THE EFFECTIVENESS OF MULTIFUEL REBURNING IN AN INTERNALLY FUEL-STAGEDBURNER FOR NOX REDUCTION

Results of a semi-industrial (2.5 MW(th)) furnace study on a swirl-sta bilized, internally fuel-staged burner are presented. The burner desig n relies on penetration of the internal recirculation zone of a swirl- stabilized pulverized coal primary flame with a high-momentum reburn f uel jet. A high-volatile bituminous coal was used as the primary fuel; reburn fuels included two high-volatile bituminous coals, heavy fuel oil, natural gas and coke oven gas. Process parameters investigated in cluded primary flame zone stoichiometry, reburn fuel fraction and stoi chiometry, reburn fuel velocity and injector position, and overall exc ess air level or tertiary air stoichiometry. For uncontrolled baseline firing, the NO(x) emission was 1328 ppmv (0% O2). With fuel staging, NO(x) emission could be reduced to < 150 ppmv (0% O2), independent of reburn fuel type. Reburn fuel fractions in the range 20-30% gave the m inimum NO(x) levels over the range of conditions studied without signi ficantly affecting burnout. Reburn fuel velocity and reburn injector p osition did not significantly affect NO(x) emission.