Our plant has four cement mills (closed circuit with first generation separator) - we use about 20 per cent slag, the output is 100tph ,the dimension of every mill is 15.5 x 4.4, the liners in the first chamber are lifting and in second chamber classifier. Are there any ways to increase mill production? How about for a raw mill?

There are numerous ways to increase the production from your cement mills. In the short term use of grinding aids combined with optimisation of the ball charge and drafting would be the best method. Longer term (and at greater cost) you could upgrade the separators to third generation or install a roll press to pre-crush the clinker ahead of the mills. With regard to raw mills you can again use grinding aids or install pre-grinding equipment.

I wish to investigate the differences in grinding of slag over clinker. We have a 100tph OPC cement ball mill. Could this mill grind slag? What modification would be needed? Is it always necessary to supply hot air when grinding slag? What sort percentage drop in production should be expected?

Yes, your ball mill can grind slag. If it were to be permanently converted to slag grinding then a change to a finer ball grading would be necessary. Slag is normally ground finer than cement and has a smaller grain size to begin with. Certainly there is a limit to the drying capacity of a mill based on the heat generated in the mill alone. To determine whether you need to add hot air you need to develop a heat balance of the mill and test various scenarios with different moisture contents of slag and feed rates. Slag is much harder than cement clinker and therefore you could expect as much as a 50 per cent reduction in output from the mill.