Abstract: A gaseous constituent such as SO.sub.2, HCl, or HF is removed from a gas stream in a granular bed filter containing granules coated with a sorbent material which is reactive with the gaseous constituent. Granules carrying reacted sorbent material are removed from the granular bed filter, cleaned of reacted sorbent material and coated with further sorbent material for reuse in the granular bed filter. Electrification of the filter bed permits simultaneous, highly efficient removal of particulates entrained in the gas stream.

Abstract: Electrified filter bed apparatus includes inner and outer cylindrical bed-retaining structures for confining a granular bed therebetween. The inner cylindrical structure may comprise a cage of superposed frusto-conical louvers and the outer structure may comprise a similar cage or a perforated cylindrical, liquid-drainage sheet. A cylindrical bed electrode for electrically charging the bed granules is suspended between the retaining structures. The tubular bed surrounds an internal gas passage from which polluted gas flows through the bed from the inside out. Gas enters the internal passage from above through an ionizer section of the apparatus. The ionizer section may include a disc-type ionizer assembly in an ionizer tube. The tube may form an extension of the inner louver cage. A corona discharge may be formed between the disc and the ionizer tube by providing electric current to the discs, whereby the corona discharge electrically charges particulate material within the gas stream.

Abstract: Fly ash and fine dust in a gas stream from a coal combustor, for example, are efficiently collected in a 2-stage, tubular, granular bed filter. The stages of the filter are arranged one above the other so that the granules may move from the upper stage to the lower stage under the influence of gravity. Larger particulate in the gas stream is first collected by the lower stage, and then the remaining particulate is electrically charged and collected by the upper stage. Both stages are electrified sufficiently to rigidify the granular beds and adhere the particulate to the granules, so that the granules and the collected particulate move downwardly through the filters as a plug. Granules that exit from the lower stage are cleaned and returned to the upper stage. Non-porous granules may be used to prevent fine particulate from becoming embedded in the granules.

Abstract: Fly ash and fine dust in a gas stream from a coal combustor, for example, are efficiently collected in a 2-stage, tubular, granular bed filter. The stages of the filter are arranged one above the other so that the granules may move from the upper stage to the lower stage under the influence of gravity. Larger particulate in the gas stream is first collected by the lower stage, and then the remaining particulate is electrically charged and collected by the upper stage. Both stages are electrified sufficiently to rigidify the granular beds and adhere the particulate to the granules, so that the granules and the collected particulate move downwardly through the filters as a plug. Granules that exit from the lower stage are cleaned and returned to the upper stage. Non-porous granules may be used to prevent fine particulate from becoming embedded in the granules.

Abstract: Pollutant emissions produced in the manufacture of asphaltic roofing are controlled by the use of electrified bed filters. Filter bed granules coated with pollutants are removed from the beds periodically and are used in the manufacture of the roofing. A prefilter is employed to remove varnishing pollutant components in the supermicron size range to prevent fouling of an electrical charger.