Why is crude oil desalting necessary and how is it done?

Crude desalting removes salt, water, and sediment before distillation. Salt causes: corrosion in distillation towers (especially from HCl formed from MgCl2 and CaCl2), fouling of heat exchangers, and catalyst poisoning in downstream units. Process: crude is mixed with wash water (3-10% volume), passed through mixing valve or static mixer to form emulsion, then separated in electrostatic desalters (electric field breaks emulsion, water/salt settles). Operating conditions: 100-150C, 5-15 bar. Two-stage desalting achieves 90-95% salt removal. Key parameters: temperature, water injection rate, mixing intensity, and electrical field strength. Brine water is treated before disposal. Essential first step in all refineries.