Compressed air energy storage method

Abstract

The purpose of the present invention is to provide an economical compressed air energy storage (CAES) method in which the cost of a compressed air energy storage (CAES) device is reduced and the volume space of an air storage unit is effectively utilized. An air reservoir (300) is configured from a plurality of containers (301), and a film having a space having a free shape is disposed inside each of the containers. In the air compression step, in each container, a space on one surface side of the membrane is filled with a buffer gas in advance, air is stored in a space on the other surface side of the membrane, the buffer gas is made into a volume-reduced fluid, and the amount of air stored in the space on the other surface side of the membrane is increased. The fluid is heated and vaporized, and the amount of air remaining in the space on the other surface side of the film is reduced. Thus, the available volume of the space of the air storage unit is increased, and the amount of clean air stored in the internal space of each container (301) can be increased.

Description

Technical Field

[0001] The present invention relates to a compressed air energy storage (CAES) method, which temporarily stores surplus power generated during a period when the power system or the like supplies more power than required as energy of compressed air, and utilizes the compressed air to recover it again as power during a period when the supply is insufficient. More specifically, it relates to a compressed air energy storage method that can effectively utilize a storage device for compressed air.

[0002] In a CAES device composed of a compressed air storage part using a steel container such as a steel pipe, the steel material cost of this part becomes expensive, and there is a tendency for cost-effectiveness to decrease. In the present invention, an object is to improve the volume utilization efficiency of the compressed air storage part space by using a buffer gas, thereby reducing the equipment cost in the compressed air energy storage method.

[0003] Here, the buffer gas is defined as follows. If air is sent into a container that is pre-filled with a certain gas, the gas is pressurized by the pressure of the air and its volume is reduced. At the same time, the presence of the gas has the effect of preventing a sharp drop in pressure in the container into which the air is sent. If it is assumed that there is a membrane-like component that isolates the two gases in the container, it is possible to selectively discharge only the air from the container. In this process, the volume of the gas remaining in the container increases as the pressure decreases. As a result, the gas has the effect of squeezing the air out of the container. In this way, during the process of air entering and exiting, the gas that pre-fills the container acts as a buffer medium with elasticity for the air in the container. The buffer gas defined here refers to a gas that is pre-filled with a predetermined amount of gas in a state where it is isolated from the compressed air by a membrane-like component in a compressed air storage unit. The more the gas changes in volume compared to air during compression and expansion, the greater the buffering effect that can be obtained.

[0004] The CAES method is classified into adiabatic type, non-adiabatic type, or a compromise type of the two, but any method requires an air storage unit. Therefore, the present invention that uses a buffer gas to improve the volume utilization efficiency of the air storage unit space can be commonly applied to these various methods, and any method can achieve an effect. Background Art

[0005] The demand for electricity varies according to the season, time period, etc. Furthermore, if the supply of electricity from renewable energy that varies according to meteorological conditions such as sunlight or wind power, day and night, etc. is added, it becomes a problem to maintain the balance between the demand and supply of electricity in the power system. In the case of surplus electricity in the power system, it is required to temporarily store the electricity and transfer it to other time periods with high demand for reuse. With the expansion of the introduction of electricity from highly variable renewable energy, the role of power storage technology as a means of effectively utilizing surplus electricity is becoming increasingly important.

[0006] Pumped hydro power generation, which uses physical energy based on height differences, is an excellent method of storing electricity, and the overwhelming majority of electricity storage facilities currently in operation are of this type. Similar to pumped hydro power generation, as a physical method of storing electricity, the compressed air energy storage (CAES) method, which converts electricity into compressed air energy and stores it, is also an excellent method of storing electricity, and large-scale electricity storage facilities that store compressed air by setting up cavities in underground rock salt layers have been in operation for many years. This method drives a compressor to store electricity as compressed air energy, and when electricity is needed, the compressed air drives an expander and recovers it again as electricity. Basically, a CAES device consists of an electric motor, a compressor, a heat exchanger for removing compression heat, a storage unit for compressed air, a heating mechanism for compressed air, an expander, and a generator. Below, in Figure 1 Reference numerals are used in FIG. 1 to illustrate an example of the CAES approach.

[0007] In this example, when power is input, air 10 is compressed in two stages by a low-pressure compressor 120 and a high-pressure compressor 130 driven by a motor 110 via a shaft 121 to become compressed air. Next, it is stored in an air storage unit 300. In the past, the storage unit of the CAES device used a hollow part of a rock salt layer located underground, but there are various options such as other strata or steel high-pressure containers located on the ground. Aftercoolers 140 and 150 are attached to each compressor, and the compression heat generated in each compressor is removed. Cooling water 30 and 32 are supplied to the aftercoolers 140 and 150, respectively, and the cooling water 31 and 33 that have absorbed the compression heat are discharged. When power is needed, the high-pressure expander 230 and the low-pressure expander 220 are driven by the compressed air stored in the air storage unit 300. At this time, the compressed air is heated by supplying fuel 20 and 21 to the high-pressure side burners 250 and the low-pressure side burners 240 provided in the air input unit of each expander. At the same time, the generator 210 driven by the high-pressure side burner 250 and the low-pressure side burner 240 and the shaft 221 operates, and the compression energy of the air is converted back into electricity. In the heating process, the high-temperature exhaust gas from the low-pressure expander 220 is heat-exchanged with the stored air from the air storage unit 300 through the regenerative heat exchanger 260, and the thermal efficiency can be improved by utilizing the recovered heat. The air 11 that has passed through the regenerative heat exchanger 260 is discharged to the atmosphere.

[0008] The conventional CAES method can be classified into adiabatic and non-adiabatic methods. In the non-adiabatic method, the compression heat generated during air compression is cooled and removed to the outside of the system. During power recovery, fuel is supplied to the inlet of the expander, which requires heating of the compressed air. The non-adiabatic CAES method has long been implemented on a large scale. Figure 1 A typical example of this method is shown.

[0009] In the adiabatic CAES method, the compression heat generated when air is compressed is stored and reused during power recovery. In this method, no fuel is used during power recovery, and thermal efficiency can be improved compared to the non-adiabatic method. Figure 1 In the adiabatic CAES method, heat recovery is performed in a portion corresponding to the aftercoolers 140 and 150 set in a non-adiabatic manner. In order to store this recovered thermal energy, a storage unit is required, which is called TES (Thermal Energy Storage). Due to the presence of this heat storage unit, adiabatic CAES can be in a variety of forms, and a typical example thereof is shown in non-patent document 1.

[0010] On the other hand, in the adiabatic CAES method, the inlet temperature of the expander during power recovery is lower than that of the non-adiabatic method using combustion heat. In addition, due to the loss of storage heat, there is a tendency for the power that can be recovered in the adiabatic CAES method to be lower than that in the non-adiabatic CAES method. As a result, the power generation per unit compressed air volume of the adiabatic method decreases, and there is a tendency for the equipment price per recovered power volume to be higher than that of the non-adiabatic method. As a countermeasure, in Patent Document 1, a hybrid CAES system of adiabatic and non-adiabatic is proposed.

[0011] A CAES method has also been proposed for using the volume space of a compressed air storage unit without waste. For example, there is a method as follows: when air is compressed, the compressed air storage unit is filled with water in advance, and water is discharged as the amount of air in this part increases. When the compressed energy of the air is recovered as power, water is injected into the air storage unit again, and the entire amount of air inside is replaced with water, thereby making maximum use of the volume of the storage unit. This method also has the advantage of always keeping the pressure of the air storage unit constant. However, in this method, a large-capacity water tank needs to be set up at a sufficiently high position corresponding to the storage pressure of the air, and the constraints of the terrain become a problem.

[0012] As a method for improving the volumetric efficiency of the air storage space, there is a method of using compressed gas as a substitute for non-compressible water. In Patent Document 2, the following method is proposed: carbon dioxide is used in a porous sandstone layer or other stratum located at a high depth, and the buffering effect of the compressed gas is used to store air. In this CAES method, the stratum for storing air is filled with a sufficient amount of carbon dioxide in advance. If compressed air is sent here, the density of carbon dioxide increases as the pressure increases. If the operating conditions at this time are near or above the critical pressure, the density of carbon dioxide increases and decreases rapidly, and thus its volume also increases and decreases rapidly. When the air is discharged, the volume of carbon dioxide increases suddenly with the decrease in the pressure of the storage layer, and the air can be driven out of the storage layer, and the storage amount in the air storage layer increases. In this way, carbon dioxide effectively acts as a buffer gas in the porous stratum, and the improvement of the volume utilization efficiency of the air storage space can be sought.

[0013] In this method, there is the following concern: inside the stratum, the boundary surface of air and carbon dioxide directly contacts each other, and the fluids of the two are mixed. Here, the following situation is used to avoid excessive mixing: the pressure becomes high in the low position in the layer. That is, in the sandstone layer, the lower the layer, the higher the fluid density of carbon dioxide, so it is possible to reduce mixing with the low-density air remaining in the upper layer. However, in this method, it is difficult to apply this method to the storage part set on the ground such as steel containers due to the constraints of the site selection conditions such as the characteristics of the stratum or the terrain.

[0014] It would be convenient if the CAES equipment could be installed on the ground without being affected by the site selection conditions. In this case, a realistic option is to use a steel pipe or a steel container as the air storage unit. However, in this method, the volume of the container space is too large, and there is a concern that the cost of the steel material for this part is expensive. As an example of this countermeasure, there is the following method: as shown in Patent Document 3, the compressed air is liquefied to reduce the storage capacity and is stored in a device installed on the ground. In addition, in this method, liquid air can be stored at normal pressure, so the installation cost of the air storage unit can be significantly reduced. However, in this method, there are problems such as the expensive air liquefaction equipment and the reduced energy efficiency associated with the generation of cold and heat required for liquefaction.

[0015] Various attempts have been made to develop an above-ground CAES facility using a steel container such as a steel pipe, including the above-mentioned liquefaction method. The present invention also belongs to this process and aims to realize an economical CAES method by effectively utilizing the volume of the air storage space formed by the steel pipe or steel container, which has a high equipment cost. Prior Art Literature Patent Literature

[0016] Patent Document 1: EP 3 255 266 B1 Patent Document 2: WO 2009 / 146101 A2 Patent Document 3: WO 2007 / 096656 A1 Non-patent literature

[0017] Non-patent literature 1: de Biasi, “Fundamental analyses to optimize adiabatic CAESplant efficiencies”, Gas Turbine World, September-October (2009). Non-patent document 2: Eckroad, S., "Handbook of Energy Storage for Transmissionor Distribution", EPRI Report-1007189 (2002). Summary of the invention Problems to be solved by the invention

[0018] The object of the present invention is to provide an economical CAES method. To achieve this object, it is necessary to effectively utilize the volume space of the air storage unit. From this point of view, the above-mentioned problems in the conventional CAES method are solved to achieve the above-mentioned object.

[0019] In the conventional CAES method, the following point can be cited: although the cost of the air storage unit accounts for a high proportion of the overall equipment, the volume utilization efficiency of this part is very low. For example, in the CAES method in which air is stored in cavities in a rock salt layer located underground, it is well known that the utilization efficiency of the cavity volume is low. According to non-patent document 2, the variable pressure ranges during operation of the CAES equipment of Hunterf (Germany) and McIntosh (USA) are shown respectively, but in either case, the expansion process is terminated in a state where compressed air with a pressure exceeding 60% of the maximum storage pressure during the compression process remains. In this way, in the conventional CAES method, there is room for improvement in the volume utilization efficiency of the air storage unit, and the overall cost of the equipment can be reduced by improving this point.

[0020] In the compression process of the CAES method, the pressure of the air storage unit increases with time, and in the expansion process, it decreases with time. If the pressure of the air storage unit decreases excessively during the expansion process, the expander cannot function sufficiently, and it is necessary to stop the expansion process at the time when the pressure drops to a predetermined value. Therefore, if some method can be used to reduce the amount of air remaining in the storage unit at a pressure equivalent to the end of the expansion process, the volume utilization efficiency of the air storage unit space can be improved.

[0021] In CAES equipment that utilizes deep cavities such as rock salt layers, porous sandstone layers, abandoned mine shafts, or deep water in lakes or oceans, the cost of the air storage unit can be alleviated to a certain extent by utilizing the benefits of natural conditions as they are. However, the places where such natural conditions can be utilized are limited, and it would be convenient if CAES equipment could be installed at required locations without being restricted by site selection. In this case, as an example, it is envisioned that compressed air is stored in steel containers such as steel pipes installed on the ground, but a large amount of steel is required for this, and the cost becomes expensive. If the volumetric utilization efficiency of the air storage space can be improved, the cost of CAES equipment that stores compressed air in steel containers can also be reduced.

[0022] As a method for effectively utilizing the volume space of the air storage unit, there is a CAES method of replacing the air in the storage unit with water. However, this method is also restricted by the terrain, and it is not realistic to adopt it in the CAES method that is the subject of the present invention.

[0023] As mentioned above, in Patent Document 2, a method for improving the volume utilization efficiency of underground air storage parts such as porous sandstone layers by using buffer gas is shown. Here, carbon dioxide is used as a buffer gas, and the characteristics of pressure changes and sudden changes in fluid density near or beyond the critical point of the substance are utilized. In this method, there is a concern that air as a working gas and the buffer gas will mix at the boundary surface between the two, but in the underground strata, the high-density buffer gas remains in the lower layer of the air, and the density of the buffer gas increases as the pressure increases as it goes to the lower layer, so the mixing of the two gases can be suppressed to a minimum.

[0024] If it is assumed that high-pressure air is stored in a steel container including a steel pipe and a buffer gas is used here, a method to avoid the mixing problem of the buffer gas and the air becomes a subject. In the above-mentioned example of storing air in a sandstone layer, the thickness of the stratum has a height difference expressed in units of 100m, and here, the sudden change in the fluid density based on the buffer gas is used to prevent excessive mixing between the two. On the other hand, it is difficult to realize a structure with such a height difference inside a steel container. If it is possible to prevent mixing with air inside the air storage section by some method and exert the buffering effect of the gas, it can be expected that the volume utilization efficiency of the air storage section space will be improved. As a countermeasure, in the present invention, the buffer gas is isolated from the air as the working gas in the storage section to prevent mixing between the two.

[0025] By changing the pressure from below the critical pressure to a pressure near the critical point or above, the buffer effect can be improved by utilizing the change in the fluid density of the buffer gas. Therefore, an ideal substance is selected as the buffer gas considering the relationship with the pressure change in the compression and expansion process.

[0026] In the example of storing air in the sandstone layer, the buffer effect is obtained by the increase or decrease in volume due to the change in density of the buffer gas caused by the pressure change. However, the change in density depends not only on the pressure but also on the temperature. If both the pressure and the temperature have an effect on the fluid density, the function as a buffer gas can be further improved. Therefore, in the present invention, the buffer effect based on temperature is also effectively utilized. Therefore, the disposal method of the buffer gas considering cooling and heating is studied.

[0027] In the non-adiabatic CAES method that consumes fuel, the compression heat generated in the compression process is removed, but in the adiabatic method, the compression heat is recovered and reused. In addition, a compromise CAES method that performs heating through the use of fuel and recovery of compression heat has also been proposed. The present invention does not belong to a specific CAES method, and various selections can be made on the use of compression heat and fuel. Solutions to Solve Problems

[0028] The present invention provides an air storage method for a CAES facility that solves the above-mentioned problems. More specifically, the present invention provides a method for effectively utilizing the volume space of an air storage unit in a CAES facility.

[0029] The compressed air energy storage method involved in the first embodiment of the present invention includes: a compression process of converting electricity into compressed air energy and storing the compressed air in one or more containers; and an expansion process of expanding the stored compressed air and recovering the electricity, and the compression process and the expansion process are performed alternately. The container is provided with a single or multiple membranes inside each container of the entire or a part of the container, and the membrane forms a space with a surface that can be deformed freely. A plurality of partial spaces are formed inside the container. The compressed air energy storage method has the following series of operations: at the beginning of the compression process, inside the container, a compressed air is formed. Part of the space on one side of the two surfaces of the aforementioned membrane is filled with buffer gas, and compressed air is stored in the partial space on the other side of the two surfaces of the aforementioned membrane inside the container without being mixed with the buffer gas during the compression process. Moreover, the amount of compressed air stored in the partial space on the other side is increased by leaving the buffer gas inside the container or guiding the buffer gas to the outside of the container to change the buffer gas into a fluid with a reduced volume. In the expansion process, the amount of compressed air remaining in the container is reduced by vaporizing the fluid inside or outside the container and restoring it to buffer gas in the partial space on one side inside the container. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram showing the overall structure of a conventional non-adiabatic compressed air energy storage (CAES) facility. Figure 2 This is a schematic diagram showing the overall configuration of a CAES facility according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0031] (First Embodiment) Reference Figure 2 , the first embodiment of the present invention is described below. In a CAES (i.e., compressed air energy storage) device, the air storage section 300 is a device commonly required by various CAES methods such as adiabatic, non-adiabatic, or a compromise of the two. In the first embodiment of the present invention, as an example, the case of an air storage section 300 composed of a steel pipe or a steel container 301 is described, but it can be commonly applied to a CAES device having an air storage section 300 with a container 301 other than steel. In addition, for Figure 1The equipment configuration and operation method of the non-adiabatic CAES equipment shown except for the air storage unit 300 can be appropriately followed by the first embodiment of the present invention.

[0032] Reference Figure 2 The overall process of the compressed air energy storage method of the present invention is described below. Figure 2 The overall structure of the CAES device based on the first embodiment is shown together with the reference numerals. The CAES device based on the first embodiment 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 heat exchanger 320, an air storage unit 300, a CO2 storage unit 310, a low-pressure expander 220, a high-pressure expander 230, a regenerative heat exchanger 260, etc. In this embodiment, the air storage unit 300 is configured with a container 301, and the container 301 is as shown in FIG. Figure 2 As shown by the portion surrounded by the dotted line, it is formed by a plurality of linear steel pipes arranged in parallel.

[0033] In the present invention, a membrane surface is arranged in the air storage part to separate the buffer gas and the air, thereby forming a partial space and preventing the mixing of the two, and selectively exhausting the air to the outside of the system. In this way, the volume utilization efficiency of the air storage part space is improved, and the net storage air volume can be increased.

[0034] The material of the membrane is described. The membrane may be made of any material as long as it has the strength and durability to cope with the pressure and temperature of the fluid that changes into the gas phase and the liquid phase. For example, it may be formed of a thin, strong, non-stretchable resin film-like member.

[0035] Next, the overall process of the compressed air energy storage method is described. Before the air compression process begins, carbon dioxide is pre-filled into a predetermined space inside each container 301. The filling process is included in the expansion process of compressed air following the previous compression process in the compression process and the expansion process that are performed alternately. Buffer gas is pre-injected into a partial space surrounded by the container inner surface of each air container 301 and one side of the membrane. The membrane expands due to the filled buffer gas, and the other side opposite to the aforementioned one side becomes in a state of being in close contact with the container inner surface.

[0036] In the following compression process, the compressed air is stored in a partial space isolated from the buffer gas by a membrane. In the compression process, the air 10 introduced from the atmosphere is pressurized in turn by the low-pressure compressor 120 and the high-pressure compressor 130 to become compressed air, and is finally stored in the air storage section 300 via the aftercooler 150 and the three-way valve 151. The low-pressure compressor 120 and the high-pressure compressor 130 are both driven by the motor 110 via the shaft 121. The compression heat generated in the low-pressure compressor 120 and the high-pressure compressor 130 is removed by heat storage in the heat storage tank 160 described later and heat exchange in the aftercooler 150. In this process, the buffer gas isolated from the compressed air is also compressed at the same time, and the buffer gas is squeezed out of the container 301 by the pressure of the compressed air.

[0037] In order to reuse the compression heat from the low-pressure compressor 120 in the expansion process, the compression heat is temporarily stored in the heat storage tank 160 by the following method. As a method for storing compression heat, there is also a method of transferring heat to a fluid such as heat medium oil through the heat transfer surface of a heat exchanger, but here a direct heat transfer method is adopted in which a granular solid composed of a small-diameter rock not shown in the figure stored in the heat storage tank 160 is used as a heat medium. This method requires a pressure container, but the advantages are good heat transfer characteristics and less pressure loss. The heat storage tank 160 is an upright cylindrical shape, and high-temperature air from the low-pressure compressor 120 is sent in from its top. The thermal energy stored in the heat storage tank 160 is used in the expansion process immediately before, so at the beginning of the compression process, the temperature of the heat storage tank 160 decreases compared to when the compression heat is stored. In the compression process, the heat storage amount in the heat storage tank 160 increases with time, and the temperature boundary line between the high-temperature side and the low-temperature side of the heat medium initially at the top of the heat storage tank 160 gradually moves toward the bottom. Thus, the compression heat is removed, the temperature of the compressed air is lowered, and the heat is stored in the heat storage tank 160. In the expansion process, in contrast to the compression process, low-temperature air is sent to the lower part of the heat storage tank 160, and the air 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 increase the temperature of the air introduced into the high-pressure expander 230 in the expansion process as described later.

[0038] The air cooled by the heat storage tank 160 from the low-pressure compressor 120 is guided to the high-pressure compressor 130, and is stored in the air storage section 300 through the aftercooler 150. The low-temperature water from the low-temperature water tank 340 is used to remove the compression heat in the aftercooler 150. In the present invention, the volume increase or decrease of the buffer gas based on the state change of heating and cooling is required. The compression heat removed by the aftercooler 150 heats the low-temperature water to generate high-temperature water and is stored in the high-temperature water tank 330. The high-temperature water is used as a heat source for heating the low-temperature fluid whose volume is reduced by cooling the buffer gas in the expansion process. The low-temperature water required for heat removal in the aftercooler is generated by the temperature drop caused by heat exchange with the above-mentioned low-temperature fluid in the heat exchanger 320 as described later. The low-temperature water is stored in the low-temperature water tank 340 and is used by alternately circulating between the high-temperature water tank 330. Furthermore, the cooling water 30 , 31 is supplied to the low-temperature water tank 340 via three-way valves 331 , 341 disposed between the heat exchanger 320 and the low-temperature water tank 340 and between the high-temperature water tank 330 and the heat exchanger 320 , respectively.

[0039] Simultaneously with the compressed air, the buffer gas is pressurized by the pressure of the compressed air inside the container 301. At this time, if the critical pressure is exceeded and the temperature drops further, the volume of the fluid is greatly reduced. In addition, the cooling of the buffer gas introduced into the container can also guide the buffer gas to the outside of the container 301 and cool it to reduce the volume. As the amount of air introduced into the interior of the container 301 increases, the shape of the partial space formed by the membrane in each container 301 into which the compressed air is introduced becomes close to the shape of the internal space of the container as the container 301 in terms of inner diameter and length. Therefore, when each container 301 is filled with compressed air and the buffer gas is discharged to the outside of the container 301, the membrane is in a state of close contact with the inner surface of the container 301.

[0040] In the compressed air expansion process, the fluid pressurized by the compressed air and further reduced in volume by cooling is heated and vaporized, and is introduced again into one side of the membrane in each container 301 to restore the buffer gas state before the compression process.

[0041] In the expansion process, the pressure of the air stored in the air storage unit 300 decreases as the air is discharged. In the expansion process, in order to gradually reduce the space occupied by the air in the air storage unit 300 and correspondingly gradually expand the space occupied by the buffer gas to replace it, it is necessary to heat the buffer gas stored in the buffer gas storage unit 310 as a fluid that is cooled and reduced in volume in the compression process and introduce it into the air storage unit 300 again. The pressure of the air storage unit is reduced to 5 (MPa), so that in the middle of the expansion process, the buffer gas becomes a low-temperature gas-liquid mixed phase fluid. In order to use this fluid as a buffer gas, the heat energy stored in the high-temperature water tank 330 in the compression process is used as its heating source. The low-temperature mixed phase fluid is heated by heat exchange with the high-temperature water from the high-temperature water tank 330 in the heat exchanger 320, and is sent to the air storage unit 300 as a buffer gas. In this way, the air in the air storage unit 300 is squeezed out by the buffer gas, and finally, the space occupied by all the air in the container 301 is replaced by the space occupied by the buffer gas.

[0042] The compressed air discharged from the air storage unit 300 is always kept at a constant pressure, for example, 5 (MPa) by a pressure reducing valve (not shown), and is guided to the high-pressure expander 230 through the rear half of the regenerative heat exchanger 260. The low-temperature compressed air leaving the air storage unit is heated by the regenerative heat exchanger through the high-temperature exhaust heat from the low-pressure expander 220 described later. Next, the air is used as a driving force to perform the initial power recovery using the high-pressure expander. The high-pressure expander 230 drives the generator 210 through the shaft 221 together with the low-pressure expander 220.

[0043] The low-temperature air leaving the high-pressure expander 230 is guided to the bottom of the heat storage tank 160 storing the compression heat generated by the low-pressure compressor 120 in the compression process. The air is directly heated by convection contact with the granular solid heat storage material stored in the tank.

[0044] When the compression process starts, the pressure of the air storage unit 300 is set to 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, the gas in the air storage section 300 is squeezed out by the accumulated pressure of the air and is cooled by cooling water (inlet side: 32, outlet side: 33) in the heat exchanger 320. The pressure of the air storage section 300 eventually becomes 9 (MPa), and the pressure of the gas is equal to the air pressure. In this state, the gas exceeds the critical pressure and becomes a supercritical fluid. In this embodiment, the temperature of the fluid is reduced to 35 (°C). The density of the substance under this condition becomes 630 (kg / m 3), its volume is reduced to 19% of that at the beginning of the compression process. On the other hand, in the expansion process of the stored compressed air, the air is replaced by carbon dioxide, and the volume of the air storage unit 300 is almost entirely used. As mentioned above, the spatial volume utilization efficiency of the air storage unit in the conventional compressed air energy storage method is 40% or less. Although a buffer gas storage unit 310 for storing the cooled fluid from the buffer gas is required in addition to the air storage unit, it is foreseeable that even if this part is offset, the volumetric efficiency of the present embodiment will become a value more than twice that of the conventional method. That is, it is possible to store more than twice the air in the same volume space.

[0045] The heated air leaving the top of the heat storage tank 160 returns to the front half of the regenerative heat exchanger 260, where it is further heated and guided to the burner 240. The high-temperature gas leaving the burner 240 including the fuel 20 consumed here is guided to the low-pressure expander 220, where power is recovered again. The temperature of the exhaust gas from the burner 240 is very high, and as described above, heat energy above a predetermined temperature is recovered by passing through the front half and the rear half of the regenerative heat exchanger 260 until the air 11 that has passed through the regenerative heat exchanger 260 is released to the atmosphere from a high temperature to a low temperature.

[0046] In the present invention, in order to increase or decrease the volume of the buffer gas used in the air storage unit 300 due to the change in state, it is necessary to cool or heat the carbon dioxide as the buffer gas. Figure 2 As shown, the cooling and heating are performed by guiding the air to the outside of the air storage unit 300 composed of a plurality of steel pipes. In this case, a container is required to store carbon dioxide, which becomes a fluid whose volume is reduced due to cooling during the air compression process. The carbon dioxide leaving the air storage unit 300 is cooled by cooling water in the heat exchanger 320. At this time, the three-way valve 331 is switched to send cooling water from the cooling tower (not shown) to the heat exchanger 320. As a container for storing cooled carbon dioxide, there is provided Figure 2 The CO2 storage unit is also composed of a container 311 as in the air storage unit 300. Figure 2 As shown in the range surrounded by the dotted line, it is formed by a plurality of linear steel pipes arranged in parallel.

[0047] (Second Embodiment) In this embodiment, the use of a steel pipe arranged horizontally in the air storage unit, the use of carbon dioxide as a buffer gas, etc. Figure 2The structure shown is also basically the same as the first embodiment. However, inside each container, the following two spaces are formed: the two ends of a group of single membrane surfaces having a length equivalent to half the circumference of the circular inner surface of the container are fixed in parallel along the inner wall surface in the direction of the tube length, and the steel tube is divided into upper and lower parts, and the ventilation between the two is cut off by the membrane surface. In this case, the membrane surfaces of the two spaces defined by the membrane become mutually complementary concave and convex shapes, and the shapes of the two spaces separated by the membrane are reversed in the middle of each of the air compression and expansion processes. In the expansion process of the compressed gas before the compression process, a partial space is filled with buffer gas, and the membrane surface of the partial space becomes convex, and the storage of air starts from the space on the other side of the membrane. In this embodiment, the air storage section 300 is also configured with a container 301, and the container 301 is as shown in FIG. Figure 2 The air storage unit 300 is arranged on the ground. The overall structure of the CAES device is similar to that of the air storage unit 300. Figure 2 The first embodiment shown in FIG. Figure 2 The buffer gas storage section 310 shown is also common in that it is stored in a plurality of containers 311 arranged in parallel as shown in the dotted line. That is, the second embodiment is a modified example as follows: except that the installation method of the membrane inside the container 301 of the air storage section 300 is different from that of the first embodiment, the overall structure, operating conditions and methods of the CAES device are common to the first embodiment, and the installation method of the membrane is different from that of the first embodiment. Therefore, their description is replaced by the first embodiment that has been described. As a further modified example, for example, the following modified examples can be listed: in the middle part of the length direction of the steel pipe, one end of the cylindrical membrane is fixed to the inner wall surface at right angles to the length of the pipe, and the membrane divides the length direction into two parts and separates it into a space of increasing and decreasing volume.

[0048] Each embodiment described above can be appropriately changed. In the following, a modified example is described. Regardless of which embodiment example is described above, the motor, low-pressure compressor, and high-pressure compressor are combined as a group including the respective accompanying devices (for example, coolers, etc.), but the whole device can also be composed of multiple groups. Similarly, it is also possible to configure multiple groups for the generator, low-pressure expander, and high-pressure expander.

[0049] In addition, for at least a portion of the fluids stored in the partial spaces formed by the membrane in any of the above-mentioned embodiments, the fluids stored in the partial spaces may be replaced. Specifically, compressed air may be stored in the partial spaces on one side of the membrane, and buffer gas may be stored in the partial spaces on the other side of the membrane. Alternatively, buffer gas may be stored in the partial spaces on one side of the membrane, and compressed air may be stored in the partial spaces on the other side of the membrane.

[0050] In addition, the container 301 may be made of something other than steel. For example, it may be made of concrete or reinforced concrete. Furthermore, it may be made of steel and the entire inner surface of the container 301 may be sprayed with a resin material or a sheet such as a resin sheet. By doing so, it is possible to improve the initial airtightness and prevent or reduce the decrease in airtightness due to damage or degradation caused by earthquakes during long-term use.

[0051] The above embodiments describe preferred examples of the present invention, and the application of the method for improving the space volume utilization efficiency of the air storage unit described in this specification is not limited to these examples. Therefore, as a method for efficiently utilizing the space volume of the compressed air storage unit of the present invention, it can also be combined with other CAES methods.

[0052] The compressed air energy storage method of the present invention has the following operation: compressing air, storing compressed air in a partial space different from the space inside the container filled with buffer gas, and changing the buffer gas into a fluid with a reduced volume, thereby increasing the amount of compressed air stored, and then vaporizing the reduced fluid to restore it to buffer gas, thereby reducing the amount of compressed air remaining inside the container. By filling the air storage part with buffer gas before the expansion process before the air compression process ends, the space of the air remaining in this part can be replaced with the space of the buffer gas and eliminated. In the next compression process, the buffer gas introduced into the air storage part due to the pressure accumulation of the air is also compressed, and its volume is reduced. If the gas is cooled, it becomes a fluid with a further reduced volume. As a result, in the compression process, the air storage space is expanded without being affected by the residual air in the expansion process, and the amount of air newly added therein can be increased. If the gas is cooled below the critical pressure, it becomes a liquid, but if it is cooled under pressure conditions exceeding the critical pressure, it becomes a fluid whose volume is reduced without undergoing a phase change to a liquid. Here, both the cooled liquid and the supercritical fluid are collectively referred to as fluids with reduced volume. If the fluid is heated and restored to the state of the buffer gas at the beginning of the compression process, the air stored in the air storage section can be replaced and discharged as described above, and the air storage section space can be effectively utilized. However, if the air as the working gas and the buffer gas are mixed, there is a problem that the buffer gas is also discharged from the system together with the air during the expansion process. Therefore, in the present invention, a membrane surface that separates the buffer gas and the air is arranged in the air storage section to form a partial space and prevent mixing between the two, so that the air is selectively discharged to the outside of the system. In this way, the volume utilization efficiency of the air storage section space is improved, and the net storage air volume can be increased. Therefore, an economical CAES method can be provided.

[0053] It is desirable that the buffer gas used in the air storage section of the compressed air energy storage method of the present invention is single carbon dioxide or a mixture containing carbon dioxide as a main component.

[0054] The buffer gas used in the air storage section of the compressed air energy storage method of the present invention uses a single carbon dioxide or a mixture with carbon dioxide as the main component. In the respective processes of compression and expansion, carbon dioxide has a greater density change than air, so a high buffering effect can be obtained in the air storage section. Therefore, the volume utilization efficiency of the air storage section space can be significantly improved. Therefore, an economical CAES method can be provided.

[0055] Regarding the pressure range of the buffer gas in the compressed air energy storage method of the present invention, it is preferred that the minimum pressure in the expansion process is used in a range below the critical pressure of the buffer gas, and the maximum pressure in the compression process is used in a range above 90% of the critical pressure of the buffer gas.

[0056] With regard to the pressure range of the buffer gas used in the compressed air energy storage method of the present invention, the minimum pressure in the expansion process is used in the range below the critical pressure of the buffer gas, and the maximum pressure in the compression process is used at more than 90% of the critical pressure of the buffer gas. Generally speaking, no matter what kind of substance it is, under pressure conditions near the critical point or above, the density changes rapidly due to a small change in pressure. Generally speaking, under pressure conditions exceeding 90% of the critical pressure, a sudden change in density is observed. In the case of using carbon dioxide as a buffer gas, the density of the gas changes with respect to the pressure change near the critical point of the substance as follows. The density of carbon dioxide at a pressure of 5 (MPa) and a temperature of 40 (°C) is approximately 120 (kg / m 3 If the temperature is kept the same and the pressure of carbon dioxide is raised to 9 MPa, which is higher than the critical pressure of 7.4 MPa, its density will be approximately 4 times higher, to 480 kg / m 3 ). Thus, the carbon dioxide changes from a pressure below the critical pressure to a pressure near the critical pressure or above the critical pressure, thereby causing a sharp density change. Therefore, a high buffering effect can be obtained under such conditions. Therefore, an economical CAES method can be provided.

[0057] The compressed air energy storage method of the present invention preferably stores compression heat generated by compression of air in the compression step, and utilizes the compression heat stored in the expansion step for at least one of heating the air and heating the buffer gas.

[0058] The compressed air energy storage method of the present invention stores the compression heat generated in the compression process, and utilizes the compression heat stored in the expansion process for at least one of heating the air and heating the buffer gas. The compression heat generated in the compression process is recovered / stored, and the compression heat is utilized for heating the compressed air in the expansion process, and is also utilized as a heating source for the fluid whose volume is reduced by cooling the buffer gas. Therefore, the energy utilization efficiency can be improved, and the thermal energy required for heating the buffer gas from the outside can be eliminated or reduced. Therefore, an economical CAES method can be provided.

[0059] The above is an example of density change relative to pressure, but in addition to the change in pressure, the present invention also utilizes the density change caused by the temperature change accompanying the cooling and heating of the buffer gas. Therefore, in the present invention, both pressure and temperature contribute to the density change, which can further enhance the buffer effect.

[0060] Preferably, the compressed air energy storage method of the present invention includes a heat storage step of storing compression heat, and the heat storage step includes at least a step of absorbing compression heat by water and storing the absorbed heat water in a tank.

[0061] The compressed air energy storage method of the present invention has a heat storage step for storing compression heat, and the heat storage step includes at least a step of absorbing compression heat by water and storing the absorbed water in a tank. Therefore, the compression heat can be used for heating instead of being wasted. Therefore, an economical CAES method can be provided.

[0062] According to the present invention, in a CAES device, in addition to air as a working gas, a buffer gas is introduced into an air storage section formed of a steel pipe or a steel container, so that the amount of stored air is increased in the air compression process, and the amount of residual air in the air storage section can be reduced in the air expansion process. As a result, the amount of air stored in the air storage section is increased, and the volume of the storage space can be effectively utilized. The equipment cost of the air storage section formed of a steel container including a steel pipe becomes expensive, but by improving the volume utilization efficiency of this part, the equipment cost of the CAES method equipped with the above-mentioned air storage container can be reduced.

[0063] The air storage part composed of a steel container such as a steel pipe is convenient as an above-ground installation part, and the cost reduction of this part can contribute to the realization of an economical above-ground CAES method. As long as the CAES equipment can be installed on the ground, the installation site of the equipment can be selected without being restricted by the site selection conditions such as the stratum as in the past.

[0064] One of the advantages obtained by the above embodiment is that the volume of the compressed air storage space can be effectively utilized to the maximum extent by using the buffer gas. In the method of storing compressed air in a steel container including a steel pipe, the problem is that the equipment cost of the air storage becomes expensive, but this can be solved by the present invention using the buffer gas, thereby reducing the cost of the CAES equipment installed on the ground. Description of Reference Numerals

[0065] 10.11 Air 20, 21 Fuel 30, 31, 32, 33 Cooling water 110 Motor 120 Low pressure compressor 121, 221 shaft 130 High pressure compressor 140, 150 Aftercooler 151, 331, 341 three-way valve 160 heat storage tank 210 Generator 220 Low pressure expander 230 High pressure expander 240, 250 Burners 260 Regenerative Heat Exchanger 300 Air storage unit 301 (Compressed air storage) container 310 Buffer gas storage unit 311 (Buffer gas storage) container 320 Heat Exchanger 330 High temperature water tank 340 Low temperature water tank

Claims

1. A compressed air energy storage method, comprising: A compression process that converts electricity into compressed air energy and stores the compressed air in one or more containers; and an expansion process of expanding the stored compressed air and recovering the electric power, the compression process and the expansion process being performed alternately, The container has a single or multiple membranes disposed inside the entire or a part of each container, wherein the membranes form a space having a surface whose shape can be freely deformed, and multiple partial spaces are formed inside the container. At the start of the compression step, the partial space formed on one side of the two surfaces of the film inside the container is filled with a buffer gas. In the compressing step, the compressed air is stored in the container in the partial space on the other side of the two surfaces of the film without being mixed with the buffer gas, and The amount of the compressed air stored in the partial space on the other surface side is increased by leaving the buffer gas inside the container or by guiding the buffer gas to the outside of the container so that the buffer gas is changed into a fluid with a reduced volume. In the expansion step, the amount of the compressed air remaining in the container is reduced by vaporizing the fluid present inside or outside the container and restoring the buffer gas in the partial space on the one side inside the container.

2. The compressed air energy storage method according to claim 1, wherein: As the buffer gas, carbon dioxide alone or a mixture containing carbon dioxide as a main component is used.

3. The compressed air energy storage method according to claim 1 or 2, wherein: For the buffer gas pressure range, The minimum pressure in the expansion step is used in a range below the critical pressure of the buffer gas. The maximum pressure in the compression step is used to be 90% or more of the critical pressure of the buffer gas.

4. The compressed air energy storage method according to any one of claims 1 to 3, wherein: The compression heat generated by the compression of the air in the compression process is stored. The compression heat stored in the expansion step is used for at least one of heating the compressed air and heating the buffer gas.

5. The compressed air energy storage method according to claim 4, wherein: having a heat storage step for storing the compression heat, The heat storage step includes at least a step of absorbing the compression heat by water and storing the heat-absorbed water in a tank.

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