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Transcript
2/20/2015
Fire
• Most modern fuels are substances we burn
– Coal, gasoline, gas, oil, propane, charcoal, wood
Chapter 4 Energy
CHM 107
GCC
• The rate we are burning them is not
sustainable. Sustainability is more than just
availability as we shall see.
– These fuels are non renewable
– They produce waste that has ill effects on our
environment
Energy Consumers
• US top E consumer per person
• US casual about E usage
• 70% of US energy comes from fossil fuels
–
–
–
–
Coal, oil, natural gas
Burning them releases CO2, PM, CO, NOx and SOx
Why are those gases a problem?
Also produces Hg, mercury, in the ash
4.1 Burning Carbon Fuels
NOx and SOx
• Short hand ways to write
–
–
–
–
NO and NO2
SO2 and SO3
Gases that cause acid rain
Main pollutants
• The media refers to them this way
Powerplants
• Powerplants use chemical energy stored in fossil fuels
and burn them (combustion) to release the energy stored
in their bonds.
• They convert this chemical energy into heat then into
kinetic energy then to electrical energy
• Burning coal creates heat, which boils water that changes
into steam that flows along pipes to the steam turbines
which then turn in a magnetic field generating electricity.
• The steam is then condensed back to liquid water which
flows back to the furnace to be boiled again. This is
about 42% efficient.
1
2/20/2015
Energy
Burning Coal
• Potential – stored energy
– Chemical energy is stored in the bonds of fuel and
foods
• Kinetic energy – energy of motion
– After digestion of food we can move
• Combustion of coal converts potential energy to
heat (boiling water) which turns into mechanical
energy (turning turbines) which converts into
electrical energy.
Coal Power Plant
Fossil Fuels
• Where did fossil fuels get their energy? From the
sun originally captured by plants
• 6 CO2 + 6 H2O  C6H12O6 + 6 O2
• Green plants capture sun energy via
photosynthesis and produce glucose and oxygen
gas. When they die they decompose partially
getting buried under dirt. Temperature and
pressure turns them into coal and oil and natural
gas.
• We will consume in a few centuries what took
hundreds of millions of years to produce.
1st Law of Thermodynamics
• Energy can not be created nor destroyed, only
converted from one form to another
• Forms include chemical, electrical, nuclear,
mechanical, radiation, heat, friction, sound
• Chemical energy = energy stored in bonds,
chemical reactions like combustion releases this
energy
2
2/20/2015
4.2 Energy Efficiency
• Coal power plants are between 35-50% efficient.
You lose heat between each step in the process.
Car engines are only about 15% efficient!
• How do we measure energy?
– calorie (cal) – heat needed to raise one gram of water
by one degree Celsius.
– Joule (J) One heart beat is one J.
Main Fuel Sources
•
•
•
•
Up to 1880 the main source was wood
Then coal became number one until 1950
Oil has been number one since 1950
Coal and oil are fossil fuels (so is natural gas)
– Review – What are fossil fuels?
Food Calories
• Science measures energy in Joules or calories but food
uses Calories which is really a kilocalorie or 1000
calories
• There are 1000 calories in a Calorie
• There are 4.184 Joules per calorie
• How many calories are in a Snickers bar that contains
245 Calories? How many Joules?
4.3 Coal – Solid Fossil Fuel
• Made up of C, H, O, N, S atoms
• 85% is C, carbon
• Typical coal plant uses 1.5 millions tons of
coal per year
• Formula: C135H96O9NS
• Trace amount of Hg
• Traces of arsenic
• Traces of lead
Types of Coal
•
•
•
•
More oxygen means less energy per gram
Lignite – lowest grade, similar to peat
Sub-bituminous – medium grade
Bituminous – higher grade, more pressure
in its formation
• Anthracite – highest grade, little left in US
3
2/20/2015
Problems with Coal
Coal Mining – One Tough Job
• Mining is dangerous
– China had 4700 deaths in 2006 alone
– Accidents in mines, black lung
• Mining ruins the environment, erosion occurs
• Groundwater exposed to mines becomes acidified and high
in Fe and Al, which is bad for fish and human
consumption.
• Coal is dirty, makes soot, NOx, SOx, PM
• Coal blackens buildings, costs money to restore
• Coal has mercury concentrates in the ash
• Coal burning produces CO2 a GHG (coal accounts for 40%
of global CO2 emissions)
Black lung
Coal
Train
Just a Joke!
What is good about coal?
• Cheap
• US has plenty of it (25% of the world’s supply)
• What about clean coal?
– Well that just means putting scrubbers on existing coal
plants to help them remove pollutants from the smoke
stacks. This should be done anyway. There is no new
different better coal, same old coal. None of this
addresses CO2 emissions.
4
2/20/2015
USA Has Lots of Coal Reserves
Coal’s Future?
• Between 1999 and 2009
– North America stayed about the same
• But 214 new coal plants proposed, 1/3 refused, 1/3
in court, many can’t find funding
– Europe decreased a bit
– Africa increased a bit
– Asia doubles its usage! Now using about 4x the
amount of the US.
4.4 Petroleum – liquid fossil fuel
Texas Landscaping
• Easy to transport since flows, so more popular
than coal, but way more expensive
• Petroleum is 48 kJ/g vs high grade coal at 30 kJ/g
• US does NOT have enough oil, so we import it
– From where?
Petroleum = crude oil
Hydrocarbons - Alkanes
• Petroleum must be refined
• It is a mix of many hydrocarbons (1-60 C per molecule)
– Compounds with Hydrogen and Carbon (H and C)
– Simple hydrocarbons = Alkanes – all single covalent bonds
between carbon atoms
– Less sulfur than coal so less SOx
• To separate the hydrocarbons you use distillation
– Heat up the crude oil until it boils
– Collect the vapors then condense back to liquid form
– Smallest hydrocarbon boils off first, collect it first, and then so
on
– The more carbon atoms, the higher the boiling point
5
2/20/2015
Distillation
Alkanes up to
Octane
Why do we care about Hydrocarbons?
• Once in the gas phase, the vapors travel up
the tower. Smaller mass compounds travel
up the highest, larger mass compounds
travel shorter distances up the tower.
• Vapors are condensed back into liquid form
at the different levels of the tower and
collected.
Petroleum Refinery
Fossil Fuel;
Petroleum
“Addicted to Oil”
One Barrel of Crude Oil 2009
•
•
•
•
•
•
19.2 gal gasoline
10.0 gal diesel
3.8 gal jet fuel
1.7 gal heavy oil fuel
1.7 gal methane – butane
7.3 gal other (plastics, pharmaceuticals,
fabrics, etc)
• China is now the 2nd largest car market
• Oil reserves will be depleted in 50-100 years
• Shell’s CEO said “after 2015 easy access oil
and gas will no longer keep up with demand.”
• US Dept of Energy says that peak oil will
occur between 2026 and 2047.
6
2/20/2015
Natural Gas
Natural Gas = gas fossil fuel
•
•
•
•
•
•
Gas Stove
90% methane, CH4, simple hydrocarbon
Provides head for 2/3 homes in US
Burns cleaner than coal or oil, less impurities
No mercury ash produced
Little NOx produced, almost no SO2
Makes less CO2 than oil or coal
Fracking
• Involves drilling down into shale that contains natural gas
about 1-2 miles down
• Water that contains a “cocktail” of substances is injected under
pressure into the shale to create “cracks” into which the gas can
flow to the surface for collection
• Environmental impacts include the risks contaminating ground
water, depleting fresh water, degrading air quality, potentially
triggering earthquakes, noise pollution, surface pollution, and
the consequential hazards to public health and the environment
• The cocktail is usually chemicals that are not disclosed by the
companies, sand, and water
• Over one million “frac jobs” have been performed in the US
4.5 Heat vs. Temperature
Temperature vs Heat
• Temperature – kinetic every of atoms. Cold is
atoms moving slowly, hot is atoms moving
quickly. Does not depend on volume.
• Heat – depends on volume. Heat is energy
that flows from hot to cold.
• A donut is 425 Calories. How many J is this?
Recall that Cal = 1000 cal, cal = 4.184 J.
Which has higher temperature? Which has more heat?
7
2/20/2015
Heats of Combustion
Energy Changes
• Heat given off when it burns. Reported in units
of kJ/mol or kJ/gram.
• Heat of combustion of methane is 802.3 kJ/mol.
• Chemical reactions are either exothermic or endothermic
• Exothermic = heat exiting
CH4 + 2 O2  CO2 + 2 H2O + 802.3 kJ
• Convert that to kJ/g using molar mass.
– Heat is produced as a product of the reaction
– Combustion produces heat
– Reactant heat is higher than the product heat, thus heat released,
the energy change is negative (goes down)
• Endothermic = heat in
– Heat is needed as a reactant in the reaction
– Cold packs take in heat
– Reactant heat is lower than the product heat, thus heat is
absorbed, the energy change is positive (goes up)
Exothermic
• Recall a chemical
reaction is
• reactants g products
• Reactant heat higher than
product heat so heat is
lost, heat exits,
exothermic
• Heat is produced
• Ex: combustion, hot pack
 DH is negative
4.6 Energy changes in Molecules
• Chemical reactions are when reactant molecule
bonds are broken and the atoms rearrange into
new different product molecules forming new
product bonds
• You should be able to tell which bonds are
broken and which ones form
• Example
– H2 + Cl2 g 2 HCl + E
– Is this reaction exothermic or endothermic?
Endothermic
• Recall a chemical
reaction is
• reactants g products
• Reactant heat lower than
product heat so heat is
taken in, heat enters,
endothermic
• Heat is absorbed
• Ex: photosynthesis must
absorb sun’s energy, cold
pack
 DH is negative
We Need Fuel and Energy
• US is about 5% of the world’s population, but
uses 30% of the world’s energy. We are addicted
to energy. Only Canada uses about the same per
person as us.
• The country using the most energy overall is
China, but they also have the most people, and
they use way less per person than us.
• We average 16 tons of coal per person per year.
Exothermic
8
2/20/2015
Electricity Consumption
country
Total MW
population
Per capita
China
4,190,000,000
1.3 billion
364
US
3,741,485,000
298 million
1460
Europe
2,950,297,000
459 million
700
Japan
963,852,000
128 million
868
Russia
857,617,000
142 million
785
India
600,649,000
1.1 billion
51
Brazil
600,029,000
786 million
226
Canada
549,476,000
32 million
1410
2005 Data
4.7 Making Gasoline
• Gasoline is hydrocarbons with 5-12 C atoms
• These smaller hydrocarbons are in way more
demand than those with 13 or more C atoms
• Need a way to break larger hydrocarbons into
smaller ones = Cracking
– C16H34 g C8H18 + C8H16
– Is this balanced???
• Anyone remember leaded gasoline? Finally
banned in US in 1996 by Clean Air Act
A “Cracker”
heats
hydrocarbons
to 400-450oC
to crack them.
Cracking
• Thermal cracking involves very high
temperatures.
• Catalytic cracking involves using a catalyst
at lower temperatures.
• Octane is C8H18 and there are several
isomers with this formula. (same formula,
different structure)
9
2/20/2015
4.8 New Fuels
• Coal can last another 150 years, but can’t be used
in cars since it is not liquid. Cheap oil will run
out in 30-50 years. We must change our ways
whether we want to or not. Big money to be
made in what replaces oil.
• We can make synthetic oil from coal, but right
now this is way too expensive. And it produces
twice the amount of CO2. Why is this bad?
Synthetic Gasoline
• We can make it from coal (Fischer-Tropsch process)
but it requires a catalyst.
• A catalyst lowers the energy necessary to make a
reaction proceed to products. And catalysts are not
consumed during the reaction so they can be reused
over and over and over.
• South Africa synthesizes most of its gasoline this way.
• However making gasoline from coal creates twice as
much GHG as burning oil creates. This is bad news for
the planet.
4.9 Ethanol Biofuel
• Burning fossil fuels is not sustainable – we will run
out of them eventually, we can’t grow them, and
they cause harm to our lungs and the planet.
• What are the options? One is to use biofuels which
are renewable fuels made from plants.
• Wood not viable, wood takes CO2 out of the air,
we need more trees, not less. Also trees grow slow.
• We can ferment corn to make ethanol. Corn grows
quickly so is sustainable.
Catalysts lower the energy required
for a reaction to proceed forwards
How to make Ethanol
• How to ferment corn
– Mix corn kernals and water
– Use enzymes to break down the starch molecules into
glucose
– Yeast cells cause glucose to turn into ethanol
– Distill and purify the ethanol
• Often mixed with gasoline already = gasohol
– Usually 10% ethanol – can be used in all cars
– E85 is 85% ethanol – can be used in FFV (flex fuel
vehicle). There are 6 million in the US now.
10
2/20/2015
Brazil
• 4 million out of 13 million cars run on pure
ethanol produced from fermenting sugar
cane
• The rest run on an ethanol / gas mix
• You get less miles per gallon with ethanol
however but the octane rating is higher.
(The higher the octane rating, the smoother
the fuel and less knocking)
Ethanol Review
• Mix of 90% gas and 10% ethanol can be used in all cars
now
• Must modify cars to run on 100% ethanol
– Brazil has about 30% cars on ethanol
• FFV (flex fuel vehicles) run on up to 85% ethanol (E85)
and 15% gas, sold in Europe and US
–
–
–
–
–
–
Few engine modifications
Same performance levels, less mpg
Produced since the 1980’s, you may have one and not know it
Labeled on gas cap or fuel door
Sweden has 1455 E85 stations, 1802 in US
US has 8.3 million E85 cars
Switch Grass
Problems with Ethanol from Corn
•
•
•
•
•
Energy to make it is more than what we get from it
More expensive than gasoline now
Lower gas mileage
Not enough land to grow that much corn
Corn uses lots of fertilizers and pesticides, bad for water
supply and soil. Transportation of these chemicals
requires burning gasoline and emits CO2.
• Corn degrades the soil. People are starving, corn could
be used as food instead of fuel.
• Many think switch grass is way better than corn as an
ethanol source
4.10 Other Biofuels = Biomass
Biomass
•
•
•
•
Biodiesel
Garbage
Biogas
Solar, wind, hydrogen and geothermal are
renewable and alternative energy sources
– Alternative energy means NOT fossil fuel
– Renewable means produced quickly, readily available
• Nuclear is alternative but not renewable because
Uranium is not produced quickly
11
2/20/2015
Biodiesel
• Increasing production, can be made by
individual consumers
• Made from vegetable oil, can get for free from
restaurants
• Can be used pure or mixed with gasoline in
diesel engines
How to
Make
Biodiesel
– B20 means 80% diesel and 20% biodiesel
• Non toxic and biodegradable
• Releases more energy than required to make it
(better than corn ethanol)
How to make biodiesel
• Vegetable oils contains triglycerides
– React with methanol and NaOH (catalyst)
– Produce 3 biodiesel molecules and glycerol waste
– Glycerol can be sold to make a glycol
Biodiesel
• Does produce CO2 when burned, but is carbon
neutral (the plant took in the CO2 first)
Garbage as energy source
• Cheap, there is lots of it, renewable, abundant
• Solves 2 problems
– What to do with trash
– How to make energy
• Burning trash leaves about 10% behind that goes to
landfill
• Can recover metals to reuse
• Incinerator emissions below standard levels or regular
incinerators
• Japan and Germany are leaders in burning trash as fuel
Biogas
• Collect gas vapors from landfill and use to
heat homes
• Collect gas from sewage or manure on a
farm to provide the heating for the farm
• Good for small scale applications
• 25 million users in rural China in 2008,
expected to double this decade
12
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Conservation
Biomass
Cycle
• Best way to control costs is still conservation – use less
energy in the first place!
• Oil will peak this century, costs will continue to rise,
something must replace it
• Recycling is key! One can recycled saves enough
energy to run a TV for 3 hours
• Drive fuel efficient cars – uses less fuel and saves
money (2008 numbers)
– Europe average 40 mpg
– Japan average 45 mpg
– US average 19.8 mpg
Summary: Energy Sources
4.11 The Way Forward
•
•
•
•
We will need more energy in the future
25% of energy is consumed by 5% (US)
China and India are emerging economies
Do we have enough energy for all people to live at
NO
US standard of living?
• Must make smart choices. In US cars/trucks are 70%
of oil usage and 1/5 CO2 emissions – our mpg is low,
could improve here.
• Mass transit – 47% of Japan’s travel vs only 6% of
US travel
• Our actions leave global footprints
13