 6 fills the inner cavity of the high-pressure storage tank 5 with gas through the high-pressure side gas filling pipeline 602. When the liquid level of the high-pressure storage tank 5 drops, the high-pressure gaseous carbon dioxide is filled into the high-pressure storage tank 5 through the carbon replenishment system 6 to maintain the pressure of the high-pressure storage tank. The filling rate is controlled by the high-pressure side pressure valve 609. At this time, a small amount of gaseous carbon dioxide liquefies into liquid under the constant working condition of 6MPa in the underground high-pressure storage tank 5. The main purpose of high-pressure side gas filling is to ensure that the pressure inside the tank is stable at 6MPa to ensure the carbon dioxide liquefaction pressure.

[0082] The carbon replenishment system 6 is also equipped with a carbon dioxide leakage monitoring device to ensure that the daily carbon dioxide leakage rate in the low-pressure gas storage facility meets the design requirements.

[0083] The pre-embedded pipeline system 3 includes: a low-pressure side gas outlet pipe 301, a low-pressure side gas return pipe 302, a high-pressure side liquid outlet pipe 303, a high-pressure side liquid return pipe 304, and a vent 305; the low-pressure side gas outlet pipe 301 and the low-pressure side gas return pipe 302 are respectively located on the side where the low-pressure gas storage tank 2 is located, and are respectively connected to the gas-containing cavity 202; the high-pressure side liquid outlet pipe 303 and the high-pressure side liquid return pipe 304 are respectively located on the side where the high-pressure liquid storage tank 3 is located, and are respectively connected to the inner cavity of the high-pressure liquid storage tank 3; the vent 305 is located on the side where the low-pressure gas storage tank 2 is located, and is connected to the interlayer cavity 201. The vent 305 is connected to an external ventilation device, which is used to fill and release air in the interlayer cavity 201, thereby controlling the carbon dioxide pressure in the low-pressure gas-containing cavity 202;

[0084] The ground-level plant 4 serves as a space for accommodating power equipment, and houses a variable frequency compressor 401, an expander 402, a heat storage tank 406, and a pumping device 409. The gas chamber 202 of the low-pressure gas storage tank 2 is connected to the input end of the compressor 401 via a low-pressure side outlet pipe 301, and the output end of the compressor 401 is connected to the inner cavity of the high-pressure liquid storage tank 5 via a high-pressure side return pipe 304. The high-pressure side outlet pipe 303 of the high-pressure liquid storage tank 5 is connected to the input end of the expander 402, and the output end of the expander 402 is connected to the gas chamber 202 of the low-pressure gas storage tank 2 via a low-pressure side return pipe 302. The heat storage tank 406 is installed on the high-pressure side outlet pipe 303 and the high-pressure side return pipe 304 of the high-pressure liquid storage tank 5, and is connected to them respectively. The pumping device 409 is installed on the high-pressure side outlet pipe 303.

[0085] The working principle of compressed carbon dioxide energy storage can be divided into two processes: energy storage and energy release. During energy storage, the low-pressure gaseous carbon dioxide 403 in the gas chamber 202 of the low-pressure gas storage tank 2 is compressed into high-pressure gaseous carbon dioxide 404 by the multi-stage compressor 401. At the same time, the heat of compression is stored in the heat storage tank 406 through the heat storage medium. The carbon dioxide is further pressurized and heated until it is liquefied and finally stored in the high-pressure liquid storage tank 5. That is, electrical energy is stored in the form of heat energy and potential energy. During energy release, the high-pressure liquid carbon dioxide 405 in the high-pressure liquid storage tank 5 utilizes the heat of compression recovered by the heat storage tank 406 in the energy storage stage and is connected to the liquid carbon dioxide vaporizer 606 through pipelines. It is heated to the state of high-pressure gaseous carbon dioxide 404 and then enters the multi-stage turbine expander 402 to drive the motor to generate electricity. The gaseous carbon dioxide changes from a high-pressure state to a low-pressure state and is finally stored in the gas chamber 202 of the low-pressure gas storage tank 2. That is, heat energy and potential energy are converted into electrical energy output, thus forming a closed loop system.

[0086] During energy storage, the inlet of the first-stage compressor 401 on the low-pressure side is usually at a constant pressure, typically 0.1 MPa. Therefore, when the storage pressure in the gas chamber 202 of the low-pressure gas storage tank 2 is 1 MPa, a pressure relief valve 407 needs to be installed on the low-pressure side outlet pipe 301 before introducing low-pressure gaseous carbon dioxide 403 into the compressor 401. By adjusting the valve, the stored low-pressure gaseous carbon dioxide 403 is slowly reduced from 1 MPa to 0.1 MPa, so that the pressure when it enters the compressor 401 remains constant at atmospheric pressure. Similarly, during the energy release process, a check valve 408 is installed on the low-pressure side return gas pipeline 302. The low-pressure gaseous carbon dioxide 403 output by the last stage expander 402 is usually slightly higher than the atmospheric pressure by 0.1 MPa. It is gradually and smoothly filled into the gas chamber 202 of the low-pressure gas storage tank 2 through the check valve 408 to prevent the pressure fluctuation in the storage tank from affecting the power output efficiency of the expander, thereby reducing the temperature and pressure loss caused by thermal balance and reducing energy consumption until the pressure in the gas chamber 202 of the low-pressure gas storage tank 2 changes back from the atmospheric pressure of 0.1 MPa to 1 MPa.

[0087] The high-pressure liquid storage tank 5 maintains a constant pressure of 6 MPa. Gaseous carbon dioxide is supplied to the high-pressure liquid storage tank 5 through the carbon replenishment system 6 to maintain the pressure of the high-pressure storage tank. At this time, some of the gaseous carbon dioxide liquefies into liquid under the constant 6 MPa condition in the underground high-pressure liquid storage tank 5. The high-pressure liquid carbon dioxide 405 in the high-pressure liquid storage tank 5 is pumped into the high-pressure side outlet pipe 303 through the pumping device 409. At the same time, the carbon dioxide filling rate is monitored by the pressure gauge 605 and controlled by the high-pressure side pressure valve 609. When the high-pressure liquid storage tank 5 is pumped out, the pressure inside the tank is briefly lower than the liquefaction pressure, and some of the liquid carbon dioxide vaporizes into high-pressure gaseous carbon dioxide 404 to reach a thermal equilibrium state inside the tank. The high-pressure liquid storage tank 5 is always in a high-pressure state during maintenance, which avoids the problem of cyclic alternating load in the underground gas storage tank for compressed carbon dioxide energy storage.

[0088] The drainage system 7 includes: a water collection tank 701, a drainage pipe 702, a drainage well cover 704, a drainage ditch 705, and an intelligent drainage sensor 703. Due to the long-term operation of the underground gas storage facility, varying degrees of surface seepage water will appear in the surrounding rock. To ensure the normal operation of the system, it is necessary to promptly drain the groundwater outside the surrounding rock of the low-pressure gas storage facility 2. Therefore, a drainage pipe 702 is pre-buried along the surrounding rock outside the gas storage facility to ensure that the flexible airbag membrane does not bear external water pressure. The water collection tank 701 is located below the entrance of the second section of the construction access roadway 1 (i.e., the intersection of the second section of the roadway and the low-pressure gas storage facility 2). The drainage ditch 705 is located on both sides of the bottom of the construction access roadway 1 to collect groundwater condensation. The drainage ditch 705 is connected to the water collection tank 701. The drainage ditch 705 maintains a certain slope, which can be 1%, and eventually flows into the collection pool 701. One end of the drainage pipe 702 is connected to the collection pool 701, and the other end is connected to a pumping device (such as a submersible pump) introduced to the ground. The drainage sensor 703 is embedded in the collection pool 701 to monitor the water level in the collection pool 701 in real time. When the water level in the pool reaches the maximum limit level, the water in the collection pool 701 is discharged through the drainage pipe 702 and the submersible pump. The size of the collection pool 701 is designed according to the drainage capacity and operating requirements of the submersible pump. The amount of water accumulated can be calculated based on the changes in air temperature and humidity in the interlayer cavity 201. The drainage well cover 704 is used to cover the collection pool 701 to prevent personnel from falling in and can be opened for maintenance.

[0089] A preferred embodiment is that the outer surface of the flexible airbag membrane 205 is coated with a waterproof and corrosion-resistant coating.

[0090] A preferred approach is to use wire mesh and sprayed concrete support on the inner surfaces of the low-pressure gas storage tank 2 and the construction access roadway 1 to prevent rockfalls.

[0091] A preferred embodiment is that the pressure-bearing valve 207 is a stainless steel valve that can withstand high pressure and can be opened and closed, used for equipment and personnel to enter and exit during maintenance and repair.

[0092] In a preferred embodiment, the compressor 401 in the surface workshop 4 can be further divided into a first-stage inlet compressor 4011 with a variable frequency compressor 4011 and a second-stage outlet compressor 4012. The expander 402 can be further divided into a first-stage inlet expander 4022 with a fixed frequency expander 4021 and a second-stage outlet expander 4021. In this case, the pressure relief valve 407 and the check valve 408 can be replaced with ordinary valves. When the compressor 401 and expander 402 closest to the low-pressure gas storage tank 2 are variable frequency and variable pressure, the dynamic pressure change requirements within the low-pressure gas storage tank 2 can be met. At the same time, multiple fixed frequency compressors 4012 and fixed frequency expanders 4022 can be connected in series. See the arrangement diagram below. Figure 8 ;

[0093] A preferred option is that the high-pressure liquid storage tank 5 can be selected as a vertical shaft storage or a horizontal tunnel storage, depending on the specific conditions of the rock mass. Figure 7 However, all of them must meet the storage depth requirements and ensure constant pressure inside the storage facility;

[0094] A preferred approach is that the drainage system 7 can choose a high-water-self-drainage and low-water-pumping approach based on the specific terrain conditions. That is, when the water level in the collection pool 701 is low, it is pumped out by pumping equipment, and when the water level in the collection pool 701 is high, drainage pipes are pre-buried according to the terrain to drain the water out of the gas storage facility along the mountain slope.

[0095] Example 2:

[0096] This embodiment provides a method for constructing a compressed carbon dioxide energy storage system based on an underground gas storage chamber. The specific steps are as follows:

[0097] Step 1: After entering the site, the construction of the construction traffic tunnel 1 shall be carried out first. After the tunnel is connected, the support lining and transportation system shall be arranged and installed in a timely manner. Based on the hydrogeological conditions of the underground space, the advanced support design and sealing grouting measures shall be carried out.

[0098] Step two: Based on the construction access roadway 1, carry out a small-scale leveling project on the low-pressure side large cavity pit, namely the low-pressure gas storage 2. Manually or mechanically grind and repair the original outline 203 of the low-pressure side cavern into the leveled outline 204 of the cavern, that is, level the irregular parts of the underground space and eliminate sharp corners to prevent puncturing the flexible working gasbag membrane 205 that encapsulates carbon dioxide. Then, the stability of the cavern itself needs to be rechecked, and corresponding wire mesh and shotcrete support measures are implemented in weak locations to prevent rockfalls.

[0099] Step 3: Assemble the flexible airbag membrane 205 and the skeleton support mesh chain 206, and fix them in the corresponding positions through the anchoring device. At the same time, according to the design, pre-embed monitoring chips for physical parameters such as temperature and pressure in the surrounding rock wall of the low-pressure gas storage 2.

[0100] Step 4: After the low-pressure gas storage 2 is completed, continue to excavate horizontally into the inner side of the underground mountain through the construction access roadway 1, and then excavate downward to form a vertical shaft-type hollow cylindrical high-pressure liquid storage 5 until the excavation meets the burial depth of the high-pressure liquid storage 5. Then, carry out the construction and arrangement of the high-pressure side lining 502 and the high-pressure side sealing layer 501 in sequence. At the same time, physical parameter monitoring chips need to be pre-embedded in the surrounding rock wall.

[0101] Step 5: After all the storage tunnels have been excavated, the construction of all the pipe holes of the pre-embedded pipeline system 3 will be carried out. At the same time, the construction of the drainage system 7 will be carried out. Similarly, the water collection pool 701, drainage ditch 705, drainage pipeline 702 and intelligent drainage sensor 703 will be laid out. Note that the drainage ditch 705 needs to be set with a certain slope so that the water can flow into the water collection pool 701.

[0102] Step 6: After the underground engineering construction is completed, the innermost side of the construction traffic tunnel 1 and the upper part of the high-pressure liquid storage tank 5 shall be sealed with plugs. At the same time, pressure-bearing valves 207 shall be installed at both ends of the low-pressure side gas storage cavern, and entry valves 101 shall be installed at the cavern inlet.

[0103] Step 7: Connect the various pre-buried pipelines in the underground gas storage facility to the power equipment and carbon replenishment system 6 in the ground plant 4, and carry out the construction of the ground plant 4, which houses the compressor 401, expander 402, heat storage tank 406 and pumping device 409.

[0104] Example 3:

[0105] Based on Example 1, this embodiment can be adjusted to suit the characteristics of different underground space scenarios:

[0106] 1) Natural underground space: Widely distributed and large in size, comprehensive utilization of natural resources can reduce excavation investment, soft rock is suitable for low-pressure side gas storage; usually poor stability and hydrogeological conditions, requiring reshaping according to specific working conditions, the stability of the cave itself needs to be reassessed, and corresponding support and sealing structural measures should be taken; groundwater should be intercepted and drained accordingly, and unnecessary gas storage spaces should be sealed with concrete.

[0107] 2) Abandoned underground spaces: The types of storage facilities are diverse, turning waste into treasure, but mineral pressure assessment is required to avoid areas where minerals are still being mined and to prioritize abandoned and depleted mine shafts; at the same time, the design should be based on the complex layout and shape of the caves and the characteristics of the caves. If the underground gas storage space does not meet the design scale, corresponding expansion treatment can be carried out; at the same time, a surrounding environmental and water conservation assessment should be carried out to avoid the impact of restarting abandoned spaces on the surrounding ecological environment.

[0108] 3) Artificially excavated space: The construction of the reservoir is flexible. Areas with good geological conditions such as deep and hard rock mass are preferred to reduce the thickness of steel plate sealing layer and concrete lining. The cross-section of the artificially excavated cavern is selected as a circular cross-section with uniform stress to reduce energy loss caused by air pressure eddies. The gas storage pressure of this type of underground space is often high. The low-pressure side gas storage pressure can be appropriately increased to reduce the volume of gaseous carbon dioxide and increase the installed capacity.

[0109] 4) Mixed underground space: When the underground low-pressure side space is limited, a high-strength pressure-bearing cable net or frame + mesh structure is constructed on the ground low-pressure side. The goal is to enable the low-pressure storage to withstand at least 1 MPa of low internal pressure, which is different from the previous storage pressure that could only withstand 0.1 MPa of normal pressure. The high-pressure side storage is still placed in the underground space because the liquid volume is small. The mixed layout of the above-ground space can greatly increase the installed capacity.

[0110] 5) Dispersed underground space: When the gas storage space on a single low-pressure side is small, gas can also be stored by combining multiple bags or by using multiple underground caverns connected in series to meet the needs of large-scale energy storage. The bags and the interfaces of each gas pipeline must be sealed to prevent gas leakage. Other working principles and construction methods are the same as those in Examples 1 and 2.

[0111] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A compressed carbon dioxide energy storage system based on an underground gas storage facility, characterized in that, include: Low-pressure gas storage, high-pressure liquid storage and carbon replenishment system; The low-pressure gas storage facility is located in a shallow underground cavern, utilizing natural underground space, abandoned underground space, or artificially excavated space. A flexible airbag membrane is installed inside the low-pressure gas storage facility. The flexible airbag membrane is fixed to the inner wall of the low-pressure gas storage facility by anchoring components and a skeleton support mesh chain. The flexible airbag membranes are connected to form a closed gas-containing cavity, and a sandwich cavity is formed between the inner wall of the low-pressure gas storage facility and the outer wall of the flexible airbag membrane. The gas chamber stores low-pressure gaseous carbon dioxide released by the expansion turbine, and the storage environment pressure is maintained at 0.1-1 MPa. High-pressure liquid storage tanks utilize underground vertical abandoned spaces or newly excavated vertical caves to store ambient-temperature high-pressure liquid carbon dioxide released by compressors at temperatures below 25°C. The storage environment pressure is maintained at 6MPa. The burial depth of high-pressure liquid storage tanks is greater than that of low-pressure gas storage tanks, with a burial depth greater than 100m. The carbon replenishment system is located on the ground. The carbon replenishment system stores and replenishes gas in the gas chamber of the low-pressure gas storage tank through the low-pressure side inflation pipeline until it exceeds 0.1 MPa. The flexible air bladder membrane expands and adheres to the inner wall of the low-pressure gas storage tank. The carbon replenishment system inflates the inner cavity of the high-pressure liquid storage tank through the high-pressure side inflation pipeline. The carbon replenishment system is equipped with a carbon replenishment interface, and both the low-pressure side inflation pipeline and the high-pressure side inflation pipeline are connected to the carbon replenishment system through the carbon replenishment interface. The low-pressure side inflation pipeline is equipped with a low-pressure side pressure valve, and the high-pressure side inflation pipeline is equipped with a high-pressure side pressure valve; a pressure gauge is installed at the carbon replenishment interface; based on the expansion rate and adhesion of the flexible air bladder membrane of the low-pressure gas storage tank and the liquid volume and pressure in the high-pressure liquid storage tank, the replenishment rate and pressure of carbon dioxide into the low-pressure gas storage tank and the high-pressure liquid storage tank are controlled by the low-pressure side pressure valve and the high-pressure side pressure valve, respectively. The carbon replenishment system is also equipped with a carbon dioxide leakage monitoring device to ensure that the daily carbon dioxide leakage rate in the low-pressure gas storage facility meets the design requirements.

2. The compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1, characterized in that, The compressed carbon dioxide energy storage system also includes: a compressor, an expander, a heat storage tank, and a pumping device; The compressor, expander, heat storage tank, and pump are all located on the ground. The gas chamber of the low-pressure gas storage tank is connected to the input end of the compressor through a low-pressure side outlet pipe, and the output end of the compressor is connected to the inner cavity of the high-pressure liquid storage tank through a high-pressure side return pipe. The high-pressure side outlet pipe of the high-pressure liquid storage tank is connected to the input end of the expander, and the output end of the expander is connected to the gas chamber of the low-pressure gas storage tank through a low-pressure side return pipe. The heat storage tank is installed on the high-pressure side outlet pipe and the high-pressure side return pipe of the high-pressure liquid storage tank and is connected to them respectively. The pump is installed on the high-pressure side outlet pipe. During energy storage, the compressor inlet is at constant pressure, with an inlet pressure of 0.1 MPa. When the storage pressure in the gas chamber of the low-pressure gas storage tank is 1 MPa, a pressure relief valve is installed on the low-pressure side outlet pipe before introducing low-pressure gaseous carbon dioxide into the compressor. By adjusting the valve, the stored low-pressure gaseous carbon dioxide is slowly reduced from 1 MPa to 0.1 MPa, so that the pressure entering the compressor remains constant at atmospheric pressure. Similarly, during the energy release process, a check valve is installed on the low-pressure side return gas pipe. Since the low-pressure gaseous carbon dioxide output by the expander is 0.1 MPa higher than atmospheric pressure, the check valve gradually and smoothly introduces the low-pressure gaseous carbon dioxide (0.1 MPa higher than atmospheric pressure) into the gas chamber of the low-pressure gas storage tank until the pressure in the gas chamber of the low-pressure gas storage tank changes back from atmospheric pressure of 0.1 MPa to 1 MPa. The high-pressure liquid storage tank is maintained at a constant pressure of 6 MPa. Gaseous carbon dioxide is introduced into the high-pressure liquid storage tank through a carbon replenishment system to maintain the pressure. At this time, a small amount of gaseous carbon dioxide liquefies into liquid under the constant 6 MPa condition in the underground high-pressure liquid storage tank. The high-pressure liquid carbon dioxide in the high-pressure liquid storage tank is pumped into the high-pressure side outlet pipe through a pumping device. At the same time, the carbon dioxide filling rate is controlled by a pressure gauge and a high-pressure side pressure valve. When the high-pressure liquid storage tank is pumped out and the pressure inside the high-pressure liquid storage tank is lower than the liquefaction pressure, some of the liquid carbon dioxide vaporizes into high-pressure gaseous carbon dioxide to achieve a thermal equilibrium state inside the tank.

3. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, The compressed carbon dioxide energy storage system also includes construction traffic tunnels; The construction traffic tunnel is used for the passage of construction workers and the transportation of construction machinery during the construction period. It consists of two tunnel sections, namely the first tunnel section and the second tunnel section. Both tunnel sections are connected to the low-pressure gas storage facility. The first tunnel section is located in front of the low-pressure gas storage facility, and the second tunnel section is located behind the low-pressure gas storage facility and is connected to the high-pressure liquid storage facility. The cross-section of the construction traffic tunnel adopts the shape of a city gate; an entry valve is installed at the entrance of the first tunnel section, and pressure-bearing valves are installed at the exit of the first tunnel section and at both ends of the second tunnel section to seal the construction traffic tunnel; the rock wall of the construction traffic tunnel is lined with reinforced concrete. The inner wall of the low-pressure gas storage is a surrounding rock structure. The reinforced concrete lining of the construction access roadway and the surrounding rock structure of the low-pressure gas storage are both low-pressure side linings. The low-pressure side lining is supported by shotcrete and anchor according to the surrounding rock conditions. The outermost side of the low-pressure side lining is the low-pressure side surrounding rock.

4. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, When the low-pressure gas storage facility uses an existing underground large cavity space as a low-pressure cavern, the inner wall surface of the low-pressure cavern needs to be polished smooth, trimmed to remove sharp edges and supported, and the low-pressure cavern needs to meet three conditions: stability, no external water pressure, and no sharp corners.

5. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 3, characterized in that, The high-pressure liquid storage tank consists of a three-layer structure, from the inside out: a high-pressure side sealing layer, a high-pressure side lining, and a high-pressure side surrounding rock. The high-pressure side lining is made of concrete, and its thickness is greater than that of the low-pressure side lining. The stress and temperature fields of the high-pressure side sealing layer are transmitted to the high-pressure side surrounding rock through the high-pressure side lining. The high-pressure liquid storage tank adopts a hollow cylindrical structure with an open top. The top opening of the high-pressure liquid storage tank is sealed with a concrete plug. The temperature control standard for the air intake of the high-pressure liquid storage tank is the local natural ground temperature.

6. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, The carbon replenishment system may employ a carbon capture device or a carbon dioxide liquid tank. When a carbon capture device is used, the carbon capture device can directly obtain high-pressure gaseous carbon dioxide. The outlet of the carbon capture device is directly connected to the carbon replenishment interface. The carbon capture device can be directly connected to the low-pressure gas storage tank through the low-pressure side gas filling pipeline and directly connected to the high-pressure liquid storage tank through the high-pressure side gas filling pipeline to replenish the low-pressure gas storage tank and the high-pressure liquid storage tank respectively. When using a carbon dioxide liquid tank, the liquid carbon dioxide in the tank needs to be vaporized to obtain high-pressure gaseous carbon dioxide. The outlet of the commercial carbon dioxide liquid tank is connected to a liquid carbon dioxide vaporizer through a ground filling pipeline. The liquid carbon dioxide vaporizer is used to vaporize the liquid carbon dioxide into high-pressure gaseous carbon dioxide and discharge it. The outlet of the liquid carbon dioxide vaporizer is connected to the carbon replenishment interface.

7. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, The carbon replenishment system stores and replenishes gas in the gas-bearing cavity of the low-pressure gas storage tank through a low-pressure side inflation pipeline. The interface between the low-pressure side inflation pipeline and the gas-bearing cavity is pre-embedded at the bottom of the low-pressure gas storage tank. The gas-bearing cavity is inflated by the carbon replenishment system until the flexible gas bladder membrane expands and completely adheres to the smooth inner wall surface of the low-pressure gas storage tank, and the pressure reaches atmospheric pressure of 0.1 MPa. The inflation rate is controlled by the low-pressure side pressure valve. At the same time, the carbon replenishment system inflates the inner cavity of the high-pressure liquid storage tank through a high-pressure side inflation pipeline. When the liquid level in the high-pressure liquid storage tank drops, high-pressure gaseous carbon dioxide is injected into the high-pressure liquid storage tank through the carbon replenishment system to maintain the pressure of the high-pressure liquid storage tank. The inflation rate is controlled by the high-pressure side pressure valve.

8. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 3, characterized in that, The compressed carbon dioxide energy storage system also includes a drainage system; The drainage system includes: a water collection tank, a drainage ditch, drainage pipes, drainage manhole covers, and an intelligent drainage sensor. The water collection pool is located below the entrance of the first section of the construction access roadway. The drainage ditch is located on both sides of the bottom of the construction access roadway and is connected to the water collection pool. The drainage ditch maintains a certain slope and eventually flows into the water collection pool. The drainage pipeline is laid along the periphery of the low-pressure gas storage tank to collect underground pressurized water and ensure that the flexible airbag membrane does not bear external water pressure. One end of the drainage pipeline is connected to the water collection pool, and the other end is connected to the surface pumping equipment. The intelligent drainage sensor is embedded in the water collection pool to monitor the water level in real time. When the water level in the pool reaches the maximum limit, the water in the water collection pool is discharged through the drainage pipeline and submersible pump. When the water level is higher than the set value, the drainage pipeline can be pre-embedded according to the terrain to drain the water from the mountain. The drainage well cover is used to cover the water collection pool and can be opened for maintenance.

9. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, The low-pressure gas storage tank is equipped with a vent, which communicates with the interlayer cavity. The vent is connected to an external ventilation device, which is used to fill and release air into the interlayer cavity, thereby controlling the carbon dioxide pressure in the low-pressure gas storage cavity.

10. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, The outer surface of the flexible airbag membrane is coated with a waterproof and corrosion-resistant coating.

11. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 3, characterized in that, The inner surfaces of the low-pressure gas storage facility and the construction access roadway are supported by wire mesh and sprayed concrete.

12. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, The high-pressure liquid storage tank adopts a horizontal tunnel-type storage method.

13. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 1 or 2, characterized in that, When the single low-pressure side gas storage space is smaller than the required space, multiple flexible gasbag membranes can be combined for gas storage.

14. A compressed carbon dioxide energy storage system based on an underground gas storage facility as described in claim 2, characterized in that, The compressor in the ground plant can be a variable frequency compressor with a first-stage inlet and a fixed frequency compressor with a second-stage outlet. The expander can be a fixed frequency expander with a first-stage inlet and a variable frequency expander with a second-stage outlet.

15. A method for constructing a compressed carbon dioxide energy storage system based on an underground gas storage facility, characterized in that, The compressed carbon dioxide energy storage system described herein is the compressed carbon dioxide energy storage system according to any one of claims 1-14, and the specific steps of the method are as follows: Step 1: After entering the site, the construction of the construction traffic tunnels shall be carried out first. After the tunnels are connected, the support lining and transportation system shall be arranged and installed in a timely manner. Based on the hydrogeological conditions of the underground space, advanced support design and sealing grouting measures shall be carried out. Step 2: Based on the construction traffic tunnel, carry out a small-scale leveling project on the low-pressure gas storage facility, and manually or mechanically grind and repair the original outline of the low-pressure side cavern to form a level cavern outline; then the stability of the cavern itself needs to be rechecked, and corresponding wire mesh and sprayed concrete support measures are carried out at weak locations. Step 3: Assemble the flexible airbag membrane and the skeleton support chain, and fix them in the corresponding positions with anchoring devices. At the same time, according to the design, pre-embed monitoring chips for physical parameters of temperature and pressure in the surrounding rock wall of the low-pressure gas storage. Step 4: After the low-pressure gas storage tank is completed, continue to excavate horizontally into the underground mountain through the construction access roadway, and then excavate downward to form a vertical shaft-type hollow cylindrical high-pressure liquid storage tank until the excavation meets the burial depth of the high-pressure liquid storage tank. Then, carry out the construction and layout of the high-pressure side lining and high-pressure side sealing layer in sequence. At the same time, physical parameter monitoring chips are pre-embedded in the surrounding rock wall of the high-pressure liquid storage tank. Step 5: After all the storage tunnels have been excavated, construction will be carried out on all the pipe holes, and the drainage system will be constructed at the same time, including the installation of water collection tanks, drainage ditches, drainage well covers, drainage pipes and intelligent drainage sensors. Step 6: After the underground engineering construction is completed, the innermost side of the construction traffic tunnel and the upper part of the high-pressure liquid storage tank are sealed with plugs. At the same time, pressure valves are installed at both ends of the low-pressure side gas storage cavern, and an entry valve is installed at the entrance of the construction traffic tunnel. Step 7: Connect the various pre-buried pipelines in the underground gas storage facility to the carbon replenishment system, compressor, expander, heat storage tank and pumping device, and construct the above-ground plant to house the compressor, expander, heat storage tank and pumping device.

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