REBURNING USING BIOMASS FOR NOX CONTROL

This study examines the use of wood reburning for NOx reduction in a c yclone-fired boiler. Reburning is an in-furnace NOx control technology that uses fuel injected above the main firing system to reduce NO for med in the main heat release zone. Bench- and pilot-scale work done ov er the past several years suggests that NOx reductions up to sixty per cent are possible using reburning under the right conditions. The prac tical implementation of reburning technology depends upon the ability to contact the reburning fuel with NO formed in the cyclone barrel at the optimum stoichiometry for he maximum time. Thus, reburning effecti veness in practical systems is determined by the performance of he mix ing system. This paper describe the results of a computer modeling stu dy of the TVA Alien Station Unit No. 2 to evaluate various reburning f uel injection and overfire air injection designs and estimate he NOx r eduction potential using wood as a reburning fuel. Results of this stu dy showed the best mixing was obtained using opposed fired rebuming in jectors located as close to the cyclone barrels as possible with oppos ed-wall overfire air injectors at as high a velocity as pressure drop constraints allow. Under these conditions, NOx reductions of similar t o 45% are expected. When the wood carrier air is replaced by fuel gas, the expected NOx reduction increases to similar to 55%. Further NOx r eduction was possible if the stoichiometric constraints in the reburni ng zone could be relaxed to allow deeper staging. (C) 1998 Elsevier Sc ience B.V.