Oil desalting systems

The process of removing water-soluble salts from an oil stream is called oil desalting. Nearly all crude oil is produced with some entrained water, which normally contains dissolved salts, principally chlorides of sodium, calcium, and magnesium. The majority of the produced salt water is removed in the separation and treating process. However, a small amount of entrained water remains in the crude oil. The crude oil is sent to the refinery where it is heated as part of the various refinery processes. The entrained water is driven off as steam. However, the salts in the water does not leave with the steam but crystallizes and remains suspended in the oil or may deposit as scale within heat exchange equipment. In addition, entrained salt crystals will usually deactivate catalyst beds and plug downstream processing equipment. 

Due to these problems, refineries usually reduce crude oil salt contents to very low levels prior to processing. Refineries usually achieve the needed salt content by specifying in purchase contracts a maximum salt content, as well as maximum water content. A common salt specification would be 10 pounds per thousand barrels (PTB), 10 PTB (0.003 kg/m ). To satisfy the refinery specification, upstream production facilities may be required to perform some oil desalting. 

This part of the chapter describes the methods and equipment commonly used to desalt crude oil. 

It is possible to automate the globe valve to avoid over mixing. A differential pressure controller is used to control the pressure drop through the globe valve. This system automatically adjusts for changing flow rates and maintains a set pressure drop. Since this system s set point can be adjusted in the field, it allows an operator to optimize its performance. 

The pressure drop through the mixing valve varies from approximately 10-50 psi (70-340 kPa). The required pressure drop through the mixing valve varies from 10-50 psi (70-340 kPa). The required pressure drop can be decreased if a premixing device is installed upstream 

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P. R. Hart. Method of breaking reverse emulsions in a crude oil desalting system. Patent CA 2126889,1995. 

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