Evaporation Technology

Falling Film Evaporator

The most widely used evaporator in the process industry. Vertical shell-and-tube heat exchanger with a wrap-around or laterally arranged centrifugal separator.

The Falling Film Evaporator, with capacity ranges of up to 150t/h and relatively small floor space requirement, is the most widely used evaporator in the process industry.

Particularly well suited for temperature-sensitive products, liquids containing small quantities of solids and with a low to moderate tendency to form incrustations.

Particular features

  • Best product quality.
    Thanks to its gentle evaporation, mostly under vacuum, and extremely short residence times in the falling film evaporator.
  • High energy efficiency.
    Due to its multiple-effect arrangement or heating by thermal or mechanical vapor recompressor.
  • Usage of recovered waste heat.
    The evaporator can be heated by exhaust airstreams or hot water thanks to the flexible design of the heating side.
  • Simple process control and automation.
    Because of its small liquid content, it reacts quickly to changes in energy supply, vacuum, feed quantities, concentrations and more.
  • Flexible operation.
    Quick start-up and easy switchover from operation to cleaning, plus uncomplicated changes of product.

Working Principle

Working Principle of Falling Film Evaporator

The liquid to be concentrated is supplied to the top of the heating tubes and distributed in such a way as to flow down on the inside of the tube walls. 

The liquid film starts to boil due to the external heating of the heating tubes and is partially evaporated as a result. The downward flow, caused initially by gravity, is enhanced by the parallel, downward flow of the vapor formed.

Residual film liquid and vapor are separated in the lower part of the calandria and in a wrap-around or laterally arranged centrifugal separator. It is essential that the entire film heating surface, especially in the lower regions, is evenly and sufficiently wetted with liquid. Where this is not the case, dry spots will result that will lead to incrustation and the build-up of deposits. 

For complete wetting is important that a suitable distribution system is selected for the head of the falling film evaporator. Wetting rates are increased by using longer heating tubes, dividing the falling film evaporator into several compartments or by recirculating the product.

falling-film-evaporator-workflow
evaporation-type-01

Heating options for thermal separation plants

Traditionally, an evaporator or crystallizer is heated by live steam, but waste heat can be used as energy source as well, as long as the amount of energy required for the thermal separation process is given.

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