GB2579557A

GB2579557A - Storage device for constant composition liquefied calibration mixtures

Info

Publication number: GB2579557A
Application number: GB1819673.3A
Authority: GB
Inventors: Edward Holland Paul; Walker Joey; Miklos Vargha Gergely
Original assignee: Invertone Ltd
Current assignee: Invertone Ltd
Priority date: 2018-12-03
Filing date: 2018-12-03
Publication date: 2020-07-01
Also published as: GB201819673D0

Abstract

The invention provides a device for storing a liquefied calibration mixture in substantially a single liquid phase and dispensing it therefrom, comprising a sealable vessel 100 defining an inner vessel volume; a collapsible container 103 defining an inner container volume disposed within the inner vessel volume; and a valve assembly 105 comprising a pressurising fluid valve 107 in fluid communication with the inner vessel volume and a volatile compound valve 109 in fluid communication with the inner container volume.

Description

Storage Device for Constant Composition Liquefied Calibration Mixtures

Technical Field of the Invention

The present invention relates to devices for storing volatile compounds in a single liquid phase and dispensing them therefrom, and methods of dispensing from and priming the device.

Background to the Invention

It is known in the art to compress mixtures of volatile compounds, such as gases, into a compressed gaseous and/or liquid state/phase and to store them in a pressurised vessel, such as a cylinder, until they are required for their intended use, wherein controlled dispensing of the mixture from the cylinder is performed, for example by releasing a valve to allow some gas to vent therefrom. Such cylinders may be used for storage in dispensing of constant composition liquefied calibration mixtures, for example. Examples of such mixtures are liquid petroleum gas (LPG) which comprises a mixture of mostly propane and butane, and natural gas liquids (NGLs) which generally consist of various small-chain hydrocarbon components in the CI-C6 range.

Standard gas cylinders for such applications generally comprise a dual-phase system, wherein a mixture of volatile compounds compressed into a liquid state is contacted by a pressurising fluid (typically an inert gas such as helium) present in the headspace of the cylinder. The pressurising fluid exerts an extra pressure on the mixture and thus forces the mixture through a dip tube and out of the cylinder in a single liquid phase form when the outlet valve is opened, which is needed for proper sampling of the standard mixture. Depleting the cylinder results in the mixture repartitioning/fractionating between the gaseous phase and liquid phase, whereby a higher proportion of the more volatile compounds in the mixture enter the gaseous phase. This leads to a problem wherein there is inconsistent distribution of the constituent compounds being dispensed from the cylinder over the course of the complete depletion cycle.

For liquefied standard mixtures usually dual port valve cylinders are used, with a gas port and a liquid port valve. To the liquid port a dip tube is connected inside the cylinder which, together with the pressurizing fluid makes it possible to sample homogenous (bubble free) liquid samples. However, the increase in volume of the gaseous phase over a depletion cycle in such systems has been found to still result in inconsistent distribution of constituent compounds over the cycle, as there is still a tendency for the mixture to re-partitionifractionate between the liquid and gas phases.

A third type of cylinder which has been designed to overcome this problem is the constant (over) pressure cylinder (piston cylinder). Piston cylinders comprise a cylinder with a piston located therein that defines two chambers within the cylinder either side of it. One chamber contains a pressurising fluid and the other a liquid volatile compound mixture. The pressure of the pressurising fluid on the piston (and therefore on the liquid mixture) is always kept above the vapour pressure of the liquid mixture.

As the mixture is depleted, the piston is moved by the pressurising fluid to decrease the volume of the chamber containing the mixture. There is therefore no gaseous phase able to form in the chamber containing the liquid mixture and the mixture remains as a single liquid phase over the complete depletion cycle. Piston cylinders therefore substantially mitigate the problem of re-partitioning/fractionation described above.

Piston cylinders are however more complex and expensive to manufacture, operate and maintain than standard gas cylinders, and are more prone to malfunctions.

It would therefore be advantageous to provide a device for storing mixtures of volatile compounds in a single liquid phase, which keeps the mixture as a single liquid phase over a complete depletion cycle, but which is less complex and/or expensive to manufacture, operate and/or maintain, and is less prone to malfunction, especially compared to known piston cylinder-type devices.

It would be further advantageous to provide a device which could be at least partially manufactured using standard gas cylinder manufacturing techniques and/or equipment and/or could be assembled from at least part of a standard gas cylinder which has already been manufactured (for example by retrofitting a standard gas cylinder).

Summary of the Invention

According to a first aspect of the invention there is provided a device for storing a mixture of volatile compounds in substantially a single liquid phase and dispensing it therefrom, comprising: a sealable vessel defining an inner vessel volume; a collapsible container, defining an inner container volume, disposed within the inner vessel volume; and a valve assembly comprising a pressurising fluid valve in fluid communication with the inner vessel volume and a volatile compound valve in fluid communication with the inner container volume.

A "volatile" compound is defined herein as a compound which is an evaporable liquid or gaseous at ambient temperatures and pressures and which may require some level of compression and/or cooling to be condensed into the liquid phase.

The volatile compounds may comprise compressible and/or condensable compounds.

The mixture of volatile compounds may comprise a mixture of volatile hydrocarbons. In some embodiments, the mixture of volatile compounds may comprise a mixture of two or more volatile hydrocarbons selected from the group of methane, ethane, ethene, propane, propene, butane, isobutane, butenes, butadiene, pentanes and other volatile hydrocarbon liquids.

The mixture of volatile compounds may comprise at least one sulphur-containing and/or oxygen-containing compound, such as sulphur-containing and/or oxygen-containing gases and/or volatile liquids. The mixture of volatile compounds may comprise at least one alcohol, such as methanol and/or glycol.

In preferred embodiments, the mixture of volatile compounds comprises natural gas liquids (NGLs).

In especially preferred embodiments, the mixture of volatile compounds comprises liquid petroleum gas (LPG) LPG typically consists primarily of a mixture of propane and butane.

The mixture of volatile compounds may comprise a constant composition liquefied calibration mixture.

The pressurising fluid may comprise a gas, a pressurised gas and/or a compressed gas. In preferred embodiments, the pressurising fluid comprises an inert gas, such as helium gas.

The vessel may comprise a cylinder. In some embodiments, the vessel may be formed from at least one metal or alloy, such as aluminium or steel. In other embodiments, the vessel may be formed from at least one composite material, such as carbon fibre. In yet other embodiments the vessel may be formed from a polymeric material.

The collapsible container may comprise an at least partially deformable outer wall which may be deformed under pressure, for example under pressure exerted on it by a mixture of volatile compounds or a pressurising fluid. The volume of the collapsible container is therefore able to be increased or reduced through deformation of the outer wall.

The collapsible container may comprise a collapsible bag or pouch.

The collapsible container may be formed from at least one polymeric material, such as at least one plastics material. The collapsible container may be formed from a plastics material selected from the group of polyethylene, polypropylene, polyethylene terephthalate, polyamide, polyester and polyvinyl chloride, or any mixture or co-polymer thereof The collapsible container may comprise at least one substantially impermeable barrier or layer on the inside and/or outside surfaces thereof, in order to stop permeation of liquid components through the wall of the container. The at least one barrier or layer may comprise at least one metal layer, such as at least one layer of aluminium (for example aluminium foil).

In preferred embodiments, the collapsible container comprises biaxiallyoriented polyethylene terephthalate (BoPET) (preferably multi lave: BoPET); known under the trade name Misilarg. In especially preferred embodiments, the collapsible container comprises metallised BoPET (or multi-layer BoPET), such as BoPET with a layer of metal (preferably aluminium, such as aluminium foil) on the inside and/or outside surface thereof.

In some embodiments, the collapsible container may be formed from at least one metal or alloy, such as titanium or stainless steel.

In some embodiments, the collapsible container may be formed from at least one composite material.

The volatile compound valve may comprise a shut-off valve or a control valve. The pressurising fluid valve may comprise a shut-off valve or a control valve.

The valve assembly may comprise a pressurising fluid conduit, such as a pipe, in fluid communication with the inner vessel volume, and which has the pressurising fluid valve connected thereto or formed therein. In such embodiments, the pressurising fluid valve therefore controls the flow of pressurising fluid through the pressurising fluid conduit, i.e. into or out of the inner vessel volume of the sealable vessel.

The valve assembly may comprise a volatile compound conduit, such as a pipe, in fluid communication with the inner container volume, and which has the volatile compound valve connected thereto or formed therein. In such embodiments, the volatile compound valve therefore controls the flow of volatile compounds through the volatile compound conduit, i.e. into or out of the inner container volume of the collapsible container.

The valve assembly may comprise a pressure regulator, such as those commonly known in the art.

In some embodiments, a portion of the volatile compound conduit may extend into the inner vessel volume. In such embodiments, the portion of the conduit which extends into the inner vessel volume may be substantially non-deformable and/or non-collapsible. In other embodiments, the portion of the conduit which extends into the inner vessel volume may be substantially deformable and/or collapsible and may, for example, comprise the same material as the collapsible container.

In preferred embodiments, the portion of the conduit which extends into the inner vessel volume is deformable and/or bendable but not collapsible, e.g. the conduit can be bent and/or otherwise deformed, but cannot be substantially collapsed such that the volume within is closed off, in use. The portion may be formed from a polymeric material, such as polyether ether ketone, for example.

In other embodiments, the volatile compound conduit does not extend into the inner vessel volume. In such embodiments, the collapsible container may be connected to a wall of the sealable vessel at its opening.

In some embodiments, the collapsible container may be integrally formed with the volatile compound conduit and/or valve assembly. In other embodiments, the collapsible container may be connectable (i.e. detachable) to the volatile compound conduit and/or valve assembly.

The sealable vessel and/or valve assembly may be specifically manufactured for incorporation into the invention described herein.

However, in other embodiments, the sealable vessel and/or valve assembly may comprise a vessel, such as a cylinder, which has already been manufactured, for example a cylinder and/or valve assembly which has/have already been manufactured for use as part of, or already used as part of, a standard gas cylinder.

The design of the device of the invention is therefore advantageous as the sealable vessel may, in some embodiments, comprise a vessel, such as a cylinder, and/or a valve assembly which has either already been manufactured, or, if not, can be easily and cheaply manufactured using already-established manufacturing methods and equipment.

In embodiments wherein the sealable vessel and/or valve assembly have already been manufactured for another use, or have already been used for another purpose, the device of the invention may be assembled simply by retrofitting the valve assembly and/or sealable vessel with, as appropriate, a sealable vessel, a valve assembly (which may comprise an operably connected collapsible container) and/or, in appropriate embodiments (i.e. those comprising a collapsible container operably connectable/detachable to the valve assembly), a collapsible container.

According to a second aspect of the invention, there is provided a volatile compound mixture storage and dispensing device comprising a device of the first aspect of the invention, wherein a pressurising fluid is located within the inner vessel volume and a volatile compound mixture is located in the inner container volume, and wherein the pressure of the pressurising fluid is greater than the vapour pressure of the volatile compound mixture.

As the pressure of the pressurising fluid is greater than the vapour pressure of the volatile compound mixture, the volatile compound mixture is therefore present as a single liquid phase.

According to a third aspect of the invention there is provided a method of priming a device of the first aspect of the invention to provide a device of the second aspect of the invention, comprising filling the collapsible container with a volatile compound mixture and filling the inner vessel volume with a pressurising fluid such that the pressure of the pressurising fluid is greater than the vapour pressure of the volatile compound mixture.

In some embodiments, the inner vessel volume and collapsible container may be filled at substantially the same time.

In some embodiments, the method may comprise filling the collapsible container first, and subsequently filling the inner vessel volume.

In preferred embodiments, the method may comprise filling the inner vessel volume first, and subsequently filling the collapsible container. In such embodiments, the method may comprise filling the inner vessel volume with a pressurising fluid such that the pressure of the pressurising fluid is lower than the vapour pressure of the volatile compound mixture that the collapsible container is to be filled with, and subsequently filling the collapsible container, which increases the pressure of the pressurising fluid to above the vapour pressure of the volatile compound mixture (due to the decrease in available volume for the pressurising fluid).

In especially preferred embodiments, the method may comprise filling the inner vessel volume with a pressurising fluid such that the pressure of the pressurising fluid is greater than the vapour pressure of the volatile compound mixture that the collapsible container is to be filled with and subsequently filling the collapsible container. In such embodiments, the pressure of the pressurising fluid increases further as volatile compound mixture is filled with volatile compound mixture. Such embodiments are advantageous as they allow for an easy method of ensuring that the pressure of the pressurising fluid (assuming no leaks in the system) remains above the vapour pressure of the volatile compound mixture, no matter how much volatile compound mixture is present in the collapsible container, as the pressure of the pressurising will never fall substantially below its initial charging pressure.

In embodiments wherein the inner vessel volume is filled before the collapsible container, the method may comprise filling the collapsible container by applying a pressure or overpressure to the volatile compound mixture, which may be provided by a piston (such as a piston cylinder), for example. The pressure or overpressure may be required to overcome the pressure already being exerted on the collapsible container by the pressurising fluid.

According to a fourth aspect of the invention there is provided a method of at least partially dispensing a volatile compound mixture from a device of the second aspect of the invention comprising the steps of a) at least partially opening the volatile compound valve such that at least a portion of the volatile compound mixture flows out of the collapsible container, valve assembly and/or device; and b) maintaining the pressure of the pressurising fluid within the inner vessel volume above the vapour pressure of the volatile compound mixture within the collapsible container.

The method may comprise substantially completely depleting the device of the volatile compound mixture. In other embodiments, only a portion of the volatile compound mixture may be dispensed.

As volatile compound mixture is dispensed, the walls of the collapsible container begin to deform and collapse inwards under the influence of the pressure exerted by the pressurising fluid. As such, none of the volatile compound mixture within the collapsible container can enter the gaseous phase within the container, and so remains as a single liquid phase throughout the dispensing cycle.

In some embodiments, substantially all of the volatile compound mixture may be dispensed from the collapsible container and optionally also from the valve assembly. In other embodiments, only a portion of the volatile compound mixture may be dispensed from the collapsible container and optionally also from the valve assembly.

In some embodiments, the method may comprise adding extra pressurising fluid to the inner vessel volume over the depletion cycle to keep the pressure of the pressurising fluid above the vapour pressure of the volatile compound mixture.

However, in preferred embodiments, no further/additional pressurising fluid needs to be added to the inner vessel volume over the depletion cycle, as the initial overpressure of pressurising fluid is sufficient such that the pressure remains greater than the vapour pressure of the volatile compound mixture over the dispensing/depletion cycle.

According to a fifth aspect of the invention, there is provided an assembly comprising a valve assembly operably connected to a collapsible container.

The valve assembly and the collapsible container may be substantially as described in relation to the first aspect of the invention, and may comprise any suitable combination of features as described therein.

In some embodiments, the collapsible container may be attachable and/or detachable to/from the valve assembly.

Such an assembly may be fitted or retrofitted to a sealable vessel, such as a cylinder.

According to a sixth aspect of the invention, there is provided a kit comprising: a) a sealable vessel; b) a collapsible container; and c) a valve assembly comprising a pressurising fluid valve, and a volatile compound valve operably connectable to the collapsible container.

According to a seventh aspect of the invention, there is provided a kit comprising: a) a sealable vessel; and b) a valve assembly comprising a pressurising fluid valve, and a volatile compound valve operably connected to a collapsible container. l0

Detailed Description of the Invention

In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figures I a-c illustrate an embodiment of a device of the first and second aspects of the invention, in use in an embodiment of the method of the fourth aspect of the invention.

Figures la-c illustrate an embodiment of a device 100 of the first and second aspects of the invention in use in an embodiment of the method of the fourth aspect of the invention. The device 100 comprises a sealable vessel in the form of a sealable aluminium cylinder 101 which defines an inner vessel volume, a collapsible aluminium-lined MYLAR (RTM) container 103 disposed therein which defines an inner container volume, and a valve assembly 105 comprising a pressurising fluid conduit 106 in fluid communication with the inner vessel volume and connected to a pressurising fluid valve 107, and a volatile compound conduit 108 in fluid communication with the inner container volume and connected to a volatile compound valve 109. The volatile compound conduit 108 comprises a substantially nondeformable and/or non-collapsible portion 110 which extends into the inner vessel volume. The device 100 further comprises a pressurising fluid 102, which may for example be helium gas, contained within the inner vessel volume. and a volatile compound mixture 104, for example LPG, contained within the collapsible container 103. The volatile compounds mixture 104 is compressed into a single liquid phase within the collapsible container 103 by pressure exerted on the outside of the collapsible container 103 by the pressurising fluid 102.

In order for the device 100 to be primed for use (i.e. primed from an embodiment of a device of the first aspect of the invention to an embodiment of a device of the second aspect of the invention), pressurising fluid 102 (such as helium gas) is pumped through the pressuring fluid conduit 106 (with the pressurising fluid valve 107 open) into the inner vessel volume of the sealable vessel 101, and the mixture of volatile compounds 104 is pumped through the volatile compound conduit 108 (with the volatile compound valve 109 open) into the inner container volume of the collapsible I1 container 103. The pressure of pressurising fluid 102 exerted on the outside of the collapsible container 103 is controlled so as to be above the vapour pressure of the volatile compound mixture 104 within the collapsible container 103 (i.e. there is an overpressure). The filling of the two components can be performed in any order, but preferably comprises first filling the inner vessel volume and subsequently filling the collapsible container. The valves 107, 109 are then closed and the device 100 is ready for use.

In use during a depletion cycle as illustrated in Figures la-c, the volatile compound valve 109 is at least partially opened, and the volatile compound mixture 104 begins to flow out of the collapsible container 103 along the volatile compound conduit 108. As the volume of the volatile compound mixture 104 in the collapsible container 103 gradually depletes, the walls of the collapsible container 103 begin to deform and collapse inwards under the influence of the pressure exerted by the pressurising fluid 102, as shown in Figure lb. Upon further depletion, the collapsible container collapses further, as shown in Figure 1 c.

As the collapsible container 103 collapses, its volume is thus decreased. Additionally, the pressurising fluid 102 pressure is maintained above the vapour pressure of the volatile compound mixture 104, which is preferably achieved by setting the initial pressure of the pressurising fluid 102 high enough such that it remains above the vapour pressure of the volatile compound mixture 104 over the complete depletion cycle. These two factors combined ensures that none of the volatile compound mixture 104 enters the gaseous phase, and so the mixture 104 remains substantially as a single liquid phase during the complete depletion.

The above embodiment is described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMSA device for storing a liquefied calibration mixture in substantially a single liquid phase and dispensing it therefrom, comprising: a sealable vessel defining an inner vessel volume; a collapsible container, defining an inner container volume, disposed within the inner vessel volume; and a valve assembly comprising a pressurising fluid valve in fluid communication with the inner vessel volume and a volatile compound valve in fluid communication with the inner container volume.
2. A volatile compound mixture storage and dispensing device comprising a device according to claim 1, wherein a pressurising fluid is located within the inner vessel volume and a volatile compound mixture is located in the inner container volume, and wherein the pressure of the pressurising fluid is greater than the vapour pressure of the volatile compound mixture.
3. A device as claimed in claim 1 or 2, wherein the mixture of volatile compounds comprises a mixture of two or more volatile hydrocarbons selected from the group of methane, ethane, ethene, propane, propene, butane, isobutane, butenes, butadiene and pentanes.
A device as claimed in claim 3, wherein the mixture of volatile compounds comprises liquid petroleum gas.
5. A device as claimed in any preceding claim, wherein the collapsible container is formed from at least one polymeric or plastics material, at least one metal, at least one alloy and/or at least one composite material.
A device as claimed in claim 5, wherein the collapsible container comprises biaxially-oriented polyethylene terephthalate (BoPET).
7. A device as claimed in any preceding claim, wherein the sealable vessel comprises a cylinder and the collapsible container comprises a collapsible bag or pouch.
A device as claimed in any preceding claim, wherein the valve assembly comprises a pressurising fluid conduit in fluid communication with the inner 9. 10. 11. 12. 13. 14. 15.vessel volume, which has the pressurising fluid valve connected thereto or formed therein, and a volatile compound conduit in fluid communication with the inner container volume, which has the volatile compound valve connected thereto or formed therein.
A method of priming a device as claimed in claim 1 or any one of claims 3 to 8 when dependent on claim 1, comprising filling the collapsible container with a volatile compound mixture and filling the inner vessel volume with a pressurising fluid such that the pressure of the pressurising fluid is greater than the vapour pressure of the volatile compound mixture.
A method as claimed in claim 9, wherein the method comprises filling the inner vessel volume first, and subsequently filling the collapsible container.
A method as claimed in claim 10, wherein the method comprises filling the inner vessel volume with pressurising fluid such that the pressure of the pressurising fluid is above the vapour pressure of the volatile compound mixture that the collapsible container is to be filled with, and subsequently filling the collapsible container with the volatile compound mixture.
A method as claimed in claim 11, wherein the method comprises filling the collapsible container by applying a pressure or overpressure to the volatile compound mixture.
A method of at least partially dispensing a volatile compound mixture from a device as claimed in any one of claims 2 or claims 3 to 8 when dependent on claim 2, comprising the steps of; a) at least partially opening the volatile compound valve such that at least a portion of the volatile compound mixture flows out of the collapsible container, valve assembly and/or device; and b) maintaining the pressure of the pressurising fluid within the inner vessel volume above the vapour pressure of the volatile compound mixture within the collapsible container.
A method as claimed in claim 13, wherein the method comprises adding no additional pressurising fluid to the inner vessel volume.
A kit comprising: a) a sealable vessel; b) a collapsible container; and c) a valve assembly comprising a pressurising fluid valve, and a volatile compound valve operably connectable to the collapsible container.
16. A kit comprising: a) a sealable vessel; and b) a valve assembly comprising a pressurising fluid valve, and a volatile compound valve operably connected to a collapsible container.