Effect of heating rate on migration and transformation of N during pyrolysis of Shengli brown coal

Abstract

The effects of heating rate on migration, transformation and occurring forms of nitrogen during pyrolysis of Shengli brown coals were studied in a fixed-bed/fluidised-bed quartz reactor. The results indicate that the yields of NH3 and HCN from the fast pyrolysis were much higher than those from the slow pyrolysis. The difference in the yields of NH3 and HCN between the fast and slow heating rates increases with the increasing pyrolysis temperature. The maximum productions of NH3 and HCN mostly occur at 973 K, which is attributed to the enhanced condensation and secondary reactions with the increasing pyrolysis temperature. The release rate of char-N is faster than the weight loss rate of char itself at fast heating rate. The results from X-ray photoelectron spectroscopy (XPS) analysis imply that the pyrolysis process has facilitated the transformation of pyrrolic (N-5) to quaternary type nitrogen (N-Q) and pyridinic (N-6). It seems that the fast heating rate favors the formation of N-6 while the content of N-Q in char is relatively high at the slow heating rate.