US2672947A - Voltage control in precipitators - Google Patents

Description

March 23, 1954 H. KLEMPE'RER VOLTAGE CONTROL IN PRECIPITATORS Filed May 3, 1951 3 Sheets-Sheet l Ln "In QMQ WW 97' ENE) March 23, 1954 H. KLEMPERER 2,672,947

VOLTAGE CONTROL IN PRECIPITATORS Filed May a, 1951 3 Sheets-Sheet 2 6 U P P L I E '2 3 4 5 a 7 a .9 POWER f/fi/VS KLEMPE'FE/P INVENTOR.

/l ra/m5 Y March 23, 1954 H. KLEMPERER VOLTAGE CONTROL IN PRECIPITATORS 3 Sheets-Sheet 5 Filed May 3, 1951 t\ INVENTOR.

BY? 7 f A rraxP/vtr Patented Mar. 23, 1954 UNITED STATES PATENT OFFICE.

VOLTAGE CQNTROL IN PRECIPITATQRS Hans Klemperer, Belmont, Mass., assignor to The Air Preheater Corporation, New York, N. Y.

Application May 3, 1951, Serial No. 224,356

8 Claims.

This-invention relates to electrostatic precipi tators for the removal from combustion or other impure gases of fine solid particles or impurities and particularly to an improved automatic control of the-particle collecting and cleaning or discharge cycles of such precipitators;

It is a general object of the invention to proviously electrostatically charged in the ionizin zone are deposited and collected on a suitable collecting surface. provision of collecting sections having a total cross sectional area for flow of gases greater than that required for flow of the gascolumn to be treated. Less than the total number of gas chanels provided are utilized at a given time and the remainder of the channels are in a cleaning zone outside the path of flow of the gas column so that the collecting surfaces may be cleaned without interrupting the gas. cleaning function of the apparatus as a whole. In particular the inven tion contemplates apparatus of the kinddescribed inwhich means are provided for automatically reducing the voltageapplied to the chargedelements of the precipitator prior to the cleaning period at which time the voltage i completely out off. The voltage is partially restored in a transition period and the charged elements have 1;

the full voltage again applied thereto as they fully resume their collecting function.

A salient feature of the invention'is'theprovision of electronically controlled device operative to reduce, cut off and subsequently first partially and then fully restore the charging voltage, all with the object of avoiding the excessive wear of electrical contacts and related mechanical partsthat would be entailed if conventional switchesof ad q ate size were utilized directly I to repeatedly and frequently reduce and cut off etc; the relatively high voltage utilized for charging the elements of anelectrical precipitator.

The invention contemplates For a better understanding of themore detailed nature'of thein'vention and the manner in which its several objects are attained-refer;- ence is made to the ensuing portion of this specification taken in conjunction with the accompanying drawings in which by way-of example; but without limitation, an embodiment of appa ratus for carrying the invention into effect is disclosed. In the drawings: Figure l is a more or less schematic central longitudinal section through a gas cleaning appa ratus embodying the invention;

Figure 2 is a section taken on the line 2;2 of" Fig. 1;

Figure 3 is a section taken on the line 3-3 of Fig. 1';

Figure 4 is a diagrammatic view illustrating the electrical arrangements for applying an electrical precipitator voltage to the various sections of the and Figure 5 is a schematic wiring diagram show ing the electronically controlled devices 'for'applying a high tension charging voltage to elements of the precipitator together with cyclically controlled means for reducing the voltage in a transition period prior to the cleaning operationwhen the voltage i cut off following which there is a second transition period when the voltage is partially restored prior to the application or full voltage as the collecting cycle is repeated;

Referring now more particularly to the pre-" cipitator shown in Figs. 1 to 3,the reference character It indicate a duct delivering gases containing fines from a furnace or other apparatus and II is a discharge duct for carrying away the cleaned gases. Between ducts l0 and II a stationary housing structure I2 is located.

The housing l2 includes an'inner cylindrical shell l3 spaced from the outer shell and joined there: to by a plurality of radially extending partitions I4 (Fig. 2) to divide the annular space between the shells into a. series of sector-like compart ments I5 providing the space for the collecting section l6 of the cleaner. The collecting surface is provided by a plate structure 11 forming-fineach compartment a bank comprising a multiplicity of open ended gas channels l8'-of"h exagonal cross section. At the upper and lower ends of the plate structure, the marginal spaces between the bank of channels l8 and the shells and partitions of the housing are closed by suit+ able plates to force all of the gas passing through the housing to flow through the collecting chan nels 44. v v Each of the gas channels l8 is'traversed longi tudinally by a centrally located electrode 20 which in the embodiment illustrated is in the form'of a solid rod but which also may be a hollow tube or other form. The electrodes 20 are supported by grids 2| of metal plate, there being one such grid for the bank of electrodes in each compartment I of the housing. The grids are electrically insulated from the framework of the housing, the grid 2| being supported by insulating connections 22 carried by the outer housing shell i2 and insulating support 23 carried by the inner shell l3.

At the'lower or inlet ends of the gas channels other grids similar to grids 2| are provided, these also being supported by insulators. Current is supplied to each compartment t rough an individual feeder 24 so that through the structure just described the electrodes may be electrically charged.

In the lower portion of the space between the shells l2 and E3 the ionizing section 25 is located, the construction of which is similar to that previ ously described, the radial partitions that form the compartments being coextensive in length with the shells of the casing structure so that the ionizing section as well as the collecting section is divided and located in a series of compartments, the several parts of the ionizing section being energized through the feed connections 25.

The casing structur is formed to provide a chamber 39 to which the gas inlet Ii! leads and communicating through an annular opening 3! with the annular space in which the ionizing and collecting sections 25, it respectively are located. Within this chamber there is located a rotatably mounted hopper 32 projecting at its lower end through a suitably sealed opening 33 in the casing structure, being carried by a suitabl bearing and having an external discharge outlet 34.

At the upper end of the shell structure a rotatably mounted casing 35 is provided, which comprises a sector-shaped wing 36 providing a chamber 31 housing a cleaning element in the form of a pipe 38 rotatable with the casing 35 by means of the gearing 39. PipeBB is connected to a source of high pressure fluid, such as steam or air. The casing 35 operates to isolate a compartment to be cleaned from the compartments through which gas is flowing in the same manner as the hopper eifects this separation at the lower end of the apparatus, and it will be evident that as the hopper 32 and casing 35 ar rotated electrode banks in different compartments it 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 described in the copending application of Per Hilmer Karlsson Serial No. 747,167 filed May 10,1947 now Patent No. 2,582,133, issued Jun 27, 1951 which also discloses forms in which the collecting sections and sometimes the ionizing sections rotate with respect to a stationary cleaning station.

From suitable sources which may be of any appropriate known kind, the electrodes of the ionizing and collecting sections of the apparatus are electrically charged, preferably being given a high negative potential. In actual practice negative potentials of the order of 15,000 volts from a direct current source have been found to be satisfactory in operation, although utilization of the apparatus is not limited to this particular kind or value of electrical charge.

Current is supplied from the 230 or 440 volt 60 cycle line designated 50 in Fig. 5 to the primary ofthe transformer 5| for the rectifier tubes 52 through the ignitron tubes 53, 54 connected in back to back relation. The ignitron tubes 53, 54 are controlled by the thyratron tubes 55, 56 which are normally biased off. An impulse transformer 51 periodically overrides the bias to energize the grids 58 of the thyratrons 55, at a phase angle set by a phase shifter 59 comprising a variable resistor 6| and condenser 62 in series and parallel relation, respectively, with the primary of the impulse transformer 57. The resistor and condenser are in series with the secondary of a transformer 63 which is on an auxiliary circuit 64 from which the filament transformers 65 for the thyratrons also are supplied.

With th apparatus thus charged through the various leads 24, the impure gases carrying the fines to be collected fiow from the supply duct E0 in a multiplicity of streams through the gas channels of the ionizing section in which section the solid particles acquire a negative charge. The gas carrying the charged particles then flows through the multiplicity of gas channels in the collecting section, and in this section, due to the repulsion of the negatively charged particles from the likewise negatively charged electrodes, the particles travel in oblique paths away from the electrodes until they impinge upon and adhere to the plate structure of the collecting section forming the walls of the channels. As the fines are deposited on the collecting surfaces of the present apparatus, films of solid deposit are built up upon these surfaces, and it has been found that the efiiciency of the apparatus falls off relatively rapidly as the thickness of such films or layers of deposits increase. If the apparatus is to operate with a high degre of efliciency from the standpoint of the percentage of fines removed, the collecting surfaces require relatively frequent cleaning.

Voltage reduction prior to cleaning Preceding the cleaning cycle for each bank of electrodes it the position of the rotary cleaning nozzle 38 and hopper 32 results in making the cam 66 of rotary disc 58 effective to close contacts 10 to energize relay ll. This may occur when the cleaning pipe 33 is several compartments or banks of electrodes in advance of the bank to be cleaned. This results in opening contacts ll! that short part of resistor tl and causes the phase shifter to acting through impulse transformer 51 to impose biasing voltage impulses on the grid 58 of the thyratrons 55, 56 which therefore are later in the phase so as to delay the starting phase of the ignitrons 53, 54 and this action results in reducing the voltage impressed on the primary of high voltage transformer 5i, and thereby reduces the direct voltage of current supplied by rectifiers 52 through lead E l to the electrode bank or precipitator section or sections lccated in the transition zone or period prior to cleaning.

In accordance with the present invention the required cleaning may be intermittently or continuously effected without interruption of the continuous particle precipitating action applied to a continuously flowing column of gases. As will be apparent from the foregoing description of the apparatus, when the cleaning element 3i and hopper 32 are alined in turn with the several compartments each is temporarily out off from the gas stream and bank of electrodes then located in the cleaning zone and may readily be cleaned of accumulated deposits by means of the jet blast which is arranged so that it can be applied to direct the blast through all of the gas aezaeez channels of the bank or. compartment. as it turns.

When a compartment of collecting surface is to,

be cleaned,- it is desirable that the associated Current disconnected during cleaning When the cleaning element is positioned over any electrode bank the rotary cam 69 closes contacts 12 and energizes the related relay 13 to open contacts 13] in the leads 14 from the secondary coilyof impulse transformer 57 to the grids 58 of thyratrons 55, 55 and interrupts the supply of starting impulses to these thyratrons so that the ignitrons 53, 54 become completely de-energized and, no current passes to the secondary coil of rectifier transformer with the result that during the cleaning cycle voltage is entirely out off from the lead 24 extending to the precipitator sector being cleaned.

. When the cleaning of the electrodes has been completed and the cleaning element 38 moved beyond a particular bank of electrodes, the rotary cam. rides beyond the related switch 12 which closes energizing the relay 13 whose contacts 13! engage and restore the biasing voltage to the grids 58' of the thyratrons 55, 56. These in turn cause the ignitrons 53, 54 to function on the part of the cycle permitted by regulation of the impulse transmitter 51 by the phase shifter 69; and restore the charging current. Subsequently as the cleaning element 38 moves away from a particular bank of electrodes the cam 66 of switch moves away and switch 10 closes energizing the relay 1| whose contacts HI open removing the short circuit around part of the resistor 6| so that the phase shifter 50 causes the impulse transformer 51 to transmit biasing impulses at a later phase in the cycle to the grids 58 of the thyratrons 55, 56. This results in restoring full voltage to the electrodes and the gas cleaning cycle is again fully elfective and the electrodes have full voltage applied thereto until the cleaning period is again reached whereupon the voltage impos'ed upon a bank of electrodes that are to be cleaned is first reduced and'thencut 01f as described above.

Over voltage An over-voltage relay. 8!! is provided with normally open contacts 81 in a line 8| connecting the voltage reducing relay H directly with the one lead of the auxiliary supply circuit 64. The. relay 8!! is. controlled by the triode 82 whose grid 83.normally has a potential applied thereto that blocks off the tube and prevents its conduction. In ordinary operation of the precipitatora small amount'of current drawn from the high voltage line 24 will flow through glow lamp. 84 to ground, at 85 through resistor 86 in a branch 81. around the k. v. meter 88 and part of its resistance 89 through which the ionizer is shunted to ground. If the high voltage in the ionizer section of the precipitator is momentarily reduced because of flash over or other faulty condition,-the voltage tapped by branch 81 is not high-enough to keep glow tube 84 ionized.- As afresult triode 82 loses the bias on its grid 83 an rcu e it w o...en s ze t v r-,rol ee 6 r relay 80. The relay 8i! closes contacts-802 looking itself in and the contacts Bill which energize the relay H and cause a reduction of the voltage applied to the precipitator as described in detail above. Operation at low voltage could continue indefinitely until relay 8!] were reset through manual release button 853. However, since the flashover is of short duration it issafe to restore the ionizer to full voltage after a short interval to permit disruption or disappearance of the fiashover. To automatically restore full voltage the rotary contacts 15 are opened once in each cycle of rotation of the precipitator. Consequently if at such time relay is energized and its contacts 802 are closed, the opening of'rotary contacts l6 de-energizes relay so that contacts 80! open and in turn result in de-energizing reg lay H and full voltage is restored as described above.

Short circuit lock-out The high voltage rectifier bridge 52 is grounded at through resistor and ammeter 9|. voltage developed across this resistance in case of a short circuit permits sufficient current to flow in the branch line to energize relay 92 which looks itself in through contacts 92! in line 93 leading to power supply'transformer 94.

On energization of relay 92 the contact circuits controlled thereby are opened as contacts 922 open in the primary of transformer 63 associated with the phase shifter 60. This automatically cuts off all control circuits and ignitrons 53, 54 become de-energized so that no power is supplied to high voltage transformer 5|.

By manual operation of release button 95' or cyclic opening of contacts 16 by cam ll once during each rotation of the cleaning element in the precipitator cycle the relay 92 is de-energized thus permitting contacts 922 to close and restart the precipitator cycle. Thus the unit automatically discontinues operation wherever a heavy flash over occurs but it restarts itself again after the cleaning cycle.

What I claim is:

1. In an electrostatic precipitator having separate banks of electrodes located in the path of a stream of particle laden gases, means movable relatively to said banks of electrodes operable to clean collected particles from the.electrodes of each bank in succession, and individual power supply means for separately applying a charging voltage to each bank of electrodes; the improvement comprising switching means responsive to and controlled by the position of said cleaning means relatively to each bank of electrodes'for reducing the charging voltage applied to '-the latter electrode immediately prior to the cleaning period.

2. In an electrostatic precipitator having separate banks of electrodes located in the path of a stream of particle laden gases, means movable relatively to said banks of electrodes operable to clean collected particles from the electrodes of each bank in succession and individual power supply means for separately applying a charging the charging voltage applied to the" latter elec-,.

trode immediately prior to the cleaning period; and means responsive to and controlled by ,the

position of said cleaning means for-completely. cutting, off. thewvoltage during the cleaninsperiod.

The

3; A precipitator as recited in claim 2 provided with switching means responsive to the position of the cleaning apparatus relative to each bankof electrodes for partially restoring the charging voltage at the end of the cleaning period and for subsequently fully restoring the charging voltage.

4. In an electrostatic precipitator apparatus having electrodes charged from a rectifier connected to the secondary or" a transformer whose primary is connected to an electrical power source by a circuit including ignitron tubes controlled by thyratron-tubes including grids; means normally effective to bias off said grids; an impulse transformer having its secondary circuit connected to apply starting impulses to the grids of said thyratrons tubes for overriding the bias applied thereto; an auxiliary power source; an auxiliary transformer having its primary circuit connected to said auxiliary power source; a phase shifting circuit connecting the secondary of said auxiliary transformer with the primary of said impulse transformer; a condenser in one side of said circuit; a resistance in the other side of said circuit; a circuit including normally engaged contacts changing the phase of said phase shifting circuit; a relay for disengaging said contacts; means for periodically cleaning said electrodes; a normally open switch controlling said relay; and means synchronously associated with electrode cleaning means and operative to close said switch a predetermined time before said cleaning means becomes effective to clean said electrodes.

5. In an electrostatic precipitator apparatus having electrodes charged from a rectifier connected to the secondary of a power transformer whose primary is connected to an electrical power source by a circuit including ignitron tubes controlled by thyratron tubes including grids; means normally effective to bias off said grids; an impulse transformer having its second-- ary circuit connected to apply starting impulses to the grids of said thyratron tubes for overriding the bias applied thereto; an auxiliary power source; an auxiliary power transformer having its primary circuit connected to said auxiliary power source; a circuit connecting the secondary of said auxiliary power transformer in parallel with the primary of said impulse transformer; means for periodically cleaning said electrodes; normally engaged contacts in the grid circuits of said thyratron tubes; a relay connected to be energized from said auxiliary power source; a normally closed switch controlling said relay; and means synchronously associated with said electrode cleaning means and operative to open said switch during the time said cleaning means is effective to clean said electrodes, whereby the de-energization of said relay separates said contacts and opens the grid circuits of said thyratron tubes so as to'render said ignitron tubes ineffectual to supply current to said rectifier tubes and precipitator electrodes during the cleaning period.

6. In an electrostatic precipitator having a plurality of separate banks of electrodes located inthe path of a stream of particle laden gases; means movable relatively to said banks of electrodes operable to clean collected particles from the electrodes of each bank in succession; individual power supply means including ignitron tubescontrolled by thyratron tubes for separately applying a charging voltage to each bank of electrodes; means controlled by the position of said cleaning means relatively to each bank of electrodes for reducing the charging voltage applied to the latter electrode immediately prior to the cleaning period; and means for completely cutting off the voltage during the cleaning period including normally engaged contacts in the grid circuits of said thyratron tubes, a relay energized from said auxiliary power source, a normally closed switch controlling said relay, and means synchronously associated with said electrode cleaning means and operative to open said second switch during the time said cleaning means is effective to, clean said electrodes.

'7. In an electrostatic precipitator apparatus having electrodes charged from a rectifier connected to the secondary of a power transformer Whose primary is connected to an electrical power source by a circuit including ignitron tubes con trolled by thyratron tubes including grids; means normally effective to bias oif said grids; an impulse transformer having its secondary circuit connected to apply starting impulses to the grids of said thyratron tubes for overriding the bias applied thereto; an auxiliary power source; an auxiliary power transformer having its primary circuit connected to said auxiliary power source;

a circuit connecting the secondary of said auxiliary power transformer in parallel with the primary of said impulse transformer; a resistance in one side of said circuit; a condenser in the other side of said circuit; a circuit including normally engaged contacts shorting part of said resistance; a relay connected to said auxiliary power source and energizable to separate said contacts to disrupt said short circuit; means for periodically cleaning said electrodes; a normally open switch controlling said relay; means synchronously associated with said electrode cleaning means and operative to close said switch a predetermined time before said cleaning means becomes effective to clean said electrodes, whereby the energization of said relay opens said contacts to remove the short circuit of part of said resistance to modify the voltage supplied by said auxiliary transformer to said impulse transformer so as to cause the latter to apply the bias countering impulses to the grids of said thyratrons at a later cyclic phase so as to cause said ignitron tubes to act to reduce the charging voltage applied bysaid rectifier to said electrodes.

8. In an electrostatic precipitator apparatus having electrodes charged from a rectifier connected to the secondary of a power transformer whose primary is connected to an electrical power source by a circuit including ignitron tubes controlled by thyratron tubes including grids; means normally effective to bias off said grids; an impulse transformer having its secondary circuit connected to apply starting impulses to the grids of said thyratron tubes for overriding the bias applied thereto; an auxiliary power source; an auxiliary power transformer having its primary circuit connected to said auxiliary power source; a circuit connecting the secondary of said auxiliary power transformer in parallel with the primary of said impulse transformer; a resistance in one side of said circuit; a condenser in the other side of said circuit; a circuit including normally engaged contacts shorting part of said resistance; a relay connected to said auxiliary power source and energizable to separate said contacts to disrupt said short circuit; means for periodically cleaning said electrodes; a normally open switch controlling said relay; means synchronously associated with said electrode cleaning means and operative toclose said switch a predetermined time before said cleaning means becomes effective to clean said electrodes, whereby the energization of said relay opens said contacts to remove the short circuit of part of said resistance to modify the voltage supplied by said auxiliary transformer to said impulse transformer so as to cause the latter to apply the bias countering impulses to the grids of said thyratrons at a later cyclic phase so as to cause said ignitron tubes to act to reduce the charging voltage applied by said rectifier to said electrodes; normally closed contacts in the grid circuits of said thyratron tubes; a second relay connected to be energized from said auxiliary power source; a normally closed switch controlling said second relay; and means 10 synchronously associated with said electrode cleaning means and operative to open said second switch during the time said cleaning means is effective to clean said electrodes whereby the de-energization of said second relay opens the grid circuits of said thyratron tubes so as to render said ignitron tubes ineffectual to supply current to said rectifier tubes and precipitator electrodes during the cleaning period.

HANS KLEMPERER.

References Cited in the file of this patent UNITED STATES PATENTS Number

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