Electrostatic precipitators (ESP)
Cold side (dry) ESP is located after the air preheater and operates in a temperature range of 130-180°C. The cold side ESP, with fixed/rigid electrodes, makes up a large portion of the current market although ESP with moving electrodes are becoming more widely used. Hot side (dry) ESP, used mainly in the USA and Japan, is located before the air preheater where the operating temperature range is 300-450°C. A 1990 study showed 150 hot side ESP were built in the USA between 1935 and 1990. In wet ESP, a liquid film is maintained on the collection plates using spray nozzles. The process eliminates the need for rapping as the liquid film removes any deposited fly ash particles. Thus, problems with re-entrainment, fly ash resistivity and capture of fine particles become obsolete. However, wet ESP require saturation of the flue gas stream with water, generate waste water and sludge and operate at low temperatures.
Both ESPs and fabric filters are highly efficient particulate removal devices with design efficiencies in excess of 99.5%. Particulate removal efficiencies in ESP and fabric filters can be further improved by flue gas conditioning.
ESPs are the particulate emissions control technology which is most widely used on coal-fired power generating facilities. The trend is expected to continue at least for the next couple of decades. The choice between ESP and fabric filtration generally depends on coal type, plant size and boiler type and configuration. Both technologies are highly efficient particulate removal devices with design efficiencies in excess of 99.5%.
Conditioning the fly ash in the flue gas is an established technique used to restore the performance of an ESP in coal-fired power plants with high-resistivity fly ash resulting from burning low sulphur coals. Elemental sulphur, ammonia (NH3), and sulphur trioxide (SO3) are the main conditioning agents currently used.
Removal efficiency >99->99.99%
Particle size range 0.01- >100 µm
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