NOx REDUCTION FROM A 44 MW WALL-FIRED BOILER UTILIZING OXYGEN ENHANCED COMBUSTION

Praxair has developed a novel method of using oxygen to bring about additional NOx reduction from low NOx combustion systems burning pulverized coal or other nitrogen containing fuels. This paper presents results of field tests in a commercial wall-fired boiler burning pulverized bituminous coal. In pilot- and full-scale burner testing NOx emissions were reduced by as much as 60%, to below 0.15 lb/MMBtu, when a small portion of low-NOx burner combustion air was replaced with locally injected oxygen. Oxygen injection allowed burner operation at lowered stoichiometric ratio, and raised the temperature of the primary combustion zone to favor NOx reduction kinetics. Oxygen addition also reduced carbon in ash. These promising results led to beta testing in a commercial 44 MW wall-fired boiler beginning fourth quarter of 2002. Testing as part of the demonstration project showed greater than 40% reduction in NOx emissions, reduction in LOI, enhanced flame stability, and unanticipated opacity reductions.