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 NH 3 and HCN from the fast pyrolysis were much higher than those from the slow pyrolysis. The difference in the yields of NH 3 and HCN between the fast and slow heating rates increases with the increasing pyrolysis temperature. The maximum productions of NH 3 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.