Release of Nitrogen Species during Rapid Pyrolysis of Model Coals

To gain an in-depth insight into the release of nitrogen species during rapid pyrolysis of coals, two model coals containing pyrrolic or pyridinic nitrogen are synthesized, and rapid pyrolysis of model coals is performed in an entrained flow system between 800 and 1300 degrees C. The effects of pyrolysis temperature, minerals, particle size, and the interaction between the two forms of nitrogen are discussed. The results show that a moderate amount of HCN and small amounts of NO and NO2 rather than NH3 are formed. As the temperature rises, the HCN release increases first and then decreases, and exhibits very similar trends for the two forms of nitrogen. Because of the better thermal stability of pyridinic nitrogen, the releases of both HCN and NOx are lower for pyridinic nitrogen than for pyrrolic nitrogen. When the two forms of nitrogen are pyrolyzed together, the interaction between the nitrogen species released makes the HCN release decrease and approach the HCN release from pyridinic nitrogen alone. For pyrrolic nitrogen, Fe addition suppresses the HCN release at all temperatures and Na addition promotes the HCN release obviously at 1000 degrees C or above, whereas Ca addition increases the HCN release with increasing temperature first and then decreases. For pyridinic nitrogen, all the metal additions suppress the HCN release and Fe has the strongest catalytic effect. As the catalyst content increases, the HCN release decreases drastically. The HCN release from pyridinic nitrogen increases slightly with increasing particle size at 800 or 1000 degrees C. When the temperature achieves 1200 or 1300 degrees C, the particle size dependence of HCN release is not observed.