ELECTROSTATIC PRECIPITATOR (ESP) www.engineersportal.in

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. www.engineersportal.in

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COMPONENTS USED IN ELECTROSTATIC PRECIPITATOR Electrodes 440V 50HZ 3φ AC supply High voltage transformer Rectifier insulators Hooper Rapper www.engineersportal.in

BASIC DIAGRAM OF AN ELECTROSTATIC PRECITATOR 20 – 80 KV dc 440V, 50Hz Clean gas Discharge electrode High voltage transformer Dust gas Control cabinet Rectifier Collector electrode www.engineersportal.in Hooper

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 as per 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. www.engineersportal.in

Conveyors: Drag conveyor Screw conveyor Pneumatic conveyor for transporting dust from ESP

Discharge electrode :- Electrodes : - Collector 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. Discharge electrode www.engineersportal.in

WORKING OF ELECTROSTATIC PRECIPITATOR Stage - 1 Several things happen very rapidly (in a matter of a millisecond) in the small area around the discharge electrode. Electric field is emerged due to dc terminal arrangement. The applied (-) voltage in discharge electrode is increased until it produces a corona discharge, which can be seen as a luminous blue glow around the 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. www.engineersportal.in

Stage - 2 As 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. www.engineersportal.in

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Types of Electrostatic Precipitators Gas Flow through a tubular precipitator Tubular Precipitators Plate Precipitators 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

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 ESPs Particles 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

Conclusion All 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 www.engineersportal.in

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