Autoclave for treating charged materials

In an autoclave for treating charged materials with vapor under pressure, the autoclave having an elongated and hollow substantially cylindrical casing wall oriented along a horizontally aligned axis and defining an inner chamber for receiving said charged materials therein the inner chamber including a curved side region oriented laterally on each side of a vertical center plane thereof and a heating device disposed within the inner chamber, the heating device being connected to a source of heated heat transfer medium to generate the vapor in the inner chamber, and being arranged within at least one of the curved side regions of the inner chamber, the improvement wherein the heating device includes as a sole means for heating at least one flue having a longitudinal axis extending substantially parallel to the vertical center plane and oriented within the at least one of the curved side regions of the inner chamber, a lower portion of the at least one of the curved side regions defining a lower inflow region of said at least one flue, the heating device further including a heat exchanger arranged within the inner chamber in said lower inflow region of said at least one flue through which heat exchanger flows the heated heat transfer medium so that a free convection flow of the vapor through said at least one flue results, the vapor circulating upwards within said at least one flue substantially in a circumferential direction of the casing wall and then circulating downwards within the inner chamber without means for forcing vapor flow within said inner chamber.