Page 258 - Air Pollution Control Engineering

05_chap_wang.qxd 05/05/2004 3:46 pm Page 237
Wet and Dry Scrubbing 237

Fig. 7. Costs of absorber towers (from US EPA).

1. Direct Annual Costs (such as electricity, chemicals, labor, etc. expenses)
a. Power (electricity) cost: Use Eq. (23) to estimate the fan power requirements, F :
p
−4
F = 1.81 × 10 (Q )(P total )(HRS) (23)
p
e,a
F = kWh/yr
p
and
Q = Q (T + 460) / 537 (24)
e,a e e
Q = acfm
e,a
where Q is the actual emission stream flow rate (scfm) and T is the emission
e e
stream temperature (°F).
It assumed that 2 wk out of the year the factory utilizing the absorber is shut
down for inventory and retooling, which provides an annual operating period
of 50 wk/yr. Additionally, it is assumed the factory uses the scrubbing system
3–8 h shift, 5 d a week.
HRS = annual operating hours (h/yr)
HRS = (3 shift/d) (8 h/shift) (5 d/wk) (50 wk/yr) = 6,000 h/yr
b. The annual electric cost (AEC) can be determined assuming that UEC is equal
to $0.059/kWh and using Eq. (25):
AEC = (UEC)(F ) = $0.059(F ) (25)
p p
AEC = $
2. Solvent cost
a. Equation (26) estimates the annual solvent requirement (ASR):
ASR = 60(L )HRS (26)
gal
ASR = gal/yr
b. The annual solvent cost (ASC) is obtained from multiplying the yearly solvent
requirement and the unit solvent cost (USC) found in Table 7. Because water
is commonly used as solvent, the USC cost for water is assumed to equal $0.20
per 1,000 gal.
ASC = (USC)(ASR) (27)
ASC = ($0.20/1000 gal)(ASR)
ASC = $