System for energy storage using fluid compression and concentration difference in liquid solution

Abstract

A system for energy storage utilizing a flow driven by a difference in concentration of a solution consisting of a solvent and a solute. The solvents and solutes can be selected, wherein the most economical components are water and salt. A system for storing energy by using fluid compression and concentration difference in a liquid solution is characterized by having an energy charging stage for storing energy and an energy discharging stage for releasing the energy. The system includes a pump, a semi-permeable separator, three reservoirs, one of which is a pressurized reservoir, and a turbine connected to a generator. Wherein, during the discharge phase, the system is capable of releasing energy stored during the charge phase.

Description

Technical Field

[0001] The present invention relates to energy storage, and more particularly to a system for storing and transporting electrical energy using fluid compression. Background Art

[0002] Pumped-storage hydroelectricity (commonly referred to as PSH) utilizes the height difference between two reservoirs to store potential energy, which can then be used to drive turbines and release the stored energy when needed. PSH is a mature technology with relatively high round-trip efficiency. However, its use is significantly geographically limited due to the required height difference between the two reservoirs.

[0003] Another energy storage method is to use electrical energy to compress air and store it in large gas storage tanks. During periods of high electrical demand, the compressed air is released and used to generate electricity through a turbine. These are known as compressed air energy storage systems (commonly referred to as CAES). However, due to compressor losses, traditional CAES systems have low efficiency. Efficiency can be improved by storing some of the heat released during the compression process and utilizing it during the expansion phase.

[0004] Currently, there are also technologies that combine PSH and CAES. In such systems, when energy demand is low, the energy is used to pump a liquid (charging phase), which ultimately compresses a gas into a pressurized container. When power is needed, a valve is opened and the liquid is delivered to a turbine connected to a generator (discharging phase). In this way, the pressure inside the container is reduced until it is too low to generate more energy in the generator. At this point, the system is ready to start the charging phase again.

[0005] By using a phase change fluid within the operating range of the system, the efficiency of the system can be increased by storing energy not only through compression but also through phase change.

[0006] The main cost of these systems is associated with the manufacture of the pressurized container. This is due to the inherent nature of the process: all energy is stored in the form of pressure. Therefore, the container must have a relatively large thickness to withstand the extremely high pressure, which increases the cost of such containers. Thus, in recent years, efforts have been made to reduce the cost of these containers.

[0007] Different from the prior art, the present invention stores energy not only in the form of the pressure of a compressible fluid, but also in the form of the chemical potential of a solvent and a solute in a liquid solution. The specific method is to pump a liquid solution from a reservoir A to a pressurized reservoir B, which is in turn connected to a semi-permeable separator that can be used for an osmotic process, allowing the solvent to be transferred to a reservoir C at low pressure through reverse osmosis while avoiding the transfer of the solute, which is stored in the pressurized reservoir B in the form of an aqueous solution. As the volume of the aqueous solution in the reservoir B increases, the volume occupied by the compressible fluid decreases, thereby increasing the pressure of the entire reservoir B and its connected devices. This enables energy to be stored not only in the form of pressure within the reservoir B at the end of the charging phase, but also in the form of chemical potential when separating the solute from the solvent in the semi-permeable separator. Once the discharging phase begins, the pressure of the pressurized container starts to drop until the solvent permeates from the low-pressure reservoir C through the semi-permeable separator into the pressurized reservoir B. Compared with the prior art, this increases the energy storage capacity of a pressurized container of a given volume and pressure. Summary of the Invention

[0008] The present invention includes and implements a system for higher energy storage using the flow driven by the concentration difference of a solution composed of a solvent and a solute. Water can be used as the solvent. The solute can be a salt or other compound dissolved in the solvent. In addition to the solution, the system also uses a compressible fluid, such as air. The present invention includes a turbine connected to a generator, an electric pump, a plurality of valves, a semi-permeable separator (which has a membrane that allows the solvent to pass through but blocks the solute), at least one reservoir A for storing a low-pressure liquid solution, at least one reservoir B for storing a compressible fluid and a part of the solution, at least one reservoir C for storing the solvent separated by the semi-permeable separator, a set of pipes for connecting the devices, and an instrument and an automatic process control system.

[0009] The present invention describes the operation in a specific case, that is, there is one reservoir A, one reservoir B, and one reservoir C, but the present invention is also applicable to a larger number of reservoirs.

[0010] To simplify the description of the present invention, the part of the system at high pressure will be referred to as the pressurized part ( Figure 5 ), which consists of the reservoir B, the pressurized chamber of the semi-permeable separator, and the pipes connecting the pump and the turbine.

[0011] Similarly, in the description of the invention, 5 valves are mentioned to illustrate the flow direction during different stages of the process. However, the present invention is not limited to this specific number of valves. All the valves shown in the figure are two-way valves.

[0012] In order to store energy and convert it into electrical energy when needed, the present invention comprises multiple stages, as shown in the pressure-concentration diagram of Figure 4 and described hereinafter.

[0013] At the start of the charging stage (point A in Figure 4), reservoir A contains a low-pressure liquid solution (which can be at atmospheric pressure), the solution containing a solvent (which can be water) and at least one solute, which can be a salt or other compound dissolved in the solvent. Reservoir A is provided with a connecting pipe for connecting valve V1 and the pump. This connecting pipe must be below the liquid level in reservoir A (see Figure 6) to ensure that the pump only sucks the liquid.

[0014] The upper part of reservoir B contains a compressible fluid (which can be air) with a density lower than that of the liquid solution. Due to its lower density than the liquid solution, the compressible fluid is always stored in reservoir B throughout the process. The interface position of the outlet pipe connecting reservoir B and valve V4 must ensure that the liquid level in reservoir B is always higher than this interface to maximize the amount of liquid in the discharging stage.

[0015] Reservoir C is in a low-pressure state, which can be atmospheric pressure. Reservoir C is connected to a semi-permeable separator, such as a semi-permeable membrane in a reverse osmosis system, which allows the solvent to flow through but blocks the solute. The pipe interface position in reservoir C should ensure that the liquid level in the reservoir is always higher than the interface (see Figure 8).

[0016] The charging stage of the system is shown as the A-B section in Figure 4. In this stage, the electrical energy generated by renewable energy is used to drive the pump to transport the aqueous solution in reservoir A to the pressurization system, thereby compressing the compressible fluid in reservoir B.

[0017] This compression means that the pressure in the pressurization system increases, including the compressible fluid and the aqueous solution. As the pressure increases, the difference between the pressure of the solution and the osmotic pressure also increases, enabling the solvent (which can be water) to pass through the semi-permeable separator into reservoir C, but the solute remains in the solution in the pressurization system. Therefore, during the charging stage, the solute concentration in the pressurization system increases. This can be clearly represented by Figure 4 the A-B line segment in

[0018] During the entire charging phase, energy is stored not only by the increase in pressure of the pressurization system but also by the increase in the chemical potential of the solution due to solute separation. That is to say, during the charging phase, a reverse osmosis process occurs where the solvent passes through the semi-permeable separator, forming two solutions with different solute concentrations: a concentrated solution within the pressurization system and a solution with a low (i.e., diluted) concentration in reservoir C. This concentration difference between the two solutions causes the solvent to pass through the semi-permeable separator from the low-pressure system to the high-pressure system during the discharging phase, which is achieved through osmosis. In this way, during the charging phase, part of the electrical energy is converted into fluid energy in the form of pressure within the pump and then stored in the form of chemical potential by separating the solutions in the semi-permeable separator. During the discharging phase, the energy in the form of chemical potential passes through the semi-permeable separator and is converted back into fluid energy in the form of pressure, and then converted back into electrical energy through the turbine driving the generator.

[0019] The pressurization system is equipped with at least one pressure sensor for detecting the working pressure and automatically stopping the injection of more solution into the pressurization system after reaching the maximum allowable pressure of the pressurization system. In Figure 1 the schematic diagram shown, it is represented by closing valve V2 and stopping the pump. At this time, the liquid volume in reservoir C may be several times larger than the liquid volume in reservoir B. Therefore, the volume of the energy storage liquid is maximized. Since reservoir B is the only reservoir that needs to withstand high pressure, the total cost of the system is reduced.

[0020] Figure 4 The B-C section in represents the stage immediately following the charging phase. At the end of the charging phase, the solution pumping stops, and the pressure of the pressurization system is greater than the osmotic pressure of the solution. Therefore, part of the solvent naturally enters reservoir C, slightly reducing the pressure of the pressurization system until osmotic equilibrium is reached. At the end of this stage, the system can generate electricity as needed.

[0021] Figure 4 The C-D section in corresponds to the discharging phase of the system, during which the liquid solution in reservoir B is introduced into the turbine connected to the generator to release its energy. In Figure 2 the schematic diagram shown, this is represented by opening valves V4 and V5.

[0022] During the discharging phase, as the volume of the aqueous solution in the pressurization system decreases, the pressure drops below the osmotic pressure of the solution, allowing the solvent to pass through the semi-permeable membrane from reservoir C into the pressurization system. In this way, the liquid originally at low pressure in reservoir C can now be used for power generation, thus increasing the total capacity of the pressurization system.

[0023] After the liquid solution flows through the turbine, it is discharged into a reservoir, which may or may not be reservoir A used during the charging phase.

[0024] The start of the exothermic stage can be automated according to grid requirements or operator operation. In the configuration shown in Figure 2, the reservoir A used in the charging stage is the same as the reservoir A used in the exothermic stage, and valves V4 and V5 remain open to connect reservoir B, the semi-permeable separator, the turbine, and reservoir A. Valve V2 remains closed to isolate the pump. Once the pressure sensor of the pressurization system detects that the minimum pressure required for the turbine has been reached or the solution in reservoir B has reached the minimum liquid level, the supply of the liquid solution to the turbine will automatically stop. In the diagram shown in Figure 2, this is represented by closing valve V5.

[0025] Figure 4 The D-A section in it represents the stage immediately following the exothermic stage. When the exothermic stage ends, the solution stops flowing, and the pressure of the pressurization system is lower than the osmotic pressure of the solution. Therefore, part of the solvent naturally enters the pressurization system from reservoir C, slightly increasing the pressure of the pressurization system until osmotic equilibrium is reached. At the end of this stage, the system is ready to enter the next charging stage.

[0026] The durations of the charging and exothermic stages depend on the size of the energy storage system and the rate at which the solution is discharged to the turbine.

[0027] The present invention provides different variant schemes for installation according to specific energy storage requirements. This has advantages over the prior art.

[0028] The first variant scheme of the present invention includes a solute separator (e.g., a physical adsorption system) that retains solutes according to the pressure of the pressurization system. That is, the higher the pressure, the greater the amount of solutes retained in the separator. This separator is located after the pump to increase the solute storage capacity within the pressurization system ( Figure 3 ). In this way, during the charging stage, part of the solutes will be stored in this separator, keeping the solute concentration in the solution at a low level, so that more solvent can pass through the semi-permeable membrane. During the exothermic stage, as the pressure decreases, the solutes stored in the solute separator will return to the solution, thus maintaining a high osmotic pressure and increasing the total capacity of the system. To maximize the solute concentration in the solution in contact with the semi-permeable separator, the solution must flow from reservoir B into the solute separator, then through the semi-permeable separator, and finally be driven to the turbine. In Figure 3 the schematic diagram shown, this is represented by keeping valves V4 and V5 open but keeping valve V3 closed, so that the solution in contact with the semi-permeable separator has the highest possible solute concentration.

[0029] The second variant scheme of the present invention is that the same device acts as a pump during the charging stage and as a turbine during the exothermic stage. Such devices have been applied to PSH energy storage systems. The exothermic stage of this scheme is asFigure 9 As shown. Its working principle is similar to the above system, except that the valves and pipes need to be arranged in different ways according to the above stages to direct the liquid in the correct direction.

[0030] Another variant of the present invention is to use a compressible fluid that changes from a gas phase to a liquid phase during the charging stage. This can increase the energy storage density of the system.

[0031] The fourth variant of the present invention is to use a solution in a supersaturated state or a solution that becomes supersaturated during the charging stage. This enables the pressure in the pressurized system to remain constant or almost constant during the discharging stage, thereby increasing the efficiency of the turbine. However, it should be noted that since there is a solid phase in the system, this may increase the risk of blockage because the solid may block the membrane or affect the normal operation of the turbine. Although the above solution provides a greater energy storage capacity, the maintenance cost may be higher compared to the solution that remains below the saturation point.

[0032] So far, we have described a system in which the liquid flowing through the turbine finally drains into reservoir A, thus closing the loop from the start of the charging stage to the end of the discharging stage. The advantage of this solution is that it avoids impurities from entering the system during each charging cycle. However, the fifth variant of the present invention is to adopt an open-loop circuit, in which the liquid solution flowing through the turbine does not drain into the same reservoir that is pumped during the charging stage. This solution is advantageous if high-quality filtered liquid is available at the user's location.

[0033] Another variant of the present invention includes a compressor for supplying and pressurizing a compressible fluid to reservoir B. This compressor can be used before the first charging stage to establish the initial pressure at the start of the charging stage. During the normal operation of the system, this compressor can also be used to control the pressure of the pressurized system through a control loop. When the pressure sensor of the pressurized system detects that the pressure drops to the lowest acceptable level, the control loop will inject the compressible fluid into reservoir B. This provides a greater storage capacity.

[0034] Finally, another variant of the present invention is that the semi-permeable separator is physically located inside reservoir C and below the liquid level of this reservoir. This helps to transfer the solvent mass from the pressurized system to the center of reservoir C during the charging stage and vice versa during the discharging stage. In addition, by placing the semi-permeable separator inside reservoir C, the total surface area required for the system can be reduced. However, from the perspective of equipment maintenance, it is ideal to have easy access to this separator. Therefore, in the preferred embodiment of the present invention, the semi-permeable separator is an independent device outside reservoir C.

[0035] All components of the system are known and easily accessible as they are common equipment in industrial fields around the world, which reduces the project development cost and avoids supply chain problems.

[0036] The system does not require unknown or exotic raw materials. Instead, the preferred fluids are water, air, and one or more solutes, thus eliminating and reducing some problems existing in the supply chains of other energy storage technologies, such as problems related to long-distance transportation of raw materials or depletion of such materials.

[0037] In addition, due to the reversibility of the system, only the lost parts need to be replaced, so its consumption is very low.

[0038] Regarding high-pressure vessels, in the present invention, the energy storage capacity per cubic meter of the pressure vessel can be increased several times, depending on the selected solute and the saturation of the liquid solution.

[0039] The present invention has some advantages similar to those of the PSH hydraulic energy storage system. However, different from typical PSH systems, this new invention is not restricted by topography, for example, there needs to be a hill or a height difference between two reservoirs.

[0040] Compared with the existing technologies combining PSH and CAES, the advantages of the present invention are that, given a certain volume and pressure, the energy storage capacity of the pressurized vessel is increased, and the pressurized vessel is considered the most expensive component in such systems. In addition, by transporting the liquid from the pressurized system to the low-pressure reservoir C during the charging stage, the compression rate of the compressible fluid in reservoir B during the charging stage is reduced. The lower compression rate allows the compressible fluid more time to transfer its thermal energy to the liquid solution, making the process closer to an isothermal process compared with the existing systems. In this way, since the whole process is closer to an isothermal process, the loss of work is minimized.

[0041] In addition, the system adopts a modular design and is easy to expand. Only by increasing the number of individual components can various energy storage capacities be covered. Brief Description of the Drawings

[0042] Figure 1 shows a schematic flow diagram of the charging stage.

[0043] Figure 2 shows a schematic flow diagram of the discharging stage.

[0044] Figure 3 shows a variant scheme of the present invention, which includes a solute separator located after the pump.

[0045] Figure 4 shows the osmotic pressure curve of the solution.

[0046] Figure 5 shows the pressurized part of the system.

[0047] Figure 6 shows a simplified schematic diagram of reservoir A.

[0048] Figure 7 shows a simplified schematic diagram of the liquid reservoir B.

[0049] Figure 8 shows a simplified schematic diagram of the liquid reservoir C.

[0050] Figure 9 shows a variant of the present invention, in which the same device acts as a pump during the charging phase and as a turbine during the discharging phase.

[0051] Figure 10 shows a variant of the present invention, which includes a compressor for pressurizing the compressible fluid from the liquid reservoir B.

Claims

1. A system for storing energy using fluid compression and concentration differences in a liquid solution, characterized in that: A reservoir (A) for storing a liquid solution; a pressurized reservoir (B) for storing a liquid solution and a compressible fluid; a reservoir (C) for storing a liquid; a pump; a semi-permeable separator; and a turbine connected to a generator, wherein the system is capable of storing energy during a charging phase, using electrical energy input to drive the pump to transfer the liquid solution from reservoir A to a high-pressure reservoir B containing a compressible fluid, wherein reservoir B is connected to a third reservoir C through a semi-permeable separator, which separates the solution into (1) a high-pressure concentrated solution in reservoir B and (2) a low-pressure liquid in reservoir C, wherein energy can be released during a discharge phase by driving the high-pressure liquid solution in reservoir B to the turbine connected to the generator, and the low-pressure liquid in reservoir C returns to the pressurized system due to its osmotic pressure, so that both the liquid solution in reservoir B and the liquid in reservoir C can be used to generate electricity.

2. The system according to claim 1, characterized in that To increase the energy storage capacity of the system, the number of reservoirs A, B or C can be increased.

3. The system according to claim 1, characterized in that The energy input into the system is stored as electrical energy.

4. The system according to claim 1, characterized in that The energy stored in the system is released in the form of electrical energy.

5. The system according to claim 1, characterized in that A solute separator is provided between the pump and the semi-permeable separator to improve the separation effect of the semi-permeable separator.

6. The system according to claim 1, characterized in that The solvent of the liquid solution is water.

7. The system according to claim 1, characterized in that The compressible fluid is air.

8. The system according to claim 1, characterized in that The liquid solution in reservoir A contains multiple solutes.

9. The system according to claim 1, characterized in that The same device acts as a pump during the charging phase and as a turbine during the discharging phase.

10. The system according to claim 1, characterized in that Compressible fluids are materials that undergo a physical phase change within the operating range of the system.

11. The system according to claim 1, characterized in that The liquid solution becomes supersaturated during the charging phase.

12. The system according to claim 1, characterized in that The liquid solution is in a supersaturated state from the beginning of the charging phase.

13. The system according to claim 1, characterized in that During the energy release phase, the liquid solution flows through the turbine and is discharged to a reservoir other than reservoir A.

14. The system according to claim 1, characterized in that A compressor is provided before the charging stage to increase the pressure of the compressible fluid in reservoir B.

15. The system according to claim 1, characterized in that The semi-permeable separator is located in reservoir C.

16. The system according to claim 1, characterized in that Pressurization is achieved by osmosis through a semi-permeable separator.

17. The system according to claim 1, characterized in that No height difference between the reservoirs is required.

18. The system according to claim 1, characterized in that Only one of the reservoirs needs to be pressurized.

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