Evaluation of sorbents and additives for dry SO2 removal

Bench scale studies of the reaction between sulfur dioxide and alkaline sorbents were performed in an integrated fixed bed reactor at low temperature, simulating the fabric filter dust layer of dry FGD systems with SO2 laden gas passing through it. Three major groups of sorbent were tested: calcitic and dolomitic hydrated lime, sodium bicarbonate, and limestone (calcite aragonite) with salt additives such as CaCl2, Ca(NO3)2, and NaNO3. Relative humidity significantly affected SO2 absorption by lime and limestone plus additives, but had less impact on NaHCO3 reactivity. Different reaction patterns for various sorbents were observed: the SO2/hydrated lime reaction rate was reduced with conversion of the sorbent, resulting in limited lime utilization, whereas the reactions between SO2 and NaHCO3 and SO2 and CaCO3 plus additives seem to proceed a constant rate, potentially leading to high sorbent utilizations. Results are discussed relating to sorbent screening for dry FGD systems.