Step 1--Assume that at 90% TPH re-
200
moval, > 99% VOC removal will occur
kW/ 20C Increase
(i.e., TPH removal controls total removal).
Calculate required treatment temperature
by rearranging eq 8 to solve for TL:
[R
]
150
+ 0.22 (QL ) - 33.72
kW 15 C Increase
p
TL =
2.61
[90 + 0.22 (75.7) - 33.72]
=
2.61
100
kW/ 10 C Increase
∴TL = 27.9C (82.3F)
Step 2--Calculate ∆C, using TL and
given initial temperature, Ti = 8.89C: ∆C
= TL Ti = 27.9C 8.89C = 19C
kW/5 C Increase
50
Step 3--Use QL and ∆C in eq 11 to
predict power requirement per unit vol-
ume of water to heat and air strip as
required:
Air Stripping Only
(actual)
[
]
-1
0.002 (75.7 lpm) + 0.0157
+ 8.83 (19C)
0
100
200
300
Liquid Flow Rate (L/min)
Figure 8. Stripping and heating power requirements vs.
174 kW
=
liquid flow rate, ShallowTray medium temperature process.
(3785 L treated)
This example shows that a low flow rate and
power requirements to yield a total power re-
quirement per volume per ∆C. The resulting pre-
significant quantity of power is required for treat-
ing TPH contaminated water to a high standard.
dictor equation for stripping and heating power
When a typical cost per kilowatt-hour is assumed
requirements per volume of liquid treated is
(e.g.,
||content||
.08/kWh), the example treatment cost is[
]
-1
much lower than literature values for steam or
kW
= 0.002 (QL ) + 0.0157
(3785 L treated)
high temperature air stripping (HTAS) costs
(Fleming 1989 and EPA 1990). The example does
+ 8.83 (∆C)
not consider emission controls, contaminant de-
(11)
struction, or disposal costs. However, the batch
A simple example can illustrate the use of eq 8
mode employed for this research is very ineffi-
and 11.
cient and could easily be made more economical
using standard insulation techniques and a con-
Example: What would be the predicted treat-
tinuous or in-line heating operation. Many new
ment power requirements for stripping a cer-
remediation sites have a steam generation ca-
tain volume of water (at 8.89C) contami-
pability for carbon regeneration, soil washing
and subsurface injection/extraction methods.
nated with 510 ppm diesel-range petroleum
Excess heat from these processes could be used
hydrocarbons (as TPH) and 3050 ppm
for water heating, or steam use could be shared
VOCs (with Henry's law constant values
≥0.003) using a ShallowTray series 2600 air
among several processes. The advantage of the
medium temperature process described is that
stripper, assuming a liquid flow rate 75.7 L/
high quality steam is not required, and less heat-
min (20 gpm) to the stripper and treatment
ing energy than competing HTAS processes is
goals of 99% VOC removal and 90% TPH
needed regardless of the source.
removal?
13
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