1156 posts
Raw materials Question 27
What would be difference in terms of clinker burning and combinability of a raw meal containing sand of low quantity (below three per cent) compared with a raw meal containing of high quantity (about six per cent) sand. In both cases the raw meal residue was kept below 14 per cent on +90mm.
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1156 posts
Re: Raw materials
You really need to analyse the composition of the sieve fractions, ie +125 micron, 45 to 125 micron and sub 45 micron for SiO2 and CaO. I expect the silica is concentrating in the coarser fractions and that this becomes more severe as the amount of sand in the mix increases. So even if the raw mixes have the same +90 micron residue I expect that the burnability of the higher silica raw mix is more difficult.
1156 posts
Raw materials Question 28
In our raw mix, iron ore is used as an additive. Its purity is around 94 per cent and it is in the proportion of 1.5 per cent in the raw meal. There is an iron rich material that is a collection of bag house fines from a steel plant. In this Fe2O3 content is around 50 per cent and also contains around 20 per cent zinc oxide. We want to know the effect of ZnO, on the burning process, brick life and on the quality of the finished product OPC, in case if use this material in our raw mix.
1156 posts
Re: Raw materials
You will need up to three per cent of the steel plant bag house fines to replace your iron oxide additive due to the relative Fe2O3 contents of the two materials. That means the ZnO content of the raw mix will be about 0.6 per cent and almost 1 per cent in clinker. The ZnO will mineralise the clinker formation, reducing the fuel consumption of the kiln and will be incorporated in the clinker minerals, C3S, C3A and C4AF. The lower burning zone temperatures should mean that the refractory brick life is improved. You can expect that the hydration of the final cement will be retarded therefore setting times will increase and early strengths will be lower. Perhaps the longer setting time will also be an advantage.
My recommendation would be to adjust the raw mix chemistry to raise the LSFand AM and compensate for these changes. This will reduce the amount of baghouse fines required and therefore the ZnO additions. The mineralising effect of the ZnO will allow a higher LSF kiln feed to be combined in the kiln. At the same time C3S and C3A content in clinker and cement will be increased offsetting the retardation effects of the ZnO.