- Electrostatic Precipitator Definition: An electrostatic precipitator is a device used in industries to remove particles from flue gases to control air pollution.
- Corona Power Ratio: Higher corona power ratios lead to higher efficiency in electrostatic precipitators by indicating more energy used per cubic foot of air filtered.
- Dust Resistivity: The electrical resistivity of dust affects the efficiency of collection, with normal resistivity being ideal for higher efficiency.
- Particle Size Impact: Larger particles are collected more efficiently than smaller ones in an electrostatic precipitator.
- ESP Efficiency Formula: The Deutsch-Anderson equation is used to calculate the efficiency of an electrostatic precipitator, considering terminal drift velocity, collection area, and volumetric air flow rate.
Electrostatic precipitators are now standard in industries due to strict regulations and rising air pollution. Installing them in thermal power plant or any other power plants where flue gases are released is necessary. Measuring their efficiency determines if they perform as expected. Different industries have varying efficiency requirements. We’ll explore how to find the efficiency of an electrostatic precipitator.
The following factors affect the efficiency of an electrostatic precipitator.
Corona Power Ratio
Before discussing the efficiency of an electrostatic precipitator, we need to understand the corona power ratio (not to be confused with corona discharge). This ratio is the power consumed (in watts) divided by the airflow (in cubic feet per minute). It indicates the energy used to filter one cubic foot of air per minute. A higher corona power ratio means higher efficiency for the electrostatic precipitator. The image below shows how efficiency varies with the corona power ratio.
The Resistivity of Dust Collected
The efficiency of an electrostatic precipitator depends on its ability to collect dust from flue gases, which is influenced by the dust’s electrical resistivity. Particles with normal resistivity are easily collected by electrostatic precipitators. However, low resistivity particles lose their charge upon reaching the collecting plates and re-enter the dust collection area, reducing efficiency—a phenomenon called re-trainment. High resistivity particles also lower efficiency as resistivity increases. Thus, the electrical resistivity of particles significantly impacts the efficiency of the electrostatic precipitator.
The Particle Size
The efficiency of an electrostatic precipitator depends on the size of the aerosol particles (dust, mist) to be collected. Larger particles are collected more efficiently, while smaller particles result in lower collection efficiency.
The formula to calculate the efficiency
The Deutsch-Anderson equation gives the efficiency of an electrostatic precipitator, and the equation is as follows:
η = fractional collection efficiency
W = terminal drift velocity in m/s
A = total collection area in m2
Q = volumetric air flow rate in m3/s
We’ll skip the formula’s derivation and focus on understanding its meaning.
Terminal drift velocity is the velocity an object attains when it falls through the air (or any other medium). Total collection area here denotes the entire area of the collecting plates. Volumetric air flow rate is the volume of gas which passes per unit time. Using the above equation, we can find out the fractional collection efficiency of an electrostatic precipitator.
