Abstract: A screw conveyor includes a steam delivery chamber, a condensate return chamber, and a helical hollow flight. In example embodiments, the condensate return chamber is defined by an inner pipe, the steam delivery chamber is defined between the outer and inner pipes, and the helical flight extends radially from the outer pipe. The screw conveyor includes a series of heating zones, each having a “closed-loop” helical passageway formed by the hollow flight and each having a corresponding steam inlet, condensate outlet, and barrier. Steam travels into the screw conveyor, through the steam inlets, and into the helical passageways, where it condenses as it heats a material conveyed by the screw conveyor. As the screw conveyor rotates, the barriers force the condensate upward until it drains through the condensate outlets and into the condensate return chamber for removal from the screw conveyor.