US3661746A

US3661746A - Uniform electric field treatment

Info

Publication number: US3661746A
Application number: US107770A
Authority: US
Inventors: Roy N Lucas
Original assignee: Petrolite Corp
Current assignee: Baker Petrolite LLC
Priority date: 1969-05-15
Filing date: 1971-01-19
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09

Abstract

A method for electrically resolving a dispersion consisting of immiscible and liquid phases. The dispersion flows along a vertical flow axis between inlet and outlet zones. An electric field for resolving the dispersion is established in a region between inlet and outlet zones through which region passes substantially all of the fluid. The electric field increases monitonically in potential in the direction of dispersion flow and has planes of constant potential transverse to the direction of dispersion flow. The phases resolved from the dispersion in the electric field are recovered from the outlet zone.

Description

United States Patent Lucas 1 May 9, 1972 [54] UNIFORM ELECTRIC FIELD 2,364,118 12 1944 Wolfe ..204/l88 TREAT NT Primary Examiner-John H. Mack [72] inventor: Roy N. Lucas, Houston, Tex. Assistant Examiner-Neil A. Kaplan [731 Assignee: Petrolite Corporation, St. Louis, Mo. Atmmey Emll Bednar and Sidney Rmg [22] Filed: Jan. 19, 1971 [57] ABSTRACT [21] Appl. No.: 107,770 A method for electrically resolving a dispersion consisting of immiscible and liquid phases. The dispersion flows along a Related Application Data vertical flow axis between inlet and outlet zones. An electric [62] Division of No 825 015 M 15 1969 Pat No field for resolving the dispersion is established in a region 3 582 l between inlet and outlet zones through which region passes substantially all of the fluid. The electric field increases 52 U.S. c1 ..204/1ss mmimnicany Pmemia' in dimm" of P flow 5 1 Int. Cl. ..B03c 5/00 and has Planes of Constant Pmemial transverse direcliim [58] Field of Search ..2o4/1 86-191 302409 of dispersion The Phases Yem'ved from the disPmio" the electric field are recovered from the outlet zone.

[56] References Cited 10 Claims, 7 Drawing Figures UNITED STATES PATENTS 1,440,776 l/l923 Eddy ..204/302 11;: s l Loses .s V

7 fwd, e I a C.

/ a a 1 1g m1 s1 u u u 1 1 PATENTEDMAY 9 I972 SHEET 1 OF 2 I N VEN TOR.

Ray /V Zara: BY

m M x u x 5 K, K. W A u i u PATENTEDHAY 9 I972 SHEET 2 OF 2 WATER INVENTOR. Fay /V. Zara; BY

ATTU/P/VEV UNIFORM ELECTRIC FIELD TREATMENT This is a division of application, Ser. No. 825,015 filed May 15, 1969, now US. Pat. No. 3,582,527, patented June I, 1971.

BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to resolving dispersions consisting of immiscible and liquid phases. More particularly, the invention relates to electric field treatment for resolving such dispersons.

2. Description of the Prior Art Electric fieldsare employed for resolving many dispersions in which the internal phase is an aqueous material such as water, caustic, or acid, etc., and the external phase is an organic liquid such as crude oil. These dispersions are passed between electrodes energized with a high voltage to create an electric field of sufficient intensity to cause the internal phase to coalesce. The term coalesce as used herein refers to the agglomeration of the dispersed internal phase while in the continuous external phase. Sufficiently large particle sizes of the internal phase are created which can be readily separated from the external phase by differences in specific gravities.

A large number of designs have been employed in electric treaters. Many methods of operation have been tested for improving the electrical resolution of dispersions. Some of these treaters were designed to employ non-uniform electric fields for effecting dispersion resolution. Other treaters were designed to employ uniform electric fields to effect the desired electrical resolution of dispersions. The latter type of treaters relate more closely to the present invention than treaters employing non-uniform electric fields.

One treater employing uniform electric fields for resolving dispersions is shown in U.S. Pat. No. l,440,776. The treater (crude oil dehydrator) was formed of an upright cylindrical metallic vessel in which were mounted horizontally a pair of vertically spaced apart foraminous electrodes. The lower electrode was grounded. The upper electrode was energized to create an electric field between the electrodes. The dispersion was introduced into the lower part of the vessel and passed upwardly through the two electrodes. The electric field caused the aqueous phase to coalesce and fall to the bottom of the vessel for removal through a suitable outlet. The organic phase passed upwardly and was removed through a suitable overhead outlet. As a result of operation of the treater, a stratified field (of undisclosed character) is alleged to be produced in the space between the electrodes.

The electrodes in the treater have a cross-section with a substantial area less than the cross-section in the treater open to fluid flow. Thus, not all the dispersion will flow through the energized electrode. For example, in a conventional similarly designed treater, this area may be in the range of between and percent of the cross-sectional area of the treater open to fluid flow. Thus, incomplete resolution of dispersions could result. Also, a non-uniform electric field exists between the peripheral edge of the energized electrode andthe adjacent metallic side walls of the vessel. This non-uniform field does not produce the same resolution of the dispersion as the uniform field which exists in regions directly between the energized and grounded electrodes. Thus, any dispersion which passes through this non-uniform field between the edge of the electrode and the adjacent metal wall of the vessel will not be treated to the same extent as the dispersion which passes through the energized electrode. Thus, the efficiency of the treater in resolving dispersions may be varied when dispersion from uniform and non-uniform electric fields is comingled. v

The purpose of the present invention is to employ a uniform electric field for resolving dispersions without passing any significant amount of dispersion through the treater other than through the uniform electric fields.

2 SUMMARY or THE INVENTION In accordance with the present invention, there is provided a method for resolving dispersions with uniform electric fields. More particularly, there is provided a method for electrically resolving dispersion formed of aqueous and organic phases. The dispersion is passed vertically between inlet and outlet zones. An electric field is established in the dispersion with monitonically increasing potentials in the direction of fluid flow. The field has planes of constant potential transverse to the direction of dispersion flow. Additionally, the electric field has sufficient intensity for resolving the dispersion at least in part into aqueous and organic phases as it passes from the inlet zone toward the outlet zone. The organic phase is recovered from the outlet zone.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section taken through a treater wherein the method steps of the present invention can be practiced;

FIG. 2 is a vertical section taken through a prior art treater which is arranged graphically to provide a ready comparison to the treater illustrated in FIG. 1;

FIG. 3 is an enlarged view of the energized and grounded electrode assembly of the treater illustrated in FIG. 1;

FIG. 4 is an enlarged fragmentary vertical section of another energized electrode embodiment used in the treater illustrated in FIG. 1;

FIGS. 5 and 6 are enlarged fragmentary vertical sections of other energized electrode embodiments used in the treater illustrated in FIG. 1;

FIG. 7 is a vertical section taken through an experimental treater employed for field testing the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to FIG. 1 of the drawings, there is shown a treater in which the steps of the present invention can be practiced. The treater is comprised of a vessel 11 having metallic wall 12 to form a vertical flow axis which is indicated by the arrowed line 13. An inlet 14 is provided to introduce dispersion to be treated into the vessel 11 at one end of the vertical flow axis. The dispersion is formed of an organic phase in which is dispersed a more dense aqueous phase. Outlets 16 and 17 to remove the organic and aqueous phases, respectively, are provided at the top and bottom of the vessel 11. If the organic phase is more dense than the aqueous phase, the treater may be inverted. Then, the organic phase would be removed through the lower outlet.

In operation of the treater, the organic phase obtained from the dispersion passes upwardly and it is removed through the outlet 16. Aqueous phase material gravitates downwardly and it is collected in a body 18 in the lower portion of the vessel 11. The aqueous phase body 18 may be withdrawn from the vessel at regulated rates so as to maintain a relatively constant interface 19 between the body 18 of aqueous phase and the dispersion and organic phase thereabove. A level control system may be provided for maintaining the interface 19 at a constant level within the vessel 11. For this purpose, a controller 21 is actuated by a float 22 for providing a signal (indicated by chain line 23) to a motor actuated control valve 24 which regulates fluid flow from the outlet 17. By this means, the aqueous phase can be removed through the outlet 17 at rates sufficient to maintain the interface 19 at any suitable level in the vessel 11.

Although the inlet 14 is shown as being disposed above the interface 19, for purposes of the present invention the inlet 14 may introduce dispersion below the interface 19, immediately at the interface 19, or at some level thereabove.

A spatial uniform electric field is provided by an electrode means within the vessel 11 so that the dispersion flowing along the vertical flow axis passes perpendicularly through planes of constant potential. In the treater illustrated in FIG. 1, the electric field is established between an energized electrode 26 and an upstream electrical ground, such as a grounded electrode 27, which are spaced vertically from one another. More particularly, the electrode 26 is constructed of an electrically conductive metal into a foraminous form and is positioned substantially horizontally in the vessel 11. The electrode 26 has a planar surface presented toward the inlet 14.

Insulators

28 and 29 may support the electrode 26 in electrical isolation from the walls 12 of the vessel 11. The electrode 26 extends substantially across the entire cross-section of the vessel 11 transverse to the flow of fluid along the vertical flow axis 13. An insulating sleeve or cylindrical member 31 is interposed between the peripheral edge 32 of the electrode 26 and the adjacent walls 12 of the vessel 11.

The electrode 26 may be formed of a steel disc provided with a plurality of openings 26a through which fluid may flow on passing along the vertical flow axis in the vessel 11. The cylindrical sleeve 31 is provided with a groove 32a to receive the peripheral edge 32 of the electrode 26. Thus, the electrode 26 and sleeve 31 comprise an integral unit which can be suspended upon the

insulators

28 and 29, or if desired, upon lower wall-mounted supports 33.

The cylindrical sleeve 31 is formed of a material having a high specific inductive capacity or dielectric constant which provides a barrier of very high resistivity compared to the fluids within the vessel 11. For substantially all practical purposes, no excessive current flows from the electrode 26 through the cylindrical sleeve 31 to the walls 12. By excessive current, it is meant a current which is greater than flows between the

electrodes

26 and 27. Suitable materials for forming the cylindrical sleeve 31 may be Teflon, polypropylene and various acrylic and other resinous materials. If desired,

ceramic insulative materials may also be employed in the sleeve 31. The cylindrical sleeve 31 has a certain thickness filling the space between the electrode 26 and walls 12. The sleeve 31 may have a lesser thickness but should have at least a minimum thickness which will not be readily punctured at the potentials to which the electrode 26 is energized during operation of the treater. Preferably, the sleeve 31 extends from a short distance above the electrode 26 downwardly throughout the region to the grounded electrode 27. In this region, the uniform electric field of the present invention is employed for resolving the dispersion.

The grounded electrode 27 is foraminous and may be constructed similar to the energized electrode 26. The grounded electrode 27 is supported beneath the sleeve 31 by supports 33 secured to the walls 12 of the vessel 11. Thus, the grounded electrode 27 is planar and disposed parallel to the electrode 26 r If desired, the grounded electrode 27 may be omitted. In this instance, the distributor connected to inlet 14, or the aqueous phase interface 19 will serve as an electrical ground spaced vertically from the energized electrode 26. The electrical field within the sleeve 31 will not be significantly changed. However, the electric field may be somewhat non-uniform in the vicinity of the distributor.

The electrode 26 is energized to potentials adequate for resolving the dispersion which enters the region between the

electrodes

26 and 27. For this purpose an external power source 34 may be provided. This power source supplies suitable potentials (AC or DC) to the electrode 26 for providing the desired result. For this purpose, one terminal of the power source 34 is connected directly to the walls 12 of the vessel 11. A high voltage conductor 36 is connected between the power source 34 and the electrode 26 through a high voltage bushing 37 mounted upon the upper surface of the vessel 11 and connected with a flexible wire 38 to the electrode 26. The power source 34 energizes the electrode 26 to sufficiently high potentials to resolve the dispersion in the region between the

electrodes

26 and 27. For example, the electrode 26 may be energized to between 3 and 35 kilovolts AC or DC for this purpose. The exact magnitude of the potentials will depend upon the characteristics of the dispersion and also of the spacing between the

electrodes

26 and 27.

Referring to FIG. 3, the arrangement of the

electrodes

26 and 27, and the sleeve 31 is shown in enlarged detail. The energized electrode 26 creates an electric field which extends vertically between the

electrodes

26 and 27. The sleeve 31 substantially reduces current flow to the walls 12 from the electrode 26 in directions parallel thereto. Therefore, substantially all current flows vertically between the electrodes. As a result, a spatially uniform electric field is created in the region between these electrodes which field has planes of constant potential normal to the vertical flow axis in the vessel 11. A plane of constant potential may be defined as a plane in which the potential is of constant magnitude throughout its extent. The plane is perpendicular to the lines of force of the electric field between the

electrodes

26 and 27. These planes of constant potential are identified by letters A, B, C, D and E for purposes of illustration. The actual spacing between adjacent planes of potential may vary depending upon the electrical characteristics of the fluids which are present in the region between the electrodes and the energizing potential applied to the .electrode 26. The dispersion moves from the electrode 27 towards the energized electrode 26in an electric field with a monitonically increasing potential. Thus, the dispersion flows at right angles to the planes of constant potential. lts traverse of the planes of constant potential provides for outstanding resolution of the dispersion into its respective aqueous and organic phases. The aqueous phase gravitates downwardly through the electrode 27 and collects intov an aqueous phase body 18 in the lower extremity of the vessel 11. The organic phase with any resolved aqueous phase passes upwardly through the electrode 26 and moves towards the outlet 16 at the upper extremity of the vessel 11. v

lt will be apparent that the sleeve 31 deflects lines of constant potential from an orientation parallel to the vertical flow axis in all flow passages along the vertical flow axis 13 within the treater. Thus, the dispersion must flow vertically at right angles through all planes of constant potential in the region which resides between

the'electrodes

26 and 27. Optimum resolution of the dispersion occurs in the uniform electric field under these conditions.

The function of the spatial uniform electric field employed in the present invention may be readily appreciated by reference to prior art treaters. ln FIG. 2 there is illustrated a prior art treater which is based upon the principles of operation described in U.S. Pat-No. 1,440,776 earlier described. This prior art treater is comprised of a vessel 40 having metallic walls 41 which provide a vertical flow axis indicated by the arrow 42. The vessel 40 carries aqueous and

organic phase outlets

43 and 44, respectively, at the top and bottom portions thereof. An inlet 46 is provided at one end of the vertical flow axis 42 in the vessel 40. The electric field established in the vessel 40 produces an organic phase which moves towards the outlet 44 and an aqueous phase which gravitates tremity of the vessel 40. Flow control means remove the aqueous' phase at a rate suitable to maintain a relatively constant interface 48 (above the body 47) at a predetermined level in the vessel 40. For this purpose, a flow control system 49 is actuated by a float 51 for providing signals indicated by chain line 52 to actuate a motor controlled valve 53 which regulates fluid flow from the outlet 43. The vessel 40 contains an energized electrode 54 and a grounded electrode 56 which are foraminous. The electrodes are mounted in vertically spacedapart horizontally oriented relationship. Thus, the

electrodes

54 and 56 are substantially identical to the

electrodes

26 and 27 in the treater of the present invention illustrated in FIG. 1. However, the energized electrode 54 has its peripheral edge spaced from the metallic walls 41 of the vessel 40 a sufficient distance that excessive currents are not drawn during treater operation. The electrode 54 is energized from a power source 57 which may be of any suitable design. The power source is grounded directly to the metallic walls 41 of the vessel 40. The power source 57 connects to a conductor 58, through an insu lating entrance bushing 59, and with a flexible lead 61 to the electrode 54. The electrode 54 is suspended from

insulators

62 and 63 within the vessel 40. Thus, the electrode may be energized to a suitable operating potential from the power source 57. 7

Upon energization of the electrode 54, a limited uniform electric field for resolving the dispersion which flows vertically through the vessel 40 is created in the central region between the

electrodes

54 and 56. A portion of the current flows vertically between the

electrodes

54 and 56 in a uniform portion of the electric field. However, substantial current also flows in directions other than vertically in the region between the

electrodes

54 and 56 to create non-uniform portions of the electric field. The uniform portion of the electric field has planes of constant potential normal to the flow axis 42. For example, if the electrode 54 is a perforated metal disc, the lines of force will be cup-shaped. These lines of constant potential for illustration are labeled A, B, C, D and E. The central part of the region between the electrodes is in the uniform portion of the electric field, and constant potential lines reside in planes transverse to the vertical flow axis 42. However, as the radial.

distance from the central region below the electrode 54 increases, the lines of force become divergent in the nonuniform portion ofthe electric field. Also, the lines ofconstant potential begin to become more compact in curved surfaces which eventually reach a vertical orientation between the peripheral edge of the electrode 54 and the adjacent metallic walls 4] of the vessel 40. Efficiency in the treater for resolving the dispersion varies as the lines of constant potential become oriented towards the vertical and become more compact.

The dispersion passing between the peripheral edge of the electrode 54 and the metallic wall 41 of the vessel 40 may be, for example, l0 percent by volume of all fluids which pass through the vessel 40. As a result, at least 10 percent of the dispersion is not resolved to the same extent as centrally between the electrodes. Additionally, the curvature of the lines of constant potential towards the vertical tends to move (by electrophoretic action) unresolved dispersion into the flow passages between the peripheral edge of the electrode 54 and the metallic wall 41 of the vessel 40. These effects combine to affect the efficiency of the prior art treater in resolving dispersions relative to the present invention.

In the treater illustrated in FIG. 1, the cylindrical sleeve 31 represents the preferred embodiment of an insulated barrier interposed between the peripheral edge of the energized electrode and adjacent metallic walls of the vessel. However, other embodiments of the insulated barrier may be employed for deflecting lines of constant potential from an orientation parallel to the vertical flow axis within flow passages residing between the energized electrode and the metallic walls of the vessel.

Another embodiment of the insulating barrier is illustrated in FIG. 4. Like parts in the treater in FIG. 4 will be designated by like numerals relative to the treater shown in FIG. 1. The electrode 26 in the vessel 11 is spaced from the metallic walls 12 by a distance .3. An imperforate insulating barrier is provided between the peripheral edge of the electrode 26 and the metallic walls 12. The insulating barrier is an annular member 66 formed of a material having a high specific conductive capacity, or dielectric constant, which provides a much higher specific resistance than the fluids which are passed through the electrode 26. For example, the annular member 66 may be formed of Teflon, or other materials such as were described relative to the sleeve 31. The member 66 may have any thickness but preferably is substantially identical in thickness to the electrode 26.

The lines of constant potential produced in the region between the

electrodes

26 and 27 will be substantially planar immediately below the electrode 26 and reside in planes A, B, C, D and E. Outwardly beyond the peripheral edge of the electrode 26, the lines of constant potential begin to curve upwardly from the planes A, B, C, D and E. These lines terminate perpendicularly along the insulated annular member 66. The annular member 66, as a high dielectric constant material, prevents the electric field from encircling the peripheral edge of the electrode 26. Additionally, the annular member 66 is imperforate and therefore seals the peripheral edge of the electrode 26 to the walls 12 of the vessel 11. Thus, substantially all fluids must move vertically along the flow axis and through the electrode 26. Fluids moving adjacent the metallic walls 12 are diverted inwardly by the annular member 66 and must pass through the openings 26a of the electrode 26. These diverted fluids traverse at substantially right angles the lines of constant potential extending between the planes of constant potential A through E and the annular member 66. Thus, all of the dispersion in the vessel 11 is treated at practically substantially identical conditions with fluid moving normal to the lines of constant potential. For all practical purposes, the embodiments shown in FIGS. 1 and 4 produce identical results.

The distance s illustrated in FIG. 4 for the annular member 66 is not critical but should be above a certain minimum dimension. Referring momentarily to the prior art treater of FIG. 2, the high-density concentration of the lines of constant potential between the peripheral edge of the electrode 54 and the walls 41 of the vessel 40 cause accumulation of aqueous phase material. This aqueous material causes chaining effects or high current paths between the electrode 54 and the walls 41. In the embodiment of FIG. 4, the annular member 66 prevents this undesired result. Thus, the accumulation of water, between the peripheral edge of the electrode 26 and the walls 12, is avoided. Excessive current flows between the electrode 26 and the walls 12 cannot occur as a result of accumulation of water therebetween.

A certain criterion is employed for determining the minimum spacing or distance s for the annular member 66. It has been found that dispersions tested in the laboratory produce an increase for current conducted through the dispersion proportional to each increase in potential until a certain critical potential is applied. Then, disproportionately larger amounts of current pass through the dispersion over a certain range of applied potentials above the critical potential. At additionally increased applied potentials, the magnitudes of current passed will be several times greater than current flows below the critical potential.

The current-potential curves for any dispersion may be determined with an apparatus to contain the dispersion about an energized electrode. Preferably, a cylindrical container coaxially carrying an energized rod electrode is used. Data is taken with sufficient rapidity that the dispersion is not resolved completely during the application of potential and measurement of the current passed through the dispersion.

The excessive current conducting properties of the dispersion above the critical voltage result from certain physical properties which cannot be presently precisely defined. It is believed that these properties occur about electrodes defining an electric field by the creation of ions, or ionized particles in the dispersion, or any gas, moisture or other impurities carried therein. This conduction may take place essentially through v collision ionization (as occurs in gases) or molecular disruption by heating, or both. It has been also suggested that the conduction in the dispersion is of an electrolytic nature. The ionization of the contained gas may be the more likely explanation of this high-current conducting phenomena since the critical voltage of a dispersion increases as the pressure upon the liquid phase is increased. Thus, for any given dispersion, the potential applied to the energized electrode to create an electric field should not create such a potential gradient between the energized electrode 26 and the adjacent walls 12 over the distance s that excessive current flows would result by reaching the critical voltage of the dispersion.

Referring now to FIG. 5, there is illustrated another embodiment of the electrode arrangement employed in the present invention wherein like parts carry like reference numerals to the embodiment illustrated in FIG. 1. The insulating barrier interposed between the peripheral edge of electrode 26 and adjacent walls 12 of the vessel 11 takes the form of an annular band 68 carried on the electrode 26. The band 68 is formed of a material having a high specific inductive capacity or dielectric constant and with a high resistivity compared to the dispersion being treated. The band 68 has a thickness 1, which may be formed of materials such as described for the sleeve 31 in the embodiment illustrated in FIG. 1. The band 68 is spaced a distance 1,, awayfrom the walls 12. This spacing 1 can be of the same magnitude as the distance s shown in the FIG. 4. However, the band 68 provides an additional function that permits the distance 1,, to be smaller than the distance s.

In a momentary reference to FIG. 4, the shortest distance through the dispersion between peripheral edge of the electrode 26 and the metallic wall 12 is the distance s. In FIG. 5, the barrier 68 has a height h providing a path of very high resistivity interposed between the peripheral edge of the electrode 26 and the adjacent walls 12. Thus, the closest electrical or line-of-sight path between the electrode 26 and the walls 12 is the line identified by the dimension 1 Thus, as long as the dimension 1 is not so short as s to create potential gradients above the critical voltage of the dispersion, the distance -1 may be any desired distance. The distance 1,, can be less than the distance 5.

The band 68 extends vertically away from the electrode 26 a sufl'icient distance I: to deflect lines of constant potential from orientation parallel to the vertical flow axis in flow passages residing between the energized electrode 26 and the 'walls 12 of the vessel 11. In the region between the

electrodes

26 and 27, and directly beneath the electrode 26, there will be formed planes A through E of the constant potential lines normal to the vertical flow axis in the vessel 11. Theselines of constant potential as they approach the metallic walls 12 of thevessel are deflected into curved paths. The band 68, as an insulating barrier, causes'these lines of constantpotential in the curved path to return to the lower extremity of the band 68. Thus, the flow passage between the band 68 and the adjacent walls 12 contains an electric field in which the lines of constant potential very closely approach orientation in horizontal planes. Also, the vertically moving fluid intersects nearly twice the number of lines of constant potential as compared to the electric field directly below the energized electrode 26. The further downwardly a line of constant potential is below the energized electrode 26, the more closely this line will orient into nearly horizontal planes of constant potential in the flow passage between the band 68 and the walls 12. For practical purposes, any dispersion flowing in these flow passages will be in an uniform electric field having substantially the same properties asthat dispersion which passes vertically through the central portions of the electrode 26.

' Anotherembodiment of the insulating barrier is illustrated in FIG. 6. Like parts in the treater in FIG. 6 will be designated by like numerals relative to the treater shown in FIG. 1. The energized electrode 26 is constructed of metal, but unlike electrode 26, has a horizontal undulated peripheral edge with varying, spacing from the adjacent metal walls 12. The electrode 26' is foraminous being formed of horizontal metal rods which electrically are substantially equivalent to perforated disc electrode 26. The rods in electrode 26' are arranged as shown in U.S. Pat. No. 2,855,359. Each rod has an end presented to the vessel 11. As a result, the peripheral edge of the electrode 26 is variably spaced from the metallic walls 12 since the ends of the rods project radially beyond other parts on the continuous electrode parameter.

Obviously, the entire peripheral edge, where required, could be surrounded by a continuous imperforate insulating barrier such as is illustrated in FIGS. 4 or 5. However, the present embodiment produces acceptable results by an individual insulating barrier integrally carried on the radially projecting ends of rods forming the electrode 26' where its peripheral edge is variably spaced from the metallic walls 12. This result is shown by constant potential planes A-E. The individual insulating barriers may be in the form of blocks,'discs or other structures. However, it is preferred for optimum electrical and hydraulic characteristics to form these individual insulating barriers on the ends of the rods as spheres or ball-like structures. I

More particularly, the ball 68, forming an individual insulating barrier, is mounted threadedly upon the end of each projecting rod contained in the electrode 26'. The ball 68, as an insulating barrier, may be formed of the same materials as earlier described relative to the annular member 68. For good results, the ball 68' can be formed of Teflon.

The ball 68' is of identical physical dimensions, 1,, 1,, 1 and h, in arrangement on the electrode 26' as was the annular band 68 on electrode 26 as shown in FIG. 5.

Although the ball 68' provides on the projecting rod ends,

the same function and results as the annular member 68, there is obviously a great saving in materials employed in the insulating barrier on these parameter portions of the electrode 26.

It will be apparent from the foregoing embodiments illustrated in FIGS. 1, 4, 5 and 6, that the insulating barrier interposed between the peripheral edge of the

electrodes

26 or 26 and the adjacent walls 12 may take any configuration as long as the insulating barrier extends away from the electrode a sufficient distance to deflect lines of constant potential from an orientation parallel to the vertical flow axis in flow passages residing between the electrode 26 and the metallic walls 12. Where the insulating barrier is so arranged, the electrode produces planes of constant potential normal to the vertical flow axis in a region residing between the energized electrode 26 and the inlet 14 through which region passes substantially all of the fluid moved along the vertical flow axis of the vessel 11. This results in a substantial improvement in the efficiency of resolving dispersions in treaters of this design.

It has been found within treaters arranged according to the present invention, that the vertical distance between the energized electrode 26 and the grounded electrode 27 may be sub stantial, and asa result, the electrode 26 can be energized to sufficiently high potentials that not only is the dispersion resolved in the region between the electrodes but any' residual dispersed aqueous phase material will be repelled from the electrode 26. Thus, the function of the electrode means of this invention provides for enhanced resolution of dispersions. Also, these structures provide for applying sufficient potentials to energize the electrode that an electrostatic phenomena may be produced which repells residual dispersed aqueous phase materials from the outlet zone and in a direction toward the inlet zone in the vessel 11.

The insulating barrier formed by either the sleeve 31, annual member 66, the band 68, or the ball 68, can be delineated as to geometry and composition in terms of the physical properties of the system. The system is comprised-of the dispersion having applied thereto a potential to create a current flow adequate to resolve the dispersion. Below the critical voltage, the electrical characteristics conform to a classic mathematical description of dE/dl R, where R," the resistance (in ohms) depends upon the geometry and the initial physical properties of the system surrounding the energized electrode, the fluid in the vessel 11 and the spacing s from the metallic walls 12.

In terms of specific resistivity po X 1,, R where '1, is the linear separation s between the electrode and the wall. To

reduce the current flow, an insulating barrier is imposed between the energized electrode and the wall. The barrier must have a specific resistivity ps and thickness 1, such that p. ,+p ue In addition, the barrier must be of sufiicient height h to provide a line-of-sight path 1 of adequate length, i.e.,

poX 1 a R,

These restrictions delineate the structure and properties of the insulating barrier which are required to reduce current flow at the critical voltage. Naturally, the vertical spacing 1 between the energized and any grounded electrode must also be such that p0 X l 2 R.

The preceding equations provide a method to determine the distance that the insulating barrier in the form of the cylindrical sleeve 31, the annular member 66, the band 68, or the ball 68', has to extend from the peripheral edge of the electrode 26 for deflecting lines of constant potential from an orientation parallel to the vertical flow axis in flow passages residing between the energized electrode 26 and the walls 12.

In treaters of the present invention, a dispersion is electrically resolved into aqueous and organic phases by several basic steps. The dispersion is passed vertically between inlet and outlet zones formed in the vessel 11 adjacent the aqueous phase and organic phase outlets l6 and 17, respectively. A

monitonically increasing electric field is established in the dispersion by function of the

electrodes

26 and 27. The field has planes of constant potential transverse to the direction of dispersion flow along the vertical flow axis in the vessel 11. The electric field has sufficient intensity for resolving substantially the dispersion before it passes from the inlet zone into the outlet zone. The organic phase resolved from the disper: sion is recovered from the outlet zone. As mentioned, the electric field may be provided by energizing the electrode 26 to a sufficient potential that residual dispersed aqueous phase materials are repelled from the outlet zone. The aqueous phase resolved from the dispersion gravitates downwardly in the electric field and is recovered adjacent the inlet zone.

Although a grounded electrode 27 has been described and shown as a metallic foraminous member, it will be apparent to those skilled in the art, that the interface 19 or a grounded distributor, may be employed to serve the purpose of the grounded electrode 27. This arrangement may be advantageous in circumstances as where the dispersion may be a crude oil containing large amounts of sediment, or for other reasons.

The scientific reasons for the highly effective resolution of dispersions in accordance with the present invention is not fully determined. The advantageous electrical resolution appears to reside in the particular configuration of the electric field employed in the region beneath the energized electrode. Resolution of the dispersion requires coalescence of the aqueous phase into sufficiently large droplets that gravitate downwardly against the upflowing dispersion. It is believed that dispersion flowing along a vertical flow axis normal to planes of constant potential produces this advantageous result. The condition of the dispersed aqueous phase in the dispersion represents an energy barrier to coalescence. The electric field supplies a means for overcoming such an energy barrier. Thus, the electric field plays a similar role in coalescing a dispersion as temperature affects chemical reactions. For example, in chemical reactions reagents may be thermodynamically unstable with respect to the products but do not react at an appreciable rate until a certain temperature level is reached. At this temperature, the desired reaction proceeds in the direction required by thermodynamics. In electrically resolving dispersions, the electrical potential is employed in an analogous fashion to temperature in electrically aided coalescence by raising the droplets to a sufiicient energy level so as to allow the coalescence to proceed in the direction required by thermodynamics.

In the specific uniform electric field employed in the present invention, the monitonically increasing electric field provided by planes of constant potential oriented normal to the vertical flow axis of the dispersion produces zones of relatively constant potential having relatively low potential gradients. Thus, one explanation of the exceptionally high resolution of dispersions according to the present invention is that it is the potential level (between these planes of constant potential) which causes resolution of the dispersion. Thus, the electrode 26 would act efiectively as a potential barrier to the passage of small droplets since the rate of coalescence of small droplets to large drops is increased by higher potential levels in the neighborhood of the electrode. The large drops gravitate downwardly to fall into the aqueous phase body 18. As a result, only small amounts of residual dispersed aqueous phase material passes through the electrode 26.

The present invention may employ either alternating or direct current potentials for energizing the electrode 26. Unexpectedly, this invention allows the known beneficial results of DC potentials in electrically resolving distillate-type dispersions to be extended to crude oils. For example, prior art methods for resolving crude oil dispersions alleged that the electric field should be created by alternating current potential. Further, creating the electric field with DC potentials to achieve the same degree of dehydration as the AC potential caused excessive current requirements. However, field testing of the present invention with an experimental treater proved the converse. It was found that crude oil dispersions could be resolved electrically to the same degree of resolution by employing DC potentials instead of AC potentials. Unexpectedly, the current consumption with DC potentials was approximately one-half of that experienced with AC potentials.

Referring now to FIG. 7, there is shown an experimental treater which was taken into an oil field to perform experiments relating to the present invention. The treater was formed of a vessel 69 provided by a steel pipe 71 having approximately a 2 foot exterior diameter and a length of about 9 feet.

Flanges

72 and 73 were secured to the ends of the pipe 71.

Cover plates

74 and 76 were secured to the

flanges

72 and 73 respectively by bolting to form end covers across the vessel 69. The sight glass assembly 77 was secured through the sidewalls of the pipe 71 at a region where the crude oil-water interface 78 was maintained. Water resolved from the crude oil accumulated in the lower portion of the vessel 69 and was removed through an effluent water outlet 79. If desired, water could be removed through a recirculating line 81 and intermixed with the incoming crude oil to form dispersions of increased water content. Treated or dehydrated crude oil was removed from the upper extremity of the vessel 69 through outlet line 82 which connected to a plurality of nozzles passed through the cover 74. Crude oil from a field source was passed into conduit 83, moved through pump 84, and regulated in rate by valve 86 to pass through an inlet distributor 87 which contained a 4-way nozzle assembly 88 that passed the crude oil uniformly into the interior of the vessel 69.

The water outlet 79 contained a valve (not shown) which regulates flow therethrough for maintaining the interface 78 at a relatively constant level in the vessel 69. Also, the crude oil outlet 82 contained a backpressure valve (not shown) for maintaining sufficient pressure to prevent undesired gas release from the crude oil in vessel 69.

An electrode assembly 89 was mounted within the vessel 69 intermediate the distributor 87 and the cover 74. The electrode assembly 89 was formed by a Teflon ring 91 having a width of approximately 6 inches with an internal diameter of about 14 inches. The Teflon ring 91 was sealed exteriorly to the pipe 71 by means of an O ring 92. An insulated feed through bushing 93 passed through the cover 74 and extended downwardly to adjacent the electrode assembly 89. A metal conductor 94 was bolted to a disc-like foraminous steel electrode 96. The electrode 96 extended into a step 97 formed on the Teflon ring 91. The bushing 93 supported the electrode assembly 89 within the vessel 69. A grounded electrode 98 was positioned on top of the Teflon ring 91 by supporting rods 99.

The grounded electrode 98 was formed of a metal disc containing a plurality of openings similar to that of electrode 96. Thus, the electrode assembly 89 had the energized and grounded electrodes mounted in the horizontal and transverse to the vertical flow axis through the treater 69.

The electrode 96 was energized from a. power source 101 which was connected to a suitable source of primary power by conductors 102. The energizing potential was passed through a conductor 103 and entrance bushing 93 to the energized electrode 96. The power supply 101 was arranged to provide a wide variation inpotentials, and either alternating or direct current potentials as was desired. The potentials applied to the electrode 96 and the current it consumed were monitored on the power source 101.

trodes was approximately 5 inches. The electrode assembly 89 was constructed so that the fluid flow along the vertical axis 3 inches above and 3 inches below the energized electrode was confined to a horizontal cross-section of 154 square inches. Within this region, the fluid flow was essentially parallel to the principal direction of the electric field and perpendicular to the planes of constant potential. At typical flow rates of 10.6 barrels per day per square foot of electrode 96 in operating the treater, approximately 12 minutes were required for fluids to traverse the region between

electrodes

96 and 98.

Under substantially equivalent operating conditions, the electrode 96 was energized first with AC potentials and then with DC potentials from the power source 101. Under near identical conditions, the DC potentials achieved the same degree of dehydration of the crude oil as the AC potential but with greatly reduced current requirements. It was unexpectedly found that the current consumption with DC potentials was approximately one-half of that experienced with AC potentials applied to the electrode 96. After the upper portions of the vessel 69 were displaced of the incoming dispersion with dehydrated crude oil, the DC potential applied to electrode 96 began to increase as a result of a higher dielectric constant of the treated crude oil.

The crude oil tested was a 17 APl oil produced by thermal recovery techniques in an East Texas oil field. The crude oil as obtained varied in water content between 40 and 80 percent by volume of intermixed water. An initial phase separation externally of the vessel 69 separated bulk water from the crude oil. The remaining dispersion was heated to above about 180 F. and then supplied to the conduit 83 for the experiment. Samples of treated crude oil were taken from outlet 82 at periodic intervals. The samples were analyzed for the base sediment and water (B S& W) content in volumetric percent. The potentials in kilovolts (KV) and current in milliamperes (MA) applied to electrode 96 were taken at the time each sample of treated crude oil was obtained. The results of this field test are shown in following Table 1.

TABLE 1.--FIELD TEST OF AC AND DC POTENTIALS Comparison of the AC with the DC potential results demonstrates reduced current levels in the DC system as well as the slight decrease in residual water carryover.

From the foregoing, it will be apparent that there has been provided a method well adapted for electrically resolving dispersions into respective aqueous and organic phases. It will be understood that certain features, and alterations, of the method may be employed without departing from the spirit of the present invention. This is contemplated by and is within the scope of the invented claims. Additionally, it is intended that the present description is to be taken as a means of illustration of the present method.

What is claimed is:

1. A method for electrically resolving a dispersion formed of aqueous and organic phases comprising the steps of:

a. passing the dispersion vertically between inlet and outlet zones;

b. establishing an electric field in the dispersion between said zones with monitonic magnitudes of increasing potentials in the direction of fluid flow, said field having planes of constant potential transverse to the direction of dispersion flow, and the electric field having sufficient intensity for resolving the dispersion at least in part as it passes from the inlet zone toward the outlet zone; and c. recovering from the outlet zone the organ c phase resolved from the dispersion in the electric field.

2. The method of claim 1 wherein the electric field increases to a sufficient potential in at least one plane of constant potential while the dispersion flows therethrough to repel at least partof residual dispersed aqueous phase from the outlet zone in a direction toward the inlet zone. 7

3. The method of claim 1 wherein the aqueous phase resolved from the dispersion gravitates downward in the electric field and is recovered adjacent the inlet zone.

4. The method of claim 1 wherein the electric field is produced by DC current flow in the dispersion. l

5. The method of claim 1 wherein each increase in potential produces a proportional increase in current conducted through said dispersion within said electric field.

6. The method of claim 1 wherein each increase in potential produces a proportional increase in current conducted through said dispersion within said electric field until the critical voltage of the dispersion is reached and excessive current flows result.

7. The method of claim 1 wherein said electric field is established by a voltage below the critical voltage of said dispersion whereby excessive current flows would result.

8. The method of claim 1 wherein the electric field is bounded in a horizontal zone by an insulating barrier within metallic walls, and said barrier has a thickness 1 and a specific resistivity R said barrier being spaced from said metallic walls a distance I the fluid to be treated providing a resistivity R resulting from proportionate changes in current flow with voltage creating said electric field and said voltage being below the critical voltage value thereof, the fluid having a I specific resistivity R, whereby excessive current flows when:

R l R; and

said insulating barrier extending vertically above and below the peripheral edge of said electric field a sufficient distance that the shortest line-of-sight path 1 produces the relation- 9. The method of claim 1 wherein said electric field has planes of constant potential transverse to the direction of

Claims

2. The method of claim 1 wherein the electric field increases to a sufficient potential in at least one plane of constant potential while the dispersion flows therethrough to repel at least part of residual dispersed aqueous phase from the outlet zone in a direction toward the inlet zone.
3. The method of claim 1 wherein the aqueous phase resolved from the dispersion gravitates downward in the electric field and is recovered adjacent the inlet zone.
4. The method of claim 1 wherein the electric field is produced by DC current flow in the dispersion.
5. The method of claim 1 wherein each increase in potential produces a proportional increase in current conducted through said dispersion within said electric field.
6. The method of claim 1 wherein each increase in potential produces a proportional increase in current conducted through said dispersion within said electric field until the critical voltage of the dispersion is reached and excessive current flows result.
7. The method of claim 1 wherein said electric field is established by a voltage below the critical voltage of said dispersion whereby excessive current flows would result.
8. The method of claim 1 wherein the electric field is bounded in a horizontal zone by an insulating barrier within metallic walls, and said barrier has a thickness 1s and a specific resistivity Rs, said barrier being spaced from said metallic walls a distance 1w, the fluid to be treated providing a resistivity R resulting from proportionate changes in current flow with voltage creating said electric field and said voltage being below the critical voltage value thereof, the fluid having a specific resistivity Ro whereby excessive current flows when: Ro.1w < R; and said insulating barrier extending vertically above and below the peripheral edge of said electric field a sufficient distance that the shortest line-of-sight path 12 produces the relationships: Rs.1s + Ro (1w - 1s) > or = R; and Ro.12 > or = R.
9. The method of claim 1 wherein said electric field has planes of constant potential transverse to the direction of dispersion flow and extending substantially across the entire vertical flow of the dispersion.
10. The method of claim 9 wherein any dispersion flow not passing directly through the planes of constant potential must traverse lines of force nearly twice the force lines in the planes of constant potential.