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

Abstract

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.

Chemical Looping Combustion of Petcoke Using Two Natural Ores in a 10 kWth Continuous Pilot Plant: A Performance Comparison

“…The temperature increase has a positive effect on petcoke conversion, as expected according to previous batch results and the established kinetic mechanism. The temperature increase has a positive and more pronounced effect on reduction capabilities of LY Mn ore with respect to ilmenite T1, and this is in agreement with literature results, where manganese ore has slower reaction kinetics at lower temperatures with respect to ilmenite …”

“…Nearly all manganese ores tested exhibited a decrease in fuel conversion after three redox cycles at 1000 °C. 3 However, manganese ore conversion could decrease when different fuels (syngas versus CH 4 ) are tested and at lower temperatures (e.g., 850 °C), 25 indicating that the reaction rate between solid fuel and ilmenite/manganese ore should be verified for the same operating consitions of fuel type, FR temperature, and air/fuel ratio. Furthermore, it is well-known that a higher temperature of operation favors solid fuel conversion.…”

Chemical Looping Combustion of a Biomass Char in Fe2O3-, CuO-, and SrFeO3−δ-Based Oxygen Carriers

“…Despite not releasing gaseous O 2 in the whole volume of the bed, the presence of non-CLOU OCs (here, Fe 2 O 3 ) was postulated to even out the spatial distribution of O 2 in the bed by the redox reactions with the combustible gases (CO) and the incoming O 2 from the fluidizing gas, a process that aligns with OCAC. − Hence, Fe 2 O 3 is a good candidate for CLC or OCAC, while CuO is a good candidate for CLOU. A similar conclusion was drawn by Kajnas et al when using iron- and manganese-based OCs as bed materials to combust gaseous CO in an OCAC setup. In an air-lean atmosphere (analogous to the devolatilization phase in this work), the conversion of CO by a Fe-based OC was greater than that by a Mn-based OC, despite the Mn-based OC being capable of releasing gaseous oxygen.…”

Investigation of the Oxygen Supply and Distribution in a Bubbling Fluidized Bed by Using Natural Ilmenite for Oxygen Carrier Aided Combustion

“…Further experiments with iron- and manganese-based OC’s in a laboratory batch reactor with gaseous fuels revealed, that all materials enhanced fuel conversion, but Mn ore performed worse. A possible explanation can be the limited gas–solid reaction kinetics between Mn-solids and CO/CH 4 at moderate temperature of OCAC (850 °C) compared to CLC (>950°C) …”