Evaporation Technology Natural Circulation Evaporator

Vertical shell-and-tube heat exchanger of short tube length, with lateral separator arranged at the top.

Operation

The liquid to be concentrated is supplied to the bottom and rises to the top of the heating tubes in accordance with the "mammoth pump" or rising film principle.

Due to the external heating of the tubes the liquid film on the inside walls of the tubes starts to boil releasing vapor. The liquid is carried to the top of the tubes as a result of the upward movement of the vapors formed. The liquid is separated from the vapors in the downstream separator and flows through a circulation pipe back into the evaporator, 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 based on the same evaporation rate.

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.

 

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 (1-3 m).

Fields of application

  • For the evaporation of products insensitive to high temperatures,  where large evaporation ratios are required.
  • For products which have a high tendency to foul  and for non-Newtonian products,  where the apparent viscosity may be reduced by the high velocities.
  • The circulation evaporator with divided boiling chamber and top-mounted separator can be  used as a high concentrator.