A wiped film evaporator (WFE), also known as a thin film evaporator or agitated thin film evaporator, is a specialized piece of equipment used in the separation of mixtures based on differences in volatility. It is particularly effective for processing heat-sensitive, viscous, or thermally unstable materials, making it a popular choice in industries such as pharmaceuticals, chemicals, food processing, and petrochemicals.

Working Principle

• Prevention of Scaling and Fouling: The high velocity of liquid circulation reduces the risk of scaling and fouling on the heat exchanger surfaces, even with solutions prone to crystallization.
• Introduction of Feed: The feed mixture, typically a liquid containing volatile and nonvolatile components, is introduced into the evaporator through an inlet at the top.
• Film Formation: The feed is evenly distributed onto the inner surface of a heated cylindrical wall by a rotating wiper blade mechanism. This wiper system continuously spreads the liquid into a thin film, typically in the range of 0.1 to 1.0 mm thickness.
• Evaporation: As the thin film of liquid flows downward under the influence of gravity and the wiper blades, the volatile components evaporate quickly due to the high surface area and close contact with the heated wall. The low residence time and the thin film ensure that heat-sensitive materials are not exposed to high temperatures for prolonged periods.
• Separation of Vapors: The evaporated vapors are then directed to a condenser, where they are condensed into a liquid form and collected as distillate. The nonvolatile components (residue) continue to flow downward along the wall and are collected at the bottom of the evaporator.
• Discharge: The residue, which is typically more viscous, is discharged from the bottom outlet, while the distillate is collected separately.

Features of Wiped Film Evaporators

• Low Residence Time: The short residence time of the product in the evaporator minimizes thermal degradation, making WFE ideal for heat-sensitive materials.
• Handling of High Viscosity: WFEs are capable of handling highly viscous liquids, slurries, and materials that may be challenging to process in other types of evaporators.
• Vacuum Operation: WFEs can operate under vacuum conditions, which lowers the boiling point of the volatile components, further protecting heat-sensitive materials.
• Scalability: Wiped film evaporators are available in various sizes, from lab-scale units for R&D to large industrial-scale systems.
• Minimal Fouling: The wiping action reduces the risk of fouling or scaling on the heated surface, maintaining consistent heat transfer efficiency.
• High Purity Separation: WFEs can achieve high levels of purity in the separated components due to the precise control of operating conditions.
• Flexibility: They are suitable for a wide range of applications, including distillation, stripping, and solvent recovery

Applications of Wiped Film Evaporators

• Pharmaceuticals: Purification of active pharmaceutical ingredients (APIs), concentration of heat-sensitive compounds, and removal of solvents from drug formulations.
• Chemicals: Separation and purification of fine chemicals, resins, polymers, and specialty chemicals.
• Food and Beverage: Concentration of flavors, fragrances, essential oils, and natural extracts.
• Petrochemicals: Recovery of valuable hydrocarbons, removal of volatile impurities from oils, and purification of lubricants.
• Biotechnology: Processing of bio-based materials, including the concentration of enzymes, proteins, and other biological products.

Advantages of Wiped Film Evaporators

• Gentle Processing: Ideal for heat-sensitive materials due to the short residence time and the ability to operate at low temperatures.
• High Efficiency: Capable of achieving high separation efficiency with minimal loss of product quality.
• Versatility: Suitable for a wide range of applications, from simple distillation to complex purification processes.
• Scalable: Can be used in both small-scale laboratory settings and large-scale industrial production.