Method for reducing emissions when burning nitrogen containing fuels

Abstract

The amount of N.sub.2 O in flue gases discharged from a fluidized bed combustion system is minimized by adding an N.sub.2 O decomposing catalyst in a reactor stage downstream of the combustor. The catalyst preferably is a calcium based sorbent, such as CaO or or limestone, although NiO and other catalysts also may be utilized. Typically, the N.sub.2 O decomposition takes place without increasing the temperature of the flue gases above the 700.degree.-1000.degree. C. level that exists combustor. However, under some circumstances, if a second fluidized bed is provided as the reactor stage, additional fuel and oxygen can be added to increase the temperature of the flue gases to insure that it is over 800.degree. C. After N.sub.2 O decomposition, the flue gases may be passed through pressurized filter tubes, or through a superheater, economizer, air preheater, optional cyclone separator, and baghouse filter. A cyclone separator is preferably provided between the combustor and reactor stage, and the removed particles are recirculated to the combustor. Removal of particles, including unused sorbent, after the reactor stage also preferably takes place, with recycle to the reactor stage (if a fluidized bed stage) and/or to the combustor.