Bag filters are Dry type air pollution control equipment that discards suspended particulate matters out of flue gas, released from material handling or from combustion for electricity generation or from liquefying hot metals. They are generally suited to withstand temperatures up to 250°C and have a particulate accumulation efficiency of as high as 99.99%, even when particle size is in sub-micron range.
Filter bags are suspended from a Tube sheet at the top of the collector and are internally supported by cylindrical wire cages to prevent them from collapsing. The dust laden Gas enters into the Bag Filter through the Hopper or casing by suction or positive pressure created by the ID Fan downstream. The heavier dust particles falls immediately into the hopper after striking the baffle plate while the lighter dust gets deposited on the outer surface of the hanging filter bags. A predetermined pulsing cycle is programmed to energize the Solenoid Valves which dislodge the dust cake from the outer surface of the filter bags. The dust falls into the hopper. The filter bags are cleaned either by time mode sequencing or by differential pressure mode.
Two types of Bag filters are available in the Market – On – Line type & Off – Line type.
In an On – Line Bag Filter, bags are cleaned Row by row even when the dust laden Gas is filtered. The sequence of cleaning is controlled automatically by sequence controller.
In an Off – line Bag Filter each compartment is similar to an on line Bag Filter. The cleaning process consists of sequentially isolating each compartment by actuating pneumatically operated Damper & cleaning the same with compressed air. Thus all the compartments are cleaned automatically one by one.
Off – line cleaning is suitable for very light & fine dust with larger Gas volume where occurrence of fluidization is a distinct possibility.