The Advantages and Disadvantages of Falling Film Evaporator

The falling film evaporator is a kind of high efficiency evaporation equipment, it is also a thin film evaporator which include rising film evaporator and scraper film evaporator.
Thin film evaporator has obvious advantages and is widely used in chemical industry, light industry and food processing industry to concentrating the liquid. The structure of falling film evaporator is quite simple, just combined with a heat exchanger and a film distributor. But it has an obvious difference between normal exchanger, the shell side is heating fluid, tube side is evaporated material. The materials in the falling film evaporator tube side are transfered from the top of the heat exchanger tube, with its own gravity to the downstream along the tube in the heat exchanger tube, and should be distributed by the film-distributor before be sent to the heat exchanger. So the materials will be film state in the heat exchanger, the water will be evaporated in the process of downstream and the raw material will be condensed. If the shell side heated by steam, the direction of steam is from top to bottom, and if the shell side is heated by oil, the direction of oil should from bottom to top.

HSD Falling Film Evaporator

The advantages of falling film evaporator:

1. The residence time of the raw material in the heat exchanger is very short, does not affect the chemical properties of heat sensitive materials;
2. The material in the heat exchange tube is film state and the flow velocity is fast, so the heat transfer coefficient is very large.
3. There is almost no pressure drop, the pipe side material is in the ambient pressure environment which can save energy.
4. The low temperature difference can be chosen because the tube side material is driven down by its own gravity along the inner wall of the tube rather than by the pressure difference.
5. There is very little retention material in tube side.

The disadvantages of falling film evaporator:

1. The effect of the evaporation is related to the distributor, and requirements for the design, manufacture and installation of the distributor are very high.
2. High requirement of installation, mainly for the requirement of verticality, assuming the tube length is 9m, and the verticality should less than 6. 4mm.
3. It is need to ensure that the inner wall of the heat exchanger tube is completely wet, but the thickness of the film can not be too large, so the raw material feed rate and heat exchanger length should be exact designed and calculated.
4. Due to the high requirements of design and manufacture, the cost is very high;
5. It is not applicable to materials that are easily scaled or containing solid suspension.

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