A kettle evaporator or kettle-type evaporator is an evaporator that consists of a tube bundle that is immersed in a liquid. The tube bundle and the liquid are in a container that serves as a separator. Such evaporators are often used to generate heating steam from liquid water.
A heatable tube bundle is usually in a horizontal position in a larger container that serves as a separator. The liquid to be evaporated is fed into the area of the tube bundle and backed up by an overflow weir so that the tube bundle is submerged. The liquid boils due to the heating, so that bubbles form, which are separated from the liquid by the large volume of the separator and discharged from the upper area. The non-evaporated liquid overflows at the weir and is then withdrawn from the evaporator.