US2142128A - Electrical precipitation method and apparatus - Google Patents

Description

Jan. 3, 1939. F. w. HOSS ET AL ELECTRICAL PRECIPITATION METHOD AND APPARATUS 1937 2 Sheets-Sheet 1 Filed April 19 Jan. 3, 1939. F, w. nose ET AL 2,142,128

ELECTRICAL PRECIPITATION METHOD AND APPARATUS Filed April '19, 1957 2 Shee'ts-Sheet 1 2 ATTORNEYS Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE ELECTRICAL PRECIPITATION METHOD AND APPARATUS Application April 19, 1937, Serial No. 137,864 In Germany April 22, 1936 14 Claims.

The present invention relates generally to improvements in method and apparatus and for 1 effecting the precipitation of suspended particles from a stream of gas and more especially to de- 5 vices of this kind in which the particles are first charged in one field and then precipitated out in a second field. In precipitators of this latter type, the gas is first passed through a discharging or ionizing field in which the particles become l electrically charged, and then the gas is passed through a separate, non-discharging field in which precipitation of the particles takes place on one or more collecting electrodes.

In electrical precipitators as usually conl structed, the gas stream flows past the electrode surfaces in a direction generally parallel thereto. The electrical field is maintained between the electrodes and so is more or less at right angles to the gas flow, which thus oflEers little or no assistance to the separation of particles from the gas but rather interferes with the separation since there is a tendency to pick up and carry along in the gas stream material that has been previously deposited.

It is a general object of our invention to provide a precipitator of increased efliciency and effectiveness which is simple and free of undesidable complexities. I

It is also a principal object to provide a precipitator of the two-field type in which the gas stream and the precipitating field exert their forces in the same direction on the suspended particles and so reinforce each other in effecting precipitation of the particles.

A further object of our invention is to provide a precipitator of the two field type in which the precipitating field has a fluid pervious electrode through which gas passes to bring about intimate contact of the gas stream with the electrode and completely precipitate suspended particles.

The method of operation of the invention comprises passing a stream of gas, containing suspended particles previously charged electrically, through a non-discharging precipitation field,

and maintaining the precipitation field in such a direction that the force it exerts on the suspended particles generally coincides with the direction of stream fiow and so aids the movement of the particles toward the collecting electrode.

These objects are attained in a precipitator of our invention by providing a pair of electrodes, one of which is a discharge electrode, and between which is maintained an electric field of 66 the discharging or ionizing type; and a second pair of non-discharging electrodes, one of which is fluid-pervious to permit the gas to pass therethrough, and between which is maintained an electrical field of a non-discharging type to precipitate the previously charged particles from the gas stream. One electrode of each pair is maintained at a common polarity, and preferably at a common potential, while the other two electrodes are both of the opposite polarity but are not necessarily both at the same potential relative to the opposing member of their respective pairs. The precipitating field is maintained between the two electrodes of the second pair in such a direction that the force exerted by the field on the suspended particles generally coincides with the direction of the gas flow through the pervious electrode, so that the electrical field and the gas flow reinforce each other in moving suspended particles.

How the above and other objects and advantages of our invention are secured will be better understood by reference to the following description and the annexed drawings in which:

Fig. 1 is a vertical section through a preferred form of precipitator illustrated somewhat diagrammatically;

Fig. 2 is a horizontal section on line 2-2 of Fig. 1;

Fig. 3 is a vertical section through a variational form of precipitator;

Fig. 4 is a vertical section through another variational form of precipitator; and

Fig. 5 is a fragmentary horizontal section through another variational form of precipitator in which all of the electrodes are arranged in a single gas conduit.

The form of precipitator illustrated in Figs. 1 and 2 comprises housings l0 and I2, which are respectively the ionizing and precipitating units and are connected by conduit l3. Discharge electrode M, such as a wire or small diameter rod, is mounted coaxially of housing Ill, being supported and insulated from the housing at its upper and lower ends by means of insulators l6. Since housing It is grounded, as at IS, the housing and discharge electrode 14 constitute a pair of electrodes between which an ionizing field is maintained by means of high tension unidirectional current supplied to the discharge electrode from any suitable source by lead IT. The potential supplied to the electrodes in this ionizing field is sufiicient to produce the well known corona or silent discharge from the discharge electrode, but is not sufiicient to bring about a disruptive or spark discharge.

Within the precipitating unit is a central electrode 20 supported by means of insulator 2 I, which ing, and made from a perforated plate or other foraminous material, such as a screen, which will permit the free passage of gas through the electrode. Electrode 23 is preferably of the same shape as electrode 20, but is open at its upper end to permit the introduction of gas as will be more fully explained. The pervious electrode 23 is spaced inwardly from the housing I2 to provide an annular passage 22 for carrying away the gas passing through said electrode. Electrodes 20 and 23 form the second pair of electrodes between which the precipitating fleld is maintained.

An annular chamber 25 is formed around the lower portion of housing I2 and communicates with the interior of the housing through a number of openings 26 through which gas may leave the housing and enter chamber 25 to reach discharge conduit 21 by means of which the cleaned gas is conveyed to a stack or other desired place. The precipitate collecting upon electrode '23 may be removed by any suitable means, such as rapping, and is prevented from entering openings 26 by means of a conical guard at 28. This precipitate falls to the bottom of the housing and may be removed from time to time by opening trap door 30 which also afi'ords access to the interior of the precipitating unit.

A non-discharging electrical fleld is maintained between electrodes 20 and 23 by means of unidirectional current supplied over lead 24 at suitable high tension to the central electrode, theopposing electrode 23 being grounded through housing I2. It is preferred that housings I II and I2 and electrode 23 are electrically connected together and grounded, and then they are always at a common potential and of one polarity. Electrodes I4 and 20 are both of a similar polarity, that is of the polarity opposite that of their opposing electrodes III and 23, respectively. However, the potential maintained between the electrodes of one pair is not necessarily the same as that between the other pair and the potentials may be varied independently of each other to obtain the best operating conditions. It is preferred, though not necessary, to maintain electrodes I4 and 20 at a negativepotential with respect to their opposing electrodes so that the gases passing through the ionizing field have the suspended particles charged negatively.

The electrical apparatus may be varied as desired to suit operating requirements. As typical of preferred practice, but without limitation thereto, we show means for supplying the precipitator with rectified high tension alternating current. Alternating current is stepped up by a transformer 32 and then passed through a full wave rectifier 34. Each of leads I1 and 24 is connected to a separate rectifier since this permits different voltages to be applied to electrodes I4 and 20, thus aflfording flexibility in operation;

' but leads n and 24 may both be connected to the In operation, the stream of gas containing suscipitator through inlet means I8 and flows upwardly and parallel to the surfaces of electrodes I0 and I4 so that the entire stream of gas passes through the ionizing field maintained between these two electrodes. The gas, now containing negatively charged particles, goes through conduit I3 to the interior of the fluid pervious electrode 23. Electrode 20 being negatively charged, repells the negatively charged particles suspended in the gas toward the positive electrode 23, so that the electrical field between these two electrodes is in substantially the same direction and in reinforcement of the fiow of gas outwardly through fluid pervious electrode 23. The negatively charged particles come into contact with electrode 23, or housing walls I2, where they lose their charge and collect on the electrode surfaces, eventually accumulating in larger masses which fall ofi, or may be shaken oil if necessary, and drop into the bottom of housing I2. The

clean gases are then discharged from the pretwo pairs of electrodes are arranged one above the other and are joined together so that they are placed in end-to-end relation. In this form,

housing IOa of the ionizing unit is mounted directly on housing I2a of the precipitating unit with the fluid pervious electrode 23a supported from housing I2a as before but placed with its open upper end in direct communication with housing Ila. From a single insulator 40 at the upper end of the ionizing unit is suspended the discharge electrode Ila and, below it, the central electrode 20a in such a way that electrodes Ida and I Ila form the pair of electrodes between which an ionizing field is maintained, and electrodes 20a and 23a form the second pair of electrodes between which a non-dischargingprecipitating field is maintained.

The electrical connections differ only in that the single high tension lead I1 is necessary to both the electrodes Ida and 20a, since in this case these two electrodes are maintained at the same potential relative to their opposing electrodes Illa and 23a which are likewise both at a common potential. As before, the gas containing suspended particles enters through inlet means I8, passes downwardly through the ionizing unit IOa, where the particles become charged in the ionizing field, and then enters the precipitating field inside pervious electrode 230 in which the charged particles are forced outwardly toward electrode 23a by means of the fleld maintained between that electrode and central electrode 234:. The gas passes through the openings in electrode 23a and is discharged through outlet means 21, while the precipitated particles are removed from the bottom of housing I20 as described.

Another variational form is illustrated inl 'ig'. 4. In this form of precipitator the ionizing unit I0 is constructed in the same way as described in connection with Fig. 1, but the construction of the precipitating unit is changed by making the inner electrode fluid pervious instead of the outer one, as in Fig. 1. In this case, the inner electrode 4| is shown as a cylindrical member of wire screen closed at its upper end by plate 42 and supported on insulators 43, which are in tator constructed as in Fig. 1 except that the turn mounted upon housing I2b. Housing I21) 15 of the precipitating unit is reduced in diameter in its upper portion opposite inner electrode ll, so that the housing acts directly as the second electrode of this pair and the precipitating field is maintained in the space between the outside of the electrode 4i and the inside of housing i2b.

The gas containing charged particles is introduced into the open lower end of electrode ll by means of nozzle 44 connected to conduit l3. Electrode 4| is preferably provided at its lower end with a non-pervious section as shown at 45 which extends for some distance below nozzle 44 and is preferably constricted at the bottom as shown. By means of this construction gas issuing from the nozzle is projected upwardly at a high velocity and is prevented by the constriction from passing out of the electrode except through the upper fluid pervious portion. If desired. the lower end of the electrode may be closed off entirely by means of an insulating member that fills the gap between nozzle 44 and electrode section 45. But this is not necessary with the illustrated construction since substantially no gas escapes through the open lower end of the e ectrode.

Housing in and i2b both have ground connections i5 and hence are maintained at a common polarity and potential. Electrodes H and 4| are preferably at a negative potential with respect to their opposing electrodes and may be supplied with a high tension current from separate sources, as illustrated in Fig. l, or from a single sourfce, as shown in Fig. 4. In the latter instance the electrical equipment includes a voltage divider l1 so that a lesser voltage may be impressed upon electrode ll than is applied to electrode H, though both electrodes are of a common polarity, i. e. negative.

In the operation of this form, gas enters through inlet means l8, passes upwardly through the ionizing unit In in which the particles become electrically charged and is then introduced inside fluid pervious electrode H by nozzle 44. The gas passing through the openings in electrode 4! enters a non-discharging field which carries the particles toward collecting electrode lZb, since electrode H is of the same polarity as discharge electrode ll, so that the precipitating field acts to reinforce the gas flow through the fluid pervious electrode. The precipitated material drops to the bottom of housing i2b, while the cleaned gases are discharged through the open upper end 48 of the housing.

There is shown in Fig. 5 a simplified form of precipitator in which all the electrodes are placed in a flue 50, typically of rectangular cross section. Discharge electrodes 5| extend across the path of the gas stream within the flue and are supported by suitable insulating means not shown. Electrodes 52 are placed between the discharge electrodes and are of sufficiently large diameter to prevent corona discharge from them. Electrodes 52 are connected directly to the walls of flue 50 and hence are grounded through ground connection i5. At a point in the flue removed from elec-.

trodes 5i and 52 and beyond them in the direction of the gas flow, a fluid-pervious non-discharging electrode 55 is mounted on insulators 56 which electrically insulate the electrode from the flue as well as provide mechanical support. Beyond electrode 55 is an opposing fluid-pervious nondischarging electrode 51 which is electrically connected to the walls of the flue and so is also grounded. While electrode 55 is indicated as being a perforated plate and electrode 51 as being wire screen, yet such perforated plates or screen may be used for either orboth of these non-discharging electrodes.

H An electrode 5i and an electrode 52 form a pair of electrodes between which an ionizing field is maintained by the application of high tension current to the discharge electrode bymeans not shown, but which may be similar to the devices previously described. Likewise, the application of high tension current to electrode 55 creates a nondischarging electric field between it and the opposing electrode 51. The gas containing suspended particles, moving toward the left as indicated by the arrow, first passes through the discharging or ionizing field between the pair of electrodes 5i and 52, so that the suspended particles become electrically charged. As these charged particles pass through electrode 55, which is charged at the same polarity as the particles, they are repelled from the electrode toward collecting electrode 51 so that the precipitating field acts to move the particles in the same direction as does the gas stream moving through electrodes 55 and 51. It will be noticed that the construction and operation of the precipitator shown in Fig. 5 is the same as described in connection with the earlier figures, but with the addition that both electrodes of the second pair, between which the precipitating field is maintained, are fluid-pervious, whereas in the earlier figures one of these electrodes was nonpervious.

Apparatus for carrying out the method of the invention including a discharge electrode, an intermediate fluid-pervious electrode through which the gas flows, and a collecting electrode which may or may not be fluid-pervious, together with means for establishing a high potential ionizing field between the discharge and intermediate electrodes and a separate substantially non-discharging field between the intermediate and collecting electrodes to efiect precipitation of the charged particles, is described and claimed in our copending application Serial No. 137,865, filed April 19, 1937.

The term non-discharging electrode, as used herein, is intended to denote an electrode of such configuration as to substantially prevent or minimize corona discharge therefrom at elevated potentials below the potential at which disruptive discharge occurs.

Having described .various embodiments of our invention, it will be realized that changes in the shape, arrangement and construction of the various features of the precipitators may be made without departing from the spirit and scope of our invention, and that the description and drawings are to be construed as illustrative of rather than descriptive upon the appended claims.

We claim:

1. In an electric precipitator in which the gas to be cleaned is first passed through an ionizing field in which the suspended particles are charged and subsequently passed through a substantially non-discharging field in which precipitation of the charged particles is effected, the combination of a pair of opposing substantially non-discharging electrodes spaced from each other, at least one of the electrodes being fluid pervious to permit the stream of gas to pass through it, and means for establishing an electric precipitating field between the two electrodes of such polarity that the field moves particles previously charged in an ionizing field in the same direction as the flow of gas through the pervious electrode.

2. In an electric precipitator in which the gas to be cleaned is first passed through an ionizing field in which the suspended particles are charged and subsequently passed through a substantially nondischarging field in which precipitation. of the charged particles is effected, the combination of a non-discharging fluid pervious electrode through which the gas passes, an opposing non-discharging electrode spaced from the fluid pervious electrode, and means for establishing an electric precipitating field between the two electrodes of such polarity that the field moves particles previously charged in an ionizing field in the same direction as the fiow of gas through the pervious electrode.

3. In an electric precipitator in which the gas to be cleaned is first passed through an ionizing field in which the suspended particles are charged and subsequently passedv through a substantially non-discharging field in which precipitation of the charged particles is effected, the combination of a non-discharging fluid pervious electrode through which the gas passes, an opposing non- .discharging electrode spaced from the fluid pervious electrode, both said electrodes being hollow and placed one within the other, and means for establishing an electric precipitating field between the two electrodes of such polarity that the field moves particles previously charged in an ionizing field in the same direction as the fiow of gas through the pervious electrode.

4. In an electrical precipitation apparatus through which fiows a stream 01' gas containing suspended particles to be removed, the combination of a pair of electrodes, one of which is a discharge electrode; means creating a high potential difference between said electrodesto establish an ionizing field; a second pair of electrodes, both of which are non-discharging and one of which is fiuid pervious to permit fiow of the gas through it; means creating a high potential difierence between the electrodes of the second pair to establish a precipitating field; one electrode of each pair being maintained at a common potential and the other two electrodes being of the same polarity, the relative polarity of the electrodes of the second pair being such as to establish the precipitating field in a direction that reinforces the gas flow throu h the pervious electrode.

5. In an electrical precipitation apparatus through which fiows a stream 01' gas containing suspended particles to be removed, the combination of a pair of electrodes, one of which is a discharge electrode; 'means creating a high potential difference between said electrodes to establish an ionizing field; a second pair oi electrodes, both of which are nondischarging and one of which is fiuid pervious to permit fiow oi the gas through it; means creating a high potential diflerence between the electrodes of the second pair to establish a precipitating field; one electrode of each pair being maintained at a common potential and the other two electrodes being of the same polarity, the relative polarity of the electrodes 01' the second pair being such as to establish the precipitating field in a direction that reinforces the gas flow through the pervious electrode carrying suspended particles to the other electrode of the second pair and to collect the particles thereon.

' 6. In an electrical precipitation apparatus through which flows a stream 01' gas containing suspended particles to be removed, the combination of a pair 01. electrodes, one of which is a discharge electrode; means creating a high potential difierence between said electrodes to establish an ionizing field; a' second pair of electrodes, both of which are non-discharging and one of which is fluid pervious to permit fiow of the gas through it; means creating a high potential difierence between the electrodes of the second pair to establish a precipitating field; one electrode of each pair being maintained at a common potential and the other two electrodes being of the same polarity, the relative polarity of the electrodes of the second pair being such as to establish the precipitating field in a direction that reinforces the gas fiow through the pervious electrode and to collect thereon suspended particles.

'7. In an electrical precipitation apparatus through which fiows a stream or gas containing suspended particles to be removed, the combination of a pair of electrodes, one (if which is a discharge electrode; means creating a high potential difference between said electrodes to establish an ionizing field; a second pair of electrodes, both of which are non-discharging and at least one of which is fiuid pervious to permit flow of the gas through it; means creating a high potential difference between the electrodes of the second pair to establish a precipitating field; the discharge electrode of the first pair and said fluid pervious electrode of the second pair being of the same polarity and the other two electrodes being maintained at a common potential, and the polarity of the electrodes of the second pair being such as to establish the precipitating field in a direction that reinforces the gas flow through said pervious electrode.

'8. In an electrical precipitation apparatus through which fiows a stream oi gas containing suspended particles to be removed. the combination of a pair of electrodes, one of which is a discharge electrode; means creating a high potential difference between said electrodes to establish an ionizing field; a second pair of non-discharging electrodes, one of which is non-pervious and one of which is fiuid pervious to permit fiow of the gas through it; means creating a high potential difference between the electrodes of the second pair to establish a precipitating field; the discharge electrode of the first pair and the non-pervious electrode of the second pair being of the same polarity and the other two electrodes being maintrode.

9. In an electrical precipitation apparatus through which flows a stream of gas containing suspended particles to be removed, the combination of a pair 01' electrodes, one of which is a discharge electrode; means creating a high potential difference between said electrodes to establish an ionizing field; a second pair of non-discharging electrodes comprising a central electrode of extended surface and an electrode surrounding and parallel to the central electrode, one oi the electrodes of the second pair being fluid pervious to permit fiow of the gas through it; means creating a high potential difference between the electrodes of the second pair to establish a precipitating field; one electrode of each pair being maintained at a common potential and the other two electrodes being of the same polarity, the relative polarity of the electrodes of the second pair being such as to establish the precipitating field in a direction that reinforces the gas flow through the pervious electrode.

10. An electrical precipitation apparatus through which fiows a stream of gas containing suspended particles to be removed, having in combination a pair of electrodes comprising an inner discharging electrode and an outer non-discharge electrode surrounding the discharge electrode, so arranged that the gas fiows generally parallel to the electrode surface; means for creating a high potential difference between said two electrodes to establish an ionizing field; a second pair of nondischarging electrodes of extended surface comprising an inner electrode and an outer surrounding electrode that is fluid pervious to permit gas flow therethrough; means for creating a high potential difference between the electrodes of the second pair to establish a precipitating field; the outer surrounding electrodes of each pair being both of one polarity and the inner electrodes being both of the opposite polarity whereby the precipitation field is of a direction to move charged particles toward the surrounding pervious electrode for collection thereon.

11. An electrical precipitation apparatus through which fiows a stream of gas containing suspended particles to be removed, having in combination a pair of electrodes comprising an inner discharging electrode and an outer non-discharging electrode surrounding the discharge electrode, so arranged that the gas flows generally parallel to the electrode surfaces; means for creating a high potential difierence between said two electrodes to establish an ionizing field; a second pair of non-discharging electrodes of extended surface comprising an inner electrode that is pervious to permit gas fiow therethrough and an outer surrounding electrode that is non-pervious; means for creating a high potential difl'erencev between the electrodes of the second pair to establish a precipitating field; the outer surrounding electrodes of each pair being both of one polarity and the inner electrodes being both of the opposite polarity whereby the precipitation field is of a direction to force charged particles, after passing through the inner electrode, toward the outer electrode for collection thereon.

12. An electrical precipitation apparatus through which flows a stream of gas containing suspended particles to be removed, having in combination a pair of electrodes comprising an inner discharging electrode and an outer non-discharging electrode surrounding the discharge electrode. so arranged that the gas flows generally parallel to the electrode surfaces; means for creating a high potential diflerence between said two electrodes to establish an ionizing field; a second pair of non-discharging electrodes of extended surface comprising an inner electrode and an outer surrounding electrode that is fluid pervious to permit gas fiow therethrough; the inner electrodes of each pair being joined together and extending substantially, end-to-end with respect to each other, and the outer electrodes of each pair being likewise joined together and extending substantially end-to-end with respect to each other; means for creating a high potential difierence between the electrodes of the second pair to establish a precipitation field; the outer surrounding electrodes of each pair being both'of one polarity and the inner electrodes being both of the opposite polarity whereby the precipitation field is of a direction to move charged particles toward the surrounding pervious electrode for collection thereon.

13. A method of electrical precipitation of suspended particles from a gas stream, that comprises subjecting a gas stream containing suspended particles to the action of a corona discharge in a high potential field to electrically charge the suspended particles; and passing the gas with the charged particles through a substantially non-discharging high potential field maintained between two opposing electrodes, in such a direction that the last mentioned field reinforces movement of particles by the gas stream toward one of said opposing electrodes.

14. A method of electrical precipitation of suspended particles from a gas stream, that comprises subjecting a gas stream containing suspended particles to the action of a corona discharge in a high potential field to electrically charge the suspended particles; and passing the gas with the charged particles through a substantially non-discharging high potential field maintained between two opposing electrodes of which one has a polarity opposite to that of the charged particles, the flow-of gas through the last-named field being in a direction toward said one electrode, and the relative polarity of the two electrodes being such as to move particles toward said one electrode in reinforcement of the movement of the.particles toward said one electrode 'by the gas stream.

FRIEDRICH H088.

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