Coal
Coal
Coal
Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
COAL
What is coal?
Coal is a combustible solid usually stratified. It mainly consists of C, H, N & O. The
carbon content increases with the geological age of the coal. It decomposes at 1000 –
12000C in the absence of air & solid residue is found is called coke.
2. Bituminous coal: It is the common commercial coal. It is black and has dull
brilliant luster burns with smokey yellow flame like bitumen. Denser and harder
and has no effect to air. Calorific value is 11000-15000 Btu/lb. It contains 80% C.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
Water in the coal is expressed as the moisture content. Nitrogen is present in coal as
proteins, alkaloids and chlorophyll. Nitrogen is present in heterocyclic linkages in large
molecules.
In short note, coal is a mixture of compounds containing mostly the condensed
carboxylic ring compounds. As a result of gradual coalification, the major part of the
coal consists of carbon in the form of graphite.
It is notable that the coal of Bangladesh is considered to be high quality due to its high
level of hit generation capacity. The total reserve is around 3300 MMT of this 5 coal
mines and the hit generation capacity is equivalent to 37 TCF of gas approximately.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
The coal reserves of existing 5 coal mines are shown in the table below:
Among the 5 coal mines, Boropukuria coal mine in Dinajpur has started commercial
production by using underground mining method from September, 2005 with the annual
target of 10 lac MT of coal extraction. A 250 MW power plant has been running by using the
extracted coal of Boropukuria through which power is being supplied to the National Grid.
7 lac MT coal, extracted from Boropukuria coal mine, is being used daily in this power plant.
Production Planning:
At present two major mines are operated to extract about 1 million tons of coal and 1.65
million tons of granite per annum on a 300 day, working days per year basis respectively from
the Barapukuria Coal Mining Company Limited and Maddhapara Granite Mining Company
Ltd. Under the new contract, the year-wise production target is given below:
Coal production from Barapukuria is now around 2,000 MT a day, down by 1,000 MT from the
average coal output of 3,000 MT.
Annual Production of granite is 1.65 Million Metric Tons (5500 metric tons daily).
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
But, in compare to surface mining & underground mining, I think that, less amount of
pollution is occurred in underground mining than surface mining, because of the close system
process of underground mining. On the other hand, Surface mining requires a large amount
of land for mining, which is not available in Bangladesh as a small country. Because, there is
shortage of land for production of crops & foods, which can affect our total production crops.
So, we can say that, Underground mining is superior than Surface mining in BCMCL.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
Give theories of formation of coal or what do you know about origin of coal?
There are two theories which can explain the origin or formation of coal.
A. Growth in situ theory:
According to this theory coal bed and the under clay represent the actual site of vegetable
matter. In other word vegetable matter grew and long years ago at the place where. We
now find coal.
a. Gasification:
Coal is gasified in fixed bed or fluidized bed. If steam and oxygen is used in gasification then
low heat content gas is produced. The difference between low & medium BTU gas is about
50% nitrogen present in low BTU gas. Low BTU gas is used by an industrial fuel and
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
intermediate of NH3 HCHO, medium BTU gas is either methanated (CO + N2 CH4 + N2O) at
higher pressure and lower temperature or catalytically water gas is hydrogenated by fisher-
tropsch process.
Catalyst
CO + H2 CH4 +H2O
This produce CH4 gas, which is known as substitute natural gas (SNG).
Low BTU Clean up Clean fuel Gas low
CO, CO2, H2, (100-250) BTU
N2, CH4, H2S
Gasification Clean fuel gas medium
(250-550) BTU
Clean fuel gas high
Medium BTU Clean up Methanation
(550-1000) BTU
Gas H2S Fischer Tropsch Clean liquid fluid
Coal
Pyrolysis Hydrotreating Clean liquid fuel
H2S
Char H2 Syn crude
Hydrotreating Clean liquid fuel
b. Pyrolysis:
Pyrolysis can be done either at low temperature (400–5000C) or at high temperature (550–
1000˚C) without contact of air. It produces gaseous, solid and liquid products. Solid is mostly
char/coke, liquid is mostly coal tar and NH3 liquor. The tar is hydrogenated to remove H2S and
used as liquid fuel.
c. Dissolution:
Solvent extraction of coal is done at temperature below and above 3000C. At low
temperature, montan wax is obtained. At high temperature, high molecular weight poly-
functional aromatic coal acids are obtained.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
Overall reaction,
n CO + 2n H2 CnH2n + n H2O
n CO + (2n+1) H2 CnH2n+2 + n H2O
9. Produced methane gas is compressed and dehydrated and supply to the pipeline as
synthetic (substituted) natural gas.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
Define ultimate and proximate analysis of coal and write the importance of both.
Ultimate analysis is the determination of C, H2, N2, O2 and S (by difference) in coal and
proximate analysis is the determination of moisture content, volatile matter, ash content and
fixed carbon. The importance of all the determinations of proximate and ultimate analysis of
coal is as follows –
1. Moisture content: Calorific value per lb is reduced by moisture. Excess surface
moisture causes difficulties in handling.
2. Volatile matter: High volatile matter containing coal have low heating values. Coals
with 20% volatile matter have the best value.
3. Fixed carbon:
Carbon content increases from low rank coal to high rank such as lignite to anthracite.
High fixed carbon ascertains high calorific value.
4. Ash content:
As the percentage of ash content increase reduces the heating value and the
production of the boilers also decrease.
5. Sulphur:
Percentage of sulphur gives the idea of corrosiveness of products of combustion.
6. Hydrogen content:
The less content of hydrogen indicates the better quality of coal.
7. Oxygen content:
The less content of oxygen also indicates the better quality of coal.
8. Nitrogen:
Nitrogen in coal comes from protein matter. Nitrogen in coal can be extracted with
H2SO4. The proportion of extractable nitrogen decreases with maturity of coal.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
What is the difference between low temperature carbonization (LTC) and high
temperature carbonization (HTC).
The differences between low and high temperature carbonization are given below –
Properties Low temperature carbonization High temperature carbonization
1. Temp. It is carried out at 500–7000C. It is carried out at 900–14000C.
2. Gaseous Small quantity 4000-9000 cft/ton. It Large quantity 10000-13000cft/ton.
product contains CH4, C2H6, paraffin and olefins. It contains CH4, H2, CO, CO2.
3. Liquid Large quantity. It contains more tar acid Small quantity. It contains little tar
product and tar base. acid & tar base.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
Why low temp. is used in coal carbonization/ write the advantages of LTC?
Low temperature carbonization is used are as follows-
1. It gives the smokeless fuel.
2. It produces a greater amount of tar which can be easily converted into liquid fuel. As a
result, a source of fuel motor fuel can be obtained.
3. The product of this process has a high hydrocarbon content and low hydrogen. So, its
calorific value is more.
Hydrogenation of Coal:
Hydrogenation is the treatment of a fuel with hydrogen at high temperatures and pressures
in the presence of catalysts. In hydrogenation, the initial fuel is transformed into new liquid,
gaseous and solid products rich in hydrogen.
Process conditions:
Temperature: 300 – 500 0C
Pressure: 200 – 250 atm
Catalyst: Mo
Process description:
When coal is pyrolysed in an atmosphere of H2 at temperature of 300–5000C and pressure of
200–250 atm in the presence of Mo as catalyst, H2 reacts with C of coal to form hydrocarbons
NH3 and H2O. The hydrocarbons thus formed react with more hydrogen to produce saturated
hydrocarbons. The latter decompose at high pressure and temperature to produce liquid
hydrocarbons, gas and coke.
In an actual practice –
1. Coal containing less than 2.5% ash is cleaned and powdered to 2 mm size and then
mixed with equal amount of heavy oil to make a paste.
2. H2 gas is obtained by the reaction of steam and water gas.
CO + H2O CO2 + H2
3. CO2 is absorbed when the mixture of H2 and CO2 is passed through an absorber
containing tri-ethanolamine (which absorbs CO2).
4. The paste of carbon and heavy oil is taken in a converter and H2 is passed through the
bottom of the converter at a temperature of 300–5000C and a pressure of 200–250
atm, both maintained constant for about 60–90 minutes.
5. The pressure then released and gases obtained are transferred to a fractionating
column. The heavy residue is withdrawn from the bottom of the converter.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
6. The gases are fractioned into crude spirit (which goes out of top), middle oil and heavy
oil as residue.
7. The middle oil transferred into another converter, where it is again heated under
pressure with hydrogen in presence of catalyst. As a result, middle oil gets converted
into crude spirit. It is mixed with first converter spirit and reformed to be used as
motor spirit.
In addition to Mo, some other catalysts such as compounds of Pb, Sn, Ge, Zn etc. and Zn
oleate can be used. It is also possible to get number of variable products by changing the
temperature, pressure, H2 concentration, time of reaction and the catalyst used.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
Dulong’s formula:
Calorific value = 1/100 [8080 C + 34500 (H – O/8) + 2240 S] kcal/kg
Where, C, H, O & S are the percentage of carbon, hydrogen, oxygen and sulphur respectively.
is the calorific value in kcal/kg. C, H, O, and S represent the percentage of carbon, hydrogen,
oxygen and sulphur.
Sulphur, therefore reduces the value of coal. So, it is important to remove sulphur from coal
to the maximum extent. Depending on the sulphur content, coal is graded as low sulphur coal
(0–1% S), medium sulphur coal (1–3% S) and high sulphur coal (more than 3% S).
Coals having too high ash content are called bone coal, bituminous shale or black slate. The
chemical composition of ash differs with different grades of coal. Ash usually contains silica,
alumina, iron oxide & small amounts of lime, alkalies, magnesia and sulphur compounds.
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Chapter 4 ACCE 5103 Md. Zahidul Islam
ASH1304MS102M, ACCE, 4th Batch
The higher the softening point of ash, the better is the quality of coal. The softening point of
coal ash generally lies between 1900-31000F. Ash having low softening point undergoes
fusion to form ash clinker, when coal is burnt. This clinker formation has adverse effects on
coal burning. So, ash is unwanted and degrades the quality of coal.
Therefore, A good quality coal should have less ash content and the ash should have high
fusion point.
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