A filter performance curve of a single bag of a fabric is shown in Figure 1. The drag is
plotted versus the dust mass, or cake, deposited on the filter.
Figure 1. Performance curve for a single woven bag
The point cr on the graph is the residual drag of the clean filter medium. The filter drag increases exponentially up to a constant rate of increase. This is the period of cake repair and initial cake buildup. Effective filtration takes place while the filter drag increases at a constant rate. When the total pressure drop reaches a value set by the system design, bag cleaning is initiated. At this point, the pressure drop decreases (almost vertically on the performance curve) to the initial point. Cake repair begins when the cleaning cycle stops and the cycle repeats. Baghouses are designed to remove most of the dust cake during the cleaning process. However, shaking or reverse-air baghouses are designed so that during the cleaning cycle some dust will remain on the bags. Therefore, a dust layer will not have to be built up again on the openings in the weave of the fabric. If the fabric is cleaned too efficiently, the cake repair cycle would be as long as the initial cake buildup, lessening the overall effective filtration time of the baghouse.
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