Hydraulic valveless gas compressor

Abstract

Invention relates to a hydraulic compressor system for compressing gas, comprising: at least one pump for pumping liquid; a gas reservoir for storing compressed gas; at least two compression tanks, each of said compression tanks comprises an expandable bladder defining a bladder cavity, wherein the expandable bladder contains a liquid in the expandable bladder cavity and the expandable bladder is configured to expand when liquid is input into the expandable bladder cavity and a tank cavity outside of the expandable bladder, wherein the cavity comprises a compressible gas wherein the expandable bladder and the tank cavity outside the expandable bladder form interdependent volumes of liquid and gas; a liquid line configured to fluidly couple the expandable bladder cavity with at least one of the one or more pumps such that the liquid is pumped into or out of the expandable bladder via the liquid line; a gas line configured to fluidly couple the gas reservoir with the tank cavity such that the gas flows into or out of the tank cavity via the gas line; wherein, during operation of the system, liquid is pumped by the one or more pumps to the expandable bladder in the first compression tank and gas is expelled from the tank cavity of the first compression tank and directed to gas reservoir where it is compressed, characterised in that Switching from compressing the first compression tank (21) to compressing the second compression tank (22); is achieved by changing the direction of flow; wherein the pump (10) direction of rotation is reversed to reverse the flow of liquid; wherein said pump (10) comprises a variable speed pump wherein the speed of said pump (10) is adjusted so that towards the end of the compression stroke the pump speed is reduced and hence the liquid flowrate is reduced to allow a smooth change-over from one compression tank to another compression tank as the automatically controlled switch over is executed or the speed of said pump is adjusted so that the maximum efficiency of the compression cycle is maintained thought continuous speed adjustment of the pump.

Description

[0001] HYDRAULIC VALVELESS GAS COMPRESSOR

[0002] TECHNICAL FIELD

[0003] The present invention relates to the field of gas compression using liquid pumps and a plurality of compression tanks.

[0004] BACKGROUND

[0005] Gas compressors are being used in a wide range of applications including industrial, health, and residential sectors. Most gas compressors are air compressors, but there are many other applications where gas compression is needed, including refrigerant compressors, natural gas compressors, oxygen compressors and compressors for highly reactive gases. Several studies have identified that the energy consumption from the use of air compressors amounts to -10% of the total energy consumption worldwide. Thus, energy savings in compressing air or gases in general could deliver a very significant economic benefit. Most common types of positive displacement compressors include reciprocating (piston, or diaphragm) or rotary (screw, vane) compressors and the use of each type of compressor depends on the fluid being compressed and the pressure and volume requirements. All positive displacement compressors use solid elements to compress the fluid and most energy is converted to heat. The inherently low efficiency of conventional air compressor systems, which lies in the region of 5-15% represents a huge waste. Certainly, any improvement in the energy efficiency of air compressor systems would contribute considerably to sustainable growth worldwide by reducing industrial energy consumption for air compression. Furthermore, conventional positive displacement compressors often use oil lubrication and expensive filtration is needed to prevent oil mist and gaseous hydrocarbons from ending up in the compressed gas reservoir. Hydro-pneumatic gas compression, where the gas is compressed using a liquid piston and a pump, is a novel concept the inventors have developed and has many advantages over conventional compressors that use solid elements to compress the fluid. Hydro-pneumatic gas compression enables isothermal cycles during compression, resulting in higher energy efficiencies when compared to adiabatic cycles. The concept of hydro-pneumatic gas compression (i.e. using liquids to compress air) is not new. Indeed, it was first described in 1879 (Mekarski, Louis, ‘Improvement in devices for using compressed air for motive power.’, 8683, Apr. 22, 1879). Although it has received relatively little attention to date, the quest for energy efficiency is driving a renewed interest in hydro-pneumatic systems for energy storage (EP3789609A1 , US20210075296A1 , WO2021250666A1 , CN110985356B) and gas compression in general (US5073090A, DE4430716A1 , CN102840183B). However, known prior art does not take full advantage of the potential of the principle of hydro-pneumatic gas compression for increased energy efficiency and do not possess the necessary robustness that would allow efficient and reliable commercial operation.

[0006] For example, US5073090A teaches a system wherein the compressor has two hollow chambers which are interconnected by a conduit system having a pump located in it. The compressor contains a sufficient volume of non-compressible transfer fluid to completely fill one of the cylinders and the conduit system. A switching system causes the pump to pump the transfer fluid into a first chamber and then pump the transfer fluid from the first chamber and into the second chamber. In such system the liquid is in open contact with the gas and potentially there is the risk of liquid inadvertently entering the storage tank as a cylinder fills with liquid. Hence, in practice, such a system is forced to operate well-below the maximum compression ratio.

[0007] Similarly, CN102840183B teaches a system where the liquid is also in open contact with gas, and liquid level sensors are used to determine the maximum fill level of the compression tank. Therefore, there is the need for an energy-efficient system that allows the system to operate near maximum theoretical efficiency, and which is robust enough to avoid risk of liquid migration into the storage tank and which is simple and reliable in its operation. The present invention aims to address many of these problems known in the art.

[0008] ADVANTAGES OF THE INVENTION

[0009] Some of the advantages of the present disclosure, which at least one embodiment herein satisfies, are as follows.

[0010] A first advantage of the invention is the provision of a method and system for compressing gases using liquid movement in a way that provides improved efficiency and reliability.

[0011] Another advantage of the present invention is the provision of a method and system for compressing gases using liquid movement in a way that enables maintenance without loss of productive time.

[0012] SUMMARY

[0013] The present invention utilises a liquid pump to move incompressible liquid in and out of compression chambers, and in doing so displace gas which is then moved into a gas reservoir tank through transfer of mass. The gas is compressed in the gas reservoir to the desired pressure. The system comprises a plurality of compression tanks, each of which comprises interdependent volumes of liquid and gas. One or more pumps move liquid through the first compression tank, forcing gas to be expelled from the first compression tank and directed to gas reservoir where it is compressed. The liquid in each of said compression tanks is contained within an expandable bladder. Dedicated passages through enable incoming liquid to be fed to the expandable bladder in the compression tank and cause it to volumetrically expand, thus forcing outflow of gas from each compression tank towards the gas reservoir communicatively connected to the compression tanks; The liquid is circulating in a closed system wherein during the first part of the cycle liquid moved out of the expandable bladder of the one compression tank and into the expandable bladder of the second compression tank, and the operation is reversed when the expandable bladder in first compression tank reaches the end of its forward stroke. Gas is supplied to the compression tanks through a low-pressure gas source. If the gas is atmospheric air, the low-pressure gas source is typically the atmosphere.

[0014] In a first aspect of the invention, a hydraulic compressor system for compressing gas, comprises at least one pump; a gas reservoir; a first compression tank, and a second compression tank. Each of the compression tanks comprises: an expandable bladder defining a bladder cavity, a tank cavity outside of the expandable bladder, wherein the cavity comprises a compressible gas; a liquid line configured to fluidly couple the expandable bladder cavity with at least one of the one or more pumps such that the liquid is pumped into or out of the expandable bladder via the liquid line; and a gas line configured to fluidly couple the gas reservoir with the tank cavity such that the gas flows into or out of the tank cavity via the gas line.

[0015] The expandable bladder contains a liquid in the expandable bladder cavity and the expandable bladder is configured to expand when liquid is input into the expandable bladder cavity. The expansion of the expandable bladder causes gas to be pressurised and achieves mass transfer of the gas from the compression tank into the gas reservoir. Amount of substance transfer (n) of gas into the gas reservoirs results in an increase of pressure in the gas reservoir according to the gas law PV=nRT where P is the pressure, V is the volume of the gas reservoir, n is the mass of gas in the reservoir, T is the absolute temperature, and R is the ideal gas constant. During operation of the system, liquid is pumped by the one or more pumps to the expandable bladder in the first compression tank and gas is expelled from the tank cavity of the first compression tank and directed to gas reservoir where it is compressed.

[0016] Because liquid flows into the inner cavity of the expandable bladder, gas and liquid are not in direct contact. At the end of the compression stroke, there is no risk of liquid getting transferred into the transfer lines that connect the compression tank and the gas reservoir. The expandable bladder expands to the maximum extent and allows greater efficiency because nearly all quantity (mass) of gas in the compression tank can be transferred to the gas reservoir. The first compression tank is configured to operate in a compression stroke and in a return stroke. During the compression stroke, liquid is configured to be pumped into the expandable bladder, via the liquid line, such that the expandable bladder expands into the tank cavity and causes compression of the gas; and wherein during return stroke, liquid is configured to flow out from the expandable bladder via the liquid line such that the expandable bladder contracts and the tank cavity expands.

[0017] The liquid line of the first compression tank is fluidly coupled to the liquid line of the second compression tank such that when the first compression tank is configured to operate in the return stroke and the second compression tank is configured to operate in the compression stroke, liquid is configured to flow out from the expandable bladder of the first compression tank and to be fed, by the pump, into the expandable bladder of the second tank; and when the second compression tank is configured to operate in the return stroke and the first compression tank is configured to operate in the compression stroke, liquid is configured to flow out from the expandable bladder of the second compression tank and fed, by the pump, into the expandable bladder of the first tank.

[0018] Switching from compressing the first compression tank to compressing the second compression tank; is achieved by changing the direction of flow; wherein the pump direction of rotation is reversed to reverse the flow of liquid; wherein said pump comprises a variable speed pump wherein the speed of said pump is adjusted so that towards the end of the compression stroke the pump speed is reduced and hence the liquid flowrate is reduced to allow a smooth change-over from one compression tank to another compression tank as the automatically controlled switch over is executed or the speed of said pump is adjusted so that the maximum efficiency of the compression cycle is maintained thought continuous speed adjustment of the pump.

[0019] In some embodiments the system further comprises: an inlet line extending between a low- pressure gas source and the tank cavity; a check valve that controls the flow of gas between the tank cavity and the low-pressure gas source; and a check valve that controls the flow of gas between the tank cavity and the gas reservoir in the gas line.

[0020] Each compression tank comprises a pressure sensor, wherein said pressure sensor is arranged to measure the pressure of the liquid within the expandable bladder. in another embodiment, the system comprises a pair of two pumps, said two pumps connected in parallel and operating as a single unit, wherein of said pair of pumps, the first pump of said pair of pumps has a higher flow capacity and can operate to a lower pressure and the second pump of said pair of pumps has a lower flow capacity and can operate at a higher pressure.

[0021] The system comprises a plurality of liquid lines, wherein each liquid line is configured to couple a hydraulic compression tank with one or more of the one or more pumps; wherein each liquid line is arranged to connect to each compression tank to one or more of the one or more pumps in a closed circuit; wherein when the hydraulic compression tank is configured to change the direction of flow by changing the direction of the pump.

[0022] In one embodiment the sensor system comprises of a pressure sensor arranged to measure the pressure of the liquid within the expandable bladder of each hydraulic compression chamber and a pressure sensor arranged to measure the pressure within the gas reservoir.

[0023] In a preferred embodiment the sensor system comprises of a pressure sensor arranged to measure the pressure of the liquid at the pump ports.

[0024] In another embodiment, the sensor system comprises a flowmeter in fluid communication with the expandable bladder of each hydraulic compression chamber, and a pressure sensor arranged to measure the pressure within the gas reservoir.

[0025] Yet in another embodiment, the sensor system CONSISTS of one flowmeter fluidically connected with pump output, and one pressure sensor fluidically connected with the reservoir no other sensors are necessary when the gas intake pressure is constant.

[0026] In one embodiment, the control system is configured to: receive data corresponding to the pressure of the liquid inside the expandable bladder before the compression stroke is started; receive date corresponding to the pressure of the liquid inside the expandable during the compression stroke is started; calculate the compression ratio (Vc / Vo); determine whether the compression ratio has reached the maximum value; and switch the isolation valves from being open to being closed, or being closed to being open, when the maximum value of the compression ratio has been reached.

[0027] In another embodiment, the control system is configured to switch the direction of the flow by changing the pump direction, when the pump reaches a stalling condition or desired pressure defined by the pump current. Yet in another embodiment, automatic switchover of system from a forward compression cycle of the first compression tank to a forward compression cycle of the second tank and reverse stroke of the first compression tank is happening with a defined time matching the system reaching the desired pressure or pump stalling.

[0028] Another aspect of the system relates to the number of compression tanks. In one embodiment there are two compression tanks. In another embodiment, there are three or more tanks wherein each tank is matched with dedicated passages through which incoming liquid may be fed forcing outflow of gas, with pressure sensors to measure liquid pressure or flowmeters to measure liquid flow.

[0029] The expandable bladder within a compression tank is elastic and is characterized by a spring constant that defines a resistance to expansion.

[0030] The expandable bladder may be of any size depending on the overall capacity of the system. The volume of the compression tanks and the expandable bladder in said expandable tanks is a function of the volume of the gas reservoir tank and the target pressure in the gas reservoir tank, divided by the number of switch-over cycles. The number of switch-over cycles is the number of cycles that liquid flows from one bladder to the other.

[0031] The system is operated in a way as to achieve maximum energy efficiency for compressing the gas; in one embodiment low pressure compressed air is fed to the gas line of the compression tank to accelerate the compression operation and reduce compression time to achieve high pressure in relatively short time.

[0032] According to a preferred embodiment, the method for compressing gas according to the invention comprises: a. providing a first compressor tank comprising: i. an expandable bladder defining a bladder cavity, wherein the expandable bladder contains a liquid in the expandable bladder cavity; ii. a tank cavity outside of the expandable bladder, wherein the cavity comprises a gas; iii. a liquid input; and iv. a gas port; v. connecting the gas port of the first compressor tank to a gas reservoir via a gas line; vi. connecting the liquid input of the first compressor tank to a first liquid line; b. operating the first compression tank in either a compression stroke or a return stroke, wherein operating the hydraulic compression tank in the compression stroke comprises: i. compressing the gas in the tank cavity of the first compressor tank by pumping a liquid into the expandable bladder cavity of the first compressor tank via the first liquid line such that the expandable bladder of the first compressor tank expands into the tank cavity; ii. displacing the gas out of the tank cavity of the first compressor tank, via the gas port, and collecting said gas in the gas reservoir; iii. further compressing the gas in the gas reservoir; and c. wherein operating the hydraulic compression tank in the return stroke comprises: i. pumping a liquid out of the expandable bladder cavity of the first compressor tank via the first liquid line such that the expandable bladder of the first compressor tank contracts, which in turn increases the volume of the tank cavity of the first compressor tank; ii. filling the tank cavity of the first compressor tank with gas from a low- pressure gas source via the gas port.

[0033] According to one embodiment, the method further comprises: a. providing a second compressor tank comprising: i. an expandable bladder defining a bladder cavity, wherein the expandable bladder contains a liquid in the expandable bladder cavity; ii. a tank cavity outside of the expandable bladder, wherein the cavity comprises a gas; iii. a liquid input; and iv. a gas port; b. connecting the gas port of the second compressor tank to a gas reservoir via a gas line, wherein the first and second compressor tanks may be connected to the same gas reservoir or different gas reservoirs; c. connecting the liquid input of the second compressor tank to a second liquid line; wherein the first liquid line and the second liquid line are in fluid communication; d. operating the first compressor tank in a compression stroke and the second compressor tank in a return stroke comprising: e. compressing the gas in the tank cavity of the first compressor tank by pumping a liquid from the expandable bladder cavity of the second compressor tank and into the expandable bladder cavity of the first compressor tank such that the expandable bladder of the second compressor tank contracts and the expandable bladder of the first compressor tank expands; f. displacing the gas out of the tank cavity of the first compressor tank, via the gas port of the first hydraulic chamber, and collecting said gas in the gas reservoir; g. filling the tank cavity of the second compressor tank with gas from a low- pressure gas source via the gas port of the second hydraulic chamber; and h. further compressing the gas in the gas reservoir.

[0034] In another embodiment, the method further comprises: a) determining that the compression stroke of the first compressor tank has been completed and / or the return stroke of the second compressor tank has been completed; and b) switching the operation of the first and second compressor tanks such that the second compressor tank is operated in a compression stroke and the first compressor tank in a return stroke comprising: compressing the gas in the tank cavity of the second compressor tank by pumping a liquid from the expandable bladder cavity of the first compressor tank and into the expandable bladder cavity of the second compressor tank such that the expandable bladder of the first compressor tank contracts and the expandable bladder of the second compressor tank expands; c) displacing the gas out of the tank cavity of the second compressor tank, via the gas port of the second hydraulic chamber, and collecting said gas in the gas reservoir; d) filling the tank cavity of the first compressor tank with gas from a low pressure gas source via the gas port of the second hydraulic chamber; and e) further compressing the gas in the gas reservoir.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Examples of preferred embodiments of the invention will now be described by referring to the accompanying drawings: Figure 1. is a schematic representation of the basic arrangement of a hydraulic valveless gas compression system according to one embodiment of the present with two compression tanks.

[0037] Figure 2 is a schematic representation of the system showing operation of compression stroke in the first tank and corresponding flow of liquid.

[0038] Figure 3 is a schematic representation of the system showing operation of reversing the flow from tank one and corresponding flow of liquid.

[0039] Figure 4 is a schematic representation of the system showing alternative means of taking pressure and flow measurements.

[0040] Figures 5 is a schematic representation of the system showing alternative means of taking pressure and flow measurements.

[0041] Figure 6 is a schematic representation of the system showing aspects of the control system.

[0042] Figure 7 is a schematic representation of the system showing an embodiment with multiple pumps used in parallel.

[0043] Figure 8 is a schematic representation showing utilisation of more than two compression tanks.

[0044] Figure 9 is a schematic representation showing utilisation of more than two compression tanks with air valves located at the manifold intake of set of tanks.

[0045] Figure 10 is a schematic representation of the system showing an embodiment with multiple pumps used in parallel and multi tanks in parallel with pressure sensor at the intake and exit of the pump.

[0046] Figure 11 is a schematic representation of the system showing an embodiment with multiple pumps used in parallel and multi tanks in parallel with pressure sensor at the manifold of a set of tanks.

[0047] REFERENCES IN THE DRAWINGS

[0048] The following is a list of references made in the figures.

[0049] 1a: First gas line from a first low-pressure gas source to the first compression tank

[0050] 1b: First gas line from a second low-pressure gas source to the second compression tank

[0051] 10: Liquid pump

[0052] 10a: Additional pump

[0053] 10n: Nth additional pump

[0054] 11 : Pump port 1

[0055] 12: Pump port 2

[0056] 2: Hydraulic compression tank 21 : First hydraulic compression tank

[0057] 210: Tank cavity of the first hydraulic compression tank

[0058] 22: Second hydraulic compression tank

[0059] 22n: Nth additional hydraulic compression tank

[0060] 220: Tank cavity in the second hydraulic compression tank

[0061] 3: Expandable bladder inside hydraulic compression tank

[0062] 30: Bladder cavity

[0063] 31 : Expandable bladder in the first hydraulic compression tank

[0064] 310: Liquid inside first bladder

[0065] 32: Expandable bladder in the second hydraulic compression tank

[0066] 320: Liquid inside second bladder

[0067] 4: Gas reservoir

[0068] 51 : First check valve of first compression tank

[0069] 52: Second check valve of first compression tank

[0070] 53: First check valve of second compression tank

[0071] 53n: First check valve of Nth additional compression tank

[0072] 54: Second check valve of second compression tank

[0073] 54n: Second check valve of Nth compression tank

[0074] 60: Pressure sensor for gas reservoir tank

[0075] 61 : Pressure sensor for the first compression tank at the pump port

[0076] 610: Pressure sensor for the first compression at the inlet of first tank

[0077] 62: Pressure sensor for the second compression tank at the pump port

[0078] 620: Pressure sensor for the second compression at inlet of the second tank

[0079] 61 n: Pressure sensor for the Nth additional compression tank at the pump port

[0080] 62n: Pressure sensor for the Nth additional compression tank at the pump port

[0081] 63: Flowmeter associated with first compression tank

[0082] 64: Flowmeter associated with second compression tank

[0083] 70: Controller

[0084] 71 : Wireless communication

[0085] 72: Computing device

[0086] 81 : Liquid pipeline having low pressure liquid

[0087] 82: Liquid pipeline having high pressure liquid

[0088] 83a: Second gas line from the first hydraulic compression chamber to the gas reservoir

[0089] 83b: Second gas line from the second hydraulic compression chamber to the gas reservoir.

[0090] DETAILED DESCRIPTION The present invention refers to a hydraulic valveless gas compression system.

[0091] The system comprises of the following main elements: one or more liquid pumps, two or more compression tanks each having an internal expandable bladder, one or more gas reservoir tanks that can be pressurised, sets of check valves each set corresponding to a compression tank, dedicated flow channels, measuring instruments, and a control system.

[0092] Details of the principles and the structure of the invention are hereinafter explained with reference to examples of alternative embodiments. These embodiments serve to highlight the principles of the invention and are not limiting in any way by means of structural arrangements.

[0093] Figure 1. is a schematic representation of the basic arrangement of a hydraulic gas compression system according to one embodiment of the present with two hydraulic compression tanks. The system comprises a liquid pump 10, a first compression tank 21 and a second compression tank 22, and a gas reservoir 4. Inside each of the compression tanks, there is an expandable bladder 31 , 32. As the pump 10 moves liquid into the first hydraulic compression tank 31, this liquid is fed into the expandable bladder in the first hydraulic compression tank 31 and the liquid in the first bladder 310 causes the expandable bladder to expand thus displacing the gas in the gas space of the first compression tank 210. Gas flows through dedicated gas lines 83a, 83b into the gas reservoir 4 where it is compressed. Each hydraulic compression tank 21 , 22 is associated with a set of check valves 51 , 52, 53, 54. Various instruments are used to measure pressure or flow. Figure 1 shows a sensing arrangement for a preferred embodiment wherein a pressure sensor 60 for the gas reservoir tank 4, and pressure sensors 61 , 62 to measure the pressure inside each of the expandable bladders of the first and second compression tanks 21 , 22. The gas reservoir 4 may comprise a bank of several individual tanks. Hydraulic compression tanks 21 , 22 comprise interdependent volumes wherein the total tank volume is equal to the gas volume 210 plus the volume of the expandable bladder 310 filled with liquid. The use of expandable bladder helps to enable utilisation of full stroke compression without risk of liquid carry-over into said gas reservoir. In the opposite case, when no bladder is used, the liquid and the gas in the hydraulic compression tank are in contact. As such, there is a high risk of liquid carry-over into the gas reservoir tank 4 when the remaining gas volume 210 in the compression tank becomes small and tends to zero.

[0094] The gas can be any gas including but not limited to air, nitrogen, hydrogen, oxygen or even refrigeration gases. The use of a bladder also enables the efficient compression of gases that are soluble in liquids without worrying about microbubbles of gas in the liquid. The use of a bladder is also important for the compression of gases that are highly reactive or corrosive such as oxygen for example.

[0095] Figure 2 is a schematic representation of the system showing operation of compression stroke in the first tank and corresponding flow of liquid. The thickened line shows the flow of liquid during the compression stroke of the first compression tank and consequently the return stroke of the second compression tank. Liquid flows in a closed circuit. During the part of the cycle when the first compression tank 21 is in a stage of a compression stroke, the pump 10 moves the liquid from the pump exit port 12 through the high-pressure liquid pipeline 82 into the expandable bladder 31 of the first compression tank to add to the liquid inside first bladder 310 and expand the expandable bladder. The gas in the first compression tank 210 is displaced and forced to move into the gas reservoir tank 4 via the dedicated gas passage 83. In this case the first check valve 51 is open to allow gas passage into the gas reservoir tank, but the second check valve 52 is held closed so no gas can escape. At the liquid side, the pump is set to direct the flow from tank 22 to tank 21. Liquid flows in a closed loop and the liquid that is supplied to the pump port 11 and exit through port 12 go through the expandable bladder of the second compression tank 32 whereby liquid inside the expandable bladder of the second tank 320, the volume of the liquid of the expandable bladder 320 reduces, the expandable bladder contracts and the gas pressure inside the second compression tank reduces, thus allowing gas from the low-pressure supply 1 b to flow into the second compression chamber 22 and the volume of the tank cavity 220 increases. The second check valve of second compression tank 54 opens to let gas in, while the first check valve of second compression tank 53 remains closed. The second compression tank 22 is in a return stroke operation while the first compression tank 21 is in compression stroke operation.

[0096] The flow of gas to the gas reservoir tank 4 via the hydraulic compression tanks 21 , 22 is achieved via gas lines, wherein each gas line comprises a first gas line 83a, 83b and a second gas line 1a, 1 b. The first gas line 83a, 83b extends between the tank cavities 210, 220 of the hydraulic compression tanks 21 , 22 and the gas reservoir. The second gas line 1a, 1 b, extends between the low-pressure gas sources and the tank cavities 210, 220 of the hydraulic compression tanks 21 , 22. The gas lines comprise all pairs of check valves 51 , 52, 53, 54 as well as the ports for pressure sensors 60.

[0097] Figure 3 is a schematic representation of the system showing the reverse cycle from tank 21 to tank 22, the flow direction of the pump 10 changes where pump port 12 is the inlet and port 11 is the exit. Figures 4 is a schematic representation of the system showing alternative means of taking measurements. Instead of pressure sensors that measure the pressure of the liquid inside each of the expandable bladders 31 , 32, flow meters are used to measure liquid flow in and out of each of the expandable bladders associated with the first and second compression tanks. The flowmeter associated with first compression tank 63 is installed at the pump port 12, and the flowmeter associated with second compression tank 64 is installed at the pump port 12.

[0098] It is possible that the operation of the system may be controlled only measurement of gas pressure in the storage tank and measurement of flow from the liquid pump. In this embodiment, one pressure sensor 60 is used to measure gas pressure in the storage tank, and two flowmeters 63 or 64 used to measure from at the pump port. Since liquid is in a closed system, one flowmeter is sufficient to indicate quantity of liquid moved into either the first or the second compression tank.

[0099] The system can be controlled by using the sensors in any of the embodiments described in figures 3 to 4. In addition, the electric current to the liquid pump can also be used to indicate when the pump is approaching maximum pressure or reaching stalling conditions.

[0100] Figures 5 is a schematic representation of the system showing alternative means of taking measurements. Combining a pressure sensor that measure the pressure of the liquid at the pump port 12 and flow meter at pump port 11. A pressure sensor at the gas tank 60 to monitor the storage pressure. The system can be fully controlled using this combination of sensors.

[0101] Figure 6 is a schematic representation of the system showing the microcontroller and system controls. The sensors 60, 61 , 62 are all connected to the input / output of a control system 70. The control system comprises processor, memory, and an electronic controller. The electronic controller is connected via control lines to the pump to control its operation. The control system also comprises wireless communication to enable it to communicate with a remote computer. A remote computer may be a handheld device, a smart phone, or a remote server.

[0102] Figure 7 is a schematic representation of the system showing an embodiment with multiple pumps used in parallel. Additional pumps 10a to 10n may be utilised with corresponding pressure sensors 61a to 62. Multiple pumps can improve efficiency and compression speed. For example, at lower pressure a one pump may operate that can deliver high liquid flow, albeit up to a lower pressure. Above a threshold pressure, a second pump may operate that can deliver liquid flow at a lower flowrate but achieve higher compression pressure. In this manner, speed is improved, energy efficiency is improved, and pump durability may also be improved. In one embodiment, the multiple pumps are two pumps operating as a pair. Said pair of two pumps is connected in parallel and they are operating as a single unit, wherein of said pair of pumps, the first pump of said pair of pumps has a higher flow capacity and can operate to a lower pressure and the second pump of said pair of pumps has a lower flow capacity and can operate at a higher pressure.

[0103] Efficiency improvements may also be achieved by utilising more than two compression tanks.

[0104] Figure 8 is a schematic representation showing utilisation of more than two compression tanks. Figure 8 shows an additional compression tank 22n and the corresponding check valves 53n, 54n installed at each compression tank 22 to 22n. The system configuration of a compression tank with the corresponding check valves and pressure sensor is such that the system is modular and utilisation of more than two compression tanks is easy and can even be done after the initial installation.

[0105] In some embodiments, efficiency improvements may be gained by utilising a variable speed pump 10 wherein the speed of said pump is adjusted so that towards the end of the compression stroke the pump speed and hence the liquid flowrate is reduced to allow a smooth change-over from one compression tank to another compression tank.

[0106] Figure 9 is a schematic representation showing utilisation of more than two compression tanks. The corresponding check valves 53n, 54n installed at the manifold of the storage tank to serve a group of compression tank. The system configuration of a compression tank with the corresponding check valves and pressure sensor is such that the system has less components and less check valves for multiple compression tank.

[0107] Figure 10 is a schematic representation showing utilisation of more than two pumps 10, 10a, 10n and more than two compression tanks 21 , 22, 22n. Depending on system demands for pressure and quantity of compressed gas, system configuration can be determined to achieve optimum performance regarding speed and energy efficiency.

[0108] Figure 11 is a schematic representation showing utilisation of more than two pumps 10, 10a, 10n and more than two compression tanks 21 , 22, 22n. The corresponding check valves 53n, 54n installed at the manifold of the storage tank to serve a group of compression tank. The pressure sensor at the liquid line is installed at the manifold entry of group of compression tank. This embodiment ensures minimum number of part per system.

Claims

Claims1 . A hydraulic compressor system for compressing gas, comprising: at least one pump for pumping liquid; a. a gas reservoir for storing compressed gas; b. at least two compression tanks, each of said compression tanks comprises:• an expandable bladder defining a bladder cavity, wherein the expandable bladder contains a liquid in the expandable bladder cavity and the expandable bladder is configured to expand when liquid is input into the expandable bladder cavity;• and a tank cavity outside of the expandable bladder, wherein the cavity comprises a compressible gas; wherein the expandable bladder and the tank cavity outside the expandable bladder form interdependent volumes of liquid and gas; c. a liquid line configured to fluidly couple the expandable bladder cavity with at least one of the one or more pumps such that the liquid is pumped into or out of the expandable bladder via the liquid line; d. a gas line configured to fluidly couple the gas reservoir with the tank cavity such that the gas flows into or out of the tank cavity via the gas line; wherein, during operation of the system, liquid is pumped by the one or more pumps to the expandable bladder in the first compression tank and gas is expelled from the tank cavity of the first compression tank and directed to gas reservoir where it is compressed, characterised in that e. Switching from compressing the first compression tank (21) to compressing the second compression tank (22); is achieved by changing the direction of flow; wherein the pump (10) direction of rotation is reversed to reverse the flow of liquid; wherein said pump (10) comprises a variable speed pump wherein the speed of said pump (10) is adjusted so that towards the end of the compression stroke the pump speed is reduced and hence the liquid flowrate is reduced to allow a smooth change-over from one compression tank to another compression tank as the automatically controlled switch over is executed or the speed of said pump is adjusted so that the maximum efficiency of the compression cycle is maintained thought continuous speed adjustment of the pump.

2. The hydraulic compressor system according to claim 1 , wherein the first compression tank (21) is configured to operate in a compression stroke and in a return stroke; wherein, during the compression stroke, liquid is configured to be pumped into the expandable bladder (31), via the liquid line (82), such that the expandable bladder (31) expands into the tank cavity (210) and causes compression of the gas; and wherein during return stroke, liquid is configured to flow out from the expandable bladder (31) via the liquid line (82) such that the expandable bladder (31) contracts and the tank cavity expands (210).

3. The hydraulic compressor system according to any one of claims 1 or 2, wherein the liquid line (82) of the first compression tank (21) is fluidly coupled to the liquid line (81) of the second compression tank (22) such that: when the first compression tank (21) is configured to operate in the return stroke and the second compression tank (22) is configured to operate in the compression stroke, liquid is configured to flow out from the expandable bladder (31) of the first compression tank (21) and to be fed, by the pump (10), into the expandable bladder (32) of the second tank; and when the second compression tank (22) is configured to operate in the return stroke and the first compression tank (21) is configured to operate in the compression stroke, liquid is configured to flow out from the expandable bladder (32) of the second compression tank (22) and fed, by the pump (10), into the expandable bladder (31) of the first tank.

4. The hydraulic compressor system according to any preceding claim, wherein the system further comprises: o an inlet line (1a, 1 b) extending between a low pressure gas source and the tank cavity; o a check valve (52, 54) that controls the flow of gas between the tank cavity and the low pressure gas source; and o a check valve (51 , 53) that controls the flow of gas between the tank cavity and the gas reservoir (4) in the gas line.

5. The hydraulic compressor system according to any one of claims 1-4, wherein the check valve is placed in the storage tank to control the flow of gas.

6. The hydraulic compressor system according to any one of claims 1-4, wherein the check valve during expanding stroke compressed air is fed to the inlet to speed up the compression process.

7. The hydraulic compressor system of any one of the preceding claims, wherein each compression tank comprises a pressure sensor (61 , 61 n, 62, 62n), wherein said pressure sensor is arranged to measure the pressure of the liquid at the pump ports (11 , 12).

8. The hydraulic compressor system of any one of the preceding claims, wherein the expandable bladder (31 , 32) is characterized by a spring constant that defines a resistance to expansion.

9. The hydraulic compressor system according to any one of the preceding claims, wherein the system comprises a plurality of liquid lines (81 , 82), wherein each liquid line is configured to couple a hydraulic compression tank with one or more of the one or more pumps (10a, 10n); wherein each liquid line is arranged to connect to each compression tank (21 , 22) to one or more of the one or more pumps (10a, 10n) in a closed circuit.

10. The hydraulic compressor system according to claim 9, wherein the system further comprises a sensor system and wherein the direction of flow is controlled by a control system (70); wherein the control system (70) is configured to switch the direction of the pump (10) based on data received from the sensors.

11. The hydraulic compressor system according to claim 10, wherein the sensor system comprises of a pressure sensor arranged to measure the pressure of the liquid within the expandable bladder of each hydraulic compression chamber (610, 620) and a pressure sensor (60) arranged to measure the pressure within the gas reservoir.

12. The hydraulic compressor system according to claim 10 or claim 11 , wherein said sensor system comprises a flowmeter (63, 64) in fluid communication with the expandable bladder (31 , 32) of each hydraulic compression chamber, and a pressure sensor (60) arranged to measure the pressure within the gas reservoir.

13. The hydraulic compressor system according to any one of claims 10-12, wherein said sensors CONSIST of a flowmeter (63, 64) fluidically connected to one of the pump ports (11 , 12), and one pressure sensor (60) fluidically connected with the reservoir no other sensors are necessary when the gas intake pressure is constant.

14. The hydraulic compressor system according to any one of claims 10-13, wherein the control system is configured to: a. receive data corresponding to the pressure of the liquid inside the expandable bladder before the compression stroke is started; b. receive date corresponding to the pressure of the liquid inside the expandable during the compression stroke is started c. determine whether the compression ratio has reached the maximum value.d. and switch the direction of the flow when the maximum value of the compression ratio has been reached.

15. The hydraulic compressor system according to any one of claims claim 11-14 11-15, wherein the control system is configured to switch the direction of the flow, when the pump (10) reaches the required pressure defined by the pump current.

16. The hydraulic compressor system according to any one of claims 11-15 11-16, wherein automatic switchover of system from a forward compression cycle of the first compression tank (21) to a forward compression cycle of the second tank (22) and reverse stroke of the first compression tank (21) is happening with a predefined time.

17. The hydraulic compressor system according to claim 1 , wherein said system comprises a pair of two pumps (10, 10a), said two pumps (10, 10a) connected in parallel and operating as a single unit, wherein of said pair of pumps (10, 10a), the first pump of said pair of pumps has a higher flow capacity and can operate to a lower pressure and the second pump of said pair of pumps has a lower flow capacity and can operate at a higher pressure.

18. The hydraulic compressor system according to claim 1 , wherein said plurality of compression tanks (22n) comprises three or more tanks wherein each tank is matched with dedicated passages through which incoming liquid may be fed forcing outflow of gas, with pressure sensors to measure liquid pressure or flowmeters to measure liquid flow the controller switches the pump direction when the required flow or pressure is reached.

19. The hydraulic compressor system according to claim 1 , wherein said plurality of pumps (1 On) comprises three or more pumps wherein each pump is in parallel with others pumps, wherein the liquid is forced by the pump to one or more compression tanks, the said pump is controlled by pressure or flow sensor at its outlets.

20. The hydraulitic compressor system according to any preceding claims, wherein controller (70) reverses the flow based on the sensor meeting the required pressure or flow.

21. A method for compressing gas using system according to any of previous claims 1-20, characterised in that the method comprising: a. providing a first compressor tank (21) comprising: i. an expandable bladder (31) defining a bladder cavity, wherein the expandable bladder contains a liquid (310) in the expandable bladder cavity; ii. a tank cavity (210) outside of the expandable bladder, wherein the cavity comprises a gas; iii. a liquid input; andiv. a gas port; v. connecting the gas port of the first compressor tank (21) to a gas reservoir (4) via a gas line (83a); vi. connecting the liquid input of the first compressor tank (21) to a first liquid line (83a); b. operating the first compression tank (21) in either a compression stroke or a return stroke, wherein operating the hydraulic compression tank in the compression stroke comprises: i. compressing the gas in the tank cavity (210) of the first compressor tank (21) by pumping a liquid into the expandable bladder (31) cavity of the first compressor tank (21) via the first liquid line (82) such that the expandable bladder (31) of the first compressor tank (21) expands into the tank cavity (210); ii. displacing the gas out of the tank cavity (210) of the first compressor tank (21), via the gas port, and collecting said gas in the gas reservoir (4); iii. further compressing the gas in the gas reservoir (4); and c. wherein operating the hydraulic compression tank in the return stroke comprises: i. pumping a liquid out of the expandable bladder (31) cavity of the first compressor tank (21) via the first liquid line (82) such that the expandable bladder (31) of the first compressor tank (21) contracts, which in turn increases the volume of the tank cavity of the first compressor tank (21); ii. filling the tank cavity of the first compressor tank (21) with gas from a low pressure gas source via the gas port (52).

22. The method of claim 21 , wherein the method further comprises: a. providing a second compressor tank (22) comprising: i. an expandable bladder (32) defining a bladder cavity, wherein the expandable bladder contains a liquid (320) in the expandable bladder (32) cavity; ii. a tank cavity outside of the expandable bladder (32), wherein the cavity comprises a gas; iii. a liquid input; and iv. a gas port;b. connecting the gas port of the second compressor tank (22) to a gas reservoir (4) via a gas line (83b), wherein the first and second compressor tanks (21 , 22) may be connected to the same gas reservoir (4) or different gas reservoirs. c. connecting the liquid input of the second compressor tank (22) to a second liquid line (81); wherein the first liquid line (82) and the second liquid line (81) are in fluid communication. d. operating the first compressor tank (21) in a compression stroke and the second compressor tank (22) in a return stroke comprising: e. compressing the gas in the tank cavity of the first compressor tank (21) by pumping a liquid from the expandable bladder (32) cavity of the second compressor tank (22) and into the expandable bladder (31) cavity of the first compressor tank (21) such that the expandable bladder (32) of the second compressor tank (22) contracts and the expandable bladder (31) of the first compressor tank (21) expands; f. displacing the gas out of the tank cavity of the first compressor tank (21), via the gas port of the first hydraulic chamber, and collecting said gas in the gas reservoir (4); g. filling the tank cavity of the second compressor tank (22) with gas from a low pressure gas source via the gas port of the second hydraulic chamber; and h. further compressing the gas in the gas reservoir (4).

23. The method of claim 2224, wherein the method further comprises: a. determining that the compression stroke of the first compressor tank (21) has been completed and / or the return stroke of the second compressor tank (22) has been completed; and b. switching the operation of the first (21) and second compressor tanks (22) such that the second compressor tank (22) is operated in a compression stroke and the first compressor tank (21) in a return stroke comprising: compressing the gas in the tank cavity of the second compressor tank (22) by pumping a liquid from the expandable bladder (31) cavity of the first compressor tank and into the expandable bladder cavity (32) of the second compressor tank such that the expandable bladder (31) of the first compressor tank contracts and the expandable bladder (32) of the second compressor tank expands;c. displacing the gas out of the tank cavity (220) of the second compressor tank (22), via the gas port of the second hydraulic chamber, and collecting said gas in the gas reservoir (4); d. filling the tank cavity (210) of the first compressor tank (21) with gas from a low- pressure gas source via the gas port of the second hydraulic chamber; and e. further compressing the gas in the gas reservoir (4).

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