SO2 CAPTURE AND N2O REDUCTION IN A CIRCULATING FLUIDIZED-BED BOILER -INFLUENCE OF TEMPERATURE AND AIR STAGING

The effects of air staging and bed temperature on sulfur capture perfo rmance in a circulating fluidized-bed boiler fired with bituminous coa l were studied. Normal air staging, no staging and intensified staging were compared at normal (850-degrees-C) and high (930-degrees-C) temp eratures. The results clearly show that high temperatures and staged c ombustion are detrimental to sulfur capture performance. Sulfur captur e was reduced by more than half with intensified staging at 850-degree s-C. At the high temperature, sulfur capture was still possible withou t staging, but at greatly reduced efficiency. In the two cases with st aging, the sulfur capture was negative in the period 2-3 h after a tem perature increase, as a result of reductive decomposition of calcium s ulfate. The temperature-dependence without staging indicates that redu cing conditions affect sulfur capture in this case as well. The increa se in temperature from 850 to 930-degrees-C halved N2O emissions, from approximately 100 to 50 ppm (at 6% O2).