NOVELTY - A torrefaction system (100) comprises: a torrefaction reactor comprising upper portion (3) and a lower portion, where upper portion is configured to dry an input of the torrefaction reactor, and a lower portion is configured to torrefy an output of the upper portion; a combustion unit (23) configured to combust a portion of a gaseous mixture vented by the torrefaction reactor to produce a flue gas; and a heat exchanger configured to exchange heat from the flue gas to the gaseous mixture.    USE - As torrefaction system which is useful for preparing a torrefied biomass fuel (claimed).    ADVANTAGE - The significant advantage of the present system design is its ability to minimize the external fuel (supplemental natural gas and biomass) needed for operation. The final advantage of the very hot upper chamber is that it substantially destroys all the organic compounds which are generated during torrefaction and are present in the torrefaction gas.    DETAILED DESCRIPTION - A torrefaction system (100) comprises: a torrefaction reactor comprising an upper portion (3) and a lower portion, where upper portion is configured to dry an input of the torrefaction reactor, and a lower portion is configured to torrefy an output of the upper portion; a combustion unit (23) configured to combust a portion of a gaseous mixture vented by the torrefaction reactor to produce a flue gas; and a heat exchanger configured to exchange heat from the flue gas to the gaseous mixture. The torrefaction reactor further includes a segregation barrier between the upper portion and the lower portion, where the segregation barrier is configured to enable gases to flow across the segregation barrier. The combustion unit comprises: an upper chamber configured to combust the gaseous mixture and a supplemental fuel to produce the flue gas; and a lower chamber configured to combust a portion of a relatively wet biomass fuel to support production of the flue gas in the upper chamber. An INDEPENDENT CLAIM is included for preparing a torrefied biomass fuel, involving: extracting moisture from a biomass input to produce a dried biomass fuel; torrefying the dried biomass fuel to produce a torrefied biomass fuel and a torrefaction gas; venting a gaseous mixture including the torrefaction gas to a heat exchanger; heating the gaseous mixture; and using the heated gaseous mixture to support the extraction of the moisture from the biomass input and the torrefaction of the dried biomass fuel.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a torrefaction system.    Input bin (1)    Airlock (2)    Dryer (3)    Cyclone separator (5)    Induction draft fan (6)    Conveyor (8)    Combustion chamber (23)    Fed pre-sized biomass (31)    Torrefaction system (100)