Abstract: A vessel comprises a cylindrical shell, which has a horizontal axis. A row of outlet openings communicate with the interior of the vessel and are spaced apart along the lowermost generatrix of the shell. An outlet manifold extends outside the vessel and communicates with said outlet openings. A row of inlet openings communicate with the interior of the vessel and are spaced apart along a second generatrix of the shell. The second generatrix is angularly spaced from the lowermost generatrix by a central angle up to 50.degree.. An inlet manifold extends outside the vessel. A plurality of pipelines are provided, each of which connects the inlet manifold to one of the inlet openings. The vessel is included in an autoclave system, which comprises a recirculating system, which connects the outlet manifold to the inlet manifold and incorporates a heater for heating liquid and a circulating pump for recycling liquid from the outlet manifold through the heater to the inlet manifold.