NOVELTY - Gas separation includes, in sequence, first feed/purge step, first flush step, second feed/purge step, and second flush step. In the first feed/purge step and second flush step, a feed gas inlet stream is provided into a first adsorbent bed (11) and a purge gas inlet stream is provided into a second adsorbent bed (13). In the first flush step and second feed/purge step, the purge gas inlet stream is provided into the first bed and the feed gas inlet stream is provided into the second bed.    USE - For e.g. recovering fuel from fuel exhaust of a solid-oxide fuel cell stack.    ADVANTAGE - A reliable, energy-efficient cycle for optimum gas separation is provided. The high-efficiency cycle allows for maximum recovery of hydrogen and maximum rejection of carbon dioxide and air.    DETAILED DESCRIPTION - Gas separation includes:    (A) a first feed/purge step including providing a feed gas inlet stream into a first adsorbent bed, collecting a feed gas outlet stream comprising separated component(s) of feed gas at a first output, providing a purge gas inlet stream into a second adsorbent bed, and collecting a purge gas outlet stream at a second output;    (B) a first flush step including providing the purge gas inlet stream into the first adsorbent bed, collecting the purge gas outlet stream comprising feed gas component that was trapped in a void volume of first adsorbent bed at the first output, providing the feed gas inlet stream into the second adsorbent bed, and collecting the feed gas outlet stream comprising a portion of purge gas that was trapped in a void volume of second bed at an output different from the first output;    (C) a second feed/purge step including providing the feed gas inlet stream into the second adsorbent bed, collecting the feed gas outlet stream comprising separated component(s) of feed gas at the first output, providing the purge gas inlet stream into the first adsorbent bed, and collecting the purge gas outlet stream at an output different from the first output; and    (D) a second flush step including providing the purge gas inlet stream into the second adsorbent bed, collecting the purge gas outlet stream comprising feed gas component(s) that was trapped in a void volume of second adsorbent bed at the first output, providing the feed gas inlet stream into the first adsorbent bed, and collecting a feed gas outlet stream comprising a portion of purge gas that was trapped in a void volume of first bed at an output different from the first output.    An INDEPENDENT CLAIM is included for a gas separation apparatus.    DESCRIPTION OF DRAWING(S) - The figure is a schematic diagram of a partial pressure swing adsorption system.    First feed gas inlet conduit (3)    Second purge gas inlet conduit (5)    Third feed gas collection conduit (7)    Fourth purge gas collection conduit (9)    First adsorbent bed (11)    Second adsorbent bed (13)