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320 Lawrence K. Wang et al.

4.2.2.1. DIRECT ANNUAL COSTS
Direct annual costs consist of utilities (electricity, refrigerant) and operating labor
and maintenance costs. The electricity cost is a function of the fan power requirement.
Equation (13) can be used to obtain this requirement, assuming a fan-motor efficiency
of 65 % and a fluid specific gravity of 1.0:
×
.
F = 181 10 −4 Q ( ea P )( )(HRS ) (13)
p
,
where F is the fan power requirement (kWh/yr), Q is the emission stream flow rate
p e,a
(acfm), P is the system pressure drop (in. H O [default = 5 in. H O]), and HRS is the
2 2
system operating hours per year (h/yr).
To obtain Q from Q , use the formula
e,a e
e (
)
Q ea = Q T + 460 537 (14)
e
,
The cost of refrigerant replacement varies with the condenser system, but is typically
very low. Therefore, assume that refrigerant replacement costs are zero unless specific
information is available. The operator labor is estimated as 0.5 h per 8-h shift, with the
wage rate given in Table 6. Supervisory costs are assumed to be 15 % of operator labor
cost. Maintenance labor is estimated as 0.5 h per 8-h shift, with the maintenance wage rate
provided in Table 6. Material costs are assumed to be 100 % of maintenance labor costs.
4.2.2.2. INDIRECT ANNUAL COSTS
These costs consist of overhead, property tax, insurance, administrative, and capital
recovery costs. Table 6 provides the appropriate cost factors.
4.2.2.3. RECOVERY CREDITS
A condenser system may have significant recovery credits. The amount of recovered
HAP can be estimated using Eq. (12). Multiplying this amount by the value of the
recovered product gives the recovery credit.

5. ENVIRONMENTAL APPLICATIONS
Air strippers (see Fig. 7) are frequently used to treat aqueous wastes and contaminated
groundwater (14–18). Units may consist of a spray tower, packed column, or a simple
aerated tank. They commonly remove parts per million or lower levels of volatiles from
dilute aqueous wastes. Many air strippers with lower emissions simply vent directly to
the atmosphere. Those with higher organic concentrations or those located in zones of
regulatory (air pollutant) noncompliance are followed by a control device (shown in
Fig. 7). The control device can be a gas-phase carbon adsorption unit, an incineration
unit, or others. Condensers alone placed directly after air strippers generally prove inef-
fective, because of low vapor-phase concentrations and high volumetric flow rates. For
high-concentration emission streams, however, condensation efficiently removes and
recovers VOCs from the emission streams prior to other final polishing control tech-
nologies, such as carbon adsorption. There are situations in which condensation can be
used alone, in some applications, to control emissions at high VOC concentrations (i.e.,
greater than 5000 ppmv). This type of VOC control is not suitable for low-boiling-point
organics (i.e., very low condensation temperatures [< 32ºF]) or high concentrations of
inert of noncondensable gases (air, nitrogen, or methane).