The Effect of Iron- and Manganese-Based Oxygen Carriers as Bed Materials in Oxygen Carrier Aided Combustion

Combustion of organic materials in fluidized bed combustion is generally performed using an over-stoichiometric air-to-fuel ratio. Despite excess air in the system, sub-stoichiometric combustion regions are present in the fluidized bed because of nonperfect mixing of reactants in the system. These regions with oxygen-deficient combustion contribute to increased levels of nonoxidized or partially oxidized carbon species. To enhance heat transfer and uniform heat distribution in the incineration chamber, an inert fluidized bed material such as silica sand is generally used. Substitution of silica sand in favor of an oxygen carrier could potentially be used to promote oxygen distribution in the incineration chamber. This is referred to as oxygen carrier-aided combustion. In this work, three alternative bed materials, previously investigated in chemical looping combustion, are investigated and compared with silica sand in over- and sub-stoichiometric combustion. The materials investigated as bed materials are a manganese ore, the mineral ilmenite, and a synthetic material mixture of Fe2O3 on a ZrO2 support. Results show that during combustion using sub-stoichiometric air-to-fuel ratios, the amount of CO in the effluent gases can be reduced using an active bed material compared to inert silica sand.