Combustion characteristics of millimeter-sized aluminum particles in fluidized bed under various O2/CO2/H2O atmospheres

Aluminum is an attractive alternative fuel, but it burns very inefficiently due to the formation of a dense Al₂O₃ layer which prevents O₂ from diffusion to the surface of Al particles. In previous experiments, the combustion of millimeter-sized Al (mAl) particles in the fluidized bed has achieved a substantial increase in the combustion efficiency, but further improvements are still needed. In this study, the effects of reaction atmosphere on the fluidized combustion of mAl particles were investigated. The experiments with different O₂/H₂O/CO₂ concentrations were conducted. The experimental results indicate that the combustion efficiency of mAl particles in fluidized bed increases as the mole fraction of O₂, H₂O or CO₂ increases, and the highest combustion efficiency can reach 38.7%. After the analysis of the oxide film on the surface of aluminum particles, it was found that it is easier to generate the unstable θ-Al₂O₃ under CO₂ atmosphere, and it is easier to generate the unstable γ-Al₂O₃ and θ-Al₂O₃ under H₂O atmosphere. The unstable Al₂O₃ film is more likely to be abraded in the fluidized bed, which leads to the effective improvement of the combustion efficiency.