Modelling the vacuum filtration of fine coal

Abstract The dewatering of fine coal using vacuum filters is widespread in Australia, and is very important to the coal industry since the fines fraction of the product coal can contain up to 50% of the moisture. Optimising and maintaining filter performance can only be achieved with the aid of a suitable model applied at plant scale. As a first step towards such optimisation, the paper describes bench-scale studies to assess a model, devised by Wakeman in the late 1970s, for calculating both moisture reduction kinetics and gas consumption during fine coal filtration. The model provided a good simulation of both desaturation kinetics and gas consumption using a range of cake thicknesses and pressure differences. The equilibrium dewatering parameters (pore size distribution index, breakthrough pressure and equilibrium saturation) that are required to run the model had to be determined by experiment, since the formulas available for calculation of these parameters provided erroneous results. Although the model is only strictly applicable to incompressible cakes, it coped well with the slight compressibility of typical (−0.5 0 mm) coal filter cakes. However, this compressibility might explain why the model was least accurate with thin cakes or at high vacuum levels. Further development of the model will be undertaken prior to applying it on commercial-scale filters.