US2863523A - Electrostatic precipitator - Google Patents

Description

Dec. 9, 1958 Y Y H. KLEMPERER l 2,863,523

ELECTRQSTATIC PRECIPITATOR Filed March 6, 1956 5 Sheets-Sheet 1 l NV E NTO R Hans Klemperer ATTO NEY Dec- 9, 1958 I H. KLEMPERER .2,863,523

ELECTROSTATIC PRECIPITATOR Filed1 March 6, 1956 l 3 Sheets-Sheet 2 4a f-f .2 Flg. 5 43 INVENTOR .WM ZTORNEY Dfw-l 9, 1958 H. KLEMPERER 2,863,523

ELECTROSTATIC FRECIPITATOR Filed March 6, 1956 3 Sheets-Sheet 3 INVENToR Hans Klemperer ATTORNEY nited States Patent C) ELECTROSTATIC PRECIPITATOR Hans Klemperer, Belmont, Mass., assignor to APRA Preciptator Corporation, New York, N. Y., a corporation of Delaware Application March 6, 1956, Serial No. 569,759

11 Claims. (Cl. 183-7) The present invention relates to electrostatic precipitators for the removal from combustion or other impure gases of ne solid particles or impurities and relates particularly to improved means for automatically controlling the application of charging voltages to the precipitator electrodes during the particle collecting and cleaning or discharge cycles of such precipitators.

The precipitator in which the invention is embodied eiects removal of impurities without interruption from a continuously flowing column of any impure gases by electrostatic means incorporated in apparatus providing an ionizing section or zone followed by a collecting section or zone in which the particles previously electrostatically charged in the ionizing zone are deposited and collected on a suitable collecting surface. The precipitator comprises a number of individual banks of electrodes arranged in collecting sections having a total cross sectional area for ow of gases greater than that required for flow of the gas column to be treated so that less than the total number of gas channels provided are utilized at a given time while the remainder of the channels are momentarily in a cleaning zone outside the path of flow of the gas column in order that the collecting surfaces may be cleaned without interrupting the gas cleaning function of the apparatus as a whole.

In particular the invention contemplates apparatus of the kind described in which means are provided for automatically regulating the voltage applied to the charged electrode elements of the precipitator in accordance with the operating conditions of a boiler, for example, with which the precipitator is associated as reected by the frequency of flashovers occurring in the precipitator as a whole, as well as the individual electrode banks.

A salient feature of the present invention is that individual power sources are provided for each of the individual collecting sections or electrode banks of the precipitator and a common regulating means controls all of these power supplies in response to the frequency of occurrence of ashovers in the precipitator as a whole. Concurrently each individual electrode bank of the precipitator may have the charging voltage that is applied thereto separately regulated in accordance with the frequency of occurrence of flashovers in the particular electrode bank.

In the drawings:

Figure l is a schematic view of a gas cleaning system incorporating individual power supplies with a common voltage regulating means for the various electrode banks in accordance with the present invention;

Figure 2 illustrates an alternative larrangement for part of the `control system illustrated in Figure 1;

Figure 3 is a schematic wiring diagram of the power supply and separate control means for a single electrode bank;

Figure 4 is a schematic wiring diagram of a modied form ofthe invention for controlling a precipitator in ICC accordance with the frequency of occurrence of flashovers.

Referring now more particularly to Figure l, the reference character 10 indicates a duct delivering gases containing impurities from a furnace or other apparatus and 11 is a discharge duct for carrying away the cleaned gases. Between ducts 10 and 11 a stationary housing 12 is located. For the purposes of this description it is assumed that the housing 12 is cylindrical and its interior divided by radial partitions into a series of sector-like compartments housing the electrode banks and collecting sections of the cleaner. The banks include lower ionizing sections and upper collecting sections. In Figure 1 the numerals 13, 14, 15 and 16 designate four out of the total of twelve, for example, individual electrode banks of the precipitator. Each compartment or bank comprises a multiplicity of open ended gas channels of hexagonal cross section and each of the gas channels is traversed longitudinally by a centrally located electrode. Current is supplied to each electrode bank through an individual feeder 20, 21, 22, 23, so that the electrodes may be electrically charged.

The casing structure is formed to provide a chamber 24 to which the gas inlet 10 leads and communicating with the space in which the ionizing and collecting sections are located. Within this chamber 24 there is located a rotatably mounted hopper 25 projecting at its lower end through a suitable sealed opening 26 in the casing structure, being carried by a suitable bearing and having an external discharge outlet 27. At the upper end of the shellstructure a rotatably mounted hood 28 is provided, which comprises a sector shaped wing providing a chamber housing a cleaning element in the form of a pipe 29 rotatable with the hood 28 by means of the suitable gearing.l Pipe 29 is connected to a source of high pressure fluid, such as steam or air. The hood 28 operates to isolate a compartment to be cleaned from the compartments through which gas is owing, the hopper 25 being maintained in registration with the hood 28 to effect this separation at the lower end of the apparatus. It will be evident that as the hopper 25 and hood 28 are rotated electrode banks in different compartments can be successively cleaned without interruption to the flow through the apparatus of the gas to be cleaned.

The foregoing precipitator structure is more fully de- -scribed in the patent to Per Hilmer Karlsson, No. 2,582,- 133, dated January 8, 1952.

Each of the electrode banks 13, 14, 15, 16 has associated therewith an individual power supply 30, 31, 32, 33, respectively, for supplying an electrical charge to the electrodes of the bank through the wires 20, .21, 22, and 23. Although only four electrode banks are shown it is to be understood that there are others in a complete precipitator and each has its individual power supply. Figure 3 illustrates the wiring arrangements of each of these power supplies.

Referring to Figure 3 the power supply for one of the electrode banks derives its energy from a three wire alternating electrical current source 40 to which the primary winding 41 of a power transformer 42 is connected. The secondary 43 of the transformer is connected to a rectifier 44 which converts the alternating current to direct current and through the wire 20, for example, supplies a high voltage charging potential to the electrodes of the bank 13 in the electrostatic precipitator. Connected in series with the primary windings 41 ofthe power transformer 42 are three reactors 46, 47, 48, whose exciting windings 50, 51, 52, are energized from .a separate source 53 of current through a rectifier 54. The primary windings 41 of power transformer 42 also vhave aaeaeae:

connected in parallel therewith three other reactors 5S, 56, 57, whose excitation windings 60, 61, 62, are energized from a tertiary coil 63 coupled to the reactor primary ofiy onek of the series reactors (e. g. 48). Theexcita tion for the parallel reactors is supplied through a rectifier 64 and: aI time constant modifying resistor 65, tol the excitation. coils 60, 61, 62, of the parallel reactors 55, 56, 5'7'.

The excitation for the series reactors 46, 47, 43, 1s governed fromv an intermediate or control reactor 66 which serves to amplify the excitation power needed. The control reactor 66 is so connected to the rectifier 34 as to be' of the self excited type displaying a high amplification andi a very fast operating time. This self saturating control reactor consists of the combination of two separate reactor components 67, 63, andv the rectifier 54. Introduction of this control reactor 66 reduces the power level for control purposes from two.. hundred fifty watts, for example, to less thanl ten watts. At this low level electro-mechanical control relays as heretofore used can be dispensed with and all necessary switching for reducing or cutting off voltage during and restoring it after the cleaning period may be performed, can be synchronizedwith the cleaning apparatus of the precipitator as disclosed in application, Serial No. 224,356, filed May 3, 1951, now Patent No. 2,672,947 issued March 23, 1954.

As shown in Figure 3, the ground resistor 75 between power rectifier 44 and ground is tapped and the voltage which corresponds to precipitator current is introduced into the control reactor excitation coils 76, 77, in a direction opposing the external excitation from a regulated separate power source 78. This is because one side of the reactor 66 windings 76, 77, is connected to the direct current source 78 so as to have the same polarity with respect to ground as the low voltage side of the power rectifier 44. Thus, the feedback circuit 80 has a degenerative and a stabilizing effect; the current in the precipitator sector limits itself by regulating the excitation of reactor 66 and hence the series reactors 46, 47, 48. The position of the slider 75A on resistor 75 defines the amount of feedback which is to be allowed. The feedback is set so that a rise in current during flashover is hardly noticeable. It is expected that due to the current limitation as derived from the feedback circuit 80 most of the ashovers in the precipitator will be blown out by the high gas velocity. A further benefit derived from the :current stabilizing action of the feedback is a more stable performance of the precipitator under varying boiler load conditions.

Circuit 80 is energized by a current carried by two opposing potentials, the constant voltage taken from source 78 and the varying voltage carried by the varying precipitator current liowing through 75. The current through 75 thus causes a current in circuit 80 which varies in inverse relation, i. e. it rises if the current in 75 falls and falls if the current in 75 rises. Therefore the excitation 77 of the control device 67, 68 varies in inverse direction with the flow of current in the precipitator and its acts to control this current in opposite sense. A rise in precipitator current causes the control device to counteract its rise. This counteraction of variations automatically performed by the controlling device is described herein by the term degenerative feedback.

The presence of the control reactor 66 considerably facilitates the extinction of flashovers. A flashover is a secondary short circuit and a manifests itself in a sudden breakdown of voltage (from 15,000 v. to about 100 v.). Flashovers behave `differently according to their points of origin. Iff they originate from dusty spots, as on the electrodes, they are most persistent. Since a precipitator sector does not remain clean during the length of its operating cycle, it is expected that some flashovers may stay. Therefore, an additional extinction circuit is needed and the trigger impulse for the extinction circuit is taken from the voltage breakdown.

In order that the voltage applied to the electrodesv of the various banks 13, 14, 15, 16, etc., may be regulated in response to the frequency of occurrence of ashover in the precipitator as a whole, the ground return leads S2, 83, 84,185, etc., of all of the power supplies 30, 31, 32, 33 (as well as others not illustrated) are connected together by a wire 86 and grounded at 87 through a common impedance 38 as shown in Figure 1. Any flashover in any power supply, i. e. in the coordinated electrode bank sector, will cause a transient voltage buildup across impedance This transient voltage is conducted through a capacity 90 to a storage device 91. Capacitance 90 serves to keep constant voltage drop across irnpedance 8S as caused by precipitator ionizing power away from storage device 91 and makes this storage device dependent on flashovers only. The storage device 91 may be a thermal, an electrostatic or a mechanical storage device for instance. A thermal device is shown consisting of a thermonegative resistance (thermistor) heatable by the current passing 90. The temperature and therefore the resistivity of the thermonegative resistance is consequently a function of theA flashover frequency in the precipitator.

A separate power source supplies direct current through the rectifier 101 to.` the excitation winding 102 of the control reactor 103 whose windings 104 and 105 are supplied with current through the rectifier 106 which is also connected to the power source 100. The output of rec'tifier1fi6 constitutes the separate power source 78 for the power supply 30 shown in. detail in Figure 3 and all of the other power supplies 31, 32 and 33 as shown in Figure 1. Connected in parallel with the excitation winding 102 of the reactor 103 is the thermo-sensitive resistance (thermistor) 91. The thermistor 91 bleeds off a part of the current which is supplied to winding 102 from the source 101- through a fixed resistor 107 and an adjustable resistor 108.

Flashover currents from any of the power supplies 30, 31, 32 pass the inductors 88 to ground 87. The change in voltage across 33 is conducted through a coupling capacity 90 to a heater winding which heats the thermistor body of thermistor 91. Therefore the temperature of the thermistor body depends on the occurrence. of flashovers and not on the direct current flowing through 88. As the body of thermistor 91 heats up it drains current away from excitation winding 102 of reactor 103 by means of which the current flowing thro-ugh reactor coils 104 and 105 and the coordinated rectifier 106 is reduced and the control reactor 103 common to the power supplies 30, 31, 32 gets less excitation, the result being that the power output of all supplies is simultaneously reduced. As boiler conditions vary, the flashover frequency in the precipitator will vary and the power output of the power supplies will automatically be increased or decreased by variation of the common voltage controlling all individual power supply control reactors.

An electrostatic storage device as an alternate is shown in Figure 2 wherein the points or terminals 92, 93, 94, 95 correspond to the similar terminals in Figure l. The voltage impulse passing capacitance 90 is rectified at 110 and stored on a capacitor 111. The energy is slowly bled off or dissipated at a rate determined by the size of a resistor 12 which thus corresponds to the natural cooling off of the thermal device shown in Figure l. The voltage stored by the capacitor-111 applied to reduce a constant negative bias on the grid 113 of an electronic tube 114. The plate resistance of this tube is therefore a function of the flashover frequency in the precipitator and this governs the voltage applied by the power units 30 to 33 to the electrode banks.

The common power supply regulator of Figure 1 Will operate only if all or the majority of power supplies start flashing. It will ordinarily not be affected by an increased fiashover rate in a single power supply because the integrator 8S is set to such sensitivity that 12 times higher impulse rate would be needed to properly excite the storage device 91. A high flashover rate in a single power supply, i. e. in the coordinated electrode bank, excites sufliciently its individual regulator 75 (Figure 3) which is adjusted to respond to these impulses only. The relative inertias of the individual regulators with respect to the inertia of the common regulator are adjustedadjustments are made by varying the respective thermal or electrical capacities-so that individual differences in ashover rates between the sectors adjust themselves before the common regulator responds.

Control of voltage applied to an individual electrode bank as the flashover frequency in the electrode bank rises is shown in Figure 3. The heating winding 72 of the thermistor 73 for bank 30 is connected to the related ground resistor 75 through a wire 79 on one side and on the other through the same resistor in adjustable manner through a wire 81A. Since the thermistor 73 is connected by the wire 70 into the circuit 74 of the activating windings 76 and 77 of the reactor 66, the heating of the thermistor 73 results in bleeding current from these energizing windings and reduces the power supplied by the reactor 54 to the power supply transformer 42 and rectifier 44 which supplies the precipitator sector 13. The tube circuit of Figure 2 could also be utilized for the individual power supplies for the electrode banks in place of the thermistor 73.

In Figure 4 a thermistor 120 which reflects the frequency of flashovers in any of the precipitato- r sections 13, 14, 15, 16 is arranged to transmit a control signal through the wires 121 and 122 to a speed control device 123 which acts upon a drive motor 124 to regulate the speed of rotation of the cleaning nozzle 29 so that as the rate of ashovers increases, the speed of the cleaning nozzle is accelerated with the result that the cleaning cycle for the precipitator occurs more frequently.

As described in detail with reference to Figure l a resistance 88 is provided in the common ground return line of all power supplies 30, 31, 32, 33, etc. Every ashover in any electrode bank 13, 14, 15, 16, etc., will appear as a voltage pulse across the resistor 88. This signal is passed by means of condensor 90 to an integrating device, thermal, electrostatic or mechanical. If a certain level is reached in the integrating device 120 the speed control 113 of the precipitator is inuenced, by relay or tube control, and speeds up the drive motor 114 for the cleaning apparatus. Resetting is eiected by cooling down or discharge of the integrating device when ashovers have subsided.

What I claim is:

l. In an electrostatic precipitator; energy storage means responsive to transient voltage uctuations in the precipitator produced by ashovers therein; means associated with said energy storage means for dissipating the energy stored therein at a predetermined rate; and means responsive to the residual energy stored in said energy storage means for controlling the operation of said precipitator.

2. In an electrostatic precipitator; having a bank of electrodes, electrical supply means for charging the electrodes of said bank, and control means associated with power supply for regulating the power supplied to said bank; energy storage means responsive to transient voltage iluctuations in the precipitator produced by flashovers therein; means associated with said energy storage means for dissipating the energy stored therein at a predetermined rate; and means responsive to the residual energy stored in said energy storage means for operating said control means to vary the output of said power supply means.

3. In an electrostatic precipitator having a group of separate banks of electrodes, a plurality of power units each individual to one of said electrode banks for supplying a high voltage current thereto, and individual control means in each power supply unit controlling the current supply to the related electrode bank independently of other electrode banks; a common regulating means for said control means; a common circuit connecting all of said power supplies to an electrical ground; means responsive to transient voltage fluctuations in said ground circuit for measuring the frequency of occurrence of flashovers in said group of electrode banks as a whole; and means responsive to said measuring means and acting on the said fcornmon current regulating means that is associated with said group of electrode banks for proportionately varying the output of all said power units simultaneously.

4. In an electrostatic precipitator having a group of separate banks of electrodes, a plurality of power units each individual to one of said electrode banks for supplying a high voltage current thereto, and individual control means in each of said power supply units separately controlling the current supply to the related electrode bank; a common regulating means for said control means; a common circuit `connecting all of said power supplies to an electrical ground; energy storage means responsive to the transient iluctuations in said ground circuit produced by ashovers in said group of electrode banks as a whole; means for dissipating the stored energy at a predetermined rate; `and means responsive to the energy stored in said energy storage means for operating said common current regulating means.

5. In an electrostatic precipitator having a group of separate banks of electrodes, a plurality of power units each individual to one of said electrode banks for supplying a high voltage current thereto, and individual control means in each power supply unit separately controlling the current supply to the related electrode bank independently of other electrode banks; a common regulating means for said control means; a common circuit connecting all of said power supplies to an electrical ground; electronic means for controlling said regulating means; and electrical means associated with said common ground circuit for making the output of said electronic means responsive to the transient voltage uctuations in said ground circuit produced by flashovers in said group of electrode banks as a whole.

6. In an electrostatic precipitator having a group of separate banks of electrodes, a plurality of power units each individual to one of said electrode banks for supplying a high voltage current thereto, and individual control means in each of said power supply units and each separately controlling the current supply to the related electrode bank independently of other electrode banks; a common regulating means for said control means; a common circuit connecting all of said power supplies to an electrical ground; a thermistor for controlling said regulating means; and electrical means associated with said common ground 'circuit for mak-ing the temperature of said thermistor responsive to the transient voltage fluctuation in said ground circuit produced by lashovers in said group of electrode banks as a whole.

7. In an electrostatic precipitator having a group of separate banks of electrodes, a plurality of power units each individual to one of said electrode banks for supplying a high voltage current thereto, and individual control means in each power supply unit controlling the current supply to the related electrode bank independently of other electrode banks; a common regulating means for said control means; a common circuit connecting all of said power supplies to an electrical ground; an impedance in said circuit; means responsive to transient uctuations in the voltage drop across said impedance for measuring the frequency of occurrence of llashovers in said group of electrode banks as a whole; and means responsive to said measuring means 'and acting on the said common current regulating means that is associated with the control means for the power units of said group of electrode banks for proportionately varying the output of all said power units simultaneously.

8. In an electrostatic precipitator having a bank of electrodes, an electrical power supply unit for charging said electrode bank; means in said power supply unit for controlling the current supplied to said bank of electrodes; an electrical grounding circuit for said electrode bank; means responsive to transient voltage uctu'ations in said ground circuit for measuring the frequency of occurrence of ashovers in said bank of electrodes; and means responsive to said measuring means and acting on said current control means for said bank to proportionately vary the output of said power unit in a direction to reduce said transient voltage fluctuations.

9. In an electrostatic precipitator having a plurality of separate electrode banks; means operable to clean said electrode banks in cyclically repeated sequential relation; :a drive motor for said cleaning means; speed regulating means for said motor; and means responsive to transient voltage fluctuations in said precipitator produced by flashovers for measuring the frequency of occurrence of Hashovers in said plurality of electrode banks as a whole acting upon said motor regulating means for varying the rate of cleaning of said electrode banks.

10. In 'an electrostatic precipitator having a bank of electrodes for ionizing entrained particles in a gas stream, electrical power supply means for charging said electrode bank; means in said power supply means for controlling the current supplied to said bank of electrodes; collecting surfaces for deposition of said particles; an electrical ground circuit for said surfaces; regulable means operable cyclically for cleaning said collecting surfaces; means responsive to transient voltage fluctuations in said ground circuit for measuring the frequency of occurrence of flashovers in said bank of electrodes; and means responsive to said measuring means and acting on said current'control means for said electrode bank to proportionately vary the output of said power unit in a direction to reduce said transient voltage fluctuations.

1.1. "In an electrostatic precipitator having separate banks of electrodes, individual power units for'said ele'ctrode banks for supplying a high voltage current thereto, and individual control means in each power supply unit controllingthe current supply to the related electrode bank independently of other electrode banks; a common regulating means for said control means; a common circuit connecting all of said power supplies to an electrical ground; means responsive to transient voltage fluctuations in said ground circuit for measuring the frequency of occurrence of ashovers in said precipitator as a whole; means responsive to said measuring means and acting on the said common current regulating means that is associated with all said electrode banks for proportionately varying the output of all power units of the pricipitator simultaneously; individual energy storage means for each electrode bank responsive to transient voltage fluctuations produced in the related electrode bank by ashovers therein; separate means associated with each energy storage means for dissipating the energy stored therein at a determined rate; and individual means for each electrode bank responsive to the residual energy stored in the related energy storage means for operating the control means in the power unit for the particular bank to Vary the output of said power unit independently of those for other banks.

References Cited in the le of this patent UNITED STATES PATENTS 2,642,149 Backer et al. June 16, 1953 FOREIGN PATENTS 149,367 Australia Dec. 10, 1952 705,604 Great Britain Mar. 17, 1954

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