Abstract: A process for treating a gaseous mixture, particularly air, by pressure swing adsorption (PSA), of the type in which three adsorbers (1 to 3) are used in each of which is carried out, for a given nominal production, a cycle comprising the following successive stages, the cycle being offset from one adsorber to the other by a third of the nominal duration (T) of the cycle:(a) a substantially isobaric adsorption phase at a high pressure (PM) of the cycle, by circulation of the mixture through the adsorber in a so-called co-current direction;(b) a desorption phase comprising a stage (b2) of pumping to a low pressure (P.sub.m) of the cycle less than atmospheric pressure, via a vacuum pump (7) of constant speed and continuous operation whose output is in the vicinity of atmospheric pressure; and(c) a repressurization phase of the adsorber to the high pressure of the cycle. During a reduction of the production flow rate, the mean intake pressure of the vacuum pump is raised for the duration of the cycle.

Abstract: A pressure swing adsorption unit comprises at least two absorbers, each absorber having at least a port connectable to at least one pumping unit. The pumping unit includes a first pumping stage and a second pumping stage. Each of the pumping stages are capable of discharging into an outlet conduit. A circuit is provided for selectively and alternately connecting a port to a source of feed gas and to the pumping unit such that the first and second pumping stages are sequentially fluidly connected in parallel, and then in series to reduce the pressure at the port to an intermediate vacuum level, and then to a low vacuum level.

Abstract: A flow of air which has been compressed cooled dried is treated in a unit for separation by cryogenic distillation to give a flow of nitrogen; the oxygen enriched residual gases are, in part, sent at the inlet of a unit for separation by adsorption in which the outlet substantially produces oxygen. If the flow of oxygen is insufficient, additional air is injected. If the flow of oxygen is too important, an excess flow of residual gases is withdrawn. This apparatus enables to provide, at a lesser cost, independent flows of nitrogen and oxygen which are adjustable at will.

Abstract: In a unit for the production of oxygen by separation of air by adsorption with regeneration of the adsorbers (1-5) under vacuum, the sub-atmospheric depressurization is ensured with rejection to the atmosphere by pumping with two successive pumping devices: one, for example of the type of a volumetric compressor (13), operates to a pressure of the order of 0.5.times.10.sup.5 Pa absolute, while the other, for example of the type of a centrifugal compressor (14), operates alone to a pressure of the order of 0.2.times.10.sup.5 Pa absolute.