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A Comprehensive Guide to Electrostatic Precipitators
2024-12-19
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What’s an electrostatic precipitator?
Electrostatic Precipitator, or Electronic Static Precipitator, is usually abbreviated as ESP. An ESP Precipitator is a device that removes particles (such as dust and smoke) from a gas stream by using electrostatic attraction. ESP device shapes air passages inside. Each air passage is passing through electrostatic charged poles or boards. Mixed air is to be ionized instantly, the dust and smoke carry negative charge and soon attract to the positive boards. Air, as a kind of molecules, with little weight, still get out, leave the solid particles (dust and smoke) stuck behind. So, the mixed air gets filtrated and purified.
The working principle of electrostatic precipitator
Electrostatic attraction or electrostatic force is the basic working principle enables electrostatic precipitator process the ESP filtration. If the two charges are different, with one being positive and one negative, then they will attract to each other. Air, including the mixed dust, smoke and oil droplet are charged with negative current when passing through the electric field. Charged particles such as dust, smoke and oil droplet turn attractive and bond to the boards with the opposite current. So, pure air is separated and vent out.
The working principle of electrostatic precipitator
The working principle of electrostatic precipitator
Coulomb's law describes the strength of the electrostatic force (attraction or repulsion) between two charged objects. The electrostatic force is equal to the charge of object 1 times the charge of object 2, divided by the distance between the objects squared, all times the Coulomb constant (k).
The work procedures of ESP filtration
Charge the static electric field and sustain corona discharge effect
A transformer rectifier is needed to supply high-voltage static electricity. The static electric field contains electrodes (usually in form of wires or rods), and their counterpart is the collection plates. Electrodes are negatively charged by the rectifier, while the collection plates or other surrounding structures are grounded (or positively charged). When this static electric field is being charged, a corona discharge effect is taking place. The corona effect is a phenomenon where the strong electric field ionizes the air around the electrode, creating a region of plasma. This happens when the electric field is strong enough to strip electrons from nearby air molecules, turning them into ions. The Corona effect can appear as a faint glow around the electrode under certain conditions. The electric field also is called corona discharge field.
Particles go through Corona discharge field with air flow and get charged with static electricity
Particles such as dust, smoke and oil fog mixed with air flow and go through the corona discharge field. The corona discharge continuously generates a supply of ions that attach to particles in the air flow, charging them as they pass through. Dust, smoke and oil fog attract to the collection board due to static attraction force draw them. Clean air vent out simultaneously as these particles stuck to the collection board. The ESP filtration works.
Removing Collected Particles
The ESP precipitator in different applications deal with different particles. The removal methods of the dirt are also different.
Dust Removal
Dust accumulates on the plates over time, forming a layer of dust. The ESP is designed to allow continuous collection while the system remains operational. As dust builds up, the efficiency of the ESP can remain high since the electric field still penetrates through the dust layer to attract new dust.
Removing Collected Dust by Rapping or Shaking
Periodically, the ESP undergoes a process known as rapping or shaking to dislodge the accumulated dust from the collection plates. This is usually done mechanically by vibrating or striking the plates to cause the dust layer to fall into hoppers located below the ESP. Once in the hoppers, the dust can be collected for disposal or recycling, depending on the type of dust and industrial requirements.
Oily Smoke Removal
Removing oily smoke from an Electrostatic Precipitator (ESP) is more challenging than handling dry dust because the oil particles can create a sticky, sometimes viscous layer on the collection plates, which is harder to dislodge. Kleanland solves this problem by using stainless steel plates or SS tubes as the particle collector, as they are durable and easier to clean when dealing with sticky residues. During normal operation, oily residues are in liquid form and they drop with gravity to the bottom of the device, where an drain and an oil tray being beneath for collecting the greasy oil.
Self-cleaning of ESP system
When the collection boards accumulate very thick dust or oil, and the filtration efficiency drops. Kleanland integrated self-cleaning system inside the ESP device. For ESP range hood, steam washing system can connect to the hood. Kleanland provides independent steam generator, complete tubing and programed controller for commercial kitchen. ESP kitchen hoods get cleaned periodically by automatic program and sustain their best performing characteristics. For in-duct ESP device, steam cleaning also available. Built-in spray washing with water or solvent added water also is Kleanland mature solution for in-duct ESP device and industrial ESP device.
The difference between dry ESP and wet ESP
Dry Electrostatic Precipitator (ESP)
Firstly, electrostatic precipitators possess similar structure under the same working principal. Dry ESP are designated to process dry particles because the procedure is dry. Applications such as power generation, cement, steel, and waste incineration are dry process. Smoke and dust are the major particles to deal with. Electricity strength, ESP cavity size, airflow direction are configured for extract the smoke and dust. Rapping or shaking mechanism is applied to dislodge the accumulated dust from the collection plates. Theoretically, It’s possible to add wet washing system to dry ESP, but it’s not necessary to do so. Some dust turns to very corrosive once wettened. Some airflow is high temperature as high as above dew point, so water cleaning is not suitable internally.
Wet Electrostatic Precipitator (ESP)
Wet ESP has built-in water systems. Three types of water system may involved with ESP. One is the self-washing water. The water is set to spray the ESP tubes and plates periodically as a cleaning method. The second is the fire protection water system. Integrated with sensor, water is set to spray to stop internal burning. The third water system is with the heat sink. ESP has its operational temperature range. But inlet gas from some application carries higher temperature, so heat sink is positioned because ESP to reduce the gas temperature.
The sum-up points of dry and wet EPS are below:
Dry ESP involve no water because the whole process is dry
Rapping or shaping is better solution than water washing for dust removal
Some dust turns corrosive once wettened and harms ESP device
Dry ESP handle airflow hotter than dew point, water is not applicable
The Types of ESP collector
A century ago, Dr. Frederick Cottrell invented electrostatic precipitator. ESPs have become a basic solution for controlling particulate emissions. Alongside the evolvement, major types of ESP collector can be categorized into the below 5 types:
Hexagon honeycomb type ESP
Round tubular type ESP
Varied Width Tubular type ESP
Tube and Plate Combined ESP
Wire and plate combined ESP
Industrial Ultra-wide Plate ESP
Dual phase Industrial Electrostatic Precipitator
Triple Phase Industrial Electrostatic Precipitator
Hexagon honeycomb type ESP
Hexagon honeycomb type ESP collectors are very conventional design of ESP collector. The negative electrode is installed along the central axis of the hexagon tube. Because the hexagon shape is not round, the side and angle have different radius to the central axis. This may cause equivalent static discharge within the hexagon cavity. The pro of hexagon EPS is that, the array of hexagon tubes uses up all the sectional area as airflow passage. While rigid round tubular arrays waste a little sectional space at the joining place of every three circles.
Round tubular type ESP
Round tubes working as the particle collector are perfect. The central axis is electrode in form of either rod or wire. No mater hexagon tube or rigid round tube, they can be placed vertically or horizontally, the consideration are airflow efficiency and residue dislodge. Further, they are size difference among the suppliers for both hexagon collector and tubular collector.
Varied Width Tubular type ESP
Round tubes working as the particle collector are perfect. The central axis is electrode in form of either rod or wire. No mater hexagon tube or rigid round tube, they can be placed vertically or horizontally, the consideration are airflow efficiency and residue dislodge. Further, they are size difference among the suppliers for both hexagon collector and tubular collector.
Tube and Plate Combined ESP
Plate is a good particle collector, and it’s convenient to clean as long as it sustains plain and even. Negative electrode stays in between the plates to charge the gas stream. The electrodes can be shaped as rods or wires. Their charging capability is weaker than following dual plate combination.
Wire and plate combined ESP
Plate is a good particle collector, and it’s convenient to clean as long as it sustains plain and even. Negative electrode stays in between the plates to charge the gas stream. The electrodes can be shaped as rods or wires. Their charging capability is weaker than following dual plate combination.
Industrial Ultra-wide Plate ESP (Kleanland)
Kleanland is the number 1 brand of industrial electrostatic precipitator in China. Just like China’s progress in other industries like EV cars or semiconductors, Kleanland also has taken the lead in ESP as they were the first manufacturer of ESP range hood in China three decades ago. Kleanland pushes the industrial electrostatic precipitator up to the next level. Kleanland's latest launch is the ultra-wide plate electrostatic precipitator. A single unit, as concise as can load into a container, which can handle 20,000 to 40,000 cubic meter airflow per hour. The space distance between electrodes is up to 85mm, adding one more thinner intense cell of 69mm as post-filter. Honeycomb ESP cells also can blend in seeing to the scenarios of application. This monster ESP filter is extremely high efficient and energy saving comparing to other competitor's products. With electrodes' space from 85mm to 69mm, these ESP filtration cells of varied width are applied, as to capture particles of different sizes respectively. The front stage collects particulate smoke and water droplets and charges the small particles. The back stage collects small particle smoke. Different voltages can be applied to each electric field, achieving a balance between low power consumption and high purification efficiency.
Dual Phase Plate ESP
Dual phase plate electrostatic precipitators are equipment with 2 giant plate type ESP, and each has different electrode width. This innovative electrode design, featuring a spacing of up to 85mm, coupled with an additional 69mm thin-cell post-filter, ensures superior performance.
Triple Phase Industrial Electrostatic Precipitator
Triple phase plate electrostatic precipitators are equipment with 2 plate type ESPs and 1 tubular ESP. The 2 giant plate type ESPs have different electrode width. 85mm the 1st phase filtration is 85mm spacing, the 2nd phase filtration is 69mm spacing. Additionally, a third filtration uses tubular ESP cell, to reinforce the filtration efficiency up to 98.5% down to 0.1 micron. Basing on the emission scenarios and venting requirement. There are two combination options, one is 2 plate cells plus 1 tubular cell, the other is 1 plate cell plus 2 tubular cells.
