Evaporator
Evaporation is the removal of solvent as vapor from a solution, slurry or suspension of solid in a liquid. The aim is to concentrate a non-volatile solute, such as organic compounds, inorganic salts, acids or bases from a solvent. The most common solvent in most of the evaporation systems is water. Evaporation differs from the other mass transfer operations such as distillation and drying. Evaporation is normally stopped before the solute starts to precipitate in the operation of an evaporator.
Evaporator consists of a heat exchanger for boiling the solution with special provisions for separation of liquid and vapor phases. Most of the industrial evaporators have tubular heating surfaces. The tubes may be horizontal or vertical, long or short; the liquid may be inside or outside the tubes.
Falling Film Evaporators
The falling film principle requires an even distribution of the feed liquid. To achieve this distribution one or more distribution trays are in the top head of the evaporator over the complete tube sheet. Our proven distribution system makes sure that the inner surface of each individual tube is properly wetted.
The liquid film moves down the tubes by gravity force. Heat applied through the tube wall effects boiling-off the light fraction from the film. The picture shows a co-current operating evaporator with vapour and liquid leaving the bottom of the evaporator into the separator vessel.
Forced Circulation Evaporators
The feed liquid is fed into the circulating stream which is moved by a pump through a heat exchanger and a separator vessel. The heat applied through the tube walls superheats the liquid which flashes into the separator vessel where the vapour separates from the concentrated liquid. The high velocity of the liquid effects good heat transfer values but requires a large circulation pump. Further, the high velocity reduces the tendency for fouling and scaling.
Forced circulation evaporators can handle liquids with solids or salts precipitating them during the concentration step.
Agitated Thin Film Evaporator
Agitated thin film evaporator consists of a vertical steam-jacketed cylinder and the feed solution flows down as a film along the inner surface of large diameter jacket
Liquid is distributed on the tube wall by a rotating assembly of blades mounted on shaft placed coaxially with the inner tube. The blades maintain a close clearance from the inner tube wall. The main advantage is that rotating blades permits handling of extremely viscous solutions. The device is suitable to concentrate solutions having high viscosity.