DELIQUORING OF BULK MATERIAL IN DECANTING CENTRIFUGES

摘要

Decanting centrifuges are widely used for separation and deliquoring of suspensions. With granular solids with particle sizes above 40μm (typically 100 μm), capillary forces can be overcome by mass forces and an effective desaturation of the porous mass on the beach can be achieved. Until now, the prediction of deliquoring performance of decanters solely based on simple laboratory tests has not been possible, mainly due to the lack of understanding about the impact of construction and processing parameters on the deliquoring results. The existing models are only applicable for the scale-up of pilot scale experiments [1] [2] [3]. rnIn order to reduce the costs of layout and scale -up experiments, to optimize the design of decanters and to improve the possibilities for the prediction of deliquoring results a new model was developed. It is based on the calculation of the liquid flow in the moving bulk at the cone of decanters. Basic assumptions for the new model are: (a) coulomb friction and rigid bulk [3], (b) DARCY’s law is applicable, (c) simple flow pattern: liquid flows directly to the gap between drum and screw, (d) one-dimensional liquid flow calculation, and (d) film flow is neglected. rnSome of these assumptions were verified during preliminary tests using decanting centrifuges and a gravity flow apparatus. The assumption that the bulk is being transported as a rigid bulk was confirmed through the observation of the bulk at the cone of a decanter, for both common and large mass throughputs. Circulation of the bulk only occurred for very small mass throughputs. The flow patterns of the liquid inside triangular shaped bulks emerging from liquid ponds were studied in a simple flow apparatuses [4]. rnCalculation results of the introduced model are not only the residual moisture of the discharged solids, but also additional information about transport torque and power. This additional information helps to improve the understanding about the influence of machine, product and process properties on the deliquoring in decanters. rnBesides the description of the new model, the preliminary tests are shortly presented. The results of the simulation are shown and discussed.