WET Electrostatic Precipitators
A wet electrostatic precipitator (WESP or wet ESP) uses air streams that are 100% relative humid to operate. In industrial process gas streams, WESPs are frequently employed to remove liquid droplets, such as sulfuric acid mist. The WESP is also frequently utilised in situations when the gases have significant moisture content, contain flammable particulate matter, or have sticky-type particles.
Electrostatic Precipitator Prinicipal
An electrostatic precipitator is a tool for reducing air pollution that is used to remove solid particles from tainted air streams. Electron emitting electrodes, commonly referred to as corona electrodes, ionise contaminated air when it enters an ESP chamber. The charged suspended particles move to a collection plate after being charged by the electron field. Rapping or rapping against the collection plates with rappers periodically clears off accumulated particle matter (mallets type hammers). Heavy particles fall to the ESP's base where hoppers catch them and store them for disposal.
One micron or smaller particles are separated from gas streams using electrostatic precipitators. Desalters also employ this method to remove salts and silt from the crude oil feeds.
What Is Electrostatic Precipitator?
An electrostatic precipitator is a filtration tool used to remove small particles from flowing gases, including smoke and fine dust. It is a typical air pollution control device. They are employed by businesses like thermal energy plants and steel mills.
The first electrostatic precipitator, which was used to gather vapours of lead oxide and sulfuric acid that were released during various acid-forming and smelting processes.
Construction and Working of an Electrostatic Precipitator:
Electrostatic precipitators essentially consist of a vertical stack of flat metal plates and a vertical row of thin wires. Plates range in size from less than 0.5 inches to around 7 inches. The distance between the plates depends on the specific application.
Between the plate stack and the rows of vertical wires, a horizontal gas stream flows. Between the plate and the wires, thousands of volts of negative charge are applied. By doing this, the gas stream's dust content is improved. The complete setup is contained in a metal container.
There is an input for impure gases on one side of the container and an outlet for filtered gases on the other. Dust particles collide with the free electrons that are present in the metal container as impure gases enter it.
After that, the unattached electrons will bond with the dust particles. Therefore, dust particles will acquire a negative charge. The positive plates will pull these negatively charged particles in their direction.
As a result, the charged dust particles will migrate in the direction of the positive plates. At this point, the dust particles will become neutral and fall to the ground under the influence of gravity.
GENERAL INFORMATION
Electrostatic precipitators, like the one in this image, function by subjecting feed stream particles to an electrostatic field. Due to their small size, the particles are easily charged. The oppositely charged collectors subsequently gather and remove the charged particles.
The collectors accumulate debris and need to be cleaned sometimes. Although usually discarded, the particles could nevertheless be treated further if profitable.
Different types of particles can be extracted from a gas stream by electrostatic precipitators. The table below illustrates the wide range of collection sizes seen in gas streams, ranging from tiny particles like x-rays and smog to huge ones like fly ash and finely ground coal.
Wet Electrostatic Precipitators
As seen in the animation here, charged particles (green) are gathered onto the collectors in wet electrostatic precipitators. A liquid (blue), usually water, pours down the plates as the particles gather on the collector. Particles on the plates are gathered and removed by the water.
Usage Examples
Electrostatic precipitators are used to regulate air pollution and minimise particle emissions in a variety of industries. The boiler from a refinery can be seen in the image below with a wet electrostatic precipitator installed to treat flue gas contaminants.
The following is a small list of typical industrial applications for ESPs.
Refuse & sewerage sludge dryers and incinerators
Coal- and oil-fired boilers, coal driers and coal mills
Production plants for the cement, limestone, gypsum, pulp and paper industry (kilns, mills, driers and coolers)
Electro-metallurgical, chemical, gas and detergent manufacturing plants
SO2, SO3, acid mist and ammonia control (wet ESPs)
WET Electrostatic Precipitator Applications
The applications of electrostatic precipitators include the following :
An electrostatic precipitator is most frequently used in industrial smoke applications. Although it appears to be a gas, it is actually a buildup of solid materials floating in the atmosphere.
These substances have the ability to be excited, allowing for the creation of massive, industrial precipitators.
Dry particles like cement, ash, and other such materials are collected using dry electrostatic precipitators.
Wet particles like oil, tar, glue, acid, etc. are removed using wet electrostatic precipitators.
Electrostatic In steam plants, precipitators are employed to filter the dust out of the flue gases.
For the removal of acid and oil mists, machine shops and chemical factories utilise electrostatic precipitators.
These are employed to purify gases from blast furnaces or metallurgical heating systems.
In the medical sector, ESPs are utilised to eliminate bacteria and fungi.
To sanitise the air, ESPs are employed in air conditioning systems.
To recover the materials in the gas flow, ESPs are employed.
In facilities like dry mills and rutile plants, ESPs are utilised in zirconium sand to separate the rutile.
