AU731003B3

AU731003B3 - A system and method for removing a gas from a plurality of vessels

Info

Publication number: AU731003B3
Application number: AU72273/00A
Authority: AU
Inventors: Damon Howes; Kim McFarland; Jon Offszanka; Michael Patterson
Original assignee: Water Corp
Current assignee: Water Corp
Priority date: 1999-11-19
Filing date: 2000-12-15
Publication date: 2001-03-22
Anticipated expiration: 2006-11-16

Description

THE PATENTS ACT 1990 PETTY PATENT SPECIFICATION (original) NAME OF APPLICANT: ADDRESS OF APPLICANT: ACTUAL INVENTOR: ADDRESS FOR SERVICE: WATER CORPORATION PO Box 100 Leederville, Western Australia, 6902

AUSTRALIA

DAMON HOWES, KIM McFARLAND, JON OFFSZANKA MICHAEL

PATTERSON

LORD COMPANY Patent Trade Mark Attorneys 4 Douro Place West Perth, Western Australia, 6005

AUSTRALIA

Petty Patent Specification for the invention entitled: "A SYSTEM AND METHOD FOR REMOVING A GAS FROM A PLURALITY OF VESSELS" The following statement is a full description of this invention, including the best method of performing it known to me/us:

TITLE

"A SYSTEM AND METHOD FOR REMOVING A GAS FROM A PLURALITY OF VESSELS" FIELD OF THE INVENTION The present invention relates to a system and method for removing a gas from a plurality of vessels and, in particular, to a system and method of removing chlorine from a plurality of vessels.

It is known to use chlorine for industrial purposes as an oxidant, bleach, reactant or disinfectant. Chlorine for use in such purposes is commonly transported and stored in pressure vessels as liquefied gas under pressure.

Several methods have commonly been used to withdraw chlorine from a vessel, one method being to draw chlorine gas from the vapour space above'the liquid chlorine in the vessel, additional liquid chlorine simultaneously vapourising to replace the withdrawn chlorine gas. In order for the liquid chlorine to vapourise, heat must be supplied from the surrounding environment across the walls of the pressure vessel.

However, since heat is supplied from the surrounding environment to vapourise the liquid chlorine, if the rate of withdrawal of chlorine gas from the vessel becomes too high, the vessel will begin to drop in temperature and, eventually, ice will form on the vessel. As a consequence, pressure inside the vessel will drop, the amount of chlorine gas available for withdrawal will reduce and the maximum rate of chlorine withdrawal will reduce.

In order to overcome the above mentioned disadvantage, an alternative method has been used wherein liquid chlorine is drawn from the vessel and subsequently evaporated at a remote location. However, while this alternative method overcomes the above mentioned disadvantage, a consequence of handling liquid chlorine is that significantly high operational and maintenance costs are involved and the public and the environment are exposed to significantly higher risks.

Instead of drawing liquid chlorine from the vessel, a further alternative method has been used to overcome the above mentioned disadvantage. This method involves connecting a plurality of vessels together so that the maximum rate of chlorine withdrawal from each vessel is not exceeded and ice does not form on any of the vessels, providing a pressurised manifold, and forcing chlorine gas from the vessel under positive pressure. However, the use of such positive pressure methods for removing chlorine from a vessel dramatically increases the risk of a chlorine leak and therefore the risk to the public and the environment.

The present invention seeks, therefore, among other things, to provide a system and method for removing a gas from a vessel which overcomes at least one of the above mentioned disadvantages.

SUMMARY OF THE PRESENT INVENTION In accordance with an aspect of the present invention, there is provided a gas withdrawal system comprising a plurality of vessels arranged to contain gas, a drawing means arranged to withdraw gas from the vessels and control means, characterised in that each vessel has a respective actuated valve operatively associated with the vessel such that when the respective actuated valve is in an open position withdrawal of gas from a vessel via the drawing means is permitted and when the respective actuated valve is in a closed position withdrawal of gas from a vessel via the drawing means is prevented, each vessel also having a respective sensing means, each sensing means being arranged to generate a first signal when the gas pressure in the corresponding vessel reaches a predetermined low level, means being provided for transmitting each first signal to the control means, wherein the control means is arranged to generate a second signal in response to the first signal to effect closure of the actuated valve of the corresponding vessel when gas pressure in the corresponding vessel reaches the predetermined low level.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic diagram of a gas removal system in accordance with the present invention; and Figure 2 is a flow chart indicating operation of a part of the system shown in Figure 1.

DESCRIPTION OF THE INVENTION The following embodiment of the invention will be described in relation to removing chlorine from a plurality of vessels, although it will be appreciated that the invention is also applicable to other gases in particular volatile gases.

Referring to Figure 1, there is shown a gas removal system 10 which includes a plurality of vessels, in this example first, second, third and fourth vessels 12, 14, 16 and 18 respectively, and an outlet pipe 20 which receives chlorine gas from the vessels 12, 14, 16, 18 through a manifold 22. The outlet pipe 20 is connected to negative pressure generating means, for example a vacuum pump (not shown).

The first, second, third and fourth vessels 12, 14, 16, 18 include respective first, second, third and fourth vessel outlet valves 24, 26, 28 and 30 respectively, each of the vessel outlet valves being provided on a vessel and being manually operable to selectively open or close the vessel.

Adjacent the first, second, third and fourth vessel outlet valves 24, 26, 28, 30 are respectively provided first, second, third and fourth vacuum regulators 32, 34, 36 and 38 respectively.

Adjacent the first, second, third and fourth vacuum regulators 32, 34, 36, 38 are respectively provided first, second, third and fourth actuated valves 40, 42, 44 and 46 respectively, each actuated valve being arranged to selectively open or close the communication path between the adjacent vacuum regulator 32, 34, 36, 38 and the outlet pipe The vacuum regulators 32, 34, 36, 38 include respective first, second, third and fourth pressure switches 48, 50, 52 and 54 respectively, and respective first, second, third and fourth vacuum activated valves 56, 58, 60 and 62 respectively. Each pressure switch 48, 50, 52, 54 is adapted to generate a signal indicative that the respective vessel is substantially empty when the pressure in the respective vessel falls below a predeterminded level. Each vacuum activated valve 56, 58, 60, 62 operates such that the vacuum activated valve opens when the pressure in the outlet pipe 20 is sufficiently low relative to atmospheric pressure.

The system 10 also includes control means in the form of a control unit 64. The control unit 64 includes an input 66 for receiving information from a user, a plurality of communication lines 68 for transferring information between the control unit 64, the first, second, third and fourth pressure switches 48, 50, 52, 54 and the first, second, third and fourth actuated valves 40, 42, 44 and 46. The control unit 64 also includes an output 70 for providing information to a user, for example information as to the status of each vessel or whether a fault has been detected in the system General operation of the system 10 is shown in the flow chart 72 in Figure 2.

By virtue of the input 66, a user enters information into the control unit 64 as to which vessels are disabled and therefore not to be connected to the output pipe 20, for example because the vessel is empty, and which vessels are available since they contain chlorine. The user also enters the number of vessels which are desired to be simultaneously online and therefore connected with the outlet pipe 20. Once this information has been entered into the control unit 64, the control unit 64 selects the desired number of vessels to be simultaneously online from the available vessels and opens the actuated valves associated with the selected vessels by sending a signal from the control unit 64 to the appropriate actuated valves via the appropriate communication lines 68.

The control unit 64 attributes a status to each vessel which may be either 'disabled' wherein the operator has indicated that the vessel is disabled, for example because the vessel is empty, 'online' wherein the vessel is in communication with the outlet pipe 'standby' wherein the vessel is not disabled, contains chlorine and the vessel is not in fluid communication with the outlet pipe 20, or 'empty' wherein the vessel does not include chlorine but has not been given 'disabled' status by a user.

Chlorine is then drawn from the online vessels to the outlet pipe 20 by the vacuum pump. When a vessel becomes substantially empty the pressure in that vessel reduces.

The pressure in each online vessel is continuously sensed by the respective pressure switches of the vessels in order to determine whether the vessels are substantially empty. Signals indicative of whether the chlorine vessels are substantially empty or not are sent to the control unit 64 via the communication lines 68. When the pressure in a vessel reaches a predetermined low level indicative that the vessel is empty or substantially empty, a signal is sent from the control unit 64 to the respective actuated valve of the empty or substantially empty vessel so as to close the actuated valve of the vessel. The control unit 64 then searches for a further available vessel having standby status and a signal is sent from the control unit 64 to the respective actuated 6 valve of the standby vessel so as to cause the actuated valve to open. It will be understood that since this vessel contains chlorine and is now in fluid communication with the outlet pipe 20, the status of the vessel changes from 'standby' to 'online'.

It will be appreciated that although four vessels are indicated in the above embodiment, it is envisaged that the invention is applicable to other numbers of vessels.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

1. A gas withdrawal system comprising a plurality of vessels arranged to contain gas, a drawing means arranged to withdraw gas from the vessels and control means, characterised in that each vessel has a respective actuated valve operatively associated with the vessel such that when the respective actuated valve is in an open position withdrawal of gas from a vessel via the drawing means is permitted and when the respective actuated valve is in a closed position withdrawal of gas from a vessel via the drawing means is prevented, each vessel also having a respective sensing means, each sensing means being arranged to generate a first signal when the gas pressure in the corresponding vessel reaches a predetermined low level, means being provided for transmitting each first signal to the control means, wherein the control means is arranged to generate a second signal in response to the first signal to effect closure of the actuated valve of the corresponding vessel when gas pressure in the corresponding vessel reaches the predetermined low level.

2. A gas withdrawal system according to Claim 1, characterised in that, in use, the plurality of vessels comprises a first number of vessels arranged with their respective actuated valves in an open position, and a second number of vessels arranged with their respective actuated valves in a closed position, and wherein the control means is also arranged to generate a third signal in response to the first signal to effect opening of the actuated valve of one of the second number of vessels when gas pressure in one of the first number of vessels reaches the predetermined low level.

3. A gas withdrawal system according to any one of the preceding claims, characterised in that the control means is arranged to receive instructions from a user and subsequently generate a specific signal to close a particular one of the actuated valves.