Redox performance of manganese ore in a fluidized bed thermogravimetric analyzer for chemical looping combustion

Abstract A key issue for commercial application of chemical looping combustion (CLC) technology is the selection of oxygen carriers (OCs) with good fluidization and high reactivity during the long-term redox operation. Conventional fluidized bed reactors and thermogravimetric analyzer (TGA) are fail to simultaneously satisfy the fluidization and real-time mass measurement of bed materials. A fluidized bed thermogravimetric analyzer (FB-TGA) combining the advantages of fluidized bed and TGA is believed to be a novel powerful tool for screening OCs for industrial CLC units. In this work, an innovative FB-TGA with a high weight measurement accuracy is designed to reflect the lifetime, redox reactivity, particle sintering and agglomeration characteristics of OCs during the CLC. Manganese ore was selected as a representative OC and redox cyclic tests with hydrogen as the reduction gas were conducted. Results indicate that the Mn3O4-MnO system acts as the main redox pair. The redox chemical reactions may intensify the attrition of manganese ore particles. This may be due to the pore-opening effect of H2 during the reduction of manganese ore, reducing mechanical strength and accelerating attrition of particles. In the reducing atmosphere, it is speculated that the generation of manganese silicates with a low melting point results in particle sintering and agglomeration at the bottom of the bed. The particle agglomeration gradually spreads inward and upward, and eventually leads to total collapse of the fluidized bed. Therefore, a high-grade manganese ore with less silicon element is more suitable for industrial CLC pilots.