Variation of gas composition and energy utilization in biomass CLG process with Fe and Ca oxides through thermodynamic simulation

Abstract

Chemical looping gasification (CLG) proves to be effective route for biomass thermal conversion for quality gas production. Fe2O3 and CaO were applied in sawdust thermal decomposition as oxygen carrier and CO2 absorption agent to improve syngas composition and yield. The CLG process was investigated based on experiment and process model simulation. Process model was developed based on thermodynamic equilibrium and kinetics of 22 representative reforming reactions in CLG, with the model applicability validated with experimental results. The effect of Fe2O3 and CaO addition on CLG process, including product distribution, gas composition, energy balance and exergy efficiency, was analyzed through extensive simulation under varied combination of reaction temperature(773 ∼ 1273 K), blending ratio of Fe2O3 (0 ∼ 2) and CaO (0 ∼ 2) conditions in order to clarify the effect of variables. Especially the interaction between Fe2O3 and CaO addition on process performance was discussed to discover the potential synergetic effect on mechanism. The blending of Fe2O3 or CaO changed the gas composition with improved oxidation and reforming reactions. Optimum syngas production with maximum H2 and CO yield 682 mL/g was achieved at 1073 K CLG process. And the blending ratio of oxidant was an important factor influencing the energy balance and exergy efficiency, with the equivalent point between CLG reaction heat and char combustion heat appeared at 0.4–0.45 Fe2O3 addition. The results achieved from process simulation would be informative for CLG process mechanism understanding and efficient syngas conversion.