Crude oil is a combination of hydrocarbons that, depending on the pressure and temperature at which they are placed, have become solid, liquid, and gas. Crude oil carries some water, inorganic salts, solid particles and water-soluble metals when leaving the well. To increase the quality of oil, the percentage of these non-oil impurities must be reduced. Therefore, in order to prevent damage caused by the entry of these materials into the facilities of oil refineries, the output oil must be desalinated before entering the refinery.

 The desalination unit is one of the main units in oil refineries that is used for desalination of crude oil before refining. As the first step in the oil refining process and to prevent corrosion, scale formation and catalysts in the process units, these materials must be separated from the oil before refining.

Chemical method and electrical method are the two main methods of desalination of crude oil. In the chemical method, hot water and a chemically active elements are added to the crude oil and heated until the impurities dissolve in the water and stick to the water. Finally, the resulting mixture is kept in a tank to separate from each other. In the electrical method, using electrodes with very high voltage, suspended particles in the water are collected in the lower part of the tank. Both methods are continuous methods. However, the following methods can be mentioned for oil desalination: