NOVELTY - The reactor comprises an elongated, tubular, circular in cross-section, axially rotatable shell having a length and a biomass input adjacent to one end of the shell and other end remote from the input, a hollow, frustoconical wall section having an outer surface and an inner surface, a larger diameter end and a smaller diameter end and a length less than the length of the shell, a fighting structure that is secured to the inner surface of the frustoconical wall section and extends inwardly from the inner surface, and a housing surrounding to a portion of the length of the shell.    USE - The reactor is useful for treating biomass such as wood or crop residues, and food waste or animal waste, where the biomass is useful for producing torrefied and charcoal end products.    ADVANTAGE - The reactor is capable of energy efficiently treating the biomass.    DETAILED DESCRIPTION - The reactor comprises an elongated, tubular, circular in cross-section, axially rotatable shell having a length and a biomass input adjacent to one end of the shell and other end remote from the input, a hollow, frustoconical wall section having an outer surface and an inner surface, a larger diameter end and a smaller diameter end and a length less than the length of the shell, a fighting structure that is secured to the inner surface of the frustoconical wall section and extends inwardly from the inner surface, and a housing surrounding a portion of the length of the shell and defining an indirect heating zone with the shell. The larger diameter end of the frustoconical wall section is operably coupled with a shell end remote from the input such that the shell and frustoconical wall section rotate together. The fighting structure is oriented spirally along the length of the inner surface. The shell has a hot gas inlet operable to receive hot gas for indirectly thermally treating biomass within the shell, and a gas outlet. The smaller diameter end of the frustoconical wall section defines a treated biomass outlet. The flighting structure comprises a number of individual spiral walls circumferentially spaced from one another around the frustoconical wall. The reactor further comprises a series of internal flights along the length of the shell, a stationary outer housing present in communication with the smaller diameter end of the frustoconical wall section, and a rotary airlock adjacent to the biomass output. Each series of internal flights includes a first segment secured to the internal surface of the shell, and a second segment oriented at an angle relative to the first segment. The housing has an upper gaseous outlet, and a lower solids outlet. The shell extends the full length of the shell.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic vertical sectional view of a reactor for treating biomass.    Lowermost frame assembly (43)    Cylindrical main body (44)    Input end wall (46)    Central projection (50)    Tubular inlet. (52)