Types of Plumes and Their Behavior in Different Environmental Conditions
Table of Contents
TYPES OF ENVIRONMENT
a) Neutral- Environmental lapse rate becomes equal to Dry Adiabatic Lapse Rate
b) Unstable – Environmental lapse rate becomes more than the Dry Adiabatic Lapse Rate
c) Stable – Environmental lapse rate becomes less than the Dry Adiabatic Lapse Rate.
TYPES OF PLUMES
The behavior of gases emitted from the Stack depends upon the prevailing Environmental Conditions.
(1) Looping Plume:
A plume is formed when the environmental lapse rate becomes more than the Dry Adiabatic Lapse Rate
i.e. occurs in a super adiabatic environment.
When the environmental lapse rate exceeds the dry adiabatic lapse rate, a looping plume forms, creating a super adiabatic environment. Due to the instability brought on by the temperature difference between the plume and the surrounding air, the plume in this case displays a looping tendency, rising, falling, and then rising again.
(2) Neutral Plume
The Neutral Plume is the first kind of plume we’ll look at. When the dry adiabatic lapse rate and the ambient lapse rate are equivalent, this happens. In these circumstances, the plume experiences an upward vertical rise as a result of buoyancy since the gases being released have the same temperature as the air around them.
Environmental lapse rate becomes equal to Dry Adiabatic Lapse Rate.
- Upward vertical rise occurs
(3) Coning plume:
The Coning Plume occurs when the ambient lapse rate falls just short of the dry adiabatic lapse rate, resulting in a sub-adiabatic environment. The plume has a conical shape and exhibits some stability, although it is still moving vertically upward.
Environmental lapse rate becomes slightly less than the Dry Adiabatic Lapse i.e under Sub Adiabatic Lapse rate. The environment is slightly stable.
(4) Fanning plume :
When the environmental lapse rate falls far below the dry adiabatic lapse rate, a highly stable sub-adiabatic environment is created, in contrast to the Coning Plume. Due to this stability, the plume does not move vertically upward and instead spreads out horizontally.
The environmental lapse rate becomes less than the Dry Adiabatic Lapse i.e. under Sub Adiabatic Lapse rate. The environment is highly stable (Invasion occurs).
(5) Lofting plume:
The Lofting Plume appears when a super adiabatic layer is located above a sub-adiabatic environment. The inversion prevents the plume from moving downhill, but it does allow it to mix upward.
- When super adiabatic lies above sub adiabatic environment.
- Downward motion is prevented by inversion but upward mixing occurred.
(6) Fulminating plume:
The Lofting Plume’s opposite is represented by the Fulminating Plume. In this case, an inversion layer is present above a hyper-adiabatic environment, which causes contaminants to be trapped below the inversion layer.
Just the reverse Lofting condition when inversion lies above a super adiabatic environment.
Pollutants cannot move above the top of the stack because of inversion.
(7) Trapping plume :
The Trapping Plume is the last kind of plume we’ll examine. The plume becomes stuck between two inversion levels when a super adiabatic layer is sandwiched between them.
The condition occurred when super adiabatic lies between two inversion layers, hence plume gets
Chimney Height
A) Function of PM
h=74(Q_p)^{0.27}
Where h is chimney height in m Qp is Particulate matter in tonne/hr
B) Function of SO2
h=14(Q_s)^{\frac{1}{3}}
Qs is S02 emission in kg/hr
Where Δh= rise of plume above the stack in m
Vs= stack gas velocity (m/sec)
D= inside exit dia. of a stack in m
u= wind speed in m/sec
P= atmospheric pressure in mill-bars
Ts= Stack gas temperature in Kelvin
Ta= Air temperature in Kelvin
Limits of Air pollution
| Pollutant | Permissible Exposure Limit (8-hour time-weighted averages) |
| Benzene | 1 ppm |
| Bromine | 0.1 ppm |
| Cadmium | 5 μg/m^3 |
| Carbon dioxide | 5000 ppm |
| Carbon disulfide | 200 ppm |
| Carbon monoxide | 50 ppm |
| Chlorine | 1 ppm |
| Chloroform | 50 ppm |
| Cresol | 5 ppm |
| Fluorine | 0.1 ppm |
| Hydrogen cyanide | 10 ppm |
| Iodine | 0.1 ppm |
| Lead | 50 μg/m^3 |
| Methanol (Methyl alcohol) | 1 mg/10 m^3 |
| Nitric oxide | 200 ppm |
| Nitrogen dioxide | 25 ppm |
| Sulphur dioxide | 5 ppm |
| Sulfur dioxide | 5 ppm |
| Vinyl chloride | 1 ppm |
AIR POLLUTION SOURCE CONTROL TECHNOLOGY
(a) Setting chamber- use the force of gravity to settle down the particles
(b) Cyclones-use centrifugal forces a principle of inertia, efficient in removing larger particles but not efficient for smaller particles.
(c) Venturimeter scrubbers use a liquid stream to remove smaller particles. Efficiency is about 99%
(d) Esps (Electrostatic precipitators)
- Use electrical forces to remove particles
- Give electrical charges to particles. Causing them to be attracted to the metal plates.
- Very high efficiency
- Used in cement, pulp & paper, petroleum, and steel industries
The control of gaseous pollutants method adopted is
(a) absorption →gaseous pollutants absorption in liquid
(b) adsorption →solid surface, activated carbon
(c) condensation →converted into a liquid by↓es +ve
(d) incineration(combustion)
Also Read:- Air Pollution: A Comprehensive Analysis of Harmful Substances Impacting Humans, Animals, and the Environment
