Process and installation for supplying nitrogen with the aid of semi-permeable membranes using a variable membrane geometry

A process for supplying a flow of nitrogen to a site having flowrate requirements which vary between a nominal flowrate and a range situated above said nominal flowrate comprising the steps of:

• a) passing compressed air into a main line in a separating assembly formed by at least two membrane separation lines mounted in parallel, each including a membrane separator having an outlet side and a permeate side, wherein at least one of the separation lines can be shut off from the main line, said separating assembly having one of the following configurations:
• a1) when the flowrate requirements are situated at a level of the nominal flowrate, all of the membrane separators of the assembly are in operation, none of the separating lines being shut off;
• a2) when the flowrate requirements of the site exceed a predetermined flowrate, at least one of the lines of the separating assembly is shut off, keeping at least one separation line and its membrane separator in operation;
• b) advancing nitrogen gas obtained at the outlet side of each of the membrane separators in operation in step a) to a collector itself connected downstream of the main line;
• c) evacuating oxygen-enriched gas obtained at the permeate side of each of the membrane separators in operation in step a);
• and
• d) directing nitrogen gas delivered by the collector towards at least one user station via a control device for controlling flowrate delivered by the collector, optionally increasing or reducing this flowrate.

An installation suitable for supplying a flow of nitrogen to a site having flowrate requirements which vary between a nominal flowrate and a range situated above said nominal flowrate, comprising, along a main line, between an air compressor and at least one user station:

• (i) a separating assembly formed by at least two membrane separation lines mounted in parallel, each line including a membrane separator having a permeate side and an outlet side, at least one of the separating lines including means for shutting it off, and each membrane separator being provided with a line for the evacuation of its permeate towards the exterior and with a line for the evacuation of its outlet;
• (ii) a collector situated between the separating assembly and a downstream part of the main line, and to which all of the lines for the evacuation of the outlet from the membrane separators of the separating assembly are connected;
• and
• (iii) a device for controlling flowrate delivered by the collector, situated between the collector and the user station.