Preheating and combustion characteristics of anthracite under O2/N2, O2/CO2 and O2/CO2/H2O atmospheres

Abstract

In this study, the anthracite was preheated by a circulating fluidized bed under O2/N2, O2/CO2 and O2/CO2/H2O atmospheres. And the preheating and combustion characteristics of anthracite were studied. Compared with the O2/N2 atmosphere, the structural characteristics of preheated char was improved more obviously under the O2/CO2 and O2/CO2/H2O atmospheres when the oxygen concentration was 31%, which mainly reflected in the increase of BET surface and the increase of small aromatic rings. HCN was mainly NOx precursor during the preheating under different atmospheres. In addition, a novel comprehensive evaluation of ignition and stable combustion characteristics for preheated fuel was proposed. And the minimum thermal power required for preheated char combustion and the combustion heat of preheated coal gas were main factors affecting on the ignition and stable combustion characteristics. The highest combustion efficiency of anthracite was 98.85% under the O2/N2 atmosphere (the oxygen concentrations of primary gas, secondary gas and tertiary gas were 31.0%, 36.0% and 35.0%), and the lowest NO emission in tail flue gas was 24.24 mg/MJ under the air atmosphere.