Page 263 - Materials Chemistry, Second Edition

246 Practical Design Calculations for Groundwater and Soil Remediation

• COC concentration in the effluent liquid, C out
• COC concentration in influent air, G in

Example 6.12: Sizing an Air Stripper for Groundwater Remediation
A packed-column air stripper is designed to reduce chloroform concentra-
tion in the extracted groundwater. The concentration is to be reduced from
50 mg/L to 0.05 mg/L (50 ppb). Size the air stripper by determining the air
flow rate, cross-sectional surface area, and packing height.
Use the following information in calculations:

• Henry’s constant for chloroform = 128 atm
• Stripping factor = 3
• Temperature of the water = 15°C
• Extracted groundwater flow rate = 120 gpm
• K a = 0.01/s
L
• Type of packing = Jaeger 3” Tri-packs
• Hydraulic loading rate = 20 gpm/ft 2
• Chloroform concentration in the influent air = 0

Solution:
(a) As shown in Example 6.11, the dimensionless value of the
Henry’s constant is equal to 0.098, and the air flow rate has been
determined to be 493 ft /min.
3
(b) Use Equation (6.19) to determine the required cross-sectional area:
Q 120 gpm
= = = 6ft 2
A stripping 2
surfaceloading rate 20 gpm/ft
Diameter of the air stripping column = (4 × A/π) 1/2
= (4 × 6/π) = 2.76 ft
1/2
So, d = 3 ft

(c) Use this newly found diameter to find the hydraulic loading rate:
Cross-sectional area of the column = πd /4 = π(3) /4 = 7.1 ft 2
2
2
Hydraulic loading rate to the column (Q ) = Q/A
L
= [(120 gpm)(ft /7.48 gal)] ÷ 7.1 ft = 2.26 ft/min = 0.0377 ft/s
2
3
(d) Use Equation (6.23) to determine the HTU value:
L 0.0377 ft/s
HTU = = = 3.77 ft
( Ka) 0.01/s
L