US3039252A

US3039252A - Electrical precipitator power system

Info

Publication number: US3039252A
Application number: US558633A
Authority: US
Inventors: Guldemond John; Harold E Van Hoesen
Original assignee: Research Corp
Current assignee: Research Corp
Priority date: 1956-01-12
Filing date: 1956-01-12
Publication date: 1962-06-19
Anticipated expiration: 1979-06-19

Description

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WATTMETER m E. w m m m n m s R wm EC WE Tm E mw um wm mm um mw .|II A Imm O INPUT VOLTAGE ATTORNEY June 19, 1962 J- GULDEMOND' EN 3,039,252

ELECTRICAL PRECIPITATOR POWER SYSTEM O AVERAGE CORONA POWER IN PRECIPITATION 2a. ,v4 H.V. 2 Vol-TAGE a TRANsI-'ORMER REGULATOR '61 v RECTIFIER 2 k I g3 I sIGNAL R3 f 43 CURRENT 300C MOTOR VOLTAGE OPERATOR (REVERSIBLE I SIGNAL ELECTRONIC n/20. WATTIVIETER LOWER RAISE I I I I II 4 L COIVIRARATOR INVENTOR CONTROL JOI-IN GULDEMONO POWER HAROLD E. VAN `HOEsEN ATTORNEY June 19, 1962 J. GULDl-:MOND ETAL 3,039,252

ELECTRICAL PRECIPITATOR POWER SYSTEM 4 Sheets-Sheet 3 Filed Jan. 12, 1956 ATTORNEY June 19, 1962 J. GULDEMOND ETA. 3,039,252

ELECTRICAL PRECIPITATOR POWER SYSTEM Filed Jan. l2, 1956 4 Sheets-Sheet 4 zg E.

POINT ON CURVE FG 3 E c D E D E K5A- l J l 1 L l L 1 K55 u u u Ll u KSC n VE n n n n n50 VL n n n n K5E n n n VL n KAA MB I L J PGA u 1 3B J u l 1 K1A n "L VL 142A n n PREFERRED OPERATING RANGE POWER SPARKING RATE INVENTOR JOHN GULDEMOND HAROLD E.VAN HOESEN ATTORNEY United States Patent 3,039,252 ELECTRICAL PRECIPITATOR POWER SYSTEM John Guldemond, Bound Brook, and Harold E. Van

Hoesen, Somerville, NJ., assignors to Research Corporation, New York, N.Y., a corporation of New York Filed Jan. 12, 1956, Ser. No. 558,633 7 Claims. (Cl. 55105) This invention relates to the control of electric precipitators and has for its primary object the provision of a highly effective system for` insuring that precipitator operation is maintained continuously at the point of highest eiciency.

Recent developments in precipitator control have been directed toward the maintenance of an optimum sparking rate and control of the precipitator voltage in accordance with deviations from a desired rate of sparking. While this represents an improvement over earlier manual or automatic control efforts, it has been found that the eiliciency of a precipitator cannot always be maintained at a satisfactory level by controlling the rate of arcing or sparking. Since the operation of electrostatic precipitators involves the charging of particles in the gas flowing through them, and since the charging is accomplished primarily by corona current or `discharge in the precipitator, it is clear that the useful work that the precipitator performs is related to the corona power.

In a conventional precipitator system employing fullwave rectification of high voltage alternating current, there should be a deiinie period of corona current flow during each half cycle. Even if the operating conditions are such that arc-over occurs, there will have been corona current dlow during-any given half cycle up to the time when such arc-over occurs, and during this time particles in the gas stream have been receiving useful charge. On arc-over the charge on these particles is not lost but conltinues to move the particles toward the collecting electrode. Oscillograph traces have shown that the corona impulses are substantially in phase with the voltage of the low tension circuit. However, during arc-over in the precipitator, the voltage drops to a very low value, very close to zero, and the power is accordingly reduced. Since the power in the circuit is a function of the product of the in-phase current and voltage, it will be apparent that precipitator collection efficiency is closely related to the electrical power expended in the precipitator. It is, *theren fore, an object of the present invention to provide a highly eicient control arrangement for a precipitator by measuring the power expended in the precipitator and controlling precipitator voltage as a function of this power. Since this method involves simultaneous correlation of precipitator voltage and current, it will be clear that it differs considerably from prior techniques using yonly one factor, such as current, voltage, or sparking to control the precipitator operation.

Control of precipitator operation in accordance with the response of a wattmeter which measures precipitator input power is effective to secure the highest efficiency since, as explained above, during efficient and normal operation of the precipitator, there is the highest power input to the precipitator. During arc-over the voltage drops substantially to zero and the voltage coil of the wattmeter will not be energized during 'this period of time. VDuring the short period or interval when the precipitator is recharged and before corona current starts to ow, the current and voltage are out of phase and again the wattice meter will not be substantially actuated. Therefore, the wattmeter is only actuated during. the period when there is a flow of corona current. The wattmeter maybe either of a conventional type or may be a special electronic de* vice for producing an output which is the instantaneous product of the inphase current and voltage.

It will be seen from the above that in order to obtain the maximum precipitator eicicncy, it is necessary to operate at the highest possible power input. However, the maximum useful power that can be utilized by the precipitator is limited by internal spanking and arcing; and since the tendency to arc-over increases with increasing precipitator voltage, it will be clear that there is an optimum input Voltage for each operating condition of the precipitator, above and below which the power, and there- `fore the efficiency, decreases. In other words, the average p-ower versus input voltage curve has a maximum point. VIt is a principal object of the invention to provide a system for determining this maximum point and controlling the precipitator voltage so as to maintain operation at or very close to this maximum point.

According to the invention, the maximum point may be determined by periodically or continuously sampling the precipitator power, or a parameter which varies as a function of the precipitator power, and control-ling the precipitator input voltage in accordance with the result of such sampling, i.e., whenever the precipitator electrode power begins to decrease, the last change made in the operating input condition is reversed so as to bring the precipitator power back toward its maximum value for the given operating condition. v

Other objects of the invention are to provide a compact, economical, rapid and relatively inexpensive control System of high reliability for insuring operation of an electric precipitator at maximum elhciency.

The Specific natu-re of the invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown yin the accompanying drawings, in which:

FIG. l is a schematic circuit diagram of a precipitator control arrangement illustrating the basic principle of the invention;

FIG. 2 is a graph showing the relationship between precipitator power and efficiency;

FIG. 3 is a graph showing the relationship between the precipitator input voltage and the effective power developed;

FIG. 4 is a schematic circuit diagram showing the principle of a system for operating at true peak power;

FIG. 5 is a schematic circuit diagram showing a practical embodiment of the circuit of FIG. 4;

FIG. 6 is a timing chart showing the sequence of operations of the switches in FIG. 5; and

FIG. 7 is a graph showing the relationship between power and sparking rate in a precipitator.

Referring to FIG. l, commerci-al alternating current is supplied through mains 2 to a voltage regulator 4 for control-ling the voltage input to the customary high voltage transformer, which together with its attendant rectifier is indicated by block 6. The control element of the voltage regulator may be a variable series rheostat or any other type of regulator controlled by motor 10, which may be driven in either direction depending upon whether circuit K1 or K2 is energized, It will be obvious that any suitable type of motor may be used.

The high voltage output from unit 6 is applied to precipitator 16 through circuit 18, in which is inserted a series resistor 22 of suitable low Value to serve as a shunt resistor for the current coil 24 of wattmeter 26. It will be apparent that instead of resistor 22 a current transformer with suitable rectification may be used. For precipitator voltage measurement there is provided across the precipitator terminals a resistance

divider comprising resistors

28 and 30, although here again, it will be apparent that any suitable transformers and rectiers may be used if desired, since the precipitator current and voltage, although unidirectional, contain a sufliciently large pulsating component to be measurable in this way.

Voltage coil 32 -of wattmeter 26 is connected across resistor 30, which is of suicient value to provide proper operation of the wattmeter. The wattmeter needle 34 is shown as a grounded switching element capable of making contact in its extreme left hand position with switch K1 to operate motor 10 in a direction to raise the precipitator voltage, and in its extreme right hand position with switch K2 to correspondingly lower the precipitator voltage. Moving element 34 may be normally springbiased into contact with switch K1, which actuates the voltage control to increase the power to the precipitator by increasing the transformer voltage of the energizing equipment. When the power to the precipitator has reached the desired amount, the wattmeter element 34 moves to the right, the control circuit is then opened, and the precipitator energization is held constant at that p-articular value. However, should the power line voltage change and the power become too high, the right hand contact K2 will be closed and the energization of the precipitator reduced to the preselected value. In this oase, a predetermined maximum operating condition is assumed and switch K2 is set so that this Value is never 'actually attained, but only approached to a reasonable approximation. The predetermined maximum is established lby preliminary testing of the precipitator installation. However, it will be Aapparent that this relatively simple system cannot -actually maintain operation at peak eiiiciency, but can only approximate such operation, since if it were allowed to operate too close to the peak of the power curve, a point would soon be reached at which a reduction in power would occur whenever the input voltage is increased, and `further operation of the wattmeter `switching system would then only make matters worse.

FIG. 2 'shows the relationship between precipitator power and precipitator eiiiciency. I-t will be apparent that as the power is increased up to the dotted ordinate 37, the efficiency also increases, but beyond this point, there is relatively little advantage to be gained by increasing the power input `to the precipitator. Thus, by adjusting the device of FIG. `l to a point near the optimum power value, a reasonably high eiiiciency m-ay be maintained by simple means.

FIG. 3 shows the relationship of precipitator power developed to rectifier input voltage. It will be seen that the power increases to a maximum at the point of arcover, beyond which as previously explained, it decreases due to the collapsed Voltage drop in the arc. In order to maintain operation at this point, it is necessary to be able to detect `the point of maximum power input. FIG. 4 shows the principles of a control system for accomplishing this.

Referring to FIG. 4, the voltage regulator 4a, corresponding to regulator 4 in FIG. 1, controls the voltage of transformer and rectifier circuit 6a which energizes precipitator 16a, `and the power is measured yby wattmeter 26a, which is preferably an electronic wattmeter, `as will be described in detail below. The output of wattmeter 26a is periodically sensed and its Value is stored in data storage circuit 40, yand is periodically compared in comparator circuit 44 with its last previous value, to see whether the power is increasing or decreasing, and the voltage regulator 4a is controlled in such a way as to continuously maintain the power at its maximum point.

be a motor drive arranged to periodically close switches 42a through 42d in a predetermined sequence and for predetermined durations as will now be explained,

Switch 42e controls the direction of travel of the motor operator 43 for the voltage regulator 4a, and it is initially biased in the raise direction. When the system is initially put into operation, assuming the input voltage to be at zero point in FIG. 3, then the following sequence of events occurs:

(l) Switch 42a closes for the iirst period of the timer and raises the voltage output of regulator 4a to point A on the characteristic curve of FIG. 3.

(2) Switch 42a opens and switch 42b closes and the wattmeter reading corresponding to point A is stored in the data storage device. f

(3) Switch 42b opens and switchl 42a closes again, raising the operating point to point B on the curve before switch 42a opens.

(4) Switches 42C and 42d close and wattmeter data stored at point A are compared with data at point B. Since the power input at B is greater than at A, switch 42e remains in the raise position.

(5) Same as step 1, above etc. The above operation continues, until point E is reached. At this point, a rise in voltage input from regulator 4a causes a loss in power output at point E. The comparator 41 senses this decrease and throws switch 42e into the lower position. On the next cycle, :the control device 4a lowers the input voltage until stable operating conditions are established between points C and E; and the control system will continue to slowly hunt between these points to maintain maximum power conditions.

It is evident that by increasing the sampling rate from device 26a the amplitude of the hunting can be reduced to practical values and in effect can be made to approach point D in FIGURE 3.

FIG. 5 shows in greater detail the components of a complete system for carrying out the above cycle of operations. Reference characters correspond generally to those of the preceding figures with the subscript b added.V A conventional ballast element Sis added to thecircuit since such a device would generally be employed in a practical precipitator circuit.

The electronic wattmeter 26b is of generally conventional design, for which no novelty is claimed, and will be described only briefly. Its function is to produce an output voltage on line 51 which is proportional to the product of the voltage on line 52 and that on line 53. The voltage on line 52, which corresponds to the current in the power circuit, is supplied to a control grid of tube 54. The voltage on line 53, corresponding to the voltage in the precipitator circuit, is iirst inverted by means of tube 56 -t-o obtain the proper polarityv and phase inversion, and then supplied to the control grid of tube S7, voltage divider 58 being provided for calibration and initial setting. It will be apparent that if the tubes are operated over a certain portion of their characteristic curves, the output on line 51 will be proportional to the product of the inputs on

lines

52 and 53. This output is supplied to 4comparator 44b through a switching arrangement, to be described below, such that the power f reading immediately before a change in input is stored in data storage condenser 61 and the power reading immediately after a change in input voltage is stored in condenser 62, after which the voltages on these two condensers can be compared to ascertain the nature and direction of the change in power produced by the change in input voltage. This change, through control circuit 64, is used to operate motor i43h so as to either increase or decrease the setting of voltage regulator 4b and correspondingly change the input voltage supply to the precipitator. Since the control circuit has more components than that described in the simpliiied arrangement of FIG. 4, the reference characters of the control circuit cannot correspond exactly to those of FIG. 4. In order to simplify the description of the control circuit, which centers about the operation of the sequence timer, the motor of this timer will be designated K5, it being understood that this corresponds generally to sequence motor 42 in FIG. 4. The contacts which are successively and periodically operated by sequence motor K5 will be designated as K5A through K5E. A dotted line from K5 to each of these respective contacts indicates that there is a mechanical connection between them such that continuous operation of K5 causes operation of the respective contacts K5A through Km in the relationship shown by the timing chart of FIG, 6. A complete physical showing of this relationship would be very complex and diicult to follow, and since sequence timer circuits for controlling the operation of a plurality of switches in accor-dance with any desired pattern are well known, and form no part of the present invention, the disclosure will not be encumbered with such a detailed showing. It will be noted that when contact K5E is closed, current will ilow from the condenser 61 or 62 having the higher charge to the other condenser through either relay K1 or K2 to thus energize one of these relays and correspondingly close contacts K1A or K2A. The resulting operation of either relay of K3 or K4 will similarly close contacts K3A or KM to determine the direction of operation of motor 43b when contact K5A is closed, The following typical sequence of operations is diagrammed in the timing chart of FIG. 6.

It is assumed that the voltage is initially at point B of FIG. 3 and that condenser 61 is therefore charged to a voltage corresponding to this value and condenser 62 -is charged to a voltage corresponding Ito point A of FIG. 3. Also contacts of timer K5A and K5B are closed.

Contact K5E closes briefly to compare the two volt-age levels. Since condenser 62 has the higher voltage charge, current will ilow through relay coil K1, thereby closing contact K1A. After K1A closes, relay K3 will seal in and close its contacts KSA and KSB, thereby causing motor 43h to operate the voltage regulator in the raise direction. While lthe voltage regulator is raising the voltage, contacts K5@ close briefly to store a Voltage corresponding to a point somewhere between point B, FIG. 3, and point C, FIG. 3. After the voltage is stored in condenser 61, contact K5C -opens and K5D closes briefly thereafter to store a voltage corresponding to a point C, FIG. 3. After this voltage is stored in condenser 62, contacts K5D, K5A, and K5B open. This resets the circuit for comparison; and again Km closes, recreating a cycle of events until point E, FIG. 3, is reached, at which time condenser 61 will have a greater charge than 62 and when cornpared will cause the voltage regulator 4b to reduce the voltage to point D, FIG. 3. The operation will continue to hunt between points D and E, FIG. 3, thereby maintaining operation near the point of maximum corona power and likewise precipitator efficiency. Points D and E can be made to substantially coincide by increasing the sampling rate as previously stated.

Thus K5C closes briey just before the regulator setting is changed to memorize the last preceding power level; K5D closes after the regulator -setting is changed to give the new power level; K5E then closes to compare the two levels, and either relay K1 or K2 is energized to raise or lower the input Voltage depending on whether the last input voltage change produced an increase or a decrease in power level. After the top of the characteristie curve of FIG. 3 is passed, the next increase in voltage will produce a decrease in power level (point E), so relay K2 will be energized the next time to decrease the input voltage when the servomotor next cycles. This reduction in voltage will now increase the power level, as point D is again reached; and as the old value on condenser 61 (point E) is now lower than the new value on 62 (point D), current will again flow ythrough K1 when K5E is closed and relay K3 will now be engaged to increase the voltage. The next step will again cause a return to point E with another reversal, and the point of operation will continue to swing between points D and E of the curve, maintaining operation near the point of maximum efficiency.

FIG. 7 shows the relationship between power and sparking rate, which is sometimes used as a criterion of performance in a precipitator. It can be seen that as the sparking rate increases, the power input falls off due to the lowering of voltage, as explained above. It is also apparent that while controlling the power at its optimum value, it also selects and maintains the optimum sparking rate commensurate with maximum precipitator efficiency. The theory of this maximum power control is not inconsistent with prior sparking rate controls and in effect automatically chooses the optimum Value of sparking.

It will be apparent that other ways of measuring power than that shown may be employed, also instead of the simple and direct control system shown, any known type of automatic control system for precipitator may be employed.

IIt will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as detined in the appended claims.

We claim:

1. An electrical precipitator charging system comprising input voltage regulator means, means for intermittently sensing the power consumption of the electrical precipitator system, means for comparing successive power levels sensed by said intermittent sensing means, and means responsive to the comparative values of successive power levels to actuate said input voltage regulator means in a sense determined by the direction of change of successive power levels.

2. A precipitator system comprising input voltage regulator means settable to different input voltage values, precipitator electrodes, high-voltage rectifier means for supplying operating potential to said precipitator electrodes, means for measuring the power consumption of said precipitator electrodes at a first given time, means for changing the setting of said input voltage regulator means, means yfor measuring the power consumption at a second time after the voltage regulator setting has been changed, means for comparing the results of the first and second measurements, and means for controlling a second change in the setting of the input voltage regulator means in accordance with the result of said cornparison.

3, The invention according to claim 2, said means for measuring power comprising wattmeter means producing a voltage output which is a function of the precipitator electrode power consumption.

4. The invention according to claim 3, said means for comparing comprising `a first memory device for storing the voltage value of said wattmeter means given by the first measurement, and a second memory device forrstoring the voltage value given by said second measurement.

5. The invention according to claim 4, said memory devices comprising a first and a second storage condenser, and sequence timer means for briefly closing a first circuit to impress said irst voltage on said rst condenser, then closing a second circuit to impress said second voltage briefly on said second condenser, a circuit between said condensers responsive to direction of current flow, and switch means under control of said sequence timer for closing said last circuit whereby current flow between said condensers in a direction determined by their respective stored voltages.

6. The invention according to claim 5 including directional responsive control means actuated by current flow in said last circuit -for determining the direction of said change in regulator setting.

7. An electrical precipitator charging system comprising input voltage regulator means, means to vary said References Cited in the le of this patent UNITED STATES PATENTS Corbett July 1, 1941 Hall Apr. 13, 1954 Hage July 2, 1957 Foley Oct. 6, 1959