Compressed air energy storage system

Abstract

This invention provides a compressed air energy storage system that can reduce compression power and increase expansion power. [Solution] The system includes an air tank 12 for storing compressed air, a pair of tanks A and B that can be switched to communicate with either the air tank 12 or the atmosphere and are capable of storing a mixture of water and air, an air compression means 14 that supplies water from tank B, which is connected to the atmosphere, into tank A to raise the water level and isothermally compress the air in tank A, and a power generation means 16 that supplies compressed air from the air tank 12 into tank A to lower the water level, isothermally expands the compressed air in tank A to pressurize the water in tank A, and uses the hydroelectric energy of the pressurized water to generate hydroelectric power, and the water used for hydroelectric power generation by the power generation means 16 is recovered into tank B, which is connected to the atmosphere.

Description

Technical Field

[0001] The present invention relates to a compressed air energy storage system.

Background Art

[0002] Conventionally, CAES (Compressed Air Energy Storage) technology for storing electrical energy as compressed air has been known (see, for example, Patent Documents 1 and 2). The CAES system is roughly classified into three types: GT-CAES, conventional CAES, and A-CAES.

[0003] GT-CAES (Gas Turbine Compressed Air Energy Storage) converts the input power of the air compressor drive motor into compressed air by adiabatic compression during charging and accumulates it in an air tank. The generated adiabatic compression heat is cooled and discarded unused. During power generation, the high-pressure air accumulated as a fuel oxidant when generating power with a gas turbine is injected and burned together with natural gas or the like to generate power. Overseas, there is one each in Germany and the United States that has been operating for decades. Similar to a normal thermal power plant, there is a problem of generating a large amount of CO2.

[0004] Conventional CAES converts the input power of the air compressor drive motor into compressed air by adiabatic compression during charging and accumulates it in an air tank. The generated adiabatic compression heat is cooled and discarded unused. During power generation, the accumulated high-pressure air is supplied to an air turbine or the like by adiabatic expansion to generate power. Conventional CAES is used as a power storage device for solar power generation and wind power generation that cannot be fully utilized. Although it does not generate CO2, there are problems such as discarding the adiabatic compression heat generated during charging, a rapid drop in the accumulated pressure due to adiabatic expansion during power generation, a short power generation time, and a low charge-discharge efficiency RTE (Rated Total Efficiency).

[0005] A-CAES (Adiabatic CAES) is a system being developed and tested in various countries to solve the problems of the above-mentioned GT-CAES and conventional CAES. In A-CAES, during charging, the input power of the air compressor drive motor is converted into compressed air by adiabatic compression and stored in an air tank. The generated adiabatic compression heat is cooled by air cooling via a heat exchanger with a heat-resistant heat transfer medium, and the compression heat is transferred to the heat transfer medium and stored in an insulated heat transfer medium tank. During power generation, the stored high-pressure air is supplied to an air turbine etc. by adiabatic expansion to generate electricity. The high-pressure air supplied from the air tank to the air turbine is heated and expanded via a heat exchanger with a high-temperature heat transfer medium in an insulated heat transfer medium tank, extending the power generation time and improving the charge / discharge efficiency (RTE). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-106548 [Patent Document 2] Japanese Patent Application Publication No. 9-149564 [Overview of the project] [Problems that the invention aims to solve]

[0007] The A-CAES system described above required a large-capacity insulated heat storage tank proportional to the power generation time, thus necessitating equipment to minimize heat loss. This resulted in a large number of components and increased costs. Furthermore, because it uses adiabatic compression and expansion for charging and discharging, it generates more power (compression power) and less power (expansion power) compared to charge-discharge systems using isothermal compression and expansion. Therefore, even with reheating during expansion using a high-temperature heat transfer medium, there were limitations to improving the charging and discharging efficiency.

[0008] To solve these problems, the inventors investigated a charge-discharge method that reduces compression power and increases expansion power. As a result, they arrived at the present invention, which uses a charge-discharge method based on isothermal compression and isothermal expansion.

[0009] The present invention has been made in view of the above, and aims to provide a compressed air energy storage system that can reduce compression power and increase expansion power. [Means for solving the problem]

[0010] To solve the above-mentioned problems and achieve the objective, the compressed air energy storage system according to the present invention comprises an air tank for storing compressed air, a pair of tanks whose communication destination can be switched to either the air tank or the atmosphere and which are capable of storing a mixture of water and air, an air compression means for supplying water from the tank communicating with the atmosphere to the other tank to raise the water level and isothermally compressing the air in the tank, and a power generation means for supplying compressed air from the air tank to the tank to lower the water level, isothermally expanding the compressed air in the tank to pressurize the water in the tank, and generating hydroelectric power using the hydroelectric energy of the pressurized water, wherein the water used for hydroelectric power generation by the power generation means is recovered in the tank communicating with the atmosphere.

[0011] Furthermore, another compressed air energy storage system according to the present invention is characterized in that, in the above-described invention, the tank is a vertically elongated vertical tank or a horizontally elongated horizontal tank, and a laminated core made of thermally conductive vertical plates stacked at predetermined intervals in the horizontal direction is provided inside the tank.

[0012] Furthermore, another compressed air energy storage system according to the present invention is characterized in that, in the above-described invention, the tank is a vertically elongated vertical tank or a horizontally elongated horizontal tank, and the upper part of the tank is provided with an injection means for spraying water downward. [Effects of the Invention]

[0013] The compressed air energy storage system according to the present invention comprises an air tank for storing compressed air, a pair of tanks whose communication destination can be switched to either the air tank or the atmosphere and which can store a mixture of water and air, an air compression means that supplies water from the tank communicating with the atmosphere to the other tank to raise the water level and isothermally compress the air in the tank, and a power generation means that supplies compressed air from the air tank to the tank to lower the water level, isothermally expands the compressed air in the tank to pressurize the water in the tank, and generates hydroelectric power using the hydroelectric energy of the pressurized water. The water used for hydroelectric power generation by the power generation means is recovered in the tank communicating with the atmosphere, so by using a charge and discharge method using isothermal compression and isothermal expansion, the compression power can be reduced and the expansion power can be increased.

[0014] Furthermore, according to another compressed air energy storage system of the present invention, the tank is a vertically elongated vertical tank or a horizontally elongated horizontal tank, and a laminated core made of thermally conductive vertical plates stacked at predetermined intervals in the horizontal direction is provided inside the tank. This laminated core promotes heat exchange between water and air, and has the effect of easily realizing isothermal compression and isothermal expansion.

[0015] Furthermore, according to another compressed air energy storage system of the present invention, the tank is a vertically elongated vertical tank or a horizontally elongated horizontal tank, and the upper part of the tank is provided with an injection means for injecting water downwards. This means that heat exchange between water and air is promoted by the injection means, and isothermal compression and isothermal expansion can be easily achieved. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a schematic diagram showing an embodiment of the compressed air energy storage system according to the present invention. [Figure 2] Figure 2 is an explanatory diagram of the compression stroke showing an embodiment of the compressed air energy storage system according to the present invention. [Figure 3] Figure 3 is an explanatory diagram of a compression stroke showing an embodiment of a compressed air energy storage system according to the present invention. [Figure 4] Figure 4 is an explanatory diagram of an expansion stroke showing an embodiment of a compressed air energy storage system according to the present invention. [Figure 5] Figure 5 is an explanatory diagram of Example 1 of the present invention, where (1) is a vertical sectional view, (2) is an enlarged view of a main part, and (3) is a horizontal sectional view. [Figure 6] Figure 6 is an explanatory diagram of Example 2 of the present invention, where (1) is a vertical sectional view, (2) is an enlarged view of a main part, and (3) is a horizontal sectional view. [Figure 7] Figure 7 is an explanatory diagram of Example 3 of the present invention, where (1) is a front sectional view and (2) is a side sectional view.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of a compressed air energy storage system according to the present invention will be described in detail based on the drawings. Note that the present invention is not limited by these embodiments.

[0018] As shown in FIG. 1(1), a compressed air energy storage system 10 according to an embodiment of the present invention includes an air tank 12 for storing compressed air, a pair of tank units A and B capable of storing a mixture of water and air, a water pump 14, and a hydroelectric turbine 16. In this embodiment, charging and discharging are performed by isothermal compression and isothermal expansion of air using only air and water without CO2 generation due to combustion of fossil fuels or the like.

[0019] Tank units A and B are composed of a pair of two pressurized tanks 18 of the same structure. Each tank unit A and B may consist of one pressurized tank or three or more pressurized tanks. A water inlet 20 and an air communication port 22 are provided at the top of the pressurized tank 18, and a water supply and drainage port 24 is provided at the bottom of the pressurized tank 18. Tank units A and B can switch the communication port 22 (communication destination) to either the air tank 12 or the atmosphere via a discharge / intake switching unit 26. In the example in Figure 1(1), tank unit A is connected to the air tank 12, and tank unit B is connected to the atmosphere.

[0020] The discharge / intake switching unit 26 includes a pipe 28 connected to the air tank 12, two branch pipes 30 branching from the pipe 28, pressure regulating valves 32 provided on each branch pipe 30, and piping units A1 and B1 connected to the ends of each branch pipe 30, respectively. Piping units A1 and B1 each have a pipe 34 communicating with the branch pipe 30, an exhaust silencer 38 provided on one side of the pipe 34 via a solenoid valve 36, and an intake check valve 42 and an intake filter 44 provided on the other side of the pipe 34 via a solenoid valve 40. The exhaust silencer 38 is provided on the exhaust port side, and the intake filter 44 is provided on the intake port side. Between the solenoid valve 40 and the intake check valve 42, a pipe 46 is connected to the pipe 34, which communicates with the communication port 22 at the top of the pressurized tank 18. A water level sensor 48 is provided between the solenoid valve 40 and the intake check valve 42 to detect the water level in the pressurized tank 18 and the piping 46. A pressure sensor (not shown) is also provided between the solenoid valves 36 and 40 in the piping 34 to detect pressure.

[0021] The flow path switching by the discharge / intake switching unit 26 is performed automatically by a control device (not shown) that controls the pressure regulating valve 32, solenoid valves 36 and 40 based on the water level detection signal from the water level sensor 48. For example, during the compression stroke in tank unit A, the solenoid valves 36 and 40 of piping units A1 and B1 are closed to perform compression. At this time, tank unit B is in communication with the atmosphere. Subsequently, the compression stroke is terminated when the pressure sensor detects a signal indicating that the discharge pressure has been reached. Alternatively, the compression stroke may be terminated when the water level sensor 48 detects a signal indicating that the water level in the pressurized tank 18 has reached a predetermined set water level. Subsequently, the solenoid valve 40 and pressure regulating valve 32 on the piping unit A1 side are opened to connect tank unit A and the air tank 12, and the discharge of compressed air to the air tank 12 is started. Subsequently, when the water level in the piping 46 on the piping unit A1 side rises and reaches a predetermined set water level, the water level sensor 48 outputs a water level detection signal corresponding to that set water level. Based on this output, the solenoid valve 40 on the piping unit A1 side is closed, ending the discharge process.

[0022] Here, at the end of the discharge stroke, it is preferable to recover the energy of the compressed air that remains undischarged between the water level below the water level sensor 48 on the piping unit A1 side and the solenoid valve 40 into the tank unit B under atmospheric pressure. In this case, a recovery pipe 65A is provided to connect the piping 46 on the piping unit A1 side and the communication port 22 of the tank unit B, and after the end of the discharge stroke, the solenoid valve 67A provided in the recovery pipe 65A is opened for a short time to recover the remaining compressed air into the tank unit B. Similarly, after the tank unit B has finished the discharge stroke, it is preferable to recover the energy of the compressed air that remains undischarged between the water level below the water level sensor 48 on the piping unit B1 side and the solenoid valve 40 into the tank unit A under atmospheric pressure. In this case, a recovery pipe 65B is provided to connect the piping 46 on the piping unit B1 side and the communication port 22 of the tank unit A, and after the end of the discharge stroke, the solenoid valve 67B provided in the recovery pipe 65B is opened for a short time to recover the remaining compressed air into the tank unit A.

[0023] Meanwhile, during the expansion stroke in tank unit A, on the piping unit A1 side, the solenoid valve 40 and pressure regulating valve 32 are opened and the solenoid valve 36 is closed, while on the piping unit B1 side, the pressure regulating valve 32 is closed and solenoid valves 36 and 40 are opened to start intake. Subsequently, when the water level in the pressurized tank 18 of tank unit A reaches a predetermined set water level, the water level sensor 48 outputs a water level detection signal corresponding to that set water level. Based on this output, the pressure regulating valve 32 on the piping unit A1 side is closed. Subsequently, when the water level in the pressurized tank 18 of tank unit A drops and reaches a predetermined set water level, the water level sensor 48 outputs a water level detection signal corresponding to that set water level. Based on this output, the expansion stroke in tank unit A is terminated. After that, the expansion stroke in tank unit B begins. In this case, the solenoid valve 36 on the piping unit A1 side is opened, the solenoid valve 36 on the piping unit B1 side is closed, and the pressure regulating valve 32 on the piping unit B1 side is opened. At this time, tank unit B and air tank 12 are in communication, and tank unit A is in communication with the atmosphere.

[0024] The water level sensor 48 detects the water level in the pressurized tank 18 and the water level in the piping 46. It is preferable to use a detection method such as a laser type that can detect variable water levels for the water level sensor 48. Based on the detected water level, the amount of residual compressed air at the end of compression and discharge, and the end of the discharge stroke can be detected. It is preferable to install the water level sensor 48 above the piping 46 so that it can detect the water level rising through the piping 46 after filling the pressurized tank 18. The compression stroke is terminated when a signal indicating that the discharge pressure has been reached is detected by the pressure sensor, and then the discharge stroke begins, discharging as much compressed air as possible into the air tank 12. The end of the discharge stroke is detected by the water level detection signal from the water level sensor 48. For example, as shown in Figure 1(2), the end of the discharge stroke is detected when the detected water level reaches a set detection water level set above the piping 46. Alternatively, as shown in Figure 1(3), the end of the compression stroke may be detected when the detected water level reaches a set detection water level set in the pressurized tank 18.

[0025] Here, the amount of air remaining between the solenoid valve 40 in the discharge / intake switching unit 26 and the water surface in the piping 46 is compressed air that is not discharged to the air tank 12, so minimizing this amount is necessary to improve the performance of the air compressor. For this reason, it is desirable to set the position of the water surface in the piping 46 detected by the water level sensor 48 at the end of the discharge stroke as close to the solenoid valve 40 as possible. Furthermore, it is desirable to make the space between the water surface in the piping 46 and the solenoid valve 40 as small as possible. In this way, the amount of compressed air remaining between the solenoid valve 40 and the water surface in the piping 46 at the end of the discharge stroke can be reduced.

[0026] Furthermore, as water is discharged from the pressurized tank 18, the residual compressed air expands, and when it falls below atmospheric pressure, air is drawn into the pressurized tank 18 via the intake check valve 42, and the pressurized tank 18 is filled with air. The end of air filling may be determined by the detection timing of the water level detected by the water level sensor 48 in the pressurized tank 18 on the compression stroke side. In order to prevent water from remaining in the pressurized tank 18 during the intake stroke, the switching timing of tank units A and B may be adjusted according to the water level detected by the water level sensor 48 to prevent water from remaining in the pressurized tank 18 during the air filling stroke.

[0027] The water pump 14 supplies water from one tank unit B (or A) to the other tank unit A (or B), which is connected to the atmosphere. The water pump 14 is an air compression means that raises the water level in the pressurized tank 18 by supplying water (water piston), and isothermally compresses the air in the pressurized tank 18. In this embodiment, by raising and lowering the water level in tank units A and B with the water supply from the water pump 14, isothermally compresses air when the water level rises and performs atmospheric intake by pressure drop when the water level falls. The example in Figure 1(1) shows a case where two water pumps 14 are arranged in parallel. The suction side of the water pump 14 is connected to a pipe 52 that communicates with the water inlet and outlet 24 at the bottom of the pressurized tank 18 via a pipe 50, and the discharge side is connected to pipes 54A and 54B that communicate with the water inlet 20 at the top of the pressurized tank 18. Solenoid valves 56A to 56D are installed in piping 52, and solenoid valves 58A and 58B are installed in pipings 54A and 54B, respectively. Piping 50 is connected to piping 52 between solenoid valves 56B and 56C. In addition, piping 60A and 60B branch off from the discharge piping 54A and 54B, respectively, and solenoid valves 62A and 62B are installed in these pipings 60A and 60B, respectively. Piping 60A is connected to piping 52 between solenoid valves 56A and 56B, and piping 60B is connected to piping 52 between solenoid valves 56C and 56D.

[0028] Switching of the water supply path from the water pump 14 is performed automatically by a control device (not shown) that controls solenoid valves 56A-56D, 58A, 58B, 62A, 62B, etc., based on the water level detection signal from the water level sensor 48. For example, when supplying water from tank unit B (pressurized tank 18), which is in communication with the atmosphere, to tank unit A (pressurized tank 18), solenoid valves 56C, 56D, 58A, and 58B are opened, and the other solenoid valves are closed, and water is supplied from the water inlet / outlet port 24 of tank unit B (pressurized tank 18) to the water inlet port 20 of tank unit A (pressurized tank 18) via the water pump 14. The supplied water raises the water level inside tank unit A (pressurized tank 18), and isothermally compresses the air inside tank unit A (pressurized tank 18). The compressed air, compressed to the target pressure, is discharged to the air tank 12. During the compressed air discharge stroke, the water supply from the water pump 14 may be switched from the water inlet 20 at the top of the pressurized tank 18 to the water inlet / outlet 24 at the bottom. In this case, solenoid valves 56A, 56C, 56D, and 62A should be opened, and the other solenoid valves should be closed.

[0029] In this way, once the discharge of compressed air to the air tank 12 is complete, the water flow from the water pump 14 can be switched, for example, from a flow from tank unit B to tank unit A to a flow from tank unit A to tank unit B. This makes it possible to continuously draw in and compress atmospheric air in tank units A and B.

[0030] The water supply to the pressurized tank 18 has two functions. First, it supplies water to the pressurized tank 18 and compresses the air inside by raising the water level. Second, it uses the water supplied to the pressurized tank 18 to absorb the heat of air compression through heat exchange. Therefore, the water supply to the pressurized tank 18 ensures a compression cycle time that allows for heat exchange, so that the heat generated by isothermal compression can be transferred to the water in each cycle, enabling isothermal compression within the pressurized tank 18. In addition, a cooling area for heat exchange is ensured as the water surface area. Furthermore, water with a constant flow rate is mixed with the compressed air to maintain the heat transfer coefficient required during heat exchange. By using isothermal compression, a heat exchanger to recover the heat of compression is unnecessary, and a heat transfer medium tank for heat storage is also unnecessary.

[0031] The air tank 12 supplies compressed air into the pressurized tank 18, lowering the water level in the pressurized tank 18, and pressurizes the water in the pressurized tank 18 by isothermal expansion of the compressed air in the pressurized tank 18. The air supplied from the air tank 12 to the pressurized tank 18 is supplied with an expansion cycle time that allows for heat exchange, so that the heat generated by isothermal expansion can be transferred to the water in each cycle, enabling isothermal expansion within the pressurized tank 18. In addition, a heating area for heat exchange is ensured as the water surface area. Furthermore, it is preferable to mix water with a constant flow velocity into the compressed air so that the heat transfer coefficient required during heat exchange can be maintained.

[0032] The hydroelectric turbine 16 functions as a power generation means that generates hydroelectric power using the hydroelectric energy of pressurized water pressurized in the pressurized tank 18 by air supply from the air tank 12. The hydroelectric energy of the pressurized water is the potential energy (head) corresponding to the pressure of the pressurized water. In the example in Figure 1(1), the hydroelectric turbine 16 is shown when it is installed in a pipe 64 branched from pipe 52 via solenoid valves 66A and 66B. In this configuration, for example, when generating hydroelectric power using the hydroelectric energy of pressurized water pressurized in tank unit A (pressurized tank 18), solenoid valves 66A and 66B are opened and the other solenoid valves are closed, and pressurized water is supplied to the hydroelectric turbine 16 from the inlet and outlet 24 of tank unit A (pressurized tank 18) via pipes 52 and 64. As the hydroelectric turbine 16 rotates with the supplied pressurized water, a generator (not shown) generates electricity. The water after rotating the hydroelectric turbine 16 (water used for hydroelectric power generation) is recovered into tank unit B (pressurized tank 18) via pipe 52.

[0033] Next, the operation and function of the compressed air energy storage system 10 during the compression and expansion strokes will be described. <Compression Stroke> As shown in Figure 2(1), at the start of compression, tank unit A is connected to air tank 12, and tank unit B is connected to the atmosphere. The pressure regulating valve 32 on the air tank 12 side is closed. Assume that tank unit A is filled with pressurized air and tank unit B is filled with water.

[0034] As shown in Figure 2(2), when water from tank unit B is supplied to the water inlet 20 at the top of tank unit A by the water pump 14, the air inside tank unit A is isothermally compressed by the effect of rising water level (water piston action). Meanwhile, air is drawn into tank unit B.

[0035] As shown in Figure 2(3), when the compressed air pressure in tank unit A reaches the target pressure, the pressure regulating valve 32 is opened, and the discharge of compressed air from tank unit A to air tank 12 begins. During the discharge process, the water supply from water pump 14 is switched to the water inlet / outlet port 24 at the bottom of tank unit A, and after the discharge is complete, it is switched back to the water inlet port 20 at the top.

[0036] As shown in Figure 2(4), compressed air is discharged from tank unit A into air tank 12 and pressurized. Once tank unit A is filled with water, the discharge is stopped.

[0037] Next, the discharge / intake switching unit 26 switches the connection between the air tank 12 and tank units A and B to the atmosphere.

[0038] As shown in Figure 3(1), at the start of compression, tank unit B is connected to air tank 12, and tank unit A is connected to the atmosphere. The pressure regulating valve 32 on the air tank 12 side is closed. Tank unit B is filled with pressurized air, and tank unit A is filled with water.

[0039] As shown in Figure 3(2), when water from tank unit A is supplied to the water inlet 20 at the top of tank unit B by the water pump 14, the air inside tank unit B is isothermally compressed by the effect of rising water level (water piston action). Meanwhile, air is drawn into tank unit A.

[0040] As shown in Figure 3(3), when the compressed air pressure in tank unit B reaches the target pressure, the pressure regulating valve 32 is opened, and the discharge of compressed air from tank unit B to air tank 12 begins. During the discharge process, the water supply from water pump 14 is switched to the water inlet / outlet port 24 at the bottom of tank unit B, and after the discharge is completed, it is switched back to the water inlet port 20 at the top.

[0041] As shown in Figure 3(4), compressed air is discharged from tank unit B into air tank 12 and pressurized. Once tank unit B is filled with water, the discharge is stopped.

[0042] Subsequently, tank units A and B are switched, and isothermally compressed air is continuously stored in the air tank 12 through the compression cycle. In this way, during the compression stroke, the input power of the drive motor of the water pump 14 is converted into compressed air and stored.

[0043] <Expansion process> As shown in Figure 4(1), at the start of expansion, tank unit A is connected to the air tank 12, and tank unit B is connected to the atmosphere. Tank unit A is filled with water, and tank unit B is filled with air. The water inlet / outlet port 24 at the bottom of tank unit A and the water inlet / outlet port 24 at the bottom of tank unit B are connected by piping 64, enabling water supply to the hydroelectric turbine 16. The pressure regulating valve 32 on the air tank 12 side is opened, and compressed air from the air tank 12 is supplied to tank unit A.

[0044] As shown in Figure 4(2), the water in tank unit A is pressurized by the isothermal expansion of compressed air within tank unit A. The pressurized water is continuously supplied to the hydroelectric turbine 16 via pipes 52 and 64, and hydroelectric power is generated. The water used for hydroelectric power generation is drained into tank unit B via pipe 52. The air in tank unit B is released into the atmosphere due to the rising water level.

[0045] Once water is filled into tank unit B, the discharge / intake switching unit 26 switches the connections of tank units A and B to the air tank 12 and the atmosphere. That is, tank unit B is connected to the air tank 12, and tank unit A is connected to the atmosphere.

[0046] As shown in Figure 4(3), at the start of expansion, tank unit B is filled with water and tank unit A is filled with air. The pressure regulating valve 32 on the air tank 12 side is opened, and compressed air from air tank 12 is supplied to tank unit B.

[0047] As shown in Figure 4(4), the water in tank unit B is pressurized by the isothermal expansion of compressed air within tank unit B. The pressurized water is continuously supplied to the hydroelectric turbine 16 via pipes 52 and 64, and hydroelectric power is generated. The water used for hydroelectric power generation is drained into tank unit A via pipe 52. The air in tank unit A is released into the atmosphere due to the rising water level.

[0048] Subsequently, the discharge / intake switching unit 26 switches between tank units A and B, generating pressurized water with isothermally expanded air through the expansion cycle, and continuously supplying this water to the hydroelectric turbine 16. In this way, during the expansion stroke, the compressed air in the air tank 12 is converted into a pressure head equivalent to the drop of hydroelectric power generation, and the generated electricity is discharged.

[0049] Thus, according to this embodiment, by using a charge-discharge method based on isothermal compression and isothermal expansion, it is possible to reduce the compression power and increase the expansion power compared to the conventional charge-discharge method based on adiabatic compression and adiabatic expansion.

[0050] Incidentally, in the compression process described above, the ambient temperature air filled in the compression tank (pressurized tank 18 where air compression occurs) will rise in temperature by the amount of compression power unless it is cooled after each expansion cycle. Isothermal compression is achieved by minimizing this temperature rise. Therefore, in order to minimize the temperature difference ΔTc between the temperature of the water used as a cooling medium in the compression tank and the temperature of the air that has risen due to compression, it is necessary to maximize the amount of heat exchange Qc (heat exchange amount Qc = Uc × Ac × ΔTc) between the water and air in the compression tank. Ac is the heat exchange area and Uc is the heat transfer coefficient. The amount of heat exchange Qc is determined from the design specifications of the compressed air energy storage system 10, and the temperature difference ΔTc is determined from the target expansion polytropic index. A heat exchange mechanism in the compression tank is required that satisfies a cooling capacity Uc × Ac = Qc / ΔTc suitable for the structure of the compression tank.

[0051] The absolute value of the difference in compression power between adiabatic compression and isothermal compression does not change significantly from low to high pressure, and therefore the power that can be reduced by isothermal compression also does not change significantly. To prevent the cooling capacity Uc × Ac from changing significantly even when the pressure rises due to changes in the water level in the compression tank, it is desirable to have a structure in which the heat exchange area Ac and the heat transfer coefficient Uc change with the water level. Examples of such structures include a structure in which a laminated core is built into the compression tank and a structure in which water is injected into the compression tank, but the specific details will be described later.

[0052] The amount of water injected into the compression tank, Qwc, is set to match the target isothermal compression cycle time, tc seconds. The amount of water injected, Qwc, is set to Qwc(m 3 / s)=Vc(m 3 It can be calculated using ) / tc(s), where Vc is the compression tank capacity.

[0053] Furthermore, during the expansion process described above, when compressed air from the air tank 12 is supplied to the expansion tank (the pressurized tank 18 where air expansion occurs), the water in the expansion tank is pressurized by the pressure of the air and supplied to the hydroelectric turbine 16. The temperature of the supplied air, which is at the temperature inside the air tank 12, decreases by the amount of expansion power with each expansion cycle. Isothermal expansion is achieved by minimizing this temperature drop. Therefore, in order to minimize the temperature difference ΔTe between the temperature of the water, which acts as the heating medium in the expansion tank, and the temperature of the air that has decreased due to expansion, it is necessary to maximize the amount of heat exchange Qe (heat exchange amount Qe = Ue × Ae × ΔTe) between the water and air in the expansion tank. Ae is the heat exchange area, and Ue is the heat transfer coefficient. The amount of heat exchange Qe is determined from the design specifications of the compressed air energy storage system 10, and the temperature difference ΔTe is determined from the target expansion polytropic index. A heat exchange mechanism within the expansion tank is required that satisfies the heating capacity Ue × Ae = Qe / ΔTe, which is suitable for the structure of the expansion tank.

[0054] The difference in expansion power between adiabatic and isothermal expansion becomes overwhelmingly larger as the expansion stroke becomes lower pressure. Therefore, it is desirable to have a structure with a heat exchange area Ae and heat transfer coefficient Ue that can ensure a sufficient amount of heat exchange Qe from heating by injected water, especially in the latter half of the expansion stroke when the amount of water in the expansion tank decreases. Examples of such structures include a structure with a laminated core built into the expansion tank and a structure that supplies injected water to the expansion tank, but the specific details will be described later.

[0055] The heat exchange area during the expansion stroke is limited to the water surface in the expansion tank, which is insufficient compared to the compression stroke. Therefore, it is desirable to provide means to enhance the heat exchange capacity. For example, to increase the heat exchange area Ae that can contribute to heating the expanding air, a circulating water pump is installed to circulate the water drained from the bottom of the expansion tank, and the drained water is sprayed from the top of the expansion tank. The circulating water pump draws water from a pipe branched from a pipe connected to the water inlet / drain port 40 at the bottom of the expansion tank, and discharges water from the circulating water pump to a pipe connected to the water inlet 20 at the top of the expansion tank. For example, as shown in Figure 4(1), a circulating pipe 68 may be provided that branches from the upstream pipes 52 and 64 of the power generation turbine 16 and leads to the water inlet 20, and a circulating water pump may be installed in this pipe 68. This ensures that the expanding air space during expansion is filled with sprayed water (injected water) without hindering drainage for expansion, thereby securing a heat exchange area Ae and enabling isothermal expansion. The circulating water pump should consume the minimum necessary power and use the minimum amount of water necessary to enable isothermal expansion, and it is desirable to minimize the differential pressure between the intake and discharge of the circulating water pump. Furthermore, as the expansion cycle repeats, the temperature of the circulating injection water decreases by the amount of heat exchange.

[0056] Compressed air from the air tank 12 to the expansion tank is supplied at the same time as the switching timing of the solenoid valves, etc., of the pair of pressurized tanks 18. Target expansion stop pressure Pe2 (MPaG), tank capacity V (m³ 3 The initial air supply pressure Pe1 (MPaG) and the supply air volume Ve1 (m³) are equivalent to the calculated air mass Ge2 (kg) at the time of air supply. 3 ) is supplied with air.

[0057] The circulating water pump starts injecting water into the expansion tank, which has a volume V, at the same time as compressed air is supplied into the expansion tank from the air tank 12, and the supply pressure Pe1 (MPaG) is (V-Ve1)(m 3 It expands by ) and stops when it reaches a pressure of Pe2 (MPaG).

[0058] To reduce the polytropic index of expansion, a heat exchanger for heating the circulating water may be inserted into the piping path of the circulating water pump. The circulating water may be heated with high-temperature water from sources such as air conditioning hot water, industrial waste heat, or solar heat, thereby increasing the temperature difference between the expanding air and the injected water during expansion and increasing the amount of heat required for heating.

[0059] Compressed air from air tank 12 is supplied to the expansion tank at an air volume of Ve1(m³). 3 Pressurized water is generated by the inflow of a certain amount, and this pressurized water is supplied to the hydroelectric turbine 16. In the case of constant-pressure constant-head power generation, it is desirable to use a hydroelectric turbine 16 that is appropriate for the head and the amount of water supplied, as the head (m) of this pressurized water is the difference in water pressure.

[0060] As water is supplied to the hydroelectric turbine 16, the suction pressure Pe1 (MPaG) decreases, and the head of water at the hydroelectric turbine 16 decreases. Therefore, the type of turbine may be changed and selected according to the magnitude and volume of the changing head, or multiple hydroelectric turbines 16 may be connected in series or parallel to generate electricity.

[0061] (Example 1) Next, Example 1 of the present invention will be described. As shown in Figure 5, Embodiment 1 of the present invention uses a vertically elongated vertical tank 18A as the pressurized tank 18. The vertical tank 18A is cylindrical with a lid and bottom. Inside the vertical tank 18A is a laminated core 72 made of thermally conductive vertical plates 70 stacked at predetermined intervals (for example, a pitch of several mm) in the horizontal direction. The vertical plates 70 are rectangular in shape and elongated in the vertical direction, and for example, aluminum plates can be used. The bottom of the laminated core 72 is fixed to the bottom inside the vertical tank 18A, and the top of the laminated core 72 is positioned close to the top end inside the vertical tank 18A. The laminated core 72 is square when viewed from above, and a roughly annular space is formed between the outer surface of the laminated core 72 and the inner wall of the vertical tank 18A when viewed from above.

[0062] The bottom of the vertical tank 18A is provided with a water inlet and outlet 24, and the top of the vertical tank 18A is provided with a water inlet 20 and a communication port 22 for air discharge and suction. The water inlet 20 at the top of the vertical tank 18A communicates with a plurality of water injection ports 76 provided on the lid 74. The water injection ports 76 are arranged in a grid pattern within a square-shaped area facing the laminated core 72. The water inlet and outlet 24 and the water inlet 20 are connected to pipes 52 and 54 (54A or 54B), respectively. A circulation pipe (not shown) and a circulating water pump are connected to pipe 54. Inside the vertical tank 18A is the water level WL.

[0063] <Compression Stroke> During the compression stroke, water WJ is injected into the laminated core 72 from a water injection port 76 at the top of the laminated core 72, forcibly mixing the air in the space inside the laminated core 72 with the injected water WJ, and the surface area of ​​the wetted vertical plate 70 and the surface area of ​​the flowing water droplets become the heat exchange area. In this way, a large cooling area can be secured relative to the tank volume during the compression stroke. Since the water flowing down the narrow inter-plate channel entrains air, it is preferable to provide an air outlet for the flowing air in the laminated core 72, and to have a structure that allows air to circulate vertically in the space between the inner surface of the vertical tank 18A and the outer surface of the laminated core 72. To ensure air circulation even with changes in water level, it is preferable to appropriately distribute flow path holes, such as punched holes, at vertical intervals on each vertical plate 70 so that internal air can escape to the outer surface of the laminated core 72.

[0064] <Expansion process> During the expansion stroke, the water pump 14 is stopped, and pressurized water is supplied from the water inlet / outlet port 76 at the bottom of the vertical tank 18A to the power generation turbine 16 (not shown) via pipes 52 and 64. Meanwhile, a portion of the pressurized water flowing through pipe 52 is supplied to the pipe 54 at the top of the vertical tank 18A via a circulation pipe (for example, pipe 68 in Figure 4(1)) using a circulating water pump with a small differential pressure. Water WJ is then injected into the vertical tank 18A from the water injection port 76 to wet the surface of the laminated core 72, thereby ensuring a heated area and heat transfer coefficient. A characteristic of the vertical tank is that the air space expands as the water level drops during expansion, increasing the wetted surface area and the amount of water droplets within the space. This increases the area heated by the heat generated by the expansion power, which increases from the adiabatic expansion power of isothermal expansion, making it possible to maintain isothermal expansion performance.

[0065] Thus, according to this embodiment, the laminated core 72 promotes heat exchange between water and air, making it possible to easily achieve isothermal compression and isothermal expansion.

[0066] (Example 2) Next, we will describe Example 2 of the present invention. As shown in Figure 6, Embodiment 2 of the present invention is characterized in that, in the vertical tank 18A of Embodiment 1 above, an injection nozzle 78 (injection means) is provided on the upper lid 74 instead of the water injection port 76. Note that in the example in Figure 6, the laminated core 72 is omitted. The injection nozzle 78 injects water WJ into the vertical tank 18A and is connected to the water inlet 20 at the top of the vertical tank 18A. The injection nozzles 78 are provided at four locations at the vertices of a square when viewed from above. The laminated core 72 can also be omitted.

[0067] <Compression Stroke> During the compression stroke, water WJ is injected into the vertical tank 18A from the injection nozzles 78. The injection nozzles 78 are preferably positioned to allow tangential water injection along the inner wall of the vertical tank 18A, generating a swirling flow from top to bottom along the inner surface of the vertical tank 18A. This improves the heat transfer coefficient through water surface oscillation and airflow generated by the water flow. The injection nozzles 78 may also be configured to inject directly downwards into the vertical tank 18A to ensure a sufficient water droplet area and improve the heat transfer coefficient by directly mixing with air. Multiple injection nozzles 78 may be provided at different positions on the lid 74. In this case, it is preferable that the water injection angle of each injection nozzle 78 be a narrow angle corresponding to the number of nozzles and the tank length, effectively cooling the entire space of the vertical tank 18A.

[0068] <Expansion process> During the expansion stroke, the water pump 14 is stopped, and pressurized water is supplied to the power generation turbine 16 from the water inlet / outlet port 24 at the bottom of the vertical tank 18A via pipes 52 and 64. Meanwhile, a portion of the pressurized water flowing through pipe 52 is supplied to pipe 54 at the top of the vertical tank 18A via a circulating water pump with a small differential pressure (for example, pipe 68 in Figure 4(1)), and water WJ is injected into the vertical tank 18A from the injection nozzle 78 to wet the surface of the laminated core 72, thereby ensuring a heated area and heat transfer coefficient. A characteristic of the vertical tank is that the air space expands as the water level drops during expansion, increasing the wetted surface area and the amount of water droplets within the space. This increases the area heated by the heat generated by the expansion power, which increases from the adiabatic expansion power of isothermal expansion, making it possible to maintain isothermal expansion performance.

[0069] Thus, according to this embodiment, the injection nozzle 56 promotes heat exchange between water and air, making it possible to easily achieve isothermal compression and isothermal expansion.

[0070] (Example 3) Next, we will describe Example 3 of the present invention. As shown in Figure 7, Embodiment 3 of the present invention uses a horizontally elongated horizontal tank 18B as the pressurized tank 18. The horizontal tank 18B is a horizontally elongated cylindrical shape with its end faces closed by flanges 80. A water inlet and outlet 24 is provided in the longitudinal center of the bottom of the horizontal tank 18B, and an air vent 22 is provided in the longitudinal center of the top of the horizontal tank 18B. Water inlets 20 are provided at both ends of the horizontal tank 18B. Pipes 52 and 54 are connected to the water inlet and outlet 24 and the water inlet 20, respectively.

[0071] A spray pipe 82 for spraying water downwards is provided horizontally on the upper surface of the horizontal tank 18B. The spray pipe 82 is inserted and fixed into the interior of the horizontal tank 18B from flanges 80 at both the left and right ends of the horizontal tank 18B and communicates with the water inlet 20. Water nozzles 84 (spraying means) are provided at intervals along the longitudinal direction of the spray pipe 82 at the lower part of the spray pipe 82. The water nozzles 84 may be arranged in one row at the very bottom of the spray pipe 82, or in multiple rows such as two rows. Alternatively, a spray nozzle may be provided instead of water nozzles 84. In this case, the spray nozzle may be screwed into and fixed to the water nozzles 84.

[0072] During the compression stroke, spray-like water WJ is injected from the water injection port 84 or injection nozzle via the injection pipe 82 towards the horizontally elongated water surface WL at the bottom of the horizontal tank 18B, thereby promoting heat exchange between the air and water in the horizontal tank 18B.

[0073] As described above, the reduction effect of isothermal compression on compression power is lower in the low-pressure range compared to adiabatic compression, but the absolute value of the reduced power does not change significantly. Therefore, in the case of the horizontal tank 18B, it is preferable to have a structure in which the cooling area Ac and the heat transfer coefficient Uc change as the water level rises, so that the value of Uc × Ac, which is the heat exchange capacity, does not change significantly. Specifically, in the high-pressure range, the cooling area Ac gradually decreases, but it is preferable to have a structure in which the stirring effect is improved by bringing the water surface WL and the injection nozzle closer together, thereby maintaining the isothermal cooling capacity by improving the heat transfer coefficient Uc.

[0074] When prioritizing the maximization of the heat exchange area Ac, it is preferable to inject the water WJ through injection nozzles, inject the water WJ as mist droplets with an angle in the injection direction, and set the number of injection nozzles and each injection angle so that the entire air space in the horizontal tank 18B is filled with water droplets.

[0075] If maximizing the heat transfer coefficient Uc is the priority, the injection of the water WJ may be made a direct injection with low direct water resistance to match the characteristics of the horizontal tank where the distance to the water surface WL is short. By causing the injected water WJ to collide with the water surface WL with a flow velocity, mutual mixing of air and water is promoted, thereby improving the heat transfer coefficient. The amount of water WJ supplied to the horizontal tank 18B by the water pump 14 Q (L / min) is adjusted to match the structural characteristics where the distance between the injection nozzle position and the water surface WL is short. The water particle size, injection velocity, and injection angle are adjusted to match the heat exchange area A (m²) in the low-pressure region. 2 ) and the heat transfer coefficient U (kcal / m 2 It is preferable to set the head of the water pump 14 to the minimum while adhering to this condition so that the product of (°C / h) is maximized.

[0076] Thus, isothermal compression and isothermal expansion can be easily achieved with this embodiment as well.

[0077] As described above, the compressed air energy storage system according to the present invention comprises an air tank for storing compressed air, a pair of tanks whose communication destination can be switched to either the air tank or the atmosphere and which can store a mixture of water and air, an air compression means that supplies water from the tank communicating with the atmosphere to the other tank to raise the water level and isothermally compress the air in the tank, and a power generation means that supplies compressed air from the air tank to the tank to lower the water level, isothermally expands the compressed air in the tank to pressurize the water in the tank, and generates hydroelectric power using the hydroelectric energy of the pressurized water. The water used for hydroelectric power generation by the power generation means is recovered in the tank communicating with the atmosphere, so by using a charge and discharge method using isothermal compression and isothermal expansion, the compression power can be reduced and the expansion power can be increased.

[0078] Furthermore, according to another compressed air energy storage system of the present invention, the tank is a vertically elongated vertical tank or a horizontally elongated horizontal tank, and a laminated core made of thermally conductive vertical plates stacked at predetermined intervals in the horizontal direction is provided inside the tank. The laminated core promotes heat exchange between water and air, and isothermal compression and isothermal expansion can be easily achieved.

[0079] Furthermore, according to another compressed air energy storage system of the present invention, an injection means for injecting water downward is provided in the upper part of the tank, so that heat exchange between water and air is promoted by the injection means, and isothermal compression and isothermal expansion can be easily achieved. [Industrial applicability]

[0080] As described above, the compressed air energy storage system according to the present invention is useful for CAES that stores electrical energy as compressed air, and is particularly suitable for reducing compression power and increasing expansion power. [Explanation of symbols]

[0081] 10 Compressed air energy storage system 12 air tanks 14. Water pump (air compression means) 16. Hydroelectric turbine (means of power generation) 18. Pressurized tank (tank) 18A Vertical Tank 18B Horizontal Tank 20 Water inlet 22 connecting ports 24 Inlet and outlet 26 Discharge / Intake Switching Section 28, 34, 50, 52, 54A, 54B, 60A, 60B, 64 Piping 30 branch pipes 32 Pressure regulating valve 36, 40, 46, 56A~56D, 58A, 58B, 62A, 62B, 66A, 66B Solenoid valves 38 Exhaust Silencer 42 Intake check valve 44 Intake filter 48 Water level sensor 65A, 65B Recovery pipe 67A, 67B Solenoid valve 70 Vertical Plate 72 stacked core 76 Water injection port (injection means) 78. Spray nozzle (spraying means) 80 flange 82 Injection pipe 84 Water injection port (injection means) A, B Tank Unit (Tank)

Claims

1. A compressed air energy storage system comprising: an air tank for storing compressed air; a pair of tanks whose communication destination can be switched to either the air tank or the atmosphere, and which are capable of storing a mixture of water and air; an air compression means for supplying water from the tank communicating with the atmosphere to the other tank to raise the water level and isothermally compressing the air in the tank; and a power generation means for supplying compressed air from the air tank to the tank to lower the water level, isothermally expanding the compressed air in the tank to pressurize the water in the tank, and generating hydroelectric power using the hydroelectric energy of the pressurized water, wherein the water used for hydroelectric power generation by the power generation means is recovered in the tank communicating with the atmosphere.

2. The compressed air energy storage system according to claim 1, characterized in that the tank is a vertically elongated vertical tank or a horizontally elongated horizontal tank, and a laminated core made of thermally conductive vertical plates stacked at predetermined intervals in the horizontal direction is provided inside the tank.

3. The compressed air energy storage system according to claim 1 or 2, characterized in that the tank is a vertically elongated vertical tank or a horizontally elongated horizontal tank, and the upper part of the tank is provided with an injection means for spraying water downward.

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