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

• Zero-dimensional oxy-polishing reactor model is made and validated with 100 kW data. • The model can extract the detailed reaction path for many gases. • Useful information for oxy-polishing optimization was got with the reactor model. • Coal-biomass mixing combustion was demonstrated with a 100 kW CLC pilot. 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 NH 3 which was then oxidized to NO in the POC. The concentrations of HCN and NO 2 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 (O 2 , H 2 , CO, NO, CH 4 ) to 3.3 %.