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In falling film evaporators, liquids and vapours flow downwards in parallel flow. The liquid to be concentrated is preheated to boiling temperature. An even, thin film enters the heating tubes via a distribution device in the head of the falling film evaporator, flows downwards at boiling temperature and is partly evaporated. This gravity-induced downward movement is increasingly augmented by the concurrent vapour flow.
In falling film evaporators, sufficient wetting of the heating surface by liquid is extremely important for trouble-free operation of the plant. Apart from the heating tube dimensions, it is very important to choose a suitable distribution device to achieve full wetting. Due to the low liquid content and high flow velocity in the heating tubes, the residence time of the product is very short. Therefore, heat sensitive products can be evaporated extremely carefully. The concentrate is collected at the bottom of the falling film evaporator. Droplets are separated from the vapours in the centrifugal separator.
Falling film evaporators can be started up quickly and changed to cleaning mode or another product easily. This is an important precondition for good controllability and automatic control of the operation of multiple effect plants, to produce a consistent product.
Watch our video animation to see a falling film evaporator in action.