Abstract
"Dry scrubbing" is the term used to denote the removal of a gaseous component from an effluent stream by reaction with a dry sorbent material in particulate form. In one particular industrial application of dry scrubbing, a dry sorbent is injected into the process gas upstream of a particulate collection system, which may typically be a filter or an electrostatic precipitator. (Here we consider only a rigid ceramic filter, for reasons which are discussed later.) In this case, reaction occurs both in the entrained flow downstream of the injection point and also on the ceramic filter. The residence time of the sorbent on the filter is typically many times what it is in the entrained flow section, so that it would seem promising to utilise the fixed bed of sorbent built-up on the filter surface in order to perform the desired reaction. This study has shown that this approach can lower sorbent usage, by comparison with that necessary for reaction in entrained flow, thus reducing capital and operating costs. In order to design effective dry scrubbing plants based on the ideas set out above it is necessary to understand the physical and chemical processes taking place on the surface of the filter medium during the build-up and subsequent removal of the deposited filter cake. For this reason experimental studies have been carried out on the physical aspects of cake formation using a single-candle apparatus and on the chemical aspects using a single-cycle hot coupon rig apparatus. Results from the single-candle filtration apparatus have indicated the conditions at which ceramic filters should operate for stable filtration and cleaning behaviour at ambient conditions; these results provide a basis to work on for high temperature filtration and dry scrubbing. Low filtration velocities and high filter cake loadings have been shown to be paramount in achieving stable conditioning and filtration behaviour, and hence improving the filtration efficiency. A high temperature single-cycle dry scrubbing rig has been designed to investigate the effects of different sorbent injection strategies on the dry scrubbing process. The experimental data have been used to validate and improve the mathematical model of Duo et al. (1993). These studies can ultimately enable the modelling and optimisation of industrial scale dry scrubbing facilities.