US2684760A - Electrical precipitator and electrode structure therefor - Google Patents

Description

July 27, 1954 H. A. WINTERMUTE ELECTRICAL PRECIPITATOR AND ELECTRODE STRUCTURE THEREFOR 2 Sheets-Sheet 2 Filed Oct. 12., 1 951 I INVENTOR I Han "y -14. MnTermuZ ATTORNEYS Patented July 27, 1954 ELECTRICAL PRECIPITATOR AND ELEC- TRODE STRUCTURE THEREFOR Harry A. Wintermute, Plainfield, N. J., assignor to Research Corporation, New York, N. Y., a

corporation of New York Application October 12, 1951, Serial No. 250,965

9 Claims. (01. 209-427) This invention relates to an electrical precipitator and to an electrode structure therefor. More particularly, the invention relates to an electrical precipitator for removing suspended solid particles from gas streams and for classifying the precipitated particles. The collecting electrode structure of the invention is especially constructed in a unique arrangement and plays an important part in the classification of the precipitated particles.

Fly ash from boilers, particularly boilers burning powdered or finely pulverized coal, is suspended in the flue gases. This ash is chiefly composed of (1) fine ash particles that are low in carboniferous material and hence cannot be reburned advantageously and (2) particles of unburned coal and relatively large particles of coked coal that are high in carbon and low in ash content and that can be returned to the boiler together with the powdered coal feed. If the high carbon fraction of the fly ash can be separated from the fine ash particles, the former can be returned to the furnace and burned either alone or together with the powdered coal feed.

An object of the invention is to provide an electrical precipitator that efficiently removes suspended particulate material from gases.

Another object is to provide a precipitator that effects classification of the precipitated material.

Another object is to provide an electrical precipitator that removes fly ash from flue gases and separates the precipitated ash into combustible and non-combustible portions.

Another object is to provide a collecting electrode structure for an electrical precipitator that functions to classify material deposited thereon.

These and other objects of the invention as may appear hereinafter are achieved in an electrical precipitator including a housing; gas inlet means and gas outlet means providing for the passage of a stream of gas to be cleaned through the housing; complementary discharge and collecting electrodes disposed in spaced relation in the gas stream path in the housing, the collecting electrodes comprising a solid extended surface member having an active face exposed to the gas stream path and an opposite face removed from the gas stream path, the extended surface member having an opening therethrough narrow in the direction of gas flow, a conductive plate member positioned behind the opening and in spaced relation thereto, and means providing a semi-conductive path electrically connecting the extended surface member to the conductive plate member; means for cleaning the surfaces of the collecting electrodes; and means for separately removing the material collected on the extended surface member and the conductive plate mem ber.

Typically, the collecting electrode structure of the invention includes a solid extended surface member having an active face adapted to be exposed to a stream of gas to be cleaned and an opposite face adapted to be removed from the gas to be cleaned, the extended surface member having an opening therethrough narrow in the direction of gas flow, a conductive plate member positioned behind the opening in the extended surface member and in spaced relation thereto, and means providing a semi-conductive path as the sole path electrically connecting the extended surface member to the conductive plate member.

The invention will be described in greater detail with reference to the drawings in which:

Fig. 1 is a longitudinal, vertical, sectional view of one form of electrical precipitator embodying the invention;

Fig. 2 is a transverse sectional view thereof taken along the plane of the line 2--2 of Fig. 1;

Fig. 3 is a horizontal sectional view thereof taken along the plane of the line 3-3 of Fig. 1;

Fig. 4 is an enlarged fragmentary detail view of a portion of the precipitator of Figs. 1 to 3 showing the construction of a flight conveyor and electrode rapper mechanism;

Fig. 5 is a sectional view taken along the plane of the line 5-5 of Fig. 4;

Fig. 6 is a vertical, axial, sectional view of another form of electrical precipitator in accordance with the invention; and

Fig. 7 is a sectional view taken along the plane of the line 1--1 of Fig. 6.

Referring to the drawings, particularly to Figs. 1 to 3 thereof, the electrical precipitator shown has a housing I0 provided with a gas inlet duct H and a gas outlet duct l2. Gas to be cleaned flows through the housing in the direction of the arrows of Fig. 1. The usual dust-receiving hoppers l3 and M are located at the bottom of the housing. The hoppers communicate with the precipitation chamber and are provided with conventional outlets (not shown) at their hottoms for removal of dust.

Within the housing are disposed collecting electrodes [5 and complementary discharge electrodes H5. The collecting electrodes are generally vertically disposed and parallel to the flow of gas through the precipitator; they are spaced transversely of the precipitator. The discharge 3 electrodes are disposed intermediate the collecting electrodes.

Collecting electrodes l5 are assembled from a plurality of identical elements I! that are H- shaped in horizontal cross-section. The panels Ila and Ill) are preferably of Transite or other similar construction material that is semi-conducting or has a high electrical resistance. These panels are secured to a spacer strip l8, preferably of conducting metal. The H-shaped elements are suspended from a frame ill by brackets 28 that are suitably attached to the frame and to the spacer strips [8.

These H-shaped elements are spaced apart in the longitudinal direction to provide vertical slots 2! that extend vertically across the path of the gas stream and are relatively narrow in the direction of flow of the gas stream.

Suspended from the frame [9 are a plurality of conductive metallic plates 22. These plates depend into the hollow interior of the collecting electrode structure and one such plate is provided for each pair of oppositely disposed slots 2|. The plates extend in the vertical direction for substantially the full length of the slots and they are somewhat wider than the slots. The plates are spaced midway between opposed slots and are centered with respect thereto.

The bottoms of the H-shaped members are closed by strips 23 and conduits 24, interconnect the bottoms of the members. An endless flight conveyor or drag chain has its upper run 25 extending through the bottoms of the H-shaped members and conduits M. The conveyor chain is trained over a driven sprocket 26 and an idler sprocket 27 and the lower run 28 of the conveyor is returned through space provided in the hopper area below the precipitation chamber. Material that settles in the bottoms of the hollow collecting electrodes is moved by the flight conveyor to a hopper'29. As seen in Fig. 3, the conveyor system is driven by a sprocket wheel 3t from a conventional motor (not shown).

It will be seen that the collecting electrode structure is grounded through the frame is and housing I9.

Discharge electrodes l5 are suspended from an insulated framework 3!, supported by hangers 32, depending from a beam 33, supported on insulators 3 3 carried by the roof of the precipitator housing. As shown in Fig. 3, the discharge electrodes are positioned between slots ii in the spaces intermediate adjacent collecting electrode structures. Thus, as will be expplained more fully hereinafter, one discharge electrode is associated with and serves two slots.

The discharge electrodes are specifically shown as rods having discharge points 35. The discharge points are spaced in the vertical direction. Preferably, the points are oriented so that a pair of opposed points are directed towards the cooperating slots of the collecting electrodes.

In operation, a source of high tension, preferably unidirectional, current is applied across the complementary discharge and collecting electrodes. As is usual in the art, one terminal of a source of such current, preferably the negative terminal, is connected to the insulated discharge electrode system and the other terminal of the source is connected to the collecting electrode system through ground. With the electrodes thus energized, gas to be cleaned, for example flue gas from a powdered coal burning furnace, is passed through the precipitator. In accordance with well known principles, the suspended 4 particles of ash and carbonaceous material are charged in the interelectrode space. The charged particles are attracted to and deposited on the collecting electrode structure.

Because of the difference between the areas of the panels [1 and the slots 2| of the collecting electrodes, most of the suspended material is attracted to and deposited on the panels I"! which, being of a semi-conductive material, soon acquire a negative charge intermediate the ground potential of the plates 22 and the discharge'electrodes H5. The carbonaceous particles, being relatively highly conductive, rapidly lose their-charge to the panels I! and, under the influence of the gas stream and the electrical conditions, these particles dance along the panels I! in the direction of gas flow until they reach one of the slots 2!. 'Here they are driven out of the gasstream by corona discharge and transported to the grounded plates 22 in the hollows of the collecting electrodes and are there precipitated. The somewhat negative charge of the panels I! assists in causing a strong coronav discharge to terminate on the grounded plates 22 and aids in trapping the carbonaceous particles.

Ash particles low in carbon are much less conductive than the carbonaceous particles and the former to a large extent remain as a deposit on the panels ll.

Thus a separation or classification of the carbonaceous particles and ash particles is effected at the collecting electrodes. When the electrodes are rapped, the ash particles fall into the hoppers 53 and i4 and the carbonaceous particles fall into the bottoms of the hollow collecting electrodes from which they are removed to the separate hopper 29 by the flight conveyors.

Although any suitable rapping device may be employed, one such device particularly adapted to the precipitator shown in Figs. 1 to 3 is illustrated in Figs. 4 and 5. In this rapping device, the motion of the flight conveyor is utilized to effect rapping.

Referring to Figs. 4 and 5, wherein like reference numerals refer to corresponding parts of the precipitator of Figs. 1 to 3, the H-shaped members of the collecting electrode structure, including the panels 17 and spacer strip l8, depend into a trough 3% in which is carried the upper run 25 of the flight conveyor. The H-shaped members are suspended from a flexible bracket 20 and are free to swing to a limited extent in the trough 35. Stop members 31 and 38 carried by the trough limit the swinging movement .of the H-shaped members.

The chain conveyor has flights 39 spaced at intervals .therealong for scraping the bottom of the trough. The flights are provided with upstanding flexible fingers 48 that extend somewhat above the level of the lower edge of the spacer strips l8. As the conveyor moves through the trough, the fingers 46 engage the spacer strips l8 and snap under the lower edges thereof to impart a rapping or vibratory movement to the H-shaped members. This action dislodgesprecipitated material from the collecting electrodes. Sufiicient vibratory motion is transmitted through the frame 19 to the metallic plates 22 to insure that the latter are kept practically free from deposits.

Referring to Figs. 6 and 7, the precipitator shown is of the cylindrical, vertical gas flow type. The precipitator has a cylindrical Transite or wooden shell tll including a gas inlet and dustreceiving chamber 42 at the bottom into which gas to be cleaned is conducted through the inlet pipe 43. At the top is a gas outlet chamber 44 provided with an outlet pipe 45. The precipitation zone extends between a lower diaphragm 46 and an upper diaphragm 41.

A gas channel is provided through the precipitation zone by a plurality of axially aligned, vertically spaced, semi-conductive rings 48, formed of Transite or the like. These rings are supported on spider arms 49, that may be of Bakelite or metal and are fitted into holes 59 in the rings and supported on the casing M by screws 5i. The spaces 52 between the rings are relatively narrow with respect to the vertical dimension of the rings.

Opposite each space 52 and surrounding the same is a metallic or conductive ring 53. These rings are carried by conductive spider arms 54 secured to the casing 4| by screws 55.

An insulating bushing 56 supports a discharge electrode 57 that extends axially into the assembly of rings 48 and has discharge points 58 positioned opposite the openings 52.

A cleanout door 59 gives access to the chamber 42 and another cleanout door 60 opens into the chamber 6i included between the diaphragms 46 and 47.

A conductive, metallic, cylindrical sheath 62 surrounds the shell 4i and electrically grounds the rings 48 and 53 through the spider arms and the screws 5i and 55 that make contact with the sheath.

From the description given hereinbefore, of the apparatus of Figs. 1 to 3 and its operation, the operation of the apparatus of Figs. 6 and 7 is readily understood. The precipitator electrodes are energized and gas to be cleaned is conducted through the precipitator in the direction of the arrows of Fig. 6. As in the operation of the apparatus of Figs. 1 to 3, the ash particles are deposited on the interior surfaces of the rings 48 and the highly carbonaceous particles are deposited on the surrounding rings 53. Deposits removed from the rings 53 fall on the diaphragm 46 and are removed through the door 6t while deposits removed from the rings 48 fall into the chamber 42 from which they are removed through the door 59.

The surfaces of the collecting electrodes that e directly exposed to the gas stream may be called active surfaces. These surfaces are electrically connected to the conductive plate members positioned behind the openings and removed from the gas solely through semi-conductive paths in order that the active surfaces may acquire a charge intermediate that of the conductive plates and that of the discharge electrodes. This semi-conductive path may be provided in a variety of ways. Where the members providing the active surfaces are constituted of a semi-conductive material such as Transite, the material of the member itself usual- 1y provides the necessary electrical resistances. The active surface members may be of conductive metal and the necessary resistance may be obtained by mounting the metallic members on elements of semi-conductive material.

From the foregoing description, it will be seen that the present invention provides an electrical precipitator and collecting electrode structure therefor that accomplishes the objects of the invention.

Transite and Bakelite materials are referred to herein as examples of semi-conductive materials. The former is a consolidated composition of portland cement, fine sand and comminuted 6 asbestos and the latter is a phenol-formaldehyde condensation resin.

Similar subject matter is disclosed in my Patent 2,668,600, filed April 6, 1953.

I claim: 5'

1. A collecting electrode for differential collec tion by electrical precipitation of materials suspended in a gas comprising an elongated boxlike structure having a hollow interior and providing active material-collecting surfaces on the exterior thereof, two of the opposed walls of said structure having opposed parallel elongated slots therethrough, a conductive plate member in said structure intermediate said slots and in spaced relation thereto, and means providing a semiconductive path electrically connecting said boxlike structure to said connductive plate member.

2. An electrical precipitator comprising a housing; gas inlet means and gas outlet means providing for the passage of stream of gas to be cleaned through said housing; complementary discharge and collecting electrodes disposed in spaced relation in the gas stream path in said housing, said collecting electrode comprising an extended surface member having an active face exposed to the gas stream path and an opposite face removed from the gas stream path, said extended surface member having an opening therethrough narrow in the direction of gas flow, a conductive plate member positioned behind said opening and in spaced relation thereto, and means providing a semi-conductive path electrically connecting said extended surface member to said conductive plate member; and means for separately removing the material collected on said extended surface member and said conductive plate member.

3. An electrical precipitator as defined in claim 2 wherein said discharge electrode is disposed adjacent to the narrow opening of said collecting electrode.

4. An electrical precipitator comprising a housing; gas inlet means and gas outlet means providing for the passage of a stream of gas to be cleaned through said housing; a plurality of vertically extending, spaced collecting electrodes in said housing arranged in parallel relation to the direction of gas stream flow, each of said collecting electrodes comprising an elongated box-like structure having a hollow interior, two of the opposed walls of said structure having opposed, parallel elongated slots therethrough extending transverse to the direction of gas stream flow, a conductive plate member in said structure intermediate said slots and in spaced relation thereto, and means providing a semi-conductive path electrically connecting said box-like structure to said conductive plate member; complementary discharge electrodes disposed in parallel, spaced relation to the slots of said collecting electrodes; means for rapping said collecting electrodes; hopper means receiving material removed from the exterior surfaces of said collecting electrodes; and separate hopper means receiving material removed from the conductive plate members and the interiors of said box-like collecting electrode structures.

5. A collecting electrode for differential collection by electrical precipitation of materials suspended in a gas comprising a collecting member providing a solid extended collecting surface, said collecting member having an elongated opening therethrough narrow in the direction of gas flow, a conductive collecting member po- 7 sitioned behind the elongated opening and in spaced relation thereto, and-=means providing a semi-conductive path electrically connecting said conductive collecting member and said collecting member.

65A collecting electrode as defined in claim 5 wherein said collecting member comprises Transite and said conductive collecting member comprisesmetal.

7. A collecting electrode comprising an extended surface member having an active face exposedto the gas stream path and an opposite face removed from the gas stream path, said extended surface member having an opening therethrough narrow in the direction of gas flow, a conductive extended surface member of greater extent than said opening positioned behind and in alignment with said opening and in spaced relation thereto, and means providing a semi-conductive path electrically connecting said extended surface member to said conductive extended surface-member.

8. The invention as defined in claim? wherein the extended surface -member comprises a first hollow cylinder, and said-conductive extended surface member comprises a second hollow cylinder.

9. The invention-as defined in claim 8 wh rein said first hollow cylinder comprises Tran ite and said second hollow cylinder comprises met 1.

References'Citedin the file of thispatent UNITED STATESPATENTS Number Name Date 1,335,758 Schmidt Apr. 6, 1920 2,283,964 Wyckoff May 26, 1942 FOREIGN PATENTS Number Country Date 360,809 Great Britain Nov. 12, 1931 365,018 Great Britain Jan. 14, 1932 536,810 Germany Nov. 17, 1931 539,879 Germany Dec. 3, 1981 691,165 Germany May 17, 1940

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