Page 202 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 185

(c) Assuming isentropic expansion, use Equation (5.20) to deter-
mine the theoretical power requirement as:

(3.03 10× − 5 k )   P 2  k ( − 1)/ k 
hp theoretical = PQ 1   − 1

1
k 1−    P 1   
−
×
5
(3.03 10 )(1.4)
= [(14.7)(144)][(40)(2)]
−
1.4 1
−
  (14.7)(144) (1.4 1)/1.4 
×    − 1 = 0.55 hp
   1,905   

Assuming an isentropic efficiency of 80%, the actual horsepower
required is determined by using Equation (5.21) as:
0.55
hp actual = hp theoretical = = 0.7 hp
E 80%

Discussion:
In soil-venting applications, the difference between the inlet and final
discharge pressures is relatively small. Consequently, the theoretical
power requirements for isothermal and isentropic compression are
very similar, as illustrated in this example.

5.3 Soil Washing/Solvent Extraction/Soil Flushing
5.3.1 Description of the Soil-Washing Process
The majority of the organic and inorganic COCs contained in soil is associ-
ated with fines (i.e., clay or silt) that have large specific surface areas. These
fine particles, in turn, are attached to sand and gravel, which are much larger
in size, by compaction and adhesion. In this section, three technologies (soil
washing, solvent extraction, and soil flushing) are discussed. They use
solvents to extract or separate COCs from the soil matrix.
Soil washing is a water-based washing process. The major removal mecha-
nisms include desorption of COCs from the soil grains, consequent dissolu-
tion into the washing fluid, and/or suspension of the clay and silt particles