Multiphase flow models in quantifying constant pressure dead-end filtration and subsequent cake compression: 2. Concentrated slurry filtration and cake compression

Separation of liquid from concentrated slurry is a significant process in laboratory and engineering applications. In an earlier paper (X.M. Wang, S. Chang, P. Kovalsky, T.D. Waite, Multiphase flow models in quantifying constant pressure dead-end filtration and subsequent cake compression. 1. Dilute slurry filtration, J. Membr. Sci., in press), we investigated the applicability of the Smiles and Tiller multiphase flow models to description of the filtration behavior of dilute yeast slurries and here extend the analysis to consideration of concentrated slurries. Smiles’ and Tiller's models are employed to quantify dynamic filtration behavior while a numerical technique derived from Smiles’ method is utilized for cake compression stage characterization. The numerical method for Smiles’ model for concentrated slurry filtration is the same as that for dilute slurry, while an iteration step is added to the method for Tiller's model. The results obtained indicate that the Smiles and Tiller models are equivalent in quantifying filtration behavior and cake structure of concentrated slurry and reveal that the cake structure and the ensuing filtration behavior are affected by the initial slurry solid fraction. The cake formed from slurry with a higher initial solid fraction tends to have a lower average solid fraction and a lower average specific resistance than is the case for lower initial slurry solid fractions. The variance of superficial liquid velocity through the cake during concentrated slurry filtration is much more significant than is the case during dilute slurry filtration suggesting that caution should be exercised in employing the conventional filtration model in concentrated slurry filtration data analysis. During the compression stage, the compression rate is relatively constant at the beginning then drops sharply before adopting a relatively stable value at longer times. Concomitantly, the solid compressive pressure of the upper surface of the cake increases slowly at the beginning, quickly after that and then slowly again.