The invention relates to a treatment chain for thermochemically converting a wet biomass feed (1) by gasification, which comprises a device (4) for gasifying the feed (3), and a reactor (9) for steam conversion of the CO, which includes water supply means (10), for delivering a syngas (17) having a defined H2/CO ratio, a drying chamber (2) into which the wet feed (1) is injected prior to its subsequent treatment in the gasification device (4), this drying chamber (2) being supplied with a hot gas (15) withdrawn downstream from the gasification device (4) and recycled by pressurizing means (13) into the drying chamber (2).