In chemical looping combustion (CLC), the choice of the oxygen carrier material is crucial with respect to overall system performance and cost. Materials based on manganese ores are promising candidates due to their favorable thermodynamic properties, high availability, and low price. As these ores tend to be comparably soft and prone to attrition, the challenge is to find materials which combine the above-mentioned advantages with sufficient mechanical durability. In this study, three manganese materials were screened for their suitability as oxygen carriers in the chemical looping process. The materials were subjected to continuous operation with fuel in a 10 kW chemical looping unit and evaluated in terms of gas conversion, carbon capture efficiency, and particle lifetime. All oxygen carriers showed good performance and reached more than 90% gas conversion at relevant conditions. Particle lifetime based on fines production was in the range of 99–284 h, which is a considerable improvement compared to a manganese ore previously tested in this unit. One material was ruled out as a potential candidate for up-scaling due to agglomeration tendencies.

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Particles of the perovskite material CaMn0.875Ti0.125O3−δ have been examined as an oxygen‐carrier material for chemical‐looping with oxygen uncoupling (CLOU). The aim of the work has been to determine the effect of the fuel‐to‐bed mass ratio for oxidizing solid fuels, and to determine the influence of SO2 on the reactivity with fuel. Two solid fuels have been used: a Mexican petroleum coke and a Colombian coal. The oxygen‐carrier material used in this study was CaMn0.875Ti0.125O3−δ and was developed and manufactured by the Norwegian research institute SINTEF. The experiments were conducted in a discontinuous quartz glass batch fluidized‐bed reactor with an inner diameter of 10 mm. The particle bed rests on a porous plate, and thermocouples 5 mm under and 10 mm above the plate were used for measuring the temperature. In the oxidation phase a flow of 1000 mL min−1 with 5 % oxygen in nitrogen was used. During the solid fuel experiments the bed was fluidized with 600 mL min−1 nitrogen and 0.1 g of solid fuel added to the reactor from the top. In the experiments with gaseous fuels the bed was fluidized with 900 mL min−1 total flow, consisting of 450 mL min−1 CH4 and 450 mL min−1 with 0.25–0.5 % SO2 in nitrogen. It was found that the Colombian coal was oxidized considerably faster than the petroleum coke, and this is unexpected because the kinetics for O2 release from the oxygen carrier were expected to determine conversion rate rather than the reactivity of the fuels. The overall rate of conversion increased for experiments with larger bed mass as an expected result. The SO2 had a negative effect on the reactivity of the oxygen carrier, likely because of formation of CaSO4.

Carbon capture and storage of CO 2 from combustion of biomass, i.e., bio-energy carbon capture and storage (BECCS), makes it possible to obtain so-called negative emissions-the atmosphere is cleansed from carbon dioxide. The purpose of the present study was to investigate the suitability of different manganese ores as oxygen carriers in chemical-looping combustion of biomass fuels. For this screening study, a laboratory-scale, circulating fluidized-bed CLC system with a nominal fuel input of 300 W th was used. The primary focus was to investigate the reactivity of these oxygen carriers towards biomass fuels, and find a reactive oxygen carrier with sufficient mechanical stability that could be suitable for large-scale chemical-looping combustion of biomass. A synthetic "biomass volatiles" gas was used to study how the different gas components react with the oxygen-carrier particles. Additional experiments were conducted with methane and a syngas. Parameter studies concerning temperature and specific fuelreactor bed mass (bed mass per fuel thermal power in kg/MW th) were carried out. With the synthetic biomass volatiles, conversion of fuel carbon to CO 2 as high as 97.6 % was achieved. For a majority of the investigated ores, essentially all C2 and C3 hydrocarbons were converted, as well as a very high fraction of the CO. Reactivity towards CH 4 was generally lower, but improved at higher temperatures. The resistance of the oxygen carriers towards mechanical degradation was measured in a jet-cup attrition test rig. The measured attrition was estimated as "intermediate" for four of the five tested materials, while one of the ores displayed high attrition.

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