US2640559A - Electrical precipitator circuits - Google Patents

Description

June 2, 1953 HlLLs 2,640,559

ELECTRICAL PRECIPITATOR CIRCUITS Filed Jan. 21, 1946 F/gJ f |NV\ENTOR MMAZM maintaining point 55 positive with respect to point 56 even after the cycle of oscillation has reversed and rectifier I6 is no longer conducting. During a portion of the cycle in which the voltage generated in coil causes point 54 to be positive with respect to point 53 current flows through rectifier I! and resistor [3 in such a manner that point 51 is caused to be negative with respect to point 55. Electrodes l2 and I3 charge in the manner of a condenser and thus 1 maintain point 51 negative with respect to point 55 even after rectifier l! is no longer conducting. It is evident from the above that if the frequency of oscillation of the power source is chosen sufficiently high that electrodes H], H, l2, and [3 remain substantiallycharged, in spite of the current drains due to resistors 18 and I9 and the normal current drain incident to precipitation between the various sets of electrodes and the current drain due to the ionizing electrodes l4 and I5, throughout a complete cycle of oscillation that the voltage difference appearing between points 55 and 51 will be substantially twice the peak value of the alternating voltage appearing between terminals of the high voltage winding 20. Ionizing electrodes i4 and [5 are connected to resistors 18 and 3 at such points and 3| that the correct voltages are applied to the ionizing electrodes for the particular mechanical configuration of the electrodes that is used. The

voltage available for the ionizing electrodes is substantially twice the peak voltage induced in coil 20 and is unidirectional and of substantially constant amplitude. This high voltage simplifies the construction of the ionizing electrodes making possible the use of a relatively few electrodes such that in some precipitators only one electrode I5 might be needed. If the entire voltage difference existing between points and 51 were applied to the ionizing electrodes and the precipitating electrodes were designed such that each set drew the same current the necessity for resistors l8 and [3 would be eliminated. The electrostatic field that exists between electrodes of pluralities l0 and H that are directly in the line of the air or gas stream with electrodes or pluralities l2 and i3 is in the same direction relative to the direction of flow of the gas stream as the field existing between the corresponding electrodes of pluralities l2 and [3. The reason for this is that the acceleration caused in a particle of a given sign of charge transverse to the direction of the gas fiow will be in the same direction when the particle is being carried by the gas between electrodes IO and II as it was when the particle was being carried between electrodes l2 and I3 so that the effects of all of the electrodes will be additive in removing the particle from the gas stream.

- In another embodiment of my invention as shown in Fig. 2 it is to be understood that rectifying devices 36 and 31 are to be operated in their proper manner, that is if they are filament type vacuum tubes the filaments are to be connected to suitable sources of energy so that they may be heated as for instance coils on a transformer similar to 2| and 22 of Fig. 1. Reference character 38 represents an alternating current generator of suitable frequency which may be similar to the oscillator described with respect to Fig. 1. Two pluralities of precipitating or collecting electrodes 32 and 33 are insulated from each other and connected across resistor 39 as shown in the diagram. During a portion of the oscillation cycle when point 58 is positive with respectto 4 point 60 current fiows through rectifier 36, resistor 39 and generator 38 in such a manner that point 59 is negative with respect to point 58 in the circuit and precipitating electrodes 32 and 33 are charged to a potential difference equal to that existing across resistor 39. If the frequency of generator 38 is sufficiently high the potential difference existing across resistor 39 will be held substantially constant throughout a complete cycle of oscillation of generator 38 by the capacitance existing between plates 32 and 33. A constant unidirectional voltage is therefore maintained between the collecting plates for use in precipitating charged particles from the gas flowing between the plates. During a portion of the oscillation cycle when point 60 is positive with respect to point 58 rectifier 3! allows current to fiow through resistor 40, rectifier 31 and generator 38 in such a manner that point 42 in the circuit is caused to be positive with respect to point 58. Resistor 40 has very little capacitance across it so that the potential of point 42 with respect to that of point 58 continually varies in the manner of rectified sine waves. The ionizing electrodes are connected between points 42 and 59 of the circuit so that the voltage applied to them is a pulsating unidirectional voltage having a minimum value substantially equal to the voltage of the collecting plates and a maximum value much greater than that of the voltage of the collecting plates, depending on the position of tap 42 on resistor 40. This embodiment of the invention allows the use of a comparatively simple collecting electrode structure with the advantages of a constant amplitude unidirectional voltage applied to the collecting electrodes and still provides a voltage for the ionizing electrodes that can be adjusted to have an average amplitude of 1.63 times the peak value of the alternating voltage existing across generator 38. I have found that with this particular embodiment of my invention that the cleaning of smoke particles, or droplets, from air is almost as complete with the same electrode arrangement as if a constant amplitude unidirectional voltage were used to excite the ionizing electrodes that had an amplitude equal to the peak value of the voltage that I apply to the ionizing electrodes in my invention. The reason for this experimental observation is that, as is well known the power lost in corona on an electrode excited at high voltage can be expressed mathematically as the sum of two components; one component being independent of the frequency of the high voltage exciting source and the other component being proportional to the frequency of this source. This latter component of power loss actually exceeds the component of power loss that is independent of frequency for frequencies greater than approximately 25 cycles per second, and as the greater power loss to corona on the ionizing electrode is associated with greater ionization for the same electrode voltage, the precipitating eificiency of the precipitator is approximately as high with the embodiment of my invention shown in Fig. 2 as if a constant amplitude unidirectional voltage were used to excite the ionizing electrodes that had an amplitude equal to the peak value of the voltage that I apply to the ionizing electrodes in my invention. The position 42 at which electrode 35 is connected to resistor 40 is chosen so that for a given electrode spacing and voltage gradient the optimum cleaning will be obtained without causing undue formation of ozone and oxides of nitrogen.

In another embodiment of my invention as shown in Fig. 3 reference character 48 represents a source of high frequency voltage. Charactor 41 represents a rectifying device operated in its proper manner in the same way that devices 36 and 31 in Fig. 2 were described as operating. Two pluralities of collecting plates 43, and 44 are connected so that the voltage output of generator 48 after being rectified by rectifier 4! is applied between them. During a portion of the oscillation cycle of generator 48 when the anode of rectifier 41 is positive with respect to its cathode current flows through devices 4'! and 48 so as to charge up the condenser formed by plates 43 and 44 to substantially the peak value of the alternating voltage output of generator 48. The frequency of generator 48 is chosen high enough (above one kilocycle per second) that the voltage difference existing between plates 43 and 44 remains substantially constant throughout an oscillation cycle of generator 48. Ionizing electrodes 45 and 46 are connected to tap points 59 and 5| on resistor 49 which resistor is connected between the collecting plates 43 and 44. The positions of tap points 50 and 51 are chosen such that the correct ionizing voltage difference is applied between electrodes 45 and 46 for the particular electrode arrangement used. In the event that points 50 and 5| are connected so that the full voltage of the source is applied to the ionizing electrodes resistor 49 would not be needed. It is obvious that in this embodiment of my invention a voltage substantially equal to the peak value of the voltage output of generator 48 is available for exciting the ionizing electrodes 45 and 46. Although the operation of high-frequency power supplies in which the high voltage transformer is made a part of the oscillating circuit of an oscillator is well known and although the inherent electrical capacitance of the elements of an electrical precipitator has been made use of (Lissman, U. S. Pat. 2,326,237), the precipitator herein described makes use of a novel combination of a high-frequency power supply and an electrical precipitator structure such that the normal advantages of both are realized and in addition the combination makes possible the complete elimination of the most expensive parts of the high frequency power supply, its high voltage condensers, and in addition makes possible the simultaneous excitation of the collecting electrodes of the precipitator with constant amplitude unidirectional voltage and excitation of the ionizing electrodes with unidirectional voltage of amplitude varying at a high frequency. Because of this combination the collecting electrodes of the precipitator, being excited with constant amplitude voltage, can be excited at a voltage that is at all times as high as possible without the electrodes arcing over, and yet at no time goes higher and causes the plates to arc over; and at the same time the ionizing electrodes are excited by a voltage varying in amplitude at a high frequency such that greatly increased ionization is obtained with the same electrode arrangement and excitation voltage that would give far inferior ionization if the ionization voltage had constant amplitude or varied in amplitude at frequencies only of the order of commercial power line frequencies. This increased ionization together with the collecting electrode voltage remaining high for the whole period of an oscillation cycle causes the precipitator to have unusually high precipitating efficiency while at the same time an actual saving of equipment is obtained.

While three embodiments of my invention have been described for the purpose of illustration, it should be understood that the invention is not limited to the exact circuits and arrangements of apparatus herein described, or specifically covered by my claims, as modifications thereof may be suggested by those skilled in the art Without departure from the essence of the invention.

What is claimed is:

1. An electrical precipitator for purifying gas comprising an ionizing device including a plurality of electrodes between which an ionizing discharge is adapted to occur, a precipitating means including a plurality of spaced, parallel collector plates upon which impurities in said gas are collected, means for charging a portion of said plates to a predetermined potential relative to a neutral point, means for charging another portion of said plates to a potential in the opposite polarity relative to said neutral point,

means for deriving a potential substantially equal to the combined potential across said two portions of said collector plates, and means for applying said derived potential across said ionizing electrodes.

2. A precipitator as claimed in claim 1 in which the means for charging the first mentioned portions of the plates is one section of a voltage doubler, and the means for charging the second mentioned portions of the plates is the other section of the voltage doubler.

3. A precipitator as claimed in claim 2 in which the voltage doubler is connected to an alternating current source operating at a frequency above one kilocycle per second, and includes a pair of half-wave rectifiers, one for each of said sections, for converting the alternating current to direct current.

4. A precipitator as claimed in claim 1 in which the means for charging the portions of the plates includes an alternating current source having a frequency above one kilocycle per second, and a pair of half-wave rectifiers for converting the alternating current to direct current.

5. An electrical precipitator comprising a first collector plate, a second collector plate spaced from said first collector plate, a first half-Wave rectifier, a source of alternating current, a first ionizer electrode, a second ionizer electrode, a second half-wave rectifier, and a circuit connecting said first rectifier, said source and said plates in series, and connecting said ionizer electrodes, said plates, said source and said second rectifier in series.

ELMER G. HILLS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,297,933 Yonkers, Jr Oct. 6, 1942 2,326,237 Lissman Aug. 10, 1943 2,336,625 Milton Dec. 14, 1943 2,462,890 Newman Mar. 1, 1949 2,598,337 Andrews May 27, 1952 FOREIGN PATENTS Number Country Date 456,405 Germany Feb. 24, 1928 649,446 Germany Aug. 24, 1947

Images