An energy based comparison of vertical roller mills and tumbling mills

•Test results of energy optimized grinding of three different mineral materials•Comparison of vertical roller mills with tumbling mills on the lab and pilot scale•Lab scale tumbling mills arranged in the (energy) optimized comminution sequence•Energy control by torque measurement, dispersity control by permeametry•Based on energy expense for grinding only the tested vertical mills are more efficient.

The Institute of Mineral Processing at the Montanuniversitaet Leoben in cooperation with the company CEMTEC has developed a pilot scale, 200 mm table diameter, vertical roller mill for energy controlled laboratory tests. The mill provides the technical options to vary process parameters like air-flow, mass flow, grinding force and classifier speed in a wide range and is equipped to analyze the internal circulating load. In order to address grinding efficiency (defined as the increase in mass specific surface vs. net specific energy input) the energy consumption of two pilot scale vertical roller mills (200 mm and 670 mm table diameter) was compared to that of a sequence of laboratory comminution equipment covering the same size range. The sequence consisting of a laboratory jaw crusher and three laboratory tumbling mills of differing grinding media was operated following the principles of energy optimized comminution according to the OCS-method. With respect to the grinding energy only all the results for marble, siderite and hematite ore show energy savings when using the vertical roller mill at optimized settings. The methods used are outlined including the special features of the equipment.