About Crude Oil Dehydration/Desalting

Electrostatic desalting is employed for both oil field and refinery applications, to facilitate the removal of inorganic chlorides and water-soluble contaminants from crude oil. In refinery applications, the removal of these water-soluble compounds prevents or minimizes damage to downstream distillation equipment.

Typical PFD for various configurations of desalter packages

       

The dehydration process of a desalter will reduce a portion of the free brine as it exits the vessel. A certain quantity of brine will continue to exit as an emulsion. Depending on the product specifications, one, two, or three stages of desalting may be required to satisfy the process design requirements. Recycling reduces dilution/wash water consumption and disposal costs of the effluents.

The salinity of the brine and the size and number of brine droplets will determine the quantity of salt in the crude. Throughout the world, salt content may range from moderate amounts to to as high as saturation (approximately 350,000 ppm).

GasTech's Dual Wave electrostatic desalting process consists of:

1. Introduction of fresh or low salinity dilution water into the crude oil stream altering the emulsion composition.
2. Dehydration or extraction of the entrained water droplets from the oil stream as it passes through an electrostatic AC/DC high voltage field.

Removes:

• Aqueous brine and formation water
• Metallic chlorides such as sodium chloride and calcium chlorides
• Inorganic solids

The removal of these impurities is accomplished by advanced electrostatic separation technology which subjects emulsified oil and water to a controlled high voltage electrical field. The action of the electrical field causes the emulsified droplets suspended in the oil to become polarized, coalesce into larger droplets and settle out by gravity.

Design

GasTech's electrostatic dehydration and desalting process is designed to meet the client's requirements for dehydration and desalting while minimizing organic oily water contaminants in the effluent water.

Technologically advanced process and equipment design features, which have been developed through operational experience, provide plant optimization, flexibility and minimize maintenance downtime.

GasTech design features include:

• 100% turndown, via designs based on computerized simulation of inlet/outlet hydraulic distribution headers creating even flow distribution.
• The installation of top mounted degassing vessels eliminating the need for upstream low-pressure separation equipment.
• High voltage electrode assemblies providing the correct voltage gradient and electrical field intensity necessary to process the required crude oil feed stream.
• GasTech provides the latest state of the art high voltage entrance bushing system available to the industry. This protects the power unit from damage caused by crude oil leakage.
• Non-overloading, 100% impedance transformer/reactor unit. "Current limiting" reactor and standard "external 5 position offload voltage tap changer" (12kV, 16.5kV, 20kV, 23kV, 25kV) is incorporated into each transformer design.
• External replacement of transformer entrance bushing without having to drain, steam-out or enter the pressure vessel.
• Hydraulic effluent water header specifically designed to minimize sludge build-up inside vessel.
• "Rag" layer system for removal of difficult emulsion pad build-up.
• Custom designed electrostatic internals for offshore production platforms or "motion" applications.
• Internal jetting system for dislodging and removal of sediment, sand and other solids from the bottom of vessels.
• Steam injection systems for ease in clean out and removal of difficult contaminants such as asphalt compounds, heavy paraffin compounds, and organic and inorganic solids.
• Static mixer for optimum contact of dilution water with the emulsified formation stream to enhance chloride removal.