US3844742A

US3844742A - Electrode cleaning mechanism for electrostatic dust precipitator

Info

Publication number: US3844742A
Application number: US00333019A
Authority: US
Inventors: H Petersen
Original assignee: FLSmidth and Co AS
Current assignee: FLSmidth and Co AS
Priority date: 1972-02-18
Filing date: 1973-02-16
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29
Also published as: DE2307960A1; FR2172348A1; BR7301155D0; JPS4890070A; CA986851A; SE381409B; ES411703A1; ZA73820B; SU733506A3; FR2172348B1; DE2307960C2; FI53539C; AU5221073A; CH545657A; GB1330612A; FI53539B; IT979146B

Abstract

An electrode cleaning mechanism for electrostatic dust precipitators is disclosed which has at least one eccentrically mounted electrode vibrated by a rapping mechanism which includes a tumbling hammer that is rotated about a horizontal shaft so that it continually swings down in a pivotal pendular movement until the impact surface of the hammer strikes against the end of a rapping bar which is thus sharply moved axially out of a rest position to jar the electrode. The rapping bar is urged back to its rest position after jarring the electrode by the weight of the eccentrically mounted electrode which is connected to the rapping bar during this return movement.

Description

United States Patent [191 Petersen 1 Oct. 29, 1974 1 ELECTRODE CLEANING MECHANISM FOR ELECTROSTATIC DUST PRECIPITATOR [75] Inventor: Helge Hogh Petersen, Copenhagen,

Denmark [30] Foreign Application Priority Data Feb. 18, 1972 Great Britain 7713/72 [52] US. Cl 55/112, 55/130, 55/148, 55/154, 173/94 [51] Int. Cl B03c 3/76, B03c 3/45, B030 3/86 [58] Field of Search 55/112, 12, 13, 108, 109, 55/113, 114, 148,149, 154, 156, 273, 272, 283, 299, 300, 130; 173/102, 94, 90, 115

3,200,565 8/1965 Gustafsson 55/112 3,201,923 8/1965 Gustafsson et a1 55/112 3,219,130 1l/1965 Steuernagel et al. 173/102 FOREIGN PATENTS OR APPLICATIONS 564,703 2/1958 Belgium 55/112 437,626 11/1935 Great Britain 55/112 721,846 l/l955 Great Britain 55/112 821,752 10/1959 Great Britain... 55/112 469,909 12/1928 Germany 55/112 505,794 8/1930 Germany 55/112 Primary Examiner-Dennis E. Talbert, Jr. Attorney, Agent, or FirmPennie & Edmonds [5 7] ABSTRACT An electrode cleaning mechanism for electrostatic dust precipitators is disclosed which has at least one eccentrically mounted electrode vibrated by a rapping mechanism which includes a tumbling hammer that is rotated about a horizontal shaft so that it continually swings down in a pivotal pendular movement until the impact surface of the hammer strikes against the end of a rapping bar which is thus sharply moved axially out of a rest position to jar the electrode. The rapping bar is urged back to its rest position after jarring the electrode by the weight of the eccentrically mounted electrode which is connected to the rapping bar during this return movement.

17 Claims, 3 Drawing Figures PATENTEUBCTZS I874 sum 10! 2 ELECTRODE CLEANING MECHANISM FOR ELECTROSTATIC DUST PRECIPITATOR BACKGROUND OF THE INVENTION This invention relates generally to electrostatic dust precipitators used for removing dust from gases as, for example, smoke gases generated in the production of cement. Such precipitators are usually constructed with wire or band shaped discharging electrodes and plate-like collecting electrodes and the dust precipitated is commonly deposited on the collecting electrodes. To prevent accumulating layers of dust on these electrodes with consequent reduction in the efficiency of the precipitator it is necessary to clean the collecting electrodes by removing dust deposited on the electrodes at regular intervals. More particularly, therefore, this invention relates to electrode cleaning mechanism for such precipitators.

Usually, the collecting electrodes are cleaned by shaking or vibration created by rapping or striking the collecting electrodes or their attachment irons. On one known construction the collecting electrodes are assembled in rows and the cleaning mechanism includes a common rapping bar for each row; the rows being vibrated as a result of tumbling hammers striking the rapping bars in a predetermined sequence. This construction, however, involves several drawbacks. First of all, the continuous rapping and vibration to which the mechanism is subjected produces very high mechanical stresses, particularly in the tumbling hammers and the rapping bars producing, consequently, heavy wear and a decrease in the life of the entire mechanism. Furthermore, the gases to be relieved of dust are usually so hot that the various components of the mechanism are subjected to heat expansion tending to produce uneven loading as the tumbling hammers strike the rapping bars, inturn, producing increased stress and undue wear on the mechanism in a very short time. According to this invention, an electrostatic dust precipitator is provided which overcomes the drawbacks associated with known cleaners.

SUMMARY OF THE INVENTION In accordance with the teachings of this invention, the electrode cleaning mechanism comprises a first support means for eccentrically mounting at least one electrode and a second support means for mounting a rapping bar for reciprocal axial movement between a rest position and second position spaced axially from the rest position. The cleaning mechanism further includes means for connecting each electrode to the rapping bar for movement with the rapping bar. The mechanism further includes a rotatable shaft and a tumbling hammer mounted on the shaft for rotational therewith. The tumbling hammer is also mounted on the shaft for free pendular pivotal movement relative thereto during an arcuate segment bringing it into relatively sharp contact with the end of the rapping bar. Thereby, the rapping bar is moved in a generally axial direction from the rest position to the second position thus imparting a jarring motion to eachelectrode; such jarring or vibration of the electrode acting to dislodge any dust particles deposited thereon during the precipitation operation.

Advantageously, the force imparted to the rapping LII bar by thehammer is directed through the axis of the rapping rod and the connection means between the electrode and the rapping bar are specially constructed such that the impact reaction between the rapping bar and the electrode is directed substantially along the axis of the rapping bar. In order to eliminate wearproducing reaction forces on the rotational shaft and the tumbling hammer (and any support structure therefor), the distance between the point of impact with the rapping bar and the pivot axis of the hammer is substantially equal to the radius gyration of the hammer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a cleaning mechanism constructed according to this invention.

FIG. 2 is a perspective view of an alternative embodiment of a cleaning mechanism constructed according to this invention.-

FIG. 3 is a perspective view of a portion of either embodiment showing a special mounting arrangement according to this invention.

DETAILED DESCRIPTION OF THE INVENTION The constructions shown in the drawings each have at least one plate-shaped collecting electrode 1 and a rapping bar 2 loosely connected with each electrode. As shown in FIG. 2, each collecting electrode is movably and eccentrically suspended from a fixed support 4 by means of fittings 3 connected to its upper end. In the construction shown in FIG. 2, two electrodes are suspended from support 4 and one rapping bar is common to both collecting electrodes. In the FIG. 1 construction there are also two electrodes however each is independently suspended from support 4 (not shown in FIG. 1) and each electrode has an individual rapping bar.

Attached to one end of each tubular rapping bar is a rounded anvil 8 which defines the impact surface for the respective rapping bar as will become clear as the description proceeds. The cleaning mechanism further includes a tumbling hammer 9 for each rapping bar. Each tumbling hammer has a substantially flat impact surface 9a and is pivotable about pin 10a extending through an arm 10 which is fixed to a rotatable shaft 11 by a releasable U-shaped clamping bow 12 secured with two nuts (not shown). The shaft 11 rests in a series of stationary bearings 13, of which only'one is shown in the drawing for the sake of clarityQThe shaft 11 is driven by a motor and suitable gearing not shown in the drawing.

In both constructions shown in the drawings each rapping bar 2 is non-rigidly connected to the respective collecting electrode by a specially constructed connection means in such a manner that the reaction between the rapping bar and the electrode has its line of action substantially along the axis of the rapping bar. As shown this connection means includes a tongue 5 passing completely through a slot extending diametrically through the tubular rapping-bar and an impact member 7 fixed to the shaft within the slot. The impact member has a round surface engaging tongue 5 at a point located on the axis of the respective rapping bar. To further insure that the tongues 5 and impact members 7 are disposed in contact with each other, wedge-shaped plate sections 19 may be fixed to the rapping bar for the first and the last collecting electrodes of a row, as shown.

In the embodiment shown in FIG. 1 the support means for each rapping bar comprises a bolt 6 extending transversely through the end of tongue 5 which projects from the underside of the rapping bar rod. The rapping bar rests on the bolt 6 as shown.

Each rapping bar is supported for axial movement between the rest position shown in the drawings and a second position axially spaced from the rest position in the direction extending from left to right as viewed in the drawings. In the rest position the electrodes 1, as shown, are oriented substantially upright. In the second position, the electrodes are tilted slightly in the direction of arrow 22; this tilting being permitted by the relative loose connection between fittings 3 and support 4. Because of the eccentric mounting of the electrodes on support 4, its own weight will move each electrode back to the upright position, in turn, moving the respective rapping bar back to the rest position.

In the constructions shown in the drawings the flat impact surface 9a of the tumbling hammer lies in a plane perpendicular to the axis of the rapping bar at the moment of impact. Furthermore, in the constructions shown the center of round anvils (i.e., the point of impact) is located at a distance from the pivot axis of the tumbling hammer on the arm 10 at the moment of impact which is substantially-equal to the calculated radius of gyration of the tumbling hammer; the radius of gyration being calculated as (g[T/21r]) where T is the period of oscillation if the hammer were allowed to swing as a simple pendulum and g is the gravitational constant.

Since the flat impact surface of each tumbling hammer is, at the actual moment of impact, disposed at right angles to the axis of the rapping bar the result obtained is that each rapping bar is struck centrally at its longitudinal axis by the corresponding tumbling ham mer. Mechanical stress in the structure will consequently be as low as possible and at the same time the entire force of the impact is transmitted in the form of vibration to the collecting electrodes without being lost in deformations of other structural parts. In this connection it is very important that the length of each tumbling hammer calculated from its center of rotation or pivot axis to its center or point of impact be substantially equal to the radius of gyration (i.e., to the length of an equivalent simple pendulum) since thereby there will normally be substantially no reaction from the impact on the tumbling hammer supporting structure.

The longitudinal axis of the rapping bar and the direction of impact generally coincide even if minor displacements occur in the relative positions of the tumbling hammer and the rapping bar in a plane perpendicular to the axis of the rapping bar, such displacements being due, for instance, to deformations of a housing or casing of the precipitator or differences in the heat expansion of the precipitator housing 20 and collecting electrodes.

In the embodiment illustrated in FIG. 2 each rapping bar 2 is supported independently of electrodes 1. The support means for each rapping bar in this embodiment includes

brackets

14 and 15. The bracket 14 is provided with a stop element or bow 16 and the respective' rapping bar cooperates with a stop block 17 to ensure correct position of the rapping bar in a longitudinal direction. As shown block 17 is attached in spaced relation to the end of rapping bar 2 opposite its impact end with the bow 16 positioned in the space therebetween.

As previously explained the weight of the electrodes 1 in returning to the rest position will force the rapping bar 2 to the left as viewed in FIG. 2 until the bow 16 is intercepted by the stop block 17. In its state of test each rapping bar will therefore always adopt the same rest position after each blow of the hammer.

In the construction shown in FIG. 1 improper longitudinal or axial movement of the rapping bars from the rest position is controlled by the inertia on the system itself and therefore special retaining means to insure proper positioning of the rapping bars at rest position is not required. The bracket 15 is attached to a support 18 which simultaneously serves to support the stationary bearings 13 through which the shaft 11 extends as previously described.

The rapping bar support means shown in FIG. 1 and the support means shown in FIG. 2 both permit reciprocal axial movement of the respective rapping bar in the direction of arrow 20 between a rest position and a second position axially spaced from the rest position. With the support means shown in-FIG. 2 the rapping bar slidably engages

brackets

14 and 15 to permit this axial movement. Other support means for the rapping bars permitting the required axial movement such as various hinge or spring arrangements will be apparent to those skilled in the art.

The rapping bar support means shown in FIG. 2 has several advantages. First, the position of the support brackets will not be affected by any heat expansion of the electrodes 1 or their support means. Secondly, this mode of suspension allows the tumbling hammers and supporting structure such as shaft 11 and bearings 13 to be mounted on the rapping bar support means. In removing dust from hot kiln gases where the components of precipitator may be subjected to substantial heat expansion, this is advantageous because the relative positions of tumbling hammers and rapping bars is' essentially unaffected by structural changes due to misalignmentor heat expansion. Thus it is much easier to insure optimum spacing between the hammer pivot axis and the point of impact with the respective rapping bar as above described.

In operation, shaft 11 is rotated counter clockwise as indicated by arrows in the drawings. For each revolution, the tumbling hammer imparts a knock to the corresponding rapping bar. During the next revolution of shaft 11 following the knock the tumbling hammer is lifted by the arm 10 and eventually assumes an equilibrium position resting on arm 10. The tumbling hammer continues to occupy this position until equilibrium is destroyed or lost at which time the hammer falls in a free pendular movement down upon the anvil 8 on the end of the rapping bar thereby imparting another knock. This intermittent knocking occurs throughout operation of the precipitator with each knock acting to jar dust deposits from the electrodes.

The tumbling hammer strikes the anvil at its center (i.e., at a point located on the center line or axis of the rapping bar) and the force created by the impact is transferred from the rapping bar via the rounded impact members 7 to the tongues 5 and, in turn, to the collecting electrodes along the axis of the rapping bar. Since the tumbling hammer strikes centrally and the energy from the impact is transmitted centrally via the rounded impact members maximum power will be utilized for vibration of the collecting electrodes. As a result no uneven impact forces will be experienced and the rapping mechanism will have a long lifetime.

As mentioned previously arms which mount the tumbling hammers 9 are secured to the shaft 11 by means of releasable clamping bows 12. This arrangement provides the capability to arbitrarily adjust the position of each tumbling hammer along shaft 11 and to adjust the relative angular displacement or position of the hammers of a multi-hammer construction thus varying the sequence in which the tumbling hammers strike the respective rapping bars and associated electrodes. Thus precise adjustment of each tumbling hammer in relation to the respective rapping bar can be easily accomplished. Also, this adjustment capability permits easy correction of misalignments arising during operation.

in the event the electrostatic precipitator is exposed to heavy stress due to very hot gases, the tumbling hammers, their suspension and their driving system may, according to this invention, be located outside the precipitator housing with the rapping bars projecting through the wall of the housing in sealed relationship thereto. For example and with reference to FIG. 3, the electrodes may be mounted in a precipitator housing or casing which is supported on a structure 21. The casing 20 has one or more bottom hoppers 22 for collecting the dust falling from the electrodes. The hammers 9 and supporting structure are mounted outside the casing 20. The rapping bars 8 extend into the casing through openings in the casing and are sealed by flexible membranes 23 as shown.

Although the cleaning mechanism constructions shown in the drawings act to clean collecting electrodes, it is also within the scope of this invention that the tumbling hammers and rapping bars can be utilized for rapping the support for the discharge electrodes or other mechanical devices associated with the discharge electrodes.

I claim:

1. An electrostatic dust precipitator having at least one dust collecting electrode provided with a rapping mechanism for cleaning the electrode which comprises:

f. at least one tumbling hammer adjustably mounted on the rotatable shaft for rotation therewith and in a manner which provides free pendular pivotal movement relative to said shaft during rotation thereof through an arcuate segment of each revolution thereof, said hammer having a substantially flat impact surface spaced from the center of rotation and thedistance from the center of rotation to its point of impact with the anvil portion of the rapping bar is substantially equal to the radius of gyration of the hammer such that when the tumbling hammer strikes the anvil portion of the rapping bar the rapping bar is moved in a generally axial direction from the rest position to the second position to thereby impart a jarring motion to each electrode in a manner which facilitates repeated dislodgement of dust particles collected thereon.

2. A precipitator according to claim 1 wherein the hammer is so configured to strike the end of the rapping bar to impart an axially directed force such that the rapping bar moves from a first rest position to a second position, said force acting through the axis of the rapping bar.

3. The electrode cleaning mechanism according to claim 1 further comprising a second support means for mounting the shaft which mounts the tumbling hammer to support the shaft independently of said electrodes.

4. The electrode cleaning mechanism according to claim 1 wherein the tumbling hammer is adjustably mounted on the shaft whereby its longitudinal and angular position relative to the shaft can be varied.

5. The electrode cleaning mechanism according to claim 1 wherein:

a. the tumbling hammer and the shaft are disposed externally of the precipitator housing with the rapping bar extending into the precipitator; and

b. means are provided for sealing the rapping bar at its point of entry into the precipitator housing.

6. The electrode cleaning mechanism according to claim 5 wherein said sealing means includes a membrane surrounding the rapping bar.

7. The electrode cleaning mechanism according to claim 1 wherein:

a. the impact surfaces of the hammer and rapping bar contact each other at a point located generally on the axis of the rapping bar; and

b. the impact surface of the hammer is moving in a direction extending substantially parallel to the axis of the rapping bar at the moment of impact.

8. The electrode cleaning mechanism according to claim 7 wherein the distance separating the point of contact between the hammer and rapping bar and the pivot axis of the hammer is substantially equal to the radius of gyration of the hammer.

9. The electrode cleaning mechanism according to claim 7 wherein:

a. said connection means includes:

1. a slot extending diametrically through the rapping bar;

2. a tongue member connected to the electrode and extending into said slot; and

3. an impact member fixed to the shaft within the slot at a position between the tongue and the impact end of the rapping bar, said impact member being disposed inengagement with the tongue at a point located generally on the axis of the rapping bar whereby the impact reaction between the rapping bar and the electrode is directed substantially along the axis of the rapping bar.

10. The electrode cleaning mechanism according to claim 9 wherein the distance separating the point of contact between the hammer and rapping bar and the pivot axis of the hammer is substantially equal to the radius of gyration of the hammer.

11. The electrode cleaning mechanism according to claim 9 further comprising a second support means for mounting the shaft which mounts the tumbling hammer to support the shaft'independently of said electrodes.

12. The electrode cleaning mechanism according to claim 9 wherein:

a. the tongue extends completely through said slot;

and

b. the second support means includes a pin extending through the tongue in underlying relationship to the rapping bar.

13. The electrode cleaning mechanism according to claim 9 wherein:

a. the impact end of the rapping bar has a rounded impact surface;

b. the impact member has a rounded impact surface engaging the tongue; and

c. the impact surface of the hammer is substantially flat and lies in a plane oriented substantially perpendicular to the axis of the rapping bar at the moment of impact therebetween.

14. The electrode cleaning mechanism according to claim 13 wherein the distance separating the point of contact between the hammer and rapping bar and the pivot axis of the hammer is substantially equal to the radius of gyration of the hammer.

15. The electrode cleaning mechanism according to claim 9 wherein:

a. the second support means includes:

l. a bracket means slidably mounting the rapping bar for said reciprocal axial movement; and

2. retaining means cooperatively engaging the rapping bar and bracket means for preventing axial movement of the rapping bar in a direction extending from the said second position to the said rest position beyond the said rest position.

16. The electrode cleaning mechanism according to claim 15 wherein:

a. said retaining means includes:

1. block element attached to the rapping bar in spaced apart relation to the end thereof opposite to its impact end; and

2. a stop element attached to the bracket means and positioned in the space between the block and the said opposite end of the rapping bar.

17. The electrode cleaning mechanism according to claim 15 wherein the shaft mounting the tumbling hammer is mounted on second support means.

Claims

1. An electrostatic dust precipitator having at least one dust collecting electrode provided with a rapping mechanism for cleaning the electrode which comprises: a. a first support means for eccentrically mounting said electrode: b. an elongated rapping bar associated with said electrode, said rapping bar having an anvil portion at one end thereof; c. a second support means for mounting said rapping bar in a manner which permits reciprocal axial movement between a rest position and a second position spaced axially from the rest position; d. means for connecting each electrode to the rapping bar for movement therewith; e. a rotatable shaft with means for supporting the shaft perpendicular to said rapping bar; and f. at least one tumbling hammer adjustably mounted on the rotatable shaft for rotation therewith and in a manner which provides free pendular pivotal movement relative to said shaft during rotation thereof through an arcuate segment of each revolution thereof, said hammer having a substantially flat impact surface spaced from the center of rotation and the distance from the center of rotation to its point of impact with the anvil portion of the rapping bar is substantially equal to the radius of gyration of the hammer such that when the tumbling hammer strikes the anvil portion of the rapping bar the rapping bar is moved in a generally axial direction from the rest position to the second position to thereby impart a jarring motion to each electrode in a manner which facilitates repeated dislodgement of dust particles collected thereon.

2. a tongue member connected to the electrode and extending into said slot; and

3. an impact member fixed to the shaft within the slot at a position between the tongue and the impact end of the rapping bar, said impact member being disposed in engagement with the tongue at a point located generally on the axis of the rapping bar whereby the impact reaction between the rapping bar and the electrode is directed substantially along the axis of the rapping bar.

5. The electrode cleaning mechanism according to claim 1 wherein: a. the tumbling hammer and the shaft are disposed externally of the precipitator housing with the rapping bar extending into the precipitator; and b. means are provided for sealing the rapping bar at its point of entry into the precipitator housing.

7. The electrode cleaning mechanism according to claim 1 wherein: a. the impact surfaces of the hammer and rapping bar contact each other at a point located generally on the axis of the rapping bar; and b. the impact surface of the hammer is moving in a direction extending substantially parallel to the axis of the rapping bar at the moment of impact.

9. The electrode cleaning mechanism according to claim 7 wherein: a. said connection means includes:

11. The electrode cleaning mechanism according to claim 9 further comprising a second support means for mounting the shaft which mounts the tumbling hammer to support the shaft independently of said electrodes.

12. The electrode cleaning mechanism according to claim 9 wherein: a. the tongue extends completely through said slot; and b. the second support means includes a pin extending through the tongue in underlying relationship to the rapping bar.

13. The electrode cleaning mechanism according to claim 9 wherein: a. the impact end of the rapping bar has a rounded impact surface; b. the impact member has a rounded impact surface engaging the tongue; and c. the impact surface of the hammer is substantially flat and lies in a plane oriented substantially perpendicular to the axis of the rapping bar at the moment of impact therebetween.

15. The electrode cleaning mechanism according to claim 9 wherein: a. the second support means includes:

16. The electrode cleaning mechanism according to claim 15 wherein: a. said retaining means includes: