Electrostatic Coalescence and Crude Oil Dehydration

Overview

During industrial processes like the dehydration of crude oil, the dissociation of the water molecules from the water-oil mixture is an essential requirement of a coalescer. Notwithstanding the fractional distillation that is subjected to the crude oil, impurities like water should be removed to improve the quality of the product. Electrostatic coalescence is an ideal technology for separation of molecules that act as impurities in crude oil.¹ As the name suggests, the impurities (water included) are separated from the mixture through an electrostatic mechanism.

The use of an electrostatic coalescer was first recorded in the late 1990s. Al-Qhatani and Elkamel hold the opinion that the quality of crude oil is enhanced upon dehydration.² Their study further recommends electrostatic coalescence due to reduction in the cost of extraction and transportation. In addition, the purified oil is made safe for the environment. Electrostatic coalescence is often carried out on petroleum products like paraffin, which require zero minimum content of impurities to enhance their combustion.

In this research paper, attention is given to the applicability of the process to the breakdown of water molecules from the crude oil emulsion. An in-depth analysis of the concept of coalescence is provided. Some of the parameters examined include the working principle of an electrostatic coalescer. The issue of electrostatics and dipolar attraction are examined.³ The coalescence of the unwanted molecules is realised through this working principle. In addition, the paper examines the configuration of the machine, with special attention to the nature of the electrodes.

The findings of this research paper will lay the ground for more studies on electrostatic coalescence. In line with the same, recommendations will be provided at the end of the paper to establish a framework for further application of electrostatic coalescence in the dehydration of crude oil. The increased demand for clean and cost-effective methods of crude oil dehydration makes a case for the use of electrostatic coalescence by oil companies.⁴

In general, the paper seeks to affirm the benefits of the electrostatic coalescer and, by extension, the science of coalescence. Given the fact that crude oil requires dehydration, it follows that any company in the oil mining industry requires an electrostatic coalescer. One of the advantages of this machine is its low cost. Most electrostatic coalescers are efficient in terms of cost.⁵ An analysis of the different types of these machines reveals their low maintenance requirements. Most electrostatic coalescers have little energy demands, making them ideal for the industrial process that is crude oil dehydration.

Electrostatic Coalescers

Electrostatic coalescers are the instruments used for the coalescence process described in the introduction of this paper. The machines induce coalescence on impurities like water, which are found on crude oil. They achieve this through the use of electric fields.⁶ The droplets are often uncharged.⁷ When that is the case, the Alternating Current (AC) field produced by the coalescer ensures that the droplet becomes polarised. The polarised droplet develops an electric field around it. The coalescence is achieved when droplets in close proximity get attracted to each other.⁸

An actual electrostatic coalescer is a large tank with several electrodes that are used to produce an AC field.⁹ Owing to the magnitude of the crude oil that requires purification, the machine has a cylindrical structure. The structure helps it to hold large volumes of oil. The coalescer is essentially a metallic grid that extends horizontally to allow for the flow of crude oil. Inside the cylindrical space, the electrodes are spaced about 50 mm apart. The high voltage is, in a way, separated from the fluid. To achieve the said polarisation, electricity is supplied at powers of up to 100 volts.¹⁰ Within the coalescer, there is a transformer that ensures the power is amplified further. The high voltage gets to the electrodes to initiate the polarisation process.

There are several types of electrostatic coalescers. Technology has evolved to ensure that the underlying principle is respected every time a new coalescer is developed. The original electrocoalescers have evolved to different brands as exhibited by the compact new versions.¹¹ Regardless of the modification, the major objective of the machine is to ensure maximum polarisation of the water molecules. The said polarisation is realised only when the voltage supplied to the electrodes is high enough. Other factors that promote coalescence include the nature of the electrodes and the frequency.

Working Principle

Every machine respects a certain mode of operation to ensure its objective is met. The electrostatic coalescer is no exception. Notwithstanding developments on the original model, all other electrostatic coalescers operate on the same principle.¹² Most coalescers operate under high voltage, which is amplified by a transformer. Also, there are electrodes within the machine which help to induce the electrostatic field to the fluids which are passed through. See figure 1

A look at figure 1 reveals the essential components of an electrostatic coalescer. The machine is structured in such a way that crude oil enters the vessel, and the water is filtered out in another section. The pure crude is extracted from yet another opening. At a preferred distance between the two openings, there is a series of electrodes, whose function has been aptly discussed in the previous sections. A coalescer also requires an aperture that separates the water which accumulates towards the outlet.¹³ The same is illustrated in figure 1. Depending on the type of machine, the transformer is placed strategically to ensure high voltage in the electrodes.

Electrostatic coalescence separates water from the crude oil using the same principle as a filter. However, the coalescer relies on a combination of gravitational and centrifugal forces to ensure that the water molecules are mechanically extracted from the mixture. Figure 1 illustrates how a typical coalescer works. Essentially, crude oil passes through two tanks. The oil enters the vessel and flows through gravity. The electrostatic field relies on centrifugal forces to draw out water molecules from the emulsion.

Electrostatic Forces

Electrostatic coalescence obtains its functionality from the principle of electrostatics. Just as the name suggests, electrostatics is a contributing factor to the actual coalescence of the water molecules. The high voltage creates an electric field which in turn lays the foundation for the attraction of the molecules.¹⁴ The electric field creates elements with different charges. As such, the Coulombs law comes into force to explain the charge difference between the molecules and consequently, the attraction that will exist.

In the previous section, it was clear that the coalescence of the molecules is determined by the electrical field supplied to the electrodes in the coalescer. However, the phenomenon is completed once there is the electrostatic force which explains induction.¹⁵ Courtesy of the electrostatic force, the polarised molecules are able to induce charges on the adjacent molecules. Again, the role of the electric field is brought to the fore. To ensure that the molecules are able to induce charge, there needs to be a high electric field. The same further explains the need for a high voltage to create the desired electric field.

The principle of the electrostatic force, as explained by the Coulomb’s Law, is such that the molecules will have disparities in the charges.¹⁶ Consequently, there are two main charges which arise due to the polarisation. There are negative and positive charges. Depending on the distances between the molecules an electrostatic force exists attracting the species with opposite charges drawing them together. The coalescence is therefore realised as a result of the electrostatic forces’ bringing together of the various molecules intended for elimination.

Dipolar Attraction

An electrostatic coalescer relies on several principles of physics to fulfil its objectives and the dipolar attraction is a key aspect of the process.¹⁷ As mentioned, molecules of water are often polarised, and they induce polarity to the molecules which are adjacent. It is therefore important to examine dipolar attraction and how the phenomenon fits into the process of electrostatic coalescence. Dipolar attraction is, therefore, best understood by examining the strongest known intermolecular bonding, which is the hydrogen bonding.¹⁸

When hydrogen bonds with compounds like Fluorine to yield Hydrogen Fluoride (HF), the resultant molecule has a net charge of zero. However, on either side of the molecule, there is a partial negative and positive charge. The partial charges attract the adjacent molecules with an opposite partial charge. The underlying principle of attraction is that two species are brought together. The same explains the coalescence or the coming together of the water molecules.¹⁹

The high voltage supplied to the electrodes in the machine serves to polarise the water molecules.²⁰ The principle of dipolar attraction necessitates the attraction of the partially charged water molecules. It is important to note that this separation process is best suited for use in the elimination of molecules that are ‘polar’ in nature. Water is a common example of a polar molecule. The actual coalescence relies on molecules to be drawn together. In the separation of water from crude oil, the coalescing of the water molecules makes it easier for the formation of a suspension which can then be separated.

Configuration of Electrostatic Coalescers

Having examined the operations of an electrostatic coalescer, it is relevant that discussions on its configuration be outlined. The most conspicuous part of the machine is the cylindrical tank.²¹ From figure 1, it is apparent that there are inlets outlets found on the machine. The fluid inlet is required to be at the top of the cylindrical tank with the outlet at the bottom.²²

The electrodes used to polarise the fluid are often cylindrical for the single objective of increasing the surface area of the fluid exposed to electric current.²³ The electrodes are required to be vertical with respect to the entire tank. They are placed in series to ensure that the fluids get maximum exposure to the electric field to ensure that as many molecules as possible are polarised. The positioning of the electrodes is done in such a way that the fluids spend a total of 10 seconds between the inlet and the outlet.

It has already been mentioned that the electrodes are supplied with high voltage. However, there are certain cases where the initial power supplied is insufficient for the whole process. The same explains the usage of a transformer among a number of transformers. A typical coalescer requires an average of 20,000 volts. To achieve objective emulsification, the machine requires a series of insulators and electrode hangers.²⁴ Also, the machine ought to be fit with sufficient entrance bushings; the additional material is necessary to contain the high voltage required for the process.

The high electric power required for the process poses several challenges to the extent of damage to the coalescer itself. For instance, the hg quantity of water that will have coalesced can transfer the current onto the tank itself, bringing the danger of short-circuiting.²⁵ The best way of avoiding such a situation is to ensure that the energised electrodes do not get in contact with the grounded ones.²⁶ The practice is common in coalescer where the electrodes are bare metals without any form of insulation. In other cases, it is advisable to eliminate the emulsion, which is typically water. However, this practice is slowly being phased out owing to the time factors.

The spacing of the electrodes is also an important aspect of an electrostatic coalescer. The ideal spacing of the electrodes and the ground ought to be approximately 19 inches.²⁷ When the spacing is made in such magnitudes, the electrostatic field is kept at an optimum level. The same ensures sufficient coalescing of the water molecules.

Available Technology

The dehydration of crude oil emulsions is an important process in the petroleum industry. Evidence of the same can be illustrated by the many patents that exist with regards to electrostatic coalescence. Eow and Ghadiri carried out a study to determine the enhancement of water droplets during this process.²⁸ Their study revealed 7 different technologies touching on electrical mechanisms of crude oil dehydration. The figure below outlines several patents associated with electrostatic coalescence in terms of technique and design of the apparatus.

Figure 2 is a summary of the various patents that exist in terms of technological advancement. The numbers in parentheses represent a particular patent with respect to the electrostatic coalescer and the process itself. The study by Eow and Ghadiri highlighted 42 patents, giving an impression that the technology around this process is as diverse as the advancements recorded.³⁰

Notwithstanding the various techniques illustrated in the diagram, the technology associated with electrostatic coalescence revolves around a general principle. The coalescing vessel must have a tank fitted with sufficient electrodes. The difference in these electrodes can be found in their design. For instance, the study by Eow and Ghadiri point out to the possibility of grids.³¹ Technological advancement of the process itself relies on the polarization effect due to the electrostatic field created within the vessel. Interestingly, there are studies that suggest that the process can be realised depending on certain electrostatic fields.³²

Technological advancements are also made to respond to various challenges touching on the effectiveness of electrostatic coalescence. Ole-Moren carried out a study to examine the electrostatic field theory.³³ Their findings were that electrostatic coalescence is impeded when electrodes do not have sufficient insulation. Thus, dehydration of crude oil depends on coalescers where there is an advancement to ensure electrode insulation is appropriate.

The patents illustrated in Figure 2 are representations of technology intended to improve the separation of the species in an emulsion. Centrifugal force and its association to electrostatic coalescence are often considered when technological advancements are made to the coalescence process and the apparatus. Separately, Ole-Moren,³⁴ Green and Perry³⁵ and Eow and Ghadiri³⁶ separately suggest that centrifugal force helps to avoid the need to reduce the viscosity of the oil. Coupled with electrostatic coalescence, centrifugal forces enhance the actual detachment of water molecules from the crude oil, which is often highly viscous.

Heating and Electrical Treatment

Electrostatic coalescence is a separation process that incorporates certain thermodynamic principles. When it comes to the separation of water from crude oil, the element of heat becomes crucial to ensuring the coalescence is effective. In a study to determine the strengths and shortcomings of electrostatic coalescence, Less & Vialgines point out to the importance of heat to the process.³⁷ The same is illustrated in Figure 2 as one of the patented technologies within electrostatic separation methods.

The analysis of heating and electrical treatment reveals two more categories. Eow & Ghadiri, while reviewing available technology in the field, suggest that mechanical separation and gas involvement as the subcategories of this technology.³⁸ The heating aspect of technology relies on the resistivity of the electrodes. In most cases, the electrodes are created such that they form a coil. Thus, when the electrode is in contact with the emulsion, the 200º temperatures emitted act over a high surface area. The heat is able to convert water in the emulsion into steam. Such a procedure is able to increase the efficiency of separation.

One of the challenges of separating water from crude oil is the high viscosity of the fluid. Less & Vilagines, in their study, argue that temperature helps to reduce viscosity.³⁹ A similar assertion is made by Ole-Moren who argues that temperature increases the kinetic energy of fluids⁴⁰. High kinetic energy contributes to reduced viscosity. Thus, whenever heat is an essential aspect of separation since, through a reduced viscosity, the water droplets are easily separated from a crude oil-water emulsion.

Technologically, the electrical part of the treatment is used to attain the high temperatures required. Less &Vilages argue that the vaporization of the water molecules is a mechanical separation.⁴¹ The relevance of this particular technology has seen the creation of a device which is termed as a “treater”. From figure 2 it is apparent that this technology has been patented. Eow and Ghadiri refer to an electrostatic emulsion treating method.⁴² The specific apparatus used for the process was patented (US Patent: 4191977) basing on the heating and electrical heating mechanism.

Chemical and Electrical Treatment

The separation of water from crude oil relies on the understanding that water is also a chemical. Figure 2 illustrates three categories of this treatment method. Specifically, the categories include secondary electrical treatment, phase inversion and gravitational settling. Masliyah and Bhattachariee point out that there are advanced theories in favour of the separation of the detachment of molecules from petroleum emulsions.⁴³ However, the two argue that coalescence is the most preferred principle. The study by Eow and Ghadiri finds that phase inversion does not yield a chemical reaction of the components of the emulsion. However, the said inversion facilitates the physical coalescence of molecules in the emulsion. Ole- Moren, while examining the

Filtration

Electrical separation, as applied in thermodynamics, has been known to make use of filtration alongside electrical treatment. As illustrated in Figure 2, filtration is an essential aspect of separating different molecules in a given emulsion. Eow and Ghadiri, explain that the actual filtration relies on the principle of miscibility.⁴⁴The actual process has been found to be successful in cases where the medium required for filtration is miscible with the fluid that is in a dispersed phase. The mechanism was aptly demonstrated in a study by Cotrell (as cited in Eow and Ghadiri).⁴⁵ The filtration, as applied in the study, was localized at the electrodes.

Pressure and Electrical Treatment

The dehydration of crude oil is an industrial process. As pointed out by Eow and Ghadiri, petrochemical processes always incorporate the element of pressure.⁴⁶ For that matter, there are several studies which point out to the usefulness of pressure and electrical treatment with regard to dehydration of crude oil. In one such study, Eddy (as cited in Less & Vilagines)⁴⁷ illustrates the method and equipment required for the separation of water from petroleum. In their study, they make reference to a particular dehydrating apparatus whose patent is US: 2 083 801. The scholar also carried out a similar study in which the treatment of oil, in a vacuum, is scrutinized. In both cases, pressure and electrical treatment find relevance.

As mentioned earlier, the pressure is an essential requirement in many industrial chemical processes. According to Eow and Ghadiri, there is a higher coalescence of water droplets, in an emulsion, in places where the pressure is lower than that of the atmosphere.⁴⁸ The droplets which make up the emulsion contained some entrapped gas. Thus, at low pressure, the gas will expand at a faster rate allowing for their demulsification. The electric effect allows for an even faster coalescence rate owing to the increased kinetic energy of the water molecules.

Research is still ongoing to determine the specifics of how the pressure affects the demulsification. However, most studies indicate that low pressure in conjunction with electrical heating helps to increase the rate of coalescence. Less and Vilagines point out that low pressure and electrical heat support a higher expansion of the oil molecules relative to the water molecules⁴⁹. The variance in the expansion of the molecules brings about a corresponding disparity in their specific gravity. In effect, the separation between the molecules depends on the gravitational disparity.

Mixing and Electrical Treatment

The separation of water molecules from crude oil is possible through a technology referred to as mixing and electrical treatment. As illustrated in, there are 4 categories in which this type of technology is applied in electrostatic coalescence. In a study carried out by Pestridge and Johnson (as cited in Eou and Ghadiri), electric field strength modulation is one such category of this technology.⁵⁰ Specifically, the same was applied in an apparatus used in the study. The electrostatic mixer, used in the study by Pestridge and Johnson (as cited in Eou and Ghadiri) and separator is a device patented owing to the said modulation (US Patent 4 606 801). Other categories of this technology include agglomeration, vibration and gas-phase & pulse DC fields.

Electrostatic coalescers are prone to short-circuiting. However, mixing and electrical treatment is seen as a means through which the same is avoided. According to Less and Vilagines, short-circuiting occurs when chains of water droplets form around the electrode.⁵¹ The mixing prevents the formation of the chains. It also helps to disintegrate any such chains which might exist prior to the separation process. The technology of mixing and electrical treatment has been used in various separation techniques. An example is evident in the study by Cotrell (as cited in Eow and Ghadiri) who were studying the rate of separation courtesy of electrostatic coalescence. Their study found that the electrostatic field causes a stir at the surface of the emulsion. It is the stir that is referred to as ‘mixing’, and the same helps in inhibiting of the formation of water droplets around the electrodes.

Electrical Treatment

As mentioned in earlier sections of this review, kinetic energy is a required aspect of separation of water molecules courtesy of electrostatic coalescence. Hussein, Mohamed and Mohamed, in their book, dedicate a chapter on the purification of crude oil.⁵² The three scholars point out that electrical treatment is essential in ensuring the electrostatic field is sufficient for the dehydration of crude oil. In a separate study, Chimenti (as cited in Less and Vilagines) examines the separation of molecules with phase dispersion.⁵³ From their findings, it is apparent that the positioning of the electrodes greatly affects the electrostatic field generated.

Upon scrutiny of, it is apparent that electrical treatment is realised through the parallel positioning of the electrodes and the diverging and converging stream. Eow and Ghadiri observed that the emulsion flows uniformly through the electrodes.⁵⁴ At the same time, their study finds that the diverging and converging streams.

Examples of Electrostatic Coalescers based on the Available Technology

The technologies described in the preceding sections find applicability in many conventional coalescers. Green and Perry, courtesy of their Engineers Handbook, suggest that various brands of coalescer exist owing to the various technologies available.⁵⁵ Some of the common types of electrostatic coalescers include the VIEC and the compact electrostatic coalescer (CEC). The technological disparities are geared at bringing about efficiency in terms of the coalescence. The following are examples of coalescers.

Compact Electrostatic Coalescer

The Compact Electrostatic Coalescer is characterised by flow-through chambers that are circular in geometrical structure.⁵⁶ The same is in response to the suggestions by Hussein, Mohamed and Mohamed, who argue that such a structure enhances centrifugal forces.⁵⁷The electrodes are fitted into the circular chambers allowing for maximum exposure to the crude oil. The circular geometrical structure enhances the dehydration owing to the surface area exposed.

The CEC comprises a separator for the elimination of the emulsion in the crude. The separator has a downward trajectory, relying on the force of gravity.⁵⁸ Contrary to other coalescers, the CEC does not have a lot of internal components. The same improves the performance in terms of coalescence owing to the exposure of the crude to the electrostatic field.⁵⁹ A coalescer with little internal components can handle large volumes of crude. Consequently, a company does not require many CECs, thus saving on cost.

The CEC is currently in use in companies like Statoil. However, the patent to the design is held by Aker Solution.⁶⁰ The 2 separator units in the CEC improve the coalescence of the water droplets courtesy of the mixing and electrical treatment. The two compartments can easily be retrofitted depending on the need. The CEC is essentially easy to assemble, making it applicable in companies that do not have specialists in the field.

Vessel Internal Electrostatic Coalescer

Crude oil can be extracted offshore. Eow and Ghadiri argue that coalescers ought to respond to the versatility of crude oil extraction.⁶¹ Similarly other studies suggest that internal components of a coalescer ought to respond to the water content in a given emulsion.⁶² As mentioned earlier, the mixing and electrostatic treatment helps to minimise such challenges like short circuiting. The Vessel Internal Electrostatic Coalescer applies the said technology to make it suitable for the dehydration of crude oil extracted offshore. The high water content level in the emulsion requires that chain formation of water molecules, around the electrodes, be kept at an absolute minimum.⁶³ The VIEC achieves the same courtesy of the mixing and electrostatic treatment.

The VIEC is structured to generate a high electrostatic field for the maximum separation of water droplets in the crude oil. The coalescer is made up of a metallic grid. The grid is horizontally placed in a pressurised chamber. Within the vessel there is a transformer that will be used to amplify the primary voltage. As mentioned earlier coalescers with such a design have a high risk of short circuiting owing to the increasing electrostatic field.

The VIEC also overcomes short circuiting by means of a frequency converter. The said converter increases the operating frequency of the transformers.⁶⁴ Also, the coalescer is well insulated since the conditions in the first stage of the separator are quite harsh. Thus, the VIEC has a structural design that enhances tolerance to the harsh conditions. In terms of the electronics involved, the VIEC makes use of AC-DC technology. Currently the VIEC is in use in major engineering firms like Wartsila and ABB.

Most Effective

Efficient electrostatic coalescers are responsible for high quality oil. Technological advancements of a coalescer must ensure the said efficiency. Thus, such advancement should focus on both the apparatus and process as suggested by Eow and Ghadiri.⁶⁵ It is therefore safe to say that the CEC and the VIEC appear to be the two most preferred coalescers owing to their technologies. In both cases the electrostatic field and short circuiting is well catered for in the design. However when the two are compared even further, the VIEC carries the day.

From the discussions, the VIEC is evidently versatile. The machine can be used both offshore and onshore.⁶⁶Also, the machine has illustrated its potential to be efficient in terms of the coalescence of the unwanted material. The ability for the VIEC to overcome the hurdles of short circuiting also contributes to the reasons why the machine would be a preference to others. Its applicability by companies like Wartsilla indicates that the VIEC is the most effective when it comes to crude oil dehydration.

Operating Considerations

Industrial chemical processes require certain factors to be considered to ensure the overall success of the process. In the context of this research paper, dehydration of crude oil is indeed quite relevant to ensure the quality of oil that is passed on to the market. Thus, a case has been made for the applicability of electrostatic coalescence as a preferred method for the said dehydration. However, just like any other chemical process, electrostatic coalescence has its limitations.⁶⁷ A look at the said limitations will reveal the operational considerations that ought to be factored in the process.

Crude oil is a fluid with high viscosity. Tatterson found that viscous fluids tend to clog the components of a coalescer.⁶⁸ Consequently, the coalescence efficiency is reduced. Separate studies by Wojciech, Marek, Marek, Sipowicz and Hans suggest that intense clogging can result in stoppage of the entire process.⁶⁹ Among the considerations, therefore, should be the need to overcome the said limitation.

During the process of crude oil extraction, there is often a high chance of solid particles getting embedded in the fluid.⁷⁰ The solids will later pose a threat to the coalescer by blocking some of the internal component. It is important to appreciate the fact that most coalescer mediums have fine pore structures. The solid particles in the crude oil affect the dehydration process. They do this by blocking the said pores. As a result, the coalescence efficiency is greatly reduced.

One way of overcoming this limitation is courtesy of a pre-filter element.⁷¹ Technicians can ensure that the coalescer is fitted with the pre-filter. Preferably the element should be fitted at the inlet to sieve out any solid particles present in the crude oil. However, there are certain manufacturers who ensure that their coalescer is fitted with a pre-filter at the time of purchase.

Other operating considerations include the generation of an electric field.⁷² To achieve optimum dissociation of the water molecules from the crude oil, the operating frequency must be high for the production of a high electrostatic field. The high electrostatic field, in turn, enhances the polarisation of the water molecules in the emulsion resulting in higher coalescence. However, the high electrostatic field poses a risk of short circuiting. It is therefore advisable for technicians to opt of coalescers that rely on AC power technology. Such machines are less likely to experience short circuiting.⁷³

Affecting Factors

Electric Field

The electrostatic field, supplied to the crude oil – water mixture is generated by a suitable electric current. Stewart, Maurice, Arnold and Ken, argue that the efficiency of separation of the emulsion relies on the electrostatic field.⁷⁴ Most coalescers rely on AC which has been mentioned in previous sections of the study. However, Direct Current (DC) also plays a major role in the electrostatic coalescence. When it comes to the dehydration of crude oil wit presumably low water content, DC is the preferred source of electrostatic field. Also, in cases where there is a high aqueous content in the emulsion, a pulsed DC is applied.

Mitgard finds that coalescence of the molecules has a direct association with the strength of the electrostatic field.⁷⁵ The same is brought about by the electrostatic force that exists between any 2 conducting drops. When there is an increase in separation between the said drops the electrostatic induction expected is decreased. The converse is also true and both have an effect on the rate of coalescence of the molecules intended for separation.

Nature of Electrode

The design of an electrode and the coating has an effect on the coalescence of the molecules.⁷⁶ Coalescers that have thinner electrodes are often associated with a higher rate of coalescence. There exists an interfacial relaxation between the continuous phase and the insulation. The charging up of the drops is largely affected by the said relaxation.⁷⁷However, the nature and size of the coating material used regulates the frequency in which the drops are charged up. Perspex and Teflon are but examples of coatings that can be used on the metal electrodes.

In the event that the electrode is thick, due to the coating, short circuiting is minimised.⁷⁸ However, if the electrode is itself thick, then the electrostatic field tends to decrease with accumulation of water. Thus, it is important to ensure that the electrodes used in the coalescer maintain an electrostatic field sufficient for the formation of enough suspension.

Applied Frequency

In the event that the electrostatic field, within the coalescer, is brought about by a pulsed DC, the electrical relaxation is affected by the frequency applied.⁷⁹ When the applied frequency is high, the implication is that the relaxation time is extended. Thus, there is a high coalescence rate. The same is also related with the insulation on the electrode since the higher the frequency, the higher the rate at which the coating peels off from the electrode.⁸⁰

In general, the efficiency of a coalescer is realised when the frequency is low.⁸¹ Typically, most machines will perform at frequencies of 10Hz. However, the coalescence will continue to perform well up to a limit of 200Hz. The implication is that, whereas an increase in frequency can result in a decline of the coalescence abilities the frequencies can operate up to a certain limit.

Future Technology

The need to ensure crude oil is properly dehydrated has driven researchers and engineers to push to the limits the possibilities of improving on the electrostatic coalescer. Going by the factors that promote coalescence the machines of the future will most likely adjust on aspects like the nature of the electrode or the electric field distribution. One such adjustment is seen in the electrostatic coalescer owned by Wartsila.⁸² As mentioned earlier, the company has a Vessel Internal Electrostatic Coalescer.

The modifications made on the machine have improved its performance in offshore crude oil dehydrations. In the earlier sections of this paper, it was established that separators are a crucial component of an electrostatic coalesce. Future technology seeks to advance on the same by reducing the number of separators but maintaining the coalescence effect.⁸³ Since the objective of any coalescence is to rid petroleum products of any impurities, the separators must be modified for optimum performance.

Advances in material science have made it possible for the synthesis of new materials. Since the coalescence is seen as a separation mechanism, researchers are considering the use of microporous material in the coalescer.⁸⁴ The material can be used to sieve unwanted particles of water to a point that they are negligible. Thus, the extremely high voltage will not be necessary owing to the scarcity of the water molecules. Nanotechnology is also another avenue that can be used to enhance the performance of the electrodes.⁸⁵ Nanoelectrodes have the possibility of increasing the surface area which the liquid is exposed.

The futuristic models of the electrostatic coalescer do not alter the working principle. Coalescence of the unwanted material remains the objective of the machine. Therefore, any modifications made on the original version of the coalescer are done with the intention of making it efficient rather than alter the principle of performance.⁸⁶ Future technologies on the machine’s improvement are keen to address certain fundamental aspects like the capacity of fluid that will be in the chamber. The same will determine the number of inlets and outlets and the volume of the tank.

Applications

Electrostatic coalescence has a variety of applications in terms of industrial chemical processes. The production of fluids, devoid of all sorts of unwanted emulsions, is essential to ensuring their quality. Qui, Gong and Liu carried out a study to find out new methods of demulsification.⁸⁷One of their findings was that the technology of electrostatic coalescence is finding acceptability in eco-friendly industries processes. The applicability of the variety of coalescers relies on their designs, based on the existing technologies.⁸⁸ Some of the components of emulsions include water and amines. Depending on the nature of the dehydration process, electrostatic coalescers find applications in varied fields.

The electro-pulsed inductive coalescer (EPIC) is one such instance where the separation through coalescence is involved. The EPIC was first illustrated by Eow and Ghadiri while making a review of the applicability of electrostatic coalescers.⁸⁹ The researchers found that the said coalescer derives its applicability from the electrostatic coalescence principles, most of which have been discussed herein. Among the technologies used in the coalescer is the electrical treatment. The central electrode relies on an electrostatic field produced by a direct current. The operation of this particular coalescer is illustrated in figure 3.

As illustrated, the fluid is introduced to the system by means of an inlet that is situated in a tangential manner. The EPIC was illustrated in a review carried out by Eow and Ghadiri, which sought to examine existing technology.⁹¹ From their review, it was apparent that the EPIC is structured in a way that the fluid spirals its way upward in the vessel. The upward movement was essential to ensure that the emulsion is exposed to continuous electric pulses. When that happens, droplet coalescence is enhanced. The coalescer is used in a variety of desalting and dehydration processes in major petroleum companies.

As mentioned earlier, the VIEC is versatile and can be used both onshore and off-shore. The coalescer is used in such oil companies as the ABB Corporation.⁹² By virtue of having several offshore oil rigs, the company attests to water as being the most common impurity in the crude oil. Thus, the need to eliminate all traces of water calls for the utilisation of the machine. The quality of oil released from the machine is improved by making adjustments to the separator. The VIEC at ABB Corporation addresses the said traditional inefficiencies of the separator making it a leader in the industry.

Industrial chemical processes require that products be as pure as possible. The electrostatic coalescer satisfies this requirement in the oil sector.⁹³ Fossil fuels bur and release toxic fumes to the environment. However, courtesy of the electrostatic coalescer, trace elements that might become toxic are removed. The coalescence process is important in the mining of oil. It enhances the quality of the oil generated. The process is also a cost effective mechanism in the dehydration of crude oil. The same is realised by eliminating mechanical processes of impurity removal. The water eliminated from the petroleum products

Recommendations

The discussions in this paper have revealed the importance of electrostatic coalescence with respect to removal of impurities from crude oil. However, the performance of the machine remains a key obstacle to realising 100% results. Some of the key issues to be addressed include the electrostatic field. An effective coalescence of the water molecules requires sufficient voltage supplied to the electrodes.⁹⁴ However, high power production can sometime increase the cost of production by making the coalescence process costly. In that regard, this paper recommends the usage of solar panels as sources of the power.

Also, there needs to be sufficient insulation within the machine to prevent endless short circuiting.⁹⁵ As such, research is necessary to come up with effective material that can be used in the machine. This paper recommends a comprehensive research on suitable material for use on the electrodes. The same is informed by the effects of too much insulation. Heavily insulated electrodes tend to reduce the surface area in which the fluids are exposed. Thus the reduced coalescence efficiency exhibited in such cases.

Further recommendation is made to oil companies that are offshore to make use of electrostatic coalescence. It is evident that oil from offshore rigs will have high water content as opposed to the oil extracted inland.⁹⁶ The only way such oil products can find competitiveness in the international market, is if their purity levels meet the required quality standards. The VIEC is an emergent electrostatic coalescer which can be used by offshore oilrigs to eliminate water from the crude oil extracted.

The advantages of the VIEC outweigh the benefits of the traditional coalescer. The major improvement done on this machine is evident in its ability to overcome the issue of short circuiting. Consequently, this research recommends that companies in the crude oil business make use of the VIEC given its effectiveness in terms of coalescence and versatility. The machine’s capability to be used both offshore and onshore reduces the cost that a company would incur in the event it has the two drilling sites.

Conclusion

Electrostatic coalescence is a separation mechanism that relies on dipole coalescence of molecules. To achieve the actual separation, electrophoresis results in chain formation of the unwanted material in chain droplets.⁹⁷ One of the most significant issue is the nature of the electrodes and the design. Effective coalescence results from electrodes that are relatively thin. It is important to avert short circuiting. The VIEC is an example of a coalescer that addresses the demands of crude oil dehydration economically

Effective coalescers are important in crude oil dehydration processes for the production of high quality petroleum products.⁹⁸ To achieve the same, it is important that research be carried out to ensure that the coalescence mechanism is improved upon. Thus, it will become crucial to see new designs of electrostatic coalescers that address efficiency by making adjustments to the internal components of the machine. The improvement of electrostatic coalescer is considered as advancement in industrial chemical processes particularly in natural science.

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Footnotes

1. Khalid, Al-Qahtani and Ali, Elkamel. Planning and Integration of Refinery and Petrochemical Operations (New Jersey: Wiley-VHC, 2010), 54.
2. Al-Qahtani and Elkamel, 55.
3. Al-Qahtani and Elkamel, 35.
4. Oji, Akuma and Charles, Opara. “Electrocoalescence of Field Crude Oil using High Voltage Direct Current.” International Journal of Engineering Science and Technology 4, no. 5 (2012): 1850.
5. Akuma and Opara, 1851.
6. Denn Morton. Chemical Engineering: An Introduction (Cambridge: Cambridge University Press, 2011), 36
7. Denn, 43.
8. Denn, 50.
9. John, Eow and Mojtaba, Ghadiri. “Electrostatic Enhancement of Calescence of Water Droplets in Oil: A Review of the Technology.” Chemical Engineering Journal 85 (2002): 358.
10. Eow and Ghadiri: 359.
11. Eow and Ghadiri: 361.
12. John, Eow, Mojtaba, Ghadiri, Adel, Sharif and Williams, Trevor. “Electrostatic Enhancement of Coalescence of Water Droplets in Oil: A Review of the Current Understanding.” Chemical Engineering Journal 84 (2001): 174.
13. Eow, Ghadiri, Sharif and Trevor: 174.
14. Midtgard Ole-Moren. “Electrostatic Field Theory and Circuit Analysis in the design of Coalescers with Pulsed dc Voltage.” Chemical Engineering Journal, 151, no. 1-3 (2009): 169.
15. Ole-Moren: 170.
16. Jacob Masliyah and Subir Bhattachariee. Electrokinetic and Colloid Transport Phenomena (New Jersey: Wiley-Interscience, 2006), 33.
17. Don Green and Robert Perry Perry’s Chemical Engineers’ Handbook. (New York; McGraw-Hill, 2007), 60.
18. Green and Perry, 60.
19. Green and Perry, 61.
20. Martin Henschke, Lars Schlieper and Andreas Pfennig. “Determination of a Coalescence Parameter from Batch-Settling Experiments.” Chemical Engineering Journal 85, no. 2-3, (2002): 370.
21. Abdel-Aal Hussein, Aqquour Mohamed and Fahim Mohamed. Petroleum and Gas Field Processing (Florida: CRC Press, 2003), 71.
22. Hussein, Mohamed and Mohamed, 78.
23. Hussein, Mohamed and Mohamed, 81.
24. Ajaja Katja. “Oil and Water Separation at its Best.” Twentyfour7, 2012. Para. 3. Web.
25. Hussein, Mohamed and Mohamed, 86.
26. Hussein, Mohamed and Mohamed, 87.
27. Green and Perry, 60.
28. John Eow and Mojtaba Ghadiri “Electrostatic Enhancement of Calescence of Water Droplets in Oil: A Review of the Technology”: 358.
29. Eow & Ghadiri, 359.
30. Eow & Ghadiri, 359.
31. Eow & Ghadiri, 359.
32. Green & Perry, 68.
33. Ole-Moren, 169.
34. Ole-Moren, 169.
35. Green and Perry, 68.
36. Eow and Ghadiri, 359.
37. Less, Simone and Vilagine, Regis. “The Electrocoalescers’ Technology; Advances, Strengths and Limitations for Crude Oil Separation.” Journal of Petroleum Science and Engineering 81 (2012): 57.
38. Eow and Ghadiri 359.
39. Less and Vilagines, 57.
40. Ole-Moren, 169.
41. Less and Vilagines, 57.
42. Eow & Ghadiri, 359.
43. Masliyah and Bhattachariee, 45.
44. Eow and Ghadiri, 359.
45. Less and Vilagines, 58.
46. Eow.
47. Less and Vilagnes, 58.
48. Eow and Ghadiri, 360.
49. Less and Vilagines, 58.
50. Eow and Ghadiri, 360.
51. Less and Vilagines, 60.
52. Hussein, Mohamed and Mohamed, 186.
53. Less and Vilagines, 60.
54. Eow and Ghadiri, 361.
55. Don, Green and Perry Robert. Perry’s Chemical Engineers’ Handbook (New York; McGraw-Hill, 2007), 88.
56. Johnsen, Einer. Erferinger Med Electrostatic Coalescer (Statoil 2007), 3.
57. Hussein, Mohamed and Mohamed, 86.
58. Einer, 3.
59. “Compact Electrostatic Coalescer” para. 4.
60. Johnsen, 5.
61. Eow and Ghadiri, 360.
62. Akuma and Opara, 1851.
63. Piasecki Wojciech, Florkowski Marek, Fulczyk Marek, Jakub Sipowicz and Kristian Hans “Novel Oil-Water Separation Technology.” ABB Review (n.d.): 67.
64. Wojciech, Marek, Marek, Sipowicz and Hans: 72.
65. Eow and Ghadiri, 359.
66. Wojciech, Marek, Marek, Sipowicz and Hans: 73.
67. Benjamin Tatterson. Process Scaleup and Design (North Carolina: Gary Tatterson, 2002), 87.
68. Tatterson, 93.
69. Wojciech, Marek, Marek, Sipowicz and Hans: 72.
70. Tatterson, 98.
71. Akuma and Opara. “Electrocoalescence of Field Crude Oil using High Voltage Direct Current.”: 1851.
72. Tatterson, 108.
73. Tatterson, 112.
74. Stewart, Maurice and Arnold, Ken. Surface Production operations: Design of Oil Handling Systems and Facilities. (Texas: Gulf Professional Publishing, 2007), 45.
75. Midtgard. “Electrostatic Field Theory and Circuit Analysis in the design of Coalescers with Pulsed dc Voltage”: 173.
76. Akuma and Opara. “Electrocoalescence of Field Crude Oil using High Voltage Direct Current.”: 1852.
77. Mitgard, 173.
78. Maurice and Ken, 79.
79. ACS Separations & Mass Transfer Products. Liquid-Liquid Coalescer Design Manual (Texas: ACS Industries, n.d.), 7.
80. ACS Separations & Mass Transfer Products, 8.
81. ACS Separations & Mass Transfer Products, 7.
82. “Wartsila Vessel Internal Electrostatic Coalescer”, para 3.
83. Masliyah and Bhattachariee. Electrokinetic and Colloid Transport Phenomena, 73.
84. James Speight. The Refinery of the Future. (New York: William Andrew, 2010), 61.
85. Jonathan Cox and Bo Zhang “Nanoelectrodes: Recent Advances and New Directions.” Annual Review of Analytical Chemistry 5, (2012): 253-272.
86. Speight, 67.
87. Qui Guohui, Gong Xingguo and Liu Yikun. “”New Research Progress of the Demuslification of Produced Liquid by Liquid Polymer Flooding,” Journal of Chemical and Pharmaceutical Research 6 no 1 (2014): 634.
88. Morton. Chemical Engineering: An Introduction, 126.
89. Eow and Ghadiri, 366.
90. Eow and Ghadiri, 363.
91. Eow and Ghadiri, 363.
92. Kristian. “Novel Oil-Water Separation Technology”: 69.
93. Kristian. “Novel Oil-Water Separation Technology”: 10.
94. Joseph Hilyard The Oil & Gas Industry: A Nontechnical Guide. (Oklahoma: Pennwell Corp., 2012), 98.
95. John Eow and Mojtaba Ghadiri “Electrostatic Enhancement of Calescence of Water Droplets in Oil: A Review of the Technology”: 361.
96. Vasily Simanzhenkov and Raphael Idem. Crude Oil Chemistry (Florida: CRC Press, 2003), 168.
97. Simanzhenkov and Idem, 170.
98. Eow, Ghadiri, Sharif and Williams “Electrostatic Enhancement of Coalescence of Water Droplets in Oil: A Review of the Current Understanding”: 170.