ECT Studies of Bead Fluidization in Vertical Mills

David M. Scott and Oliver W. Gutsche

DuPont Central Research & Development, Experimental Station PO Box 80304, Wilmington, Delaware 19880-0304 USA scottdm@esvax.dnet.dupont.com

ABSTRACT ? Vertical media mills require sufficient fluidization of the grinding media in order to be efficient. Fluidization is determined by the agitator speed and, in the case of recirculating mills, also by the flow rate through the recirculation pump. Inadequate fluidization lowers the efficiency of the mill, and excessive flow through the mill causes hydraulic packing at the output screen. The optimum operating conditions (agitator speed and flow rate) for such mills are presumed to be those which evenly distribute the grinding media throughout the mill. Electronic Capacitance Tomography (ECT) has been used to determine the media packing (beads per unit volume) and bead fluidization in an agitated vertical mill. The tomographic data is used to measure average packing along the axis and radius of a vertical mill for a number of agitation speeds. Several geometries and bead/fluid combinations have been studied. The results of this study are being used to identify optimal operating conditions instead of performing an extensive series of grinding experiments.

Keywords: ECT, fluidization, milling, process optimization