Formation of NO_x Precursors During Chinese Pulverized Coal Pyrolysis in an Arc Plasma Jet

摘要

The formation of NO_x precursors (HCN and NH_3) from the pyrolysis of several Chinese pulverized coals in an arc plasma jet was investigated through both thermodynamic analysis of the C-H-O-N system and experiments. Results of thermodynamic analysis show that the dominant N-containing gaseous species is HCN together with a small amount of ammonia above the temperature of 2000 K. The increase of H content advances the formation of HCN and NH_3, but the yields of HCN and NH_3 are decreased with a high concentration of O in the system. These results are accordant with the experimental data. The increasing of input power promotes the formation of HCN and NH_3 from coal pyrolysis in an arc plasma jet. Tar-N is not formed during the process. The yield of HCN changes insignificantly with the changing of the residence time of coal particles in the reactor, but that of NH_3 decreases as residence times increase because of the relative instability at high temperature. Adsorption and gasification of CO_2 on the coal surface also can restrain the formation of HCN and NH_3 compare to the results in an Ar plasma jet. Yields of HCN and NH_3 are sensitive to the coal feeding rate, indicating that NO_x precursors could interact with the nascent char to form other N-containing species. The formation of HCN and NH_3 during coal pyrolysis in a H_2/Ar plasma jet are not dependent on coal rank. The N-containing gaseous species is released faster than others in the volatiles during coal pyrolysis in an arc plasma jet, and the final nitrogen content in the char is lower than that in the parent coal, which it is independent of coal type.