Intrinsic Reduction Kinetics Investigation on a Hematite Oxygen Carrier by CO in Chemical Looping Combustion

In the present work, the intrinsic reduction kinetics of a chemical looping oxygen carrier, hematite, reduced by CO has been investigated. Initially, the pore structure features of the hematite OC were tested to provide the necessary parameters for the kinetics analysis. Then, temperature-programmed reduction experiments were conducted in a thermogravimetric analyzer. The results showed that the weight loss rate appears to be a bimodal distribution and the appropriate experimental temperature range for the intrinsic kinetics testing of the first reduction stage of hematite is 400-650 degrees C. Additionally, a series of experiments were further conducted in a batch fluidized bed system with different temperatures and different CO concentrations. After elimination of the internal and external diffusion limitations, the intrinsic activation energy and pre-exponential factor were determined as 74.48 kJ/mol and 1.2 x 10(12) s(-1), respectively. The analysis of the internal and external diffusion effects was beneficial to understand the reaction characteristics of this kind of hematite oxygen carrier. As concluded, the shrinking core series model, the external diffusion control, and the small apparent activation energy obtained from many previous studies were compatible with this analysis and can be explained by this work. The research results attained in this study can also contribute to the development of a practical model for computational fluid dynamics simulation.