In-Situ Hydrocarbon Capture and Reduction of Emissions of Dioxins by Porous Bed Material Under Fluidized Bed Incineration Conditions

Abstract

This work is intended to reduce emissions of dioxins and unburned gas from fluidized bed waste incinerators. Combustion of plastic pellets was conducted using a bench-scale bubbling fluidized bed combustor. Porous alumina was used as a bed material instead of conventional bed material (sand). First, we evaluated the effect of bed material on capture of volatile matter in the bed in a nitrogen atmosphere. Porous alumina captured volatile matter while sand did not. Feeding gas asymmetrically to enhance internal circulation of solids in the bed increased volatile capture efficiency of the porous alumina bed, whereas no improvement was found for the sand bed. Next, we performed combustion of plastic pellets by air. Emission of unburned gas was lower for the porous alumina bed than for the sand bed under a uniform gas feed condition. This is attributable to volatile matter capture by bed material that lengthens residence time of volatile matter in the combustor. However, non-uniform air feed for internal circulation was ineffective for suppressing unburned gas emissions. This may be caused by formation of an oxygen-deficient zone in the combustor. Finally, dioxin emissions were measured during PVC pellet combustion in a uniformly fluidized bed. The porous alumina bed was more effective for dioxin emission suppression than the sand bed.