- Electrostatic Precipitator Definition: An electrostatic precipitator is a device that removes dust particles from flue gases to reduce air pollution.
- ESP Working Principle: Electrostatic precipitators work by using positive and negative electrodes to charge and collect dust particles from flue gases.
- Electrode Setup: The device has negative rods or wire mesh and positive plates, creating a voltage gradient to ionize the air between them.
- Dust Collection Process: Negatively charged dust particles are attracted to positive plates, where they deposit and fall due to gravity.
- Pollution Control: Electrostatic precipitators help keep the air clean by filtering out ash particles from flue gases before they are released into the atmosphere.
An electrostatic precipitator is a flue-gas cleaner that charges dust and ash, then pulls those particles onto collecting plates. Coal-fired furnaces send a lot of fly ash with the gas. The precipitator sits in that duct so most of the ash never reaches the stack.
If that gas left the chimney uncleaned, the ash would pollute the air. An electrostatic precipitator, or a fabric filter, is the usual plant answer. Collection can exceed 99 percent on a well-run unit, but some fine dust still escapes.
The unit is placed between the last heat-recovery surface and the induced-draught fan or chimney. Oil- and gas-fired boilers make far less fly ash, so they may not need a full-size precipitator.
An electrostatic precipitator does this work for a furnace system. The gas flows through a metal casing with an inlet on one side and a cleaned-gas outlet on the other.
Working Principle of Electrostatic Precipitator
The working principle of the electrostatic precipitator uses two electrode sets. Discharge electrodes run at high negative voltage. Collecting plates sit at the positive side of the same DC supply and are often earthed.
Discharge electrodes are wires, rods or a mesh. Collecting electrodes are parallel plates.
The plates and discharge electrodes stand vertically and alternate across the gas path. 
The discharge set is tied to the negative pole of a high-voltage DC supply. The plates are tied to the positive pole.
Earthing the positive side of that supply is common. The discharge electrodes then sit well below earth potential.
Spacing and voltage set a steep gradient. Near the thin discharge electrode the field is high enough to start a corona in the gas.
The gas between the electrodes is the flue gas, mostly nitrogen, carbon dioxide, water vapour and leftover oxygen. Negative corona around the wires or mesh is the usual industrial choice.
Corona ionizes the gas and frees electrons. Those electrons attach mainly to gas molecules. The resulting negative ions then charge the dust. The casing already has the inlet and outlet described above.
As the gas passes the corona, dust particles pick up the negative charge from those ions. Direct attachment of free electrons to dust is a smaller part of the charging in industrial flue gas.
The charged particles then drift toward the collecting plates under the electric field.
They stick on the plate surface and build a dust layer.
Charge leaks into the earthed plate. The layer does not usually drop under gravity alone. Rappers or hammers periodically shake the plates so the cake falls as sheets into the hoppers. Some of that dust is re-entrained in the gas.
After several fields in series, most of the ash mass has been removed. The cleaned gas then goes to the fan and the chimney. Fine particles and rapping puffs still make up the remaining emission.
An electrostatic precipitator adds draught loss and uses rectifier power. It does not generate megawatts in the thermal power plant. Its job is to cut stack dust so the plant can meet air-quality limits.
Hoppers under the electrostatic precipitator catch the rapped cake. A water spray on the plates belongs to a wet precipitator. Dry units rely on rapping, not a continuous wash.
