NO release during chemical looping combustion with iron ore as an oxygen carrier

• NO release in chemical looping combustion of solid fuels was investigated.
• Iron ore can oxidize NH3/HCN to NO only when Fe2O3 was reduced to Fe3O4.
• NO release during coal CLC was investigated in a 1 kWth CLC prototype.
• The elevated temperature and the use of H2O favor reducing NO release.

Chemical looping combustion (CLC) is one of the promising technologies to capture CO2 with low cost. Owing to the existence of nitrogen in fuel, the emission of fuel-NOx is a significant concern during the CLC process. This work evaluated NO release in the CLC process of bituminous coal and petcoke using iron ore as an oxygen carrier in a fluidized bed. The effect of several factors was evaluated, including bed material, fuel type, temperature and gasification medium. The results indicate that in the fuel reactor (FR), fuel-NOx due to the reaction between NH3/HCN and iron ore was supported only when the iron ore was reduced from Fe2O3 to Fe3O4. Compared with the case of an inert bed material, NO yield during the gasification in an iron ore bed material was relatively higher due to the enhanced char-gasification and the oxidization effect of iron ore. For the bituminous coal, NO release in FR was mainly due to the volatile release and subsequent oxidation by iron ore. For the petcoke process, NO release in FR could mainly be ascribed to the char-gasification and subsequent oxidization of NOx-precursors by iron ore. The elevated temperature and the use of H2O/N2 in comparison to CO2 could efficiently enhance the fuel conversion and NOx precursors release in FR. Thus, NO yield in FR increased, whereas that in AR correspondingly decreased. Furthermore, the NO release during continuous coal CLC was investigated in a 1 kWth CLC prototype based on the iron ore oxygen carrier. Overall, the elevated fuel reactor temperature and the use of H2O as gasification medium are beneficial to reduce NO release in the CLC system.