A cryogenic distillation tower for separating a feed stream. The tower includes a distillation section. A controlled freeze zone section is situated above the distillation section and forms a solid from the feed stream. The controlled freeze zone section includes a spray assembly in an upper section and a melt tray assembly in a lower section. The melt tray assembly includes at least one vapor stream riser that directs the vapor from the distillation section into liquid retained by the melt tray assembly, and one or more draw-off openings positioned to permit a portion of the liquid to exit the controlled freeze zone section. The portion of the liquid indirectly exchanges heat with a heating fluid. One or more return inlets return the portion of the liquid to the melt tray assembly after it has been heated in the heat exchanger.