Distillation

After desalting, the crude oil is pumped through a series of heat exchanger and its temperature raised to about 550°F (288°C ) by heat exchange with product and reflux streams.

It is then further heated to about 750°F (399°C ) in a furnace and charged to flash zone of atmospheric fractionators.

Fractionation

Separation

Atmospheric DistillationRectifying section

Flash zone

Stripping section

Reboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns.

They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation.

Reboiler

In this reboiler type, steam flows through the tube bundle and exits as condensate.

The liquid from the bottom of the tower, commonly called the bottoms, flows through the shell side.

There is a retaining wall separating the tube bundle from the reboiler section so that the tube bundle is kept covered with liquid.

Kettle Reboiler

The vapour moves up the column, and as it exits the top of the unit, it is cooled by a condenser.

The condensed liquid is stored in a holding vessel known as the reflux drum.

Some of this liquid is recycled back to the top of the column called the reflux.

The condensed liquid that is removed from the system is known as the top product.

Condensor

Bubble caps and trays

Temperature above 370-380 °C is not favourable in atmospheric column as high molecular weight compounds in crude will go thermal cracking and form coke.

Formation of coke will result in plugging tubes

Therefore residue from atm column is sent to vacuum distillation column.

Vacuum Distillation

In Vacuum distillation the pressure is reduced to less than its vapor pressure (usually less than atmospheric pressure) causing evaporation of the most volatile liquid(s) (those with the lowest boiling points).

 This distillation method works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure.

Vacuum Distillation