Application of fluidization to obtain washability data

Abstract

There is considerable interest in developing new approaches to obtaining washability data, especially in coal preparation. Here, the traditional “sink float” method has been used for decades. Obtaining the data, however, is costly, and often the analysis time required is too long for the data to be useful as part of a feed-back control strategy. Further, the dense liquids used to conduct the analysis can be problematic, on health and environmental grounds. The purpose of this paper is to describe a new method for conducting washability analysis, using fluidization. Although we have used this method on coal particles smaller than 2 mm, the method may be applied to particles of any size or density. Although the process of fluidization is well established, its application to obtaining washability data appears to be novel. Narrow size fractions of the sample are obtained using conventional sieving. One of the narrow size fractions is placed into the fluidized column, where it segregates readily producing a pressure profile, with the less dense particles at the top and the progressively denser particles below. The pressure profile of the suspension is measured using differential pressure transducers. Samples of the suspension are removed from the vessel, the change in the suspension pressure profile measured, and the dry weight of the discharged sample determined. These data are then used to obtain the particle density.