Removal of salts is important for reducing corrosion in the distillation tower and downstream processing units. If not removed the salt will form acids when heated that will result in corrosion. Also, the salt can form deposits on heat exchanger surfaces over time, resulting in fouling.
Desalting also removes suspended solids such as sand, dirt and rust particles picked up in transport.
How it works
In the desalter, the crude oil is heated and then mixed with 5-15% volume of fresh water so that the water can dilute the dissolved salts. The oil water mix is put into a settling tank to allow the salt-containing water to separate and be drawn off. Frequently an electric field is used to encourage water separation. Demulsifying chemicals are also used. For high levels of salt, and/or to achieve very low final concentrations, two or three stage desalting may be used.
Typical desalted crude will have concentration of 1 pound/thousand barrels (PTB).