Abstract:
A method for coalescing a disperse phase component in a primarily gas process fluid includes passing the process fluid through a structure. The structure includes an outer wall with an electrically insulating material formed on an entire inner surface of the outer wall to define an entirely insulated flow path for receiving the process fluid and the flow path is free of any portion of the structure. A plurality of planar, spaced-apart electrode plates is positioned within the entirely insulated flow path and positioned substantially parallel to one another and substantially the entirety of each of the plurality of electrode plates is coated with an insulative material. At least one insulating member disposed in a space between and spaced apart from two adjacent electrode plates. A power source is applied to the electrode plates to generate an electrical field to coalesce droplets of the disperse phase component.

Description:
BACKGROUND 
       [0001]    The disclosed subject matter relates generally to separating fluids and, more particularly, to separating primarily gas process fluids in an electrostatic coalescer. 
         [0002]    The separation of water from a hydrocarbon liquid is an important process in the oil production industry. In an oil dominated regime, small water droplets can occur in the continuous oil phase due to shearing in upstream piping, for example. The droplet size is an important contributing factor to the speed of the separation. Small droplets of water in oil separate slowly from the oil compared to larger droplets due to the immiscibility of the liquids and the differences in specific mass. 
         [0003]    One conventional approach for oil/water separation makes use of gravity and requires large residence times inside separators. Large residence times are needed for an acceptable separation performance, and therefore this approach is not suitable for an in-line application with high flow rates. Other techniques that use chemicals to break the emulsions require later removal of the chemicals, thereby increasing cost. Still other techniques that employ heating are less effective at breaking emulsions. 
         [0004]    The separation of liquids from fluid streams that are primarily gas is also an important process in industry. In many cases, gases with a high economical value are obtained containing very fine droplets of liquids. Examples may be natural gas or many other gases used in the chemical industry, such as chlorine or sulfur dioxide. Also, in process industry, vapors may partly condense, which may also result in gas containing fine liquid droplets, especially in high gas speed applications (i.e., the high speeds provide significant force to draw the droplets along). Further, any obstacle in the flow path may generate high and low pressure areas, resulting in more condensation at the obstacle than compared to low gas speed application, where the pressure differences are much lower. 
         [0005]    As these droplets can corrode piping and are harmful for pumps and other processing equipment, they should be removed before packing or transporting the commercial gas or using the gas in a process industry. Further, consumers want their products as pure as possible, and extraneous liquids lower the quality of these gases. In the petrochemical industry, especially off shore, where natural gas is obtained together with salt water and oil, it is beneficial to remove the water and/or other liquids as near to the well as possible. A significant effort is spent drying the natural gas to remove water vapor to concentrations far below saturation with water absorbers. However, such efforts may be inefficient if the gas to be dried contains liquid water in addition to vapors. 
         [0006]    Conventional techniques for removing liquids from gases typically aim at improving the traditional separation of liquids from gases by using gravitation-like forces. One very old technique is based on the observation that a piece of cloth hanging in a fog will collect water from the fog, thus decreasing the fog intensity and providing water. The cloth acts as a condensation center for the droplets and gravitation will, in the case of water, cause excess water to flow down. This technique is the basis for the separation of liquids from gases using a mesh wire. 
         [0007]    Another technology involves increasing the gravitational forces to make the suspension of liquid droplets more instable in the gas. Gravitational forces can be increased by spinning the medium, which results in a centripetal force of many times normal gravitation. In this manner, the separation proceeds at a rate many times faster than under gravitation alone, resulting in a much smaller apparatus. 
         [0008]    Still, for large scale in-line operation both mesh wire technologies and accelerators have their disadvantages. A mesh can become clogged and requires the gas molecules to follow complicated paths through the mesh, costing mechanical energy. Increasing gravitational forces by spinning also requires mechanical energy that is generally drawn from the gas to be separated. This consumed mechanical energy results in a pressure drop, which increases the required number or size of the pumps. Further, both techniques require sensitive equipment that is vulnerable to erosion. 
         [0009]    This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
       BRIEF SUMMARY 
       [0010]    The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an exhaustive overview of the disclosed subject matter. It is not intended to identify key or critical elements of the disclosed subject matter or to delineate the scope of the disclosed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
         [0011]    One illustrative method for coalescing a disperse phase component in a primarily gas process fluid includes passing the primarily gas process fluid through a structure. The structure comprises an outer wall with an electrically insulating material formed on an entire inner surface of the outer wall so as to define an entirely insulated flow path for receiving the process fluid and the flow path is free of any portion of the structure. A plurality of planar, spaced-apart electrode plates positioned within the entirely insulated flow path and positioned substantially parallel to one another is provided. A space is defined between two adjacent planar, spaced-apart electrode plates and substantially the entirety of each of the plurality of planar, spaced-apart electrode plates is coated with an insulative material. At least one insulating member is disposed in the space and spaced apart from the two adjacent planar, spaced-apart electrode plates. A power source is applied to the planar, spaced apart electrode plates so as to generate an electrical field to coalesce droplets of the disperse phase component. 
         [0012]    Another illustrative method for coalescing a process fluid including water droplets entrained in a primarily gas hydrocarbon-containing process fluid includes passing the process fluid through a structure. The structure comprises an outer wall with an electrically insulating material formed on an entire inner surface of the outer wall so as to define an entirely insulated flow path for receiving the process fluid and the flow path is free of any portion of the structure. A plurality of planar, spaced-apart electrode plates positioned within the entirely insulated flow path and positioned substantially parallel to one another is provided. A space is defined between two adjacent planar, spaced-apart electrode plates and substantially the entirety of each of the plurality of planar, spaced-apart electrode plates is coated with an insulative material. At least one insulating member is disposed in the space and spaced apart from the two adjacent planar, spaced-apart electrode plates. A power source is applied to the planar, spaced apart electrode plates so as to generate an electrical field to coalesce at least a portion of the water droplets. An inductor is coupled in parallel with the planar, spaced-apart electrode plates. The inductor and the planar, spaced-apart electrode plates define a resonant circuit. An alternating current signal is applied to the planar, spaced apart electrode plates at a frequency corresponding to a resonant frequency of the resonant circuit in the presence of the process fluid, the frequency of the alternating current signal is varied based on a positive feedback signal received from the resonant circuit to maintain resonance. 
         [0013]    Yet another illustrative method for coalescing a process fluid including water droplets entrained in a primarily gas hydrocarbon-containing process fluid includes passing the process fluid through a structure. The structure comprises an outer wall with an electrically insulating material formed on an entire inner surface of the outer wall so as to define an entirely insulated flow path for receiving the process fluid and the flow path is free of any portion of the structure. A plurality of planar, spaced-apart electrode plates positioned within the entirely insulated flow path and positioned substantially parallel to one another is provided. A space is defined between two adjacent planar, spaced-apart electrode plates and substantially the entirety of each of the plurality of planar, spaced-apart electrode plates is coated with an insulative material. At least one insulating member is disposed in the space and spaced apart from the two adjacent planar, spaced-apart electrode plates. A power source is applied to the planar, spaced apart electrode plates so as to generate an electrical field to coalesce at least a portion of the water droplets. An inductor is coupled in parallel with the planar, spaced-apart electrode plates. The inductor and the planar, spaced-apart electrode plates define a resonant circuit. An alternating current signal is applied to the planar, spaced apart electrode plates at a frequency corresponding to a resonant frequency of the resonant circuit in the presence of the process fluid. A current of the alternating current signal is sensed, and the frequency is changed to minimize the sensed current. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    The disclosed subject matter will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0015]      FIG. 1  is a simplified diagram of a fluid separation system in accordance with one illustrative embodiment of the present subject matter; 
           [0016]      FIG. 2  is a simplified cross-section view of an electrostatic coalescer in the system of  FIG. 1 ; 
           [0017]      FIG. 3  is a diagram of a flow disrupting element that may be used in the electrostatic coalescer of  FIG. 2 ; 
           [0018]      FIG. 4  is a simplified block diagram of a control circuit of the electrostatic coalescer of  FIG. 1 ; 
           [0019]      FIG. 5  is a simplified diagram of a positive loop that may be employed in an AC generator in the control circuit of  FIG. 4 ; 
           [0020]      FIG. 6  is a simplified block diagram of an autogenerator circuit that may be employed in the control circuit of  FIGS. 4 and 5 ; 
           [0021]      FIG. 7  is a simplified block diagram of an alternative embodiment of a control circuit of the electrostatic coalescer of  FIG. 1 ; 
           [0022]      FIG. 8  is a simplified block diagram of a fluid separation system incorporating an external energy source with an electrostatic coalescer; 
           [0023]      FIGS. 9 and 10  are cross-section views of an alternative embodiment of an electrostatic coalescer with intermediate insulating members disposed between electrode plates; and 
           [0024]      FIGS. 11 and 12  are cross-section views of an electrostatic coalescer in accordance with another illustrative embodiment of the present invention. 
       
    
    
       [0025]    While the disclosed subject matter is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosed subject matter as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0026]    One or more specific embodiments of the disclosed subject matter will be described below. It is specifically intended that the disclosed subject matter not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the disclosed subject matter unless explicitly indicated as being “critical” or “essential.” 
         [0027]    The disclosed subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the disclosed subject matter with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
         [0028]    Referring now to the drawings wherein like reference numbers correspond to similar components throughout the several views and, specifically, referring to  FIG. 1 , the disclosed subject matter shall be described in the context of a fluid separation system  10 . The system  10  includes an electrostatic coalescer  15  disposed upstream of a separator  20 . The electrostatic coalescer  15  is resident in a fluid stream defined by piping  25 . 
         [0029]    For purposes of the following discussion, a fluid stream may be a primarily liquid stream of a primarily gas stream. In the illustrated embodiment, the electrostatic coalescer  15  is operable to increase the size of liquid droplets in a process fluid, such as a hydrocarbon fluid. For example, the coalesced liquid may be water present in a liquid hydrocarbon stream or a gas stream (e.g., natural gas). Of course, the particular fluid provided to the electrostatic coalescer  15  may vary, and fluids other than hydrocarbon fluids may be processed. The liquid coalesced from the process fluid may also vary, with water being only one illustrative example. In another example, liquids may be separated from the process gases (e.g., chlorine or HCl). Water droplet sizes in chlorine gas streams may be enlarged by the electrostatic coalescer  15  to more effectively remove water from the chlorine, before dealing with the gaseous water vapor. 
         [0030]    The separator  20  operates to remove at least a portion of the liquid present in the process fluid and provides a process fluid outlet  30  and a coalesced liquid outlet  35 . The construction and operation of the electrostatic coalescer  15  is described in greater detail below with respect to  FIGS. 2 and 3 . The application of the present subject matter is not limited to any particular embodiment of the separator  20 . Exemplary separator types include horizontal/gravity separators and enhanced gravity separators (e.g., cyclone based separation technology). In some embodiments, the electrostatic coalescer  15  and the separator  20  may be integrated into a single unit. 
         [0031]    Estimations and experience of electro-coalescence in liquid-liquid systems show that the necessary value of electrical field to produce coalescence in a liquid-gas system should be in the range 10 3 -10 4  V/cm. Typical values of electrical fields, which cause auto electron emission (i.e., the only charging mechanism for the droplets by electrostatic fields) are in the range larger than 10 7  V/cm, so the above electrical field will not produce any charging of the droplets. 
         [0032]    In cases where the fluid being processed by the electrostatic coalescer  15  is primarily gas, it is possible to generate an electric field across a gas due to the fact that gases are good insulators. In such an electric field, charged particles are attracted to one of the electrode plates  45 . Uncharged particles will be polarized, and due to dipole-dipole interaction, an attractive force between them will appear, while they remain unattracted by the electrode plates  45 . The forces generated by the electrical field in the coalescer  15  are too weak to ionize the free particles. 
         [0033]    Although this description illustrates the separation of water from a hydrocarbon fluid, the electrostatic coalescer  15  may be applied to applications with other emulsions where the specific resistance of the continuous phase is larger than about 10 7  Ohm*m and where the electric permeability of continuous and disperse phases are different. For example, the water droplet sizes in hydrocarbon gas streams may be enlarged by the electrostatic coalescer  15  to more effectively dry the gas. In general, more conductive emulsions may require higher frequencies of the applied voltage. 
         [0034]    In general, the electrostatic coalescer  15  is more effective in causing coalescence when the water cut is at least about 2%. This amount may vary depending on the particular process fluid and flow rate. In cases where the water cut of the process fluid is less than an efficient value, a water injection port  37  may be disposed upstream of the electrostatic coalescer  15  to increase the water content of the process fluid prior to coalescence and separation. 
         [0035]      FIG. 2  illustrates a cross-section view of the electrostatic coalescer  15 . In the illustrated embodiment, the diameter of an outer wall  40  of the electrostatic coalescer  15  roughly corresponds to the diameter of the piping  25  in which it is installed to provide an in-line arrangement. Fluid passing through the piping  25  passes through the electrostatic coalescer  15  at substantially the same flow rate. A plurality of electrode plates  45  are provided in the electrostatic coalescer  15  through which the fluid travels. In some embodiments, obstructive elements  52  may be provided in the areas where no electrical field is generated to ensure the exposure of all of the fluid to the electrical fields. 
         [0036]    The electrostatic field generated by the electrode plates  45  polarizes liquid droplets in the process stream to locally neutralize the electrostatic field. The polarized droplets are not attracted by the homogeneous field to one of the electrodes  45  because the net charge of the droplet is zero. The polarized droplets do feel the gradient of the electrostatic field at short range of other droplets. In this manner, the droplets are attracted to one another. 
         [0037]    The particular geometry of the electrode plates  45  (e.g., arrangement, number, thickness, etc.) may vary depending on factors associated with the particular implementation, such as process fluid, piping diameter, fluid pressure, expected flow rate, etc. For example, the spacing of the electrode plates  45  may vary depending on the processed fluid. The electrode plates  45  in a gas coalescer may be spaced more closely together than in a liquid coalescer. This reduced spacing may be achieved by reducing the diameter of the coalescer  15  as compared to that of the piping  25  to allow the same number of electrode plates  45  to be used, but spaced more closely. Alternatively, the diameter may not be reduced, but the number of electrode plates  45  may be increased. In some applications, long electrode plates  45  having a length several times the diameter of the electrostatic coalescer  15  may be used to increase the residence time or to lower the required field strength. 
         [0038]    As illustrated in  FIG. 2 , the inside surface of the outer wall  40  and the electrode plates  45  are coated with a protective layer  50 . Generally, the protective layer  50  protects the electrode plates  45  from erosive or corrosive effects of the process fluid (e.g., due to particles or chemicals in the process fluid) and may also serve as an electrical insulator to reduce the likelihood of arcing between adjacent electrode plates  45 . Exemplary materials for the protective layer  50  include epoxy, electrically non-conducting ceramics, plastic coatings, etc. formed using processes such as molding, chemical vapor deposition, physical vapor deposition sintering, etc. Alternatively, electrically insulating layers may be combined with other protective layers on the outside surfaces to meet the mechanical requirements of the application (e.g., abrasion resistance or corrosion resistance). For example, an insulating epoxy coating may be covered by a ceramic conducting coating. The particular insulator and/or abrasion resistant coating selected may vary depending on mechanical requirements, cost, and material electrical properties (e.g., dielectric constant). 
         [0039]    The electrode plates  45  may be sized and arranged to provide for a relatively high Reynolds number, thereby providing turbulent flow of the process fluid through the electrostatic coalescer  15 . Turbulent flow causes the velocity of the process fluid to vary in a random manner, causing an increase in the small-scale movements of the fluid. This increase in movement makes it more likely that water droplets in the process stream will come in close proximity with one another. At this close proximity, the dipolar interaction induced by the electrostatic field described above will be stronger, thereby increasing coalescence. 
         [0040]    In one embodiment illustrated in  FIG. 3 , one or more flow disrupting elements  52  may be provided in the electrostatic coalescer  15  to enhance microturbulence between the electrode plates  45 . The flow disrupting element  52  may be fabricated from an electrically insulative material, such as a ceramic, plastic, or other electrically-non-conductive solid material. The flow disrupting element  52  includes a plurality of pillars  53  interconnected by cross members  54  in a grid arrangement. The grid disrupts the flow of process fluid through the electrostatic coalescer  15  to increase turbulence. The flow disrupting element  52  may be positioned between adjacent electrode plates  45 . The sizing of the flow disrupting element  52  may vary depending on the particular arrangement and sizing of the electrode plates  45 . Flow disrupting elements  52  may not be required in implementations where the flow rate and Reynolds number are sufficiently high to provide turbulent flow. 
         [0041]    In an application where the fluid stream exhibits a high degree of laminar flow, the central part of the stream will have a much higher speed than the part along the walls. This flow characteristic may result in a short residence time between the electrode plates  45  In addition to or in place of the flow disrupting elements  52  to induce turbulence, flow guides may be provided to make the distribution of flow over the electrode plates  45  more even in terms of kg/hour, resulting in a better use of the electrostatic coalescer  15 . 
         [0042]    Referring to  FIG. 4 , a simplified block diagram of a control circuit  55  of the electrostatic coalescer  15  is provided. The properties of the process fluid affect the net electrical characteristics of the electrostatic coalescer  15 . Hence, the electrostatic coalescer  15  is modeled as a capacitor  60  in parallel with a resistor  62  representing the net capacitance and resistance defined by the arrangement of the electrode plates  45  and the process fluid passing through them. The control circuit  55  includes an inductor  64  and an alternating current (AC) generator  66 . Collectively, the inductor  64  and the capacitor  60  and resistor  62  that model the electrostatic coalescer  15  and process fluid define a resonant circuit  68 . In general, the AC generator  66  maintains its output frequency at the resonant frequency of the resonant circuit  68  to minimize the current needed to drive the electrostatic coalescer  15 . The AC generator  66  generates a variable frequency sinusoidal waveform that is applied to the electrode plates  45  to foster coalescence in the process fluid. 
         [0043]    In one embodiment, the AC generator  66  may be an autogenerator circuit. As known to those of ordinary skill in the art, an autogenerator is generally an amplifier with large amplification having an exit connected to the entrance, commonly referred to as a positive loop. The positive loop includes a resonant circuit that defines the frequency of oscillation. In this embodiment, the resonant circuit  68  is coupled to the positive loop of the AC generator  66 , thereby providing for passive frequency adjustment of the AC generator  66  corresponding to the resonant frequency of the resonant circuit  68 .  FIG. 5  illustrates how the resonant circuit  68  is incorporated into the positive loop of the AC generator  66  through a comparator  85 . Because of the positive feedback, the AC generator  66  operates at the resonant frequency of the resonant circuit  68 . Because the inductor  64  is fixed, the frequency adjusts according to the varying properties of the process fluid and the resulting capacitance of the electrostatic coalescer  15 . As the properties of the fluid change over time, the AC generator  66  automatically maintains its output at the varying resonant frequency, thereby minimizing the current requirements required for driving the electrostatic coalescer  15 . 
         [0044]      FIG. 6  is a simplified block diagram of the autogenerator circuit that may be employed for the AC generator  66 . The autogenerator circuit includes a power unit  70  that receives an AC input voltage (e.g., 220V, 50 Hz) and generates DC output voltages (e.g., +300V, +50V, +12V, +9V, etc.) for powering the other units of the circuit. A driving generator  72  produces driving pulses at double frequency. A signal conditioner  74  produces signals for a frequency phase adjustment unit  76  and for switching the gates of transistors in a power amplifier  78 . The power amplifier  78  is a push-pull amplifier. The frequency phase adjustment unit  76  compares the phases of the driving generator  72  and an output signal and adjusts the frequency of the driving generator  72  to achieve resonance with varying load characteristics. A resonance transformer  80  forms a sinusoidal output signal with an amplitude up to 3 kV, for example for powering the electrostatic coalescer  15 . A positive feedback path exists between the resonance transformer  80  and the frequency phase adjustment unit  76 . 
         [0045]    A control unit  82  controls the frequency and amplitude of the output signal, and in response to a condition that exceeds defined limits, sets the AC generator  66  into a safe mode (i.e., low power). An indicator unit  84  indicates the parameters of the output signal. An interface  86  may be provided for connecting the AC generator  66  to an external computing device  88 , such as a personal computer, controller, or some other general purpose or special purpose computing device for allowing tracking of device parameters, such as frequency, amplitude and consumed power, or to allow operator intervention or system configuration. 
         [0046]      FIG. 7  illustrates an alternate embodiment of a control circuit  90 , where an AC generator  95  is a signal generator that outputs a configurable frequency signal. For example, the AC generator  95  may be a voltage controlled oscillator. The voltage at a resistor  100  represents a measure of the output current of the control circuit  90  for driving the electrostatic coalescer  15 . The AC generator  95  measures the output current and automatically adjusts its output frequency to minimize the value of the measured voltage, which corresponds to a resonance condition. Hence, the AC generator  95  actively adjusts its output frequency based on the measured drive current to obtain the resonant frequency of the resonant circuit  68 . 
         [0047]    Generally, the frequency of the oscillation is above 1 kHz due to the relaxation time associated with most types of crude oil, which is in the range of 0.02-0.003 seconds. In the illustrated embodiment, it is assumed that the capacitance is about 0.1 μF and the nominal frequency is about 10 kHz, which provides for and inductance of about 3 mH. Of course, the inductor  64  may be sized differently based on different assumptions about the process fluid and geometry of the electrostatic coalescer  15 . The Q value corresponding to the resonance condition that results in the diminishing of the drive current is given by: 
         [0000]        Q= 2ω L/R  
 
         [0048]    Monitoring the frequency of the control circuit  55 ,  90  provides information regarding the capacitance of the electrostatic coalescer  15 , and therefore the water cut. The power consumption of the electrostatic coalescer  15  is defined by the resistance of the process fluid. The electrical resistance of the process fluid and the value of the water cut characterize the quality of the process fluid being processed. The resistance can provide information regarding the salinity of the process fluid. The water cut of the process fluid entering the electrostatic coalescer  15  effectively defines the final wafer cut after the separator  20 . Hence, by utilizing the water cut and resistance information, diagnostic tools may be defined to characterize the process fluid. 
         [0049]    In some embodiments, the efficiency of the coalescence may be enhanced by providing an external energy source that operates in conjunction with the electrostatic coalescer  15 . As shown in  FIG. 8 , an energy source  105  may be coupled to the electrostatic coalescer  15 . Exemplary energy sources include microwave or ultrasound devices. Exposing the process fluid to a microwave or ultrasonic energy field may increase the coalescence provided by the electrostatic coalescer  15 . The need for an external energy source  105  may depend on characteristics such as the size of the electrostatic coalescer  15 , the characteristics of the process fluid, the flow rate, etc. Information gathered from the resonant frequency of the resonant circuit  68 , which defines the characteristics of the process fluid, may be used to tune the external energy source  105 . For example, experiments may be conducted to identify the optimal frequency or amplitude characteristics of the microwave or ultrasound signals based on the characteristics of the process fluid. A correlation between the determined resonant frequency and the external energy source characteristics may then be determined to increase the effectiveness of the external energy source  105 . 
         [0050]    In another embodiment illustrated in  FIG. 9 , an electrostatic coalescer  110  may be provided with an intermediate insulating member  115  disposed between the electrode plates  120 A,  120 B to define a first flow path between the insulating member  115  and the first electrode plate  120 A and a second flow path between the insulating member  115  and the second electrode plate  120 B. One or more insulating members  115  may be disposed between the pair of electrode plates  120 A,  120 B to define additional flow paths therebetween (e.g. a third flow path between adjacent insulating members  115 ). Although only two electrode plates  120 A,  120 B are illustrated, different configurations may be used, including the arrangement shown in  FIG. 2 , where parallel plate electrodes are used. In such a case one or more insulating members  115  may be disposed between each pair of electrode plates  45 . Of course other geometries may also be used. 
         [0051]    For purposes of illustration, the electrode plate  120 A is grounded, and the electrode plate  120 B is coupled to a power source  125 , such as one of the power sources  66 ,  95  described above, or a different power source. Typically, the electrode  120 B is coated with a protective layer  130  to protect the electrode plate  120 B from erosive or corrosive effects of the process fluid (e.g., due to particles or chemicals in the process fluid). The protective layer  130  may also serve as an electrical insulator to reduce the likelihood of arcing. The grounded electrode plate  120 A may or may not have a protective layer  130 . The resonant circuit  68  described above may or may not be implemented in the electrostatic coalescer  110 . 
         [0052]    The insulating member  115  disposed between the two electrode plates  120 A,  120 B increases coalescence efficiency. Coalescence of droplets in another medium relies on the polarization of conducting liquid particles in an electrical field. Due to the required high field, and the preference not to use very high voltages, the electrodes are normally disposed in close proximity to one another. Under normal circumstances, water droplets that happen to be in-line with the electrical field, will be aligned in a “chain” of water droplets that do not coalescence effectively because the attraction to a droplet in the middle of the chain to one side will be equal to that to the other side, negating the attraction, while the droplets on the electrode will not release. Only droplets on free ends will move and, thereby, coalesce. This chain of droplets reduces the field strength, and therefore the coalescence, which reduces the efficiency of the coalescence. In some cases, where high field and long chains are present, sparking can occur. The higher the water concentration, the more droplets are present, and therefore the higher the influence of this effect. The insulating member  115  tends to break up these chains or even prevent them from forming, resulting in a higher coalescence efficiency. 
         [0053]    The insulating member  115  may be hydrophilic (i.e., water attracting) or hydrophobic (i.e., water repelling). The attractive forces between water and a hydrophilic surface are relatively small compared to those found in electric fields. The dielectric constant of the material used for the insulating member  115  may vary depending on the particular implementation. If an insulator with high dielectric constant (i.e., higher than the surrounding medium) is used, the influence the droplets experience from each other, even assuming contact between the droplets and the surface of the insulator, will be smaller than the thickness would predict. Therefore, in situations where not much space is present between electrodes  120 A,  120 B, a thin, high dielectric constant insulator may be used. On the other hand, due to mechanical requirements, the insulating member  115  may, in some cases, be rather thick, which would result in a preference for an insulator with a low dielectric constant. Where a material with a high dielectric constant is combined with one with a low constant in an electrical field, the electrical field strength will concentrate in the high dielectric constant material. A lower dielectric constant material for the insulating member  115  will support the goal of building the electrical field over the medium to be coalesced by reducing the fields in the insulating member  115 , thereby allowing a smaller applied voltage and resulting in safer operations with less power consumption. 
         [0054]    Providing multiple insulating members  115  between the electrode plates  120 A,  120 , as shown in  FIG. 10 , tends to further increase the efficiency of the coalescence. The region between the insulating members  115  will be free of water droplet chains, which were found to reduce efficiency. By placing the insulating members  115  close to the electrodes  120 A,  120 B (i.e., without merging with them, which would reduce the insulator function), a higher efficiency can be obtained. 
         [0055]    In contrast to electro coalescence of water in water-in-oil systems, the conductivity of gases is far less than the conductivity of crude oils. This circumstance makes it possible to use a DC voltage power source to create an electrical field in the gas media. In some applications, the electrostatic coalescer  15  may be employed in a gas application and a controlled resonance AC power source may be used. 
         [0056]      FIG. 11  illustrates an alternative embodiment of an electrostatic coalescer  150  that may be employed in an application where the process fluid is primarily gas. The electrostatic coalescer  150  includes an outer wall  155  and external electrodes  160  coupled to a power source  165 . The outer wall may be an electrically insulating material. An enclosure  170  may be provided around the external electrodes  160  for protective purposes. In the illustrated embodiment, the power source  165  is a DC power source, however, an AC source may also be used. The use of the external electrodes  160  allows the electrical field to be generated while minimizing the obstruction of the flow. 
         [0057]    In yet another embodiment shown in  FIG. 12 , the electrostatic coalescer  150  described in reference to  FIG. 11  may be provided with one or more electrically conductive members  175  disposed between the external electrodes  160  to increase the electrical field strength. The conductive members  175  are not connected to any power source, so they do not operate as electrodes. The conductive members  175  may be coated to provide the required characteristics, as described above in relation to the electrode plates  45 . Interposed conductive members  175  may also be used in the embodiment illustrated in  FIG. 2 . 
         [0058]    Although the electrostatic coalescers  15 ,  110 ,  150  are illustrated and described herein as being in-line devices, it is contemplated that the techniques described herein may be applied to other types of coalescers, such as vessel based coalescers. 
         [0059]    The use of an electrostatic force to coalesce liquid droplets in a fluid flow allows more efficient downstream removal of the droplets, thereby reducing the demands on the removal equipment and lowering its cost or increasing the amount of liquid that can be removed, thereby providing a higher purity processed fluid. 
         [0060]    The particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.