The tube bundle is immerged in a pool of liquid at the base of the column in an oversize shell (Figure 1.11). Kettle reboiler is also called a “submerged bundle reboiler”. The height of the tube bundle is usually 40-60% of the shell ID. The submergence of the tube bundle is assured by an overflow weir at height of typically 5-15 cm from the upper surface of topmost tubes. Advantage: suitable for vacuum operation and high vaporization rate up to about 80% of the feed.
Limitations: low heat transfer rate than other types as there is no liquid circulation (low velocity); not appropriate for fouling fluids; kettle reboiler is not suitable for heat sensitive materials as it has higher residence time.