Multistage cascade sweep-process for membrane gas separation

摘要

A nitrogen generator for producing nitrogen gas from air having a plurality of stages of membrane units each containing a plurality of hollow fiber membranes having a feed input at least one of the plurality of membrane units containing a sweep input to inject a sweep gas longitudinally on the external surface of the hollow fiber membranes, the generator further containing: a) a conduit for collecting a non-permeate stream of a membrane stage N and using the same as a feed stream for a membrane stage N+1; b) a conduit for collecting only a permeate stream from at least the membrane stage N, and feeding all of the permeate stream from the membrane stage N to a sweep input of at least one previous membrane stage, such that the sweep gas is injected longitudinally and counter-current to the non-permeate gas on the external surface of the hollow fiber membranes, and that the sweep gas is mixed with the gas permeating through the hollow fiber membranes to make the permeate stream; and c) a conduit for collecting a permeate of a first membrane stage and a non-permeate of the last membrane stage.