Use of calcined and noncalcined calcium-based sorbents for H2S capture in fluidized bed gasifiers

This work describes the H2S uptake by two limestones and a dolomite under atmospheric conditions in a thermobalance at temperatures between 450 and 850 degrees C and with sorbent particles between 0.4 and 1.6 mm. The effects of reaction temperature and sorbent particle size were analyzed, working with calcined, half-calcined and noncalcined sorbents. For the dolomite the sulfidation reaction, in both full-calcined and half-calcined conditions, increased with increasing reaction temperature and with decreasing its particle size. However, for the limestones a very different behaviour between calcined and noncalcined conditions was found. In calcined conditions conversions up to 100% were reached, the sulfidation rate did not depend on particle size at low temperatures (<500-550 degrees C), however the conversions increased with decreasing particle size at high temperatures (>500-550 degrees C). In noncalcined conditions the sulfidation rate of the limestones did not depend on particle size in all of the range tested. The initial reaction rates increased with increasing reaction temperature until 750 degrees C and it was nearly constant from this temperature, but when the conversion increased the reaction rate dropped sharply at the highest temperatures, giving a maximum conversion at 650 degrees C. This drop in the reaction rate at the highest temperatures was mainly due to sintering of the CaCO3.