Modelling media movement during cleaning of pulse-jet fabric filters

Pulse-jet fabric filters are one of the most common items of plant for removing particles from process gases. During operation, a cake of dust builds up on the outside of the filter fabric. The growth of this cake increases the pressure drop of the filter and makes periodic cleaning necessary. The cake is generally removed by injecting a short pulse of gas into the clean side of the filter in a direction which is the reverse of the normal flow. This pulse causes the cake to be thrown off the surface of the fabric. The dynamics of the fabric motion during this type of cleaning pulse are modelled and compared with experimental measurements performed on an industrial scale pilot plant filter. Building upon earlier work, a picture of how the cake is removed from the fabric during the cleaning process is presented. Equations describing the propagation of the cleaning pulse down the filter and the acceleration that it produces are presented. The pulse is transmitted in a wavelike manner causing the fabric to expand so rapidly that it propels the cake off the fabric surface. The fabric expansion controls the cleaning process. The model is extended to consider cage design and to allow for the slackness of fit between the bag and the supporting cage. Good agreement is demonstrated between theoretical prediction and experimental results.