6 COAL Abstract Coal is the primary source of energy for most of the countries in the world. Although the main use of coal is in the generation of electricity, recently synthesis of liquid fuel from coal is becoming attractive, although coal liquefaction is a very old and well known process that was developed just after World War I. This may relieve pressure on petroleum as the only source of automobile fuel. However, a major concern in the use of coal is emissions of various pollutants including gases that cause acid rain and C02 emissions - a major contributor to global warming. Two approaches are pursued to reduce emissions from coal power plants. Most of the recent coal power plants are designed to produce supercritical steam, increasing the efficiency to about 50%. Another approach is to develop zero emission coal power plants. In this chapter, a comprehensive discussion on the use of coal and associated issues are presented. 6.1 Introduction Coal has a long and rich history. The commercial use of coal can be traced back to 1000 BC by China. However, there is evidence that coal has been used for heating by the cave men. Archeologists have also found evidence that the Romans in England used coal in the second and third centuries (100-200 AD). The first scientific reference to coal may have been made by the Greek philosopher and scientist Aristotle, who referred to a charcoal like rock. It was during the Industrial Revolution in the 18th and 19th centuries that demand for coal surged. The introduction of the steam engine by James Watt in 1769 was largely responsible for the growth in coal use. Coal was discovered in the United States by explorers in 1673. However, the Hopi Indians used coal for cooking, heating and to bake the pottery during the 1300s. Commercial coal mines started operation around 1740s in Virginia. During 159 T.K. Ghosh and M.A. Prelas, Energy Resources and Systems: Volume 1: Fundamentals and Non-Renewable Resources, 159-279. © Springer Science + Business Media B.V. 2009 Licensed to Jiri Martinec 160 6 Coal the Civil War, weapons factories were beginning to use coal. By 1875, coke (which is made from coal) replaced charcoal as the primary fuel for iron blast furnaces to make steel. The use of coal for electricity generation started around the nineteenth century. The first practical coal-fired electricity generating station, developed by Thomas Edison, went into operation in New York City in 1882, supplying electricity for household lights. Coal was the primary source of energy until 1960s. The use of oil for transportation overtook coal as the largest source of primary energy in the 1960s. However, coal still plays a vital role in the world's primary energy mix, providing 24.4% of global primary energy needs in 2003 and 40.1% of the world's electricity. The production and consumption of coal by various regions and some selected countries are given in Tables 6.1 and 6.2. As can be seen from Table 6.2, the use of coal world wide is increasing slowly. In Table 6.3 shows how long the coal will last at the current rate of use and with modest increase in the next few years. Table 6.1. Yearly coal production of selected countries in million tonnes. Countries Years Share of the 2003 2004 2005 2006 World (%) USA 972.3 1008.9 1026.5 1053.6 19.3 Canada 62.1 66.0 65.3 62.9 1.1 Mexico 9.7 9.9 10.0 11.1 0.2 Total North America 1044.1 1084.8 1101.8 1127.7 20.5 Brazil 4.7 5.4 6.3 6.3 0.1 Colombia 50.0 53.7 60.6 65.6 1.4 Venezuela 7.0 8.1 8.1 8.1 0.2 Other S. & Cent. America 0.5 0.3 0.8 0.7 - Total S. & Cent. America 62.2 67.5 75.7 80.7 1.7 Bulgaria 27.3 26.6 26.4 27.5 0.2 Czech Republic 63.9 62.0 62.0 62.4 0.8 France 2.2 0.9 0.6 0.5 - Germany 204.9 207.8 202.8 197.2 1.6 Greece 71.0 71.6 70.6 70.6 0.3 Hungary 13.3 11.5 9.6 10.0 0.1 Kazakhstan 84.9 86.9 86.6 96.3 1.6 Licensed to Jiri Martinec 6.1 Introduction 161 Countries Years Share of the 2003 2004 2005 2006 World (%) Poland 163.8 162.4 159.5 156.1 2.2 Romania 33.1 31.8 31.1 35.1 0.2 Russian Federation 276.7 281.7 298.5 309.2 4.7 Spain 20.5 20.5 19.4 18.4 0.2 Turkey 49.3 49.9 61.7 63.4 0.4 Ukraine 80.2 81.3 78.7 80.5 1.4 United Kingdom 28.3 25.1 20.5 18.6 0.4 Other Europe & Eurasia 66.2 65.2 63.9 66.7 0.5 Total Europe & Eurasia 1185.7 1185.1 1192.0 1212.4 14.5 Total Middle East 1.0 1.1 1.1 1.1 - South Africa 237.9 243.4 244.4 256.9 4.7 Zimbabwe 2.8 3.8 2.9 2.9 0.1 Other Africa 2.0 2.0 1.8 1.8 - Total Africa 242.7 249.2 249.0 261.6 4.8 Australia 351.5 366.1 378.8 373.8 6.6 China 1722.0 1992.3 2204.7 2380.0 39.4 India 375.4 407.7 428.4 447.3 6.8 Indonesia 114.3 132.4 146.9 195.0 3.9 Japan 1.3 1.3 1.1 1.3 - New Zealand 5.2 5.2 5.3 5.8 0.1 Pakistan 3.3 3.3 3.5 4.3 0.1 South Korea 3.3 3.2 2.8 2.8 - Thailand 18.8 20.1 20.9 19.4 0.2 Vietnam 19.3 26.3 32.6 38.9 0.7 Other Asia Pacific 37.5 40.0 41.9 43.1 0.7 Total Asia Pacific 2651.8 2997.7 3267.0 3511.7 58.5 TOTAL WORLD 5187.6 5585.3 5886.7 6195.1 100.0 commercial solid fuels only, i.e. bituminous coal and anthracite (hard coal), and lignite and brown (sub-bituminous) coal. Annual changes and shares of total are based on data expressed in tonnes oil equivalent. Because of rounding some totals may not agree exactly with the sum of their component parts. Source: Reference [1], Licensed to Jiri Martinec 162 6 Coal Table 6.2. World coal consumption by regions and of selected countries. Region/Country 2002 2003 2004 % of World in 2004 World Total 5,262.80 5,698.15 6,098.78 Asia & Oceania 2,448.45 2,795.88 3,190.25 52.31 North America 1,151.89 1,182.43 1,182.53 19.39 Europe 1,030.01 1,052.40 1,036.30 16.99 Eurasia 398.01 413.30 429.40 7.04 Africa 184.44 200.33 205.83 3.37 Central & South America 35.92 37.57 38.21 0.63 Middle East 16.07 16.23 16.27 0.27 China 1,412.96 1,720.24 2,062.39 33.82 United States 1,065.84 1,094.86 1,107.25 18.16 India 434.44 448.62 478.16 7.84 Germany 278.98 277.29 279.95 4.59 Russia 240.23 243.43 257.52 4.22 Japan 173.47 185.24 203.72 3.34 South Africa 169.56 186.60 195.14 3.20 Australia 145.37 142.64 150.09 2.46 Poland 149.45 155.49 153.10 2.51 Ukraine 71.51 75.39 77.50 1.27 Korea, South 81.47 83.13 90.56 1.48 Greece 76.81 78.16 80.34 1.32 Turkey 73.16 70.65 69.59 1.14 Canada 72.21 68.88 57.76 0.95 Kazakhstan 66.24 72.32 72.86 1.19 Czech Republic 64.65 65.58 63.43 1.04 United Kingdom 64.17 68.78 67.16 1.10 Taiwan 56.32 60.67 62.90 1.03 Spain 50.53 46.68 48.67 0.80 Korea, North 31.99 32.58 33.07 0.54 Other Countries 8.00 Source: Reference [1], Licensed to Jiri Martinec Table 6.3. Years coal will last at various consumption rate. Consumption time in year with the following growth rate annually Current consumption Country (2004) Total reserve 0% 2% 2.50% 3.00% 3.50% 4% 4.50% 5% China 2,062.39 126,215 61.20 40.36 37.59 35.26 33.28 31.56 30.05 28.72 United States 1,107.25 271,677 245.36 89.69 79.57 71.84 65.71 60.70 56.53 52.99 India 478.16 93,031 194.56 80.16 71.63 65.03 59.75 55.40 51.75 48.63 Germany 279.95 72,753 259.88 92.12 81.58 73.56 67.21 62.04 57.73 54.08 Russia 257.52 173,074 672.08 134.84 116.61 103.26 93.01 84.85 78.19 72.64 Japan 203.72 852 4.18 4.06 4.03 4.00 3.97 3.94 3.92 3.89 South Africa 195.14 54,586 279.73 95.25 84.18 75.78 69.14 63.76 59.28 55.49 Australia 150.09 90,489 602.90 129.75 112.47 99.77 89.99 82.19 75.81 70.48 Poland 153.1 24,427 159.55 72.36 65.09 59.39 54.78 50.97 47.75 44.98 Ukraine 77.5 37,647 485.77 119.77 104.32 92.88 84.02 76.92 71.09 66.21 Greece 80.34 3,168 39.43 29.36 27.78 26.41 25.21 24.14 23.18 22.32 Turkey 69.59 4,066 58.43 39.09 36.47 34.26 32.37 30.73 29.28 28.01 Canada 57.76 7,251 125.54 63.42 57.52 52.83 48.99 45.78 43.04 40.68 Kazakhstan 72.86 37,479 514.40 122.39 106.47 94.70 85.60 78.32 72.34 67.34 Czech Republic 63.43 6,259 98.68 55.03 50.35 46.56 43.42 40.76 38.48 36.50 UK 67.16 1,653 24.61 20.21 19.42 18.71 18.06 17.47 16.94 16.44 Spain 48.67 728 14.96 13.22 12.87 12.54 12.24 11.96 11.69 11.45 Korea, North 33.07 661 19.99 16.98 16.41 15.89 15.42 14.98 14.58 14.20 164 6 Coal 6.2 Origin of Coal Two main theories have been suggested by scientists on the origin of coal or how coal is formed [2-4]. According to the first theory, coal formed in situ, where the vegetation grew and fell, and such a deposit is said to be autochthonous in origin. The starting constituents of coal are believed to be plant debris, trees, and bark that accumulated and settled in swamps. Composition of coals differs throughout the world due to the kinds of plant materials involved in the formation (type of coal), in the degree of metamorphism or coalification (rank of coal), and in the type of impurities included (grade of coal). However, there is a great controversy on the bearing of plant constituents, particularly cellulose and lignin, on coal formation. The unconsolidated accumulation of plant remains is called peat. The beginning of most coal deposits started with thick peat bogs where the water was nearly stagnant and plant debris accumulated. The plant debris converted into peat by microbiological action. Over the years, these layers of peat became covered with sediment and were subjected to heat and pressure from the subsidence of the swamps. The cycles of accumulation and sediment deposition continued and were followed by diagenetic (i.e., biological) and tectonic (i.e., geological) actions and, depending upon the extent of temperature, time, and forces exerted, formed the different ranks of coal observed today [5-19]. A number of researchers concluded that cellulose in plants was the main path towards the ultimate formation of coal [20-28]. Both the theories were reviewed by several groups and their applicability to various deposits around the world was discussed. However, it became certain from these reviews that one single theory could not be applied to explain all the deposits [29-48]. A metamorphic process, called coalification as shown in Fig. 6.1, eventually formed the coal. The metamorphic process is thought to have occurred in several stages and the factors assumed to affect the content, makeup, quality, and rank of the coal are given below. • Temperature • Pressure • Time • Layering process • Fresh water/sea water • Swamp acidity • Types of plant debris • Types of sediment cover Licensed to Jiri Martinec 6.2 Origin ofCoal 165 Plant materials are first converted to peat that has high moisture content and a relatively low heating value. However, as the process of coalification continues under greater pressure and temperature, peat starts to loose moisture and other types of coal formed. Fig. 6.1. Coal formation process. (Adapted from [49]). Licensed to Jiri Martinec 166 6 Coal The mineral content in coal comes from the salts that were part of the body of water. This generally leads to different mineral contents in various coal deposits. Ash content is due to the mud (may be considered as a mixture of mineral) that was deposited along with the plant matter. Different bodies of water had different rates of mud deposit. In the USA, eastern coal is the oldest and formed from the organic debris in a shallow sea. Eastern coal is high in sulfur because the seas it formed in were high in sulfur salts. Nearly all eastern coal is bituminous. There is a small amount of anthracite in the east. Western coal is relatively young. It formed mostly in fresh water swamps. It contains less sulfur because there was relatively little sulfur salts in the water. It has more ash because the rate of mud deposit in a swamp is high. Western coal is mostly sub-bituminous or lignite. The second theory stipulates that coal formed through the accumulation of vegetal matter that has been transported by water to another location [3, 4], According to this theory (i.e., allochthonous origin), the fragments of plants were carried away by streams and deposited on the bottom of the sea or in lakes where they build up strata, which later became compressed into coal. Major coal deposits were formed in every geological period since the Upper Carboniferous Period, 350-270 million years ago. The main coal-forming periods are shown in Fig. 6.2, which shows the relative ages of the world's major coal deposits. Paleozoic _ Devonian I c5T5ön5Tröuä^Krmiän" Mc sozoic Ccnozoic Triassir. Jurassic Cretaceous Tertiary | Eastern USA UK I | Western Europe | | Eastern Europe I I C,S South America ] China Australia India South Africa Western USA Eastern Canada Other Far East □ □ Western Canada I 3S0 30D —I- 2S0 100 SO 200 150 Age (Million Years) Fig. 6.2. Ages of coal at different parts of the world. (Printed with permission from [50]). Licensed to Jiri Martinec 6.3 Classification 167 6.3 Classification Coal is generally divided into two main categories: Anthracite (or Hard Coal) and Bituminous (or Soft Coal). The classification is mainly based on the carbon content and moisture content of the coal. As the coalification process continues the rank of the coal increases. The rank of coal is defined as the degree of changes (metamorphism) that occurs as a coal matures from peat to anthracite. The coal may be classified in a number of ways as described below. There are a number of subdivisions within these categories too. 1. By ash content Low ash (<5%) High ash (>20%) 2. Its structure Anthracite (nearly pure carbon) Bituminous (more bound hydrogen) Sub-Bituminous (less bound hydrogen) Lignite 3. Heating values Anthracite: 22-28 x 106 BTU/ton Bituminous: 25 x 106 BTU/ton Lignites: 12xl06 BTU/ton 4. Sulfur content Low (<1%) High (about 7%) 5. Coke grade Metallurgical coke (premier grade) Non metallurgical coke (low grade) 6. Caking properties Caking Non-caking The American Society of Testing and Material (ASTM) has a standard classification of coals by ranks and is provided in their D388-84, which is given in Table 6.4. The four main constituents of coal are volatile matters, hydrogen, carbon, and oxygen. The percentage of these elements determines the heating value of coal rank. The C/H and (C+H)/0 ratios are also important for determining combustion characteristics of coal. These values for different ranks of coal are shown in Table 6.5. Licensed to Jiri Martinec Table 6.4. Classification of coal by rank according to ASTM standard 388. Fixed carbon limits (%) (dry mineral matter free basis) Volatile matter limits (%) (dry, mineral matter free basis) Calorific value limits (BTU/lb) (moist mineral Agglomerating character Equal to or Less than Greater than Equal to or less Equal to or Less than Class Group greater than than greater than I. Anthracite 1. Meta-anthracite 2. Anthracite 3. Semi-anthracite 98 92 86 98 92 2 8 2 8 14 - - Non-agglomerating II. Bituminous 1. Low volatile bituminous coal 78 86 14 22 - - Commonly 2. Medium volatile bituminous 69 78 22 31 - - agglomerating coal — 69 31 — 14,000 — 3. High volatile A bituminous coal 4. High volatile B bituminous coal 5. High volatile C bituminous coal - - - - 13,000 11,500 10,500 14,000 13,000 11,500 Agglomerating III. Subbitumi- 1. Subbituminous A coal - - - - 10,500 11,500 Non-agglomerating nous 2. Subbituminous B coal 3. Subbituminous C coal — — — — 9,500 8,300 10,500 9,500 IV. Lignite 1. Lignite A 2. Lignite B - - - - 6,300 8,300 6,300 Non-agglomerating (a) This classification applies to coals composed mainly of volatile: coals rich in liptinite or inertinite do not fit into this classification system. (b) Standard units for ASTM classification for calorific value are BTU/lb. To convert to SI units of kJ/kg, multiply BTU/lb by 2.326. (c) Moist refers to coal containing its natural inherent moisture but not including visible water on the surface of the coal. (d) If agglomerating, classify in low-volatile group of the bituminous class. (e) Coals having 69% or more fixed carbon on a dry, mineral matter free basis are classified according to fixed carbon only, regardless of calorific value. (f) It is recognized that there may be non-agglomerating varieties in these groups of bituminous class, and that there are notable exceptions in the high volatile C bituminous group. (g) Agglomerating coals in the range 10,500-11,500 BTU/lb are classed as high volatile C bituminous coal. Source: ASTM Standard D388-84 (1984). ON Table 6.5. Classification profile chart. o o - S3 Average analysis -moisture and ash free basis .icensed Volatile Hydrogen Carbon Oxygen Heating value C/H (C+H)/0 matter (%) (wt%) (wt%) (wt%) (kJ/kg) ratio ratio Anthracite i-i-o Meta 1.8 2.0 94.4 2.0 34,425 46.0 50.8 c_ Anthracite 5.2 2.9 91.0 2.3 35,000 33.6 42.4 Semi 9.9 3.9 91.0 2.8 35,725 23.4 31.3 Bituminous tinec< Low-vol. 19.1 4.7 89.9 2.6 36,260 19.2 37.5 Med-vol. 26.9 5.2 88.4 4.2 35,925 16.9 25.1 :marti High-vol. A 38.8 5.5 83.0 7.3 34,655 15.0 13.8 High-vol. B 43.6 5.6 80.7 10.8 33,330 14.4 8.1 CD High-vol. C 44.8 4.4 77.7 13.5 31,910 14.2 6.2 O © Sub-bituminous —h 3 Sub-bitu. A 44.7 5.3 76.0 16.4 30,680 14.3 5.0 CD Sub-bitu. B 42.7 5.2 76.1 16.6 30,400 14.7 5.0 c Sub-bitu. C 44.2 5.1 73.9 19.2 29,050 14.6 4.2 br.cz> Lignite Lignite A 46.7 4.9 71.2 21.9 28,305 14.5 3.6 To convert kJ/kg to BTU/lb, divide by 2.326 Source: Reference [51] 6.3 Classification 171 The use of coal depends on its rank and their use is summarized in Table 6.6. Table 6.6. Use of coal depending on its rank. Types of coal % of World Uses reserves Low rank coals Lignite 17 Sub-bituminous 30 Hard coal Bituminous 52 Thermal steam coal Metallurgical coking coal Anthracite 1 Mainly power generation Power generation Cement manufacture Industrial uses Power generation Cement manufacture Industrial uses Manufacture of iron and steel Domestic/Industrial uses Smokeless fuel Source: Reference [52], The reserve of different ranks of coal in various countries is given in Table 6.7. Table 6.7. Coal: proved reserves at the end 2006 (in million tones). Country Anthracite and bituminous Sub-bituminous and lignite Total Share of world total R/ľ ratio USA 111,338 135,305 246,643 27.1% 234 Canada 3,471 3,107 6,578 0.7% 105 Mexico 860 351 1,211 0.1% 109 Total North 115,669 138,763 254,432 28.0% 226 America Brazil - 10,113 10,113 1.1% * Colombia 6,230 381 6,611 0.7% 101 Venezuela 479 - 479 0.1% 60 Other S. & Cent. America 992 1,698 2,690 0.3% * Total S. & Cent. America 7,701 12,192 19,893 2.2% 246 Bulgaria 4 2,183 2,187 0.2% 80 Czech Republic 2,094 3,458 5,552 0.6% 89 (Continued) Licensed to Jiri Martinec 172 6 Coal Table 6.7. (Continued) Country Anthracite and bituminous Sub-bituminous and lignite Total Share of world total R/P ratio France 15 - 15 ♦ 30 Germany 183 6,556 6,739 0.7% 34 Greece - 3,900 3,900 0.4% 55 Hungary 198 3,159 3,357 0.4% 337 Kazakhstan 28,151 3,128 31,279 3.4% 325 Poland 14,000 - 14,000 1.5% 90 Romania 22 472 494 0.1% 14 Russian Federation 49,088 107,922 157,010 17.3% * Spain 200 330 530 0.1% 29 Turkey 278 3,908 4,186 0.5% 66 Ukraine 16,274 17,879 34,153 3.8% 424 United Kingdom 220 - 220 ♦ 12 Other Europe & Eurasia 1,529 21,944 23,473 2.6% 352 Total Europe & Eurasia 112,256 174,839 287,095 31.6% 237 South Africa 48,750 - 48,750 5.4% 190 Zimbabwe 502 - 502 0.1% 176 Other Africa 910 174 1,084 0.1% * Middle East 419 - 419 ♦ 399 Total Africa & Middle East 50,581 174 50,755 5.6% 194 Australia 38,600 39,900 78,500 8.6% 210 China 62,200 52,300 114,500 12.6% 48 India 90,085 2,360 92,445 10.2% 207 Indonesia 740 4,228 4,968 0.5% 25 Japan 359 - 359 ♦ 268 New Zealand 33 538 571 0.1% 99 North Korea 300 300 600 0.1% 20 Pakistan - 3,050 3,050 0.3% * South Korea - 80 80 ♦ 28 Thailand - 1,354 1,354 0.1% 70 Vietnam 150 - 150 ♦ 4 Other Asia Pacific 97 215 312 ♦ 7 Total Asia Pacific 192,564 104,325 296,889 32.7% 85 TOTAL WORLD 478,771 100.0% 147 Licensed to Jiri Martinec 6.4 Coal Properties and Structure 173 Country Anthracite and bituminous Sub-bituminous and lignite Total Share of world total R/P ratio European Union 25 17,424 17,938 35,362 3.9% 65 European Union 27 17,450 20,593 38,043 4.2% 63 OECD 172,363 20,0857 373,220 41.1% 177 Former Soviet Union 94,513 132,741 227,254 25.0% 464 Other EMEs 211,895 96,695 308,590 33.9% 86 *More than 500 years. ♦Less than 0.05%. Proved reserves of coal - Generally taken to be those quantities that geological and engineering information indicates with reasonable certainty can be recovered in the future from known deposits under existing economic and operating conditions. Reserves/Production (R/P) ratio - If the reserves remaining at the end of the year are divided by the production in that year, the result is the length of time that those remaining reserves would last if production were to continue at that rate. Source: References [1, 53], The exports and imports of coal by various countries are given in Appendix VI. 6.4 Coal Properties and Structure The analysis of coal is carried out not only to determine its rank, but also its combustion characteristics. The results of these analyses can be used to predict coal behavior and the corresponding environmental impact during its use. Analysis of coal must be carried out using established protocols and standard methods described by American Society for Testing and Materials (ASTM), International Organization for Standardization (ISO) and British Standards Institution (BSI) test method numbers. These standards are listed in Table 6.8. Descriptions and objectives of these analyses are described in Table 6.9. Table 6.8. ASTM and corresponding ISO methods for coal analysis. Parameter ASTM method ISO method BSI Ultimate analysis ISO 17247:2005 BS 1016-6 Proximate D-5142 ISO 17246 BS 1016 P104 Sulfur D-4239 ISO 334 and ISO 351 BS 1016 P106 S106.4.2 Carbon & hydrogen D-5373 ISO 609 and 625 BS 1016 P106 SS106.1.1 (Continued) Licensed to Jiri Martinec 174 6 Coal Table 6.8. (Continued) Parameter ASTM method ISO method BSI Nitrogen D-5373 ISO 333 BS 1016 P106 S106.2 BTU D-2015 Forms of sulfur D-2492 ISO 157 BS 1016 P106 S106.5 HGI D-409 Trace elements by ICP D-6357 Trace elements by rf-source N/A GDMS Moisture D-1412 ISO 589 BS 1016 P104 S104.1 Specific gravity D-167 Sulfur in ash D-5016 Ash fusion temp. D-1857 ISO 540 BS 1016 P113 Mineral ash D-4326 ISO 1171 Sieve analysis D-4749 BS 1016 P109 Sample prep. D-2013 BS1017P1 Washability D-4371 Chloride D-4208 Mercury D-3684 ISO 15237 Arsenic ISO 601 BS 1016P10 Phosphorous ISO 622 BS 1016-9 Petrographic analysis ISO 7404 BS 6127 Mineral matter ISO 602 Abrasiveness ISO 12900 BS1016 Pill Table 6.9. Description and objectives of various coal analysis techniques. Properties Description of the analysis Chemical properties Proximate analysis Determination of the "approximate" overall composition of a coal, i.e., moisture, volatile matter, ash, and fixed carbon content. Ultimate analysis Absolute measurement of the elemental composition of coal excluding ash elements. Atomic ratio The H/C and O/C chemical analysis of coal. Elemental analysis Measurement of elements in coal including ash elements. Sulfur forms Chemically bonded sulfur in coal: organic, sulfide, or sulfate. Physical properties Density True density measured by helium displacement, minimum of 1.3 g/mL at 85-90% C. Licensed to Jiri Martinec 6.4 Coal Properties and Structure 175 Properties Description of the analysis Specific gravity Pore structure Surface area Reflectivity Mechanical properties Elasticity Strength Hardness/abrasiveness Friability Grindability Dustiness index Thermal properties Calorific value Heat capacity Thermal conductivity Plastic/agglutinating Agglomerating index Free-swelling index Electrical properties Electrical resistivity Dielectric constant Magnetic susceptibility Ash properties Elemental analysis Mineralogical analysis Apparent density - use of fluid that does not penetrate pores. Specification of the porosity of coals and nature of pore structure between macro, micro, and transitional pores. Determination of surface area by nitrogen or carbon dioxide adsorption. Useful in petrographic analyses. Quality of regaining original shape after deformation: rheology, deformation, flow. Specification of compressibility strength in psi. Scratch and indentation hardness by Vickers hardness number: abrasiveness of coal Ability to withstand degradation in size on handling, tendency toward breakage, two tests: tumbler test and drop shatter test. Relative amount of work needed to pulverize coal against a standard, measured by Hardgrove grindability index. Dust produced when coal is handled in a standard manner: index of dutiness Indication of energy content in coal. Heat required to raise the temperature of a unit amount of coal by 1°. Rate of heat transfer through unit area, unit thickness, unit temperature difference. Changes in a coal upon heating and caking properties of coal, measured by Gieseler plastometer test. Grading based on nature of residue from 1 g sample when heated at 950°C: Roga index Measure of the increase in volume when a coal is heated without restriction, indication of plastic and caking properties. Electrical resistivity of coal in ohm-cm, coal is considered a semiconductor. Electrostatic polarizability, related to the % electrons of aromatic rings. Diamagnetic, paramagnetic and ferromagnetic characteristics of coal. Major elements found in coal ash, 90% of ash is made up ofSiC-2, A1203, and Fe203. Analysis of the mineral content in coal ash._ (Continued) Licensed to Jiri Martinec 176 6 Coal Table 6.9. (Continued) Properties Description of the analysis Trace element analysis Analysis of trace elements found in coal, 22 elements occur in most samples, averages show some enrichment in ash. Ash fusibility Temperature at which ash passes through defined stages of fusing and flow. Petrographic properties Maceral composition Specification of the maceral components of coal, important to describing how a coal will react in coal conversion and what coal products will be given off. Vitrinite reflection Important to maceral analysis and rank calculation Sample information Sample history Sampling date and agency, sample type. Mine information Mine life expectancy, reserves, annual production and mining method. Sample location Country, state, county, township, city, coal, province, and region. Seam information Age of seam, group, formation and seam thickness. Source: Reference [54], 6.5 Coal Structure The structure of coal is extremely complex and depends on the origin, history, age, and rank of the coal. The molecular (chemical) and conformational structures of coal are studied to determine its reactivity during combustion, pyrolysis, and liquefaction processes [55-120]. Structures were derived using data obtained from various analyses including coal atomic composition, analysis of product from chemical reactions, coal liquefaction, and pyrolysis. Molecular models derived by various researchers for bituminous coal are shown in Fig. 6.3. Carlson [58] studied the three dimensional structures of coal using computer simulation and further analyzed the structures suggested by Given [121], Solomon [122], Shinn [123], and Wiser [124]. Licensed to Jiri Martinec 6.5 Coal Structure (b) Solomon [122] Licensed to Jiri Martinec 178 6 Coal (d) Wiser [124] Fig. 6.3. Structures of coal as suggested by various researchers. Licensed to Jiri Martinec 6.6 Coal Mining 179 6.6 Coal Mining The mining techniques used for extraction of coal depend on the quality, depth of the coal seam, and the geology of the coal deposit. The coal mining process can be classified into two categories depending on the mode of operation. 1. Surface Mining (a) Strip mining (b) Mountain top mining 2. Underground Mining (a) Room and Pillar mining (b) Longwall mining A schematic depiction and various terminology associated with coal mining is given in Fig. 6.4. Underground 3^ace Drag.i„e re^ng Surface Mining Fig. 6.4. A Schematic depiction of the range of different surface and underground types of coal mining, illustrating types of access to coal deposits and mining terminology [125], 6.6.1 Surface Mining Surface mining is the most common type of mining of coal in the world. It is called strip mining. It accounts for around 80% of production in Australia, while in the USA it is used for about 67% of production. It is similar to open-pit mining in many regards. Surface mining is used when a coal seam is usually within 200 feet of the surface. The layer of soil and rock covering the coal (called the "overburden") is first removed from the surface to expose the coal, but is stored near the site Licensed to Jiri Martinec 180 6 Coal (Fig. 6.5). A variety of heavy equipment including draglines, power shovels, bulldozers, and front-end loaders are used to expose the coal seam for mining. After the surface mining, the overburden is replaced; it is graded, covered with topsoil, fertilized and seeded to make the land useful again for crops, wildlife, recreation, or commercial development. About 32% of coal in the USA can be extracted by surface mining, and about 63% of all U.S. coal is mined using this method today. Surface mining is typically much cheaper than underground mining. Reclaimed ground Shovels and trucks remove coal Dragline excavales overburden Overburden dug by shovels and hauled by dumptrucks Coal Topsoil and subsoil are reomoved by scrapers and stored Direction of mining Direction of pit advancement Fig.6.5. A schematic representation of surface mining. (Adapted from [126]). Another type of surface mining is called mountain top mining. This type of mining is a relatively new process for coal mining from a depth of about 1,000 ft below the surface. In this process, the land is first clear-cut and then leveled by explosives. Dozens of seams are exposed on a single mountain by the blasts, lowering the mountain's height each time, sometimes by hundreds of feet [127]. Most mountain top mining in the United States occurs in West Virginia and Eastern Kentucky, and together they use more than 1,000 t of explosives per day for surface mining [128], 6.6.2 Underground Mining Underground mining is used when the coal seam is several hundred feet below the surface. A vertical "shaft" or a slanted tunnel is constructed, called a "slope", to get the machinery and people down to the mine. Mine shafts may be as much as 1,000 ft deep. Licensed to Jiri Martinec 6.6 Coal Mining 181 6.6.2.1 Room and Pillar Mining In room-and-pillar mining, a significant amount of coal is left behind to support the mine's roofs and walls (Fig. 6.6). Sometimes, this amount could be as much as half of the coal mined. Large column formations are necessary to keep the mine from collapsing. In this method, a set of entries, usually between 3 and 8, are driven into a block of coal. These entries are connected by cross-cuts, which are usually at right angle to the entries. The entries are commonly spaced from 50 to 100 ft apart, and the cross cuts are usually about 50-150 ft apart. In the conventional room and pillar method, several operations known as undercutting, drilling, blasting, loading and roof bolting operations are performed to get to the coal. Recent advancement includes continuous room and pillar method that eliminates undercutting, drilling and blasting. The cutting and loading functions are performed by a mechanical machine - the continuous miner. The coal is loaded onto coal transport vehicles and then dumped onto a panel-belt conveyor for further transport out of the mine. Once the coal has been cut, the strata above the excavated coal seam are supported by roof bolts. Fig.6.6. A schematic representation of room and pillar mining. (Adapted from [129]). 6.6.2.2 Longwall Mining In this method, a mined-out area is allowed to collapse in a controlled manner (EIA [130]). Huge blocks of coal, up to several hundred feet wide, can be removed and high recovery and extraction rates are feasible (Fig. 6.7). However, Licensed to Jiri Martinec 182 6 Coal the coal bed should be relatively flat-lying, thick, and uniform. The block of coal is further cut into small pieces using a high-powered cutting machine (the shearer). The sheared, broken coal is continuously hauled away by a floor-level conveyor system. The use of longwall mining in underground production has been growing in the USA both in terms of amount and percentages, increasing from less than 10% of underground production (less than 10 million annual tons) in the late 1960s, to about 50% of underground production (over 200 million annual tons). Fig. 6.7. A schematic representation of logwall mining. (Adapted from [131]). Underground mining currently accounts for about 60% of world coal production, although in several important coal producing countries surface mining is more common. 6.7 Cost of Coal and Its Mining A number of costs are associated with coal mining and its delivery price. The mining of coal involves various types of costs. However, with the use of modern and more efficient equipment, the cost of mining has gone down significantly. Some of the activities that are associated with the cost of coal mining include restoration of the land, mine drainage, and water usage. All these factors determine the cost of coal that is delivered to end users. The average price of coal at various regions in the USA and the price to the end users are given in Table 6.10. The production cost of coal depends on the method of mining and also varies from region to region. In Table 6.11 is shown the cost of coal at various states in the USA for different mining methods. Licensed to Jiri Martinec Table 6.10. Average price of coal delivered to end use sector by census division and state, 2005, 2004 (dollars per short ton). o CD CO CD Q. 03 a. D CD O A 3 05 3-D CD O 3 CD < C ß V 2005 2004 Annual percent change Census division and state Electric utility plants Other industrial plants Coke Plants Electric utility plants Other industrial plants Coke plants Electric utility plants Other industrial plants Coke plants New England 65.39 85.57 - 52.14 65.54 - 25.40 30.60 - Middle Atlantic 51.97 W W 42.92 W W 21.10 15.60 28.5 East North Central 30.45 53.89 89.97 26.69 41.22 63.30 14.10 30.70 42.1 West North Central 16.47 24.00 - 15.34 21.93 - 7.40 9.50 - South Atlantic 51.21 W W 43.29 W W 18.30 25.60 36.8 East South Central 36.91 W W 32.22 W 59.16 14.60 28.80 W West South Central 21.55 W - 20.72 W - 4.00 12.70 - Mountain 23.30 35.93 - 21.87 31.92 - 6.50 12.60 - Pacific 21.33 50.62 - 19.91 42.94 - 7.10 17.90 - US Total 31.22 47.63 83.79 27.30 39.30 61.50 14.40 21.20 36.2 W = Withheld to avoid disclosure of individual company data. Includes manufacturing plants only. Source: References [132-134], 184 6 Coal Table 6.11. Average open market sales price of coal by state and underground mining method. 2005 (Dollars per short ton). Coal producing state Continuous" Conventional6 Longwallc Other" Total Alabama W - W - 54.75 Colorado W - W - 21.69 Illinois w - w - 29.18 Indiana 33.17 - - - 33.17 Kentucky Total W 38.71 w - 38.70 Eastern W W w - 43.55 Western W W - - 27.48 Maryland W - - - W Montana W - - - W New Mexico - - w - W Ohio w - w - 25.25 Oklahoma w - - - W Pennsylvania Total" 46.07 40.17 w W 36.23 Anthracite W W - W 46.74 Bituminous W W w - 36.18 Tennessee 49.89 - - - 49.89 Utah 25.17 - 21.02 - 21.45 Virginia 42.47 63.89 W - 48.01 West Virginia Total 46.54 W W - 41.99 Northern 31.88 W 32.60 - 32.52 Southern 47.85 - 53.00 - 49.06 Wyoming - - - - - U.S. Total 39.04 W 33.90 w 36.42 aMines that produce greater than 50% of their coal by continuous mining methods. bMines that produce greater than 50% of their coal by conventional mining methods. °Mines that have any production from longwall mining method. A typical longwall mining operation uses 80% longwall mining and 20% continuous mining. dMines that produce coal using shortwall, scoop loading, hand loading, or other mining methods. or a 50/50% percent conventional/conventional split in mining method. W = Withheld to avoid disclosure of individual company data. Open market includes all coal sold on the open market to other coal companies or consumers. An average open market sales price is calculated by dividing the total free on board (f.o.b) rail/barge value of the open market coal sold by the total open market coal sold. Excludes mines producing less than 10,000 short tons, which are not required to provide data. Excludes silt, culm, refuse bank, slurry dam, and dredge operations. Totals may not equal sum of components because of independent rounding. Source: References [135, 136], Licensed to Jiri Martinec 6.8 Transportation of Coal 185 Cost of coal is also different in different countries, particularly for the coal importers. In this case, the cost includes that of raw materials, insurance and freight. The cost in US dollar for Europe and Japan is given in Table 6.12. Table 6.12. Coal price in other countries. US dollars per tonne Northwest Europe marker price f US Central Appalachian coal spot price index" Japan coking coal import cif price Japan steam coal import cif price 1987 31.30 — 53.44 41.28 1988 39.94 - 55.06 42.47 1989 42.08 - 58.68 48.86 1990 43.48 31.59 60.54 50.81 1991 42.80 29.01 60.45 50.30 1992 38.53 28.53 57.82 48.45 1993 33.68 29.85 55.26 45.71 1994 37.18 31.72 51.77 43.66 1995 44.50 27.01 54.47 47.58 1996 41.25 29.86 56.68 49.54 1997 38.92 29.76 55.51 45.53 1998 32.00 31.00 50.76 40.51 1999 28.79 31.29 42.83 35.74 2000 35.99 29.90 39.69 34.58 2001 39.29 49.74 41.33 37.96 2002 31.65 32.95 42.01 36.90 2003 42.52 38.48 41.57 34.74 2004 71.90 64.33 60.96 51.34 2005 61.07 70.14 89.33 62.91 2006 63.67 62.98 93.46 63.04 aPrice is for CAPP 12,500 BTU, 1.2 S02 coal, fob. cif = cost + insurance + freight (average prices); fob = free on board. Source: Reference [137], 6.8 Transportation of Coal The electric power sector uses more than 90% of the coal produced in the United States and is transported to more than 400 coal-burning power plant sites. About 58% of coal is transported by rail, 17% by water-ways, 10% by trucks, 3% are mine mouth plants with conveyor systems and the rest 12% by other methods (This includes barge) [138, 139]. However, these numbers do not include mode of trans- Licensed to Jiri Martinec 186 6 Coal portation of coals to main transportation ports. The EIA figures report methods by which coals are delivered to its final destination (see Table 6.13), and do not describe how many tons may have traveled by other means along the way - almost one third of all coal delivered to power plants is subject to at least one trans-loading along the transportation chain [138]. For example, the U.S. Army Corps of Engineers reported that 223 million tons of domestic coal and coke were carried by water at some point in the transport chain in 2004 [140], Recently transportation of coal as a slurry through pipelines has been explored. This type of transportation method not only requires water for transportation, but also need a number of pumping station to boost the pressure in the pipeline. It requires about 1 ton of water for 1 ton of coal and a booster pump for every 100 km when flowing at a velocity of 1-2 m/s. Table 6.13. Mode of transportation of coal to end users (thousands short tons). Delivery methods Electricity generation Coke plant Industrial (except coal)a Residential/ commercial Total Great 8,644 1,144 1,341 — 11,128 Lakes Railroad 625,830 10,414 46,031 1,975 684,249 River 71,062 3,722 7,915 406 83,105 Tidewater 3,391 - 530 - 3,936 Piers Tramway. 79,997 1,014 31,975 - 115,262 Conveyor and Slurry Pipeline Truck 73,441 453 50,266 2,741 128,900 Others - - - - 28,005 Total 863,802 17,095 150,309 5,122 1,064,348 aThis category includes coal that is transported to plants that transform it into 'synthetic' coal that is then distributed to the final end-user - a substantial component goes to electricity generation plants. Source: Reference [139], 6.9 Coal Cleaning The objectives of coal cleaning are to remove ash, rock, and moisture from coal to reduce transportation costs and improve the power plant efficiency. Coal cleaning is now also focused on removing sulfur to reduce acid-rain-related emissions. The benefits of coal cleaning are: Licensed to Jiri Martinec