The main devices and systems used to separate fly ash from flue gas before it is released into the atmosphere include:

1. Electrostatic Precipitator (ESP)

An Electrostatic Precipitator (ESP) uses a high-voltage electrical field to electrically charge fly ash particles. The charged particles are attracted to collecting plates, where they accumulate and are periodically removed by rapping mechanisms.

ESP is one of the most widely used fly ash removal devices in large thermal power plants because it can handle a large volume of flue gas and effectively remove fine particulate matter.

2. Bag Filter (Fabric Filter)

A bag filter, also called a fabric filter, removes fly ash by passing flue gas through specially designed filter bags. The ash particles are trapped on the surface of the bags, while the cleaned gas passes through.

The accumulated ash is periodically removed from the bags using methods such as pulse-jet cleaning or mechanical shaking.

3. Wet Scrubber

A wet scrubber uses water or another liquid to capture particulate matter from flue gas. The flue gas comes into contact with the liquid, causing fly ash particles and certain gaseous pollutants to be captured.

Wet scrubbers can be useful when both particulate matter and gaseous pollutants need to be controlled.

4. Inertial Separators

Inertial separators separate ash particles by taking advantage of the difference in inertia between the gas and solid particles. When the direction or velocity of the flue gas changes, heavier particles cannot follow the gas stream as easily and are separated.

Common types include:

• Settling chambers
• Baffle chambers
• Cyclone separators

These systems are generally more effective for removing relatively larger particles and may be used as pre-collectors.

5. Fabric Hybrid Filter

A fabric hybrid filter combines the principles of an electrostatic precipitator and a fabric filter. The electrical field helps charge and collect particles, while the fabric filter provides additional filtration.

This combination can achieve high particulate removal efficiency and is useful where stringent emission limits are required.

Conclusion

The major fly ash removal devices used for separating fly ash from flue gas are Electrostatic Precipitators (ESP), bag filters, wet scrubbers, inertial separators, and fabric hybrid filters. The selection of a particular system depends on factors such as plant capacity, particle characteristics, flue gas conditions, required emission limits, and overall plant design.

In large coal-fired thermal power plants, ESP is one of the most commonly used systems for fly ash removal from flue gas.