Kettle Heat Exchangers are very simple and reliable. They may require pumping of the column bottoms liquid into the kettle, or there may be sufficient liquid head to deliver the liquid into the Heat Exchanger. In this Heat Exchanger type, steam flows through the tube bundle and exits as condensate. The liquid from the bottom of the tower, commonly called the bottoms, flows through the shell side. There is a retaining wall or overflow weir separating the tube bundle from the reboiler section where the residual reboiled liquid (called the bottoms product) is withdrawn, so that the tube bundle is kept covered with liquid. Kettle reboilers are reliable in that they can handle high vaporization of up to 80 percent and are easy to maintain. The liquid from the bottom of the tower flows through the tube bundle and exits as condensate. A restraining device (baffle) controls the liquid level over the bundle.