Process for the separation/recovery of gases

A process for the separation/recovery of gases with the aid of a membrane/PSA system from a stream where the desired component is present at low molar concentration and/or low pressure, which consists essentially of the following steps:

• compressing and directing the compressed feed stream containing the desired component at moderate temperature and pressure to a membrane unit of high permeability and medium selectivity whereby are separated a low pressure stream enriched in the desired component—the permeate stream—and a lean stream or retentate, enriched in non-desired component(s) of pressure close to that of the feed;
• saving energy by conveying the pressure inventory from the retentate stream to the permeate stream so as to elevate the permeate pressure;
• directing the permeate stream at elevated pressure to a PSA system which selectively adsorbs non-desired components, for purification of the desired component;
• recovering the desired component from the PSA system;
• desorbing the purge stream containing the non-desired components from the PSA system;
• compressing and recycling the purge stream from the PSA system to the membrane separation unit, combining said purge stream from the PSA system with the feed stream and resuming the permeation/purification cycle.

A process for the separation/recovery of gases with the aid of a membrane/PSA system from a stream where the desired component is present at very low molar concentration and moderate pressure which consists essentially of the following steps:

• directing the feed stream containing the desired component at moderate temperature and pressure to a first membrane unit of high permeability and medium selectivity whereby are separated a first, low pressure stream enriched in the desired component
• the first permeate stream—and a first lean stream or first retentate, enriched in non-desired component(s) of pressure close to that of the feed;
• saving energy by conveying the pressure inventory from the first retentate stream to the first permeate stream so as to elevate the permeate pressure;
• directing the first permeate stream enriched in the desired component to a second membrane unit of high permeability and medium selectivity whereby are separated a second, low pressure stream enriched in the desired component—the second permeate stream—and a second, lean stream or second retentate, enriched in non-desired component(s) at pressure close to that of the feed;
• saving energy by conveying the pressure inventory from the second retentate stream to the second permeate stream so as to elevate the second permeate pressure;
• directing the second permeate stream at elevated pressure to a PSA system which selectively adsorbs non-desired components, for purification of the desired component;
• recovering the desired component from the PSA system;
• desorbing the purge stream containing the non-desired components from the PSA system;
• recycling and combining the purge stream from the PSA system with the first permeate stream to be compressed and directed to the second membrane unit.