Crude oil desalting Back

Action Dehydration
Method Absorption (chemical or electrostatic)
Purpose Remove contaminants (water, inorganic salts, suspended solids and water-soluble trace metals)
Feedstock Crude oil

Desalted crude oil
Waste water

Product(s) goes to

Atmospheric distillation
Waste water treatment

The crude oil which arrives in refinery storage often contains trashes from the oil field, such as water, inorganic salts, suspended solids, water-soluble trace metals and iron oxides that have flaked off pipelines or tank walls. As a first step before refining, to reduce corrosion, plugging and fouling of the distillation unit and to prevent catalyst poisoning during processing, these trashes are eliminated by desalting (dehydration).

Much of the suspended solids, minerals and iron oxides settle out in the crude oil tanks, ending up in the tank bottom as bottom sediment & water (BS&W).

Typical methods of desalting include the use of water as an extraction agent. Water and a chemical surfactant (e.g. a caustic) are heated with the crude, so that salts and other contaminants dissolve in the water. The mixture will then be kept still in a tank where these components settle out. In electrical desalting, a high voltage charge is used to concentrate suspended water, which settles out in the bottom of the tank. Surfactants may be added only when the crude has a large amount of suspended solids. Both desalting methods are continuous. A third and less common method is filtering heated crude using diatomaceous earth.

Waste water and contaminants are discharged from the bottom of the settling tank to the waste water treatment facility. The result is the desalted crude which is continuously sent to the crude distillation unit.

DMA Generation M

The DMA Generation M density meters measure the density and concentration of liquids. They provide preset measuring methods and integrated conversion tables for many applications. The FillingCheckTM function automatically detects filling errors and gas bubbles in the sample to avoid measuring errors.

Accuracy, density:
0.0001 g/cm³ (DMA 4100 M)
0.00005 g/cm³ (DMA 4500 M)
0.000005 g/cm³ (DMA 5000 M)

Repeatability s.d., density:
0.00005 g/cm³ (DMA 4100 M)
0.00001 g/cm³ (DMA 4500 M)
0.000001 g/cm³ (DMA 5000 M)

Benefits of DMA Generation M at Crude oil desalting


Crude oil varies greatly in appearance depending on its composition. Sulfur content and API gravity are characteristic for its origin. API gravity ranges from approx. 20 (heavy) to almost 50 (light). DMA 4100 M and DMA 4500 M can directly measure API gravity (calculated from true density), a necessary parameter for quality control of incoming goods (crude oil). The conversion from density to API gravity is implemented according to ASTM D1250 (product group A: crude oil).  A sample changer is used for high sample throughput (Xsample 452) and allows for highly repeatable results (Xsample 352/452).


Even the quality of a caustic (NAOH) – required if crude oil contains large amounts of solid particles – is easily monitored with a density meter, which reports the concentration in % w/w.