Fuel is a combustible substance containing carbon as its main constituent. During combustion of fuel, carbon and other elements combine with oxygen while releasing heat. Coal and crude oil are the main fuel sources, formed from fossilized remains of plants and animals. A good fuel is cheap, safe to store and transport, does not spontaneously combust, has a high calorific value, moderate ignition temperature, and is easily controllable with low moisture and non-harmful combustion products. Fuels are classified as primary (coal, oil, natural gas) or secondary (coke, gasoline) based on occurrence, and as solid (coal, coke), liquid (gasoline, diesel) or gaseous (coal gas, natural gas

2. Fuel is a combustible substance containing carbon as
the main constituent which on burning gives a large
amount of heat. During the process of combustion of
fuel, the atoms of carbon, hydrogen etc combine with
oxygen with simultaneous liberation of heat.
Main source of fuel is coal and crude petroleum oil, they
were formed from fossilized remains of plants and
animals.

3. Characteristics of a good fuel:
 Cheap and readily available
 Safe and economical for storage and transport
 Doesn’t undergo spontaneous combustion
 Have higher calorific value
 Have moderate ignition temperature
 Easily controllable
 Have low moisture content
 Products of combustion should not be harmful.

4. Classification of fuels
Fuels are classified based on
1. Occurrence and
2. The state of aggregation.(physical state)
Based on occurrence:
Primary fuels: occurs in nature
eg: coal,petroleum,naturalgas
Secondary fuels: Derived from primary fuels.
eg: coke,gasoline,coal gas

5.  Based on physical state :
Solid fuels : eg: coal,coke.
Liquid fuels : eg : gasoline,diesel
Gaseous fuels : eg: coal gas, natural gas

6. SOLID FUELS
 COAL: It is important primary fuel that has been
formed as a result of alteration of vegetable matter
under some favourable conditions.
 Coalification or metamorphism: The process of
conversion of vegetable matter to anthracite is called
coalification or metamorphism of coal.

7. Coal has been classified in several ways.
Coal is classified based on the carbon content

8. Progressive transformation of wood to anthracite results in
 Decrease in moisture content
 Decrease in volatile content
 Decrease in hydrogen,oxygen,nitrogen and sulphur contents
 Increase in carbon content
 Increase in hardness
 Increase in calorific value
 Peat: Peat is regarded as the first stage in the transformation of
wood into coal. Brown, fibrous, jelly like mass. Un-economical
fuel. Contains 80-90% of H2O.
 Composition C = 57%, H= 6%, O = 35%, ash 2.5 to 6%.
Calorific value = 5400 kcal/kg.

9.  Lignite: (Brown coal) soft, brown, colored lowest rank
coal moisture content is 20 to 60%.
Composition: C = 60%, O = 20%, Calorific value = 6,500 to
7,100 kcal/kg
 Bituminous coal: Bituminous coal (common coal) Black
to dark colored. This coal is largely used in industries for
making metallurgical coke, coal gas and for domestic
heating. It has laminated structure it is sub classified based
on carbon content.
Composition is % of C = 78 to 90%, VM = 20 to 45% ,
CV = 8000 to 8500 kcal/kg.

10.  Anthracite: Highest rank of coal. These coals have very
low volatile matter, ash & moisture. This coal is very hard,
dense and lustrous in appearance. % of C = 98 % has
lowest volatile matter hardest, dense, lustrous. CV = 8650
to 8700 kcal/kg.

11. Analysis of coal:
In order to assess the quality of coal the following two
types of analysis are made
 Proximate analysis
 Ultimate analysis
Proximate analysis involves in the following
determinations
 Moisture content
 Volatile matter
 Ash content
 Fixed carbon

12. Moisture content:
 About 1 gram of finely powdered air-dried coal sample is
weighed in a crucible. The crucible is placed inside an
electric hot air-oven, maintained at 1000 to 1050C. The
crucible is allowed to remain in oven for 1 hour and then
taken out, cooled in a desiccator and weighed. Loss in
weight is calculated then the % of moisture is calculated
as
Percentage of Moisture = __Loss in weight of coal__ X 100
Weight of air dried coal

13. Volatile Matter:
 The dried sample of coal left in the crucible is then covered
with a lid and placed in an electric furnace or muffle furnace,
maintained at 9500 + or - 200C. The crucible is taken out of
the oven after 7 minutes of heating. The crucible is cooled
first in air, then inside desiccators and weighed again. Loss in
weight is reported as volatile matter on percentage-basis.
Percentage volatile matter=_Loss in weight ofcoal_ X 100
Weight of air dried coal

14. Ash content:
 After the analysis of volatile matter,the residual coal in the
crucible is then heated without lid in a muffle furnace at
7000 + or - 500 C for ½ hour. The crucible is then taken
out, cooled first in air, then in desiccator and weighing is
repeated, till a constant weight is obtained. The residue is
reported as ash on percentage-basis.
 percentage of ash = __Weight of ash left__ X 100
Weight of air dried coal

15. Fixed carbon:
 Percentage of fixed carbon =
100 - % of (Moisture + Volatile matter + ash contnet)

16. Significance of proximate analysis
1. Moisture content:
 Reduces calorific value of coal
 Moisture in coal consumes more heat in the form of
latent heat of evaporation and hence more heat is to be
supplied to the coal
 Increases the transport cost
2. Volatile matter:
 Reduces calorific value of coal
 A high volatile matter containing coal burns with a long
flame, high smoke
 Coal with high percentage of volatile matter do not coke
well

17. 3. Ash content:
 Reduces calorific value of coal
 ash causes the hindrance to the flow of air and heat, thereby
lowering the temperature and blocks the air supply through
the fuel;
 Increases transporting, handling and storage.
 Involves additional cost in ash disposal.
4. Fixed carbon:
 Higher percentage of fixed carbonon coal have higher
calorific value
 Helps in designing the furnace and shape of the fire box

18. Ultimate analysis of coal:
Carbon and Hydrogen:
 A known amount of coal sample is burnt in a current of
oxygen in a combustion apparatus. C and H of the coal are
converted into CO2 and H2O respectively. The gaseous
products of combustion are absorbed respectively in KOH
and CaCl2 tubes of known weights. The increase in weights
of KOH tube is due to formation of H2O while increase in
weights of CaCl2 tube is due to formation of CO2.
C + O2 ------ CO2
H2 + ½ O2  H2 O

19. calculations
2KOH + CO2  K2CO3 + H2O
CaCl2 + 7 H2O  CaCl2.7H2O
 Let m= weight of coal sample taken
 X=increase in weight of KOH tube
 y=increase in weight of KOH tube

20. a) % of Hydrogen
 H2 + ½ O2  H2 O
2 18
 18 gms of H2 O contains 2 gms of hydrogen
 y gms of H2 O contains =2*y gms of hydrogen
18
 m gms of coal contains =2*y * gms of hydrogen
18
 100 gms of coal contains=2*y *100 gms of hydrogen
18 m
 % of hydrogen in coal =2*y *100 gms of hydrogen
18 m
% of hydrogen in coal = increase in wt of CaCl2 tube* 2 *100
wt of coal sample taken 18

21. a) % of Carbon
 C + O2 ------ CO2
 12 44
 44 gms of CO2 contains 12 gms of carbon
 X gms of CO2 contains =12*x gms of carbon
44
 m gms of coal contains =12*x * gms of carbon
44
 100 gms of coal contains=12*x *100 gms of carbon
44 m
 % of carbon in coal =12*x *100 gms of carbon
44 m
% of carbon in coal = increase in wt of KOH tube*12 *100
wt of coal sample taken 44

22. Nitrogen content:
 The determination of nitrogen content is carried out by
Kjeldahl’s method. About 1 gram of accurately weighed
powdered coal is heated with concentrated H2SO4 along with
K2SO4 (catalyst) in a long-necked Kjeldahl’s flask. Nitrogen in
the coal is converted into ammonium sulphate and a clear
solution is obtained.
2N + 3H2+ H2SO4→(NH4)2SO4
 After the solution becomes clear, it is treated with excess of
KOH and the liberated ammonia is distilled over and absorbed
in a known volume of standard HCl solution.
 (NH4)2SO4+2NaOH →NH3+Na2SO4+2H2O
NH3+HCl→NH4Cl

23. Calculation
 Let the weight of coal sample taken = m gms
 Initial volume of N/10 HCl=V1 ml
 Volume of unused N/10 HCl=V2ml
 The acid neutralised by ammonia=(V1-V2) ml
 We know that,
 1000ml of 1N HCl = 1 mole of HCl= 1 mole of NH3 = 14 gms
of N2 (or 17 gms of NH3)
 (V1-V2)ml of N/10 HCl=14*(V1-V2)*N/10 gms of N2
1000*1N
 m gms of coal contains=14*(V1-V2)*N/10 gms of N2
1000*1
 100gms of coal contains=14*(V1-V2)*N/10 * 100 mgs of N2
1000*1 m

24. % of N2 in coal = 14*volume of acid consumed*Normality *100
1000*weight of coal sample
(or)
% of N2 in coal = 1.4*volume of acid consumed*Normality *100
weight of coal sample

25. Sulphur content
 A known amount of coal sample is burnt completely in
bomb calorimeter. During this determination, Sulphur is
converted in to Sulphate,which is extracted with water.
The extract is treated with Barium chloride solution, so
that sulphates are precipitated as Barium Sulphate. This
precipitate is filtered, washed and heated to constant
weight. From the weight of barium sulphate obtained,the
sulphur present in the coal can be calculated as follows.

26. calculation
 Let m= weight of coal sample taken
X=Weight of BaSO4 obtained
 S+2O2→SO4 → BaSO4
32 BaCl2 233
 233 gms of BaSO4 contains 32 gms of sulphur
 X gms of BaSO4 contains =32*x gms of sulphur
233
 m gms of coal contains =32*x gms of sulphur
233
 100 gms of coal contains=32*x *100 gms of sulphur
233 m
 % of sulphur in coal =32*x *100 gms of sulphur
233 m
 % of sulphur in coal = Weight of BaSO4 obtained X 32 X 100_
Weight of coal sample taken X 233


27. Ash:
Ash determination is carried out as in proximate analysis.
Oxygen:
Percentage of Oxygen = 100 – % of ( C + H + S + N + Ash)

28. Importance of ultimate analysis:
Carbon and Hydrogen:
 Greater the percentage of carbon and hydrogen, better is
the coal in quality and calorific value.
 % of carbon helpful in classification of coal.
 Higher % of coal reduces the size of combustion
chamber req.uired

29. Nitrogen:
 Nitrogen has no calorific value and hence, its presence
in coal is underirable. Thus, a good quality coal should
have very little Nitrogen content.

30. Sulphur:
 Sulphur, although contributes to the heating value of
coal, yet on combustion produces acids like SO2,
SO3, which have harmful effects of corroding the
equipments and also cause atmospheric pollution.
Sulphur is, usually, present to the extent of 0.5 to
0.3% and derived from ores like iron, pyrites,
gypsum, etc., mines along with the coal. Presence of
sulphur is highly undesirable in coal to be used for
making coke for iron industry. Since it is transferred
to the iron metal and badly affects the quality and
properties of steel. Moverover, oxides of sulphur
pollute the atmosphere and leads to corrosion.

31. Oxygen
 Oxygen content decreases the calorific value of coal. High
oxygen-content coals are characterized by high inherent
moisture, low calorific value, and low coking power.
Moverover, oxygen is an combined form with hydrogen in
coal and thus, hydrogen available for combustion is lesser than
actual one. An increase in 1% oxygen content decreases the
calorific value by about 1.7% and hence, oxygen is
undesirable. Thus, a good quality coal should have low
percentage of oxygen

32. carbonisation
 When coal is heated strongly in the absence of
air(desrtructive distillation) it is converted into
lustrous, dense, porous and coherent mass known as
coke. This process of converrting coal into coke is
known as Carbonisation.
 When coals are heated strongly the mass becomes soft
plastic and fuses to give a coherent mass known as
caking coals.
 When coals are heated strongly the mass becomes
hard, porous and strong then they are known as coking
coals.

33. Types of Carbonisation
 Based on temperature ,Carbonisation is classified into two
types.
 1. Low temperature carbonisation(LTC):
Carbonisation carried out at 500˚C- 700˚C
 2. High temperature carbonisation(HTC):
Carbonisation carried out at 900˚C- 1300˚C

34. Metullurgical coke
 When bituminous coal is heated strongly in the
absence of air, the volatile matter escapes out and the
mass becomes hard,strong,porous and coherent which
is calles Metallurgical coke.
 Characteristics of good Metallurgical coke:
 1.Purity: The moisture, ash, sulphur and phosphorous
contents should be low because it reduces the calorific
value. sulphur and phosphorous contaminate the
metal.
 Porosity: It should be highly porous so that oxygen will
have intimate contact with carbon and combustion
will be complte and uniform.

35.  3.Strength: It should have high mechanical strength.
 4.Calorific value: It should be very high.
 5.Combustibilty: It should burn easily.
 6.Reactivity: Reactivity should be low because reactive
cokes produce high tempertaure on combustion.
 7. Cost: It should be readily available.

36. Manufacture of Metallurgical coke
 There are so many types of ovens are used for the
manufacture of metallurgical coke. But the important
one is Otto-Hoffman’s by product oven.
Otto-Hoffman’s by product oven: In order to
 Increase the thermal efficiency of carbonisation
process and,
 Recover valuable by products(coal gas,
ammonia,benzol oil, tc.) Otto-Hoffman developed
modern by product coke oven

37. Otto-Hoffmann’s process

38. Otto Hoffman’s by-product Coke Oven
The oven consists of a number of silica chambers.
Each chamber is about 10 - 12 m long, 3 - 4 m height and
0.4 - 0.45 m wide. Each chamber is provided with a
charging hole at the top, it is also provided with a gas off
take valve and iron door at each end for discharging coke.
Coal is introduced in to the silica chamber and the
chambers are closed. The chambers are heated up to
1200°C by burning pre heated air and the producer gas
mixture in the interspaces between the chambers.

39.  The air and gas are preheated by sending them through 2nd and
3rd hot regenerators. Hot flue gases produced during carbonization
are allowed to pass through 1st and 4th regenerators until the
temperature has been raised to 1000˚C.While 1st and 4th are being
heated by hot flue gases, the 2nd and 3rd regenerators are used for
heating the incoming air and gas mixture.
For economical heating, the directions of inlet and flue gases are
changed frequently. The above system of recycling the flue gases to
produce heat energy is known as the regenerative system of heat
economy. When the process is complete, the coke is removed and
quenched with water.
 Time taken for complete carbonisation is about 12 - 20 hours. The
yield of coke is about 70 %.The valuable by products like coal gas,
tar, ammonia, H2S and benzene, etc are removed from the flue gas.

40.  Recovery of by products
i) Tar
 The coke oven gas is first passed through a tower in
which liquor ammonia is sprayed. Tar and dust gets
dissolved and collected in a tank below, which is heated
by a steam coil to recover back the ammonia sprayed.
ii) Ammonia
 The gas is then passed through the other tower where
water is sprayed. Ammonia gets converted to NH4OH.

41. iii) Naphthalene
 The gases are then passed through the tower in which
cooled water is sprayed. Here Naphthalene gets condensed.
iv) Benzene and other aromatic compounds
 The gas is then passed through the next tower in which
petrol is sprayed. Benzene and other aromatic compounds are
dissolved in the oil and recovered.
v) Hydrogen sulphide
 The gas then enters into a purifying chamber packed with
moist Fe2O3, which removes any sulphur compound present.
Hence Hydrogen sulphide is retained.
The final gas left out is pure coal gas, which is used as a
gaseos fuel.

42. Advantages of Otto Hoffman’s process:
 Valuable by products like ammonia,coal gas, napthalene
etc are recovered.
 Carbonisation time is less.
 Heating is done externally by producer gas.

43. LIQUID FUELS:
 PETROLEUM:
Petroleum or crude oil is naturally occurring
liquid fuel. It is a dark brown or black coloured viscous oil
found deep in earth’s crust.The oil is usually floating over a
brine solution and above the oil,natural gas is
present.crude oil is mixture of paraffinic,olefinic and
aromatic hydrocarbons with small amounts of organic
compunds like N,O and S.
Average composition of crude oil is as follows.
Constituents Percentage
C 80-87
H 11-15
S 0.1-3.5
N+O 0.1-0.5

44. Classification of petroleum
 Petroleum is classified into three types.
1. Paraffinic –Base type crude oil: Contains saturated
hydrocarbons from CH4-C35H72 with smaller amount of
napthenes and aromatics.
2. Napthenic or Asphaltic base type crude oil: Contains
cycloparaffins or napthenes with a smaller amount of paraffins
and aromatics.
3. Mixed base type crude oil: It contains both Paraffinic and
asphaltic hydrocarbons.

45.  Refining of petroleum:
Crude oil obtained from the mine a mixture of oil,water
and unwanted impurities. After the removal of water and other
impurities the crude oil is subjected to fractional distillation.
During Fractional distillation ,the crude oil is separated into
various fractions.
The process of removing impurities and separating the
crude oil into various fractions having different boiling
points is called Refining of petroleum.
It involves the following steps.
Step I: Separation of water(cottrell’s process)
Step II: Removal of harmful sulphur compounds..
Step III: Fractional distillation

46. Step I: Separation of water(cottrell’s process) :
The crude oil from oil well is extremely stable emulsion
of oil and salt water. The crude oil is allowed to flow between
two highly charged electrodes,where colloidal water droplets
combine ti form large drops, whioch is then seperated out from
oil.
Step II: Removal of harmful sulphur compounds:
Sulphur compounds are removed by treating the crude
oil with copper oxide. The copper sulphide formed is separated
out by filtration.

47. Step III: Fractional distillation
 Purified crude oil is then heated to about 4000C in an iron
retort, produces hot vapor which is allowed to pass
through fractionating column. It is a tall cylindrical tower
containing a number of horizontal stainless trays at short
distances and is provided with small chimney covered
with loose cap. As the vapors go up they get cooled
gradually and fractional condensation takes place. Higher
boiling fraction condenses at lower trays and the lower
boiling fractions condenses at higher trays. The gasoline
obtained by fractional distillation is called Straight-run
gasoline.
 .

48. Fractional distillation

50. S.NO NAME OF
FRACTION
BOILING
RANGE
RANGE OF
ATOMS
USES
1 Uncondensed
gases
Below 30 C1-C4 LPG
2 Petroleum ether 30-70 C5-C7 Solvent
3 gasoline 40-120 C5-C9 Fuel for IC engines
4 Naptha or
solvent spirit
120-180 C9-C10 As a solvent in paints
and in dry cleaning
5 Kerosene oil 180-250 C10-C16 Fuel for stoves and jet
engines
6 Diesel oil 250-320 C15-C18 Diesel engine fuel
7 Heavy oil 320-400 C17-C30 Fuel for ships and for
production of gasoline
by cracking

51. Name of fraction uses
Lubricating oil Lubricants
Petroleum jell or vaseline Medicine and cosmetics
Grease Lubricant
Paraffin wax In candles, boot polishes
Pitch at above 400 c For making roads,water
proof roofing
Refractionation of Heavy oils:
Heavy oils on refractionation gives

52.  Synthetic petrol:
 Gasoline obtained from fractional distillation of crude oil is
called straight run petrol.As the use of gasoline is increased the
ammount of straight run gasoline is not enough to meet the
requirement of the present community. Hence we are in need of
finding out a method of synthesizing Petrol.
 Hydrogenation of coal:
 Coal contains about 4.5% of H 2 to aboout 18% in petroleum. So
coal is hydrogen deficient compound.
 If coal is heated with hydrogen to higher temperature under high
pressure,it is converted to gasoline.
The preparation of liquid fuels from solid coal is called
hydrogenation of coal or synthetic petrol.

53.  An important method available for the hydrogenation of
coal is Bergius process (direct method).
 Manufacture of Synthetic petrol:
 Bergius process:
In this process the low ash is finely powdered and
turned into a paste using heavy oil and a catalyst (5% iron
oxide or tin or nickel oleate) is mixed with it. The paste is
pumped along with hydrogen gas in the converter, where
the paste is heated to a temperature of 400 – 4500C and
mixed with H2 under a pressure of 200 – 250 atm for 1 ½
hours. Initially hydrogen combines with the different
impurities like S, N, O present along with C in the coal.

54.  i.e. H2 + S ---------- H2S
 H2 + 1/2O2 ------------- H2O
 3H2 + N2 ------------ 2NH3
 During the process hydrogen combines with coal to form
saturated higher hydrocarbons which undergo further
decomposition at higher temperature to yield a ,mixture of
lower hydrocarbons. The mixture is led to a condenser,
where the crude oil is obtained.
 The crude oil is then fractionated to yield
 i) Gasoline
 ii) Middle oil
 iii) Heavy oil

55.  The top fraction is condensed, and synthetic gasoline is
recovered. The middle oil is then hydrogenated in
presence of a solid catalyst to give more gasoline and the
heavy oil fraction is recycled to make a paste with fresh
batchof coal powder. The yield of gasoline is about 60%
Coal +heavy oil
+catalyst

56. Coal +heavy oil
+catalyst

57. Orsat’s gas analysis

58.  It consists of water – jacketed measuring burette,
connected in series to a set of three absorption
bulbs, through stop cocks.
 The other end is provided with a three way stop
cock, the free end of which is further connected to
a U – tube packed with glass wool (for avoiding the
incoming of any smoke particles, etc.) The
graduated burette is surrounded by a water jacket
to keep the temperature constant of gas during the
experiment.
 The lower end of the burette in connected to a
water reservoir by means of along rubber tubing.
 The absorption bulbs are usually filled with glass
tubes, so that the surface area of contact between
the gas and the solution is increased.

59.  The absorption bulbs have solutions for the
absorption of CO2, O2 and CO respectively. First
bulb has potassium hydroxide solution, and it
absorbs only CO2.
 The second bulb has solution of alkaline pyrogallic
acid and it can absorb CO2 and O2.
 The third bulb contains ammonium cuprous
chloride) and it can absorb CO2, O2 and CO.
 Hence, it is necessary that the flue gas it passed
first through potassium hydroxide bulb, where
CO2 is absorbed, then through alkaline pyrogallic
acid bulb, when only O2 will be absorbed (because
CO2 has already been removed) and finally
through ammonical cuprous chloride bulb, where
only CO will be absorbed.