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)

6

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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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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5

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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BITS Pilani, K K Birla Goa Campus

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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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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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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

ET ZC362-L9

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