CYCLIC MEMBRANE SEPARATION PROCESS

摘要

A cyclic process for controlling environmental emissions of volatile organic compounds (VOC) from vapor recovery in storage and dispensing operations of liquids maintains a vacuum in the storage tank ullage. In the first part of a two-part cyclic process ullage vapor is discharged through a vapor recovery system in which VOC are stripped from vented gas with a selectively gas permeable membrane. In the second part, the membrane is inoperative while gas pressure rises in the ullage. In one aspect of this invention, ambient air is charged to the membrane separation unit during the second part of the cycle. In another aspect, a vacuum is drawn in the membrane separation unit. The charging of air or drawing of vacuum purges VOC from the membrane unit and thus reduces overall VOC emissions.