Generalities about Coal and briefly mention to its spread

Author Khalil Bahar Firouzi
Published At 14 December 2003


Before 1990 decade, coal was most important fuel resource in most of industrial countries especially the THE US and it has provided about 90% from their energy need. After that, due to some changes was done in position of oil and natural gas in international markets and importance of coal is decreased


First part: Coal Geology 1-1-       Introduction Before 1990 decade, coal was most important fuel resource in most of industrial countries especially the THE USand it has provided about 90% from their energy need. After that, due to some changes was done in position of oil and natural gas in international markets and importance of coal is decreased. Nevertheless currently coal is first source for electricity production because it is very cheaper than other fossil fuels and it is more abundant rather has other countries. In the U.S, it is as most important industrial country, in 2000 has been for coal consumption for electricity production with 983 million tons (91% from its total consumption) that more than half of consumption electricity from the U.S. Before decade of 1970, natural gas is cheapest consumption fuel for electricity production. In year of 1970, mean amount of price is 28 € for each million of Btu energy from natural gas, 31 € coal and it is 42 € from oil. From 1976, coal was converted to cheapest fuel for electricity production. In 1999, natural gas has a price of 2.59 $ in each million btu to must expensive fuel while oil is with 2.56 $ for petroleum and coal with 1.22 in next degrees. Although cost of power production has been increased from coal nevertheless they are very lower than natural gas and oil. Its price is 24.28 tonne per dollar. Price fluctuations of coal in the the US market is since 1990 to 1999 as a table. Their descending trend of price is well. Table No (1) – coal price fluctuation (dollar in short tone) in decade 90. Other important usage of coal is coke production from that which is used for melting of iron and steel minerals. Mean price of coals which are used for coke has been decreased at the beginning of 1980. Since 1993 to 2000, from 47.44 $ per tonne to 44.45 $ per tone. As it is characterized from table (1) and coal price is extractional in mine in 1999 is about one dollar lower than 1998 while this decrease has been continued in 17 permanent years. Because coal has much abundance and its price is low for long terms so they use power production plans in the the US (the digits where implied to them are in internet website of related to energy information (Energy information sheets) are extracted. From other usage of coal is lignite and its special usage is for oil and gas production from this coal, about 38 gallon have been obtained in each tone. Lignite coals have high potential rather than high grade coal in this field. Coal has other usages in other industries like loom, cement, sugar and … Fig number (1) has shown other usages of coal. This material is seen mainly in time horizons from late Paleozoic and Mesozoic but tertiary coals are formed big reservoirs all over the world and their relative advantage is easier formining activities. Tertiary coals are with many usages for electricity production. So implement of explorative operation is for coal saving in rein region does have not only economical justification but also discovering of reservoirs in it results in providing of some resources from energy for development of power production industry and other industries is in the region. Cimitation in oil and gas resources and far distance from studied region are from justification resources on exploration of other resources. 1-2-       Definition: Coal is a coal with carbon with carbon which is formed due to aggregation, alteration and conservation of present flora material in the land and it is regarded as a fossil fuel. Coal is a solid explosive material and dark (except for thin section) and non – crystalline that its color is light color to dark is variable. Its luster is varied from opaque to glitter. Coal density is 1 to 1.8 gr/cm3 and its hardness is from 0.5 to 2.5. Coal is brittle and it finds hackly. Its chemical members include carbon, hydrogen and oxygen with some amount of nitrogen and sulfur. Ash part and or mineral matter can be completely variable. There is a general reverse relation between oxygen and in less amount of hydrogen and carbon with coal. Coal is a very complicated molecule which are mainly from carbon rings and carbon atoms may be substituted by oxygen, nitrogen and or sulfur atoms. So sulfur may include environmental problems including acid rain are caused. Mentioned cases are as some definitions that has been represented by Shackleton (1986). 1-1-       Aggregation and formation of coal For aggregation and formation of coal have two theories which each of them use special evidence. These two theories include in situ and drift. In situ theory: Most of coals are as the have been formed in its growth location. These coals are known to authochthonous. Evidences which support theory determination are: 1.     Non sorted flora fragments. 2.     Their lower soils have some traces for roots which have penetrated down wards. 3.     Usually classtic materials in them that indicative of calm still water condition. 4.     There are many evidences for fresh water lagoons which are indicative of considerable thickness of peat. 5.     Big coal circles are indicative of aggregation in sea surface and or near to that with week subsidence. Drift theory: Some of coals are as they have been formed from transportation material to new location and they are transported as allochthonous coals. There are evidences which are supported as follows: 1.     Under all of coals are in lower soil seat earth. 2.     Sedimentary structures are indicative of transported materials in coal. 3.     Very fine nature in some of coals is indicative of very fine detrital materials and representative of sorting by natural sedimentary processes. 4.     This reality is that all of coals are not with cyclothem. Each both methods may be occurred and origin of each coal deposit should not be emphasized as bias but it should be studied with precise observations.         1-4- coal origin: Geological evidences indicate that coal is from rest of flora. Main flora material, cellulose and lignite but they have much extensive diversion from minor members like proteins, essential oils, organic acids and their salts, tanines and … mentered to chemical composition of flora material. Cellulose formula is C6H10O5 and lignite formula is almost C12H18O9. So there is a big difference from relative comparison of carbon, oxygen and hydrogen are present in these two compositions. Anyway, lignite composite is a aromatic composition in other words are from annual groups of atoms. In stead of cellulose composition has aliphatic nature. In this regard, some of investigator believe that lignite is main material has coal origin because broken products have aromatic structure and they are as coal. In addition to, each of two aggregation methods may be occurred and origin of each coal deposit should not be as bias. In addition to, lignite is resistant against to invade organisms while cellulose is disrupted easily and CO2 and CH4 and aliphatic acids. Anyway it is under similar condition to coal formation. Cellulose can be converted to aromatic composition. Of course coal formation story is more than simple conversion to lignite and or cellulose to coal material. Cellulose and lignite do not have nitrogen in their composition is important in coal. Some parts of this nitrogen can be from minor member like proteins of bacteria reaches to 13% too. Coal oxygen seems that it is hydroxyl (or phenol), carboxyl, metaoxylo, carbonate groups are present. In coals with higher row (High rank coals) are preserved with phenol and carbonyl but they decrease other compositions. Conversion of flora material is divided into two stages which is mainly biochemical and orher one is metamorphic. Biochemical stage is mainly from conversion of flora material to peat that microorg anisms have active role from recycling aspect. Peat formation is surrounded following processes: 1.     Leaching of solution in water. 2.     They interrupt cellulose composition, peat nature to much level depends on this stage. 3.     Transitional aggregation of microorganism cells is due to increase nitrogen. When condition is unsuitable for bacteria activity, bio chemical stage terminates practically. These conditions are produced due to burial condition under inorganic sedimentation and or it is caused due to cause toxic condition in organic material. After biochemical stage, metamorphism or in other words warm operation and pressure is responsible for coalification. Progression changes can be followed from wood to peat and then coal can be followed by chemical decompositions. Table No. 2 has a mean composition, wood, peat and three additive rows, i.e., lignite, bitumen coal, bitumen coal and anthracite (Mason, 1982).        %O       %N      H%       C%          2/43        92/0       23/6       65/49     چوب       56/36        72/1        28/6       44/55     تورب        5/20       13/1       24/5      95/72    لیگنیت        69/8       52/1      55/5      24/84   ذغالسنگ بیتومین       72/2        97/0      81/2       50/93   آنتراسیت Rank is a scale which has influenced coal in metamorphic degree. Various suggestions are about geological factors and determining coal row has been represented and some of these suggestions are: 1.     Burial time, Paleozoic coals have mainly high degree and tertiary coals in lower rows. However there are many characterized exceptions that impression time does not have straight influence on coal row. 2.     Operation of resulted heat from earth movements or igneous intrusive bodies. 3.     Pressure from folding and faulting. 4.     Pressure and temperature resulted from burning. Among these factors, last factor is easier than other evaluated factors and it is as a result of a rule (Hilte rule) has been formulated. According to this rule, in a series of coal is accompanied with increase in depth, amount of carbon is increased and it is decreased with elusive material. Hilte rule is about coal basin and it was characterized that elusive materials are generally with a rate of about 0.2 to 0.8 in stead of each foot. Relation is surveyed between depth and elusive material in some of coal circles has been surveyed and general pattern of depth distribution – elusive material for coal from England from low grade bitumen (with 42% from elusive material) to anthracite (5% of elusive material). Some evidences have been found (mason, 1982) that are main cause of rank increase in burial depth except for contact metamorphism. He has estimated conversion depth of peat to coal bitumen in low rank about 7.500 ft and for conversion of peat to coal is 5% of elusive material about 19.000 ft. These data can be used as reversely i.e. primary depth of coal layers that their modern position results from tectonical movement and or erosion. From chemical aspect, transition of wood to anthracite is mainly accompanied with carbon and oxygen decrease. Hydrogen is decreased too but decrease velocity is very little. This process is mainly is a new renovation process. Ratio of H/O (weight percent) is 1/8 in cellulose and 1/7 in wood and it is increased up to 1/1 in anthracite. Figure No. 3 shows changes in chemical composition of cellulose, peat to anthracite, based on carbon and hydrogen. Last alteration product of coal materials is graphite production. This alteration is compared to alteration of rocks even though present organic material is reacted in coal with temperature and faster pressure in minerals. Coal composition is a very sensible index from alteration degree. This topic is not only about coal but also about embedding rocks too. Anyway it is in anthracite stage that host rocks has changed and they are hard and they can not be named metamorphic rocks. Coal origin is surveyed from other dimension that survey of sedimentary environment and deposition models can be surveyed as follows too. Sedimentary sequences which have interlayers of coal and or peat all over the world and it is from upper Paleozoic to resent (fig No.2). Coal results from aggregation of flora members in special deposition environments and coals with rows and structural complexities are caused. Considerable similarities are present between sedimentary sequences with coal because they are special condition for formation and their remaining is needed. Sequences with different aspects are far from each other from geographical aspect and it has lithological similarity and they show reaction and from structural aspect. 1-5- deposition models Recognition of deposition models for description of origin for coal containing and their relation to embedding sediments in them have been formed in comparison with environments under condition of modern peats and old coal-bearing sequences. Of course there is no model that all of coal-bearing deposits are embedded. Many coal deposits are with special sedimentary regimes. Formal sedimentary model which is used by many people is based on cyclothem which is in iterative cycle as a series of occurred lithotypes. Finally this topic is amended to a model that lateral and vertical changes in the sequence are recognized in new environments like flood, delta and coastal barriers. Coastal and back barriers facieses Coastal sedimentary model is with cleaned barrier sandstone which is finer towards sea and it has some interlayers of calcareous shales and red and towards land, it is converted to dark gray shales in lagoons with a faunal association of brackish water and lagoonal marginal areas which are dominant in those plants. Barrier sandstones have been reworked mainly and they are mainly with quartz to adjacent environments. Back barrier lagoonal sediments with shale and siltstones with coarse grains (coarsening upwards) and it is rich from organic materials and they are with thin coverage and characterized coal sections. These sequences of regions have bioturbidity with stripes and concretions o carbonates (siderite) which is deposited as chemical composition. Lower delta plain facies In deposits of this facies, it is coarsening upward sequence are from mudstone and siltstone are dominant. Lower parts in these sequences are accompanied with limestones as dispersed irregular limestones with grey to dark mudstones and siderite are characterized. Sandstones are in upper parts and they are indicative of increase in environment energy as filled bays by sediments. When these bays are filled good enough and plants can grow and they form coal. When this bay is not filled completely, sandstone and siltstone which have been cemented by siderite and they have been bioturbated by animal activity. Due to terminate bioturbation, fillings are from fine grained mudstones in lower deposits of delta that are deposited from silt and organic members and from suspension after turbulence. Is some of aggregation regions are from organic material have been filled in these canals and it results in forming lens coals. Except for coals which are formed in filled canals, there is no dry and long periods, raised lagoons may be developed and these lagoons are able to extent upwards. 1-6- composer members of coal Coals are formed in two parts of macerals and minerals. 1-6-1- Macerals A coal maceral is an individual unit like a part of plant part. Macerals are also named as coal minerals. Macerals are named as coal minerals. Maceral name is usually to inite. Types of maceral are explained as follows: 1.     Viterinite or humnite which includes kaolinite (jello plant remnants and without characterized structure), telenite (a golden jello of translucent that it has a cellular structure) and semi-telenite (deficit from humus jell). 2.     Exinite or liptinite include smaller and more resistant plant materials: a)    Alginate, derived from mushroom b)    Spornite, derived from pollen