US3532614A - Method and apparatus for the electric treatment of dispersions - Google Patents

Description

United States Patent O M 3,532,614 METHOD AND APPARATUS FOR THE ELECTRIC TREATMENT OF DISPERSIONS William L. Shirley, Houston, Tex., assignor to Petrolite Corporation, St. Louis, Mo., a corporation of Delaware Filed Apr. 3, 1968, Ser. No. 718,484 Int. Cl. B03c 5/00; B01tl 13/02 U.S. Cl. 204-191 6 Claims ABSTRACT OF THE DISCLOSURE Dispersions are electrically treated and their constituent phases separated by applying an uninterrupted high unidirectional potential to the electrodes for a normal period of dispersion treatment. Such treatment is interrupted only during periods of increased conductivity in the interelectrode space, when there is applied to the electrodes a series of short unidirectional pulses. A spark gap in a conducting state can interconnect the unidirectional source and the energized electrode of the treater to supply the uninterrupted potential for normal treatment. During periods of high conductivity the gap sputters in coaction with other elements in the circuit to deliver a pulsed potential to the treater.

BACKGROUND OF THE INVENTION This invention relates to the electric treatment of dispersions of relatively high electrical resistivity as compared with dispersions of extremely high electrical resistivity. The invention is particularly concerned with the treatment of dispersions of exotic liquids in which the continuous phase is a liquid other than petroleum or a petroleum distillate. Such dispersions are encountered in chemical synthesizing processes. They are dispersions in which the external or continuous phase is a liquid of relatively high electrical resistivity with the internal or dispersed phase being of different composition and density. The internal or dispersed phase comprises a liquid immiscible with and finely dispersed in the externalphase liquid. A small amount of solids may or may not be present either dispersed in the external-phase liquid or in the droplets of the internal-phase liquid.

It is known that crude oil emulsions can be resolved by subjection to high-voltage alternating-current electric fields. It is also known that some dispersions of very high resistivity, e.g. dispersions of petroleum distillates, can be continuously resolved in an electric treater between electrodes energized by a high-voltage source of unidirectional potential that is continually connected to the elec-' trodes of the treater to maintain therebetween electrostatic fields capable of treating the dispersion during continued supply thereof to the interelectrode treating space.

It has previously been proposed to dehydrate crude oil emulsions by supplying to the electrodes of an electric dehydrator an alternating-current potential that is less than the output potential of the high-voltage step-up transformer that is used. The reduced potential is the result of a voltage-dropping impedance connected serially between the transformer and the dehydrator. It has been proposed to bring the electrode voltage up to the output potential of the transformer periodically. In Fisher 1,864,722 this is done by a rotary switch which increases the electrode potential each half cycle of the AC. wave, producing a peaked wave form, occurring at a frequency of 120 times per second when using a standard 60-cycle A.C. supply. In Fisher 1,864,723 the electrode potential is increased to that of the transformer by a spark gap across the voltage-dropping impedance, the spark gap 3,532,614 Patented Oct. 6, 1970 being normally nonconductive and becoming conductive only when increased current to the electrodes builds up a voltage drop across the impedance equal to the breakdown voltage of the gap. This effects a peaking of the electrode potential in each of a succeeding series of half cycles, each second long, until the electrode current decreases and the voltage across the impedance drops to a value such that the arc is no longer maintained, after which the normal reduced-voltage potential is reapplied to the electrodes. The objective of Fisher 1,864,723 is to apply a normal A.C. potential (actually a reduced potential as compared with the output voltage of the transformer) and peak the voltage wave when electricallyagglomerated water masses line up between the electrodes to form highly-conductive chains in the treating space of the dehydrator, the peak voltage wave being applied in a series of half cycles until the chains are disrupted. Such a system has not found commercial acceptance. It is wasteful of electrical energy, requires a transformer of unusually high output voltage exceeding the voltage of the desired peaks, involves the extra expense of a voltagedropping impedance, and has been found commercially unsuitable in the art.

The patent to Heinrich et al. 2,000,017 proposes the electrostatic cleaning of fluids that tend to short-circuit the electrodes before an eifectively high potential can be applied therebetween. Treatment is by regular and continued application of high-frequency unidirectional pulses to the electrodes, the pulses being of a length of 10- seconds and being uniformly and continually repeated at intervals of 10- seconds. A spark gap is used in conjunction with impedance elements that are in series and in parallel therewith, the gap becoming conductive at intervals of 10* seconds to supply to the electrodes high-frequency pulses derived from energy stored in condensers. Alternatively the gap can be a part of a rotary switch acting in sequence to charge a large condenser, discharge it to a smaller condenser and connect the latter to discharge to the electrodes to supply the treating energy. In Heinrich et al. 2,000,018 emulsions are similarly treated by high-frequency pulses of a duration of 10- or 10' seconds separated by time intervals at least ten times as long to provide relatively long periods of rest between the extremely short pulses during which no potential is applied to the electrodes. In no instance in either Heinrich patent is the unidirectional source connected directly to the electrodes solely through a spark gap, nor is there any normal treatment with an uninterrupted unidirectional potential followed by a period of pulsing. The high-frequency treatment of these patents has not solved the problems existing in the art of resolving liquid dispersions and has not met with any significant commercial acceptance in that art.

SUMMARY OF THE INVENTION The present invention relates to electric treatment of certain dispersions that are not electrically treatable between electrodes energized by an uninterrupted highvoltage unidirectional potential because of a tendency to produce in the interelectrode space during such electric treatment a system that progressively increases in conductivity. The dispersions of the invention are of diiferent character than those heretofore known as capable of resolution by the aforesaid methods of the prior art. They often diifer from the latter in being of somewhat lower resistivity, being therefore sometimes referred to hereinafter as dispersions of medium resistivity. They respond only temporarily to treatment by uninterrupted highvoltage unidirectional potentials applied to the electrodes, being of a character to produce in the interelectrode space a system of increasing conductivity that causes the treater to bog down and become totally inoperative until it is 3 dained or other measures taken to remove it from the flow line and effect treatment of its contents. Resistivities of such dispersions will normally be in the range of about to 10 ohm cms., more commonly in the range of about 10 to 10 ohm cms.

While the invention can be applied to the treatment of various dispersions of the above type it is particularly applicable to the treatment of dispersions of exotic liquids in which the continuous phase is a liquid other than petroleum or a petroleum distillate. Such dispersions are encountered in chemical synthesizing processes. The external or continuous phase may be a chemical substance of relatively high electrical resistivity, with the internal or dispersed phase being of a different composition and density. The internal or dispersed phase comprises a liquid immiscible with and finely dispersed in the external-phase liquid. A small amount of solids may or may not be present either dispersed in the external-phase liquid or in the droplets of the internal-phase liquid.

The invention relates in general to a method and apparatus whereby the normal treatment of the dispersion by an uninterrupted high unidirectional potential is continued for a significant period of time but is stopped before the treater bogs down. The potential applied to the electrodes is then pulsed until the conductivity of the dispersion between the electrodes is reduced, whereupon the normal uninterrupted unidirectional potential is reapplied to the electrodes for a further significant period of time. In this respect the invention involves no peaking of any existing potential but rather the continued application of a high unidirectional potential to the electrodes, substantially equal to the output voltage of the source, for a prolonged time during which normal treatment will be effected, followed by a rapid pulsing of the potential applied to the electrodes of the treater, usually for a shorter period of time. This pulsing occurs only if and when the conductivity in the treating space increases to a point where the desired treating action from the normal unidirectional potential ceases. The pulsing effects treatment of the dispersion constituents in such increased-conductivity state. It is continued only during a corrective period ending when the conductivity of the interelectrode system is decreased to the point where treating action from the normal unidirectional potential is again effective. It is an object of the invention to provide a method and apparatus operating in this way.

In the preferred embodiment of the invention a spark gap is connected serially between the source of unidirectional potential and the treating electrodes. The spark gap is set or controlled so that it remains conductive during normal operation of the treater and becomes transiently nonconductive upon an increase in current to the electrodes above a predetermined value. When the gap becomes nonconductive, the invention contemplates the generation of pulses that will be delivered to the treating electrodes and that will effect treatment of the moreconductive system then present therebetween. The pulsing will be continued until the adverse condition in the interelectrode treating space has been cleared, whereupon the normal uninterrupted unidirectional potential of the source will again be applied to the electrodes and normal treating resumed.

Using such a spark gap, the normal treating condition will be evidenced by a corona-like glow between the electrodes of the gap, producing no more than a slight continuous sound. However a rapid stuttering of the gap will evidence the production of the pulses while return of the gap to its normal conductive condition will evidence reapplication of the uninterrupted unidirectional potential to the electrodes and the return of the treater to normal operation.

It is an object of the invention to resolve dispersions by unidirectional potentials in the above manner and to shift from one mode of operation to another only as required for effective treatment. A further object of the invention is to provide apparatus and circuitry that will automatically shift from one normal mode of operation to the pulsed operation to clear an adverse condition and later return automatically to the normal operation. Further objects and advantages of the invention will be evident to those skilled in the art from the following descrip tion of exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 exemplifies a simple circuit that can be used to practice the invention.

FIG. 2 exemplifies a typical drooping. characteristic curve of the high-potential source of FIG. 1; and

FIG. 3 is a time-voltage curve illustrating approximately the variations in voltage and current applied to the electrodes during treatment in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS SHOWN In FIG. 1 is illustrated a high-voltage source of unidirectional potential 10 including a full wave rectifier circuit 11 with its input terminals connected across the high-voltage winding of a transformer 12. With the spark gap system to be described, the source 10 should have a drooping characteristic, providing an output voltage that progressively decreases with increased current. This type of characteristic is preferably obtained by use of a highreactance transformer with the high reactance being the result of internal design or the presence of a reactor in the primary circuit, the secondary of the transformer being connected to the rectifier circuit 11 to provide the desired source of high-voltage unidirectional potential of the above character. FIG. 2 illustrates a typical characteristic curve with the ordinate E representing output voltage and the abscissa I representing output current. The output voltage drops progressively as the current increases.

One output terminal 15 of the rectifier 11 is grounded or otherwise connected to one electrode of an electric treater 17, shown merely diagrammatically as including a grounded container 18 acting as one electrode, with a cylindrical energized electrode 20 therein and insulated therefrom, providing an interelectrode treating space 22 therebetween. In practice a treater with multiple electrodes and multiple treating spaces will be used, such as the treater shown in Pats. Nos. 2,855,356, 2,976,228, 3,205,- 160, 3,205,161, etc.

As diagrammatically shown in FIG. 1, the dispersion to be treated is pressured by a pump 24 and supplied through a pipe 25 to a distributor 26. The treated externalphase liquid, containing little or no internal-phase liquid dispersed therein, is withdrawn at 27 from an upper position. The internal-phase liquid that has been coalesced by the electric action and separated in the treater is withdrawn therefrom at 29 in well-known manner. The dispersion that is actually treated is sometimes synthesized by pumping water or other aqueous material into the stream advancing inside the pipe 25, using a pump 30 for this purpose and using a valve 31 or other mixing means to mix the two streams intimately and form the dispersion that is to be treated.

As exemplified in FIG. 1, the high-voltage terminal 33 of the rectifier 11 is connected through a spark gap 35 having gap electrodes 35 and 35" to a lead 36 that traverses a bushing 37 and is connected to the energized electrode or electrodes of the treater 17. In the preferred practice of the invention the connection between the spark gap electrode 35" and the treater is exclusively through the lead 36 with no auxiliary circuitry on the treater side of the gap that would modify the wave form to be later discussed. Stated otherwise, the gap electrode 35 is preferably directly connected to the electrode 17 of the treater to maintain the potential of the latter the same as the potential of the gap electrode 35" at all times. A storage capacitor 40 is employed on the source side of the gap for a purpose to be disclosed. This capacitor 40 will usually be across the high-voltage terminals of the rectifier '11 and is shown as being connected between the high-voltage lead to the gap and ground. The setting of the gap 35 is critical in the practice of the invention and some means is preferably provided for adjusting the spacing between the gap electrodes 35', 35 to vary the gap therebetween, such means being suggested by the double-headed arrow 42.

FIG. 3 suggests the voltage and current relationships when the treater is operated in accordance with the present invention. The voltage E applied to the electrodes is suggested by the heavy full-line curve while the current I to the electrodes is suggested by the heavy dotted-line curve. Both are plotted in the ordinate direction, against time plotted in the abscissa direction. Breaks in the curves indicate times in the normal operation period and/or in the corrective period during which conditions preceding the break are continued.

If the treater were to be energized directly from the source 10, without the gap 35 and the capacitor 40, the voltage and current curves following initial energization would be more or less as shown at the extreme left in FIG. 3. If the treater was loaded at the time of such energization the voltage B would rise slowly as shown by the dashed voltage line 45 while the current would rise instantaneously and drop back to a relatively stable value as suggested by the dashed line 46. As the treater clears, the voltage E would rise to some steady-state normaltreating voltage 50 and the current would decrease to a relatively stable value indicated at 52. If the treater was clear when first energized, the voltage would rise abruptly to 50 and the current would rise abruptly to 52.

With those dispersions that can be successfully treated under equilibrium conditions and during continued supply of the dispersion to the treater for a matter of days or weeks, these stable conditions of voltage and current can be maintained indefinitely. However with those mediumresistivity dispersions with which the invention is concerned this relatively stable treatment would continue only for some significant period of time, usually above seconds and often measurable in tens of seconds or tens of minutes, but then the system undergoing treatment in the electric field would increase in conductivity and the current would correspondingly increase along the line 53. As a result of the increasing load and the reactance of the source 10, particularly the high reactance transformer 12 forming a part thereof, the output voltage will decrease as suggested at 54. Unless corrective measures are taken, proposed for the first time by the present invention, the treater would bog down and be rendered inoperative.

When the interelectrode current rises to a predetermined value the invention comprehends switching to a different mode of operation during a corrective period, preferably a mode of operation in which the potential is supplied to the treater electrodes in pulses. Such pulses are suited to treat the then-present interelectrode system of higher conductivity to coalesce the dispersed material which then settles from the field and increases the resistivity of the system between the electrodes to such a point that the normal steady-state unidirectional voltage can again be applied for a succeeding period of normal operation. The corrective period is usually of a time duration measured in seconds, tens of seconds or minutes, the time being often only about 1-20% of the duration of the normal operating periods.

With the circuit of FIG. 1 this is accomplished by setting the gap 35 in such relation to the source 11, the condenser 40 and the treater 17 that the gap remains conductive during the significant normal-operation period ending when the current rises to a predetermined value. The gap then begins to stutter, evidencing successive conditions of non-conductivity and conductivity, with the gap-related elements producin ga series of potential pulses that are applied during the corrective period.

The relationships are shown roughly in FIG. 3. Be-

tween the times t and t the source 11 will be charging the capacitor 40 but the potential applied to the treater will be zero until the potential across the gap electrodes 35', 35 reaches a value 56 at which the gap breaks down or becomes conductive. In practice, this conductive state is evidenced by the relatively-quiet corona-like glow between the gap electrodes, which changes to a sputteringtype discharge that continues during the corrective period. At the time t the gap 35 becomes conductive and the voltage and current curves are thereafter approximately as indicated by the heavy lines. There may or may not be a minor transient in the voltage curve 57 as a result of the charge in the capacitor 40 and the sudden breakdown of the gap 35. Any such transient at this time or during other times are not of significance as concerns the general mode of operation of the invention.

As the interelectrode current rises at 53 toward the end of the normal operation period the voltage of the source 11 decreases, as suggested at 54, until the gap 35 becomes non-conductive by a time t when the voltage between the gap electrodes drops to a value insufficient to maintain the gap in conductive condition. This voltage value is somewhat less than the break-down voltage of the gap. The gap 35 is set to become non-conductive at a time, such as t when the current rises to a predetermined value 58.

At t E and I fall rapidly to zero. Between t and t the output voltage of the rectifier 11 is increasing and the voltage applied to the capacitor 40 is correspondingly increasing. By the time t is reached the voltage across the gap electrodes has again built up to the value 56' at which the gap becomes conductive, whereupon the capacitor 40 sends a voltage surge or pulse to the electrodes, suggested at 60. As the conductivity of the interelectrode system has not decreased between t and t and may indeed have increased, there is a current pulse 61 the peak value of which is determined largely by the capacitance of the capacitor 40. The peak value of this pulse is above the predetermined current value 58. The current draws the voltage of the source down until the gap again becomes nonconductive and the current and voltage drop to zero at t The time between t and t, is determined in part by the size of the capacitor 40. The potential pulse between t and t may or may not be modified by transients but the peak value of the main pulse never exceeds the potential of the unidirectional source 10. The treater electrodes remain unenergized between L, and t whereupon conditions between t and are repeated a number of times during the corrective period, effecting treatment of the interelectrode 'system and progressively increasing its resistivity. When its resistivity again becomes high enough that the current pulses do not exceed the value 58 the arc remains conductive and another period of normal operation follows.

It is within the scope of the invention to employ various other means to create pulses at a time in the normal operation period at which the electrode current exceeds the predetermined value, with this pulse treatment being continued until the resistivity of the interelec-.

trode system has increased to a point where the normal steady-state unidirectional potential can be applied during a succeeding period of normal operation.

The invention is applicable to the treatment of a wide variety of dispersions having various continuous-phase liquids but it is particularly applicable to the treatment of dispersions of exotic liquids encountered in chemical synthesizing processes and which require purification or separation of an existing dispersed-phase liquid. The continuous phase of such dispersions is a liquid other than petroleum or a petroleum distillate. For example the invention has been used with success in the separation of an aluminum chloride complex from crude ethyl benzene, in separating a strong caustic from a solution of aniline hydrochloride, in the separation of metals dissolved in 7 a solvent that was the internal phase to be separated from an amine solution, etc.

Exemplary of its use in the treatment of dispersions encountered in chemical synthesizing processes, the invention has been successfully applied to the treatment of an amine solution for separation of beryllium dissolved in a solvent; to the separation of a strong caustic from a solution of aniline hydrochloride for purpose of neutralization; to the treatment of ethyl benzene to separate therefrom a dispersed phase of aluminum chloride complex; etc.

By way of specific example, a stream of crude ethyl benzene (gravity 335 API) was mixed with about .45% by volume of aluminum chloride complex containing about 28% aluminum chloride and about 72% of complexed hydrocarbons and delivered to an electric treater of the type shown in FIG. 1. With an uninterrupted DC. voltage of 5 kv. or 6 kv. applied to the electrodes and with an initial electrode current of about 4 ma. or somewhat more, initial treatment was good, the amount of dispersed complex being reduced from .5% to about .05%. However after a period of normal operation for an unpredictable time, ranging from several minutes up to an hour or more, the electrode current then increased either gradually or fairly rapidly to 15 ma. or more and the treater bogged down. Attempts to substitute an AC. source were not successful as the treater bogged down rapidly. The circuit of FIG. 1 was then substituted with the gap distance set at approximately inch to be conductive when 6 kv. was applied. The arc was steady with occasional stuttering interruptions for short periods of time, indicating that the potential was pulsed when a conductive condition started to develop in the treater. The current drawn was significantly less than during the application of uninterrupted D.C., being in the range of about 5-2.0 ma., and the effectiveness of the separation was improved, the residual amount of dispersed complex being about .02% or slightly more. The treater remained on stream without bog down. An increase of the applied voltage to 8 kv. stopped the stuttering but increased the current and decreased the efiectiveness of the separation. However when the gap was widened with this higher voltage the current was reduced to less than .5 ma. and periods of stuttering were observed, the elfectiveness of treatment being improved.

I claim:

1. A process for treating those dispersions (1) that comprise an external phase of liquid of high resistivity and a dispersed internal phase of liquid immiscible therewith and (2) that tend progressively to produce an interelectrode system of increasing conductivity when treated between electrodes energized by an uniterrupted highvoltage unidirectional potential, said process including the steps of:

disposing such dispersion between such electrodes;

delivering to said electrodes for a significant period of time greater than about ten seconds such uninterrupted high-voltage unidirectional potential, and continuing such uninterrupted delivery of such potential until the interelectrode current rises to a predetermined value as the result of the increased conductivity of the interelectrode system undergoing treatment;

then applying to said electrodes short unidirectional high-voltage pulses during a corrective period ending when the conductivity of the interelectrode system undergoing treatment between the electrodes is reduced, thus completing a cycle beginning at the start of said significant period of time and ending at the end of said corrective period;

then reapplying the uninterrupted high-voltage unidirectional potential to said electrodes for another such significant period of time as the start of the next cycle; and

repeating said cycle.

2. A process as defined in claim 1 in which said dispersion has a resistivity of about 10 to 10 ohm cms., and in which said pulses are applied throughout a corrective period that is of a time duration only about 1-20% of the significant period of time during which said uninterrupted potential is applied to said electrodes.

3. A process for treating dispersions encountered in chemical synthesizing processes that have resistivities of about 10 to 10 ohm cms. and that comprise an external phase liquid other than petroleum or a petroleum distillate with the internal phase of the dispersion comprising droplets of a liquid immiscible with the external phase liquid, which dispersions tend progressively to produce an interelectrode system of increasing conductivity when in a treating space between electrodes energized by an uninterrupted high-voltage unidirectional potential, said process including the steps of:

continuously delivering said dispersion to said treating space;

supplying to said electrode for a significant period of time of at least about ten seconds such uninterrupted high-voltage unidirectional potential and continuing such supply of such potential until the interelectrode current rises to a predetermined value as the result of the increased conductivity of the interelectrode system undergoing treatment;

then applying to said electrodes during a shorter corrective period a series of short unidirectional highvoltage pulses until the conductivity of the interelectrode system undergoing treatment between the electrodes is reduced, thus completing a cycle beginning at the start of said significant period of time and end iug at the end of said corrective period;

then reapplying the uninterrupted high-voltage unidirectional potential to said electrodes for another such significant period of time as the start of the next cyc e;

repeating said cycle during continued delivery of the dispersion to said treating space; and

separating the constituents of the electrically treated dispersion into a treated external-phase liquid contaimng little or no internal-phase liquid dispersed therem and an internal-phase liquid containing little or none of the external-phase liquid.

4. A process as defined in claim 3 in which said uninterrupted high-voltage unidirectional potential is supplied to said electrodes for a significant period of time that is of a duration of at least ten seconds, and in which said potential pulses are applied to said electrodes for a shorter corrective period of time that is of a duration only about 120% of said significant period of time.

5. A process as defined in claim 3 in which the peak potential of said pulses is no more than said high-voltage unidirectional potential applied uninterruptedly to said electrodes during said significant period of time.

6. process for treating those dispersions (1) that comprise an external phase of liquid of high-resistivity and a dispersed internal phase of liquid immiscible therewith and (2) that tend progressively to produce an interelectrode system of increasing conductivity when treated between electrodes energized by an uninterrupted highvoltage unidirectional potential, said process involving the use of a high-voltage unidirectional source of potential having one terminal connected to one electrode and having a high-voltage terminal connected to the other electrode through a spark gap, and :by use of a storage capacitor on the source side of such spark gap connected thereto and to said high-voltage source, which process includes the steps of:

continuously delivering said dispersion to said treating space;

controlling said spark gap to supply said high-voltage unidirectional potential uninterruptedly to said electrodes during a normal treating period terminating only when the interelectrode current rises to a predetermined value as the result of the increased conductivity of the interelectrode system undergoing treatment between the electrodes, said spark gap being controlled to remain conductive during such normal treating period;

controlling said spark gap to become nonconductive when the interelectrode current rises to said predetermined value and to act in conjunction with said storage capacitor to produce during a shorter corrective period a plurality of short unidirectional high-voltage pulses applied to said electrodes, said pulses during said corrective period controlling said spark gap to then return to its conductive condition at the end of said corrective period, thus completing a cycle beginning at the start of said normal treating period and ending at the end of said corrective period and immediately starting another such cycle; and

repeating said cycle during continued delivery of the dispersion to said treating space.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner US. Cl. X.R.

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