The evaporated liquid is transported to the top of the heater through a circulation pump and evenly distributed to each heat exchange tube through a dedicated film distributor. The material flows downwards in a film like manner along the inner wall of the pipe under the action of gravity, evaporating while flowing. The generated secondary steam enters the separation chamber together with the concentrated liquid, and is filtered by the high-efficiency demister at the top to remove entrained bubbles, droplets, and impurities, providing a high-quality and clean secondary heat source for subsequent heat recovery.