Thin film /Wiped film evaporator working principle with animated video
An agitated thin film evaporator (TFE) or wiped film evaporator (WFE or "wiffe") provides short residence time and open, low pressure drop configuration, allowing continuous, reliable processing of many heat sensitive, viscous, or fouling materials without product degradation.
The thin film evaporators quickly separate more volatile from less volatile components using indirect heat transfer and mechanical agitation of a flowing product film under controlled conditions. Either the vaporized component (distillate) or the concentrated component may be the product depending on the application.
How It Works
The agitated thin film evaporator (also commonly referred to as a "wiped film evaporator") consists of two major assemblies: a cylindrical heated body and a rotor.
Product is introduced above the heated zone and is evenly distributed over the evaporator's inner surface by the rotor. As the product spirals down the wall, the high rotor tip speed generates highly turbulent flow resulting in the formation of bow waves (see illustration above) and creating optimum heat flux and mass transfer conditions.
Volatile components are rapidly evaporated via conductive heat transfer. Vapors flow either counter-currently or co-currently through the unit, depending on the application requirements. In both cases, vapors are ready for condensing or subsequent processing (i.e. fractionation) after exiting the vapor discharge section.
Nonvolatile components are discharged at the outlet. Continuous agitation and mixing by the rotor blades minimizes fouling of the thermal wall where the product or residue is most concentrated.
The combination of 1) extremely short residence time, 2) narrow residence time distribution, 3) high turbulence, and 4) rapid surface renewal permits the thin film evaporator to successfully handle heat-sensitive, viscous and fouling-type fluids.
Legend
Feed Inlet
Product Stream Through the Evaporator
Product Bow wave
Counter-Current Vapor Outlet
Co-Current Vapor Outlet
Concentrate Outlet
Design Principles
It offers thin film / wiped film evaporator designs in a wide range of configurations.
Rotor Designs
Fixed Clearance for all horizontal designs and most vertical applications for less viscous liquids, generally less than 50,000 cps
Wiped Film/Hinged Blade for materials with very high fouling tendencies or vaporization ratios
Rotor Orientation
Vertical is used for most applications. The vertical configuration provides reliable, efficient processing of viscous and fouling fluids. Units are available with either an internal or external bottom bearing.
Horizontal designs are ideal for applications where longer residence times are required for mass transfer and reactions, or where headroom is limited. The tapered configuration allows adjustment of the rotor clearance to control residence time, and assures heat transfer surface wetting at low throughput rates.
Vapor Flow
Countercurrent is used for most vertical applications since it maximizes both heat and mass transfer efficiencies and accommodates internal vapor/liquid entrainment separation.
Co-Current is the best choice for applications where there is heavy vapor loading, foaming, or flashing.
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