physics of energy and the environment - university of...

Physics 161:

Physics of Energy and the Environment

Prof. Raghuveer Parthasarathy

[email protected]

Fall 2008

Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008

November 4, 2008

R. Parthasarathy

University of Oregon

Fall 2008

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.

R. Parthasarathy


Fall 2008

Advice• One comment now:

• 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 explainmaterial 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? How would I know?)


R. Parthasarathy


Fall 2008

Advice

• Does the following look familiar?


R. Parthasarathy


Fall 2008

Hydroelectric powerPhysics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008

• ΔEgrav=ΔEkinetic=ΔEelectric

• Power = ΔEgrav / 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?

R. Parthasarathy


Fall 2008

Hydroelectric powerPhysics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008

• Power = (M/t)gh

• 1000 W = (M/t) (9.8 m/s2) 100 m

• 1000 W = (M/t) (10 m/s2) 100 m

• 1000 W = (M/t) 1000 m2/s2.

• (M/t) = 1 kg/s

• Units? Consistently SI, so must be kg/s; or could express W in terms of kg, m, s.

≈ 10 m/s2

R. Parthasarathy


Fall 2008

Advice

• Exact slides from lecture 5!

• Exceptionally similar to a midterm problem!


R. Parthasarathy


Fall 2008

Advice

Procedure:

A. Review notes

B. Do I understand this?

Yes: Good.

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)


R. Parthasarathy


Fall 2008

Last Lecture• ≈ 85% of our energy comes from Fossil Fuels• Fossil Fuels: Hydrocarbons (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


R. Parthasarathy


Fall 2008

Fossil fuels• Fossil fuels

– Coal

– Oil and Natural Gas


R. Parthasarathy


Fall 2008

Petroleum• Petroleum: Oil and Natural Gas

• Ancient marine life → ocean floor sediments. Pressure, temperature → rock + organic liquids and gases


PetroleumPetroleum: these liquids and gases, though often used to refer to liquid onlyR. Parthasarathy


Fall 2008

Petroleum• Petroleum in many sedimentary rocks: typically useless

• Accumulates in porous rock, trapped by impermeable rock


R. Parthasarathy


Fall 2008

R. Parthasarathy


Fall 2008

Petroleum

• In these rare geological structures, useful reservoirs of petroleum. (Useful = economically feasible)

• How to find these deposits? – Not easy!

– Reflections of sound waves, for example

– Only 1 in 10 exploratory drillings strike oil


R. Parthasarathy


Fall 2008

PetroleumHistory: First oil well• 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


R. Parthasarathy


Fall 2008

PetroleumPetroleum: What is it?• A mixture of hydrocarbons

• The gas part: natural gas– mostly methane, CH4 (the simplest, lightest hydrocarbon) [Remember]

– [Draw: CH4]


carbon

hydrogen

from “World of Molecules”

Size 4 × 10‐10 m

R. Parthasarathy


Fall 2008

PetroleumPetroleum: 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


R. Parthasarathy


Fall 2008

Petroleum Products

Note: higher molecular weight→ higher boiling point


Roofing, pavingResidue in boilerHighPitch and tar

CandlesMelts at 52‐5720 and upParaffin (wax)

LubricationSemisolid18 and upGreases

LubricationAbove 35016 to 20Lubricating oil

Furnace OilUp to 37515 to 18Fuel oil

Stove, diesel, jet fuel175 to 27512 to 16Kerosene

Motor fuel30 to 2005 to 12Gasoline

Solvent; dry cleaning30 to 905 to 7Petroleum ether

Gaseous fuel‐164 to 301 to 5Gas

Typical usesBoiling point (°C)# CarbonsFraction

R. Parthasarathy


Fall 2008

Gasoline• In gasoline

– e.g....

– heptane C7H16 [draw]

– octane C8H18 [draw]

– nonane C9H20 [draw]

– decane C10H22 [draw]

• (Greater octane / heptane ratio → less “knocking” in engines)

• Energy content ≈ 50 MJ / kg [Energy released from chemical bonds (chemical energy)}


carbon hydrogen

R. Parthasarathy


Fall 2008

Petroleum Products

Petroleum isn’t just for burning

≈ 7% (in “Other”) →lubricants, roadmaking, petrochemical feedstocks


R. Parthasarathy


Fall 2008

Petrochemical Feedstocks•→ Plastics! (& countless medicines, paints, food ingredients, and other chemicals)

• Why? Organic chemistry: Carbon


Poly‐methyl‐methacrylate, i.e. “acrylic glass,” “plexiglass”

A polymer: chainlike, repeating molecule

[Draw]

A future view of petroleum use... “Did they actually burn such valuable stuff?”

R. Parthasarathy


Fall 2008

Petroleum Products

Note: higher molecular weight→ higher boiling point


Roofing, pavingResidue in boilerHighPitch and tar

CandlesMelts at 52‐5720 and upParaffin (wax)

LubricationSemisolid18 and upGreases

LubricationAbove 35016 to 20Lubricating oil

Furnace OilUp to 37515 to 18Fuel oil

Stove, diesel, jet fuel175 to 27512 to 16Kerosene

Motor fuel30 to 2005 to 12Gasoline

Solvent; dry cleaning30 to 905 to 7Petroleum ether

Gaseous fuel‐164 to 301 to 5Gas

Typical usesBoiling point (°C)# CarbonsFraction

R. Parthasarathy


Fall 2008

Distillation• How do we separate these components of crude oil? (Note the different boiling points) [Ask]

• Fractional distillation– vaporize crude 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


R. Parthasarathy


Fall 2008

Distillation• Fractional distillation

– vaporize crude oil (> 400 °C)– 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. decreaseenergyinst.org.uk

R. Parthasarathy


Fall 2008

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

R. Parthasarathy


Fall 2008

Distillation• (Pictures)


energyinst.org.uk

Distillation unit, CorytonRefinery, UKOil Refinery near Rodeo, SF Bay

area, California, USA – QT Luong

R. Parthasarathy


Fall 2008

Coal• Coal: From decaying plant matter, on land, 100’s of millions of years ago.

• Acidic swamps. Ferns, etc. decay (anaerobic, without O2); compressed into layers → peat.


cut peat, Scotland. (photo: U. Wyoming)

R. Parthasarathy


Fall 2008

Coal• Coal: From decaying plant matter, on land, 100’s of millions of years ago.

• Acidic swamps. Ferns, etc. decay (anaerobic, without O2); compressed into layers → peat.

• Geology: Buried further. Slowly...– Temperature, pressure

– Most oxygen, hydrogen leaves

– A black solid: Coal


R. Parthasarathy


Fall 2008

Coal• Coal: Trapped chemical energy from long‐dead plants

• Mostly carbon

• Many varieties, grades– e.g. anthracite, ≈ 80% carbon

– e.g. bituminous, ≈ 50% carbon– the rest is oxygen, hydrogen, sulfur, ...


(an example of a chemical structure of coal. Each vertex is a C. [Wikipedia: Karol Glab])R. Parthasarathy


Fall 2008

ReviewWhat is this a structure of?

A. methane

B. hexane

C. octane

D. coal


CH

HH H

R. Parthasarathy


Fall 2008

ReviewWhat is this a structure of?

A. methane

B. hexane

C. octane

D. coal


CH

HH HC

H

HCH

HCH

HCH

HCH

HR. Parthasarathy


Fall 2008

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‐H


CH

HH HC

H

HCH

HCH

HCH

HCH

H

R. Parthasarathy


Fall 2008

ReviewArrange 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


R. Parthasarathy


Fall 2008

ReviewArrange 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


D. methane > hexane > decane


4H / 1C 14H / 6C – certainly < 4!

All C’s except ends have 2 H per C. Longer → ratio approaches 2

> Coal (lots of C)

R. Parthasarathy


Fall 2008

Burning

• Why is the relative amount of H vs. C important?

• Let’s see what it means to burn a fuel... (i.e. combustion)


R. Parthasarathy


Fall 2008

Burning• Burning: a chemical reaction

• Burning methane:CH4 + 2 O2 → CO2 + 2 H2O + Energy

• Meaning:


1 methane molecule

Combines with 2 oxygen molecules (each O2 has two oxygen atoms)

... to form...

one carbon dioxide (CO2) moleculeand 2 water molecules

and release energy*

* 55 MJ per kg of methane

R. Parthasarathy


Fall 2008




and release energy*Note:

• 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

R. Parthasarathy


Fall 2008




Note:

• 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 H2O is 2 H and 1 O, please don’t tell me.

R. Parthasarathy


Fall 2008




Note:

• Chemical elements are conserved (except in nuclear reactions)

• Necessarily: 1 methane molecule → 1 CO2 molecule

R. Parthasarathy


Fall 2008

Burning octane• Burning octane:

2 C8H18 + 25 O2 → 16 CO2 + 18 H2O + Energy• Equivalent to

C8H18 + 12.5 O2 → 8 CO2 + 9 H2O + 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 CO2 molecules


and release energy*

* 48 MJ per kg of octane

R. Parthasarathy


Fall 2008

Burning• In general:

hydrocarbon + # O2 → # CO2 + # H2O + Energy# = various numbers, to balance the equation

• CO2, H2O, and energy are the products!

• CO2: The major greenhouse gas; → climate change

• H2O: mostly harmless

• Energy: What want. Energy from breaking C‐C and C‐H chemical bonds (& forming C‐O and H‐O bonds)


R. Parthasarathy


Fall 2008




• All the carbon from the hydrocarbon → CO2


So: you should be able to figure out the following:

R. Parthasarathy


Fall 2008

Carbon emissions

Arrange methane, hexane, and coal by carbon dioxide emission per molecule burned, starting with the most emission (i.e. > means “more CO2

emission than...”)

A. all are the same

B. coal > hexane > methane


D. methane > hexane > coal


R. Parthasarathy


Fall 2008

Carbon emissions

Arrange methane, hexane, and coal by carbon dioxide emission per molecule burned

A. all are the same

B. coal > hexane > methane


D. methane > hexane > coal


Coal: lots of C per molecule; Methane: only one (→ 1 CO2)R. Parthasarathy


Fall 2008

Carbon emissions

Arrange oil, natural gas, and coal by carbon dioxide emission per molecule burned, starting with the most emission (i.e. > means “more CO2

emission than...”

A. all are the same

B. oil > coal > natural gas

C. coal > oil > natural gas

D. natural gas > oil > coal


R. Parthasarathy


Fall 2008

Carbon emissionsCO2 is the major greenhouse gas (will discuss more later). I.e. it’s bad!


Natural gas emits less CO2 than other fossil fuels.

Should examine per unit of energy, rather than per molecule; trend still holds (Fig.)

Unfortunately, there’s lots of coal...

R. Parthasarathy


Fall 2008




• A key point: CO2 is an unavoidable product of fossil fuel combustion! If there’s combustion, there’s CO2 emission!


R. Parthasarathy


Fall 2008

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