Torrefaction/carbonization-enhanced gasification-steam reforming of biomass for promoting hydrogen-enriched syngas production and tar elimination over gasification biochars

•Torrefaction/carbonization was coupled with biochar-assisted steam gasification.•Gasification biochar was recaptured as an assisted-reforming agent and co-reactant.•WS-280 was superior to other feedstocks in terms of gas and tar formation behaviors.•C[10 %O2] was more favorable for H2-rich syngas production (>112 mmol/greactants)•The lowest tar yield (3.36 Nm3) was gained from GSR of WS-280 over C[10 %O2]