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Chemical and Process Engineering Resources

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Category: Separation Technology
Question: How can VOCs (volatile organic compounds) be recovered from beds of activated carbon?
Keywords: v1i2,voc,recover,carbon,activated,adsorption,groundwater,remeidation
Answer: The use of activated carbon is a popular method of removing volatile organic components from air streams. Typically, these spent carbon beds are either sent back to the manufacturer and fresh beds are used or the carbon is regenerated by using steam to destroy the VOC within the carbon bed.Another, more recent, technology related to vapor phase carbon absorption is the Brayton-cycle heat pump (BCHP). This technology created by Idaho National Engineering Laboratory offers a method for VOC recovery and recycling. A Brayton-cycle heat pump can condense volatile organic compounds (VOCs) from an air stream, which offers the potential for both recovery and either on-site or off-site recycle of a wide range of VOCs. The VOC-laden air stream can come from either vapor vacuum extraction of soil or air stripping of contaminated ground water.A truck-mounted BCHP is used to regenerate the adsorbers on a periodic basis. When the bed becomes saturated, hot nitrogen from the regenerator is used to desorb the VOCs from the bed. The nitrogen passes through a chiller, is compressed, and is then cooled in a recuperator, where 50% to 80% of the organics are recovered. The partially depleted nitrogen stream is then expanded through a turbine, lowering the temperature to as low as -150oF and condensing the remaining organics. The now-clean nitrogen passes through the recuperator to cool the VOC-laden nitrogen before returning to the carbon bed. The only outputs will be the clean off-gas and a small amount of recovered organics.The economics of such a system are not available at this time. This system has been employed in a system where air was used to strip VOCs from groundwater. The VOC-laden air was then sent to the carbon beds and the BCHP system was used to recover the contaminants.