Evolution prediction of coal-nitrogen in high pressure pyrolysis processes

A pyrolysis model which can describe the effects of pressure on the evolution of coal-nitrogen has been constructed based on the FLASHCHAIN® model in order to relate the gas release mechanism under high pressure conditions to the polymer reactions in coal. Various kinds of nitrogen-containing gaseous species in the evolved volatiles and their secondary decomposition and coupling processes have been also clarified by considering the elementary reactions of pyrrole-type nitrogen as the primary type of bound nitrogen in the first evoluted heavy species (tar vapor). The results show that the recombination reactions of metaplast are activated in a coal by the increase in pressure, resulting in a lesser amount of tar vapor and more intermediate chars. Thus, the conversion ratio of coal-nitrogen to gaseous volatile-nitrogen increases with the increase of pressure and N-gas converted from the fuel-N is much larger than the tar-N, and becomes more significant in high pressure conditions. Due to the chemical kinetics of the gas phase reactions, a shift in the distributions of tar-N vapor and gas-N with the increase of pressure can be predicted, and larger amounts of H2CCHCN and bipyrrole gases are rapidly formed through three-body reactions, while HCN gas decreases greatly compared with the reaction at normal pressures. The changes of gas composition are in close agreement with the experimental results.