Case Studies of Models of Tube Mill and Air Separator Grinding Circuits

"A research program on modelling cement grinding circuits has been in operation at Hacettepe University, Ankara, for four years. It has concentrated so far on tube mill and air separator grinding circuits for cement clinker, with emphasis on plant sampling surveys, including axial sampling inside the tube mills. The data used for model development have come from 33 surveys in 9 plants.The operating conditions have been:- mill sizes - 3.2 to 4.8 metres diameter and 8.5 to 15 metres long,- mill feed rates - 46 to 158 tonnes per hour,- air flow through mills - 25000 to 125000 cubic metres per hour,- cement clinker work indexes - 10.3 to 18,- separator sizes - 2. to 3.1 metres diameter,- separator feed rates - 132 to 689 tonnes per hour,- separator speeds - 12.3 to 21 metres per second.The ball mill model is Whiten’s perfect mixing model and the separator model is the Tromp curve with a fish-hook. This paper emphasises the importance of calculating the breakage rates and the discharge functions with three case studies at five different circuits which were selected for discussion because they show how particular features of circuit operation can be included in the general models. Size distribution graphs are used to illustrate every aspect of the discussion"