Abstract
The desalting process of an electrostatic desalting unit was studied using the collision time of two droplets in a water-in-oil (W/O) emulsion based on force balance. Initially, the model was solved numerically to perform a process analysis and to indicate the effect of the main process parameters, such as electric field strength, water content, temperature (through oil viscosity) and droplet size on the collision time or frequency of collision between a pair of droplets. In decreasing order of importance on the reduction of collision time and consequently on the efficiency of desalting separation, the following variables can be classified such as moisture content, electrostatic field strength, oil viscosity and droplet size. After this analysis, a computational fluid dynamics (CFD) model of a biphasic water–oil flow was developed in steady state using a Eulerian multiphase framework, in which collision frequency and probability of coalescence of droplets were assumed. This study provides some insights into the heterogeneity of a desalination plant which highlights aspects of design performance. This study further emphasizes the importance of two variables as moisture content and intensity of electrostatic field for dehydrated desalination by comparing the simulation with the electrostatic field against the same simulation without its presence. The overall objective of this study is therefore to show the necessity of including complex phenomena such as the frequency of collisions and coalescence in a CFD model for better understanding and optimization of the desalting process from both process safety and improvement.
Highlights
Crude oil is a non-renewable and a naturally occurring unrefined petroleum product that consists mainly of hydrocarbons and other inorganic substances [1]
The initial distance between droplets depends only on the water content and droplet size as expressed by Equation (10), so this is why the distances between droplets are different at initial time for Figure 3a,c, while for the rest of variables the initial distances are the same in all cases
Time for collision between two droplets is related to the rate of coalescence which influences the rate separation between water and oil in an electrostatic desalting unit
Summary
Crude oil is a non-renewable and a naturally occurring unrefined petroleum product that consists mainly of hydrocarbons and other inorganic substances [1]. These hydrocarbons have to be separated before they can be used as a fuel. Crude oil is extracted mostly from underground oil fields and from under the sea bed. It is extracted from wells containing gases, water and a small amount of inorganic salts. The process of removal of saline water from raw crude oil is called desalting. 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]
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