Abstract
The filtration efficiency of a shallow fluidized bed of silica sand has been measured at 800DEGREESC and 1000DEGREESC for redispersed fly ash from a fluidized combustor and char fines from the NCB fluidized gasifier. Efficiency is much higher for fly ash, because of better retention due to stronger adhesion forces, but the filtration of both dusts is limited by retention on the surface of the collector. Retention can be enhanced by addition of a liquid retention aid to the collector, or by operating under conditions where the dust is sufficiently soft to experience better adhesion. For fly ash complete retention is achieved by operating the filter at 1000DEGREESC, near the sintering point of the ash. For gasifier fines retention is improved substantially by using heavy fuel oil as a retention aid, but further development is needed to improve efficiency towards the theoretical limit of collection.