Liquid piston device and method for compressing and expanding gas

Abstract

The invention relates to a method for compressing and / or expanding a gas by means of a liquid piston device comprising: at least two cylinders (10, 10 '); a liquid line (21) interconnecting the cylinders (10, 10 '); a liquid drive unit (20) by means of which a fluid (14) can be conveyed from one cylinder (10, 10 ') to the other cylinder (10, 10'); a low-pressure gas reservoir (40) connected to each cylinder (10, 10 ') via a low-pressure line (41); low-pressure valves (11, 11 ') for the respective cylinders (10, 10'), by means of which low-pressure lines (41) leading to the cylinders (10, 10 ') can be opened and closed; a high-pressure gas reservoir (50) connected to each cylinder (10, 10 ') via a high-pressure line (51); and high-pressure valves (12, 12 ') for the respective cylinders (10, 10'), by means of which high-pressure lines (51) leading to the cylinders (10, 10 ') can be opened and closed.

Description

Technical Field

[0001] The present invention relates to methods for compressing and / or expanding gases using a liquid piston device, liquid piston devices for carrying out these methods, and various uses of the liquid piston device. Background Technology

[0002] Piston compressors are commonly used to compress gases, especially in high-pressure ranges. Compared to rotary compressor systems, this technology allows for higher pressures through proper sealing of the piston chamber. However, it is precisely this sealing that presents challenges in terms of cost and maintenance, and piston lubrication must also be ensured. If pure compressed gas is required, contamination of the gas that may occur through contact with the driving medium must also be prevented.

[0003] Liquid piston systems solve this challenge by using a liquid as the piston instead of a solid piston moving within a cylinder. The rising liquid level compresses the gas in the cylinder. This also ensures the pressure chamber is sealed. Liquid pistons require no lubrication, significantly reducing maintenance costs.

[0004] The liquid facilitates heat exchange with the compressed gas, which has a beneficial effect on the efficiency of the compression process because it reduces temperature fluctuations. Furthermore, a fixed heat exchanger can be installed in the cylinder through which the liquid can flow, further enhancing heat exchange. This is impossible in conventional piston compressors because the piston is fixed. Finally, in a liquid piston system, the dead zone volume of the gas can be minimized by properly distributing the liquid within the compression chamber.

[0005] A liquid piston system can also be used as an expander by reversing the process. In this case, compressed gas pushes a liquid column out of the cylinder and drives a liquid motor. In a liquid piston system, this reversal can typically be achieved using the same device used for compression with a suitable valve circuit. This means that a bidirectional system can be easily implemented.

[0006] Liquid piston compressors are used in high-pressure applications, such as for supplying compressed gas, filling compressed gas cylinders, and in compressed gas filling stations. Liquid piston expanders can be used in any situation where compressed gas expands from a higher pressure level to a lower pressure level, such as when extracting compressed gas from a storage facility or pipeline. Bidirectional systems are primarily used in compressed gas storage systems, such as compressed air energy storage systems.

[0007] Prior art, such as DE 102004046316 A1, discloses a liquid piston system specifically used as a compressor. In particular, hydrogen is compressed, and an ionic liquid is used to avoid contaminating the gaseous medium to be compressed.

[0008] WO 2017198725 A1 illustrates a bidirectional liquid piston system, specifically designed for use in multi-stage energy storage systems for the compression and expansion of gases. A heat exchanger within the cylinder enhances heat exchange between the gas and the liquid.

[0009] DE 102012003288 B3 illustrates a bidirectional liquid piston system that further facilitates heat exchange through an optimized heat exchanger design. Furthermore, dead zone volume is minimized by employing an adaptive tilting arrangement of the cylinders.

[0010] WO 2008139267 A1 illustrates a bidirectional liquid piston system in which a portion of the liquid is directly sprayed into the compression or expansion chamber. This also increases heat exchange between the liquid and gas and achieves near-isothermal conditions, which is beneficial for efficiency.

[0011] WO 2008031527 A1 illustrates a liquid piston system that replaces level measurement in multiple cylinders with level measurement in a leak tank. This optimizes cost and allows for the installation of fixed heat exchangers in the cylinders without interfering with level measurement. However, this system is designed only for compressors.

[0012] Liquid piston systems known from existing technologies still have potential for further optimization at various levels. First, dead-zone volumes still exist that impair the efficiency of gas compression and expansion. Second, compression and expansion still result in significant heating or cooling of the gas, which can lead to liquid evaporation or condensation and gas condensation. Third, systems for measuring liquid levels, which are necessary for control systems, are sometimes complex and expensive. Summary of the Invention

[0013] The object of this invention is to provide a method for compressing and / or expanding a gas, and a liquid piston device for carrying out these methods, minimizing dead zone volume. Another optional object is to provide a liquid piston device and a corresponding method by which the compression and / or expansion process is more isothermal. Yet another optional object is to provide a liquid piston device having a simple system for measuring the liquid level within the liquid piston device.

[0014] These tasks are solved by two methods having the features of claims 1 and 2 of this patent application and two liquid piston devices having the features of claims 3 and 4 of this patent application. Further features and embodiments are revealed in the dependent claims, the advantages of which will be explained in the following description. Attached Figure Description

[0015] Figure 1A schematic diagram of a liquid piston device with two cylinders for compressing and expanding gas.

[0016] Figure 2 A schematic diagram of an application for compressed gas energy storage systems.

[0017] Figure 3 A schematic diagram of general energy flow.

[0018] Figure 4 A schematic diagram of an application for compressed gas supply.

[0019] Figure 5 A liquid piston device with a liquid management system.

[0020] Figure 6 A liquid piston device with a thermal management system.

[0021] Figure 7 A liquid piston device with a management system for leaking fluid.

[0022] Figure 8 A liquid piston device with pressure and level sensors.

[0023] Figure 9 Details of a cylinder with a turbulent pin. Detailed Implementation

[0024] The accompanying drawings illustrate possible implementations, which will be explained in the following description.

[0025] The core of this invention is a liquid piston device, which allows gas 13, such as ambient air, nitrogen, or oxygen, to be compressed from a low-pressure gas reservoir 40 to a higher pressure and stored in a high-pressure gas reservoir 50. This liquid piston device includes at least two cylinders 10, 10', which are connected to each other via a liquid line 21 (see...). Figure 1A liquid drive unit 20, including a hydraulic pump, is positioned on the liquid line 21 for transferring fluid 14 from one cylinder 10, 10' to another cylinder 10, 10'. Each cylinder 10, 10' is connected to a low-pressure gas reservoir 40 via a low-pressure line 41, allowing gas 13 to flow from the low-pressure gas reservoir 40 into each cylinder 10, 10' through the low-pressure line 41. The low-pressure gas reservoir 40 is preferably a container in which gas 13 is at a low pressure, for example, between 1 bar and 100 bar. However, the low-pressure gas reservoir 40 may also be simply ambient air, with air from the environment entering the cylinders 10, 10'; or the low-pressure gas reservoir 40 may be a low-pressure compressor and / or expander, for example, pre-compressing the gas to a certain pressure level; and / or the low-pressure gas reservoir 40 may be a gas generator, providing a gaseous component, such as nitrogen, from ambient air (see [link to relevant documentation]). Figure 2 The low-pressure line 41 is equipped with low-pressure valves 11 and 11', which can be used to control the flow of gas 13 from the low-pressure gas reservoir 40 to the individual cylinders 10 and 10'. The individual cylinders 10 and 10' are connected to the high-pressure gas reservoir 50 via a high-pressure line 51, allowing gas 13 to flow from the individual cylinders 10 and 10' into the high-pressure gas reservoir 50 through the high-pressure line 51. The high-pressure gas reservoir 50 is preferably a container adapted to receive and / or store gas 13 at high pressure (e.g., 10 bar to 1000 bar). However, the high-pressure gas reservoir 50 may also be or may include a high-pressure compressor and / or expander, for example, a high-pressure compressor and / or expander that recompresses the gas to even higher pressure levels. The high-pressure line 51 is equipped with high-pressure valves 12 and 12', which can be used to control the flow of gas 13 from the individual cylinders 10 and 10' to the high-pressure gas reservoir 50.

[0026] During operation of the liquid piston device, liquid 14, such as water, oil, or other suitable liquid, is present in cylinders 10, 10'. To compress the gas and store the compressed gas in the high-pressure gas reservoir 50, the liquid drive unit 20 delivers liquid 14 from the first cylinders 10, 10' to the second cylinders 10, 10' via liquid lines 21. The following description of the compression process is based on... Figure 1 Here, it is arbitrarily assumed that the liquid drive unit 20 delivers liquid 14 from the first cylinder 10 on the left to the second cylinder 10' on the right. During this process, a compression process occurs in the second cylinder 10', followed by a discharge process. • During the compression process, the low-pressure valve 11' and high-pressure valve 12' of the second cylinder 10' are closed, so that the internal gas 13 is compressed by the incoming liquid 14.

[0027] Once the desired pressure level is reached, the discharge process begins: the high-pressure valve 12' opens, and the compressed gas is pushed into the high-pressure gas reservoir 50 by the incoming liquid 14.

[0028] Simultaneously, the low-pressure valve 11 connected to the first cylinder 10 opens, and the high-pressure valve 12 connected to the first cylinder 10 closes, causing the liquid 14 removed from the first cylinder 10 to be replaced by gas 13 from the low-pressure gas reservoir 40. Once the second cylinder 10' is filled with liquid 14, the delivery direction of the low-pressure valves 11, 11' and the high-pressure valves 12, 12', as well as the liquid drive unit 20, can be switched to continue the compression process by utilizing the compression and discharge of the gas 13 located in the first cylinder 10, and so on. Preferably, the amount of liquid 14 contained in the liquid piston device is greater than the volume of the cylinders 10, 10'. This ensures that when one cylinder 10, 10' is filled, the other cylinder 10, 10' will never be completely emptied, and that liquid 14 is always present in the liquid drive unit 20.

[0029] When the liquid piston device is in operation, the mechanical or electrical energy input to drive the liquid drive unit 20 is stored in the high-pressure gas reservoir 50 in the form of compressed gas. This stored energy can then be released as output drive energy by expanding the stored pressurized gas through the liquid piston device. Thus, the liquid drive unit 20 subsequently acts as a hydraulic motor, which can drive vehicles, machines, or generators. The following description of the expansion process is based on... Figure 1 It is arbitrarily assumed that pressurized gas 13 is fed into the second cylinder 10' on the right. In this second cylinder 10', the intake process occurs first, followed by the expansion process: • During the intake process, the high-pressure valve 12' of the second cylinder 10' opens and the low-pressure valve 11' closes, allowing a certain amount of gas 13 to enter the second cylinder 10' from the high-pressure gas reservoir 50 which is under high pressure.

[0030] Once the desired amount of gas 13 is present in cylinder 10', the expansion process begins. During the expansion process, the high-pressure valve 12' and the low-pressure valve 11' of the second cylinder 10' are closed, and the high-pressure gas 13 introduced expands within the second cylinder 10'.

[0031] During the intake and expansion processes, the liquid 14 in the second cylinder 10' is driven through the liquid line 21 and through the liquid drive unit 20, which then acts as a hydraulic motor. The liquid 14 then enters another cylinder 10, 10', for example... Figure 1In the first cylinder 10 on the left, the high-pressure valve 12 is closed and the low-pressure valve 11 is open. The gas 13 in the first cylinder 10 is then discharged through the low-pressure line 41 and enters the low-pressure gas reservoir 40, which subsequently acts as a gas tank. Once the first cylinder 10 is filled with liquid 14, the low-pressure valves 11, 11' and the high-pressure valves 12, 12' can be switched to continue the expansion process by allowing pressurized gas stored in the high-pressure gas reservoir 50 to enter the first cylinder 10 and expand, and so on.

[0032] Advantageously, the amount of gas 13 introduced into cylinders 10 and 10' during the intake process is calibrated so that after the gas 13 expands in one cylinder, the other cylinder 10 and 10' is fully filled with liquid 14. Otherwise, after the expansion process, liquid equilibration occurs, during which additional liquid 14 is introduced into the other cylinder 10 and 10' until the other cylinder is fully filled. In this case, the low-pressure valves 11 and 11' in both cylinders 10 and 10' are open, and the high-pressure valves 12 and 12' are closed.

[0033] The compression and subsequent expansion of gas 13 provides a bidirectional liquid piston device that can be used to store and release energy in a manner similar to a battery. Liquid piston devices have numerous applications, some of which are briefly mentioned below. Temporary storage of surplus energy is one of the biggest challenges in generating electricity from renewable energy sources, whose output depends on weather (sunlight, wind, etc.) and cannot be adjusted according to actual current electricity demand. Therefore, one possible application of this liquid piston device is to store surplus energy (e.g., during the day when the sun generates electricity via a solar power system but energy demand is low), which can then be used later (e.g., at night when the solar power system is no longer generating electricity but electricity demand is high). This liquid piston device can also be used to provide economical peak load management for electricity procurement. Temporary energy storage allows energy to be generated from the grid during low-load periods and stored for consumption during high-load periods. The liquid piston device according to the invention has further applications in industrial sectors requiring compressed gases. For example, the compressed gas required by machinery can be produced in advance during low-load periods, temporarily stored at higher pressures, and then extracted during high-load periods at any lower pressure level. Because the gas is stored at high pressure, a capacity of up to 47 kWh / m³ is achieved at 300 bar. 3 The useful energy density is achieved, and the required storage volume is reduced to a reasonable size. To change the volumetric flow rate and pressure level and adapt it to demand, multiple stages of liquid piston devices can be used in series and / or in parallel.

[0034] The compression of a gas generates heat, while the expansion of a gas generates cold (see...). Figure 3 Liquid piston devices have the advantage of being usable in processes requiring pressurized gas as well as heat or cold (see...). Figure 4 For example, during low-load periods, when compressed gas storage facilities are being filled, heat is used for operation or to heat buildings. There are many applications that utilize electricity and cooling during expansion, as the demand for both forms of energy often occurs simultaneously. Generally, cooling is also required when electricity is needed, for example, for cooling machines or data centers, because electricity is always partially converted into heat. Another particularly advantageous application of this liquid piston device is in the nitrogen supply of laser cutting machines, where, in addition to nitrogen, the machine requires electricity and cooling.

[0035] The liquid piston device according to the invention is also applicable to compressed gas storage systems according to WO 2019219801 A1, wherein the liquid piston system is combined with a compressed gas tank filled with liquid, so that the gas can be stored at a constant pressure. This liquid piston device can perform all or part of the functions of the working machine and / or shifting device described in WO 2019219801 A1.

[0036] To improve compression efficiency, the dead zone volume of the compressed gas 13 in cylinders 10 and 10' should be minimized. This means that at the end of compression in cylinders 10 and 10', there should be as little gas 13 as possible, and cylinders 10 and 10' should be filled with liquid 14 as completely as possible. This prevents the gas 13, which is at a high pressure level, from expanding back to the pressure level of the low-pressure gas reservoir 40 after the discharge process, thus preventing energy loss. Ideally, cylinders 10 and 10' should be filled with liquid 14 exactly up to the associated high-pressure valves 12 and 12', no more and no less. However, it is impossible to fill cylinders 10 and 10' with perfect precision; therefore, in practice, cylinders 10 and 10' are either not fully filled or are overfilled. Since incomplete filling of cylinders 10 and 10' creates a dead zone volume, which is undesirable, according to the invention, liquid 14 is at least delivered to the high-pressure line 51, after reaching the high-pressure valves 12 and 12' (i.e., liquid 14 flows through the high-pressure valves 12 and 12' and continues to flow into the high-pressure line 51). The liquid piston device according to the invention is specifically designed to perform this process step and includes a control system for controlling the liquid drive unit 20 and the high-pressure valves 12 and 12' and low-pressure valves 11 and 11'. This control system is programmed such that the liquid 14 delivered to cylinders 10 and 10' by the liquid drive unit 20 fills the cylinders 10 and 10', and the liquid 14 is at least delivered to the high-pressure line 51 and after reaching the high-pressure valves 12 and 12'. Therefore, the dead zone volume in cylinders 10 and 10' is minimized, and optimal discharge of compressed gas 13 into the high-pressure gas reservoir 50 is ensured. To further reduce the dead zone volume, it can be specified that the high-pressure pipeline 51 or the high-pressure valves 12 and 12' have openings at the upper ends of the cylinders 10 and 10', so that the cylinders 10 and 10' can be completely filled with liquid 14.

[0037] The same applies to expansion: to improve expansion efficiency, the dead zone volume of the remaining gas 13 in cylinders 10 and 10' should be minimized. This means that before the expansion process begins, and before the corresponding high-pressure valves 12 and 12' open, cylinders 10 and 10' must be filled with liquid 14 as completely as possible. This prevents gas from the high-pressure gas reservoir 50 from expanding at a lower pressure level into the gas 13 still in cylinders 10 and 10' without doing work when the high-pressure valves 12 and 12' open. According to the invention, liquid 14 is specified to enter cylinders 10 and 10' and push the gas 13 contained in cylinders 10 and 10' into the low-pressure gas reservoir 40 to fill cylinders 10 and 10', and is delivered at least to the low-pressure line 41 and reaches the low-pressure valves 11 and 11' (i.e., the liquid 14 flows through the low-pressure valves 11 and 11' and continues to flow into the low-pressure line 41). The liquid piston device according to the invention is specifically designed to perform this process step and includes a control system for controlling the liquid drive unit 20 and the high-pressure valves 12, 12' and low-pressure valves 11, 11'. This control system is programmed such that the amount of gas 13 supplied to cylinders 10, 10' via the high-pressure valves 12, 12' during the intake process is calibrated such that after the gas 13 expands in the cylinder, another cylinder 10, 10' is fully filled with liquid 14, and the liquid 14 is delivered at least to the low-pressure line 41 and reaches the low-pressure valves 11, 11'. This minimizes or completely eliminates the dead volume in cylinders 10, 10'. To further reduce the dead volume, the low-pressure line 41 or the low-pressure valves 11, 11' may be configured to open at the upper end of cylinders 10, 10', allowing cylinders 10, 10' to be fully filled with liquid 14.

[0038] The solution according to the invention—that is, overfilling cylinders 10, 10' with liquid 14 to the associated high-pressure valves 12, 12' or low-pressure valves 11, 11' connected to cylinders 10, 10' to minimize dead-zone volume in cylinders 10, 10'—can be used independently of each other to improve compression efficiency and / or expansion efficiency. If the liquid piston device is used only as a compressor for storing energy as compressed gas, then driving liquid 14 to high-pressure valves 12, 12' only during the compression process may be sufficient. Conversely, if the liquid piston device is used only as an expander for obtaining the stored energy, then driving liquid 14 to low-pressure valves 11, 11' only during the expansion process may be sufficient. If the liquid piston device is used bidirectionally as both a compressor and an expander, this measure can be applied during both the compression and expansion processes.

[0039] However, to ensure that no liquid 14 enters the high-pressure gas reservoir 50 or the low-pressure gas reservoir 40, a dedicated liquid management system is provided. The liquid management system provides a closed system for the liquid 14, preventing leakage and thus eliminating the need for refilling. Providing a closed system is crucial for the efficiency of the liquid piston device, as any amount of pressurized liquid exceeding the system boundary represents a loss of pressure energy. Therefore, the fluid 14 driven into the high-pressure line 51 and / or the low-pressure line 41 must be intelligently returned to the cylinders 10, 10'. Depending on whether the liquid 14 is driven into the high-pressure line 51 during compression or into the low-pressure line 41 during expansion, according to the invention, a liquid separator is provided between the high-pressure valves 12, 12' and the high-pressure gas reservoir 50, or between the low-pressure valves 11, 11' and the low-pressure gas reservoir 40 (see [link to relevant documentation]). Figure 5 If liquid 14 is driven into high-pressure line 51 during compression and into low-pressure line 41 during expansion, liquid separators are provided between high-pressure valves 12, 12' and high-pressure gas reservoir 50, and between low-pressure valves 11, 11' and low-pressure gas reservoir 40. Each liquid separator 42, 52 is connected to return lines 43, 53 through which liquid 14 flows from liquid separator 42, 52 back to one of cylinders 10, 10'. Liquid 14 can flow back to another cylinder 10, 10', or it can flow back to the same cylinder 10, 10' from which it was discharged. However, for this to be achieved, the pressure in cylinders 10, 10' must be lower than the pressure in liquid separators 42, 52. At the end of the compression process, the fluid 14, driven into the high-pressure line 51 and collected by the associated fluid separator 52, is at high pressure and can, for example, immediately flow back to the cylinders 10, 10' that did not undergo compression. Preferably, the fluid 14 can also flow back to the cylinders 10, 10' that underwent compression, provided the pressure in the cylinders 10, 10' is low and a sufficient pressure differential exists. At the end of the expansion process in one cylinder 10, 10', the fluid 14, driven into the low-pressure line 41 connected to the other cylinder 10, 10' and collected by the associated liquid separator 42, is at too low a pressure level to spontaneously flow back to the cylinder 10, 10'. Therefore, the corresponding return line 43 is equipped with a first pump 44 that raises the liquid 14 to the pressure required for return to the cylinders 10, 10'.

[0040] Advantageously, if at least one return line 43, 53 of the liquid separators 42, 52 leads to the valve assembly 60, after the valve assembly 60, multiple branches 61, 62, 63, 61', 62', 63' of the return lines 43, 53 lead to cylinders 10, 10' and open at different points (e.g., different heights) in the cylinders 10, 10'. The multiple branches 61, 62, 63, 61', 62', 63' of the return lines 43, 53 can also lead to different points in different cylinders 10, 10'. For example, Figure 5 A valve assembly 60 with six branches 61, 61', 62, 62', 63, and 63' is shown. Three of the six branches lead to different points on one cylinder 10, 10', and the other three branches lead to different points on another cylinder 10, 10', for example, to different points on the upper, middle, and lower ends of cylinders 10, 10', respectively. Alternatively, only two branches may exist, for example, two branches opening at the lower and upper ends of cylinders 10, 10'. By controlling the valve assembly 60 accordingly, the time of fluid return from fluid separators 42, 52, the returning cylinders 10, 10', and the return position on cylinders 10, 10' can be determined as needed. The ideal time for this return is when the pressure difference between the liquid separators 42, 52 and cylinders 10, 10' is as low as possible. This means that the first liquid separator 52 loses the least amount of energy from the high-pressure gas storage tank 50 side, and the first pump 44 connected to the second liquid separator 42 consumes the least amount of energy.

[0041] Furthermore, alternative solutions for further minimizing dead zone volume include narrowing the upper portions of cylinders 10, 10' so that gas 13 is directed to high-pressure valves 12, 12' and low-pressure valves 11, 11' during the discharge process. However, since this must be ensured for both valves 11, 11', 12, 12' of cylinders 10, 10', certain spaces are created where gas 13 may be trapped by liquid 14 instead of being pushed into high-pressure line 51 and low-pressure line 41, thus creating dead zone volume. To reduce this effect, a turbulent body 80 can be attached to the upper end of cylinders 10, 10' at high-pressure valves 12, 12' and low-pressure valves 11, 11' (see [link to article]). Figure 9 This generates turbulence in the flow at the upper ends of cylinders 10, 10', particularly in the separation layer between liquid 14 and gas 13. This improves the distribution of liquid 14 and reduces the dead zone volume of gas 13. The turbulence generator 80 can have any geometry, as its very presence affects the liquid flow and generates turbulence in the liquid. A preferred shape for the turbulence generator 80 is spherical.

[0042] It is also advantageous if compression and expansion are as isothermal as possible. This allows the liquid piston device to achieve a higher pressure ratio without causing the gas 13 to be overheated during compression or overcooled during expansion. This prevents the evaporation and condensation of the liquid 14 and the condensation of the gas 13. To achieve quasi-isothermal compression and expansion, optimal heat exchange between the gas 13 and its environment is required. In the liquid piston device, a certain amount of heat exchange already occurs directly through the boundary layer between the gas 13 and the liquid 14. However, to increase this heat exchange, the liquid piston device can include a dedicated thermal management system. For example, accumulators 15, 15' can be arranged in cylinders 10, 10', which absorb additional heat during compression or release additional heat during expansion. The liquid piston concept allows the accumulators 15, 15' to be mounted directly in solid form in the compression or expansion chamber. This is significantly advantageous compared to conventional piston compression and expansion machines with fixed pistons. The heat accumulators 15, 15' are preferably arranged in the upper region of the cylinders 10, 10' because the greatest energy flow occurs in this region during compression or expansion: at the end of compression, when the cylinders 10, 10' are partially filled with liquid and the gas 13 is in the upper region of the cylinder, the gas 13 is heated to the maximum extent. Similarly, at the beginning of expansion, once the pressurized gas 13 expands in the upper region of the cylinder filled with liquid 14 at the start of the expansion process, the maximum cooling occurs. This also allows for savings of heat storage material in the lower region of the cylinders 10, 10', thereby reducing costs. During compression, the heat storage materials 15, 15' are heated by the warm gas 13 in the first step. Once the liquid 14 flows around the heat storage materials 15, 15', the absorbed heat is transferred to the liquid 14 in the second step. Similarly, during expansion, heat is first transferred from the heat storage units 15, 15' to the cooled gas 13. In the next expansion cycle, which takes place in another cylinder 10, 10', the liquid 14 reheats the accumulators 15, 15' as long as the cylinder is filled with liquid 14. The material of the accumulators preferably has high heat capacity and high heat transfer coefficient, and is therefore preferably metal. Furthermore, to further promote heat transfer, the surface area to volume ratio should be as high as possible. Additionally, for a suitable design of the accumulators 15, 15', characteristics such as low liquid retention capacity, low pressure loss, ease of manufacture, and cost optimization must be considered. Tests have shown that accumulators made of, for example, steel wool are very suitable.

[0043] Liquid 14 conducts heat from the compressed gas or cold from the expanding gas through contact with the walls of cylinders 10, 10' and other components of the liquid piston assembly (liquid line 21, liquid drive unit 20, high-pressure valves 12, 12' and low-pressure valves 11, 11', etc.). To dissipate heat more effectively during compression or to add heat in a more controlled manner during expansion, a first heat exchanger 22 can be incorporated into the liquid line 21 (see...). Figure 6 The first heat exchanger 22 can be used to heat the external circuit by supplying heat during compression, and similarly, the first heat exchanger 22 can be used to cool the external circuit by removing heat during expansion.

[0044] When cylinders 10 and 10' are filled with liquid 14, the liquid is transported or injected into cylinders 10 and 10' through liquid line 21. Preferably, the liquid is transported or injected into cylinders 10 and 10' from bottom to top through liquid line 21. This has disadvantages: liquid 14 is injected directly onto accumulators 15 and 15', and accumulators 15 and 15' are partially filled with liquid 14 before the rising liquid level reaches them. This reduces the heat exchange between accumulators 15 and 15' and gas 13. The situation is worse if accumulators 15 and 15' have closely spaced surfaces and the space between the closely spaced surfaces is filled with liquid. In this case, the effect of accumulators 15 and 15' is almost negated because the contact area between accumulators 15 and 15' and gas 13 is greatly reduced, heat exchange is significantly impaired, and the isothermal characteristics of the process are significantly reduced. Therefore, on the one hand, a low liquid retention capacity of the accumulators 15, 15' is preferred so that when the liquid level drops, the space between the surfaces is emptied and filled with gas as quickly and completely as possible. To avoid this, baffles 16, 16' can be arranged in the cylinders 10, 10', for example, at the liquid inlet 14 at the lower end of the cylinders 10, 10', where the entering liquid 14 impacts the baffles. This ensures a controlled rise in the liquid level in the cylinders 10, 10' regardless of the entry speed of the liquid 14, and that the liquid 14, 14' does not prematurely contact the accumulators 15, 15'. In some cases, such as when the liquid piston device is used to generate heat or cold, and therefore the gas 13 needs to reach higher or lower temperature levels, it may be advantageous if the isothermal characteristics of the process can be controlled. In this configuration, for example, each cylinder 10, 10' has two inlets for liquid 14 that can be controlled by valves 17, 17': a first inlet having baffles 16, 16' for controlled rise of the liquid level; and a second inlet through which liquid 14 intentionally comes into contact with accumulators 15, 15' as early as possible (see...). Figure 6This provides an additional control variable for regulating the compression process between isothermal processes (i.e., constant temperature achieved through heat exchange) and adiabatic processes (heating during compression and cooling during expansion due to the lack of heat exchange).

[0045] There are also methods for controlling the effect of the accumulator and thereby controlling the isothermal nature of the process. One or more return lines 43, 53 of the liquid separators 42, 52 can lead to the valve assembly 60 as described above, and after the valve assembly 60, multiple branches 61, 61', 62, 62', 63, 63' of the return lines 43, 53 can lead to outlets at different points on the cylinders 10, 10'. In particular, a branch leads to a first outlet, whereby the returned liquid 14 is sprayed onto the accumulators 15, 15', and a branch leads to a second outlet, whereby the returned liquid is not sprayed onto the accumulators 15, 15'. For example, the liquid returning to the cylinders 10, 10' can be controlled to be above, below, or at the level of the accumulators 15, 15'. Therefore, depending on the temperature of the liquid 14 and the accumulators 15, 15', the accumulators 15, 15' can be heated or cooled as needed. This creates another control variable for controlling the heat flow during compression or expansion. It is also possible to spray the liquid 14 returning to the cylinders 10, 10' in droplet form into the gas 13 contained within the cylinders 10, 10', for example, via branches 61, 61', 62, 62', 63, 63' with a central opening in the space below the accumulators 15, 15'. Spraying the liquid 14 in droplet form maximizes the contact area between the gas 13 and the liquid 14, thereby maximizing heat exchange. These methods can be used in conjunction with or alternate with the methods described above with baffles 16, 16'.

[0046] In some embodiments of the liquid drive unit 20, a leakage flow of liquid 14 may occur during operation. In this case, the liquid piston device may include a management system for the leaking liquid. The leaking flow may be supplied, for example, via a leak line 71 to a leak container 70, which has a low pressure level (see [link to relevant documentation]). Figure 7To close the fluid loop, fluid 14 can be brought back to the desired pressure via the second pump 73 and then returned to cylinders 10, 10' via the third return line 72. If the liquid piston assembly has a valve assembly 60, and fluid 14 returns from fluid separators 42, 52 to cylinders 10, 10' through this valve assembly 60, the third return line 72 can connect to the valve assembly 60, and the leaking fluid can return to cylinders 10, 10' together with the fluid 14 from fluid separators 42, 52. Fluid 14 in the leak container 70 also allows for more suitable heat exchange with the external loop because fluid 14 is at a lower pressure level. Therefore, a third pump 76 can be provided, which delivers fluid 14 from the leak container 70 through the second heat exchanger 75 and returns fluid 14 to the leak container 70. The lower pressure in this loop makes the design of the heat exchanger 75 simpler and more cost-effective. The third pump 76 allows for independent control of the flow rate through the second heat exchanger 75. Alternatively, the second heat exchanger 75 can be placed directly in the leak line 71 or the third return line 72, thus eliminating the need for a third pump 76. If a leak tank 70 is provided, the liquid piston assembly can be further simplified by returning the liquid from the low-pressure side liquid separator 42 directly to the leak tank 70 via the liquid line 77. This eliminates the need for a separate first pump 44 and a corresponding return line 43. However, the pressure in the low-pressure side liquid separator 42 must be higher than the pressure in the leak tank 70.

[0047] Another aspect of the invention is the measurement of pressure and state within the liquid piston assembly, which may be advantageous for the control of the liquid piston assembly. Pressure and state values ​​in cylinders 10, 10', liquid separators 42, 52, and leakage container 70 can contribute to better control of the liquid piston assembly. Since all containers are always filled with at least a small amount of liquid, pressure sensors P1, P2, P3, P4, and P5 can be used to measure the pressure in the liquid at the lower end if necessary (see...). Figure 8This makes pressure measurements smoother because the inertia of the liquid filters out unwanted fluctuations in the pressure measurement. Effective level measurement in liquid piston systems is often challenging, especially when accumulators 15 and 15' are installed inside cylinders 10 and 10'. This invention solves this problem effectively and economically by using two level sensors L1, L2, L3, L4, L5, L6, L7, L8 at different heights in cylinders 10 and 10' and liquid separators 42 and 52 (e.g., using one level sensor at the upper end of cylinders 10 and 10' and one level sensor at the lower end of cylinders 10 and 10'). If a leaking container 70 is present, the leaking container 70 can also be equipped with two level sensors L9 and L10 at different heights. This allows the detection of the maximum or minimum liquid level 14 in each of these containers. Other states of the liquid level in cylinders 10, 10' can be estimated with sufficient accuracy using the position or state of the shaft of the liquid drive unit 20 (e.g., using a sensor N1 regarding the number of cycles). Information about the number of cycles can be used to determine the amount of liquid 14 being delivered to or from cylinders 10, 10'. Therefore, by combining the maximum and minimum states determined by level sensors L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, the liquid level of liquid 14 can be continuously evaluated. This means that the state of the liquid piston assembly can be detected using a pressure sensor, a simple level sensor, and the sensor N1 regarding the number of cycles, and optimal control of the liquid piston assembly can be achieved using a liquid pump and valves.

[0048] The liquid drive unit 20 is preferably designed such that the flow and rotation direction of the liquid drive unit 20 remain the same regardless of the operating mode (compression or expansion). This reduces complexity and saves on components and costs. For this purpose, the liquid drive unit 20 may include valves that allow control of the flow direction of the fluid 14 as needed. The liquid drive unit 20 may include a hydraulic pump and a hydraulic motor for alternating compression and expansion, or a reversible hydraulic pump that can also function as a hydraulic motor.

Claims

1. A method for compressing gas using a liquid piston device, the liquid piston device comprising: At least two cylinders (10, 10'). Liquid lines (21) connect the cylinders (10, 10') to each other. The liquid drive unit (20) can drive fluid (14) from one cylinder (10, 10') to another cylinder (10, 10'). A low-pressure gas reservoir (40) is connected to each cylinder (10, 10') via a low-pressure line (41). Low-pressure valves (11, 11') for each cylinder (10, 10') allow the opening and closing of the low-pressure lines (41) leading to the cylinders (10, 10'). A high-pressure gas reservoir (50) is connected to each cylinder (10, 10') via a high-pressure line (51). High-pressure valves (12, 12') for each cylinder (10, 10'), which allow the opening and closing of the high-pressure lines (51) leading to the cylinders (10, 10'), and A first liquid separator (52) is disposed between the high-pressure valves (12, 12') and the high-pressure gas reservoir (50) for separating liquid (14) from gas (13) entering the first liquid separator (52) through the high-pressure line (51), and the first liquid separator (52) is connected to one of the cylinders (10, 10') via a first return line (53) for the separated liquid (14). The liquid drive unit (20) drives liquid (14) from the first cylinder (10, 10') through the liquid line (21) to the second cylinder (10, 10'), so that the gas (13) in the second cylinder (10, 10') is compressed by the liquid (14) and pushed into the high-pressure gas reservoir (50) through the high-pressure line (51). Its features are, After filling the second cylinder (10, 10'), the liquid (14) is driven at least into the high-pressure line (51) and then to the high-pressure valve (12, 12').

2. A method for expanding a gas using a liquid piston device, the liquid piston device comprising: At least two cylinders (10, 10'). Liquid lines (21) connect the cylinders (10, 10') to each other. The liquid drive unit (20) can drive liquid (14) from one cylinder (10, 10') to another cylinder (10, 10'). A low-pressure gas reservoir (40) is connected to each cylinder (10, 10') via a low-pressure line (41). Low-pressure valves (11, 11') for each cylinder (10, 10') allow the opening and closing of the low-pressure lines (41) leading to the cylinders (10, 10'). A high-pressure gas reservoir (50) is connected to each cylinder (10, 10') via a high-pressure line (51). High-pressure valves (12, 12') for each cylinder (10, 10') can be used to open and close the high-pressure lines (51) leading to the cylinders (10, 10'). A first liquid separator (42) is disposed between the low-pressure valves (11, 11') and the low-pressure gas reservoir (40). The first liquid separator (42) is adapted to separate liquid (14) from gas (13) entering the first liquid separator (42) through the low-pressure line (41). The first liquid separator (42) is connected to one of the cylinders (10, 10') via a first return line (43) for the separated liquid (14). A first pump (44) is installed on the first return line (43) to drive the separated liquid (14). In this process, pressurized gas (13) is fed from the high-pressure gas reservoir (50) into the second cylinder (10, 10'), and the gas (13) is expanded in the second cylinder (10, 10'). Thus, liquid (14) is driven from the second cylinder (10, 10') through the liquid line (21) and through the liquid drive unit (20) into the first cylinder (10, 10'). Its features are, After filling the first cylinder (10, 10'), the liquid (14) is driven at least into the low-pressure line (41) and then to the low-pressure valve (11, 11').

3. A liquid piston device for carrying out the method according to claim 1, the liquid piston device comprising: At least two cylinders (10, 10'). Liquid lines (21) connect the cylinders (10, 10') to each other. The liquid drive unit (20) can drive liquid (14) from one cylinder (10, 10') to another cylinder (10, 10'). A low-pressure gas reservoir (40) is connected to each cylinder (10, 10') via a low-pressure line (41). Low-pressure valves (11, 11') for each cylinder (10, 10') allow the opening and closing of the low-pressure lines (41) leading to the cylinder (10, 10'). A high-pressure gas reservoir (50) is connected to each cylinder (10, 10') via a high-pressure line (51). High-pressure valves (12, 12') for each cylinder (10, 10'), which allow the opening and closing of the high-pressure lines (51) leading to the cylinders (10, 10'), and A first liquid separator (52) is arranged between the high-pressure valve (12, 12') and the high-pressure gas reservoir (50) for separating liquid (14) from gas (13) that enters the first liquid separator (52) through the high-pressure line (51), and the first liquid separator (52) is connected to one of the cylinders (10, 10') through a first return line (53) for the separated liquid (14).

4. A liquid piston device for carrying out the method according to claim 2, the liquid piston device comprising: At least two cylinders (10, 10'). Liquid lines (21) connect the cylinders (10, 10') to each other. The liquid drive unit (20) can drive liquid (14) from one cylinder (10, 10') to another cylinder (10, 10'). A low-pressure gas reservoir (40) is connected to each cylinder (10, 10') via a low-pressure line (41). Low-pressure valves (11, 11') for each cylinder (10, 10') allow the opening and closing of the low-pressure lines (41) leading to the cylinders (10, 10'). A high-pressure gas reservoir (50) is connected to each cylinder (10, 10') via a high-pressure line (51). High-pressure valves (12, 12') for each cylinder (10, 10') can be used to open and close the high-pressure lines (51) leading to the cylinders (10, 10'). A first liquid separator (42) is disposed between the low-pressure valves (11, 11') and the low-pressure gas reservoir (40) for separating liquid (14) from gas (13) entering the first liquid separator (42) through the low-pressure line (41). The first liquid separator (42) is connected to one of the cylinders (10, 10') via a first return line (43) for the separated liquid (14). A first pump (44) is located on the first return line (43) for driving the separated liquid (14).

5. A bidirectional liquid piston device according to claims 3 and 4 for implementing the method according to claim 1 and the method according to claim 2. Its features are, A first liquid separator (52) is used to separate liquid (14) from gas (13) entering through the high-pressure line (51). The first liquid separator (52) is arranged between the high-pressure valves (12, 12') and the high-pressure gas reservoir (50). The first liquid separator (52) is connected to one of the cylinders (10, 10') via a first return line (53) for the separated liquid (14). A second liquid separator (42) is used to separate liquid (14) from gas (13) entering through the low-pressure line (41). The second liquid separator (42) is arranged between the low-pressure valve (11, 11') and the low-pressure gas reservoir (40). The second liquid separator (42) is connected to one of the cylinders (10, 10') through a second return line (43) for the separated liquid (14). A first pump (44) is provided on the second return line (43) to drive the separated liquid (14) to one of the cylinders (10, 10').

6. The liquid piston device according to any one of claims 3 to 5, Its features are, At least one of the return lines (43, 53) leads to the valve assembly (60), and after the valve assembly (60), multiple branches (61, 61', 62, 62', 63, 63') of the return lines (43, 53) lead to the cylinders (10, 10') and open at different points in the cylinders (10, 10').

7. The liquid piston device according to any one of claims 3 to 6, Its features are, Two liquid level sensors (L1, L2, L3, L4, L5, L6, L7, L8) are installed at two different heights in the cylinders (10, 10') and / or the liquid separators (42, 52), and the liquid drive unit (20) is provided with a sensor (N1) for the number of cycles to determine the amount of liquid (14) delivered out of or into the cylinders (10, 10').

8. The liquid piston device according to any one of claims 3 to 7, Its features are, The upper end of the cylinder (10, 10') is attached to the high pressure valve (12, 12') and the low pressure valve (11, 11'). A turbulent body (80) is attached to the cylinder (10, 10').

9. The liquid piston device according to claim 6, Its features are, A heat accumulator (15, 15') is arranged in the upper region of the cylinders (10, 10'). Branches (61, 61', 62, 62', 63, 63') open at a point in the cylinders (10, 10'), and during operation, the returned liquid (14) reaches the accumulator (15, 15') from said point. The other branches (61, 61', 62, 62', 63, 63') open at other points in the cylinder (10, 10'), and during operation, the returned fluid (14) cannot reach the accumulator (15, 15') from the other points.

10. The liquid piston device according to any one of claims 3 to 9, Its features are, The accumulator (15, 15') is arranged in the upper region of the cylinder (10, 10'), and a baffle (16) is arranged at the inlet of the liquid line (21) into the cylinder (10, 10'), the baffle (16) being arranged such that during operation, the liquid (14) entering the cylinder (10, 10') through the liquid line (21) impacts the baffle (16) and does not directly reach the accumulator (15, 15').

11. The liquid piston device according to claim 10, Its features are, The liquid line (21) has two inlets for the fluid (14) in the cylinder (10, 10') that can be controlled by valves (17, 17'): a first inlet equipped with a baffle (16); and a second inlet without a baffle (16), which is oriented such that during operation, the incoming liquid (14) flows directly onto the accumulator (15, 15').

12. The liquid piston device according to any one of claims 3 to 11, Its features are, The liquid drive unit (20) has a leakage flow of liquid (14) during operation. The liquid drive unit (20) is connected to the leak container (70) via a leak line (71). A second pump (73) and a third return line (72) are provided, which can be used to return the liquid (14) from the leak container (70) to the cylinder (10, 10'). A third pump (76) is provided, which enables the fluid (14) to be transported from the leak container (70) through the second heat exchanger (75) and returned to the leak container (70).

13. The liquid piston device according to any one of claims 3 to 12, Its features are, The liquid drive unit (20) includes a valve that controls the flow direction of the liquid (14) within the liquid drive unit (20), such that the flow direction of the liquid (14) within the liquid drive unit (20) is always the same, and therefore the rotation direction of the liquid drive unit (20) is always the same.

14. The use of the liquid piston device according to claim 5 for storing energy in the form of compressed gas and subsequently releasing the stored energy.

15. The liquid piston device according to claim 4 is used for the purpose of simultaneously providing compressed gas, electrical energy and cooling to a machine.

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