Evaporator Technology

Falling film

In this type of evaporator the solution to be evaporated flows inside the tubes of a vertically arranged tube bundle. A special liquid distribution system at the top ensures an equal liquid feed to each tube and ensures that an even liquid film is obtained on the circumference of each tube. The flow of liquid per tube is called the wetting rate. Higher feed concentrations require higher wetting rates to prevent over concentration and fouling.

• The heating fluid for evaporation is introduced outside the tubes in the shell and is generally steam or vapor. The vapor generated by the evaporation is separated from the concentrated liquid at the bottom of the vessel and goes through a droplet separator which can be either integrated into the evaporator shell or separated with a vapor connection and a highly efficient cyclone inlet.
• The most common type of evaporator. Well adapted for thermosensitive fluids.

Forced circulation

The forced circulation system is a combination of a heat exchanger, for product heating, and a flash vessel. A high flow pump circulates the solution to be evaporated inside the heater where it is heated a few degrees over the boiling temperature by steam or another heating fluid. The heated solution then evaporates by flashing in the vessel. This type of evaporator can use either tubular or plate heaters according to the application.

Well adapted for :

• viscous products and very fouling solutions,
• solutions with suspended solids,
• solutions close to crystallisation.  

Horizontal wetted tube

The solution to be evaporated flows around the outside of the tubes in a horizontal tube bundle while the heating fluid flows through the inside of the tubes. This type of evaporators offers a number of advantages:

• utilises heat from either steam or a hot fluid in circulation,
• the space within the tube bundle allows the evaporated vapors to flow around the tubes at low velocity and enables a very low evaporation temperature,
• low risk of liquid priming
• easy mechanical cleaning of the outside tube surface and possibility of tube bundle dismounting (for limited heat exchange surface),
• low building height requirements and easy retrofit in existing buildings,
• large choice of manufacturing materials,