CHAPTER 13: Energy

ENVIRONMENTAL SCIENCE

13e

14e

15e

CHAPTER 13:

Energy

13-1 What Major Sources of

Energy Do We Use?• Concept 13-1A About three-quarters of

the world’s commercial energy comes

from nonrenewable fossil fuels, and the

rest comes from nonrenewable nuclear

fuel and renewable sources.

• Concept 13-1B Net energy is the amount

of high-quality energy available from a

resource minus the amount of energy

needed to make it available.

Evaluating Energy Resources

• Energy from the sun

• Indirect forms of renewable solar

energy

– Wind

– Hydropower

– Biomass

• Commercial energy (energy sold in the marketplace)

– Fossil fuels -- nonrenewable

Net Energy

= (available E from resource) –

(E needed to find, extract, process and get E to consumer)

• Net E is like your net spendable income

(wages minus taxes and deductions)

• Net energy ratio= Ratio of energy produced to energy used to

produce it

Example

• 10 units of energy in oil in the ground we have

to use.

• Waste 8 units of energy to find, extract,

process, and transport the oil to users.

– Only 2 units of useful energy available.

• Net energy ratio = 10/8 = 1.25

• The higher ratio, the greater the net energy

(when <1, net energy loss).

Fig. 13-A, p. 299

5.8

Transportation

4.9Natural gas

4.11.4

1.2

1.1 (but can reach 1.5)

Gasoline (refined crude oil)

Ethanol from sugarcane residue

Coal liquefaction

Oil shale

Space Heating (House)

Oil

Electric heating (nuclear plant)

Passive solar

Natural gas

Active solar

Coal gasification

Electric heating (coal-fired plant)

Electric heating (natural-gas-fired plant)

High-Temperature Industrial Heat

Direct solar (concentrated)

Coal gasification

Oil

Natural gas

Underground-mined coal

Surface-mined coal

0.9

1.5

4.7

4.9

25.8

0.3

0.4

0.4

1.9

1.5

4.5

4.9

28.2

8.0

5.4

Ethanol from corn

Ethanol from switchgrass

Net energy ratios for

various energy

systems

About 82% of the

commercial energy

consumed in the world

comes from

nonrenewable energy

resources—

76% from fossil fuels (oil,

natural gas, and

coal) and 6% from

nuclear power

13-2 What Are the Advantages and

Disadvantages of Fossil Fuels?

• Concept 13-2 Oil, natural gas, and coal

are currently abundant and relatively

inexpensive, but using them causes air

and water pollution, degrades large areas

of land, and releases greenhouse gases to

the atmosphere.

Dependence on Oil

• Petroleum (crude oil)

– Also called light oil

– Trapped underground or

under ocean with natural

gas

– Fossil fuels*

• Extraction – global peak

production

• Transportation

• Refining

• Petrochemicals

Asphalt

GasesLowest Boiling Point

Highest Boiling Point

Gasoline

Aviation fuel

Heating oil

Diesel

oil

Heated

crude

oil

Furnace

Naphtha

Greaseand wax

= chemical products obtained from

petroleum by refining

*Fossil fuelis a general term for buried combustible geologic

deposits of organic materials, formed from decayed

plants and animals that have been converted to

• crude oil

• Coal

• natural gas

• heavy oils

by exposure to heat and pressure in the earth's

crust over hundreds of millions of years.

How Long Will Crude Oil

Supplies Last?• Crude oil is the single largest source of

commercial energy in world

• Proven oil reserves

– Can be extracted profitably at today’s

prices with today’s technology

– 80% depleted between 2050 and 2100

• Major Oil-Supplying Nations

– OPEC

• How long will conventional oil last?

Fig. 13-5, p. 301

Disadvantages

Need to find

substitutes within 50

years

Large government

subsidies

Environmental costs

not included in

market price

Artificially low price

encourages waste

and discourages

search for alternatives

Pollutes air when

produced and burned

Releases CO2 when

burned

Can cause water

pollution

Ample supply for

42–93 years

Low cost

High net energy

yield

Easily transported

within and

between countries

Low land use

Technology is well

developed

Efficient

distribution system

Trade-Offs

Conventional Oil

Advantages

Oil Sand and Oil Shale

• Oil sand (tar sand)

– Bitumen

– Kerogen

• Shale Oil

Oil Sand and Oil Shale

• Oil sand (tar sand)

– Bitumen (Hot water or stream

extraction)

– Kerogen

• Shale Oil

– World reserves

– Major environmental

problems

Heavy Oils from Oil

Shale and Tar Sand

High cost (oil shale)

Low net energy yield

Environmental costs

not included in

market price

Large amounts of

water needed for

processing

Severe land

disruption

Severe water

pollution

Air pollution and CO2

emissions when

produced and

burned

Technology

well-developed

(tar sand)

Efficient

distribution system

in place

Easily transported

within and

between countries

Large potential

supplies, especially

tar sands in

Canada

Moderate cost

(tar sand)

Trade-Offs

Advantages Disadvantages

Natural Gas Is a Useful and

Clean-burning Fossil Fuel (1)

• Natural gas a mixture of gases of which 50–

90% is methane (CH4)

– Conventional natural gas*

– Unconventional natural gas

• Liquefied petroleum gas (LPG)

– Less carbon dioxide emitted per unit of

energy than with crude oil, tar sand,

shale oil

Natural Gas Is a Useful and

Clean-burning Fossil Fuel (2)

• Liquefied natural gas (LNG)– World supply of

conventional natural gas

– 62-125 years

Fig. 13-8, p. 304

Conventional Natural Gas

Nonrenewable resource

Releases CO2 when burned

Government subsidies

Environmental costs not

included in market price

Methane

(a greenhouse gas) can

leak from pipelines

Difficult to transfer from

one country to another

Can be shipped across

ocean only as highly

explosive LNG

Ample supplies

High net energy yield

Low cost

Less air pollution than

other fossil fuels

Lower CO2 emissions than

other fossil fuels

Easily transported by

pipeline

Low land use

Good fuel for fuel cells,

gas turbines, and motor

vehicles

Trade-Offs

Advantages Disadvantages

Unconventional natural gas

• Coal-bed methane gas

• Methane hydrate

Coal (solid fossil fuel) Is a Plentiful

But Dirty Fuel (1)

• Used in electricity production

• World’s most abundant fossil fuel

• U.S. reserves should last about 250 years

Increasing moisture content Increasing heat and carbon content

Peat

(not a coal)

Lignite

(brown coal)Bituminous

(soft coal)

Anthracite

(hard coal)

Heat Heat Heat

Pressure Pressure Pressure

Partially decayed plant

matter in swamps and

bogs; low heat content

Low heat content; low

sulfur content; limited

supplies in most areas

Extensively used as a fuel

because of its high heat

content and large supplies;

normally has a high sulfur

content

Highly desirable fuel

because of its high heat

content and low sulfur

content; supplies are

limited in most areas

Coal Is a Plentiful

But Dirty Fuel (2)

• Sulfur and particulate pollutants

• Mercury and radioactive pollutants

• Heavy carbon dioxide emissions

• Pollution control and environmental costs

• China major builder of coal plants

Stack

Waste heat

Cooling tower

transfers

waste

heat to

atmosphere

Pulverizing

mill

TurbineCoal bunker

GeneratorCooling loop

Condenser

Boiler

Filter

Toxic ash disposal

Fig. 13-10, p. 306

Heat produced by burning coal in a furnace boils water to produce steam

that spins a turbine to produce electricity. The steam is cooled, condensed,

and returned to the boiler for reuse.

Waste heat can be transferred to the atmosphere or to a nearby source of

water. Water is pumped through a condenser and back

to the water source to remove the waste heat.

10%

286%Coal-fired electricity

150%Synthetic oil and

gas producedfrom coal

Coal 100%

Oil 86%

Natural gas 58%

92%Tar sand

Nuclear power fuel cycle

Geothermal

17%

Fig. 13-11, p. 306

CO2 emissions per

unit of electrical

energy produced

for various energy

resources

Fig. 13-12, p. 307

Disadvantages

Severe land disturbance,

air pollution, and water

pollution

Severe threat to human

health when burned



Large government

subsidies

High CO2 emissions

when produced and

burned

Radioactive particle and

toxic mercury emissions

Air pollution can be reduced with

improved technology

Well-developed technology

Low cost

High net energy yield

Ample supplies (225–900 years)

Trade-Offs

Coal

Advantages

Case Study: The Growing

Problem of Coal Ash

• Highly toxic

• Often stored in ponds

– Ponds can rupture

• Groundwater

contamination

• EPA: in 2009 called for

classifying coal ash as

hazardous waste

– Opposed by coal

companies

Clean Coal Campaign

• Coal industry

– Rich and powerful

– Fought against labeling carbon dioxide a greenhouse gas

• “Clean coal” touted by coal industry

– Mining harms the environment

– Burning creates carbon dioxide and toxic chemicals

• Plan to capture and store carbon dioxide

Converting Coal into Gaseous

and Liquid Fuels

• Synfuels

• Coal gasification

– Synthetic natural gas (SNG)

• Coal liquefaction

– Methanol or synthetic gasoline

• Extracting and burning coal more

cleanly

Fig. 13-13, p. 309

Disadvantages

Low to moderate net energy yield

Higher cost than coal

Requires mining 50% more coal

Environmental costs not included

in market price

High environmental impact

Large government subsidies

High water use

Higher CO2 emissions than coal

Large potential supply

Vehicle fuel

Moderate cost

Lower air pollution

than coal when

burned

Trade-Offs

Synthetic Fuels

Advantages

13-3 What Are the Advantages and

Disadvantages of Nuclear Energy?

• Concept 13-3 The nuclear power fuel

cycle has a low environmental impact

and a very low accident risk, but its

use has been limited because of high

costs, a low net energy yield, long-

lived radioactive wastes, vulnerability

to sabotage, and the potential for

spreading nuclear weapons

technology.

How Does a Nuclear Fission

Reactor Work?

• Nuclear fission

• Light-water reactors

• Boil water to produce steam to turn

turbines to generate electricity

• Radioactive uranium as fuel

• Control rods, coolant, and

containment vessels

Coolwaterinput

Small amounts ofradioactive gases

Periodic removal andstorage of radioactive

wastes and spentfuel assemblies

Periodic removaland storage of

radioactiveliquid wastes

Control rods

Heat exchanger

Containment shell

Steam

Water

Uraniumfuel input(reactor core)

Hotcoolant

Coolant

Moderator

Coolantpassage

Shielding

Waste heat

Water source(river, lake, ocean)

Useful electricalenergy

About 25%

GeneratorTurbine

Hotwateroutput

Condenser

Pressurevessel

Fig. 13-14, p. 310

Pump

Waste heatPump

Pump

Pump

Safety and Radioactive Wastes

• On-site storage of radioactive

wastes

• Safety features of nuclear power

plants

• Expensive

• Nuclear fuel cycle

• Reactor life cycle

• Large amounts of very radioactive

wastes

• Disposal of waste is difficult

Fig. 13-15, p. 311

Fuel assemblies

Fuel fabricationEnrichment

of UF6

Temporary storage

of spent fuel assemblies

underwater or in dry

casks

Low-level radiationwith long half-life

Geologic disposalof moderate and high-levelradioactive wastes

(conversion of enriched

UF6 to UO2 and fabrication

of fuel assemblies)

Uranium-235 as

UF6 Plutonium-

239 as PuO2

Decommissioning

of reactor

Reactor

Spent fuel

reprocessing

Conversion

of U3O8

to UF6 (uranium hexafluoride)

Fig. 13-16, p. 312

Open fuel cycle today

Recycling of nuclear fuel

Mining uranium ore

(U3O8 )

What Happened to Nuclear

Power?

• Optimism of 1950s is gone

• Comparatively expensive source of

power

• No new plants in U.S. since 1978

• Disposing of nuclear waste is difficult

• Three Mile Island (1979)

Case Study: Chernobyl Disaster

• Ukraine (1986)

• Explosions and partial meltdown

• Huge radioactive release to

atmosphere

• Estimated death toll: 9,000–212,000

• Radioactive fallout and long-term

health effects

• Lesson – worldwide consequences

Fig. 13-17, p. 313

Conventional Nuclear Fuel Cycle

Cannot compete

economically without huge

government subsidies


High environmental impact

(with major accidents)



Risk of catastrophic accidents

No widely acceptable solution

for long-term storage of

radioactive wastes

Subject to terrorist attacks

Spreads knowledge and

technology for building

nuclear weapons

Large fuel supply

Low environmental

impact (without

accidents)

Emits 1/6 as much CO2

as coal

Moderate land disruption

and water pollution

(without accidents)

Moderate land use

Low risk of accidents

because of multiple

safety systems (except for

Chernobyl-type reactors)

Trade-Offs

DisadvantagesAdvantages

Dealing with Radioactive Wastes

• High-level radioactive wastes

• Long-term storage: 10,000–240,000

years

• Deep burial

• Detoxify wastes?

Case Study: Dealing with Radioactive

Wastes in the United States

• Yucca Mountain, Nevada

• Concerns over groundwater

contamination

• Possible seismic activity

• Transportation accidents and

terrorism

• 2009: Obama ends Yucca funding

What Do We Do with Worn-Out

Nuclear Power Plants?

• Decommissioning old nuclear power

plants

• Dismantle power plant and store

materials

• Install physical barriers

• Entomb entire plant

Fig. 13-18, p. 314

Coal vs. Nuclear

Ample supply of

uranium


Low air pollution

Lower CO2 emissions

Much lower land

disruption from

surface mining

Moderate land use

High cost (even with

huge subsidies)

Ample supply

High net energy

yield

Very high air

pollution

High CO2

emissions

High land

disruption from

surface mining

High land use

Low cost (with

huge subsidies)

Coal Nuclear

Trade-Offs

What Is the Future for Nuclear

Power?

• Reduce dependence on foreign oil

• Reduce global warming

• Advanced light-water reactors

• Nuclear fusion

• How to develop relatively safe nuclear

power with a high net energy yield?

CHAPTER 13: Energy

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