Crude oil desalting

As many refineries around the world are increasingly processing “dirty sour crude” rather than “light sweet crude”, desalting is often a bottleneck, since the originally planned desalting capacity is insufficient to process the same volume of “dirtier” crude.  In addition, desalting is increasingly being carried out at wellhead sites (particularly offshore).

Desalting is commonly performed using electrostatic separating tanks, 50-100m3, operating at relatively high pressures of about 20 Bar, and temperatures up to 160oC.  The crude oil is heated and mixed with sweet water (and often demulsifiers) in order to dilute the salt, and the emulsion is separated in the electro-separators.

 

Crude Oil Desalting Process Flow
Crude Oil Desalting Process Flow

 

The two-stage desalting process eliminates about 90% of the salt; 10% of the salt is present in the oil in the smallest droplets (10 microns and less), which do not coalesce with the introduced sweet water and pass untouched through the electro-separation dehydrators. This salt, which remains in the oil, is the major cause of corrosion in refinery distillation equipment, and a major driver of catalyst replacement cycles.

Our turbulent mixer/coalescer, with a volume of approximately 5m³, and driven by a 70kw electric motor, is placed in-line before the electrostatic separator, either replacing the mixing valve used to introduce sweet water and the demulsifier optionally following it. Throughput for this size device will be approximately 35,000 barrels per day, so for a 100,000 barrels per day desalting line (a refinery may have several lines), 3 mixers would be required.

The controlled turbulence in the mixer will reduce the final salt concentration in the desalter output of crude oil by more than half, which will result in a significant reduction of corrosion and catalyst damage and the associated expenses.

Alternatively, Turbulent Mixers can be used to approximately double the throughput of an existing desalting line without increased chloride content in the desalted crude output. A third option is to replace the first stage of a conventional two-stage electro-separation desalting line, with a Turbulent mixer.