• 
• Evaporation occurs on the wall of a cylindrical evaporator as the feed product falls down the cylinder wall and is heated above its boiling point by heat applied to the exterior of the cylinder.
• Excludes the disadvantages of batch-distillation:
  • Lower pressure in the evaporator is possible
  • Reduces the residence time at high temperature, even in large units.

Result: Thermal decomposition is being avoided

Types of Thin Film Evaporators

• Single Tube Falling Film Evaporator w/external condenser
• Multiple Tube Falling Film Evaporator w/external condenser
• Falling Film Degasser (packing) w/external condenser
• Wiped Film Evaporator w/external condenser
• Short Path Evaporator w/internal condenser

Thin Film (Wiped Film) Evaporators

• Residence time:
  less than 1 minute
• Pressure range:
  down to 1 mbar
• Not an equilibrium device
• ~ 1 theoretical plate
• Condenser is external to Evaporator
• 30oC rule —

   pressure f( temperature)

Falling Film Evaporators

Residence time: several minutes

often with recycling

Pressure range: down to several mbar Not an equilibrium device

~ 1 theoretical stage

Short Path Evaporators
(a subset of Wiped Film Evaporator)

• Residence time:
  less than 1 minute
• Pressure range:
  down to 0.001 mbar
• Not an equilibrium device
• ~1 theoretical plate
• Condenser is inside the Evaporator
• 30oC rule

Wiped Film   vs. Short Path

• Thin Film Evaporator
  – External condensation
  –  Lowest operation   pressure: ~ 1 mbar
  –  Main application:
  Separation of high   contents of volatiles

• Short Path Distillator
  – Internal condensation
  –  Lowest operation   pressure: 0.001 mbar
  –  Main application:
  Distillation of heat   sensitive products