Page 106 - Air Pollution Control Engineering

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86 Lawrence K. Wang et al.

b.
3) Air-to-cloth ratio (Table 4) ft/min
4) Net cloth area, A :
nc
)
A nc = Q e,a (AC ratio
2
where A is the net cloth area (ft ), Q = maximum flow rate at actual conditions
nc e,a
(acfm) = Q (T + 460)/537 (which is to be used if given Q instead of Q ), and
e e e e,a
A/C ratio = air-to-cloth ratio (ft/min)
A = /
nc
A = ft 2
nc
5) Gross cloth area, A :
tc
A = A nc × Factor
tc
2
where A is the gross cloth area (ft ) and Factor is the value from Table 5 (dimen-
tc
sionless).
A = ×
tc
A = ft 2
tc
6) Baghouse configuration ___________
7) Materials of construction ___________
5. Determination of baghouse operating parameters
1) Collection efficiency (CE) = __________
2) System pressure drop range __________ in. H O
2
Example 7
Fabric filtration is one of the selected control techniques for a municipal incinerator.
Conduct a preliminary design for a fabric filtration system (select filter fabrics, decide
cleaning method, and determine A/C ratio). The pertinent engineering data appear on the
“HAP Emission Stream Data Form” (see Table 11).

Solution
1. Gather engineering data on HAP emission stream characteristics from Table 11:
1) Flow rate, Q = 110,000 acfm
e,a
2) Moisture content, M = 5% vol
e
3) Temperature, T = 400°F
e
4) Particle mean diameter, D =1.0 µm
p
5) SO content = 200 ppm (vol)
3
6) Particulate content = 3.2 gr/scf − flyash
7) HAP content = 10% (mass) cadmium
2. Fabric-filter Preliminary Design. In this case, fabric selection depends on the emission
stream temperature of 400°F, the SO content of 200 ppmv, and the flyash particulate
3
type. Table 3 indicates that filter fabrics capable of withstanding 400°F emission
stream temperature are ceramics (Nextel 312 TM ), nylon aromatic (Nomex), fluorocar-
bon (Teflon), and fiberglass. Because there is a high potential for acid damage (i.e., a
high SO content), however, Nomex bags should not be considered. To obtain an indi-
3
cation of the A/C ratio, use Table 4. This table shows that an A/C ratio of around 2.5 is