NOVELTY - The rotary furnace (1) comprises a rotating tube in which solid materials are introduced, a first heating unit external to the rotating tube allowing to form a part for heat treatment in the absence of oxygen, a second unit for heating the load (2) formed by a heating element (4), and a deflector panel (5) surrounding the element heating at the opposite side of the load and placed inside the rotating tube. The heating element is straight, longitudinal and present along the entire length of the rotary furnace. A section of the heating element is polygonal, round, oval, or flat.    USE - The rotary furnace is useful for heat treatment of solid biomass by roasting and using heat radiation (all claimed).    ADVANTAGE - The rotary furnace is simple and compact, and is capable of economically heat treating the solid biomass by roasting with less consumption of energy and without exothermic reactions.    DETAILED DESCRIPTION - The rotary furnace (1) comprises a rotating tube in which solid materials are introduced, a first heating unit external to the rotating tube allowing to form a part for heat treatment in the absence of oxygen, a second unit for heating the load (2) formed by a heating element (4), and a deflector panel (5) surrounding the element heating at the opposite side of the load and placed inside the rotating tube. The heating element is straight, longitudinal and present along the entire length of the rotary furnace. A section of the heating element is polygonal, round, oval, or flat, and concave or convex. The heating element has a width of 1/60 and 2/3 of the internal diameter of the furnace tube and a height of 1/20 and 4/4 of the width of the heating element, and is fixed by its ends independently of the tube of the furnace. The position of the heating element in the tube of the furnace is eccentric with respect to the central longitudinal axis of the tube of the furnace in the direction opposite to that where the load is placed. The heating element is hollow or filled, sealed or perforated, and is heated by circulating a hot gas inside the heating element or by combustion. The deflector panel is longitudinal and constituted of single part or several parts related to one another, and has a length same as the heating element. A central part is arranged above the heating element, and two sides are arranged on both sides of the central part. The deflector panel is present in the form of half tube, and comprises angles formed by the connection of different parts. The two sides of the deflector panel have a size, which allows the sides to exceed the heating element, and are oriented to form an angle allowing radiations to cover the surface of the bed of the load.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional view of a rotary furnace.    Furnace (1)    Load (2)    Bed surface (3)    Heating element (4)    Panel (5)    Heat zone. (6)