Synergistic effect of hydrogen atmosphere and biochar catalyst on tar decomposition and methane-rich gas production during biomass pyrolysis

•Synergistic effect of hydrogen atmosphere and char in pyrolysis-catalytic reforming of biomass.•Synergistic of hydrogen atmosphere and biochar catalyst degrades heavy tar components.•Increased hydrogen concentration and higher reforming temperature promotes CH4 production.•Biochar inhibited the polycondensation of macromolecular compounds in tar.•Tar conversion efficiency and the yield of CH4 increased with increasing biochar layer height. This study investigated the synergistic effect of a hydrogen atmosphere and biochar for tar removal and CH4-rich gas production during the pyrolysis-catalytic reforming of biomass using a lab-scale dual-stage fixed-bed furnace. The biomass feedstock was pyrolyzed under a hydrogen atmosphere at 850 °C, and then the evolved vapors were passed to a second stage with pyrolysis gases reformed in the presence of biochar as a catalyst. The influence of reforming temperature, hydrogen concentration, and the mineral and layer height of the biochar catalyst were investigated. Using such a synergistic pattern not only effectively promoted tar decomposition but also generated methane-rich gas and continuously regenerated the biochar catalyst. In particular, the tar conversion efficiency reached 93.72 % with the use of biochar under a hydrogen concentration of 20 % at a reformer temperature of 850 °C. The CH4 yield increased evidently with increasing hydrogen concentration and reforming temperature. The maximum CH4 yield in producer gas of 36.52 vol% was obtained at a catalytic temperature of 850 °C and a hydrogen concentration of 100 %. The catalytic activity of minerals in biochar has a significant effect on tar decomposition and producer gas components, which was proven by the decrease in CH4 yield when demineralized biochar was used for reforming the catalyst. The tar conversion efficiency and yield of CH4 tended to increase with increasing biochar catalyst layer height. Finally, a hydropyrolysis-catalytic reforming mechanism of a hydrogen atmosphere and biochar catalyst in tar removal and methane-rich gas production was proposed.