Comparison of sulphur retention by coal ash in different types of combustors

Abstract

During coal combustion, a part of the total sulphur in coal will be retained as solid compounds in ash. In the present paper, the retention of sulphur by ash of typical Chinese coal used for electric power generation was correlated with the contents of alkaline elements relative to sulphur in the parent coal. Comparison was performed among the capabilities of sulphur retention by coal ashes in laboratory ashing procedure, pulverised coal-fired combustor and fluidised bed combustor (FBC). It was shown that calcium plays a dominant role in sulphur retention of laboratory-prepared ash and the sulphur retention percentage increases with the increase of Ca/S molar ratio of the parent coal, while the contributions of other elements are limited. The sulphur retention behaviour in pulverised coal-fired combustor is significantly different from that in laboratory ashing procedure. The contribution of calcium is reduced markedly, while the roles of the other alkaline elements are obviously enhanced. Using the literature data from foreign coals, it was found that the sulphur retention in FBC is comparable with that in laboratory ashing procedure. It was suggested from the results obtained in this study that the sulphur retention of laboratory-prepared ash can be applied to fluidised bed combustion because the behaviour of calcium is similar to that of lime in FBC.