High ash coal
Does anyone have any experience or knowledge regarding the use of high ash anthracite in their kilns. The coal in question is a low volatile coal (anthracite) with 7% volatile matter and gross calorific value of 23 MJ/kg (air dried). The problem is that the ash content is very high in the range 26-35% (air dried). The ash constituents consist of 57% silica, 27% AL2O3, 7% Fe2O3 and 5% CaO.
Would be grateful for any insights into the use of this or similar types of fuels.
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re High ash coal
With low volatile matter/high ash coals you have to consider the following;-
(a) KILN RINGS: High-ash coals are more likely to result in ash rings within the kiln.
(b) COAL FINENESS: Low volatile matter coals need to be ground finer. The 'rule of thumb' is that the R90 um target should be half of the volatile matter content, which in your case means you would have to grind the anthracite to ~3.5% on 90um sieve. (In addition, a special burner tip design is often needed for anthracite coal.)
(c) LIMESTONE REQUIREMENTS: Compared to low ash coals, high-ash coals require a considerably higher raw meal LSF to achieve a given clinker LSF target. ie more high-grade limestone from the quarry.
(d) VARIABILITY: If the ash content, volatile matter or GCV in the coal have high variability, there will be significant impact on the flame dynamics, clinker chemistry and kiln stability.