Coalescence of Water Droplets in Crude Oil Emulsions: Analytical Solution

Abstract

In petroleum refineries, water is used in desalting units to remove the salt contained in crude oil. Typically, 7 % of the volume of hot crude oil is water, forming a water-and-oil emulsion. The emulsion flows between two electrodes and is subjected to an electric field. The electrical forces promote the coalescence of small droplets of water dispersed in crude oil, and these form bigger droplets. This paper calculates the forces acting on the droplets, highlighting particularly the mechanisms proposed for droplet-droplet coalescence under the influence of an applied electric field. Moreover, a model is developed in order to calculate the displacement speed of the droplets and the time between droplet collisions. Thus, it is possible to simulate and optimize the process by changing the operational variables (temperature, electrical field, and water quantity). The main advantage of this study is to show that it is feasible to increase the volume of water recycled in desalting processes, thus reducing the use of freshwater and the generation of liquid effluents in refineries.

Numerical Study of Electrostatic Desalting Process Based on Droplet Collision Time

“…The effect on the inlet flow rate of fresh water showed similar results to that of Aryafard et al [13]. Bresciani et al [7] proposed a mechanism for droplet-droplet collision and coalescence in the presence of an external electric field. A model was developed to determine the time between collision and displacement speed of water droplets considering the forces acting on the droplets.…”

“…Additionally, the geometry of such electrostatic desalting unit is extremely complex. Desalting of crude oil involves two steps, the first is to mix the oil stream with a stream of freshwater intensively, which results in reducing the stability of the water-in-oil emulsion and the second is to separate the saline water present in the emulsion [7,8]. Depending on the amount of gas, salt and water present in the extracted crude oil, two different separation techniques are used.…”

“…These emulsions consist of water droplets dispersed in oil and the third component being the emulsifying agent to stabilize the system. The volume of water that is present in the W/O emulsion is usually 7% of the extracted hot crude oil [7]. Therefore, electrostatic desalting is one of the most popular methods to remove saline water from crude oil by applying an external electrostatic field.…”

“…Treatment of saline water present in emulsified form (desalting) is a sophisticated process as it depends on various factors such as the concentration of demulsifying agents, wash water, concentration of salt in water, rate of mixing with wash water [2], temperature and rate of dilution [10]. Several researchers [5,7,10,11] have studied the effect of these factors on desalting efficiency. Aryafard et al [12] simulated the process using a single stage desalting process in which a demulsifier is added to the raw crude oil stream at the beginning.…”

Coalescence of Binary Droplets in the Transformer Oil Based on Small Amounts of Polymer: Effects of Initial Droplet Diameter and Collision Parameter

“…The simulation results demonstrated that the emulsion will form droplets of larger diameter through a filter with larger pore spacing, but it is difficult for the larger-diameter droplets to coalesce; thus, it is difficult to separate water and oil [ 18 ]. Bresciani et al [ 19 ] investigated the effect of the electric field on the coalescence mechanism of droplets, and a mathematical model was established to calculate the collision velocity and the coalescence time of the droplet. The results indicated that the coalescence of droplets could be accelerated by changing operating parameters such as temperature and electric field.…”