Working Principle

The operation process in the WFE is simple but yet effective. Feed is introduced at the top of the unit and spread on the shell inner surface by the rotating distribution plate. Specially designed wipers wipe the feed thus creating and renewing the film. This thin film enables an efficient heat transfer even for highly viscous fluids. The low boiling component evaporates and passes through an entrainment separator. This minimizes the carry over of liquid droplets along with the vapors. The vapors are removed through the vapor line to an external condenser (optional) and condensed. For specific applications which demand low pressure drop, the central section of the evaporator is provided with a condenser, thus making the unit a short path/molecular distillation unit. In this case, the vapors are allowed to condense on the outside of the tube bundle and flow out of the vaporator via the condensate outlet provided at the centre.

The high boiling component flows along the shell wall and is discharged from the product outlet. Wiper action is important in promoting downward flow. The product/concentrate should be in fluid form at the operating temperature. Different designs of rotors are available depending upon the product, its viscosity and the process pressure.

Milestones

Features

• Low rotational speed
• No bottom bearing
• Higher power to take care of feed fluctuations
• Chevron rotor with interchangeable panels for ease of cleaning
• Double groove gasket for high vacuum WFE
• Conical bottom with auger
• Top vapour outlet/li>
• Large internal condenser
• Swing / Hinge wiper blades
• Open rotor (no entrainment separator)

Falling Film Evaporator

A Falling Film Evaporator is used for concentration and evaporation of relatively low viscosity liquids. Steam, hot water or hot oil is used as the heating media and the process is carried out under atmospheric or vacuum condition. The Evaporator is used for volume reduction where dilute products are concentrated to a medium concentration. The process is continuous. The liquid to be concentrated is fed from the top and a distributor ensures proper feed distribution in each of the tubes. The distributor also ensures that all tubes are wetted and that the liquid flows in a film. The liquid and vapour both travel vertically downward. Due to a relatively thin film, the heat transfer coefficient is better than that obtained in reactors and simple shell and tube evaporators. If further concentration is required, the concentrated product can then be fed to the WFE.

Total Solutions

Dalal Engineering supplies complete systems consisting of one or more wiped film evaporators, falling film evaporators, auxiliary condensers, sub-coolers, receivers for residue and concentrate, vent condenser, vacuum system, interconnecting piping with instrumentation, valves etc.

A prototype Wiped Film Evaporator system is available at its Thane factory where trials can be conducted to determine feasibility and equipment with guaranteed performance can be offered.