Apparent kinetics derived from fluidized bed experiments for Norwegian ilmenite as oxygen carrier

• Apparent reduction kinetics are obtained for a rock ilmenite oxygen carrier.
• Reduction and oxidation cycles are performed in a laboratory fluidized bed reactor.
• Temperatures vary from 850 to 950 °C and fuel gases from 50 to 100 vol.%.
• Different modified power laws and the changing grain size model are fitted to the experimental data.
• A model with temperature dependent solids conversion exponent indicates good agreement with the experimental data.

Chemical-looping combustion (CLC) is one of the most promising methods for CO2-capture. Regarding the use of solid fuels in CLC, it is assumed that the lifetime of the oxygen carrier material will be lowered preferring low cost and environmental sound materials. In this work apparent kinetics for the reduction of a natural rock ilmenite from Norway are derived from experimental data while utilizing CO, H2 and CH4 as fuel gases. CO, H2 and CH4 are the main combustible gases in solid fuel CLC. The experiments were carried out in a laboratory batch fluidized bed reactor. The reactor was heated to bed temperatures varying from 850 to 950 °C. Different fuel gas concentrations were achieved by diluting the fuel flow with nitrogen. For H2, pulsed reduction experiments have been accomplished to allow the calculation of conversion dependent rates.The experimental conversion rates were fitted to different model approaches in order to derive the apparent kinetic parameters. Thereby the oxygen carrier conversion was represented by the mass based conversion ω. The results are compared to published data. The reaction order with respect to the gas phase is close to the reported values. Only the reaction order obtained for CH4 with the fitted power law deviated with about 40%, what could indicate a limitation of available surface for the heterogeneous decomposition of CH4. Although the overall agreement between fitted power laws and experimental data was appropriate, their extrapolation outside the experimental data range has to be done with care.