Background of the Invention

Field of the invention

The present invention, at least in its presently preferred embodiments, primarily relates to the compression of hydrogen gas and any other gaseous substance using a high pressure water pump which is highly energy efficient due to near isothermal compression.

Description of the Prior Art

The flow rate of the smallest commercial hydrogen compressor available on the market is significantly greater than the rate of gas production by small electro lysers. For this reason a buffer tank is needed between the electrolyser and compressor to compensate for their mismatch.

The use of compressed air to pump water is well known in the prior art. The known prior art related to a water pump using compressed air includes US Pat. No. 6,942,463 where a combination water pump and air compression system is disclosed for performing two separate functions within one unit by providing compressed air and water.

US Patent No. 4, 478,553 discusses isothermal compression using impeller blades to produce a mixture of compressed water and air.

The use of a water column to increase the air pressure is also known in the prior art in gas turbine and power plant based applications.

US Patent No. 4,797,563 discloses a power plant where a water stream is used to create compressed air for the burners of a turbine without additional compression.

US Patent No. 5,537,813 discloses a method of increasing the operational capacity and efficiency of a combustion turbine system having a compressor, combustor and turbine generator by treatment of the inlet air prior to its introduction into the compressor; this is done by establishing a vertically descending flow of inlet air; introducing treatment water into the flow of inlet air to create a downward velocity greater than that of the inlet air to create drag-induced pressure increase in the inlet air.

Hydraulic air compressors have been in existence since approximately 1890 when they were used throughout North America and Europe to provide compressed air for mining camps. The prior arts also include US Patents Nos. 543410, 543411, 543412, 618243, 892772, 199819, 3643426, 3797234, 4343569, 4391552.

While these prior art disclosures fulfil their respective objectives for compression of air, none of these inventions are suitable for compression of hydrogen gas.

Summary of the Invention

The present invention provides a gas compressor comprising a source of high pressure fluid and a pressure vessel having a gas inlet for the gas to be compressed, a gas outlet for the compressed gas and a fluid inlet for the high pressure fluid. The compressor is arranged to introduce the high pressure fluid into the pressure vessel via the fluid inlet whereby to compress a volume of gas in the pressure vessel.

Embodiments of the present invention provide a safe and leak tight gas compressor due to the use of a water seal making it ideal for compression of explosive gases such as hydrogen. This invention allows a low pressure gas such as hydrogen from an atmospheric water electrolyser to increase the gas pressure significantly in a much more economical way than costly pressurised electrolysers or conventional hydrogen compressors. This new compressor can have a significantly lower number of parts and thus lower capital cost compared to a centrifugal air compressor, a piston-type compressor or a diaphragm-type gas compressor. Furthermore, this invention can eliminate the need for any buffer tank of hydrogen gas as the flow rate of the compressor can be in the range from 10 cc per minute to literally several hundred normal cubic meters per hour as this depends only on the flow rate of the water pump. Moreover, the current invention, at least in preferred embodiments, is capable of producing hydrogen or any other gas up to 700 bar by using multiple stage

compression at near isothermal compression at a higher efficiency.

The present invention, at least in its preferred embodiments, increases the efficiency, reduces the capital cost, lower the maintenance cost and covers a very broad spectrum of operational range from very low flow rate to very high flow rate and a wide range of operating pressure which is not available in the prior art.

The fluid in the pressure vessel may be in direct contact with the gas to be

compressed. For example, water may be pumped into a vertically-oriented pressure vessel in direct contact with the gas by a water pump. The water seal and the rising water column acts as a hydraulic piston. In this case, the compressor may not have a source of nitrogen gas for purging air, because the water may be filled up to the outlet of the pressure vessel to purge any air from the system.

However, in one embodiment, the pressure vessel comprises a barrier member for separating the high pressure fluid from the gas within the pressure vessel. In this way, the fluid does not come in contact with the subjected gas under compression. The barrier member may be in the form of a piston received within the pressure vessel. The pressure vessel may be orientated in use such that fluid is introduced at the bottom of the pressure vessel and gas is introduced at the top of the pressure vessel. In this way, the piston, other barrier member or the volume of fluid in the pressure vessel may expand the volume available to the gas in the pressure vessel under the action of gravity. Thus, the compressor may comprise a mechanical piston installed inside a vertically oriented pressure vessel. The mechanical piston may be driven upward due to the back pressure created by the high pressure fluid source.

In one embodiment, the barrier member is in the form of an inflatable bag connected to the fluid inlet of the pressure vessel. An inflatable water bag has never before been used inside a pressure vessel to prevent direct contact between water and the subjected gas to be compressed. The inflatable water bag may be dimensioned to occupy the internal space of the pressure vessel when inflated, in order to pressurise the gas while keeping the switchable air vent on the inlet water pipe open to atmosphere. The internal shape and volume of the pressure vessel may be substantially identical to the external shape and volume of the inflatable water bag. The bag may be made of any flexible or composite materials such as reinforced rubber, fibre reinforced plastic etc. Water may be pumped at high pressure into the inflatable water bag to occupy the internal space of the pressure vessel and subsequently pressurise the gas in the pressure vessel while keeping the switchable air vent on the inlet water pipe open to atmosphere; under this condition water does not come into contact with the gas under compression in the pressure vessel. Typically, the high pressure fluid is a liquid. In preferred embodiments, the high pressure fluid is water. Any non-compressive liquid or hydraulic fluid can be used instead of water. The gas compressor of the invention may use any suitable liquid medium such as water, water-solvent mixture, antifreeze mixture, various solvents with high boiling point, hydraulic oil etc. The pressure vessel may be connected to a mains source of high pressure fluid. Alternatively, the source of high pressure fluid may comprise a pump arranged to pump fluid to the fluid inlet of the pressure vessel. The source of high pressure fluid may comprise a tank and the pump may be arranged to pump fluid from the tank to the fluid inlet of the pressure vessel. The gas compressor may comprise at least one further pressure vessel having a gas inlet and a fluid inlet for the high pressure fluid. The pump may be arranged to pump fluid from the first pressure vessel to the fluid inlet of the further pressure vessel whereby to compress a volume of gas in the further pressure vessel. The pump may be arranged subsequently to pump fluid from the further pressure vessel to the fluid inlet of the first pressure vessel whereby to compress a volume of gas in the first pressure vessel. It is possible for the first and further pressure vessels to be provided with respective pumps, but this is not preferred.

The first pressure vessel and the further pressure vessel may be configured such that pumping of fluid from the first pressure vessel to the further pressure vessel causes a pressure drop in the first pressure vessel, whereby to draw gas into the first pressure vessel via the gas inlet. Pumping of fluid from the further pressure vessel to the first pressure vessel may cause a pressure drop in the further pressure vessel, whereby to draw gas into the further pressure vessel via the gas inlet. In this way, a reciprocating system is provided.

The gas inlet of the first pressure vessel and the gas inlet of the further pressure vessel may be connected to the same source of gas.

The compressor may comprise at least one further pressure vessel having a gas inlet connected to the gas outlet of the first pressure vessel and a fluid inlet for the high pressure fluid. The compressor may be arranged to introduce the high pressure fluid into the further pressure vessel via the fluid inlet whereby to compress further a volume of gas in the further pressure vessel. In this way, the desired pressure of the gas can be achieved in stages.

Efficiently, the fluid inlet of the further pressure vessel may be connected to the same source of high pressure fluid as the fluid inlet of the pressure vessel.

In a preferred application of the invention, the gas inlet of the (or each) pressure vessel is supplied with gas from a water electrolyser. In this application, and others, the gas is hydrogen. The gas compressor may be connected to a source of gas to be compressed or may be directly connected to an electrolyser to compress hydrogen and oxygen gas.

The fluid inlet of the pressure vessel and/or the further pressure vessel may comprise a spray nozzle for spraying the high pressure liquid into the (further) pressure vessel. This is advantageous in that a greater surface area of the liquid may be presented to the gas in the pressure vessel for absorbing impurities in the gas.

In one configuration, the gas compressor may comprise one or more of a bottom water tank, a high pressure water pump, at least one an inflatable water bag installed inside a pressure vessel, a gas inlet valve to the pressure vessel, a high pressure gas outlet purge valve from the pressure vessel, a nitrogen gas purging valve, switchable atmospheric air vents located on top of the bottom water tank, a piping configuration and valve mechanism, monitoring and control devices for pressure, temperature, flow rate and fluid level, non return valves installed after the high pressure gas-purge valve and after the outlet of the water pump, inline gas sensors, a liquid condensing and separation unit, an oxygen removal unit for removing oxygen from hydrogen gas, a gas drying unit and an electronic control system.

The nitrogen gas purging valve may be connected to the pressure vessel or to the hydrogen electrolyte tank of the electrolyser. The operating range of the compressor may be from lOmbar gauge pressure up to 700 bar in multiple stages depending on the output pressure of the water pump and the volume of the pressure vessel.

The outlet gas purge valve may deliver compressed gas or a compressed mixture of gases.

A liquid vapour condensing unit, a liquid separation unit, an oxygen removal unit, a gas drier and a liquid absorption unit may be fitted after the gas outlet purge valve of the pressure vessel.

A gas sensor may detect the purity of gas and send an electrical voltage and/or current signal to the electronic control box. The compressed gas may be vented to the atmosphere if the purity of the gas is not at a desired level or for any maintenance work.

In operation, when the switchable air vent is open, the outlet gas-purge valve and the inlet gas valve of the pressure vessel are closed allowing the water level to fall under differential pressure from the inflatable water bag or from the pressure vessel itself into the bottom water tank.

The multiple valve system may facilitate the emptying of water from the pressure vessel or the inflatable water bag by active pumping of water back into the bottom water tank.

In typical operation, the gas to be compressed is fed into the empty pressure vessel followed by compression by pumping water into the inflatable water bag or directly into the pressure vessel, as described above. The inflatable water bag may be mechanically supported inside the pressure vessel when inflated. The differential pressure on the inflatable water bag or air bag may be controlled within a safe operating pressure. The greater contact area with the gas as provided by the inflatable water bag or water seal ensures faster cooling of the gas at near isothermal condition and thus higher efficiency than conventional mechanical gas compressors. The flow rate of the gas to be compressed may be in the range of 10 cubic centimetres per minute to several hundred normal cubic metres per hour. The compressor may have an operating temperature in the range from minus 60 degrees C to 200 degrees C. The liquid medium and liquid pump is selected as per the optimum operating temperature, flow rate and operating pressure.

The invention also provides a gas compressor directly coupled with an atmospheric electro lyser, wherein the de-oxo-drier removes the traces of oxygen gas present in hydrogen gas followed by gas drying.

The main purpose of the present invention is to produce extremely low cost hydrogen gas compressors; however this invention is also applicable for any other gasses. Embodiments of the present invention use an inflatable water bag and a high pressure water pump to operate at near isothermal conditions to produce a highly efficient gas compressor.

The operating range of the compressor is from 10 mbar gauge pressure up to very high pressure such as 700 bar in multiple stages depending on the output pressure of the water pump and the volume of the pressure vessel. The flow rate of the gas compressor is in the range of 10 cubic centimetres per minute to several hundreds normal cubic metres per hour.

The operating temperature of the gas compressor is in the range from minus 60°C to 200°C.

The gas compressor may have an optional nitrogen gas feed point to the pressure vessel to purge any gaseous substance from the system where hydrogen and other explosive gases are compressed instead of air or any other non-combustible gasses. After the compressed gas is delivered to the supply line, the gas compressor prepares itself for the next compression cycle; it does so in a sequential method such as:

i) Keep open the switchable air vent located at the bottom water tank,

ii) Keep the outlet gas-purge valve closed

iii) Close the inlet gas valve of the pressure vessel in closed position;

The higher gas pressure inside the pressure vessel will deflate the water bags; the gas compressor operates the multiple valves as per the above sequence to empty the water from the pressure vessel or from the inflatable water bag by pumping water back into the bottom water tank.

For the next compression cycle, the gas is fed into the empty pressure vessel followed by pumping of water into the inflatable water bag or directly into the pressure vessel.

Brief description of the Drawings

The invention will be better understood with reference to Figure 1 which is a schematic diagram of various components of this invention; the sample calculation as shown in Table 1 provides an example of the compression ratio but following the same principle different compression ratios will be achieved by changing the physical parameters of this invention; Table 2 describes the sequence of valve control corresponding to Figure 1 ; there will be several ways to perform the operation using the same physical configuration and/or different configurations using the same components. Figure 2 shows an alternative configuration of a gas compressor according to an embodiment of the invention; Table 3 describes the sequence of valve control corresponding to Figure 2.

Description of the preferred embodiment

While the present invention will be described more fully hereinafter with reference to the accompanying drawing in which aspects of the preferred manner of practicing the present invention are shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate art may modify the invention herein described while still achieving the favourable results of this invention;

accordingly the description which follows is to be understood as being a broad teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention.

As best illustrated in Figure 1 hydrogen gas is supplied to a compressor according to an embodiment of the invention from a source of hydrogen gas via an adjoining pipe (1) and a first valve (2) to a gas inlet port (3) of a first pressure vessel (4); the source of this hydrogen as shown in Figure 1 is a hydrogen-electrolyte tank (5) of an electrolyser stack (6). The hydrogen electrolyte tank has a nitrogen gas inlet port (7) and a nitrogen gas purging valve (8).

The first pressure vessel (4) has a gas outlet port (9) and an inflatable water bag (10) securely fitted inside the pressure vessel by a leak free port (11). The gas and water do not come into direct contact within the first pressure vessel (4). A pressure sensor (12), and a temperature sensor (13) are fitted into the first pressure vessel to monitor the inside pressure and temperature of the first pressure vessel.

The inflatable water bag (10) is made of flexible materials such as reinforced rubber, composites, fibre reinforced plastic bags etc. The safe operating pressure of the inflatable water bag is about 10-15 bar and the design pressure is 25bar. The differential pressure between the inside and outside pressure of the fully inflated water bag never exceeds 15 bar because the water bag is supported when fully inflated by the wall of the pressure vessel; the physical volume change from the deflated to the inflated water bag is up to 20 times or even more; therefore the gas can be compressed up to 20 times by the fully inflated water bag resulting in 20 times increase in gas pressure inside the first pressure vessel (4).

The inflatable water bag receives intake water from a bottom water tank (16) which has two level sensors for low level sensor (17) and high level sensor (18); the water tank has an air vent valve (19) fitted on a pipe (20) securely connected to the water tank;

A high pressure water pump (21) has a suction pipe (22) connected to the bottom water tank (16) securely fitted in place using standard pipe fittings; an outlet pipe (23) from the water pump has a second valve (24) and a non-return valve (25); after the non-return valve (25) an outlet pipe (23) is connected to one port of a T-junction (26); the second port of the T-junction (26) facilitates the return flow of water into the water tank (16) while bypassing the water pump (21) via an adjoining pipe (56) and a sixth valve (55); the remaining port of the T-junction (26) pumps water via an adjoining pipe (27) up to another T-junction (28). The second port of the T-junction (28) is connected to the inflatable water bag via the leak free port (11) via a pressure regulator (29), a low pressure pipe (30) and a third valve (31).

The first pressure vessel (4) is securely connected to a leak free port (32) of a second pressure vessel (33) via an adjoining pipe (14) and a fourth valve (14).

The second pressure vessel (33) has a gas outlet port (34); an inflatable water bag (35) is securely fitted inside the pressure vessel via a leak free port (36); the gas and water do not come into direct contact within the second pressure vessel (33); a pressure sensor (37), and a temperature sensor (38) are fitted into the second pressure vessel to monitor the inside pressure and temperature of the second pressure vessel (33).

The gas outlet port is connected to a high pressure gas delivery pipe (39) a seventh valve (40), and a non return valve (41).

A water inlet port (32) of the inflatable water bag (35) of the second pressure vessel (33) is connected to the remaining port of the T-junction (28) via an adjoining pipe (42); a fifth valve(43) is securely fitted on a pipe (42) to control the flow of water into the inflatable water bag (35).

A gas purity sensor (44) is connected on an outlet pipe (39) after the non-return valve (41) and joined to a T-junction (45).

An air vent (46) is connected to one of the ports of the T-junction (45) by an adjoining pipe (49); an air vent valve (47) and a flame arrestor (48) are fitted on to the pipe (49); this air vent is used to vent gases to the atmosphere into a safe place for maintenance purpose and if the gas purity is not suitable. The remaining port of the T-junction (45) is connected by an adjoining pipe (50) to a gas-water separator (51).

A de-oxo unit (52) is connected to produce high purity (99.999%) hydrogen; a drier (53) assembly is connected to produce very dry hydrogen gas i.e. up to -60°C dew point; the de-oxo unit (52) has a palladium catalyst bed which helps the reaction between the traces of oxygen gas present in hydrogen gas with hydrogen itself to form water vapour at around 140°C; the pure moist hydrogen is then dried in a drier (53); the drier contains a molecular sieve bed to produce very dry hydrogen gas. A non return valve (54) is fitted after the de-oxo drier.

Figure 2 shows an alternative configuration of an embodiment of a gas compressor according to the invention, which combines four functionalities of gas compression, gas drying, gas cooling and gas cleaning at low cost and greater efficiency.

As shown in Figure 2, a liquid pump 108 runs continuously by circulating liquid between two interconnected vessels 101 and 102 by forward and backward motion of the liquid from the first vessel 101 to the second vessel 102, and then from the second vessel 102 back to the first vessel 101. The reciprocating motion of the liquid is controlled by an arrangement of several valves, as will be described below.

At the start of the process the first vessel 101 is full of liquid and the second vessel 102 is full of gas. The liquid from the first vessel 101 is supplied by the pump 108 into the second vessel 102 to compress gas in the second vessel 102. At this stage a first valve 104 between the input side of the pump 108 and the first vessel 101 is open, while a second valve 105 between the output side of the pump 108 and the first vessel 101 is closed. Similarly, a third valve 106 between the output side of the pump 108 and the second vessel 102 is open, while a fourth valve 107 between the input side of the pump 108 and the second vessel 102 is closed. A fifth valve 111 between the first vessel 101 and a low pressure electro lyser stack 103 is open, while a sixth valve 112 between the second vessel 102 and the low pressure electro lyser stack 103 is closed. A seventh valve 113 between the first vessel 101 and a high pressure gas delivery line 116 is closed. An eighth valve 114 between the second vessel 102 and the high pressure gas delivery line 116 is also closed. The gas in the second vessel 102 is compressed up to 700 bar or higher from ambient pressure in a single stage by gradual filling of liquid by the high pressure liquid pump 108. These pumps are commonly used in high pressure cleaning applications, the offshore drilling industry and water-jet cutting tools, and can produce even more than 2000 bar discharge pressure; thus this arrangement provides the required compression ratio in a single stage without any upper limit as this depends only on the capacity of the high pressure hydraulic pump. The compressed gas is then discharged by opening the eighth valve 114 into the high pressure gas delivery line 116 while keeping the third valve 106 and the sixth valve 112 closed. An output valve 109 is opened to deliver high pressure gas or fill up a buffer tank for storage. The gas inlet of the first vessel 101 is controlled by the fifth valve 111 which is connected to the electro lyser cell 103 producing hydrogen and oxygen gas or any other sources of gas. The electrolyser cell 103 may be as described in GB 2469265. During the compression process in the second vessel 102 a vacuum is created in the first vessel 101 due to its gradual drop in liquid- level. The first vessel 101 therefore fills with gas from the electrolyser 103. This vacuum helps to draw gas bubbles out from the electrolyser cell 103 more effectively. Effective and faster removal of gas bubbles from the electrolyser cells improves the ionic conductivity of the cell thus improving cell efficiency significantly. This overcomes a major problem of present atmospheric electrolysers in which gas sticks to the electrode surface due to the surface tension acting between gas bubbles and the electrode surface.

After discharging high pressure gas from the second vessel 102, the liquid is then pumped backward from the second vessel 102 to the first vessel 101. At this stage the first valve 104 between the input side of the pump 108 and the first vessel 101 is closed, while the second valve 105 between the output side of the pump 108 and the first vessel 101 is open. Similarly, the third valve 106 between the output side of the pump 108 and the second vessel 102 is closed, while the fourth valve 107 between the input side of the pump 108 and the second vessel 102 is open. The fifth valve 111 between the first vessel 101 and a low pressure electrolyser stack 103 is closed, while the sixth valve 112 between the second vessel 102 and the low pressure electrolyser stack 103 is open. The seventh valve 113 between the first vessel 101 and the high pressure gas delivery line 116 is closed. The eighth valve 114 between the second vessel 102 and the high pressure gas delivery line 116 is also closed. High pressure gas is created in the first vessel 101 while the second vessel 102 draws in new gas from the electro lyser 103 due to the vacuum created. The compressed gas is then discharged from the first vessel 101 by opening the seventh valve 113 into the high pressure gas delivery line 116 while keeping the second valve 105 and the fifth valve 111 closed. The output valve 109 is opened to deliver high pressure gas or fill up a buffer tank for storage.

The above process is repeated to continually charge and discharge each of the vessels 101, 102. Table 3 shows the position of the valves during the gas compression and gas discharge in both vessels 101, 102.

The embodiment of Figure 2 provides gas drying functionality. During compression inside the first vessel 101 and the second vessel 102 and moisture and other impurities are condensed and drop out naturally to produce high pressure dry gas, thus eliminating the need for a gas drier before the compressor. Conventional piston-based compressors need a gas drier before the compressor.

The embodiment of Figure 2 provides gas cooling functionality. The high pressure liquid is expanded inside the first vessel 101 and the second vessel 102 at low pressure first which produces a cooling effect that controls the temperature near isothermally during compression. Some heat will be dissipated from the surface of the pressure vessel. This cooling first during compression eliminates the need for a conventional cooling circuit, thus saving in cost and making the compressor more energy efficient. The embodiment of Figure 2 provides gas cleaning functionality. The liquid can be any fluid such as water, various chemicals mixed in water, caustic solutions, sodium hydroxide, potassium hydroxide, ferric sulphate solution, acidic water, etc. The selection of liquid depends on the impurities present in the inlet gas which is cleaned by the liquid during compression. The liquid is sprayed by nozzles 110, 115 inside the pressure vessels 101, 102 to scrub various impurities by physical absorption or by chemical reaction. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH) solution is used to remove C0 ₂ from biogas during compression. Hydrogen sulphide (H ₂ S) is removed by scrubbing in ferric sulphate solution or by washing of the raw gas in water. Removal of tar, oil, hydrocarbon, particulate and other impurities is achieved by various scrubbing techniques with relevant liquid solution.

In summary, the present invention primarily relates to the compression of hydrogen gas and any other gaseous substance using high pressure water pump. The present invention provides a safe and leak proof gas compressor due to the use of water seal making it ideal for compression of explosive gases such as hydrogen. This invention allows a low pressure gas such as from an atmospheric water electrolyser to increase the gas pressure significantly in a much more economical way than costly pressurised electro lysers or conventional hydrogen compressors. The flow rate of the smallest commercial hydrogen compressor available on the market is significantly greater than the rate of gas production by small electrolysers; for this reason a buffer tank is needed between the electrolyser and compressor to compensate for their mismatch; however this invention eliminates the need for any buffer tank of hydrogen gas as the flow rate of this compressor is in the range from 10 cc per minutes to literally several hundred normal cubic metres per hour as this is depends on the flow rate of the water pump. This new compressor has a significantly less number of parts thus lower capital cost compared to a centrifugal air compressor, piston type or a diaphragm type gas compressors. This invention is applicable to other gasses such as air, oxygen, nitrogen, carbon dioxide, natural gas etc. This invention produces the highly energy efficient gas compressor due to near isothermal compression.

The invention has been outlined broadly to cover the main features of the invention by using an inflatable water bag or air bag or any other inflatable device along with a water pump and other components as shown in Figure 1 and Table 1 and the corresponding valve sequence as shown in Table 2; it is understood that the invention is not limited to the configuration of Figure 1 or Figure 2; the invention is capable of being embodied in several different configurations by re-arranging the components of Figure 1 and/or Figure 2 in different ways; it is also understood that the terminology and the phrases used to describe the invention can be rearranged to provide a broader scope of this invention.

Embodiments of the present invention provide a new hydrogen compressor at an extremely low cost; this compressor is not sensitive to engineering tolerances in its manufacturing; this invention is also applicable for any other gasses too. The gas compressor comprises a source of high pressure fluid and a pressure vessel having a gas inlet for the gas to be compressed, a gas outlet for the compressed gas and a fluid inlet for the high pressure fluid. The compressor is arranged to introduce the high pressure fluid into the pressure vessel via the fluid inlet whereby to compress a volume of gas in the pressure vessel.