Activity 3 Energy from Coal · Digging Deeper COAL AS A FOSSIL FUEL There are only four primary sources of energy available for use by humankind.They are solar radiation,the Earth’s

Coordinated Science for the 21st Century825

Activity 3 Energy from Coal

GoalsIn this activity you will:

• Classify the rank of coalusing physical properties.

• Interpret a map of coaldistribution in the UnitedStates.

• Understand that fossils fuelsrepresent solar energystored as chemical energy.

• Understand what coal ismade of and how coalforms.

• Be able to explain in yourown words why coal is anonrenewable resource.

Think about It

Coal is the largest energy source for electricity in the UnitedStates. Known coal reserves are spread over almost 100 countries.At current production levels, proven coal reserves are estimated to last over 200 years.

• How does coal form?

• Why is coal referred to as “stored solar energy”?

What do you think? Record your ideas in your EarthCommnotebook. Be prepared to discuss your responses with your small group and the class.


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Investigate

Part A: Types of Coal1. Obtain a set of samples of four

different types of coal. Examine thesamples. Look for evidence of plantorigin, hardness, luster (the way lightis reflected off the surface of thesample), cleavage (tendency to split

into layers), and any othercharacteristics that you thinkdistinguish the four types of coal.Discuss similarities and differenceswith members of your group.

a) In your EarthComm notebook,create a data table and recordyour observations.

2. Use your completed data table, toanswer the following questions:

a) How might the samples be related?

b) Put the samples in order fromleast compacted to mostcompacted.

c) Which sample do you thinkcontains the most stored energy?Why do you think so?

3. The next step of this activity will be ademonstration. You will observe yourteacher igniting a small piece of coalheld over a Bunsen burner. Thesample will be removed from theflame and you will observe how thesample burns. Four types of coal willbe tested.

a) Note the speed of ignition, colorof the flame, speed of burning,and odor. Note any othercharacteristic that you thinkdistinguishes the samples.Summarize your observations in a data table or chart.

b) In your EarthComm notebook,summarize the major differencesyou observed.

c) Review your answer to Step 2(c).Have your ideas changed?Explain.

A

C D

B

Wear goggles. Clean up all loose piecesof coal. Wash your hands after you are done.


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Part B: Coal Resources

1. Examine the map of coal resources inthe United States.

a) Summarize the major trends,patterns, or relationships in thedistribution of coal and the locationsof coal-fired power plants.

2. Refer to the map to answer thefollowing questions about coalresources in the United States. Recordyour responses in your EarthCommnotebook.

a) How many states contain coaldeposits? Which states are they?

b) What are the main types of coalpresent in the following regions:east-central, southeast, and west-central?

c) Can you infer from the map which state has or produces the most coal? Why or why not?

d) Measure how far your community is from a source of coal.

e) Look at the distribution of coal-firedpower plants. Why do you think coalis used in these plants rather thanpetroleum or natural gas?

f) What type of coal is closest to yourcommunity?

3. Refer to the map to answer thefollowing questions about coal-firedpower plants in the United States.Record your responses in yourEarthComm notebook.

a) Is there a coal-fired power plant inyour state? If so, where is it located?


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b) How far from your community isthe closest coal-fired power plant?Where is the plant located?

c) In what part of the country are themost coal-fired power plants found?Why do you think this is so?

d) Identify the states that have coal-fired power plants but do not have coal deposits.

e) How might distance from coaldeposits affect the cost ofelectricity produced by a coal-firedpower plant?

4. Examine a geologic map of yourcommunity or state. A geologic mapshows the distribution of bedrock atthe Earth’s surface. The bedrockshown on the map might be exposedat the surface, or it might be coveredby a thin layer of soil or very recentsediment. Every geologic map containsa legend that shows the kinds of rocksthat are present in the area.

a) Write down or note the names ofthe different rock types present inyour community, the names of therock units, their ages, and theirlocations.

5. Compare the geologic map to themap that shows the distribution ofcoal deposits in the United States.

a) Are any of the rocks present inyour community associated withcoal deposits? What kinds of rocks are they? How old are the rocks?

b) Are any of the rocks present inyour community likely to yieldcoal deposits in the future? Which ones? How do you know?

6. Go to the EarthComm web site tovisit the Department of Energy’sEnergy Information Administrationweb page. Click on your state to open a new web page. Use the “Energy Consumption, Prices, andExpenditures” profiles page to answer the following questions:

a) In your state, approximately what percentage of primary energy consumption for residentialpurposes comes from coal?

b) In your state, what percentages of primary energy consumption for commercial, industrial, andtransportation purposes comefrom coal?

c) How would an increase in thepopulation of your communityaffect this usage?

Reflecting on the Activity and the Challenge

In this activity you described four typesof coal and observed how the differenttypes of coal react when burned. Youthen examined maps to determine thedistribution of coal deposits in the UnitedStates and also to determine if coaldeposits are found near your community.You looked at the location of coal-fired

power plants relative to coal deposits andthought about how the distance betweenthe two can affect the cost of electricityproduction. These activities will help youto determine how coal is used as anenergy resource in your community andthe impacts of its use.




Digging Deeper

COAL AS A FOSSIL FUEL

There are only four primary sources of energy available for use byhumankind.They are solar radiation, the Earth’s interior heat, energy fromdecay of radioactive material in the Earth, and the tides.You can assume thatstarlight, moonlight, and the kinetic energy of meteorites hitting the Earthare so small that they can be neglected.The energy in coal is energy fromsolar radiation that is stored as chemical energy in rock.

The energy in coal originates as solarenergy. Plants in the biosphere store thissolar energy by a process calledphotosynthesis. During photosynthesis,green plants convert solar energy intochemical energy in the form of organic(carbon-based) molecules. Only0.06% of the solar energy that reachesthe Earth is stored throughphotosynthesis, but the amount of energythat is stored in the Earth’s vegetation isenormous. Photosynthesis yields thecarbohydrate glucose (a sugar) and water,as shown in the equation below:

Sunlight used

6CO2 + 6H2O C6H12O6 + 6O2Carbon dioxide Water removed Solar energy Glucose (sugar) Oxygenremoved from from hydrosphere stored as for biosphere released toatmosphere chemical atmosphereand biosphere energy

The energy stored in glucose (a sugar) and other organic molecules can bereleased when broken in a reaction with oxygen (oxidized). Oxidationoccurs through respiration, decomposition, or combustion (burning).

Chemical energy released

6O2 + C6H12O6 6H2O + 6CO2Oxygen Glucose Heat released Water Carbonremoved from to organism returned to dioxidefrom biosphere by respiration or hydrosphere returnedatmosphere to environment to and biosphere by decomposition atmosphere

or combustion and biosphere

Geo Wordsphotosynthesis: theprocess by which plantsuse solar energy, togetherwith carbon dioxide andnutrients, to synthesizeplant tissues.

organic (carbon-based)molecules: moleculeswith the chemicalelement carbon as a base.

oxidation: the chemicalprocess by which certainkinds of matter arecombined with oxygen.

respiration: physical andchemical processes bywhich an organismsupplies its cells andtissues with oxygenneeded for metabolism.

decomposition: thechemical process ofseparation of matter intosimpler chemicalcompounds.Figure 1 Solar radiation is one of the

primary sources of energy on Earth.

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You can see from the reactants (on the left sides of the two equations) andthe products (on the right sides of the two equations) that photosynthesisand oxidation are the reverse of each other.

The energy that enters the biosphere by photosynthesis is nearly equal to theenergy lost from the biosphere by oxidation, as shown in Figure 2. Most of thecarbon in the biosphere is soon returned to the atmosphere (or to theocean) as carbon dioxide, but a very small percentage is buried insediments. It is protected from oxidation and becomes part of thelithosphere (in the form of peat, coal, and petroleum) for future use as fossilfuels.The rate of storage of energy used by organisms for photosynthesis isvery slow. However, these processes have been active throughout much ofEarth’s history.Therefore, the amount of energy stored as fossil fuels isenormous (32 × 1020 Btus). Fossil fuels are consumed far faster than theyform, and therefore they are classified as nonrenewable resources.

heat energylost to space

plants

coal

oil

ocean

electricalenergy

solarenergy

chemical energy (fossil fuels)

Figure 2 The flow of energy from the Sun, to plants, to storage in fossil fuels, and loss backinto space.

Geo Wordssediments: loose particulatematerials that are derived frombreakdown of rocks orprecipitation of solids in water.

lithosphere: the rigidoutermost shell of the Earth,consisting of the crust and theuppermost mantle.

nonrenewable resource: anenergy source that is poweredby materials that exist in theEarth and are not replacednearly as fast as they areconsumed.




The Formation of Coal

Most coal starts out as peat. Peat is an unconsolidated and porous depositof plant remains from a bog or swamp. Structures of the plant matter, likestems, leaves, and bark can be seen in peat.When dried, peat burns freely,and in some parts of the world it is used for fuel.Today, most peat comesfrom peat bogs that formed during the retreat of the last ice sheets,between about ten thousand and twenty thousand years ago.

Coal, by definition, is a combustible rock with more than 50% by weight ofcarbonaceous material. Coal is formed by compaction and hardening of plantremains similar to those in peat.The plant remains are altered physically andchemically through a combination of bacterial decay, compaction, and heat.Most coal has formed by lush growth of plants in coastal fresh-waterswamps, called coal swamps, in low-lying areas that are separated from anysources of mud and sand. Plants put their roots down into earlier depositsof plant remains, and they in turn die and serve as the medium for the rootsof even later plants. In such an environment, the accumulation of plant debrisexceeds the rate of bacterial decay of the debris.The bacterial decay rate isreduced because the available oxygen in organic-rich water is completelyused up by the decay process.Thick deposits of almost pure plant remainsbuild up in this way. Coal swamps are rare in today’s world, but at varioustimes in the geologic past they were widespread.

For the plant material to become coal,it must be buried by later sediment.Burial causes compaction, because ofthe great weight of overlying sediment.During compaction, much of the originalwater that was in the pore spaces ofthe plant material is squeezed out.Gaseous products (methane is one) ofalteration are expelled from thedeposit.The percentage of the depositthat consists of carbon becomes greaterand greater.As the coal becomesenriched carbon, the coal is said toincrease in rank. (See Figure 3.) Thestages in the rank of coal are in thefollowing order: peat, lignite, sub-bituminous coal, bituminous coal, anthracite coal, and finally graphite (a purecarbon mineral). It is estimated that it takes many meters of original peatmaterial to produce a thickness of one meter of bituminous coal.

Geo Wordspeat: a porous depositof partly decomposedplant material at or notfar below the Earth’ssurface.

coal: a combustible rockthat had its origin in thedeposition and burial ofplant material.

heat

time

pressure

peat

lignitecoal

Figure 3 Increasing time, pressure, and heatresult in the formation of progressivelyhigher ranking coal.


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Geo Wordssedimentary rock: a rock,usually layered, that resultsfrom the consolidation orlithification of sediment.

As shown in Figure 4, coal is always interbedded with other sedimentaryrocks, mainly sandstones and shales. Environments of sediment depositionchange with time.An area that at one time was a coal swamp might laterhave become buried by sand or mud from some nearby river system.Eventually, the coal swamp might have become reestablished. Upon burial,the plant material is converted to coal, and the sand and mud formsandstone and shale beds. In this way, there is an alternation of othersedimentary rock types with the coal beds. Some coal beds are onlycentimeters thick, and are not economically important. Coal beds that aremined can be up to several meters thick.

Types of Coal

The type of coal that is found in a given region depends partly on thecomposition of the original plant material (together with any impurities thatwere deposited in small quantities and at the same time). But mainly the typeof coal depends on the depth and temperature of later burial. Coal that isburied very deeply attains high rank, because of the high pressures andtemperatures associated with deep burial. Low-rank coals (lignite and sub-bituminous) have not been buried as deeply.

The rocks we see

coal

coal

coal

coal

sandstone

limestoneconcretion

dark shale

dark shale

siltstone

coal

coal

coal

coal

sandstone

limestoneconcretion

dark shale

dark shale

siltstone

widespread swamps

the land builds outward

seas flood the coasts

swamps

the landscapes in which the rocks formed

Figure 4 Rocks reflect the environments of the past.




Coal varies greatly in composition. One of the most important features of coalcomposition is sulfur content. Sulfur is important because it is released into theatmosphere as sulfur dioxide when the coal is burned.The sulfur dioxide thencombines with water in the atmosphere to form sulfuric acid, causing acid rain.The sulfur content of coal can range from a small fraction of 1% to as much as5%, depending mainly on the sulfur content of the original plant material.Thecarbon content of coal increases with increasing rank of coal, from lignite toanthracite, as illustrated in Table 1.The heat content is also an important featureof coal.The greater the heat content, the smaller the mass of coal that needs tobe burned to produce the needed heat.The heat content of coal increases withthe rank of the coal, because it depends mainly on the carbon content.

The carbon content of coal supplies most of its heat energy per unit weight.The amount of energy in coal is expressed in British thermal units (Btu) perpound.A Btu is the amount of heat needed to raise the temperature of onepound of water one degree Fahrenheit. Peat can be used as a source of fuel,but it has a very low heat content per pound of the fuel burned. Lignite (alsocalled brown coal), the least buried and usually the youngest type of coal, isused mainly for electric power generation. Sub-bituminous coal is a desirableheat source because of its often low sulfur content. Sub-bituminous coal isfound in the western United States and Alaska. Bituminous coal is the mostabundant coal in the United States, with a large deposit in the AppalachianProvince of the East. Bituminous coal is used mainly for generating electricityand making coke for the steel industry.Anthracite, found in a very smallsupply in the eastern United States, has been used mainly for home heating.

Some of the constituents of coal are not combustible.The part of coal that isnot consumed by burning is called ash. Most of the ash consists of sand, silt, andclay that was deposited in the coal swamp along with the vegetation.The purestcoal has only a small fraction of 1% ash.The ash content of usable coal can bemuch higher. Some of the ash remains in the combustion chamber, and somegoes up the flue.Ash in coal is undesirable because it reduces the heat contentslightly. It also must be removed from the combustion chamber and discarded.

Table 1 Percentages of Carbon and Volatile Matter in Coal

Coal Rank Carbon Content (%) Volatile matter (%) Btus per pound

Lignite 25–35 up to ~50% 4000–8300

Sub-bituminous 35–45 up to ~30% 8300–13,000

Bituminous 45–86 less than 20% 10,500–15,000

Anthracite 86–98 less than 15% 15,000

1. Explain how solarenergy is stored andreleased by theprocesses ofphotosynthesis andoxidation.

2. Describe, in your ownwords, the formationof coal, from plantmatter to anthracite.

3. Why is the heatcontent of coal (inBtu/pound) importantin determining howthe coal is used?

4. What is the origin ofthe sulfur content ofcoal, and why is sulfuran undesirableconstituent of coal?

Check YourUnderstanding


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Understanding and Applying What You Have Learned

1. How much impact do you thinkthe proximity of your communityor state to a coal deposit has onthe use of coal for energygeneration? Support your responsewith the information you collectedin the investigation.

2. Discuss what happens to the carboncontent of peat if it is allowed todecay in the presence of oxygen.

3. Use what you have learned aboutcoal in this activity to provide tworeasons why it would be a betteridea to burn anthracite in a homefireplace than lignite.

4. What are the advantages to usingcoal to meet energy needs? Whatare the disadvantages?

Preparing for the Chapter Challenge

You have learned how coal depositsform, and you looked at thedistribution of coal deposits in theUnited States and your community.You also considered how reliant yourcommunity is on coal as an energyresource. Write a paper in which you

consider how the number of coaldeposits in the United States, alongwith the time required to produce acoal deposit, shape the way that yourcommunity uses coal today and howit will use coal in the future, in lightof projected population growth.

Inquiring Further

1. Model the formation of coal

Line a plastic shoebox (or two-liter bottle with the top cutoff) with plastic wrap. Pour waterinto the container to a depth offour inches. Spread about twoinches of sand on the bottom.Drop small leaves, sticks, andpieces of fern on the sand. Let itstand for two weeks. Record whatyou observe as changes in colorand decomposition occur. Gentlysift fine sand or mud on top of the

plant layer to a depth of twoinches. Wait two weeks and drainany remaining water. Let it sit anddry for another two weeks.Remove the “formation” out ofthe container. Slice it open to seehow you have simulated coalwhere the plants were, and fossilimprints from the plant leaves.

2. Plants associated with coal

Research the ancient plants whoseremains formed the United Statescoal deposits.

Wash your hands after handling any material in this activity. Wear goggles.Complete the activity under adult supervision.


Documents

Activity 3 Energy from Coal · Digging Deeper COAL AS A FOSSIL FUEL There are only four primary sources of energy available for use by humankind.They are solar radiation,the Earth’s