An experimental and kinetic modeling study of the reduction of NO by coal volatiles in a flow reactor

The reduction of NO by reactions with primary coal tar and other volatiles under fuel-rich conditions was investigated using a tubular-flow reactor coupled to a fluidized-bed reactor. The primary coal volatiles were generated at high heating rate (10⁴ K s^-1) conditions in the fluidized-bed reactor. The results were compared to those from experiments performed using the same experimental setup but with CH₄ instead of the primary coal volatiles. The experimental results show that reactions of coal volatiles result in greater NO reductions than reactions with CH₄. In addition, NO reduction by coal volatiles occurs at much lower oxygen concentrations, indicating the higher reactivity of the coal volatiles compared to that of CH₄. Increases in the yields of HCN and HNCO were found to occur concurrently with the decrease in NO during the experiments with the coal volatiles, suggesting that the NO is reduced to these two species under the conditions employed in this study. Kinetic modeling of the experiments with coal volatiles was performed using a highly simplified model for the coal tars, in which the tar was modeled as structures representative of the major species known to be present in primary tar: n-heptane to represent the longchain aliphatics, toluene and phenol to represent the aromatics, and a pseudospecies, designated as tar-N, to represent the nitrogen-containing components in primary tar. Despite the simplified tar-nitrogen chemistry employed (the nitrogen in tar was assumed to evolve via the first-order global reaction, tar-N → HCN), the modeling results show reasonable predictions of the major gas-phase species. Yields of HNCO and NH₃ however are poorly predicted.