System for eliminating air leakage and high purity oxygen of a psa

Abstract

A first compressor (10) supplies air under pressure to a first stage pressure swing adsorption system (D) which separates oxygen and argon from atmospheric air. A second stage pressure swing adsorption system (E) separates the oxygen from the argon. Each time the compressor (10) is shut off, pressure in molecular sieve beds (22a, 22b) and (90a, 90b) tend to equalize causing mixing of retained primary product gas a feed stock gas. When the compressor (10) is restarted, the intermixed gas is supplied with the primary product gas for the first few cycles. During the first few cycles, a diverter valve (130) diverts the primary product gas to a vent (132) such that the reduced purity primary product gas is not supplied downstream. Thereafter, primary product gas is drawn into a suction tank (110) which is maintained at a reduced pressure by a second compressor (112). A second compressor (112) is a piston type compressor that compresses gas by reciprocating movement of the piston (150) and a cylinder (152) draws primary product gas in on a suction stroke and compresses it on a compression stroke. During the suction stroke, gas tends to be drawn between the piston and the cylinder from a crankcase (158). Primary product gas is fed by a line (162) into the crankcase to maintain the crankcase charged with the primary product gas. In this manner, any primary product gas which leaks between the piston and the cylinder is primary product gas and does not dilute the primary product gas which is compressed and supplied downstream by the compressor.