We have a problem related with high sand usage to make the consistent raw material mix. Sand addition for silica correction is roughly five per cent into raw material results roughly three per cent quartz content in the raw meal over 45 micron residue. Consequently the overall effect is frequent free lime formation in the clinker due to high quartz content in the raw meal, negatively effecting quality and high heat consumption in burning. In order to tackle with the problem following activities are already done
1. The burner pipe is replaced by a new design burner pipe with high momentum to improve burning and have stronger flame.
2. New coal dosing system is installed to have stable and accurate kiln fuel feed. Also with this system, we started to grind petcoke and other types of coal separately to facilitate burning. However the problem still persists.

I agree with you that the high quartz content above three per cent over 45 micron is the root of the problem. The new burner and the improved coal dosing can only be advantages but they are unlikely to solve this problem of low reactivity of the kiln feed. There are many white cement factories that are operating with very high silica sand additions. These would be the best references. My suggestion of a remedy would be to introduce duplex grinding where the rejects from the raw mill classifer are separately ground and reintroduced to the raw mix. This is a radical solution and requires process modifications to introduce, however it will solve the problem.

I cannot foresee that reduces the load of dust entering a filter will have any detrimental effect on its performance. Certainly no problem with an ESP. Your point regarding fine dust blinding the cloth of fabric filters maybe valid, but I would be surprised.

In an air-swept mill false air is usually introduced at the bottom of the ascension pipe in order to ensure there is sufficient volume, density and velocity of air to lift the ground material up the ascension pipe and through the separator. The amount of dust being carried up the ascension pipe is the same, however the volume of air is greater therefore the overall effect is a dilution of the dust load. In principle the false air will cause a reduction of the temperature and this will reduce the resistivity of the dust improving the electrostatic precipitation.