Effect of the cooling and reheating during coal pyrolysis on the conversion from char-N to NO/N2O

Coal chars employed in the previous studies were usually prepared from coal pyrolysis at high temperatures and then cooled down to the room temperature. As these chars were burned out, they had undergone an additional process: cooling and reheating. The influence of this process on the conversion from char-N to nitrogen oxides had mostly been neglected. In this paper, the influence of cooling and reheating during coal pyrolysis on the conversion from char-N to NO and N₂O is studied on a drop tube/fixed bed reactor. Results indicate that the process of cooling and reheating can cause a fall of NO emission during the coal char combustion. The discrepancy between the experiments with and without cooling and reheating at low temperatures is greater than that at high temperatures. For a high rank coal sample, the difference can be up to 20% in the temperature range of 973–1073 K. In addition, the discrepant nitrogen, which would have been converted into NO in the experiments without cooling and reheating, does not retain in the char during the char combustion. Most of this nitrogen is oxidized into N₂O through the reduction of NO.