A type of horizontal shell-and-tube type heat exchanger in which liquid to be evaporated is contained on the shell side and condensing steam or a hot liquid used to provide the heat contained on the tube side (see Fig. 24). The shell contains a relatively small bundle of hairpin tubes in a two-pass arrangement in a floating head and tube sheet, and sits in a pool of the boiling liquid, the depth being determined by an overflow weir. A flow of fresh liquid continuously enters from the bottom while vapour leaves from the top of the shell. The condensing steam in the tubes is removed through a trap. Kettle reboilers are typically used with distillation columns to boil up the bottom material and return vapour back into the column for separation.

Fig. 24