Impact of co-firing lean coal on NOx emission of a large-scale pulverized coal-fired utility boiler during partial load operation

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 NO X emission particularly at low load operations. Historic operation data were systematically analyzed to investigate the characteristics of NO X 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 NO X emission. Keeping the ratio at properly lower level achieved lower NO X emissions at low load operations. Based on the analyses, in-situ tests successfully brought NO X emissions of co-firing down close to 300 mg/m 3 at the load of 700 MW, demonstrating the effectiveness of combustion optimization for controlling NO X emissions at partial load operation of co-firing.