Unit 26
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Unit 26. Environmental Problems associated with the use of fossil fuels. How air pollutants are formed?. By the incomplete combustion of fuels / petrol By the burning of impurities in fuels (such as sulphur dioxide from sulphur impurities.). Test for gases in car exhaust.

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Unit 26

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Unit 26

Environmental Problems associated with the use of fossil fuels


How air pollutants are formed?

  • By the incomplete combustion of fuels / petrol

  • By the burning of impurities in fuels (such as sulphur dioxide from sulphur impurities.)


Test for gases in car exhaust

  • Test for carbon dioxide

  • Turns lime water milky.

  • Test for carbon monoxide

  • Turns citrated blood cherry red.

  • Test for acidic gases

  • Turns universal indicator red.


Air pollutants from car exhausts

  • Carbon monoxide – from the incomplete combustion of petrol.

  • Unburnt hydrocarbons – such as benzene, C6H6, which is carcinogenic / causing cancer.

  • Carbon particulates (black smokes) – unburnt carbon particles from the incomplete combustion of fuel

  • Too small to be filtered by the hairs in the nose.

  • Causing serious lung diseases .


Air pollutants from car exhausts

  • Nitrogen oxides

  • High temperature in the cylinders of the car engine and electric sparks / lightening (thunderstorm)

  • Oxidation of nitrogen

  • N2(g) + O2(g) 2NO(g)

  • Oxidation of nitrogen oxide by air

  • 2NO(g) + O2(g)  2NO2(g)


Nitrogen oxides

  • Poisonous gases

  • Irritate and attack respiratory system

  • Dissolving in rainwater to form acid rain.

  • 2NO2(g) + H2O(l) HNO2(aq) + HNO3(aq)


Photochemical smog

  • Nitrogen oxides together with unburnt hydrocarbons produce photochemical smog.

  • Smog is poisonous.


Lead compounds

  • Tetraethyl lead – added to petrol for improving the burning of petrol

  • Lead compounds accumulate in our bodies. They have harmful effects on red blood cells and brain cells.


Pollutants from industry

  • From factories, power stations and incinerators

  • Same as that from car exhausts

  • With one more air pollutant (from the burning of sulphur impurities)

  • Sulphur dioxide


Sulphur dioxide

  • From the burning of coal or low grade petroleum

  • From the waste gas of incinerators as rubbish (waste paper) contains sulphur compounds as impurities.

  • Irritates the respiratory systems & affects the normal function of lungs

  • Causes cancer and even death.

  • SO2(g) + H2O(l) H2SO3(aq)


Acid rain

  • Is rainwater from non-polluted air acidic?

  • pH 5.6

  • Carbon dioxide dissolves in rainwater to form carbonic acid.

  • CO2(g) + H2O(l) H2CO3(aq)

  • Sulphur dioxide and nitrogen dioxide dissolve in rainwater to form acid rain.


Effect of acid rain

  • Harm to water lives

    • Acid rain makes rivers and lakes more acidic. Harmful to water lives and even kills them.

  • Damage to forests

    • Forests seriously damaged by acid rain. Trees are stunted. Leaves drop off and the trees die.


Effect of acid rain

  • Damage to metalwork

    • Speeding up the rate of corrosion of metals

  • Damage to building materials

    • Acid rain attacks buildings made up of limestone.


Greenhouse effect

  • Carbon dioxide in the atmosphere acts like glass of a greenhouse. It allows high energy radiation from the sun to penetrate the atmosphere and warms the Earth’s surface. The high energy radiation is re-radiated as infra-red radiation. However, the infra-red radiation is trapped by the atmosphere (carbon dioxide). The Earth is thus warmed up.


Greenhouse gases

  • Carbon dioxide, methane, nitrogen oxides, ozone and chlorofluorocarbons are greenhouse gases.


Ways to reduce the greenhouse effect (to reduce carbon dioxide emission)

  • Plant more trees

  • Stop burning fossil fuels

  • Stop cutting down trees.


Methods for reducing air pollution

  • Using unleaded petrol in cars.

    • For reducing the amount of lead compounds in air.


Methods for reducing air pollution

  • Installing catalytic converter in car exhaust system

  • It is a honeycomb structure.

  • Installed in the exhaust system of cars.

  • On structure, platinum and other transition metal are deposited.


Catalytic converters

carbon dioxide (CO2)

nitrogen (N2)

water (H2O)

carbon monoxide (CO)

nitrogen oxides (NOx)

hydrocarbons (HC)

stainless steel case

honeycomb-shaped

support


Shortcoming of catalytic converters

  • Solid lead compounds deposit on the surface of catalyst and block the honeycomb.

  • Catalytic converters can only be fitted with motor-cars which are run on unleaded petrol.


How does catalytic converter work?

  • Nitrogen oxide reacts with carbon monoxide when they pass over the catalyst.

  • 2NO(g) + 2CO(g) N2(g) + 2CO2(g)

  • The carbon monoxide and unburnt hydrocarbons are oxidized in the presence of catalyst to form harmless products.

  • 2CO(g) + O2(g)  2CO2(g)

  • 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(l)


Using scrubbers in power stations

  • Removing up to 95% of carbon dioxide.

  • Two methods of scrubbing

    • Dry scrubbing

    • Wet scrubbing


Dry scrubbing

  • Powdered limestone (CaCO3) is blown into the combustion chamber where it decomposes.

  • CaCO3(S) CaO(s) + CO2(g)

  • The calcium oxide reacts with sulphur dioxide to form calcium sulphite.

  • CaO(s) + SO2(g)  CaSO3(s)

  • These products are washed away as a slurry – a mixture of solids and water.


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Using scrubbers in power stations


Wet scrubbing

  • Sulphur dioxide is removed by the action of calcium oxide and water (I.e., calcium hydroxide solution).

  • CaO(s) + H2O(l) Ca(OH)2(aq)

  • Ca(OH)2(aq) + SO2(g)  CaSO3(s)+ H2O(l)


By the electrostatic precipitators in industry

  • Removes 99% of the particulates.


Electrostatic precipitators

  • Dirty gases pass through a strong electric field.

  • The particles become charged.

  • The charged particles are then collected on plates of opposite charge.


Role of Governemnt

  • Legislation

  • Monitoring and investigating

  • planning


Oil splliage

  • Petroleum is toxic and flammable.

  • Pollutes beaches and spoils recreation resorts.

  • Blocks the oxygen supply of water lives.

  • Clogs the feathers of birds and prevents them from flying abd swimming.

  • Poisoned sea birds and fishes.


Cleaning up oil spillage

  • Using detergents to emulsify the oil.


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