Carbon dioxide energy storage system utilizing series-parallel connection combination of abandoned coal mine roadways and implementation method of carbon dioxide energy storage system

Abstract

The invention discloses a coal mine abandoned roadway series-parallel connection combined carbon dioxide energy storage system and an implementation method thereof.The implementation method comprises the steps that a to-be-used abandoned roadway is selected out and transformed into a high-position storage cavern, a middle-position storage cavern and a low-position storage cavern, and gaseous CO2, gas-liquid mixed CO2 and supercritical liquid CO2 are stored in the high-position storage cavern, the middle-position storage cavern and the low-position storage cavern respectively; excavating an equipment chamber to install an energy storage device, and connecting the high-position storage cavern, the middle-position storage cavern, the low-position storage cavern and the energy storage device through pipelines; under the driving of external electric quantity, gaseous CO2 is pressed into the middle-position storage cavern from the high-position storage cavern, and gas-liquid mixed CO2 is pressed into the low-position storage cavern from the middle-position storage cavern, so that energy storage is realized; the supercritical liquid CO2 in the low-position storage cavern expands to push the turbine to generate power and then enters the middle-position storage cavern, and the gas-liquid mixed CO2 in the middle-position storage cavern expands to push the turbine to generate power and then enters the high-position storage cavern, so that power generation is realized. According to the invention, CO2 industrial utilization and mine underground space development can be synergistically realized.

Description

Technical Field

[0001] The present invention relates to the technical field of underground space development of abandoned mines and carbon dioxide utilization, and in particular to a carbon dioxide energy storage system utilizing a series-parallel combination of abandoned coal mine tunnels and a realization method thereof. Background Art

[0002] Long-term large-scale mining of coal resources has led to the depletion of shallow resources. The mining depth of some coal mines has reached more than 800 meters underground, and deep mining has become an inevitable trend. When coal mines are mining shallow resources, many shallow tunnels have been scrapped. When deep mining is carried out, many abandoned tunnels will be formed in the deep. Simple sealing treatment will cause waste of these shallow and deep underground space resources. How to achieve high-value industrialized coordinated utilization of shallow and deep abandoned tunnels has become an urgent problem to be solved.

[0003] At present, the capture, utilization and storage of carbon dioxide has become a problem that needs to be solved urgently. Studies have found that carbon dioxide can exist stably in a critical state under conditions deeper than 800 meters underground, which provides a theoretical basis for CCUS (carbon capture, utilization and storage) in deep coal mines. However, at present, there are very limited methods to organically combine the comprehensive utilization of abandoned tunnels within the full mining depth of coal mines with CCUS to build a compressed carbon dioxide energy storage system within the entire coal mining range. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a carbon dioxide energy storage system utilizing a series-parallel combination of abandoned coal mine tunnels and its implementation method, so as to synergistically solve the problems of CO2 resource utilization and underground space development in mines.

[0005] Technical solution: A method for implementing a carbon dioxide energy storage system using a series-parallel combination of abandoned coal mine tunnels, comprising the following steps:

[0006] S1, evaluate the stability and sealing of abandoned mine tunnels through tests and experiments, select abandoned tunnels to be used, and divide them into high-level abandoned tunnels, medium-level abandoned tunnels and low-level abandoned tunnels according to their burial depth;

[0007] S2, transforming high-level abandoned tunnels, middle-level abandoned tunnels and low-level abandoned tunnels into high-level reservoirs, middle-level reservoirs and low-level reservoirs, and storing gaseous CO2, gas-liquid mixed CO2 and supercritical liquid CO2 in them in turn;

[0008] S3, excavate equipment chambers near high-level abandoned tunnels, middle-level abandoned tunnels and low-level abandoned tunnels, support the equipment chambers, and then install compressors, expanders, coolers, reheaters and turbines inside the equipment chambers;

[0009] S4, the high-level storage tank, the middle-level storage tank and the low-level storage tank are connected in series and parallel through pipelines, and connected to the compressor, the expander, the cooler, the reheater and the turbine to form a carbon dioxide energy storage system.

[0010] Further, in step S1, the stability and sealing of abandoned coal mine tunnels are studied and evaluated through field tests, indoor tests and numerical simulations. The specific steps are as follows:

[0011] S11, using a laser radar scanning system to detect abandoned tunnels in a coal mine, establish a three-dimensional model of the abandoned tunnel, identify the rock structure surface of the abandoned tunnel, and determine the damage of the surrounding rock of the abandoned tunnel;

[0012] S12, drilling and sampling in abandoned tunnels, and conducting indoor tests to obtain the geomechanical parameters and permeability of the tunnel surrounding rock;

[0013] S13, based on the detection and test data, a numerical model of the abandoned tunnel is established and calculated to obtain the stress, displacement and plastic zone distribution of the surrounding rock of the abandoned tunnel;

[0014] S14. Comprehensively consider the stress, displacement, plastic zone distribution and permeability of the surrounding rock of abandoned tunnels, and establish a stability and sealing evaluation system for abandoned coal mine tunnels.

[0015] Furthermore, the abandoned tunnels to be used should meet the following conditions: the surrounding rock grade of the tunnel is Class I and Class II, and the surrounding rock permeability is less than 1×10 -14 m 2 The 24h air leakage rate of the tunnel is less than 1%.

[0016] Furthermore, in step S1, the buried depth of the high-level abandoned tunnel is less than 600m, the buried depth of the middle-level abandoned tunnel is between 600 and 800m, and the buried depth of the low-level abandoned tunnel is greater than 800m; and multiple high-level abandoned tunnels, or multiple middle-level abandoned tunnels, or multiple low-level abandoned tunnels can be arranged at the same level.

[0017] Furthermore, in step S2, the transformation of the abandoned tunnels includes support construction, flexible membrane installation and monitoring device installation; specifically, as follows: first, the high-level, middle-level and low-level abandoned tunnels are leveled, and their weak parts are reinforced and supported; then, a flexible membrane with good impermeability is installed on the lining structure formed by the support; finally, a pressure monitoring device, a temperature monitoring device, a humidity monitoring device and a CO2 concentration monitoring device are installed on the flexible membrane, and finally a high-level reservoir, a middle-level reservoir and a low-level reservoir are formed.

[0018] Furthermore, in step S3, the volume of the equipment chamber does not exceed 150m 3 The whole section construction method is adopted to build the tunnel in one time, and anchor mesh spraying combined support is carried out for it.

[0019] Further, in step S4, the steps for connecting the high-position reservoir, the middle-position reservoir and the low-position reservoir in series and parallel through pipelines are as follows:

[0020] S41, connecting multiple high-position reservoirs, multiple middle-position reservoirs and multiple low-position reservoirs at the same level in parallel through horizontal pipelines to form a high-position reservoir group, a middle-position reservoir group and a low-position reservoir group in sequence;

[0021] S42, high-level storage groups, middle-level storage groups and low-level storage groups at different levels are connected in series through vertical pipelines to form a CO2 storage group in the underground space of the mine.

[0022] Further, in step S4, the compressor, expander, cooler, reheater and turbine are connected to the high-level reservoir, the middle-level reservoir and the low-level reservoir through pipelines, thereby forming a carbon dioxide energy storage system.

[0023] A carbon dioxide energy storage system is constructed by using any of the above-mentioned methods for realizing a carbon dioxide energy storage system using a series-parallel combination of abandoned coal mine tunnels, comprising a high-position reservoir, a middle reservoir and a low-position reservoir, wherein the high-position reservoir, the middle reservoir and the low-position reservoir are connected in series and parallel through pipelines, and connected to a compressor, an expander, a cooler, a reheater and a turbine to form a carbon dioxide energy storage system;

[0024] The high-position reservoir is connected to the input end of the first compressor through a pipeline, the output end of the first compressor is connected to the inlet end of the first cooler, and the output end of the first cooler is connected to the middle-position reservoir through a pipeline;

[0025] The intermediate reservoir is connected to the input end of the first expander through a pipeline, the output end of the first expander is connected to the input end of the first reheater, the output end of the first reheater is connected to the input end of the first turbine, and the output end of the first turbine is connected to the high-level reservoir through a pipeline;

[0026] The middle reservoir is connected to the input end of the second compressor through a pipeline, the output end of the second compressor is connected to the inlet end of the second cooler, and the output end of the second cooler is connected to the low reservoir through a pipeline;

[0027] The low-level reservoir is connected to the input end of the second expander through a pipeline, the output end of the second expander is connected to the input end of the second reheater, the output end of the second reheater is connected to the input end of the second turbine, and the output end of the second turbine is connected to the middle-level reservoir through a pipeline.

[0028] Furthermore, driven by the external excess electricity, the gaseous CO2 in the high-level reservoir enters the second compressor for compression and is cooled by the second cooler to form a gas-liquid mixed CO2, which is then injected into the middle-level reservoir; at the same time, the gas-liquid mixed CO2 in the middle-level reservoir enters the first compressor for compression and is cooled by the first cooler to form a supercritical liquid CO2, which is then injected into the low-level reservoir;

[0029] The supercritical liquid CO2 in the low-level reservoir enters the second expander to expand and do work and is heated by the second reheater to form a gas-liquid mixed CO2. The gas-liquid mixed CO2 enters the second turbine to drive the turbine to generate electricity, and the gas-liquid mixed CO2 discharged from the output end of the second turbine is injected into the middle-level reservoir; at the same time, the gas-liquid mixed CO2 in the middle-level reservoir enters the first expander to expand and do work and is heated by the first reheater to form a gaseous CO2. Subsequently, the gaseous CO2 enters the first turbine to drive the turbine to generate electricity, and the gaseous CO2 discharged from the output end of the first turbine is injected into the high-level reservoir.

[0030] Compared with the prior art, the present invention has the following significant effects:

[0031] 1. Based on the phenomenon that carbon dioxide can stably exist in a supercritical state at a depth of more than 800 meters underground, the present invention utilizes the series-parallel combination of abandoned coal mine tunnels to construct a carbon dioxide energy storage system, thereby realizing the coordinated development of space resources in the shallow, middle and deep abandoned tunnels of the mine and the industrial utilization of carbon dioxide; at the same time, since the storage reservoir is constructed underground, with the help of deep temperature and pressure conditions, only a small amount of energy is consumed when compressing carbon dioxide, which is conducive to reducing the operating cost of the energy storage system.

[0032] 2. Driven by external electricity, gaseous CO2 is pressed from the high-level reservoir into the middle-level reservoir, and the gas-liquid mixed CO2 is pressed from the middle-level reservoir into the low-level reservoir to achieve energy storage; the supercritical liquid CO2 in the low-level reservoir expands to drive the turbine to generate electricity and then enters the middle-level reservoir, and the gas-liquid mixed CO2 in the middle-level reservoir expands to drive the turbine to generate electricity and then enters the high-level reservoir to achieve power generation; the comprehensive utilization of abandoned tunnels within the entire mining depth of the coal mine is organically combined with CCUS to achieve the combination of industrial utilization of CO2 and development of underground space in mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the process of the present invention;

[0034] Figure 2 It is a pipeline connection schematic diagram of the present invention;

[0035] Figure 3 It is a cross-sectional schematic diagram of the high-position reservoir, the middle-position reservoir and the low-position reservoir of the present invention;

[0036] Figure 4Schematic diagram of the carbon dioxide energy storage system of the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0038] like Figure 1 As shown, a method for constructing carbon dioxide energy storage by using series-parallel combination of abandoned coal mine tunnels, the specific steps are as follows:

[0039] Step 1, determine the available abandoned lanes;

[0040] Through testing and experimentation, the stability and sealing of abandoned mine tunnels were evaluated, and abandoned tunnels to be used were selected. The details are as follows: First, the abandoned tunnels of a coal mine were detected by using a laser radar scanning system, a three-dimensional model of the abandoned tunnel was established, and the rock structure surface of the abandoned tunnel was identified to determine the damage of the surrounding rock of the abandoned tunnel; then, drilling and sampling were carried out in the abandoned tunnel, and indoor experiments were carried out to obtain the geomechanical parameters and permeability of the tunnel surrounding rock; then, based on the above-mentioned detection and experimental data, a numerical model of the abandoned tunnel was established and calculated to obtain the stress, displacement and plastic zone distribution of the abandoned tunnel surrounding rock; finally, considering the stress, displacement, plastic zone distribution and permeability and other indicators, a stability and sealing evaluation system for abandoned mine tunnels was established, and the surrounding rock grades I and II and the surrounding rock permeability less than 1×10 -14 m 2 The abandoned tunnels with a 24h gas leakage rate of less than 1% are divided into high-level abandoned tunnels, medium-level abandoned tunnels and low-level abandoned tunnels according to their burial depth. Among them, the burial depth of high-level abandoned tunnels is less than 600m, the burial depth of medium-level abandoned tunnels is between 600 and 800m, and the burial depth of low-level abandoned tunnels is greater than 800m; and multiple high-level abandoned tunnels, multiple medium-level abandoned tunnels, or multiple low-level abandoned tunnels can be arranged at the same level, such as Figure 4 shown.

[0041] Step 2, constructing a carbon dioxide reservoir;

[0042] The high-level abandoned tunnels, the middle-level abandoned tunnels and the low-level abandoned tunnels are renovated as follows:

[0043] First, the high, middle and low abandoned tunnels are leveled and their weak parts are reinforced and supported;

[0044] Then, a flexible membrane 2 with good impermeability is installed on the lining structure 1 formed by the support;

[0045] Finally, a pressure monitoring device 3, a temperature monitoring device 4, a humidity monitoring device 5 and a CO2 concentration monitoring device 6 are installed on the flexible membrane. Figure 2 shown.

[0046] Finally, a high-level reservoir 7, a middle-level reservoir 8 and a low-level reservoir 9 are formed, in which gaseous CO2, gas-liquid mixed CO2 and supercritical liquid CO2 are stored in turn.

[0047] Step 3, installing the energy storage device;

[0048] Equipment chambers 10 are excavated near high-level, middle-level and low-level abandoned tunnels, and compressors, expanders, coolers, reheaters and turbines are installed inside the equipment chambers after they are supported.

[0049] Step 4, constructing a carbon dioxide energy storage system;

[0050] like Figure 4 As shown, first, multiple high-level storage tanks 7, multiple middle-level storage tanks 8 and multiple low-level storage tanks 9 at the same level are connected in parallel through horizontal pipelines 21 to form high-level storage tank groups, middle-level storage tank groups and low-level storage tank groups in turn; then, high-level storage tank groups, middle-level storage tank groups and low-level storage tank groups at different levels are connected in series through vertical pipelines 22 to form a CO2 storage tank group in the underground space of the mine; finally, the CO2 storage tank group in the underground space of the mine is connected to a compressor, an expander, a cooler, a reheater and a turbine to form a compressed carbon dioxide energy storage system. Figure 3 As shown, the specific pipeline connections are as follows:

[0051] The high-level reservoir 7 is connected to the input end of the first compressor 11 through a pipeline, the output end of the first compressor 11 is connected to the inlet end of the first cooler 12, and the output end of the first cooler 12 is connected to the middle-level reservoir 8 through a pipeline;

[0052] The intermediate reservoir 8 is connected to the input end of the first expander 13 through a pipeline, the output end of the first expander 13 is connected to the input end of the first reheater 14, the output end of the first reheater 14 is connected to the input end of the first turbine 15, and the output end of the first turbine 15 is connected to the high-level reservoir 7 through a pipeline;

[0053] The middle reservoir 8 is connected to the input end of the second compressor 16 through a pipeline, the output end of the second compressor 16 is connected to the inlet end of the second cooler 17, and the output end of the second cooler 17 is connected to the low reservoir 9 through a pipeline;

[0054] The low-level reservoir 9 is connected to the input end of the second expander 18 through a pipeline, the output end of the second expander 18 is connected to the input end of the second reheater 19, the output end of the second reheater 19 is connected to the input end of the second turbine 20, and the output end of the second turbine 20 is connected to the middle-level reservoir 8 through a pipeline.

[0055] The carbon dioxide energy storage system constructed by the present invention stores energy by compressing carbon dioxide or generates electricity by expanding carbon dioxide, as follows:

[0056] 1. Compressed carbon dioxide energy storage

[0057] Driven by external excess electricity, the gaseous CO2 in the high-level reservoir 7 enters the second compressor 16 for compression and is cooled by the second cooler 17 to form a gas-liquid mixed CO2, which is then injected into the middle reservoir 8; at the same time, the gas-liquid mixed CO2 in the middle reservoir 8 enters the first compressor 11 for compression and is cooled by the first cooler 12 to form a supercritical liquid CO2, which is then injected into the low-level reservoir 9.

[0058] In this embodiment, the external surplus electricity used in the process of compressing carbon dioxide energy storage comes from the surplus electricity of renewable energy and the valley filling electricity during the off-load period of the power plant.

[0059] (II) Expanding carbon dioxide to generate electricity

[0060] The supercritical liquid CO2 in the low-level reservoir 9 enters the second expander 18 to expand and do work, and is heated by the second reheater 19 to form a gas-liquid mixed CO2. The gas-liquid mixed CO2 enters the second turbine 20 to drive the turbine to generate electricity, and the gas-liquid mixed CO2 discharged from the output end of the second turbine 20 is injected into the middle-level reservoir 8; at the same time, the gas-liquid mixed CO2 in the middle-level reservoir 8 enters the first expander 13 to expand and do work, and is heated by the first reheater 14 to form gaseous CO2. Subsequently, the gaseous CO2 enters the first turbine 15 to drive the turbine to generate electricity, and the gaseous CO2 discharged from the output end of the first turbine 15 is injected into the high-level reservoir 7.

Claims

1. A method for implementing a carbon dioxide energy storage system using a series-parallel combination of abandoned coal mine tunnels, characterized in that: The following steps are involved: S1, evaluate the stability and sealing of abandoned mine tunnels through tests and experiments, select abandoned tunnels to be used, and divide them into high-level abandoned tunnels, medium-level abandoned tunnels and low-level abandoned tunnels according to their burial depth; S2, transforming the high-level abandoned tunnel, the middle-level abandoned tunnel and the low-level abandoned tunnel to form a high-level reservoir (7), a middle-level reservoir (8) and a low-level reservoir (9), and storing gaseous CO2, gas-liquid mixed CO2 and supercritical liquid CO2 therein in turn; S3, excavating an equipment chamber (10) near the high-level abandoned tunnel, the middle-level abandoned tunnel and the low-level abandoned tunnel, supporting the equipment chamber (10), and installing a compressor, an expander, a cooler, a reheater and a turbine inside the equipment chamber (10); S4, the high-level storage tank (7), the middle-level storage tank (8) and the low-level storage tank (9) are connected in series and parallel through pipelines, and connected to a compressor, an expander, a cooler, a reheater and a turbine to form a carbon dioxide energy storage system.

2. The method for realizing the carbon dioxide energy storage system using series-parallel combination of abandoned coal mine tunnels according to claim 1 is characterized in that: In step S1, the stability and sealing of abandoned coal mine tunnels are studied and evaluated through field tests, indoor tests and numerical simulations. The specific steps are as follows: S11, using a laser radar scanning system to detect abandoned tunnels in a coal mine, establish a three-dimensional model of the abandoned tunnel, identify the rock structure surface of the abandoned tunnel, and determine the damage of the surrounding rock of the abandoned tunnel; S12, drilling and sampling in abandoned tunnels, and conducting indoor tests to obtain the geomechanical parameters and permeability of the tunnel surrounding rock; S13, based on the detection and test data, a numerical model of the abandoned tunnel is established and calculated to obtain the stress, displacement and plastic zone distribution of the surrounding rock of the abandoned tunnel; S14. Comprehensively consider the stress, displacement, plastic zone distribution and permeability of the surrounding rock of abandoned tunnels, and establish a stability and sealing evaluation system for abandoned coal mine tunnels.

3. The method for realizing the carbon dioxide energy storage system using series-parallel combination of abandoned coal mine tunnels according to claim 1 is characterized in that: The abandoned tunnels to be used should meet the following conditions: the surrounding rock grade of the tunnel should be Class I and Class II, and the surrounding rock permeability should be less than 1×10 -14 m 2 The 24h air leakage rate of the tunnel is less than 1%.

4. The method for realizing the carbon dioxide energy storage system using series-parallel combination of abandoned coal mine tunnels according to claim 1 is characterized in that: In step S1, the buried depth of the high-level abandoned tunnel is less than 600m, the buried depth of the middle-level abandoned tunnel is between 600 and 800m, and the buried depth of the low-level abandoned tunnel is greater than 800m; and multiple high-level abandoned tunnels, or multiple middle-level abandoned tunnels, or multiple low-level abandoned tunnels can be arranged at the same level.

5. The method for realizing the carbon dioxide energy storage system using series-parallel combination of abandoned coal mine tunnels according to claim 1 is characterized in that: In step S2, the reconstruction of the abandoned tunnel includes support construction, flexible membrane installation and monitoring device installation; specifically, the following steps are performed: first, the high-level, middle-level and low-level abandoned tunnels are leveled, and their weak parts are reinforced and supported; then, a flexible membrane (2) with good impermeability is installed on the lining structure (1) formed by the support; finally, a pressure monitoring device (3), a temperature monitoring device (4), a humidity monitoring device (5) and a CO2 concentration monitoring device (6) are installed on the flexible membrane, and finally a high-level reservoir (7), a middle-level reservoir (8) and a low-level reservoir (9) are formed.

6. The method for realizing the carbon dioxide energy storage system using series-parallel combination of abandoned coal mine tunnels according to claim 1 is characterized in that: In step S3, the volume of the equipment chamber (7) does not exceed 150m 3 The whole section construction method is adopted to build the tunnel in one time, and anchor mesh spraying combined support is carried out for it.

7. The method for realizing the carbon dioxide energy storage system using series-parallel combination of abandoned coal mine tunnels according to claim 1 is characterized in that: In step S4, the steps for connecting the high-position reservoir (7), the middle-position reservoir (8) and the low-position reservoir (9) in series and parallel through pipelines are as follows: S41, connecting a plurality of high-position reservoirs (7), a plurality of middle-position reservoirs (8) and a plurality of low-position reservoirs (9) at the same level in parallel through a horizontal pipeline (21), so as to form a high-position reservoir group, a middle-position reservoir group and a low-position reservoir group in sequence; S42, connecting high-position storage groups, middle-position storage groups and low-position storage groups at different levels in series through vertical pipelines (22) to form a CO2 storage group in the underground space of the mine.

8. The method for realizing the carbon dioxide energy storage system using series-parallel combination of abandoned coal mine tunnels according to claim 1 is characterized in that: In step S4, the compressor, expander, cooler, reheater and turbine are connected to the high-level reservoir (7), the middle-level reservoir (8) and the low-level reservoir (9) through pipelines, thereby forming a carbon dioxide energy storage system.

9. A carbon dioxide energy storage system, constructed by using the method for realizing a carbon dioxide energy storage system using a series-parallel combination of abandoned coal mine tunnels as described in any one of claims 1 to 8, characterized in that: The high-position storage tank (7), the middle-position storage tank (8) and the low-position storage tank (9) are connected in series and parallel through pipelines, and connected to a compressor, an expander, a cooler, a reheater and a turbine to form a carbon dioxide energy storage system; The high-position reservoir (7) is connected to the input end of the first compressor (11) through a pipeline, the output end of the first compressor (11) is connected to the inlet end of the first cooler (12), and the output end of the first cooler (12) is connected to the middle-position reservoir (8) through a pipeline; The intermediate reservoir (8) is connected to the input end of the first expander (13) through a pipeline, the output end of the first expander (13) is connected to the input end of the first reheater (14), the output end of the first reheater (14) is connected to the input end of the first turbine (15), and the output end of the first turbine (15) is connected to the high-level reservoir (7) through a pipeline; The middle reservoir (8) is connected to the input end of the second compressor (16) through a pipeline, the output end of the second compressor (16) is connected to the inlet end of the second cooler (17), and the output end of the second cooler (17) is connected to the low reservoir (9) through a pipeline; The low-level reservoir (9) is connected to the input end of the second expander (18) through a pipeline, the output end of the second expander (18) is connected to the input end of the second reheater (19), the output end of the second reheater (19) is connected to the input end of the second turbine (20), and the output end of the second turbine (20) is connected to the middle-level reservoir (8) through a pipeline.

10. The carbon dioxide energy storage system according to claim 9, characterized in that: Driven by the external surplus electricity, the gaseous CO2 in the high-level reservoir (7) enters the second compressor (16) for compression and is cooled by the second cooler (17) to form a gas-liquid mixed CO2, which is then injected into the middle-level reservoir (8); at the same time, the gas-liquid mixed CO2 in the middle-level reservoir (8) enters the first compressor (11) for compression and is cooled by the first cooler (12) to form a supercritical liquid CO2, which is then injected into the low-level reservoir (9); The supercritical liquid CO2 in the low-level reservoir (9) enters the second expander (18) to expand and perform work and is heated by the second reheater (19) to form a gas-liquid mixed CO2. The gas-liquid mixed CO2 enters the second turbine (20) to drive the turbine to generate electricity. The gas-liquid mixed CO2 discharged from the output end of the second turbine (20) is injected into the middle-level reservoir (8); at the same time, the gas-liquid mixed CO2 in the middle-level reservoir (8) enters the first expander (13) to expand and perform work and is heated by the first reheater (14) to form gaseous CO2. Subsequently, the gaseous CO2 enters the first turbine (15) to drive the turbine to generate electricity. The gaseous CO2 discharged from the output end of the first turbine (15) is injected into the high-level reservoir (7).

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