Mechanism study of nitric oxide reduction by light gases from typical Chinese coals

Abstract

Coal devolatilization plays an important role in NO formation and reduction. In this study, the coal pyrolysis experiment was performed in an entrained flow reactor to obtain the light gas release characteristics. Six typical Chinese coals with volatile content ranged from 8.8% to 38.3% were studied. The pyrolysis temperature was in the range from 600 to 1200 °C. A significant rank dependence of HCN, CO and C2H2/C2H4/C2H6 was observed and their release for high volatile coals was higher than that for low volatile coals. The HCN–N/NH3–N ratio ranged from 0.00 to 0.66 for anthracite coals and ranged from 1.63 to 3.90 for high volatile coals. Based on the experimental results, the effect of coal pyrolysis gas on NO reduction in a plug flow reactor at reducing atmosphere was kinetically calculated. The optimal excess air ratio(αopt) corresponding to the maximum NO removal efficiency decreased with an increase in reduction temperature. For the light gas from the HL coal pyrolyzed at 800 °C, the αopt decreased from 0.73 to 0.17 when the reduction temperature increased from 927 to 1327 °C. The rate of production analysis indicated that NO removal efficiency was determined by 3 competing reaction paths: NO reduction, NO formation and oxygen consumption by combustible species.