This invention relates to Electrostatic Precipitator (ESP), which is a pollution
control equipment widely used for collecting dust particles from flue gas
exhausted by thermal power plants, cement plants, steel plants and glass plants
etc. The invention in particular relates to an improved rapping which eliminates
periodical modification of the casing columns whose depths are reduced while in
operation. More particularly, the invention relates to an improved rapping
hammer for electrostatic precipitator to restrict emission levels and increase
efficiency.
BACKGROUND OF THE INVENTION
An Electrostatic Precipitator (ESP) is a particulate collection device that removes
particles from a flowing gas (such as air) using the force of an induced
electrostatic charge. Electrostatic precipitators are highly efficient filtration
devices that minimally impede the flow of gases through the device, and can

easily remove fine particulate matter such as dust and smoke from the air
stream.
The efficiency of ESP is ensured by carrying out effective rapping of collecting
electrode by a rapping hammer. Hammers are mounted in a shaft and are
positioned co-linear with the collecting electrode. Each row of collecting
electrodes is provided with a rapping hammer to dislodge the precipitated ash
sticking over these collecting plates. The total load of ESP intemals(Collecting
and emitting systems) gets transferred to the casing column and is positioned in-
between fields. The collecting electrode row which is disposed in between the
fields is provided with a rapping hammer which normally fouls with the casing
column and its impact leading gets reduced to insignificant force for dislodging
ash from the collecting electrodes. Hence, the sustained electro static
precipitation is hampered and affects the ESP performance. To avoid this,
conventionally, the casing column member depth is reduced by gouging process
and additional stiffeners are envisaged at this location as part of strengthening
the member whose depth has been reduced. In a typical 660MW ESP, approx.
100 nos of casing columns are to be periodically modified with increased

fabrication process leading to increase in manufacturing cycle time, additional
material consumption and increase in Non Destructive test (NDT) costs. To
eliminate these complex and voluminous work, the conventional rapping hammer
was revisited and new rapping hammer design was evolved to ensure ESP
performance.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved rapping
hammer for electrostatic precipitator to restrict emission levels and increase
efficiency.
Another object of the invention is to propose an improved rapping hammer for
electrostatic precipitator to restrict emission levels and increase efficiency which
provides effective impact force on collecting electrode to dislodge attached fly
ash particle without fouling with the casing columns.
A still another object of the invention is to propose an improved rapping hammer
for electrostatic precipitator to restrict emission levels and increase efficiency

which reduces manufacturing cycle time by eliminating depth reduction of
column member and consequently avoiding frequent repair work on the columns.
A further object of the invention is to propose an improved rapping hammer for
electrostatic precipitator to restrict emission levels and increase efficiency which
increases efficiency of the ESP and reduces operational cost.
SUMMARY OF THE INVENTION
The dust laden flue gas gets treated inside ESP before letting the flue gas to
atmosphere. The dust gets collected on the surface of collecting electrode. To
have effective, sustained collection and enhanced performance, the collected
dust particles are dislodged by providing an impact force. Tumbling hammer is
one of the means to provide impact force on the collecting electrode to dislodge
deposited dust particle.
Hammers are mounted along the shaft and positioned co-linear with the
collecting electrode. The rapping shaft is motor driven and rotates the hammer in
sequential way to hit the collecting electrode to avoid re-entrainment of
dislodged dust particle.

The rapping hammers are positioned near the easing column and occasionally
interfere with the hammer. This leads to fouling of the hammer including
restriction in rotation and free-fall of the hammer to exert the fouling and
restriction of rapping force on the collecting electrodes. The hammer results into
non-rapping of particular row of the collecting electrode and ash could not be
dislodged. Hence, further collection of dust does not become possible, which
leads to escape of dust and more emission through the stack.
According to the prior art, the casing column used to be gouged locally and
strengthened by providing additional stiffener plate requiring additional trimming,
welding and NDT test of weld. Such activities leads to increase in manufacturing
cycle time and cost of manufacturing.
6. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows an isometric view of a typical Electrostatic Precipitator (ESP).

Figure 2 - schematically shows view of the ESP depicting the collecting and
discharge electrodes and rapping hammer.
Figure 3- Shows Casing column member depth reduction and additional stiffeners
welding according to the prior art.
Figure 4 - Shows 2-D drawing of the rapping hammer according to the invention.
Figure 5 - Shows 2-D drawing of a rapping hammer according to the prior art.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
An Electrostatic precipitator as shown figure-1 &. 2 essentially consists of two sets
of electrodes called Collecting Electrodes and Emitting Electrodes and (also called
discharge electrodes). A unidirectional high voltage is applied between these
electrodes, connecting its negative polarity to the emitting electrodes and the
positive polarity to collecting electrodes, which are also earthed. The dust laden
flue gas from the boiler passes between rows of collecting and discharge
electrodes.

The high voltage induces ionization of gas molecules adjacent to the negatively
charged emitting electrodes. The positive charges of the ions travel towards the
discharge electrodes and the negative charges travel towards the collecting
electrodes. On their way to the collecting electrodes, the negative charges get
deposited on the dust particles.
Thus the dust particles get electrically charged. In the presence of high electric
field between the electrodes, the charged dust particles experience a force which
causes the particles to move towards the collecting electrodes and finally get
deposited on them. Minor portions of the dust particles, which have acquired
positive charges, get deposited on the emitting electrodes also. Periodically these
are dislodged from the electrodes by a process called Yapping * by using a
hammer. The particles then fall into the hoppers at the bottom.
Negative charge electrodes are mounted in a support frame and are negatively
charged. Total load of the collecting and emitting frames are transferred to
ground through a plurality of casing column.

The improved rapping hammer of the invention is made out of a Round bar (01)
and concentric hole is made to fix with holding flats (02). Two numbers of
holding flat is fixed with the Round bar (01) at both ends through a first pin-
(03). Washer (05) is provided on both sides of the first pin-03 Holding flat (02)
at other end is positioned with a second pin (04) which assembled with an
inner arm for performing the desired function.

WE CLAIM:
The invention relates to an improved rapping hammer for electrostatic
precipitator to restrict emission levels and increase efficiency, the ESP comprises
at least one set of collecting electrodes and emitting electrodes which upon
application of a unidirectional high voltage respectively connecting position and
negative polarity of the voltage, wherein the dust laden flue gas from the boiler
when allowed to pass between rows of collecting and discharge electrodes
causing ionization of gas molecules adjacent the negatively charged emitting
electrodes, the positive charges of ions and the negative charges of the ions
travel respectively towards the discharge electrodes and the collecting
electrodes, wherein when the negative charges of ions on their way to the
collecting electrodes get disposed on the dust particles making the dust
electrically charged, and wherein the majority of the dust get deposited on the
collecting electrodes and a minor portion acquiring positive charge get deposited
on the emitting electrodes, the deposited dust particles being periodically
dislodged from the electrodes by electrically operating the rapping hammer, the
rapping hammer mounted on a rapping shaft co-linear with the collecting
electrodes and positioned adjacent to the casing columns of the ESP and driven
by an electric motor to sequentially hit the collecting electrodes for ash
dislodging, the improvement is characterized in that:-

the rapping hammer is formed of a round bar (01) with concentric holes
at two ends;
one each holding flat (02) detachably attached to the first and second end
of the round bar (01) via a first pin (03) and a second pin (04)
respectively through said connecting holes; and
the sub-assembly of the round bar (01) and the flat (02) fixedly
assembled to an inner arm.