| Solid-liquid separation (SLS) is frequently encountered in the chemical process industries. The empirical constitutive equations (ECE) relating porosity and specific cake resistance to effective pressure are important tools in designing a successful SLS operation. Because of the complexity of particulate systems, parameters of ECE are normally only applicable to a particular process or equipment. Repetitive analysis is required for each system encountered.; Several methods have been used in obtaining parameters of ECE. The compression-permeability cell technique bears various flaws including wall friction, nonuniformity in particulate bed structure, and tedious experimental procedures and data analysis. The filtration method as devised by Tiller and Leu is beset by sedimentation phenomena. A new experiment was designed to circumvent these difficulties. A particulate bed is formed by low pressure filtration. Liquid with identical composition to the suspending medium in the slurry is pumped through the structure in a series of increasing constant pressure steps. Filtrate flow rate, cake thickness, pressure drop across the cake, and solid content in the cake are used to derive the parameters of ECE. Prediction of pressure distribution in cakes using these parameters showed reasonable agreement with experimental data.; The partial differential equation governing particulate structures as a function of time and space was solved to study the transient structure changes during the stepwise pressure increase. Predicted structure response using the derived parameters of ECE was compared satisfactorily with experimental data.; In order to understand the effects of the three prevailing microscopic properties (shapes, size distribution and degree of aggregation) of particulate systems on the macroscopic behavior of cakes and sediments, two types of kaolins received extensive investigation under different flocculant/dispersant conditions. The resulting parameters of ECE were correlated to the compressible extent of a bed, (epsilon)(,sm) - (epsilon)(,s1). The low stress solidosity is considered as an index of degree of aggregation, which can be obtained by a simple gravitational filtration test. Knowing (epsilon)(,s1) of a kaolin suspension, the parameters of ECE can be obtained from the correlation equations. Comparison between experimental data and correlation predictions were reasonable. |
