AIR POLLUTION CONTROL course material by Prof S S JAHAGIRDAR,NKOCET,SOLAPUR for BE (CIVIL ) students of Solapur university. Content will be also useful for SHIVAJI and PUNE university students

1. L-34
GASEOUS CONTROL
TECHNOLOGIES
Air Pollution and Control
Elective- I

2. CONTENTS OF UNIT- VIII
L-32 Principles of removal of gaseous
pollutants, details of incineration, absorption
adsorption systems.
L-33 Vehicular pollution, composition,
quantity and control.
Status of air pollution in India, Air pollution
control act and strategy for effective control of
air pollution.

5. 1) ABSORPTION
The
removal of one or more selected
components from a gas mixture by
absorption is probably the most
important operation in the control of
gaseous pollutant emissions.
Absorption is a process in which a
gaseous pollutant is dissolved in a
liquid.
Water is the most commonly used
absorbent liquid.

6. As
the gas stream passes through the
liquid, the liquid absorbs the gas, in
much the same way that sugar is
absorbed in a glass of water when
stirred.
Absorption is commonly used to recover
products or to purify gas streams that
have high concentrations of organic
compounds.
Absorption equipment is designed to get
as much mixing between the gas and
liquid as possible.

8. Absorbers
are often referred to as
scrubbers, and there are various types
of absorption equipment.
The principal types of gas absorption
equipment include
1. spray towers,
2. packed columns,
3. spray chambers, and
venture scrubbers.
4.
 The packed column is by far the most
commonly used for the absorption of
gaseous pollutants.

9. The
packed column absorber has a
column filled with an inert (nonreactive) substance, such as plastic or
ceramic, which increases the liquid
surface area for the liquid/gas interface.
The inert material helps to maximize
the absorption capability of the column.
In addition, the introduction of the
gas and liquid at opposite ends of
the column causes mixing to be more
efficient because of the counter-current
flow through the column.

10. In
general, absorbers can achieve
removal efficiencies grater than 95
percent.
 One potential problem with absorption
is the generation of waste-water, which
converts an air pollution problem to
a water pollution problem.

12. KEY TERMS
1. Absorbent: the liquid, usually water mixed
with neutralizing agents, into which the
contaminant is absorbed
2. Solute: the gaseous contaminant being
absorbed, such as SO2, H2S, and so forth
3. Carrier gas : the inert portion of the gas
stream, usually flue gas, from which the
contaminant is to be removed
4. Interface : the area where the gas phase and
the absorbent contact each other
5. Solubility : the capability of a gas to be
dissolved in a liquid

14. SPRAY
TOWER

15. Plate
Tower

16. PACKED
TOWER

18. PACKING MATERIAL USED IN PACKED TOWER

19. BUBBLE
CAPPED TRAY
TOWER

22. 2) ADSORPTION
 Adsorption
1.
2.
3.
is used when
The pollutant gas is incombustible or
difficult to burn
The pollutant is sufficiently valuable to
warrant recovery
The pollutant is in very dilute
concentration in the exhaust system

23. The
technique is based on the
reaction of gases on the solid
adsorbents.
The adsorption may be physical or
chemical.
In this method gas is passed through
a bed of adsorbents packed in the
specially designed towers to allow the
maximum contact between the two

24.  Physical
adsorption depends on the
temperature and pressure conditions.
Adsorption is promoted by increase in
pressure and decrease in temperature
 Chemical adsorption depends on the
reactivity of the gases and their bond forming
capacity with the surface of the adsorbent,
which provides surface for the reaction.
 Adsorbent can be regenerated for continuous
reuse.
 In some cases if is not economical to
regenerate, it better to dispose the pollutant
together with the adsorbent

25. Adsorption
is mostly pollutant specific.
e.g – Activated carbon, silica gel and
diatomaceous earth are suitable for
adsorption of water vapours from a gas
phase. It can also adsorb SO2 and NH3.
Activated carbon is most suited for
removal of organic gases from gas
stream.

26.  Carbon
adsorption systems are either
regenerative or non-regenerative.
 Regenerative system usually contains
more than one carbon bed. As one bed
actively removes pollutants, another bed
is being regenerated for future use.
 Non-regenerative systems have
thinner beds of activated carbon. In a
non-regenerative adsorber, the spent
carbon is disposed of when it becomes
saturated with the pollutant.

27. Regenerative Carbon Adsorption System

28. NonRegenerative
Carbon
Adsorption
System

29. PART-II
GASEOUS POLLUTION CONTROL

30. 3) COMBUSTION
In
many cases it is not possible to
remove the required amount of specific
pollutant from an exhaust stream by
techniques such as absorption or
adsorption.
The other technique available is
Combustion
Combustion refers to rapid oxidation of
substances (usually referred as fuels)
with evolution of heat.

31. •
•
To summarize, Combustion is
defined
as
rapid,
hightemperature
gas-phase
oxidation.
Simply, the contaminant (a
carbon-hydrogen substance) is
burned with air and converted
to carbon dioxide and water
vapor.

32.  Combustion
process involves three distinct
components
1. Fuel : -A solid, liquid or gaseous substance
with energy rich C-C or C-H bonds among
others, which are broken up during
combustion
2. Oxidant:- A substance which aids in
combustion process by breaking the
chemical bonds allowing the release of heat.
3. Diluent:- A substance that does not take
part in the combustion process but acts as
carrier of the fuel or the oxidants. Most
common diluents is Nitrogen present in
the air

33. I) FLARE OR
DIRECT FLAME COMBUSTION

34. Flare

35.  Combustible
gases are burned in open air, which
produces flare
 The flare is usually employed to remove
hydrocarbons and organic vapours, odorous
compounds in refineries and chemical works.
 It can also burn gases such as NH3, HCN or other
toxic or dangerous gases.
 If aromatic hydrocarbons are present, they
burn with Smokey flame. This can be avoided
by injecting a steam into the flame, which
reacts and forms hydrogen and CO both burn
smokelessly.
 However such steam-injected flare are little noisy

36. ADVANTAGES OF FLARE
Can be an economical way to dispose of
sudden releases of large amounts of
gas;
2. In many cases do not require
auxiliary fuel to support combustion;
and
3. Can be used to control intermittent or
fluctuating waste streams.
1.

37. DISADVANTAGES OF FLARE
1. Can produce undesirable noise, smoke,
heat radiation, and light.
2. Can be a source of SOx, NOx, and CO;
3. Cannot be used to treat waste streams
with halogenated compounds; and.
4. Released heat from combustion is lost

38. 4) INCINERATION OR AFTERBURNING
is method of reducing
gases, liquid and solid waste streams by
chemically altering the pollutant species
once they are formed.
 It is used to remove combustible air
pollutants (gases, vapours or odours)
 Incineration

39. I) THERMAL INCINERATION
+
Air

41. this method combustibles in the gas
stream are brought above auto
ignition temperatures and burn
with oxygen usually present in the
gas stream.
If sufficient oxygen is not
available, air is added by means of
blower fan.
Thermal incineration is carried out in
the temperature range of 10000 F to
15000F
Because of this cost is less and NOx
formation is also less.
In

42. Important
considerations in Design of
thermal incinerators are the “Three Ts”
Time- residence time should be 0.2 to
0.8 sec with 0.5 sec as a reasonable
guideline
Temperature (refer next slide)
Turbulence- complete mixing is very
important in case of odour control than
hydrocarbons, Less residence time is
required if proper mixing occurs

43. APPROXIMATE AVERAGE TEMPERATURE
REQUIREMENTS
Average temperature
range (0K)
Hydrocarbon oxidation
780 – 1030
Carbon monoxide
oxidation
950- 1060
Odour control via
oxidation
750 - 980

45. Thermal
Incinerator

46. ADVANTAGES
 Incinerators
are one of the most
positive and proven methods for
destroying VOC, with efficiencies up
to 99.9999% possible.
 Thermal incinerators are often the
best choice when high efficiencies
are needed and the waste gas is
above 20% of the LEL (Low explosive
limit).

47. II) RECUPERATIVE
INCINERATION

49.  Whichever
may be the method,
Temperature of gases leaving the
system vary from 700 to 2000 0F
 Thus considerable energy at high
temperatures is associated with the gas
stream.
 So that heat can be used to preheat the
contaminated gas entering into the
reactor.
 Heat exchanger used for this purpose
is called as recuperator or regenerator
 Use of recuperator reduce use of fuel and
makes it economical.
 Initial cost is high.

51. ADVANTAGES
1.
2.
3.
99.9999% efficiency can be achieved
Recuperative incinerators usually are more
economical than straight thermal
incinerators because they recover about
70% of the waste heat from the exhaust
gases.
This heat can be used to preheat incoming
air, and of ten times, sufficient waste heat
will be available for process heating, or to
generate steam or hot water

52. DISADVANTAGES
 Thermal
incinerators, including recuperative types,
are not well suited to streams with highly
variable flow because of the reduced residence
time and poor mixing during increased flow
conditions which decreases the completeness
of combustion.
 Incinerators, in general, are not recommended for
controlling gases containing halogen- or sulfurcontaining compounds because of the
formation of highly corrosive acid gases.

53. III) CATALYTIC INCINERATION

55. A
catalyst accelerates rate of chemical
reaction without undergoing a chemical
change itself.
 Residence time is in the range of 0.3 to 0.9
sec.
 Combustion reaction occurs on the surface
of the catalyst
 Most gases containing combustible
pollutants from industrial processes
are at a fairly low temperature.
Therefore some type of preheating
burner is used to bring waste gas up to
temperature , at which catalyst will be
effective.

56. range is 590 to 810 0K
Efficiency is 95% to 98%
Effluent gases are CO2, vapours and
nitrogen
Temperature
TEMPERATURE RANGES FOR DIFFERENT
POLLUTANT GASES
Industrial pollutant
Solvents
Average temperature
range (0K)
530 – 730
Vegetable and animal fats
530 - 640
Chemical process exhausts 480 - 670

57.  Catalyst
should be
Cheap
- Long lasting
- Should be able to function at required
temperatures.
- Capable of formed into variety of
shapes
 Examples of catalyst are
Platinum
Palladium
-

59. Catalytic
Incinerator

60. ADVANTAGES
1. Lower fuel requirements;
2. Lower operating temperatures;
3. Little or no insulation requirements;
4. Reduced fire hazards; and
5. Less volume/size required

61. DISADVANTAGES
1. High initial cost;
2. Catalyst poisoning is possible;
3. Particulate often must first be removed;
and
4. Spent catalyst that cannot be regenerated
may need to be disposed

62. THEORY QUESTIONS
Write short notes on
1. Absorption 2. Adsorption 3. Catalytic
incineration 4. Recuperation 5. Flare
6. Thermal incineration
A. Gaseous control of pollutants (note:- List all and
explain any one or two in detail)
B. Combustion method of gaseous pollution
control (note:-list all methods under combustion and
incineration and explain any one with figure)