Kinetics of CaMn 0.775 Ti 0.125 Mg 0.1 O 2.9-? perovskite prepared at industrial scale and its implication on the performance of chemical looping combustion of methane

The reaction kinetics of a CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite, prepared at ton-scale to be used as an oxygen carrier in a CLC process with methane, was determined. The variation of the reaction rates, oxygen transport capacity, and oxygen uncoupling behaviour of the selected material with the number of cycles was evaluated in a thermogravimetric analyser. The perovskite was activated for the reduction reaction with all the combustible gases, i.e., H2, CO and CH4. On the contrary, the oxidation rate barely changed throughout the cycles. The oxygen transport capacity underwent a slight decrease during the activation period. Kinetics of reduction, oxidation and oxygen uncoupling reactions were determined for the fresh and activated material assuming a grain model controlled by chemical reaction at low values of solids conversion and diffusion through the product layer at high values of solids conversion. This model predicted correctly the solids conversion vs. time curves as a function of temperature and gas concentration for the oxygen carrier reactions evaluated in this kinetics study. The kinetics data were introduced in a validated mathematical model of a fuel reactor to analyse the amount of solids required to fully combust CH4. A solids inventory of 350 kg/MWth was estimated in the fuel reactor at a temperature of 1243 K. However, this value could be reduced to 160 kg/MWth if the material operates under activation conditions within the CLC unit. © 2020 Elsevier B.V.