Fuel contains mainly ‘C’ which undergoes
combustion and liberates large amount of heat
energy.
C+ O2  CO2 + heat (Exothermic)
Burning of a substance (in presence of O2) or
oxidation of a compound is called combustion.
CLASSIFICATION OF FUELS
CHEMICAL
FUELS
SECONDARY
OR DERIVED
FUELS
PRIMARY OR
NATURAL
FUELS
SOLID:
Wood,coa
l, lignite
LIQUID:
Crude oil
GASEOUS:
Natural gas
SOLID:
coke,charcaol
,petroleum
LIQUID:
Petrol,kero
sene,diesel
.
GASEOUS:co
al gas, water
gas, biogas
Characteristics of a good fuel :
 HCV
 Moderate ignition temperature.
 Low moisture content
 Low non-combustible matter
 Combustion products should not be harmful
 Low cost
 Easy to transport
 Should undergo spontaneous combustion
 Should leave less carbon residue.
Primary solid fuels :
1) Wood : Its C.V. depends on nature of wood, but now it is
not used as main fuel.
2) Coal : Is a stratified rock contains organic material derived
from decay of plant material.mineral mater and moisture.
Mechanism of coal formation :
Insitu theory : Coal formation takes place at the place of
vegetation itself.
Transportation theory : Trees uprooted and carried to Delta
area and deposited under earth. When this wood burns at
high temp, high press, in absence of air, cellulose material
of wood decompose liberating CO2 and CH4 gases.
Classification of coal:
WOOD ----- PEAT----- LIGNITE ----- BITUMINOUSCOAL-----ANTHRACITE COAL
PEAT: Brown, fibrous, jelly like mass. It is the first stage of
coalification. Uneconomical fuel. Used if deficiency of high rank
coal is prevailing. Contains
80-90% of H2O. Composition C = 57%, H= 6%, O = 35%, ash 2.5
to 6%. Calorific value = 5400 kcal/kg.
Lignite: (Brown coal) soft, brown, colored lowest rank coal
moisture content is 20 to 60%. Used for steam generation
inthermal power plants and for production of producer gas.
Composition : C = 60%, O = 20%, Calorific value = 6,500 to 7,100
k.cal/kg
Bituminous coal : (common coal) Black colored. It has laminated
structure.used in making coal gas and metallurgical coke.and also
for steam generation inthermal plants and for domestic heating. it
is sub classified
based on carbon content.
70 – 95% carbon, 8600 kcal/kg calorific value.
Anthracite: Highest rank of coal. Used in households and for steam
raising.also used in metallurgical purposes where no smoke and
high local heat is desired.
% of C = 98 % has lowest volatile matter hardest, dense, lustrous.
CV = 8650 to 8700 kg.
Coal analysis :
Depending on data required there are two types of analysis.
Proximate analysis : Empirical analysis
 Moisture, Volatile matter, ash, Fixed carbon content as % of original
weight of coal sample are recorded.
1) Moisture : 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
105 to 1100C. 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 reported as
moisture.
% of moist = (Loss in weight/Weight of Coal) x 100
2) Volatile matter : The dried sample of coal left in the crucible in (1) is then
covered with a lid and placed in an electric furnace or muffle furnace,
maintained at 925 + 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.
% of volatile matter = loss in weight due to the removal of volatile matter/wt
of dry coal taken




3.Ash: The residual coal in the crucible in (2) is
then heated without lid in a muffle furnace at 700
+ 500 C for ½ hour. The residue is reported as
ash on percentage-basis.
Thus,
% of Ash = (weight of ash left/weight of coal) x
100
4 )Fixed carbon : 100 – (% of moist + % of
volatile matters) + % of ash)
Significance :
Low moisture content, Low volatile matter, Low ash content, high
fixed carbon content are the features of good quality coal.
Disadvantages of high ash content :

Lower C.V. of fuel

Disposal of ash is a problem

Ultimate analysis :
determines % of C, H,O…

1.Carbon and Hydrogen: About 1 to 2 gram of accurately
weighed 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 these are
then determined.
C+O2  CO2
(12)
(44)
H2 + ½ O2  H2O
(2)
(18)
2KOH+CO2  K2CO3 + H2O
CaCl2+H2O  CaCl2 .7 H2O
%C
=
increase in wt of KOH tube/ wt of coal sample taken X 12/44 X 100
%H2 =
increase in wt of CaCl2 tube/ wt of coal taken X 2/18 X100
2) Nitrogen (Kjeldhal’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. 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 acid solution. The
unused acid is then determined by back
titration with standard NaOH solution.
From the volume of acid used by ammonia
liberated, the percentage of N in coal is
calculated as follows:
Nitrogen  H SO Heat
 ( NH ) SO
2 4
42 4
NaOH
( NH ) SO 2


 Na SO  2 NH
 2H O
42 4
2 4
3
2
NH  H SO  ( NH ) SO
3
2 4
42 4
% of N2=
Volume of acid used X Noramality of acid X 14 X100
Weight of coal sample taken X 1000
Volume of acid X Noramality of acid
=
X 1.4
Weight of coal sample taken
 3) Sulphur :

Sulphur is determined from the washings obtained from the
known mass of coal, used in bomb calorimeter for
determination of a calorific value. During this determination, S
is converted in to Sulphate. The washings are treated with
Barium chloride solution, when Barium sulphate is precipitated.
This precipitate is filtered, washed and heated to constant
weight.
S+ O2  SO4-2 + BaCl2  BaSO4
(32)
(233)
% of Sulphur =
wt of BaSO4 / Wt of sample taken X 32/233 X 100.

4) Ash: ash determination is carried out as in proximate
analysis.
5.Oxygen:
Percentage of Oxygen = 100 – percentage of
( C + H + S + N + Ash)
LIQUID FUELS


The main source of liquid fuels is petroleum
which on distillation gives several fractions.
Petroleum is a complexes mix. Of
paraffinic,olefinnic, aromatic hydrocarbons.



C = 80 – 87 % H = 11.1to 15% S = 0.1 3.5% N = 0.4- 0.9%
REFINING OF CRUDE OIL:
The crude oil is separated into various
fractions by fractional distillation.
Stages in refining

A) Separation of water (Cottrell's process)

B) Removal of harmful sulphur compounds

C) Fractional distillation.
A) Separation of water(Demulsification):
 The crude oil coming out from the well, is in the
form of stable emulsion of oil and salt water,
which is yellow to dark brown in colour.
The demulsification is achieved by Cottrell’s
process, in which the water is removed from the oil
by electrical process. The crude oil is subjected to
an electrical field, when droplets of colloidal water
coalesce to form large drops which separate out
from the oil.

Removal of harmful Sulphur
compounds:
Sulphur compounds are removed by
treating the crude oil with copper
oxide.
Treatments results in the formation of
copper sulphide in solid from which
can be removed by filtration.
What is fractional
distillation?
Fractional distillation is the separation of a material into
its separate fractions.
The main use of this is in the distillation of crude oil into
various substances such as petrol and diesel.
Fractional distillation:



The crude oil is heated to about 4000c in a
pipe still where by all volatile constituents
are evaporated.
The hot vapors are then passed through a
tall cylindrical tower, known as
fractionating column, containing a no. of
horizontal stainless steel trays at short
distances.
These trays are provided with individual
chimneys which are covered.
What are the products?
The products of crude oil (and their boiling points) are as
follows:
EGEE 102-Pisupati
23
Fractions of
Petroleum
Fraction
Boiling
Range /C
No of carbon
atoms per
molecule
Uses
Petroleum
Gas
Below 40
1-4
Fuel for
cooking
Fractions of
Petroleum
Fraction
Boiling
Range /C
No of carbon
atoms per
molecule
Uses
Petrol
(Gasoline)
40 - 75
5 -10
Fuel for car
engines
Fractions of
Petroleum
Fraction
Boiling
Range /C
No of carbon
atoms per
molecule
Uses
Naphtha
75 - 150
7 - 14
Chemical
feedstock
Fractions of
Petroleum
Fraction
Boiling
Range /C
No of carbon
atoms per
molecule
Uses
Kerosene
160 - 250
11 - 16
Fuel for jet
engines,
cooking
and heating
Fractions of
Petroleum
Fraction
Boiling
Range /C
No of carbon
atoms per
molecule
Uses
Diesel
250 - 300
16 - 20
Fuel for
diesel
engines
Fractions of
Petroleum
Fraction
Boiling
Range /C
No of carbon
atoms per
molecule
Uses
Lubricants
300 - 350
20 - 35
Making
waxes and
lubricating
oils
Uses of the products
• Petrol- fuel for cars
• Gases- keeping houses warm
• Naphtha- making plastics
• Kerosene- aeroplane fuel
SYNTHESIS OF PETROL
Fischer - Tropsch method:
Water gas (CO+H2) produced by passing steam over heated
coke , is mixed with hydrogen.
The gas is purified by passing through Fe2O3 & then into a
mix. Of Fe2O3,Na2CO3.
The purified gas is compressed to 15 – 25 atm & then led
through a converter, mainted at about 200 – 300 c .
A mix of satured & unsatured hydrocarbons result:
nco + 2nH2 - CnHn + nH2O
nco +(2n +1) H2 -- CnHn+2 + nH2O
The crude oil thus obtained is then fractionated to yield:
A) Gasoline
B) high boiling heavy oil
BERGIUS PROCESS





The low ash coal is finely powdered and made into a paste
with heavy oil and than catalyst is incorporated.
The whole is heated with H2 at 450oc , at pressure 200 –
250 atm for about 1.5 hrs during which H2 combines with
coal to form saturaed hydrocarbons, which decompose at
prevailing high liquid.
The issuing gases are led to condenser , where a liquid
resembling crude oil is obtained , which is then fractioned
to get:
A) Gasoline – 60%
B) Middle oil & heavy oil
GASEOUS FUELS







The most imp gaseous fuels are Natural gas , producer gas
, water gas ….
Natural gas:
It is obtained from well dug in the oil bearing regions.
It is mainly composed of methane , ethane & other gases.
Composition of natural gas is:
Methane: 88.5% ethane 5.5%, propane 3.7% butane
1.8% pentane H2, CO, CO2 higher hydro carbons 0.5%.
The calorific value of natural gas varies from 8000-14000
kcal/m3
Uses:





It can be conveyed over very large distances in
pipelines, it is finding increasing use as domestic
& industrial uses.
It is also used as a raw material for:
i) The manufacture of carbon black & hydrogen
which in turn used as filler for rubber & ammonia
synthesis respectively.
Methanol , formaldehyde & other chemicals.
Methane on microbiological fermentation gives
synthetic proteins which are used as animal feed.
FLUE GAS ANNALYSIS BY ORSAT’S
APPARATUS



Principle of analysis is that the gas to be
analyzed is to be taken in burette which is
connected to several pipettes containing
suitable solutions.
The gas is forced through three pipettes
one after the another.
The certain constituent get absorbed or
volumes of the unabsorbed gases are
found from which from the volume of the
particular constituent is known.
Orsat’s apparatus:
 It consists a 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.
 The absorption bulbs have solutions for the absorption of
CO2, O2 and CO respectively.

First bulb has potassium hydroxide solution (250 g KOH in
500ml of boiled distilled water), and it absorbs only CO2.

The second bulb has solution of alkaline pyrogallic acid (25
g pyrogallic acid + 200g KOH in 500 ml of
distilled water) and it can absorb CO2 and O2.

The third bulb contains ammonium cuprous chloride(100g
cuprous chloride + 125ml liquor ammonia + 375 ml of
water) and it can absorb CO2, O2 and CO.

It gives valuable information for regulating combustion in
the furnace.
Presence of free CO shows in complete combustion & air
supply to be increased.
If there is a large amount of free O2 if shows large excess
of air.


 Calorific value
•
Calorific value is the total quantity of heat
liberated when a unit mass of fuel burn
completely.
•
Measured at 25˚C.
•
Heat or energy produced
•
Gross calorific value (GCV): vapour is fully
condensed
•
Net calorific value (NCV): water is not fully
condensed.
NCV = GCV – (mass %hydrogen)(9)(λv)kJ/kg
λv –latent heat of water vapour at reference
temperature, normally at 298.15K.
λv at 298.15K = 2442.5kJ/kg.
41
Units of calorific values:
For solid and liquid calorific value are
Joules/kg
calori / gram
kcalori/kg
B.T.U/lB
Relation
[ in SI system]
[ in cgs system]
[ in mks system]
[ British system ]
1kcal/kg = 1.8B.T.U/lB.
For gases; kcal/cubic meter.
BTU/cubic feet.
Relation
1kcal/cubic meter = 0.107BTU/IB.
42
Determination of calorific value by
Junker’s gas calorimeter:
AIM :To determine calorific value of gaseous fuel by Junkers gas
calorimeter
APPARATUS: The apparatus mainly consists of a cylindrical shell with
copper coil arranged in two passage configuration with water inlet
and outlet to circulate through the copper coil, a pressure regulator,
a wet type gas flow meter & a gas Bunsen burner.
DESCRIPTION: Determination of calorific value (heat value) of
combustible gases is essential to assess the amount of heat given
away by the gas while burning a known amount of gas to heat a
known amount of fluid (water) in a closed chamber.
PROCEDURE:





Install the equipment on a flat rigid platform near an
uninterrupted continuous water source of ½” size and a drain
pipe.
Connect the gas source to the pressure regulator, gas flow
meter and the burner respectively in series
Insert the thermometer / temperature sensors, into their
respective places to measure water inlet and outlet
temperatures and a thermometer to measure the flue gas
temperature at the flue gas outlet
Start the water flow through the calorimeter at a study
constant flow rate and allow it to drain through over flow.
Start the gas flow slowly and light the burner out side the
calorimeter
Regulate the flow of gas at a steady rate to
any designed flow (Volume)
 Insert the burner into the calorimeter and allow the out let water





temperature to attain a steady state
Swing the out let to a 1000 ml jar and start. The stop watch
simultaneously, record the initial gas flow meter reading at the
same time
Note down the time taken to fill 1000ml and at the same time the
final gas flow reading recorded by the gas flow meter
Tabulate all the reading and calculate the calorific valve of the gas
under test
Repeat the experiment by varying the water flow rate or gas flow
for different conditions.
After the experiment is over stop the gas flow, water flow, and
drain the water from the calorimeter, keep the equipment clean &
dry.
Calculations:

Let V = volume of gas burnt in certain time ‘t’ at S.T.P
W = weight of water collected in ‘t’





T1 = temp of incoming water
T2 = temp of outgoing water
HCV =W(T2-T1)/V K.cal /m3
Suppose m= mass of steam condensed in certain time ‘t’
in graduated cylinder from Vm3 of gas . The latent heat of
steam= 587 K.cal/kg. thus the lower calorific value (LCV) is
given as:
LCV= [HCV- m/v X 587] K.cal/m3.
COMBUSTION
Combustion reactions are exothermic reactions
accompanied by evolution of heat and light and the
temperature rises considerably. The amount of oxygen
or air required for combustion of a given sample of fuel
can be calculated.
Calculation of Air Quantities
To determine the amount of oxygen and hence the amount of air
required for combustion for a unit quantity of fuel, the following
chemical principles are applied.
(1) Substances always combine in definite proportions given by
molecular mass.
C + O2 → Co2
12 32 44
12 g of carbon requires 32 g of oxygen and 44 g of CO2 is formed.
Cracking: Is defined as “the decomposition of
bigger hydrocarbon molecules into simpler ,low
boiling hydrocarbons of lower molecular
weight”.
Gasoline is the most imp fraction of crude petroleum.
The yield of this fraction is only 20% of the crude oil.
The yield of heavier petroleum fraction is quite high.
Therefore, heavier fractions are converted into more
useful fraction, gasoline.

This is achieved by a technique called
cracking.

Cracking is the process by which heavier
fractions are converted into lighter
fractions by the application of heat, with or
without catalyst. Cracking involves the
rupture of C-C and C-H bonds in the
chains of high molecular weight
hydrocarbons.

e.g:
C H Cracking

 C H
C H
5 12 5 10
10 22
Decane
n - pentane pentene
B.Pt 174ο C
B.Pt  36ο C
C H Cracking

 C H
C H
5 12 3 6
8 18
Nearly 50% of today’s gasoline is obtained by
cracking. The gasoline obtained by cracking is far
more superior than straight run gasoline.
The process of cracking involves the full chemical
changes:
•Higher hydrocarbons are converted to lower
hydrocarbons by C-C cleavage. The product obtained
on cracking have low boiling points than initial
reactant.
•Formation of branched chain hydrocarbons takes
place from straight chain alkanes.
•Unsaturated hydrocarbons are obtained from
saturated hydrocarbons.
•Cyclization may takes place.
Cracking can also be used for the production of olefins
from naphthas, oil gas from kerosene.
KNOCKING

The instantaneous combustion
causes a shock wave to set up. This
is known as ‘ knocking’ ‘pinkinf’
‘detonation’. It depends on the
characteristics of the fuel , besides
design factors. This ratting noise
produced in he internal combustion
engine is called knocking.
In a spark-ignition petrol engine, a phenomenon that
occurs when unburned fuel-air mixture explodes in the
combustion chamber before being ignited by the spark.
The resulting shock waves produce a metallic knocking
sound. Loss of power occurs, which can be prevented by
reducing the compression ratio, re-designing the geometry
of the combustion chamber, or increasing the octane
number of the petrol.(formerly by the use of tetraethyl
lead anti-knock additives, but now increasingly by MTBE
– methyl tertiary butyl ether in unleaded petrol.
An antiknock agent is a gasoline
additive used to reduce engine
knocking and increase the fuel's
octane rating.
 The typical antiknock agents in use
are:
 Tetra-ethyl lead (phased out)
 Methyl cyclo pentadienyl manganese
tricarbonyl (MMT)
 Ferrocene, Iron pentacarbonyl,
Toluene, Isooctane
