ABATEMENT OF N2O EMISSIONS FROM CIRCULATING FLUIDIZED-BED COMBUSTION THROUGH AFTERBURNING

A method for the abatement of N2O emission from fluidized bed combustion has been investigated. The method consists of burning a secondary fuel after the normal circulating fluidized bed combustor. Liquefied petroleum gas (LPG), fuel oil, pulverized coal, and wood, as well as sawdust, were used as the secondary fuel. Experiments showed that the N2O emission can be reduced by 90% or more by this technique. The resulting N2O emission was principally a function of the gas temperature achieved in the afterburner and independent of afterburning fuel, but the amount of air in the combustion gases from the primary combustion also influences the results. No negative effects on sulfur capture or on NO or CO emissions were recorded. In the experiments, the primary cyclone of the fluidized bed boiler was used for afterburning. If afterburning is implemented in a plant optimized for this purpose, an amount of secondary fuel corresponding to 10% of the total energy input should remove practically all N2O. During the present experiments the secondary fuel consumption was greater than 10% of the total energy input due to various losses.