Describe the key mechanism behind a desalter's salt removal in crude oil processing.

• A. Desalter uses mixing with water to wash salts, then electrostatic separation to settle water with salts from oil.
• B. Desalter removes salts by simple filtration.
• C. Desalter uses heating to evaporate salts.
• D. Desalter uses biological treatment.

Answer: (C)

Desalting a crude aims to transfer inorganic salts from oil into a separate water phase and then remove that water. The oil is washed with water so salts dissolve into the wash water. An electric field is applied to promote coalescence of the water droplets dispersed in the oil, so they grow and separate by gravity into a water-rich phase that is drained off. Heating often helps by reducing oil viscosity and improving mixing and droplet coalescence, but the salt removal itself comes from the water wash and electrostatic separation, not from evaporation. Filtration, evaporation of salts, or biological treatment don’t describe the actual mechanism used in a desalter.