Design and testing of a moving bed VOC adsorption system

Abstract

AbstractA 0.28‐2.8 m3/min (10‐100 cfm) moving bed carbon adsorption pilot plant has been developed for testing of low (10–200 ppm) concentration VOC emissions. The pilot plant uses a cross‐flow arrangement with the air flowing horizontally through the adsorption bed while the carbon adsorbent particles flow vertically downward. At the bottom of the system, the “used” activated carbon is regenerated using a direct contact heat exchanger. The regenerated carbon is then transported to the top of the moving bed via a screw feeder and pneumatic transport tube. A small gas flow containing the VOCs removed from the used adsorbent is emitted continuously from the adsorbent regenerator. When a carbon flow rate of 2.3 kg/hr (5 lbs/hr), a face velocity of 0.32 m/sec (63 ft/ min), and an emissions stream containing 30 ppm ethanol were used, the observed collection efficiency was approximately 90%. The ability to regenerate the carbon was tested by first operating the system in a static mode, that is air being drawn into the system while the adsorption bed was not moving. This was continued until approximately 70% of the inlet gas VOCs passed through the system without being adsorbed. The carbon flow was then started and the VOC concentration in the off gases of the absorbent regenerator was measured as the partially saturated carbon passed through the system. The VOC concentration in the gases emitted from the adsorbent regenerator was about a factor of ten higher than the VOC concentration in the air entering the adsorption bed.