Description of the filter cloth deformation during backwashing filtration

Abstract

The separation of fine particles with filter cloth is a commonly used technique to remove particles from process streams under low-cost and low-maintenance conditions. Such kind of filter apparatus can be found, i.e., in front of distillation columns with the adjusted size. Here, it is possible to have a filter apparatus with filter elements ≤ 2.5 m in length and ≤ 100 elements in one vessel. For a constant and stable process conditions, a periodical regeneration of the filter cloth is absolute required. One option for realizing this procedure is discharging the built-up filter cake in liquid phase (backwashing filtration). Due to the reverse flow, a deformation of the filter cloth occurs. This deformation depends on the assembly situation, mechanical pre-loading of the weave, the environment of the system, the weave type and, of course, the backwashing pressure. The interaction of this variables results in an adjusting of the space between the filter elements and correspond with the required backwashing volume in l/m2.Influence of a contact between two filter elements is not known but can have a negative impact in case of remaining filter cake on surface. Too much space reduces the economy of the apparatus because less filter surface needs the same apparatus footprint. Thus, by knowing how the filter cloth expand, the space can be adjusted on the particular separation task. This can lead to an improvement of the filter surface per apparatus footprint and can be advantageously compared to competing separations procedures. The deformation of the filter cloth during the backwashing treatment is described and discussed in the context of this investigation on the basis of elementary mechanics.