C O A L A N D I T S A V A I L A B I L I T Y 1Presentation Transcript
COAL AND ITS AVAILABILITY
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Centre For Advanced Management & Power Studies
Coal is called a fossil fuel because it was formed from the remains of vegetation that grew as long as 400 million years ago.
It is often referred to as "buried sunshine," because the plants which formed coal captured energy from the sun through photosynthesis to create the compounds that make up plant tissues.
The most important element in the plant material is carbon, which gives coal most of its energy.
It is found in seams/coal bed which vary from a few inches to 100’ or more in thickness.
On the basis of amount of ground cover or over burden the coal can be mined by the surface method (complete removal of overburden) or deep (underground) method.
In early times,horses and mules pulled the cart from the miner(who worked at the face of the mine) to the adit (the entry portal of the mine).
If a surface adit could not be made due to the depth of the mine then a large elevator or a skip bucket brought the coal to the surface.
The individual coal miner in the deep mine was replaced by machines in the mid 20 th century.
Mining methods are always changing as machinery and technology improves.
Today use drag lines and power shovel remove entire hilltops to uncover whole seams.
The long wall mining machines needs just 3 miners to cut a 500’ wide swath through the coal seam.
Such advances in productivity are the reason why more tonnage of coal is mined in the world today with fewer than 10 percent of the coal miners employed in 1940-50.
WHAT IS COAL?
Coal is a readily combustible rock containing more than 50% by a weight of carbonaceous material,formed from compaction and in duration of variously altered plant remains similar to those in peat.Most coal is fossil peat.
Peat is an unconsolidated deposit of plant remains from a water saturated environment such as a bog or mire,structure of vegetal matter can be seen and when dried peat burns freely.
HOW IS COAL FORMED?
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 compound.
Peat deposits contain everything from pristine plant parts (roots, barks, spores etc) to decayed plants, decay products & even to charcoal if the peat caught fire.
Peat deposits formed in a waterlogged environment where plant debris is accumulated, peat bogs and peat swamps are examples.
For the peat to become coal it must be burried by sediment. Burial causes the compaction of peat and much water is squeezed out during the first stage of burial.
Continued burial and addition of heat and time causes the complex hydrocarbon compounds in the deposit to start to breakdown and alter in the varieties of ways.
The gaseous alteration products (methane is one) are typically expelled from the deposit and the deposit becomes more and more carbon rich (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).
It is estimated that because of squeezing and water loss it took vertical 10 feet of original peat material to produce 1 vertical foot of bituminous coal.
WHAT ARE THE COMPONENTS OF COAL?
Coal an organic deposit, is made up of organic grains called macerals.
Coal petrographers are the people who study coal under the microscope, separate the macerals into three macerals groups, each of which are composed of several macerals 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 materials.
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 richer in carbon, it includes fusinite, most of which is fossil charcoal derived from ancient peat fires.
KINDS OF COAL
Anthracite is coal with the highest carbon content, between 86 and 98 percent.
Heat value of nearly 15,000 BTUs-per-pound.
Most frequently associated with home heating, anthracite is a very small segment of the world coal market .
The most plentiful form of coal in the world, bituminous coal is used primarily to generate electricity and make coke for the steel industry.
The fastest growing market for coal, though still a small one, is supplying heat for industrial processes.
Bituminous coal has a carbon content ranging from 45 to 86 percent carbon and a heat value of 10,500 to 15,500 BTUs-per-pound.
Ranking below bituminous is sub bituminous coal with 35-45 percent carbon content.
Heat value between 8,300 and 13,000 BTUs-per-pound.
Although its heat value is lower, this coal generally has a lower sulfur content than other types, which makes it attractive for use because it is cleaner burning.
Lignite is a geologically young coal which has the lowest carbon content, 25-35 percent.
Heat value ranging between 4,000 and 8,300 BTUs-per-pound.
Sometimes called brown coal, it is mainly used for electric power generation
COAL USED BY DIFF. INDUSTRIES IN INDIA (1992-93) (MILLION TONNES) 163.11 180.07 TOTAL NIL 1.57 CAPTIVE POWER ETC 6 17.4 28.41 36.15 BRICK KILN 5 OTHERS 20 3.31 3 FERTILIZERS 4 4.9 8.05 10.57 CEMENT 3 64.2 104.74 107.62 POWER UTILITIES 2 11.4 18.59 22.73 STEEL & COKE OVEN 1 % OF FUEL ACTUAL DISPATCH ASSESSED DEMAND INDUSTRIAL SECTOR SR.NO
UNDERGROUND MINING METHODS
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.
Mountaintop removal and
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.
C ontour 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
HOW DID THE COAL-BEARING ROCKS FORM?
The alternation of coals with shale's, sandstones, and thin limestone's records alternating periods of sea-level changes.
As sea level rose, swamps spread across. Ultimately, the seas covered the swamps.
Shallow seas covered parts of land 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 land.
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 peat, mud, and sand, buried by increasing layers of sediments, slowly became compacted. Eventually the peat transformed into coal and the grains in the mud's and sands became cemented, transforming them into shale's 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.
Coal washing, technically called coal benificiation, is a process by which the quality of raw coal is improved by either reducing the extraneous matter that gets extracted along with the mined coal or the associated ash or both.
Coal washing can either be dry deshaling or wet washing.
In dry deshaling, the non-coaly shale and sandstone are removed without using any liquid media.
In wet washing on the other hand, coal is first crushed to a smaller size and put in a liquid media whose specific gravity is adjusted to separate the lighter coal (low in ash) from the heavier coal (high in ash).
The heavier coal, high in ash content, which is left behind as the residue after washing is called the reject.
ADVANTAGES THAT ARE CLAIMED FOR USING WASHED COAL IN THERMAL POWER STATIONS:
Reduction in emissions of particulate matter
Owing to reduced ash content in coal, reduction in size of coal handling plant at power station end.
Reduction in size of ash disposal unit; smaller ash ponds
Reduction in ash will result in less wear and tear of ball mills, induced draught and forced draught fans; less leakage of boiler tubes and less consumption of fuel oil for flame stabilization
The capital cost of the power station will come down for the same design capacity
Railways will carry thermal coal with less ash resulting in increased freight carrying capacity for the railways
Reduction in freight charges to the power station
Better control in thermal power station operations and the control settings would not need to be changed frequently to take care of fluctuations in the heat value in coal feed
THE SATPURA-NANDAN EXPERIMENT
At the behest of Ministry of Coal (the then Deptt. of Coal) in the year 1987, National Productivity Council (NPC) carried out the oft quoted experiment to assess the benefits accruing to a power plant using washed coal. In this experiment, the performance of two identical units of 210 MW of Satpura power stations were compared for one month by burning raw coal in one unit and the washed coal from Nandan washery in another.
The report has tried to prove conclusively that the use of washed coal is highly beneficial but many experts opine differently. It seems that the very basis of the experiment was faulty. Some of the relevant points are listed below:
1 The units were designed to consume coal with higher heat value (HHV) of 4000-4500 kCal/kg while the raw coal fed was of lower heating value at 3637 kCal/kg compared to washed coal of 5071 kCal/kg. The performance would otherwise improve if raw coal conforming to the design parameters were used.
2 Coal sources were different. While the raw coal came from Patherkeda and Pench coalfields, the input for washed coal was from Kanhan coalfields. It should have been same in both cases for proper evaluation.
3 The average moisture content of raw coal was found to be 7.9% while that of washed coal was reported to be only 3.57%. This is anomalous because the process of washing will increase the moisture content in all cases.