PROCESS FOR FILLING GAS STORAGE CONTAINER

A gas storage container, such as a gas cylinder, is filled with a gas mixture comprising a first gas and a second gas under pressure by feeding a liquid/solid mixture comprising liquefied first gas and solidified second gas into the gas storage container; closing the gas storage container to the passage of gas into or out from the container; and allowing said liquefied first gas and said solidified second gas to become gaseous within said closed gas storage container. Such a process is easier and more energy efficient as compared to direct compression processes, and is safer and results in less wastage as compared to direct liquid injection processes.

RegardingFIG. 1, a gas cylinder2has an outer vessel4defining an interior space6for holding gas under pressure. The outer vessel4is made from steel and has an opening8for receiving a fluid flow control unit10for controlling fluid flow into and out of the cylinder2. The fluid flow control unit10has a fill inlet12suitable for filling a liquid/solid mixture of a liquefied first gas and a solidified second gas into the cylinder, with a pressure cap14, and a customer outlet16having a control valve18. The fluid flow control unit10also has a pressure relief valve20.

An inner vessel22made from aluminium is provided entirely within the bottom half of the interior space6. The inner vessel22defines a part24of the interior space for holding cryogenic fluid26in spaced relationship with respect to the outer vessel. A support28provides the spaced relationship between the inner vessel22and the outer vessel4. The inner vessel22has a mouth30for receiving the liquid/solid mixture from the fluid flow control unit10via a conduit32, or dip tube, made from aluminium. The end34of the conduit32extends below the mouth30of the inner vessel22, thereby ensuring that spray from the conduit32is caught by the inner vessel22. The end34of the conduit32does not usually extend so far below the mouth30of the inner vessel22such that it would be below the surface of the liquid/solid mixture26after the inner vessel22has been charged with the mixture.

The mouth30is open to the remaining part of the interior space6and thereby provides fluid flow communication between the inner vessel22and the remaining part of the interior space6.

The cylinder2is filled by removing the pressure cap14and feeding liquid/solid mixture down the conduit32into the inner vessel22. The control valve18on the customer outlet16may be open to allow displaced gas to escape from the cylinder2.

The amount, e.g. volume or mass, of the liquid/solid mixture to be fed to the cylinder2is pre-determined based on the target pressure of the gas in the cylinder (and, hence, the volume of the cylinder, the densities of the liquefied first gas and solidified second gas, and the gas mixture), and feed to the cylinder is metered to ensure that the correct amount of cryogenic fluid is added. Once the required amount of the liquid/solid mixture has been added to the cylinder2, the inlet12is closed off with the pressure cap14, and the control valve18in the customer outlet16is closed. The mixture is then allowed to become gaseous by evaporation and where appropriate by sublimation, thereby filling the cylinder2with gas to the desired pressure.

Example

A 23.5 L steel gas cylinder having a large (40 mm) neck was equipped with a fluid flow control unit having a cryogenic fluid filling aperture and tube, a customer valve and a safety relief valve. A Mylar™ bag was connected to the liquid filling tube and provided inside the cylinder. The resultant cylinder and internals were similar to the type described in U.S. Pat. No. 3,645,291.

A slurry of 97 wt % liquid argon/7 wt % solid carbon dioxide was prepared by spraying liquid carbon dioxide from a nozzle on to the surface of a vented tank of liquid argon. After sufficient carbon dioxide had been added, the resultant slurry was checked for free-flowing characteristic and colour. An opaque white watery liquid was achieved.

The system was pre-cooled with LIN before filling. After pre-cooling, about 4.2 litres (6 litres total with a loss of 1.8 litres due to blow back and spitting, etc.) of the mixture was poured through the central tube in a coaxial nozzle into the fill tube and the bag. The customer valve was open when the mixture was poured in, and then both the customer valve and the liquid filling aperture closed after the mixture had been poured in. The pressure and temperature of the cylinder were then logged over time. Carbon dioxide content was measured every few hours over several days until it returned to an equilibrium value of 7%.

The graph inFIG. 2depicts how the observed pressure inside the cylinder increases over time as the LAr/CO2slurry becomes gaseous. The pressure inside the cylinder increases rapidly over the first 30 seconds due primarily to evaporation of the LAr from the slurry. After about 30 seconds, substantially all of the LAr has evaporated. The pressure continues to increase (albeit at a lower rate) due to sublimation of the solid CO2left over from the slurry after the liquid argon has evaporated.

The graph inFIG. 2also indicates that the temperature at the coldest point of the cylinder (the middle) does not drop below −20° C. at any point during the filling process. These results indicate that the outer vessel of the cylinder can be made from materials such as steel which tend to be less resistant to cryogenic temperatures.

The Inventors expect that the loss of mixture due to blow back and spitting, etc. would be significantly reduced if the mixture is charged to an internal can in the base of the cylinder.

Advantages of preferred embodiments of the present invention include:Easier and more rapid filling of a gas storage container with a gas mixture when compared to direct compression processes;More energy efficient filling of gas storage containers when compared to direct compression processes;More reliable and safer filling of gas storage vessels when compared to direct liquid injection processes; andLess wastage of liquefied gases during filling of gas storage containers.

It will be appreciated that the invention is not restricted to the details described above with reference to the preferred embodiments but that numerous modifications and variations can be made without departing form the spirit or scope of the invention as defined in the following claims.