Effect of Operating Conditions and H2S Presence on the Performance of CaMg0.9Mn0.9O3-δ Perovskite Material in Chemical Looping Combustion (CLC)

Chemical looping combustion (CLC) is considered a promising technology for CO2 capture and sequestration (CCS), since the CO, generated during the combustion process of a gaseous fuel is inherently separated. Recently, perovskite-type particles based on Mn have been investigated for use as oxygen carrier materials in CLC processes. These materials present some advantageous characteristics, in comparison with metal oxides, such as reduced cost, environmentally friendly behavior, and the oxygen uncoupling effect. In this sense, the objective of this study was to assess the performance of the CaMn0.9Mg0.1O3-delta perovslcite as an oxygen carrier.. The influence of different parameters such as the solids inventory, oxygen carrier-to-fuel ratio (phi), operational time, and sulfur content of fuel on CH4 combustion efficiency, was studied in a continuous 500-W-th CLC unit. In addition, the evolution of oxygen carrier reactivity, mechanical integrity, and agglomeration behavior, relative to operating time, was analyzed. When combustion tests were carried out without sulfur addition, it was observed that a very high excess of oxygen over the stoichiometric conditions (phi > 11) was needed to reach full CH4 conversion. Under these conditions, the oxygen uncoupling effect was relevant to fully convert the fuel, and some O-2 appeared at the outlet of the fuel reactor with concentrations close to 1 vol %. The presence of H2S in the fuel gas produced the deactivation of the oxygen carrier in terms of an important decrease in the reactivity and oxygen uncoupling capacity, resulting in a relevant drop in the combustion efficiency, decreasing from full combustion to 72% after 17 h of operation with H,S addition. Moreover, the presence of H,S caused an unstable circulation of solids, because of agglomeration problems. Therefore, in order to use this reactive oxygen carrier with H2S-containing fuels in future CLC industrial plants, it would be necessary to fully desulfurize them due to the high sensitivity to sulfur poisoning of this material.