US 3086341 A
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Apr-ll 23, 1963 H. BRANDT 3,086,341
SHAKING DEVICE FOR ELECTRIC FILTERS AND A METHOD FOR OPERATING SAME Flled Nov 4 1960 2 Sheets-Sheet l five/7601*: HERBERI BRMIDI AGENT April 23, 1963 H. BRANDT SHAKING DEVICE FOR ELECTRIC FILTERS AND A METHOD FOR OPERATING SAME 2 Sheets-Sheet 2 Filed Nov. 4, 1960 [fiver/Z01": HERBERT BRANDT fi MM 7 Agent United States Patent 3,086,341 SHAKING DEVICE FOR ELECTRIC FILTERS AND A METHOD FOR OPERATING SAME Herbert Brandt, Rothemuhle, near Olpe, Germany Filed Nov. 4, 1960, Ser. No. 67,358 Claims priority, application Germany Nov. 4, 1959 3 Claims. (Cl. 55-412) This invention relates to a shaking device for electric filters and a method for operating same.
A problem in cleaning flue gases is to remove the dust from the collecting surfaces or anodes, after it has settled on these and to convey it to a dust collector, in most cases a hopper. In plate electric filters, that is electric filters of which the collecting surfaces consist of flat areas, plane or shaped plates or hollow frames or boxes, the dust is generally removed from the collecting plates by shaking them by means of vibrators which may be weighted hammers or spring-loaded heaters. The three orthogonal axes are available for the actuation of the devices f r shaking the plates. These run from above or below in the plane of the plate, horizontally in the plane of the plate and perpendicularly to the plane of the plate.
An object of the present invention is to solve the problem aforesaid using vibration in the last-named principal direction, that is perpendicular to the plate surface.
The vibration of the plate in this direction is, for physical reasons, the most effective for dislodging the dust. in this way, such powerful vibrations can be released that the plates bend up to the limit of their elasticity as long as permanent distortion of the plates is prevented which would lead to unequal spacing of the plates and therefore also between them and corona-discharge electrodes arranged opposite both sides of the plate. The bending of the plates under perpendicular pressure has been effectively and thoroughly investigated scientifically and can be calculated for any shape of plate and for all plate materials. This kind of shaking most eifectively reduces the notable disadvantage of plate distortion in continuous operation.
The bending of the plates through permanent distortion, which occurs in the course of time, leads to a considerable reduction in the dust-removing efiiciency of the filter and makes frequent servicing necessary to straighten the plates. A permanent distortion of this type arises with excessively powerful or frequent shaking, due to the long waves generated with a small frequency and a large bending amplitude. These long waves are, however, less effective for cleaning purposes because the number of vibrations per time unit is relatively small.
On the other hand, the short, high-frequency waves which develop as harmonics during the shaking are effective for cleaning. They have low amplitude and high percussive force per wave length and are themselves experienced as a vibratory shaking of the plate surface.
The present invention is based on this knowledge. It utilises the rule of the art that the plates, which are suspended at the top in the casing and guided beneath, should be struck not at one place but at two places, at different depths, it being further intended that at one striking point, the plate is struck on one side and at the other on the other side. The striking points are preferably so located that they lie at equal distances from each other and from the ends of the plate, that is, at one third or two thirds of the plate depth respecively. Whereas the one-sided shaking or beating hitherto adopted produces an elastic bending of the plate according to the fundamental frequency in the mode of a half wave, with such vibration from both sides, by the arrangement of the impact points at one third or two thirds of the plate depth, the longest wave obtained is the second harmonic with a wavelength 3,086,341 Patented Apr. 23, 1963 of /al. This vibration, however, is not directly transmitted through the impact points in the vibration nodes at /sl and %l so that only the third harmonic with four half waves over the plate length and four times the frequency of the fundamental vibration, absorbs the percussion energy with fourfold greater deflecting force per half wave by which means the amplitude amounts to only A of the amplitude of the fundamental vibration.
Thus, with this arrangement in accordance with the invention, a greater shaking force is permissible before the limit of the onset of permanent distortion is reached. This permissibly greater percussion energy further produces a more powerful cleaning by reason of the more effective shorter waves, which then also produce far greater deflecting forces.
'On account of inevitable but desirable small difference in the timing of the vibration of a plate from one and from the other side, the synchronising of the tapping on both sides produces a superposition of short waves, intensifying the cleaning action, with simultaneous supperssion of the longest waves determined by the plate length, which could cause permanent distortion.
The provision of two impact points on each plate offers the further possibility of fitting two holding screws, each of which is flush with the impact points of the plates on the side opposite to the tapped side. These holding screws serve the purpose of preventing any bulging of the plate through back pressure arising in known forms of shaker. During operation, the holding screws are loosened; during the straightening of the plates, they are screwed in to an adjusted stop, whereby the plates are pressed back into the original position. After this shaping by pressure, they are again screwed on the surface so that the plates are able to vibrate freely and are quite ready for service.
As long as only one impact point per plate is used, the plate cannot be pressed back satisfactorily into the former shape because the elasticity of very long plates is so great that the elastic recoil makes it impossible to straighten themsufiiciently in this, simple manner. Also, the suspensions and guides of the plates are soheavily stressed by the unilateral pressure that they become warped or loosened. With simultaneous use of two holding screws in accordance with the present invention, on the contrary, which grip from both sides at intervals of about one third of the plate length, the plate can easily be pressed back into the previous alignment owing to its reduced elasticity.
The present invention further solves the problem of leaving a little play for 'anvils arranged on the plates, through which the impact is transmitted from one plate to the next, arranged parallel to it, the clearance being less than the amplitude of the plates when tapped. By means of this play or clearance, it results that on impact of the hammer, not all the plates together, instantaneously, participate in the :same vibration, but each plate only on receiving its first blow transmits the vibration to the next, and that by this means, the plates beat against each other to promote the cleaning action by these phase-displaced vibrations.
Since, with percussion in a direction perpendicular to the plate surface, the shaking action decreases with increasing distance from the plate to the casing wall, in accordance with the invention, further-more, with the lateral shaking arrangement, the width of the casing is sufiiciently restricted so that the last plate is still adequately cleaned. One advantage of the invention is thereby attained. Through the impacting of each plate from both sides of the casing, the width of the casing may, in fact, be doubled. The outermost plate in each shaking device which is impacted with the least force, obtains, vice-versa, the most powerful impact from the other tapping device, as being the first plate struck. It is obvious that by this shaking from both sides all the plates are vibrated approximately equally in spite of their different distances from the casing wall.
An exemplary form of embodiment of the invention is shown in the accompanying drawing, in which:
FIG. 1 is a sectional plan view through a plate filter,
FIG. 2 is an elevation corresponding to FIG. 1, and
FIG. 3 shows the plates of a plate filter in perspective view.
In FIGS. 1 and 2, the corona-discharge conductors or cathodes have been omited in the interests of clarity. In FIG. 3 the casing and anvils are not shown.
As shown, in all the figures, the collecting plates 1 are arranged, as is usual, in parallel rows and joined with only small gaps to large surfaces which delimit channels through which pass the gases to be cleaned.
Side walls 2 of the filter casing support a cover 3 and carriers for the suspension of the collecting plates 1. The bottom of the casing is in the form of a hopper 4. Dust dislodged from the collecting plates 1 falls into the hopper 4. Irons 5 guide the plates suspended from the said carrrers.
Each anvil 6 is connected at one side to a plate 1, and at the other side is supported against the adjacent plate flush, or, preferably, with a gap which is less than the amplitude of the plate vibration. In accordance with the invention, each plate is provided with a second anvil 7 which provides the supporting connection to the parallel adjacent plate at the lower impact point. In the figures, the anvils 6 in the upper plane are shown lying about two thirds of the way up the plate and the anvils 7 in the lower plane about one third of the way up the plate. In FIG. 3, the points of attachment 6a of the anvils 6 to the plates are shown as blocked circles whereas the impact points 7a of the anvil 7 are shown as open circles.
The outer plates adjacent the outer walls 2 carry at the impact points anvils 8 which lead through openings 9 in the wall 2. The device which vibrates the plates in order to clean them strikes on this anvil 8 and is shown in the drawing as a hammer 10 of the usual type which is raised at the required time intervals, falls and by its own weight produces a blow on the anvil 8 which transmits the impact to the outside plate and from this through the anvils 6 and 7 to the other plates.
A holding screw 11 consists of a screw bolt 12 guided in a female thread 13 in the casing wall 2. The screw bolt is fitted with a pressure plate 14 and an adjustable stop 15 to fix the amount to which the plate is to be pressed back.
1. A rapping device for a set of collecting electrodes in an electrical precipitator, said electrodes being vertically suspended, equidistant metallic plates arranged parallel to one another and having their vertical center lines in a common vertical plane, said electrode plates being arranged perpendicularly to said common plane and said rapping device being positioned in said common plane, said rapping device comprising a first hammer on one side of said set of plates, a first series of aligned anvils at about one third of the height of the plates, :1 first one of said anvils being arranged to be rapped by said first hammer, succeeding ones of said anvils being arranged one after the other between adjacent ones of said plates and a last one of said anvils constituting an adjustable impact point, a second hammer on the opposite side of said set of plates, a second series of aligned anvils at about two thirds of the height of the plates, a first one of said second series of anvils being arranged to be rapped by said second hammer, succeeding ones of said latter anvils being arranged one after the other between adjacent ones of said plates and a last one of said latter anvils constituting an adjustable impact point.
2. The rapping device of claim 1, wherein said succeeding anvils in the first and second series of anvils have one of their ends slightly spaced from the adjacent plate, in the rapping direction, and the other one of their ends fixed to the adjacent plate.
3. The rapping device of claim '1, wherein said last anvils in the first and second series of anvils consist of a set screw with an impact plate at the screw end facing said set of plates.
References Cited in the file of this patent UNITED STATES PATENTS 1,110,699 Lechtenberg Sept. 15, 1914 1,356,086 Plaisted Oct. 19, 1920 1,882,949 Ruder Oct. 17, 1932