Wiped Film Evaporators (WFE) or Rolled Film Systems
Traditional Wiped Film evaporators have been around for a long time. There are a number of manufacturers which offer equipment acceptable in the low vacuum range, where the distillation conditions might not be challenging. Designing robust wiper systems which perform reliably without damaging the evaporator surface in long term operating campaigns is the most challenging engineering feature associated with Wiped Film Evaporation design. The UIC Distillation Division addressed this issue years ago and concluded a "Rolled Film Evaporator" offered a multitude of operational advantages over the traditional wiper approach. Rolled Film Evaporator advantages include:
- Consistent wiped film thickness distributed over the evaporator surface
- Provides a homogeneous material layer across the evaporator with mixing action
- Promotes higher distillation rates as the roller's extended surface increases the evaporator's theoretical surface area by 15% - 25%
- Minimizes wiper maintenance and wear-and-tear on the evaporator with a simple roller mechanism which rarely fails
- No bottom seals are necessary which minimizes the potential for vacuum leaks.
This special wiper system is used in the UIC rolled Film evaporators and Short Path Evaporators. This roller wiped film system has proven it has tremendous advantages in many applications over the years. The roller system consists of a cylindrical "basket", composed of guide rods on which rollers are fixed. The rollers are made of a glass fiber reinforced PTFE compound. The roller wiped film system is driven by a motor from outside the distillation chamber. The centrifugal force presses these rollers into the liquid film flowing downwards. Since there is no mechanical load on the evaporation surface, scratches and "fouling" are avoided. The roller wiped film system guarantees a uniform, laminar mixing of the thin film on the entire evaporator surface. Due to overlapping of the rollers and wiping on the unheated areas, so-called "dead-zones" are avoided. At the same time, the liquid thin film on the rollers is continuously renewed. This results in a very low residence time of the evaporating feed on the evaporator surface. Build-up or caking of material on the evaporator surface and on the rollers, which might happen with other wiping systems, is completely avoided with the UIC designed roller wiped film system.
The large clearance between rollers and guide rods facilities a "floating roller" which assures an even distribution of the feed material on the evaporator without causing damage to the evaporator. The necessity for a bottom bearing for the wiper basket is precluded by the floating action of the roller, so problems related to product penetrating into the lower bearing, or vacuum leaks through the bearing are eliminated.Learn about Short Path