Effect of the oxygen concentration on the oxy-fuel preheated combustion characteristics and NOx control path of different coal rank fuels

The oxy-fuel combustion with low NOx emissions for pulverized coal is multi-disciplinary sought in recent decades. In this work, a 30 kW preheating combustion experimental investigation of bituminous coal, semi-coke, lignite, and anthracite was implemented to obtained the effect of the oxygen concentration on the oxy-fuel preheated combustion characteristics and NOx control path of different fuels. The results showed that increasing the oxygen concentration of the preheating device was beneficial for enhancing the intensity of fuel modification, especially for high-rank coal and semi-coke with low volatile contents and high fixed carbon contents. This was primarily evident in the augmentation of the gas's calorific value, the increased conversion ratio of fuel to preheated coal gas, and the generation of numerous small pore structures. When the oxygen concentration of primary stream was increased to 37 %, the calorific value of the preheated coal gas produced by semi-coke under an O2/CO2 atmosphere reached 2.25 times greater than that under air atmosphere. The conversion ratio of anthracite to preheated coal gas under O2/CO2 atmosphere reached 4.6 times greater than that under air atmosphere. Compared with air preheating combustion technology, oxy-fuel preheating combustion technology had a more obvious advantage in reducing NOx emissions, but the regulation paths for reducing NOx vary for different fuels. In the study of NOx emission characteristics during the oxy-fuel preheating process of different fuels, the lowest NO emissions of bituminous coal, semi-coke, and anthracite combustion were 16.31 mg/MJ, 14.51 mg/MJ, and 13.83 mg/MJ, respectively. The lowest NOx emission of lignite combustion was 18.56 mg/MJ.