US2790128A - Discontinuing charge to precipitator electrodes during cyclic cleaning periods - Google Patents

Description

Aprll 23, 1957 KLEMPERER v 2,790,128

' DISCONTINUING CHARGE To PRECIPITATOR ELECTRODES A DURING CYCLICYCLEANING PERIODS Filed Feb. 18, 1952 2 heets-Sheet 2 H0 iv/fa q j K2] f LINE WLTHGE DISC ONTINUING CHARGE T PRECIPITATOR ELECTRODES DURING CYCLIC CLEANING PERIODS Hans Klernpe'rer, Belmont, Mas's., assignor, by niesne assignments, to Apra Precipitator Corporation, New York, N. Y.,' a corporation of Delaware Application February 18, 1952, Serial No. 272,238

4' Claims. (Cl. 321-25) United States Patent O arrangement is disclosed in the patent of Hilmer Karlsson,

No. 2,582,133 issued on January 8, 1952. In apparatus of this type the cleaning operation is carried out much more frequently than in previous types of precipitator-s, being effected, for example, for each individual bank of electrodes once per minute for a duration of five (5) seconds. At the time the cleaning is carried out by means of a jet of steam or air, the charging voltage must be discontinued and such frequent interruption of the electrical circuit on the power side is impractical when using movable contacts. The present invention contemplates the utilization of purely electrical and non-mechanical means operative to cut off the voltage to the electrodes at the frequent intervals required for cleaning purposes. This is accomplished by the cooperative use of a series connected saturable reactor with a saturable parallelly connected reactor in the power circuit.

The invention will be best understood upon consideration of the following detailed description of an illustrative embodiment thereof when read in conjunction with the accompanying drawings in which:

Figure 1 is a schematic view of part of an electrostatic precipitator embodying the present invention for cutting off the charging voltage.

Figure 2 is a wiring diagram of the electrical circuit for controlling the charge applied to the electrode banks of the precipitator.

Figure 3 is a graph illustrating the voltage-current relationship in the electrostatic precipitator.

Figure 4 is a graph showing the voltage-current relationship of a series connected saturable reactor in comparison with that of a parallel reactor; and

Figure 5 is a graph similar to Figure 4 illustrating the voltage reduction that may be attained when employing a series reactor in conjunction with a parallel reactor and cutting off the charging voltage to the precipitator electrodes.

Referring first to Figure 1, there is shown a high velocity gas precipitator of the type disclosed in the Karlsson Patent No. 2,582,133 issued January 8, 1952 consisting of a rotor 10 divided into a plurality of compartments by radial partitions with banks 12 of gas ionizing and particle collecting electrodes 13. Each bank of electrodes is separately charged from a separate power supply 14 through the wire 24. The rotor 10 is turned by a suitable motor so that it moves with respect to a cleaning device illustrated generally at 16. In an alternative 2,790,128 Patented Apr. 23, 1957 form, the banks of electrodes are stationary and the cleaning nozzle and an associated collecting hopper turn with respect to the banks of electrodes so that the banks may be successively subjected to the cleaning operation.

In Figure 2 the numerals 20 and 21 designate a source of altemating current of 240 to 480 volts, 60 cycles, supplying a high voltage transformer 12 to which is connected the rectifier bridge designated as a whole by the numeral 23 from which the charging voltage is applied to a bank of precipitator electrodes through the wire 24,- it being understood that the control circuit arrangement shown in Figure 2 is duplicated for each bank of electrodes inthe precipitator so that they may be individually controlled. Connected in parallel with the primary of the power transformer 12 is a saturable reactor designated as a whole by the number 25 while one side of the power line has a second saturable reactor 26 connected in series relationship therein, as in the lead 21. The current for magnetizing the reactors 25 and 26 is derived from auxiliary power supplies 30 to which are connected the rectifier bridges 31 and 32 which convert the alternating current to be applied to the reactors to direct current. The rectified current applied to the saturable reactors 25, 26 is periodically varied, for example, by means of an auto-transformer 33 with variable secondary and a variable resistance 34, respectively having movable contact elements 35, 36 which may be mechanically driven by time control mechanisms 37, 38 or by a train of elements synchronized with the precipi tator rotor 10 or itscleanin'g apparatus. The series and parallel reactors have the magnetizing current applied to them in out of phase relationship; that is to say, when the magnetizing current for the series reactor 26 is being increased the current for the parallel reactor 25 is being simultaneously decreased and at the same rate. This is illustrated in Figure 4 wherein the curves 40 show the voltage-current relationship of a series reactor as the magnetizing current is periodically increased and de=v creased while the curves 41 show similar relation for the parallel reactor. The point of intersection of the two groups of curves 40 and 41 give operating points or values for the charging voltage applied to the bank of electrodes in the precipitator. Referring to Figures 3 and 5 it may be seen that while a parallel reactor alone in the power circuit of the electrostatic precipitator would produce charging voltages between the points A and B with the point A at such a high voltage value that the glow discharge would not be extinguished and the current to the precipitator electrodes would not be cut off. On the contrary the utilization of a parallel reactor and a series reactor in conjunction with each of them in the relationship shown in Figure 2 enables the voltage applied to the bank of precipitator electrodes to be reduced to a much lower value.

The increase of direct current magnetization of the saturable series reactor reduces the impedance and permits increased current flow. For example, a 500 volt drop across the reactor is reduced to 50 volts. The parallel reactor 25 constitutes a variable shunt which affects the current flowing through the series reactor 26 and transformer 12 in the precipitator circuit and with the disappearance of the glow discharge at 10,000 volts for example, the impedance of the transformer 22 becomes infinite so that the current normally supplied to the bank of electrodes is completely cut off during the interval required for cleaning the electrodes by means at a jet of steam or air. The parallel reactor 25 is employed because use of the series reactor 26 alone would unduly delay the interruption of the electrode charging voltage. In short, the parallel reactor 25 speeds up the action of the circuit whereas the series reactor would be too slow in demagnetizing.

What I claim is:

1. In a power supply system for an electrostatic precipitator, an alternating current source, a high voltage transformer with its primary connected to said source, a rectifier connected to the secondary winding of said transformer, a saturable reactor having its main Winding connected in series relation with said primary winding, a saturable reactor having its main winding connected in parallel with said primary winding, magnetizing windings for said reactors, means for energizing the magnetizing windings of said series and parallel connected reactors from direct current supply means; control means associated with said energizing means so arranged as to be operable to increase or decrease the energization of the magnetizing windings of said parallel and series connected reactors; and cyclically operating means actuating said control means so arranged as to elfect periodic variation of the energization of the magnetizing windings of said series connected reactor in out of phase relationship with the energization of the magnetizing windings of said parallel connected reactor.

2. In a power supply system for an electrostatic precipitator, an alternating current source, a high voltage transformer with its primary winding connected to said source, a rectifier connected to the secondary windingof said transformer, a saturable reactor having its main winding connected in series relation with said primary winding, a saturable reactor having its main winding connected in parallel with said primary winding, magnetizing windings for said reactors, means for applying magnetizing currents to the magnetizing windings of said series and parallel connected reactors; control means as sociated with said current applying means so arranged as to be operable to periodically increase or decrease the energization of the magnetizing windings of said parallel and series connected reactors; and cyclically operating means acting continuously on said control means for periodically increasing and decreasing the energization of the magnetizing windings of said series connected reactor in out of phase relationship with the energization of the magnetizing windings of said parallel connected reactor.

3. In a power supply system for an electrostatic precipitator, an alternating current source, a high voltage transformer with its primary winding connected to said source, a rectifier connected to the secondary winding of said transformer, a saturable reactor having its main Winding connected in series relation with said primary winding, a saturable reactor having its main winding connected in parallel with the said primary winding, magnetizing windings for said reactors, means for energizing the magnetizing windings of said series and parallel connected reactors; control means associated with said reactor energizing means so arranged as to be operable to increase or decrease the energization of the magnetizing windings of said parallel and series connected reactors; and cyclic operating means actuating said control means so as to periodically increase and decrease the energization of the magnetizing windings of said series connected reactor so as to periodically cut-off and then restore the supply of current by said rectifier to the precipitator.

4. In a power supply system for an electrostatic precipitator, an alternating current source, a high voltage transformer with its primary connected to said source, a rectifier connected to the secondary winding of said transformer, a saturable reactor having its main winding connected in series relation with said primary winding, a saturable reactor having its main winding connected in parallel with said primary winding, magnetizing wind ings for said reactors, means for energizing the magnetizing windings of said series and parallel connected reactors from direct current supply means; the combination with said energizing connection of control means so arranged as to be operable to increase or decrease the energization of the magnetizing windings of said parallel and series connected reactors; and cyclically actuated means acting on and operating said control means so arranged as to eifect periodic variation of the energization of the magnetizing windings of said series connected reactor in out of phase relationship with the energization of the magnetizing windings of said parallel connected reactor.

References Cited in the file of this patent UNITED STATES PATENTS 2,126,790 Logan Aug. 16, 1938 2,139,232 Hysko Dec. 6, 1938 2,297,740 Brown Oct. 6, 1942 2,351,681 Haug June 30, 1944 2,509,380 Walker May 30, 1950 2,575,600 Smith Nov. 20, 1951 OTHER REFERENCES Selenium Rectifiers," I. R. Smith, Westinghouse Engineer, vol. 12, No. 4, July 1952, pages 131-2.

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