Background of the Invention

Field of the invention

The present invention, at least in its presently preferred embodiments, primarily relates to the cleaning/upgrading of low pressure raw biogas or a mixture of gases into pure methane gas as pressurised gas without using any conventional gas compressor. Description of the Prior Art

The flow rate of the smallest commercially viable biogas upgrade system available on the market is significantly greater than the output of typical small to medium scale biogas projects. For this reason small to medium scale biogas projects are currently not viable even though the potential for small to medium scale biogas projects are significantly greater than large scale biogas projects. Therefore a suitable small to medium scale biogas upgrade technology will open up a new market opportunity worldwide.

There are several biogas upgrade technologies available in the market: water scrubbing technology, membrane based gas upgrade technology, pressure swing absorption technology, and cryogenic technology, each method having their pros and cons. The present invention relates to water scrubbing based technology but in a different manner. The water scrubbing based technology is well known in the prior art, which uses a conventional gas compressor to increase the gas pressure first. The pressurised gas is then injected at the bottom of a tall tower where water is sprayed from the top of the tower. The rising raw biogas is mixed with the falling water under 4-6 bar pressure when the Carbon Dioxide (C02) and Hydrogen Sulphide (H2S) are absorbed into the water under pressure. The cleaned methane (CH4) is then collected from the top of the tower. The water is then pumped into a flash tank at ambient pressure. Air is injected into the flash tank to react with hydrogen sulphide (H2S) to form elemental sulphur and water. C02 is then released from the top of the flash tank at atmospheric pressure. The main problem in the conventional water scrubbing method is that i) raw biogas which contains corrosive H2S and moisture etc is compressed first which severely reduces the lifetime of the conventional gas compressors; ii) this requires more maintenance work; iii) The capital cost of the conventional gas compressor is very high; iv) they are highly energy intensive; v) They must be intrinsically safe due to the risk of explosion; vi) The noise level of this gas compressor is very high; vii) the quality of the cleaned biogas is only 97% or less; viii) the height of the water scrubbing tower is very large due to low pressure scrubbing and demands greater flow rate of gas to be commercially viable; ix) it uses air to react with the hydrogen sulphide (H2S) in the flash tank thus diluting C02 with nitrogen, when pure C02 can have a high market value if not diluted with nitrogen.

Summary of the Invention

Viewed from a first aspect, the invention provides a gas compressor and upgrade system comprising a source of high pressure fluid and a pressure vessel having a gas inlet for a gas mixture 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 and to absorb soluble gases into the high pressure fluid in the pressure vessel or chemically react the high pressure fluid in the pressure vessel with impurities contained in the gas mixture, whereby to separate constituent gases from the gas mixture. The system further comprises a flash tank in fluid communication with the pressure vessel for releasing the absorbed gases at ambient pressure from the high pressure fluid.

The system may be arranged to neutralise hydrogen sulphide by mixing the hydrogen sulphide with oxygen inside the flash tank. The mixing of the hydrogen sulphide with oxygen may be aided by floating balls inside the flash tank. A gas cylinder or an oxygen producing plant may be arranged to provide oxygen gas into the flash tank. The system may further comprises a double walled coil with internal perforation for injecting oxygen to combust traces of hydrogen sulphide from the flash tank, whereby to eliminate the smell of hydrogen sulphide. The double walled coil may comprise an electrical coil heater to facilitate complete combustion of hydrogen sulphide even in cold temperature. 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. The pressure vessel may be orientated in use such that fluid is introduced at the top of the pressure vessel and gas is introduced at the bottom of the pressure vessel.

Typically, the high pressure fluid is a liquid, for example water.

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 tank may be open to atmospheric pressure. The tank of the source of high pressure fluid may be the flash tank. The system 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.

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, and pumping of fluid from the further pressure vessel to the first pressure vessel causes a pressure drop in the further pressure vessel, whereby to draw gas into the further pressure vessel via the gas inlet.

Viewed from a further aspect therefore, the invention provides a gas compressor system comprising: a pressure vessel having a gas inlet for a gas to be compressed and a fluid inlet for a high pressure liquid; at least one further pressure vessel having a gas inlet and a fluid inlet for the high pressure liquid; a liquid tank and a pump system arranged to pump liquid from the liquid tank into the pressure vessel via the fluid inlet whereby to compress a volume of gas in the pressure vessel and subsequently to pump liquid from the liquid tank into the further pressure vessel via the fluid inlet whereby to compress a volume of gas in the further pressure vessel, wherein the tank is open to atmospheric pressure. Such an arrangement has the advantage that the tank can act as a heat exchanger for the high pressure liquid and the use of a tank in the fluid pathway between the pressure vessels reduces the requirement for accurate valve timings in operation.

The system may be configured to drain liquid from the pressure vessel into the liquid tank after compression of the gas in the pressure vessel and subsequently to drain liquid from the further pressure vessel into the liquid tank after compression of the gas in the further pressure vessel. The liquid may be drained from the pressure vessel and the further pressure vessel under the action of gravity. The liquid may be drained from the pressure vessel and the further pressure vessel by the pumping system. The system may be configured to drain liquid from the pressure vessel while liquid is pumped into the further pressure vessel and to drain liquid from the further pressure vessel while liquid is pumped into the pressure vessel. The first pressure vessel and the further pressure vessel may be configured such that draining of fluid from the first pressure vessel causes a pressure drop in the first pressure vessel, whereby to draw gas into the first pressure vessel via the gas inlet, and draining of fluid from the further pressure vessel causes a pressure drop in the further pressure vessel, whereby to draw gas into the further pressure vessel via the gas inlet.

Typically, the compressor system comprises a controller, such as a microcontroller for controlling the operation of the system as described herein.

The pumping system may comprise a single pump and a valve system. The pumping system may comprise a respective pump for the pressure vessel and the further pressure vessel. 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 system 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. 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.

The gas inlet of the (further) pressure vessel may be supplied with gas from a low pressure gas source such as a biogas plant, landfill site, gas well or electrolyser. The gas may be biogas.

Lightweight hollow, movable, floating balls, may be provided inside the (further) pressure vessel to facilitate gas mixing, physical absorption and chemical reaction with the high pressure fluid. The flash tank may comprise one or more of floating balls, an oxygen mixing system, a gas barrier and a gas screen-mesh.

The fluid inlet may comprise a spray nozzle arranged to spray the high pressure liquid into the pressure vessel. The (or each) pressure vessel may comprise an upper fluid port and a lower fluid port. The compressor system may be configured to operate in a first stage of operation in which the upper fluid port is the fluid inlet, the lower fluid port is closed and the high pressure liquid is sprayed into (or otherwise enters) the pressure vessel through the upper fluid port (to absorb the soluble gases from the gas mixture and compress insoluble gases in the pressure vessel by means of a rising liquid column). The compressor system may be configured to operate in a second stage of operation in which the lower fluid port is the fluid inlet, and the compressed gas is purged from the pressure vessel, by high pressure liquid entering the pressure vessel through the lower fluid port to maintain the compressed gas under pressure (to prevent dissolution of the soluble gases). In the second stage of operation the upper fluid port may be the gas outlet. The compressor system may be configured to operate in a third stage of operation in which the pressurised high pressure liquid

(containing dissolved gases) is drained from the pressure vessel by opening the lower fluid port into the flash tank under gravity, while feeding more gas mixture into the pressure vessel through the upper fluid port for the next cycle. The soluble gases may be de-absorbed from the liquid at atmospheric pressure and collected via a gas outlet of the flash tank. Fresh liquid may be separated from any dissolved gas, for example by means of gas-water separating membranes. The compressor system may be configured to repeat the first, second and third stages of operation in a cycle. The (or each) pressure vessel may comprise a liquid level sensor in the form of a float comprising at least one magnetic component, whereby the position of the float within the pressure vessel can be detected from the exterior of the pressure vessel by a magnetically sensitive device. Viewed from a further aspect therefore, the invention provides a gas compressor system comprising a pressure vessel having a gas inlet for a gas mixture to be compressed, a gas outlet for the compressed gas and a fluid inlet for a high pressure fluid, wherein the (or each) pressure vessel comprises a liquid level sensor in the form of a float comprising at least one magnetic component, whereby the position of the float within the pressure vessel can be detected from the exterior of the pressure vessel by a magnetically sensitive device.

The pressure vessel may be substantially cylindrical. The outer surface of the float may be complementary to the inner surface of the pressure vessel.

The present invention, at least in its preferred embodiments, solves the above problems as this has already been demonstrated by a working prototype system. The present invention provides a gas compressor comprising a source of high pressure fluid and a pressure vessel having a gas inlet for the raw biogas 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. Water is used as an example as a working fluid to absorb the C02 and H2S from the raw biogas while compressing the raw biogas inside the pressure vessel. This invention eliminates the need for a separate conventional gas compressor and it combines the water scrubbing method as an integral part of the gas compression process. Hollow lightweight balls are filled inside the pressure vessels to facilitate rigorous gas mixing with water due to added surface contact area between the gas and water. A small amount of oxygen gas is supplied from a source into the flash tank to react with H2S to produce elemental sulphur and water. This maintains the high purity of C02 which is collected at the top of the flash tank. A double-walled coil is used to inject more oxygen to completely neutralise any trace H2S from the C02 gas stream by combustion of H2S in the presence of iron oxide, or alumina catalyst which is facilitated by an electric coil heater if needed.

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 methane. This invention allows a low pressure gas such as methane from any source, e.g. anaerobic digestion biogas plants, landfill sites, crude gas wells to increase the gas pressure significantly in a much more economical way than costly conventional compressors. This new compressor-gas upgrade system has a significantly lower number of parts and thus lower capital cost compared to a conventional system. Furthermore, this invention is highly scalable as the flow rate of the compressor can be in the range from 10 cc per minute to literally several thousands normal cubic meters per hour as this depends on the flow rate of the water pump. Moreover, the current invention, at least in preferred embodiments, is capable of producing methane at up to 700 bar by using multiple stage compression by following the same principle.

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.

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 for selective absorption of the impurities in the gas stream. The gas compressor of the invention may use any suitable liquid medium such as water, water- solvent mixture, antifreeze mixture, sodium hydroxide, potassium hydroxide, various solvents with high boiling point, hydraulic oil, ethylene glycol, and various compounds of ethylene glycol etc. Ethylene glycol and its various compounds when sprayed via nozzle creates a high surface area liquid which will absorb moisture from the compressed gas; therefore when a water absorbent liquid is sprayed as the compressing liquid this compressor can also dry the gas. 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 raw biogas 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 raw biogas 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 are 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 biogas plant. In this application, and others, the gas is raw biogas. The gas compressor may be connected to a source of gas to be compressed.

In one configuration, the gas compressor may comprise one or more of a bottom water tank, a high pressure water pump, a gas inlet valve to the pressure vessel, a high pressure gas outlet purge valve from the pressure vessel, 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, a gas drying unit and an electronic control system.

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 and level of gas clean up.

The outlet gas purge valve may deliver compressed and cleaned methane 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 an 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 typical operation, the gas to be compressed is fed into the empty pressure vessel followed by compression by pumping water into the pressure vessel, as described above.

The flow rate of the gas to be compressed may be in the range of 10 cubic centimetres per minute to several thousands normal cubic metres per hour. The compressor may have an operating temperature in the range from minus 60 degrees C to above 100 degrees Centigrade. The liquid medium and liquid pump is selected as per the optimum operating temperature, flow rate and operating pressure.

The gas compressor may have an optional nitrogen gas feed point to the pressure vessel to purge any gaseous substance from the system when explosive gases are compressed.

In one embodiment a compressor comprises a pressure vessel containing a gas mixture, having one top opening, and one bottom opening, and a liquid is sprayed into the pressure vessel from the top opening to absorb the soluble gases from the gas mixture and compress the un-soluble gases at the top section of the pressure vessel due to the rising liquid column by keeping the bottom opening closed.

The purified compressed gas may be purged out from the top opening by pumping in more liquid into the pressure vessel from its bottom opening, to maintain a constant pressure inside the pressure vessel to prevent reappearance of the soluble gases under low pressure.

The pressurised liquid containing dissolved gases may be drained by opening the bottom opening of the pressure vessel, into an atmospheric pressure tank under gravity, while feeding more gas mixture into the pressure vessel through its top opening for the next cycle. After purging out all the insoluble gases from the top of the pressure vessel, the soluble gases may also be released from the top of the pressure vessel from a different outlet at a greater than atmospheric pressure by operating an on/off valve. The remaining soluble gases may be de-absorbed from the liquid at atmospheric pressure and collected via a gas outlet of the atmospheric pressure tank and fresh liquid may be separated from any dissolved gas.

The fresh liquid may be again sprayed from its top opening into the pressure vessel to scrub the soluble gases from a gas mixture and pressurise the non-soluble gases and the process may then be repeated as described above.

Brief description of the Drawings

Exemplary embodiments of the invention will be better understood with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of various components of a compressor system according to an embodiment of the invention;

Figure 2 is a schematic diagram of various components of a compressor system according to a further embodiment of the invention; and

Figure 3 is a schematic diagram of various components of a compressor system according to a yet further embodiment of the invention.

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.

Figure 1 shows the configuration of an embodiment of an integrated gas upgrade system 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 1, 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. The hollow light weight movable balls facilitate better mixing of raw biogas with water as an example, which then absorb C02 and H2S from the biogas by leaving clean methane at the top of the pressure 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 gas source

103 is open, while a sixth valve 112 between the second vessel 102 and the low pressure gas source 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 as this depends only on the capacity of the high pressure hydraulic pump. The compressed, cleaned methane 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 low pressure gas source 103. 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 low pressure gas source 103. This vacuum helps to draw more gas from low pressure gas source 103 more effectively.

After discharging high pressure gas from the second vessel 102, the liquid which contains C02 and H2S under pressure is then poured downward from the second vessel 102 to the bottom flash tank 121 at ambient pressure. C02 and H2S gas bubbles will form inside the flash tank 121 under ambient pressure. Oxygen gas is supplied from an oxygen source 1 18, via a connecting oxygen pipe 128, into the flash tank 121. The flash tank is filled with lightweight, movable, floating balls 120, which facilitates mixing between the H2S and oxygen to produce elemental sulphur and water inside the flash tank 121. A screen gas barrier 126 and a screen-mesh 127 is used inside the flash tank 121 to prevent gas bubbles going to the water intake side of the water pump 108. An inlet pipe 122 feeds gas free water to the pump 108.

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 gas source 103 is closed, while the sixth valve 112 between the second vessel 102 and the low pressure gas source 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. The hollow lightweight movable balls facilitate better mixing of raw biogas with water as an example, which then absorb C02 and H2S from the biogas by leaving clean methane at the top of the pressure vessel 101. High pressure pure methane gas is created in the first vessel 101 while the second vessel 102 draws in new gas from the low pressure gas source 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. After discharging high pressure gas from the first vessel 101, the liquid which contains C02 and H2S under pressure is then poured downward from the first vessel 101 to the bottom flash tank 121 at ambient pressure. C02 and H2S gas bubbles will form inside the flash tank 121 under ambient pressure. Oxygen gas is supplied from a oxygen source 118, via a connecting oxygen pipe 128, into the flash tank 121. The flash tank is filled with lightweight, movable, floating balls 120, which facilitates mixing between the H2S and oxygen to produce elemental sulphur and water inside the flash tank 121. A screen gas barrier 126 and a screen-mesh 127 is used inside the flash tank 121 to prevent gas bubbles going to the water intake side of the water pump 108. An inlet pipe 122 feeds gas free water to the pump 108. A configuration of high surface area, double-walled coil 123 with internal perforation 124 for injecting oxygen via the oxygen pipe 128 is used to combust the traces of hydrogen sulphide to completely eliminate the smell of hydrogen sulphide.

The above process is repeated to continually charge and discharge each of the vessels 101, 102.

The embodiment of Figure 1 provides gas drying functionality. During compression inside the first vessel 101 and the second vessel 102 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 and after the compressor at an elevated gas pressure such as above 100 up to 700bar bar. Ethylene glycol and its various compounds when sprayed via nozzle creates a high surface area liquid which will absorb moisture from the compressed gas; therefore when a water absorbent liquid is sprayed as the compressing liquid this compressor can also dry the gas by chemical reaction. The embodiment of Figure 1 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.

The invention is capable of being embodied in several different configurations by re- arranging the components of Figure 1 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 gas upgrade system at an extremely low cost; this invention 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.

In another example as shown in FIGURE 2, wherein a pressure vessel containing a gas mixture (for example shale gas or natural gas), having one top opening and multiple ports for various valves (VI, V2, V3), and one bottom opening and multiple ports for Valve V4 and V5. A liquid for example water, is sprayed into the pressure vessel from the top opening via valve 2, to absorb the soluble gases (e.g. C0 ₂ , H ₂ S, NH ₃ , Siloxanes, amines, etc ) from the gas mixture, and compress the un-soluble gases (e.g. CH4, other hydrocarbon gases etc) at the top section of the pressure vessel due to the rising liquid column by keeping the bottom opening (i.e. valve V4 and V5) closed. The purified compressed gas is then purged out from the top opening via valve V3, by the pumping in more liquid into the pressure vessel from its bottom opening via valve V4, to maintain a constant pressure inside the pressure vessel to prevent the reappearance of the soluble gases under low pressure. This is needed to prevent the C0 ₂ being re-appeared from the solution if depressurised while CH ₄ is still left in the pressure vessel. Then the pressurised liquid containing the dissolved gases (e.g. C0 ₂ , H ₂ S, ¾, Siloxanes etc) is drained, by opening the bottom opening of the pressure vessel via valve V5, into the atmospheric pressure tank under gravity, while feeding more gas mixture into the pressure vessel through its top opening via Valve VI, for the next cycle. The soluble gases (e.g. C0 ₂ , H ₂ S etc) is then de-absorbed from the liquid at atmospheric pressure and collected via a gas outlet of the atmospheric pressure tank and a fresh liquid is separated from any dissolved gas. The fresh liquid is then again sprayed from its top opening via Valve V2, into the pressure vessel to scrub the soluble gases from a gas mixture and pressurise the non-soluble gases and the process is then repeated for the next cycle. The liquid can be water and any other chemical (amines, lime water, soda water, KOH solution, NaOH solution, glycol and its compounds, anti-freeze, acidic solution, depending on the impurities to be absorbed, adsorbed, or reacted to the liquid as a chemical scrubber.

As a further variation of the configuration, after purging out the insoluble gases (e.g. CH4) from the top of the pressure vessel, the soluble gases (e.g. C02) can also be released from the top of the pressure vessel via a different valve outlet at a greater than atmospheric pressure. The remaining soluble gases (e.g. C02) may be further separated by draining the water in the atmospheric pressure tank to produce fresh liquid for the next cycle.

In summary as per the configuration as shown in FIGURE 1 and FIGURE 2, a gas compressor and gas upgrade system 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. The compressing fluid absorbs the impurities contained in the input gas stream under high pressure. The absorbed gases are released and neutralised with the help of oxygen at ambient pressure. Figure 3 shows the configuration of another embodiment of a compressor system according to the present invention. Corresponding reference numerals to those used in Figure 1 have been used for corresponding components.

As shown in Figure 3, 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 gas source 103 is open, while a sixth valve 112 between the second vessel 102 and the low pressure gas source 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. Temperature and pressure sensors 133 are provided between the pump and both the first and second vessels. This is used to monitor the compressor.

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 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 purge port 131 can also be used to deliver gas to a separate pipeline or storage tank. In addition, a gas pressure relief valve 129 enables gas venting through the gas vent port 130 in the case of excess pressure build-up. A gas temperature and pressure sensor 132 monitors the gas being delivered through the output valve 109 and is used to control valve timings.

The gas inlet of the first vessel 101 is controlled by the fifth valve 111 which is connected to the low pressure gas source 103. 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 low pressure gas source 103. This vacuum helps to draw more gas from low pressure gas source 103 more effectively.

After discharging high pressure gas from the second vessel 102, the liquid is then poured downward from the second vessel 102 to the bottom tank 121 at ambient pressure. The bottom tank 121 has a liquid fill and vent port 134 for controlling the level of liquid in the tank. A pressure release valve 135 is provided connected to the bottom tank 121 as a safety measure if the pressure becomes too great.

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 gas source 103 is closed, while the sixth valve 112 between the second vessel 102 and the low pressure gas source 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 pure gas is created in the first vessel 101 while the second vessel 102 draws in new gas from the low pressure gas source 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. After discharging high pressure gas from the first vessel 101, the liquid is then poured downward from the first vessel 101 to the bottom flash tank 121 at ambient pressure.

The above process is repeated to continually charge and discharge each of the vessels 101, 102.

Our application GB2487815 discloses a high pressure hydrogen compressor and the content of that application is incorporated herein by reference. In broad terms, this application discloses the use of a compressor of the type described in GB2487815 to clean a gas, such as biogas. Such a compressor comprises: a source of high pressure liquid 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 liquid. The compressor is arranged to introduce the high pressure liquid into the pressure vessel via the fluid inlet whereby to compress a volume of gas in the pressure vessel. According to an invention disclosed herein, the gas is a gas mixture and the high pressure liquid mixes with the gas in the pressure vessel to dissolve selectively components of the gas mixture.

The high pressure liquid may be water. The source of high pressure liquid may comprise a pump arranged to pump liquid to the fluid inlet of the pressure vessel. The source of high pressure liquid may comprise a tank and the pump may be arranged to pump liquid from the tank to the fluid inlet of the pressure vessel. The compressor may comprise at least one further pressure vessel having a gas inlet and a fluid inlet for the high pressure liquid. The pump may be arranged to pump liquid 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 liquid 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. The first pressure vessel and the further pressure vessel are configured such that pumping of liquid 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, and pumping of liquid from the further pressure vessel to the first pressure vessel causes a pressure drop in the further pressure vessel, whereby to draw gas into the further pressure vessel via the gas inlet. 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 fluid inlet of the further pressure vessel may be connected to the same source of high pressure liquid as the fluid inlet of the first pressure vessel.

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.

The gas mixture may comprise one or more of carbon dioxide, hydrogen sulphide and methane. The carbon dioxide and/or the hydrogen sulphide may be dissolved into the high pressure liquid. The carbon dioxide and/or the hydrogen sulphide may be recovered subsequently from the high pressure liquid. The methane may exit the gas outlet of the pressure vessel(s) as compressed gas. The compressed gas exiting the gas outlet of the pressure vessel(s) may be substantially pure, for example

substantially pure methane. In addition to the above, our patent application PCT/GB2012/050270 discloses various configurations of a gas compressor, including features disclosed in

GB2487815, that may be used in relation to the present invention and the content thereof is incorporated herein. Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this

specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.