In our plant, we have a typical problem of high wear rate of mill liners. The basic reason identified is the percentage of free silica in silica (one of the components of raw meal) is very high about 50 per cent and the consumption of this material is also very high (around 14 per cent) due the very high quality of limestone (low grade limestone, clay or shale is not available in near vicinity) and thus making kiln feed free silica around 9 to 10 per cent. We are of the opinion that the recirculation of the O-Sepa is causing a cummulative effect on the percentage of free silica inside the mill, which is the reason why we see that the total life time of the diaphragm plates is continually reducing (from six months to four months to three months). We would like to know, are you aware of any recent developments in design which can provide an arrangements to remove this high density coarse grain material out of the mill to avoid high abrasion of mill liners and diaphragm plates?

The silica will inevitably build up in the recirculating load of the mill as this is the hardest component of the raw mix. The limestone is preferentially ground leaving the silica in the rejects. Unfortunately I don't know of any means to avoid this.

Our plant has four cement mills (closed circuit with first generation seprator) - 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.