Alkali interactions with a calcium manganite oxygen carrier used in chemical looping combustion.

Chemical-Looping Combustion (CLC) of biofuels is a promising technology for cost-efficient CO 2 separation and can lead to negative CO 2 emissions when combined with carbon capture and storage. A potential challenge in developing CLC technology is the effects of alkali metal-containing compounds released during fuel conversion. This study investigates the interactions between alkali and an oxygen carrier (OC), CaMn 0.775 Ti 0.125 Mg 0.1 O 3-δ , to better understand the fate of alkali in CLC. A laboratory-scale fluidized bed reactor is operated at 800–900 °C in oxidizing, reducing and inert atmospheres to mimic CLC conditions. Alkali is fed to the reactor as aerosol KCl particles, and alkali in the exhaust is measured online with a surface ionization detector. The alkali concentration changes with gas environment, temperature, and alkali loading, and the concentration profile has excellent reproducibility over repeated redox cycles. Alkali-OC interactions are dominated by alkali uptake under most conditions, except for a release during OC reduction. Uptake is significant during stable reducing conditions, and is limited under oxidizing conditions. The total uptake during a redox cycle is favored by a high alkali loading, while the influence of temperature is weak. The implications for the understanding of alkali behavior in CLC and further development are discussed. • KCl aerosol particles are introduced to a fluidized bed of calcium manganite oxygen carrier particles. • Alkali is absorbed by the oxygen carrier under most studied conditions. • Alkali is released when the oxygen carrier is undergoing reduction. • Alkali uptake increases considerably with increasing gas phase alkali concentration. [ABSTRACT FROM AUTHOR]