Clicker Question
What fraction of CU electricity and heat come from its own
cogeneration facility burning natural gas in 2015?
A) 100%
B) 80%
C) 50%
D) 20%
E) 0%
“The Cogeneration plant currently
meets all the electrical
requirements for the campus.
Additionally, it exports an average
of 8 MW of electricity to PSCo.
The plant is operated and
maintained by the staff within
Facilities Management.” (2003)
Reading Assignment
Chapter 5.1-5.4 for today and all of Chapter 5 for Friday.
Homework Assignment
Homework #4 will be posted on Wednesday and due the following
Wednesday, February 17, 2016.
Note that Exam #1 in class is coming up on
Wednesday, February 10, 2016.
Make sure to come 5 minutes early!
-- My office hours are Monday 1-2 pm,
Tuesday 11 am –12 pm
Also available by appointment – just email me.
-- The class Teaching Assistants will also be available in the Physics Help
Room (downstairs on the Duane 2B level).
Prasanth Prahladna : Tuesdays 3-4 pm, Paul Quelet : Wednesdays 10-11 am,
Ivan Kurz: Wednesdays 11 am – 12 pm
If we want to generate 100 MegaJoules of energy in electricity,
we typically need to burn 300 MegaJoules worth of chemical
energy of coal (i.e. 33% efficiency heatwork).
Book uses the notation 100 MJe and 300 MJth
What happened to the other 200 MegaJoules?
Just heating the atmosphere or a lake or river… (wasted).
However, if we have a need for heat energy nearby, we can
use some (often not all) of this “wasted energy” !
• Heating the passenger compartment of a car or bus.
• Heating buildings or a factory.
• Selling steam in New York City for building heat.
Cogeneration
1
“In Sweden, nearly half the population lives in houses
heated by ''district heating'': heat distributed from cogeneration electricity utility plants.
Unfortunately, the climate in most of our country dictates that
peak electricity production occurs in the summer, because of
widespread air-conditioning, and so most waste heat is
produced in the summer, when it is not needed.
* Over 75% efficient !
Our most successful on-site cogeneration plants are in
heavy industries, such as pulp and paper, where there is a
steady year-round demand for heat to operate a process.”
NYTimes
85% of US energy supply comes from fossil fuels !
Fossil Fuels
This includes:
• Petroleum = gas (methane) and liquid (oil)
“natural gas”, propane, butane,
gasoline, kerosene, etc.
• Coal
• Tar Sand and Oil Shale are sometimes considered
separately from petroleum but are still fossil fuels.
Clicker Question
Petroleum  Molecules of carbon and hydrogen
(“Hydrocarbons”)
Example: “Alkanes” with saturated “single bonds” (i.e. each
carbon has 4 bonds)
H
H H
H C H
H C C H
H
H H
Methane
Ethane
Methane (CH4) – one carbon atom
Ethane (C2H6) – two carbon atoms
Propane (C3H8) – three carbon atoms
Butane (C4H10) – four carbon atoms
And so forth….
How many carbon atoms in Octane?
A) 2
B) 4
C) 7
D) 8
E) 10
H H H H H H H H
H C C C C C C C C H
H H H H H H H H
2
“Burning” Methane
How are fossil fuels formed?
Fundamental byproducts!
CH 4  2 O2  CO2  2 H2O
Provides 45,000 – 55,000 Btu/kg when you oxidize.
Origin is from plants (and some animals, but not much
dinosaur in there ).
Chemical energy is released when burning.
Mostly microscopic, early ocean life.
Solar Energy as Input
for Plants
(Photosynthesis)
Chemical Potential Energy
Intermediate state
Higher
Cellulose
CO2  H 2O  ...  Energy  (C6 H10O5 ) n  O2
Solar
Energy
Cellulose
Carbohydrates !
Burning
CO2+H2O + …
If you burn a piece of wood, you are reversing this process
and freeing energy. Similar “burning” occurs via bacterial
decomposition.
However, in the absence of Oxygen, this does not happen.
H
H
H
C
H
H
Methane
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
Sometimes instead of bacterial decomposition or burning…
Hexane
Dead material sinks to the bottom of the water.
If buried where there is no oxygen (e.g. in sand or mud),
high pressure and temperatures can actually remove the
oxygen from the molecules.
H
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
H
H
Octane
Coal: C-C-C-C-C
Plus impurities
H
Heat, Pressure, Oxygen absent
Plant material, wood, cellulose, …
(C6H10O5) - (C6H10O5)- (C6H10O5) - (C6H10O5)
Carbohydrates  Hydrocarbons
The Production of Fossil Fuels
Heat, Oxygen present
CO2, H2O, …
3
Liquid, gas hydrocarbons flow, until they are trapped in a
natural area (impermeable rock).
Over geological time scales (108 = 100 million years),
reservoirs may end up under LAND, but can also be under
WATER too.
Gas and Oil Trap
Surface
• Coal formed relatively close to the surface
Relatively low temperatures and lower pressures
• Oil formation requires higher temperatures and pressures
• Oil decomposes into natural gas at very high temperature
Natural gas (CH4 = Methane) almost always present
Oil prospecting – Finding the trap
Geologists locate promising areas. Test drill (“wildcat” well).
If you find oil, this is considered a “proven reserve” (i.e.
economically recoverable, known to exist)
Sound source
Receiver
Surface
Impermeable rock trap
Impermeable rock trap
Porous materials
Porous materials
Upward pressure forces oil
(and gas) into trap
Upward pressure forces oil into trap
4