US2722283A - Electronic precipitator - Google Patents

Description

Nov. 1, 1955 H. KLEMPERER A ELECTRONIC PRECIPITATOR 4 Sheets-Sheet 1 Filed March 50, 1951 ms/1 van-n6 Pawn? 500,

Ava/[M7025 HIM/S A'L EMPERER 64 EN 5. fl/VO/FEWS Nov. 1, 1955 H. KLEMPERER ETAL 2,722,283

ELECTRONIC PRECIPITATOR Filed March 30, 1951 4 Sheets-Sheet 2 IN VEN TO R s HANS KLEMPERER 61. ENN E. A NDREWS ATTORNEY Nov. 1, 1955 H. KLEMPERER ETAL ELECTRONIC PRECIPITATOR Filed March 30, 1951 4 Sheets-Sheet 3 BY EMQ 4 Sheets-Sheet 4 Filed March 30, 1951 DISK spa/2K OVER bOLTAGE CORONA MAx. COLLECTOR VOLTAGE WITHOUT RATIO OF DIAMETER 76 OF INNEI? @LLECTOR ELECTTWDE OR FIG. 5

D/AMETEI? 66 OF DISK TO D/AMETEI? OF 500v MEMBER 35.

VOLTAGE OF DISK IONIZEI? AND CVL/NDE/Z COLLECTOR g E W! EFFECT OF CYLINDER IONIZ/ SPACER OF DIS/($46 Q RAT/0 0F D/AMETER 0 48 TO DIAMETER s s v mmm N m mm m M w T W A mm DIMENSIONS OF SPACERS 48 nv /o/v/zE/2 SECTION United States Patent ELECTRONIC PRECIPITATOR Hans Klemperer, Belmont, and Glenn E. Andrews, Lexington, Mass., assignors, by mesne assignments, to APRA Precipitator Corporation, New York, N. Y., a corporation of Delaware Application March 30, 1951, Serial No. 218,450

2 Claims. (Cl. 183-7) This invention relates to electronic precipitators for removing particles from moving gases.

In certain types of electronic precipitators for flue gases, it has been customary to use two structurally separate units, an ionizer unit and a collector unit. In the ionizer unit fine wire electrodes were used in producing the corona discharge for charging particles in the flue gases. The particles were then, by means of a high potential differential in the collector unit, directed toward and precipitated on the walls of the collector unit. While the operating potentials in both units were very high, both units operated at different potentials. The operating potential of the collector unit for proper operating conditions was maintained generally higher than the potential in the ionizer unit. A primary reason for this was that the ionizer unit could not withstand the higher operating potential of the collector unit. If its potential were raised to that in the collector unit, arcing and general dielectric breakdown would occur. As a result, separate power supplies for each of these units were required along with separate insulating and separating structures for each unit. This entailed not only expensive duplication of construction but, also, because of the fineness of the wire required in the ionizer electrodes in the ionizer unit, it entailed an undesirable weak structure particularly susceptible to the very high temperature and corrosive conditions of flue gases as is usually the condition under which flue gas precipitators operate.

Pursuant to the present invention, it has been found that desirable ionizing characteristics are obtained by using a series of projections or fins in the ionizer electrode. It also has been found that the use of these fins permits not only an increase in operating potential of the ionizing electrode to that of the collector electrode without causing arcing or breakdown, but also an ionizer electrode structure which is rigid and highly resistant to injury under operating conditions of the precipitator. This invention, therefore, involves the use of projections or fins in ionizer electrodes in the precipitators.

The present embodiment of the invention incorporates the above in a flue gas electronic precipitator in a novel construction which, besides being more eflicient, is less expensive, less bulky, more readily manufacturable, and more readily usable with lower maintenance required than in precipitators heretofore in use. The embodiment consists generally of a housing containing a collection of hollow body members, each having an inlet and an outlet for passing therethrough flue gases to be cleaned. In each of the hollow body members is defined an ionizer and a collector section. A bus bar grill-work at each end of the housing is fixed securely to, and insulated from,

the walls of the housing by means of high voltage insulators. This bus bar grill-work through suitable adapters thereon provides a support as well as electrical coupling to a power source for an ionizer and collector electrode in the ionizer and collector sections, respectively, of each hollow body member. The collector electrode may con- Sist of an elongated rigid member while the ionizer electrode, in addition to an elongated rigid member of smaller cross-sectional dimension than that of the collector electrode, includes projections or fins extending laterally at spaced intervals along the elongated member. Relative dimensions of the collector electrode with respect to the ionizer electrode elements as the elongated body member, the fins and spacing thereof are Very important to proper operation and will be hereinafter more fully described.

The collector electrode is rigidly fixed at one of its ends to an end of the ionizer electrode to form a long rigid unitary electrode which, when supported at its extremities, as explained above, is highly resistant to shock and other operating conditions of the precipitator. A relatively simple, easily manufacturable and economical structure is provided by making the collector electrode of cylindrical hollow tubing and a rod for the elongated member of the ionizer electrode with the tubing and rod being rigidly connected end to end in axial alignment with each other. The fins are provided by disks having openings located centrally thereof and fitting the above-mentioned rod. The disks are then held in place between suitable spacers formed by sleeve members fitted over the rod and secured in place by a screw and nut arrangement.

These and other features, objects and advantages of the invention will become more apparent from the following description taken in connection with the accompanying drawings illustrating one embodiment of the invention, and wherein:

Fig. 1 is an isometric view of an electronic precipitator shown partly in section;

Fig. 2 is an elevational view shown partly in section of the electrode structure used in the embodiment in Fig. 1;

Fig. 3 is a graph for comparing operation-of disk and wire type precipitators;

Fig. 4 is a graph showing effect of S/D ratio on operation of the precipitator;

Fig. 5 is a graph showing eiiect of E/ B ratio on operation of the precipitator; and

Fig. 6 is a graph showing effect of C/D and S/B ratios on operation of the precipitator.

Referring to Fig. 1 in more detail, the illustrative embodiment comprises a housing 10 provided with tapered. sides 12 to form a pie-shaped segment so as to permit the assembly of several of such housings to form a large substantially circular unit similar in appearance to that shown in the co-pending application of Kenneth W. MacKenzie, Serial No. 99,461, filed June 16, 1949. At the outer wall 14 and inner wall 16 of the housing 10, there are located top and bottom high voltage insulators 18 and 20, respectively. Attached, as by screws 22 to the housing 10, the insulators 18 and 20, respectively, have mounted therein bus bar structures 24 and 26 for providing top and bottom supports, respectively, for an ionizing electrode structure 28 and collector electrode structure 30 through adapters 32 ant 34, respectively. An ionizing electrode 28 and collector electrode 30 are supported, as explained above, axially ofeach of a plurality of long tubular precipitator body members 35 parallel to each other and forming a honeycomb appearing network in said housing.

The collector electrode 30 may consist of a hollow cylindrical metallic tube, preferably of such material as stainless steel, fitted over a lug 36 at the bottom of adapter 32. Adapter 32 may be held in place in the bus bar grill-work, as by pin 38. The bottom end 40 of the collector electrode 30 has rigidly fixed thereto a rod 42, as by a screw 44, to form the body portion of the ionizer electrode 28. Disks 46 having an opening located substantially centrally thereof are fitted over the rod 42 and are maintained rigidly in place in space relation to each other by spacer sleeve members 48 like- I wise fitting over the rod 42. The disks and spacers are held in place by a washer 50 and nut 52 on the threaded end 54 of the rod 42 (Fig. 2). Threaded end 54 of the rod 42 is also fitted into a recess 56 in the supporting adapter 34 which is fixed to the bottom bus bar grill-Work 26, as by a pin 58. The material used in the ionizer electrode 28 is preferably stainless steel to withstand the high corrosive and high temperature flue gas operating conditions. Suitable resistance to these conditions may also be obtained by using tungsten in the disks or fins 46. Other parts, as the tubular body member 35, adapters 32 and 34, and bus bar grill- work 24 and 26, are likewise preferably made of stainless steel to withstand operating conditions.

In operation a high potential differential is maintained between the electrodes 28 and 30 and the tubular body members by a suitable power source 60. In this instance the electrodes 28 and 30 are maintained at a negative potential and the body members 35 are connected to ground 62.

The potential across the electrodes 28 and 30 is such that a corona discharge occurs at the periphery of each of the disks 46 on the ionizer electrode 28 with no corona discharge occurring at the collector electrode 30. Gases to be cleaned, as gases from furnace stacks, which may be at elevated temperatures in excess of 1000 degrees Fahrenheit, are passed upwardly through the tubular body members 35, each of which has an ionizer section located at the end occupied by the ionizer electrode 28, and a collector section located at the end occupied by the collector electrode 30. As the gases pass through the ionizer section, particles therein are electrostatically charged with a negative charge by the corona discharge from disks 46. As the charged particles which have not adhered to the ionizer section walls pass upward through the collector section with the gases, they are directed by the Potential differential between collector electrode 30 and the tubular body member 35 toward the walls of the body member 35, where they adhere and accumulate. These accumulated particles may later be removed by disconnecting the potential source 60 and blowing air or steam through the body members 35 or by any other suitable means.

As has been mentioned above, the dimensioning of the various elements is important to proper operation. In operation, it is desirable to create as high an ionization current as possible in the ionizer electrode 28. A high ionization current permits charging a larger number of particles per unit time and thereby the accommodation of larger gas volumes. Referring to Fig. 3, it is seen that the use of disks in the ionizer electrode produces a greatly increased ionization current over that possible by a wire electrode at the same potential differential. The graphs in Fig. 3 are for a one foot long wire ionizer electrode .030 of an inch in diameter and a one foot length 64 of fin type ionizer electrode 28 having disks 42 with three quarter inch diameter 66 and a thirty-thousandths of an inch thickness 68 with a one inch spacing 70 between disks on an elongated member 42 with separators 48 having three-eighths of an inch diameter 74. Both electrodes were operated in a tubular member 35 having a two and one-half inch cross-sectional dimension.

The ratio of the spacing 70 between disks 46 to the diameter 66 of the disks 46, herein termed the S/ D ratio, has been found to be a very important factor in achieving a high ionizing current. At a given fixed operating potential the ionizing current varies with the S/D ratio. The ionizing current is maintained relatively high through only a small range of S/D ratios. This may be seen in Fig. 4, which is a graph of ionizing current versus S/D ratio. Optimum ionization current occurs within a region substantially eighty per cent of the peak ionization current region. This lies between the S/D ratios of .43 and 1.2 which is therefore the region preferred for use in the present embodiment.

Another important consideration for proper operation is that of the ratios of the diameter 76 of the collector electrode 30 and the diameter 66 of the disks 46 to the smallest cross-sectional dimension in the hollow tubular body member 35 and herein termed the E/B ratio. The E/ B ratio is desired as high as possible consistent with preventing arc-over from the disks 46 and preventing corona discharge at the collector electrode 30. The effect of the E/B ratio in the collector electrode 30 and disks 46 may be seen by curves 80 and 82, respectively, in Fig. 5. It is seen that the curves 80 and 82 intersect at a point 84 which indicates the region of preferred E/B ratios and is found at or near a value of .24, and preferably between the values .15 and .40. It should be noted here that the point of intersection 84 of curves 80 and 82 gives a single E/B ratio value for both the collector electrode 30 and the disks 46. Thus for this ratio the diameter 76 of the collector electrode 30 and the diameter 66 of the disks 46 are the same. It is preferred that the diameters 66 and 76 be maintained the same or nearly the same, not only because a maximum operating voltage may be used with minimum arc-over risk, but also because it improves the gas flow conditions through the precipitator. The actual operating voltage will be somewhat below the point 84 to provide a safety factor or tolerance.

Having found the diameter 66 of the disks 46 as explained above, it becomes important to determine the diameter 74 to be used for the spacers 48. It has been found that the ratio of the diameter 74 to the diameter 66 of the disks 46, herein termined the C/D ratio, has a great effect upon ionizing current flow from the disks 46 in the ionizing electrode 28. The smaller the C/D ratio for a given diameter 66 of disks 46, the higher is the ionizing current from disks 46. However, as the C/ D ratio decreases, the operating potential at which the spacer will itself start to have a corona discharge, is decreased. It is undesirable for a corona discharge to occur from the spacers 48 since the net etfect would be to decrease the ionizing current from the disks 46, thereby decreasing overall ionizing current flow. Thus it is important to maintain as small a diameter 74 of spacers 48 as possible consistent with preventing corona discharge at the spacers 48. Also the cross section of rod 42 should be large enough to provide a rugged mounting and support for the disks in order to keep them aligned axially in the body member 35. Referring to Fig. 6, the curve 86 gives the corona starting voltage of the spacers 48 as effected by the ratio of diameter 74 of spacers 48 to the inside diameter of the tubular body members 35 and herein termed the C/D ratio. The curve 88 gives the effect of the ratio of diameter 74 of spacers 48 to diameter 66 of disks 46, or C/D ratio, upon ionizing current flow in the ionizer electrode 28. It has been found that the preferred region of operation lies between C/D ratios .33 and .60 shown by arrows 90 (Fig. 6). Thus if a diameter 66 of three-quarters of an inch is used for disks 46 and a body member 35 having a two and a half inch inside diameter, the diameter 74 of spacers 48 will lie preferably between .25 and .45 inch. These dimensions correspond to C/B ratios of .1 and .18, respectively, for determining from curve 86 (Fig. 6) the proper operating voltage.

This invention is not limited to the particular details of construction or materials herein described as equivalents will suggest themselves to those skilled in the art. It is therefore intended that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An electronic precipitator comprising an external tubular member of uniform polygonal cross section along its length; an internal elongated member inside one end of said external tubular member forming a collector electrode of uniform circular cross section along its length; an ionizing electrode in the other end of said member, said ionizing electrode comprising an elongated rigid member fixed at one end to one end of said collector electrode and having disks extending laterally from said rigid member, said collector electrode and said disks having substantially equal diameters in the region of connection of said ionizing electrode to said collector electrode, the ratio of the diameter of the elongated rigid member to the diameter of said disks in said region being less than .6 and being large enough to substantially prevent ionization at the surface of said rigid member; and means holding said electrodes in place comprising an extension of said collector electrode and an extension of said ionizing electrode beyond the respective ends of said tubular member, bus bars positioned beyond the ends of said tubular member, said extensions having slots therein engaging said bus bars, said extensions being insulatedly supported with respect to said tubular member whereby said collector electrode and said ionizing electrode are held along the axis of said tubular member.

2. An electronic precipitator comprising an external tubular member of uniform polygonal cross section along its length; an internal elongated member inside one end of said external tubular member forming a collector electrode of uniform circular cross section along its length; an ionizing electrode in the other end of said member, said ionizing electrode comprising an elongated rigid member fixed at one end to one end of said collector electrode and having disks extending laterally from said rigid member, said collector electrode and said disks having substantially equal diameters in the region of connection of said ionizing electrode to said collector electrode, the ratio' of the diameter of the elongated rigid member to the diameter of said disks in said region being less than .6 and being large enough to substantially prevent ionization at the surface of said rigid member, the ratio of the spacing between said disks and the diameter of said disks being on the order of 1.2; and means holding said electrodes in place comprising an extension of said collector electrode and an extension of said ionizing electrode beyond the respective ends of said tubular member, bus bars positioned beyond the ends of said tubular member, said extensions having slots therein engaging said bus bars, said extensions being insulatedly supported with respect to said tubular member whereby said collector electrode and said ionizing electrode are held along the axis of said tubular member.

References Cited in the file of this patent UNITED STATES PATENTS 1,322,163 Conover Nov. 18, 1919 1,339,480 Schmidt May 11, 1920 1,440,887 Nesbit Jan. 2, 1923 1,473,806 Bradley Nov. 13, 1923 2,192,249 White Mar. 5, 1940 2,244,278 White June 3, 1941 FOREIGN PATENTS 44,547 France Apr. 7, 1949

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