Measuring the fast oxidation kinetics of a manganese oxygen carrier using microfluidized bed thermogravimetric analysis

Oxygen carriers play critical roles in chemical looping combustion. A key task in investigating the oxygen carrier reactivity is to measure the redox kinetics in the fluidization state. However, this is still a challenge because one must perform the redox kinetics measurement in a fluidizing environment in order to simulate the strong mass and heat transfer occurring in a practical fluidized bed reactor. Herein, we report a new method, called the microfluidized bed thermogravimetric analysis (MFB-TGA), to measure the kinetics of the redox reactions, specifically the fast oxidation reaction of a manganese ore oxygen carrier. MFB-TGA is based on a real-time mass measurement of a solid sample inside a fluidized bed. The experimental data measured by MFB-TGA are interpreted with a K-L two-phase fluidized bed model to incorporate the effect of the gas concentration change in the emulsion phase. We conclude that the oxidation kinetics of this manganese ore are much faster than those of other oxygen carriers in the published works. Based on the measured oxidation reaction kinetics, the reaction time required in the air reactor is only 2.3-4 s. Therefore, a new design concept for CLC where the air reactor is operated under a dilute-phase transport regime is put forward. The new design of the air reactor has the potential to reduce cost and avoid the hot pot problem, which is a promising choice for future CLC application. In brief, this MFB-TGA method can be applied to measure the fast gas-solid reaction kinetics of any type of oxygen carriers, and thus contributes to providing reliable redox kinetics for chemical looping combustion.