Fractionation Distillation

 Fractionation Distillation column blog contains

  • Fractionation Distillation
  • Fractionation column operation
  • Material Balance
  • Feed Plate & Feed line
  • Total Reflux (Infinite Reflux Ration)
  • Minimum Reflux Ratio
  • Optimum Reflux Ratio

Fractionating distillation

A fractionating column a cylindrical shell divided into two sections by a series of perforated trays a reboiler and condenser.

Fractionating distillation

A liquid mixture to be separated is introduced in the cylindrical column more or less centrally. 

The column itself is divided into two section rectifying and stripping section. 

The section above the feed plate or tray is called the rectifying section, where in vapour is washed to remove the less volatile component with the liquid return to the column from top, the portion below the feed plate including feed plates is called the stripping section.

Where in liquid is used stripping of more volatile component by using vapour perforated trays are nothing but gas liquid containing device on which gas and liquid are come into intimate contact of mass transfer to occur .

Vapors are generated in a reboiler and are feed to the bottom of the column. The liquid removed from the fractionators rich in less volatile component is called the bottom product. temperature is maximum at the bottom and minimum at the top. 

The part of the condensed liquid returning to the top column is called reflux.

Why reflux is important?

When vapor reaches up side, it cool down and travel back to bottom section ( Stripping section).

When cooled reflux is added it reduces top section (rectifying section) temperature and creates temperature gradient which cool down non product components. and allow to pass only product vapour.

Temperature Gradient, energy exchange & Importance of reflux

Distillation of fluid mixture A & B is fed to any tray or reboiler.

Fluid A Boiling point 80℃ Fluid B Boiling point 85℃

[ Boiling temperature is depending upon concentration of individual components concentration.

When fluid mixture fed to column heated vapour temperature it has 90℃ If we supply steam for 85℃ then vapour will not reach up to top section. It is not possible to supply heat to all section so these vapour mixture will act as heating media.

Both Fluid A & B start vaporizing and travelling to upper section.

When vapour reach at some trays above it starts cool down and fluid B partially start condensing. In this condensation Minor portion of fluid A will also condensate.

Above this tray same phenomena will occur but the difference is Fluid A concentration will also increases

When vapour goes out from top section to condenser minor portion of Fluid B will be present in product.

So, how we can reduce concentration of Fluid B in product?

Answer - We have to retain fluid B in column

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