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CHAPTER 48
COALS, LIGNITE, PEAT
James G. Keppeler, P.E.
Progress Energy Corporation
48.1 INTRODUCTION 15 35
48.1.1 Nature 15 35
48. 1 .2 Reserves— Worldwide
and United States 15 35
48.1.3 Classifications 15 37
48.4 PHYSICAL AND CHEMICAL
PROPERTIES— DESCRIPTION
AND TABLES OF SELECTED
VALUES
15 40
48.5 BURNING
CHARACTERISTICS 15 41
48.2 CURRENT USES— HEAT,
POWER, STEELMAKING,
OTHER
15 39
48.6 ASH CHARACTERISTICS 15 43
48.3 TYPES
15 39
48.7 SAMPLING
15 45
48.8 COAL CLEANING
15 46
48.1 INTRODUCTION
48.1.1 Nature
Coal is a dark brown to black sedimentary rock derived primarily from the unoxidized remains of
carbon-bearing plant tissues. It is a complex, combustible mixture of organic, chemical, and mineral
materials found in strata, or "seams," in the earth, consisting of a wide variety of physical and
chemical properties.
The principal types of coal, in order of metamorphic development, are lignite, subbituminous,
bituminous, and anthracite. While not generally considered a coal, peat is the first development stage
in the "coalification" process, in which there is a gradual increase in the carbon content of the fossil
organic material, and a concomitant reduction in oxygen.
Coal substance is composed primarily of carbon, hydrogen, and oxygen, with minor amounts of
nitrogen and sulfur, and varying amounts of moisture and mineral impurities.
48.1.2 Reserves—Worldwide and United States
According to the World Coal Study (see Ref. 3), the total geological resources of the world in
"millions of tons of coal equivalent" (mtce) is 10,750,212, of which 662,932, or 6%, is submitted
as "Technically and Economically Recoverable Resources."
Millions of tons of coal equivalent is based on the metric ton (2205 Ib) with a heat content of
12,600 Btu/lb (7000 kcal/kg).
A summary of the percentage of technically and economically recoverable reserves and the per-
centage of total recoverable by country is shown in Table 48.1.
As indicated in Table 48.1, the United States possesses over a quarter of the total recoverable
reserves despite the low percentage of recovery compared to other countries.
It is noted that the interpretation of "technical and economic" recovery is subject to considerable
variation and also to modification, as technical development and changing economic conditions dic-
tate. It should also be noted that there are significant differences in density and heating values in
various coals, and, therefore, the mtce definition should be kept in perspective.
In 1977, the world coal production was approximately 2450 mtce,3 or about V^oth of the recov-
erable reserves.
Mechanical Engineers' Handbook, 2nd ed., Edited by Myer Kutz.
ISBN 0-471-13007-9 © 1998 John Wiley & Sons, Inc.
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Table 48.1
Percentage of
Recoverable3 of
Geological Resources
5.5
1.3
6.8
13.9
15.3
42.6
59.7
23.7
6.5
2.2
24.3
Percentage of Total
Recoverable Reserves
4.9
0.6
14.9
5.2
1.9
9.0
6.5
6.8
25.2
16.6
8.4
100.0
"Technically and economically recoverable reserves. Percentage indicated is based on total geological
resources reported by country.
Source: World Coal Study, Coal— Bridge to the Future, 1980.
Australia
Canada
Peoples Republic of China
Federal Republic of Germany
India
Poland
Republic of South Africa
United Kingdom
United States
Soviet Union
Other Countries
Table 48.2 Demonstrated Reserve Base3 of Coal in the United States on January, 1980,
by Rank (Millions of Short Tons)
State*
Alabama**
Alaska
Arizona
Arkansas
Colorado**
Georgia
Idaho
Illinois'*
Indiana
Iowa
Kansas
Kentucky
Eastern**
Western
Maryland
Michigan**
Missouri
Montana
New Mexico**
North Carolina
North Dakota
Ohio**
Oklahoma
Oregon
Pennsylvania
South Dakota
Tennessee**
Texas'*
Utah**
Virginia
Washington**
West Virginia
Wyoming**
Totalc
Anthracite
Bituminous
3,916.8
697.5
410.0
288.7
9,086.1
3.6
4.4
67,606.0
10,586.1
2,197.1
993.8
Subbituminous
Lignite
1,083.0
14.0
Total0
4,999.8
6,154.5
410.0
410.7
17,281.3
3.6
4.4
67,606.0
10,586.1
2,197.7
993.8
5,443.0
96.4
25.5
25.7
4,189.9
3,979.9
12,927.5
21,074.4
822.4
127.7
6,069.1
1,385.4
1,835.7
10.7
12,927.5
21,074.4
822.4
127.7
6,069.1
120,428.0
4,521.4
10.7
9,952.3
19,056.1
1,637.8
17.5
30,280.8
366.1
983.7
12,659.7
6,477.6
3,471.4
1,481.3
39,776.2
69,924.0
472,713.6
103,277.4
2,683.4
15,765.2
2.3
9,952.3
19,056.1
1,637.8
17.5
7,092.0
23,188.8
366.1
983.7
12,659.7
1.1
6,476.5
3,345.9
303.7
39,776.2
4,460.5
239,272.9
125.5
1,169.4
8.1
65,463.5
182,035.0
7,341.7
44,063.9
a Includes measured and indicated resource categories defined by USBM and USGS and represents
100% of the coal in place.
b Some coal-bearing states where data are not sufficiently detailed or where reserves are not currently
economically recoverable.
cData may not add to totals due to rounding.
**Data not completely reconciled with demonstrated reserve base data.
815043739.007.png
According to the U.S. Geological Survey, the remaining U.S. Coal Reserves total almost 4000
billion tons,4 with overburden to 6000 ft in seams of 14 in. or more for bituminous and anthracite
and in seams of 21/2 ft or more for subbituminous coal and lignite. The U.S. Bureau of Mines and
U.S. Geological Survey have further defined "Reserve Base" to provide a better indication of the
technically and economically minable reserves, where a higher degree of identification and engi-
neering evaluation is available.
A summary of the reserve base of U.S. coal is provided in Table 48.2.5
48.1.3 Classifications
Coals are classified by "rank," according to their degree of metamorphism, or progressive alteration,
in the natural series from lignite to anthracite. Perhaps the most widely accepted standard for clas-
sification of coals is ASTM D388, which ranks coals according to fixed carbon and calorific value
(expressed in Btu/lb) calculated to the mineral-matter-free basis. Higher-rank coals are classified
according to fixed carbon on the dry basis; the lower-rank coals are classed according to calorific
value on the moist basis. Agglomerating character is used to differentiate between certain adjacent
groups. Table 48.3 shows the classification requirements.
Agglomerating character is determined by examination of the residue left after the volatile deter-
mination. If the residue supports a 500-g weight without pulverizing or shows a swelling or cell
structure, it is said to be "agglomerating."
The mineral-matter-free basis is used for ASTM rankings, and formulas to convert Btu, fixed
carbon, and volatile matter from "as-received" bases are provided. Parr formulas—Eqs. (48.1)-(48.3)
are appropriate in case of litigation. Approximation formulas—Eqs. (48.4)-(48.6) are otherwise
acceptable.
Parr formulas
ff A 1 C C
Dry, MM-Free FC = 10Q _ (M +~^ + 0.555) x 100
(48.!)
Dry, MM-Free VM = 100 - Dry, MM-Free FC
(48.2)
Moi* MM-Free Btu = 100 ^^To.SSS) X 10°
(483)
Approximation formulas
FC
Dry, MM-Free FC - 1QQ _ (M + UA + 0.15) * ™
(48.4)
Dry, MM-Free VM = 100 - Dry, MM-Free FC
(48.5)
Moist, MM-Free Btu = 1QQ _ <** + QJ5) X 100
(48.6)
where MM = mineral matter
Btu = British thermal unit
FC = percentage of fixed carbon
VM = percentage of volatile matter
A = percentage of ash
S = percentage of sulfur
Other classifications of coal include the International Classification of Hard Coals, the Interna-
tional Classification of Brown Coals, the "Lord" value based on heating value with ash, sulfur, and
moisture removed, and the Perch and Russell Ratio, based on the ratio of Moist, MM-Free Btu to
Dry, MM-Free VM.
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Table 48.3 ASTM (D388) Classification of Coals by Rank3
Fixed Carbon
Limits, Percent(Dry,
Mineral-
Matter-Free Basis)
Equal to or Less
Less Than Than
Volatile Matter
Limits, Percent
(Dry, Mineral-
Matter-Free Basis)
Greater Equal to or
Than Less Than
Calorific Value
Limits, Btu/lb
Moist,* Mineral-
Matter-Free Basis)
Equal to or Less
Less Than Than
Agglomerating
Character
Class
Group
I Anthracitic
1 . Metaanthracite
2. Anthracite
3. Semianthracite0
1. Low-volatile bituminous
2. Medium-volatile bituminous
3. High- volatile A bituminous
4. High-volatile B bituminous
5. High-volatile C bituminous
98
—
—
2
92
98
2
8
Nonagglomerating
86
92
8
14
II Bituminous
78
86
14
22
69
78
22
31
Commonly
agglomerating*
—
69
31
—
14,000* —
13,000^ 14,000
11,500
13,000
10,500
11,500
Agglomerating
III Subbituminous
1. Subbituminous A
2. Subbituminous B
3. Subbituminous C
1. Lignite A
2. Lignite B
10,500
11,500
9,500
10,500
8,300
9,500
IV Lignitic
6,300
8,300
—
6,300
"This classification does not include a few coals, principally nonbanded varieties, that have unusual physical and chemical properties and that come within the limits of fixed
carbon or calorific value of the high- volatile bituminous and Subbituminous ranks. All of these coals either contain less than 48% dry, mineral-matter-free fixed carbon or have
more than 15,500 moist, mineral-matter-free British thermal units per pound.
* Moist refers to coal containing its natural inherent moisture but not including visible water on the surface of the coal.
clf agglomerating, classify in the low-volatile group of the bituminous class.
^Coals having 69% or more fixed carbon on the dry, mineral-matter-free basis shall be classified according to fixed carbon, regardless of calorific value.
elt is recognized that there may be nonagglomerating varieties in these groups of the bituminous class and that there are notable exceptions in the high- volatile C bituminous
group.
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48.2 CURRENT USES—HEAT, POWER, STEELMAKING, OTHER
According to statistics compiled for the 1996 Keystone Coal Industry Manual, the primary use of
coals produced in the United States in recent years has been for Electric Utilities; comprising almost
90% of the 926 million tons consumed in the U.S. in 1993. Industry accounted for about 8% of the
consumption during that year in a variety of Standard Industrial Classification (SIC) Codes, replacing
the manufacturing of coke (now about 3%) as the second largest coal market from the recent past.
Industrial users typically consume coal for making process steam as well as in open-fired applications,
such as in kilns and process heaters.
It should be noted that the demand for coal for coking purposes was greater than the demand for
coal for utility use in the 1950's, and has steadily declined owing to more efficient steelmaking,
greater use of scrap metal, increased use of substitute fuels in blast furnaces, and other factors. The
production of coke from coal is accomplished by heating certain coals in the absence of air to drive
off volatile matter and moisture. To provide a suitable by-product coke, the parent coal must possess
quality parameters of low ash content, low sulfur content, low coking pressure, and high coke strength.
By-product coking ovens, the most predominant, are so named for their ability to recapture otherwise
wasted by-products driven off by heating the coal, such as coke oven gas, coal-tar, ammonia, oil,
and useful chemicals. Beehive ovens, named for their shape and configuration, are also used, albeit
much less extensively, in the production of coke.
48.3 TYPES
Anthracite is the least abundant of U.S. coal forms. Sometimes referred to as "hard" coal, it is shiny
black or dark silver-gray and relatively compact. Inasmuch as it is the most advanced form in the
coalification process, it is sometimes found deeper in the earth than bituminous. As indicated earlier,
the ASTM definition puts upper and lower bounds of dry, mineral-matter-free fixed carbon percent
at 98% and 86%, respectively, which limits volatile matter to not more than 14%. Combustion in
turn is characterized by higher ignition temperatures and longer burnout times than bituminous coals.
Excepting some semianthracites that have a granular appearance, they have a consolidated ap-
pearance, unlike the layers seen in many bituminous coals. Typical Hardgrove Grindability Index
ranges from 20 to 60 and specific gravity typically ranges 1.55 ± 0.10.
Anthracite coals can be found in Arkansas, Colorado, Pennsylvania, Massachusetts, New Mexico,
Rhode Island, Virginia, and Washington, although by far the most abundant reserves are found in
Pennsylvania.
Bituminous coal is by far the most plentiful and utilized coal form, and within the ASTM defi-
nitions includes low-, medium-, and high-volatile subgroups. Sometimes referred to as "soft" coal,
it is named after the word bitumen, based on general tendency toward forming a sticky mass on
heating.
At a lower stage of development in the coalification process, carbon content is less than the
anthracites, from a maximum of 86% to less than 69% on a dry, mineral-matter-free basis. Volatile
matter, at a minimum of 14% on this basis, is greater than the anthracites, and, as a result, combustion
in pulverized form is somewhat easier for bituminous coals. Production of gas is also enhanced by
their higher volatility.
The tendency of bituminous coals to produce a cohesive mass on heating lends them to coke
applications. Dry, mineral-matter-free oxygen content generally ranges from 5% to 10%, compared
to a value as low as 1% for anthracite. They are commonly banded with layers differing in luster.
The low-volatile bituminous coals are grainier and more subject to size reduction in handling.
The medium-volatile bituminous coals are sometimes distinctly layered, and sometimes only
faintly layered and appearing homogeneous. Handling may or may not have a significant impact on
size reduction.
The high-volatile coals (A, B, and C) are relatively hard and less sensitive to size reduction from
handling than low- or medium-volatile bituminous.
Subbituminous coals, like anthracite and lignite, are generally noncaking. "Caking" refers to
fusion of coal particles after heating in a furnace, as opposed to "coking," which refers to the ability
of a coal to make a good coke, suitable for metallurgical purposes.
Oxygen content, on a dry, mineral-matter-free basis, is typically 10-20%.
Brownish black to black in color, this type coal is typically smooth in appearance with an absence
of layers.
High in inherent moisture, it is ironic that these fuels are often dusty in handling and appear
much like drying mud as they disintegrate on sufficiently long exposure to air.
The Healy coal bed in Wyoming has the thickest seam of coal in the United States at 220 ft. It
is subbituminous, with an average heating value of 7884 Btu/lb, 28.5% moisture, 30% volatile matter,
33.9% fixed carbon, and 0.6% sulfur. Reported strippable reserves of this seam are approximately
11 billion tons.4
Lignites, often referred to as "brown coal," often retain a woodlike or laminar structure in which
wood fiber remnants may be visible. Like subbituminous coals, they are high in seam moisture, up
to 50% or more, and also disintegrate on sufficiently long exposure to air.
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