ASPECTS OF THE CHEMISTRY OF CALCIUM-SULFATE IN COAL ASH

Equimolar mixtures of iron sulfide, calcium carbonate and other select ed additives were ignited in air at 1200 K, and it was shown that abou t 70% of the sulfur was retained in the residue as calcium sulfate. Th ese reaction conditions were selected to represent those applicable wh en calcium carbonate is used in fluidized bed combustion. Calcium oxid e is efficient in trapping sulfur oxides. It was further shown, howeve r, that under the same well defined reaction conditions alumino-silica tes react with CaSO4, to some extent, to release a proportion of the s ulfur (approximately 30%). This result is consistent with a previous c onclusion that acidic oxides in coal reduce the efficiency of calcite for sulfur oxide removal from flue gases.