Distillation is the fractionate process of crude oil into light hydrocarbons (C1 – C4), gasoline, kerosene, diesel, petrol, and atmospheric reside. The products need to be further processed in the refinery before selling them out. However, some of the products can be sold directly.
The raw product used in the refinery distillation is crude oil, which is a mixture of hundreds hydrocarbons, with paraffins, aromatics and naphthenes.
Gasoline, petrol, diesel, kerosene, etc, are named fractions in the distillation process.
Crude oil has to be desalting before going to the distillation process. The pressure used in distillation it the atmospheric pressure (slightly above it), which gives the name of theatmospheric distillation.
There are three reasons why it is necessary to have a 1 atm pressure for the distillation process:
-We need to raise the boiling point of the light carbons in order to be able to condense the C3 and C4
-The uncondensed gas needs to be under sufficient pressure in order to flow to the next processing equipment
-Allow pressure drop in the column
The desalted crude oil needs to be preheated before going to the distillation column. The preheat exchangers are used to heat the crude oil before going to distillation. Usually these heat exchangers take the heat from the distillates that have just gotten off the distillation column.
The preheated crude oil is then introduced into a furnace and
heated to a temperature
approximately to 340 Celsius degrees. The unwanted products are vaporized in this phase.
The remaining crude oil is then flashed from the furnace to the flash zone in the distillation column, where the vapor and the liquid will separate. The vapor goes up to the top of the column and the liquid down to the bottom of the column. The liquid will still have some of the distillates that need to be fractionated, so they will be recuperated by the steam stripping.
After the steam stripping process, the remaining liquid is discharged from the distillation column. This final product it is also known as reduced crude. Depending on the refinery, the reduced crude oil can go to a further vacuum distillation to recover some other products, such as vacuum gas oil (VGO), bitumen, fuel oil production.
Depending of the type of crude oil, the distillation column may contain also a prefractionator to recover most of the light-ends (for the crude oils with very high percentages of light-ends).
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