ESP Training Manual

TRAINING MANUAL FOR ELECTROSTATIC PRECIPITATOR
INDEX
SL. DESCRIPTION PAGE
NO. NO.
1. PRINCIPLE OF ELECTROSTATIC PRECIPITATOR OPERATION 1
2. SELECTION AND SIZING OF ELECTROSTATIC PRECIPITATORS FOR 9

COAL FIRED BOILER
3. MECHANICAL DESIGN OF ELECTROSTATIC PRECIPITATOR 14
4. FLOW MODEL STUDIES IN THE FIELD OF ELECTROSTATIC 28

PRECIP1TATOR
5. ELECTRICAL SYSTEMS FOR ELECTROSTATIC PRECIPITATORS 32
6. 36
PRE-COMMISSIONING STABILISATION OF EP AND PERFORMANCE
TESTING OF EP
7. 39
EP OPERATION AND MAINTENANCE
8. RECENT DEVELOPMENTS IN ELECTROSTATIC 43
PRECIPITATOR
Page 1
PRINCIPLE OF ELECTROSTATIC PRECIPITATOR OPERATION
INTRODUCTION
Electrostatic precipitation utilizes the forces acting on electrically charged particles in

the presence of an electric field to effect the separation of solid or liquid particles from a
gas stream. In the precipitation process dust suspended in the gas is electrically charged
and passed through an electric field where electrical forces cause the particles to migrate
towards the collection surface (fig-1). The dust separated from the gas by retention on
the collection electrode and subsequently removed from the precipitator. Various
physical configurations are used to accomplish the followings:
(a) Corona generation

(b) Particle charging
(c) Particle collection
(d) Particle removal
CORONA GENERATION
Corona as applied to electrostatic precipitators is a gas discharge phenomenon
associated with the ionization of gas molecules by electron collision in regions of high
electric field strength. The process of corona generation requires a non-uniform electric
field which is obtained by the use of a small diameter wire as one electrode and a plate
or cylinder as the other electrode. The application a high voltage to this electrode
configuration results in a high electric field near the wire. The electric field decreases
inversely with the radius from the wire surface.
The corona process is initiated by the presence of electrons in the high field region near
the wire. Electrons for corona initiation are supplied from natural radiation or other
sources and since they are in a region of high electric field they are accelerated to high
velocities and possess sufficient energy so that on impact with gas molecules in the
region they release orbital electrons from the gas molecules.
The additional free electrons are also accelerated and enter into the ionization process.
This avalanche process continues until the electric field decreases to the point that the
electrons released do not acquire sufficient energy for ionization.
Within the region defined by the corona glow discharge where ionization is taking place,
there are free electrons and positive ions resulting from electron impact ionization. The
behavior of these charged particles depends upon the polarity of the electrodes, and the
corona is termed negative corona if the discharge electrode is negative or positive corona
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if the discharge electrode is positive.
Both positive and negative coronas are used in industrial gas cleaning application,
however the negative corona is most prevalent within the temperature range of most
industrial applications.
In the case of the negative corona, positive ions generated in the corona region as a
result of electron impact are attracted towards the negative wire electrode and electrons
towards the positive plate or cylinder electrode. Beyond the corona glow region the
electric field diminishes rapidly and if electronegative gases are present electrons will be
captured by ht egas moleculeson impact. The negative ions thus generated move towards
the collection electrode and serve as the principal means for charging the dust.
In the corona process there must be a source of electrons to initiate and maintain the
avalanche process. The electrons are supplied from naturally occurring ionizing
radiation photo-ionization due to the presence of the corona glow, and in the case of high
temperature operations, from thermal ionization at the electrode surface. For negative
corona, electrons are also provided by secondary emission from the impacts between the
positive ions and the discharge electrodes.
In most industrial gas cleaning applications, there are sufficient quantities of

electronegative gases such as Oxygen so that practically all of the electrodes are
attached to gas molecules. Gases such as nitrogen, helium, argon etc., do not form
negative ions and hence a stable negative corona is not possible in these gases.
In positive corona the electrons generated by the avalanche process, flow toward the
collection electrode. Since the positive ions are the charge carriers, they serve to provide
an effective space charge and the presence of an electronegative gas is not required for
positive corona. Sources of electrons for initiating and maintaining avalanche in a
positive corona are cosmic radiation and photo ionization due to the corona glow.
Positive and negative coronas differ in several important aspects. In appearance the
positive corona is rather uniform sheath surrounding the discharge electrode. In contrast
negative corona appears as localized discharges from points on a clean wire and as
localized tufts along the dust coated electrode. The voltage-current characteristics of the
negative corona are superior to those of positive corona at the temperature at which
most precipitators operate. Higher operating voltages and currents can be reached prior
to disruptive sparking.
Most industrial gas cleaning precipitators utilise negative corona because of its
Page 3
inherently superior electrical characteristics, which leads increase in efficiency at the
temperatures at which they are used.
Geometry of the electrodes, gas composition and gas conditions have important
influences on corona generation. The diameter of the discharge wire and the electrode
spacing determine the voltage gradient and hence the variation in electric field strength.
The electric field varies as the reciprocal of the radius near a small diameter wire. Hence
with a very small wire, the electric field near the surface can be quite high often in the
range of 50-100 kV/cm. The avalanche process requires the presence of high electric field
over a given distance. In general the small diameter wire requires high electric field
strength for initiation of corona. For a given spacing, however the onset of corona occurs
at a lower voltage for the smaller diameter wire. Also for a given voltage higher currents
are obtained with smaller diameter discharge electrodes.
Temperature and pressure influence the generation of corona by changing the gas
density. In the avalanche process the time available for accelerating an electron between
collisions is a function of gas density. With increased molecular spacing, higher velocities
can be achieved between collisions. Thus ionizing energy can be achieved with low
electric fields for low gas densities.
A second effect, in the case of the negative corona is that the increased molecular spacing
results in the penetration of free electrons further into the inter-electrode region before
capture to form a negative ion. Thus results in an increased average mobility in the
inter-electrode space and hence higher current.
Corona generation studies of basic nature are most often made with clean electrodes
under laboratory conditions. These conditions are highly idealized in comparison to
industrial precipitator. In practical precipitators, the presence of a dust entering the
electrodes space becomes charged by attachment of negative are positive ions. Because of
the much lower mobility of the charged dust it constitutes a significant space charge,
The magnitude of the space charge depends upon the size and quantity of the dust and
magnitude of its charge. The effect of the space charge is to reduce the electric field in
the vicinity of the corona glow region and thus it tends to quench the corona and reduce
the current. This effect is particularly significant at the inlet section of a precipitator
where dust concentrations are highest.
A second important consideration of the effects of dust on corona generation is the

deposit formed on both collection and discharge electrodes. On the collection electrodes
dust deposits alter the electric field and sparking conditions as a result of the voltage
Page 4
drop with in the dust layer. This effect limits the voltage and current at which the
predpitatorcan operate and is its chief influence on corona generation.
PARTICLE CHARGING
There are two physical mechanisms by which gas ions impart charge to dust particles in
the precipitator. Particles in an electric field cause localized distortion of the field so that
electric field lines intersect the particles. Ions present in the field tend to travel in the
direction of maximum voltage gradient which is along electric field lines. Thus ions will
be intercepted by the dust particles resulting in a net charge flow to the particles. The
ion will be held to the dust particle by an induced image charge force between the ion
and dust particles. As additional ions collide with and are held to the particle, it becomes
charged to a value sufficient to divert the electric field lines such that they do not
intercept the particle. Under this condition no ions contact the dust particle and it
receives no further charge. The electrostatic theory of the process shows that the
saturation value of the charge on the particle is related to the magnitude of the electric
field-in the region where charging takes place, the size of the particle and the dielectric
constant of the particle.
The saturation charge is proportional to the square of the particle diameter thus larger
particles are more easily collected than small ones. This mechanism of charging is called
field- dependent charging.
For small particles (diameter less than 0.2 microns) field dependent charging mechanism
is less important and collision between the particles and gas ion is governed primarily by
thermal motion of the ions. The factors influencing charging rate are particle diameter
free ion density and thermal velocity for the ions.
Since the range of thermal velocities has no upper boundary there is no saturation value
associated with diffusion charging. However, as the charge on a particle increases the
probability of impact decreases so that there is a decreasing charging rate associated
with an increasing particle charge, this second charging process is called diffusion
charging.
In practical precipitators, field dependent charging is usually of most interest but in

some applications, particles are present in the range where diffusion charging is
predominant mode (less than 0.2 microns) as well as the area in which both mechanisms
are significant.
Page 5
Particle charging theory indicates several important factors governing precipitator
performance. Since the magnitude of the particle charge is dependent upon the
magnitude of the electric field in the field dependent mode it is important that field
strength be kept as high as practical in the region where charging takes place.
A second factor of importance is the rate of charging of the particles. Practical

precipitators generally introduce heavy concentrations of uncharged dust in the inlet
section of the precipitator. The electric field in the precipitator determines the maximum
value of the particle charge due to field dependent charging and also the force acting on
a charged particle.
Electric field strength is determined by the electrostatic component, which is related to

the precipitator geometry and the applied voltage and by the space charge component
which is related to the presence of charged particles (ions an charged particulate) in the
inter electrode space. The design of the precipitator can be varied to the alter the
geometry of the discharged electrode and the electrode spacing. This factor can
determine the magnitude of the electrostatic component. Variation in the electrode
geometry can also alter the corona current, which in turn influences the electric field by
changing the space charge contribution.
PARTICLE COLLECTION:
The forces acting on a charged particle in a precipitator are gravitational, inertia,
electrical and aerodynamic. The latter two are the principal ones of the importance in
electrostatic precipitation.
If a particle is suspended in a laminar gas flow stream in a pipe and wire precipitator a
force due to the electric field and particulate charge will act on the particle in the
direction of the collection electrode. This force is opposed by the viscous drag force of the
gas.
In sufficient time, which is short for small particles, the particle would reach a terminal
velocity at which point the electrical and viscous drag forces could be equal. In
precipitator terminology, this is called the migration velocity. The other force acting on
the particle is the aerodynamic force by the gas stream. The motion of the particle will be
along the line defined by the vector sum of these two forces. Under laminar flow all
particles would be collected in a given length of the precipitator and the collection
efficiency for shorter lengths would be linearly related to precipitator length.
In practical size precipitators, however, laminar force is practically never achieved.
Page 6
Consequently the turbulent gas flow causes particles to flow random path through the
precipitator. The magnitude of the forces due to the turbulent gas flow is large compared
to the electrical forces. However at the boundary layer, the gas flow is laminar and
particles entering boundary layer will be collected. The collection efficiency is therefore
related to the probability of a particle entering the boundary layer.
Studies by Anderson, Deutsch and White of particle collection in turbulent gas stream
have shown theoretically that collection efficiencies are exponentially related to the
collection surface, the gas volume handled and the migration velocity of the particle. The
quantum known generally as the Deutsch, Anderson of the form (efficiency = 1-Exp).
A principal practical use of the Deutsch-Anderson equation has been in relating

measured collection efficiency to the collecting surface area and gas volume. In such
cases the term 'W as calculated from the Deutsch-Anderson equation is a parameter
rather than the migration velocity given by theoretical considerations. In this case it is
called effective migration velocity or precipitation rate parameter. The term is useful in
describing the effectiveness with which a given dust can be collected and is widely used
in design and analysis of precipitators.
From a theoretical as well as a practical standpoint the distribution of particles within the
precipitator is important. There is some evidence to indicate that particle distribution with in the
precipitator may not be uniform and that diffusional forces may also play a role in collection
efficiency.
REMOVAL
Once collected the dust must be removed from the precipitator. This can be accomplished
by flowing liquid down the collection electrode to wash the collected dust or by rapping
the electrodes to impart an acceleration to dislodge the dust, which falls into a hopper for
subsequent removal.
In dry removal system rapping of the collection electrode to remove the dust is normally
done on periodic basis. Successful rapping depends upon accumulation of sufficient
thickness of the material on the plate so that it falls in large agglomerates into the
hopper. There is always some re-entrainment of the dust so that effective rapping must
minimize the amount material reentrained in the gas stream.
The acceleration required to remove the collected dust varies with the properties of the
dust and gas stream. Forces of cohesion and adhesion consist of molecular, electrical and
mechanical forces. Some dusts adhere tenaciously to the collection surface and require
substantial acceleration to dislodge them. Variations in operating temperature gas
Page 7
composition or both can alter the forces required for successful rapping.
Electrical forces which are related to current density and dust resistivity are also
significant in holding the collected material to the plate and therefore affect the forces
required for rapping. Since current densities are higher at the discharge electrode than
at the collecting electrode greater forces are often required to maintain them relatively
free of dust deposits than are required at the collection plates.
Reentrainment of the dust during rapping is evidenced by increased dust loadings at the
precipitator exit following a rap. To minimize this effect only small section of the
precipitator are rapped at one time.
CONCLUSION
The basic principle of electrostatic precipitator operation remain the same irrespective of
the process of application and they fall broadly on the topics covered above.
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SELECTION AND SIZING OF ELECTROSTATIC PRECIPITATORS FOR COAL

FIRED BOILER INTRODUCTION
A fundamental task in precipitation technology is the design of optimum precipitator

system for given applications. Precipitator design has changed in character during the
past several years from a routine and casual function to a more serious enterprise
involving high performance and high financial stakes. This change has been forced by
the implementation of stringent air pollution control standards which require
substantially invisible stack emissions.
FACTORS AFFECTING THE SIZE OF ESP

Precipitator performance depends fundamentally on physical and chemical properties of
the gas and particulate treated. In a power plant these properties are governed by the
coal burnt the furnace design and the overall operation of the boiler. Precipitator design
and performance are strongly dependent on the properties of the coal burnt in the
furnace. All coals of Indian origin contain significant amount of ash or residues of
combustion consisting chiefly of inert oxides and silicates. Characteristic of coal vary
greatly because of the wide distribution of coal deposits and the many different
geological formation in which these deposits occur. The variability and uncertainty of
coal properties are reflected in the ash generated and these uncertainties and variations
can make the problem of fly ash collection singularly difficult. A typical value of Indian
coal and ash analysis is furnished in Annexure. In order to cope successfully with
particulate air pollution from coal fired power plants it is necessary to apply consistently
a high order of appropriate technology.
DESIGN PARAMETERS
Basic parameter used in the precipitator design are gas flow, electrical resistivity,
specific collection area, gas velocity, aspect ratio, treatment time and number of fields in
gas flow direction. The value of these parameter vary with particle and flue gas
properties with gas flow and with required collection efficiency. The migration velocity
achieved in actual operation depends strongly on many factors such as accuracy of
precipitator electrodes alignment uniformity and smoothness of gas flow rapping of
electrodes and size and electrical stability of the T/R sets.
GAS FLOW
The total quantity of gas flow is a fundamental factor in determination of the size and
Page 9
performance of the electrostatic precipitator. In general precipitator size for a given
efficiency is proportional to the gas volume but for a given precipitator size efficiency
drops off with increasing gas volume in accordance with the equation.
ή =1- e- (w *A)/Q
Where ή = efficiency of precipitator in percent
A = collection area in Sq.Metre
Q = flue gas volume in Cub.Metre / Sec.
W = migration velocity in M/sec.

The quantity of combustion gas produced in a boiler depends on the composition of coal
burnt the excess air used for combustion and the air in leakage through the furnace, flue
gas ducts, air preheater and electrostatic precipitator. The flue gas flow through the
precipitator also is a function of gas temperature and pressure. Actual operating gas
flows may be more than the design value due to the reasons enlisted above and
consequently increased stack emissions.
ELECTRICAL RESISTIVITY OF ASH

Experience over many years has shown that fly ash from low sulphur coals similar to
that of ours usually has high electrical resistivity and is difficult to precipitate. Theory
and experience indicate that when the dust resistivity exceeds a critical value of about
10 to the power of 10 Ohm-cm the precipitator operating voltage is limited which in turn
reduces precipitator efficiency. The loss in performance increases quite rapidly for
resistivities greater than 10 to the power of 10 ohm-cm and resistivity is there fore a
major factor in precipitator technology. Detailed studies made by us indicate resistivity
of the order of 10 to the power of 10 ohm-cm for fly ashes resulting from combustion of
coal. Higher electrical resistivities of the fly ash result in much lower values of migration
velocities and consequently a precipitator having large specific collection surfaces for
meeting the prescribed performance guarantees.
COLLECTION SURFACE (SPECIFIC COLLECTION AREA)

The collection surface required for a given flow and efficiency is usually expressed as
specific collection area (SCA) i.e. the collecting surface provided for unit gas flow rate.
Practical values of SCA usually range between 100 to 200 for efficiency range of 99% and
99.9%.
Page 10
GAS VELOCITY
This is relationship between the total gas flow and cross sectional area provided for a
precipitator. The cross section as taken the open area available for gas flow between the
end collecting plates disregarding the plate baffles. Primary important of the gas velocity
through the precipitator is its relation to rapping and re-entrainment losses. Above some
critical velocity these loss tend to increase rapidly because of the aerodynamic force on
the particles. The critical velocity depends on the quality of the gas flow plate
configuration, precipitator size and other factors but for most fly ash precipitators
velocity is 1.2 m/sec.
ASPECT RATIO
This parameter is defined as the ratio of the total length of the electrode zone to the
height of the electrode. It is important in precipitator design because of its effect on
rapping losses. Collected dust released from the plates is carried forward by the flow of
the gas. If the length of the collecting zone is too short compared to the height some of
the falling dust will be carried out of the precipitator before it reaches the hoppers
thereby substantially increasing the dust loss.
For efficiencies of 99 % and higher the aspect ratio should be at least 1 to 1.5 to minimize
carry over of collected dust.
TREATMENT TIME
This parameter is defined as the time taken by the flue gas to pass through the length of
the collecting electrode zone. Some of the dust can be carried out of the precipitation
zones due to insufficient treatment when gas velocities exceed about 1.2m/sec. and the
duct length is less than 9 metres. The treatment time in that case is only about 7 sec. for
efficiencies of 99% and higher the treatment time should be at least 15 seconds to ensure
satisfactory treatment and collection of the dust.
NUMBER OF FIELDS IN SERIES

Theory and practical experience confirms the fact that precipitator performance im-
proves with the number of fields in series (degree of high-tension sectionalisation). There
are several fundamental reason for this improvement. Electrical alignment and spacing
are more accurate for smaller sections. Smaller rectifiers needed are inherently more
stable under sparking conditions and the sparks which occur are less intense and
damaging to performance. Outage of one or two electrical sections has a much smaller
effect on efficiency where a relatively large number of high-tension sections are used.
Page 11
The optimum degree of high-tension sectionatisation is a balance between the increase
in efficiency obtained with more sections and the increased cost of providing the
additional sections. This balance is highly dependent on ash property, gas temperature,
efficiency required and the space availability.
EMISSION REGULATIONS
The central! board for the prevention and control of water pollution Act-1984 stipulates
the permissible emission limits for thermal power plants are as under:
Boiler Size Old After 1979 Existing

General Protected area (SPM)
< 200 MW 600 mg/Nm3 350 mg/Nm3 150 mg/Nm3 150 mg/Nm3
>= 200 MW ----- 150 mg/Nm3 150 mg/Nm3 *
As per the Environment (Protection) Second Amendment Rules, 1993 Schedule VI (Part-
D) enforced from January 1, 1994. The Amendment empowers State Boards to specify
more stringent standards for the relevant parameters with respect to specific industry or
location. Andhra Pradesh State pollution control board made the limit as 115 mg/Nm3.
A protected area is one that is already polluted from being in a metropolitan industrial
location or the area is sensitive because of proximity to national parks/ forests/ historical
monuments/health resorts etc. While specifying the emission or the collection efficiency
the compliance with the stipulations shall be ensured.
CONCLUSION
In this paper the effect of various critical parameters have been discussed and adequate
amount of design conservatism shall be adopted for obtaining the desired level of
efficiency. This is more demanding in case of retrofit application where the conditions
are varying widely.
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ANNEXURE
01. PROXIMATE ANALYSIS RANGE

Total Moisture % 9-10
Volatile matter % 23 – 25
Fixed carbon % 29 – 33
Ash % 39 – 32
02. ULTIMATE ANALYSIS
Carbon % 40 – 45
Hydrogen % 2.5 – 3
Nitrogen % 0.8-1.0
Sulphur % 0.4 - 0.8
Oxygen % 8.3 - 8.7
Total moisture % 9-10
Ash % 39 – 32
03. ASH ANALYSIS
Silica % 59
Alumina % 21
Iron Oxide % 7.5
Calcium Oxide % 6.5
Magnesium Oxide %
Sodium Oxide %
Potassium oxide % 3
Phosphorous pentoxide %
Sulphur trioxide %
Titanium %
Page 13
MECHANICAL DESIGN OF ELECTROSTATIC RECIPITATOR
INTRODUCTION
Electrostatic Precipitator is a dust cleaning system provided after coal/oil fired boiler. It
removes fly ash from flue gas coming out of the boiler. Due to the stringent particulate
emission regulation the present efficiency requirements are in the region of 99.3% to
99.9%. It is rather essential to provide a correctly sized ESP with a sound internal
arrangement. The alignments of internals, effective rapping system and uniform flue gas
distribution are important requirements apart from healthy electrical system. The
performance of internals can be achieved by proper and careful erection. Faulty erection
method will lead to improper alignment of internals, which cannot be rectified at later
stage.
SUPPORTING STRUCTURE AND SUPPORT BEARINGS

The supporting structure of ESP is a rigid frame structure capable of supporting the load
of entire ESP collected dust and additional vertical loads because of horizontal forces due
to wind and earthquake (fig 1). Diagonal members are provided to transfer the
horizontal forces on the ground without generating any moments in the members. So all
the members area designed for axial forces alone. Site welding of the joints are critical
and should be carried out with great care. Support bearings are provided between casing
columns and supporting structure to ensure that the casing moves freely over supporting
structure due to thermal expansion. These structural bearings are provided with PIPE
lining to take horizontal movement and spherical surface to take angular movement.
Side guides are provided to take horizontal forces coming on the support. The guides of
bearing should be kept parallel to the line joining fixed foot of EP and the particular
support point. Mirror finished surfaces should be protected from any damage.
CASING
Casing is made of 6mm mild steel plates with required stiffeners. Internal bracings are
provided to transfer the horizontal forces due to wind and earthquake to the support
bearing level. Casing columns are subjected to axial compression. The entire internals
collected dust self-weight and additional load due to horizontal forces are supported by
casing. Casing walls are designed to take lateral load due to wind and under pressure.
Casing strength is calculated for the above mentioned loads at higher temperature
(normally 150° C and exceptionally 300° C). All the internal bracings and columns will
Page 15
come between the electrical fields and the gaps are maintained in such a way, that no
mechanical fouling or electrical sparking takes place. Both emitting and collecting
system are hung from the top of casing. The site welding of casing components should be
carried out carefully so those no leakage exists. The alignment of internals depends to a
great extent on the alignment of casing. Bolted connections are provided between the
components to facilitate erection. All the joints are to be welded before the internals are
loaded.
OLD CASING
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NEW CASING
This type of casing is known as IB casing . Following are features of the IB casing:
 The side walls are made of horizontal panels

 It has two types of roof beam known as longitudinal and transverse roof beamThe
columns are sent separately and site assembled internal horizontal and diagonal
bracings are provided in between the electrical fields
 Casing columns are positioned in such a manner that the portal beam immediately
below bearings is avoided.
The above change in the design of casing has resulted in considerable reduction in
erection of casing time.
HOPPERS
Pyramidal hoppers are provided under the casing of ESP to collect the dust. The hoppers
should not be treated as storage place for dust. It is preferred to evacuate the hoppers at
the earliest. Long storage of dust leads to clogging of hoppers. The hoppers are designed
with a valley angle of not less than 55° to facilitate free fall of dust in hopper. Hopper
bottoms are provided with electrical
heaters to avoid any condensation of
moisture resulting in clogging of hopper.
Hoppers are made of mild steel plate
with adequate stiffness to take up dust
pressure. The hoppers are connected to
each other in the form of ridge. The
ridges are made of wide flange rolled,
reams and rolled channels only. Both
manufacturing and erection are easy.
According to the size of hopper it is sent
in number of wall panels which are to be welded together at site to form hopper. The
welding should be proper so that leakages do not exist. The wall stiffeners should be
outside the hopper. Depending on customer option the bottom part of hopper is provided
with smooth stainless steel inside liner, poke holes or combination of the above. Hoppers
are provided with inspection door. On customers option hoppers are provided with ash
level indicators.
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EMITTING SYSTEM
Emitting system consists of rigid emitting frame (like a cage) suspended from four points
on the top and emitting electrodes in the form of open spiral (fig 4). The four suspension
points are supported on support insulators to give electrical insulation to the emitting
frame. The frames are designed to take up the retention forces of emitting electrodes
which is 20 Kgs force per electrode.
Members of emitting frame are generally
rectangular hollow section. The frame
parts are manufactured in special
fixtures to obtain a closer tolerances on
the dimensions. Special packings are
provided for frame parts. Since this is a
Live part of ESP which will be at 70 kV
(peak) no sharp projection is desirable.
Care should be taken while
manufacturing and erecting these
components. The weld joints of frame
should be made carefully since these
frames are subjected to rapping and any
crack in the weld will lead to failure in due course of time.
By using four points suspension as mentioned earlier the frame design is totally in-
sensitive to expansion and so rigid that the operation and maintenance crew can climb
on it without disturbing the alignment. The advantages with our rigid frame design for
the emitting system are:
No electrodes are passing the top or lower collecting electrode edges thus spark erosion
hazard is thereby totally eliminated.
No need for ceramic stabilizers at the bottom part of the emitting system for perfect
positioning.
A detailed sketch of the emitting system is enclosed. Support insulators are housed in
weather tight insulator housings which are provided with electrical space heaters and
thermostats. Heaters prevent any condensation on the insulator surface.
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EMITTING ELECTRODES
The discharge electrodes consist of hard drawn spiral wires. The spiral discharge
electrodes are sent to the erection site in the form of spring like coils. At the site these
coils are attached, and stretched out between top and bottom holder in each level of the
discharge framework. These spiral electrodes are fastened with hooks to the discharge
frame.
Several advantages of this type of electrode are:

Because of their coil spring form the
emitting electrodes are self tensioning
(approximately 15-20 kgs/spiral which
means they resist these electrical field
and remain positioned on the centre
line of the gas passage. This stabilized
positioning permits the highest possible
operating voltage.
By utilizing the self-tensioning effect of

the spiral electrode coils no weights are
required to keep the electrode hanging
plumb. The absence of weights makes it possible to terminate the discharge electrodes
prior to their passing the edge of the collecting plates. This eliminates flash-over and the
need for shield in the discharge electrodes.
The self-tensioning spiral discharge electrodes allow for better transmission of the
rapping forces. Because of the intermediate frames each separate discharge electrode is
kept short. Short wires well tensioned are not prone to swinging. The spiral wire
electrode provides a uniform current distribution over the full height of the collecting
plates since the corona discharge will occur around the entire surface of the wire as
opposed to a solid emitter with pronounced peaks where the corona discharge will occur
only at the tip of each peak.
RAPPING MECHANISM FOR DISCHARGE ELECTRODE

During electrostatic precipitation a traction of the dust will be collected on the discharge
electrodes and the corona will be suppressed as the dust layer grows. It is therefore
necessary to rap the discharge electrodes Occasionally. This rapping is done with a
rapping system employing tumbling hammers which are mounted on a horizontal shaft
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In a staggered fashion. These hammers hit specially designed shock beams to which one
intermediate part of the discharge frame is attached. In this manner the vibrations
generated by the hammers are transmitted to the discharge electrodes.
One such rapping mechanism is

provided for each electrical bus
section. The drive of the rapping
mechanism is through a shaft
insulator which is installed in one of
the insulator compartments located on
the roof of the precipitator (fig 6). The
operation of the gear motor for the
rapping mechanism is controlled by
synchronous programmer which is
adjusted to optimum conditions at the
time of commissioning. Subsequent
adjustments can easily be carried out during operation should conditions vary.
COLLECTING SYSTEM
The design of the collecting system is based on the concept of dimensional stability. The
upper edges of the collecting plates are provided with hooks which are hung from
support members welded to the roof structure. The lower edge of each plate has a shock
receiving lug which is securely guided by the rapping system. By using an eccentrically
mounted suspension hook for the collection on plates good and positive contact between
the shock iron and the shock bar is guaranteed. This results in a dimensionally stable
collecting system compatible with the discharge system.
In order to maintain the collection efficiency at the design level it is essential that the
discharge electrode and the collecting system are dimensionally stable.
Collecting system mainly consists of collecting suspension frames collecting electrodes

and shock bar (fig 7) Collecting suspension frames are made of slotted angles which are
to be fixed to the roof beams. They should be properly aligned with the emitting system.
Special care is taken during manufacturing to get a closer tolerance on the dimension.
They are properly packed and sent to site.
Collecting electrodes are made of 1.6mm thick mild steel sheets formed in G profile of
400mm width. A special roll forming machine is used to get a closer tolerance on G
Page 20
profile. Hook and guide are welded on one end and shock iron (which goes inside the
shock bar) on the other end on a fixture. Side slot if required, are made on the roll
forming machine itself. The electrodes are bundled together and dipped in rust
preventive oil tank. Collecting electrode bundles should be properly handled to avoid any
damage to the electrodes. Minor local dents can be rectified at site with the help of
correcting tool. Before erecting the electrode should be checked for any damage rusting
and straightness.
Shock bar is provided to transmit the rapping acceleration effectively to all the collecting
electrodes in the row. It is suspended under the Collecting electrodes and guided
transversely by shock bar guides. Collecting electrodes are loosely connected to the shock
bars. The anvil portion of shock bar is stress relieved after welding. The shock bar
should be checked for straightness before erection.
RAPPING MECHANISM FOR COLLECTING ELECTRODE

An essential parameter when designing the internal equipment of a precipitator is the
design of the rapping mechanism for the collecting system. It is essential that this
system is thoroughly cleaned during rapping. The acceleration of the plate resulting
from the rapping action has the greater influence of the cleaning efficiency. In order to
achieve efficient cleaning the rapping system is constructed so as to provide the required
accelerations over all the plates.
Each collecting plate of the system

offered has a shock lower end. The plates
in one row of each field are interfaced to
one another by means of these shock
receiving plates located in slots in the
shock bar maintaining the required
spacings. The shock bars are kept in
alignment by means of guides.
Each collecting plate is hung on an

eccentric hook to ensure that the shock
receiving plate of the collecting electrode
is constantly resting against the shock bar. In this manner the highest possible energy is
transferred to the collecting plate when the tumbling hammer hits the corresponding
shock bar.
The system employs tumbling hammers which are mounted on a horizontal shaft in a
Page 21
staggered fashion with one hammer for each shock bar. As the shaft rotates slowly each
of the hammers in turn over balances and tumbles hitting its associated shock bar. The
shock bar transmits the blow simultaneously to alt of the collecting plates in one row
because of their direct contact with the shock bar. A uniform rapping effect is therefore
provided over the whole row of collecting plates.
It is of prime importance in any rapping system to avoid excessive re-entrainment of the

dust into the gas stream during the rapping procedure. With the design of our rapping
mechanism, the electrodes are given acceleration which causes the collected dust to
shear away from the collecting plates and fall down in large agglomerates. These large
agglomerates which result from a single shearing action greatly reduces the possibility of
dust re-entrainment during rapping.
The rapping frequency should be as low as possible in order to minimize the dust re-
entrainment from rapping. The frequency of the rapping mechanism offered by us is
adjustable within wide limits. There is one set of rapping equipment provided for each
series field so that the frequency can be suited to the conditions in that individual area.
All internal parts of the rapping mechanism are accessible for inspection being placed in
side access passages, before, between and after the collecting plates.
All physical data essential for designing plate suspension eccentricity and rapping
intensity for this type of dust has been tested in our laboratories.
This type of tumbling hammers rapping mechanism has been used by our collaborators
for fly ash application for over 20 years as well as in all other precipitator applications.
From full scale tests carried out in our laboratory the acceleration in any point of a
system similar to the one quoted has been determined. Table 1 shows the effectiveness of
the rapping mechanism measured on the collecting plates. The numbers 2 and 6 in the
direction of flow indicates the position of the plate in relation to the tumbling hammer.
When judging the effectiveness of the collecting system it is also essential to keep in
mind the total collecting area being rapped at any instance. The higher the percentage of
the total collecting is being rapped at any time the greater the re-entrainment of dust
into the gas. With out tumbling hammer rapping mechanism only a very small
percentage of the collecting area for each precipitator is rapped at one time.
This improves the overall efficiency of the precipitator and avoids puffing at the stack
outlet. The functional capabilities of the tumbling hammer system and its operational
reliability have made it a Flakt standard utilised in all installations.
Page 22
TABLE 1
COLLECTING ELECTRODE PLATE
ACCELERATION IN Gs
PLATE HEIGHT
COLLECTING PLATE No. 9M 12M 18M

2
Top part of the plate 460 400 360
Middle part of ptate 560 480 430
Bottom part of plate 880 880 880
COLLECTING PLATE NO.

6
Top part of the plate 190 160 150
Middle part of ptate 230 200 180
Bottom part of plate 360 360 360

The latest design is with 250mm wide collecting electrodes of 1.5mm thick sheet (fig 8).
The hook will be provided on the collecting suspension frames and the slots will be
provided on collecting electrode. The shock bar will be firmly connected to the collecting
electrodes with the help of huck bolts (similar to rivet). Three emitting electrodes per
collecting electrode will be provided instead of two as in the case of 400mm electrodes.
GAS DISTRIBUTION SYSTEM

The gas velocity within the precipitator is approximately 1/20 of the velocity in the
dueling before the precipitator. It is therefore essential that the precipitator is equipped
with arrangements that will give an even gas distribution over its entire cross sectional
area. The desirable gas distribution cannot be achieved solely through the design of the
ducts. Special gas distribution plates are placed before the precipitator itself (fig 9).
Recognizing the importance of preventing areas of high gas velocities construction of the
gas distribution arrangement consists of two separate rows of baffles located at the inlet
of the casing.
The velocity distribution within the precipitator casing is checked prior to

commissioning. During these gas distribution tests any necessary alterations to the flow
pattern will be made by the installations of horizontal baffle plates sealing off required
Page 23
areas of the gas distribution screens.
In addition to the gas distribution plates at the inlet of the precipitator the outlet funnel
of the precipitator is also provided with one row of gas screening plates to improve the
flow pattern near the outlet.
The gas distribution screens at the inlet of the precipitator are provided with a rapping
Mechanism if required. This rapping mechanism is similar to rappers used for the
emitting and collecting systems described earlier.
INSULATOR COMPARTMENTS
Each electrical bus section is supported from insulators located in insulator
compartments outside the casing roof. The weather tight insulator compartments for the
high voltage support insulators are of double walled construction with thermal
insulation between the walls. Each insulator compartment is furnished with an access
door for inspection and service. To avoid dust entering up into the insulator a screen
tube is installed
immediately below it.
Each of the insulator for the

electrical bus sections has
associated with it a one kW
heating element which
effectively heats the air
space of the insulator
compartments and prevents
condensation and
deposition of the moisture
on the insulator. The
elements are of tubular type
and are formed to encircle
each insulator in order to provide uniform heating within the chamber. The electrical
heaters are thermostatically controlled. There is a special arrangement in each insulator
compartment which makes it possible to suspend the discharge electrode system by
means of a temporary jacking hook if the insulator must be exchanged.
Page 24
INLET AND OUTLET NOZZLES
Inlet and Outlet nozzles are provided for each precipitator fabricated of 6mm mild steel
plate. The nozzles are adequately stiffened and braced to stresses due to wind load
earthquake load and suction pressure.
INTERLOCK SYSTEM
The ESP is a high voltage (70 kV) system and hence proper protection devices should be
provided to prevent any operational maintenance personnel to enter into ESP when it is
charged. An elaborate mechanical key type interlock system is provided for the purpose.
All the inspection doors insulator housing and disconnecting switches are interlocked to
rectifier transformer control panels. Unless the rectifier transformers are de energized
and the fields are grounded, a person cannot open any inspection door disconnecting
switch or insulator housing.
PERIPHERALS
Apart from the earlier mentioned features, ESP is provided with galleries and stairs,
rectifiers handling system, pent-house (optional), hopper approach platform (optional),
outer roof, rectifier transformer with controls, auxiliary control panels LT distribution
board, disconnecting switches etc.
Galleries and stairs are provided to make all the inspection doors, electrical equipments
etc. accessible for operation and maintenance purpose. It is designed to take live load of
500 Kg/M2 of load. Platform and stair widths are generally not less than 1.0 metre and
0.80 metre respectively.
Rectifier handling system is provided on top of ESP to lift T/R sets from ground to the
top or vice versa. A hand-operated pulley block is provided on a monorail placed in such
a way that it can handle any T/R set on the ESP.
Pent-house is provided on top of ESP on customer's option. This provides coverage for
insulator housings, disconnecting switches, TR sets etc.
Hopper approach platform (customer option) is provided under ESP to make the hopper
inspection doors and hopper heaters easily accessible. This is required for maintenance
purposes,
Water washing system (customer option) is an elaborate system for washing the
Page 25
collecting electrode surfaces (mainly) when any maintenance work is required to be
carried out. Washing is possible only when ESP is not charged. Clean water with low
chlorine content should be used for cleaning the ESP internals.
A chequered plate outer roof is provided on top of ESP as maintenance platform. ESP top
insulation is provided in between roof panel of ESP casing and outer roof. If the pent-
house is provided the outer roof would be flat, otherwise, it would have a two degree
slope for rain water drainage. It is designed to take up 500 kg/m2 of live load. Rainwater
drainage channels are provided to prevent rainwater to fall hazardously.
THERMAL INSULATION SLAGGING

The precipitator casings, the hoppers and the roof of the precipitator will be insulated as
per the company's standard procedures with both sides Gl wire netting of mineral wool
mattress (slag) of adequate thickness to ensure a maximum surface temperature of 65°C
over an ambient temperature of 45°C and air velocity of 3 metres/second (figs 11 & 12).
The insulator materials and protective covering wilt be new and unused and is
guaranteed to withstand continuously and without deterioration the maximum
temperature to which they wilt be subjected under the specified applications. The
density of the insulation with mineral wool blanket insulating material will be 150
kg/cu.m. The mattresses will be installed by using stud of 6mm. Casing support binding
wires and insulation retainers. The mattresses are held by studs and the joints of the
mattresses are sewn together.
The wool mattress is tied by galvanized binding wires of 186 across the hooks/ studs.
After application of insulation the outer casing will be laid. The sheathing material for
all insulation will be aluminum sheet of thickness not less than 1 mm.,
ELECTRICS
Rectifier transformer (TR) sets are provided on top of ESP. The control panels (electronic
controllers) are housed in EP control room situated on the ground. They are connected by
power and control cables. TR sets are connected to emitting system through
disconnecting switches with the help of bus duct. Disconnecting switches are provided to
enable maintenance personnel to disconnect and ground the emitting systems before any
maintenance work is taken up.
Auxiliary control panels (ACP) housed in EP control room are provided to give power
supply and control the auxiliary equipments of ESP like heaters, rapping motors etc.
These field mounted equipments are connected to ACP by cables.
Page 26
LT distribution board housed in EP control room is provided to distribute the power
supply to different panels. The above mentioned features are applicable for a typical
electrostatic precipitator for collecting fly ash. The EPs used for the collection of soda ash
coming out of a soda ash recovery boiler (paper industries) are different in many ways as
compared to the EPs used for fly ash collection.
Page 27
FLOW MODEL STUDIES IN THE FIELD OF ELECTROSTATIC PRECIP1TATOR
ABSTRACT
Flow mode! studies is an effective method to ensure uniform distribution of gases in the
electrode section of the electrostatic precipitator. A good understanding of the field
dynamic behavior is important to arrive at a reliable inference from such studies. The
need for approach to results and conclusion of model studies conducted are outlined.
INTRODUCTION
The basic design philosophy of electrostatic precipitator emphasizes the need for good
gas distribution inside the electrode chamber.
THEORETICAL ASPECTS
Large installation of these days handling over three million cubic meters of gas every
hour with their associated limitations on space result in layouts giving rise to serious
flow distribution problems. The precipitator by itself is a low pressure device, hence the
flow pattern established by the inlet flue system upstream the precipitator established
the flow pattern within the electrode chamber.
Poor gas flow which includes unbalanced gas velocities, flow separation jet and pulsating
flow result in reduction in precipitator performance by unbalanced loading and by re-
entrainment.
Conducting studies in site and introducing necessary corrective measures are both
laborious time consuming, constantly and impracticable. Flow model studies thus offers
an apt method to tackle flow distribution at the design stage itself enabling design of
flow correcting devices and better design of flue system.
APPROACH TO MODEL STUDY
The following model requirements are considered while constructing the model :-
i). Geometric similarity -the same scale being used for ail parts comprising the model. As
regards the surface roughness the effect of scale was compensated by using materials of
smooth surface.
ii).Kinematic similarity - the flow lines in model and full scale plant shall have similar
patterns.
Page 28
iii). Dynamic similarity - Here it was assumed that from a practicality point, is
sufficient to ensure that the Reynold's number was maintained in the region of turbulent
flow at all section of the model, A critical area being that of the electrode section.
The following assumptions are made ;-

ii) The temperature distribution at the inlet of the precipitator is equalized by mixing in
the preceding duct work.
ii) Dust is evenly distributed in the gas and that a good gas distribution at the inlet to
the electrode chamber will suffice. Hence, a primary aim of the model study is to ensure
an even distribution of gases in the electrode chamber.
TEST SET-UP AND INSTRUMENTATION

The model comprises of the electrostatic precipitator, the inlet flues and the outlet flues
scaled down to 1/10. The main shell is fabricated from 1.6 mm sheet steel/flexi glass.
Flexi glass and windows and test measurement points provided at various sections to
enable measurements and visualization of flow patterns. Vane type anemometers are
used to measure the velocity distribution inside the electrode chamber.
Prandtl tubes are used in conjunction with electronic micro-manometer to measure the
distribution ducts. Computer is used through keyboard terminals to evaluate and
analyze the measured values.
TEST PERFORMANCE:
The testing involves the measurement and analysis of flow distribution, introduction of
flow correcting devices, flow pattern visualization using smoke stream and measurement
and analysis of flow pattern after introduction of flow correcting devices.
Flow correction is done in stages measuring, analysing and correcting section by section
starting from the inlet dueling then the outlet dueling and finally the precipitator
chamber. Guidevanes installed for improving the flow pattern in ducts
are basically designed based on the literature available on duct losses and at the times
extrapolation on these.
The vanes in the funnel inlets to the electrostatic precipitator is arrived at an

experimental basis keeping in line with the recommendation given in literature. The
deflector plates provided on the screens are arrived at totally on experimental basis-
GAS DISTRIBUTION IN DUCTS:

Measurements are made in various duct streams before the precipitator to check for the
equal distribution of flow in the various streams. Where necessary guide vanes are
Page 29
installed in addition to those already installed to obtain the required flow distribution
between screens.
GAS DISTRIBUTION IN PRECIPITATOR CHAMBER:

After distribution in the various streams of the ducts have been nearly equalised the
distribution in the precipitator chamber is studied. Vanes are provided based on
literature available in the entry funnel. Thereafter repeated tests are conducted with
various locations of deflector plates on the distribution screens till the required locations
for the acceptable distribution is obtained.
Distribution studies are made keeping the Reynold number in the gas duct region
between the collection electrodes (which is critical region in the model) above the critical
value i.e. 4000 at 60% gas flow conditions. Smoke screens are also used to check visually
the flow stream inside the casing.
DUST DROP OUT STUDIES:

Dust drop out studies are carried out by injecting dust into the duct keeping the flow
well below 50% of the normal flow. This ensure that dust drop out takes place in the
ducts. Thereafter the flow is slowly increased to normal flow. Region on dead zone areas
and duct build zones are identified by those regions where dust remains even after
normal flow is obtained.
PRESSURE DROP STUDIES:

Pressure drop measurements are made as a difference of the total pressure at the test
sections of interests. In the case of precipitator the total pressure difference between the
test section in the duct near the inlet funnel of the precipitator and the test section at
the duct near the outlet funnel of the precipitator gives the pressure drop in the model.
This is further scaled to full scale plant by correcting at for the flow conditions like
density, temperature and gas flow.
ACCEPTANCE CRIETERIA FOR GAS DISTRIBUTION :

1). Minimum number of velocity readings taken in any section inside the precipitator
shall not be less than one ninth the area of that section in sq. feet.
2). Readings shall cover a minimum of every third gas page in section.
3). The spacing between two levels of readings by the sections shall not be greater than
10% of the collecting electrode heights.
Page 30
4). The test section shall be at the leading edge of the first field and the leading edge of
last field.
5). The final velocity pattern in any section shall have 80% of the readings not more than
1.15 times the average value of that section.
6). The average value of the various parallel streams shall be within + or -10 degree, of
the total average.
7). Low velocity may be accepted in the top and bottom levels in view of gas effect.
CONCLUSION :
The performance requirement of the present day precipitators is welt above 99%. The
basic design of the precipitator is to provide required collecting area for every unit of gas
volume to be handled. This brings out the importance of gas distribution. The model
study is the tool available to study this distribution and to ensure the recovery level of
distribution.
The flow correction devices like guide vanes in ducts, vanes in the inlet funnel of the
precipitator and the deflector plates on the screens are finally adopted in the full scale
plant and a final test conducted at a full scale plant to ensure that the distribution is as
desired and determined in the model studies.
Page 31
ELECTRICAL SYSTEMS FOR ELECTROSTATIC PRECIPITATORS

The following is a general description of the electrical equipment offered as a part of the
electrostatic precipitator for each Boiler. All the equipments specified herein are
designed in accordance with the accepted engineering practices.
HIGH VOLTAGE TRANSFORMER - RECTIFER { HVR )
The HVR Unit is an assembly consisting of a 415 volts single-phase high transformer
and a full wave rectifier bridge designed for electrostatic precipitator service and
contained in a tank filled with insulating oil. The tank also houses a current limiting
linear reactor connected in series with the primary winding of the transformer and a HF
choke connected to the negative terminal of Rectifier Bridge. A high voltage measuring
and feedback resistor column is also mounted in the transformer tank.
The linear reactor limits the short circuit current during sparking in side the
precipitator to safe value. The HF choke protect the transformer rectifier from surges
occurring during sparking inside the precipitator.
Regulated AC input voltage available from electronic controller is fed to the transformer
primary and full wave rectified negative DC out put is taken through a HV bushing.
The positive end of the rectifier bridge is connected to earth through current feedback
shunt. The transformer rectifier is designed for heavy duty operation of 24 Hrs. a day
with frequent sparking inside the precipitator.
The transformer tank is a fully welded construction suitable for outdoor service. The
insulating and cooling medium of HVR is an oil of dielectric strength and good heat
transfer characteristics and is adequately protected from contamination.The HVR is
fitted with the following instrumentation and appurtenances.
1. BUCHCHOLZ RELAY.
2. OIL TEMPERATURE INDICATOR.
3. WEATHER PROOF TERMINAL BOX HOUSING "LV" TERMINALS
FOR MEASURING AND CONTROL CIRCUITS, POSITIVE
TERMINAL ALONG WITH PROTECTIVE SURGE ARRESTORS,
SHUNT RESISTOR, SPARK DETECTOR.
4. A HIGH VOLTAGE DC NEGATIVE BUSHING WITH
PROVISION OF BUS DUCT CONNECTIONS.
5. CONSERVATOR WITH OIL LEVEL INDICATION AND BREATHER.
6. ROLLERS.
7. RATING PLATE.
8. LIFTING LUGS.
Page 32
ELECTRONIC CONTROLLER
The electronic controller unit feeding regulated input to HVR is a microprocessor based
controller suitable for indoor application and of dead front free standing floor mounted
type.
The electronic controller houses the following components:
* Switch fuse unit
* Main contractor
* A pair of thyristor in anti parallel connection
* Microprocessor based automatic control module with fault annunciation

system.
* Firing card.
* Overload relay.metere,control transformers, CTs etc.
* Cable glands lugs and control terminal blocks.

The panel front is fitted with ARECA-2 (BHEL’S ADVANCED PRECIPITATOR
CONTROLLER) comprising of digital display for measurement of secondary voltage
(average, peak, valley), current, spark counter, current set push buttons, management
net work /stand alone selector switch and also analog meters for current and voltage
measurement.
The automatic voltage control system operates so as to maintain constant current from
transformer rectifier unit under dynamic conditions of electrostatic precipitators load.
ARECA-2 controls the precipitator by changing the ignition angle of the Thyristors
connected to the primary of the transformer rectifier set. Precipitator current voltage
and phase angle of the primary voltage are used as Input data. The actual precipitator
current which varies continuously due to field conditions is compared with set value and
the error signal is processed to control firing angle of the Thyristor to regulate the input
voltage to the transformer to achieve set constant current inside the precipitator. When
a spark occurs the current is interrupted for a preset time to allow de-ionization and
rebuilds to a value slightly lower than the current at which the spark occurred. The
current decrease and the rate of rise to the set value are deciding the spark rate.
ARECA-2 provides facility like intermittent charging and peak sensing mode of
operating to suit the process for improving precipitator operation or for energy saving.
Page 33
Electronic controller provides the following protections /indications.
1. Protection for T/R from oil temperature high and internal faults.
2. Thermal over load protection.
3. Under voltage indication.
4. DC Voltage high.
5. Transformer temp.high.
6. AC Current high.
7. Peak detector.
A brief write up on ARECA-2 is given below.
ARECA-2 is a 16-bit microcontroller based unit for regulation and control of the
electrical power input to the HVR /Electrostatic precipitator.
ARECA-2 maintains the spark rate at a suitable level for great variations of gas
temperature, dust compositions, flow rate etc.
It regulates the rectifier in such a way that the current through the precipitator Is
corrected constantly as the conditions for the sparking are changed there by minimising
the loss of energy.
The electrostatic precipitator functioning can be monitored on the ARECA-2 control

module. The figures on the control module display show the precipitator current, voltage,
spark rate current limit etc. The figures are obtained in succession by pressing suitable
keypad combinations as given in ARECA-2 user manual.
AUXIL1ARY CONTROL PANELS (ACP)

The auxiliary control panels provided for Electrostatic Precipitators houses the power
and control circuits required for energizing rapping motors and heating element of the
precipitator.
The complete unit is modular and draws out type with individual modules for each
feeder. Each module houses the power and control circuits with push buttons, and
indicating lamps mounted on the door of the compartments.
The heating elements for hoppers and support insulators are thermostatically controlled.
Indications for operation of heating element as well as ammeters to read line currents of
heater feeders are provided. The operation of rapping motor is sequentially controlled
through programmers. Annunciation/indication for rapper motor 0/L trip/rapper motor
Page 34
ON or OFF are provided. The rapper motors are also provided with local start/stop
facility,
GEARED MOTORS
Each collecting and emitting system is provided with one geared motor unit coupled to
the rapper shaft and located out side the casing. The geared motor consists of helical
reduction gear with an integral DOL Start squirrel cage induction motor as prime
mover. The motors are suitable for 415V,3 phase. 50Hz AC input and of weather proof IP
55 enclosure. The geared box unit is proving with oil filling drain plugs and level
indicators.
DISCONNECTING SWITCH (OFF LOAD ISOLATER)

HV disconnecting switch is provided for isolation of associated transformer rectifier. In
the OFF Position of the dis-connecting switch the emitting system of the associated bus
section is earthed there by proving safety for the personnel during any maintenance
work on the dead HV SYSTEM.
INSULATORS
Following insulators are used in the electrostatic precipitator:

1. Each bus section consists of four support insulators for supporting the emitting system
and are located inside individual insulator housing mounted on roof of precipitators.
These insulators are surrounded by heating elements to prevent condensation of deposits
causing any flash over.
2.Shaft insulator is provided to isolate each geared assembly from the associated
emitting rapping shaft, this also is provided with heating elements to avoid any
condensation on its surface which could result in flash over of the same,
3.0ne bushing insulator is provided corresponding to each field and is mounted in the
+insulator housing, this act as a bushing in the H.V bus duct system providing necessary
support and clearance for the H.V bus section. The insulators are of high quality
porcelain designed to with stand the operating temperatures.
LT SWITCH BOARD
LT switch board shall be single /double front, dead front. floor mounting and modular
type. All the incomer feeders and bus coupler shall be fully drawout type. The out going
feeders (Switch fuse units) Shall be fixed type. This feeds power to electronic controllers
and auxiliary control panels.
Page 35
PRE-COMMISSION1NG STABILISATION OF EP AND

PERFORMANCE TESTING OF EP
INTRODUCTION
Once the erection of EP is over, electrical work can start. Electrical jobs include the
erection of HVR sets electronic controllers, the auxiliary control panels geared motors
the heaters and the laying of inter connecting cables. After this process pre-
commissioning activities involved in the pre commissioning of EP include.
* Checking up of internals for tolerance

* Checking up of internals for completion
* Checking of heaters
* Trial run of rapping motors
* OCC of HVR sets
* Air load test of fields
* Gas distribution test on EP
* Gas loading
The internals should be checked for any debris or welding protrusions which will cause
heavy sparking during charging. Any of the internals should be checked for welding
completion as given in the drawings. It should be checked whether all the items as given
in the drawings have been properly erected. This is particularly applicable for screw for
the shaft insulator where the inter-changing is quite possible between left and right
types.
Next, we can take-up charging of heaters and the rapping gears. It should be ensured
that ail these requirements are properly earthed so that safety of the operating
personnel is ensured. The rapping frequency for the various collecting and emitting field
should be set as given in the manual. The motors can be put on trial run for Eight hours
continuously,
To find out the healthiness of the HVR sets OCC test has to be done. After OCC is done,
the transformers may be connected to the fields and VI curves on static air load as well
as with ID and FD fans running may be taken,
With ID and FD fans running at rated current the gas distribution test is conducted on
EP to find out the co-efficient of variations below 20 %. To achieve this limits the guide
vans and blanking plates given have to be made use off. Finally these plates should be
welded to the screens.
Page 36
Finally the EP can be charged with flue gas. The EP can be charged once the flue gas
temperature is above due point and the combustion of coal/oil is complete. So that
chances for fire is avoided. The various fields may be set with different current values as
given in the manual. Also the spark limit of 5-10 sparks/minute have to be ensured by
proper S&T pot setting. Some coals may lead to back corona problem because of high
resistivity. In such coals, intermittent charging with 'ON' - 'OFF' controller of ICE
controller will help.
PERFORMANCE TESTING
In the performance testing of EP measurement of the operating flue gas volume,

temperature and the concentration of the dust is done both at the inlet and outlet. This
dust sampling should be done in such a way that velocity of sampling is same as the flue
gas velocity in the duct at that point. Pitot traverse is done after splitting the ducts to
number of equal areas using the Pitot tubes and micro-manometer. Here velocity is
measured as the dynamic pressure
Next dust sampling is done using the fiber glasses thimbles with proper size nozzles.
vacuum pump and the gas meter in series. The thimble entraps all the dust coming
alongwith the sampled flue gas and the gas meter records the gas volume sampled.
m
Then concentration of dust (c) is C = ——
x
Where : m = mass of dust collected
x = volume of gas sampled
If C1 is the inlet dust concentration and C2 is the outlet dust concentration the
efficiency of EP is,
C1 -C2
n=
C1
CONCLUSION
Page 37
As the performance level of equipment goes up, the methods of measurement are also
keeping apace. The measurement accuracy will depend on the equipments used for
resting. Hence a proper selection of equipments and procedure will go a long way in
establishing a foolproof method.
Page 38
EP OPERATION AND MAINTENANCE
INTRODUCTION
Now-a-days, Electrostatic Precipitators are the main pollution control equipments for
the utility steam generators and they are very much suitable for treating large volume of
flue gas emanating from steam generators at very high efficiencies of the order of 99.8%
plus with low pressure drop. Though it is rugged and very simple in construction still it
needs some maintenance works for its proper upkeep. Points that need attention during
short and major shutdowns are discussed below.
CAUSES FOR POOR PERFORMANCE:

The main parameters to judge the EP performance is the emission from the chimney.
However, it will be very difficult to differentiate when the emissions are below 150
mg/Nm3. High ash emission may result from one or more of the following:
1. Fields not in service due to electrode snapping.

2. HVRs/Control panels are not working.
3. Ash removal system not working.
4. Voltage-current level is low.
One of the major reasons for the field tripping is ash bridging- this is caused by the poor/
inadequate ash handling system, and non- functioning of the surface heaters. Snapped
electrodes also cause the field to trip. Reverse rotation of the rapping system also may
lead to slippage of the collecting electrodes from the hooks and thereby snorting the
fields.
The HVRs are placed on EP roof top and control panels in the air conditioned control
room. Any malfunction of either of the HVR or the panel affects the EP field and hence
EP performance. One of the ways to overcome this situation would be put this particular
field to the adjacent transformer alongwith its own field i.e. to put two fields in parallel
to a HVR. Though it is not a long term solution this will help to reduce the emission until
the defective HVR/EC is rectified.
The voltage current level in the EP may be low because of:
* High ash deposit on the emitting/collecting electrodes

* Poor alignment of emitting and collecting system.
* Heavy sparking caused by high resistivity dust.
Page 39
Continuous rapping of say for 10-15 minutes will reduce the ash deposit on the
electrodes. Initial deposits on the emitting electrodes some times, takes six months to
peel off. The problem of poor alignment can be attended only during-a shutdown.
Problem associated with high resistivity dusts can be solved by resorting to either
conditioning by SO3 & NH3 or to pulse charging.
One need not over emphasize the importance of adequately designed ash evacuation sys-
tem. ash accumulation in hoppers not only leads to bridging of emitting and collecting
system causing the field to trip but also damage to the internals.
Cases of failures of rapping shafts, displacement of shockbar guides, bending of

collecting electrodes because of ash reaching the level of manhole door have come to our
notice. Proper upkeep of heating elements in the hoppers and operating the ash removal
system regularly will obviate this problem.
OPERATION OF EP AND LOG MAINTENANCE

Electrostatic precipitator is one of the equipments which has very few moving /rotating
parts and hence needs minimum maintenance. Nevertheless, reliable and sustained good
performance will result if a little attention is paid to the operation and maintenance of
this rugged and magnificent equipment. Hourly logging of the voltage current levels of
the various fields as well as the operation of the heaters, rapping motors will aid in
analyzing problem if any at a later date. Typical log sheet is enclosed (Annexure-1).
ON LINE MAINTENANCE
* Drive for rapping system

* High voltage power supply system
* Heating elements for hopper insulator housing and
* Ash level indicator
* Ash handling system
SHORT AND LONG

Whenever the unit is under shut down the opportunity may be availed to inspect the
internals, During a short shutdown extending say upto a fortnight the following Jobs can
be attended to.
* Snapped emitting electrodes, if any can be removed

* Ash deposit on the shaft support insulators can be removed.
* visual inspection of alignment between emitting and collecting
system as well as rapping systems can be made.
* Places of air/water leakage if any, can be identified
Page 40
* Minor deformation to the collecting electrodes can be rectified.
However if there is any major defect /damage in the internals that can be attended to
only during major overhauls.
SPARES
One has to plan well for spares before starting the shut down jobs on electrostatic
precipitators. It is found that items like shock bar guides and raping hammers etc; are
required for replacement. Hence adequate stock of these items as well as other spares
will be a wise proposition. The annexure II gives a recommended list of spares for three
years operation.
Page 41
ANNEXURE-1
RECOMMENDED SPARES FOR ELECTROSTATIC PRECIPITATOR 200 MW
Sl.no Items Qty/Boiler
1. Support insulator 10
2. Shaft Insulator Assy. 16
3. Bushing Insulator Assy 04
4. Heating Element/Hopper 06
5. Heating Element for Insulator housing 06
6. Heating Element for Shaft Insulator 06
7. Foot mounted Gear Motor 06
8. Timers 06
9. Synchronous Programmer 02
10. Thermostat for Insulator Housing 02
11. Thermostat for Hoppers 06
12. Emitting electrode 600
13. Inner arm 40
14. Outer arm for Emitting Electrode 16
15. Outer arm for Collecting Electrode 16
16. Plain bearing 06
17. Set ring 08
18. Sleeve Pin for Shock bar guide 02
19. Shock bar 08
20. Carbon Bush 06
21. Shock bar guide front 24
22. Shock bar guide rear 14
23. Sleeve for Shock bar guide 06
24. Pin Insulator for disconnecting switch 10
Page 42
RECENT DEVELOPMENTS IN ELECTROSTATIC PRECIPITATOR
INTRODUCTION
In recent years there has been an increasing demand for fly ash removal efficiencies of
99.8% and above. Air (prevention and control of pollution)Act 1981 stipulates emission
standard which requires the collection efficiency of the electrostatic precipitator to be
very high. In India, we use mainly tow sulphur coals. Because of the high resistive
nature it becomes difficult to collect Indian fly ash and hence the size of EP is large.
Studies conducted by us resulted in development of ICE-C controller, BAPCON
controller and pulse rectifier, which is well suited for low sulphur coals.
Recent experimental work has shown that wider spacing EP results in increased mi-
gration velocity. The potential of plate spacing as a parameter for optimizing design can
be evaluated only by conducting experiments. If migration velocity can be increased as
plate space is increased it might be possible to hold collection efficiency constant and
reduce the specific collection area and therefore the initial cost of a precipitator. BHEL
has taken up R&D experiments on wide spacing with pilot and full scale tests.
Establishing of basic research facilities to analyze the various parameters and to

evaluate the various components is required for any company to attain strong
technological base. BHEL has already established its ELECTROSTATIC
PRECIPITATOR LABORATORY to analyze various parameters and help in selecting,
designing, evaluating improving and maintaining a trouble free long lasting and
economic electrostatic precipitator.
RECENT DEVELOPMENT
The development of new ESP technology notably in the high voltage supply area Is
opening up new possibilities for substantial energy savings reduced dust emissions and
increased availability. Today there are plants in commercial operation in which energy
savings of between 70 and 90 percent are achieved and where emissions are reduced up
to 85 percent.
The efficiency of dust collection in an ESP follows an exponential curve. Any desired
collecting efficiency can be achieved If the precipitator is sized large enough. The
following formula Is used universally for calculating the required collection area (A) m2
for a given dust collecting efficiency and a given volume flow(Q) m3/s
Page 43
n =1-e- (WK x A)/Q

In the formula K is a constant and WK a dust constant characteristic of a given dust
composition. WK is called the migration velocity. If the dust is difficult to collect i.e. if it
has a low WK a high A is required to achieve the desired collecting efficiency. WK is
determined largely on the basis of the ESP supplier's experience from operating plants.
Developments have taken place recently in the field of electrostatic precipitator

controllers to obtain substantial energy savings reduced dust emissions increased
availability and cost reduction. Major developments are as follows:-
** Development of ICE-C controller

** Devolopment of BAPCON controller
** Development of multipulse transformer set
** Introduction of wide spacing ESP
DEVELOPMENT OF BAPCON CONTROLLERS

BHEL’S ADVANCED PRECIPITATOR CONTROLLER (BAPCON) is based on
intelligent microprocessor to regulate and control power input to the electrostatic
precipitator. Thyristor controlled rectifiers of any make can be connected to BAPCON.
For different gas temperatures, dust compositions, gas flows etc., BAPCON maintains
the spark rate at optimum level. For different conditions of sparking current through the
electrostatic precipitator will be corrected by controlling the primary current of the
transformer rectifier. The EP functioning can be monitored on the BAPCON control
panel. If the value of the parameter is out of set limits BAPCON gives an audio and
visual alarm. Co-ordinated control of all the EP functions can be achieved by connecting
number of BAPCON units to a centralized management system called INTEGRATED
OPERATING SYSTEM.
BAPCON controls the EP power by controlling the firing angle of the rectifier thyristors.
EP current and voltage as well as phase angle of the primary voltage are used as control
inputs. Initially EP current is slowly increased toward the set current limit.
When a spark occurs the EP current is blocked for one cycle and then the CP current is
restarted. At this point the EP current suddenly raises to (IS-S) level. The spark rate will
be controlled by the set values of S&K controls.
INTERMITTENT CHARGING:
The number of half cycles the thyristors should conduct can be selected. The selected
Page 44
number indicates the number of half cycles the thyristor should conduct. Intermittent
Charging operation be selected for improving precipitation or energy saving. Often both
are possible.
BASE CHARGE:
When we adapt very high charge ratio, the valley voltage drop and thereby average
voltage will also go down. To improve the valley voltage and also to eliminate the effect
of uni-polar charging of HVRs base charging facility is provided. The small charging is
introduced (base charge) in between the two main intermittent charging pulses to
increase the valley voltage.
AUTOMATIC OPTIMISATION:
The BAPCON controllers are provided with the feature of automatic optimisation.
BAPCON samples the VI characteristics of the fields at regular programmable intervals
and selects the best possible chrge ratio.
Figure-3 shows the general arrangement of BAPCON controllers developed by BHEL

which are in operation at Tuticorin TPS and DESU power station. The improved
performance has been obtained by using BAPCON controllers. The major advantages
are:-
1. Reduced power consumption.
2. Increased efficiency and performance of EP
3. Can be retrofitted in existing power controllers of EP with thyristor control.
4. Automatic selection of best intermittent charge ratio for varying operating

conditions
5. Base Charging facility increase the valley voltage and hence the performance
DEVELOPMENT OF MULTIPULSE TRANSFORMER SET

A recently developed technology for Electrostatic precipitators is pulsed energisation
extensive research and development during the last decade has introduced several pulse
concepts of which a few are commercially available today reduced outlet emissions have
been emphasized but tests by BHEL shows that remarkable power savings also can be
obtained. When upgrading or retrofitting existing ESPs to comply with new emission
Page 45
regulations the ESP. Pulsed energization now offers a number of specific benefits in
addition to improved performance and power savings. These includes installation with
mum ESP downtime, minimum supervision and maintenance and low investment since
only the transformer/rectifier (T/R) set is changed and the internals of the ESP do not
have to be modified. Different designs of internals have been used successfully and found
that the deterioration of EP efficiency due to poor current distribution and back corona
conditions can be reduced by pulsed operation.
As it takes some time in the order of some seconds for a high resistivity dust for the
charges in the dust layer to disappear the current density where back corona starts is
equal to the time average current density as a first approximation. Thus high sharp peak
currents at low frequencies from the discharge electrode have little effect on back corona.
By increasing the voltage for short periods intensive corona is formed and good current
distribution is obtained at regular intervals.
MULTIPULSE CONCEPT
Figure-4 shows the circuit diagram of the Flakt pulse supply. A storage capacitor placed
after high voltage rectifier is charges. The energy is transferred via an inductance to the
ESP by thyristors. The energy oscillates between the ESP and the storage capacitor until
an essential portion has been used by the ESP.
Figure-5 shows the high voltage wave form for the MFC system. When the energy. When
the energy generated in the storage capacitor is released, the pulse is generated. The
pulse amplitude declines in line with progressive use of the energy to form corona in the
ESP. By means of pulses peak voltages higher than used for conventional energization
are used in the ESP without leading to sparking. Better corona current distribution
results in enhanced efficiency and due to the application of pulsed currents back corona
formation is suppressed.
A separate conventional base rectifier is not required for the DC since the multipulse
unit is designed to supply an inherent base voltage up to the corona onset voltage. Any
change in the corona onset voltage is automatically tracked. Table At shows technical
data for the MPC units at Gnsted unit-2 power station.
Page 46
TABLE 1
Pulse amplitude 40 kV
Pulse width 90 Micro sec.
Pulse frequency up to 300 Hz
Corona current 200mA
Pulse/burst up to 8
Size 1.2x1.2x1m
Weight 1,470kg,
RAPCON FOR PRECISION TIMINGS OF RAPPER MOTORS

RAPCON(rapper controller) is a microprocessor based unit that controls and Surveys the
operation of rapping motors in Electrostatic Precipitators. One RAPCON unit can control
up to 16 rapping motors. RAPCON starts and stops the rappi1lg motors as programmed
and will give an alarm if a rapping motor fails.
RAPCON is a component of BHEL's Integrated Operating System (IOS), but can also
used as a stand alone unit. In BHEL 's Integrated Operating System a maximum of
eight RAPCONs will communicate on a data with other control units.
From RAPCON each rapping motor can be manually started or stopped during
operation, without interfering with other rapping motors. The Operation State of each
rapping motor is indicated with light emitting diodes on the RAPCON Panel.
The RAPCON is pre-programmed with number of Rapping Sequences, any of which can
be selected depending on the field failure condition of the Electrostatic Precipitator.
INTEGRATED OPERATING SYSTEM

Integrated Operating System (IOS) is a PC based management system developed for
Electrostatic Precipitator applications and is one of the most sophisticated systems
available today. Controlling and supervising an Electrostatic Precipitator with IOS
ensures an effective control of the entire process in the precipitator. Remote control of
entire ESP operation can be achieved from a single point e.g. at UCB. The set point of
the various BAPCONs and RAPCONs can be changed from IOS. The status of the ESP
and printout of the same can be obtained in the IOS-PC. The ESP can also be optimised
Page 47
for best performance with the help of IOS, using optional control algorithms to achieve,
 Maximum dust collection, by optimising charge ratio.
 Minimum power comsumption with allowed emission, by increasing charge ratio and
reducing current.
 .Automatic ESP startup and shutdown procedure at minimum time and cost.
The IOS is adaptable to the varying requirements of the different objectives

like above.
The IOS is using Distributed Digital Control (DDC) co,ncept. It incorporates specialised
sub-controllers which are independent and can control and supervise their part following
their local preset, paramenters. The comprehensive control of the precipitator can be set
in the IOS. On-line help is also available in the IOS with easy access.
INTRODUCTION OF WIDE SPACING EP

The Electrostatic precipitators can remain competitive with other particulate control
devices like fabric filter if their capital cost can be reduced while keeping their
performance. Recent experimental work has shown that wider spacing EP results in
increased migration velocities. Presently we use spacing of 300mm between any two
collecting electrode rows. World wide many suppliers have started using wide spacing
EP.BHEL has taken up evaluation and demonstration of wide spacing EPs in India. Full
scale trails wee conducted with 400mm spacing at Tuticorin thermal power plant. The
performance results were obtained with full scale experiments at Tuticorin and Fig.-7
shows the comparison of performance for wide spacing EP. Results shows that by using
400mm spacing performance of EP can be maintained, when compared to 300mm
spacing, the following improvements/changes may be obtained with wide spacing EPs.
** Increasing the pitch to an optimum value to get

higher migration velocity.
** Higher operating voltage.
** More stable electrical operation.
** Permissible range of alignment error can be increased.
** Maintenance will be easier. Personnel can enter
the inter electrode space easily.
** High collecting performance even for sub-
micron particles.
** Total weight is reduced.
BHEL is introducing 400 mm spacing for EP applications. In addition R & D
Page 48
experiments with 600mm wide spacing in Indian power plant for evaluating the
performance of this modification is also being taken-up. Based on the trials to be
conducted EP spacing for Indian application, can be optimized.
LABORATORY FACILITIES AVAILABLE AT BAP-RANIPET
A) R&D Laboratory ;-
BHEL has established its own R&D laboratory at its manufacturing plant. The total cost
of the facility is Rs.50.0 lakhs including building, electrical accessories ad laboratory
equipments. The following facilities are available.
a) FLOW MODEL TEST FACILITY

b) EP COMPONENT TEST FACILITY
FLOW MODEL TEST FACILITY.

Flow model test facility is used for obtaining better air distribution patterns by
conducting tests on scale models of electrostatic precipitator and associated dueling. The
results are useful for BHEL and customer. Such model studies are conducted based on
the contractual requirement of customers. The facility is used for: -
** Obtaining better gas distribution inside EP chamber for improved performance.
** Optimized pressure drop in the system which will result in a reduction in the
operation cost of the boiler system.
Page 49
EP COMPONENT TEST FACILITY

Facilities were established to analyze the characteristics of dust and to obtain better
performance and reliability by developing and testing new profiles of collecting and
emitting electrodes and other components of EP. Table-1 gives a list of various
equipments and facilities available and their uses.
TABLE-1
LIST OF VARIOUS EQUIPMENTS/FACILITIES AVAILABLE AND THEIR
USES
Sl.no. Test facility Major use
1. Resistivity meter Resistivity of fly ash with varying air
temperature & dew point.
2. Bahco classifier Fly ash size distribution from 3 microns and

above.
3. Current distribution test rig Current distribution on collecting electrode
4. Corona study rig Corona aspect of various electrode system.
5. Spark erosion test rig Spark erosion endurance of emitting

electrode
6. Thermal relaxation testrig Thermal relaxation of emitting electrode
7. Image intensifier Recording of corona discharge and spark

discharge.
8. Ozone level monitor Monitoring of ozone level due to corona.
9. Portable smoke density meter smoke density measurement
10. Data logger On line computation and logging of data for

flow model tests & current distribution test.
11. Acceleration measuring system To measure rapping accelerations on

electrodes of EP.
12. HV-HF active divider To measure repetitive and fast HV pulses.
Page 50
B. PILOT ELECTROSTATIC PRECIPITATOR

The performance of EP can be described in terms of dust characteristics gas flow
temperature and electrical characteristics. But is difficult to conduct experiments to
evaluate the effectiveness of each variable in full scale EPs. It is desirable to construct a
dedicated pilot EP with enough flexibility for an experimental investigation of the effects
of individual functional units on overall performance. BHEL has acquired a pilot scale
EP which is being tested at Ennore thermal power station. Major design features are :-
** Gas temperature can be varied from ambient to 350 Deg.C.
** Gas velocity variation from 0.3m/sec. upwards.

** Sampling ports at outlet of EP fly ash collected in each field can be measured from its
hoppers.
** Total gas volume flow is measured at EP outlet.

** The collection plates are 2Mtr. high plate to plate spacing can be varied. Width of gas
path is 1 metre.
** Specific collection area of EP is 64M2/M3/Sec. at a plate spacing of 250mm and gas

velocity of 0.6m/sec,
There are three electrical sections in the direction of gas flow with only one gas path.
Pilot EP can be moved to any power station and the performance characteristics can be
obtained.
C. COLLECTING ELECTRODE TEST TOWER

We have established this test facility for acceleration and life testing of collecting
electrodes, guides, shock bars and hammers.
SUMMARY
Presented till now are important developments that have taken place around the world
and also- in India. BHEL has taken up efforts for better customer satisfaction and also
keeping up with the various new trends in the world. Based on R&D results on wide
spacing EP, BHEL's ESP collaborator M/s. Flakt Industri, Sweden has started supplying
electrostatic precipitators with 400mm wide spacing EP and is expected as a standard
for few contracts. BHEL's laboratory facilities will be used for analyzing and
understanding the various programmes associated with electrostatic precipitator
operation.
Page 51

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TRAINING MANUAL FOR ELECTROSTATIC PRECIPITATOR

SL. DESCRIPTION PAGE

1. PRINCIPLE OF ELECTROSTATIC PRECIPITATOR OPERATION 1

2. SELECTION AND SIZING OF ELECTROSTATIC PRECIPITATORS FOR 9

3. MECHANICAL DESIGN OF ELECTROSTATIC PRECIPITATOR 14

4. FLOW MODEL STUDIES IN THE FIELD OF ELECTROSTATIC 28

5. ELECTRICAL SYSTEMS FOR ELECTROSTATIC PRECIPITATORS 32

PRINCIPLE OF ELECTROSTATIC PRECIPITATOR OPERATION

Electrostatic precipitation utilizes the forces acting on electrically charged particles in

(a) Corona generation

In most industrial gas cleaning applications, there are sufficient quantities of

A second important consideration of the effects of dust on corona generation is the

In practical precipitators, field dependent charging is usually of most interest but in

A second factor of importance is the rate of charging of the particles. Practical

Electric field strength is determined by the electrostatic component, which is related to

In practical size precipitators, however, laminar force is practically never achieved.

A principal practical use of the Deutsch-Anderson equation has been in relating

SELECTION AND SIZING OF ELECTROSTATIC PRECIPITATORS FOR COAL

A fundamental task in precipitation technology is the design of optimum precipitator

FACTORS AFFECTING THE SIZE OF ESP

Where ή = efficiency of precipitator in percent

A = collection area in Sq.Metre

Q = flue gas volume in Cub.Metre / Sec.

W = migration velocity in M/sec.

ELECTRICAL RESISTIVITY OF ASH

COLLECTION SURFACE (SPECIFIC COLLECTION AREA)

NUMBER OF FIELDS IN SERIES

Boiler Size Old After 1979 Existing

01. PROXIMATE ANALYSIS RANGE

MECHANICAL DESIGN OF ELECTROSTATIC RECIPITATOR

SUPPORTING STRUCTURE AND SUPPORT BEARINGS

 The side walls are made of horizontal panels

Several advantages of this type of electrode are:

By utilizing the self-tensioning effect of

RAPPING MECHANISM FOR DISCHARGE ELECTRODE

One such rapping mechanism is

Collecting system mainly consists of collecting suspension frames collecting electrodes

RAPPING MECHANISM FOR COLLECTING ELECTRODE

Each collecting plate of the system

Each collecting plate is hung on an

It is of prime importance in any rapping system to avoid excessive re-entrainment of the

COLLECTING PLATE No. 9M 12M 18M

Top part of the plate 460 400 360

Middle part of ptate 560 480 430

Bottom part of plate 880 880 880

COLLECTING PLATE NO.

Top part of the plate 190 160 150

Middle part of ptate 230 200 180

Bottom part of plate 360 360 360

GAS DISTRIBUTION SYSTEM

The velocity distribution within the precipitator casing is checked prior to

Each of the insulator for the

INLET AND OUTLET NOZZLES

THERMAL INSULATION SLAGGING

FLOW MODEL STUDIES IN THE FIELD OF ELECTROSTATIC PRECIP1TATOR

APPROACH TO MODEL STUDY

The following assumptions are made ;-

TEST SET-UP AND INSTRUMENTATION

The vanes in the funnel inlets to the electrostatic precipitator is arrived at an