PHYS Energy and Environmental Physics

Transcription

1 PHYS Energy and Environmental Physics Lecture 5 Fossil Fuels II Oleh Klochan

2 This Lecture Energy Content of Fossil Fuels Problems with Fossil Fuels Production issues Pollution Availability

3 Hydrocarbons Fossil fuels contain hydrocarbons molecules containing hydrogen and carbon. C n H m e.g. CH 4 (methane), C 5 H 12 (pentane), C 6 H 6 (benzene) When the fuel is burnt in oxygen the carbon combines with oxygen to make CO 2 and the hydrogen combines with oxygen to make H 2 O.

4 Burning Hydrocarbons Methane CH 4 CH 4 + 2O 2 CO 2 + 2H 2 O Pentane C 5 H 12 C 5 H O 2 5CO 2 + 6H 2 O The energy released in these reactions varies for different hydrocarbons.

5 Fuel Energy Content of Fuels Energy (kj/kg) Hydrogen (H 2 )* 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.

6 Hydrogen Hydrogen (H 2 ) 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.

7 Hydrogen to Carbon The more hydrogen atoms relative to carbon atoms in a fuel the higher its energy content. So methane (CH 4 ) the main constituent of natural gas with four carbons to every hydrogen has the highest energy. Oil products (e.g. octane C 8 H 18 ) typically have just over two hydrogen atoms per carbon and have less energy. Coal with a little over one hydrogen per carbon has low energy. Ethanol (C 2 H 5 OH) is also quite low since it contains oxygen and so is already partly oxidised.

8 Hydrogen to Carbon More Carbon More Hydrogen Coal Oil Natural Gas More Energy per kg

9 Problems with Fossil Fuels Problems associated with Production Accidents (coal mining, oil rig explosions) Pollution (e.g. oil spills) Pollution and Health Problems due to Use Sulfur dioxide, nitrogen dioxide (producing particulates or aerosols) Climate Change Greenhouse Gases (Mostly CO 2 ) Availability issues Peak Oil

10 Accidents UK Coal Mining Deaths ( ) 85,745 (average 1058 per year) China Coal Mining deaths ( ) 51,267 (average 5126 per year) Sizhuang Coal Mine in Shizong county of the city of Qujing, November 10, A powerful gas explosion hit two underground platforms (43 miners dead).

11 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.

12 Pollution Due to Fossil Fuel Use Pollution due to fossil fuel burning can be: Greenhouse pollution Primarily due to CO 2 which is an inevitable product of hydrocarbon burning. CH 4 and N 2 O are also greenhouse gases. Main cause of global warning. Other Pollution Toxic gases such as CO, SO 2, Nitrogen oxides. Particulate pollution. Acid Rain. Health problems and other environmental damage.

13 Pollution Pollution can arise from: Sulfur dioxide Coal and oil contain about 1% of sulfur that burns to make sulfur dioxide (SO 2 ). Nitrogen oxides Nitrogen in fossil fuels burns to produce nitrogen oxides including N 2 O (Nitrous oxide) and NO 2 (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.

14 Acid Production Sulfur dioxide and nitrogen oxides can undergo further reactions. 2SO 2 + O 2 2SO 3 SO 3 + H 2 O H 2 SO 4 (sulfuric acid) NO 2 + OH HNO 3 (nitric acid)

15 Acid Rain These acids dissolve in rain producing the phenomenon of acid rain. Even unpolluted rain is slightly acidic because of dissolved CO 2. 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.

16 Acid rain has damaging effects on natural vegetation and forests and on freshwater ecosystems. Acid Rain Build up of acid in lakes can lead to loss of fish populations. Trees killed by acid rain ph of rain in eastern US

17 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

18 Fine Particle Pollution Fine particle or particulate pollution is due to tiny particles less than 10µm (0.01mm) in diameter. These can be sulfate aerosols or solid particles of ash or soot. Burning of fuels is a major source. Particulates are a serious health problem. The particles are small enough to lodge deep in the lungs and do substantial damage.

19 Fine Particle Pollution Measured by PM 10 index. Particles of 10 µm diameter or smaller in µg m 3 Or: PM 2.5 index. Particles of 2.5 µm diameter or smaller in µg m 3

20 Health Effects Statistically high levels of fine particle pollution (PM 10 or PM 2.5 ) 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.

21 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

22 Fine Particle Pollution Air Pollution (PM) Paris, France Melbourne, Australia Sydney, Australia London, UK Australian standard Los Angeles, USA Tokyo, Japan Beijing, China Shenyang, China Jakarta, Indonesia Lucknow, India Kanpur, India Chonquing, China Tianjin, China Kolkata, India Delhi, India Cairo, Egypt micrograms/m3

23 Air pollution Aug

24 Pollution is worst in developing countries where environmental regulations are not strong. However, significant pollution problems still exist in developed countries Cairo one of the most polluted cities. Smog in Los Angeles

25 Air Quality Standards Standards have been established for many air pollutants. For example: Pollutant Sulfur Dioxide Nitrogen oxides Averaging Australian US Period Standard Standard 1 day 0.08 ppm 0.14 ppm 1 year 0.03 ppm 0.05 ppm PM 10 1 day 50 µg m µg m 3

26 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.

27 Controlling Pollution Scrubbers remove SO 2 from power station exhaust gases by passing the gas through a slurry of calcium carbonate (crushed limestone) in water. The SO 2 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.

28 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 CO 2 produced by fossil fuel burning. Methane (CH 4 ) 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.

29 Greenhouse Gases Gas Sources GWP Lifetime Concentration CO 2 Fossil Fuels years Methane Rice fields, cattle 385 ppm years 1.7 ppm Nitrous Oxide Fertilizers, deforestation years 0.3 ppm CFCs Aerosols, refrigerators years ppm GWP is relative global warming potential compared with CO 2

30 CO 2 (Keeling Curve) Build up of CO 2 accounts for only about half of CO 2 produced (e.g. by fossil fuel burning). Highest concentration of CO2 in 2 million years

31 CO 2 Production Methane CH 4 CH 4 + 2O 2 CO 2 + 2H 2 O Pentane C 5 H 12 C 5 H O 2 5CO 2 + 6H 2 O CO 2 is a normal product of burning any hydrocarbon fuel.

32 Hydrogen to Carbon More Carbon More Hydrogen Coal Oil Natural Gas More CO 2 Pollution More Energy per kg

33 CO 2 From Fossil Fuels Coal 90.5 Diesel fuel 68.8 Petrol 66.9 Natural Gas kg of CO2 per GJ of energy Coal is the dirtiest fuel in terms of CO 2 production per unit of energy. Natural Gas is the cleanest, and oil is intermediate.

34 Carbon Capture and Storage Can we remove CO 2 from power station emissions in the same way as scrubbers remove SO 2? 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.

35 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 CO 2 to leak into the atmosphere.

36 Carbon Capture Carbon dioxide can be captured by dissolving in an organic solvent that selectively absorbs CO 2. The CO 2 can then be released from the solvent by heating it.

37 Transport CO 2 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).

38 Carbon storage The CO 2 can be stored underground in locations such as depleted oil and gas reservoirs.

39 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.

40 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. Demand for oil Since demand for oil is continuing to rise: Oil Production After peak production will fall Price of oil should rise steeply when the peak is reached. Is this what we are seeing now?

41 Oil Prices

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

43 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.

44 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 average temperature to well below 2 C above pre-industrial levels; to aim to limit the increase to 1.5 C, since this would significantly 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 with the best available science. Video

45 Next lecture Alternatives to fossil fuels

46 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 (C 8 H 18 ) in the hydrocarbon mix.

47 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)

48 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.

49 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 (CH 3 CH 2 ) 4 Pb. 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.