As most oil fields are growing older, resulting in wet crude oil production, it is necessary to provide desalting =dehydration systems to separate the oil and water before the oil can be further processed. Oil desalting=dehydration is the process of removing water-soluble salts from an oil stream. With the increasing regulations on effluent water and the ever- increasing cost of producingabarrel of oil, the use of emulsion-treatment plants has become an important practice in crude oil processing. Treat- mentofemulsions has always ranged from simple methods such as gravity settlement to highly sophisticated methods such astri-volted desalting and dehydration systems.
The development of desalting systems has always been evaluated in terms of quantities of salt and water being removed. In a desalting unit, when crude oil is heated as part of various desalting =dehydration or refining processes, the water maybe driven off as steam. The salts in the water, however, do not leave with the steam. They crystallize and may either remain suspended in oil or form scale within heat-exchange equipment. Entrained salt crystals may deactivate catalyst beds and plug processing equipment. Because of these potential problems, refineries usually reduce crude oil salt content to very low levels prior to processing. To reduce the amount of desalting required at the refinery, some oil purchasing contracts specify a maximum salt content as well as a maximum water content. Atypical salt specification would be 10Pounds per Thousand Barrels (10.0 PTB). To satisfy such purchase specifications, producers maybe required to perform some oil desalting.
Among the many reasons desalting =dehydration units are installed is to avoid transporting high viscosity liquids, ''water-in-oil''emulsions, which require more pumping energy. Furthermore, salts and water are removed in day-to-day operation for three reasons: corrosion, scale accumulation, and lowering of activity of catalysts.