PHYS 1211 - Energy and Environmental Physics

Lecture 5

Fossil Fuels II

Oleh Klochan and Michael Ashley

This Lecture

• Energy Content of Fossil Fuels

• Problems with Fossil Fuels

– Production issues

– Pollution

– Availability

Hydrocarbons

• Fossil fuels contain hydrocarbons —molecules containing hydrogen and carbon.

• CnHm

• e.g. CH4 (methane), C5H12 (pentane), C6H6 (benzene)

• When the fuel is burnt in oxygen the carbon combines with oxygen to make CO2and the hydrogen combines with oxygen to make H2O.

Burning Hydrocarbons

• Methane CH4

CH4 + 2O2 CO2 + 2H2O

• Pentane C5H12

C5H12 + 8O2 5CO2 + 6H2O

The energy released in these reactions depends on the particular hydrocarbonsinvolved.

Energy Content of Fuels

Fuel Energy (kJ/kg)

Hydrogen (H2)* 140,400

Methane (Natural Gas) 55,000

Petrol# 47,000

Ethanol* 31,000

Bituminous Coal 29,000

Lignite 17,000

* Not a fossil fuel# Other oil products such as Diesel, Avgas, Fuel oil are similar.

HydrogenHydrogen (H2) has the highest energy

content of any fuel. It is used to fuel the

space shuttle and Europe’s Ariane 5

rocket. However, it is not a naturally

available fuel (despite being the most

common element in the universe).

Hydrogen to carbon ratio

The more hydrogen atoms relative to carbon atoms in a fuel

the higher its energy content.

So methane (CH4), the main constituent of natural gas, with

four hydrogen atoms to every carbon atom, has the highest

energy.

Oil products (e.g. octane C8H18) typically have just over two

hydrogen atoms per carbon and have less energy.

Coal with a little over one hydrogen per carbon has

comparatively low energy.

Ethanol (C2H5OH) is also quite low in energy since it

contains oxygen and so is already partly oxidised.

Hydrogen to Carbon

More

HydrogenMore

Carbon

More

Energy

per kg

Coal Oil Natural

Gas

Problems with fossil fuels

• Problems associated with production– Accidents (coal mining, oil rig explosions)

– Pollution (e.g. oil spills, fracking chemicals)

– Large amounts of water usage (washing coal, fracking)

• Pollution and health problems due to use– Sulfur dioxide, nitrogen dioxide (producing particulates

or aerosols)

– Radioactive nuclei emitted into the atmosphere

• Climate change– Greenhouse Gases (mostly CO2, but also methane)

• Availability issues– “Peak Oil”

Accidents

• UK Coal Mining Deaths (1873-1953)

– 85,745 (average 1058 per year)

• China Coal Mining deaths (2000-2009)

– 51,267 (average 5126 per year)

Sizhuang Coal Mine in Shizong county of the city of Qujing , November 10, 2011. A powerful gas explosion hit two underground platforms (43 miners dead).

Recent Events

Soma coal mine explosion

(May 2014) in Turkey (301

deaths)

BP Deepwater Horizons oil rig

explosion (Apr 2010) caused 11

deaths and a major oil spill with

4.9 billion barrels of oil released

into the Gulf of Mexico.

Pollution Due to Fossil Fuel Use

Pollution due to fossil fuel burning can be:

• Greenhouse pollution– Primarily due to CO2 which is an inevitable product of

hydrocarbon burning.

– CH4 and N2O are also greenhouse gases.

– Main cause of global warning.

• Other Pollution– Toxic gases such as CO, SO2, Nitrogen oxides.

– Radioactivity.

– Particulate pollution.

– Acid Rain.

– Health problems and other environmental damage.

Pollution

• Pollution can arise from:

• Sulfur dioxide– Coal and oil contain about 1% of sulfur that burns to make

sulfur dioxide (SO2).

• Nitrogen oxides– Nitrogen in fossil fuels burns to produce nitrogen oxides

including N2O (Nitrous oxide) and NO2 (Nitrogen Dioxide).

• Carbon Monoxide– Incomplete burning of fuels can produce CO.

• Heavy Metals– Trace elements in coal contribute to pollution including

mercury, arsenic, lead and other heavy metals, some of which are radioactive.

Acid Production

• Sulfur dioxide and nitrogen oxides can undergo further reactions.

2SO2 + O2 2SO3

SO3 + H2O H2SO4 (sulfuric acid)

NO2 + OH HNO3 (nitric acid)

Acid Rain

These acids dissolve in rain producing the phenomenon of acid rain.

Even unpolluted rain is slightly acidic because of dissolved CO2. It has a typical pH of 5.6 (where 7 is neutral and low numbers are acidic).

In industrial areas rain with pH of 4 is not uncommon.

Acid Rain

Trees killed by acid rain

Acid rain has damaging effects on natural vegetation and forests and on freshwater ecosystems.

Build up of acid in lakes can lead to loss of fish populations.

pH of rain in eastern US

Sulfate Aerosols

• The sulfuric acid from fossil fuel pollution forms tiny particles that remain suspended in the air.– These are known as sulfate aerosols.

• Sulfate aerosols have a significant effect on the climate.– They reflect sunlight back to space and have a

cooling effect.

– They also contribute to “fine particle pollution”

• Removing aerosols will lead to an increasein global warming.

Fine Particle Pollution

• “Fine particle” or “particulate” pollution is due to tiny particles less than 10mm (0.01mm) in diameter.

– These can be sulfate aerosols or solid particles of ash or soot.

– Burning of fuels is a major source.

– An interesting supercomputer simulation of fine particulates over Australia in December 2006

• Particulates are a serious health problem.

– The particles are small enough to lodge deep in the lungs and do substantial damage.

Fine Particle Pollution

• Measured by PM10 index. Particles of 10 mm diameter or smaller in mg m–3

• Or: PM2.5 index. Particles of 2.5 mm diameter or smaller in mg m–3

Health Effects

• Statistically high levels of fine particle pollution (PM10 or PM2.5) can be linked to:

– High death rates from respiratory and cardiovascular causes - including strokes.

– Increased number of heart attacks.

– Increase in severe asthma attacks.

– Increased risk of lung cancer.

– Many other respiratory health problems.

Air Pollution

• Air pollution from coal fired power stations in the USA is estimated to cause about 30,000 deaths per year. (Abt Associates report,

2000)

• The WHO estimates that world-wide deaths from outdoor air pollution are 865,000 per year. – India 120,600 deaths per year

– China 275,600 deaths per year

Fine Particle Pollution

0 20 40 60 80 100 120 140 160 180

micrograms/m3

Cairo, Egypt

Delhi, India

Kolkata, India

Tianjin, China

Chonquing, China

Kanpur, India

Lucknow, India

Jakarta, Indonesia

Shenyang, China

Beijing, China

Tokyo, Japan

Los Angeles, USA

London, UK

Sydney, Australia

Melbourne, Australia

Paris, France

Air Pollution (PM)

Australianstandard

Air pollution

Aug 2 – 2017

http://aqicn.org

Cairo —one of the most

polluted cities.

Pollution is worst in developing countries where environmental regulations are not strong.

However, significant pollution problems still exist in developed countries

Smog in

Los Angeles

Air Quality Standards

Pollutant Averaging

Period

Australian

Standard

US

Standard

Sulfur

Dioxide

1 day 0.08 ppm 0.14 ppm

Nitrogen

oxides

1 year 0.03 ppm 0.05 ppm

PM10 1 day 50 mg m–3 150 mg m–3

Standards have been established for many air pollutants. For example:

Controlling Pollution

• Pollution in the developed world has been significantly reduced by “clean air” policies.

• These have included.

– Emission controls for cars including the fitting of catalytic converters, and use of unleaded fuel.

– Incorporation of technology to limit sulfur emissions and particulates from fossil fuel power stations.

Controlling Pollution

Scrubbers remove SO2 from power station exhaust gases by passing the gas through a slurry of calcium carbonate (crushed limestone) in water. The SO2 reacts with the carbonate to make Calcium sulfate.

Electrostatic precipitators remove particulates from power station exhaust gases by charging the particles and passing the gas through an electric field.

Greenhouse Pollution

• Greenhouse pollution is the release of the gasses that contribute to global warming through the greenhouse effect.

• The main source of greenhouse pollution is the CO2 produced by fossil fuel burning.

• Methane (CH4) is also a greenhouse gas so unburnt natural gas dues to leakage or incomplete combustion also contributes.

• Nitrous oxide (discussed earlier) is also a greenhouse gas.

Greenhouse Gases

Gas Sources GWP Lifetime Concentration

CO2Fossil Fuels 1 100

years

385 ppm

Methane Rice fields,

cattle21 12 years 1.7 ppm

Nitrous

Oxide

Fertilizers,

deforestation310 120

years

0.3 ppm

CFCs Aerosols,

refrigerators1300-

12000

70-100

years

0.003 ppm

GWP is relative global warming potential compared with CO2

CO2 (Keeling Curve)

• Build up of CO2 accounts for only about half of CO2

produced (e.g. by fossil fuel burning).

• Highest concentration of CO2 in 2 million years

CO2 Production

• Methane CH4

CH4 + 2O2 CO2 + 2H2O

• Pentane C5H12

C5H12 + 8O2 5CO2 + 6H2O

CO2 is a normal product of burning any hydrocarbon fuel.

Hydrogen to Carbon

More

HydrogenMore

Carbon

More

Energy

per kg

Coal Oil Natural

Gas

More CO2

Pollution

CO2 From Fossil Fuels

49.9

66.9

68.8

90.5

0 10 20 30 40 50 60 70 80 90 100

kg of CO2 per GJ of energy

Natural Gas

Petrol

Diesel fuel

Coal

Coal is the dirtiest fuel in terms of CO2 production per unit of energy. Natural Gas is the cleanest, and oil is intermediate.

Carbon Capture and Storage

• Can we remove CO2 from power station emissions in the same way as scrubbers remove SO2?

• This is the idea behind Carbon Capture (Carbon Sequestration) or so called “clean coal” technologies.

• If we can do this we can continue to use coal while complying with greenhouse gas reduction targets.– For Australia with abundant coal reserves this is very

attractive.

Carbon Capture and Storage

• While sulfur is a trace constituent, carbon is one of the main components of the fuel.– There is a lot more material to remove and store.

• Such schemes will involve:– Capture of the carbon dioxide from the exhaust gases.

– Transport to a suitable storage location.

– Long term storage in a way that will not allow CO2 to leak into the atmosphere.

Carbon Capture

• Carbon dioxide can be captured by dissolving in an organic solvent that selectively absorbs CO2.

• The CO2 can then be released from the solvent by heating it.

Transport

• CO2 could be transported by pipeline.

• Alternatively it could be compressed and transported as a liquid

• Similar to transportation of liquid petroleum gas.

• America's coal-fired power plants generate 1.5 billion tons per year. Capturing that would mean filling 30 million barrels with liquid CO2 every single day (x1.5 the volume of crude oil consumed).

Carbon storage

The CO2 can be

stored underground

in locations such as

depleted oil and

gas reservoirs.

Hubbert’s Peak

• In 1956 US Geologist M. King Hubbert predicted that US oil production would peak in the early 1970s.

– His prediction was ridiculed by experts at the time, but until recently had proved correct.

US oil production peaked in 1971 and was in decline up to 2008.

“Peak Oil”

Applying the same methods to world oil production predicts

that we are now close to the peak (so called “Peak oil”) This

implies that we have burnt about half the world’s total oil

supply.

Oil

Production

After peak

production

will fall

Demand for oilSince demand for oil is continuing

to rise:

Price of oil should rise steeply

when the peak is reached.

Is this what we are seeing now?

Oil Prices

US Oil production is now increasing again (due to unconventional oil sources)

Are we really near the Peak?• Current proven oil reserves should last for about 50

years at current production rates.

• In 2008 the figure was 41.6 years.

• We are finding new reserves of oil much faster than we are using it.

• So some experts argue that there is plenty of oil.– Higher prices will make it economic to explore in more

remote areas (the arctic and deep ocean) and extract oil from sources such as oil shales (oil source rock not yet “cooked” into oil). We have already seen the example of oil from tar sands.

– Even if they are correct we will still likely to have to adjust to considerably higher oil prices.

Paris climate conference 2015

At the Paris climate conference (COP21) in December 2015, 195 countries

adopted the first-ever universal, “legally binding” global climate deal.

• a long-term goal of keeping the increase in global averagetemperature to well below 2°C above pre-industrial levels;

• to aim to limit the increase to 1.5°C, since this wouldsignificantly reduce risks and the impacts of climate change;

• on the need for global emissions to peak as soon as possible,recognising that this will take longer for developing countries;

• to undertake rapid reductions thereafter in accordance withthe best available science.

• Video

Next lecture

• Alternatives to fossil fuels

Octane Rating of Fuels

• Liquid Fuels (e.g. Petrol) are also classified according to their “octane rating”.

• This is an often misunderstood quantity.

• Octane rating is unrelated to the energy content of the fuel.

– Despite the fact that “high octane” seems to have entered our language with the meaning of “high energy”

• Octane rating is also not a measure of the quantity of octane (C8H18) in the hydrocarbon mix.

Octane Rating

• Octane rating measures the resistance of a fuel to predetonation (also known as “knock” or “pinging”).

• This occurs when the fuel mixture in the engine is ignited as a result of compressional heating, rather than by the spark plug.

Heating by adiabatic compression

(see lecture 5)

Octane Rating

• This predetonation effect can reduce performance and in some cases cause damage to the engine.

• The problem is increased for higher compression ratio engines, which offer higher engine performance.

– Cars with these engines may need to use higher octane fuel.

– However there is no advantage in using higher octane fuel in a engine designed for regular fuel.

Octane Rating

• The octane rating of a fuel is determined by the mix of hydrocarbons, and by additives.

• A widely used “anti-knock” additive was tetraethyl lead (CH3CH2)4Pb.

• However, concern about the toxicity of the lead has resulted in the phasing out of leaded petrol for motor fuel in most countries.

• Tetraethyl lead is still used in aviation fuels.