Page 270 - Air Pollution Control Engineering

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Wet and Dry Scrubbing 249

3
D is the density of the polluted air stream (lb/ft ), L = 0.10 saturated lb water/lb
e w,s
dry air (from Fig. 4), L = 0.031 inlet lb water/lb dry air (from Fig. 4), and D is
w,a w
3
the density of water vapor, (lb/ft ).
Using the ideal gas law, an approximate density of any gas encountered in an air
pollution control project can be made:
D = (PM) / (RT) (30)

3
where D = D is the density of emission (lb/ft ), P is the pressure of the emission
e
stream (1 atm), M is the molecular weight of the specific pollutant gas (29 lb/lb-mol),
3
R is the gas constant (0.7302 atm-ft /lb-mol °R), and T = T is the temperature of the
e,s
gas (°R).
The density of the emission stream is calculated from Eq. (30):
3
D = (1) (29) / [(0.7302) (127 + 460)] = 0.0676 ft /lb
e
The density of water vapor is determined from Eq. (30):
3
D = (1) (18) / [(0.7302) (127 + 460)] = 0.042 ft /lb
w
3
where D = D is the density of emission (lb/ft ), P is the pressure of the emission
w
stream (1 atm), M is the molecular weight of the specific pollutant gas (18 lb/lb-mol),
3
R is the gas constant (0.7302 atm-ft /lb-mol °R), and T = T is the temperature of the
e,s
gas (°R).
Substituting into Eqs. (29a) and (29) yields
Q = (106,590)(0.0676)(0.10 − 0.031)(1/0.042) = 11,838 cfm or 11,800 cfm (29a)
w
The saturated emission stream flow rate is determined by substituting into Eq. (29):
Q = [(110,000) (127 + 460) / (400 + 460) ] + 11,800 = 86,800 acfm (29)
e,s
The calculated saturated gas flow rate will then be used for sizing a commercially
available venture scrubber.
G. Permit Application for Submission
The controlling regulatory agency (most likely, but not necessarily limited to, the state)
will use the following (or similar) table evaluate the merits of the permit application.
The values in the table are calculated from the example used here for discussion pur-
poses:
Calculated versus observed (reported) performance data
Calculated value Observed value

Particle mean diameter, D 1.0 µm
p —
Collection efficiency, CE 99.9%
—
Pressure drop across Venturi, P 47 in. H O
v 2 —
The regulatory agency can be expected to conduct an independent investigation, as per
Example 14. If such are independent review yields results not significantly different
than the results submitted by the applicant (Example 14, in this example), approval of
the permit application for the Venturi scrubber can be expected by the agency.

General industry experience indicates that one of the critical parameters that the agency
will scrutinize is actual and estimated pressure drops for the Venturi scrubber. As pre-