Environmental consequences of combustion processes

1
CHAPTER 3
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)
2
Combustion
Source WCI 2005
3
Combustion chamber
4
Combustion

• Emissions of concern
• Particulates/fly and bottom ash
• Carbon dioxide
• Sulphur oxides
• Nitrogen oxides
• Carbon monoxide
• Waste

5
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
6
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.

7
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

8
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.

9
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

10
Results of emissions

• Local pollution with particulates and gases
• Smog
• Acid rains
• Greenhouse effect/ Global warming
• Thermal pollution from cooling waters
• Waste generation

11
Local air pollution
12
Layers of Earths Atmosphere
13
Composition of the Atmosphere
14
Atmospheric concentration of selected species
Compound Concentration, ?g/m3 Concentration, ?g/m3
Compound Unpolluted Polluted
CO lt200 10000-30000
NO2 lt20 100-400
HC (except CH4) lt300 600-3000
O3 lt5 50-150
PANs lt5 50-250
Source Sieminski M., Srodowiskowe zagrozenia
zdrowia, Warszawa 2001
15
Smog
16
Smog

• 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

17
Sulphur smog / London smog

• History
• 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.
• Mechanism
• Inefficient combustion of high-sulphur coal gt
  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, gt 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.

18
Sulphur smog / London smog
Batter Sea power station, London, UK
19
Sulphur smog / London smog

• Impacts
• Deterioration of human made structures and
  materials
• Deterioration of flora
• Respiratory problems, allergies, asthma, lung
  damage
• Mitigation
• Burning of lower S-content coal
• Desulphurisation of flue gases
• Clean Air Acts, Sulphur Protocol

20
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
• History
• 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

21
Photochemical smog / LA smog
22
Photochemical smog / LA smog
Los Angeles
23
Photochemical smog / LA smog
LA Santiago Las Vegas
24
(No Transcript)
25
Photochemical smog / LA smog

• Impacts
• Impaired visibility
• Eye and respiratory system irritants
• Damage to lung tissue
• Vegetation damage
• Contribution to acidic deposition
• Materials destruction (rubber and some plastics)

26
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

27
Acid Rain
28
Acid Rain

• History
• 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.

Source Van Loon G.W., Duffy S.J., 2000.
29
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

30
Mechanism of acid rain formation
31
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

32
Impacts of acid rain

• 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

33
Impacts of acid rain

• 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

34
Mitigation

• Conventions/Targets
• 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

35
Ozone Depletion
36
Ozone Depletion

• Stratospheric Ozone absorbs harmful ultraviolet
  (lt340nm) 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

37
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

38
Ozone layer depletion

• Impacts
• 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)

39
Ozone Whats 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

40
Chlorine Content in Stratosphere