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.

I work at a plant 4500tpd, based on FLS design, with a five-stage preheater and precalciner, Our problem is repeated blockage in cyclone stage five (some four times at period of five months). We calculated the sulphate/alkali ratio before each blockage, we found it between 1.45 to 1.7. As we know the normal value should be less than 1.2. The LSF between 92 and 105, also the analysis result of a sample from the blockage material are: SiO₂=19.5, Al₂O₃ =4.76, Fe₂O₃ =3.63, CaO=62.1, SO₃=2.31, K₂O=1.37, Na₂O=0.93. Can you advise if the values of SO₃/AlK ratio to cause the blockage in Cyclone 5 or is it another reason?

From the information you have sent there seem to be two problems, (i) the SO₃/Alkali ratio between 1.45 and 1.7 is very high and would be expected to cause very hard dense coatings, (ii) the variability of the LSF from 92 to 105 is much too high and would be expected to cause major process and quality variability. However. the samples from the blockage do not show very high SO levels and have an SO₃/alkali ratio of 0.87 which should not cause any problems. The other cause could be premature calcination in the cyclone 5 due to variable LSF. This would happen with the change to low LSF, easy burning material.