Desulphurization by limestone injection at high temperature

An isothermal flow reactor was used to characterize the physical and chemical processes during calcination and sulphation of limestones. The experimental data from the flow reactor were compared to a calcination model, which assumed that calcination was proportional to the specific surface area (BET) of undecomposed calcium carbonate, and to two sulphation models, a random pore model and a grain model in the case of product layer diffusion control. The results indicate that the limestones undergo significant physical changes during the calcination process. The calcium carbonates calcined in less than 0.3 second under typical combustion conditions. The calcination results were quite well predicted up to 80% conversion with the calcination model used. The results of the sulphation and the simultaneous calcination and sulphation suggest that under conditions typical of sorbent injection in the boiler, the major portion of the calcium sulphate formation will occur very rapidly (during about 0.3 s). Electron microprobe analyses showed that the sulphur seemed to be mainly on the outer surface of the reacted particles.