Applications of Chemical Kinetics in Environmental Systems - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 416

5. The specification of absorption column diameter is usually done on
the basis of the mechanical design of the column internals and is
essentially independent of the compound to be stripped.
6. A crossflow scrubber is more efficient than countercurrent or co-
current scrubbers for the removal of particulates from an air stream.
7. Adoublingofcarbondioxidepartialpressureintheatmosphereeffec-
tively increases the global average surface temperature by the same
amount.
8. The reaction of ozone with oxides of nitrogen accounts for 60-70%
of ozone destruction in the lower troposphere.
6.38 2 A local industry produces a process air stream that contains vinyl chlo-
ride (molecular weight 62.5) at a concentration of 1000 ppmv. The mass
flow rate of air is 1.9 kg/s at a temperature of 25 ◦ C and a total pressure of
1 atm. The environmental group has proposed using an activated carbon
bed to remove vinyl chloride. Density of air is 1.2 kg/m 3 . Given that the
adsorption bed is 5 m 2 in area and 0.35 m in thickness, determine the fol-
lowing: (a) The lifetime of the bed before regeneration. Answer in hours.
The carbon used is Ambersorb XE-347 for which the Freundlich isotherm
parameters for vinyl chloride are K Freun = 4.16 and n = 2.95, that is,
C e = K Freun W sat , where W sat is the saturation adsorbed concentration
(g/g). The adsorption bed density is 700 kg/m 3 . The overall mass transfer
coefficient is 30 s − 1 . (b) What is the overall flux of vinyl chloride through
the bed?Answer in kg/m 2 s.What is the mass rate through the bed in kg/h?
6.39 2 Construct a two-box model for a lake that consists of an epilimnion (a well-
stirred upper region) and a hypolimnion (the cold portion of the lake). r p is
the rate of removal (precipitation, sedimentation), r b is the rate of burial,
r d is the rate of addition to hypolimnion by dissolution, Q exc is the rate
of exchange of water between epilimnion and hypolimnion. Write a mass
balance equation for the steady-state concentration of a pollutant in the
hypolimnion. Note that at steady state r b = r p − r d . Consider a lake where
the average river water flow is 100 m 3 /s, an average rainfall deposition of
20 m 3 /s, and a mean burial rate of 200 mg/s for phosphorus. If the influent
to the lake has a P loading of 5 μ g/L from agricultural pesticide runoff into
the river, is the lake prone to eutrophication (i.e., biological productivity)?
Mean P concentration for biological productivity in lakes is 5 μ g/L.
6.40 3 Estimate the time to breakthrough for 1,2-dichlorobenzene to reach a
well 1 km from a source in the groundwater that has a Darcy velocity
of 8 m/y. The soil has a 3% organic carbon, porosity of 0.4, and a density
of 1.2 g/cm 3 . Both advection and dispersion are important in this case.
Breakthrough is defined as the time at which the concentration reaches
1% of the feed (source).
6.41 2 The following two contaminants are present in a gasoline mixture: hex-
ane and octane. If a gasoline spill has occurred in the subsurface due to
an underground storage tank rupture and contaminated the groundwater,
how quickly will these chemicals be detected in a monitoring well 100 m
away?The arrival time of a conservative tracer (chloride ion) was observed
to take only 50 days. The soil had an organic carbon fraction of 1% and a
porosity of 0.45. The soil density was 1.3 g/cm 3 .