INFLUENCE OF OPERATING PARAMETERS ON NOX EMISSIONS FROM A CIRCULATING FLUIDIZED-BED COMBUSTOR

A parametric study of NO(x) emissions has been carried out on a 150 mm2 x 7.3 m tall pilot scale circulating fluidized bed combustor with coals of various ranks, including anthracite, bituminous, subbituminous and lignite, as well as one petroleum coke. Increasing either temperature or excess air was found to increase NO(x) emissions significantly in the ranges studied. The effect of staged combustion on NO(x) emission depended on the level at which the secondary air was introduced. A reduction of NO(x) emission was usually, but not always, observed when secondary air was introduced 3.4 m above the base. Limestone addition promoted NO(x) formation for high volatile bituminous coal, due to the catalytic effect of limestone on oxidation of volatile nitrogen. However, adding limestone during petroleum coke combustion reduced NO(x) emissions. A relationship exists between fuel nitrogen to NO(x) conversion and the volatile content of the fuel, with fuels of higher volatile content emitting more NO(x).