Composite energy storage system and operation method for renovation of waste power plants based on thermal-pressure decoupling

Abstract

The present invention discloses a composite energy storage system and operation method for the transformation of waste power plants based on thermal-pressure decoupling, including a compressor compressed air energy storage unit, a double-tank near-isothermal compressed air energy storage unit, a solar molten salt energy storage unit and an expansion generator set; the compressor compressed air energy storage unit and the double-tank near-isothermal compressed air energy storage unit are used for compressed air energy storage; the solar molten salt energy storage unit is used for efficiently collecting heat and heating the air after near-isothermal compression, thereby improving the energy density of the near-isothermal compressed air; the expansion generator set is used for high-temperature and high-pressure air expansion to generate power; the present invention utilizes the idle resources of waste power plants, and according to the different pressure bearing capacities of various equipment in the waste power plants, the various equipment are transformed into three types of low, medium and high pressure vessels, and a double-tank near-isothermal compression device is introduced to make full use of the high-pressure vessel, providing a technical direction for the transformation of waste power plants in the future.

Description

Technical Field

[0001] The present invention belongs to the technical field of physical energy storage, and in particular relates to a composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling and an operation method thereof. Background Art

[0002] The modernization and upgrading of coal-fired power plants is a crucial means of improving coal utilization efficiency, reducing coal consumption, and promoting the absorption of clean energy. With the recent construction of numerous large-capacity, high-performance coal-fired power plants and renewable energy generation units, many small-capacity coal-fired power plants will be phased out. However, according to statistics, the average service life of these units is only 12 years, resulting in the idleness and waste of obsolete thermal power plant equipment. Furthermore, with the rapid increase in total installed capacity of renewable energy, addressing issues such as instability and intermittency in renewable energy generation has become a key issue in the large-scale utilization of renewable energy.

[0003] Isothermal compressed air energy storage technology uses specific temperature control methods (such as liquid pistons and sprays) to keep the air temperature within a narrow range during compression, thereby achieving a near-isothermal compression process. This technology is independent of fossil fuels, consumes little power for compression, has a simple structure, and offers high efficiency. However, the gas temperature before expansion is nearly equal to the ambient temperature, resulting in a low energy density. Summary of the Invention

[0004] To address the issue of idle and wasted equipment in obsolete thermal power plants, the present invention aims to provide a composite energy storage system and operating method for the transformation of obsolete power plants based on thermal-pressure decoupling. The entire system transforms the obsolete power plant's high-pressure vessels, such as the steam drum, water-cooled wall, and primary heating circuit, into high-pressure gas storage vessels (with a pressure of 18 MPa), transforms the obsolete power plant's medium-pressure vessels, such as the reheat circuit, into medium-pressure gas storage vessels (with a pressure of 3.9 MPa), and transforms the obsolete power plant's low-pressure vessels, such as the exhaust steam circuit, into low-pressure gas storage vessels (with a pressure of 1 MPa), thereby fully utilizing the obsolete power plant's idle equipment. Furthermore, by utilizing the obsolete power plant's vacant land, a solar molten salt energy storage system can be established, which can be coupled with a near-isothermal compressed air system to address the low energy storage density of the near-isothermal compressed air system.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling, including a multi-stage compressed air energy storage unit, a solar molten salt energy storage unit and an expansion generator set; each stage of the multi-stage compressed air energy storage unit is provided with a gas storage container and a heat accumulator, the hot side of the heat accumulator is connected to the compression device and the gas storage container, and the cold side of the heat accumulator is connected to the gas storage container and the expansion generator set, and the gas storage container adopts a waste thermal power plant pressure vessel and pipeline corresponding to its working pressure; the compressed air energy storage unit with the highest pressure level is provided with a double-tank near-isothermal compression The device serves as compression power; the compressed air outlet of the multi-stage compressed air energy storage unit is connected to the working fluid inlet of the expansion generator set, and the expansion generator set includes a low-pressure expander, a medium-pressure expander and a high-pressure expander set, and the low-pressure expander, the medium-pressure expander and the high-pressure expander set are all connected to the generator; the working fluid outlets of the low-pressure expander, the medium-pressure expander and the high-pressure expansion set are connected to the heat recovery inlet of the solar molten salt energy storage unit, multiple high-pressure expanders are arranged in the high-pressure expansion set, and a molten salt heat exchanger is arranged between the high-pressure expanders, the hot side of the molten salt heat exchanger is connected to the solar molten salt energy storage unit, and the cold side of the molten salt heat exchanger is connected to the high-pressure expander.

[0006] The multi-stage compressed air energy storage unit includes a compressor compressed air energy storage unit and a double-tank near-isothermal compressed air energy storage unit. The compressor compressed air energy storage unit includes a low-pressure compressor, a first heat accumulator, a low-pressure gas storage container, a medium-pressure compressor, a second heat accumulator and a medium-pressure gas storage container. The air inlet of the low-pressure compressor is connected to the atmosphere, and the low-pressure compressor, the hot end of the first heat accumulator, the low-pressure gas storage container, the medium-pressure compressor, the hot end of the second heat accumulator, the medium-pressure gas storage container, the double-tank near-isothermal compressed air energy storage unit and the high-pressure gas storage container are connected in sequence. The outlet of the high-pressure gas storage container, the cold end of the first heat accumulator and the cold end of the second heat accumulator are connected in sequence; the cold end inlet and outlet of the first heat accumulator correspond to the outlet of the low-pressure gas storage container and the working fluid inlet of the low-pressure expander respectively, and the cold end inlet and outlet of the second heat accumulator correspond to the outlet of the medium-pressure gas storage container and the working fluid inlet of the medium-pressure expander respectively.

[0007] The solar molten salt energy storage unit includes a solar collector, a high-temperature molten salt storage tank, a first molten salt heat exchanger, a second molten salt heat exchanger, and a low-temperature molten salt storage tank; the solar collector, the high-temperature molten salt storage tank, the hot end of the first molten salt heat exchanger and the low-temperature molten salt storage tank are connected in sequence, and the solar collector, the second molten salt heat exchanger and the low-temperature molten salt storage tank are connected in sequence; the outlet of the low-temperature molten salt storage tank is connected to the inlet of the solar collector; the hot end outlets of the first molten salt heat exchanger and the second molten salt heat exchanger are connected to the top of the low-temperature molten salt storage tank; the high-pressure expansion unit includes a first high-pressure expander, a second high-pressure expander and a third high-pressure expander; the working fluid inlet of the first high-pressure expander is connected to the outlet of the multi-stage compressed air energy storage unit as the working fluid inlet of the high-pressure expansion unit; the first high-pressure expander, the cold end of the first molten salt heat exchanger, the second high-pressure expander, the cold end of the second molten salt heat exchanger, the third high-pressure expander and the air inlet of the low-temperature molten salt storage tank are connected in sequence, and the air inlet of the low-temperature molten salt storage tank serves as the heat recovery inlet after the air of the expansion unit does work.

[0008] An insulation layer is set in the low-temperature molten salt storage tank, which includes three layers of insulation materials. The thickness of each layer of insulation material is 100-150mm. The first insulation material and the third insulation material are 400-500mm apart. The second insulation material in the middle is arranged in a wave shape. Each minimum wave unit is approximately a semi-ellipse. The three vertices of the semi-ellipse intersect with the first or third insulation material respectively, and the empty space in the middle is filled with air; a conical guide plate is set on the top of the low-temperature molten salt storage tank, and a plurality of circular holes are opened on the conical guide plate in the circumferential direction. The radius of the two circles of circular holes close to the central axis of the conical guide plate is the same, and the radius of the remaining circles increases by 1.5 times as they go out of the conical guide plate; the heat exchange pipe in the low-temperature molten salt storage tank adopts a serpentine tube.

[0009] The low-pressure gas storage container can withstand a pressure of 1MPa. It is transformed from the steam side space of the medium-pressure heater of the abandoned thermal power plant and the related steam extraction and drainage pipes, deaerator and its related system pipes, auxiliary steam system equipment pipes, continuous and related system pipes, boiler room industrial water pipes, closed water system pipes, original compressed air system pipes, steam turbine body steam seal pipes, steam turbine body drainage pipes and circulating water pipes. By adding valves and pipes, the low-pressure containers are connected in series, and the redundant outlets are blocked to transform them into low-pressure gas storage containers.

[0010] The medium-pressure gas storage vessel can withstand a pressure of 3.9MPa. It is modified from the reheater system, reheat cold section pipeline, high-pressure heater steam side space and related steam extraction and drainage pipeline, low-pressure heater water side space, condensate pipeline, and boiler fuel system pipeline of an abandoned thermal power plant. The valve between the desuperheater and the high-pressure cylinder outlet is closed, and a valve is installed between the reheater steam pipeline and the medium-pressure cylinder. A connecting pipe is connected between the upper outlet header of the furnace top and the inlet header of the screen-type reheater to the steam side space of the high-pressure heater and related steam extraction and drainage pipelines, thereby transforming the medium-pressure vessel into a medium-pressure gas storage vessel.

[0011] The high-pressure gas storage container can withstand a pressure of 18Mpa and is transformed from the economizer system, boiler drum, water cooling system, superheater, high-pressure heater water side space, main water supply pipe, main steam pipe, and boiler drum connecting high-pressure pipe of an old thermal power plant. The entire transformation process does not require the disassembly of the equipment and pipes of each system. Each system can be converted into a high-pressure gas storage container by controlling the switching of existing valves and installing valves and pipes; the valve between the main steam pipe and the high-pressure cylinder of the turbine is closed, and a three-way pipe is installed in the section where the check valve and electric gate valve are located between the single line on the left side of the boiler and the economizer inlet header, and connected to the main water supply pipe and other high-pressure containers, and the redundant outlets are blocked to transform it into a high-pressure gas storage container.

[0012] The double-tank near-isothermal compressed air energy storage unit includes a high-pressure gas storage container and a double-tank near-isothermal compression device. The double-tank near-isothermal compression device includes a first high-pressure water tank, a second high-pressure water tank and a water pump. The first high-pressure water tank and the second high-pressure water tank are connected in parallel. The tops of the first high-pressure water tank and the second high-pressure water tank are connected to the first air outlet pipe of the medium-pressure gas storage container, the tops of the first high-pressure water tank and the second high-pressure water tank are connected to the air inlet pipe of the high-pressure gas storage container, and the bottoms of the first high-pressure water tank and the second high-pressure water tank are connected by a water pump and a liquid delivery pipe. In the preset stage, the liquid levels of the first high-pressure water tank and the second high-pressure water tank in the double-tank near-isothermal compressed air energy storage unit remain consistent.

[0013] The present invention is based on the operation method of the composite energy storage system of the waste power plant transformation with thermal-pressure decoupling. The compressor compressed air energy storage unit and the double-tank near-isothermal compressed air energy storage unit are provided with a heat accumulator and a double-tank near-isothermal compression device to decouple the thermal energy and pressure energy of the compressed air and store them separately. The pressure energy after the air is compressed is stored in each corresponding gas storage container, and the thermal energy is stored in the heat accumulator. The solar molten salt energy storage unit heats the low-temperature molten salt to a high temperature and stores it. When the system releases energy, the compressed air flows through the heat accumulator to heat and heat it, and then enters the low-pressure expander, the medium-pressure expander and the high-pressure expansion unit to perform work and generate electricity. The air after work enters the low-temperature molten salt tank to heat the low-temperature molten salt to prevent the molten salt in the low-temperature tank from being too low in temperature and causing the molten salt to solidify. The air after heat exchange is discharged into the atmosphere.

[0014] The compressed air coming out of the low-pressure gas storage container and the medium-pressure gas storage container flows through the first heat accumulator and the second heat accumulator respectively to be heated and then enter the low-pressure expander and the medium-pressure expander respectively to generate power. The air after work enters the low-temperature molten salt tank to heat the low-temperature molten salt to prevent the molten salt in the low-temperature tank from being too low in temperature and causing the molten salt to solidify. The air after heat exchange is discharged into the atmosphere; the gas in the high-pressure gas storage container first enters the first heat accumulator and the second heat accumulator to be heated and then enters the first high-pressure expander to work. The air after work enters the cold end of the first molten salt heat exchanger to exchange heat with the high-temperature molten salt at the hot end, and then enters the second high-pressure expander to expand To generate electricity, the air after work enters the cold end of the second molten salt heat exchanger to exchange heat with the high-temperature molten salt at the hot end. After being heated to a high temperature again, it enters the third high-pressure expander to generate electricity. The air coming out of the third high-pressure expander enters the low-temperature molten salt tank to heat the low-temperature molten salt to prevent the molten salt in the low-temperature tank from being too low and causing the molten salt to solidify. The air after heat exchange is discharged into the atmosphere to complete the energy release. The high-temperature molten salt pump transports the high-temperature molten salt to the first molten salt heat exchanger and the second molten salt heat exchanger. The molten salt after heat exchange returns to the low-temperature molten salt tank for storage. When there is sufficient sunlight, it can be transported to the solar collector by the low-temperature molten salt pump to be heated to a high temperature and stored in the high-temperature molten salt tank.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects:

[0016] The present invention transforms pressure vessels of different pressure levels and their associated pipelines in waste power plants into gas storage containers, thereby reusing idle equipment in waste power plants and saving the cost of compressed air energy storage systems. A nearly isothermal double-tank near-isothermal compression device is applied to the transformation of waste power plants. Compared with commonly used compressors, the double-tank near-isothermal compression device, as a liquid piston, can compress gas to an ultra-high pressure state, allowing idle high-pressure equipment in waste power plants to be more fully utilized. A heat accumulator and a double-tank near-isothermal compression device are provided to decouple the thermal energy and pressure energy of compressed air, thereby storing them separately, so that the thermal energy and pressure energy can be fully used as needed during energy release. The nearly isothermal compressed air energy storage system is coupled with a double-tank solar molten salt energy storage system to realize the system's start and stop at any time, utilizing solar energy, a clean energy source, without the need for fossil fuels and pollution, and the problem of low air energy density in the near-isothermal compressed air energy storage system is also solved.

[0017] Furthermore, by transforming the high-pressure vessels such as the steam drum, water-cooled wall, and primary heating circuit of the abandoned power plant into high-pressure gas storage vessels (with a pressure of 18 MPa), transforming the medium-pressure vessels such as the reheat circuit of the abandoned power plant into medium-pressure gas storage vessels (with a pressure of 3.9 MPa), and transforming the low-pressure vessels such as the exhaust steam circuit of the abandoned power plant into low-pressure gas storage vessels (with a pressure of 1 MPa), the idle equipment of the abandoned power plant was reused, saving the cost of the compressed air energy storage system;

[0018] Furthermore, the waste heat after work is recovered by using low-temperature molten salt, which can increase the temperature of the low-temperature molten salt and prevent the molten salt from solidifying.

[0019] Furthermore, the insulation layer of the low-temperature molten salt storage tank is composed of three layers of insulation materials. The second insulation material in the middle is shaped into a wave shape. Each minimum wave unit is approximately a semi-ellipse. The three vertices of the semi-ellipse are tangent to the first or third insulation material respectively, and the empty space in the middle is filled with air, which greatly increases the heat transfer resistance and enhances the thermal insulation performance of the low-temperature molten salt storage tank. The wavy insulation material composed of semi-ellipses greatly enhances the compressive resistance of the insulation layer.

[0020] Furthermore, a conical guide plate is added to the top of the low-temperature molten salt storage tank, with circular holes on it, and the circular holes become larger and larger along the radial direction, which can make the probability of molten salt falling from all places above close, so that the molten salt falls evenly from above, preventing the middle part of the heat exchange pipe located below from being constantly washed by the molten salt, thereby extending the service life of the heat exchange pipe. The heat exchange pipe below is distributed in a serpentine shape, so that the molten salt can be heated evenly, thereby increasing the heat exchange area. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram of a composite energy storage system for transforming an abandoned power plant according to the present invention.

[0022] Figure 2 This is a structural schematic diagram of a low-temperature molten salt storage tank of the present invention.

[0023] Figure 3 This is a cross-sectional schematic diagram of a low-temperature molten salt storage tank of the present invention.

[0024] Figure 4 This is a top view of a conical guide vane of the present invention.

[0025] Figure 5 This is a schematic diagram of the insulation layer structure of a low-temperature molten salt storage tank according to the present invention.

[0026] Among them: 1- low-pressure compressor, 2- first heat accumulator, 3- low-pressure gas storage container, 4- low-pressure first outlet valve, 5- medium-pressure compressor, 6- second heat accumulator, 7- medium-pressure gas storage container, 8- medium-pressure first outlet valve, 9- first inlet valve, 10- second inlet valve, 11- first high-pressure water tank, 12- second high-pressure water tank, 13- water pump, 14- first exhaust valve, 15- second exhaust valve, 16- high-pressure gas storage container, 17- high-pressure outlet valve, 18- first high-pressure expander, 19- first molten salt heat exchanger, 20- second high-pressure expander, 21- second molten salt heat exchanger Device, 22-third high-pressure expander, 23-low-temperature molten salt storage tank, 24-low-temperature molten salt pump, 25-solar collector, 26-high-temperature molten salt storage tank, 27-high-temperature molten salt pump, 28-low-pressure second outlet valve, 29-low-pressure expander, 30-medium-pressure second outlet valve, 31-medium-pressure expander, 32-exhaust gas inlet, 33-low-temperature molten salt outlet, 34-low-temperature molten salt inlet, 35-exhaust gas outlet, 36-conical guide vane, 37-heat exchange tube, 38-insulation layer, 39-first insulation material, 40-second insulation material, 41-third insulation material, 42-double-tank near-isothermal compression device. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings:

[0028] See also Figure 1 , a composite energy storage system for the transformation of waste power plants, including a compressor compressed air energy storage unit and a double-tank near-isothermal compressed air energy storage unit for compressed air energy storage, a solar molten salt energy storage unit for collecting heat and heating compressed air, and an expansion generator set for gas expansion power generation; the expansion generator set includes a low-pressure expander 29, a medium-pressure expander 31, a first high-pressure expander 18, a second high-pressure expander 20 and a third high-pressure expander 22, the low-pressure expander 29, the medium-pressure expander 31, the first high-pressure expander 18, the second high-pressure expander 20 and the third high-pressure expander The machine 22 is connected to the generator; the compressor compressed air energy storage unit includes a low-pressure compressor 1, a first heat accumulator 2, a low-pressure gas storage container 3, a medium-pressure compressor 5, a second heat accumulator 6, and a medium-pressure gas storage container 7. The air inlet of the low-pressure compressor 1 is connected to the atmosphere, and the air outlet is connected to the hot end inlet of the first heat accumulator 2, the hot end outlet of the first heat accumulator 2 is connected to the inlet of the low-pressure gas storage container 3, the first outlet of the low-pressure gas storage container 3 is connected to the inlet of the medium-pressure compressor 5, the outlet of the medium-pressure compressor 5 is connected to the hot end inlet of the second heat accumulator 6, and the hot end outlet of the second heat accumulator 6 is connected to the medium-pressure gas storage container 7.

[0029] refer to Figure 1The double-tank near-isothermal compressed air energy storage unit includes a high-pressure gas storage container 16 and a double-tank near-isothermal compression device 42. The double-tank near-isothermal compression device includes a first high-pressure water tank 11, a second high-pressure water tank 12, a water pump 13 and corresponding intake and exhaust pipelines and a water pump circulation pipeline; Figure 1 As shown, the intake and exhaust pipelines include an intake pipeline and an exhaust pipeline connected in parallel to the two high-pressure water tanks, the intake and exhaust pipelines are connected to the top of the first high-pressure water tank 11 and the second high-pressure water tank 12, and the intake pipelines corresponding to the first high-pressure water tank 11 and the second high-pressure water tank 12 are respectively provided with a first intake valve 9 and a second intake valve 10; the exhaust pipelines corresponding to the first high-pressure water tank 11 and the second high-pressure water tank 12 are respectively provided with a first exhaust valve 14 and a second exhaust valve 15; the exhaust pipeline is connected to the inlet of the high-pressure gas storage container 16; the water pump and its circulation pipeline are connected to the bottom of the first high-pressure water tank 11 and the second high-pressure water tank 12.

[0030] refer to Figure 1 The solar molten salt energy storage unit includes a solar collector 25, a high-temperature molten salt storage tank 26, a first molten salt heat exchanger 19, a second molten salt heat exchanger 21, and a low-temperature molten salt storage tank 23. The outlet end of the solar collector 25 is connected to the inlet end of the high-temperature molten salt storage tank 26, and the outlet end of the high-temperature molten salt storage tank 26 is connected to the hot end inlet of the first molten salt heat exchanger 19 via a high-temperature molten salt pump 27. The hot end outlet of the first molten salt heat exchanger 19 is connected to the top of the low-temperature molten salt storage tank 23, the hot end outlet of the second molten salt heat exchanger 21 is connected to the top of the low-temperature molten salt storage tank 23, and the outlet of the low-temperature molten salt storage tank 23 is connected to the inlet of the solar collector 25 via a low-temperature molten salt pump 24.

[0031] refer to Figure 1 The second outlet of the low-pressure gas storage container 3 is connected to the low-pressure second outlet valve 28, which is connected to the cold end inlet of the first heat accumulator 2. The cold end outlet of the first heat accumulator 2 is connected to the low-pressure expander 29. The tail gas at the outlet of the low-pressure expander 29 is passed into the low-temperature molten salt storage tank 23 for tail heat recovery. The second outlet of the medium-pressure gas storage container 7 is connected to the medium-pressure second outlet valve 30. The second outlet valve 30 is connected to the cold end inlet of the second heat accumulator 6. The cold end outlet of the second heat accumulator 6 is connected to the medium-pressure expander 31. The tail gas at the outlet of the medium-pressure expander 31 is passed into the low-temperature molten salt storage tank 23 for tail heat recovery. The outlet of the high-pressure gas storage container is connected to the high-pressure gas outlet valve 17, the high-pressure gas outlet valve 17 is connected to the second heat accumulator 6 and the first heat accumulator 2 and then to the first high-pressure expander 18, the outlet of the first high-pressure expander 18 is connected to the cold end inlet of the first molten salt heat exchanger 19, the cold end outlet of the first molten salt heat exchanger 19 is connected to the second high-pressure expander 20, the outlet of the second high-pressure expander 20 is connected to the cold end inlet of the second molten salt heat exchanger 21, the cold end outlet of the second molten salt heat exchanger 21 is connected to the third high-pressure expander 22, and the exhaust gas at the outlet of the third high-pressure expander 22 is passed into the low-temperature molten salt storage tank 23 for exhaust heat recovery.

[0032] refer to Figure 1 、 Figure 2 and Figure 3 There is a conical guide plate 36 with holes on the top of the low-temperature molten salt storage tank 23. The circular holes on the guide plate become larger and larger with the radial direction. The radius of the two circles closest to the central axis of the cone is the same. The radius of the circle farther away from the central axis is 1.5 times larger than the radius of the previous circle closer to the central axis. It is used to average the probability of molten salt falling from various places above, preventing the middle part of the heat exchange pipe below from being constantly washed by molten salt, so that the heat exchange pipe can be used for a longer time.

[0033] refer to Figure 2 、 Figure 4 and Figure 5 The heat exchange tubes 37 in the low-temperature molten salt storage tank 23 are arranged in a serpentine shape, which is mainly used to recover the waste heat of the exhaust gas to heat the low-temperature molten salt and prevent it from solidifying. The external insulation layer 38 of the low-temperature molten salt storage tank 23 is composed of three layers of insulation materials, including the first insulation material 39 on both sides, the third insulation material 41 and the wavy second insulation material 40 in the middle, which are used to enhance the thermal insulation performance of the low-temperature molten salt storage tank 23 and the compressive resistance of the insulation layer.

[0034] Based on the above system, the present invention provides a composite energy storage system for the transformation of waste power plants, including the following steps:

[0035] During the presetting stage, the liquid levels in the two water tanks are kept level by adjusting the water pump 13 .

[0036] During the energy storage phase, the low-pressure compressor is connected to the atmosphere, opening the low-pressure first outlet valve 4 and the medium-pressure first outlet valve 8, while closing the low-pressure second outlet valve 28, the medium-pressure second outlet valve 30, and the high-pressure outlet valve 17. The opening or closing of the inlet and exhaust valves depends on the compression process. Air is compressed by the low-pressure compressor 1 to the pressure of the low-pressure gas storage vessel 3, then cooled by the first heat accumulator 2 before entering the low-pressure gas storage vessel 3. It then enters the medium-pressure compressor 5, where it is compressed to the pressure of the medium-pressure gas storage vessel 7. It then enters the medium-pressure gas storage vessel 7 and enters the dual-tank near-isothermal compression device for further compression. First, the first air inlet valve 9 is opened, the second air inlet valve 10, the first exhaust valve 14, and the second exhaust valve 15 are closed, and air enters the first high-pressure water tank 11. The water pump 13 presses the water in the first high-pressure water tank 11 from the bottom into the second high-pressure water tank 12. After the air in the second high-pressure water tank 12 is compressed to the pressure of the high-pressure gas storage container 16, the second exhaust valve 15 is opened to allow the high-pressure air to enter the high-pressure gas storage container 16 for storage. After the gas level in the second high-pressure water tank 12 is equal to the clearance height, the first air inlet valve 9 and the second exhaust valve 15 are closed. Then, the second air inlet valve 10 is opened, and the water pump presses the water in the second high-pressure water tank 12 from the bottom into the first high-pressure water tank 11. After the air in the first high-pressure water tank 11 is compressed to the pressure of the high-pressure gas storage container 16, the first exhaust valve 14 is opened to allow the high-pressure air to enter the high-pressure gas storage container 16 for storage. After the gas level in the first high-pressure water tank 11 is equal to the clearance height, the second air inlet valve 10 and the first exhaust valve 14 are closed, and then the first air inlet valve 9 is opened. This cycle continues until the high-pressure gas storage vessel 16 is full of gas, at which point all valves in the dual-tank near-isothermal compression device 42 are closed, halting operation. Similarly, when the low-pressure gas storage vessel 3 and the medium-pressure gas storage vessel 7 are filled with air corresponding to their respective pressures, all valves are closed. In the solar molten salt energy storage system, the molten salt in the low-temperature molten salt storage tank 23 is pumped by a low-temperature molten salt pump 24 to the solar thermal collector 25, where it is then stored in the high-temperature molten salt storage tank.

[0037] During the energy release stage, the compressed air coming out of the low-pressure gas storage container 3 and the medium-pressure gas storage container 7 flows through the first heat accumulator 2 and the second heat accumulator 6 respectively to be heated, and then enters the low-pressure expander 29 and the medium-pressure expander 31 respectively to perform work and generate electricity. The air after work enters the low-temperature molten salt tank 23 to heat the low-temperature molten salt to prevent the molten salt in the low-temperature tank from being too low and causing the molten salt to solidify. The air after heat exchange is discharged into the atmosphere. After coming out of the high-pressure gas storage container 16, the gas first enters the second heat accumulator 6 and the first heat accumulator 2 for heating, then enters the first high-pressure expander 18 to perform work, and then enters the first molten salt heat exchanger 19 to exchange heat with the high-temperature molten salt at the hot end. The temperature is raised to high-temperature and high-pressure air and then enters the second high-pressure expander 20 to expand and generate work. The air after work enters the second molten salt heat exchanger 21 to exchange heat with the high-temperature molten salt at the hot end. After heating to a high temperature state again, it enters the third high-pressure expander 22 to perform work and generate electricity, completing the energy release. The high-temperature molten salt pump 27 transports the high-temperature molten salt to the first molten salt heat exchanger 19 and the second molten salt heat exchanger 21. The molten salt after heat exchange is returned to the low-temperature molten salt tank 23 for storage. The air from the third high-pressure expander 22 enters the low-temperature molten salt tank 23, where it heats the low-temperature molten salt to prevent the molten salt in the low-temperature tank from freezing due to the low temperature. The air after heat exchange is discharged into the atmosphere.

[0038] The present invention transforms idle high-quality equipment in abandoned power plants. By evaluating the strength of pressure vessels in the power plants, the existing pressure-bearing pressure pipes and pressure vessels are used to construct a near-isothermal compressed air energy storage system. The solar molten salt energy storage system is coupled to heat the air after near-isothermal compression to solve the problem of low near-isothermal compressed air storage density. The heat accumulator and the double-tank near-isothermal compression device are used to decouple the thermal energy and pressure energy of the compressed air, thereby storing them separately, so that the thermal energy and pressure energy can be fully used as needed during energy release.

Claims

1. A composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling, characterized in that: It includes a multi-stage compressed air energy storage unit, a solar molten salt energy storage unit and an expansion generator set; each stage of the multi-stage compressed air energy storage unit is provided with a gas storage container and a heat accumulator, the hot side of the heat accumulator is connected to the compression device and the gas storage container, and the cold side of the heat accumulator is connected to the gas storage container and the expansion generator set, and the gas storage container adopts a waste thermal power plant pressure vessel and pipeline corresponding to its working pressure; the compressed air energy storage unit of the highest level pressure is provided with a double-tank near-isothermal compression device as compression power; the compressed air outlet of the multi-stage compressed air energy storage unit is connected to the expansion generator set The working fluid inlet of the expansion generator set includes a low-pressure expander (29), a medium-pressure expander (31) and a high-pressure expander set, and the low-pressure expander (29), the medium-pressure expander (31) and the high-pressure expander set are all connected to the generator; the working fluid outlets of the low-pressure expander (29), the medium-pressure expander (31) and the high-pressure expansion set are connected to the heat recovery inlet of the solar molten salt energy storage unit, a plurality of high-pressure expanders are arranged in the high-pressure expansion set, and a molten salt heat exchanger is arranged between the high-pressure expanders, the hot side of the molten salt heat exchanger is connected to the solar molten salt energy storage unit, and the cold side of the molten salt heat exchanger is connected to the high-pressure expander.

2. The composite energy storage system for waste power plant reconstruction based on thermal-pressure decoupling according to claim 1 is characterized in that: The multi-stage compressed air energy storage unit includes a compressor compressed air energy storage unit and a double-tank near-isothermal compressed air energy storage unit. The compressor compressed air energy storage unit includes a low-pressure compressor (1), a first heat accumulator (2), a low-pressure gas storage container (3), a medium-pressure compressor (5), a second heat accumulator (6) and a medium-pressure gas storage container (7). The air inlet of the low-pressure compressor (1) is connected to the atmosphere. The hot end of the low-pressure compressor (1), the first heat accumulator (2), the low-pressure gas storage container (3), the medium-pressure compressor (5), the hot end of the second heat accumulator (6), the medium-pressure storage container (7) The gas container (7), the double-tank near-isothermal compressed air energy storage unit and the high-pressure gas storage container (16) are connected in sequence, and the outlet of the high-pressure gas storage container (16), the cold end of the first heat accumulator (2) and the cold end of the second heat accumulator (6) are connected in sequence; the cold end inlet and outlet of the first heat accumulator (2) are respectively connected to the outlet of the low-pressure gas storage container (3) and the working fluid inlet of the low-pressure expander (29), and the cold end inlet and outlet of the second heat accumulator (6) are respectively connected to the outlet of the medium-pressure gas storage container (7) and the working fluid inlet of the medium-pressure expander (31).

3. The composite energy storage system for waste power plant reconstruction based on thermal-pressure decoupling according to claim 1 is characterized in that: The solar molten salt energy storage unit comprises a solar collector (25), a high-temperature molten salt storage tank (26), a first molten salt heat exchanger (19), a second molten salt heat exchanger (21), and a low-temperature molten salt storage tank (23); the solar collector (25), the high-temperature molten salt storage tank (26), the hot end of the first molten salt heat exchanger (19), and the low-temperature molten salt storage tank (23) are connected in sequence, and the solar collector (25), the second molten salt heat exchanger (21), and the low-temperature molten salt storage tank (23) are connected in sequence; the outlet of the low-temperature molten salt storage tank (23) is connected to the inlet of the solar collector (25); the hot end outlets of the first molten salt heat exchanger (19) and the second molten salt heat exchanger (21) are connected to the low-temperature The top of the molten salt storage tank (23); the high-pressure expansion unit includes a first high-pressure expansion unit (18), a second high-pressure expansion unit (20) and a third high-pressure expansion unit (22); the working fluid inlet of the first high-pressure expansion unit (18) is connected to the outlet of the multi-stage compressed air energy storage unit as the working fluid inlet of the high-pressure expansion unit; the first high-pressure expansion unit (18), the cold end of the first molten salt heat exchanger (19), the second high-pressure expansion unit (20), the cold end of the second molten salt heat exchanger (21), the third high-pressure expansion unit (22) and the air inlet of the low-temperature molten salt storage tank (23) are connected in sequence, and the air inlet of the low-temperature molten salt storage tank (23) serves as the heat recovery inlet after the air of the expansion unit does work.

4. The composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling according to claim 3 is characterized in that: A heat-insulating layer is provided in the low-temperature molten salt storage tank (23), and the heat-insulating layer includes three layers of heat-insulating materials, each layer of heat-insulating materials has a thickness of 100-150 mm, the first heat-insulating material (39) and the third heat-insulating material (41) are 400-500 mm apart, and the second heat-insulating material (40) in the middle is provided in a wave shape, and each minimum wave unit is approximately a semi-ellipse, and the three vertices of the semi-ellipse intersect with the first or third heat-insulating material respectively, and the empty space in the middle is filled with air; a conical guide plate is provided on the top of the low-temperature molten salt storage tank (23), and a plurality of circular holes are provided on the conical guide plate along the circumferential direction, the radius of the two circles of circular holes close to the central axis of the conical guide plate is the same, and the radius of the remaining circles increases by 1.5 times as they go outward of the conical guide plate; the heat exchange pipe in the low-temperature molten salt storage tank (23) adopts a serpentine tube.

5. The composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling according to claim 1 is characterized in that: The low-pressure gas storage container (3) has a pressure resistance of 1 MPa and is transformed from the steam side space of the medium-pressure heater of the abandoned thermal power plant and the related steam extraction and drainage pipes, the deaerator and its related system pipes, the auxiliary steam system equipment pipes, the continuous and related system pipes, the boiler room industrial water pipes, the closed water system pipes, the original compressed air system pipes, the steam seal pipes of the steam turbine body, the steam turbine body drainage pipes and the circulating water pipes. By installing valves and pipes to connect the low-pressure containers in series and blocking the redundant outlets, the low-pressure gas storage container is transformed.

6. The composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling according to claim 1 is characterized in that: The medium-pressure gas storage vessel (7) has a pressure resistance of 3.9 MPa and is transformed from the reheater system, reheat cold section pipeline, high-pressure heater steam side space and related steam extraction and drainage pipeline, low-pressure heater water side space, condensate pipeline, and boiler fuel system pipeline of an old thermal power plant. The valve between the desuperheater and the high-pressure cylinder outlet is closed, a valve is installed between the reheater steam pipeline and the medium-pressure cylinder, and a connecting pipe is connected between the furnace top outlet header and the screen-type reheater inlet header to the high-pressure heater steam side space and steam extraction and drainage pipeline to transform it into a medium-pressure gas storage vessel.

7. The composite energy storage system for waste power plant reconstruction based on thermal-pressure decoupling according to claim 1 is characterized in that: The high-pressure gas storage container (16) with a pressure of 18 MPa is transformed from the economizer system, boiler drum, water cooling system, superheater, high-pressure heater water side space, main feed water pipeline, main steam pipeline, and boiler drum connecting high-pressure pipeline of an old thermal power plant. By controlling the opening and closing of existing valves and installing valves and pipelines, each system is transformed into a high-pressure gas storage container; the valve between the main steam pipeline and the high-pressure cylinder of the steam turbine is closed, and a three-way pipe is installed in the section where the check valve and electric gate valve are located between the single line on the left side of the boiler and the economizer inlet header, and connected to the main feed water pipeline, and the redundant outlet is blocked to transform it into a high-pressure gas storage container.

8. The composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling according to claim 1 is characterized in that: The double-tank type near-isothermal compressed air energy storage unit includes a high-pressure gas storage container (16) and a double-tank near-isothermal compression device (42). The double-tank near-isothermal compression device (42) includes a first high-pressure water tank (11), a second high-pressure water tank (12) and a water pump (13). The first high-pressure water tank (11) and the second high-pressure water tank (12) are connected in parallel. The tops of the first high-pressure water tank (11) and the second high-pressure water tank (12) are connected to the first air outlet pipe of the medium-pressure gas storage container (7). The tops of the first high-pressure water tank (11) and the second high-pressure water tank (12) are connected to the air inlet pipe of the high-pressure gas storage container (16). The bottoms of the first high-pressure water tank (11) and the second high-pressure water tank (12) are connected by the water pump (13) and the liquid delivery pipe. In the presetting stage, the liquid levels of the first high-pressure water tank (11) and the second high-pressure water tank (12) in the double-tank type near-isothermal compressed air energy storage unit remain consistent.

9. The method for operating a composite energy storage system for the transformation of waste power plants based on thermal-pressure decoupling according to any one of claims 1 to 8, characterized in that: The compressor compressed air energy storage unit and the double-tank near-isothermal compressed air energy storage unit are provided with a heat accumulator and a double-tank near-isothermal compression device to decouple the thermal energy and pressure energy of the compressed air and store them separately. The pressure energy after the air is compressed is stored in each corresponding gas storage container, and the thermal energy is stored in the heat accumulator. The solar molten salt energy storage unit heats the low-temperature molten salt to a high temperature and stores it. When the system releases energy, the compressed air flows through the heat accumulator and is heated and then enters the low-pressure expander (29), the medium-pressure expander (31) and the high-pressure expander group to generate power. The air after the work enters the low-temperature molten salt tank (23) to heat the low-temperature molten salt to prevent the molten salt in the low-temperature tank from being too low and causing the molten salt to solidify. The air after heat exchange is discharged into the atmosphere.

10. The operating method according to claim 9, characterized in that: The compressed air from the low-pressure gas storage container (3) and the medium-pressure gas storage container (7) flows through the first heat accumulator (2) and the second heat accumulator (6) to be heated and heated, and then enters the low-pressure expander (29) and the medium-pressure expander (31) to generate power. The air after the work enters the low-temperature molten salt tank (23) to heat the low-temperature molten salt to prevent the molten salt in the low-temperature tank from being too low and causing the molten salt to solidify. The air after heat exchange is discharged into the atmosphere; the gas in the high-pressure gas storage container (16) first enters the first heat accumulator (2) and the second heat accumulator (6) to be heated and heated, and then enters the first high-pressure expander (18) to perform work. The air after the work enters the first molten salt heat exchanger (19) to exchange heat with the high-temperature molten salt at the hot end at the cold end. After the temperature is increased to high-temperature and high-pressure air, it enters the second high-pressure expander (20) for expansion. The air after the work enters the second molten salt heat exchanger (21) to exchange heat with the high-temperature molten salt at the hot end at the cold end. After the temperature is raised to a high temperature state, the air enters the third high-pressure expander (22) to generate power. The air coming out of the third high-pressure expander (22) enters the low-temperature molten salt tank (23) to heat the low-temperature molten salt to prevent the molten salt in the low-temperature tank from being too low and causing the molten salt to solidify. The air after the heat exchange is discharged into the atmosphere to complete the energy release. The high-temperature molten salt pump (27) transports the high-temperature molten salt to the first molten salt heat exchanger (19) and the second molten salt heat exchanger (21). The molten salt after the heat exchange returns to the low-temperature molten salt tank (23) for storage. When there is sufficient sunlight, the low-temperature molten salt pump (24) transports the high-temperature molten salt to the solar collector (25) to heat it to a high temperature and store it in the high-temperature molten salt tank (26).

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