(443f) Nonequilibrium Compression Effects in the Dewatering of Fibrous Suspensions: Analysis Using Dual Porosity Dual Permeability Approach

Dewatering of many suspensions is effected by applying pressure and building up a solid cake or fibrous mat. The pressure applied for dewatering is transmitted in part to the solid phase which deforms in response. In many conventional filtration and expression processes, the solid phase deforms elastically. However, in many other processes, plastic and time dependent deformation occurs. Common situations are filter cakes formed from flocculated suspensions or suspensions containing nanoporous and compressible particles. Papermaking pulp fibers are an example of deformable nanoporous structures which can express water from their internal structure when subjected to compression during the papermaking operation.

We have developed a new approach to analyze the dewatering process where the cake solids are themselves porous and compressible using a dual compressibility/permeability concept. Our model yields two linked diffusion type equations which are solved simultaneously to yield the water fluxes and concentration profiles throughout the system.

We discuss applications of this approach and compare its predictions with other conventional single medium approaches . The predictions are also compared with experimental data and the validity of the dual medium approach is established.