Electrostatic Precipitators

As air enters the electrostatic precipitator, the particles pass through an electrical field that gives an electrical charge to the particles. The charged particles pass through a series of alternately charged collector plates. Particles are repelled by plates with the same polarity and attracted to plates with opposite polarity — similar to how a powerful magnet works.
Dual-stage electrostatic precipitators include two parts: the charging and the collecting sections. In the charging section, the incoming smoke, grease, mist, and other particulates pass by ionizer wires which impart a positive electrical charge to these contaminants. The positively charged contaminants are then drawn through the collection section which contains a secondary electrical field with negatively charged aluminum plates. Since opposite charges attract, the positively charged contaminants collect on the negatively charged aluminum plates, removing them from the air stream.
Air velocity: 1.5 - 2.5 m/s

ESP Advantages:

• ESPs are very efficient (up to 99% efficiency)
• This is more effective to remove very small particles like smoke, mist and fly ash. Its range of dust removal is sufficiently large (0.01 micron to 1.00 micron).
• This is also most effective for high dust loaded gas (as high as 100 grams per cu. meter)
• The draught loss of this system is the least of all forms(1 cm of water)
• The dust is collected in dry form and can be removed either dry or wet.
• They are generally more economical than other particulate control devices:
Operating costs are reduced by low energy consumption, minimal maintenance requirements and reduced cost on spare parts
• Can be designed to handle wet and dry gas compositions
• Can handle large volumes of gas flow with low pressure drop
• Can function at high temperatures (as high as 700 degree F – 1300 degree F)
• Pressure and temperature changes are small
• Difficult material like acid and tars can be collected
• They withstand extremely corrosive material
• Low power requirement for cleaning
• Dry dust is collected making recovery of lost product easy
• Large flow rates are possible
• It provides ease of operation.

ESP Disadvantages:

• High initial capital costs
• Dry ESPs can only control particulate emissions, not gas composition emissions
• Once installed, ESPs take up a lot of space and cannot be easily redesigned
• May not work properly on high electrical resistive particles
• Materials with very high or low resistivity are difficult to collect
• Inefficiencies could arise in the system due to variable condition of airflow (though automatic voltage control improves collector efficiency) • They can be larger than bag Filters (fabric collectors) and cartridge units, and can occupy greater space
• Dust loads may be needed to be reduced before precipitation process (pre-cleaner may be needed)
• The direct current is not available with the modern plants, therefore considerable electrical equipment is necessary to convert low voltage (400 V) A.C to high voltage (60000 V) D.C. This increases the capital cost of the equipment as high as 40 to 60 cents per 1000 kg of rated installed steam generating capacity.
• The running charges are also considerably high as the amount of power required for charging is considerably large.
• The efficiency of the collector is not maintained if the gas velocity exceeds that for which the plant is designed. The dust carried with the gases increases with an increase of gas velocity.
• Because of closeness of the charged plates and high potential used, it is necessary to protect the entire collector from sparking by providing a fine mesh before the ionizing chamber. This is necessary because even a smallest piece of paper might cause sparking when it would be carried across adjacent plates or wires.