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80 Lawrence K. Wang et al.

Table 10
Annual costs for Fabric Filters
Cost item Factor
Direct Costs (DAC)
Utilities
Electricity $0.059/kWh
3
Compressed air $0.16/10 scfm
Replacement parts, bags
Operating labor
Operator $12.96/h
Supervisor 15% of operator labor
Maintenance
Labor $14.26/h
Material 100% of maintenance labor
Waste disposal Variable
Indirect costs (IAC)
Overhead 0.60(operating labor + maintenance)
Administrative 2% of TCC (total capital cost)
Property tax 1% of TCC
Insurance 1% of TCC
Capital recovery a 0.1175(TCC − 0.05C − 1.08 C )
L B
n
a Capital recovery factor is estimated as i(1+i) /[(1+i) − 1],
n
where i is the interest rate, (10%) and n is the equipment life, (20 yr).
Source: ref. 8.
a 99.999% removal rating for 0.003 µm at maximum flow rate. The ceramic medium is
processed at temperatures above 2000°C, eliminating organic contaminants. It is capable
of producing flow rates up to 2700 L/min (29).
The most recently developed filtration processes use membrane filtration media.
Because substances that permeate nonporous membranes are reasonably volatile, appli-
cation of a vacuum always causes the permeate to be desorbed from the membrane in
the vapor state. Hence, the term “pervaporation” applies if the feed to the membrane fil-
ter is liquid, because the contaminant appears to evaporate through the membrane (30,31).
If the feed is vapor, or a gas–vapor mixture, the process is called “vapor permeation”
(30). More new technologies are reported elsewhere (32–36).

7. DESIGN EXAMPLES AND QUESTIONS
Example 1
The process flow diagram for a typical shaker fabric filter appears in Fig. 3. Give a general
process description for the fabric filtration process.
Solution
Fabric filters are air pollution control devices designed for controlling particulate matter
emissions from point sources. A typical fabric filter consists of one or more isolated com-
partments containing rows of fabric bags or tubes. Particle-laden gas passes up along the
surface of the bags, then radially through the fabric. The upstream face of the bags retains
particles while the clean gas stream vents to the atmosphere. The filter operates cyclically