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Crude Oil Desalting

  • Objectives of crude oil desalting process

The crude oil entering the refinery processing system contains numerous undesirable impurities such as corrosion byproduct, polymer, drilling mud, inorganic salts and sands (Eow & Ghadiri, 2002). The amount of salt in the crude oil differs depending on the source and when a mixture of crude oil from different sources makes the salt content to vary greatly (Al-Otaibi et al., 2005). Without removing these impurities, the system has the potential of producing dangerous gasses such as hydrogen chloride, corrosion, damages due to erosion and abrasion and calcium naphthenate compound (Al-Otaibi et al., 2003). For example, the inorganic salts in the crude oil can be decomposed resulting in the production of hydrogen chloride gas and the presence of humidity, it turns into liquid hydrochloric acid (Mahdi et al. 2008). The acid corrodes different parts of the machinery and system, and the solution is eliminating the possibility of production of hydrogen chloride gas (Manning & Thompson, 1995). Therefore, the objectives of the process include increased crude throughput, better corrosion control, less coking, scaling, plugging of furnace tubes and heat exchanger (Aryafard, Farsi & Rahimpour, 2015). In addition, crude oil desalting contributes to less erosion by solids in pumps, furnace, and exchanger and control valves. Hence, crude oil desalting is an important component that improves the efficiency of petroleum production processes.

  • The Crude Oil Desalting Process and Operations

The following diagram summarizes the crude oil desalting process:

petroleum and petro chemistry processing

The desalting process adheres to some specific steps (Aryafard, Farsi & Rahimpour, 2015). The steps include dilution water dispersion and injection, emulsification of diluted water, distribution of emulsion in an electrostatic field, electrostatic coalescence and water droplet settling.

The process starts with the crude oil passing through the cold preheat train, and with the help of crude charge pumps, the crude oil is passed to the desalters (Manning & Thompson, 1995). Recycled water from previous desalters outputs is injected to the crude oil that contains sediments (Al-Otaibi et al., 2005). The mixture then enters into the static mixer, which is aimed at creating a maximizing effect on the interfacial surface area for the purpose of optimal contact between the crude and water liquid (Aryafard, Farsi & Rahimpour, 2015). The water is introduced near the emulsifying device to prevent separation, and the sources of water include stripping water and high salty sea water (Al-Otaibi et al., 2003). The static mixers are also strategically placed in a manner to which it improves the contact between the wash water inject and the crude oil in the line.

The emulsification process is crucial is aimed at improving the contact between the wash water and the oil, and then the emulsion enters the Desalters, which results into two phases via electrostatic coalescence (Al-Otaibi et al., 2003). An external electric source creates the polarization effect, and the polarization of water droplets contributes to pulling the droplets out from the water-oil emulsion phase (Aryafard, Farsi & Rahimpour, 2015). The salt in the water droplets is also separated during the process (Al-Otaibi et al., 2005). Effluent water is discharged from the water treatment system, and the effluent water can be used for another process during operation.

In the entire process, numerous fundamentals of electrical desalting should be considered (Manning & Thompson, 1995). Some of these fundamentals include wash water addition, wash and rate water quality, mixing/contact, coalescence, performance control variables and salt removal efficiency vs. dehydration efficiency (Al-Otaibi et al., 2005). Adhering and following these different components are important in fulfilling the crude oil desalting requirements.

  • The Crude Oil Feed and Final Products

The feed products in the crude oil desalination process are the crude oil and wash water. The output of the process are effluent water, and oil transferred to the appropriate furnace (Al-Otaibi et al., 2005). In the crude oil, there are other components and contents, which includes water-soluble trace metals, suspended solids, inorganic salts and water (Aryafard, Farsi & Rahimpour, 2015). The desalting process aims at removing these products to prevent the systems from fouling, plugging, and corroding of equipment and other systems (Al-Otaibi et al., 2003).

  • Different Crude Oil Desalting Technologies

Different types of desalting systems exist: three stage desalter, two stage desalter, single stage desalter, and single stage dehydrator.

  • Single stage dehydrator – the process employs a liquid desiccant dehydrator aimed at absorbing water vapor from the gas stream (Al-Otaibi et al., 2003).

  • Single stage desalter – it method is applicable or suitable for dehydrating produced crudes. The stage allows desalting to introduce less saline than what is original contained in the feedstock (Al-Otaibi et al., 2005).

  • Two stage desalter – the two phase is made of dehydration/desalter or/and desalter/desalter. The aim of the two stage desalter is to improve the quality of the final product with the target of purity at 98-99% (Manning & Thompson, 1995).

  • Three stage desalter – the crude oil is forced to undergo three phases: two options exist in the process. The first option is desalter/desalter/desalter and the second option is dehydration/desalting/desalting (Aryafard, Farsi & Rahimpour, 2015).

In the use or design of the system, some of the considerations include crude properties, power consumption and transactor size, the number of stages and vessel size (Al-Otaibi et al., 2005). In desalting process, there are desalter components, which include level control devices, mud wash, transactors and electrodes, distribution system and process vessel (Aryafard, Farsi & Rahimpour, 2015). In addition to these different processes, different types of desalting applications distillate treating, FCC feed desalting, and heavy crude desalting.

  • Conclusion

The objectives of crude oil desalting are removing impurities that may create additional challenges in cleaning crude oil. The consequences of not removing the impurities include corrosion of some parts of the equipment because of hydrogen chloride and creating other problems such as plugging and other issues preventing the efficiency of petroleum production. The production and operational process of crude oil desalting involve numerous phases and steps. These first step is mixing the crude oil with water that is less saline, and while the process continues, other processes are incorporated. For example, electrification is incorporated to improve the desalination process and depending on the output requirements, the technique employed should conform to the expected outcome. The feed products are the crude oil and the wash water while the final product is petroleum and other products associated with crude fuel. Moreover, wastes such as effluent water is discharged and other salt related components, which are released during numerous phases of the production process. There are many types of technologies used in fulfilling the crude oil desalting. Some of these techniques include single stage dehydrator, single stage desalter, two stage desalter and three stage desalter. The applicability of the techniques depends on the use of the final products and the nature of the original crude oil. The size of the facilities, the power consumption and vessel size informs on the design considerations.


Al-Otaibi, M. B., Elkamel, A., Nassehi, V., & Abdul-Wahab, S. A. (2005). A computational intelligence based approach for the analysis and optimization of a crude oil desalting and dehydration process. Energy & Fuels, 19(6), 2526-2534.

Al-Otaibi, M., Elkamel, A., Al-Sahhaf, T., & Ahmed, A. S. (2003). Experimental investigation of crude oil desalting and dehydration. Chemical Engineering Communications, 190(1), 65-82.

Aryafard, E., Farsi, M., & Rahimpour, M. R. (2015). Modeling and simulation of crude oil desalting in an industrial plant considering mixing valve and electrostatic drum. Chemical Engineering and Processing: Process Intensification, 95, 383-389.

Eow, J. S., & Ghadiri, M. (2002). Electrostatic enhancement of coalescence of water droplets in oil: a review of the technology. Chemical Engineering Journal, 85(2), 357-368.

Mahdi, K., Gheshlaghi, R., Zahedi, G., & Lohi, A. (2008). Characterization and modeling of a crude oil desalting plant by a statistically designed approach. Journal of Petroleum Science and Engineering, 61(2), 116-123.

Manning, F. S., & Thompson, R. E. (1995). Oilfield processing of petroleum: Crude oil (Vol. 2). Pennwell books.