Formation of NH3 During Temperature-Programmed and Isotherm Pyrolysis of Different Rank Coals

Abstract

Coals from Yanzhou, Yima, Zunyi and Ximeng mines were used to study the formation of NH₃ during pyrolysis in a fixed-bed reactor under argon atmosphere. Results show that the release of NH₃ is mainly affected by coal properties and its heating course. Total and accumulated yields of NH₃ basically takes the order of volatile content in coal, but the relative stability of heterocyclic nitrogen is very important. Low rank coal with high volatile content is favorable for NH₃ formation. NH₃ mainly yields from the rapid cracking of heterocyclic structure containing pyrrolic nitrogen at low temperature, initially releases at 400 ºC and presents the maximum at 700 ºC. The yield of NH₃ in holding stage increases with increasing pyrolysis final temperature and reaches maximum at 600 ºC. When the temperature is below 600 ºC, the yield of NH₃ in holding stage (Yc) is higher than that in heating stage (Yp). From 600 ºC to 800 ºC, Yc is lower than Yp because of the release of volatile is easy and rapid at high temperature.