a shipboard system provides dry , oil - free utility air and inert gas for use on a marine vessel . a compressor converts ambient air into a pressurized air stream . the air stream is cooled by heat exchange with sea water in the vicinity of the vessel . the air stream is then dried in a dehydration membrane module , and some of the product of the dehydration module is taken for use as utility air . the remainder of the dried air is passed through an air separation module which includes a polymeric membrane . the product of the air separation module includes a nitrogen - enriched gas which is used as an inert gas on the vessel . the compressor is the only mechanically moving component of the system .