Note: Descriptions are shown in the official language in which they were submitted.
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RAPPING APPARATUS FOR AN ELECTROSTATIC PRECIPITATOR
Background of the Invention
The invention relates to electrostatic precipitators and
in particular to a rapping mechanism therefore.
During operation of electrostatic precipitators dust
collects on the electrodes. In order to maintain a high dust
collection efficiency, the dust must be periodically removed from
the electrodes. One method of removing this dust is rapping the
electrodes to shake the dust free.
A simple low maintenance apparatus for effecting this
rapping involves locating anvils which contact selected collector
plates. A hammer is eccentrically located to a rotating shaft such
; that it is raised above the shaft during the rotation. As it passes
top dead center, the hammer swings free under the force of gravity
and strikes the anvil.
It is essential to rap the electrodes with sufficient
force to break the dust loose. Preferably the dust breaks loose
from the electrodes in flakes dropping to the hopper located there-
below. If excessive rapping force is used, the flakes are disin-
tegrated reforming as dust which is then carried on through the
prec;pitator with the gas. Other rapping mechanisms such as electro-
magnetic coils which shake an entire electrode field have been
designed with varying rapping intensity so that the optimum rapping
intensity for a particular precipitator can be obtained.
Adjusting the rapping intensity of free-fall hammers
requires shutting down the apparatus and changing the hammers. This
is inconvenient and costly because of the many shutdowns and the
difficulty of predicting the rapping performance under particular
C780Y90 operating conditions. Furthermore should operating conditions
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change, a shutdown is required for modification of the rapping
intensity.
In addition to the problem of disintegration of the
flakes when rapping with unnecessary force, the excess force
creates unnecessary wear and tear on the equipment.
In Russian Patent No. 450,592 a plate is arranged
passing within the normal free fall path of a rapping hammer.
The plate is pivoted above the top position of the hammer, and is
movable to various locations, each cutting a sector thru the free
fall path.
'~lith such an arrangement the plate must also intercept
the path of the hammer in its fully cocked position. It must,
therefore, move with each rotation of the hammer. If the plate is
spring loaded it can limit the minimum hammer fall only from the
position where the hammer and plate are perpendicular, re~ardless
of the initial plate position. Alternately -the plate must be
independently actuated to release the hammer from some point
between its initial contact point and the limit position clescribed
above. Such an apparatus involves wear, restricted adjustment
flexibility, and/or complicated operating mechanism.
Summary of the Invention
It is an object of the invention to vary the rapping
intenstty of a free-fall hammer-type rapper in a simple manner
which may be effectuated without shutting down the equipment.
The electrostatic precipitator of the invention is of
the type using suspended plate-shaped electrodes and including an
anv;l which is rapped to remove the dust from the electrodes. A
free-fall hammer associated with each of the rapping bars is
attached to a rotating shaft so that it falls against the anvil
~0 from the top dead center position, with the weight and size being
selected to obtain the maximum desired rapping intensity with this
free-fall. An attenuator plate is adjustably located to a fixed
position within this free-fall area of the hammer so that the hammer
is intercepted during its fall by the attenuator plate. The subse-
quent fall from the attenuator plate to the anvil is adjusted bylocating the attenuator plate. The attenuator plate may be adjusted
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from outside the apparatus, thereby varying the rapping intensity
of the free-fall hammer.
Brief Description of the Dra~!in~s
Figure 1 is a general arrangement o-f the electrostatic
precipitator,
Figure 2 is a detail view of the anvil beam hammer and
attenuator plate, and
Figure 3 is a plan view of the impact area of the anvil
illustrating several hammers.
Description o~ the Preferred Embodiment
A casing 10 is arranged to confine a flow of gases 12
passing horizontally through the precipitator. A plurality of
plate-shaped collector electrodes 14 are each pivotally suspended
from pins 16 and aligned so as to be parallel with the flow of
gases. A plurality of these electrodes are arranged in a plurality
of transverse parallel rows.
A plurality of anvil beams 18 are supported from each of
the transverse rows of electrodes. They are operatively attached
to the row of electrodes so that an impact on the anvil beam will
be transmitted to the freely suspended collector plates for the
purpose of shakiny dust therefrom. Each of the anYil beams has an
impact location 20 at one end thereof.
A slowly rotating shaft 22 is located above one end of
the anvil. Eccentrically attached to the shaft by pivot pin 24 is
a hammer 26. As the shaft is rotated, the hammer moves to the top
dead center location 28 from which upon further rotation of the shaft
it falls through the free-fall zone 3n downwardly striking the anvil
1>3 at impact location 20. Operation as described provides the
maximum impact for a particular size and weight hammer.
An attenuator plate 32 is mounted with an axis 34 parallel
to the shaft 22 and located outside the free-fall zone 30. The
attenuator plate may be anaularly adjusted to any selected position
aroundits axis by moving the external adjustment arm 36 which is
located outside the precipitator by extension of the axis 34.
Arcuate plate 38 has a plurality of locking points such that the
80990 external arm may be locked into any locking point, thereby setting
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a relative position of the attenuator plate within the apparatus.
The attenuator plate 32 is held in the locked position during day-
to-day operation of the precipitator. ~Ihen it is desired that the
rapping intensity be changed, the plate is moved to an alternate
locked position. This change in position may be accomplished with
the precipitator in operation by moving arm 36 to a new locked
position with respect to plate 38.
The attenuator plate is extended inwardly from the axis
34 so that in selected locations it will pass within the free-fall
zone 30. In such a location, the attenuator plate will intercept
the free-fall of the hammer. As the shaft 22 is further rotated
and pin 24 moves away from the attenuator plate, the head 40 of
the hammer pulls free from the attenuator plate and falls against
the anvil with reduced force.
lS The attenuator plate may be of any shape or form provided
only that it intersect the free-fall path to intercept the fall of
the hammer. It may extend further into the free-fall zone than
illustrated if more adjustab;lity is required. Locatins the atten-
uator plate with free space between it and the shaft prcvides means
for the hammer to pull free from the attenuator plate so that it may
impact with the reduced force.
It can be seen, upon inspection of Figure 2, that release
of the hammer from attenuator plate 32 is caused by the rotation
of shaft 22 carrying pin 24 away from plate 32. The plate must be
located so that the head 40 clears the plate before shaft 22 binds
the hammer 26. The bindin~ position is the relative position
between hammer 26 and shaft 22 illustrated as the cocked position
at the top dead center location 28. More specifically~ the distance
between the centerline of shaft 22 and the closest portion of
attenuator plate 32 must be greater than the distance between the
centerline and the outer edge of hammer ao when it is at the top
dead center location 28.
As best seen in Figure 3, the attenuator plate extends
across a number of the transverse parallel rows to intersect with
the free-fall hammers of each line of electrodes. These hammers are
conventionally located at different positions around the shaft so
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that the timing of the impacts on the anvil as well as the
attenuator plate are stagqered.
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