Experimental combustion characteristics and NOx emissions at 50% of the full load for a 600-MWe utility boiler: Effects of the coal feed rate for various mills

For realizing higher boiler efficiency and lower NOx emissions at a half load of a 600-MWe utility boiler, a novel approach is proposed for various coal feed rates. In this study, at 50% of the full load, industrial-size experiments were conducted at various coal feed rates with measurements of local gas temperatures and species concentrations (in the burner region and near-wall region, respectively), the carbon content of the fly ash, the carbon content of the slag, and the NOx emissions. The pulverized-coal ignition positions of two burners at low loads were at 0.2–0.3 m from the burner nozzle outlet; hence, satisfactory ignition performance was realized. At larger coal feed rates of mill A, both the ignition performance and the NO reduction performance improved. The unburnt carbon in the fly ash decreased monotonically and the carbon in the slag increased monotonically, with settings from 50%:50%–36%:64% (namely, changing the coal-feed rate pair of the middle and bottom mills from 50%:50%–43%:57%–36%:64%).