Liquid piston device and method for compressing and expanding a gas

Abstract

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

Description

[0001]gry 12 / P 1 / 44 2024-09-19 Liquid piston device and method for compression and expansion of a gas The present invention relates to methods for compression and / or expansion of a gas using a liquid piston device, liquid piston devices for carrying out these methods, and various uses of the liquid piston devices. Piston compressors are usually used to compress a gas, particularly over a high pressure range. In contrast to rotary compressor systems, this technology makes it possible to achieve higher pressures by means of suitable sealing of the piston chamber. However, it is precisely this sealing that represents a challenge in terms of costs and maintenance effort, and lubrication of the piston must also be ensured. If pure compressed gas is required, contamination of the gas, which can occur through contact with the drive medium, must also be prevented.Liquid piston systems solve this challenge by using a liquid as the piston instead of a solid piston that moves within the cylinder. The rising liquid level compresses the gas in the cylinder. This also ensures the tightness of the pressure chamber. Lubrication is not necessary with a liquid piston, and maintenance requirements are significantly reduced. The liquid promotes heat exchange with the compressed gas, which has a beneficial effect on the efficiency of the compression process because temperature fluctuations are reduced. It is also possible to install a solid heat exchanger in the cylinder, around which the liquid can flow, further increasing heat exchange. This is not possible with conventional piston compressors due to the solid piston.Finally, in liquid piston systems, the dead space of the gas can be minimized by appropriately distributing the liquid in the compression chamber. Liquid piston systems can also be used as expanders by reversing the process. Compressed gas pushes the liquid column out of the cylinder and drives a liquid motor. This reversal is generally possible in liquid piston systems with the same equipment used for compression, by employing appropriate valve circuits. This allows a bidirectional system to be implemented with little effort. Liquid piston compressors are used in higher pressure ranges, for example, in the supply of compressed gas, in the filling of compressed gas cylinders, and in compressed gas filling stations.The liquid piston expander can be used wherever compressed gas is expanded from a higher pressure level to a lower pressure level, for example when withdrawing compressed gas from a reservoir or a pipeline. The bidirectional system is primarily used in compressed gas storage systems, such as compressed air energy storage systems. Liquid piston systems that serve exclusively as compressors are known from the prior art, for example from DE 102004046316 A1. In particular, hydrogen is compressed and an ionic liquid is used as the liquid in order not to contaminate the gaseous medium to be compressed. WO 2017198725 A1 shows a bidirectional liquid piston system that is used in particular in a multi-stage energy storage system for the compression and expansion of a gas. A heat exchanger in the cylinder increases the heat exchange between gas and liquid.DE 102012003288 B3 shows a bidirectional liquid piston system which, with an optimized heat exchanger design, further promotes heat exchange. In addition, the dead space volume is minimized by an adapted inclined arrangement of the cylinders. WO 2008139267 A1 shows a bidirectional liquid piston system in which a portion of the liquid is sprayed directly into the compression or expansion chamber. This also increases heat exchange between liquid and gas, and virtually isothermal conditions are achieved, which is advantageous for efficiency. WO 2008031527 A1 shows a liquid piston system which replaces the measurement of the liquid level in several cylinders with a level measurement in the leakage tank. This optimizes costs and enables the installation of fixed heat exchangers in the cylinder without interfering with the level measurement.However, this system is only designed as a compressor. The liquid piston systems known from the prior art still have further optimization potential on various levels. Firstly, there is still a dead space volume that impairs the efficiency of the compression and expansion of the gas. Secondly, the compression and expansion still cause the gas to heat up or cool down significantly, which can cause the evaporation or solidification of liquids as well as the condensation of the gas. Thirdly, the systems used to measure the liquid level, which are necessary for controlling the system, are sometimes complex and cost-intensive. The present invention therefore has the object of providing methods for the compression and / or expansion of a gas and liquid piston devices for carrying out these methods, which minimize the dead space volume.A further, optional object is to provide a liquid piston device and a corresponding method with which the compression and / or expansion process is more isothermal. A further, optional object is to provide a liquid piston device with a simple system for measuring the liquid level therein. These objects are achieved by the two methods with the features of claims 1 and 2 and the two liquid piston devices with the features of claims 3 and 4. Further features and embodiments emerge from the dependent claims, and their advantages are explained in the following description.The figures show: Figure 1 Schematic drawing of a gry 12 / P 6 / 44 2024-09-19 liquid piston device with two cylinders for the compression and expansion of a gas Figure 2 Schematic drawing for the application in a compressed gas energy storage system Figure 3 Schematic drawing of the general energy flows Figure 4 Schematic drawing for the application in compressed gas provision Figure 5 Liquid piston device with the liquid management system Figure 6 Liquid piston device with the heat management system Figure 7 Liquid piston device with the management system for the leakage liquid Figure 8 Liquid piston device with the pressure and liquid level sensors Figure 9 Detail of a cylinder with swirl pin The figures represent possible embodiments, which are explained in the following description.The invention is based on a liquid piston device with which gas 13, for example ambient air, nitrogen or oxygen, can be compressed from a low-pressure gas reservoir 40 with lower pressure to a higher pressure and stored in a high-pressure gas reservoir 50. This liquid piston device comprises at least two cylinders 10, 10', which are connected to one another by a liquid line 21 (see Figure 1). Located on this liquid line 21 is a liquid drive unit 20 comprising a hydraulic pump, with which a liquid 14 can be conveyed from one cylinder 10, 10' to the other cylinder 10, 10'. Each cylinder 10, 10' is connected to the low-pressure gas reservoir 40 by a low-pressure line 41, so that a gas 13 can pass from the low-pressure gas reservoir 40 through the low-pressure line 41 into each cylinder 10, 10'.The low-pressure gas reservoir 40 is preferably a container in which gas 13 is located at low pressure, for example, below 1 to 100 bar. However, the low-pressure gas reservoir 40 could also simply be the environment, with air from the environment passing into the cylinders 10, 10' through the low-pressure line 41, or a low-pressure compressor and / or expander, which, for example, pre-compresses gas to a certain pressure level and / or a gas generator, which provides a certain gas component, for example, nitrogen, from ambient air (see Figure 2). The gry 12 / P 8 / 44 2024-09-19 low-pressure line 41 is provided with low-pressure valves 11, 11', with which the passage of gas 13 from the low-pressure gas reservoir 40 to each cylinder 10, 10' can be controlled.Each cylinder 10, 10' is connected to the high-pressure gas reservoir 50 by a high-pressure line 51, so that a gas 13 from each cylinder 10, 10' can pass through the high-pressure line 51 into the high-pressure gas reservoir 50. The high-pressure gas reservoir 50 is preferably a container suitable for the extraction and / or storage of gas 13 under high pressure of, for example, 10 to 1000 bar. However, the high-pressure gas reservoir 50 can also be or comprise a high-pressure compressor and / or expander, which, for example, further compresses gas to an even higher pressure level. The high-pressure line 51 is provided with high-pressure valves 12, 12', with which the passage of gas 13 from each cylinder 10, 10' to the high-pressure gas reservoir 50 can be controlled. During operation of the liquid piston device, a liquid 14, for example water or oil or another suitable liquid, is present in the cylinders 10, 10'.For the compression and storage of compressed gas in the high-pressure gas reservoir 50, the liquid drive unit 20 conveys liquid 14 through the liquid line 21 from a first cylinder 10, 10' to a second cylinder 10, 10'. The following gry 12 / P 9 / 44 2024-09-19 description of the compression method is based on Figure 1, in which it is arbitrarily assumed that the liquid drive unit 20 conveys liquid 14 from the first cylinder 10 on the left side to the second cylinder 10' on the right side. In this case, a compression process takes place in the second cylinder 10' first, followed by an expulsion process: ^ During the compression process, the low-pressure valve 11' and the high-pressure valve 12' of the second cylinder 10' are closed, so that the gas 13 contained therein is compressed by the incoming liquid 14.^ As soon as the desired pressure level is reached, the expulsion process starts: The high-pressure valve 12' opens, and the compressed gas is pushed into the high-pressure gas reservoir 50 by the incoming liquid 14. Meanwhile, the low-pressure valve 11 connected to the first cylinder 10 is open, and the high-pressure valve 12 connected to the first cylinder 10 is closed, so that the liquid 14 exiting the first cylinder 10 is replaced therein with gas 13 from the low-pressure gas reservoir 40. Once the second cylinder 10' is filled with liquid 14, the low and high pressure valves 11, 11', 12, gry 12 / P 10 / 44 2024-09-19 12' and the conveying direction of the liquid drive unit 20 can be switched to continue the compression process with the compression and expulsion 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 a cylinder 10, 10'. This ensures that when one cylinder 10, 10' is filled, another cylinder 10, 10' is never completely emptied and that there is always liquid 14 in the liquid drive unit 20. During operation of the liquid piston device, the incoming mechanical or electrical energy used to drive the liquid drive unit 20 is stored in the form of compressed gas in the high-pressure gas reservoir 50. This stored energy can later be released as outgoing drive energy by expanding the stored compressed gas through the liquid piston device, with the liquid drive unit 20 then serving as a hydraulic motor with which a vehicle, a machine, or a power generator can be driven.The following description of the expansion process is based on Figure 1, in which it is arbitrarily assumed that gry 12 / P 11 / 44 2024-09-19 pressurized gas 13 is admitted into the second cylinder 10' on the right-hand side. In this case, an admission process and then an expansion process take place in this second cylinder 10': ^ During the admission process, the high-pressure valve 12' of the second cylinder 10' is open and the low-pressure valve 11' is closed, so that a certain amount of gas 13 under high pressure passes from the high-pressure gas reservoir 50 into the second cylinder 10'. ^ As soon as the desired amount of gas 13 is in the cylinder 10', the expansion process starts. During the expansion process, the high-pressure valve 12' and the low-pressure valve 11' of the second cylinder 10' are closed and the admitted high-pressure gas 13 expands therein.During both the intake process and the expansion process, the liquid 14 located in the second cylinder 10' is driven through the liquid line 21 and through the liquid drive unit 20, which then serves as a hydraulic motor. The liquid 14 then enters another cylinder 10, 10', for example, the first cylinder 10 on the left side of Figure 1, in which the high-pressure valve 12 is closed and the low-pressure valve 11 is open. The gas 13 located in the first cylinder 10 is then expelled through the low-pressure line 41 and reaches the low-pressure gas reservoir 40, which then serves as a gas sink.Once the first cylinder 10 is filled with liquid 14, the low- and high-pressure valves 11, 11', 12, 12' can be switched to continue the expansion process with the intake and expansion of the compressed gas stored in the high-pressure gas reservoir 50 in the first cylinder 10, and so on. It is advantageous if the amount of gas 13 admitted into a cylinder 10, 10' during the intake process is calibrated such that, after the expansion process of this gas 13 in this cylinder, the other cylinder 10, 10' is completely filled with liquid 14. Otherwise, a liquid equalization process takes place after the expansion process, during which additional liquid 14 is introduced into the other cylinder 10, 10' until it is completely filled. In both cylinders 10, 10' the low pressure valves 11, 11' are open and the high pressure valves 12, 12' are closed.The compression and subsequent expansion of gas 13 creates a bidirectional liquid piston device that can store and release energy similar to a battery. The liquid piston device therefore offers numerous applications, a few of which are briefly mentioned below. The temporary storage of excess energy is one of the greatest challenges in power generation using renewable energy sources, whose output is weather-dependent (sun, wind, etc.) and cannot be adapted to actual current power demand.One possible application of the present liquid piston device is the storage of excess energy (for example, during the day when the sun is generating electricity via a solar system but there is a low energy demand), which can be used later (for example, in the evening when the solar system is no longer generating electricity but there is a greater electricity demand). The present liquid piston device can also be used, for example, to provide economical peak load management when purchasing electrical energy. The intermediate storage of energy allows energy to be drawn from the electrical grid during off-peak times and stored for use during peak times. The liquid piston device according to the invention finds further applications in industrial sectors where compressed gas is required.For example, the compressed gas required for a machine can be produced in advance during off-peak times, temporarily stored at a higher pressure, and then retrieved at any desired lower pressure level during peak load times. Because the gas is stored at high pressure, a useful energy density of up to 47 kWh / m³ is achieved. 3at 300 bar, and the required storage volume is reduced to an appropriate size. In order to vary the flow rates and pressure levels and adapt them to requirements, several stages of the liquid piston device can be used in series and / or parallel. Heat is also generated during gas compression, and cold is generated during expansion (see Figure 3). The liquid piston device can be advantageously used in a process that requires compressed gas and, at the same time, heat or cold (see Figure 4). This is the case, for example, in applications where, during off-peak times, the heat is used to charge the compressed gas storage device to power a process or heat a building. There are many applications for the use of electrical energy and cold during expansion, as the demand for these two forms of energy usually coincides. Generally, if electricity is needed, cold is also needed, e.g.for cooling machines or data centers, since electricity is always partially converted into heat. Another particularly advantageous application of the present liquid piston device is in the supply of nitrogen for laser cutting machines, wherein the machine requires electricity and cooling in addition to the nitrogen. The presented liquid piston device is also suitable for use in the compressed gas storage system according to WO 2019219801 A1, in which a liquid piston system in conjunction with a liquid-filled compressed gas tank enables gas to be stored at constant pressure. The present liquid piston device can take on all or part of the function of the working machine and / or the displacement device described in WO 2019219801 A1. In order to increase the efficiency of the compression, the dead space volume of the compressed gas 13 in the cylinders 10, 10' should be minimized.This means that at the end of compression, as little gas 13 as possible remains in a cylinder 10, 10', and the cylinder 10, 10' is filled as completely as possible with liquid 14. This prevents the high-pressure gas 13 from expanding back to the pressure level of the low-pressure gas reservoir 40 after the expulsion process, thereby preventing energy from being lost. To achieve this, a cylinder 10, 10' should ideally be filled with liquid 14 exactly up to the connected high-pressure valve 12, 12', no more and no less. However, a completely precise filling of the cylinder 10, 10' is not feasible, so in practice the cylinder 10, 10' is either not completely filled or the cylinder 10, 10' is overfilled. Since the incomplete filling of the cylinder 10, 10' creates dead space volume and is undesirable, according to the invention the liquid 14 is conveyed at least to the high pressure line 51 after the high pressure valve 12, 12' (ieThe liquid 14 flows through the high-pressure valve 12, 12' and continues into the high-pressure line 51. A liquid piston device according to the invention is specifically designed to carry out this method step and comprises a control system with which the liquid drive unit 20 and the high- and low-pressure valves 11, 11', 12, 12' can be controlled. The control system is programmed such that the liquid 14, which is conveyed into the cylinder 10, 10' by the liquid drive unit 20, fills the cylinder 10, 10' and is conveyed at least as far as the high-pressure line 51 and downstream of the high-pressure valve 12, 12'. The dead space volume in the cylinder 10, 10' is thus minimized, and an optimal expulsion process of the compressed gas 13 into the high-pressure gas reservoir 50 is ensured.To further reduce the dead space volume, it can also be provided that the high-pressure line 51 or the high-pressure valve 12, 12' opens at the upper end of the cylinders 10, 10' so that the cylinders 10, 10' can be completely filled with the liquid 14 gry 12 / P 17 / 44 2024-09-19. The same applies to expansion: To increase the efficiency of the expansion, the dead space volume of the remaining gas 13 in the cylinders 10, 10' should be minimized. This means that at the beginning of the expansion process, the cylinders 10, 10' must be filled as completely as possible with liquid 14 before the corresponding high-pressure valve 12, 12' opens. This prevents gas from the high-pressure gas reservoir 50 from expanding into the lower-pressure gas 13 still in the cylinder 10, 10' at a lower pressure level when the high-pressure valve 12, 12' opens, without performing work.For this purpose, the invention provides that the liquid 14, which enters the cylinder 10, 10' and pushes the gas 13 contained therein into the low-pressure gas reservoir 40, fills the cylinder 10, 10' and is conveyed at least as far as the low-pressure line 41 and past the low-pressure valve 11, 11' (i.e., the liquid 14 flows through the low-pressure valve 11, 11' and continues into the low-pressure line 41). A liquid piston device according to the invention is specifically designed to carry out this method step and comprises a controller with which the liquid drive unit 20 and the high- and low-pressure valves 11, 11', 12, 12' can be controlled.The gry 12 / P 18 / 44 2024-09-19 control system is programmed so that the amount of gas 13 admitted into a cylinder 10, 10' through the high-pressure valve 12, 12' during the intake process is calibrated such that after the expansion process of this gas 13 in this cylinder, the other cylinder 10, 10' is completely filled with liquid 14 and the liquid 14 is transported at least as far as the low-pressure line 41 and past the low-pressure valve 11, 11'. In this way, the dead space volume in the cylinders 10, 10' is minimized or completely eliminated. In order to reduce the dead space volume even further, it can additionally be provided that the low-pressure line 41 or the low-pressure valve 11, 11' opens at the upper end of the cylinders 10, 10' so that the cylinders 10, 10' can be completely filled with the liquid 14. The solution according to the invention, ie the overfilling of a cylinder 10, 10' with liquid 14 up to the associated high pressure orLow-pressure valves 11, 11', 12, 12' for minimizing the dead space volume in the cylinder 10, 10' can be used independently of each other to improve compression efficiency and / or to improve expansion efficiency. If the liquid piston device is used only as a compressor to store energy as compressed gas, it may be sufficient if liquid 14 gry 12 / P 19 / 44 2024-09-19 is driven to the high-pressure valve 12, 12' only during the compression process. Conversely, if the liquid piston device is used only as an expander to draw on stored energy, it may be sufficient if liquid 14 is driven to the low-pressure valve 11, 11' only during the expansion process. If the liquid piston device is used bidirectionally as a compressor and expander, the measure can be used in both the compression process and the expansion process.However, to ensure that no liquid 14 enters the high-pressure gas reservoir 50 or the low-pressure gas reservoir 40, a special liquid management system is provided. This also provides a closed system for the liquid 14, from which it cannot escape and therefore no refilling is necessary. Providing a closed system is important for the efficiency of the liquid piston device because any pressurized liquid quantity lost beyond the system boundary also represents lost pressure energy. The liquid 14 forced into the high- and / or low-pressure lines 41, 51 must therefore be intelligently returned to the cylinders 10, 10'.Depending on whether liquid 14 is forced into the high-pressure line 51 during the compression process or liquid 14 is forced into the low-pressure line 41 during the expansion process, according to the invention a liquid separator 42, 52, for example a cyclone separator, is arranged either between the high-pressure valve 12, 12' and the high-pressure gas reservoir 50 or between the low-pressure valve 11, 11' and the low-pressure gas reservoir 40 (see Figure 5). When liquid 14 is forced into the high-pressure line 51 during the compression process and liquid 14 is forced into the low-pressure line 41 during the expansion process, a liquid separator 42, 52 is arranged between the high-pressure valve 12, 12' and the high-pressure gas reservoir 50 as well as between the low-pressure valve 11, 11' and the low-pressure gas reservoir 40.Each liquid separator 42, 52 is connected to a return line 43, 53, through which the liquid 14 flows from the liquid separator 42, 52 back into one of the cylinders 10, 10'. The liquid 14 can flow back into another cylinder 10, 10' or into the same cylinder 10, 10' from which it was expelled. However, for this to happen, the pressure in the cylinder 10, 10' must be lower than in the liquid separator 42, 52. The liquid 14, which is forced into the high-pressure line 51 at the end of the compression process and collected by the connected liquid separator 52, is under high pressure at this time and can, for example, flow directly back into a cylinder 10, 10' in which no compression process is taking place.Preferably, this liquid 14 could also flow back into a cylinder 10, 10' in which a compression process is taking place, as long as the pressure in the cylinder 10, 10' is lower and a sufficient pressure difference is present. However, the liquid 14, which at the end of the expansion process in one cylinder 10, 10' is forced into the low-pressure line 41 connected to the other cylinder 10, 10' and collected by the associated liquid separator 42, is at a pressure level too low to spontaneously flow back into a cylinder 10, 10'. Therefore, the corresponding return line 43 is provided with a first pump 44, which brings the liquid 14 to the pressure required for return to the cylinders 10, 10'.It is advantageous if at least one return line 43, 53 of a liquid separator 42, 52 leads to a valve group 60 and, after the valve group 60, several branches 61, 62, 63, 61', 62', 63' of the return lines 43, 53 lead to a cylinder 10, 10' and open at different points, for example at different heights, of the cylinder 10, 10'. Several branches 61, 62, 63, 61', 62', 63' of the return lines 43, 53 can also lead to different points of different cylinders 10, 10'. For example, Figure 5 shows a valve group 60 with six branches 61, 61', 62, 62', 63, 63', three of which lead to different locations of a cylinder 10, 10' and three of which lead to different locations of another cylinder 10, 10', for example at the top end, in the middle and at the bottom end of the cylinders 10, 10'.It is also possible for only two branches to lead to each cylinder 10, 10', which, for example, open at the lower and upper ends of the cylinder 10, 10'. With the appropriate control of the valve group 60, the time, as well as the cylinder 10, 10' and the position on the cylinder 10, 10', of the return of the liquid from the liquid separator 42, 52 can be determined as desired. The ideal time for this return is when the pressure difference between the liquid separator 42, 52 and the cylinder 10, 10' is as small as possible. Thus, the least energy is lost from the first liquid separator 52 on the side of the high-pressure gas reservoir 50, and the first pump 44 connected to the second liquid separator 42 has to consume the least energy.Additional, optional solutions for further minimizing the dead space volume include narrowing the upper portion of cylinders 10, 10' to direct the gas 13 toward the high- and low-pressure valves 11, 11', 12, 12' during the discharge process. However, because this must be ensured for both valves 11, 11', 12, 12' of cylinder 10, 10', certain spaces are created where the gas 13 can be enclosed by the liquid 14 instead of being pushed into the high- and low-pressure lines 41, 51, thus generating dead space. To reduce this effect, a swirl element 80 can be mounted at the upper end of the cylinder 10, 10' near the high- and low-pressure valves 11, 11', 12, 12' (see Figure 9). This creates swirl in the flow at the upper end of the cylinder 10, 10', particularly the swirl of the separating layer between liquid 14 and gas 13.This improves the distribution of liquid 14 and reduces the dead space volume of gas 13. Swirl body 80 can have any desired geometry, as its mere presence influences the liquid flow and creates turbulence therein. A preferred shape for swirl body 80 is spherical. It is also advantageous if compression and expansion are as isothermal as possible. This allows higher pressure ratios to be achieved with the liquid piston device without the gas gry 12 / P 24 / 44 2024-09-19 13 heating up too much during compression or cooling down too much during expansion. This prevents evaporation and solidification of liquid 14 as well as condensation of gas 13. To achieve quasi-isothermal compression and expansion, the best possible heat exchange must be enabled between gas 13 and its surroundings.A certain amount of heat exchange already occurs in the liquid piston device directly through the boundary layer between gas 13 and liquid 14. However, to increase this heat exchange, the liquid piston device can include a special heat management system. For example, a heat accumulator 15, 15' can be arranged in a cylinder 10, 10', which absorbs additional heat during compression or releases additional heat during expansion. The liquid piston concept allows for the installation of a heat accumulator 15, 15' in the form of a solid body directly in the compression or expansion chamber. This is a significant advantage over conventional piston compression and expansion machines with fixed pistons.The heat accumulator 15, 15' is preferably arranged in the upper region of the cylinders 10, 10' because the greatest energy flows occur in this region of compression or expansion: The greatest heating of the gas 13 occurs at the end of compression, when the cylinder 10, 10' is already partially filled with liquid and the gas 13 is located in its upper region. Analogously, the greatest cooling occurs at the beginning of the expansion, as soon as the pressurized gas 13 expands in the upper region of the cylinder filled with liquid 14 at the beginning of the expansion process. This also saves heat storage material in the lower region of the cylinders 10, 10' and thus reduces costs. During compression, the heat accumulator 15, 15' is heated up in a first step by the heating gas 13.As soon as the liquid 14 flows around the heat accumulator 15, 15', the absorbed heat of the liquid 14 is transferred in a second step. Similarly, during expansion, heat is first transferred from the heat accumulator 15, 15' to the cooling gas 13. In the next expansion cycle, which takes place in a different cylinder 10, 10', the liquid 14 then heats the heat accumulator 15, 15' again as soon as the cylinder is filled with the liquid 14. The material of the heat accumulator preferably has a high heat capacity and a high heat transfer coefficient and is therefore preferably a metal. Furthermore, the surface area-to-volume ratio should be maximized to further promote heat transfer. Furthermore, for a suitable design of the heat accumulator 15, 15', properties such as low liquid retention capacity, low pressure drop, simple manufacturing, and optimized costs must be considered.Tests have shown that a heat storage device made of steel wool, for example, is well suited. The liquid 14 already dissipates the heat of the compressed gas or the cold of the expanded gas through contact with the walls of the cylinders 10, 10' and the other components of the liquid piston device (liquid line 21, liquid drive unit 20, high- and low-pressure valves 11, 11', 12, 12', etc.). In order to dissipate heat even more effectively during compression or to add heat more controlled during expansion, a first heat exchanger 22 can be integrated into the liquid line 21 (see Figure 6). Via the first heat exchanger 22, an external circuit can be heated by supplying heat during compression and, analogously, cooled by removing heat during expansion.When filling the cylinders 10, 10' with liquid 14, the liquid is preferably conveyed or sprayed into the cylinders 10, 10' from bottom to top through the liquid line 21. This results in the disadvantage that the liquid 14 is sprayed directly onto the heat accumulator 15, 15', partially filling it with liquid 14 before the rising liquid level reaches the heat accumulator 15, 15'. This reduces the heat exchange between the heat accumulator 15, 15' and the gas 13. The situation is even worse if the heat accumulator 15, 15' has surfaces that are close to one another and the space between them is filled with liquid.In this case, the effect of the heat accumulator 15, 15' is virtually neutralized because the contact area between the heat accumulator 15, 15' and the gas 13 is greatly reduced, significantly impairing heat exchange and significantly reducing the isothermal nature of the process. Therefore, on the one hand, a low liquid retention capacity of the heat accumulator 15, 15' is preferred in order to empty the spaces between the surfaces as quickly and completely as possible and fill them with gas when the liquid level drops. To avoid this, a baffle plate 16, 16' can be arranged in a cylinder 10, 10', for example, at the inlet of the liquid 14, 14' at the lower end of the cylinders 10, 10', against which the incoming liquid 14 impacts.This ensures that, regardless of the inlet velocity of the liquid 14, a controlled increase in the liquid level in the cylinder 10, 10' is achieved, and that the liquid 14, 14' does not come into undesired premature contact with the heat accumulator 15, 15'. In certain cases, for example, when the liquid piston device is used to generate heat or cold (griy 12 / P 28 / 44 2024-09-19) and the gas 13 must therefore be brought to a higher or lower temperature level, it can be advantageous if the isothermal nature of the process is controllable.In this case, for example, the liquid line 21 can be provided with two inlets for the liquid 14 in each cylinder 10, 10', which can be controlled by a valve 17, 17': a first inlet with a baffle 16, 16' for the controlled increase in the liquid level, and a second inlet through which the liquid 14 deliberately comes into early contact with the heat accumulator 15, 15' (see Figure 6). This provides another control variable for controlling the compression process between the isothermal process (i.e., with a constant temperature thanks to heat exchange) and the adiabatic process (with heating during compression and cooling during expansion due to the lack of heat exchange). There is another method for controlling the effect of the heat accumulator and, therefore, the isothermal nature of the process.One or more return lines 43, 53 of the liquid separators 42, 52 can lead to a valve group 60 as already described above, and after the valve group 60, several branches 61, 61', 62, 62', 63, 63' of the return lines 43, 53 can lead to outlets at various points on the cylinders 10, 10', gry 12 / P 29 / 44 2024-09-19 in particular to a first outlet, through which the returned liquid 14 sprays onto the heat accumulator 15, 15' and to a second outlet, through which the returned liquid does not spray onto the heat accumulator 15, 15'. For example, the liquid return to a cylinder 10, 10' could be controllably above, below or at the level of the heat accumulator 15, 15'. Thus, depending on the temperature of the fluid 14 and the heat accumulator 15, 15', the latter can be heated or cooled as needed. This creates an additional control variable for controlling the heat flows during compression or expansion.It is also conceivable to spray the liquid 14 returned to the cylinder 10, 10' into the gas 13 contained therein in the form of droplets, for example via a branch 61, 61', 62, 62', 63, 63', which opens into the center of the empty space below the heat accumulator 15, 15'. Spraying the liquid 14 in the form of droplets maximizes the contact area between the gas 13 and the liquid 14 and thus also the heat exchange. These methods can be used cumulatively or alternatively to the method with the baffle plate 16, 16' described above. Certain embodiments of the liquid drive unit 20 exhibit a leakage flow of the liquid gry 12 / P 30 / 44 2024-09-19 14 during operation. In this case, the liquid piston device can have a management system for the leakage liquid. The leakage flow can, for example, be led via a leakage line 71 into a leakage container 70 which has a lower pressure level (see Figure 7).To close the fluid circuit, the fluid 14 can be brought back to the required pressure by a second pump 73 and then returned to the cylinders 10, 10' via a third return line 72. If the liquid piston device has a valve group 60 with which fluid 14 is returned from the fluid separators 42, 52 to the cylinders 10, 10', the third return line 72 can lead to this valve group 60 and the leakage fluid can be returned to the cylinders 10, 10' together with the fluid 14 from the fluid separators 42, 52. The fluid 14 in the leakage container 70 also enables a more suitable heat exchange with an external circuit, since this fluid 14 is at a lower pressure level. A third pump 76 can therefore be provided, which transports the liquid 14 from the leakage container 70 through a second heat exchanger 75 and returns it to the leakage container 70.The lower pressure in this circuit makes the design of the heat exchanger 75 simpler and more cost-effective. This third pump 76 allows the flow through the second heat exchanger 75 to be controlled independently. Alternatively, the second heat exchanger 75 can be placed directly in the leakage line 71 or in the third return line 72, thus eliminating the need for the third pump 76. If a leakage tank 70 is present, the liquid piston device can be further simplified by returning the liquid from the liquid separator 42 on the low-pressure side through the liquid line 77 directly into the leakage tank 70. Thus, a separate first pump 44 and corresponding return line 43 are not necessary. However, the pressure in the liquid separator 42 on the low-pressure side must be higher than in the leakage tank 70.A further aspect of the invention is the measurement of the pressure and the state in the liquid piston device, which can be advantageous for its control. In principle, the pressure values ​​and the state in the cylinders 10, 10', in the liquid separators 42, 52, and in the leakage container 70 can contribute to better control of the liquid piston device. Since all containers are always at least partially filled with a liquid, the pressure can be measured in the liquid at the lower end using pressure sensors P1, P2, P3, P4, P5 if necessary (see Figure 8). This dampens the pressure measurement more because the inertia of the liquid filters out unwanted fluctuations in the pressure measurement. Efficient liquid level measurement in liquid piston systems is generally challenging, especially when a heat accumulator 15, 15' is installed inside the cylinders 10, 10'.The present invention solves this problem efficiently and cost-effectively with two liquid level sensors L1, L2, L3, L4, L5, L6, L7, L8 each at different heights in the cylinders 10, 10' and in the liquid separators 42, 52, for example with one liquid level sensor at the upper end and one liquid level sensor at the lower end of the cylinders 10, 10'. If a leakage container 70 is present, it can also be provided with two liquid level sensors L9, L10 at different heights. This allows the maximum or minimum state of the liquid 14 level to be detected in each of these containers. The other states of the liquid level in the 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., with a sensor for the number of revolutions N1.Using the information on the number of revolutions, the quantity of fluid 14 conveyed from or into the cylinders 10, 10' can be determined, and thus, using the maximum and minimum states determined by the fluid level sensors L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, a continuous estimation of the fluid level can be made. Thus, the state of the fluid piston device can be detected using the pressure sensors, the simple fluid level sensors, and the sensor for the number of revolutions N1, and the fluid piston device can be optimally controlled using the fluid pumps and valves. The fluid drive unit 20 is preferably designed such that its flow and rotation directions are always the same, regardless of the compression or expansion operating mode. This reduces complexity and allows for savings in components and costs.For this purpose, the fluid drive unit 20 can comprise valves with which the flow direction of the fluid 14 can be controlled as desired. The fluid drive unit 20 can comprise a hydraulic pump and a hydraulic motor that are used alternatively for compression and expansion, or a reversible hydraulic pump that can also serve as a hydraulic motor.

Claims

gry 12 / P 34 / 44 2024-09-19 Patent claims 1. Method for compressing a gas with a liquid piston device comprising at least two cylinders (10, 10'), a liquid line (21) which connects the cylinders (10, 10') to one another, a liquid drive unit (20) with which a liquid (14) can be conveyed from one cylinder (10, 10') to the other cylinder (10, 10'), a low-pressure gas reservoir (40) which is connected to each cylinder (10, 10') via a low-pressure line (41), a low-pressure valve (11, 11') for each cylinder (10, 10') with which the low-pressure line (41) to the cylinder (10, 10') can be opened and closed, a high-pressure gas reservoir (50) which is connected to each cylinder (10, 10'), a high-pressure valve (12, 12') for each cylinder (10, 10'), with which the high-pressure line (51) to the cylinder (10, 10') can be opened and closed, and a first liquid separator (52),which is arranged between the high-pressure valve (12, 12') and the high-pressure gas reservoir (50), for separating the liquid (14) and the gas (13) which are fed through the high-pressure line (51) into the, gry 12 / P 35 / 44 2024-09-19 first liquid separator (52), and is connected to one of the cylinders (10, 10') by a first return line (53) for the separated liquid (14), wherein in the method the liquid drive unit (20) conveys a liquid (14) through the liquid line (21) from a first cylinder (10, 10') into a second cylinder (10, 10'), so that the gas (13) located in the second cylinder (10, 10') is compressed by the liquid (14) and pushed through the high-pressure line (51) into the high-pressure gas reservoir (50), characterized in that the liquid (14), after filling the second cylinder (10, 10'), is fed at least into the high-pressure line (51) downstream of the high-pressure valve (12, 12') is transported in. 2.Method for expanding a gas with a liquid piston device comprising at least two cylinders (10, 10'), a liquid line (21) which connects the cylinders (10, 10') to one another, a liquid drive unit (20) with which a liquid (14) can be conveyed from one cylinder (10, 10') to the other cylinder (10, 10'), a low-pressure gas reservoir (40) which is connected to each cylinder (10, 10') via a low-pressure line (41). gry 12 / P 36 / 44 2024-09-19, a low-pressure valve (11, 11') for each cylinder (10, 10'), with which the low-pressure line (41) to the cylinder (10, 10') can be opened and closed, a high-pressure gas reservoir (50) which is connected to each cylinder (10, 10') via a high-pressure line (51), a high-pressure valve (12, 12') for each cylinder (10, 10'), with which the high-pressure line (51) to the cylinder (10, 10') can be opened and closed, and a first liquid separator (42) which is arranged between the low-pressure valve (11, 11') and the low-pressure gas reservoir (40), for separating the liquid (14) and the gas (13) which are fed through the low-pressure line (41) into the first Liquid separator (42) enter, is suitable for being connected by a first return (43) for the separated liquid (14) to one of the cylinders (10,10') and a first pump (44) is provided on the first return line (43) for conveying the separated liquid (14), wherein in the process pressurised gas (13) from the high-pressure gas reservoir (50) is admitted into a second cylinder (10, 10') and the gas (13) expands therein, whereby liquid (14) from the second cylinder (10, 10') through the liquid line (21) and through the, gry 12 / P 37 / 44 2024-09-19 fluid drive unit (20) is driven into a first cylinder (10, 10'), characterized in that the fluid (14) is conveyed, after filling the first cylinder (10, 10'), at least into the low-pressure line (41) downstream of the low-pressure valve (11, 11'). 3.A liquid piston device for carrying out the method according to claim 1, comprising at least two cylinders (10, 10'), a liquid line (21) connecting the cylinders (10, 10') to one another, a liquid drive unit (20) with which a liquid (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), a low-pressure valve (11, 11') for each cylinder (10, 10') with which the low-pressure line (41) to the cylinder (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), a high-pressure valve (12, 12') for each cylinder (10, 10'), with which the high pressure line (51) to the cylinder (10,. gry 12 / P 38 / 44 2024-09-19 10') can be opened and closed and a first liquid separator (52) arranged between the high-pressure valve (12, 12') and the high-pressure gas reservoir (50), suitable for separating the liquid (14) and the gas (13) entering the first liquid separator (52) through the high-pressure line (51), and connected to one of the cylinders (10, 10') by a first return line (53) for the separated liquid (14). 4.Liquid piston device for carrying out the method according to claim 2, comprising at least two cylinders (10, 10'), a liquid line (21) which connects the cylinders (10, 10') to one another, a liquid drive unit (20) with which a liquid (14) can be conveyed from one cylinder (10, 10') to the other cylinder (10, 10'), a low-pressure gas reservoir (40) which is connected to each cylinder (10, 10') via a low-pressure line (41), a low-pressure valve (11, 11') for each cylinder (10, 10') with which the low-pressure line (41) to the cylinder (10, 10') can be opened and closed, a high-pressure gas reservoir (50) which is connected to each cylinder (10, 10') via a high-pressure line (51). gry 12 / P 39 / 44 2024-09-19, a high-pressure valve (12, 12') for each cylinder (10, 10'), with which the high-pressure line (51) to the cylinder (10, 10') can be opened and closed, a first liquid separator (42) arranged between the low-pressure valve (11, 11') and the low-pressure gas reservoir (40), suitable for separating the liquid (14) and the gas (13) entering the first liquid separator (42) through the low-pressure line (41), is connected to one of the cylinders (10, 10') by a first return line (43) for the separated liquid (14), and a first pump (44) on the first return line (43) for conveying the separated liquid (14). 5.Bidirectional liquid piston device according to claims 3 and 4 for carrying out the method according to claim 1 and the method according to claim 2, characterized by a first liquid separator (52) for separating the liquid (14) and the gas (13) entering it through the high-pressure line (51), which first liquid separator is arranged between the high-pressure valve (12, 12') and the high-pressure gas reservoir (50) and is connected to one of the cylinders (10, 10') by a first return line (53) for the separated liquid (14), and. gry 12 / P 40 / 44 2024-09-19 a second liquid separator (42) for separating the liquid (14) and the gas (13) entering it through the low-pressure line (41), which second liquid separator is arranged between the low-pressure valve (11, 11') and the low-pressure gas reservoir (40) and is connected to one of the cylinders (10, 10') by a second return line (43) for the separated liquid (14), a first pump (44) being provided on the second return line (43) for conveying the separated liquid (14) to one of the cylinders (10, 10').

6. A liquid piston device according to one of claims 3 to 5, characterized in that at least one return line (43, 53) leads to a valve group (60), and after the valve group (60), several branches (61, 61', 62, 62', 63, 63') of the return line (43, 53) lead to a cylinder (10, 10') and open at different points on the cylinder (10, 10').Liquid piston device according to one of claims 3 to 6, characterized in that two liquid level sensors (L1, L2, L3, L4, L5, L6, L7, L8) are mounted at two different heights in the cylinders (10, 10') and / or in the liquid separators (42, 52), and that. gry 12 / P 41 / 44 2024-09-19 the fluid drive unit (20) is provided with a sensor for the number of revolutions (N1) for determining the amount of fluid (14) conveyed from or into the cylinders (10, 10').

8. A fluid piston device according to one of claims 3 to 7, characterized in that a swirl body (80) is mounted at the upper end of a cylinder (10, 10') near the high- and low-pressure valves (11, 11', 12, 12'). 9.A liquid piston device according to claim 6, characterized in that a heat accumulator (15, 15') is arranged in the upper region of a cylinder (10, 10'), a branch (61, 61', 62, 62', 63, 63') opens in the cylinder (10, 10') at a point from which the returned liquid (14) reaches the heat accumulator (15, 15') during operation, and another branch (61, 61', 62, 62', 63, 63') opens in the cylinder (10, 10') at a different point from which the returned liquid (14) does not reach the heat accumulator (15, 15') during operation.

10. A liquid piston device according to any one of claims 3 to 9. gry 12 / P 42 / 44 2024-09-19 characterized in that a heat accumulator (15, 15') is arranged in the upper region of a cylinder (10, 10'), and a baffle plate (16) is arranged at the mouth of the liquid line (21) in the cylinder (10, 10') in such a way that, during operation, the liquid (14) entering the cylinder (10, 10') through the liquid line (21) impacts the baffle plate (16) and does not reach the heat accumulator (15, 15') directly.

11. A liquid piston device according to claim 10, characterized in that the liquid line (21) has two inlets for the liquid (14) in a cylinder (10, 10'), which are controllable by a valve (17, 17'): a first inlet provided with a baffle plate (16), and a second inlet without a baffle plate (16), which is oriented such that, during operation, the incoming liquid (14) reaches the heat accumulator (15, 15') directly.Liquid piston device according to one of claims 3 to 11, characterized in that the liquid drive unit (20) has a leakage flow of the liquid (14) during operation, the liquid drive unit (20) via a leakage line (71) with a leakage container (70). gry 12 / P 43 / 44 2024-09-19 is connected, a second pump (73) and a third return (72) are provided, with which the liquid (14) can be returned from the leakage container (70) to a cylinder (10, 10'), a third pump (76) is provided, with which the liquid (14) can be conveyed from the leakage container (70) through a second heat exchanger (75) and returned again to the leakage container (70).

13. A liquid piston device according to one of claims 3 to 12, characterized in that the liquid drive unit (20) comprises valves with which the flow direction of the liquid (14) within the liquid drive unit (20) can be controlled such that the flow direction of the liquid (14) in the liquid drive unit (20) and thus the direction of rotation of the liquid drive unit (20) is always the same.Use of the liquid piston device according to claim 5 for storing energy as compressed gas and later releasing the stored energy.

15. Use of the liquid piston device according to claim 4 for the simultaneous provision of compressed gas, electrical energy, and cooling for a machine.

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