Use of Manganese Ores as Oxygen Carriers in Chemical-Looping Combustors for Solid Fuels

Other conference contribution, 2016

Manganese ores are highly promising oxygen-carrier candidates due to high reactivity and high availability. It has been observed that some manganese ores may be sensitive to attrition, and the challenge has thus become to find a highly reactive manganese ore, or combination of ores, with sufficient mechanical integrity. This study summarizes the operational experience with manganese ores achieved at Chalmers UT. In an early study using Buritirama manganese ore as oxygen carrier a in 10 kW unit for solid fuels, it was shown that the gas conversion using petcoke as fuel increased from 80% with ilmenite to 85% with Buritirama. Simultaneously, there was a four-fold increase in gasification rate resulting in much higher carbon capture efficiency. However, the mechanical stability of the Mn ore was inferior to ilmenite, judged by the production of fines. In a subsequent study, ilmenite was mixed with the Buritirama manganese ore during operation in a 100 kW unit. The mixture of ilmenite and manganese ore gave significant improvements in gas conversion in comparison to only ilmenite. The highest gas conversion observed during testing with bituminous coal was as high as 91.5%, as compared to 84% with only ilmenite during similar conditions in the 100 kW unit. Another three manganese ores were recently investigated in the 10 kW unit. These ores appeared to form less fines as compared to Buritirama ore. All oxygen carriers showed high performance and reached more than 90% gas conversion at relevant conditions, using wood char as fuel. The estimated lifetime of the oxygen carrier based on fines production was in the range of 100 to 300 hours – a considerable improvement compared to the Buritirama ore. The most promising of the three ores tested in the 10 kW unit, Sinfin, was selected for use in the 100 kW unit. 52 hours of operation with different fuels has been achieved with the new oxygen carrier, called Sinaus, which is similar but not identical in composition to Sinfin. Preliminary results show that gas conversion is higher, and solid-fuel conversion much higher than with ilmenite as oxygen carrier. The evaluation also shows that the lifetime is lower than for ilmenite.