An improved rapid thermal conversion process for efficiently converting wood, other biomass materials, and other carbonaceous feedstock (including hydrocarbons) into high yields of valuable liquid product, e.g., bio-oil, on a large scale production, is disclosed. In the process, biomass material, e.g., wood, is fed to a conversion system where the biomass material is mixed with an upward stream of hot heat carriers, e.g., sand, that thermally convert the biomass into a hot vapor stream. The hot vapor stream is rapidly quenched with quench media in one or more condensing chambers located downstream of the conversion system. The rapid quenching condenses the vapor stream into liquid product, which is collected from the condensing chambers as a valuable liquid product.