Environmental Engineering Reference
In-Depth Information
gas-phase mass transfer coefficient (
k
g
) on each side of the composite film is the
same.
For steady-state mass transfer, does it make any difference which side of the film
is the feed phase? Prove your answer and state why. The diagram has feed on the
left. Assume
P
f
and
P
p
are constant.
P
1
=
m
1
C
1
C
12
=
m
2
C
12
m
3
C
2
P
2
=
3.6
An organic extraction from water into various solvents is being considered. Some
solvents and their distribution coefficients (
m
) are:
Solvent
A
B
C
m
3
30
90
The distribution coefficient is based on mass concentrations in each phase.
(a) Determine the number of equilibrium stages needed to reduce the organic con-
centration from 1000 ppm to 1 ppm for
mV
/
=
=
L
1and2(
V
solvent mass
flowrate and
L
=
aqueous feed mass flowrate).
(b) For
mV
/
L
=
1, determine
V
for each solvent for
L
=
10 kg
/
min.
3.7
Irrigation run-off exits three different farms and merges into a single stream. The
average flowrates, phosphate levels and nitrogen levels in each run-off stream are
shown in the table. Perform an overall and component mass balance to obtain the
total flowrate, phosphate and nitrogen levels of the merged stream.
Flowrate (L/min)
Phosphate (mg/L)
Nitrogen (mg/L)
Stream 1
1200
30
25
Stream 2
1450
15
35
Stream 3
1300
25
30
3.8 A distillation column separates a feed stream of 50 wt% methanol and 50 wt% water.
The feed enters at a rate of 100 kgmol/hr. The overhead product can contain no more
than 1 mol% water and the bottoms product can contain no more than 4 mol%
methanol. What are the rates of the overhead and bottom streams?
3.9 A ternary system of 60 wt% methanol, 10 wt% butanol, and 30 wt% water is the
feed stream for an alcohol/water separation unit. There are three exit streams. The
composition of one exit stream is 95 wt% methanol, 4.5 wt% butanol, and 0.5 wt%
water. The second stream has 96 wt% butanol, 3 wt% methanol and 1 wt% water. The
third stream is 95 wt% water with 2.5 wt% each of methanol and butanol. Calculate
the total mass flowrate of the three exit streams per kg feed.
3.10 Storm sewer drains from three subdivisions feed into a single canal that flows to
a municipal water treatment facility. Each subdivision pays the municipal facility
based upon the total quantity of water and the concentration of organics in the water.
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