tailieunhanh - AIR POLLUTION CONTROL TECHNOLOGY HANDBOOK - CHAPTER 16

16 Membrane Separation OVERVIEW Membrane separation has developed into an important technology for separating VOCs and other gaseous air pollutants from gas streams during the past 15 years. The first commercial application was installed in 1990, and more than 50 systems have been installed in the chemical process industry The technology utilizes a polymeric membrane that is more permeable to condensable organic vapors, such as C3+ hydrocarbons and aromatics, than it is to noncondensable gases such as methane, ethane, nitrogen, and hydrogen. The air stream to be treated is separated into a permeate that contains concentrated VOCs and a treated residue. | 16 Membrane Separation OVERVIEW Membrane separation has developed into an important technology for separating VOCs and other gaseous air pollutants from gas streams during the past 15 years. The first commercial application was installed in 1990 and more than 50 systems have been installed in the chemical process industry The technology utilizes a polymeric membrane that is more permeable to condensable organic vapors such as C3 hydrocarbons and aromatics than it is to noncondensable gases such as methane ethane nitrogen and hydrogen. The air stream to be treated is separated into a permeate that contains concentrated VOCs and a treated residue stream that is depleted of VOC. Because the technology concentrates the VOC gas stream it can be used with a condenser to recover the VOC. It is best suited for relatively low-flow streams containing moderate VOC concentration. The typical overall VOC recovery process consists of two steps 1 compression and condensation and 2 membrane A mixture of vapor and air is compressed to about 45 to 200 psig. The compressed mixture is cooled and condensed vapor is recovered. Uncondensed organics are separated from the gas stream and concentrated in the permeate by the membrane. The treated gas is vented from the system and the permeate is drawn back to the compressor inlet. POLYMERIC MEMBRANES The polymeric membrane consists of a layer of nonwoven fabric that serves as the substrate a solvent-resistant microporous support layer for mechanical strength and a thin film selective layer that performs the separation. It is manufactured as flat sheet and is wrapped into a spiral-wound module. Feed gas enters the module and flows between the membrane sheets. Spacers on the feed and permeate side of the sheets create flow PERFORMANCE Membranes are best suited for treating VOC streams that contain more than 1 000 ppmv of organic vapor where recovered product has value. Typical VOC recovery .

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