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Fabric Filtration 65

Fig. 1. Schematic diagram of a reverse-pulse baghouse.

in the gas flow while the cleaning process takes place in intermittent collectors. In these
systems, gas flow is greatest immediately after the filter medium has been cleaned and
decreases as the cake builds up. A typical cycle for an intermittent system is operating
for 0.25–4 h and cleaning for 5 min.
A fourth major way in which fabric filters can be classified is by service. Particulate
removal is the major service performed by fabric filters. However, they also can be used
for gaseous control by adsorption and chemical adsorption (chemisorption), which are
well-proven industrial techniques. For example, solid alumina can be used to adsorb
chlorine; gaseous ammonia can be injected to react with sulfur oxides to form a solid
particulate, which can be filtered; sodium and/or calcium compounds can be added as