A Laboratory Scale Investigation of Dry Coal Benefeciation in an Air Fluidized Bed: Effects of Particle Size, Shape and Density

Abstract

Coal is a fossil fuel that forms under the earth by natural processes. The Potential markets for coal include power generation, export, domestic, metallurgical, liquefaction and cement processing industries. In Kenya, coal is found in arid areas of Kitui County but mining and processing operations are yet to begin. One factor that could impede the development of a coal processing plant in Kitui, besides environmental related challenges (such as the carbon footprint) is the scarcity of water. A need thus exists to research on dry coal beneficiation methods to avoid reliance on the conventional wet processing methods. Dry coal beneficiation with an air dense-medium fluidized bed is one of the dry coal processing methods that have proved to be efficient. In this study a (40 x 40x 60) cm air fluidized bed was employed for dry coal beneficiation tests. The effects of coal particles size and shape as well as the bed density on beneficiation process were assessed. A relatively uniform and stable average bed density of 1.64 g/cm3 was achieved using a mixture of silica and magnetite as fluidizing media. Coal particles of different particle size ranges which varied from (+9.5 -16mm), (+16 -22mm), (+22-31.5mm) and (+37-53mm) were utilized in the tests. Three different particle shapes namely blockish (+16-22mm), flat (+16 -22mm) and sharp pointed prism particles (+16–22mm) were used. The (+37 -53mm) and (+22 -31.5mm) particles separated faster and more efficiently than the (+16-22mm) and (+9.5 -16mm) particles. Further, the separation efficiency of the particles improved at longer bed depths with relatively uniform and stable bed densities. Therefore, prescreening of the coal particles into relatively narrow ranges would be important in the optimization of dry coal beneficiation using an air fluidized bed since different particle size ranges and shapes have different optimum operating conditions required for efficient separation.