The effectiveness of multi-fuel reburning in an internally fuel-staged burner for NO x reduction

Abstract

Results of a semi-industrial (2.5 MW(th)) furnace study on a swirl-stabilized, internally fuel-staged burner are presented. The burner design relies on penetration of the internal recirculation zone of a swirl-stabilized pulverized coal primary flame with a high-momentum reburn fuel 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 included primary flame zone stoichiometry, reburn fuel fraction and stoichiometry, reburn fuel velocity and injector position, and overall excess air level or tertiary air stoichiometry. For uncontrolled baseline firing, the NO x emission was 1328 ppmv (0% O 2). With fuel staging, NO x emission could be reduced to < 150 ppmv (0% O 2), independent of reburn fuel type. Reburn fuel fractions in the range 20–30% gave the minimum NO x levels over the range of conditions studied without significantly affecting burnout. Reburn fuel velocity and reburn injector position did not significantly affect NO x emission.