|
Crude Distillation The crude still are the first major processing units in the refinery. They are used to separate the crude oils by distillation into fractions according boiling point. So that each of the processing units following will have feedstocks that meet their particular specification. 1. Desalting : minimize fouling and corrosion caused by salt deposition. Prevent catalyst deactivation. Removal of suspended solids from crude oil( such as very fine sand, clay) 2. atmospheric distillstion 3. vacuum distillation
Light End Unit
Atmospheric Distillation: Following desalting, crude oils are heated to approximately 750 F and pumped into the atmospheric distillation column. This column runs at atmospheric pressure, hence the name. The column separates the lighter fractions of petroleum from the bottoms product that is sent to the vacuum distillation column (see table at bottom). A typical atmospheric column requires 30-50 trays depending on the number of fractions/sidedraws. Generally, 5-8 trays are needed per sidedraw. Vacuum Distillation: The heavier fractions of crude oil that do not boil at the atmospheric column's furnace temperature (750 F) are sent to another column under a vacuum of 25-40 mmHg. This allows the heavier fractions to boil without experiencing thermal cracking in the column. Thermal cracking occurs at very high temperatures, >850 F, and breaks compounds into smaller/ lighter fractions and also forms coke deposits in the column. In addition, steam can be added to bring down the partial pressure of the crude further. The necessary temperature to vaporize the oil decreases as the amount of steam increases. Typical furnace outlet temperatures for the vacuum column are 730-850 F.
|
|
