How to select best Evaporator type: Thermal Separation & Turnkey Plants

Some industrial processes require the concentration of a solution, evaporating the solvent. Evaporation plants are widely used for concentration of liquids in the form of solutions, suspensions and emulsions.

3V Tech designs and supplies tailor-made evaporation plants, which can be arranged as skid-mounted units or suitable systems for on-site installation.

Typical applications

• Improving quality and/or stability of the final product
• Pre-concentration step for final product crystallization or drying
• Solute purification from process or waste streams
• Solvent recovery from process or waste streams
• Volume reduction for lower transport or disposal cost

Evaporator types

3V Tech's evaporation systems, operating under vacuum in the most of cases or at atmospheric condition, optimally use and combine the following technologies:

Evaporation systems, operating under vacuum in the most of cases or at atmospheric condition, optimally use and combine the following technologies:

• Falling film evaporators FFE
• Forced circulation evaporators FCE
• Thin/Wiped film evaporators TFE
• Short path evaporators SPE

Vertical Agitated Thin Film Evaporator TFE/L - HVconsists of a cylindrical, heated, vertical vessel and a high-speed rotor that maintains a film of product against the wall in highly turbulent conditions, a distributor mounted in front of the inlet of the product and a dynamic droplet separator.

• Vertical arrangement, from 0,15 to 40 m2 (larger on request)
• Best choice for general applications
• Suited for vacuum from 1-2 mbar abs to the atmosphere, or positive pressure
• Non-contacting L-type lobed rigid rotor with fixed and well-defined clearance from the heated wall
• The rotor sweeps the heated surface with a gap of some mm, this results in a great liquid turbulence
• Wide range of viscosity
• Moderate concentration ratios
• Special execution for high viscosity applications (type HV), with toothed lobed rotor

The Vertical Agitated Thin Film Evaporator TFE - HHV consists of a cylindrical, heated, vertical vessel and a high-speed rotor that maintain a film of product against the wall in highly turbulent conditions, a distributor mounted in front of the inlet of the product and a dynamic droplet separator

• Non-contacting rotor with toothed paddles
• The rotor with fixed toothed paddles push the product towards the bottom
• Positive transport of very viscous material which do not flow easily by gravity
• Moderate concentration ratios
• Operating at very high temperature (350°)
• Bottom pillow is normally a sleeve bearing, working into the process atmosphere, with several lubrication options, but it's possible to supply needle bearings also, with sealing from the process side

The Vertical Thin Film Dryer EF/V type has similar dimensions and a general construction as the Agitated Thin Film Evaporator TFE/L but its wipers has no fixed clearance and generally touch the heated stator vessel.

It is mainly used for high evaporation ratio, drying or material with very high fouling tendency.Wipers are available in several shapes and materials.
The Horizontal Thin Film Dryer EF/H is mainly used for pumpable paste or sludge. 

The necessary residence time is controlled by adjusting the blade configuration along the length and the circumference of the rotor. The counter-current flow assure that entrained fine particles are re-agglomerated in contact with the wet feed. Final product forms should be free flowing or pastes, melts etc.

The Short Path Evaporator SPE is an Agitated Thin Film Evaporator TFE/P with a built-in condenser in the evaporation chamber, mounted coaxially to the rotor, which results in a very short distance between the heating and condensing surfaces.

The Short Path Evaporator SPE is the best solution for molecular distillation and purification of extremely heat-sensitive substances and products with very high boiling point, under extreme vacuum conditions. For this type of applications, the pressure drop of the external condenser would be unacceptable.

In a multi-stage system, Short Path Evaporators can be used as final stage in combination with a Thin Film Evaporators

The Tubular Falling Film Evaporator FFE is the right solution to concentrate streams containing a small amount of suspended solids, low-medium viscous fluids and heat sensitive products.

It is particularly suited to energy saving multiple-effect (ME) evaporation, Thermal Vapor Recompression (TVR) or mechanical vapor recompression (MVR) arrangement due the very small operating temperature difference between heating medium and process side ("driving force").

In a multi-stage system, Falling Film Evaporators can be used in combination with Thin Film Evaporators/Dryers or with Forced Circulation Evaporators/Crystallizers.

• Very high heat transfer coefficient, especially for low viscous product under turbulent conditions
• Small mean temperature differences between heating medium and process side
• Short residence time in the heating tubes, mainly in one-trough operation, therefore also low liquid hold-up
• Negligible pressure drop in the heating tubes, therefore only in deep vacuum applications the pressure drop has to be considered
• Operation at low absolute pressure
• Sensitive to fouling from precipitating solids, nucleate boiling is to be avoided
• The Tubular Forced Circulation Evaporator FCE is the right solution to concentrate streams containing a big amount of suspended solids, medium-highly viscous fluids and products with high tendency to fouling. This kind of evaporator is also widely used as crystallizer, where special separator designs are used to separate crystals from the recirculated crystal slurry.

• Medium to high heat transfer coefficient, especially for low viscous product under turbulent conditions
• High circulation flow-rate inside the heat exchanger
• Evaporation does not take place on the heating surface, but in the flash separator
• Long residence time due the high recirculation, therefore also high liquid hold-up
• Vacuum operation or at atmospheric condition
• Not suitable for sensitive product, due the long residence time

General guidelines for evaporator selection

• Where high capacity is required, usually falling film evaporators  FFE bare the first choice
• When solids content and fouling tendency prevail, forced circulation evaporators FCE are the best suited
•  Where the product is difficult to handle due the extreme temperature sensitivity, high viscosity, high boiling point or heavy solids, a technology such as agitated thin/wiped film evaporator TFE is required
• Short path evaporators SPE are suitable for special applications underextreme vacuum condition with high boiling products.

• Often, a combination of two or more evaporator types is foreseen in multiple-effect or in pre-concentrator plus a high concentrator system

Now if you have to select an evaporator take a chance to compare different types to use better equipment for your applications!