The influence of dust and gas properties on cake adhesion in fabric filters

Abstract

The operation of fabric filters in specific applications is often regarded as unpredictable, and design is normally based on experience on a variety of differing dust types, and applications. The paper reports part of a research programme aimed at identifying the major variables which influence both the operating pressure drop of a bag filter, and which affect the stability of its operation. The paper details experimental work on a two-bag test facility, and on a small industrial-scale filter in which dust cakes were prepared for determination of cake density, thickness, porosity and adhesion characteristics. Cake adhesion was measured using two techniques, and the influence of the filter medium, cake areal mass and dust type was determined. Experiments using four types of dust and two types of filter medium are reported, as well as the influence of electrostatic charging of the dust, humid gas and the presence of liquid water. This work is aimed at the development of a technique which characterises the ‘stickness’ of filter cakes which can then be applied to a wide range of filter types, and it is expected that detailed knowledge of the forces generated by the specific cleaning system can be determined separately. The results show that PVC dust is much more adhesive than carbon black and chalk. A fourth type of dust tested (glass/fibres) was found to be less adhesive than all the others. Results tend to be scattered, and to some extent accuracy is unpredictable; this is thought to be as a result of a combination of factors, including the influence of the dust conditioning, humidity, electrostatics and cake compression resulting from cake restructuring.