Coal- A details study of coal
What is Coal? How Coal is Used? What is Coal Mining? History of Coal mining in Assam and Coal Mining Areas of Assam, Tirap Colliery and methods of Work
Classification of Coal, Physical and Chemical Properties of Coal, Composition of Coal, Volatile matter of Coal, Ash Content of Coal
Coal-A details Study of Coal
What is Coal?
Coal is a hard, black substance found in deposits of sedimentary rocks. Coal is a fossil fuel that formed from the remains of ancient plants that lived and died or buried deep in the earth millions of years ago when parts of the earth were covered with huge forests. Coal is also known as a non-renewable energy source because coal takes millions of years to form.
Coal is mainly used to produce energy but it can also be used to manufacture steel and coal is an important source of some of the chemicals that are used in pharmaceuticals, fertilizers and pesticides.
The energy that we get from coal came from the energy that plants (flora) absorbed from the sun millions and billions of years ago. All living plants store energy from the sun. After the plant die, this energy is usually released as the plants decay, under certain conditions, the plants decay is interrupted and preventing the release of the stored solar energy.
Coal reserves and production:
Coal reserves are the beds of coal still under the ground that can be mined. The United States has the World’s largest known coal reserves.
How coal is used?
About 90% of the coal mined is used to make electricity. The steel industries, the Iron industries and other various industries use coal for smelting metals. Paper, bricks, limestone and cement industries also use coal to make various products.
Coal mining:
Coal mining is a process of physical extraction of coal resources to yield coal. Coal companies mainly use two methods for coal mining-
1. Surface mining and
2. Underground mining
Coal mining areas in Assam:
The history of coal mining in Assam-
In 1834, the coal mineral extraction was done on a small scale that was carried out at Cherapunji (during 1834, this area was under the State of upper Assam). In 1840, the Coal was first mined near Jaypore (presently this area under Dibrugarh district) by the Assam Tea company. The most important stage in 1882 was the development of the coal mining industry in Assam was the incorporation Assam Railway and Trading company for the exploitation of the Coal of upper Assam.
The most important coal mines in Assam are situated in the Ledo (Tinsukia district) and Jaypore (Dibrugarh district) areas of upper Assam. Pure forms of coals are extract from these areas. In the Mikir hills, two small coal areas exist- one at the Koilajan and other at Seelbhata. The coal mining activities in the Khasi hill is mostly concentrated around the Laitryngew area. In addition to these small coal areas, three mines exist in the Khasi hills. Messrs Thanginath coal area and the Mawsynram coal area are important among them (all these places are presently under the state of Meghalaya).
Places of Underground mining, namely Borgolai, Ledo, Tipong, Jaypore (under Dibrugarh and Tinsukia districts).
Places of opencast mining, namely, Tikak and Tirap (under Tinsukia district).
Tirap Colliery:
Location/ Geography/ Latitude/ Longitude
Tirap Colliery is one of the three operating opencast mine of North Eastern Coalfields (NEC). The Tirap Colliery is mainly situated in the Margherita Sub-division of Tinsukia district of north eastern state of Assam, near the border of Arunachal Pradesh. The Tirap Colliery mine is approachable by National Highway 38 located 10 kilometers away from the North Eastern Coalfields (NEC)(a unit of Coal India Limited), Margherita area Office. Ledo railway station is the nearest railway station that is located about 6 kilometers away and 60 kilometres away from the district Headquater Tinsukia.
Tirap gaon (no.1 and no.2 villages)- this place is known for opencast coal mining since 1st November, 1983.
Tirap Colliery lies between the latitude of 27°15’’ and 27° 5’’N and longitudes of 95°40’’ and 95°50’’E. The general elevation is 140 meters above mean sea level near the plains of Buri Dehing River, rising to 300- 500 metres on the Patkai Naga range and is characterized by rugged topography due to this presence of hills. The average annual rainfall ranges between 300 to 425 cm. The Tirap colliery climate is mainly belongs to short summer, rainy season and a fairly cold winter and the tropical monsoon starts from april to September. The Tirap colliery mainly consists of various types of plants like Macaranga denticulate, Mesua ferra, Michenia Champaka, Dipterocarpus retusus, Schima wallichi, Syzygium sp. etc.
Methods of work in Tirap Colliery:
Mechanized mining with hydraulic excavator and dumper combination is being practiced in Tirap Colliery. Drilling is done by mechanized drills and blasting is conducted under proper supervision.
CLASSIFICATION OF COAL
Coal is mainly classified as Anthracite, Bituminous, Sub-bituminous, Lignite. The ranking of coal is depends on the type of the coal and the carbon content of the coal. The types of coal are described below_
PEAT
Peat is considered to be a precursor of coal, it has industrial importance as a fuel in some regions. Peat is a highly effective absorbent for fuel and oil spills on land and water. It is also used as a conditioner for soil to make it more able to retain and slowly release water.
ANTRACITE
Anthracite also known as Hard coal. Anthracite has brittle texture. It is composed mainly of carbon with little volatile and no moisture content oldest coal from geological perspective. Anthracite mainly contains 86% to 97% carbon, highest amount of carbon. Have highest energy content. Classified as the highest rank of coal and is used primarily for residential and commercial space heating. It contains approximately 22-28 million Btu per ton with an ignition temperature of approximately 925- 970 degrees Fahrenheit. Anthracite used in metal industry due to high heat value.
BITUMINOUS
Bituminous also known as soft coal. Bituminous contains lower amount of carbon than Anthracite, it is about 45% to 86%. Bituminous has shiny luster and layered texture. Great pressure results in the creation of Bituminous or soft coal. Have higher heating value (in the range of 19-30 million Btu per ton) than lignite but less than anthracite. Ignites easily burns long with a relatively long flame. If improperly fired bituminous coal is characterized with excess smoke and soot. It is used primarily as fuel in steam electric power generation with substantial quantities used for heat and power applications in manufacturing and to make coke. Have moisture content of less than 20% and an ignition range of 700-900 degrees farenheit.
SUB-BITUMINOUS
Sub-bituminous has 35% to 45% carbon content. Properties range from those of lignite to those of bituminous coal is used primarily as fuel for stream electric power generation and is an important source of light aromatic hydrocarbon for the Chemical synthesis industry. Generally sub-bituminous contains 20-30% moisture. It contains 16-24 million Btu per ton.
LIGNITE
Lignite is also known as Brown coal. Lignite or brown coal is very lowest rank of coal and used almost exclusively as fuel for electric power generation. Lignite has 25% to 35% carbon content. It has crumbly texture. Very soft coal composed mainly of volatile matter and 70% moisture content. Have low fixed carbon (carbon is in free state) and youngest coal from geological perspective. Increases in maturity by becoming darker and harder and is then classified as sub bituminous coal. After a continuous process of burial and alteration chemical and physical changes occur until the coal is classified as bituminous dark and hard coal.
GRAPHITE
Technically the highest rank is difficult to Ignite and is not commonly used as fuel. Graphite is mostly used in pencils and when powdered as a lubricant.
COMPOSITIONS OF COAL
The composition of coal varies widely. Coal is composed chiefly of rings of six carbon atoms join together in an extremely complex composition of layered arrangement not only hydrogen but have significant amount of Oxygen as well as Nitrogen. The structure also includes varying amount of sulphur and other environmental pollutants.
The sulphur and nitrogen content are important as emissions of their chemical oxides during cold burning can cause acid rain.
PHYSICAL PROPERTIES OF COAL
MOISTURE CONTENT
Each type of coal has a certain set of physical parameters which are mostly controlled by moisture content, volatile content and carbon content. Coals are mined wet hence moisture content is one of the important property of coal adventitious moisture refers to groundwater and other extraneous moisture which is readily evaporated whereas inherent moisture is held within the coal itself and is analysed quantitatively. Moisture may occur in four possible forms within coal.
HYDROSCOPIC MOISTURE-
In hydroscopic moisture, water held by capillary action within the microfractures of the coal.
DECOMPOSITION MOISTURE-
In decomposition moisture, water help within the coal decomposed organic compounds.
SURFACE MOISTURE-
In surface moisture,water held on the surface of coal particles.
MINERAL MOISTURE-
In mineral moisture, water which comprises part of the crystal structure of hydrous silicates such as clays. Moisture decreases the heat content per kg of coal. Typical range is 0.5 to 10%. It increases heat loss due to evaporation and superheating of vapour, paper helps to a limit, in binding fines and aids radiation heat transfer.
VOLATILE MATTER OF COAL
Volatile matter in coal refers to the components of coal, except for moisture which are liberated at high temperature in the absence of air under specified conditions. Volatile matter is usually a mixture of short and long chain hydrocarbons, aromatic hydrocarbon and some sulphur. It is an index of the gaseous fuels present. Typical range of volatile matter is 20-30%. Volatile matter proportionately increases flame length and helps in easier ignition of coal.
ASH CONTENT OF COAL
Ash content of coal refers to the non-combustible residue left after coal is burnt. It represents the bulk mineral matter after carbon, oxygen, sulphur and water including from clays has been driven off during combustion. Analysis is fairly straight forward with the Coal thoroghly burnt and ash material expressed as a percentage of the original weight. Ash is an impurity that will not burn. Typical range is 5-40% and it reduces handling and burning capacity increases handling costs,effect combustion efficiency and boiler efficiency and causes clinkering and slagging.
FIXED CARBON OF COAL
Fix carbon is the solid fuel left in the Furnace after volatile matter is distilled off. This differs from the ultimate carbon content of the coal because some carbon is lost in the hydrocarbon with the volatile. It consists mostly of carbon but also contains some hydrogen, oxygen, sulphur and nitrogen not driven off with the gases. Fixed carbon is used as an estimate of the amount of coke that will be yielded from a sample of coal. Fixed carbon is determined by removing the mass of volatiles determined by the volatility test above from the original mass of the coal sample.
Fix carbon is derived by subtracting from 100 the value of moisture, volatile matter and ash.
Fixed carbon= 100 – (moisture+ volatile matter+ ash)
RANK OF THE COAL
The degree of metamorphism or coalification undergone by a coal as it matures from peat to anthracite has an important bearing on its physical and chemical properties and is referred to as the rank of the coal.
RELATIVE DENSITY OR SPECIFIC GRAVITY
Relative density or Specific gravity of the coal depends on the rank of the coal and degree of mineral impurity. It determines the properties of composite and the blends. It is normally determined by the loss of a samples weight in water. This is the best achieved using finely ground coal as bulk samples are quite porous.
CHEMICAL PROPERTIES OF COAL
= Coal is a combustible black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams.
= Coal and fossil fuel is the largest source of energy for the generation of electricity worldwide as well as one of the largest anthropogenic sources of CO2 releases.
= Coal is useful resource of human consumptions.
= Coal is primarily burned as a fossil fuel for the production of electricity and for heat.
= Coal is used for industrial purposes such as refining metals.
= Coal form when dead plant matter is converted into peat, which is turn, converted into ignite then anthracite.
