An investigation of the performance of and the flow of solids and air in a vertical shaft impactor

Abstract

The operation of the Breakring vertical shaft impactor was investigated mathematically and experimentally. In particular, the performance of the crusher, the action of solids and air in the impeller and the mechanism responsible for the localised abrasion of the impeller wear parts were investigated. Computer programs were developed, which modelled the performance of the Breakring for impellers having simple, idealised wear part profiles. Contour plots were produced, which illustrated the dependence of impeller power, absolute particle exit speed and anvil angle for normal impact on the wear part sweep angle and the coefficient of friction between the feed material and the wear part. The significance of the contours was investigated. A computer program was developed, which modelled the action of a single particle in the Breakring impeller for wear parts having various complex profiles. The results indicated that the cause of the localised wear part abrasion was the reattachment of feed material to the wear part, following separation at the downstream end of the depression caused by action of material after entry to the impeller. The accuracy of the results was confirmed by the profiles of abraded wear parts and various other factors. A full-scale model impeller was constructed. The flow of air in the model and, following failure of the model, the flow of air and solids in a prototype impeller were investigated by a surface flow visualisation technique and high speed cinematography. The results neither verified the wear-mechanism outlined above nor indicated any other wear-mechanism. It was concluded that the wear mechanism indicated by the mathematical modelling was accurate and that there is no indication of abrasion by airborne fines.