NO_x and N₂O Emission Characteristics From Circulation Fluidized Bed Combustion of Blends of Paper Mill Sludge and Coal

With the rapid economic development and the increase in population in the whole world, the amount of municipal sewage (MS) is increasing and lead to a rapid increasing in amount of municipal sewage sludge (MSS). Combustion of municipal sewage sludge may be a viable solution for its disposal in some cases and so is its co-combustion with coal. Whereas significant information is available on NO_x and N₂O emissions characteristics of sludge and coal individually, not much has been reported on sludge/coal blends. In the present paper, investigations in NO_x and N₂O emission characteristics from circulation fluidized bed combustion of blends of municipal sewage sludge and coal were conducted in a 0.2MW_th circulating fluidized bed test facility with cross section of 0.23×0.23m² and height of 5.9m. Coal sample selected was a kind of lignite, while a kind of paper mill sludge was used as sludge sample. The influences of sludge/coal mixing rate, excess air ratio and second air ratio on NO_x and N₂O emission characteristics have been studied. Test results show that co-combustion of sewage sludge and coal is feasible. With the increasing in proportion of sludge of the sludge/coal blends, the temperatures in dense bed and freeboard decrease rapidly, and the emissions of NO_x decrease while the emission of N₂O increases obviously. With the increasing in excess air ratio, the emission concentrations of NO_x and N₂O increase. While with the increasing in secondary air ratio, the emission concentrations of NO_x and N₂O decrease.