Impact of co-firing lean coal on NO x emission of a large-scale pulverized coal-fired utility boiler during partial load operation

Abstract

The present work aimed at combustion optimization of a 1,000 MW tower-type ultra-supercritical boiler co-firing a lean coal with bituminous coals for reducing NOX emission particularly at low load operations. Historic operation data were systematically analyzed to investigate the characteristics of NOX emission. Through comparing between lean coal co-firing and sole bituminous coal firing, it was confirmed that, besides the big difference in quality and combustion characteristics of the lean coal from the bituminous coals, the excess air ratio in main combustion zone had a significant effect on NOX emission. Keeping the ratio at properly lower level achieved lower NOX emissions at low load operations. Based on the analyses, in-situ tests successfully brought NOX emissions of co-firing down close to 300 mg/m3 at the load of 700 MW, demonstrating the effectiveness of combustion optimization for controlling NOX emissions at partial load operation of co-firing.