www.engineersportal.in. elctrostatic principle :- an electrostatic precipitator (esp) is an device...
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ELECTROSTATIC PRECIPITATOR (ESP)
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ELCTROSTATIC PRINCIPLE :-
An electrostatic precipitator (ESP) is an device that removes dust particles from a flowing gas (such as air) using the force of an induced electrostatic attraction (i.e, like charges repel; unlike charges attract)
Electrostatic precipitators are highly efficient filtration devices that allow the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.
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COMPONENTS USED IN ELECTROSTATIC PRECIPITATOR
Electrodes
440V 50HZ 3φ AC supply
High voltage transformer
Rectifier
insulators
Hooper
Rapper
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20 – 80 KV dc
BASIC DIAGRAM OF AN ELECTROSTATIC PRECITATOR
440V, 50Hz
Control cabinet High voltagetransformer
Rectifier Dust gas
Clean gas
Hooper
Discharge electrode
Collectorelectrode
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Control cabinet
Control cabinet is used to interconnect the 3φ ac supply and transformer through wires.
Transformer
Transformer is used to step up or step down the voltage asper the design of Electrostatic precipitator.
Rectifier
Rectifier is used to convert the given ac supply into dc supply.
Hooper
Hooper is used to store the dust particles and ash content coming out from the Electrostatic precipitator.
Conveyors:
Screw conveyor
Drag conveyor
Pneumatic conveyor for transporting dust from ESP
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Electrodes : -
Based on DC current flow terminals elctrodes can be divided as below:-
Discharge electrode :-
Electrodes wire which carries negatively charged high voltage (between 20 to 80KV) act as discharge or emitting electrodes.
Collector electrode :-
Electrode wire which carries positively charged high voltage act as Collecting electrodes.
Collector electrodes
Discharge electrode
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WORKING OF ELECTROSTATIC PRECIPITATOR
Several things happen very rapidly (in a matter of a millisecond) in the small areaaround the discharge electrode. Electric field is emerged due to dc terminalarrangement. The applied (-) voltage in discharge electrode is increased until it produces a corona discharge, which can be seen as a luminous blue glow aroundthe discharge Electrode.
Due to the formation of corona discharge, free electrons are emitted with high velocity from discharge electrode.
This fast moving free electrons strikes the gas molecule thus emission of free electron from gas molecules takes place.The positive ion molecule move towards discharge electrode by electrostatic attraction
As a result using gas molecule more free electrons are emitted near the discharge electrode.
Stage - 1
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Stage - 2As the electrons leave the strong electrical field area around the discharge electrode, they start slowing down. This free electron again strikes the gas molecule but this time they are captured by gas molecule and became negatively charged ion.
As the gas molecule are negatively ionized they move towards the (+) electrode (i.e., collector electrode).
This negative gas ion fills the space of Dust particle and becoming negatively charged particle.
This particle are captured by collector electrode using electrostatic attraction.
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Types of Electrostatic PrecipitatorsTubular
Precipitators
Plate Precipitators
Gas Flow through a tubular precipitator
Gas flow through a plate precipitator
Cold-side ESPs
Cold side ESPs 1) volume of flue gas
that is handled is less 2) less costly 3) overall size of the
unit is smaller 4) used to remove fly
ash from boilers that
burn high sulfur coal
Cold side ESP’s
Hot Side ESPs
used in high-temperature applications (Cement kiln)
the gas volume treated in the ESP is larger
the overall size of the precipitator is larger making it more costly
structural and mechanical problems occur in the precipitator shell
Wet Side ESPs
Wet ESPs are used for industrial applications where the potential for explosion is high
When dust is very sticky, corrosive, or has very high resistivity
It does not have problems with rapping reentrainment or with back corona
Dry Side ESPsParticles are
charged and collected in a dry state
Dust particles collected are removed by rapping
Used in steel furnaces, cement kilns and fossil-fuel-fired boilers
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ConclusionAll ESPs, no matter how they are grouped,
have similar components and operate by charging particles or liquid aerosols, collecting them, and finally removing them from the ESP before ultimate disposal in a landfill or reuse in the industrial process
The precipitator should be designed to provide easy access to strategic points of the collector for internal inspection of electrode alignment, for maintenance, and for cleaning electrodes, hoppers, and connecting flues during outages
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ANY QURIES…?