2. Course Objectives
• To understand the various processing techniques and limitations of
fossil fuels
• To analyze the processing techniques of Biofuels and Biomass as a
Potential renewable energy source
• To understand the necessity of harnessing alternate energy sources
such as Solar, wind, nuclear, fuel cell, geothermal and tidal.
3. Course Outcomes
• CO1 – List the available renewable and non-renewable energy
resources and relate to fulfil global energy demand.
• CO2 - Summarize the various characterization techniques used in solid
and liquid fuels
• CO3 - Execute the effective utilization of potential conventional energy
source by advanced conversion technologies
• CO4 – Analyze the potential utilization of biomass and bio-fuels as a
substitute for the fossil fuel applications
• CO5 - Assess the available non-conventional (renewable) energy
resources and techniques to utilize them effectively.
• CO6 – Facilitate the design and applications of related devices using
renewable energy sources
4. Examination Scheme
• Endsem-50%, (100 marks)
• Midsem-25%
• IA (Continuous evaluation includes: quiz(5), open book assignment(5),
Problem Solving / Design Problem / Case Study (5)
References:
1. Fuels and Combustion – Samir Sarkar
2. Non-conventional Energy Sources – G.D. Rai
3. Solar Energy by Sukatame, Tata McGraw Hill, New Delhi
4. Energy Technology by Rao & Parulaker.
5. The guidelines for the Mid Semester Examination are as follows:
1. Only ONE Mid Semester Exam will be conducted in a semester.
2. For evaluation of the course, 25% weightage will be given to the Mid Semester Examination,
25% weightage will be given to the Internal Assessment and 50% weightage will be given to
the End Semester Exams.
3. The Course Coordinator Faculty / Faculty teaching the Course should share the outlay
i.e. Components of the Internal Assessment with the students in the first week of the
ensuing odd semester.
4. In order to pass the course, it is mandatory for every student to score at least (minimum) 35%
marks in the End Semester Examination of that course.
5. During the Mid Semester Exam, no Classes / Laboratories shall be conducted.
6. Units
1. Overview of energy scenario
Coal (Solid fuel: Fundamental definitions, properties and various
measurements of fuels, Coal classification, composition and basis, Coal
preparation and washing Different types of coal combustion
techniques, Coal liquefaction, Coal Gasification, etc.)
2. Liquid and Gaseous Fuels
Petroleum, Crude & Vacuum distillation, Processing of crude
Producer gas, Water gas, Hydrogen gas
Biofuels, Biorefinery
7. Units
1. Renewable Energy Sources
Solar (Measurement of solar radiation, solar energy collectors – flat
plate collector, air collector, collectors with porous absorbers,
concentrating collectors, applications & advantages of various
collectors, solar pond)
Wind (nature, power, forces, conversion and estimation. Components
of wind energy system, types, design considerations)
2. Alternate Sources
Fuel Cell
Nuclear Energy – fission, fusion
Geothermal Energy
Tidal Energy
9. What is GDP?
How is it related to energy consumption?
The production/consumption of energy and GDP interact with
each other, because energy determines the economic and social
development of countries, and GDP growth leads to an increase in
energy demand. Many studies conducted in recent decades
confirm the strong relationship between these two variables
10.
11. Energy Consumption
Energy is primarily used by four different sectors:
• Domestic sector
• Transportation sector
• Industrial sector
• Health, education and welfare
What are some other uses?
14. Conventional Energy Sources
Oil
- The most dominant energy source.
- However the consumption of oil is decreasing
with increased use of non-conventional energy
sources
- India’s share is barely 1.2%
15. Conventional Energy
Sources
Natural Gas
- Total reserve = 6183 trillion cubic feet
- The top 20 countries alone account for
5602 trillion cubic feet
- Middle east and Eurasia are the primary
sources
- End-user – primarily industrial sector
17. Commonly used definitions
Proximate Analysis: The proximate analysis of a fuel indicates the moisture, volatile
matter, fixed carbon and ash content of the fuel in terms of percentage of weight
1. Moisture: The water content expelled from the fuel by specified methods without
causing any chemical change to the fuel
2. Volatile matter: Total loss in weight minus the moisture when the fuel is heated out of
contact with air to a sufficiently high temperature under specified conditions
3. Ash: Inorganic residue left when the fuel is completely burnt in air under specified
conditions
4. Fixed Carbon: The residue obtained by subtracting the sum of percentages by weight
of moisture, volatile matter and ash from 100. It is essentially carbon containing
minor amounts of nitrogen, sulphur, oxygen and hydrogen.
18. Ultimate Analysis: The ultimate analysis of a fuel gives its elementary
composition. It is the analysis in terms of the percentage by weight of the
elements: carbon, hydrogen, oxygen, nitrogen and sulphur which constitute the
pure fuel, free from moisture and inorganic constituents.
1. Combustion: Process by which heat is liberated from fuel by its high
temperature reaction with an oxidant which is usually oxygen present in the
air. The quantity of heat evolved by the combustion of unit quantity of fuel is
its calorific value or heating value.
2. Gross calorific value at constant volume/pressure: Amount of heat released by
a specified quantity (initially at 25°C) once it is combusted and the products
have returned to a temperature of 25°C, which takes into account the latent
heat of vaporization of water in the combustion products. (solid and liquid
fuels are burnt at constant volume while gaseous fuels are burnt at constant
pressure).
3. Net Calorific value: CN=CG-52.5H (H is the % of hydrogen in fuel; for solid
and liquid fuels), CN=CG-4.7V (V is the volume percentage of total hydrogen
of gaseous fuels)
19. 4. Ignition Point: Minimum temperature at which a fuel ignites in an oxidizing
atmosphere without the help of any external source of fire. It is a characteristic
property.
5. Flash point and fire point: Both characteristic properties. What are these?
Difference between flash point/fire point and ignition point?
6. Rank of coal: What is it?
7. Carbonization of coal: Process of heating of coal without contact with air to a
sufficiently high temperature, so that the coal undergoes decomposition and
yields a residue which is richer in carbon content than the original fuel. The
natural process is termed as coalification.
8. Gasification: Solid/liquid fuel gaseous fuel
20. 9. Caking: Coal that softens and agglomerates on heating and after volatile matter
has been driven off at high temperatures; produces a hard gray cellular mass of
coke. All caking coals are not good coking coals
10. Coking: Carbonisation of coal in a commercial oven at about 1000 deg C to
result in formation of hard lump which is known as coke.
11. Cracking: Thermal decomposition with or without catalysts. (what is
hydrocracking?)
A hydrocracking unit, or hydrocracker, takes gas oil, which is heavier and has a higher boiling range than
distillate fuel oil, and cracks the heavy molecules into distillate and gasoline in the presence of hydrogen
and a catalyst.
12. Orsat analysis: Related to gaseous fuel, the composition of which is
determined by analysis in a standard apparatus known as orsat apparatus. % of
CO2, O2, CO, and N2 (It was patented before 1873 by Mr. H Orsat as the Ellison
Orsat Apparatus.)
13. Flue Gas: Gaseous product of combustion of fuels in oven and furnaces. When
combustion is complete, what are the residue products?
21. Basis for reporting results of analysis:
Fuels are heterogeneous in nature. Therefore to quantitatively report analytical
data on an accepted basis we need some forms of basis. (Especially for solid fuels)
1. Run-of-mine (rom) [As obtained from mine]
2. As-received [When customer analyses]
3. Air-dried [As the name suggests, can be same as (2) as during transport air
drying occurs. However standardization exists, as air drying generally
happens at 40 deg C with 60% relative humidity]
4. Dry
5. Dry-and-ash-free (daf)
6. Dry-and-mineral-matter-free (dmmf)
7. Moist-mineral-matter-free or simple mineral-free
22. Solid Fuels
Solid materials that are used as a fuel to produce energy by combustion
with oxygen enriched air.
Can be both natural and processed fuels. Widely used in industries and
domestic appliances.
Some examples:
Naturally occurring: wood, peat, coal
Derived from naturally occurring: charcoal, coke, lignite briquettes
Other examples of widely used fuels that might not be as efficient ??
23. Biomass
What is Biomass?
Atmospheric CO2 is fixed in the form of biomass – primary product of
photosynthesis in the terrestrial and aquatic regions of the earth.
Secondary products are human, animal and industrial wastes and residues.
Prehistoric times biomass was perhaps the only source of useful energy and
currently only provides 11% of world’s energy.
Biomass has the potential to provide 10 times that of world’s needs. What is the
bottleneck?
How much does India depend on biomass?
24. Wood
1. Wood can be used for carbonisation and
gasification purposes.
2. Charcoal is the end product of carbonisation and
producer gas is the gaseous product of gasification.
3. Incomplete combustion can also produce
charcoal.
Carbonisation of wood is characterized by several
temperature regimes:
• At around 100-170 deg C loosely bound water
evaporates,
• between 170-270 deg C, CO and CO2 are
released,
• and an exothermic step starts beyond 270 deg
C.
25. Charcoal
Wood carbonisation charcoal.
On cooling wood gas, and two layers of liquid. Upper
pyroligneous acid, lower wood tar
Open pits are fairly obsolete nowadays (only 15%
charcoal is recovered)
Paraboloidal mud kilns are common in India. The
dimensions are about 2.5m in height, and 3m radius.
The channel at the center acts as a chimney (vertical)
and the horizontal one is used to introduce fire.
Time taken for carbonisation is about 7-10 days.
Retorts used in factories however give better yields and
some by-products can also be recovered.
4 types of retorts: Externally fired batch retorts,
Externally fired continuous vertical retorts, internally
heated batch vertical retorts and internally heated
continuous vertical retorts.
27. Charcoal continued..
1. Internally heated retorts are of recent design, and use forced recirculation of heated inert gases given off
during carbonisation, have high thermal efficiency and lend themselves to efficient mechanical handling of
the wood and charcoal.
2. Wood charcoal is a source of fairly pure carbon. It easily ignites and burns at low rates. For clean and
smooth burning in heating ovens, wood charcoal is a good but costly fuel. It used to be a very important fuel
and reducing agent in metallurgical processes. Coke has now replaced it in most cases owing to cost and
other technical reasons.
3. Charcoal has however retained its use in some special cases. It is extensively used as a fuel in blacksmiths'
and metal workers forges, and in numerous other cottage industries.
4. Gasification plants may also use charcoal as the fuel material. During the Second world war, road vehicles
using producer gas obtained from wood charcoal were used in many countries, including India. With suitable
treatment wood charcoal is widely used as an absorbent in gas purification, solvent recovery and liquid
purification. It has a high surface area of 150-450 m^2/g.
5. Other forms of biomass like sawdust, nutshells, bagasse, barks, twigs and coconut shells can also be
carbonized to give charcoal.
28. Cattle dung
• Amount of cattle dung used in India 100 million tonnes everyday as domestic
fuel.
• Equivalent to 40 million tonnes of coal.
• This is hugely problematic. Why so?
• What is the better usage of cattle dung?
29. Peat
Peat is a naturally occurring solid fuel (used primarily as domestic fuel) consisting of partly decomposed
plant material that accumulated in situ under marshy conditions.
Peat bogs grow at slow, but measurable rate. In general, peat accumulates in an active swamp at the rate
of about 3 m in 2,500 years. Associated with very large content of water. In fact, the amount of solid
matter in peat bogs is 10%, or less.
Near the surface of the deposit, peat is light brown in colour and highly fibrous in nature. With an
increase in the depth, the colour becomes darker and finally black, when the vegetable origin and
structure is not so obvious. A part of the water content of freshly won peat can be drained off while a
much larger part is removed by drying in air. The air-drying operation may require 40-50 days.
Peat represents the first stage in the conversion of vegetable matter into coal. Large deposits of peat are
found in Russia, Germany, Poland, Finland, USA, Sweden, Norway, Ireland, Canada, Indonesia and
Scotland. Russia has 60% of the world's total reserves of peat. The only significant deposit of true peat in
India is in the swamps of the Nilgiri hills in southern India at an elevation of 2,000 m. The composition and
properties of peat vary widely from place to place, depending on the nature of the original plant material
and the agencies and extent of decay. Raw peat consists of decayed plant material.
32. Lignite
Forms of lignite: Woody or fibrous brown, Earthy brown compact and friable,
Brown coal showing split.
Properties:
1. High moisture content (30-50%), on exposure to atmosphere moisture content
reduces to equilibrium value 12 to 20%
2. Can ignite spontaneously and break.
3. Therefore transportation is a problem.
4. High Oxygen (therefore low calorific value)
5. Tar obtained by the low temperature carbonisation used as raw material for
production of synthetic petroleum.
6. Used for manufacture of producer gas,
7. Gasified into synthesis gas for ammonia production.
34. Sub-bituminous
• In many countries this fuel is regarded as a variety of mature lignite resembling true coal in colour and
appearance. In India it is regarded as a separate class and the term sub-bituminous coal is preferred.
• It is black in colour with a dull, waxy lustre.
• It is denser and harder than lignite and has a lower moisture content of 12% to 25%. Most sub-bituminous coals
appear banded like bituminous coal. The bands are parallel to the bedding plane, but are poorly jointed and
easily split into slabs instead of breaking into rectangular lumps.
• Like lignite, sub-bituminous coal disintegrates on exposure to atmosphere and is therefore difficult to transport.
• Sub-bituminous coal is available in the USA, Russia, Germany, Canada, Australia and India. Some of the tertiary
coals in Assam, Kashmir and Rajasthan are of the sub-bituminous type.
• The sub-bituminous coal has 70%–78% carbon, 4.5%-5.5% hydrogen and about 20% oxygen (all on a dmmf
basis). The air-dried moisture is 10%-20%. The volatile matter is 40% (dmmf) and above. The calorific value is
6800-7600 kcal/kg, dmmf.
• It ignites easily and may be used in raising steam for various purposes. If low in sulphur, it may also be used for
manufacturing gaseous fuels.
35. Bituminous
• Most common and widely used variety of solid fossil fuel. The term 'bituminous’ is a misnomer. Coal does not
contain true bitumen. Moreover the so-called bitumen extractable from coal with the help of organic solvents
cannot define coal and its properties. The name is perhaps due to the fact that it burns with a smoky yellow
flame similar to that of bitumen, and that the pitch obtained from coal tar is of a bituminous nature.
• Bituminous coal is black and usually banded. The bands are parallel to the bedding plane. The coal breaks along
vertical joints or cleats into rectangular, columnar and cubical places. Sometimes the fracture is conchoidal. The
lustre varies from bright to dull, Bituminous coal is denser and harder than lignite and sub-bituminous coal, and
does not disintegrate into slacks exposure to atmosphere. Owing to the good heating qualities and ease of
handling, bituminous coal is the major fuel in most countries.
• Coal occurs in strata called seams which are bound between the upper and lower layers of rocks, and have
longitudinal and lateral extensions. Coal seams are parallel to the bedding planes which, may or may not be
parallel to the earth's surface. The whole of the coal-bearing rocks in a region is collectively known as the coal
measures. The seams vary widely in thickness, Longitudinal and lateral extension and depth of occurrence. For
comfortable mining a seam should be at least a metre in thickness. The thickest coal seam (156 m) of India
Rajmahal coalfield, WB, and the deepest is at Raniganj, WB.
fracture with smooth,
curved surfaces that
resemble the interior
of a seashell
37. Bituminous
Methods of Mining:
1. Underground Mining:
1. Board and pillar: used in medium to thick seams at relatively shallow depth. Here tunnels are driven by
blasting along and across the extension of coal seam. The tunnels divide the seam into many blocks known
as coal pillars. Coal is won by driving tunnels and by depillaring to the extent possible. Then conveyor belts
along with lifts are used to transport coal.
2. Long wall: Used for mining at great depths. Involves driving of pairs of roads along with linked access roads
into the area under mining. These roads are also connected to the mine shafts. This is important because
we need air circulation (forced or otherwise).
2. Open cast mining: Advanced method. Incorporates a line with a bucket scooping up tonnes of coal at a time.
Machineries like bulldozers or bucket wheel excavators can also be used. Top soil is removed to expose coal
seams which are then progressively extracted. This kind of mining involves restoration of the land after coal has
been extracted. In India more than half the coal is mined using this method.
41. Bituminous -- Uses
1. Combustion in domestic ovens, industrial furnaces, boilers, railway locomotives (dying
out), and thermal power stations.
2. Carbonisation coke, semi-coke
3. Gasification producer gas, water gas, coal gas (a mixture of gases (chiefly hydrogen,
methane, and carbon monoxide) obtained by the destructive distillation of coal and
formerly used for lighting and heating) and liquid fuels like coal tar fuels.
4. Source of wide range of chemicals , fertilisers, and synthetics liquid fuels.
42.
43. Semi-anthracite
1. Intermediate between bituminous coals and anthracites.
2. Harder than bituminous, ignites more easily.
Some properties:
1. Moisture percent: 1 to 2
2. Volatile matter, per cent dmmf = 10 to 15
3. Calorific value kcal/kg dmmf = 8500 to 8800
Semi-anthracites do not occur in India
44. Anthracite
1. Hardest form of solid fossil fuel. They are non-caking. Has sub-metallic lustre and
sometimes even graphitic appearance. It doesn’t soil the hand.
2. Low volatile matter, 3 to10% dmmf and high carbon content, above 90% dmmf.
3. Air dried moisture = 2-4%, Hydrogen content is about 3-4%
4. Calorific value = 8500-9000 kcal/kg
Uses: boilers, domestic stoves, and metallurgical furnaces. Also as coke, or precision
electrodes etc.
45. Anthracite
1. True anthracites do not occur in India
2. However, tertiary coals in Jammu and lower Gondwana coals in Darjeeling have
properties approaching those of anthracite and are known as anthracitic coals.
3. 100 to 150 Mt of such coals in these two places
46. Cannel and Boghead coals: Anyone heard of these? Where were they used?
1. Humic vs sapropelic coals both vegetable origin, former derived from higher plants
(peat, lignite, bituminous and anthracite) and latter smaller plant organisms.
2. Sapropelic coal hydrogen-rich including, derived from sapropels (loose deposits
of sedimentary rock rich in hydrocarbons) and characterized by a dull black, sometimes waxy
lustre. The origin could be algae as well.
3. Not widespread. Is not found in India.
4. In earlier years cannel and boghead were used in the UK extensively for manufacture of
town gas a gas of high illuminating power.
Natural coke/slv (special low volatile) fuel: Result of carbonisation of coal insitu by igneous
intrusion. Can be used as coke substitute.
47. Origin of Coal
Chemical and geological studies conclusively show coal forms from vegetable and some
lower animals.
Larger remains like tree trunks, bark, twigs, leaves and plant residues are visible with naked eye
and smaller structures such as wood cells, spores and algae are identified with the help of
microscope.
The ranks represent the degrees in the conversion of the original plant material.
Two theories on origin of coal:
• Autochthonous (the growth insitu) The plants grew and decayed in the same area
where coal is found today.
• Allochthonous (drift theory) The vegetable matter was driven from the original place of
occurrence by water into the neighbourhood lakes, lagoons or estuaries.
48. Origin of Coal
• Either theory accounts for the wide area occupied by coal seams and can
also explain their uniform thickness.
• Points in favour of the insitu theory:
• In existing peat bogs the decayed vegetable matter is accumulating in
situ,
• the underclays of the coal bed and sometimes the rocks associated with
coal contain upright fossil roots which are numerous and therefore
suggest the occurrence of a fossilized forest,
• The coal seams are fairly constant in composition over a wide area.
49. Origin of Coal
• Points in favour of drift theory:
• Large quantities of plant material are carried downstream by rivers and
sometimes deposited near the estuary (example?),
• There are similarities between coal and sedimentary rocks,
• Tree stems without roots in a seam are found quite often.
50. Origin of Coal
Collected evidences indicate that the majority of coal seams in the world are of the in situ origin while there
is little doubt that some coals have been formed by the drift method.
The characteristic features of the Gondwana coal seams support the common belief that these coals were
formed from plant materials of terrestrial vegetation which were transported into lakes, river valleys and
estuaries or even into the sea.
Many coalfields consist of coal seams and sedimentary rocks in a sequence that is repeated several times
which corresponds to a cyclic process of accumulation of plant debris and cover by sedimentary rocks. Such
formations of stratified coal seams and sedimentary rocks are known as coal measures.
There were two important stages in the formation of coal from vegetable matter
1. Peat stage or biochemical stage,
2. Metamorphism or dynamo-chemical stage.
51. Origin of Coal
The first stage: Plant material underwent decay under moist conditions by bacterial attack. The decay
continued until the absence of an adequate supply of oxygen and the development of toxins which ended the
microbe activities. This could have been caused either by rapid and complete burial of the peat deposits
under a cover of inorganic sediment or by flooding by stagnant water, followed later by a covering of
sedimentary earth.
The second stage: The agencies causing changes in this stage are:
1. pressure of overburden,
2. tectonic pressure caused by severe earth movement, for example, during the folding orbuckling of the
earth's strata.
3. Regional temperature increasing by 0.5°C to 3.5°C for every 100 m increase in depth.
4. Contact with igneous intrusions (molten rocks and lava).
These agencies were partly or wholly operative for a very long time, spread over geological ages. The result
has been coals of different maturity or rank. By and large the rank of coal rises with the increase in the age of
the geological system of the coal deposits
53. Origin of Coal
Thus bituminous coals are found in paleozoic and mesozoic deposits and lignite in tertiary deposits. However
high tectonic pressure and proximity of lava might bring about-accelerated metamorphism as in the deposits
of anthracite coal in Jammu and Darjeeling.
The effect of depth of occurrence on the maturity of coal is obvious. Both temperature and pressure rise with
the increase in depth. Again the rate of a chemical change doubles for a rise of about LOC. Hence the coals in
the lower seams of coal measures are generally more mature thanthose in higher seams. This variation of
rank with depth is known as Hilt's law.
The precise nature of the changes that took place in the gradual conversion of plant materials into coal is
not known. It may however be inferred that the bacterial attack in the first stage of coal formation brought
about chemical reactions under predominantly oxidising atmosphere, in which almost all the ingredients of
plants took part and produced the humic acids and other components of peat.
Later peat was buried under mineral rocks and pressed into more compact material, Chemical reactions such
as dehydration, decarboxylation and dehydrogenation, and others took place to remove H2O, CO2, CO, CH4,
and H2S.
54. Composition of coal
Basically organic mass (complex organic compounds of carbon, hydrogen,
nitrogen, oxygen and sulphur), with some quantities of inorganic substances
like water and mineral matter.
Can also contain adsorbed gases, methane, CO2, and CO.
Coal petrograph: Study of coal components by visual methods, with or
without the help of a microscope. Therefore we have macroscopic
components and microscopic components.
56. Analysis and properties of coal
Bureau of India Standards publications standardize the detailed methods of
analysis and testing in India.
Proximate analysis
Ultimate Analysis
Calorific value
Other chemical and physical properties include: solubility, specific gravity,
surface area and porosity, angle of repose, grindability, specific heat,
reflectance and refractive index.
57. Moisture
Coal is always associated with moisture. Because of it’s origin.
External and inherent moisture. When wet coal is exposed to the atmosphere, the
external moisture evaporates but the apparently dry coal still contains some
moisture which can be removed only on heating above 100°C. External moisture
may also be called accidental or free moisture, while inherent moisture may be
referred to as equilibrium, or air-dried, or hygroscopic moisture.
The quantity of external moisture depends mainly on the mode of occurrence and
handling of coal, but the air-dried moisture is related to the inherent hygroscopic
nature of the coal. Excessive quantities of free moisture are.
In order to get reproducible and correct values of air-dried moisture, it is
necessary first to equilibriate the coal sample in a standard atmosphere of
specified temperature and humidity before the actual determination is done.
58. Air Dried Moisture
1. Observe loss in weight by heating to
about 105 deg C
2. Moisture content decreases with
increasing rank. Peat has 25%,
bituminous has 0.5%.
3. Value increases slightly for anthracite
(upto 3%)
4. Coal is hygroscopic. At 96-99% relative
humidity, the qty of moisture held by
coal is known as near-saturation
moisture or capacity moisture.
60. Ash and Mineral matter
Coal contains mineral matter, which gets converted to ash during combustion. Mineral matter can be inherent or
extraneous.
Extraneous External substance that gets associated during coal formation or rocks and dirts getting mixed up
during mining
Removing mineral matter is important. However inherent one can’t be removed by mechanical means.
Mineral matter alumino silicates (clay or shale), calcites and pyrites.
Mineral matter does not contribute to calorific value of coal.
1% rise in coal ash can lead to fall in boiler efficiency by 0.3-4%.
Coal cleaning can be used to remove or reduce contents of mineral matter beforehand.
We can calculate mineral matter content from ash values:
MM= 1.08A + 0.55 S (Parr formula)
MM = 1.09 A + 0.5 Spyr +0.84 CO2 – 1.1 SO3,ash + SO3,coal + 0.5 Cl (King, Maries and Crossley formula)
MM=1.1A
MM=mineral matter, A=ash, S= total sulphur, Spyr=pyritic sulphur, CO2=carbon dioxide from carbonates,
SO3,ash=sulphate in ash, SO3,coal=sulphate in pure coal, and Cl= Chlorine all in percentages
61. Volatile Matter
The volatile matter and fixed carbon, both expressed as a percentage on dmmf basis add up to 100 parts of
pure coal (organic mass).
When volatile matter is reported on air-dried and daf basis it includes parts of the mineral matter as well. On
dmmf basis however it represents only the volatile products from the organic mass.
There is a correlation between volatile matter and maturity of coal. With the increase in the maturity or rank
of coal, its volatile matter content decreases, However, there seems to be a critical value of volatile matter,
32%-33% dmmf, above which this relationship is not valid.
Carbon
Carbon = Fixed carbon + volatile matter, For anthracite volatile matter is very small, thus values of carbon =
fixed carbon.
Carbon content can be determined by complete combustion (in pure O2) and finding the amount of CO2.
Correction is made for carbonates
62. Hydrogen
Calculated by complete combustion of coal and calculating the amount of H2O formed. Corrections are made
for moisture content of the coal and/or water of hydration of minerals.
Nitrogen
Kjeldahl method is used, sample is digested in fuming sulphuric acid (oleum) containing a catalyst when
nitrogen is converted into ammonium sulphate. Ammonia is then estimated and the nitrogen content is
calculated. Nitrogen content has no correlation with coal
Sulphur
Present as pyrites, organic sulphur and sulphates. Sulphur content has no correlation with rank. Determined
by Eschka method or Bomb method.
Eschka: convert sulphur to sulphates by heating coal with an oxidising mixture of magnesium oxide and
sodium carbonate and then estimating the sulphate.
Bomb: Total sulphur is converted to sulphates during determination of calorific value in Bomb calorimeter.
63. Oxygen
Determined by method of difference. If carbon, hydrogen, nitrogen, and sulphur are
expressed in percent on dmmf basis, their sum is subtracted from 100. What is the
disadvantage? Oxygen has correlation with rank. O2 goes down with increase in rank.
Phosphorus
Content is too small to be considered mostly.
64. Calorific value
1. Basic property of fuel, indicating the quantity of heat evolved by their complete combustion.
2. Bomb calorimeter is used to calculate calorific value of coal.
3. Goutal (1902) formula: CG=82F+aV, CG=gross calorific value, kcal/kg air dried, F= fixed carbon percent air
dried, V= volatile matter, percent air dried, and a=a constant depending upon volatile matter expressed as
percent daf (V’).
4. Central Fuel Research Institute formulae:
For M<2%, CG=91.7 F + 75.6 (V-0.1A) – 60 M
For M>2%, CG=85.6[100-(1.1A F+M)]-60M
5. Original Dulong formula: CG=80.8C+344(H-O/8), [Assumption: heat of formation of coal is 0, sulphur not
accounted for]
6. Modified Dulong formula: CG=80.8C+345(H-O/8)+22.2 S
65. Caking properties
1. Caking coal part of bituminous group alone. Caking properties influence not only production of coke
but also performance of coal in combustion and gasification.
2. Caking, swelling, agglutinating and plastic properties interrelated. Different tests include
1. Free swelling index Standardized test used in India, coal is heated on a flame under specified
conditions. The swollen residue is compared with standard profiles and assigned numbers from 0
to 9 increasing by 0.5. Higher the number better the caking and swelling properties. Limitation?
2. The caking index is the maximum whole number ratio of sand to coal in a 25 g mixture of the two,
which on heating under standard conditions produces a residue capable of supporting a weight of
500 g without producing more than 5% loose grains.
3. It is a measure of the binding or agglutinating property of the coal undergoing carbonisation. The
higher the agglutinating propensity, the higher the amount of sand that can be bound by coal and
hence the higher the caking index. It is a modified Grey-Campredon test and responds well to high-
ash Indian coals. The Bureau of Indian Standards (BIS) has adopted it as one of the three tests for
caking properties. The demerit of the test lies in its trial-and-error approach.
66. Caking properties
1. Low temperature Gray-King carbonisation assay
1. Powdered coal is heated under standard conditions, 600°C.
2. The residue is visually compared with standard profiles and a letter A to G or G, to G, is assigned.
This letter represents the Gray-King (LT) Coke Type. 'A' means non-caking. Letters from 'B' to 'G'
indicate the increasing order of caking and swelling capacity.
3. This is one of the three standard tests in India and is now judged the best suited for Indian coals. If
the coal has higher than 17% ash, then the sample has to be washed before testing.
67. Caking properties
1. Sapozhnikov test
1. This plastometric test measures the maximum thickness of the plastic layer that is formed when
coal is carbonised under well-defined conditions.
2. In the case of bituminous coals, the caking capacity first increases with the rank, attains a
maximum and then decreases with further rise in the maturity. The coals of the highest coking
capacity are often called fat coals. These coals are rare in India.
3. Why some coals are caking and others non-caking is an interesting problem for investigation. The
caking properties are perhaps due to a chemical process in which the macromolecular structure of
the coal mass is thermally broken down and some products of relatively low molecular weight
remain in a softened state for a sufficiently long time in the reaction zone. As a result the entire
mass takes the form of a plastic matter which is converted into a solid lump, resolidified, on further
heating. In this way the powdered caking coals are capable of producing lumpy semicoke and coke.
The non-caking coals cannot produce the plastic state and on carbonisation yield only a sintered
mass in place of coke.
68. Specific gravity and bulk density
1. The true specific gravity of average bituminous coal varies between 1.27 and 1.45.
Formula: g=k+A/100, g=sp. gravity, k=constant having avg value of 1.25, A=percentage of ash
2. Specific gravity seems to increase with rank, peat 1.15-1.25, lignite 1.25-1.3, bituminous 1.27-1.45, and anthracite 1.4-
1.7
Inference from the plot??
69. Angle of repose
1. The angle that a heap of coal forms with the horizontal is of importance in its storage and in transport in conveyors
and feed hoppers. Not reproducible and the error margin is always 2 or 3 degrees.
2. 18-30mm 41 deg
12-8mm 40 deg
6-12 38 deg
0-6 32 deg
Porosity, surface area, and heat of wetting
70. Grindability
2 methods of determining ease of grinding coal to fine sizes, namely
1. ball mill method measures the amount of work done in grinding a presized material to a given fineness
2. Hardgrove method measures the increase of surface produced by the application of a standard amount of
work and expresses the result as Hardgrove grindability index, G, which ranges between
20 and 100 for most coals. G= 13+6.93W, w=weight of coal in grams passing through
200 mesh sieve after 50 gm of coal of size 16-30 mesh are ground in std mill for 60 revs.
71. Action of heat on coal
When a sample of powdered coal is heated out of contact with air, it loses occluded gases consisting of CH4, C2H6, N2
and CO2 at temperatures below 100°C.
Moisture is evolved between 100°C and 150°C. The organic mass of coal then starts decomposing with the evolution of
gaseous and vaporous products.
The decomposition is called active when oil appears in the vaporous products. Peat and young lignites start
decomposing at 100°C or less.
The initial temperature of decomposition of bituminous coals is 200C to 300°C while active decomposition starts at
300°C to 375°C for these coals. The evolution of volatile products of thermal decomposition of bituminous coals is
marked by two peaks or maxima, one corresponding to the primary devolatilisation in the temperature range 350°C to
550'C and the other corresponding to the secondary devolatilisation around 700°C.
Pyrogenic water, primary tar and gases evolved during the primary, while gases (mainly hydrogen) are evolved during the
secondary devolatilisation . Peat and lignite show pronounced primary devolatilisation and insignificant seconday
devolatilisation. Anthracite is characterised by the absence of primary devolatilisation and occurrence of 2ndary
devolatilization only.
Heating above 2000 deg C graphitization happens used to manufacture graphite electrodes.
72. Classification of coal
Problems:
1. Heterogeneous mixture of uncertain proportions
2. The organic mass is also heterogeneous
Primary classification:
1. Humic coals derived from higher plants
2. Sapropelic coals sediments or lower plants
3. Liptobiolites from selected parts of higher plants
Ranks of coal
Classification of Indian coal
3 basis parameter: calorific value, volatile matter, and Grey-King coke
Low temperature Gray-King carbonisation assay: Powdered coal is heated under standard conditions, 600°C. The residue
is visually compared with standard profiles and a letter A to G or G1 to G9 is assigned. This letter represents the Gray-King
(LT) Coke Type. A' means non-caking. Letters from 'B' to 'G' indicate the increasing order of caking and swelling capacity.
This is one of the three standard tests in India and is now judged the best suited for Indian coals. If the coal has higher
than 17% ash, then the sample has to be washed before testing.
73. • Basic Parameters
• GCV
• VM
• Gray King coke type
• Supplementary parameters
• Maximum thickness of plastic layer (MTPL: Sapozhnikov test, test determines the
layer of plastic formation on carbonisation, only bituminous coal shows plastic
formation. The caking properties are perhaps due to a chemical process in which the
macromolecular structure of the coal mass is thermally broken down and some pdts
of relatively low molecular wt remain in softened state for a long time in the
reaction zone. Plastic matter which from molten state can solidify. Noncaking
coals yield only a sintered mass.)
• Air equilibrated moisture at 60% relative humidity and 40 deg C
