Reduction of nitrogen oxides by injection of urea in the freeboard of a pilot scale fluidized bed combustor

Abstract

The ‘thermal deNOx’ process using urea has been investigated in a 1 MW fluidized bed combustor. NOx reductions of up to 76% were obtainable by using this method. The experimental results show that urea is at least as active as NH3, which is commonly used in this application, but which is far more toxic and corrosive. Emission levels of 200 mg m−3 for NOx could be achieved by injecting the urea at a height of 2 m above the distribution plate in a molar ratio urea:NOx = 1.5. The SO2 emission value also appeared to be reduced when the urea was injected at a urea: NOx molar ratio > 4