A type of heat exchanger associated with distillation columns for boiling the liquid from the bottom of the column to totally or partially vaporize it and be returned to the column to drive the separation. Reboilers usually consist of a horizontal cylindrical body containing hairpin tubes for heating with a characteristic vapour dome above the boiling liquid. Vertical thermo-syphon reboilers are also used. Condensing steam, waste heat, or a hot liquid from the process is usually used as the heating medium. See kettle reboiler.