What is the purpose and basic principle behind a desalter in crude oil processing?

• A. Desalter removes salts from crude oil using simple filtration.
• B. Desalter removes salts from crude oil to prevent corrosion and catalyst poisoning; uses mixing with water to wash salts, then electrostatic separation to settle water with salts from oil.
• C. Desalter removes salts by distillation of oil.
• D. Desalter removes salts by bioremediation.

Answer: (B)

Desalting crude oil is about removing inorganic salts that are carried along with entrained water in the oil, so they don’t cause corrosion or poison refinery catalysts downstream. The process achieves this by first washing the oil with fresh water to dissolve and carry the salts into the water phase. Then an electrostatic separator uses an electric field to charge and coalesce the tiny water droplets so they rapidly separate from the oil, forming a water-rich layer that is removed. This combination of a water wash to pull salts out and electrostatic separation to speed up and improve the demixing is what makes a desalter effective. Filtration, distillation, or bioremediation don’t remove these dissolved inorganic salts from crude oil in the same way, so they aren’t the right mechanisms here.