US2509548A - Energizing electrical precipitator - Google Patents

Description

ma 30, 1950 H. J, WHITE 2,509,548

ENERGIZING ELECTRICAL PRECIPITATOR Filed May 27, 1948 Patented May 30, 1950 ENERGIZIN G ELECTRICAL PRECIPITATOR Harry J. White, Lawrenceville, N. J., assignor to Research Corporation, New York, N. Y., a corporation of New York Application May 27, 1948, Serial No. 29,623

14 Claims.

The present invention relates to electric systems comprising an electrical precipitator for removing suspended particles from gases and a charging circuit for energizing the precipitator. In particular it relates to a charging circuit in which electrical power is supplied to an electrical precipitator in a series of evenly spaced, short duration current pulses of controlled characteristics, provision being made in the circuit for maintaining a supply of such power without interruption arising from the changeable and unpredictable load conditions which are commonly met with in electrical precipitators.

The usefulness of such a circuit depends to I large extent upon the overall efiiciency with which energy is transformed and transferred from one form to another and from one piece of equipment to another. This in turn depends upon the nature, relative rating, and arrangement of the equipment comprised in the circuit. It also depends upon the characteristics of the load, or loads, included in the system and the influence of the load upon the functioning of the energizing circuit.

An electrical precipitator for cleaning gases comprising spacially positioned and insulated complementary electrodes provides a very unpredictable electric load because, in its operation, mixtures of gas and suspended solid and/or liquid particles flow through the inter electrode spaces and these mixtures change in physical, chemical, and electrical characteristics due to changes at the origin of the mixtures, for instance, in the operating conditions in the furnace which may produce such mixtures. The gas may change in composition or temperature and the particles may change in composition, size, and concentration. At times of rapping the precipitator electrodes, the electrical conditions in the spaces between the electrodes, due to falling material, are greatly changed. Such changes alter the dielectric constant of the mixture, thus changing the capacitance of the precipitator; they bring about changes in the conductivity of the gases, and so change the electric power, due largely to corona discharges, required by the precipitator; and, without warning, spark-overs take place between the electrodes which temporarily short circuit the precipitator and initiate transients which will, unless prevented from doing so, travel back through the power supply circuit.

It is an object of the present invention to avoid these objectionable features and conditions by providing a high efficiency circuit for the production of unidirectional current pulses and supplying the unidirectional pulses to the complementary electrodes of a precipitator through a unidirectional current passing device, such as a diode or a metal oxide rectifier.

Preferably the pulse energy is generated at relatively low voltage thus reducing equipment and operating costs and making it possible to transfer the pulse energy under low voltage conditions to the immediate vicinit of the precipitator. At the precipitator, a pulse transformer is provided which steps up the voltage of the pulses but which changes them practically not at all, otherwise. These pulses then flow through a one-way current transfer means to the precipitator. The oneway means causes retention in the precipitator, for use therein, of all energy that reaches it. This makes for economical operation, suppresses transients, and provides conditions which permit the charging circuit to function in an orderly and desired manner. The duration and peak value of the pulses can be largely controlled, conditions which have much to do with the efiiciency of the operation of the precipitator. Use of a pulse transformer is not essential but is preferred in energizing precipitators at high potentials.

The term pulses is used herein to denote a succession of discrete increments of electrical energy separated by intervals of substantially greater duration than the duration of the increments of electrical energy.

Generally, the pulse charging system of the invention comprises a condenser, circuit elements including a series conductive impedance connecting a source of current to the condenser, circuit elements including a periodic circuit closing device, for example, a rotary gap switch, and an inductance connected in series with the condenser to provide a pulsing circuit, and circuit elements including a unidirectional current passing device connecting the pulsing circuit with complementary electrodes of an electrical precipitator. The pulse charging system may be energized with unidirectional current or with alternating current synchronous with the periodic circuit cl-osing device of the system.

The invention will be more particularly described with reference to the accompanying drawing in which Figs. 1 to 5 are diagrammatic representations of five different charging circuits embodying the principles of the invention.

In the various figures like elements are indicated by like reference numerals.

In the drawing circuit of Fig. 1, I!) is a source of unidirectional current, and II and I2 are the discharge electrodes and collecting electrodes of an electrical precipitator, I3 is an inductance,

I 4 a rotary gap switch, I5 a condenser, It an inductance, I I a pulse transformer and I8 a diode.

For the supply .of pulses at :a peak voltage of 60 kv. and a pulse rate of 240 :per second to an electrical precipitator of approximately 5,000 cubic feet per minute capacity, D. C. power supply I ll may provide D. 0. current at about .7200 volts. The following values of the circuit elements of Fig. 1 will provide the desired pulse energy at the precipitator:

Inductance I3: 43 h.

Rotary gap I4: 8 points, 11890 R. P. M. Condenser I5: 0.048 mf.; 15 kv. Inductance It: 17 mh.

Pulse transformer". I'I: ratio 4.7

Diode I8: Ei-macZBOR The- -provision of a condenser Lainshunt with the load is advantageous in providing further control of .the voltage characteristics of the charging pulses and particularly tor controllin the duration of potentials across "the electrodes of the :precipitator. The shunt condenser 49 is preferably much smaller :in capacity than the charging condenser 1-5 and may be decreased in size and capacity with increasing pulse freguency.

The .tunction of :coil 15 maybe-filled by the provision of sufficient inductive leakage in pulse transformer II.

The charging circuit-of Fig. '2 includes a synchronous rotary gap switch 2!! which functions a commutating switch to distribute the energizing pulses in cyclic succession to a plurality of electrical precipitators through loads 21, 22, ligand 24.

With a direct current supply Ill providing 1'3 kv., 1.8 Amp. direct current, the followingvalues ofrthe circuit elements will supply pulses of peak voltage 100 kv. at a ra-teof 480 per second prosliding -18 kw. for distribution to the tour electrical precipitators:

Inductance", I3: ,3 h.

Rotary gap I4: .8 points, 3600 R. P. M. Condenser it: 0.15 mf.; 25 kv. Inductance It: 19 mh.

Pulse transformer I1: Ratio 7 Rotary switch Z0: 8'points, 3600 RP. M.

In the charging'circuit of Fig. 3, the rotary gap'switch I4 and the condenser t5 are interchanged. In the circuit of Fig. 3, a damping circuit, comprising series res stance 25-and diode 2 5 connected across the primary terminals of the pulse transformer .I 1., is provided. Since the diode 26 conducts whenever the voltage across the primary winding of the transformer becomes posi tive any transient voltages, which might arise in theprimary .due to sparking in the precipitate:- or other operating variables, are rapidly attenuated.

Fig. 4 shows a charging circuit including a plurality ,of pulse condensers I'5a, I5b connected with D. C. power source Ill through inductance I3 and optional diode 28 and connected with inductances Iiia, I 6b and rotary gap switches I and 20 to be charged in parallel and discharged in series.

sible to vary the output frequency over a considerable range without changing the resonant frequency of the charging circuit including inductance I3 and capacity I5. A pulse transformer may be inserted in the circuit between inductance 2'! and diode I8 as in Figs. 1 to 3. The values of the circuit elements will be selected in accordance with the principles illustrated in the illustrative values given for Figs. 1 and 2 to provide the desiredpulse rate and peak voltage at the precipitator. The inductances Ilia and I 5b should be much greater than inductance 21, and inductance I 3 should be much greater than inductances Ida, I6b.

In the charging system of Fig. 5, alternating current from motor-generator set 29 is stepped up to the desired voltage by transformer 30.

"The'rotary gapzswitch I4 is driven in synchronism with the motor-generator set to close the pulsing circuit once each cycle when the A. C. voltage is zero. The pulse frequency will then be equal to the A. 0. frequency and if the charging choke I3 and pulse condenser I5 are selected to be series resonant with the A. 0. frequency the maximum pulse voltage will be 1rV, where V is the peak value of the A. C. voltage at the secondary of transformer .30.

If the transformer 33 is energized with line A. C. current, the rotary ap switch may bedriven by a synchronous motor actuated by the line power. The function of the charging choke I3 may be filled leakage inductance of transformer 38 if desired. I

It will be seen that the construction andvarrangement of the-charging systems "of the invention may be widely varied without departing from the principles of the invention.

By means of minor changes in the circuits a wide range of pulse frequencies, voltages and wave shapes can be provided, thus making it readily possible to adjust the energization of each precipitator installation to the particular condi-- tions involvedand obtain-increasedefiiciencyand smoothness of operation. 1

:Anu-mber of precipitators or precipitatorsections can be energized from a single charging circuit-by commutation arrangementsof the type shown in Fig. 2, without introducing any interaction of the precipitators with each-other.

By the introduction of a pulse transformer into the charging circuits all of the circuit voltages may be kept relatively low, for example of the order-of 5 kv. to 151W. for the direct current power supply and 10 kv. to 30 kv. for the pulsing circuit components. This makes it possible to locate the-direct current power supply and the pulse generating circuit at any convenient loca-- tion or locations, connections being made with relatively cheap power cable. The pulse transformer can be mounted close to or adjacent the precipitator and the high voltage output lead tied directly tothe precipitator by a short direct connection.

The pulse generating circuit of the invention has the advantage that short circuiting the pulse transformer, as would occur in the case of sparking in the precipitator, does not resultin any-increase in power, as contrasted with the usual precipitator energizing circuits which, when the precipitator sparks, draw heavy currents and power and .giver-iseto surges and electrode burning in the precipitator. These heavy sparking currents necessitate a large, power wasting, primary resistance in the high voltage transformer of ordinary energizing circuits in order to .pre-

vent excessive precipitator arcs and current surges on the power line. The circuits of the invention require no such power wasting resistor, nor can any ordinary amount of precipitator sparking be harmful, although excess sparking is undesirable as it reduces precipitator efficiency.

This application is a continuation-in-part of my application Serial No. 774,142 filed September 15, 1947 and now abandoned.

I claim:

1. A charging system for an electrical precipitator comprising a condenser, circuit elements including a series conductive impedance means connecting a source of current to said condenser, circuit elements including a periodic circuit closing device and an inductance means connected in series with said condenser to provide a pulsing circuit, and circuit elements including a unidirectional current passing device connecting said pulsing circuit with the complementary electrodes of a precipitator.

2. A charging system for an electrical precipitator comprising a condenser, circuit elements including a series inductance means connecting a source of current to said condenser, circuit elements including a periodic circuit closing device and an inductance means connected in series with said condenser to provide a pulsing circuit, and circuit elements including a unidirectional current passing device connecting said pulsing circuit with the complementary electrodes of a precipitator.

3. A pulse charging system for an electrical precipitator comprising a condenser, circuit elements including a series inductance means con necting a source of unidirectional current to said condenser, circuit elements including a periodic circuit closing device and an inductance means connected in series with said condenser to provide a pulsing circuit, and circuit elements including a unidirectional current passing device connecting said pulsing circuit with the complementary electrodes of a precipitator,

4. A charging system for an electrical precipitator comprising a condenser, circuit elements including a series conductive impedance means connecting a source of current to said condenser, circuit elements including a periodic circuit closing device and an inductance means connected in series with said condenser to provide a pulsing circuit, and circuit elements including a unidirectional current passing device and a shunt capacity means connecting said pulsing circuit with the complementary electrodes of a precipitator.

5. A charging system for an electrical precipitator comprising a condenser, circuit elements including a series inductance means connecting a source of unidirectional current to said condenser, circuit elements including a periodic circuit closing device and an inductance means connected in series with said condenser to provide a pulsing circuit, and circuit elements including a pulse transformer and a unidirectional current passing device connecting said pulsing circuit with the complementary electrodes of a precipitator.

6. A charging system for an electrical precipitator comprising a condenser, circuit elements including a series conductive impedance means connecting a source of unidirectional current to said condenser, and circuit elements including a periodic circuit closing device, an inductance means and a unidirectional current passing device connecting .said condenser with the complementary electrodes of a precipitator.

7. A charging system as defined in claim 6 wherein the circuit elements connecting the condenser with the complementary electrodes of the precipitator include an inductive coupler.

8. A charging system for an electrical precipitator comprising a pulse transformer, a pulsing circuit including a condenser, an inductance means and a periodic circuit closing device in series with the primary of the pulse transformer, circuit elements including a series impedance means connecting a source of unidirectional electric current to said condenser, and circuit elements including a unidirectional current passing device connecting the secondary of the pulse transformer to the complementary electrodes of the precipitator.

9. A charging system for an electrical precipitator comprising a pulse transformer, a pulsing circuit including a condenser, an inductance means and a periodic circuit closing device in series with the primary of the pulse transformer, circuit elements including a series inductance means connecting a source of unidirectional electric current to said condenser, and circuit elements including a unidirectional current passing device connecting the secondary of the pulse transformer to the complementary electrodes of the precipitator.

10. A charging system for an electrical precipitator comprising a pulse transformer, a pulsing circuit including a condenser, an inductance means and a multiple rotary switch in series with the primary of the pulse transformer, circuit elements including a series impedance means connecting a source of unidirectional electric current to said condenser, and circuit elements including a unidirectional current passing device connecting the secondary of the pulse transformer to the complementary electrodes of the precipitator.

11. A charging system for an electrical precipitator comprising a pulse transformer, a pulsing circuit including a condenser, an inductance means and a periodic circuit closing device in series with the primary of the pulse transformer, circuit elements including a series impedance means connecting a source of unidirectional electric current to said condenser, and circuit elements including a diode connecting the secondary of the pulse transformer to the complementary electrode of the precipitator.

12. A charging system for an electrical precipitator comprising a condenser, circuit elements including a series conductive impedance means and a unidirectional current passing device connecting a source of current to said condenser, circuit elements including a periodic circuit closing device and an inductance means connected in series with said condenser to provide a pulsing circuit, and circuit elements including a unidirectional current passing device connecting said pulsing circuit with the complementary electrodes of a precipitator.

13. A charging system for an electrical precipitator comprising a pulse transformer, a closed pulsing circuit including a condenser and a periodic circuit closing device connected in series with the primary of the pulse transformer, circuit elements including a series inductance means connecting a source of unidirectional electric current directly to said condenser to form a second closed circuit, and circuit elements including a unidirectional current passing device connecting the secondary of the pulse transformer to the complementary electrodes of the precipitator.

means 14. A charging-r system for an. electrical precipitator comprising, a pulse; transformer, a closedpulsing circuit including a condenser, an inductance means and a periodic circuit. closing device connected in series with the primary of the pulse transformer, circuit elements including a series inductance means connecting a source of unidirectional electric current directly to said, condenser to form a second closed circuit, circuit elements including a. unidirectional current passing. device connecting the secondary of the pulse transformer to the complementary electrodes of the precipitator, and a damping circuit including a unidirectional current passing device and a series resistor connected in shunt with the 15 primary of the pulse transformer. v

HARRY J. WHITE.

REFERENCES CITED The following references are of record in the file of this. patent:

UNITED STATES PATENTS

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