Generally, in power plants, steam generated by the burning of fuels produces certain gases. These gases are released into the atmosphere through a chimney. These gases contain several harmful particles in the air will be absorbed by the living organisms on the earth. Due to these gases, the health of humans and other organisms also will be affected. The environment will be polluted and global warming arises due to these pollutants. So, in order to overcome these issues, a filter should be used before releasing these gases from the industries into the environment. Thus, the filter which is used to filter these gases is known as Electrostatic Precipitator. Here, in this, article, we will discuss what is an Electrostatic precipitator, what is its use, components used for the operation, working principle, advantages, disadvantages, and applications.
What is an Electrostatic Precipitator (ESP)
An ESP is a device for the cleaning of dust particles from the harmful flue gases that are exposed out from the boiler of a steam power plant.
Basically, the steam generated in the boiler of a power plant utilizes hot flue gases for the production of electricity. The hot flue gases after utilization will be expelled out through a chimney provided by an induced or forced draught fan. These hot flue gases contain harmful carbonate particles which affect the lives of human beings. SO, an ESP is placed before the chimney to filter out harmful particles from the flue gases before they are exposed out to the environment.
Working Principle of ESP
An ESP works on the principle of the corona discharge effect. A high DC voltage is applied across the two plates or electrodes. The negatively charged plate attracts the dust particles which are further attracted by the positively charged electrode by the process of Ionisation. Corona discharge is shown in the figure below.
Consider an example, Observe the pollution difference between two power plants with and without ESP installation.
A power plant without ESP is shown in the figure below.
A power plant with an ESP installation is shown in the figure below.
An ESP involves four basic processes for its operation. They are
- Corona discharge
- Electrostatic attraction
- Dust particle collection, and
- Removal of these collected dust particles.
- High voltage supply source and control system
- Gas Distribution System
- Collecting plate
- Discharge Electrode
- Hammering or Rapping system
High voltage DC supply is given to the electrodes for the corona discharge to take place.
Mesh is used as both pre-filter and post-filter for the collection of dust particles. Pre-filter collects the dust before sending flue gases to the ionization process. Post-filter is used to filter out the dust particles if any found after the ionization process.
The gas distribution system is employed for the proper passage of flue gases through the pre-filtration and ionization process.
Hopper is used to collecting the dust particles collected by the collecting plate.
The collecting plate is a positively charged electrode that collects the dust particles by the attraction principle which are ionized by the highly negatively charged electrode.
The discharge electrode is a highly negatively charged electrode which ionizes the dust particles which are made to pass through it.
Hammering is done on the collecting plate at periodic intervals to collect these dust particles in the hopper.
Construction and Working of an Electrostatic Precipitator
A high voltage DC supply is given to the electrodes, one will be positively charged and the other will be negatively charged. The dust particles from the boiler are fed to the ESP. The ESP has a pre-filter placed at the front portion. The dust particles will undergo a pre-filtration process before undergoing precipitation. The working of Electrostatic Precipitator is shown in the figure below.
After Pre-filtration the particles will be subjected to experience a highly negatively charged by passing the dust particles through the negatively charged electrode placed after the pre-filter. Due to the high negative charge, the dust particles will be ionized. Due to the attraction principle, the ionized negatively charged particles will be attracted by the Positively charged electrode.
This positively charged electrode acts as a collecting electrode whereas the negatively charged electrode acts as an emitting electrode. By the process of hammering (Rapping system), the collected dust particles will be dumped inside a hopper placed at the bottom of ESP. The mechanical Rapper system is shown in the figure below.
The remaining gas particles will be subjected to post-filtration where any other particles will be filtered out. The clean gas will be sent to the chimney to expose out.
Different Types of Electrostatic Precipitators
- Wet, and
In plate type, two plates or electrodes are arranged vertically through which these gases will be passed horizontally. Due to the principle of corona discharge, the dust particles will be attracted to the positive plate by the electrostatic attraction.
Dry-type ESP is used where the dust particles to be filtered should be of dry nature. It is used in the cement industry for the handling of ash. The harmful dust particles from the ash will be filtered out using dry type ESP.
Wet type ESP is used where the dust particles to be eliminated should be of wet nature. It is used in oil refineries where the fuel used is of liquid nature.
Tube type ESP is used where the dust particles to be expelled out should be of adhesive nature. Here, the electrodes used will be of a tubular type which is given high voltage. These are arranged in different shapes like circular or hexagonal. The gases to be filtered are passed either upwards or downwards through these tubes.
- 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.
- Air Pollution can be minimized.
- More running costs
- Cost compared to other devices is high
- Requires large area
- Used in power plants, pulp industries, metallurgical industries, and oil refineries.
- Used to remove the fungus in medical industries.
- Used to remove harmful particles in the chemical industry.
Thus, in this article, we had an overview of what is an Electrostatic Precipitator. We can conclude that an ESP is a device that plays a crucial role in the process of dust elimination in a power plant. Basically, it is a filter used for the filtration of dust particles before they are exposed to the environment. Apart from this, we had also studied the use of ESP, components, working, advantages, disadvantages, and applications. Here is a question for the readers, what is the working model and design of ESP?