Evolution behaviors of nitrogen functionalities during fast CO2-rich pyrolysis of coal.

To clarify the pyrolysis mechanism of different nitrogen functionalities in coal during oxy-fuel combustion (OFC), fast pyrolysis tests of four nitrogen models containing the raw proportion of low-temperature ash were performed under a CO 2 -rich atmosphere in a vertical fixed bed at 1100 °C. The oxidation characteristics of nitrogen functionalities in the investigated coal during fast CO 2 -rich pyrolysis were further studied by comparing CO 2 -rich atmosphere with argon atmosphere. Results show that during conventional pyrolysis pyridinic nitrogen tends to be oxidized to pyridine N-oxide by oxygen functionalities in coal, afterwards high-temperature pyrolysis of the latter may lead to more NO 2 emissions. During CO 2 -rich pyrolysis quaternary nitrogen has a good potential to be oxidized to pyridonic nitrogen by oxidizing species in atmosphere, and further decomposition of the latter could generate NH 3 so as to suppress NO 2 formation. The yield of fuel-N to NO 2 corresponding to CO 2 -rich pyrolysis decreased by roughly three times than that of conventional pyrolysis. The oxidation effect of CO 2 on pyrolysis behaviors of nitrogen functionalities in coal is supposed to be another key factor of low NO x emissions during the OFC process regardless of the reduction effect of CO induced by elevated CO 2 level. [ABSTRACT FROM AUTHOR]