Effect of filter permeability on the release of captured dust from a rigid ceramic filter surface

Accumulation and release mechanisms of captured dust from a ceramic filter element were tested using five elements made of different materials and structures, Increase of the pressure drop due to the accumulation of dust was continuously monitored until it reached a predetermined value. Captured dust was then removed from the element surface by injecting a high-pressure pulse cleaning air. The behavior of the dust detachment was monitored by several means, such as pressure change at various locations along the element, movement of released dust and their high-speed video images. As a result, pressure drop of dust on the element was found to increase quickly at the beginning because of the formation of a dense dust layer on the filter surface and then a slowdown in the increase in rate due to the formation of a coarse layer. A similar trend was observed for all tested elements; however, quantitatively, it strongly depended upon the filter material and structure. To reach a predetermined pressure drop, the filtration time of each filter is different and increases with filter permeability, Furthermore, the calculated dust porosity at a large dust-load condition also indicated that it increases as filter permeability increases. These obtained results indicate the dependence of filter permeability on the structure of the accumulated dust layer. In the cleaning process. it is found that pressure traces after the injection of cleaning air also have different behaviors, depending on the filter permeability. In case of a high-permeability filter, the cleaning process starts almost immediately after injection of cleaning air. For a low-permeability filter, cleaning air is stored before the cleaning process occurred. Based on the experimental observation, the detachment behavior of captured dust from a filter surface is related to the filtration condition and filter properties. (C) 2001 Elsevier Science B.V. All rights reserved.