Fabric filters (baghouses)
Fabric filters, which generally operate in the temperature range 120-180°C, have been more widely used since the 1970s, especially at industrial scale. The choice between ESP and fabric filtration generally depends on coal type, plant size and boiler type and configuration. There are three types of fabric filters based on the cleaning mechanisms of each. The two fundamental parameters in sizing and operating baghouses are the air to cloth (A/C) ratio (m/s) and the pressure drop (mm water gauge, Pascals or in.H2O). Other important factors which affect the performance of the fabric filter include the flue gas temperature, dew point and moisture content; particle size distribution and chemical composition of the fly ash.
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.
Fabric filters are increasing their market share year by year but mainly in industry. The choice between ESP and fabric filtration generally depends on coal type, plant size and boiler type and configuration.
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. The benefits of flue gas conditioning in fabric filters include achieving lower emissions at higher bag air to cloth ratio, reducing pressure drop and improving fly ash cake cohesivity thus leading to better dislodgement in larger agglomerates and less re-entrainment. Elemental sulphur, ammonia (NH3), and sulphur trioxide (SO3) are the main conditioning agents currently used.
Removal efficiency >99- >99.9999%
Particle size range 0.01- >100 µm
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