I am a Chemical Engineer working in a company in the cement area in South America and the question is: What sort of fluorspar (acid, metallurgic) is used as fluxing agent in clinker process, what percentage of fluorspar and what quantity in the raw mix fed to the kiln. Does it imply savings in heat?

In my experience acid grade fluorspar spar is used as a mineraliser, however there is no reason why other grades should not be used. Again in my experience addition rates have been up to 0.4 per cent to kiln feed, achieving unit fuel consumption savings in excess of 200 kJ/kg clinker.

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.