1 E nvironmental consequences of combustion processes – Part I (Smog, Acid Rain, and ozone depletion) Dr. Hassan Arafat Department of Chem. Eng. An-Najah.

1

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

depletion)

Dr. Hassan ArafatDepartment of Chem. Eng.

An-Najah University

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

CHAPTER # 3

2

Combustion

Source: WCI 2005

Combustion

chamber

FUEL(COAL,

OIL, GAS,W ASTE)

CHONSCl

Si, Al, Fe,K, Ca

Hg

other

AIRN 2

O 2

COCO 2

bottom ash,slag

?

Hg o

Hg?HgO

HgCl2flyash

HCl

SO 2

SO 3

N 2

N 2ONONO 2

H 2O

FLUE GAS=>

(CLEANINGPOSSIBLE)

4

Combustion

• 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

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.

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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.

H3C C O O

O

Na

Peroxyacetyl nitrate(PAN)

H2C CH CH

O

Acrolein

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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

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Results of emissions

• Local pollution with particulates and gases

• Smog• Acid rains• Greenhouse effect/ Global warming• Thermal pollution from cooling waters• Waste generation

Local air pollution

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Layers of Earth’s Atmosphere

Thermosphere

Mesosphere

Stratosphere

Troposphere

Earth

Ozone layer

-80 -40 0 40 80

Temperature (C)

Temperature

Stratosphere

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Composition of the Atmosphere

G a s F o rm u la Pe rc e nt b y vo lu m e

N it ro ge n N 2 78 .0 8

O xyg e n O 2 20 .9 4

A rg o n A r 0.9 3 4

C a rb o n d io x ide C O 2 0.0 3 3

N e o n N e 0.0 0 18 2

H e liu m H e 0.0 0 05 2

M e tha n e C H 4 0.0 0 01 5

K ry p to n K r 0.0 0 01 1

H yd ro g e n H 2 0.0 0 00 5

N it ro us o x ide N 2O 0.0 0 00 5

X e no n X e 0.0 0 00 0 9

N o te : av e ra g e fo r d ry , c le a n a ir

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Atmospheric concentration of selected species

Compound Concentration, g/m3

Unpolluted Polluted

CO <200 10000-30000

NO2 <20 100-400

HC (except CH4)

<300 600-3000

O3 <5 50-150

PANs <5 50-250

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

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Smog

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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

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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 => 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

Batter Sea power station, London, UK

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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

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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

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Photochemical smog / LA smog

N2 + O2 NO + NO2

NO2 + UV NO + O*

O2 + UV 2O*

O2 + O* O3

O3 + VOC O2 + PAN + other smog oxidants

Overall reaction:NO2 + VOC + O2 +UV NO + O3 + PAN + other oxidants

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Photochemical smog / LA smog

Los Angeles

Photochemical smog / LA smog

LA

Santiago

Las Vegas

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World Automobile Production, 1950-2003

0

10

20

30

40

50

1950 1970 1990 2010

Source: AAMA, DRI-WEFA, Global Insight

Mill

ion

Ve

hicl

es Passenger Cars

Light Trucks

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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)

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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

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Acid Rain

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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.

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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

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Mechanism of acid rain formation

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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

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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

Herten, Germany, 1908 & 1969

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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

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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

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Ozone Depletion

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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. milesCFCs & HCFCs are the primary

causes

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Antartic/Arctic ozone holeOzone 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

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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)

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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

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Chlorine Content in Stratosphere

Year

1985 1990 1995 2000 2005 2010 2015 2020 2025 20302

4

6

8

10

12

14

Without controls

With 1996 phase-out