NOVELTY - Biomass is introduced (105) into a vertically elongated combustion chamber having a suspension burner, a heat transfer apparatus and an exhaust opening. The biomass is combusted (110) to obtain a mixture containing hot flue gas and molten ash. The heat from the hot flue gas is transferred (120) to a portion of heat collection surface to obtain a mixture having warm flue gas and non-molten ash. The warm flue gas is cooled (130) with a cold gas to obtain a mixture having cool flue gas and non-molten ash.    USE - Method used for extracting energy from biomass depleted of carbohydrate and/or oil such as plant fiber produced in grains of corn, wheat, rice and cereals, and stalk, leaf and vegetable material of grass, shrub and tree such as cane and beet, and non-molten ash as byproduct used as fertilizer, land filling material and component of phosphatic cement (claimed).    ADVANTAGE - The method enables extraction of energy from biomass depleted of carbohydrate and/or oil efficiently.    DETAILED DESCRIPTION - Biomass is introduced into a vertically elongated combustion chamber having a suspension burner at the top of the combustion chamber which projects a flame down the axis of the combustion chamber, a heat transfer apparatus with a portion of a heat collection surface located radially from the flame and below the burner, and an exhaust opening provided below the flame and below the portion of heat collection surface. The biomass is combusted to obtain a mixture containing hot flue gas and molten ash above the exhaust opening. The heat from the hot flue gas is transferred to a portion of heat collection surface substantially by radiation before contact of ash to the surface of the combustion chamber to obtain a mixture containing warm flue gas and non-molten ash and having lower molten ash content with respect to mixture obtained by combustion. The warm flue gas is cooled with a cold gas to obtain a mixture containing cool flue gas and non-molten ash and having lower molten ash content with respect to mixture obtained by transferring.    DESCRIPTION OF DRAWING(S) - The drawing shows the flowchart of extraction of energy from biomass depleted of carbohydrate and/or oil.    Introducing biomass into combustion chamber (105)    Combusting biomass (110)    Transferring heat (120)    Cooling flue gas (130)