Influence of the presence of open three-dimensional fiber structures on solid liquid cake filtration of limestone

Solid particles in a suspension can be separated effectively through cake filtration where the filter medium is decisive particularly during the initial stage when particle breakthrough can be high. To improve the filtrate quality and throughput, filtration aid additives are used, which are known to alter filter cake structure and thus reduce flow resistance but, in forming clusters, also stabilize fine particles that would otherwise pass through the filter (cake) easily. However, filter aids are costly, increase the complexity of the system and may have adverse effects for subsequent mechanical drying and washing. Instead of supplying additives, four alternative filter media were tested exhibiting an open, three-dimensional structure that reached deeply into the depth of the forming filter cake. An aqueous limestone suspension was investigated in a conventional laboratory test unit. Composite filter medium set-up delivered up to 15% faster filtration. The results indicate that the fiber structures give better performance that reach far into the cake and are oriented not only axially but also radially. In contrary to the initial hypothesis that an axial fiber structure would produce additional drainage channels along the surface of these fibers and thus support but deliquoring, the actual deliquoring performance with air blowing appeared to be slightly less efficient. Although not investigated yet, cake discharge with a 3-D filter layer present poses an additional challenge, rendering the concept of composite filters unpractical.