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Energy and Environment. E nvironmental consequences of combustion processes – Part I (Smog, Acid Rain, and ozone depletion). Dr. Hassan Arafat Department of Chem. Eng. An-Najah University. (these slides were adopted, with modification, from Ms. Paulina Bohdanowicz , KTH Institute, Sweden).

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energy and environment
Energy and Environment

Environmental consequences of combustion processes – Part I(Smog, Acid Rain, and ozone depletion)

Dr. Hassan Arafat

Department of Chem. Eng.

An-Najah University

(these slides were adopted, with modification, from Ms. Paulina Bohdanowicz , KTH Institute, Sweden)


Source: WCI 2005


In order to meet forecasted global electricity demand it is estimated that 2000 MW of additional capacity will have to be installed every week over the next 20 years

Source: WCI 2005

combustion chamber1
Combustion chamber
  • The type and quantity of compounds created depend on:
    • the type and composition of fuel,
    • combustion conditions (type of furnace, air:fuel ratio, and especially temperature)
    • CO2, depending on fuel composition and generator efficiency
    • Sulphur oxides (SOx) from sulphur oxidation - more than 95 % SO2, remaining is SO3
    • CO, depending on oxidation efficiency of fuel (up to 30% in incomplete combustion)
    • 20-90 % of N in fuel is converted into NOx. Additionally depending on the temperature of combustion and residence time, N from air combines with O from air
  • The extras ? - dioxines and furans (coming from combustion of chlorinated plastics)- highly carcinogenic and very dangerous, mainly in waste incineration plants
  • Coal: small quantities of uranium, radium and thorium present in the coal result in the radioactivity of the fly ash (of varying level)
  • Emissions of concern:
    • Particulates/fly and bottom ash
    • Carbon dioxide
    • Sulphur oxides
    • Nitrogen oxides
    • Carbon monoxide
    • Waste
flue gas composition from a typical coal fired power plant
Flue gas composition from a typical coal-fired power plant

Source: Liss R., Saunders A., Power generation and the Environment, Oxford 1990; Turns S.R., An introduction to combustion, concepts and application, Singapore 2000


Air Pollutants

  • Carbon monoxide
      • colorless, odorless, non-irritating poison
      • attaches to hemoglobin; reduces oxygen carrying capacity
      • results in headaches, drowsiness and asphyxiation
  • Hydrocarbons
      • denotes a large group of volatile organic compounds
      • some are carcinogens, poison etc.

Air Pollutants

  • Sulfur Dioxide
      • colorless corrosive gas
      • respiratory irritant and poison
      • can result in H2SO4
  • Particulates
      • small pieces of solid or liquid materials dispersed in the atmosphere
      • 0.005-100 um
      • reduction in visibility, respiratory problems

Air Pollutants

  • Nitrogen Oxides
      • critical component for smog formation
      • compounds acid precipitation problems
  • Photochemical Oxidants
      • products of secondary atmospheric reactions driven by solar energy
      • e.g., O3 PAN (peroxyacetyl nitrate), acrolein
      • strong oxidants, eye irritant etc.

Air Pollutants

  • Lead
      • released as metal fumes or suspended particles
        • 2 million metric tons per year
        • 5-10 times more in urban than rural areas when leaded gas is used
      • major source was leaded gasoline
  • Carbon Dioxide
      • generally considered non-toxic and innocuous
      • not listed as air pollutant
      • increasing concentrations have been related to global warming
waste generated per year in a 1000 mwe coal power plant
Waste generated per year in a 1000 MWe coal power plant

Coal characteristics: CV of 20 MJ/kg and a sulphur content of 1%.

Plant characteristic: efficiency 34%, electricity production 65% of the total electricity it is capable of producing (650 MW-years in one year)

comparative emission levels from a 300 mw power plant
Comparative emission levels from a 300-MW power plant
  • Source: Interstate Natural Gas Association of America. Natural Gas and the Environment. (accessed March 18, 2002)
results of emissions
Results of emissions
  • Local pollution with particulates and gases
  • Smog
  • Acid rains
  • Greenhouse effect/ Global warming
  • Thermal pollution from cooling waters
  • Waste generation
atmospheric concentration of selected species
Atmospheric concentration of selected species

Source: Siemiński M., Środowiskowe zagrożenia zdrowia, Warszawa 2001

urban air quality
19.7% of EU inhabitants are exposed to excessive levels of ozone (2000)

9.6% - Denmark

18.3% - Finland

41.2% - Greece

69.9% - Italy

95.4% - Austria

36.2% of EU inhabitants are exposed to excessive levels of particulate matter (PM10) (2000)

36.2% - Denmark

56.0% - Sweden

95.6% - Netherlands

97.6% - Greece

100.0% - Italy

100.0% - Portugal

Urban air quality
Form of air pollution in which atmospheric visibility is partially obscured by a haze consisting of solid particulates and/or liquid aerosols

Occurs mainly in urban areas but not exclusively

Smoke + fog = smog

sulphur smog london smog

dates back to the 14th century

the "Killer Smog" reported in 1952, claimed 4000 fatalities in London - by far the most devastating event of this type in recorded history.


Inefficient combustion of high-sulphur coal => high concentration of unburned carbon soot and other particulates, acidic sulfate aerosols (such as sulfuric acid, H2SO4) as well as elevated levels of sulphur dioxide.

SO2 and soot, => sulphuric acid, sulfate aerosols

Characteristic brownish haze - formed usually under conditions of high humidity and relatively low temperatures, characterised by reducing and acidic properties.

In case of humid atmospheres carbon particulates serve as condensation nuclei for water droplets resulting in formation of fog, highly irritant.

Classical smog can persist for days when atmospheric conditions allow.

Sulphur smog / London smog
sulphur smog london smog1
Sulphur smog / London smog

Batter Sea power station, London, UK

sulphur smog london smog2

Deterioration of human made structures and materials

Deterioration of flora

Respiratory problems, allergies, asthma, lung damage


Burning of lower S-content coal

Desulphurisation of flue gases

Clean Air Acts, Sulphur Protocol

Sulphur smog / London smog
photochemical smog la smog
process by which ozone is being created at low altitudes – ground level

encountered in automobile rich cities – with specific climatic conditions


mid-1940s - repeated occurrence of heavy injury to vegetable crops in the Los Angeles area - traced to high concentrations of ozone that appeared to be created at low altitudes

Photochemical smog / LA smog
photochemical smog la smog3
Photochemical smog / LA smog



Las Vegas

asian brown cloud1
Aerosols, ash, soot

3km thick

80% man-made



local wood /dung /kerosene burning,

forest fires – clearing

can travel half way round the globe in a week

solar radiation reduced by up to 15%

Hundreds of thousands of deaths annually (2mln in India alone)

Acid rain

Warming of the atmosphere

Climate changes (floods & draughts)

Other Brown Clouds: South America, Mediterranean

The regional and global impact of the haze will intensify over the next 30 years

Asian Brown Cloud
photochemical smog la smog4

Impaired visibility

Eye and respiratory system irritants

Damage to lung tissue

Vegetation damage

Contribution to acidic deposition

Materials destruction (rubber and some plastics)

Photochemical smog / LA smog

Photochemical smog / LA smog

  • How to reduce smog (main goal is to reduce VOC and NOx):
    • PCV valves
    • Leak-proof caps
    • Tune-up
    • Emission tests
    • Catalytic converters
    • Public transportation
acid rain

First studies on rain chemistry were conducted in late 1800s, but modern investigations date back to 1960s.

Nowadays the chemistry of atmospheric precipitation is fairly well known.

The phenomenon of acid rain has been known and studied from 1950s.

1960 – lowered fish production in Scandinavian lakes

In 1972 it became an international public policy issue at the first United Nations Conference on the Environment held in Stockholm.

The transboundary effect of atmospheric pollution has been officially accepted, based on the fact that sulphur and nitrogen oxides are commonly emitted in one location while the acid deposition occurs in distant area.

In Sweden and Norway around 90% of the acid deposition comes from other countries, primarily UK, Germany, Poland and other Central Europe countries. Canada receives major acid contribution form the US.

Acid Rain

Source: Van Loon G.W., Duffy S.J., 2000.

acid rain1
Acid Rain
  • Rain that is more acidic than normal because it contains sulfuric acid or nitric acid
  • result of SOx, NOx, acidic particulates in air
  • involves all forms of acid deposition, even if rain is not involved
  • Utility plants contribute to 70% SO2 production and 30% NOx production in USA
  • Coal contains as high as 5% sulfur
sox emissions of energy options
SOx emissions of energy options

Source: Boyle et al. 2003

nox emissions of energy options
NOx emissions of energy options

Source: Boyle et al. 2003

impacts of acid rain
Acidification of water ecosystems

Natural surface waters - pH of 6-8, acidified waters pH 3 (conditions unbearable for many aquatic species, which eventually die, and lakes become lifeless)

Today some 14000 lakes in Sweden are affected by acidification. Similar situation is in Canada

Nitrogen can induce eutrophication, which results in depletion of oxygen in water, further affecting the aquatic flora and fauna

Impacts of acid rain
impacts of acid rain1
Acidification of soil ecosystems

Areas with highly siliceous bedrock (granite, gneisses, quartzite, and quartzstone - acidic) – most vulnerable (Scandinavia, Canada, United Kingdom and Alps).

Acid deposition - enhances leaching of important cations such as calcium, potassium, magnesium and sodium - unavailable to plants as nutrients (soil depletion)

Reduced fertility of soil

Some metals (i.e. aluminium, and mercury) leach from acidified soils into waters

Impacts of acid rain
impacts of acid rain2
Damage of flora

A 1999 survey of European forests - one out of every four trees suffered the loss of 25% or more leaves or needles

Decay of structural materials

Marble, sandstone, rubber, metals

Herten, Germany, 1908 & 1969

Impacts of acid rain
impacts of acid rain3
Human health problems

respiratory problems including lung disorders, asthma, and bronchitis due to suspended atmospheric sulphates

indirect effect of acidification on humans is related to the presence of toxic metals in the food chain

Impacts of acid rain

the Convention on Long Range Transboundary Air Pollution (1994 Sulphur Protocol) – with amendments

5th Environmental Action Programme and by the Council of Ministers of the Environment)

1999 Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-Level Ozone

The annual cost of the multi-effect protocol is estimated at the level of 2.8 billion euro for the year 2010.

The returns, in the form of improved health and reduced corrosion to buildings would by that same year amount to euro 12.8 billion.

Plus there are benefits that do not carry a price tag…


Ozone Depletion

  • Stratospheric Ozone absorbs harmful ultraviolet (<340nm) radiation from the Sun
  • 1% loss of ozone = 2% increase in UV radiation = 106 extra cancers
  • ozone hole = 7.7 million sq. miles
  • CFCs & HCFCs are the primary causes
antartic arctic ozone hole
Ozone hole above the the Antarctic on October 3, 1999 (NASA satellites)

A record size of ozone hole was 10.5 million square miles on Sept 19, 1998

Red color would denote high ozone levels; blue denotes low

Antartic/Arctic ozone hole
ozone layer depletion

Humans (a 10% drop in stratospheric ozone levels is likely to lead globally to

300000 more skin cancers,

1.6 million more eye damage – cataracts) per year

Reptiles (damage to eggs)

Plants (reduced photosynthesis, increased sensitivity to stress)

Damage to marine ecosystems (direct and indirect)

Ozone layer depletion
ozone what s being done
Ozone: What’s Being Done?
  • Montreal Protocol (1985)
  • complete phase-out of CFCs by 2000
  • critical need to come up with inexpensive non-halogenated coolants
  • if everyone abides, ozone loss should peak between 2001 and 2005
  • ozone levels should return to normal