Introduction
In the context of oil refineries, electrostatic coalescence is a technique used in the elimination of water as well as water-soluble contaminants from crude oil. According to Lesaint et al. [1], the electrical field, which may be in the form of direct currents, alternating currents or a combination of the two, imparts a charge on water molecules and causes them to vacillate as they traverse the electrodes. The turnaround of the electrical field distorts the shape of water droplets, causing them to stretch and contract continuously. Oji and Opara [2] report that water droplets interact with each other and unite to form large droplets that move by gravity into the bottom part of the vessel for disposal.
Overall Importance of Electrostatic Coalescence
According to Pruneda et al. [3], electrostatic coalescence enables the elimination of water molecules from crude oil. It has been suggested that high quality petroleum products should not have water molecules.
Lesaint et al. [1] report that the water that is removed by electrostatic coalescence lowers the pumping costs of crude oil refinery. This is quite important because oil refineries are designed in such a way that they refine crude oil in an economical way.
Importance of Electrostatic Coalescence over Other Methods of Crude Oil Dehydration
Electrostatic coalescence does not require the use of additional chemicals to facilitate the removal of water, making it more efficient than other processes of dehydration such as chemical dehydration. Additionally, electrostatic coalescence is relatively simple and does not lead to the production of “rag waste” that is often difficult to handle in oil refineries.
Oji and Opara [2] report that electrostatic coalescence does not alter the composition of crude oil compared to heating, which has been shown to cause a thermal restructuring of the crude oil. Thermal destruction leads to production of oil that does not yield the best results in various sectors of the economy such as manufacturing and transport. During electrostatic coalescence, Less et al. [4] assert that the extremely volatile low-carbon compounds remain intact, whereas such compounds are adversely affected by heat dehydration.
When compared to other techniques such as gravity settling and filtration, electrostatic coalescence removes significant quantities of water from crude oil, thereby making the process very efficient. Ultimately, the cost of operating an electrostatic coalescence machine in the dehydration of crude oil is less than that required in other procedures such as centrifugation, distillation and fibrous packing.
Advantages of Electrostatic Coalescence
According to Lesaint et al. [1], electrostatic coalescence is an environmentally friendly technique because it minimises the utilisation of chemicals in getting rid of water from crude oil. The procedure also uses very little heat. Thus, it does not emit as much heat as other processes such as heating. In addition, the method of refining oil is relatively cheap in comparison to other methods. Therefore, it could be applied in many oil refinery plants with the main of achieving significant profits and reduction of production costs.
Disadvantages of Electrostatic Coalescence
The voltage gradient in the electrostatic field requires a delicate balance. It has been shown that at certain voltage gradients, water droplets disintegrate instead of combining, thereby increasing the forces of interaction between water and oil in the emulsion. As a result, the emulsion becomes stabilised. Hemmingsen et al. [5] report that the use of direct currents in electrostatic coalescence favours electrolytic corrosion, which may negatively impact equipment in oil refineries.
Conclusion
The advantages of electrostatic coalescence outweigh its disadvantages. Therefore, it can be concluded that electrostatic coalescence is an efficient technique of effectively removing water molecules from crude oil in oil refineries across the world.
References
C. Lesaint, W. R. Glomm, L. E. Lundgaard, J. Sjöblom. “Dehydration efficiency of AC electrical fields on water-in-model-oil emulsions.” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 2009, no. 2009, pp. 1-7, 2009.
A. Oji and C. C. Opara. “Electrocoalescence of field crude oil using high voltage direct current.” International Journal of Engineering Science & Technology, vol. 4, no. 5, pp. 1850-1857, 2012.
E. F. Pruneda, E. R. B. Escobedo and F. J. G. Vázquez. “Optimum temperature in the electrostatic desalting of Maya crude oil.” Journal of Mexican Chemical Society, vol. 49, no.1, pp. 14-19, 2005.
S. Less, A. Hannisdal. E. Bjorklund, and J. Sjoblom. “Electrostatic destabilization of water-in-crude oil emulsions: Application to a real case and evaluation of the Aibel VIEC technology.” Fuel, vol. 87, no. 12, pp. 2572-2581, 2008.
P. V. Hemmingsen, A. Silset, A. Hannisdal, and J. Sjöblom. “Emulsions of heavy crude oils. I: influence of viscosity, temperature, and dilution.” Journal of Dispersion Science and Technology, vol.26, no. 5, pp. 615-627, 2005.