Compressed gas storage system and compressed gas storage method

Abstract

The present invention improves storage efficiency by effectively using, in a simple form, the storage volume of a compressed gas storage part in which a compressed gas is stored. Provided is a compressed gas storage system (100) for storing a compressed gas which has been compressed by a compressor, said system comprising: a compressed gas storage part (300) in which a compressed gas is stored; a buffer gas storage part (310) in which a buffer gas is stored; a first cooler (306) that cools the buffer gas; a first adjustment valve (307) that is provided between the first cooler and the buffer gas storage part; a second adjustment valve (309) that is provided between a first heater and the buffer gas storage part; a second heater (312) that heats the buffer gas inside of the buffer gas storage part; and a control unit (320) that at least controls the temperatures of the first cooler, the first heater, and the second heater, and the degrees of opening of the first adjustment valve and the second adjustment valve.

Description

Compressed gas storage system and compressed gas storage method

[0001] The present invention relates to a compressed gas storage system and a compressed gas storage method.

[0002] Power generation using renewable energy sources such as wind power and solar power depends on weather conditions, and therefore output can be unstable. For this reason, technologies have been developed to level output using energy storage devices such as compressed air energy storage (hereinafter also referred to as CAES) power generation devices. CAES power generation devices use a compressor to store electrical energy as compressed air in an accumulator tank, and then use an expander to convert the compressed air stored in the accumulator tank into electrical energy.

[0003] As related technologies relating to CAES power generation devices, Patent Documents 1 and 2 disclose CO ２ On the other hand, Patent Document 3 discloses an energy storage plant that uses CO 2 , which has a larger density change than air, as a working fluid to store electricity by compression and expansion. ２ This publication discloses a compressed air energy storage method in which the compressed air in the air storage unit is used as a buffer gas for pushing the compressed air to the outside.

[0004] JP 2023-514812 A JP 2023-518151 A JP 2023-172944 A

[0005] It is preferable to improve the storage efficiency of an air storage unit that stores compressed air for a CAES power generation system by more easily and effectively utilizing the storage volume. Also, there is a demand for improving the storage efficiency of compressed gases other than the compressed air for a CAES power generation system by simply and effectively utilizing the storage volume of the compressed gas storage unit that stores the compressed gas.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to improve storage efficiency by effectively utilizing the storage volume of a compressed gas storage unit that stores compressed gas in a simple manner.

[0007] One aspect of the present invention is a compressed gas storage system that stores compressed gas compressed by a compressor, comprising: a compressed gas storage unit that stores the compressed gas; a buffer gas storage unit that stores buffer gas that pushes the compressed gas out of the compressed gas storage unit in any of a supercritical state, a liquefied state, or a solid state; a first cooler that cools the buffer gas that is transferred from the compressed gas storage unit to the buffer gas storage unit; and a second heater that heats the buffer gas in any of a supercritical state, a liquefied state, or a solid state in the buffer gas storage unit.

[0008] According to one aspect of the present invention, by controlling the state change of the buffer gas transferred between the compressed gas storage section and the buffer gas storage section, the storage volume of the compressed gas storage section that stores the compressed gas can be effectively utilized in a simple manner, thereby improving storage efficiency.

[0009] Another aspect of the present invention is a method for storing compressed gas using a compressed gas storage system including a compressed gas storage unit that stores compressed gas and a buffer gas storage unit that stores buffer gas for pushing the compressed gas out of the compressed gas storage unit, the compressed gas storage system including a first cooler that cools the buffer gas transferred from the compressed gas storage unit to the buffer gas storage unit, and a second heater that heats the buffer gas in the buffer gas storage unit, and when filling the compressed gas into a compressed gas storage tank, the compressed buffer gas in the compressed gas storage tank is The buffer gas is cooled by a first cooler and transferred to the buffer gas storage unit, and stored in one of a supercritical state, a liquefied state, and a solid state. When the compressed gas filled in the compressed gas storage tank is discharged to the outside, the buffer gas stored in the buffer gas storage unit in one of a supercritical state, a liquefied state, and a solid state is heated by the second heater and vaporized, and the vaporized buffer gas is heated by the first heater to expand and transferred to the compressed gas storage tank, and the compressed gas filled in the compressed gas storage tank is discharged to the outside via flexible deformation of the diaphragm.

[0010] According to another aspect of the present invention, by controlling the state change of the buffer gas transferred between the compressed gas storage section and the buffer gas storage section, the storage volume of the compressed gas storage section that stores the compressed gas can be effectively utilized in a simple manner, thereby improving storage efficiency.

[0011] FIG. 1 is a block diagram showing a schematic configuration of the entire CAES power generation device to which a compressed gas storage system according to one embodiment of the present invention is applied. FIG. 2 is an explanatory diagram showing a schematic configuration of a main part of a compressed gas storage system according to one embodiment of the present invention. FIG. 3 is an explanatory diagram showing an operation of one step of a compressed gas storage method by a compressed gas storage system according to one embodiment of the present invention. FIG. 4 is an explanatory diagram showing an operation of one step of a compressed gas storage method by a compressed gas storage system according to one embodiment of the present invention. FIG. 5 is an explanatory diagram showing an operation of one step of a compressed gas storage method by a compressed gas storage system according to one embodiment of the present invention. FIG. 6 is an explanatory diagram showing an operation of one step of a compressed gas storage method by a compressed gas storage system according to one embodiment of the present invention. FIG. 7 is an explanatory diagram showing an operation of one step of a compressed gas storage method by a compressed gas storage system according to one embodiment of the present invention.

[0012] The following describes in detail preferred embodiments of the present invention. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims, and not all of the configurations described in the embodiments are necessarily essential as means for solving the problems of the present invention.

[0013] In the following description, terms indicating directions such as "upper," "lower," "left," and "right" are used for convenience of explanation and do not limit the method or manner of use. Terms such as "first" and "nth" (n is an integer) following "first" in this specification and claims are used as identifying terms to distinguish different elements and do not indicate a particular order or superiority or inferiority.

[0014] The schematic configuration of a CAES power generation system to which a compressed gas storage system according to one embodiment of the present invention is applied will be described with reference to the drawings. Fig. 1 is a block diagram showing the schematic configuration of the entire CAES power generation system to which a compressed gas storage system according to one embodiment of the present invention is applied. Note that this embodiment shows an aspect in which compressed air used for power generation of the CAES power generation system is stored as compressed gas stored in the compressed gas storage system.

[0015] The compressed gas storage system 100 of this embodiment is a system that stores compressed gas compressed by a compressor. The compressed gas storage system 100 shown in Fig. 1 shows an application example in which the compressed gas storage system 100 stores, as compressed gas, compressed air used to rotate the turbine of the generator 210 of the CAES power generation system 1 to generate electricity. Note that in this specification, the compressed gas storage system 100 refers to the portion of the CAES power generation system 1 shown in Fig. 1 , excluding the generator 210.

[0016] The CAES power generation system 1 is configured to use compressors 120 and 130 in the compression process to store electrical energy as compressed air in compressed air storage unit 300. The CAES power generation system 1 is configured to use expanders 220 and 230 in the expansion process to expand the compressed air stored in compressed air storage unit 300 and rotate the turbine of generator 210 to convert the air into electrical energy. In this way, the CAES power generation system 1 goes through the compression process and expansion process to smooth out output fluctuations of power generation equipment that generates electricity using renewable energy and supply power to the power grid, and also supply power to the power grid in accordance with fluctuations in power generation demand.

[0017] As shown in FIG. 1 , the CAES power generation system 1 includes a low-pressure compressor 120, a high-pressure compressor 130, a heat storage tank 160, an aftercooler 150, a high-temperature water tank 330, a low-temperature water tank 340, a compressed air storage unit 300, a buffer gas storage unit 310, a low-pressure expander 220, a high-pressure expander 230, a regenerative heat exchanger 260, a first cooler 306, a first adjustment valve 307, a first heater 308, a second adjustment valve 309, a second heater 312, a chiller 313, a cooling pump 314, and a control unit 320.

[0018] The low-pressure compressor 120 and the high-pressure compressor 130 are configured to be driven by a motor 110 via a shaft 121, and have the function of compressing air 10 taken in from the atmosphere while sequentially increasing its pressure into compressed air. The compressed air pressurized by the low-pressure compressor 120 and the high-pressure compressor 130 is finally stored in a compressed air storage unit 300, which functions as a compressed gas storage unit for storing compressed gas, via an aftercooler 150 and a three-way valve 151. The heat of compression generated in the low-pressure compressor 120 and the high-pressure compressor 130 is removed by heat storage in a heat storage tank 160 (described later) and heat exchange in the aftercooler 150, respectively. In this compression process of compressing the air 10, as described later, a buffer gas isolated from the compressed air is also compressed at the same time, and the buffer gas is pushed out of a compressed air storage tank 301 of the compressed air storage unit 300 by the pressure of the compressed air.

[0019] The heat of compression from the low-pressure compressor 120 is temporarily stored in the heat storage tank 160 to be reused in the expansion process by the expanders 220, 230. In this embodiment, the heat storage tank 160 is a pressure-resistant container filled with a granular solid made of small-diameter rock as a heat medium, and a direct heat transfer method is applied in which high-temperature air from the low-pressure compressor 120 is sent into the top of the heat storage tank, but the heat of compression may also be stored by transferring the heat to a fluid such as thermal oil through the heat transfer surface of a heat exchanger.

[0020] Because the thermal energy stored in the heat storage tank 160 is used in the immediately preceding expansion process, the temperature of the heat storage tank 160 is lower at the start of the compression process than when the heat of compression was stored. During the compression process, the amount of heat stored in the heat storage tank 160 increases over time, and the temperature boundary line between the high-temperature side and the low-temperature side of the heat medium, which was initially at the top of the heat storage tank 160, gradually moves toward the bottom. In this way, the heat of compression generated during the compression process is removed, lowering the temperature of the compressed air, and at the same time, the heat is stored in the heat storage tank 160. During the expansion process, in contrast to the compression process, low-temperature air is sent to the bottom of the heat storage tank 160, where it is heated by the heat stored in the heat storage tank 160 and discharged from the top of the heat storage tank 160. The heat recovered here is used to warm the air introduced into the high-pressure expander 230 during the expansion process, as described below.

[0021] The air cooled from the low-pressure compressor 120 through the heat storage tank 160 is guided to the high-pressure compressor 130 and stored in the compressed air storage unit 300 via the aftercooler 150. Low-temperature water from the low-temperature water tank 340 is used to remove the heat of compression in the aftercooler 150. In this embodiment, as described below, the volume of the buffer gas changes due to heating and cooling. The heat of compression removed in the aftercooler 150 is used, for example, to heat low-temperature water to generate high-temperature water, which is then stored in the high-temperature water tank 330. As described below, the high-temperature water stored in the high-temperature water tank 330 is used as a heat source for the first heater 308, which heats the low-temperature fluid resulting from the reduction in volume of the buffer gas as it is cooled, in the expansion process. In this embodiment, the high-temperature water stored in the high-temperature water tank 330 is also used as a heat source for the second heater 312, which heats the buffer gas stored in the buffer gas storage unit 310 in a supercritical, liquid, or solid state.

[0022] The low-temperature water required for heat removal in the aftercooler 150 is generated by a temperature drop caused by heat exchange between the high-temperature water and the low-temperature fluid in the first heater 308, which functions as a heat exchanger, as described below. The low-temperature water is stored in a low-temperature water tank 340 and used by circulating alternately between the low-temperature water tank 340 and the high-temperature water tank 330. Note that the supply of cooling water 30, 31 to the low-temperature water tank 340 is performed, for example, via three-way valves 331, 341 arranged between the low-temperature water tank 340 and the first cooler 306, which functions as a heat exchanger, and between the high-temperature water tank 330 and the first heater 308, respectively.

[0023] The compressed air storage unit 300 has a function of storing compressed air obtained by compressing the air 10 with the compressors 120 and 130. In this embodiment, the compressed air storage unit 300 is configured by arranging compressed air storage tanks 301 formed of a plurality of parallel, straight steel pipes or steel containers, as shown in the area surrounded by a dotted line in Fig. 1. Note that in this embodiment, the compressed air storage unit 300 has a vertical configuration in which the vertically oriented compressed air storage tanks 301 are arranged in parallel, as shown in Fig. 1, but it may also have a horizontal configuration.

[0024] The compressed air storage unit 300 is a necessary facility in common to various CAES systems, such as adiabatic, non-adiabatic, or a hybrid of both. In this embodiment, the compressed air storage unit 300 is described as a compressed air storage tank 301 configured with a steel pipe or a steel container, as an example, but the present invention can also be applied to CAES systems equipped with a compressed air storage unit 300 having a compressed air storage tank 301 configured with a container other than steel. Furthermore, the facility configuration and operating method other than the compressed air storage unit 300 of the non-adiabatic CAES system shown in FIG. 1 can be appropriately applied to this embodiment.

[0025] In this embodiment, a film-like partition 302 (see FIG. 2) is disposed in the compressed air storage tank 301 to separate the buffer gas from the air, thereby forming a partial space and preventing mixing of the two, allowing the air to be selectively discharged outside the system. In this way, the volumetric utilization efficiency of the space in the compressed air storage tank 301 of the compressed air storage unit 300 can be improved, and the net amount of stored air can be increased. The compressed air storage unit 300 of this embodiment will be described in detail later.

[0026] The buffer gas storage unit 310 has a function of storing the buffer gas, which is compressed air stored as compressed gas and pushed out from the compressed air storage unit 300, in any of a supercritical state, a liquefied state, or a solid state stored in a high-density state. In this embodiment, the buffer gas storage unit 310 is configured by arranging buffer gas storage tanks 311 formed of a plurality of parallel, straight steel pipes or steel containers, as shown in the area surrounded by a dotted line in FIG. 1. Note that in this embodiment, the buffer gas storage unit 310 has a vertical configuration in which vertical buffer gas storage tanks 311 are aligned in parallel, as shown in FIG. 1, but it may also have a horizontal configuration.

[0027] Furthermore, because the buffer gas storage tanks 311 of the buffer gas storage unit 310 store the buffer gas in any one of a supercritical state, a liquid state, or a solid state, the required volume is smaller than that of the compressed air storage tanks 301 of the compressed air storage unit 300. Therefore, in this embodiment, in order to save space and reduce costs in the compressed gas storage system 100 and the CAES power generation apparatus 1, it is possible to install fewer buffer gas storage tanks 311 than compressed air storage tanks 301, so that the ratio of the number of buffer gas storage tanks 311 to the number of compressed air storage tanks 301 is, for example, 1:2, when the volumes of the buffer gas storage tanks 311 and the compressed air storage tanks 301 are the same. Note that the ratio of the number of buffer gas storage tanks 311 to the compressed air storage tanks 301 is not limited to 1:2 and may be, for example, 1:5. Furthermore, when the volume of the buffer gas storage tanks 311 is smaller than that of the compressed air storage tanks 301, the number of the buffer gas storage tanks 311 and the compressed air storage tanks 301 may be the same.

[0028] In this embodiment, carbon dioxide or a mixed gas containing carbon dioxide is used as the buffer gas, which acts as an elastic buffer medium for the air inside the container during the air inlet / outlet process, and whose volume changes significantly compared to air during the compression and expansion processes associated with temperature changes. Carbon dioxide is a preferred buffer gas because it can condense and expand in a relatively easy-to-produce temperature range and forms a fluid whose volume difference between its gas and liquid states is large. However, a gas containing as its main component another gas, such as ammonia, which can condense and expand in a relatively easy-to-produce temperature range and whose volume difference between its gas and liquid states is large may also be used. A detailed description of the buffer gas storage unit 310 of this embodiment will be provided later.

[0029] In this embodiment, simultaneously with the compression of the air, the buffer gas is pressurized by the pressure of the compressed air inside the compressed air storage tank 301. At this time, the CO ２ When the critical pressure of the buffer gas is exceeded and the temperature is further decreased, the volume of the buffer gas is significantly reduced. The buffer gas introduced into the compressed air storage tank 301 may be cooled by guiding the buffer gas to the outside of the compressed air storage tank 301 and then cooling it to reduce its volume. As the amount of air introduced into the compressed air storage tank 301 increases, the volume of the partial space into which the compressed air is introduced, formed by the diaphragm 302 provided in each compressed air storage tank 301, approaches nearly the same as the internal space of the compressed air storage tank 301. Therefore, when each compressed air storage tank 301 is filled with compressed air and the buffer gas is discharged outside the compressed air storage tank 301, for example, if the diaphragm 302 has a shape and size similar to the internal surface of the compressed air storage tank 301, the diaphragm 302 will be in close contact with the internal surface of the compressed air storage tank 301. In this embodiment, the diaphragm 302 is in close contact with the inner surface, including the bottom surface 301b, of the compressed air storage tank 301, but depending on the shape and size of the diaphragm 302, it may be configured so that it is not in complete contact.

[0030] In the expansion process of the compressed air, the fluid is pressurized by the compressed air and further cooled to reduce the volume of the buffer gas. The fluid is heated and vaporized, and is introduced again into one side of the diaphragm 302 (see Figure 2) in each compressed air storage tank 301, returning the buffer gas to its state before the compression process.

[0031] When electricity is needed, the high-pressure expander 230 and the low-pressure expander 220 are driven while expanding the compressed air stored in the compressed air storage unit 300. In the expansion process in which the compressed air stored in the compressed air storage unit 300 is expanded, the pressure of the compressed air stored in the compressed air storage unit 300 decreases as the compressed air is discharged. Therefore, in the expansion process, the space occupied by the air in the compressed air storage unit 300 needs to be gradually reduced, while the space occupied by the buffer gas needs to be gradually expanded correspondingly for replacement. Furthermore, in the expansion process, there is an initial phase in which the compressed air is discharged without replacement of the compressed air space with the buffer gas space.

[0032] Therefore, in this embodiment, the carbon dioxide that serves as the buffer gas in one of a supercritical state, a liquefied state, and a solid state, which is cooled and stored as a fluid with a reduced volume in the buffer gas storage unit 310 after the compression process, must be heated and then introduced back into the compressed air storage unit 300. Since the pressure of the compressed air storage unit 300 is reduced to 5 (MPa), if carbon dioxide is used as the buffer gas during the expansion process, the buffer gas becomes a low-temperature gas-liquid multiphase fluid. To use this gas-liquid multiphase fluid as the buffer gas, the thermal energy stored in the high-temperature water tank 330 during the compression process is used as its heating source.

[0033] This low-temperature multiphase fluid is heated by heat exchange with high-temperature water from the high-temperature water tank 330 in the first heater 308, which functions as a heat exchanger, and is sent as buffer gas to the compressed air storage unit 300. In this way, the air in the compressed air storage unit 300 is pushed out by the buffer gas, and eventually, the space occupied by all the air in the compressed air storage tank 301 is replaced by the space occupied by the buffer gas.

[0034] The compressed air discharged from the compressed air storage unit 300 is constantly maintained at a constant pressure (for example, 5 MPa) by a pressure reducing valve (not shown) and is guided to the high-pressure expander 230 via the rear part of the regenerative heat exchanger 260. The low-temperature compressed air leaving the compressed air storage unit 300 is heated in the regenerative heat exchanger 260 by high-temperature exhaust heat from the low-pressure expander 220 (described later). Next, this air is used as driving force to perform the first power recovery by the high-pressure expander 230. The high-pressure expander 230, together with the low-pressure expander 220, drives the generator 210 via a shaft 221.

[0035] The low-temperature air leaving the high-pressure expander 230 is led to the bottom of the heat storage tank 160, which stores the heat of compression generated in the low-pressure compressor 120 during the compression process. This air is directly heated by countercurrent contact with the granular solid heat storage material contained in the tank.

[0036] At the start of the compression process, the pressure of the compressed air storage unit 300 is set to, for example, 5 (MPa), and the temperature is set to 40 (°C). At this time, the gas density of carbon dioxide is 120 (kg / m ３ ). In the compression process, this gas in the compressed air storage unit 300 is compressed by the accumulated air pressure. The pressure in the compressed air storage unit 300 finally reaches 9 (MPa), and at the same time, the pressure of this gas also becomes equal to the air pressure. Since this gas in this state exceeds the critical pressure, it becomes a supercritical fluid and is cooled by cooling water 30 in the first cooler 306, which acts as a heat exchanger, lowering the temperature of this fluid to 35 (°C). The density of this material under these conditions is 630 (kg / m ３ ) and its volume decreases to 19% of the volume at the start of the compression process.

[0037] Meanwhile, during the expansion process of the stored compressed air, the air in the compressed air storage unit 300 is replaced with carbon dioxide, and almost the entire volume of the compressed air storage unit 300 is used. In conventional compressed air energy storage methods, the spatial volume utilization efficiency of the compressed air storage unit is often 40% or less. In contrast, in this embodiment, a buffer gas storage unit 310 is required in addition to the compressed air storage unit to store cooled fluid derived from the buffer gas. Even after offsetting this, the volume efficiency of the compressed air storage unit 300 is expected to be more than twice that of conventional methods. In other words, it is possible to store more than twice the amount of air in the same volume space.

[0038] The heated air exiting the top of the heat storage tank 160 returns to the front section of the regenerative heat exchanger 260, where it is further heated and led to the combustor 240. The high-temperature gas leaving the combustor 240, including the fuel 20 consumed here, is led to the low-pressure expander 220, where power is recovered again. The exhaust gas from this combustor 240 has a very high temperature, and as described above, thermal energy above a predetermined temperature is recovered as the temperature drops from high to low through the front and rear sections of the regenerative heat exchanger 260, and the air 11 that has passed through the regenerative heat exchanger 260 is released into the atmosphere.

[0039] In this embodiment, cooling and heating of carbon dioxide as a buffer gas is required to accommodate changes in the volume of the buffer gas used in the compressed air storage unit 300 due to state changes. In this embodiment, as shown in FIG. 1 , this cooling and heating is performed by leading the carbon dioxide to the outside of the compressed air storage unit 300, which is made up of multiple steel pipes. In this case, a container is required to store the carbon dioxide that has become a fluid after its volume has been reduced by cooling during the air compression process. The carbon dioxide discharged from the compressed air storage unit 300 is cooled by cooling water in a first cooler 306, which serves as a heat exchanger. At this time, a three-way valve 341 is switched to send cooling water 30 from a cooling tower (not shown) to this first cooler 306.

[0040] The control unit 320 has a function of controlling all or part of the components of the CAES power generation apparatus 1, including the compressed gas storage system 100. The control unit 320 includes components such as a processor 321, a memory unit 322, and a connector 323, which are connected to each other via a bus. The processor 321 includes, for example, a central processing unit (CPU). The memory unit 322 includes, for example, a hard disk, a ROM in which programs and the like are stored, and a RAM as a work area. The control unit 320 communicates with the components of the compressed gas storage system 100 via the connector 323. The control unit 320 may further include other components, such as a display device such as a liquid crystal display or a touch panel, and an input device such as a keyboard, buttons, or a touch panel. The operation of the control unit 320 may be realized, for example, by having the processor 321 execute a program stored in the memory unit 322.

[0041] The inventor has discovered that in each of the above-described compressed gas storage systems 100 and CAES power generation devices 1 including the compressed gas storage system 100, by controlling the change in state of the buffer gas transferred between the compressed air storage section 300 and the buffer gas storage section 310, the storage volume of the compressed air storage section 300, which functions as a compressed gas storage section for storing compressed gas, can be effectively utilized in a simple manner, thereby improving storage efficiency.

[0042] Based on the above-described new findings, in the compressed gas storage system 100 of this embodiment, the control unit 320 controls the operation of the first cooler 306, the first regulating valve 307, the first heater 308, the second regulating valve 309, the second heater 312, the chiller 313, and the cooling pump 314 in the compressed gas storage system 100. Details of the operation control by the control unit 320 will be described later.

[0043] Next, details of the main parts of a compressed gas storage system according to one embodiment of the present invention will be described with reference to the drawings. Figure 2 is an explanatory diagram showing the schematic configuration of the main parts of a compressed gas storage system according to one embodiment of the present invention. For simplicity of explanation, Figure 2 shows a case where the compressed air storage unit 300 and the buffer gas storage unit 310 are each provided with one compressed air storage tank 301 and one buffer gas storage tank 311.

[0044] The compressed gas storage system 100 of this embodiment is a system that stores compressed gas compressed by compressors 120, 130 (see Figure 1), and as shown in Figure 2, is equipped with a compressed air storage unit 300, a buffer gas storage unit 310, a first cooler 306, a first adjustment valve 307, a first heater 308, a second adjustment valve 309, the buffer gas storage unit 310, a second heater 312, a chiller 313, a cooling pump 314, and a control unit 320.

[0045] The compressed air storage unit 300 has a function of storing compressed gas compressed by the compressors 120 and 130 (see FIG. 1 ). The compressed air storage unit 300 includes a compressed air storage tank 301 that functions as a cylindrical compressed gas storage tank with both ends closed, and a flexible and deformable diaphragm 302 that is separably provided to isolate a space on one end side from a space on the other end side within the compressed air storage tank 301.

[0046] The compressed air storage tank 301 serves as a pressure accumulation vessel and is preferably made of a pressure-resistant metal such as carbon steel or stainless steel. The cross-sectional shape of the compressed air storage tank 301 is preferably circular, but it can also be elliptical, polygonal, or any other desired shape depending on conditions such as the installation location. The dimensions of the compressed air storage tank 301 can be set appropriately depending on conditions such as the required compressed air storage volume and the installation location. For example, when the cross-sectional shape in the width direction is circular, a tank with a diameter of 0.8 to 2.0 m and a height of 20 to 40 m can be used, but is not limited to these dimensional ranges.

[0047] The compressed air storage tank 301 has a cylindrical side surface 301a, a ceiling surface 301c that closes the upper end of the side surface 301a, and a bottom surface 301b that closes the lower end of the side surface 301a. The compressed air storage tank 301 has a first opening 301d on the ceiling surface 301c side through which compressed air can flow in and out as compressed gas, and a second opening 301e on the bottom surface 301b side through which buffer gas can flow in and out. The first opening 301d of the compressed air storage tank 301 is provided with a compressed air adjustment valve 305 that can adjust the flow rate and flow velocity of the inflow and outflow of compressed air. Note that in this embodiment, the ceiling surface 301c and the bottom surface 301b of the compressed air storage tank 301 have a substantially horizontal, planar shape, but may have other shapes, such as a hemispherical shape.

[0048] Compressed air storage tank 301 is separated into an outer space 301f surrounded by outer surface 302a of partition membrane 302 and ceiling surface 301c and side surface 301a of compressed air storage tank 301, and an inner space 301g surrounded by inner surface 302b of partition membrane 302 and bottom surface 301b of compressed air storage tank 301, with gas transfer blocked by partition membrane 302. By blocking the inside of compressed air storage tank 301 with partition membrane 302 in this way, compressed air storage unit 300 allows inner space 301g of partition membrane 302 to function as a supply space for buffer gas, and outer space 301f of partition membrane 302 to function as a supply space (storage space) for compressed air.

[0049] 2, the diaphragms 302 are hung by spring hangers 303 from the ceiling surface 301c of the compressed air storage tank 301 with their upper ends bundled together and sealed, and their lower ends are fixed by ring-shaped fixtures 304 so as to be in close contact with the side surface 301a near the bottom surface 301b of the compressed air storage tank 301 with their lower ends open and facing the bottom surface 301b. Note that the fixing location of the lower ends of the diaphragms 302 may be on the outer edge side of the bottom surface 301b of the compressed air storage tank 301, and the fixing method of the lower ends of the diaphragms 302 is not limited to fixation by the ring-shaped fixtures 304, and may be fixed in other ways, for example, by screws or adhesive.

[0050] The diaphragm 302 is not breathable, and when it is hung from the ceiling surface 301c of the compressed air storage tank 301 with its upper end gathered and closed, its lower end is maintained by its own weight in a skirt-like hanging state while in contact with the side surface 301a near the bottom surface 301b of the compressed air storage tank 301. The diaphragm 302 is made of a flexible material selected from a synthetic resin film, a rubberized cloth, and a combination thereof, and has a mass per unit area of ​​500 g / m. 2 It is preferable to use the above.

[0051] The buffer gas storage unit 310 is composed of a buffer gas storage tank 311, which is formed from a straight steel pipe or a steel container and has a function of storing buffer gas in any of a supercritical state, a liquefied state, or a solid state, and has both ends closed. As in this embodiment, a minimum liquid level may be created in the buffer gas storage unit 310 for temperature control during standby. In this case, an appropriate amount of liquefied buffer gas is left in the buffer gas storage tank 311, for example, up to a height of about 5 to 10% from the bottom.

[0052] If the buffer gas is not liquefied, the gas in the buffer gas storage tank 311 is extracted, cooled in a heat exchanger, and returned to the buffer gas storage tank 311, and the cooled gas is used to lower the temperature in the buffer gas storage tank 311. However, extracting gas is not as easy as extracting liquid by gravity, and a gas heat exchanger has a large transfer surface area, making it inefficient. For this reason, in this embodiment, the liquefied buffer gas remaining in the buffer gas storage tank 311 is used as a refrigerant to cool the storage tank, enabling efficient degassing. Note that the level of the liquefied buffer gas should be an appropriate level that ensures a liquid volume greater than the piping volume of the cooling line so that the pump does not suck in gas and run idle.

[0053] As shown in FIG. 2, a first cooler 306, a first regulating valve 307, a first heater 308, and a second regulating valve 309 are provided between the compressed air storage unit 300 and the buffer gas storage unit 310.

[0054] The first cooler 306 has a function of cooling the buffer gas transferred from the compressed air storage unit 300 to the buffer gas storage unit 310 during the compression process. The first cooler 306 cools the buffer gas using, for example, cooling water 30 (see FIG. 1 ) supplied from the outside. Note that the cooling of the buffer gas by the first cooler 306 is not limited to the cooling water 30 supplied from the outside, and may be, for example, supplied with cooling water stored in a low-temperature water tank 340, cooled by an air cooler, or cooled by other general refrigerants such as brine, hydrocarbons, or other liquefied gases.

[0055] The first regulating valve 307 is provided between the first cooler 306 and the buffer gas storage unit 310. The first regulating valve 307 functions as a pressure regulating valve that regulates the pressure of the buffer gas transferred from the compressed air storage unit 300 to the buffer gas storage unit 310 during the compression process by adjusting its opening to a desired value. In this manner, by providing the first regulating valve 307 downstream of the first cooler 306, it becomes possible to switch on / off the transfer of the buffer gas cooled in the first cooler 306 to the buffer gas storage unit 310, and to adjust the flow rate and pressure of the cooled buffer gas when transferred to a desired value. Note that, in this embodiment, the first regulating valve 307 is provided downstream of the first cooler 306, but it may be provided at any other appropriate position between the compressed air storage unit 300 and the buffer gas storage unit 310, such as upstream of the first cooler 306.

[0056] The first heater 308 has a function of heating the buffer gas transferred from the buffer gas storage unit 310 to the compressed air storage unit 300 during the expansion process. The first heater 308 heats the buffer gas discharged from the buffer gas storage unit 310 using high-temperature water supplied from the high-temperature water tank 330 (see FIG. 1). The first heater 308 can be set to an appropriate temperature depending on the gas characteristics and operating concept of the buffer gas to be transferred. Note that the heating of the buffer gas by the first heater 308 is not limited to the high-temperature water supplied from the high-temperature water tank 330 (see FIG. 1), and may be performed using, for example, an air heater, high-temperature steam, an electric heater, or excess heat from combustion exhaust heat in other process systems.

[0057] The second regulating valve 309 is provided between the first heater 308 and the buffer gas storage unit 310. The second regulating valve 309 functions as a pressure regulating valve that regulates the pressure of the vaporized buffer gas transferred from the buffer gas storage unit 310 to the compressed air storage unit 300, which functions as a compressed gas storage unit, during the expansion process by adjusting the opening degree to a desired value. In this way, by providing the second regulating valve 309 upstream of the first heater 308, it becomes possible to vaporize the buffer gas in any of a supercritical state, a liquefied state, and a solid state in the buffer gas storage unit 310 heated by the second heater 312, and then to switch on and off the transfer of the vaporized buffer gas to the compressed air storage unit 300, and to adjust the flow rate and pressure of the vaporized buffer gas during transfer to desired values. In this embodiment, the second adjustment valve 309 is provided upstream of the first heater 308, but it may be provided at any other appropriate position, such as downstream of the first heater 308, as long as it is between the buffer gas storage unit 310 and the compressed air storage unit 300.

[0058] In this embodiment, to adjust the temperature of the buffer gas in the buffer gas storage unit 310, a second heater 312 serving as a heating means and a chiller 313 serving as a cooling means are provided in parallel, as shown in FIG. 2 . The second heater 312 heats and vaporizes the buffer gas in any of the supercritical, liquefied, and solid states during the expansion stroke. Thus, the second heater 312 heats and vaporizes the buffer gas in any of the supercritical, liquefied, and solid states, and then transfers the vaporized buffer gas from the buffer gas storage unit 310 to the compressed air storage unit 300, thereby discharging the compressed air stored in the compressed air storage unit 300 from the compressed air storage unit 300. In this embodiment, the buffer gas heated and vaporized by the second heater 312 is returned to the top side of the buffer gas storage unit 310. However, the buffer gas may be transferred directly to the first heater 308 via the second adjustment valve 309 without being returned to the buffer gas storage unit 310.

[0059] The chiller 313 has a function of continuously cooling the gaseous buffer gas remaining in the buffer gas storage unit by circulating the buffer gas in a supercritical, liquefied, or solid state using a cooling pump 314. The buffer gas storage unit 310 stores buffer gas in a supercritical, liquefied, or solid state. However, if the buffer gas storage tank 311 is filled with liquid, and the temperature of the buffer gas storage tank 311 rises, excessive pressure will be applied to the buffer gas storage tank 311 due to thermal expansion of the liquid, which may result in damage to the buffer gas storage tank 311. For this reason, the chiller 313 is provided in parallel to the buffer gas storage unit 310 as a safety device to prevent damage to the buffer gas storage tank 311.

[0060] As described above, the control unit 320 has a function of controlling all or part of the components of the compressed gas storage system 100. In this embodiment, the control unit 320 has a function of controlling various operations of the first cooler 306, the first regulating valve 307, the first heater 308, the second regulating valve 309, the second heater 312, the chiller 313, and the cooling pump 314.

[0061] Specifically, when filling the compressed gas into the compressed air storage unit 300 in the compression process, the control unit 320 controls the first regulating valve 307 to be closed before filling the compressed gas. Then, the control unit 320 controls the first regulating valve 307 to be opened, and the compressed buffer gas in the compressed air storage tank 301 is cooled by the first cooler 306 and then transferred to the buffer gas storage unit 310, and the buffer gas is stored in any one of a supercritical state, a liquefied state, and a solid state.

[0062] Meanwhile, when discharging the compressed gas filled in the compressed air storage unit 300 to the outside during the expansion stroke, the control unit 320 controls the buffer gas stored in the buffer gas storage unit 310 in any one of a supercritical state, a liquefied state, and a solid state to be heated by the second heater 312 and then vaporized. The control unit 320 then controls the aperture of the second adjustment valve 309 to open the second adjustment valve 309, heat the vaporized buffer gas by the first heater 308, expand it, and transfer it to the compressed air storage unit 300. The control unit 320 then controls the diaphragm 302 to be flexible and deformed so that the compressed air filled in the compressed air storage tank 301 is discharged to the outside.

[0063] As described above, in this embodiment, by controlling the state change of the buffer gas transferred between the compressed air storage unit 300, which functions as a compressed gas storage unit, and the buffer gas storage unit 310, it is possible to increase the pressure of the buffer gas, convert it into a supercritical or liquefied buffer gas, and store it, without using a pressure-increasing machine such as a buffer gas compressor or pump. Also, by decompressing and expanding the stored buffer gas in any of a supercritical, liquid, or solid state into a gaseous buffer gas, the stored compressed air can be pushed out through the diaphragm 302. This makes it easier to effectively utilize the storage volume of the compressed air storage unit 300 and improve storage efficiency.

[0064] Furthermore, in this embodiment, when the compressed air stored in the outer space 301f of the compressed air storage tank 301 is discharged to the outside, the control unit 320 controls the aperture of the second adjustment valve 309 so that the pressure of the compressed air in the outer space 301f and the pressure of the buffer gas transferred into the inner space 301g are equal to the pressure required to move the diaphragm 302. This makes it possible to control the pressure and flow rate of the buffer gas while preventing an excessive pressure difference from occurring across the diaphragm 302, which could cause damage. Note that the "same pressure" referred to here includes both pressures that are exactly the same and pressures that are not exactly the same but are approximately the same.

[0065] Next, a method for storing compressed gas using the compressed gas storage system according to this embodiment will be described with reference to FIGS. 3 to 10, which are operation explanatory diagrams showing each step of the method for storing compressed gas.

[0066] First, in this embodiment, as shown in Fig. 3, carbon dioxide is filled in advance as a buffer gas into the inner space 301g of the compressed air storage tank 301 before the air compression process begins. This filling process is included in the compressed air expansion process following the previous compression process in the alternating compression and expansion processes. At this time, the membrane 302 expands with the filled buffer gas, as shown in Fig. 3, and one side of the membrane is in close contact with the inner surface of the compressed air storage tank 301. In this state, the compressed air is empty, and the carbon dioxide filled in the inner space 301g is released into the membrane as CO2 at a pressure of 50 barg and a temperature of 40°C, for example. ２ At this time, the first adjusting valve 307 is closed.

[0067] Next, the compression process is started by injecting air compressed by the compressor at 90 barg and 40°C into the outer space 301f of the compressed air storage tank 301. At this time, the first regulating valve 307 is closed, so that the carbon dioxide filled in the inner space 301g of the compressed air storage tank 301 is compressed by being pressed against the flexible diaphragm 302 as shown in Figure 4, and the pressure rises to, for example, 90 barg and the temperature to a range of 40 to 90°C. At this time, the carbon dioxide filled in the inner space 301g is in a supercritical state, which is the state of a substance when placed under temperature and pressure above its critical point.

[0068] After the carbon dioxide filled in the inner space 301g of the compressed air storage tank 301 is brought to a supercritical state, the first regulating valve 307 is opened when the pressure of the compressed air in the outer space 301f of the compressed air storage tank 301 and the pressure of the carbon dioxide in the inner space 301g become approximately the same. When the first regulating valve 307 is opened in this state, as shown in Fig. 5 , the carbon dioxide in the inner space 301g is cooled by the first cooler 306 to, for example, 36°C, and the pressure is reduced by the first regulating valve 307 to, for example, 71 barg and 30°C (30°C saturated liquefied carbon dioxide), and the carbon dioxide is transferred to the buffer gas storage unit 310. In this process, in order to receive the saturated liquefied carbon dioxide into the buffer gas storage tank 311, it is necessary to reduce the volume of the gas layer originally present in the buffer gas storage tank 311. Therefore, as shown in Fig. 5 , the chiller 313 is operated to cool and circulate liquid carbon dioxide at, for example, a pressure of 71 barg and a temperature of 20°C.

[0069] Thereafter, as air at a pressure of 90 barg and a temperature of 40°C continues to be injected into the compressed air storage tank 301, as shown in FIG. 6 , the carbon dioxide in the inner space 301g is almost completely depleted, and the buffer gas storage tank 311 is filled with carbon dioxide in a supercritical, liquefied, or solid state. In this manner, in this embodiment, the carbon dioxide serving as the buffer gas is stored in the buffer gas storage unit 310 in a supercritical, liquefied, or solid state. At this time, the carbon dioxide is in a saturated state, for example, at a pressure of 71 barg and a temperature of 30°C, in which gas and liquid coexist. In this embodiment, through this compression process, the carbon dioxide serving as the buffer gas is stored in the buffer gas storage unit 310 in a supercritical, liquefied, or solid state.

[0070] Next, carbon dioxide in a saturated state, for example, at a pressure of 71 barg and a temperature of 30° C., in a supercritical state, a liquefied state, or a solid state, is stored in the buffer gas storage unit 310, and the expansion process is started by heating the second heater 312. In the expansion process, the buffer gas, which has been pressurized by compressed air and then cooled to reduce its volume, is heated and vaporized, and is introduced back into the inner space 301 g of the membrane 302 in the compressed air storage tank 301, where it returns to the state of the buffer gas it was in before the compression process.

[0071] In the initial stage of the expansion process, first, as shown in Fig. 7, the second heater 312 is turned off, the second adjustment valve 309 is closed, and the compressed air adjustment valve 305 is opened. When the compressed air adjustment valve 305 is opened in this state, compressed air is discharged until the pressure of the compressed air filled in the compressed air storage tank 301 at a pressure of 90 barg and a temperature of 40°C is reduced to 50 barg, for example, as shown in Fig. 8.

[0072] In the expansion step, the space occupied by the air in the compressed air storage unit 300 is gradually reduced, and the space occupied by the carbon dioxide serving as the buffer gas is gradually expanded correspondingly to replace the air, so that the buffer gas stored in the buffer gas storage unit 310 as a fluid cooled in the compression step and reduced in volume must be heated and introduced again into the compressed air storage unit 300. For this reason, in this embodiment, the carbon dioxide stored in the buffer gas storage unit 310 in any one of a supercritical state, a liquefied state, and a solid state is gasified by heating with the second heater 312, and then the second adjustment valve 309 is opened to introduce the carbon dioxide as the buffer gas into the inner space 301g of the compressed air storage tank 301. ２ We move on to the gas delivery phase.

[0073] Specifically, the carbon dioxide in any one of a supercritical, liquefied, or solid state in the buffer gas storage unit 310 is heated by the second heater 312 to a gaseous state (30°C saturated carbon dioxide gas) at a pressure of 71 barg and a temperature of 30°C, for example, and then the second adjustment valve 309 is opened. When the second adjustment valve 309 is opened, the carbon dioxide in any one of a supercritical, liquefied, or solid state is gasified and then heated to, for example, 40°C by the first heater 308, as shown in Fig. 9, so that the carbon dioxide is transferred to the inner space 301g of the compressed air storage tank 301 at a pressure of, for example, 50 barg, similar to the pressure of the compressed air in the outer space 301f.

[0074] Thereafter, when the carbon dioxide is transferred as a buffer gas from the buffer gas storage unit 310 to the compressed air storage unit 300 with the pressure of the carbon dioxide set to, for example, 71 barg and the temperature set to 30°C, the inner space 301g is filled to 100% with carbon dioxide at a pressure of, for example, 50 barg and a temperature of 40°C, as shown in Fig. 10, and the compressed air in the outer space 301f is discharged. In this way, in this embodiment, the carbon dioxide stored in the buffer gas storage unit 310 in any of a supercritical state, a liquefied state, or a solid state is vaporized and used as a buffer gas, allowing the compressed air stored in the compressed air storage unit 300 to be efficiently discharged.

[0075] In the compressed gas storage system 100 of this embodiment, the compressed air storage unit 300 serving as the compressed gas storage unit has a vertical configuration in which vertical compressed air storage tanks 301 are arranged in parallel, as shown in Fig. 1, but it may also have a horizontal configuration. Below, another embodiment in which the compressed air storage tank serving as the compressed gas storage tank has a horizontal configuration will be described with reference to the drawings.

[0076] Fig. 11 is an explanatory diagram showing a schematic configuration of the main parts of a compressed gas storage system according to another embodiment of the present invention. In the compressed gas storage system 200 of this embodiment, the compressed air storage unit 400 serving as the compressed gas storage unit is a horizontal compressed air storage tank 401 that functions as a horizontal compressed gas storage tank extending horizontally, as shown in Fig. 11. The horizontal compressed air storage tank 401 has a columnar shape such as a cylinder or a rectangular parallelepiped, but the shape is not particularly limited as long as it is configured to be installed horizontally extending in the horizontal direction.

[0077] A first opening 401d through which compressed air can flow in and out is provided at one end of the top surface 401c of the horizontal compressed air storage tank 401. Meanwhile, a second opening 401e through which buffer gas can flow in and out is provided at the other end of the bottom surface 401b of the horizontal compressed air storage tank 401. The locations of the first opening 401d and the second opening 401e are not limited to this example. For example, the first opening 401d may be provided at any upper end of the side wall 401a of the horizontal compressed air storage tank 401, and the second opening 401e may be provided at any lower end of the side wall 401a.

[0078] In this embodiment, a flexible and deformable bag-like diaphragm 402 is provided in the horizontal compressed air storage tank 401 to separate an internal space 401g, which is in communication with the second opening 401e, from an external space 401f, which is in communication with the first opening 401d and covers the outside of the internal space 401g, and is provided in a separable manner within the horizontal compressed air storage tank 401. In this way, by providing the film-like bag-like diaphragm 402 that separates the buffer gas and the air within the horizontal compressed air storage tank 401, partial spaces are formed and mixing of the two is prevented, making it possible to selectively discharge the air outside the system.

[0079] 11, the bag-shaped diaphragm 402 has an opening fixed by a fixing means, adhesive means, or the like (not shown) so as to be able to communicate with the second opening 401e of the horizontal compressed air storage tank 401, and is a bag-shaped flexible membrane large enough to occupy the entire internal space of the horizontal compressed air storage tank 401. The bag-shaped diaphragm 402 is made of a flexible material selected from a synthetic resin film, a rubberized cloth, and a combination thereof, and has a mass per unit area of ​​500 g / m. 2 It is preferable to use the above.

[0080] As described above, in this embodiment, the storage tank of the compressed air storage unit 400 is a horizontal compressed air storage tank 401 that extends horizontally, and a bag-shaped diaphragm 402 is provided inside the storage tank to separate the outer space 401f of the bag-shaped diaphragm 402 from the inner space 401g.

[0081] Therefore, when compressed air is supplied through the first opening 401d, the compressed air enters the outer space 401f of the horizontal compressed air storage tank 401, thereby increasing the volume of the outer space 401f. As the volume of the outer space 401f increases, the compressed air that has entered the outer space 401f pushes out the buffer gas contained in the inner space 401g through the bag-shaped diaphragm 402, thereby reducing the volume of the inner space 401g. The buffer gas is then discharged through the second opening 401e and transferred to the buffer gas storage tank 311 of the buffer gas storage unit 310 via the first cooler 306 and the first adjustment valve 307.

[0082] Meanwhile, when buffer gas is transferred from the buffer gas storage unit 310 through the second opening 401e, the volume of the internal space 401g increases. As the volume of the internal space 401g increases, the buffer gas that has entered the internal space 401g pushes out the compressed air in the external space 401f through the bag-shaped diaphragm 402, thereby reducing the volume of the external space 401f. Then, the compressed air is discharged to the outside through the first opening 401d.

[0083] Next, the operation and effects of the compressed gas storage system and method according to this embodiment will be described.

[0084] The present inventors have conducted extensive research to solve the problem of improving storage efficiency by effectively utilizing the storage volume of a compressed gas storage section that stores compressed gas in a simple manner, and have discovered the following phenomenon.

[0085] That is, the inventors have found that by controlling the state change of the buffer gas transferred between the compressed gas storage unit and the buffer gas storage unit, it is possible to increase the pressure of the buffer gas and convert it into any one of a supercritical state, a liquid state, or a solid state and store it, without the need for a pressure-increasing machine such as a buffer gas compressor or a pump. Furthermore, the inventors have found that by controlling the temperature of the buffer gas that has been converted into any one of a supercritical state, a liquid state, or a solid state and stored, it is possible to efficiently discharge the compressed gas stored in the compressed gas storage unit while expanding the volume of the buffer gas using the change in gas state.

[0086] Therefore, by making the buffer gas used to discharge the compressed gas to the outside into any one of a supercritical state, a liquefied state, and a solid state so that it can be stored more compactly, and then expanding the volume of the buffer gas using the gas state change of the buffer gas that has been made into any one of a supercritical state, a liquefied state, and a solid state, it becomes possible to easily transfer the buffer gas to the compressed gas storage unit while efficiently discharging the compressed gas stored in the compressed gas storage unit to the outside without using a pressure boosting machine, etc. Therefore, by controlling the state change of the buffer gas transferred between the compressed gas storage unit and the buffer gas storage unit, it becomes possible to effectively utilize the storage volume of the compressed gas storage unit that stores the compressed gas in a simple manner and improve storage efficiency.

[0087] Furthermore, in the compression process of the CAES method, the pressure in the compressed air storage section increases over time, and in the expansion process, it decreases over time. Therefore, if the pressure in the compressed air storage section decreases too much during the expansion process, the expansion process must be stopped at the point when it falls below the specified suction pressure of the expander. However, compressed air equivalent to the residual pressure remains in the compressed air storage section, which poses a problem of not being able to extract sufficient energy.

[0088] In contrast, in the compressed gas storage system of this embodiment, the compressed gas storage section is partitioned by a flexible and deformable diaphragm, and the compressed gas stored in the compressed gas storage section is pushed out by the buffer gas through the diaphragm. This reduces the amount of compressed gas remaining in the compressed gas storage section, thereby improving the volume utilization efficiency of the compressed gas storage section. This prevents the need to increase the size of the compressed gas storage tank, which is particularly costly in terms of materials, and enables more cost-effective CAES power generation.

[0089] Furthermore, in this embodiment, compressed air can be stored in the compressed air storage unit more efficiently, and the compressed air stored in the compressed air storage unit can be easily discharged using buffer gas. Therefore, by charging at night when demand is low and discharging during the day when demand is high, thereby increasing the amount of power transmitted, it is possible to level out fluctuations in the power plant.

[0090] Furthermore, this embodiment can be applied to gases other than air as the compressed gas to be stored. For example, by applying hydrogen as the gas to be stored in the compressed gas storage system of this embodiment, it is possible to use hydrogen for power generation by burning hydrogen or for power generation using fuel cells, or to use it as a raw material gas in the synthesis of ammonia or methanol. In other words, by adding the compressed gas storage unit and buffer gas storage unit of this embodiment to existing facilities that use these hydrogen gases, the compressed gas storage system of this embodiment can also be applied in the same way.

[0091] Although one embodiment of the present invention has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

[0092] For example, a term described at least once in the specification or drawings together with a different term having a broader or similar meaning may be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration and operation of the compressed gas storage system are not limited to those described in each embodiment of the present invention, and various modifications are possible.

[0093] According to the present invention, the storage volume of a compressed gas storage unit that stores compressed gas can be effectively utilized in a simple manner, thereby improving storage efficiency.

Claims

1. A compressed gas storage system for storing compressed gas, comprising: a compressed gas storage unit for storing the compressed gas; a buffer gas storage unit for storing the compressed gas in a supercritical state, a liquefied state, or a solid state as buffer gas for pushing the compressed gas out of the compressed gas storage unit; a first cooler for cooling the buffer gas to be transferred from the compressed gas storage unit to the buffer gas storage unit; and a second heater for heating the buffer gas in the supercritical state, the liquefied state, or the solid state in the buffer gas storage unit.

2. The compressed gas storage system of claim 1, further comprising: a first heater that heats the buffer gas to be transferred from the buffer gas storage section to the compressed gas storage section; a first regulating valve that is provided between the first cooler and the buffer gas storage section; a second regulating valve that is provided between the first heater and the buffer gas storage section; and a control unit that controls at least the temperatures of the first cooler, the first heater, and the second heater, and the opening degrees of the first regulating valve and the second regulating valve.

3. A compressed gas storage system as described in claim 2, wherein the compressed gas storage section comprises a cylindrical compressed gas storage tank with both ends closed, and a flexible and deformable diaphragm that separates and allows separation between the space at one end and the space at the other end within the compressed gas storage tank.

4. The compressed gas storage system of claim 3, wherein the control unit controls the following: when filling the compressed gas into the compressed gas storage tank of the compressed gas storage unit, filling the tank with the first regulating valve closed, then opening the first regulating valve to cool the compressed buffer gas in the compressed gas storage tank with the first cooler and transfer it to the buffer gas storage unit while storing it in any of a supercritical state, a liquefied state, or a solid state; when discharging the compressed gas filled in the compressed gas storage tank to the outside, heating the buffer gas in any of a supercritical state, a liquefied state, or a solid state stored in the buffer gas storage unit with the second heater and then vaporizing it, opening the second regulating valve to heat the vaporized buffer gas with the first heater and expand it while transferring it to the compressed gas storage tank, and discharging the compressed gas filled in the compressed gas storage tank to the outside via flexible deformation of the diaphragm.

5. The compressed gas storage system according to claim 1 or 2, further comprising a chiller capable of cooling the gaseous buffer gas remaining in the buffer gas storage section.

6. The compressed gas storage tank has a cylindrical side portion, a ceiling portion that closes the upper end of the side portion, and a bottom portion that closes the lower end of the side portion, and has a first opening on the ceiling portion side through which the compressed gas can flow in and out, and a second opening on the bottom portion side through which the buffer gas can flow in and out, the diaphragms are hung from the ceiling portion of the compressed gas storage tank with their upper ends bundled together and sealed, and their lower ends open facing the bottom portion, and the lower ends of the diaphragms are fixed so that they are in close contact with the bottom portion or the side portion near the bottom portion, and the compressed gas storage tank is separated into an inner space surrounded by the inner surface of the diaphragm and the bottom portion of the compressed gas storage tank, and an outer space surrounded by the outer surface of the diaphragm and the ceiling portion and side portion of the compressed gas storage tank, with gas transfer between them being blocked by the diaphragm.

7. A compressed gas storage system as described in claim 6, wherein when the compressed gas stored in the outer space within the compressed gas storage tank is discharged to the outside, the control unit adjusts the opening of the second regulating valve so that the pressure of the compressed gas and the pressure of the buffer gas transferred to the inner space are equal to the amount required to move the diaphragm.

8. A compressed gas storage system according to claim 1 or 2, wherein a predetermined amount of liquefied buffer gas remains in the buffer gas storage section.

9. A compressed gas storage system as claimed in claim 1 or 2, wherein the buffer gas is either carbon dioxide or a gas mixture containing carbon dioxide.

10. A compressed gas storage system as described in claim 1 or 2, wherein the compressed gas storage section comprises: a horizontal compressed gas storage tank extending horizontally; a first opening provided on the top side of the horizontal compressed gas storage tank and allowing the compressed gas to flow in and out; a second opening provided on the bottom side of the horizontal compressed gas storage tank and allowing the buffer gas to flow in and out; and a flexible, deformable bag-like diaphragm that is separably provided to isolate an internal space in the horizontal compressed gas storage tank that communicates with the second opening from an external space that communicates with the first opening and covers the outside of the internal space.

11. A method for storing compressed gas using a compressed gas storage system comprising a compressed gas storage unit for storing compressed gas and a buffer gas storage unit for storing buffer gas for pushing the compressed gas out of the compressed gas storage unit, wherein the compressed gas storage system comprises: a first cooler for cooling the buffer gas to be transferred from the compressed gas storage unit to the buffer gas storage unit; a first heater for heating the buffer gas to be transferred from the buffer gas storage unit to the compressed gas storage unit; and a second heater for heating the buffer gas in the buffer gas storage unit, and when filling the compressed gas into a compressed gas storage tank, the compressed buffer gas in the compressed gas storage tank is cooled by the first cooler and transferred to the buffer gas storage unit, while being stored in any one of a supercritical state, a liquefied state, or a solid state, When discharging the compressed gas filled in the compressed gas storage tank to the outside, the buffer gas stored in the buffer gas storage unit in a supercritical state, a liquefied state, or a solid state is heated by the second heater and then vaporized, and the vaporized buffer gas is heated by the first heater to expand and transferred to the compressed gas storage tank, and the compressed gas filled in the compressed gas storage tank is discharged to the outside through flexible deformation of a flexibly deformable diaphragm that is separably provided to isolate one end space from the other end space in the compressed gas storage unit.

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