pdf file formatCoal and Slag as an Archeological Artifact
Coal and Slag Characterization for Archaeologists
or “Coal and Slag Are Everywhere”
Presented at 2003 SHA Conference
Providence, R.I.
Rod Hatt
Coal Combustion, Inc.
114 South Main Street
Versailles, KY 40383
In this workshop we will explore the analytical tools used in industry to characterizes and identify coal types. The presenter believes that in many cases this information can add clues for the archeological interpretation of a site. A main premise is that the type of coal deposited at a site can change over time as the coal supply for a region shifts. The types of coals shift over time due to many factors including reserve depletion, mining cost and perhaps most importantly, in the last 170+ years, as rail and water transportation developed. The less developed science of slag produced from combustion will also be covered.
Outline
I. What coal is
II. Short history of coal production
III. Changes in coal production over time
IV. Analytical Methods for coal characterization
V. Interpretation
VI. Slag characterization
VII. Future and data collection/retrieval
I. What coal is
A. Fossilized swamp
B. Had greenhouse gases, tremendous plant growth
C. Coalification process
i. With time, pressure, temperature, usually caused by burial under rock and mountains
ii. PEAT - Sable, hundreds to thousands of years old, think peat bogs and preservation of organic material
iii. LIGNITE - Brown coal, high moisture
iv. SUB-BITUMINOUS – Black, dull, friable, oxidizes easily
v. BITUMINOUS – Black, shiny, hard to friable, banded unless cannel coal
vi. ANTHRACITE – Black glass, conchoidal fractures
D. Geological impacts post formation, faulting, volcanic, dykes, water and water born minerals, fires, erosion…
II. Short history of coal production
A. Prehistory uses, found on surface, side of mountains, spontaneous combustion, natural combustion, scoria or red dog
B. Early civilizations, Chinese, Greeks 4th century BC used lignites
C. Primary uses in heating and smelting ores
D. Trading documented in 13th century England
E. Paris, France 1550’s coal use was objectionable and smiths were banned from using or paid fine for use
F. By the 17th century many European cities were regulating use
G. The use of the steam engine and steam power greatly increased coal production, 1690+, English coal mines and water pumps
H. Brief timeline for US coal production
Brief US Coal History Timeline
1643 Louis Jolliet and Father Jacques Marquette discover charbon de tierra (coal) on Illinois River
1748 First recorded coal production in Mankin, VA area
1762 Anthracite discovered in PA
1776 Coal used in shot and shell manufacturing during Revolutionary War
1787-9 First extensive mining at Richmond, VA for shipment to New York, Philadelphia and Boston
1790+ Anthracite mining begins in PA
1816 Baltimore, MD first city to light streets with coal gas
1817 Coal mining being conducted near St. Louis, MO
1818 Explosives first used in PA anthracite mines
1819 Mining begins in Meigs County, OH for shipment to Louisville, KY
1827 Mule power rail line installed in Mauch Chunk, PA for delivering coal to Lehigh River then to Philadelphia
1829 Delaware and Hudson Canal completed to bring Wyoming Valley anthracite to New York City
1830 Tom Thumb, first steam locomotive
1848 First coal miner’s union formed in Schuylkill County, PA
1860 Mining in Camden, AR
1866 Strip mining started near Danville, IL
1869 Golden Spike, transcontinental railroad completed
1872 Strip mining in Kansas
1875 Coal replaces charcoal as major fuel for blast furnaces
1879 Coal mining in Utah
III. Changes in coal production over time
A. The historical record of coal production is well documented back to about 1880 and many records exist prior to 1880
B. Canal, barge, and river transportation of coal were use early on
C. Significant changes in production brought by railroad service moving into mountains
D. Mines open by railroads for fuel
E. Economics of coal force expensive mines to close if alternatives are available
F. Coal reserves are finite and production can be limited as reserves deplete
Figures 1 and 2 are derived from coal production records. There are significant differences in levels of production. Figure 1 compares production levels of two types of coals, Pennsylvania anthracite and Virginian bituminous. Figure 2 shows time of maximum production for individual counties.
Figure 1. Annual production levels for two different coal fields.
http--pubs.usgs.gov-mf-maps-mf-2330-milici1.pdf
Figure 2. Maximum coal production by decades and county
By Robert C. Milici, USGS
IV. Coal Characterization
Coal is a combustible material; it will slowly oxidize in air at room temperature. The oxidizing of coal will alter its test results. It is best to consider coal oxidation in your sample. High ranks coals are more stable than low rank coals. Coals preserved under water or with limited exposure to air are preferred.
A. Coal Sampling - Experiment
Team 1 Team 2 Team 3 Team 4 Team 5
% White
The actual Value of the percent white marbles is ____. How well did we do with limited sampling? How can we improve our results?
B. Sampling procedures
1. Should include description and classification of hand samples
2. Should include storage history and preservation methods
3. Should include retention of portions for further analyses
4. Retention and storage procedures to be developed and documented
C. Should we use Statistical or Human discretion in sample preparation
1. If samples are unique or recovered from specific location consider individual analyses
2. Are they same coal, if yes consider statistical
3. Use hand sample observations, (HSO) to sort types
4. Consider core hole in sample verses crushing sample
D. Sample Quantities
1. Standard industry samplings procedures require hundreds of pounds to be collected representing
thousands of tons of material.
2. A one-inch square piece of coal contains approximately 25 grams of material.
3. Proximate and Ultimate analyses are destructive but require as little as 6 grams of material to conduct.
4. Ash chemistry material needs are inversely proportional to the amount of ash in the sample but will require a minimum of 5-10 grams of coal.
5. Coal petrology calls for 50 grams, maybe we can get away with 25 grams. Sample is preserved
in epoxy
I’m a coal expert now!
Please describe the hand samples now and make educated guess as to what they are:
Fracture Luster Banding Friability Coal Type
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
1a.
13.
14.
D. Analytical Procedures
1. Non-destructive
a. Hand Sample Observations (HSO), classification of hand samples
Terms:
Fracture - conchoidal, angular, cubic, planer,
Luster – dull, shiny, glossy, color
Banding – brightness range, thickness
Friability – crumbles, chips, dusty, hard
b. Petrology can be performed on polished sections of coal imbedded in epoxy, this will alter
sample but will also preserve it.
2. Destructive
a. Proximate and Ultimate
b. Ash chemistry
3. New Methods
a. Methods such as determining the salt water penetration or absorption rates may require new
sampling, preparation, and preservation techniques to be developed.
COAL PETROGRAPHY
This section adapted from:
Kural, O. (1994): Coal, Istanbul Technical University, Istanbul. 494 pp.
Introduction
Coal is not a homogeneous substance but is composed of discrete entities. Coal petrography is the study of coal entities under microscope and its indications to various subjects, such as mode of origin and commercial processes of coal. The smallest constituents of coals are called macerals. Macerals are analogous to the minerals of inorganic rocks.
Coal
Coal is a compact, stratified mass of former plant debris consisting largely of lignocellulosic components often interspersed with inorganic clay, silt or sand. The plant parts, with the effects of heat, change their properties, becoming denser and danker. Since the constituents of coal become darker, it is essential to observe polished sections and to use reflected light microscopy in their study.
Petrography of Coal
Microscopic Constituents of
Coals
Macerals and minerals are the microscopic constituents of coal. The term maceral
describes the shape and the nature of the microscopically recognizable (organic)
constituents of coal. A maceral is not crystalline but varies widely in its
chemical composition and physical properties. The macerals are distinguished
from one another microscopically on the basis of their differences in such
properties as reflectance, color, morphology, size and hardness. To exclude any
ambiguity in the definitions of different macerals, the ICCP has established
standard roles for petrographic microscopy, which provide that the description
of macerals and microlithotypes shall correspond to their appearance in
reflected light using oil immersion objectives with 25x to 50x magnifications.
Macerals take the suffix -inite, and microlithotypes take the suffix -ite
Macerals
Within the ICCP Handbook
(1971), the macerals are defined as the microscopically recognizable individual
constituents of coal. ISO standard 7404/1 explains macerals and the methods for
their petrographical analysis. In the lignite and bituminous coalification
stages, the macerals are classified in three groups: Vitrinite (Huminite in
lignites), Liptinite (former Exinite) and Inertinite.
Each group includes a series
of macerals that can be regarded as belonging together due to similar optical
and chemical properties.
In coal of the same rank, vitrinite (or huminite) usually contains relatively
more oxygen, the liptinite more hydrogen, and the inertinite more carbon. The
volatile matter yield is relatively highest in the liptinite. With increasing
coalification rank, the macerals change in their chemical, physical and
technological properties. There is a distinct relationship between the
reflectance of a maceral and its carbon or volatile matter yield. This means
that the rank of a coal can be determined by its reflectance on a polished
surface.
With increasing rank, the
individual macerals become less different in reflectance, making it more
difficult to differentiate between them under the microscope. When examining a
polished surface of anthracite or a higher rank of organic material, special
techniques are required to recognize the individual macerals.
Complementary methods of examination such as fluorescence microscopy or etching
polished surfaces can help to reveal the normally hidden internal structures of
the macerals and their chemical and physical properties. Shapes and structures,
which are not recognizable by the normal microscopic examination of polished
surfaces using oil immersion, are made visible in this way. The fluorescence
properties of liptinite and vitrinite are rank dependent.
The three maceral groups in
the lower ranks of coal exhibit different light absorption and, therefore,
different light reflectance. To make the measurements more meaningful for the
rank of coal, reflectance is always calibrated with standards like sapphires,
artificial garnets, diamond.
Vitrinite (Huminite in Lignites) - This maceral group is the most abundant and
important maceral group in coal. The low rank coal, being the less altered,
exhibits a greater variety of macerals than higher rank coal. The huminites are
regarded as the precursors of the vitrinites. The huminite macerals are
distinguished from each other primarily by their stage of preservation or decay
and their degree of gelification, a process by which the humic (plant) matter
passes through a soft plastic gel stage and takes on a swollen appearance. The
degree of gelification has been shown to correlate with the performance of such
industrial processes as crushing and briquetting, tar and char yields.
The vitrinite group of macerals is generally the most abundant maceral group
occurring in the higher rank coal. The carboniferous coal of the Northern
Hemisphere is usually rich in vitrinite. The reflectance of vitrinite is often
used as a measure of rank due to its sensitivity to metamorphism and its gradual
physical and chemical change when subjected to metamorphism. Compared with the
liptinites and inertinites in coal of the same rank, the vitrinites (or
huminites) have intermediate reflectance properties, hydrogen and carbon
contents, and volatile matter yields.
V. Interpretation
So you are holding a coal analyses form with numbers on it, now what? You sent in a non-representative, improperly stored, contaminated, coal sample (or precious artifact maybe). The sample no longer exists because it has been destructively tested or at best entombed in epoxy. The world is seen through many eyes and we are just new at this.
A. Rank determination - Proximate and Heating Value tests
1. Local coal
2. Potential sources
3. Transportation routes
4. Potential use
5. Smokeless
6. Coke
B. Petrographic Results
1. Rank
2. Unique or distinguishing traits
3. Match source
C. Chemical Testing
1. Sulfur - match source
2. Ash Chemistry - match slag
3. Trace - maybe similar to ore and metal work
D. Coal Type Stratigraphy
1. Did coal source change with time
2. Marine use of coal
3. Disturbances, man, weather…
VI. Slag Samples
A. Slags are produced by many processes
1. Coal combustion
2. Ore processing
3. Glass manufacturing
4. Volcanic lavas can all be classified as slags
B. Morphologies, chemistry and petrology allow for classification
1. Metallic
2. Amorphous
3. Vesicular
4. Sintered
5. Many classification systems
C. Uses
1. Max Temperature
2. Slag stratigraphy
3. Fly ash deposition
4. Saline penetration
5. Magnetic alignment
6. Nice microphotographs