Separating a gas enriched in oxygen

Claim 1

A process for separating oxygen from a feed gas containing at least oxygen, nitrogen and argon through pressure swing adsorption utilizing three adsorption columns containing an adsorbent capable of selective adsorption of nitrogen comprising repeatedly performing the steps of: (i) introducing said feed gas into a first adsorption column, in which step (viii) has previously been completed, from its feed end to pressurize the column, thereby adsorbing the nitrogen in the feed gas and obtaining a product gas; (ii) introducing a portion of the product gas obtained in step (i) into a second column, in which step (vi) has previously been completed, while continuing introduction of the feed gas to the first column; (iii) connecting the feed end of the first column, in which step (ii) has previously been completed, to the feed end of the second column, in which step (vii) has previously been completed, passing unadsorbed gas from the first column to the second column until approximate pressure equalization of the two columns is achieved; (iv) connecting the effluent end of the first column, in which step (iii) has previously been completed, to the effluent end of a third column, in which step (v) has previously been completed, and passing an amount of the gas from the first column to the third column so as to depressurize the first column; (v) evacuating the first column, in which step (iv) has previously been completed; (vi) purging the first column undergoing evacuation with an amount of gas coming from the effluent end of the second column, in which step (iii) has previously been completed, during which purge the effluent end of the first column is open, said step (vi) being effected for all or part of the period of step (v); (vii) introducing product gas into the effluent end of the first column, in which step (v) or (vi) has previously been completed, to pressurize the first column; (viii) introducing the feed gas into the first column in which step (vii) has previously been completed, and simultaneously passing gas from the feed end of the third column, in which step (ii) has previously been completed, to the feed end of the first column, until approximate pressure equalization of the two columns is achieved; wherein the said steps are followed by each column in appropriate time relationship with the other columns.