Air PollutionMeasures to
Improve
Air Quality
Cheung Wing Yu 7S (24)
Poon Shu Ying 7S (29)
Use of
Unleaded Petrol
Tetraethyllead(IV) [(CH3CH2)4Pb]
• anti-knock agent
• produces lead oxide which combine with
the free radicals produced in combustion
during burning
slows down the reaction;
makes it smoother
prevent knocking
• Lead halides is volatile and inactivate the
catalysts in the catalytic converter
• Reduce the amount of toxic lead
compounds in the air
use of unleaded petrol
Installation of
catalytic
converters in car
exhaust systems
• Major source of air pollution nitrogen oxides,
carbon monoxide, unburnt hydrocarbons
• Catalytic converter reduce the emission of
these pollutants
• Converter contains: precious metals, rhodium
and platinum, as catalyst
• In catalytic converter:
2NO+2CON2+CO2
2CO+O22CO2
• *Catalysts are poisoned by lead compounds
it is essential to use unleaded petrol
A Catalytic converter
Limitation of
Sulphur Content
in Fuels
Sulphur dioxides
• Emitted from factories and power plants
burning fossil fuels
• Dissolve in rain
water to form
acid rain:
SO3(aq)+H2O(l)H2SO4(aq)
Determination of SO2
• Bubbling air through acidified potassium
dichromate solution, the colour of the
solution will change from orange to dark
green as sulphur dioxide is a reducing
agent:
3SO2 (aq) + Cr2O72- (aq) + 2H+(aq) → 3SO42-(aq) + 2Cr3+(aq) + H2O(l)
Desulphurization
of the flue gas
Flue-gas Desulphurization (FGD)
• Sulphur compounds are the main cause of acid rain
• flue-gas desulphurization (FGD) (煙氣脫硫) process of
removing harmful sulphur pollution
• FGD can remove 90% of the sulphur dioxide emitted
from the boiler plant
• The process is environmentally beneficial but expensive,
to the cost of electricity generation.
FGD Process System
Desulphurization of the flue gas

Using limestone as the absorbent.

Boiler flue gas is directed into the absorber
inside which layers of grid packings with
fountain type spray banks installed.

The wetted walls of the grid packings serve as
surfaces for the interaction of recycle slurry
droplets containing a suspension of limestone
and reaction products with the flue gas flowing
concurrently.

A regenerative gas heater is adopted to heat up the
clean gas leaving the absorber to a temperature of
o
>80 C.

This is to minimise the effect of condensation of flue
gas and to ascertain its effective dispersion to the
atmosphere.

The filtrate generated therefore is directed to the waste
water treatment system for treatment before
discharging.
Installation of
Electrostatic
Precipitators in
Power Plants
Fly ash
• Generated by coal-fire power plants
• Cannot be burnt
• Cause pollution if released directly
install electrostatic precipitators in power
plant
Electrostatic Precipitators
• particles pass through an electrical field
• charged particles are resulted
• pass through a series of alternately charged collection
plates
• repelled by plates with the same polarity and attracted to
plates with opposite polarity
• Clean air is discharged
• Fly ash collected is used to make construction materials
(eg. cement), or for landfill purpose
Installation of low
nitrogen oxide
burners in
power plants
Nitrogen Oxides
• ‘nitrogen oxides’ (NOx) usually refers to NO and
NO2
• formed in at least 2 ways:
(i) nitrogen in the combustion air reacts with
oxygen at high temperature in a series of
complex reaction to form nitrogen monoxide
(ii) fossil fuels may contain nitrogen compounds.
When these fuels are burnt, the nitrogen content
is oxidized.
• The power plants in Hong Kong have been
equipped with low nitrogen oxide burners
• The low NOx burner system utilizes
combustion control method
 reduce NOx formation
 reduce air pollution
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