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10.2 Control of Particulate Matter Emissions 281

unfriendly corrosive environment. At higher temperatures, ceramic materials are the
best choice.

10.2.2.2 Bag-house Filters
Typical filtration systems offer collection efficiencies greater than 99 % over a large
size range. The advantage of the filtration over ESP is its independence on the
electric resistivity of the particles. This characteristic makes filter very competitive
for particles with high-resistivity. A disadvantage of a filter compared with an ESP
is the larger pressure drop and the allowable gas speed. Typically the face speed
through a filter is in the range of 0.5–5 cm/s. Otherwise, filter flooding will occur
and result in low filtration efficiency.
In order to handle a high airflow rate while maintaining the low face speed, a
high filter surface area is necessary. In industry, hundreds of cylindrical or tubular
filter bags of fabric materials are confined in a “bag-house” to create a high surface
area to allow certain amount of air flow to pass through the filters at an acceptable
low face speed.
Figure 10.2 shows two typical operation modes of bag-house filters. For an
inside-out filtration system, the gas passes through the filters from the inside and
exit from the outside of the filter bags. This “blows up” the bag filters to their
maximum volume and produces the dust cake on the inside of the bags. Outside–in

Fig. 10.2 Bag-house filter systems based on outside–in (left) and inside–out (right) operation