IE20030546A1 - Filling gas cylinders - Google Patents

Abstract

Carbon dioxide is filled into gas cylinders and used for beer and soft drink dispense and other food applications either as a single component or as a compressed gas mixture. If contaminants are introduced into gas cylinders during the filling process the quantity of these contaminants can build-up as the cylinder is refilled. According to this invention a fill cycle for filling gas cylinders (2) with carbon dioxide includes a cleaning step in which any residual components present in the cylinder (2) are flushed out and removed before the cylinder is filled. <Figure 1>

Description

Carbon dioxide is filled into gas cylinders and used for beer and soft drink dispense and other food applications in, for example, packaging, either as a single component or as a compressed gas mixture of various specifications depending upon the application. There are in place specifications and standards to prevent crosscontamination in the supply of bulk carbon dioxide and it would be desirable to ensure that carbon dioxide, and mixed gases including carbon dioxide, filled into cylinders met specified quality standards.

In order to improve both quality and safety it is now commonplace to fit residual pressure valves to gas cylinders. These provide an integral combination of nonreturn valve and a valve which maintains a small positive pressure when the cylinder is empty. This improves safety by ensuring that water or other liquid cannot simply enter the cylinder from the system to which it is connected in use or the atmosphere and thus helps to prevent corrosion. Residual pressure valves however cannot prevent contaminants from being filled into the cylinders during their filling, or from building up within a liquid carbon dioxide cylinder by distillation. The problem is exacerbated by illicit fillers who offer a refilling service and deal directly with pubs and other retail outlets. This gives rise to major safety implications as well as quality concerns. If contaminants are introduced into gas cylinders during the filling process the quantity of these contaminants can build-up as the cylinder is refilled. When carbon dioxide is withdrawn solely from the vapour phase, as is common in the case of cylinders for food and beverage use, equilibrium conditions can be rapidly and substantially altered causing the liquid carbon dioxide within the cylinder to boil. Carbon dioxide boils at a different temperature from that of the contaminants and, as a consequence, fractional distillation takes place //-/—I__j r- ____s IE 0 3 05 4 6 within the cylinder. The magnitude of the changes in level vary from component to component and, as a function of instantaneous equilibrium conditions. Some typical examples of the concentration ratios in liquid carbon dioxide or carbon dioxide vapour are given in the following table by way of demonstration.

LIQUID CO2 CO2 VAPOUR WATER 4 1 BENZENE 8 1 OXYGEN 1 12 METHANE 1 18 The residual levels of some components build up exponentially in the liquid whilst the level of others exponentially reduce from an initially high level in the gas phase. The actual levels of each component are modified again each time that the cylinder is refilled and are a function of the residual volume left in the cylinder before it is refilled, the residual contaminants, and the composition of the liquid carbon dioxide introduced into the cylinder during refilling.

At present cylinders are typically maintained horizontal or erect when being handled at a filling station and are simply placed in their horizontal or erect position on a weigh scale, have a fill-hose attached to their gas inlet and outlet and then, with the valve on the cylinder open, liquid carbon dioxide is introduced into the cylinder until a predetermined fill weight has been achieved. At that point the introduction of carbon dioxide is stopped, the cylinder valve closed, the fill hose vented and then removed.

According to this invention a fill cycle for filling gas cylinders with carbon dioxide includes a cleaning step in which any residual components present in the cylinder are flushed out and removed before the cylinder is filled. ΙΕΟ 3 05 4 6 As part of this cleaning cycle the cylinders are preferably mounted in an inverted state with the base of the cylinder above the neck portion carrying the cylinder valve and at a height sufficient to allow liquid to drain freely past the shoulder of the cylinder. With the cylinder mounted in this position the valve on the cylinder is opened and any residual pressure valve also opened. This allows any liquid within the cylinder to drain away and vents the cylinder to atmosphere pressure. Preferably liquid carbon dioxide is then introduced into the inside of the cylinder. This will jet into the cylinder through the valve in the form of a spray, to wash the inside wall of the cylinder and again this liquid carbon dioxide is allowed to drain away.

The cylinder may be left in the inverted position for filling after this cleaning operation or be filled in the normal.way. However it is preferred that the cylinders are both washed and filled at the same single station and, in this case, it may be convenient to refill the cylinders whilst in their inverted position. This is especially true when the cylinders are to be filled with a mixed gas including carbon dioxide and, in this case, preferably the cylinders are first part-filled with the filling of carbon dioxide and then the remaining gas or gases introduced into the cylinder whilst it is held in the inverted position. This causes a thorough mixing of the components and avoids the need for any subsequent treatment such as, rolling the cylinders, to cause mixing of the components before use.

A particular example of a method in accordance with this invention will now be described with reference to the accompanying drawings; in which:Figure 1 is a schematic diagram of the filling system; Figure 2 is a side elevation of the cylinder cradle showing it in its two alternative positions and carrying a range of sizes of cylinder; Figure 3 is a plan of the cylinder cradle; and, Figure 4 is a front elevation of the cylinder cradle.

IE 0 3 05 4 6 The apparatus comprises a pivoted cradle 1 for holding a gas cylinder 2 and raising the gas cylinder 2 between a horizontal and an inverted position. The cradle 1 and all of its associated equipment is mounted on the pan of a weigh scale 3 supported on load cells (not shown) . The apparatus also includes a supply hose 4 indicated only in dotted lines in Figure 1 and connected to a block 5 also mounted on the pan of the weigh scale 3 . The block 5 is also connected to a pipe line 6 including an elongate hairpin portion 7 which lies in a substantially horizontal plane. The hairpin portion 7 is, typically formed from small diameter stainless steel tube having an internal diameter of typically 6 mm and having a length of around %m. Changes in pressure inside the flexible hose 4 lead to changes in forces exerted between its ends. However, since one end is connected to the cylinder 2 which is housed on the pan of the weigh scale 3 and the other end is anchored to the block 5 which is also mounted on the of the weigh scale pan 3 changes in pressure within the flexible hose 4 have no effect whatsoever on the weight recorded by the weigh scale 3. Since the weigh scale 3 includes load cells the movement of the scale pan 3 is imperceptible, however, the hairpin arrangement 7 provides sufficient flexibility to ensure that the connection of the pipeline 6 to the scale pan 3 has no measurable effect on the weight recorded by the weigh scale 3.

The system also includes a motorised carbon dioxide supply valve 8, drain valve 9, pump 10 and a bulk tank 11 containing liquid carbon dioxide. The weigh scale 3 and motorised valves 8 and 9 are connected to a control system 12 .

The cradle 1, as shown more clearly in Figures 2, 3 and 4 includes a double row ball conveyor 20 which is connected via pivots 21 to a frame 22, a pair of arms 23, connected to the cradle 1 are joined at their free ends by a rod 24. A pneumatic piston and cylinder assembly 25 is connected and acts between the frame 22 and the rod 24. By IE 0 3 05 4 6 actuating the pneumatic piston and cylinder assembly 25 to withdraw the piston rod into the cylinder the cradle 1 is caused to pivot around the pivots 21 to raise the base of a gas cylinder 2 to an angle such as shown in Figure 2 where the base of the cylinder 2 is raised to a sufficient height above the neck portion to allow liquid to drain freely past the shoulder of the cylinder. The cradle 1 also includes an abutment 26 located at the right hand end of the ball conveyor 20 as shown in Figure 2, against which the shoulder of the gas cylinder 2 is held when the cylinder is in its raised position. The cradle may also include a cylinder clamp 28 shown most clearly in Figure 4.

A cylinder 2 is placed horizontally onto the cradle 1. The filling hose 4 is then connected to a valve 30 (Figure 2) on the neck of the cylinder. The fill hose 4 may include a probe on its end to open any residual pressure valve forming part of the valve 30. The pneumatic piston and cylinder assembly 25 is then actuated to raise the base of the cylinder 2. With the cylinder in this position and with the valve 30 of the cylinder 2 open, the motorised valve 9 is then opened and any liquid contents within the cylinder 2 drain to waste via the hose 4 and valve 9. Any liquid contents within the cylinder fall by gravity and are also driven out by any residual pressure within the cylinder. Any residual pressure is also vented to atmospheric via the valve 9. As an option the cylinder 2 can also, at this point, be connected to a vacuum pump (not shown) to remove any residual gas and contaminants.

The valve 9 is then closed and valve 8 opened to jet a small amount of liquid carbon dioxide into the cylinder to rinse it. The valve 8 is then closed and valve 9 opened again to drain the liquid carbon dioxide used for rinsing the inside of the cylinder 2 to waste. The valve 9 is then closed.

The output from the weigh scale 3 is then used as the tare weight of the empty cylinder and valve 8 opened and the cylinder 2 filled with liquid carbon dioxide from the IE Ο 3 05 4 6 bulk tank 11 via the pump 10 until the weigh scale 3 indicates the correct fill weight. The valve 8 is then closed and the pump stopped. The cradle 1 is lowered to its horizontal position by operating the pneumatic piston and cylinder assembly 25, the valve 30 on the end of the cylinder closed and then the valve 9 opened to vent the carbon dioxide from the fill hose 4 and hairpin 7. The fill hose 4 is then removed from the cylinder 2 and the filled cylinder 2 removed from cradle 1.

Claims (8)

1. A fill cycle for filling gas cylinders with carbon dioxide including a cleaning step in which any residual components present in the cylinder are flushed out and removed before the cylinder is filled.

2. A fill cycle according to claim 1, in which the cylinders are mounted in an inverted state with their base above their neck portion carrying the cylinder valve and at a height sufficient to allow liquid to drain freely past the shoulder of the cylinder.

3. A fill cycle according to claim 2, in which any residual pressure valve on the cylinder is opened when the cylinder is in its inverted state.

4. A fill cycle according to any one of the preceding claims, in which liquid carbon dioxide is jetted into the inside of the cylinder to wash the inside wall of the cylinder and is allowed to drain away.

5. A fill cycle according to any one of the preceding claims, in which the cylinders are both washed and filled at the same single station.

6. A fill cycle according to claim 5 in which the cylinders are refilled whilst in their inverted position.

7. A fill cycle according to claim 6 in which, when the cylinders are to be filled with a mixed gas including carbon dioxide, the cylinders are first part-filled with the filling of carbon dioxide and then the remaining gas or gases introduced into the cylinder whilst it is held in the inverted position

8. A fill cycle substantially as described with reference '* J to the accompanying drawings.