Geoscience Reference
In-Depth Information
Fabric filters are relatively simple to operate, provide high overall collection efficiencies up to
99+%, and are very effective in controlling submicrometer particles, but they do have limitations.
These include relatively high capital costs, high maintenance requirements (bag replacement, etc.),
high space requirements, and flammability hazards for some dusts.
17.4.4.1 Air-to-Filter (Media) Ratio
The air-to-filter (cloth) ratio is a measurement of the velocity (filtration velocity) of the air passing
through the filter media. The ratio definition is the volume of air expressed in cubic feet per minute
or cubic meters per hour divided by the filter media area expressed in square feet or square meters.
Generally, the smaller a particle diameter, the more difficult it is to filter and thereby requires a
lower A/C value. The formula used to express air-to-filter (cloth) ratio (A/C ratio), filtration velocity,
or face velocity (terms can be used interchangeably) is
v
f
=
Q
/
A
c
(17.23)
where
v
f
= Filtration velocity (ft/min, cm/s).
Q
= Volumetric air flow rate (ft
3
/min, cm
3
/s).
A
c
= Area of cloth filter (ft
2
, cm
2
).
17.4.4.2
Baghouse Example Calculations
■
EX AMPLE 17.11
Problem:
The manufacturer does baghouse sizing. A simple check or estimate of the amount of bag-
house cloth needed for a given process flow rate can be computed by using the A/C ratio, Equation
17.23 (USEPA, 1984a, p. 8-34):
v
f
=
Q
/
A
c
or
A
c
=
Q
/
v
f
For example, if the process gas exhaust rate is given as 4.72 × 10
6
cm
3
is (10,000 ft
3
/min) and the
filtration velocity is 4 cm/s (
A
/
C
is 4:1 (cm
3
/s)/cm
2
), the cloth area would be
A
c
= (4.72 × 10
6
)/4 = 118 m
2
(cloth required)
To determine the number of bags required in the baghouse, use the formula:
A
b
= π ×
D
×
h
where
A
b
= Area of bag (m, ft).
D
= Bag diameter (m, ft).
h
= Bag height (m, ft).
If the bag diameter is 0.203 m (8 in.) and the bag height is 3.66 m (12 ft), the area of each bag is
A
b
= 3.14 × 0.203 × 3.66 = 2.33 m
2
The calculated number of bags in the baghouse is
Number of bags = 118/2.33 = 51 bags
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