Synergistic effect in co-gasification of coal and biomass in supercritical water

Experiments of co-gasification of biomass and coal in supercritical water (SCW) are conducted to investigate any synergy between biomass and coal for enhancing coal gasification and hydrogen production. A thermal-catalytic reactor with continuous flow is employed to co-gasify Hua-Ting bituminous coal, sodium carboxymethylcellulose (a model compound of biomass) and their blends under a reactor with wall temperature of 650°C, pressure 25 MPa, and a residence time 30 s and 0.1% NaOH additive. The experimental results show that the produced gases consist mainly of H₂, CO₂ and CH₄, and the molar fraction of hydrogen reaches in excess of 60%; Nitrogen or sulfur is not detected in the produced gases, and contaminations with nitrogen or sulfur are discharged by liquid. A synergistic effect between coal and sodium carboxymethylcellulose is observed on the hydrogen yield and the gasification efficiency, and that the synergistic effect is mainly resulted from free radical reactions in SCW is proposed further. The present work indicates hydrogen production from co-gasification of biomass and coal in SCW is a promising new technology for clean energy conversion.