Evaporation operating principle

Evaporation is basically a separation step which uses heat transfer to separate products presenting differences at boiling point; this technology results in several different downstream processes such as concentration, crystallization and drying.

In chromatographic processes, fractions of the desired compound(s) diluted in solvents (pure or mixtures) are produced. This creates a need for concentration, evaporation and crystallization operations.

Evaporation and crystallization equipment can be configured as multiple effect, thermo-compression and mechanical recompression. They can be fully integrated in processes developed by Novasep Process.

Among many others, the following examples of applications can be given :

• concentration of chromatographic fractions,
• concentration of sugar solutions,
• crystallization (APIs, chiral compounds, organic acids, dextrose, etc.),
• salts recovery, effluent concentration (raffinates, vinasses, effluents)

The thermal separation technology offers adequate answers to many actual concerns such as:

• Energy cost monitoring
• Production of highly purified crystalline products
• Disposal of industrial waste streams through concentration
• Recovery of valuable volatile fraction

Evaporation technology

Nowadays numerous designs are industrially operating.

Stirrer evaporator: This type of evaporation is rarely used nowadays; it applies mostly for highly viscous feed and for very specific products.

Climbing film evaporator: The operation principle is quite straightforward, a powerful pump moves up the boiling feed along the tubes, and the lower portion could eventually be used to preheat the solution.

Circulation evaporator: The operations are similar to the rising film principle but the liquid recovered in the separator is sent back to the bottom of the evaporator creating a closed loop.

Forced circulation evaporator: This system used when the product has a strong tendency to foul the heating surfaces, therefore it is recirculated at a rather high rate through the tubes.

Falling film evaporator: In this case, both liquid and vapours move downwards, the key point being a uniform wetting of the tubes in order to avoid any incrustation.

 

 

 

 

 

 

 

Fluidized bed evaporator: They operate under the same principle as forced circulation evaporator and are used when the feed solution contains particles.

Plate evaporator: As the name indicates, this type of evaporators instead of using shell and tubes design are made of a series of thin, corrugated plates compressed together in a rigid frame. The feed solution and the steam flow in alternate channels.

Spiral tubes evaporator: This is a very compact system where the long heating tubes are in spiral form to minimize space.

The characteristics of the feed solution such as heat sensitivity, viscosity, turbidity, boiling points, tendency to precipitation or foaming will determine the best selection.

Evaporation plant

Typically evaporation plants consist in preheaters in order to bring the feed solution up to the required temperature in order to start evaporation on the first unit, separators for the separation of the vapour and liquid phases, condensers for residual vapours and deaeration units.

Multiple effect evaporation: The energy consumption to evaporate an aqueous solution is pretty high therefore, in order to reduce the energy cost, several systems are commonly used such as multiple effect evaporation and thermal vapour recompression. The steam consumption of the evaporator plant can be reduced by using the vapour of the first unit for heating the next one but at a lower pressure.

Vapour recompression: The principle consists in recompressing low pressure/temperature vapours at a higher pressure so they can be condensed in the evaporator heat exchanger. This can be achieved either through a thermal vapour recompression device (typically a steam ejector venturi shaped) or mechanical vapour recompression (turbo compressor).

Multiple effect evaporation with thermocompression

Browse also Novasep Process Applexion® Evaporation and Crystallization Solutions for industrial biotech.