Our Vobis pilot rising film evaporators are typically single stage systems. Operationally, as the liquid inside the tubes ascends or rises, it is heated through the walls of the tubes, and evaporation of the volatile components occurs. Disentrainment of the evaporated materials takes place in a specifically designed separate vessel.
Rising film evaporators are normally used:
For non-salting and non-scaling feed streams
To provide excellent heat transfer efficiency
For medium viscosity feeds that tend to foul
For low capital cost solution
For thermally sensitive materials for which the short residence time is an advantage (although this is limited by the high temperature differential of heating media to evaporation temperature that is required)
For foaming products for which very efficient vapor separators are required
For ease of deposit removal through increased feed rates
For solvent recovery
As the feed liquid to the rising film evaporator is fed to the bottom of the tubes and rises, heat is applied to the outside of the tubes causing evaporation of the low boiling components to occur within the tubes as the liquid rises. As the bubbles rise they grow in size, and the speed and turbulence of the liquid increases.
The combination of these operating principles:
Shortens the residence time within the tubes
Causes rapid material renewal against the heat transfer surface of the tubes
Lessens the necessary heat transfer surface area required
The rising film evaporator design has the advantages of simple, reliable and stable operation with many years of operating experience for a full ranges of applications. It is sometimes combined with falling film evaporation.