Published December 2010
Desalting is performed to reduce operating and maintenance costs and to enable products, especially the heavy ones, to meet specifications. Desalter technology has been developed and perfected over a number of decades yet continues to evolve. The most recent challenges are to refine more heavy or opportunity crude oils.
Opportunity crude oils are either new crude oils with unknown or poorly understood processing issues or are existing crude oils with well known processing concerns. Opportunity crude oils are often, but not always, heavy crude oils but in either case are more difficult to desalt, most commonly due to high solids content, high levels of acidity, viscosity, electrical conductivity or contaminants. They may also be oils that are incompatible, causing excessive equipment fouling when processed either in blends or separately.
Desalting is the first refining process applied to crude oil. The process removes salt, water and solid particles that would otherwise lead to operational problems during refining such as corrosion, fouling of equipment, or poisoning of catalysts. This is accomplished by washing the oil with water, coalescing small water droplets with electrostatic field forces into drops large enough to settle through the oil to form a bottom water phase and separating the oil and water.
We review both chemical and physical crude oil properties. We emphasize properties important to desalting, especially of opportunity crude oils: crude oil composition, emulsion properties and conductivity. We then review the technology, equipment and operating conditions for desalting heavy and opportunity crude oils.
We determine the process economics for two cases of two-stage electrostatic desalting in a refinery:
- 180,000 BPSD of heavy crude oil (0.2 vol% BS&W [bottoms sludge & water])
- 50,000 BPSD of conventional crude oil (0.4 vol% BS&W)
The economics of single-stage treaters for 50,000 BPSD of conventional crude oil containing 10 vol% water (BS&W) in oil field and in refinery settings are then determined.