16_energy

30 prices per joule well suited to on the spot heat

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Unformatted text preview: miles of mains) • Extracted as oil-drilling byproduct – was once burned off at well head as means of disposal • Mostly methane, some ethane, and a little propane, butane • 3.5 times cheaper than electricity per energy content, 3 times cheaper than gasoline (at current $2.30 prices) per joule • Well-suited to on-the-spot heat generation: water heaters, furnaces, stoves/ovens, clothes dryers – more efficient than using fossil-fuel-generated electricity Winter 2007 Lecture 16 23 Winter 2007 24 6 Energy, Sustainability 03/15/2007 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 How much do we have left? How much do we use, and where do we get it? In 1995, we used 21.9 tcf (Tera-cubic feet, or 1012ft3); about 23 QBtu (24% of total) • Out of the 21.9 tcf used, 88% was domestic – 11.8% from Canada – 0.08% from Algeria (shipped in liquified form) – 0.03% from Mexico • Have used about 1,000 tcf to date • Estimated recoverable amount: 1100 tcf • 50 years at current rate • Estimates like this do account for future discoveries d o account – present proven reserves provide only 7 years’ worth Winter 2007 25 Winter 2007 26 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 Coal Use of Coal • • • • Coal is a nasty fuel that we seem to have a lot of Primarily carbon, but some volatiles (CO, CH4) CO2 + energy Reaction is essentially C + O2 CO energy Energy content varies depending on quality of coal, ranging from 4–7 Cal/g 4– • Highly undesirable because of large amounts of ash, sulphur dioxide, arsenic, and other pollutants • Also ugly to remove from the ground Winter 2007 Lecture 16 • 88% of the coal used in the U.S. makes steam for electricity generation • 7.7% is used for industry and transportation • 3.5% used in steel production • 0.6% used for residential and commercial purposes • 0.1% used on Halloween for trick-or-treaters Winter 2007 27 28 7 Energy, Sustainability 03/15/2007 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 When will coal run out? Estimated Worldwide Coal Reserves Country Amount (1012 tons) tons Energy Equiv. (QBtu) QBtu) 4.3 Former USSR Percentage of Total 56 103,100 United States 1.5 20 35,800 Asia 0.68 9 16,400 North America 0.60 8 14,300 West Europe 0.38 5 9,200 • • We use 109 tons of coal per year, so the U.S. supply alone could last as tons long as 1500 years at current rate Using variable rate model, more like 400–600 years 400– • • This assumes global warming doesn’t end up banning the use of coal doesn’ Environmental concerns over extraction also relevant Africa 0.11 1 2,400 Australia 0.06 1 1,300 South America 0.01 0 300 Total 7.64 100 – especially relevant if oil, gas are gone 182,900 Winter 2007 29 Winter 2007 30 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 The CO2 Problem Problem Hydrocarbon Reactions • Methane reaction: CO2 + 2H2O + energy CH4 + 2O2 CO 1g 4g 2.75 g 2.25 g 55 kJ • Octane reaction: 16CO2 + 18H2 O + energy 2C8H18 + 25O2 25O 16CO 18H 1g 3.51 g 3.09 g 1.42 g 48 kJ • For every pound of fuel you burn, you get about three times that in CO2 – one gallon of gasoline ~25 pounds of CO2 – occupies about 6 cubic meters (1500 gallons) of space Winter 2007 Lecture 16 31 Winter 2007 32 8 Energy, Sustainability 03/15/2007 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 CO2 on the rise… on rise… Longer-term View • The previous graph speaks for itself • We’re generating a lot of CO2 by burning fossil fuels by We’ – at predictable rate of 3 pounds per pound of fossil fuel • Calculated contribution per year: – 4 1020 J per year worldwide, 3 1020 J from fossil fuels – average of 7,000 Cal/kg 2.9 1 07 J/kg 1013 kg of fue...
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