Model-Assisted Comparison of Chemical-Looping Combustion in Fixed and Fluidized Bed Reducers

摘要

The objective of this work is to use a global reactions scheme and the same kinetic mechanisms to accurately describe the dynamic behavior of chemical-looping combustion (CLC) Reducers in fixed and fluidized bed units, operating with CH4 as the fuel and NiO as the oxygen carrier. The kinetics in chemical-looping reduction have been established through a comprehensive analysis of all the relevant published data of fixed-bed CLC reactors and with experiments performed in-house in a fully automated fixed bed CLC reactor. The kinetic expressions are then integrated in a comprehensive three-phase (bubble/wake/emulsion) hydrodynamics model, in which reactions in the dilute phase (freeboard) are also taken into account, to predict fluidized bed CLC performance. Sensitivity studies of the effect of gas and solid exchange between bubble (wake) and emulsion, particle diameter, bubble diameter and reactions in the dilute phase on CLC efficiency are performed. Based on the model and experimental results, a comparison of fixed and fluidized bed chemical-looping combustion reactors is discussed.