Filtration is the outlet and generally one of the most versatile and efficient method for removing particulate matter from industrial gases. Fabric filters are used to remove particles from a gas stream. Fabric filters are made of a woven or felted material in the shape of a cylindrical bag or a flat supported envelope.
These elements are contained in a housing which has gas inlet and outlet connections, a dust collection hopper; and a cleaning mechanism for periodic removal of the collected dust from the fabric. In operation, dust laden gas flows through the filters, which remove the particles from the gas stream.
In principle, the dust-laden gas passes though a fabric in which the particles are trapped due to different physical mechanism. The important mechanisms by which the particles are separated from the gas stream are usually inertial impaction, direct interception and diffusion.
Advantages and Disadvantages:
(a) Advantages:
(1) Very high collection efficiencies possible (99.9 + per cent) with a wide range of inlet grain loadings and particle size variations. Within certain limits fabric collectors have a constancy of static pressure and efficiency, for a wider range of particle sizes and concentrations than any other type of single dust collector.
(2) Collection efficiency not affected by sulfur content of the combustion fuel as in ESPs.
(3) Reduced sensitivity to particle size distribution.
(4) No high voltage requirements.
ADVERTISEMENTS:
(5) Flammable dust may be collected.
(6) Use of special fibers or filter aids enables sub-micron removal of smoke and fumes.
(7) Collectors available in a wide range of configurations, sizes, and inlet and outlet locations.
(b) Disadvantages:
(1) Fabric life may be substantially shortened in the presence of high acid or alkaline atmospheres, especially at elevated temperatures.
ADVERTISEMENTS:
(2) Maximum operating temperature is limited to 550 degrees Fahrenheit, unless special fabrics are used.
(3) Collection of hygroscopic materials or condensation of moisture can lead to fabric plugging, loss of cleaning efficiency, large pressure losses.
(4) Certain dusts may require special fabric treatments to aid in reducing leakage or to assist in cake removal.
(5) Fabric bags tend to burn or melt readily at temperature extremes.