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FE Review for Environmental EngineeringProblems, problems, problemsPresented by L.R. Chevalier, Ph.D., P.E.Department of Civil and Environmental EngineeringSouthern Illinois University Carbondale
AIRFE Review for Environmental Engineering
Estimate the amount of soda ash required per m3 of exhaust gas to neutralize 20,000 g/m3 of SO2 at 20° C.
Problem Strategy Solution
• Review governing reaction• Determine the mass of soda ash needed from mole ratio
Problem Strategy Solution
232322 COSONaCONaSO
The neutralization reaction is:
MW: SO2 = 64 Na2CO3 = 106
Problem Strategy Solution
The mass of soda ash is then:
mg
SOg
CONagSOmgm CONa
125.33
64
1060.20
2
32232
Therefore, for each m3 of exhaust gas, we require33.1 mg Na2CO3
Problem Strategy Solution
Consider a box model for an air shed over a city 1 x 105 m wide with a mixing depth of 1200 m. Winds with no SO2 blow at 4 m/s against one side of the box. SO2 is emitted in the box at a rate of 20 kg/s. If SO2 is considered to be conservative, estimate the steady state concentration in the air shed.
Report your answer in mg/m3.
Problem Strategy Solution
• Draw a schematic of your system• Consider mass balance
Problem Strategy Solution
SolutionL
W = 1 x 105 m H = 1200 m
windu = 4 m/sCo = 0 mg/m3
windu = 4 m/sCe =?
Emission20 kg/s
windu = 4 m/sCo = 0 mg/m3
windu = 4 m/sCe =?
Emission20 kg/s
Ce = Co +(qL)/(uH)
L
W = 1 x 105 m H = 1200 m
Problem Strategy Solution
windu = 4 m/sCo = 0 mg/m3
windu = 4 m/sCe =?
Emission20 kg/s
Ce = Co +(qL)/(uH)
L
W = 1 x 105 m H = 1200 m
367.4110912004
20
mg
kgg
m
LLW
es
m
skg
C
Problem Strategy Solution
Consider the emission of SO2 from a coal fired power plant, at a rate of 1,500 g/s. The wind speed is 4.0 m/s on a sunny afternoon. What is the centerline concentration of SO2 3 km downwind (Note: centerline implies y=0). Stack parameters:
Height = 130 mDiameter = 1.5 mExit velocity = 12 m/sTemperature = 320°C (593° K)
Atmospheric conditions: P=100 kPa T=25° C (298° K)
Problem Strategy Solution
• Review data• Estimate effective stack height
• Determine stability class• Calculate sy and sz• Review terms and apply governing equation
Problem Strategy Solution
22
2
1exp
2
1exp,0,,
zyzy s
H
s
y
uss
QHyxC
dTTT
Pudv
Hs
ass 21068.25.1
mm
smmsm
H
44.1543.35.4
5.1593298593
1001068.25.10.4
50.112 2
H = effective stack height = h + DH = 130 m + 15.4 m = 145.4 m
Problem Strategy Solution
Atmospheric stability class: Class B
sy = ax0.894 = 156(3)0.894 = 416.6 m
sz = cxd + f = 108.2(3)1.098 + 2 = 363.5 m
Problem Strategy Solution
32
34
4
4
21
6.728
1028.7
923.01088.7
08.0exp1088.7
5.36344.145
21
exp0exp0.45.3636.416
1500,,,
mg
SOofmg
HzyxC
Problem Strategy Solution
Simplify the Gaussian dispersion model to describe a ground level source with no thermal or momentum flux, which is the typical release that occurs at a hazardous waste sites. In this situation, the effective plume rise, H, is essentially 0.
Example Solution
22
2
1exp
2
1exp,0,,
zyzy s
H
s
y
uss
QHyxC
0exp2
1exp,0,,
2
yzy s
y
uss
QHyxC
2
2
1exp,0,,
yzy s
y
uss
QHyxC
Example Solution
Consider soil under a single story house that emits 1.0 pCi/m2·s of radon gas. The house has 250 m2 of floor space, and average ceiling height of 2.6 m, and an air change rate of 0.9 ach. Estimate the steady state concentration of radon in the house, assuming that the ambient concentration is negligible.
For radon, k = 7.6 x 10-3 hr-1
Problem Strategy Solution
kV
QV
EC
V
Q
Ci
e
Volume = (250 m2)(2.6 m) = 650 m3
Q/V = 0.9Ventilation rate = Q = (650 m3)(0.9) = 585 m3/hrCi = 0E = (1.0 pCi/m2·s)(250 m2)(3600 s/hr) = 900000 pCi/hr
Problem Strategy Solution
• Review data• Review SS equation
3
11
3
1525
0076.09.0650
90000
mpCi
hrhrmhr
pCi
Ce
Problem Strategy Solution