Wiped Film Evaporator

Introduction

The Wiped Film Evaporator is used for concentration, distilling, stripping, dehydration and deodorisation of products which are heat sensitive or viscous. The equipment can handle a very wide range of feed compositions ranging from 1% to over 95% concentration. WFE has several advantages as stated in the table below. The operation is continuous with a single pass; the self cleaning continuous contact wipers produce and renew the thin film. Such an operation improves product yield, avoids residue and colour formation. It has an internal condenser (optional) that minimizes the pressure drop and maintains vacuum.

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.

Advantages

• Evaporation at low operating temperature
• Short residence time (few seconds)
• High heat transfer coefficients
• Low pressure drop on vapor side
• No degradation or loss of active ingredients
• Self cleaning\wiping of the heat transfer surface
• Suitable for viscous liquids
• Continuous operation
• Low maintenance

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.

Technical Specifications
Evaporator area m2	0.45	1.0	2.0	3.0	5.0	7.5	12.0	20.0
A (Square Cut-Out)	660	1010	1010	1320	1320	1320	1650	1895
B	1190	1710	1760	1800	1885	2249	2604	3360
C	616	1295	1770	1460	2205	2877	3590	5155
D	480	900	1200	1130	1190	2600	3000	2050
E	600	1000	1900	1690	2100	3000	3625	4000
Other sizes available as per requirement. Internal condenser optional.

E - Brochure: Dalal Wiped Film Evaporator