Pilot-scale study on NO emissions from coarse coal combustion preheated by circulating fluidized bed

Achieving stable low-NOx combustion of coarse pulverized coal could improve the energy efficiency of the combustion system. In this study, a pilot-scale experiment on coarse coal (0–1 mm) combustion preheated by circulating fluidized bed is conducted. The coarse coal could achieve a long-term stable preheating, and the assisted combustion by the high-calorific preheated coal gas (3.06 MJ/Nm3) and the higher physical sensible heat (754 °C) greatly improved the ignition performance and the combustion stability of the preheated fuel. Meanwhile, the release ratio of fuel-nitrogen during the preheating was 36.56%, while the concentrations of NOx in the preheated coal gas were all 0 ppm. During the stable combustion, the volume-based average temperature and the volume-based temperature fluctuation coefficient in the main combustion zone was approximately 1112 °C and 8.89%, and the combustion efficiency was approximately 95%. The NOx concentrations in the strong reductive zone were almost 0 ppm. As the reaction atmosphere along the combustion path gradually varied from reducing to oxidizing, fuel-nitrogen was mainly oxidized to NO, and the NO emissions was approximately 68 ppm (114 mg/m3 @6%O2). In addition, the effects of burnout air positions in strong reductive zone on NO emissions could be ignored.