part i : arang batu (coal) - universiti sains malaysiamineral.eng.usm.my/web halaman mineral/coal...

EBS 425/3 -Mineral Perindustrian Coal Technology – Part I

Disedia oleh : Dr. Kamar Shah Ariffin ( 6/30/2003) of 12

PART I : ARANG BATU (COAL)

What are fossil fuels?

• Derived from the remains of once living organisms. • Formed some 500-200 million years ago. • The three major fossil fuels are oil, coal, and natural gas.

Currently being consumed at a rate faster than they are being produced.

After food, fossil fuel is humanity's most important source of energy. There are three major fuels -- coal, oil and natural gas. Coal is used primarily to produce electricity. It therefore provides us with light, motive power from electric motors, and our many electronic devices. Oil gives us our mobility, our cars, planes, trains, trucks and boats. Natural gas is used primarily to produce heat, for our buildings, hot water, and industrial processes.

Natural gas, oil and coal are the three (fossil) fuels that are abundantly used. These fuels are remains (fossils) of life forms such as marine organisms and plant life, that flourished on our planet millions of years ago. This energy is thus a stored form of solar energy that accumulated over millions of years, and at the current and projected rates of consumption, fossil fuels will be used up in a fraction of time compared to the time it took to collect the energy from the sun.

It is a pretty safe bet that fossil fuels will be depleted. The question is when?

Fossil Fuels

• Coal, Petroleum, Oils Shale, Tar Sands • Concentrated Organic Matter (> 2% TOC) • Humic and sapropelic components • Unevenly distributed in space & time

What is Coal?

Coal is a generic term referring to a family of solid fossil fuels with a wide range of physical and chemical compositions. Coal is formed from large accumulations of plant materials that have been preserved from complete decay and later altered by chemical and physical conditions in the accumulation.

Coal is a readily combustible rock containing more than 50 percent by weight of carbonaceous material, formed from compaction and indurations of variously altered plant remains similar to those in peat [adapted from AGI's "Glossary of Geology"]. Most coal is fossil peat. Peat is an unconsolidated deposit of plant remains from a water-saturated environment such as a bog or mire; structures of the vegetal matter can be seen, and, when dried, peat burns freely [adapted from AGI's "Glossary of Geology"].

Coal is actually a heterogeneous rock composed of different kinds of organic matter which vary in their proportions in different coals, and no two coals are



absolutely identical in nature, composition or origin. A definition of coal has been proposed:

"Coal is a compact stratified mass of metamorphosed plants which have, in part, suffered arrested decay to varying degrees of completeness."

The organic material in coal was formed from plant debris which has been layed down in a peat swamp, over many millions of years. These swamps were extremely large, and it has been calculated that the thick brown coal seams in Victoria (Australia), now about 200 m thick, were formed from debris with a total thickness of five kilometres. With time, the plant debris was covered with sediments, and undergone various changes of temperature and pressure which produced a sequence of coals beginning with peat and terminating with anthracite.

The definition of the term "coal" in steel industrial point of view

The term "coal" is defined in the following way: hard coal, hard coal briquettes, coke and semi-coke derived from hard coal, lignite, lignite briquettes and coke and semi-coke derived from lignite.

The term "hard coal" includes the high and medium-ranking "A" coals (sub-bituminous coals) as defined in the "International codification system of coal" of the UN Economic Commission for Europe. The term "lignite" includes the low-ranking "C" coals (or ortho-lignites) and the low-ranking "B" coals (or meta-lignite) of the same classification. With regard to lignite, the programme shall apply to lignite used for electricity production or for combined head/electricity production, or for the manufacture of briquettes or semi-coke.

Formation of Coal Coal Creation

Between 200 and 300 million years ago, long before there were any reptiles, birds or mammals, in many parts of the world there existed warm and human climatic conditions. These conditions favored the growth of huge tropical ferns and giant trees, which grew and died in vast swamp areas. The dead plants fell into the boggy waters, which tended to exclude oxygen and bacteria, so that they only partially decomposed to produce a peat-like material. This fossilized plant debris was the beginning of coal, but only the beginning. Vegetation continued to grow for many generations and centuries, forming vast, thick peat beds which were later to turn into coal. After a time the areas of swamp gradually became submerged by shallow seas, where they were covered by sediment. These sediments would later become sedimentary rock. This cycle of swamp followed by submersion was often repeated a number of times, so that a sequence of horizontal bands of peat and inorganic, sedimentary rock was built up. This formed the first stage, called the biochemical stage. Coal formation occurred in other geologic periods as well. . Subsequently, the bands of peat were altered by the action of pressure and



temperature during the second, or geochemical stage, to form the various kinds of coal found today. As much as a 20-fold reduction in the thickness of the original plant deposits sometimes occurred. During the course of time these horizontal coal seams were further altered as they became folded, tilted and eroded. Much of this action was due to the motion of the continents, as mountains formed and were then worn away. The study of fossils is called paleontology. The creation of coal from fossils is part of geology.

Coal is formed by the physical and chemical alteration of peat (coalification) by processes involving bacterial decay, compaction, heat, and time. Coal is an agglomeration of many different complex hydrocarbon compounds, some of which owe their origin to the original constituents in the peat. Peat deposits are actually quite varied and contain everything from pristine plant parts (roots, bark, spores, etc.) to decayed plants, decay products, and even to charcoal if the peat caught fire. Peat deposits typically form in a waterlogged environment where plant debris is accumulated; peat bogs and peat swamps are examples. In such an environment, the accumulation of plant debris exceeds the rate of bacterial decay of the debris. The bacterial decay rate is reduced because the available oxygen in organic-rich water is completely used up by the decay process. Anaerobic (without oxygen) decay is much slower than aerobic decay.

In order for the peat to become coal, it must be buried by sediment. Burial causes compaction of the peat and, consequently, much water is squeezed out during the first stages of burial. Continued burial and the addition of heat and time, cause the complex hydrocarbon compounds in the deposit to start to break down and alter in a variety of ways. The gaseous alteration products (methane is one) are typically expelled from the deposit and the deposit becomes more and more carbon-rich (the other elements drop out). The stages of this trend proceed from plant debris, peat, lignite, sub-bituminous coal, bituminous coal, anthracite coal, to graphite (a pure carbon mineral).

Because of the amount of squeezing and water loss that accompanies the compaction of peat after burial, it is estimated that it took vertical 10 feet of original peat material to produce one vertical foot of bituminous coal. The peat to coal ratio is variable and dependent on the original type of peat the coal came from and the rank of the coal.



In other point of view, Coal was formed from plant life under the action of immense pressures and temperatures prevailing within the earth's crust over a period encompassing millions of years. The major elements present in the "organic portion" of coal are carbon, hydrogen, oxygen, nitrogen and sulphur. Sulphur (mostly as iron pyrite) is also present as part of the "inorganic portion" or ash in the coal along with oxides of alumina, silica, iron, alkaline earths and alkalis. Coal also contains some chlorine. Coal is classified into the following four types according to the degree of metamorphism:

• anthracite which is low in volatile matter (which forms tars, oils and gasses when coal is heated) and consists of mostly carbon (fixed carbon)

• bituminous which contains significant amounts of the volatile matter and typically exhibit swelling or caking properties when heated

• sub-bituminous is a younger coal and contains in addition to the volatile matter, significant amounts of moisture

• lignite is the youngest form of coal (when peat is not included in the broader definition of coal types) and is very high in moisture content resulting in a much lower heating value than the other types of coal.

First of the fossil fuels – drove the industrial revolution Known since ancient times, but only really important since 18th century. Abraham Darby, 1710, used to smelt iron. Later use spread across Europe. Use aided by transportation, first canals and later railroads. In United State first coal production in Virginia (1750) and Pennsylvania (1759). In Malaysia, first coal production came from Batu Arang Selangor and Labuan from Tanjung Kabung (1847-1911). Batu Arang field development initially was started in 1904, by J.A. Russell & Co (BOH tea plantation founder). The story behind Batu Arang fields is rather interesting. A Malay man had picked up pieces of coal in the jungle and brought them to Archie Russell. Currently actively mine at Nanga Merit (Lombong Merit Pila) and Beradai, Kapit division Serawak. This coal is mine to be supplied for power generation by SESCO All coal some type of carbon compound or pure carbon formed from fossilized plant material. Will only be formed when the plant growth is abundant and when environment conditions will result in rapid burial. Higher plants (needed to form humic coals) did not evolve until Devonian (400 Ma) so no large coal deposits rocks formed before that time. Most coals formed in tropical, swampy areas. River delta’s ideal because also carry sediment to bury accumulated vegetation.



Coalification As vegetation-rich layers are buried under sediments, pressure and increasing temperature change the nature of the material.

Coalification of coal

• Wide variety of terrestrial environments accumulate peat • Coalification related to time and pressure, expressed as rank • Lignite (<70% TOC; >31% volatiles), Bituminous coal (80-90% TOC;

22-31% volatiles), Anthracite (>90% TOC; 2-14% volatiles) • Macerals indicate coal constituent origin • Vitrinite - degraded structured cellular remains, glassy • Inertiniate - non-degraded cellular remains of bark & wood; fungal

remains • Liptinite - resistant biopolymers such as cutan, resins, & sporopollenin

vegetation -> peat -> lignite (brown coal) -> bituminous -> anthracite

[low rank] [high rank] At each stage volatiles lost, so is a consequent increase in carbon content. Thus high rank coals provide more energy. Layers of coal called seams. Coal Formation sequence

Peat -------> Lignite -------> Subbituminous -------> Bituminous -------> Anthracite

Energy Content

Low -------------------------------------------------------------------------------------> High

Moisture Content

High -------------------------------------------------------------------------------------> Low

Sulfur Content

High -------------------------------------------------------------------------------------> Low



What are the components of coal? Coal contains two major constituents: THE USEFUL BITS: These are the parts of the coal which are of direct benefit to a process because they produce heat, or used as a source of carbon. This part is usually termed the "organic" part of the coal substance, and originated mainly from the carbon in the original plant material.

THE USELESS BITS: These are those parts of the coal which have no value to the utilisation of the coal. Two materials are present in this category:

• The "inorganic" part of the coal substance, and is present in the form of "minerals" which remains in the coal substance by virtue of inert substances contaminating the plant material as it was being laid down in the peat swamp, and present in the form of minerals (which produce ash).

• The coal "moisture" which is retained within the porous coal structure, and on the coal surface.

Some organic constituents including nitrogen, and organic sulphur.

These components of the coal are illustrated in the simple box diagram, and it should be noted that some of the carbon, hydrogen and oxygen are the only useful bits if the coal. Some of the carbon and all the hydrogen and oxygen report to the volatiles, and the balance of the carbon reports to the fixed carbon.



Rocks are made up of grains of one or more minerals. Similarly, coal, an organic deposit, is made up of organic grains called macerals. Coal petrographers, people who study coal under the microscope, separate the macerals into three maceral groups, each of which are composed of several maceral types. These groups are liptinite, vitrinite, and inertinite and are defined according to their grayness in reflected light: liptinites are dark gray, vitrinites are medium to light gray, and inertinites are white and can be very bright. Liptinites were made up of hydrogen-rich hydrocarbons derived from spores, pollens, cuticles, and resins in the original plant material. Vitrinites were made up of wood, bark, and roots and contained less hydrogen than the liptinites. Inertinites are mainly oxidation products of the other macerals and are consequently richer in carbon. The inertinite group includes fusinite, most of which is fossil charcoal, derived from ancient peat fires.

Microscopic view of coal; yellow area is vitrinite; white grains are inertinite; gray shapes are liptinites (plant spores); dark brown areas are tiny grains of vitrinite.



Coals can also be divided into two types based on their macroscopic (not microscopic) appearance: banded and non-banded. Non-banded coals include cannel and boghead coals, both of which are dull and blocky. Cannel is derived from the word "candle," because pencil-shaped pieces were used as candles in the past. Banded coals grade from dull banded ("splint coal") to bright banded coals, depending upon whether dull bands or bright bands are dominant. The bands are divided into lithotypes. Dull bands are called durain; satiny bands are clarain; charcoal bands are fusain; and black, glassy bands are vitrain. Bright coals have lots of vitrain and clarain; dull coals are rich in durain bands. Fusain generally occurs only in thin and sporadic bands.

. Splint coals are durain-rich and can be massive (non-banded) or banded. Most vitrain- and clarain-rich banded coals break into small blocky pieces along joints called cleats. Vitrain and clarain are brittle and break easily. "Block coals" are dull coals that break into large blocks because they have fewer vitrain and clarain bands, but have a composition higher in liptinite macerals, which are tough. "Bone" and "bone coals" have a high ash content in the form of clays and silts; they form part of a continuum between dark shale and dull (banded or non-banded) coal in the following sequence: dark shale, bone (greater than 50 percent ash), boney coal (less than 50 percent ash), dull coal (cannel, boghead, or splint).



Kinds and Types of Coal

The kinds of coal, in increasing order of alteration (or rank), are lignite (brown coal), sub-bituminous, bituminous, and anthracite. These classes are further divided into subclasses based on their degree of alteration (measured by volatile-matter content, Btu's, or by petrographic means). The bituminous coals are also subdivided into types of coal as well: banded and non-banded. Non-banded massive coals are cannel, boghead, and some types of "splint" coal. Banded coals are divided into subtypes based on the nature of the bands and are either bright-banded or dull-banded. The bands are classified into four major lithotypes: vitrain (bright, black, glassy, brittle), clarain (bright, satiny texture, brittle), durain (dull, grainy texture, tough), and fusain (dull black, charcoal texture, gets hands dirty).

How did the coal-bearing rocks form?

The numerous layers of coal beds in many coal fields are intermixed with shale and sandstone (and rarely with thin limestone). Most of the major coal beds in many part of the world were formed as widespread peat swamps or mires during the Pennsylvanian Period. During the Pennsylvanian Period the area that is now Kentucky, US was near the equator and had a climate much like that of modern Indonesia. Tropical climates allowed lush vegetation to accumulate into widespread peats.



The alternation of coals with shales, sandstones, and thin limestones records alternating periods of sea-level changes. As sea level rose, swamps spread across many low area. Ultimately, the seas covered the swamps. Shallow seas covered parts of Kentucky more than 50 times during the Pennsylvanian. When sea level fell, the seas withdrew to the edges of the continent and large rivers snaked across low area. In this kind of area, the peat swamps formed on extensive coastal plains. When sea level rose, the peat deposits were covered by muddy sediments. When sea level started to lower, coastal plains and small deltas built back over the muddy sea sediments. During the next low sea level, coastal peat (in swamps) was again deposited over the coastal plain sediments. The peats, mud, and sand, buried by increasing layers of sediments, slowly became compacted. Eventually the peat transformed into coal and the grains in the muds and sands became cemented, transforming them into shales and sandstones. Remains of plants and animals buried by the sediments, were preserved and became fossils, if conditions were right. A variety of plant and animal fossils are found in the coal-bearing rocks.

Extraction of Coal Originally very labor intensive, mainly underground mining, but helped by fact that occurs in layers. In early years many horrors including child labor, 60 hour work weeks etc. (see Emile Zola’s “Germinal” for account of coal mining in late 19th France). Also very dangerous, cave-ins, explosions (due to methane gas a.k.a “fire damp” etc. Made mining hotbed of union activity. Coal Mining Methods

There are two primary methods of mining coal, surface mining and underground mining. There are over 1,000 surface mines and more than 1,000 underground mines in the US. Underground mining is more difficult and requires more miners, but much of our best coal is underground. Mining has become much safer and more efficient over the years. In 1980 there were over 220,000 coal miners in the country. Today there are fewer than 100,000. But while 1980 production was about 800,000 tons, today we produce over 1 billion tons with fewer than half the number of miners.



In many countries, there are three main mining methods employed by the majority of the mines:

• Opencast, using dragline, truck and shovel • Underground Bord and Pillar, using continuous mining machinery • Underground Longwall, using coal shearers and conveyor systems

Surface Opencast

Underground-mining methods include drift, slope, and shaft mining. Drift mines are mines that enter into the side of a hill and mine the coal within the hill. Slope mines usually begin in a valley bottom, and a tunnel is built that slopes down to the coal to be mined. Shaft mines are the deepest mines; a vertical shaft with an elevator is made from the surface to the coal. In western Kentucky, US one shaft mine reaches 1,200 feet below the surface. Surface-mining methods include area, contour, mountaintop removal, and augur mining. Area mines are surface mines that remove shallow coal over a broad area where the land is fairly flat. Rocks overlying the coal (called overburden) are commonly removed by huge dragline shovels. After the coal has been removed, the rock is placed back into the pit.



Underground - Bord and Pillar

Bord and pillar mining methods are used in flat tabular deposits (seams) from 1.5 to 7 metres in thickness where it is required to prevent subsidence (collapse) of mined-out areas from affecting the surface. . The seam is mined in a ‘streets’ and ‘avenues’ fashion (‘bords’) advancing in one direction. ‘Pillars’ of coal are left behind to support the roof and prevent collapse. Additional support is provided through the use of roofbolts.Coal is cut by continuous miners and loaded onto haulers which tip the coal onto a conveyor system. From there, it is transported out of the mine.

Contour mines are surface mines that mine coal in steep, hilly, or mountainous terrain. A wedge of overburden is removed along the coal outcrop on the side of a hill, forming a bench at the level of the coal. After the coal is removed, the overburden is placed back on the bench to return the hill to its natural slope. Mountaintop removal mines are special area mines where several thick coal seams occur near the top of a mountain. Large quantities of overburden are removed from the top of the mountains, and this material is used to fill in valleys next to the mine. Large areas of elevated flat land (where none existed before) are produced by this method. Augur mines use surface-mine benches (before they are covered up) and drill out the coal in the

side of the hill that can't be reached by contour mining.

Underground Longwall

Longwall mining is classified as a total extraction methodology and can recover over 75% of the minable coal. The mining process takes place over a face length of between 100m (shortwall) and 250m (longwall). The coal is cut from the face by a coal shearer which traverses backwards and forwards across the exposed coal face. The coal produced by the shearer is transported along the face by an armored face conveyor. At the end of the face, the coal is loaded by a stage loader onto conventional toughed conveyor belts and transported out of the mine. The roof over the shearer and armoured face conveyors is supported by hydraulically operated shields. As the coal face is cut and removed, the shields advance in the direction of mining, allowing the unsupported roof to collapse behind the mining operation.

Courtesy : Kentucky Geological Survey (KGS)

part i : arang batu (coal) - universiti sains malaysiamineral.eng.usm.my/web halaman mineral/coal...

Documents