2-ZONE MODEL FOR SOLID-LIQUID SEPARATION BY FILTRATION AND EXPRESSION

A one-dimensional modelling of constant pressure deliquoring based on not more than three material specific parameters was achieved by the f ollowing basic assumptions: two regions of void ratio are defined. Fro m the initial value down to a threshold value e(i), the solid-solid in teraction is neglected; only when the water content falls short of e(i ), an elastic network with increasing elasticity modulus is formed. Fi ltration and consolidation are not regarded as subsequent stages, but are assumed to occur at varying extents during the whole process. The profile of porosity is approximated by a rectangular function while th e profiles of liquid pressure and the elasticity modulus inside the co mpressed zone are approximated by hyperbolic functions. The compressed zone is characterized by an average solid stress sigma(c) and an aver age filtration resistance R(c) both related to the volume of the expre ssed or filtrated liquid V (maximal amount V(E)). The proportionality between sigma(c) and V and that between dR(c) and dV/(V(E) - V) are in herent empirical conditions. For the initial stage of solid-liquid sep aration, a strong non-linear profile of the filtration resistance resu lts and this is discussed usually to be due to a ''skin effect''. The model was successfully applied to the kinetics of the press-dewatering of different materials: suspension of protein, sawdust, semi-solid cl ay and sugar-beet tissue. Additional parameters describing the seconda ry consolidation were not required. Filtration was shown to be a bound ary case of the model.