Abstract
Recent environmental legislation for many chemical and combustion processes has given new impetus to the development of ceramic filters for hot gas cleaning. The work described here is concerned with the filtration and cleaning conditions which determine the performance of rigid ceramic filters. The pressure drop over the filter medium will continue to rise after the cleaning action due to the presence of a dust layer which is not removed. The time taken for this "residual" pressure drop to reach an equilibrium value is known as the conditioning period. Satisfactory performance of the filter requires the conditioning period to be short and the residual pressure drop to be low. Experimental investigations reveal that a lower residual pressure drop is achieved by filtering to a higher areal mass of dust on the filter surface before cleaning (400 g/m2) and subsequently cleaning with a higher reservoir cleaning pressure (5 bar(g)). Additionally, characteristics of the filter surface have found to be influential in minimising the residual pressure drop. The effectiveness of the cleaning action along the filter has been monitored during pulse jet cleaning. Here, a higher over pressure exists at the closed end of the filter than the open end. In both cases, the over pressure in the filter cavity is much less than the reservoir pressure. During both filtration and reverse flow cleaning, a maldistribution of flow exists along the filter candle. Development of a one-dimensional steady state model has allowed prediction of the local velocity and pressure drop along the filter in these two cases. The first steps of filter vessel design have been investigated through the use of computational fluid dynamics where it has been seen that inside the filter vessel, there are regions of intense flow re-circulation and regions of apparent "stagnation". The work described in this thesis points the way to a more rational and scientific approach to both design and operation of a rigid ceramic filter unit.