Maximum Packing Concentration of Coal Water Mixtures

Abstract

The maximum packing fraction achieved in a solid-liquid dispersion depends on particle properties such as particle size, particle size distribution and particle shape (sphericity). One means of increasing the maximum packing concentration is by adjusting the particle size distribution. This work compares models to predict and optimise the maximum packing fraction (φm) behaviour (and consequently the rheological behaviour) of a bi-modal brown coal/water mixture (CWM). One of the models used was originally developed by Ouchiyama and Tanaka, and modified by Mayadunne et al., for irregularly shaped particles, and has previously been used to fit the data for less agglomerating systems. CWM's are generally of low volume concentration due to their ag-glomerative nature. This model for packing of bi-modal mixtures requires data for the sphericity (assumed constant for a given material) and the φm behaviour of the unblended. nearly monosized materials (also assumed equal). φm of a CWM of two different coal sizes was estimated by rheological techniques at a number of shear stresses and compared to the predicted values over the range of shear stresses and different ratios of small to large particles.