An innovative Cu-Al oxygen carrier for the biomass chemical looping gasification process

Biomass chemical looping gasification (BCLG) is a novel technology that enables the production of renewable syngas without the need for an external supply of energy or power while achieving negative carbon emissions. In this work, the behavior of a synthetic Cu-based (14 wt% CuO) oxygen carrier, Cu14Al_ICB, was tested for 45 h in a 1.5 kWth continuous unit using pine sawdust as fuel. The effect of the oxygen-to-fuel ratio (λ) and gasification temperature on syngas composition and gasification parameters, including fuel conversion, carbon capture, cold gas efficiency, and syngas yield, was studied. A decrease in the oxygen-to-fuel ratio increased molar flows of H2 and CO in the syngas, while an increase in gasification temperature mainly improved char gasification, also enhancing H2 and CO generation. High amounts of syngas with low CH4 molar flows (∼2.3 mol CH4/kg of dry biomass) were obtained under any conditions due to the catalytic effect of metallic copper on CH4 reforming reactions. Syngas yield values were achieved approximating those obtained with Ni-based solids. The oxygen carrier also had a very positive effect on tar removal, reaching tar concentration values similar to those obtained by operating under chemical looping combustion conditions. The attrition rate measured with this oxygen carrier was the lowest obtained to date for any oxygen carrier operating under BCLG conditions. In addition, the mechanical properties, reactivity, and oxygen transport capacity of the oxygen carrier were maintained throughout the campaign. Therefore, the Cu14Al_ICB oxygen carrier has proved to be an excellent material for the BCLG process.