Air Pollution-Measures to

Improve Air Quality

Cheung Wing Yu 7S (24)Cheung Wing Yu 7S (24)

Poon Shu Ying 7S (29)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+2CON2+CO2 2CO+O22CO2• *Catalysts are poisoned by lead compounds

it is essential to use unleaded petrol

A Catalytic converter

Limitation of Sulphur Content in F

uels

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 r

emoving harmful sulphur pollution • FGD can remove 90% of the sulphur dioxide emitted fro

m the boiler plant• The process is environmentally beneficial but expensive,

to the cost of electricity generation.

FGD Process System

Desulphurization of the flue gas

① Using limestone as the absorbent.

② Boiler flue gas is directed into the absorber inside which layers of grid packings with fountain type spray banks installed.

③ 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.

③ A regenerative gas heater is adopted to heat up the clean gas leaving the absorber to a temperature of >80oC.

④ This is to minimise the effect of condensation of flue gas and to ascertain its effective dispersion to the atmosphere.

⑤ 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 plat

es• repelled by plates with the same polarity and attracted to pl

ates with opposite polarity• Clean air is discharged• Fly ash collected is used to make construction materials (e

g. 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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