DEHYDRATION & DESALTING
Dehydration is a process to remove water from crude to achieve required BS&W. Traditional Dehydrators employ two horizontal grids connected to a high voltage AC supply, and the emulsion flows upwards through the grids.
Desalting is a process to remove salts and other contaminants from crude. This prevents fouling of equipment in upstream operations and prevents corrosion, fouling, and coking in refinery operations. Single Stage or Two Stage Desalter Packages for salt removal efficiencies of up to 99% are used depending upon process parameters and salt removal required.
Desalters and Dehydrators work on the principal of electrostatic coalescence. Water droplets in crude assume spherical shapes. When exposed to an electrical grid, the droplets distort into an elliptical shape, or dipole. The attractive forces between the dipoles result in rapid coalescence into larger droplets. The larger droplets can then be separated by gravity. As Stoke’s law for gravity settling predicts that the settling rate increases as the square of the droplet size, typical brine droplets of 1 micron found in oilfield emulsions increase to 100 microns, thereby increasing their settling rate by a factor of 10000. This greatly reduces the size of the desalter or dehydrator compared to conventional gravity settling equipment.
Major Components of a Dehydrator/Desalter
- Inlet / Outlet Headers
- High Voltage Bushing System
- Transformer/Power Units with Control Panel
- Electrical Grids
- Mixing Valve /Static Mixer (For Desalter Only)
- Wash Water System (For Desalter Only)