We are about to lose our traditional sand supplies for our raw mix. Now we are using 78-80 per cent limestone, 15-17 per cent clay, 1-2 per cent iron ore and 2-4 per cent sand. Now we are thinking to use low grade limestone and no sand. Our management says to use iron dust through kiln firing system in place of using in the raw mill grinding. Mix design is iron dust 0.5 per cent limestone 70 per cent, low grade limestone 18.5 per cent and clay 11 per cent. My point is any raw mix is made to be through raw mill grinding and only fuel through firing system. Let me know your opinion and suggestion.

Many cement plants add high ballast and high ash fuels through the firing system. However, I do not know of any plant that is specifically doing that with iron additive. I also see no reason to do that. There are potential problems of in homogeneity in the clinker. Also you need the iron to form flux in the transition zone, not at the end of the burning zone.

What kind of changes are required in raw mix to increase the granulation with 50 per cent pet coke total CV 4.3 per cent, LSF 93, SM-2.1 per cent, AM-1.0 per cent, in kiln feed?

The granulation problems with pet coke firing arise because of the low viscosity of the flux caused by the sulphur in the pet coke. Therefore raising the silica and alumina modulii should help to improve the granulation.