Environmental Engineering Reference
In-Depth Information
The monitoring devices for the first subdivision have been rendered inoperable.
Given an overall canal flow of 6400 gpm (gallons per minute) with an organics load
of 240 mg
L, estimate the flow and organics load in the first sewer if the other
two sewers are measured at 1850 gpm with 280 mg
/
/
L organics and 2250 gpm with
L organics.
3.11 A distillation column is needed to separate methanol and water. The overhead stream
should be at least 97% methanol and the bottom stream should contain no more than
3% methanol. Apply the graphical method to estimate the minimum number of stages
to achieve this separation. Assume the equilibrium relationship,
y
*
210 mg
/
=
1.3
x
, is linear
and the operating line is the diagonal.
3.12 An absorption column is built to remove CO
2
from an air stream leaving a combustion
process. The entering gas stream is 10 mol% CO
2
and the exit gas stream must be
no greater than 0.5 mol%. The entering liquid stream contains 0.1 mol% CO
2
. The
equilibrium relationship,
y
*
V
ratio is 4.
(a) Perform a mass balance to obtain the CO
2
concentration in the exit liquid stream.
(b) Apply the graphical method to estimate the number of stages. If the overall stage
efficiency is 0.65, how many stages are required?
(c) Estimate the number of steps using the Kremser equation.
3.13 Evaluate the number of required stages for Problem 3.12 for an
L
=
2.3
x
, is linear and the
L
/
V
ratio of 3 and
5. Assume the entering and exiting gas-phase concentrations do not change. How
does the
L
/
V
ratio affect the number of stages required?
3.14 For the absorption column in Problem 3.12, estimate the number of equilibrium
stages required for equilibrium relationships of
y
*
/
3.8
x
, respectively.
How does increasing the Henry's Law relationship affect the number of required
stages?
3.15 A distillation column is designed to separate benzene and toluene. The relative
volatility ratio for this binary system is 2.5. If the overhead stream must be at least
97% benzene and the bottoms stream no greater than 6% benzene, apply the Fenske-
Underwood equation to estimate the minimum number of stages required.
3.16 For the separation defined in Problem 3.15, estimate the minimum required stages
under the following conditions:
(a) benzene in overhead
=
1.2
x
and
y
*
=
=
=
99.5%, benzene in bottoms
6%;
=
=
(b) benzene in overhead
92%, benzene in bottoms
6%;
0.5%.
What effect do both the overhead and bottoms product purity have on the required
number of stages?
3.17 Experiments are performed to characterize the flux of carbon dioxide through a
membrane. If the flux is measured at 2
(c) benzene in overhead
=
99.5%, benzene in bottoms
=
10
−
11
mol
cm
2
.
09
×
/
·
s, the concentration on
the incoming side of the membrane is 0.5 mg
/
L, and the concentration on the opposite
L, what is the overall mass transfer coefficient?
3.18 A solid carbon adsorbent is to be used to remove 53 mg
side of the membrane is 0.1 mg
/
L chlorides from a
water stream. There are two mass transfer resistances. The first, resistance to the
/
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