Evolution behaviors of nitrogen functionalities during fast CO_2-rich pyrolysis of coal

摘要

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 CO2-rich atmosphere in a vertical fixed bed at 1100 degrees C. The oxidation characteristics of nitrogen functionalities in the investigated coal during fast CO2-rich pyrolysis were further studied by comparing CO2-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 NO2 emissions. During CO2-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 NH3 so as to suppress NO2 formation. The yield of fuel-N to NO2 corresponding to CO2-rich pyrolysis decreased by roughly three times than that of conventional pyrolysis. The oxidation effect of CO2 on pyrolysis behaviors of nitrogen functionalities in coal is supposed to be another key factor of low NOx emissions during the OFC process regardless of the reduction effect of CO induced by elevated CO2 level.