Page 198 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 181

4. Only two intervals were used to analyze the period between
free-product disappearance and final cleanup. The estimate
would be more accurate if more intervals were used.
5. If the free-product phase is not present initially, solve the prob-
lem by starting from part (g).

5.2.7 Effect of Temperature on Soil Venting
In a soil-venting project, the subsurface temperature will affect both the air
flow rate and the vapor concentration. At a higher temperature, the vapor
pressure of an organic compound would be higher. On the other hand, the
higher subsurface temperature will yield a lower air flow rate because air
viscosity increases with temperature:

µ @ T 1 = T 1

µ @ T 2 T 2 (5.14)
where T is the subsurface temperature, expressed in Kelvin or Rankine
units. The ratio of the flow rates at two temperatures can be estimated by
using Equation (5.15):

QT@ 1 = T 2 (5.15)
QT@ 2 T 1

As shown in Equation (5.15), the vapor flow rate will be lower at higher
temperatures. However, since the vapor concentration will be much higher at
a higher temperature, the mass removal rate will still be higher at a higher
temperature.

Example 5.17: Estimate the Extracted Vapor Flow Rate of a Soil-
Venting Well at Elevated Temperatures
A soil-venting well (4-in. diameter) was installed at a site. The pressure in the
extraction well is 0.9 atm, and the radius of influence of this soil-venting well
has been determined to be 50 ft.
If the subsurface temperature is raised to 30°C, what will be the vapor flow
rate (all the other conditions being kept the same)? The extracted vapor flow
rate has been estimated, as shown in Example 5.10, to be 7.6 ft /min under
3
the following conditions:
• Permeability of the formation = 1 darcy
• Well screen length = 20 ft
• Viscosity of air = 0.018 cP
• Temperature of the formation = 20°C