The invention is directed to a process to continuously prepare a char product having a high BET surface area of above 400 m2/g and gaseous fraction comprising of carbon monoxide, hydrogen and hydrocarbons starting from particles of a torrefied biomass in an elongated and substantially horizontally positioned reactor furnace. A reactive gaseous mixture of steam and oxygen is supplied to the solids in the reactor and more oxygen and steam is supplied to the downstream end part of the reactor as compared to the amount of oxygen supplied to the upstream end part.