Oxy-polishing of gas from chemical looping combustion: Fuel-nitrogen transformation and model-aided gas purity optimization

Journal article, 2025

Chemical looping combustion (CLC) is a carbon capture technology for heat, power and hydrogen production. This work focuses on fuel-nitrogen transformation in fuel reactor and its further conversion in oxy-polishing step of CLC system. A 100 kW CLC pilot equipped with an oxy-polishing chamber (called POC) was used to perform experiment study and a zero-dimensional reactor model combining elementary reaction kinetics was developed and used for oxy-polishing simulation and reaction path analyses. An ilmenite and a manganese ore called Sinaus were used as oxygen carriers, and a coal and a coal-biomass mixture are the fuels in the CLC tests. It was found that in the fuel reactor, part of the fuel-nitrogen was converted to NO and the rest remained as NH3 which was then oxidized to NO in the POC. The concentrations of HCN and NO2 were negligible in the fuel reactor and POC. According to the simulation, when the oxygen excess is too low it is difficult to reach 1150–1200 °C which are temperatures needed for oxidizing the unconverted fuel gases. In a reference case, a high conversion was reached when the overall oxygen ratio was above 1.03 and temperature above 925 °C. With a fuel reactor temperature of 950 °C, the oxygen demand needed could be up to around 8 %. Based on the model, optimal geometrical designs of the POC were proposed. With a gas residence time of 3 s in the POC, it was possible to decrease the content of impurities (O2, H2, CO, NO, CH4) to 3.3 %.