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ELECTROSTATIC PRECIPITATOR

An electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate collection device that removes particles from the flue gas using the force of an induced electrostatic charge.

Precipitator Components

All electrostatic precipitators, regardless of their particular designs, contain the following
essential components:
• Discharge electrodes
• Collection electrodes
• High voltage electrical systems
• Rappers
• Hoppers
• Shell

Discharge electrodes are either small-diameter metal wires that hang vertically (in the electrostatic precipitator), a number of wires attached together in rigid frames, or a rigid electrodemade from a single piece of fabricated metal. Discharge electrodes create a strong electrical field that ionizes flue gas, and this ionization charges particles in the gas .

Collection electrodes collect charged particles. Collection electrodes are either flat plates or tubes with a charge opposite that of the discharge electrodes.

High voltage equipment provides the electric field between the discharge and collection electrodes used to charge particles in the ESP.

Rappers impart a vibration, or shock, to the electrodes, removing the collected dust. Rappers remove dust that has accumulated on both collection electrodes and discharge electrodes. Occasionally, water sprays are used to remove dust from collection electrodes.

Hoppers are located at the bottom of the precipitator. Hoppers are used to collect and temporarily store the dust removed during the rapping process.

The shell provides the base to support the ESP components and to enclose the unit.

Working of Electrostatic Precipitator

An ESP works because of electrostatic attraction (like charges repel; unlike charges attract).

An ESP uses a high voltage electrostatic field to separate dust, fume or mist from a gas stream. The precipitator consists of vertical parallel plates (collecting plates/electrodes) forming gas passages 12 to 16 in. (30.5 to 40.6 cm) apart. Discharge electrodes are electrically isolated from the plates and suspended in rows between the gas passages.

Every particle either has or can be given a charge – positive or negative. A high voltage system provides power to the discharge electrode to generate an electrical field. The particulate, entrained in the gas, is charged while passing.

The particulate is then attracted to the grounded collector plate, and forms a dust layer on the plate.
Periodic rapping separates the accumulated dust layer from both the collector plates and discharge electrodes (in case of wet ESP by spraying it with a liquid). The dust layer released by the rapping collects in hoppers and is removed by material / ash handling system.

Advantages And Disadvantages

Advantages

• Its initial cost is less.
• Less maintenance.
• Helps in protecting the environment.
• Efficiency is high.
• Works well compared to other separators.
• Easy to operate.
• Highly reliable.
• Large dust particles can be easily eliminated.
• Approximately 90 percent of dust can be cleaned

Disadvantages

• More running costs.
• Cost compared to other devices is high.
• Requires large area.