ASPECTS OF THE EFFICIENCY OF CALCIUM SALTS FOR THE RETENTION OF SULFUR IN COAL ASH DURING COMBUSTION AT 1200-K

Electron microprobe analyses were made of the residual ash particles r emaining after combustion in air at 1200 K of samples of representativ e coals used in thermal power plants and of samples of Northern Irelan d lignite. Local associations of sulphur and calcium in the small area s analysed (c. 10 mum) were ascribed to the formation of the relativel y stable CaSO4. This correlation was not linear and it was concluded t hat locally CaO reacted preferentially with the acidic oxides of silic on and aluminium to form calcium alumino-silicates. We recommend, ther efore, that in assessing the amount of CaCO3 or Ca(OH)2 that must be a dded to a given fuel to achieve effective desulphurisation, due accoun t must be taken of the ability of the constituent oxides in that coal to react with the additive.