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8/12/2019 ET ZC362-L9
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Environmental Pollution Control(ETZC362)
Dr. Jegatha Nambi Krishnan
Department of Chemical Engineering
13thFeb 2014
etzc362
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Estimation of yand z
Based on the experimental observations and
atmospheric stability, Pasquill and Gifford
have devised a method for calculating these
values.
P
z
y
Bx
Ax
903.0
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If the time interval employed in the sampling
is other than 10 min, the following correction
need to be applied which is valid till 2 hrs.
q
AAt
tCC
2
112
Where, C is the concentration and t2is the sampling time period in minutes and t1is 0
min and q has a value between 0.17 and 0.20.
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Average wind speed u
11
2
z
H
u
u
u1is usually the meteorological value of the velocity measured at Z1= 10m. Alpha is 0.25
for unstable and 0.5 for stable conditions.
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Dispersion EquationDifferent Forms
2
2
2
exp
zzy
H
u
Q
General EquationPlume with Reflection for Stack Height H
2
2
2
2
2
2
2222zzyzy
HzHzy
u
QHzyxC
expexpexp);,,(
Ground Level ConcentrationStack at Height H
2
2
2
2
220zyzy
Hy
u
Q
HyxC expexp);,,(
Ground Level Center Line ConcentrationStack at Height H
);0,0,( HxC
Ground Level Center LineGround Point Source
)0;0,0,(xC
z=0
zyu
Q
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Calculation of Effective Stack Height
H = hs+ h, where h is the stack rise.
Stack rise is dependant on stack characteristics,Meteorology, and physico-chemical nature of effluent.
* Carson-Moses Equation:
s
h
s
s
u
Q
u
dVh
21
6220290 ..
* Holland Formula:
dV
Q
u
dVh
s
h
s
s 0096051 ..
* Concawe Formula:
6940
4440
714.
.
.s
h
u
Qh
asph
TTCmQ
Ts= stack gas temperature, K
Ta= ambient temperature,
kJ/s
m= gas mass flow rate, kg/s
Vs= stack gas exit velocity, m/s
us
= wind speed at exit, m/s
d= stack exit diameter, m
All Equations assuming that no stack tip
downwash occurs: i.e. when
Vs 1.5 us
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Briggs Formula
Neutral or unstable condition (A,B,C,D)
mx
mHFx
T
TTrgVF
U
xF
H
f
sf
a
asss
f
305Hfor674
305Hfor16.2
6.1
s
4.0
s6.04.0
2
3/23/1
xf= down wind distance to final plume rise in m.
U= wind speed at stack tip m/s
F= Buoyancy flux parameter in m4/s3.
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For stable conditions (E and F)
mCZT
TgS
USFH
a
a
/01.0
4.2
3/1
S= Stability parameter
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Example
2
2
2exp)150;0,0,500(
zzy
H
u
QC
NOx emission from a stack at a rate of 100 g/s from an urban stack of
physical height 100m and a plume rise of 50m. What is the ground-level
concentration at a distance of 500 m from the stack and along the center-line on a clear sunny day? Wind speed is measured at 2 m/s at 10m.
H = hs+ h
2
2
2
2
2
2
2exp
2exp
2exp
2);,,(
zzyzy
HzHzyuQHzyxC
Centerline y = 0 Ground Level z = 0
hs= 100; h = 50H = 150
Equation for emission from a stack with Reflection
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Example -contd.
2
26
)105(2
150exp
)105)(109)(2(
10*100)150;0,0,500(
C
Data: Q = 100 g/s H = 150 m
2. Empirical Equations (from Equations 3.57 and 3.58 and tables 3.2 and 3.3)
y: From Table 3.3,
y=109 m
Z= 105 m
u =2 m/s y= 109 m z= 105 m
= 501 g/m3of NOX
x in km : 0.5 km
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A plate type electrostatic precipitator for use in a cementplant for removing dust particles consists of 10 equal
channels. The spacing between the plates is 0.15 m, and
the plates are 2 m high and 2 m long. The unit handles
10,000 m3/hr of gas. What is the efficiency of thecollection? What should be the length of the plates for
achieving 99% collection efficiency if other conditions are
the same?
Example 2
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Example 2
2
2
2
2
2exp
2exp)150;0,100,500(
yzzy
yH
u
QC
NOXemission from a stack Estimate NOXconcentration at ground level, 100m
crosswind, 500 m from the stack
2
2
2
2
2
2
2exp
2exp
2exp
2);,,(
zzyzy
HzHzy
u
QHzyxC
)1132
100(exp*501)150;0,100,500( 2
2
C = 338 g/m3
of NOX
NAAQSstandard for NO2= 100 g/m3 for annual average
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A Venturi scrubber is to be used to collect particulate matterfrom an industrial operation. The liquid flow rate through
the scrubber is 10 gpm per 1000 ft3/ min of the gas and
the relative velocity of the gas to liquid is 300 ft/sec. The
gas is air at standard temperature of 298 K and pressureof 1 atm carrying particles of density 1000 kg/m3.
determine the efficiency of the scrubber as a function of
particle diameter.
Example-2
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Given the scrubber described below, write an expressionfor collection efficiency that is function of particle size.
Assume the particles are fly ash with a density of 700
kg/m3and a minimum size of 10 m diameter.
Venturi Characteristics:Throat area: 1 sq.m
Gas flow rate: 94.4 cum/s
Gas temperature: 150 degree C
Liquid flow rate: 0.13 cum/sCoefficient K= 200
Droplet diameter= 100 m
Example-1
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BITS Pilani, K K Birla Goa Campus28thJan. 2014 (Course Code: etzc 362)
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Before installation of an electrostatic precipitator, the stack gas ofa power plant contained 5 g particulates per m3 of gas. The gasflow rate is 300 m3/min and the new precipitator can remove1800 Kg particulates /day.
1. What is the emission rate of particulates before and afterpollution control in kg/day?
2. What is the efficiency of the electrostatic precipitator?
3. Will the new system meet an emission standard of 0.7 g/m3?
Exercise Problem 1
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BITS Pilani, K K Birla Goa Campus28thJan. 2014 (Course Code: etzc 362)
5
Flow rate = 300 m3/min.
(a) Emission rate before pollution control Kg/d = 2160 kg/day
Precipitator can remove 1800 kg/day
(b) Left out will be or emission rate after pollution = 360 kg/d
(c) Efficiency = 1800/2160 = 83.33 %
(d) Concentration in air after removal
= 360 x 1000/ 300 x 60 x 24
X = 0.833 g/m3 > 0.7 g/m3.
Therefore it will not meet emission standard.
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A 915 MW power plant with a load factor of 72.5% and anefficiency of 40% uses coal as a fuel source. The coal has 1%sulphur content and a calorific value of 30 MJ/kg. The stack tipis 200 m high with a diameter of 7m. If neutral conditions
prevail, determine the following
a. Emission rate of SO2
b. Plume rise using Briggs equation
c. Maximum ground level concentration of SO2 at 1 kmdownwind from the plant. Given the following data: U10= 4m/s; Ts= 150 C; Ta= 20C; Vs = 15m/s; =0.16 (for neutralcondition)
Exercise Problem 1
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Briggs Formula
Neutral or unstable condition (A,B,C,D)
mx
mHFx
T
TTrgVF
U
xF
H
f
sf
a
asss
f
305Hfor674
305Hfor16.2
6.1
s
4.0
s6.04.0
2
3/23/1
xf= down wind distance to final plume rise in m.U= wind speed at stack tip m/s
F= Buoyancy flux parameter in m4/s3.
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BITS Pilani, K K Birla Goa Campus
Estimation of y and z
Based on the experimental observations and
atmospheric stability, Pasquill and Gifford have devised
a method for calculating these values.
P
z
y
Bx
Ax
903.0
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BITS Pilani, K K Birla Goa Campus28thJan. 2014 (Course Code: etzc 362)
5
Coal required = 199 t/h
Emission rate = 1.1 kg/s
Vs = 6.5 m/s
F = 553 m4/s3
xf = 648 m
H = 150 m
y = 66.5186 m (0.13 (1000)0.903)
z = 31.78 m (0.105 (100)0.827)
c = 9.838 x 10-23g/m3
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Calculation of hydrocarbon content