2 Fossil Fuels Robert Reuther U.S. Department of Energy Richard Bajura West Virginia University Philip C. Crouse Philip C. Crouse and Associates, Inc. 2.1 Coal ........................................................................................ 2-1 Coal Composition and Classification † Coal Analysis and Properties † Coal Reserves † Important Terminology: Resources, Reserves, and the Demonstrated Reserve Base † Transportation 2.2 Environmental Aspects....................................................... 2-14 Defining Terms ............................................................................... 2-14 References........................................................................................ 2-15 For Further Information................................................................ 2-15 2.3 Oil ........................................................................................ 2-16 Overview † Crude Oil Classification and World Reserves † Standard Fuels 2.4 Natural Gas ......................................................................... 2-21 Overview † Reserves and Resources † Natural Gas Production Measurement † World Production of Dry Natural Gas † Compressed Natural Gas † Liquefied Natural Gas (LNG) † Physical Properties of Hydrocarbons Defining Terms ............................................................................... 2-25 For Further Information................................................................ 2-25 2.1 Coal Robert Reuther 2.1.1 Coal Composition and Classification Coal is a sedimentary rock formed by the accumulation and decay of organic substances, derived from plant tissues and exudates, which have been buried over periods of geological time, along with various mineral inclusions. Coal is classified by type and rank. Coal type classifies coal by the plant sources from which it was derived. Coal rank classifies coal by its degree of metamorphosis from the original plant sources and is therefore a measure of the age of the coal. The process of metamorphosis or aging is termed coalification. The study of coal by type is known as coal petrography. Coal type is determined from the examination of polished sections of a coal sample using a reflected-light microscope. The degree of reflectance and the color of a sample are identified with specific residues of the original plant tissues. These various residues are referred to as macerals. Macerals are collected into three main groups: vitrinite, inertinite, and exinite (sometimes referred to as liptinite). The maceral groups and their associated macerals are listed in Table 2.1, along with a description of the plant tissue from which each distinct maceral type is derived. 2-1 q 2007 by Taylor & Francis Group, LLC
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2
q 2007 by Taylor & Francis Group, LLC
Fossil Fuels
Robert ReutherU.S. Department of Energy
Richard BajuraWest Virginia University
Philip C. CrousePhilip C. Crouse and Associates, Inc.
Subbituminous Subbituminous A — — — — 10,500 11,500 Nonagglomerating
Subbituminous B — — — — 9,500 10,500 Nonagglomerating
Subbituminous C — — — — 8,300 9,500 Nonagglomerating
Lignitic Lignite A — — — — 6,300 8,300 Nonagglomerating
Lignite B — — — — — 6,300 Nonagglomerating
Source: From the American Society for Testing and Materials’ Annual Book of ASTM Standards. With permission.
Fossil
Fu
els
2-3
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2-4 Energy Conversion
carbon content; moisture content; and ash content, all of which are reported on a weight percent basis.
The measurement of these four properties of a coal must be carried out according to strict specifications
codified by the ASTM. Note that the four constituents of proximate analysis do not exist, per se, in the
coal, but are measured as analytical results upon treating the coal sample to various conditions.
ASTM volatile matter released from coal includes carbon dioxide, inorganic sulfur- and nitrogen-
containing species, and organic compounds. The percentages of these various compounds or species
released from the coal varies with rank. Volatile matter content can typically be reported on a number of
bases, such as moist; dry, mineral matter-free (dmmf); moist, mineral matter-free; moist, ash-free; and
dry, ash-free (daf), depending on the condition of the coal on which the measurements were made.
Mineral matter and ash are two distinct entities. Coal does not contain ash, even though the ash
content of a coal is reported as part of its proximate analysis. Instead, coal contains mineral matter, which
can be present as distinct mineral entities or inclusions and as material intimately bound with the organic
matrix of the coal. Ash, on the other hand, refers to the solid inorganic material remaining after
combusting a coal sample. Proximate ash content is the ash remaining after the coal has been exposed to
air under specific conditions codified in ASTM Standard Test Method D 3174. It is reported as the mass
percent remaining upon combustion of the original sample on a dry or moist basis.
Moisture content refers to the mass of water released from the solid coal sample when it is heated
under specific conditions of temperature and residence time as codified in ASTM Standard Test Method
D 3173.
The fixed carbon content refers to the mass of organic matter remaining in the sample after the
moisture and volatile matter are released. It is primarily made up of carbon. However, hydrogen, sulfur,
and nitrogen also are typically present. It is reported by difference from the total of the volatile matter,
ash, and moisture contents on a mass percent of the original coal sample basis. Alternatively, it can be
reported on a dry basis; a dmmf basis; or a moist, mineral matter-free basis.
The values associated with a proximate analysis vary with rank. In general, volatile matter content
decreases with increasing rank, while fixed carbon content correspondingly increases. Moisture and ash
also decrease, in general, with rank. Typical values for proximate analyses as a function of the rank of a
coal are provided in Table 2.3.
The ultimate analysis provides the composition of the organic fraction of coal on an elemental basis.
Like the proximate analysis, the ultimate analysis can be reported on a moist or dry basis and on an ash-
containing or ash-free basis. The moisture and ash reported in the ultimate analysis are found from the
corresponding proximate analysis. Nearly every element on Earth can be found in coal. However, the
important elements that occur in the organic fraction are limited to only a few. The most important of
these include carbon; hydrogen; oxygen; sulfur; nitrogen; and, sometimes, chlorine. The scope, definition
of the ultimate analysis, designation of applicable standards, and calculations for reporting results on
different moisture bases can be found in ASTM Standard Test Method D 3176M. Typical values for the
ultimate analysis for various ranks of coal found in the U.S. are provided in Table 2.4. Other important
properties of coal include swelling, caking, and coking behavior; ash fusibility; reactivity; and
calorific value.
Calorific value measures the energy available in a unit mass of coal sample. It is measured by ASTM
Standard Test Method D 2015M, Gross Calorific Value of Solid Fuel by the Adiabatic Bomb Calorimeter,
or by ASTM Standard Test Method D 3286, Gross Calorific Value of Solid Fuel by the Isothermal-Jacket
Bomb Calorimeter. In the absence of a directly measured value, the gross calorific value, Q, of a coal (in
Btu/lb) can be estimated using the Dulong formula (Elliott and Yohe 1981):
Q Z 14; 544C C62; 028½HKðO=8Þ�C4; 050S
where C, H, O, and S are the mass fractions of carbon, hydrogen, oxygen, and sulfur, respectively,
obtained from the ultimate analysis.
Swelling, caking, and coking all refer to the property of certain bituminous coals to change in size,
composition, and, notably, strength, when slowly heated in an inert atmosphere to between 450 and 550
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TABLE 2.3 Calorific Values and Proximate Analyses of Ash-Free Coals of Different Rank
0%
20%
40%
60%
80%
100%
Lignit
e A
Lignit
e B
Subbit
umino
us C
Subbit
umino
us B
Subbit
umino
us A
High-V
olatile
C B
itum
inous
High-V
olatile
B B
itum
inous
High-V
olatile
A B
itum
inous
Med
ium-V
olatile
Bitu
mino
us
Low-V
olatile
Bitu
mino
us
Semian
thra
cite
Anthr
acite
Met
a-an
thra
cite
Mas
s pe
rcen
t
Moisture
Volatile matter
Fixed carbon
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
18,000B
tu/lb
Source: From Averitt, P., Coal Resources of the United States, January 1, 1974. U.S. Geological Survey
Bulletin 1412, Government Printing Office, Washington, DC, 1975.
Fossil Fuels 2-5
or 6008F. Under such conditions, the coal sample initially becomes soft and partially devolatilizes. With
further heating, the sample takes on a fluid characteristic. During this fluid phase, further devolatilization
causes the sample to swell. Still further heating results in the formation of a stable, porous, solid material
with high strength. Several tests have been developed, based on this property, to measure the degree and
TABLE 2.4 Ultimate Analysis in Mass Percent of Representative Coals of the U.S.
Component Fort Union
Lignite
Powder River
Subbituminous
Four Corners
Subbituminous
Illinois C
Bituminous
Appalachia
Bituminous
Moisture 36.2 30.4 12.4 16.1 2.3
Carbon 39.9 45.8 47.5 60.1 73.6
Hydrogen 2.8 3.4 3.6 4.1 4.9
Nitrogen 0.6 0.6 0.9 1.1 1.4
Sulfur 0.9 0.7 0.7 2.9 2.8
Oxygen 11.0 11.3 9.3 8.3 5.3
Ash 8.6 7.8 25.6 7.4 9.7
Gross calorific value,
Btu/lb
6,700 7,900 8,400 10,700 13,400
Source: Modified from Probstein, R. and Hicks, R., Synthetic Fuels, McGraw-Hill, New York, 1982. With permission.
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2-6 Energy Conversion
suitability of a coal for various processes. Some of the more popular tests are the free swelling index
(ASTM Test Method D 720); the Gray–King assay test (initially developed and extensively used in Great
Britain); and the Gieseler plastometer test (ASTM Test Method D 2639), as well as a host of dilatometric
methods (Habermehl et al. 1981).
The results of these tests are often correlated with the ability of a coal to form a coke suitable for iron
making. In the iron-making process, the high carbon content and high surface area of the coke are used
in reducing iron oxide to elemental iron. The solid coke must also be strong enough to provide the
structural matrix upon which the reactions take place. Bituminous coals that have good coking properties
are often referred to as metallurgical coals. (Bituminous coals without this property are, alternatively,
referred to as steam coals because of their historically important use in raising steam for conversion to
mechanical energy or electricity generation.)
Ash fusibility is another important property of coals. This is a measure of the temperature range over
which the mineral matter in the coal begins to soften, eventually to melt into a slag, and to fuse together.
This phenomenon is important in combustion processes; it determines if and at what point the resultant
ash becomes soft enough to stick to heat exchanger tubes and other boiler surfaces or at what
temperature it becomes molten so that it flows (as slag), making removal as a liquid from the bottom
of a combustor possible.
Reactivity of a coal is a very important property fundamental to all coal conversion processes (such as
combustion, gasification, and liquefaction). In general, lower rank coals are more reactive than higher
rank coals. This is due to several different characteristics of coals, which vary with rank as well as with
type. The most important characteristics are the surface area of the coal, its chemical composition, and
the presence of certain minerals that can act as catalysts in the conversion reactions. The larger surface
area present in lower rank coals translates into a greater degree of penetration of gaseous reactant
molecules into the interior of a coal particle. Lower rank coals have a less aromatic structure than higher
ranks. This corresponds to the presence of a higher proportion of lower energy, more reactive chemical
bonds. Lower rank coals also tend to have higher proximate ash contents, and the associated mineral
matter is more distributed, even down to the atomic level. Any catalytically active mineral matter is thus
more highly dispersed.
However, the reactivity of a coal also varies depending upon what conversion is attempted. That is, the
reactivity of a coal toward combustion (or oxidation) is not the same as its reactivity toward liquefaction,
and the order of reactivity established in a series of coals for one conversion process will not necessarily be
the same as that for another process.
2.1.3 Coal Reserves
Coal is found throughout the U.S. and the world. It is the most abundant fossil energy resource in the
U.S. and the world, comprising 95% of U.S. fossil energy resources and 70% of world fossil energy
resources on an energy content basis. All coal ranks can be found in the U.S. The largest resources in the
U.S. are made up of lignite and sub-bituminous coals, which are found primarily in the western part of
the country, including Alaska. Bituminous coals are found principally in the Midwest states, northern
Alaska, and the Appalachian region. Principal deposits of anthracite coal are found in
northeastern Pennsylvania.
The Alaskan coals have not been extensively mined because of their remoteness and the harsh climate.
Of the other indigenous coals, the anthracite coals have been heavily mined to the point that little
economic resource remains. The bituminous coals continue to be heavily mined in the lower 48 states,
especially those with sulfur contents less than 2.5 wt%. The lignite and subbituminous coals in the
western U.S. have been historically less heavily mined because of their distance from large population
centers and because of their low calorific values and high moisture and ash contents. However, with the
enactment of the 1990 Clean Air Act Amendments, these coals are now displacing high sulfur-containing
coals for use in the eastern U.S. A map showing the general distribution of coal in the U.S. is included as
Figure 2.1.
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Wind riverregion
Northcentralregion
WA
MT
OR
NVCA
Uintaregion
Greenriver
region
Centralia-chehalis
field
UTWY
NE
CO
KS
OKTX
NMMS
LA
MOTN
AL
KY
ILWIIA
MNSD
ND
Denverbasin
Fortunionregion
PowderriverbasinBighom
basin
Westerninteriorregion
Illinoisbasin Michigan
basin
MI
INOH
NC
SC
Warriorfield
Appalachianregion
FL
Gulf coastregion
DepositRank
Southwesterninterior
Ratonmesaregion
San juanbasin
AZ
AK
Black mesa field
Northern alaskafields
Healy-nenanafields
Matanuskavalleyfields
Kenai field
Anthracite1
Bituminous coal
Subbituminous coal
Lignite
Note: Alaska not to scale of conterminous United States. Small fields and isolated occurrences are not shown.1 Principal anthracite deposits are in Pennsylvania. Small deposits occur in Alaska, Arkansas, Colorado, Massachusetts-Rhode Island, New Mexico, Utah, Virginia, Washington, and West Virginia.
GA
VAMD
PA
DE
NJCT
RIMA
NHVT
ME
NY
Pennsylvaniaanthracite
region
WV
AR
ID
FIGURE 2.1 U.S. coal deposits.
Fossil Fuels 2-7
The amount of coal that exists is not known exactly and is continually changing as old deposits are
mined out and new deposits are discovered or reclassified. Estimates are published by many different
groups throughout the world. In the U.S., the Energy Information Administration (EIA), an office within
the U.S. Department of Energy, gathers and publishes estimates from various sources. The most
commonly used definitions for classifying the estimates are provided below.
2.1.4 Important Terminology: Resources, Reserves, and the DemonstratedReserve Base1
Resources are naturally occurring concentrations or deposits of coal in the Earth’s crust, in such forms and
amounts that economic extraction is currently or potentially feasible.
Measured resources refers to coal for which estimates of the rank and quantity have been computed to a
high degree of geologic assurance, from sample analyses and measurements from closely spaced and
geologically well-known sample sites. Under the U.S. Geological Survey (USGS) criteria, the points of
1For a full discussion of coal resources and reserve terminology as used by EIA, USGS, and the Bureau of Mines, see U.S.
Coal Reserves, 1996, Appendix A, “Specialized Resource and Reserve Terminology.”Sources: U.S. Department of the Interior,
Coal Resource Classification System of the U.S. Bureau of Mines and the U.S. Geological Survey, Geological Survey Bulletin
1450-B (1976). U.S. Department of the Interior, Coal Resource Classification System of the U.S. Geological Survey,
Geological Survey Circular 891 (1983) U.S. Department of the Interior, A Dictionary of Mining, Mineral, and Related Terms,
Bureau of Mines (1968).
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2-8 Energy Conversion
observation are no greater than 1⁄2 mile apart. Measured coal is projected to extend as a 1⁄4 -mile-wide belt
from the outcrop or points of observation or measurement.
Indicated resources refers to coal for which estimates of the rank, quality, and quantity have been
computed to a moderate degree of geologic assurance, partly from sample analyses and measurements
and partly from reasonable geologic projections. Under the USGS criteria, the points of observation are
from 1⁄2 to 11⁄2 miles apart. Indicated coal is projected to extend as a 1⁄2 -mile-wide belt that lies more than1⁄4 mile from the outcrop or points of observation or measurement.
Demonstrated resources are the sum of measured resources and indicated resources.
Demonstrated reserve base (DRB; or simply “reserve base” in USGS usage) is, in its broadest sense,
defined as those parts of identified resources that meet specified minimum physical and chemical criteria
related to current mining and production practices, including those for quality, depth, thickness, rank,
and distance from points of measurement. The “reserve base” is the in-place demonstrated resource from
which reserves are estimated. The reserve base may encompass those parts of a resource that have a
reasonable potential for becoming economically recoverable within planning horizons that extend
beyond those that assume proven technology and current economics.
Inferred resources refers to coal of a low degree of geologic assurance in unexplored extensions of
demonstrated resources for which estimates of the quality and size are based on geologic evidence and
projection. Quantitative estimates are based on broad knowledge of the geologic character of the bed or
region from which few measurements or sampling points are available and on assumed continuation
from demonstrated coal for which geologic evidence exists. The points of measurement are from 11⁄2 to 6
miles apart. Inferred coal is projected to extend as a 21⁄4 -mile-wide belt that lies more than 3⁄4 mile from
the outcrop or points of observation or measurement. Inferred resources are not part of the DRB.
Recoverable refers to coal that is, or can be, extracted from a coalbed during mining.
Reserves relates to that portion of demonstrated resources that can be recovered economically with the
application of extraction technology available currently or in the foreseeable future. Reserves include only
recoverable coal; thus, terms such as “minable reserves,” “recoverable reserves,” and “economic reserves”
are redundant. Even though “recoverable reserves” is redundant, implying recoverability in both words,
EIA prefers this term specifically to distinguish recoverable coal from in-ground resources, such as the
demonstrated reserve base, that are only partially recoverable.
Minable refers to coal that can be mined using present-day mining technology under current
restrictions, rules, and regulations.
The demonstrated reserve base for coals in the U.S. as of January 1, 2001, is approximately 501.1 billion
(short) tons. It is broken out by rank, state, and mining method (surface or underground) in Table 2.5. As
of December 31, 1999 (December 31, 2000, for the U.S.), the world recoverable reserves are estimated to
be 1083 billion (short) tons. A breakdown by region and country is provided in Table 2.6. The
recoverability factor for all coals can vary from approximately 40 to over 90%, depending on the
individual deposit. The recoverable reserves in the U.S. represent approximately 54% of the demon-
strated reserve base as of January 1, 2001. Thus, the U.S. contains approximately 25% of the recoverable
reserves of coal in the world.
2.1.5 Transportation
Most of the coal mined and used domestically in the U.S. is transported by rail from the mine mouth to
its final destination. In 1998, 1119 million short tons of coal were distributed domestically. Rail
constituted 58.3% of the tonnage, followed by water at 21.4%; truck at 11.0%; and tramway, conveyor,
or slurry pipeline at 9.2%. The remaining 0.1% is listed as “unknown method.” Water’s share includes
transportation on the Great Lakes, all navigable rivers, and on tidewaters (EIA 1999).
In general, barge transportation is cheaper than rail transportation. However, this advantage is reduced
for distances over 300 miles (Villagran 1989). For distances less than 100 miles, rail is very inefficient, and
trucks are used primarily, unless water is available as a mode of transport.
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TABLE 2.5 U.S. Coal Demonstrated Reserve Base, January 1, 2001
Bituminous Coal Subbituminous Coal Lignite Total
Region and State Anthracite Underground Surface Underground Surface Surfacea Underground Surface Total
U.S. total 7.5 213.1 53.5 121.3 61.8 43.8 338.5 162.5 501.1
States east of the
Mississippi
River
7.3 186.1 44.8 0.0 0.0 1.1 190.1 49.3 239.4
States west of the
Mississippi
River
0.1 27.0 8.7 121.3 61.8 42.7 148.4 113.3 261.7
Notes: (s)ZLess than 0.05 billion short tons. Data represent known measured and indicated coal resources meeting minimum seam and depth criteria, in the ground as of January 1, 2001.
These coal resources are not totally recoverable. Net recoverability ranges from 0% to more than 90%. Fifty-four percent of the demonstrated reserve base of coal in the United States is
estimated to be recoverable. Totals may not equal sum of components due to independent rounding.
Source: Energy Information Administration, Coal Reserves Data Base.a Lignite resources are not mined underground in the U.S.b Georgia, Maryland, North Carolina, and Tennessee.c Arkansas, Kansas, Louisiana, and Michigan.d Arizona, Idaho, Oregon, and South Dakota.
Source: Energy Information Administration, Coal Reserves Data Base.
2-1
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yC
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TABLE 2.6 World Recoverable Reserves of Coal
Region/Country Recoverable Anthracite
and Bituminous
Recoverable Lignite
and Subbituminous
Total Recoverable
Coal
North America
Canada 3,826 3,425 7,251
Greenland 0 202 202
Mexico 948 387 1,335
U.S. 126,804 146,852 273,656
Total 131,579 150,866 282,444
Central and South America
Argentina 0 474 474
Bolivia 1 0 1
Brazil 0 13,149 13,149
Chile 34 1,268 1,302
Colombia 6,908 420 7,328
Ecuador 0 26 26
Peru 1,058 110 1,168
Venezuela 528 0 528
Total 8,530 15,448 23,977
Western Europe
Austria 0 28 28
Croatia 7 36 43
France 24 15 40
Germany 25,353 47,399 72,753
Greece 0 3,168 3,168
Ireland 15 0 15
Italy 0 37 37
Netherlands 548 0 548
Norway 0 1 1
Portugal 3 36 40
Slovenia 0 303 303
Spain 220 507 728
Sweden 0 1 1
Turkey 306 3,760 4,066
United Kingdom 1,102 551 1,653
Yugoslavia 71 17,849 17,919
Total 27,650 73,693 101,343
Eastern Europe and former U.S.S.R.
Bulgaria 14 2,974 2,988
Czech Republic 2,330 3,929 6,259
Hungary 0 1,209 1,209
Kazakhstan 34,172 3,307 37,479
Kyrgyzstan 0 895 895
Poland 22,377 2,050 24,427
Romania 1 1,605 1,606
Russia 54,110 118,964 173,074
Slovakia 0 190 190
Ukraine 17,939 19,708 37,647
Uzbekistan 1,102 3,307 4,409
Total 132,046 158,138 290,183
Middle East
Iran 1,885 0 1,885
Total 1,885 0 1,885
Africa
(continued)
Fossil Fuels 2-11
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TABLE 2.6 (Continued)
Region/Country Recoverable Anthracite
and Bituminous
Recoverable Lignite
and Subbituminous
Total Recoverable
Coal
Algeria 44 0 44
Botswana 4,740 0 4,740
Central African Republic 0 3 3
Congo (Kinshasa) 97 0 97
Egypt 0 24 24
Malawi 0 2 2
Mozambique 234 0 234
Niger 77 0 77
Nigeria 23 186 209
South Africa 54,586 0 54,586
Swaziland 229 0 229
Tanzania 220 0 220
Zambia 11 0 11
Zimbabwe 553 0 553
Total 60,816 216 61,032
Far East and Oceania
Afghanistan 73 0 73
Australia 46,903 43,585 90,489
Burma 2 0 2
China 68,564 57,651 126,215
India 90,826 2,205 93,031
Indonesia 871 5,049 5,919
Japan 852 0 852
Korea, North 331 331 661
Korea, South 86 0 86
Malaysia 4 0 4
Nepal 2 0 2
New Caledonia 2 0 2
New Zealand 36 594 631
Pakistan 0 2,497 2,497
Philippines 0 366 366
Taiwan 1 0 1
Thailand 0 1,398 1,398
Vietnam 165 0 165
Total 208,719 113,675 322,394
World total 571,224 512,035 1,083,259
Notes: The estimates in this table are dependent on the judgment of each reporting country to interpret local economic
conditions and its own mineral assessment criteria in terms of specified standards of the World Energy Council.
Consequently, the data may not all meet the same standards of reliability, and some data may not represent reserves of
coal known to be recoverable under current economic conditions and regulations. Some data represent estimated recovery
rates for highly reliable estimates of coal quantities in the ground that have physical characteristics like those of coals
currently being profitably mined. U.S. coal rank approximations are based partly on Btu content and may not precisely match
borderline geologic ranks. Data for the U.S. represent recoverable coal estimates as of December 31, 2000. Data for other
countries are as of December 31, 1999.
Millions of tons.
Sources: World Energy Council, Survey of Energy Resources 2001, October 2001. U.S. Energy Information Administration.
Unpublished file data of the Coal Reserves Data Base (February 2002).
2-12 Energy Conversion
Prior to the signing of the 1990 Clean Air Act Amendments, most coal was transported to the closest
power plant or other end-use facility to reduce transportation costs. Because most coal-fired plants are
east of the Mississippi River, most of the coal was transported from eastern coal mines. However, once the
Amendments, which required sulfur emissions to be more strictly controlled, began to be enforced, the
potential economic advantage of transporting and using low-sulfur western coals compared to installing
q 2007 by Taylor & Francis Group, LLC
35
30
25
20
15
10
5
0
Per
cent
Powder river basinCentral appalachia
Other
Illinois basin
Northern appalachia
1997
Rockies
1988 1989 1990 1991 1992 1993 1994 1995 1996
FIGURE 2.2 Supply region shares of domestic coal distribution. (From Energy Information Administration, EIA-6,
“Coal Distribution Report.”)
Fossil Fuels 2-13
expensive cleanup facilities in order to continue to use high-sulfur eastern coals began to be considered.
This resulted in increasing the average distance coal was shipped from 640 miles in 1988 to 793 miles
in 1997.
In comparing shipments from coal-producing regions, the trend of Figure 2.2 shows that an increasing
share of coal was shipped from the low-sulfur coal producing Powder River Basin between 1988 and 1997
and that less coal was shipped from the high-sulfur coal producing Central Appalachian Basin. Overall,
coal use continued to increase at about 2.2% per year over this timeframe.
The cost of transporting coal decreased between 1988 and 1997, due to the increased competition from
the low-sulfur western coals following passage of the Clean Air Act Amendments in 1990. This decrease
held for all sulfur levels, except for a slight increase in medium sulfur B coals over the last couple of years,
as shown in Figure 2.3.
20
15
10
5
0
1996
Dol
lars
per
sho
rt to
n
1997199619951994199319921991199019891988
High sulfur
Low sulfur
Medium sulfur B
Medium sulfur A
All coal
FIGURE 2.3 Average rate per ton for contract coal shipments by rail, by sulfur category, 1988–1997. Notes: low
sulfurZless than or equal to 0.6 lb of sulfur per million Btu; medium sulfur AZ0.61–1.25 lb per million Btu;
medium sulfur BZ1.26–1.67 lb per million Btu; high sulfurZgreater than 1.67 lb per million Btu. 1997. (From
Energy Information Administration, Coal Transportation Rate Database.)
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2-14 Energy Conversion
2.2 Environmental Aspects
Richard Bajura
Along with coal production and use comes a myriad of potential environmental problems, most of
which can be ameliorated or effectively addressed during recovery, processing, conversion, or
reclamation. Underground coal reserves are recovered using the two principal methods of room-and-
pillar mining (60%) and longwall mining (40%). In room-and-pillar mining, coal is removed from the
seam in a checkerboard pattern (the “room”) as viewed from above, leaving pillars of coal in an alternate
pattern to support the roof of the mine. When using this technology, generally half of the reserves are left
underground. Depending upon the depth of the seam and characteristics of the overburden, subsidence
due to the removal of the coal may affect the surface many years after the mining operation is completed.
Because of the danger of collapse and movement of the surface, undermined lands are not used as
building sites for large, heavy structures.
Longwall mining techniques employ the near-continuous removal of coal in rectangular blocks with a
vertical cross section equal to the height of the seam multiplied by the horizontal extent (width) of the panel
being mined. As the longwall cutting heads advance into the coal seam, the equipment is automatically moved
forward. The roof of the mine collapses behind the shields, and most of the effects of subsidence are observed
on the surface within several days of mining. If the longwall mining operation proceeds in a continuous
fashion, subsidence may occur smoothly so that little damage occurs to surface structures. Once subsidence
has occurred, the surface remains stable into the future. Longwall mining operations may influence water
supplies as a result of fracturing of water-bearing strata far removed from the panel being mined.
When coal occurs in layers containing quartz dispersed in the seam or in the overburden, miners are at
risk of exposure to airborne silica dust, which is inhaled into their lungs. Coal workers’ pneumonoco-
niosis, commonly called black lung disease, reduces the ability of a miner to breathe because of the effects
of fibrosis in the lungs.
Surface mining of coal seams requires the removal of large amounts of overburden, which must
eventually be replaced into the excavated pit after the coal resource is extracted. When the overburden
contains large amounts of pyrite, exposure to air and water produces a discharge known as acid mine
drainage, which can contaminate streams and waterways. Iron compounds formed as a result of the
chemical reactions precipitate in the streams and leave a yellow- or orange-colored coating on rocks and
gravel in the streambeds. The acid caused by the sulfur in the pyrite has been responsible for significant
destruction of aquatic plants and animals. New technologies have been and continue to be developed to
neutralize acid mine drainage through amendments applied to the soil during the reclamation phases of
the mining operation. Occasionally, closed underground mines fill with water and sufficient pressure is
created to cause “blowouts” where the seams reach the surface. Such discharges have also been
responsible for massive fish kills in receiving streams.
The potential for acid rain deposition from sulfur and nitrogen oxides released to the atmosphere
during combustion is a significant concern. About 95% of the sulfur oxide compounds can be removed
through efficient stack gas cleaning processes such as wet and dry scrubbing. Also, techniques are
available for removing much of the sulfur from the coal prior to combustion. Combustion strategies are
also being developed that reduce the formation and subsequent release of nitrogen oxides.
The potential for greenhouse warming due to emissions of carbon dioxide during combustion (as well
as methane during mining and mine reclamation) has also been raised as a significant concern. Because
coal is largely composed of carbon with relatively little hydrogen, its combustion leads to a higher level of
carbon dioxide emissions per unit of energy released than for petroleum-based fuels or natural gas.
Defining Terms
Coalification: The physicochemical transformation that coal undergoes after being buried and subjected
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to elevated temperature and pressure. The classification of a particular coal by rank is a measure of
the extent of its coalification. Thus, coalification is a measure of the “age” of a particular coal.
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Fossil Fuels 2-15
Fixed carbon content: One of the constituents that make up the proximate analysis of a coal. It is
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normally measured by difference. That is, one measures the volatile matter content and the moisture
and ash contents, if the fixed carbon content is reported on a basis containing one or both of those
constituents, and subtracts the result(s) from 100% to find the fixed carbon content. One should not
confuse the fixed carbon content of a coal with its (elemental) carbon content found in the ultimate
analysis. Although carbon is certainly in the material making up the fixed carbon content, it is not all
of the carbon present in the original coal, and other elements are also present.
Gross calorific value: Calorific value is a measure of the energy content of a material—in this case, a coal
sample. Calorific value is measured by ASTM Standard Test Method D 2015M, Gross Calorific Value
of Solid Fuel by the Adiabatic Bomb Calorimeter, or by ASTM Standard Test Method D 3286, Gross
Calorific Value of Solid Fuel by the Isothermal-Jacket Bomb Calorimeter. The gross calorific value
takes into account the additional heat gained by condensing any water present in the products of
combustion, in contrast to the net calorific value, which assumes that all water remains in the
vapor state.
Macera1: An organic substance or optically homogeneous aggregate of organic substance in a coal sample
that possesses distinctive physical and chemical properties.
Proximate analysis: A method to measure the content of four separately identifiable constituents in a
coal: volatile matter content; fixed carbon content; moisture content; and ash content, all of which
are reported on a weight percent basis. The standard method for obtaining the proximate analysis of
coal or coke is defined by the ASTM in Standard Test Method D 3172.
Rank: A classification scheme for coals that describes the extent of coalification that a particular coal has
undergone. The structure, chemical composition, and many other properties of coals vary system-
atically with rank. The standard method for determining the rank of a coal sample is defined by the
ASTM in Standard Test Method D 388.
Type: A classification scheme for coals that references the original plant material from which the coal
was derived.
Ultimate analysis: A method to measure the elemental composition of a coal sample. Typical ultimate
analyses include carbon, hydrogen, oxygen, sulfur, and nitrogen contents, but other elements can also
be reported. These other elements are usually not present to any appreciable extent. However, if they
are reported, the sum of all the elements reported (including moisture and ash content) should equal
100%. The standard method for the ultimate analysis of coal or coke is defined by the ASTM in
Standard Test Method D 3176.
Volatile matter content: The mass of material released upon heating the coal sample under specific
conditions, defined by the ASTM Standard Test Method D 3175.
References
Elliott, M. A. and Yohe, G. R. 1981. The coal industry and coal research and development in perspective.
In Chemistry of Coal Utilization. Second Supplementary Volume, M. A. Elliott, ed., pp. 26–328.
Wiley, New York.
Habermehl, D., Orywal, F., and Beyer, H.-D. 1981. Plastic properties of coal. In Chemistry of Coal
Utilization. Second Supplementary Volume, M. A. Elliott, ed., pp. 319–328. Wiley, New York.
Villagran, R. A. 1989. Acid Rain Legislation: Implications for the Coal Industry, pp. 37–39. Shearson,
Lehman, Button, New York.
For Further Information
An excellent resource for understanding coal, its sources, uses, limitations, and potential problems is the
book by Elliott referenced under Elliott and Yohe (1981) and Habermehl et al. (1981). A reader wishing an
understanding of coal topics could find no better resource. Another comprehensive book, which includes
more-recent information but is not quite as weighty as Elliott’s (664 pages vs. 2374 pages), is The Chemistry
7 by Taylor & Francis Group, LLC
2-16 Energy Conversion
and Technology of Coal, edited (second edition, revised and expanded) by James G. Speight. For
information specific to the environmental problems associated with the use of coal, the reader is referred
to Norbert Berkowitz’s chapter entitled “Environmental Aspects of Coal Utilization” in An Introduction to
Coal Technology. For information on the standards for coal analyses and descriptions of the associated
procedures, the reader is referred to any recent edition of the ASTM’s Annual Book of ASTM Standards.
Section 5 covers petroleum products, lubricants, and fossil fuels, including coal and coke.
2.3 Oil
Philip C. Crouse
2.3.1 Overview
The U.S. Department of Energy’s Energy Information Administration (EIA) annually provides a wealth
of information concerning most energy forms including fossil fuels. The oil and natural gas sections are
extracted summaries for the most germane information concerning oil and natural gas. Fossil fuel energy
continues to account for over 85% of all world energy in 2000. The EIA estimates that in 2025, fossil fuels
will still dominate energy resources with natural gas having the most growth. The base case of the EIA
predicts that world energy consumption will grow by 60% over the next two decades. Figure 2.4 shows
steady growth in global energy consumption. The projections show that in 2025 the world will consume
three times the energy it consumed in 1970.
In the United States, wood served as the preeminent form of energy for about half of the nation’s
history. Around the 1880s, coal became the primary source of energy. Despite its tremendous and rapid
expansion, coal was overtaken by petroleum in the middle of the 1900s. Natural gas, too, experienced
rapid development into the second half of the 20th century, and coal began to expand again. Late in the
1900s, nuclear electric power was developed and made significant contributions.
Although the world’s energy history is one of large-scale change as new forms of energy have been
developed, the outlook for the next couple of decades is for continued growth and reliance on the three
major fossil fuels of petroleum, natural gas, and coal. Only modest expansion will take place in renewable
resources and relatively flat generation from nuclear electric power, unless major breakthroughs occur in
800
600
400
200
0
Quadrillion btu
History Projections
207243
285 311348 368
404 433481
532583
640
1970
1975
1980
1985
1990
1995
2001
2005
2010
2015
2020
2025
FIGURE 2.4 World energy consumption, 1970–2025. (History from EIA, International Energy Annual 2001,
DOE/EIA-0219(2001), Washington, DC, Feb. 2003, www.eia.doe.gov/iea/. Projections from EIA, System for the
TABLE 2.10 World Natural Gas Reserves by Country as of January 1, 2003
Country Reserves (trillion ft3) Percent of World Total
World 5501 100.0
Top 20 countries 4879 88.7
Russia 1680 30.5
Iran 812 14.8
Qatar 509 9.2
Saudi Arabia 224 4.1
United Arab Emirates 212 3.9
U.S. 183 3.3
Algeria 160 2.9
Venezuela 148 2.7
Nigeria 124 2.3
Iraq 110 2.0
Indonesia 93 1.7
Australia 90 1.6
Norway 77 1.4
Malaysia 75 1.4
Turkmenistan 71 1.3
Uzbekistan 66 1.2
Kazakhstan 65 1.2
Netherlands 62 1.1
Canada 60 1.1
Egypt 59 1.1
Rest of World 622 11.3
Source: Oil Gas J., 100 (December 23, 2002), 114–115.
Fossil Fuels 2-23
2.4.3 Natural Gas Production Measurement
Natural gas production is generally measured as “dry” natural gas production. It is determined as the
volume of natural gas withdrawn from a reservoir less (1) the volume returned for cycling and
repressuring reservoirs; (2) the shrinkage resulting from the removal of lease condensate and plant
liquids; and (3) the nonhydrocarbon gases. The parameters for measurement are 608F and 14.73 lb
standard per square inch absolute.
2.4.4 World Production of Dry Natural Gas
From 1983 to 1992, dry natural gas production grew from 54.4 to 75 trillion ft3. The breakdown by region
of world is shown in Table 2.11.
TABLE 2.11 World Dry Natural Gas Production
Country/Region 1983 1992 2000
North, Central, and South America 21.20 25.30 30.20
Western Europe 6.20 7.85 10.19
Eastern Europe and former U.S.S.R. 21.09 28.60 26.22
Middle East and Africa 2.95 6.87 12.01
Far East and Oceania 2.96 6.38 9.48
World total 54.40 75.00 88.10
Trillion ft3.
Source: From EIA, Annual Energy Review 1993, EIA, Washington, DC, July 1994, 305, and
International Energy Outlook-2003.
q 2007 by Taylor & Francis Group, LLC
TABLE 2.12 Relation of API Gravity, Specific Gravity, and Weight per Gallon of
Gasoline
Degree API Specific Gravity Weight of Gallon (lb)
8 1.014 8.448
9 1.007 8.388
10 1.000 8.328
15 0.966 8.044
20 0.934 7.778
25 0.904 7.529
30 0.876 7.296
35 0.850 7.076
40 0.825 6.870
45 0.802 6.675
50 0.780 6.490
55 0.759 6.316
58 0.747 6.216
Note: The specific gravity of crude oils ranges from about 0.75 to 1.01.
2-24 Energy Conversion
2.4.5 Compressed Natural Gas
Environmental issues have countries examining and supporting legislation to subsidize the development
of cleaner vehicles that use compressed natural gas (CNG). Even with a push toward the use of CNG-
burning vehicles, the numbers are quite small when compared with gasoline vehicles. Recent efforts
toward car power have been focused on hybrid electric-gasoline cars and fuel cell vehicles.
2.4.6 Liquefied Natural Gas (LNG)
Natural gas can be liquefied by lowering temperature until a liquid state is achieved. It can be transported
by refrigerated ships. The process of using ships and providing special-handling facilities adds
significantly to the final LNG cost. LNG projects planned by a number of countries may become
significant over the next 20 years, with shipments of LNG exports ultimately accounting for up to 25% of
all gas exports.
2.4.7 Physical Properties of Hydrocarbons
The most important physical properties from a crude oil classification standpoint are density or
specific gravity and the viscosity of liquid petroleum. Crude oil is generally lighter than water. A
Baume-type scale is predominantly used by the petroleum industry and is called the API (American
Petroleum Institute) gravity scale (see Table 2.12). It is related directly to specific gravity by the
formula:
4 Zð141:5Þ
ð131:5 C 8APIÞ
where fZ specific gravity. Temperature and pressure are standardized at 608F and 1 atm pressure.
Other key physical properties involve the molecular weight of the hydrocarbon compound and the
boiling point and liquid density. Table 2.13 shows a summation of these properties.
q 2007 by Taylor & Francis Group, LLC
TABLE 2.13 Other Key Physical Properties of Hydrocarbons
Compound Molecular
Weight
Boiling Point at
14.7 psia in 8F
Liquid Density at 14.7 psia
and 608F-lb/gal
Methane 16.04 K258.7 2.90
Ethane 30.07 K125.7 4.04
Propane 44.09 K43.7 4.233
Isobutane 58.12 10.9 4.695
n-Butane 58.12 31.1 4.872
Isopentane 72.15 82.1 5.209
n-Pentane 72.15 96.9 5.262
n-Hexane 86.17 155.7 5.536
n-Heptane 100.2 209.2 5.738
n-Octane 114.2 258.2 5.892
n-Nonane 128.3 303.4 6.017
n-Decane 142.3 345.4 6.121
Fossil Fuels 2-25
Defining Terms
API gravity: A scale used by the petroleum industry for specific gravity.
Discovered resources: Include all production already out of the ground and reserves.Proved resources: Resources that geological and engineering data demonstrate with reasonable certainty
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to be recoverable in future years from known reservoirs under existing economic and
operating conditions.
Recoverable resources: Include discovered resources.
For Further Information
The Energy Information Agency of the U.S. Department of Energy, Washington, DC, publishes
International Energy Outlook and other significant publications periodically.