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Condensation 313

where RE is the removal efficiency (%), HAP is the contaminant concentration in
e
entering gas stream (ppmv), and P is the partial pressure (mm Hg) of the HAP in
partial
the exit stream assuming the pressure in the condenser is constant and at atmospheric.
For this air–VOC system at equilibrium, the partial pressure of the HAP equals its
vapor pressure at that temperature. Determining this temperature permits specification
of the condensation temperature (T ). This calculation requires vapor pressure–tem-
con
perature data for the specific HAP (see Fig. 4), which can be obtained from refs. 3 and 7.
Equation (1) gives the partial pressure as a function of the desired removal efficiency for
the range likely to be encountered. Importantly, a high removal efficiency (and thus low
partial pressure) might require an unrealistically low condensation temperature (T ).
con
In this case, a lower removal efficiency must be accepted or a different control tech-
nique adopted. Information on coolants necessary for a given condensation temperature
(T ) appear in Table 1. At this step, the coolant can be selected from Table 1 based on
con
the calculated T .
con
3.3. Condenser Heat Load
Condenser heat load is the quantity of heat extracted from the emission stream to
achieve specified removal. It is determined from an energy balance, combining the heat
of condensation and sensible heat change of the HAP, and the sensible heat change in
the emission stream. This calculation neglects enthalpy changes associated with noncon-
densible vapors (i.e., air), which is typically a very small value. The calculation steps are
as follows:
1a. Calculate moles of HAP in the inlet emission stream (basis: 1 min):
, em ( ) −6
HAP = Q 392 HAP × 10 (2)
e
e
3
The factor 392 is the volume (ft ) occupied by 1 lb-mol of an ideal gas at standard conditions
(77ºF and 1 atm).
1b. Calculate moles of HAP remaining in the outlet emission stream (basis: 1 min):
[
, om ( ) − ( −6 )][ vapor ( vapor)]
HAP = Q 392 1 HAP × 10 P P − P (3)
e
e
e
where P is equal to P given in Eq. (1).
vapor partial
1c. Calculate moles of HAP condensed (basis: 1 min):
HAP = HAP − HAP (4)
con , em , om
2a. Determine the HAP’s heat of vaporization (∆H): Typically, the heat of vaporization will
vary with temperature. Using vapor pressure–temperature data as shown in Fig. 4, ∆H can
be estimated by linear regression for the vapor pressure and temperature range of interest
(see ref. 3 for details). Compare the estimated ∆H with that of the permit application and
ensure that they are in the same units. If these values differ significantly, contact the permit
applicant to determine the reason for the difference.
2b. Calculate the enthalpy change associated with the condensed HAP (basis: 1 min):
e (
H = HAP con[ ∆ H + C T − T )] (5)
con
p
HAP con