L-17Plume Rise Formulae

Air Pollution and Control

(Elective -I)

• Gases that are emitted from stacks are often pushed out by fans. As the turbulent exhaust gases exit the stack they mix with ambient air. This mixing of ambient air into the plume is called entrainment. As the plume entrains air into it, the plume diameter grows as it travels downwind. These gases have momentum as they enter the atmosphere. Often these gases are heated and are warmer than the outdoor air. In these cases the emitted gases are less dense than the outside air and are therefore buoyant.

Prof S S Jahagirdar, NKOCET2

• A combination of the gases' momentum and buoyancy causes the gases to rise. This is referred to as plume rise and allows air pollutants emitted in this gas stream to be lofted higher in the atmosphere. Since the plume is higher in the atmosphere and at a further distance from the ground, the plume will disperse more before it reaches ground level.

Prof S S Jahagirdar, NKOCET 3

Plume Rise

>

4Prof S S Jahagirdar, NKOCET

hs= Physical Stack heightH= Effective stack height

5

Buoyancy =Plume rise

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Prof S S Jahagirdar, NKOCET

1. IS formula

6Prof S S Jahagirdar, NKOCET

2. Modified Carson and Moses formula

0.5.[( . ) / ] .[( ) / ]s hh a V d u b Q u

Stability Condition

a b

Unstable 3.47 5.15

Neutral 0.35 2.64

Stable -1.04 2.24 7Prof S S Jahagirdar, NKOCET

8Prof S S Jahagirdar, NKOCET

3. Holland’s Formula

Ts= Stack gas temperature in 0 KTa =Ambient air temperature in 0 K 9Prof S S Jahagirdar, NKOCET

4. Concave formula1/2 3/42.71[ / ]hh Q u

It is modified by Thomas

0.444 0.6944.71[ / ]h Q u

10Prof S S Jahagirdar, NKOCET

5. Brigg’s formula1/3114. .( ) /h C F u

2. . .( )

4.s s a

a

g V d T TF

T

1.58 41.4Cz

11Prof S S Jahagirdar, NKOCET

• F= Flux (m4/Sec3)

• G= gravitational acceleration.

• = potential temperature gradient (Similar to dT/dZ)z

12Prof S S Jahagirdar, NKOCET

6. Davidson and Bryant formula

1 .4

. . 1s

V s Th d

u T

Where, Ts-Ta= T

13Prof S S Jahagirdar, NKOCET

Objective Questions1. Plume rise is measures from top of the stack and

is measured up to ____________________________.

2. Stack gas temperature is ___________ than the surrounding air.

3. IS: _______ suggested plume rise formula based on Brigg’s equation.

4. Values of coefficients a and b in case of modified Carson and Moses equation for unstable stability class are ____ and ____ respectively. (Similar questions for other two stability categories.) 14

Prof S S Jahagirdar, NKOCET

5. Plume rise is due to _________________ and _______________.

6. Effective stack height = ________________+____________________.

7. True or False?

Plume rise (Δh) is the height that pollutants rise above a stack and is measured from the top of the stack to the upper edge of the plume.

15Prof S S Jahagirdar, NKOCET

Theory QuestionsQ1. Explain what is ‘Plume rise’. Give any three

formulae for the same.

Q2. Give IS formula for plume rise.

16Prof S S Jahagirdar, NKOCET

Go to Problems

17Prof S S Jahagirdar, NKOCET