Fate of fuel‑nitrogen during in situ gasification chemical looping combustion of coal

Abstract

In situ gasification chemical looping combustion (iG-CLC) was a promising way to inherently sequestrate CO2. Due to the nitrogen in coal, the NOx emission was a key issue in iG-CLC. In this study, we aimed to identify the nitrogen conversion and distribution characteristics in two elementary stages of coal conversion (pyrolysis and subsequent char gasification) during the iG-CLC process in a tailor-made two-stage fluidized bed reactor. HCN was the dominant precursor of NOx in iG-CLC, almost all the NOx precursors were rapidly released during the coal pyrolysis stage, and no gaseous nitrogen pollutant was detected within the subsequent CO2-char gasification process. The generated HCN could be completely converted by the Fe-based oxygen carrier (OC) to either NO or N2. The high CO2 concentration and reducing reaction atmosphere in the fuel reactor were found to exert certain inhibitory effects on the formation of NO. Meanwhile, the operating conditions, that is, the O/fuel ratio and temperature, exhibited insignificant effects on the fate of fuel-N. Finally, the fate of nitrogen in volatiles, char, and tar of coal during iG-CLC and the potential homogeneous nitrogen conversion in the iG-CLC of coal were proposed based on the results obtained from both experiments and thermodynamic simulations.