Gas separation: processes – With control responsive to sensed condition – Concentration sensed
Patent
1998-08-21
2000-06-20
Spitzer, Robert
Gas separation: processes
With control responsive to sensed condition
Concentration sensed
95 98, 95105, 95130, 96111, 96130, 96144, B01D 53047
Patent
active
060773316
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF INVENTION
This invention relates to a molecular sieve type gas separation apparatus for separating product gas from a gas stream. A prior art molecular sieve type gas separation apparatus is described in prior European specification 0129304 and comprises in that example, three sieve beds which each contain a material which adsorbs nitrogen and other gases from a gas supply whilst permitting product gas, containing oxygen in that example, to pass from the apparatus and be used in an oxygen breathing system for example for an air crew in an aircraft.
In prior specification EP0129304, there is described an apparatus in which the operation of each sieve bed is cycled. In each cycle, each sieve bed is subjected to an adsorption charge phase in which nitrogen primarily, is adsorbed by the sieve bed, and a desorption regeneration phase in which the nitrogen, which is non product gas, is desorbed from the sieve bed. This is achieved, as is well known in the art, by introducing the gas supply to the sieve bed at a first pressure during the adsorption charge phase, and during the desorption regeneration phase, the bed is subjected to a second pressure, lower than the first.
For an air crew, it is necessary to provide increasing concentrations of oxygen in the product gas for breathing, with increasing altitude. In prior specification EP0129304, the concentration of oxygen in the product gas is varied by adjusting the overall cycle time for the or each sieve bed whilst the relative durations of the adsorption charge and desorption regeneration phases are retained substantially constant.
Although the prior art apparatus works satisfactorily in practice, there is a requirement to make the apparatus more effective.
Experiments into the operation of sieve beds have shown how the adsorbent material is better cleansed of the adsorbed gas by increasing the duration of the desorption regeneration phase in each cycle.
According to a first aspect of the invention we provide a molecular sieve type gas separation apparatus for separating product gas from a gas supply, the apparatus comprising at least one sieve bed which during an adsorption charge phase of a cycle, adsorbs non product gas in the gas supply, and in a desorption regeneration phase of the cycle desorbs the previously adsorbed non product gas, the apparatus further comprising outlet means to which product gas is delivered during the adsorption charge phase, and outlet means for non product gas during the desorption regeneration phase, sensor means responsive to the concentration of a constituent in the product gas, and control means to switch the operation of the sieve bed between the adsorption charge and desorption regeneration phases, characterised in that the control means is adapted to adjust the duration of adsorption charge phase relative to the duration of the desorption regeneration phase in each cycle.
Thus the applicants have found that by adjusting the duration of adsorption charge phase relative to the duration of desorption regeneration phase in each cycle of the sieve bed (or beds) improved control over the concentration of desired constituent in the product gas can be achieved.
Whereas in prior European specification 0129304 the cycle time is varied during an operation period, whilst the relative durations of adsorption charge and desorption regeneration phases are maintained generally constant, in the apparatus of the invention the overall cycle time for the or each sieve bed may be maintained generally constant during an operation period, whilst the relative durations of adsorption charge and desorption regeneration phases in each cycle are adjusted.
The invention provides various advantages. Particularly, the deviation of concentration of desired constituent in the product gas from a desired level can be greatly reduced in general and thus the risk of producing product gas with a lower or higher than acceptable concentration of desired constituent therein, is greatly reduced.
Furthermore, particularly where low concentrations of d
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Normalair-Garrett (Holdings) Limited
Spitzer Robert
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