R. Parthasarathy. University of Oregon

Transcription

1 Physics 161:Physics of Energy and Environment Physics 161: Physics of Energy and the Environment November 4, 2008 Prof. Raghuveer Parthasarathy

2 Physics 161:Physics of Energy and Environment Lecture 10: Announcements Vote: Don t forget! Reading: Wolfson, Chapter 5 Problem Set 5: (posted on line later today) Due NEXT Thursday, November 13, 5pm. Midterm: We *have not* finished grading the midterm, but are on track to finish by Wednesday. I therefore can't comment much today, but I'll certainly discuss it at length in class on Thursday. Sorry to keep you in suspense. For now, all I'll say from our preliminary work is that some people did well; some did poorly; and many results surprise me. I'll be trying to learn from all this how to structure the rest of the course.

3 Physics 161:Physics of Energy and Environment One comment now: Advice Be sure to study your lecture slides / notes. (I m sure many of you do this; it s clear that many do not!) Study does not mean glance at while doing other things, but rather read carefully within a day or two of class; annotate; ask yourself whether you could explain material to others. If you don t understand: ASK. This is your responsibility. If you don t ask, I have two options: assume you understand the material assume you re too lazy to care (None of the above? ow would I know?)

4 Physics 161:Physics of Energy and Environment Advice Does the following look familiar?

5 Physics 161:Physics of Energy and Environment ydroelectric power ΔE grav =ΔE kinetic =ΔE electric Power = ΔE grav / t = Mgh/t = (M/t)gh Rate of mass flow (e.g. in kg/s). Could write ΔM / Δt Consider a h = 100 meter dam, and perfect conversion of energy. What mass flow rate would give 1 kw of electrical power generation?

6 Physics 161:Physics of Energy and Environment Power = (M/t)gh ydroelectric power 1000 W = (M/t) (9.8 m/s 2 ) 100 m 1000 W = (M/t) (10 m/s 2 ) 100 m 1000 W = (M/t) 1000 m 2 /s 2. (M/t) = 1 kg/s 10 m/s 2 Units? Consistently SI, so must be kg/s; or could express W in terms of kg, m, s.

7 Physics 161:Physics of Energy and Environment Advice Exact slides from lecture 5! Exceptionally similar to a midterm problem!

8 Physics 161:Physics of Energy and Environment Procedure: A. Review notes B. Do I understand this? Yes: Good. Advice No: Ask for help. (Or study with classmates) C. Solve similar problem on exam. D. But I can t solve the problem. Are you sure your answer to B is correct? (More Thursday)

9 Physics 161:Physics of Energy and Environment Last Lecture 85% of our energy comes from Fossil Fuels Fossil Fuels: ydrocarbons (molecules composed of carbon and hydrogen) formed from the decomposition of organisms long ago Long ago = hundreds of millions of years i.e. long accumulation of stored chemical energy

10 Physics 161:Physics of Energy and Environment Fossil fuels Coal Oil and Natural Gas Fossil fuels

11 Physics 161:Physics of Energy and Environment Petroleum Petroleum: Oil and Natural Gas Ancient marine life ocean floor sediments. Pressure, temperature rock + organic liquids and gases Petroleum Petroleum: these liquids and gases, though often used to refer to liquid only

12 Physics 161:Physics of Energy and Environment Petroleum Petroleum in many sedimentary rocks: typically useless Accumulates in porous rock, trapped by impermeable rock

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14 Physics 161:Physics of Energy and Environment Petroleum In these rare geological structures, useful reservoirs of petroleum. (Useful = economically feasible) ow to find these deposits? Not easy! Reflections of sound waves, for example Only 1 in 10 exploratory drillings strike oil

15 Physics 161:Physics of Energy and Environment istory: First oil well Petroleum 1859, Titusville Pennsylvania Colonel Edwin Drake Many active oil seeps in the area Many wells had previously struck oil. The problem: they didn t want oil, they wanted water! Drake s well: 69 feet. Oil kerosene

16 Physics 161:Physics of Energy and Environment Petroleum Petroleum: What is it? A mixture of hydrocarbons The gas part: natural gas mostly methane, C 4 (the simplest, lightest hydrocarbon) [Remember] [Draw: C 4 ] carbon hydrogen Size m from World of Molecules

17 Physics 161:Physics of Energy and Environment Petroleum Petroleum: What is it? A mixture of hydrocarbons The gas part: natural gas The liquid part: crude oil various components (and impurities: sulfur, oxygen) must be separated to generate useful products: refining

18 Physics 161:Physics of Energy and Environment Fraction Gas Gasoline Kerosene Fuel oil Lubricating oil Greases Paraffin (wax) Pitch and tar Petroleum Products # Carbons 1 to 5 5 to to to to and up 20 and up igh Boiling point ( C) 164 to 30 Petroleum ether 5 to 7 30 to 90 Solvent; dry cleaning 30 to to 275 Up to 375 Above 350 Semisolid Melts at Residue in boiler Typical uses Gaseous fuel Motor fuel Stove, diesel, jet fuel Furnace Oil Lubrication Lubrication Candles Roofing, paving Note: higher molecular weight higher boiling point

19 Physics 161:Physics of Energy and Environment In gasoline e.g... heptane C 7 16 [draw] octane C 8 18 [draw] nonanec 9 20 [draw] decane C [draw] Gasoline carbon hydrogen (Greater octane / heptane ratio less knocking in engines) Energy content 50 MJ / kg [Energy released from chemical bonds (chemical energy)}

20 Physics 161:Physics of Energy and Environment Petroleum isn t just for burning 7% (in Other ) lubricants, roadmaking, petrochemical feedstocks Petroleum Products

21 Physics 161:Physics of Energy and Environment Petrochemical Feedstocks Plastics! (& countless medicines, paints, food ingredients, and other chemicals) Why? Organic chemistry: Carbon [Draw] Poly methyl methacrylate, i.e. acrylic glass, plexiglass A polymer: chainlike, repeating molecule A future view of petroleum use... Did they actually burn such valuable stuff?

22 Physics 161:Physics of Energy and Environment Fraction # Carbons Gas 1 to 5 Gasoline Kerosene Fuel oil 15 to 18 Lubricating oil Greases Paraffin (wax) Pitch and tar Petroleum Products 5 to to to and up 20 and up igh Boiling point ( C) 164 to 30 Petroleum ether 5 to 7 30 to 90 Solvent; dry cleaning 30 to to 275 Up to 375 Above 350 Semisolid Melts at Residue in boiler Typical uses Gaseous fuel Motor fuel Stove, diesel, jet fuel Furnace Oil Lubrication Lubrication Candles Roofing, paving Note: higher molecular weight higher boiling point

23 Physics 161:Physics of Energy and Environment Distillation ow do we separate these components of crude oil? (Note the different boiling points) [Ask] Fractional distillation vaporizecrude oil (> 400 C) vapor goes to a tower with a temperature gradient (T changes with height) vapors condense at various points along the tower, depending on their boiling point

24 Physics 161:Physics of Energy and Environment Fractional distillation vaporizecrude oil (> 400 C) Distillation tower with a temperature gradient vapors condense at various points along the tower, depending on their boiling point In the diagram, does T increase or decrease going from bottom to top along the tower? A. increase B. decrease energyinst.org.uk

25 Physics 161:Physics of Energy and Environment Distillation In the diagram, does T increase or decrease going from bottom to top? A. increase B. decrease Cool a bit: heavy hydrocarbons become liquid; drawn off Cool more: next lighter hydrocarbons... Cool more:... kerosene... gasoline... Lightest molecules remain gas even at coolest temperatures, at top energyinst.org.uk

26 Physics 161:Physics of Energy and Environment (Pictures) Oil Refinery near Rodeo, SF Bay area, California, USA QT Luong Distillation Distillation unit, Coryton Refinery, UK energyinst.org.uk

27 Physics 161:Physics of Energy and Environment Coal Coal: From decaying plant matter, on land, 100 s of millions of years ago. Acidic swamps. Ferns, etc. decay (anaerobic, without O 2 ); compressed into layers peat. cut peat, Scotland. (photo: U. Wyoming)

28 Physics 161:Physics of Energy and Environment Coal Coal: From decaying plant matter, on land, 100 s of millions of years ago. Acidic swamps. Ferns, etc. decay (anaerobic, without O 2 ); compressed into layers peat. Geology: Buried further. Slowly... Temperature, pressure Most oxygen, hydrogen leaves A black solid: Coal

29 Physics 161:Physics of Energy and Environment Coal Coal: Trapped chemical energy from long dead plants Mostly carbon (an example of a chemical structure of coal. Each vertex is a C. [Wikipedia: Karol Glab]) Many varieties, grades e.g. anthracite, 80% carbon e.g. bituminous, 50% carbon the rest is oxygen, hydrogen, sulfur,...

30 Physics 161:Physics of Energy and Environment Review What is this a structure of? A. methane B. hexane C. octane D. coal C

31 Physics 161:Physics of Energy and Environment Review What is this a structure of? A. methane B. hexane C. octane D. coal C C C C C C

32 Physics 161:Physics of Energy and Environment Carbon Carbon forms four chemical bonds bond: a pair of shared electrons that connect atomic nuclei some bonds are double bonds, indicated by double lines [none shown so far] 4 bonds at each C (shown: hexane) some C C some C C C C C C C

33 Physics 161:Physics of Energy and Environment Review Arrange methane, hexane, and decane by hydrogen to carbon ratio. (Can you do this without counting atoms?) A. all are the same B. decane > hexane > methane C. hexane > methane > decane D. methane > hexane > decane

34 Physics 161:Physics of Energy and Environment Review Arrange methane, hexane, and decane by hydrogen to carbon ratio. (Can you do this without counting atoms?) A. all are the same B. decane > hexane > methane C. hexane > methane > decane D. methane > hexane > decane 4 / 1C 14 / 6C certainly < 4! All C s except ends have 2 per C. Longer ratio approaches 2 > Coal (lots of C)

35 Physics 161:Physics of Energy and Environment Burning Why is the relative amount of vs. C important? Let s see what it means to burn a fuel... (i.e. combustion)

36 Physics 161:Physics of Energy and Environment Burning Burning: a chemical reaction Burning methane: C O 2 CO O + Energy Meaning: and 2 water molecules one carbon dioxide (CO 2 ) molecule... to form... and release energy* Combines with 2 oxygen molecules (each O 2 has two oxygen atoms) 1 methane molecule * 55 MJ per kg of methane

37 Physics 161:Physics of Energy and Environment Burning Burning: a chemical reaction Burning methane: Note: C O 2 CO O + Energy and release energy* Total energy is conserved same on both sides Left side (before burning): more chemical energy Right side: Chemical energy released, i.e. can be converted into other forms (typically thermal) * 55 MJ per kg of methane

38 Physics 161:Physics of Energy and Environment Burning Burning: a chemical reaction Burning methane: Note: C O 2 CO O + Energy Chemical elements are conserved (except in nuclear reactions) So 1 C atom on left side means there must be 1 C on the right side. Also: 4 O atoms on left, 4 O on right; etc. If you re unaware that molecules are made of atoms, that 2 O is 2 and 1 O, please don t tell me.

39 Physics 161:Physics of Energy and Environment Burning Burning: a chemical reaction Burning methane: Note: C O 2 CO O + Energy Chemical elements are conserved (except in nuclear reactions) Necessarily: 1 methane molecule 1 CO 2 molecule

40 Physics 161:Physics of Energy and Environment Burning octane: Burning octane 2 C O 2 16 CO O + Energy Equivalent to C O 2 8 CO O + Energy, but non integers are usually frowned upon Note# atoms of each element are balanced on each side of the equation 1 octane molecule 8 CO 2 molecules and release energy* * 48 MJ per kg of octane

41 Physics 161:Physics of Energy and Environment In general: Burning hydrocarbon + # O 2 # CO 2 + # 2 O + Energy # = various numbers, to balance the equation CO 2, 2 O, and energy are the products! CO 2 : The major greenhouse gas; climate change 2 O: mostly harmless Energy: What want. Energy from breaking C C and C chemical bonds (& forming C O and O bonds)

42 Physics 161:Physics of Energy and Environment In general: Burning hydrocarbon + # O 2 # CO 2 + # 2 O + Energy # = various numbers, to balance the equation CO 2, 2 O, and energy are the products! All the carbon from the hydrocarbon CO 2 So: you should be able to figure out the following:

43 Physics 161:Physics of Energy and Environment Carbon emissions Arrange methane, hexane, and coal by carbon dioxide emission per molecule burned, starting with the most emission (i.e. > means more CO 2 emission than... ) A. all are the same B. coal > hexane > methane C. hexane > methane > decane D. methane > hexane > coal

44 Physics 161:Physics of Energy and Environment Carbon emissions Arrange methane, hexane, and coal by carbon dioxide emission per molecule burned A. all are the same B. coal > hexane > methane C. hexane > methane > decane D. methane > hexane > coal Coal: lots of C per molecule; Methane: only one ( 1 CO 2 )

45 Physics 161:Physics of Energy and Environment Carbon emissions Arrange oil, natural gas, and coal by carbon dioxide emission per molecule burned, starting with the most emission (i.e. > means more CO 2 emission than... A. all are the same B. oil > coal > natural gas C. coal > oil > natural gas D. natural gas > oil > coal

46 Physics 161:Physics of Energy and Environment Carbon emissions CO 2 is the major greenhouse gas (will discuss more later). I.e. it s bad! Natural gas emits less CO 2 than other fossil fuels. Should examine per unit of energy, rather than per molecule; trend still holds (Fig.) Unfortunately, there s lots of coal...

47 Physics 161:Physics of Energy and Environment In general: Burning hydrocarbon + # O 2 # CO 2 + # 2 O + Energy # = various numbers, to balance the equation CO 2, 2 O, and energy are the products! A key point: CO 2 is an unavoidable product of fossil fuel combustion! If there s combustion, there s CO 2 emission!