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 performance in a circulating fluidized-bed boiler fired with bituminous coal were studied. Normal air staging, no staging and intensified staging were compared at normal (850-degrees-C) and high (930-degrees-C) temperatures. The results clearly show that high temperatures and staged combustion are detrimental to sulfur capture performance. Sulfur capture was reduced by more than half with intensified staging at 850-degrees-C. At the high temperature, sulfur capture was still possible without staging, but at greatly reduced efficiency. In the two cases with staging, the sulfur capture was negative in the period 2-3 h after a temperature increase, as a result of reductive decomposition of calcium sulfate. The temperature-dependence without staging indicates that reducing conditions affect sulfur capture in this case as well. The increase in temperature from 850 to 930-degrees-C halved N2O emissions, from approximately 100 to 50 ppm (at 6% O2).