Evaporation Technology

Natural Circulation Evaporator

Quick start-up and large specific capacity. Vertical shell-and-tube heat exchanger of short tube length with lateral separator arranged at the top.


The Natural Circulation Evaporators offer the possibility to be used as a high concentrator.

Well suited for working with products insensitive to high temperatures that require large evaporation ratios as well as with products with a high tendency to foul or with Non-Newtonian products, where the apparent viscosity may be reduced by the high velocities.

Often assembled with a divided boiling chamber and top-mounted separator as well.

Particular features:

  • Quick start-up and large specific capacity.
    The liquid content of the evaporator is very low due to the relatively short length and small diameter of the heating tubes.

Working Principle

Working Principle of Natural Circulation Evaporator

The liquid is fed to the bottom of the heating tubes. Due to the external heating of the tubes the liquid film on the inside walls of the tubes starts to boil and evaporates partially. 

As a result of the upward movement of the vapors produced, the liquid is also transported upwards – according to the thermosiphon or rising film principle. After the separation from the vapors it flows back into the evaporator through a circulation pipe, ensuring stable and uniform circulation. 

The larger the temperature difference between the heating chamber and the boiling chamber, the greater the intensity of evaporation and, consequently, the liquid circulation and heat transfer rates. 

Where the boiling chamber of the circulation evaporator is divided into several separate chambers, each one equipped with its own liquid circulation system, the heating surface required for high final concentrations can be considerably reduced compared to an undivided system. 

The final concentration is only reached in the last chamber. In other chambers, the heat transfer is considerably higher due to the lower viscosities and boiling point elevations.


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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