Gas separation: processes – Solid sorption – With plural indirect heat transfer steps on solid sorbent or...
Patent
1994-11-08
1996-05-28
Spitzer, Robert
Gas separation: processes
Solid sorption
With plural indirect heat transfer steps on solid sorbent or...
95117, 95130, 96126, 96132, B01D 53047
Patent
active
055207219
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to processes for the production of a gas by separation by adsorption of a gaseous mixture containing this gas in at least one adsorption unit comprising, associated in series, a first adsorbent bed for the retention of water and a second adsorbent bed for separation, comprising a gas production step in which the gaseous mixture passes successively through the first and second beds.
BACKGROUND OF THE INVENTION
It is known that in the processes of this type, so-called "PSA" (Pressure Swing Adsorption), there is progressively formed, in operation, a temperature gradient in the separation adsorbent bed, which results particularly, at the end of about ten hours of operation, in the creation of a particularly cold zone in the upstream portion of the separation bed, which greatly affects the production output during cyclic operation under vacuum or pressure, and this the more so as the operating pressure is higher (greater than 5.times.10.sup.5 Pa). To overcome this drawback, it has been proposed to heat the gaseous mixture to be separated, as described in U.S. Pat. No. 3,973,931 or to immerse in the upstream portion of the adsorbent bed a heat source, as described in the above-mentioned patent, or, more recently, in EP-A-502.627 which describes also an adsorbent unit of the type defined in the first paragraph. The heating of the gaseous mixture gives satisfactory results for very small installations but becomes inoperative, and moreover prohibitive, for installations with industrial capacity (greater than 0.5 ton of production gas per day). The inclusion in the adsorbent bed of effective heating means considerably increases the cost of production.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a process permitting in a simple and effective manner, involving only a small increase in the cost of production and low operating costs, substantially avoiding the formation of a cold zone, particularly in the processes of separation for the production of oxygen under a pressure greater than 7.times.10.sup.5 Pa.
To do this, according to one characteristic of the invention, the process comprises the steps of providing a portion of the intermediate gas passage, typically of a short length, establishing communication between the first and second beds and applying to this intermediate passage portion a heat flow, preferably controlled and of reduced intensity, to raise its temperature, typically to a level not less than -20.degree. C., preferably not less than 0.degree. C.
According to other characteristics of the invention: exchange relation with a source of heat, for example a gas and/or a thermal generator; greater than 7.times.10.sup.5 Pa, for the production of oxygen under pressure.
The present invention also has for its object providing an adsorption unit for practicing the above process, of the type comprising, in series in a production circuit of the gas to be separated, a gaseous mixture inlet, first and second adsorbent beds and a production gas outlet, characterized in that it comprises an intermediate circuit portion connecting at least one downstream portion of the first bed to at least one upstream portion of the second bed and associated with means for supplying a heat flux, at least to the gas passing therethrough, in at least one direction, in the intermediate circuit portion.
According to more particular characteristics of the invention: source, for example a gas or a thermal generator; superposed enclosures, for example annular, the intermediate circuit portion being, in this latter case, also annular.
BRIEF DESCRIPTION OF THE DRAWINGS
Other characteristics and advantages of the present invention will become apparent from the following description of embodiments, given by way of illustration but in no way limiting, with respect to the accompanying drawings, in which: gas under high pressure according to the invention; productivity at low pressure according to the invention; and
DETAILED DESCRIPTION OF THE INVENTIO
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Fraysse Sylvie
Marot Christine
Petit Pierre
Scudier Jean-Marc
L'Air Liquide Societe Anonyme pour l'Etude et, l'Exploitation de
Spitzer Robert
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