US3446724A

US3446724A - Energization of electric emulsion treaters

Info

Publication number: US3446724A
Application number: US474551A
Authority: US
Inventors: Joseph D Winslow Jr; Roy N Lucas
Original assignee: Petrolite Corp
Current assignee: Baker Petrolite LLC
Priority date: 1965-07-26
Filing date: 1965-07-26
Publication date: 1969-05-27
Anticipated expiration: 1986-05-27

Description

Mayu 1969 J. D. wlN'sLow, JR., ETAL 3,446,724

ENERGIZATION 0F `ELECTRC EMULSION THEATERS lFiled July 26. 1965 Sheet 60A/#041.50 CONDUCT/w05 UNIT HRM/G cour/20L.

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JOSEPH D. W/NsLo W, JR., Aoy /V. LUCAS ,sy rma/.e Arma/.ers HABE/s, Mec/,3, RUSSELL #Een May 27,v 1969 J. D. wlNsLow, JR., ETAL 3,446,724

ENERGIZATION OF ELECTRIC EMULSION THEATERS Filed .July 26.l 1965 sheet 2 @f3 CURRENT JM/TEK j l INVENTORS Joss/2H D. l/V/A/.s/ on/,L/R.,

Roy Af. LUCAS BY THE/2 ATTORNEYS HABE/5, Msc/1, Russe/.L KERN CONTRO/ L50 CONDUCTA/ms amr May 27, 1969 J. D. wlNsLow, JR., ETAL 3,446,724

ENERGIZATION OF ELECTRIC EMULSION THEATERS Sheet Filed July 26. 1965 M T.l NK ww e wo 7 5W mL SACHAL w U25 /5 We@ ..7 DMwR HY H., P0 C im J0 m H United States Patent O 3,446,724 ENERGIZATION OF ELECTRIC EMULSION TREATERS Joseph D. Winslow, Jr., Bellaire, and Roy4 N. Lucas, Houston, Tex., assignors to Petrolite Corporation, St. Louis,

Mo., a corporation of Delaware Filed July 26, 1965, Ser. No. 474,551 Int. Cl. B03c 5/00 U.S. Cl. 204-191 23 Claims ABSTRACT F THE DISCLOSURE Method and apparatus for electric treatment of dispersions between electrodes, utilizing an A.C. electric power source and modication of the A.C. wave form, whereby the voltage during an initial portion of a half cycle is substantially zero and then rises substantially instantaneously to a treating value.

This invention relates to the electric treatment and resolution of oil-continuous dispersions to separate particles dispersed in an oil. The oil phase may be a well-produced crude oil, an oil resulting from the processing of tar sands, shale oil or other oil-containing mineral deposits, a distillate or other hydrocarbon. The dispersed phase may be composed of liquid or solid particles or both whether naturally present in or added to an existing oil, the particles being dispersed in the oil in more or less permanent state. The emulsion as electrically treated may contain all of the dispersed particles present when the dispersion was produced or a residual yamount thereof remaining after preliminary settling or other treatment of the dispersion all with or without the presence of dispersed liquid droplets that may have been added lfor one purpose or another. Reference herein to emulsions or dispersions is inclusive of relatively stable or unstable emulsions or dispersions.

Such dispersions are conventionally resolved by a highvoltage alternating-current or direct-current electric field established between electrodes bridged by the dispersion. If the voltage is of suicient magnitude it will coalesce or agglomerate the dispersed particles into masses of sufcient size to gravitate from the oil. In conventional electric treaters such a iield is established by connecting the high-voltage or secondary winding of a transformer or the high-voltage terminal of ya D.C. supply to the electrodes. In an A.C. system, the low-voltage or primary winding of the transformer is connected to a source of alternating potential, such as a power circuit, the wave form of which is a sine wave. The high voltage applied to the electrodes will similarly be of a sine-wave type, either alternating, or unidirectional. A choke coil or other current-limiting voltage-reducing device is connected in the primary circuit to limit the current to the electrodes. However this choke coil or other current-limiting device causes the electrode potential to drop progressively as the electrode current increases, which is undesirable as eifective treatment occurs only above a critical voltage.

Trouble has been experienced in electrically treating dispersions of high electrical conductivity, particularly those dispersions of a conductivity greater than about l0*9 mho/cm. When treating these emulsions the electrode potential never reaches its rated value due to the action of the choke coil. The potential often reaches an intermediate value that is insulicient to cause coalescence or agglomeration of the dispersed particles. Even if the potential rises suiciently to effect some treating of the dispersions the high current costs are disadvantageous and often prohibitive and the heating resulting from higher currents is undesirable.

Current drain starts at the instant the voltage starts to ice rise from zero at the beginning of each half cycle (zero electrical degrees). It continues throughout the rise (090) and the subsequent drop (9D-180) of the voltage in each half cycle.

The invention involves a process and apparatus by which the voltage is held at substantially zero value during an initial portion of each half cycle and is then very suddenly increased to a treating value, after which current drain is permitted during the remainder of the half cycle. Expressed differently, the circuit interconnecting the power source and the treater is switched on or closed at one point in the cycle and is switched off or opened at a later point, typically at the end of a half cycle. The rise in potential is very ra-pid and preferably takes place in a time considerably less than 1/2 millisecond, resulting in a voltage surge of extremely steep wave front.

It appears that electrical treatment as presently understood involves a series of individual coalescing events, with each event being initated or actuated electrically by a pulse or portion of a half wave. It has been determined that a minimum value of applied voltage must be applied for a certain period of time in order to obtain satisfactory treatment. This minimum value of voltage will vary depending upon the equipment utilized, the material being treated, and the results desired, and can be determined by operating a system and reducing the peak voltage until unsatisfactory treating is obtained. This voltage may be referred to as the effective treating voltage. When the yapplied voltage is less than the effective treating voltage, the electric power being consumed is wasted. Also when the effective treating voltage is applied for a time interval longer than the aforesaid period the additional power consumed is wasted. Y,

It has been found that the time interval required for maximum effectiveness is about 10 to about 30 electrical degrees which, for a 60 cycle per second alternating current power source, is about 0.5 to about 1.5 milliseconds. Hence the invention contemplates the control of the time of the voltage rise or turn on point so that a treating voltage will be applied for a predetermined period before the applied potential decreases below the effective value. The surge is desirably timed to occur in the -160 range of each half cycle. Most commonly the surge is timed to occur in the 11G-150 range. In many instances best results both in treating and power saving will be obtained if the timing is in the 1Z0-150 range. The turn on or Voltage surge may be timed to occur prior to the 90 point, but little if any improvement in treating is obtained, while the power consumption is undesirably increased.

That portion of the source voltage wave between the point at which the potential drops `below the effective treating voltage and the end of the half wave at electrical degrees consumes power but does not add to the treating elfectiveness. LHence the duration thereof desirably should be kept at a minimum. This may be accomplished by having the peak value of the unmodified source voltage considerably greater than that required to produce the treating voltage so that the turn on time may be delayed to near the 180 point while still obtaining the treating voltage for the desired period. Typically the unmodified peak value may be about 11/2 to about 21/2 times that necessary to produce the treating voltage, preferably in the order of at least double the value.

By use of the invention it becomes possible to eliminate the current drain from 0 to the instant of the Surge. A corresponding saving in current results. Also it has been unexpectedly found that the current drain during the remainder of the half cycle is substantially less than that which would be expected, i.e., the load impedance is higher with the `delayed conductance operation. For example, with one system operated with the current turned on at the time and then operated with turn on at the 160 time, the load irnpedances were 15,750 ohms and 25,000 ohms, respectively. In another system operated with the current on at and then at 118, the load impedances were 65,500 ohms and 84,300 ohms, respectively. This may be due to the extremely rapid rise in potential when rst applied and to the extremely rapid treatment of the dispersion effected thereby. The extreme steepness of the wave front seems to improve the over-all treatment and the invention makes practical the treatment of some dispersions that heretofore it was not economical to treat because of the high power requirements.

lt has previously been proposed to employ rotary switches, spark gaps, condensers, etc. in the secondary or high-voltage circuit of a transformer connected to the electrodes. Such systems were unsatisfactory and did not produce the wave forms of the present invention. In such prior systems, one or more potential surges were superimposed on or substituted for the normal wave during each half cycle, during some half cycles, or randomly. In the present invention, the complete control is effected on the primary or low-voltage side of the transformer and is made effective on each half cycle of a conventional alterhating-current supply circuit or on alternate half cycles if unidirectional potentials are to be applied to the electrodes. A sine-wave supply is normally used because it is commercially available, but the invention is not limited to this specific wave form.

The invention employs electronic triggering of an A.C. circuit. An electronically-triggered unit, typically some form of conductance switch, is employed to delay conductance to the desired instant. Such a unit may employ thyratron or ignitron tubes or solid state devices such las silicon controlled rectiiers (SCRs). The triggering operation is synchronized with the A.C. supply. The apparatus includes a triggering or ring control circuit connected to the conductance delay unit to supply thereto a signal shifting the unit instantaneously or substantially instantaneously from a non-conducting condition, in which the voltage applied to the primary winding of the transformer is substantially zero, to a conducting condition, in which the then-existing potential of the A.C. circuit is applied suddenly to the transformer primary, with the transformer secondary voltage being applied to the electrodes.

The treating process and apparatus providing for input wave modification with a zero magnitude initial portion may be utilized to provide treatment results similar to that obtained with conventional equipment but with substantially lower power consumption and kv.a. demand. The process and apparatus of the invention may. also be used to provide current control by limiting the load current to a predetermined maximum while maintaining the peak treating voltage over a greater range of operating current than is possible with the conventional choke coil or air gap reactor. In this mode of control, current limiting is obtained by increasing the duration of the zero magnitude initial portion rather than by reducing the magnitude of the applied voltage.

The invention is particularly adapted for use in treating emulsions characterized by high or widely varying conductivity, i.e., systems with large current demands or wide variations in current demand. The heavy crude emulsions ordinarily fall into this category as do the emulsions produced in various processes being used for the recovery of oil from shale, tar sands, etc. Forexample, tar sands, sands impregnated with heavy petroleum, are found in most areas of the world Where petroleum is present such as in France, Poland, Romania, Russia, the Middle and F ar East, and the United States. However, the largest and most important deposits are the Athabasca tar sands found primarily in northern Alberta, Canada.

The Athabasca oil sands in northeastern Alberta contain one of the worlds largest reserves of recoverable oil. The `amount of oil in the formation is estimated to be between 300 billion and 500 billion barrels. Using a conservative estimate for the recovery ratio, there are at least billion barrels of marketable oil reserves.

The oil sand layer averages feet in thickness and is made up of layers of unconsolidated oil bearing sand interspersed with clay, shale, and lignite as well as some rock and boulders. The sand is primarily quartz with varying percentages of silt and clay. The oil saturation in the sand varies from 3 to 18%; sand with oil saturation in excess of 10% is classed as a good grade.

The oil sand overburden, which varies from 0 to 2,000 feet in thickness, dictates the method of oil recovery. With a ratio of oil sand to overburden of 1:1 or greater, some form of open pit mining is the most economical recovery method. With a larger ratio of overburden to sand, in situ recovery methods are required.

In general, the oil found in the formation is a heavy, viscous, low quality hydrocarbon containing about 4% sulfur and about 0.4 nitrogen. The specific gravity varies from about 1.002 to about 1.027, i.e., the API gravity is in the range of about 9 to 6. The viscosity is greater than 3,000 poise at 60 F.

A variety of processes have been proposed for separating the oil from the sand. These various processes produce emulsions which must be broken for ultimate recovery of the oil therefrom. Treatment of many such emulsions in conventional electric treaters, energized by conventional high-voltage sources with current-limiting devices such as a choke coil or reactance, has not been economically feasible. However, electric treating using the process and equipment herein described has been found to be effec-tive in breaking such emulsions and recovering the oil therefrom at greatly reduced power consumption.

The invention is suited for use in breaking emulsions formed by various tar sand recovery processes and in the recovery of oil from oil bearing sands and shale in other parts of the world. The invention is also suited for the recovery of oil from very heavy crudes produced from wells by conventional procedures that result in products that require demulsitication.

In recovering oil from sands it is not uncommon to encounter tar-like products that are emulsified with relatively large amounts of water and that often contain small 'amounts of clay and sand. If such systems are diluted by use of a hydrocarbon solvent, eg., naphtha, and decanted, the supernatant oil, sometimes further diluted, often contains in the neighborhood of 20% water. Such an emulsion, with or without the addition of a conditioning chemical, can be fed to an electric treater incorporating the invention and can be resolved therein better and cheaper. The emulsion is usually heated to a temperature of about 250 F. and -is satisfactorily treated `at a peak voltage gradient in the neighborhood of about 6 kv./in. to accomplish treatment and phase separation. The oil effluent is then flashed for recovery of the naphtha diluent. The resultant oil has a water content of about 1% BS and W.

It is an object of the invention to provide an electric emulsion treater having a high-voltage stepup transformer with a primary and a secondary, a container for fluid to be treated and including lan inlet and upper and lower outlets for fluid flow therethrough, electrodes mounted within said container in spaced relation for fluid flow therebetween, rst circuit means for connecting the secondary of the transformer to the electrodes to apply a high electrical potential between the electrodes, A.C. power source terminals, and second circuit means for connecting the source terminals to the transformer primary and including means for modifying the output wave of the A.C. source to make an initial portion 0f a half cycle substantially zero followed by a substantially instantaneous rise from the zero condition to the normal output wave condition.

It is an object of the invention to provide such a treater incorporating control means for varying the duration of the initial portion of a half cycle. A further object is to provide such a treater in which the duration of the initial portion may be varied manually or many be varied automatically in response to a -load signal. An additional object is to provide such a treater including means for setting the duration of the initial portion of a half cycle at a first value land means for progressively increasing the duration of such initial portion from the first value to substantially the entire half cycle as the load current of the treater increases from a first predetermined value to a second greater value for maintaining the maximum treating voltage while limiting the current to a rated maximum value. An object is to provide such a treater including means for disconnecting the source terminals from the transformer primary at predetermined times.

It is an object of the invention to provide a process for electrically treating dispersions between the electrodes characterized by applying to the electrodes a high-voltage potential applied in pulses, with each pulse being of a Wave form in which the potential is substantially zero during an initial portion of the pulse 'and rises substantially instantaneously to a high value and thereafter follows substantially a sine wave in decreasing to zero during the remainder of the pulse. A further object is to provide such a process in which the duration of the zero portion of the pulse is varied as a function of the load current with the duration increasing as the load current increases. A specific object is to provide such a. process including the step of controlling the input to the primary winding of the high-voltage stepup transformer, with the secondary winding providing the high voltage for the treating electrodes.

It is an object of the invention to provide such a process for electrically treating dispersions between electrodes which provides treatment with Ia marked reduction in power consumption. A further object is to provide a process in which the applied voltage is maintained above the effective treating voltage for a controlled relatively short period of time. An additional object is to provide a process in which the peak value of the source voltage is considerably greater than that required to produce the effective treating voltage so that the on time may be very near the end of the half Wave.

The invention also comprises novel steps and novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description. The drawings merely show and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.

In the drawings:

FIG. 1 is a diagram illustrating a preferred form of the apparatus of the invention,

FIG. 2 is an electrical schematic of one embodiment suitable for the rectifier firing control and the current limiter of FIG. l;

FIG. 3 is a graph illustrating the operation of one embodiment of the invention;

FIG. 4 is a diagram illustrating electrical wave forms; and

FIG. 5 is a graph illustrating the control characteristics of the equipment of FIG. 2.

Referring to the embodiment of FIG. 1, an electric treater is energized from an A.C. power source via a high-voltage stepup transformer 11 which typically may have a primary rated at 440 volts and a secondary rated at 16,500 volts. The construction of the treater itself is not critical to the invention and any conventional emulsion-.breaking electric treater may be utilized. A typical treater is illustrated incorporating an upright cylindrical container 12 closed at both ends. A set of foraminous electrodes is disposed in a horizontal pattern Within the container, including an electrode 13 connected to one side of the secondary winding of the transformer 11 via a conductor 14, a feedthrough or inlet bushing 15 and another conductor 16. In a D.C. treater a rectifier (not shown) may be connected between the transformer secondary and the feedthrough 15. Another foraminous electrode 17 is disposed above the electrode 13 and may be grounded. In operation the treater contains superimposed bodies of oil and separated water in which event the water at and `below the interfacial zone 18 may act as another grounded electrode. The container 12 and the other terminal of the transformer secondary winding are connected to ground, and the container itself may act as a grounded electrode.

The oil to be treated is pressured by a pump 20. In some instances a supplementary liquid is desirably mixed therewith and Conditioning chemicals may also be added to the material to be treated. A small amount of water or other liquid may be introduced from a line 21 in an amount controlled by a pump 22. A conditioning chemical may be introduced from a line 23 in an amount controlled by a pump 24. A mixing device 25 may be provided in the line to mix the various streams and the mixed emulsion is discharged into the container 12 through a nozzle 26 directed upward against a baffle 27. The treated oil leaves the container through a line 28 and water or other material coalesced by the electric field and separated from the oil leaves through a line 29. Reference may be made to U.S. Patents Nos. 2,182,145 and 2,880,158 for a more detailed description of the construction and operation of an electric emulsion treater.

The desired modification of the output wave of the A.C. source (typically a sine wave) may be obtained by introducing a controlled conductance unit 3S in the circuit bet-Ween the A.C. source and the primary of the transformer 11. The controlled conductance unit 35 differs -from a rectifier in that the conduction thereof is not controlled by the voltage developed across the anode and cathode but rather by an additional control element which permits maintaining the unit in a nonconducting condition for any desired period of time. A variety of components are presently available for use in the controlled conductance unit, which may be a half Wave or a full wave device. Suitable components include thyratrons, ignitrons, silicon controlled rectifiers, blocking bridge connected rectifiers with a silicon controlled rectifier gate, and the. like.

The controlled conductance unit 35 functions in the nature of a switch for connecting and disconnecting the A.C. line to and from the transformer primary. The line is open with the unit not conducting until a triggering or ring or gating signal is applied to the unit, at which time the unit goes into conduction, connecting the A.C. line to the transformer primary with very little loss. At a later point in time the conductance unit again becomes nonconducting, such as by a reversal of polarity thereacross as the output wave from the source goes through zero. By this means, the initial portion of a half cycle of the output wave from the source may be blocked from the transformer primary and thereby made zero by delaying the generation and/or coupling ofa firing voltage to the conductance unit.

The firing voltage is provided by a firing control 36 which typically is some form of magnetic amplifier circuit that provides a firing signal for each half cycle. The firing control will usually include means for adjusting the duration of the time delay, permitting setting of the delay to any'desired value. A manually adjustable setting device may be utilized or an automatic setting device may be employed. In the embodiment illustrated, a current limiter 37 functions as the automatic setting device for varying the duration of the initial zero portion of the half cycle. A current transformer 38 provides a signal to the current limiter which varies as a function of the load current to the treater. The current limiter provides an output which varies inversely as a function of the load current signal @for varying the time delay in the firing control to thereby limit the r.m.s. or peak load current to a predetermined maximum value.

Examples of specific circuits for the firing control 36 and the current limiter 37 are shown in FIG. 2. Of course, a wide range of electronic circuitry can be utilized for performing the functions of these two components and the circuits described should be considered illustrative of the type of component which can perform the desired function.

The controlled conductance unit 35 comprises two silicon controlled rectifiers 40, 41 which are connected in inverse parallel. The conductance unit connects the A.C. line to the load by synchronously connecting the line to the load within each half cycle of line frequency and disconnecting the line and load at the end of a half cycle. A silicon controlled rectifier is a solid state three-element device having an anode, a cathode and a gate or control element. When the anode is positive with respect to the cathode, the SCR can be switched into conduction by a positive voltage signal applied to the gate, indicated at 44 for SCR 40 and at `45 for SCR 41.

High voltage transient protection is provided by a first pair 42 of selenium rectiiiers connected head to head across the A.C. line and a second pair 43 of selenium rectiiers connected head to head across the transformer primary. If the voltage across a rectifier pair exceeds the reverse breakdown rating, the rectifier pair effectively shorts out the source of the transient voltage until that voltage passes through the zero value. On the `following cycle, the rectifier pair again effectively blocks.

The iiring control 36 provides the gate or trigger voltages for firing the SCRs into conduction. The ring control illustrated herein is a magnetic amplidier circuit which operates in synchronism with the line frequency and provides a trigger voltage each half cycle of the line frequency. The time of occurrence of the trigger voltage with respect to the zero value time of the line voltage is controllable and permits variation of the delay in Ifiring the controlled conductance unit or, stated differently, variation of the duration of the zero initial portion. The control voltage for the SCR 40 is developed across resistor 50 and the control voltage for the SCR 41 is developed across resistor 51.

The specific firing control circuit shown in FdG. 2 incorporates saturable core toroid transformers 52, 53 to form a magnetic multivibrator mode of operation with the frequency of operation controlled by the frequency of the excitation on the primary of the power supply transformer 54. The circuits associated with the transformers 52, 53 are identical, operating 180 out of phase #with each other, and only one will be described in detail. The duration of the delay is controlled by the magnitude of the currents in the reset winding 55 and the control winding 56 of the transformer '52.

The core of the transformer 52 has a hysteresis curve which is essentially square and which will oppose a change in the polarity of the residual magnetism until the product of time and polarizing current attains a certain magnitude. At this point, the polarity of the core will instantaneously flip or change, causing a sudden drop in the high impedance initially presented to the repolarizing or setting current. The magnitude of the setting current required to flip the core again is proportional to the iiux density of its residual magnetism, which in turn is proportional to the magnitude of the current used tov drive the core back to its initial or reset condition.

A core is set during the positive half cycle of line current (as determined with respect to the anode voltage of its associated SOR) and reset during the negative half cycle.

The transformer `54 is a conventional voltage transformer with the primary excited from the line voltage and with each of the

secondary windings

58, 59, 60 providing a low voltage, typically r9 volts. A potentiometer 61 is connected across the winding 59 with a resistor 62 connected between one terminal and the arm of the potentiometer. As the voltage on the dot terminals of the secondary windings of the transformer 54 swings negative,

current flows through diode 65, which is now forward biased by the polarity of the voltage, while current is blocked by the diode 66, which is reverse biased. There is current flow through the reset winding 55 of the transformer 52 and through resistor 67 and potentiometer 68, with the magnitude of current dependent upon the settings of the potentiometer 61 and the potentiometer 68. The potentiometer 68 provides an adjustment for balancing out differences between the transformers 52, S3 and their associated rectiiiers while the resistor 67 functions as a current limiting resistor. A capacitor 69 may be connected across the resistor 67 and potentiometer 68 for the purpose of smoothing the reset time current. With the potentiometer `6,1 positioned at its upper or maximum voltage setting, maximum reset, current flows in the reset winding 55.

The winding 58 of the transformer 54 is connected across the resistor 50, rectifier 72, and gate winding 73 of the transformer 52.

With the voltage at the dot terminal of the winding 58 negative, the diode 72 is reverse biased and no current can iiow in the gate winding 7'3. This permits the reset flux density of the core to be controlled only by the current in the reset winding 55 and in the control winding S6. The magnitude of current in the reset Winding 55 is controlled by manually setting the potentiometer 61. The current in the winding 56 may be provided from an external source, such as the current limiter 37 and is of a polarity to oppose the current in the winding 5S, causing a cancellation of the eiectiveness of the reset current in proportion to the magnitude of the control current in the 'winding 56. Hence a change in the magnitude of the control current in the winding 56 is effectively the same as a change in the current in the reset winding 55, so that the manual control and the external control have the same effect. For a system utilizing manual control only, the winding 56 may be omitted.

At the end of the reset half cycle, the magnitude of the reset ux density in the core 5-2 will be proportional to the amount of net current in the reset and control windings `55, `56. The time-magnitude of the setting current now required to iiip the core is proportional to this residual ux density.

In the next half cycle of the line voltage, as the voltage on the dot terminals of the transformer 54 swings positive, the diode 65 reverse biases, blocking current through the reset winding y55. The diode 712 is now forward biased. The core 52 is still in the reset state and the impedance of the gate winding 73 is very high with respect to that of the resistor 50. lHence the voltage supplied by the winding 58 is primarily dropped across the Winding 73. The reset flux in the core 52 will be overcome by the gating current in the winding 73 at some point in time during the tiring half cycle. At this time, the core suddenly saturates, dropping the impedance of the gate winding 73 to a very low level such that the voltage from the winding 58 is now primarily dropped across the resistor `50. At this point in time, the conditions required to iire the silicon controlled rectifier are satisiied--a voltage of the proper magnitude and polarity is applied across the resistor 50 connected in parallel with the gate and cathode of the SCR 40, with the anode of the SCR positive with respect to its cathodeand SCR is turned on.

A network consisting of a rectiiier a resistor 81 and a capacitor 82 functions to prevent gating signals from appearing across the resistor 50 when the tiring control unit is initially energized, since the residual magnetism of the toroid core may be low. The resistor 81 bleeds the capacitor 82 to reset the guarding function when the transformer '54 is deenergized. A resistor 83 and a diode 84 serve to maintain the energy level of the capacitor 82 during normal operation so that the gate signal is not diminished and so that there is no delay in gate signal generation when the net reset current time-magnitude is reduced.

In operation, the SCR is red into conduction during the properly phased half cycle of the line voltage at a point in time when a constant value half wave gating current overcomes the variable density of residual reset ux in a saturable core transformer. The reset flux density is a function of the magnitude of the reset current minus the magnitude of the opposing control current. The reset flux density may be varied to cause the SCR to be fired at any given time within its enabling half cycle of line voltage. In this mode of operation, r.m.s. voltage delivered to a load may be vaired from zero to substantially full line value. At the same time, the maximum voltage available is being utilized when the conductance unit is conducting. When operating under manual control, the potentiometer 61 may be utilized to determine the duration of the delay in firing. or duration of the initial zero portion of the half cycle. When operating under remote or automatic control with a current in the control winding 56, the potentiometer 61 may be set to provde a reset current which in the absence of current in the control winding 56 will maintain the conductance unit off throughout the entire conduction half cycle.

The current limiter 37 provides a controlled current to the firing control 36, with the controlled current varying as a function of the load current to the treater.

A power supply is incorporated in the current limiter and comprises a transformer 100 having its primary connected to the A.C. line source and its secondary connected across a rectifier unit 101. The power supply includes a filter capacitor 102 and a voltage regulator comprising a resistor 103 and a Zener diode 104, providing a controlled voltage of 4.7 volts on the line 105 and a higher unregulated voltage on line 106.

The load current signal from the current transformer 38 is connected to the primary winding of a stepup transformer 110 across a resistor 111, with the secondary of the transformer connected across a full wave rectifier 112 providing a D.C. voltage varying as a function of the load current.

The current limiter provides the current for the control winding 56 of the transformer 52 and the corresponding control Winding of the transformer 53 for shortening the delay period in the firing of the rectifier unit. The control current s provided by a transistor 115 through the control windings and a resistor 116. The base of transistor 115 is connected to the line 105 and the emitter is connected to the negative supply line 117 through resistors 118, 119. The current in the transistor 115 is set by a potentiometer 120 connected in series with a resistor 121, with the potentiometer arm connected through a transistor 122 to the junction point of resistors 118, 119, with the transistor 122 functioning as an emitter follower.

Ignoring for the moment the transistor 125, the control current through the transistor 115 is of a magnitude to provide a voltage drop across the resistors 118, 119 equal to the voltage across lines 105, 117, i.e., to 'bring the base and emitter of the transistor to the same point. The resistor 116 serves to increase the ratio of control winding resistance to inductance in order to increase the response time. In the particular circuit illustrated, the control winding D.C. resistance is about 200 ohms. When the base of transistor 122 is set to the top or high-voltage end of the potentiometer 120, there is no current in the transistor 115. Similarly when the base of the transistor 122 is set to the low-voltage end of the potentiometer 120, there is a maximum control current in the transistor 122 which normally is selected to counteract fully the reset current and provide conductance unit conduction throughout the conducting half cycle. By this means the potentiometer 120 provides for a manual setting of the minimum value of the delay.

This control current produced by the transistor 115 at a preset magnitude determined by the potentiometer 120 10 remains constant until reduced by action of the transistor 125.

The load current signal from the current transformer is developed across resistor 130 and capacitor 131, with one terminal of the resistor 130 connected to the base of the transistor through resistor 132 and Awith the other end of the resistor connected to the arm of a potentiometer 133 which in turn is connected across the lines 105, 117. The resistor 130 permits the charge of capacitor 131 to be dissipated when the load current signal decreases. The voltage across the capacitor 131 is maintained at a predetermined level by rectifier 136 and the setting of the potentiometer 133. When the load current signal is below the level set by the potentiometer 133, the capacitor 131 and the base of the transistor 125 are at the same level -as the base of the transistor 115. Under these conditions there is no voltage across the adjustable resistor 137 connected between the emitters of

transistors

125 and 115 and hence no current through the resistor 137.

When the load current signal voltage across the resistor 130 exceeds the preset value determined by the potentiometer 133, the capacitor 131 charges, the rectifier 136 is blocked, and the base of the transistor 125 is raised above the base of the transistor 115. Under these conditions a current flows in the resistors 137, 118, 119, with the current proportional to the voltage difference of the bases of the two transistors and with the proportionality factor determined by the setting of the adjustable resistor 137. The additional current in resistors 118, 119 tends to raise the voltage of the emitter of transistor 115 and consequently the transistor does not conduct as much as before and may be completely turned off, reducing or cutting off completely the control current.

A switch 138 provides for manual connection of the line 106 to the resistor 130 through a resistor 139. This is a manual overide switch which places an excess high voltage on the capacitor 131 producing conduction in the transistor 125 land completely cutting off conduction in the transistor 115.

In operation, the control current in the transistor 115 remains at the preset level determined by the setting of the potentiometer 120 until the line current exceeds a preset level determined by the setting of the potentiometer 133. As the line current increases above the predetermined value, the control current reduces linearly to zero at a rate determined by the setting of the resistor 137.

The controlled conductance unit, firing control and current limiter of FIG. 2 illustrate preferred circuitry for accomplishing the desired functions of these units. However, it should be kept in mind that the invention is not limited to these specific circuits and that a wide range of circuitry can be utilized to perform the functions required of these units.

The modified wave form produced by the control of the invention is illustrated in FIG. 4. The heavy dashed line illustrates the output of the controlled conductance unit with a sine wave source and with a conduction delay of about two-thirds of a half cycle or 120. The light dashed line 151 illustrates the 100% conduction voltage wave provided by the A.C. source. The duration of the initial Zero magnitude portion can be varied to provide more or less of the 100% wave as desired. The solid curve 152 illustrates a continuous A.C. voltage as would be provided by a choke coil or reactor limited system which is providing the same power to the treater as the conduction limited wave 150. It is readily seen that the conduction limited system provides a substantially greater treating voltage than does the conventional system for the same power consumption requirements. Also with the system of the invention, one can get a greater peak voltage for the same volt-ampere demand, or can get the same peak voltage with less power and/or Volt-ampere demand.

In one embodiment ofthe invention, the control can be utilized to provide operation as illustrated in FIG. 4 throughout the operating current range, with or without the automatic current limiting feature of the invention. In this mode of operation it has been found that treating results equivalent to those obtained with the continuous voltage systems can be achieved with substantially lower power consumption and/or volt-ampere demand.

Another mode of operation is illustrated in FIG. 3. The load voltage-load current curve for an electric treater with conventional reactor current limiting is shown in the dot-dash curve 154. The voltage wave form diagrams 155, 156, 157 illustrate how the current limiting is achieved by and at the expense of reduction of the peak value of the continuously applied voltage wave. As electrical coalescence of dispersed droplets in an emulsion is a direct function of voltage, it can be seen that less effective or no coalescence occurs when the applied voltage is too low; see the wave form diagrams 156 and 157.

The solid curve 160 illustrates the operation of the controller of the invention with automatic current limiting. As indicated by diagrams 161, 162, the full value of the voltage is applied continuously up to about threequarters of the rated current. Thereafter, the magnitude of the applied voltage remains the same but the wave form is modified by making the initial portion zero, with the duration of the initial portion being increased as the load current approaches the rated value, as illustrated in diagrams 163 and 164. It is readily seen from a comparison of the

curves

154 and 160 that the system of the present invention permits electric treating at considerably higher voltages throughout a major portion of the current range for systems of equal rating and equal supply voltages.

When desired, the modied wave form mode may be utilized throughout the current range, as illustrated by the dashed line 166, which merges with the solid line 160 at about the 90% rated current position. For this mode of operation, the control will be set to provide a modiied wave with an initial delay portion of a selected value such as 90 or 120. This wave form is illustrated in the diagram as 167. This mode of operation can be obtained by changing the setting of the potentiometer 120 which determines the minimum delay period, and without changing any of the other settings.

FIG. 5 illustrates the eiect of the variables in the circuitry on the curves 160 and 166 of FIG. 3. The potentiometer 61 controls the current in the reset winding 55 and determines the maximum duration of the initial zero portion. Normally this is set to provide a full 180 delay. The potentiometer 120 controls the voltage in the resistor chain 118-119 and determines the maximum value of control current and thereby the minimum duration of the delay or zero magnitude portion of the modified wave. The potentiometer 133 controls a reference voltage level tude of load current at which the current limiting action begins. This may be selected to suit a particular treating operation and normally is in the range of to 99% of rated current. The potentiometer or variable resistor 137 affects the current in the resistor chain and determines the proportionality factor or rate of limiting action, which appears as the slope of the curve 160V during the limiting operation. The setting of the point at which the limiting begins and the rate of limiting determines the current value at which current is shut off, usually at of rated load current.

The present invention provides for the control of power and for current limiting in electric emulsion treaters such as dehydrators and desalters. The present invention utilizing a modilied voltage wave with an initial zero magnitude portion provides improved treating, reduction in the size and rating of power equipment, reduction of power consumption and volt-ampere demand, and extended operating ranges. Different materials are best treated at different electrical gradients. A conventional treater has to be shut down to permit mechanical adjustment of output voltage, usually by changing taps on the transformer windings. The present invention permits changing the maximum instantaneous electrical gradient in a treater without shutting oi treater power and without any mechanical changes in treater format, by changing the conduction delay period over the range from 90 to 180. The invention permits manual control of treater operation by plant personnel by simple potentiometer settings so that variations in performance can be achieved as desired and so that variations in composition of the material being handled can be accommodated.

Test results comparing the performance of conventional equipment and equipment incorporating the system of the invention are set out in Tables I and I1. The equipment utilized in the tests of Table II was in use for the treatment of Athabasca crudes and incorporated two treaters connected in series. The same equipment was used for all three runs of Table I and the same equipment was used in all six runs of Table II. The conventional equipment utilized reactance limiting; the new equipment utilized the conductance limiting of the present invention with the delay time indicated in electrical degrees.

In Run 4, the purpose of the test was to determine the amount of power required to produce a substantially dry oil in a single treater. There was a temperature rise of F. in the oil during this treatment. In Run 6, the first treater was modiied by the addition of the control of FIG. 2, with the potentiometer 120 set to provide a minimum delay of In Runs 7, 8 and 9, the second treater Was also modified by the addition of the equipment of FIG. 2, with both potentiometers 120 set to provide a minimum delay of 120. In the tables, W/D indiat the capacitor 131 and thereby determines the magni- 55 cates water content as measured by distillation.

TABLE I Charge (percent) Eiuent (percent) Power, Run BS&W W/D Solids Eqpt: BS&W W/D Solids kwin/bbl.

34 2. 5 Conv 3 9 1. 1 20 34 2.5 New 160...- 2 12 1.6 2.9 12 7 New 160--.. 1. 5 0. 3 0.2 2. 7

TABLE II Charge Process parameters First treatment Second treatment Diluent Etluent Effluent Rate, W/D, Solids, bitumen Temp., Press., bbL/hr. Percent Percent ratio F p.s..g. W/D, Solids, Power, W/D, Solids, Power, Eqpt. Percent Percent kwh/bbl. Eqpt Percent Percent kwh/bbl,

.06 28 2.2 1 240 200 Conv 0.1 0.1 217 06 15 1. 3 1 260 200 Conv. 4. 4 0. 4 27 Conv 0. 2 0. 2 30 12 27 2. 1 8 220 200 NeW 160..-- 9. 1 1. 4 2.0 Conv 0. 2 0. 2 25 5 34 2. 5 8 210 140 New 120 1. 2 0. 9 3. 0 New 120 0. 0 0. 6 4. 6 5 29 4. 7 .4 215 140 New 120 9. 3 2. 4 1. 0 New l20 1.0 1. 8 1. 8 5 38 2. 5 4 215 140 New 120 17. 7 8. 4 1. 0 New 120 1. 8 1. 3 2. 3

The results set forth in Tables I and II clearly indicate the superior performance of the system of the invention both in single-stage treatment and in dual-stage treatment.

Although exemplary embodiments of the invention have been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiments disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

We claim as our invention:

1. A process for electrically treating dispersions between electrodes, characterized by applying to the electrodes a high-voltage potential applied in pulses, each pulse being of a wave form in which the potential is substantially zero during an initial portion of the pulse and rises substantially instantaneously to a high value and thereafter follows substantially a sine wave in decreasing to zero during the remainder of the pulse.

2. A process as defined in claim 1 in which the voltage is applied to the electrodes by a high-voltage secondary winding of a transformer, and including the step of controlling the potential applied to the primary winding of the transformer to produce said pulses.

3. A process as defined in claim 2 in which the potential applied to the primary winding is from an A.C. source having a wave form of substantially sine-wave pattern, each pulse being established by controlling the potential applied to the primary winding to remain substantially at zero potential during said initial portion, corresponding to the initial portion of a half cycle of said sine wave, and then substantially instantaneously increasing such applied potential to the sine-wave potential then being developed by said source, the applied potential following the sine wave during the remainder of the half cycle in dropping to zero at the end of the half cycle.

4. A process as defined in claim 1 including the step of applying a substantially sinusoidal high-voltage potential to said electrodes so long as the electrical resistance of said dispersion is higher than a given value, and applying said pulses to the electrodes only when the electrical resistance of said dispersion becomes lower than said value.

5. A process as defined in claim 4 in which the initial substantially-zero portions of said pulses are progressively lengthened as the electrical resistance of said dispersion between said electrodes progressively decreases below said value.

6. A process as defined in claim 1 including the step of varying the duration of the zero portion of the pulse as a function of the load current with the duration increasing as the load current increases.

7. A process as defined in claim 1 including the step of maintaining the duration of the zero portion of the pulse substantially constant While the load current is less than a predetermined amount and progressively increasing the duration as the load current increases beyond said predetermined amount.

8. A process as defined in claim 1 including the step of progressively increasing the duration of the zero portion of the pulse as the load current increases beyond a first predetermined amount with the duration extending to substantially the entire half cycle of the sine wave as the load current approaches a second predetermined amount.

9. A process according to claim 1 in which the substantially zero initial portion ends and the potential rises at a time from about to about 30 electrical degrees prior to the time the resulting electrode potential decreases below the effective treating voltage.

10. A process according to claim 1 in which the peak value of the sine wave unmodified would be from about 11/2 to about 21/2 times greater than that required to prod-uce the effective treating voltage.

11. A process according to claim 1 in which the substantially zero initial portion ends and the potential rises at a time from about 0.5 to about 1.5 milliseconds prior to the time the resulting electrode potential decreases below the effective treating voltage and in which the peak value of the sine wave unmodified about be from about 11/2 to about 21/2 times greater than that required to produce the effective treating voltage.

12. In an electric emulsion treater, the combination of:

a high-voltage stepup transformer having a primary and a secondary;

Ia container for fluid to be treated and including an inlet and upper and lower outlets for fluid ow therethrough;

a pair of electrodes disposed in said container in spaced relation for fiuid flow therebetween;

first circuit means for connecting said secondary to said pair of electrodes to apply a high electrical potential between said electrodes;

A.C. power source terminals; and

second circuit means for connecting said source terminals to said primary and including means for modifying the output wave of the A.C. source to make an initial portion of a half cycle substantially zero followed by a substantially instantaneous rise fromthe zero condition to the normal output wave condition.

13. An electric emulsion treater as defined in claim 12 including control means for varying the duration of said initial portion of a half cycle.

14. An electric emulsion treater as defined in claim 13 including:

means for generating a load signal varying as a function of the load current in said treater; and

current responsive means having said load signal as an input and providing an output to said control means in controlling relation for increasing the duration of said initial portion when the load current exceeds a predetermined value.

15. An electric emulsion treater as defined in claim 13 including:

current responsive means having said load signal as an input and providing an output to said control means in controlling relation for progressively increasing the duration of said initial portion from a first value to substantially the entire half cycle as the load current increases from a first predetermined value to a second greater value for maintaining the maximum treating voltage while limiting the current to a rated maximum.

16. An electric emulsion treater as defined in claim 12 in which said second circuit means includes a controlled conductance unit having a control element, and means for applying a voltage to said control element at the end of said initial portion of a half cycle to turn the unit on.

17. An electric emulsion treater as defined in claim 12 in which said second circuit means includes a full wave rectifier circuit having anode, cathode and control elements, and means for applying a voltage to a control element at the end of said initial portion of each half cycle to trigger the rectifier circuit into conduction.

18. An electric emulsion treater as defined in claim 12 in which said second circuit means includes means for generating conduction triggering voltages in synchronism with the A.C. power source with the triggering voltage delayed behind the zero degree time of the A.C. source wave, and means for varying the delay time.

19. An electric emulsion treater as defined in claim 18 in which said means for varying the delay time is a variable current source and including manual means for Varying the output of said current source for setting the duration of said initial portion of a half cycle.

20. An electric emulsion treater as defined in claim 18 including means for automatically varying the output of said current source as a function of the load current of the treater for maintaining a predetermined relation be- 15 tween treater load current and duration of the initial portion of a half cycle.

21. An electric emulsion treater as dened in claim 14 in which said means for generating a load signal includes a current transformer feeding a rectier yunit to produce a D.C. voltage which varies as a function of the load current.

22. An electric emulsion treater as defined in claim 14 in which said current responsive means includes a current control transistor with the output current thereof controlled by a manually set voltage until the load signal exceeds a predetermined value and with the output current thereof then controlled by the load signal voltage.

23. An electric emulsion treater as defined in claim 22 including three resistances connected in series across the load signal voltage with said transistor connected at one resistance junction point and with said manually set voltage connected at another resistance junction point.

References Cited UNITED STATES PATENTS Winslow et al.

JOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner.

U.S. C1. X.R.