NOVELTY - The biomass torrefaction method comprises rotating a reactor drum (12) about an axis (16) of rotation, where the reactor drum has flights positioned at each of locations along a longitudinal length of the reactor drum, and generating a heated gas stream (34) through the reactor drum sufficient to intermittently transport biomass particles along the longitudinal length of the reactor drum and to simultaneously torrefy the biomass particles that are lifted by the flights as the reactor drum rotates and showered through the heated gas stream under the influence of gravity.    USE - The method is useful for torrefaction of cellulosic biomass such as wood chips, giant cane chips and other cellulosic biomass.    ADVANTAGE - The method ensures continuous, consistent, safe and efficient torrefaction of cellulosic biomass with high energy value, improved tailor characteristics and less energy consumption.    DETAILED DESCRIPTION - The biomass torrefaction method comprises rotating a reactor drum (12) about an axis (16) of rotation, where the reactor drum has flights positioned at each of locations along a longitudinal length of the reactor drum, generating a heated gas stream (34) through the reactor drum sufficient to intermittently transport biomass particles along the longitudinal length of the reactor drum and to simultaneously torrefy the biomass particles that are lifted by the flights as the reactor drum rotates and showered through the heated gas stream under the influence of gravity, recirculating a portion of gas exiting the reactor drum back to an inlet (22) of the reactor drum via gas ducts for torrefying biomass particles within the reactor drum, selectively varying some of operational parameters to tailor characteristics of the resultant torrefied biomass particles, selectively varying a time of residence of the biomass particles in the reactor drum, adjusting flights within the reactor drum with respect to location or density to change the retention time of the biomass particles within the reactor drum, passing biomass particles through the reactor drum at a minimum rate of 1 ton per hour according to particle density or size, discharging torrefied biomass particles while preventing the infiltration of oxygen into the reactor drum, establishing a pressure level within the reactor drum to inhibit the infiltration of oxygen into the reactor drum, and routing exhaust gas to a device remote from the reactor drum to utilize the exhaust gas in an auxiliary or supplemental process. The operational parameters include: a speed of the heated gas stream through the reactor drum; a volumetric flow rate of the heated gas stream through the reactor drum; a temperature of the heated gas stream through the reactor drum; a pressure level within the reactor drum; a speed of the rotation of the reactor drum; oxygen content of the heated gas stream; a moisture content of the biomass particles; and/or a rate of introduction of the biomass particles into the reactor drum. The step of routing the exhaust gas to the device comprises routing exhaust gas to a burner to utilize the exhaust gas to generate a heated medium for supplying heat to a gas stream to establish the heated gas stream. The method further comprises sealing the reactor drum from an external environment, selectively purging chambers adjacent to sealing interfaces of the reactor drum with inert or semi-inert gas, transferring heat from a heated gas isolated from the reactor drum to a gas stream to establish the heated gas stream that passes through the reactor drum during operation, drying the biomass particles in a rotary type dryer system, establishing the heated gas stream such that an inlet temperature of the heated gas stream entering the reactor drum is 500 degrees F and such that an outlet temperature of the heater gas stream exiting the reactor drum is 400 degrees F, introducing the biomass particles into the continuously reactor drum while preventing the infiltration of oxygen into the reactor drum, venting the reactor drum upon a fault condition, and introducing steam into the reactor drum to assist in the torrefaction of the biomass particles. The biomass particles have an energy density of 20 GJ/ton after torrefying the biomass particles within the reactor drum, and an average size of 1/16 cubic inch to 1 cubic inch upon entry. The drying step comprises drying the biomass particles to have an average moisture content of less than 20% moisture content, wet-weight basis. The particle sizes of the discharged torrefied biomass particles are 10% while the energy density and moisture characteristics of the torrefied biomass particles are relatively constant irrespective of particle size. The introduction of the steam into the reactor drum comprises producing steam with a boiler that receives heat from a portion of gas exiting the reactor drum. The step of establishing the heated gas stream through the reactor drum comprises moving the heated gas stream through the reactor drum to directly heat the introduced cellulosic biomass particles as the heated gas stream intermittently transports the cellulosic biomass particles.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a biomass torrefaction system.    Reactor drum (12)    Longitudinal axis (16)    Inlet (22)    Airlock (26)    Heat source (30)    Heated gas stream. (34)