WO2012122599A1

WO2012122599A1 - Compressed natural gas tank float valve system and method

Info

Publication number: WO2012122599A1
Application number: PCT/AU2012/000265
Authority: WO
Inventors: Paul Anthony Whiteman; Derek Shane FEKETE
Original assignee: Mosaic Technology Development Pty Ltd
Current assignee: Mosaic Technology Development Pty Ltd
Priority date: 2011-03-14
Filing date: 2012-03-14
Publication date: 2012-09-20
Anticipated expiration: 2013-09-14
Also published as: AU2012229884A1

Abstract

A compressed natural gas (CNG) tank float valve system (10) enables improved on-vehicle CNG fuel supply. The system (10) includes a first pressure vessel (14) having a top end and a bottom end, wherein the top end includes a top opening and the bottom end includes a bottom opening. A first bottom float valve (90) is in fluid communication with the bottom opening. Gas can flow from the first pressure vessel (14) through the top opening as the level of a liquid (42) rises inside the first pressure vessel (14), and whereby the liquid (42) can flow from the first pressure vessel (14) through the first bottom float valve (90) and out the bottom opening until the level of the liquid (42) inside the first pressure vessel (14) drops and closes the first bottom float valve (90).

Description

TITLE

COMPRESSED NATURAL GAS TANK FLOAT VALVE SYSTEM AND METHOD FIELD OF THE INVENTION

This invention relates generally to a compressed gas transfer system. In particular, the invention relates to a compressed natural gas transfer system including a tank float valve system and method for use in commercial vehicles.

BACKGROUND OF THE INVENTION

Natural gas fuels are relatively environmentally friendly for use in vehicles, and hence there is support by environmental groups and governments for the use of natural gas fuels in vehicle applications. Natural gas based fuels are commonly found in three forms: Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG) and a derivative of natural gas called Liquefied Petroleum Gas (LPG).

Natural gas fuelled vehicles have impressive environmental credentials as they generally emit very low levels of SO2 (sulphur dioxide), soot and other particulate matter. Compared to gasoline and diesel powered vehicles, CO₂ (carbon dioxide) emissions of natural gas fuelled vehicles are often low due to a more favourable carbon-hydrogen ratio found in natural gas. Natural gas vehicles come in a variety of forms, from small cars to (more commonly) small trucks and buses. Natural gas fuels also provide engines with a longer service life and lower maintenance costs. Further, CNG is the least expensive alternative fuel when comparing equal amounts of fuel energy. Still further, natural gas fuels can be combined with other fuels, such as diesel, to provide similar benefits mentioned above.

A key factor limiting the use of natural gas in vehicles is the storage of the natural gas fuel. In the case of CNG and LNG, the fuel tanks are generally expensive, large and cumbersome relative to tanks required for conventional liquid fuels having the same energy content. In addition, the lack of wide availability of CNG and LNG refuelling facilities, and the cost of LNG, add further limitations on the use of natural gas as a motor vehicle fuel. Further, in the case of LNG, the cost and complexity of producing LNG and issues associated with storing a cryogenic liquid on a vehicle further limits the widespread adoption of this fuel.

Some of the above issues are mitigated concerning LPG, and this fuel is widely used in high mileage motor cars such as taxis. However, cost versus benefit comparisons are often not as favourable in the case of private motor cars. Issues associated with the size and shape of the fuel tank, the cost variability of LPG and the relatively limited supply mean that LPG also has significant disadvantages that limit its widespread adoption. Consequently, without massive investment in a network of LNG plants around major transport hubs, CNG is the only feasible form of natural gas that is likely to be widely utilised in the near future.

Methods for delivering natural gas into an internal combustion engine can be broadly categorized into two main groups:

Low pressure carburetted induction or manifold based injection:

The practice of inducting natural gas into the inlet of an internal combustion engine is well known and is similar to practices used in LPG fueled vehicles. Because of the ignition characteristics of inspirited natural gas compared to direct injection diesel, the level of liquid fuel substitution when used in a diesel engine using low pressure carburetted induction is somewhat limited. Another problem with this method concerns 'methane slippage' that results from the overlap of the timing of the inlet and exhaust valves, and/or non-combustion zones in the cylinder chamber typically in the piston-land gap. This results in a level of unburnt hydrocarbons in the engine exhaust that can negate most of the greenhouse gas emission benefits of using natural gas.

High pressure direct injection (HPDI):

In high pressure direct injection, natural gas is injected into a piston cylinder with a small quantity of pilot diesel fuel (typically between 3% and 5%) resulting in less potential for methane slippage or pre-ignition of the fuel- air mixture. A diesel engine operating on natural gas with high pressure direct injection retains the benefits of a high efficiency diesel engine, is able to achieve better than 95% displacement of the liquid fuel, and achieves significant reductions in greenhouse gas emissions and pollutants including sulphur dioxide, carbon dioxide, oxides of nitrogen and soot. Thermal tip ignition or spark ignition are alternatives to diesel pilot ignition and results in a 100 percent gas direct injection engine.

However, high pressure direct injection requires natural gas to be supplied to an engine at a consistent high pressure (typically greater than 3600 psig). For LNG this is achieved through the use of a specially designed pump capable of operating at cryogenic temperatures and delivering the fuel at the required pressure. For CNG it requires an expensive and complex gas compressor that must deliver natural gas at the required pressure from a range of pressures, typically between 10 psig (in a near empty CNG tank) and 3600 psig (in a full CNG tank). This means the gas compressor set must have the capability to reject the significant quantities of heat created by a compression ratio of up to 300:1 , and deal with a range of compression ratios down to 1 :1. This requires complex machinery and large air to gas intercoolers, consumes large quantities of energy, adds significant excess mass, and requires a large amount of space which is something not available on most vehicles.

While LNG has had some success as a liquid fuel replacement in some regions of the world, the lack of availability of LNG and its high cost means that in many regions of the world it is not feasible to use LNG. In the case of CNG, it also has had some success as a liquid fuel replacement but almost exclusively in spark ignition engines utilising the low pressure carburetted or port injection induction technology. This application is popular in government bus fleets around the world where the cleaner burning natural fuel is used in a spark ignition engine to relace a conventional diesel engine.

The unavailability of a system to maintain a high CNG pressure for direct injection engines means that CNG fuel storage systems for HPDI engines have not been considered practical, and many experts in the field have pursued LNG as the only viable natural gas fuel storage system that can be readily pumped/maintained at a high pressure as a liquid to meet the pressure requirements of direct injection.

International Patent Application Publication WO 2008/074075, titled "A Compressed Gas Transfer System", disclosed for the first time a liquid delivery system that enables the volume in a pressure vessel to be varied to maintain gas in the pressure vessel at a constant pressure. That enables a CNG tank to be maintained at a consistent high pressure (e.g., greater than 3600 psig) while the tank is emptied to supply fuel to a high pressure direct injection engine.

OBJECT OF THE INVENTION

It is an object of some embodiments of the present invention to provide consumers with improvements and advantages over the above described prior art, and/or overcome and alleviate one or more of the above described disadvantages of the prior art, and/or provide a useful commercial choice.

SUMMARY OF THE INVENTION

In one form, although not necessarily the only or broadest form, the invention resides in a system comprising:

a first pressure vessel having a top end and a bottom end, wherein the top. end includes a top opening and the bottom end includes a bottom opening; and

a first bottom float valve in fluid communication with the bottom opening;

whereby gas can flow from the first pressure vessel through the top opening as a liquid level rises inside the first pressure vessel, and whereby liquid can flow from the first pressure vessel through the first bottom float valve and out the bottom opening until the liquid level inside the first pressure vessel drops and closes the first bottom float valve.

Optionally, a first top float valve is in fluid communication with the top opening.

Optionally, gas can flow from the first pressure vessel through the first top float valve until the liquid level inside the first pressure vessel rises and closes the first top float valve.

Optionally, the first top float valve is inside the first pressure vessel.

Optionally, the first bottom float valve is inside the first pressure vessel.

Optionally, the system comprises a plurality of interconnected pressure vessels, wherein each interconnected pressure vessel includes a top float valve and a bottom float valve.

Optionally, liquid flowing from the first pressure vessel through the first bottom float valve is recycled to another of the plurality of interconnected pressure vessels.

Optionally, closure of the first top float valve is detected by at least one of the following: by a sensor that senses closure of the first top float valve, by detecting a spike in pressure at a pressure controller, or by a volumetric analysis of liquid that has been supplied to the first pressure vessel.

Optionally, liquid is transferred sequentially from the first pressure vessel through the remaining plurality of interconnected pressure vessels as gas is emptied sequentially from the first pressure vessel and the remaining plurality of interconnected pressure vessels.

Optionally, the first top float valve comprises:

an elongated body having a top end and a bottom end;

a float inside the elongated body; and

a pocket inside the elongated body for receiving the float and causing the float to remain outside a flow path prior to closure of the first bottom float valve.

Optionally, at least one "0" ring is attached to the float inside of the elongated body, whereby in use the "O" ring seals an outlet at the top end of the first top float valve.

Optionally, the elongated body of the first top float valve comprises a hollow metal cylinder.

Optionally, the hollow metal cylinder of the first top float valve comprises a hole near the bottom end of the cylinder, whereby in use liquid enters the hole near the bottom end of the cylinder and causes the float to move upward inside the elongated body.

Optionally, the first bottom float valve comprises:

an elongated body having a top end and a bottom end;

a float inside the elongated body; and

Optionally, at least one Ό" ring is attached to the float inside of the elongated body, whereby in use the "O" ring seals an outlet at the bottom end of the first bottom float valve after liquid flows from the first pressure vessel through the first bottom float valve.

Optionally, the elongated body of the first bottom float valve comprises a hollow metal cylinder.

Optionally, the hollow metal cylinder of the first bottom float valve comprises a hole near the top end of the cylinder, whereby in use gas enters the hole near the top end of the cylinder as liquid flows from the bottom end of the cylinder and causes the float to move downward inside the elongated body.

Optionally, the first top float valve is threaded into a hole at the top end of the first pressure vessel.

Optionally, the first bottom float valve is threaded into a hole at the bottom end of the first pressure vessel.

Optionally, the gas is compressed natural gas and the liquid is a salt solution.

In another form, although not necessarily the only or broadest form, the invention resides in a float valve comprising: an elongated body having a top end and a bottom end; and a float inside the elongated body;

wherein the elongated body includes a valve seat near the top end, an outlet opening through the top end, an inlet opening, and a pocket for receiving the float and causing the float to remain outside a flow path prior to closure of the float valve;

whereby in use liquid enters the inlet opening and provides a buoyancy force that pushes the float upward out of the pocket toward the top end and closes the valve by pressing the float against the valve seat and preventing flow through the outlet opening.

Optionally, the inlet opening is near the bottom end bf the valve.

Optionally, the float comprises a plurality of Ό" rings that seal against the valve seat.

In still another form, although not necessarily the only or broadest form, the invention resides in a float valve comprising:

an elongated body having a top end and a bottom end; and a float inside the elongated body;

wherein the elongated body includes a valve seat near the bottom end, an outlet opening through the bottom end, an inlet opening, and a pocket for receiving the float and causing the float to remain outside a flow path prior to closure of the float valve;

whereby in use a liquid level drops from the inlet opening to the outlet opening as liquid exits the elongated body, and the float floats downward out of the pocket with the liquid level until the float seals against the valve seat and closes the valve.

Optionally, the inlet opening is between the top end and the bottom end of the valve.

Optionally, the float comprises a plurality of "O" rings that seal against the valve seat.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will be described with the reference to the accompany drawings in which:

FIG. 1 is a system diagram illustrating a compressed natural gas transfer system, including four pressure vessels that are completely full of gas, according to an embodiment of the present invention.

FIG. 2 is a further system diagram illustrating the system of FIG. 1 , where one pressure vessel is partially emptied of gas, according to an embodiment of the present invention.

FIG. 3 is a further system diagram illustrating the system of FIG. 1 , where one pressure vessel is almost completely emptied of gas and filled with liquid, according to an embodiment of the present invention.

FIG. 4 is a further system diagram illustrating the system of FIG. 1 , where two pressure vessels are almost emptied of gas and a liquid is shown drained from one of the emptied vessels, according to an embodiment of the present invention.

FIG. 5 is a further system diagram illustrating the system of FIG. 1 , where two pressure vessels are almost completely emptied of gas and a liquid is shown fully drained from one of the emptied vessels, according to an embodiment of the present invention.

FIG. 6 is a further system diagram illustrating the system of FIG. 1 , where three pressure vessels are almost completely emptied of gas and a liquid is shown fully drained from two of the emptied vessels, according to an embodiment of the present invention.

FIG. 7 is a further system diagram illustrating the system of FIG. 1 , where three pressure vessels are almost emptied of gas and a liquid is shown filling one of the emptied vessels, according to an embodiment of the present invention.

FIG. 8 is a further system diagram illustrating the system of FIG. 1 , where all four pressure vessels are almost completely emptied of gas and a liquid is shown fully drained from three of the emptied vessels, according to an embodiment of the present invention.

FIG. 9 is a close up sectional side view illustrating a top float valve in an "open" configuration, according to an embodiment of the present invention.

FIG. 10 is a close up sectional side view illustrating the top float valve of FIG. 9 in a "closed" configuration, according to an embodiment of the present invention.

FIG. 11 is a close up sectional side view illustrating a bottom float valve in an "open" configuration, according to an embodiment of the present invention.

FIG. 12 is a close up sectional side view illustrating the bottom float valve of FIG. 11 in a "closed" configuration, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Elements of the invention are illustrated in concise outline form in the drawings, showing only those specific details that are necessary to understanding the embodiments of the present invention, but so as not to clutter the disclosure with excessive detail that will be obvious to those of ordinary skill in the art in light of the present description.

In this patent specification, adjectives such as first and second, left and right, front and back, top and bottom, etc., are used solely to define one element from another element without necessarily requiring a specific relative position or sequence that is described by the adjectives. Words such as "comprises" or "includes" are not used to define an exclusive set of elements or method steps. Rather, such words merely define a minimum set of elements or method steps included in a particular embodiment of the present invention. It will be appreciated that the invention may be implemented in a variety of ways, and that this description is given by way of example only.

FIG. 1 illustrates a compressed natural gas transfer system 10 that supplies gas at high pressure to a gas consuming engine 12. The gas consuming engine 12 is typically in the form of a vehicle engine such as a high pressure direct injection (HPDI) engine and accordingly the transfer system 10 is usually portable. However, the transfer system 10 may be stationary and supply a gas consuming device in the form of a gas turbine or any plant or process requiring a relatively constant stream of high pressure gas.

The compressed natural gas transfer system 10 includes a plurality of interconnected pressure vessels 14, 16, 18, 20 in the form of CNG tanks. The tanks are able to cater for different pressures as required. However, current pressure technology would reasonably allow operating pressures up to 5000 psig and beyond. This is typical of the pressure at which compressed natural gas is supplied to an engine in a high pressure direct injection system. However, it should be appreciated that the rating and operating pressure of the pressure vessels 14, 16, 18, 20 can be varied depending upon the requirements of the gas consuming engine 12.

An engine gas line 22 is used to connect the pressure vessel 20 to the gas consuming engine 12. An engine gas header valve 24 is used to isolate the supply of gas from the pressure vessel 20 from the gas consuming engine 12 through the engine gas line 22. An engine gas pressure regulator 26 is located along the engine gas line 22 to ensure that gas that is supplied to the gas consuming engine 12 at a desired pressure whilst the pressure vessels 14, 16, 18, 20 may operate within a pressure range.

A liquid vapour separator system 28 is also located along the gas line

22 to ensure that liquid vapour from the pressure vessel 20 does not enter the engine 12. The system 28 includes a separator tank 30, a level switch 32, and a liquid dump valve 34.

A liquid reservoir 36 is connected to the pressure vessel 20 via a liquid delivery line 38 and a liquid return line 40. The liquid reservoir 36 is filled with liquid 42. The liquid 42 is typically a salt solution including water and salt or other antifreeze product being added to the water for use in low temperature environments. Liquid inlet valves 44, 46, 48, 50 are used to permit the delivery of liquid 42 from the liquid reservoir 36 to, respectively, the pressure vessels 14, 16, 18, 20 through the liquid delivery line 38. Liquid outlet valves 52, 54, 56, 58 and a liquid return header valve 59 are used to allow liquid 42 to return from, respectively, the pressure vessels 14, 16, 18, 20 through the liquid return line 40.

A reservoir pump 60 is located along the liquid delivery line 38 to pump liquid 42 from the liquid reservoir 36 to the pressure vessels 14, 16, 18, 20. A reservoir pump pressure controller 62 is connected to the reservoir pump 60 and the liquid delivery line 38 to ensure the desired pressures within the pressure vessels 14, 16, 18, 20 are maintained. The amount of liquid 42 being delivered to the pressure vessels 14, 16, 18, 20 can be controlled by using the reservoir pump 60, which for example can be a variable speed pump, a variable displacement pump, a constant speed pump with spill valves or a combination thereof. A liquid refuelling connection 64 can be used to periodically replenish or replace liquid in the reservoir 36.

In use, the pressure vessels 14, 16, 18, 20 are filled with gas to a desired pressure as shown. Gas filling occurs through a gas refuelling connection 66 and gas valves 68, 70, 72, 76 associated, respectively, with pressure vessels 14, 16, 18, 20. A further gas transfer valve 74 is attached between the vessels 14, 16, 18 and a bottom end of the vessel 20. As shown in FIG. 1 , all vessels 14, 16, 18, 20 are full of CNG, all liquid 42 is stored in the reservoir 36, and the engine 12 is off.

Referring to FIG. 2, consider that the engine gas header valve 24, gas transfer valve 74, gas valves 68, 70, 72 and 76, and the liquid inlet valve 44 are open, the engine 12 is started, and operation of the reservoir pump 60 is commenced. The pump 60 may commence operation after pressure at the pressure regulator 26 has dropped below a designated level. Gas immediately flows from pressure vessel 20 through gas line 22 and to the engine 12. Gas also flows from the top end of vessels 14, 16, 18 and into the bottom end of vessel 20. As the pressure in vessel 14 begins to drop, liquid 42 is moved from the reservoir 26 by the reservoir pump 60 through the liquid delivery line 38 and valve 44 into the pressure vessel 14. Gas from vessel 14 also re-pressurises vessels 16, 18. Using feedback from the pressure controller 62, a flow rate is achieved that maintains relatively constant pressure of the gas within the pressure vessels 14, 16, 18, 20. Optionally, the system 10 uses a constant speed pump pressure control logic that cycles the system 10 on and off between upper and lower pressure triggers.

Referring to FIG. 3, when the gas in vessel 14 is almost all consumed, the liquid 42 reaches the bottom of a top float valve 78 in the vessel 14. A float 80 inside the top float valve 78 then floats upward with the rising level of the liquid 42 until the float 80 closes the top float valve 78. Thus the liquid 42 is not able to escape through the gas valve 68, which is then closed. This condition can be detected in a variety of ways, including for example by a sensor that senses closure of the top float valve 78, by detecting a spike in pressure at the pressure controller 62, or by a volumetric analysis of the liquid 42 that has been supplied from the reservoir 36 to the vessel 14.

The liquid inlet valve 44 is then closed, the liquid inlet valve 46 is opened, and the liquid outlet valve 52 is opened. That allows liquid 42 to begin draining from the vessel 14 and returning to the liquid reservoir 36 through a restrictor 82, which is installed in parallel with the liquid return header valve 59 in the liquid return line 40. The liquid return header valve 59 remains closed. Residual pressurised gas at a top end of the vessel 14 assists in forcing the liquid 42 out of the vessel 14. Simultaneously, the pump 60 begins to force the liquid 42 into the vessel 16, thereby maintaining a relatively high constant pressure of the gas in the vessels 16, 18, 20. Thus gas can continue to flow at a high pressure from the vessel 20 and through line 22 to the engine 12.

Referring to FIG. 4, as the gas in vessel 16 is consumed, the level of the liquid 42 in vessel 16 continues to rise, while simultaneously the level of the liquid 42 in vessel 14 continues to fall. Those skilled in the art will thus appreciate that the total volume of the reservoir 36 does not need to significantly exceed the total volume of one of the vessels 14, 16, 18, 20. As described further below, by sequentially transferring the liquid 42 from the vessel 14, back to the reservoir 36, and then to the vessel 16, less volume of the liquid 42, and hence less mass of the liquid 42, is required to be stored in and transported with the CNG transfer system 10.

Referring to FIG. 5, a process similar to that described for FIG. 3 above repeats. When the gas in vessel 16 is almost all consumed, the liquid 42 reaches the bottom of a top float valve 84 in the vessel 16. A float 86 inside the top float valve 84 then floats upward with the rising level of the liquid 42 until the float 86 closes the top float valve 84. Thus the liquid 42 is not able to escape through the gas valve 70, which is then closed.

The liquid inlet valve 46 is then closed, the liquid inlet valve 48 is opened, and the liquid outlet valve 54 is opened. That allows liquid 42 to begin draining from the bottom opening of the vessel 16 and returning to the liquid reservoir 36 through the restrictor 82. The liquid return header valve 59 remains closed until the pressure of the liquid 42 is lowered to a nominal pressure as a result of the liquid 42 draining through the restrictor 82. Residual pressurised gas at a top end of the vessel 16 assists in forcing the liquid 42 out of the vessel 16. Simultaneously, the pump 60 begins to force the liquid 42 into the vessel 18, thereby maintaining a relatively high constant pressure of the gas in the vessels 18, 20. Thus gas can continue to flow at a high pressure from the vessel 20 and through line 22 to the engine 12.

Further, as the liquid 42 was fully drained from the bottom opening in the bottom end of the vessel 14, a float 88 in a bottom float valve 90 floated down with the level of the liquid 42 and closed the bottom float valve 90. That leaves the vessel 14 ready to be refilled with gas through the refuelling connection 66 and the gas valve 68.

Referring to FIG. 6, as the gas in the vessel 18 is consumed, additional liquid 42 is drained from the bottom opening in the bottom end of the vessel 16 and is routed, through the reservoir 36, to the vessel 18. That again maintains a relatively constant high pressure in the vessels 18, 20. Also, when the vessel 16 was emptied of the liquid 42, a float 92 in a bottom float valve 94 in fluid communication with the bottom opening floated down with the level of the liquid 42 and closed the bottom float valve 94.

Referring to FIG. 7, a similar process of recycling the liquid 42 from the vessel 18, through the reservoir 36, and to the vessel 20 continues.

Referring to FIG. 8, the gas in all four of the pressure vessels 14, 16, 18, 20 is almost entirely consumed by the engine 12. In vessel 18, a bottom float valve 96 is closed by a float 98, and a top float valve 100 is closed by a float 102. Finally, if the engine 12 is run completely out of fuel, a float 104 will close a top float valve 106 in the vessel 20.

However, more commonly the CNG transfer system 10 will be refuelled before all of the gas from vessel 20 is consumed. Before such refuelling, the liquid 42 can be drained back to the reservoir 36. A bottom float valve 108 is then closed by a float 109. Next, the gas valve 76 is closed, and the gas valves 68, 70, 72 and the gas transfer valve 74 are opened. Gas then can flow through refuelling connection 66 to refill all the vessels 14, 16, 18, 20 with gas.

The flow of gas from the vessel 20 can be stopped based on a volumetric calculation of the liquid 42 that has been added to the vessel 20. Thus the top float valve 106 may be included only as a fail-safe mechanism. Also, according to an alternative embodiment of the present invention, those skilled in the art will appreciate that the top float valves 106, 100, 84, 78 all can be replaced by a single top float valve (not shown) in fluid communication with the top ends of the pressure vessels 14, 16, 18, 20, such as a single top float valve located in the separator tank 30 or in another suitable location close to the engine 12. Use of such a single top float valve also can effectively serve the fail-safe function of preventing liquid from entering the engine 12.

In another refuelling scenario, the vessels 14, 16, 18, 20 may be filled with the liquid 42 via the liquid refuelling connection 64 prior to refuelling with gas. Gas is then introduced via the gas refuelling connection 66, and the liquid 42 drains back via the liquid refuelling connection 64 to an external back pressure valve (not shown) which holds the vessels 14, 16, 18, 20 at high pressure. That allows gas transfer to occur at high pressure via the gas refuelling connection 66, and avoids traditional fast-fill CNG heating issues concerning heating and expansion of gas on transfer-which can prevent a full fill. Transferring the gas at high pressure also reduces gas velocities and de-compression/re-compression on transfer. That also helps to reduce any temperature increase of the gas as it is transferred into the vessels 14, 16, 18, 20. In this refuelling mode, the bottom float valves 90, 94, 96, 108 provide a mechanism for dealing with any differences in vessel fill rates. If any vessel 14, 16, 18, 20 becomes completely full before all the other vessels 14, 16, 18, 20 are full, a bottom float valve 90, 94, 96, 108, respectively, closes and prevents gas from escaping with the liquid 42, while allowing other vessels 14, 16, 18, 20 to complete their fills in any order.

According to an alternative embodiment of the present invention, those having ordinary skill in the art will recognise that the bottom float valves 90, 94, 96, 108 need not be positioned inside of the vessels 14, 16, 18, 20, respectively, but may be positioned outside and in fluid communication with the vessels 14, 16, 18, 20, respectively.

Further, according to yet another alternative embodiment of the present invention, the top float valves 78, 84, 100, 106 may be eliminated from the pressure vessels 14, 16, 18, 20, leaving just a top opening in the top end of each of the vessels 14, 16, 18, 20, which top opening is in fluid communication with the gas valves 68, 70, 72, 76. Liquid levels inside the vessels 14, 16, 18, 20 then can be monitored using, for example, a volumetric analysis or other sensor means, to ensure that excess liquid is not pumped out of the top end of a vessel 14, 16, 18, 20 and through a gas valve 68, 70, 72, 76.

Referring to FIG. 9, a close up sectional side view illustrates the top float valve 78 in an "open" configuration. The other top float valves 84, 100, 106 may be identical to the top float valve 78. The top float valve 78 includes an elongated body 110 having a top end 112 and a bottom end 114. As shown, the elongated body 110 consists of a hollow metal cylinder; however, those skilled in the art will recognize that various other designs of an elongated body are within the scope of the present invention. The hollow metal cylinder may be manufactured from various metals, including stainless steel, plastics, composites, or metal alloys.

The float 80 is shown resting inside the elongated body 110 in a pocket at the bottom end 114. The float 80 may be manufactured of various materials, including polypropylene, so that it floats in the liquid 42. To increase its buoyancy, the float 80 may include a hollow end portion 116. A sealing end of the float 80 includes two "O" rings 118. The top end 112 of the elongated body 110 of the top float valve 78 includes a tapered valve seat portion 120, against which the two "0" rings 118 seal when the float 80 floats to the top of the valve 78.

Holes 122 in the elongated body 110 define an inlet opening and enable gas to enter the top float valve 78 and also enable the liquid 42 to enter into the top float valve 78 and cause the float 80 to begin to float toward the top end 112. A small hole 123 in a base of the elongated body 110 further assists in allowing the liquid 42 to enter the elongated body 110 and allows the float 80 to rest out of the flow path. The position of the holes 122 near the bottom end 114 of the elongated body 110 assists to prevent a liquid level in the vessel 14 from rising above the level of the holes 122. By thus maintaining a residual volume of pressurised gas at the top end of the vessel 14, the liquid 42 can be easily drained from the bottom end of the vessel 14 as described above. ^

The top end 112 further includes a threaded portion 124 for threading the valve 78 into the top opening in the top end 112 of the pressure vessel 14. Also, a nozzle 126 enables the valve 78 to be attached to the gas line between the pressure vessel 14 and the gas valve 68. An outlet hole 128 extends from the top end 112 through the nozzle 126 and defines an outlet opening. As shown, a flow path between the holes 122 at the bottom end 114 and the outlet hole 128 at the top end 112 is unobstructed and the valve 78 is effectively open. The pocket beneath the holes 122 receives the float 80 and causes the float 80 to remain outside a flow path of gas between the holes 122 and the outlet hole 128 prior to closure of the valve 78.

Referring to FIG. 10, a close up sectional side view illustrates the top float valve 78 in a "closed" configuration. As shown, the two "O" rings 118 of the float 80 are sealingly engaged with the tapered valve seat portion 120 at the top end 112 of the valve 78. A flow path, between the holes 122 at the bottom end 114 and the outlet hole 128 at the top end 112, is therefore blocked and the valve 78 is effectively closed. Referring to FIG. 11 , a close up sectional side view illustrates the bottom float valve 90 in an "open" configuration. The other bottom float valves 84, 106, 108 may be identical to the bottom float valve 90. The bottom float valve 90 includes an elongated body 130 having a top end 132 and a bottom end 134. As shown, the elongated body 130 consists of a hollow metal cylinder; however, those skilled in the art will recognize that various other designs of an elongated body are within the scope of the present invention. The hollow metal cylinder may be manufactured from various metals, including stainless steel, or metal alloys.

The float 88 is shown floating inside the elongated body 130 in a pocket at the top end 132. This position generally will be maintained when the valve 90 is submerged in liquid (not shown), such as the liquid 42. The float 88 may be manufactured of various materials, including polypropylene, so that it floats in the liquid 42. A sealing end of the float 88 includes two "0" rings 136. The bottom end 134 of the elongated body 130 ofthe bottom float valve 90 includes a tapered valve seat portion 138, against which the two "O" rings 136 seal when the float 88 drops to the bottom of the valve 90.

Holes 140 in the elongated body 130 define an inlet opening and enable gas to enter the bottom float valve 90 and cause the float 88 to begin to float downward toward the bottom end 134. Similarly, when filling with liquid 42, the liquid 42 can enter into the bottom float valve 90 and push the float 88 off its seat and allow the float 88 to begin to float toward the top end 132. A small hole 141 in a top cap of the elongated body 130 further assists in allowing the liquid 42 to enter the elongated body 130 and allows the float 88 to rest outside the flow path. The bottom end 134 further includes a threaded portion 142 for threading the valve 90 into the bottom end of the pressure vessel 14. Also, a nozzle 144 enables the valve 90 to be attached to the liquid lines between the pressure vessel 14 and the liquid inlet valve 44 and the liquid outlet valve 52. An outlet hole 146 extends from the bottom end 134 through the nozzle 144 and defines an outlet opening. As shown, a flow path between the holes 140 and the outlet hole 146 at the bottom end 134 is unobstructed and the valve 90 is effectively open. The pocket at the top end 132 above the holes 140 receives the float 88 and causes the float 88 to remain outside a flow path of liquid between the holes 140 and the outlet hole 146 prior to closure of the valve 90.

Referring to FIG. 12, a close up sectional side view illustrates the bottom float valve 90 in a "closed" configuration. As shown, the two "O" rings 136 of the float 88 are sealingly engaged with the tapered valve seat portion 138 at the bottom end 134 of the valve 90. A flow path, between the holes 140 and the outlet hole 146 at the bottom end 134, is therefore blocked and the valve 90 is effectively closed. During a liquid filling process (as described above concerning the liquid 42), the float valve 90 is opened by liquid pressure applied through the outlet hole 146, which forces the float 88 upward from the tapered valve seat portion 138 and toward the top end 132 of the valve 90.

The architecture of the float valves 78, 90 provide several advantages. For example, the large hoop stresses experienced by the pressure vessel 14 generally require an integrated construction of the vessel 14, and also generally make it uneconomical to provide large access ports in the vessel 14. Therefore, the elongated bodies 110, 130 of the valves 78, 90, respectively, enable the valves 78, 90 to be conveniently inserted into small holes at the top end and bottom end, respectively, of the pressure vessel 14. Corresponding female threads (not shown) in the pressure vessel 14 receive the male threads of the threaded portions 124, 142.

A further advantage is obtained by integrating what is effectively a valve stem, in the form of the shape of the floats 80, 88 and the Ό" rings 118, 136, respectively, into the floats 80, 88. Thus no separate valve stems, floats, pivot arms or other linkages (which are typical of prior art float valves) are required. The result is a very robust valve that is extremely reliable, particularly under the relatively low duty cycles (e.g., valve activations of not more than twice per day) typically involved in the emptying and filling of CNG pressure vessels.

The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is not intended to be exhaustive or to limit the invention to a single disclosed embodiment. As mentioned above, numerous alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily developed by those of ordinary skill in the art. Accordingly, this patent specification is intended to embrace all alternatives, modifications and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention.

Claims

1. A system, comprising:

a first pressure vessel having a top end and a bottom end, wherein the top end includes a top opening and the bottom end includes a bottom opening; and

a first bottom float valve in fluid communication with the bottom opening;

2. The system of claim 1 , wherein a first top float valve is in fluid communication with the top opening.

3. The system of claim 2, wherein gas can flow from the first pressure vessel through the first top float valve until the liquid level inside the first pressure vessel rises and closes the first top float valve.

4. The system of claim 2, wherein the first top float valve is inside the first pressure vessel.

5. The system of claim 1 , wherein the first bottom float valve is inside the first pressure vessel.

6. The system of claim 1 , wherein the system comprises a plurality of interconnected pressure vessels, wherein each interconnected pressure vessel includes a top float valve and a bottom float valve.

7. The system of claim 1 , wherein liquid flowing from the first pressure vessel through the first bottom float valve is recycled to another of the plurality of interconnected pressure vessels.

8. The system of claim 2, wherein closure of the first top float valve is detected by at least one of the following: by a sensor that senses closure of the first top float valve, by detecting a spike in pressure at a pressure controller, or by a volumetric analysis of liquid that has been supplied to the first pressure vessel.

9. The system of claim 1 , wherein liquid is transferred sequentially from the first pressure vessel through the remaining plurality of interconnected pressure vessels as gas is emptied sequentially from the first pressure vessel and the remaining plurality of interconnected pressure vessels.

10. The system of claim 2, wherein the first top float valve comprises: an elongated body having a top end and a bottom end;

a float inside the elongated body; and

11. The system of claim 2, wherein at least one "O" ring is attached to the float inside of the elongated body, whereby in use the Ό" ring seals an outlet at the top end of the first top float valve.

12. The system of claim 11. wherein the elongated body of the first top float valve comprises a hollow metal cylinder.

13. The system of claim 12, wherein the hollow metal cylinder of the first top float valve comprises a hole near the bottom end of the cylinder, whereby in use liquid enters the hole near the bottom end of the cylinder and causes the float to move upward inside the elongated body.

14. The system of claim 1 , wherein the first bottom float valve comprises: an elongated body having a top end and a bottom end;

a float inside the elongated body; and

15. The system of claim 14, wherein at least one "O" ring is attached to the float inside of the elongated body, whereby in use the "O" ring seals an outlet at the bottom end of the first bottom float valve after liquid flows from the first pressure vessel through the first bottom float valve.

16. The system of claim 15, wherein the elongated body of the first bottom float valve comprises a hollow metal cylinder.

17. The system of claim 16, wherein the hollow metal cylinder of the first bottom float valve comprises a hole near the top end of the cylinder, whereby in use gas enters the hole near the top end of the cylinder as liquid flows from the bottom end of the cylinder and causes the float to move downward inside the elongated body.

18. The system of claim 2, wherein the first top float valve is threaded into a hole at the top end of the first pressure vessel.

19. The system of claim 1 , wherein the first bottom float valve is threaded into a hole at the bottom end of the first pressure vessel.

20. The system of claim 1 , wherein the gas is compressed natural gas and the liquid is a salt solution.

21. A float valve, comprising: an elongated body having a top end and a bottom end; and a float inside the elongated body;

22. The float valve of claim 21 , wherein the inlet opening is near the bottom end of the valve.

23. The float valve of claim 21 , wherein the float comprises a plurality of "O" rings that seal against the valve seat.

24. A float valve, comprising:

25. The float valve of claim 24, wherein the inlet opening is between the top end and the bottom end of the valve.

26. The float valve of claim 24, wherein the float comprises a plurality of "O" rings that seal against the valve seat.