Abstract: The present invention provides a cylindrical reactor vessel having a top end with an inlet and a bottom end with an outlet end. A refractory insulating lining is applied on the interior of the wall of the vessel. A cylindrical vertically disposed first inner basket having a generally closed top first end and an open second end in communication with the outlet conduit and having fluid pervious sidewalls surrounded by a vertically disposed outer cylindrical second basket defining a space therebetween for containment of subdivided contact material. The cylindrical second basket also has a top end, which is closed, and fluid pervious sidewalls. The cylindrical second basket is spaced away from the refractory lining of the vessel at a sufficient distance, to provide an annular space for fluid, admitted through the inlet, to progress downwardly through the annular space and then radially inwardly through the contact material contained in the space between the first and second basket.