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UNIT I
FUELS
Syllabus
General Aspects of Fuel: Organic fuels, Origin, classification and general aspects of
fossil fuels
...
Liquid fuels, Composition of petroleum, advantages
and refining of petroleum
...
Synthetic petrol, Bergius and Fischer Tropsch process
...
Gaseous fuels, Advantages, manufacturing,
composition and calorific value of coal, gas and oil gas
...
1

INTRODUCTION

Fuel is any combustible substance which when burnt in oxygen or air, produces
significant amount of heat which can be economically used for domestic and industrial
purposes for generating power
...

Fuel + Air " Products + Energy
As most of the fuels contain carbon and hydrogen, they are converted to CO2 and H2O
respectively with release of energy
...
6 Kcal
H2 + ½ O2 → H2O + 68
...
A typical example is
a fuel cell
...

Fossil fuels are formed from plant and animal remains buried deeply in soil or ocean
floor (under high pressure) millions of years ago
...
Examples of fossil fuels are
coal, natural gas, petroleum etc
...
Due to rapid population growth and growing energy requirements the reserves of
these fossil fuel reserves are fast depleting
...
2

CLASSIFICATION OF FUELS

Fuels are broadly classified into two types depending upon origin
...
Primary fuel: These include the naturally occurring fuels found freely on earth’s
crust
...


iii)

Gaseous fuel: Natural gas
...
Secondary or derived fuel: These are artificially manufactured or are derived
from primary fuels
...


ii)

Liquid fuel: Petrol, diesel, kerosene, LPG etc

iii)

Gaseous fuel: Water gas, producer gas, consumer gas etc
Comparison of solid, liquid and gaseous fuels

Sl
...


Cost

Solid fuel
Cheap

Liquid fuel
Costlier than solid

Gaseous fuel
Expensive

fuel
2
...


3
...


Combustion rate

Slow process

Quick

Very rapid and
efficient
...


Ash is always

Can be controlled by
controlling the air

needed
...


Combustion control

supply
...


No ash produced
...

7
...


Smoke

Invariably

Burning is clean
...


High carbon and
aromatic liquids
may produce
smoke
...


Use in internal

Not possible

Possible

Possible

combustion engine

1
...
Higher the calorific value, the more efficient is the fuel
...
Fuels
having very low ignition temperature can cause fire hazards while handling,
storage and transportation
...
Moderate ignition temperature is the ideal for a good fuel
...
High ash content reduces the calorific
value, poses problems in its disposal
...

d) Low moisture content: Presence of high moisture content decreases the
efficiency of the fuel
...
Presence of

moisture decreases the calorific value as some heat produced is used to
vaporize moisture
...
Generally, solid fuels are easier to handle then liquid and
gaseous fuels
...

f) No harmful combustion products: A good fuel should not produce harmful
combustion products such as CO, NO, NO2, SO2, H2S etc
...
An ideal fuel must burn with a clean flame
without producing any undesirable by-products
...


1
...
It gives useful information about its
heating efficiency
...

Calorific value is defined as the amount of heat energy released by the complete
combustion of unit quantity (mass or volume) of the fuel
...
It is also
expressed in joules per kg (J/Kg) for solid fuels, and joules per cubic meter (J/m3) for
gaseous fuels in SI units
...
4
...

All fuels invariably contain carbon and hydrogen
...
On cooling the
combustion products, steam gets condensed to water and liberates its latent heat
...


Theoretical higher calorific value of a fuel can be calculated by knowing the percentage
of constituents of the fuel
...


Where, C, H, O and S = percentages of carbon, hydrogen, oxygen and sulphur in the
fuel sample
8080 = Calorific value of carbon
34500 = Calorific value of hydrogen
2240 = Calorific value of sulphur
1
...
2 NET (LOWER) CALORIFIC VALUE (NCV or LCV)
Net calorific value is the amount of heat energy released when a unit mass of fuel is
burnt completely and the products of combustion are allowed to escape
...
If the combustion products like steam, CO2 are allowed to
escape into the atmosphere, the calorific value measured under these conditions does
not include the latent heat of condensation of steam
...

LCV = GCV- Latent heat of condensation of steam

If H is the percentage of fuel in the sample, 9H/100 will be the mass of water from one
gram of fuel, 0
...

Therefore, the heat taken by water for the formation of steam = 0
...

LCV = GCV – (0
...
5

ORGANIC FUELS (HYDROCARBON FUELS)

Hydrocarbons are chemical compounds made up of hydrogen and carbon
...
Alkanes
(CnH2n+2), alkenes (CnH2n), alkynes (CnH2n-2), cycloalkanes (CnH2n) form most widely
used hydrocarbon fuels
...
Higher
hydrocarbons (liquids) form important constituent of petrol(C5-C9) and diesel(C15-18)
...

Advantages of organic fuels
∑

High calorific value: Most of the organic fuels have high calorific value
...
They donot cause toxic
exhaust emissions
...


∑

Ease of transport: Hydrocarbon fuels can be easily transported in containers
...


Disadvantages of organic fuels
∑

Production of greenhouse gases: Hydrocarbons when burnt completely, water
and carbon dioxide are produced
...


∑

Pollution: When hydrocarbons are burnt in a limited supply of air, Carbon
monoxide, a poisonous gas, is released
...


1
...
Solid fuel contains organic materials (combustile) and
inorganic minerals (non combustile)
...
Inorganic or mineral part of fuel consists of silicates, phosphates,
sulphates of Fe, Ca, Na, K etc
...


The major solid fuels include wood, coal and coke
...

1
...
1 WOOD
Most widely used solid fuel is wood
...
Freshly
cut wood contains 25-50% moisture, whereas dried wood contains only less than 15%
moisture
...

The average composition of air dried wood is
Carbon (C)

=

50-60 %

Hydrogen (H) =

6-8 %

Oxygen (O)

=

40-43 %

Ash

=

1-2 %

Calorific value of air dried wood is about 3500 to 4500 Kcal/kg
...

1
...
2 COAL
Coal is a fossil fuel which is formed due to the decomposition of plant matter by the
application of heat and pressure over millions of years
...

Progressive transformation of wood to coal can be written as
Wood " Peat " Lignite " Bituminous coal " Anthracite

The process of coal formation is known as coalification
...
Coal contains primarily carbon
...
It is the largest source of energy for the generation of electricity
worldwide
...

a) Peat
b) Lignite
c) Bituminous coal
d) Anthracite
a) Peat
Peat represents the first stage of coalification
...
Peat contains approximately 60-65% carbon
...
Its calorific value is about 5000 Kcal/kg
...
In India peat deposits are found
in Nilgiri hills
...
It can have black or brown color
...
It contains 60-75% carbon
...
In India lignite deposits are found at Neyveli
...

c) Bituminous coal
It is the third stage of coalification process
...
Bituminous coal is dark and opaque
...
Its calorific
value is about 8000 Kcal/Kg
...
In India bituminous coal reserves are found in Bihar and assam
...
It is the highest ranking coal and contains
maximum percentage of carbon
...
It contains least
volatile matter
...
5-4 % and calorific value is 8500 KCal/Kg
...

Depending on the desired requirements, suitable type of coal is chosen based on
calorific value, moisture content, ash content, cost etc
...
The rate of
combustion can be increased by pulverizing (powdering) the coal
...
Pulverizing also helps in the liberation of volatile
matter too
...


∑

It involves no clinker formation
...


Disadvantages
∑

Involves extra cost for pulverization

∑

Ash disposal is a problem
...
6
...
The
process of converting coal into coke by destructive distillation is known as
carbonization
...
Such coals are called
caking coals
...
Coking coals possess lower volatile matter and are used for the
manufacture of metallurgical coke
...
Only bituminous coal can be coked
...
6
...
1

Characteristics of metallurgical coke

When bituminous coal is heated strongly (900-1200 °C) in the absence of air, moisture
and volatile matter are driven out and a dense, strong and porous mass is obtained, it is
called metallurgical coke
...
Metallurgical coke is
used as a fuel and used as a reducing agent in smelting iron ore in blast furnace
...
Purity: Sulphur, oxygen, moisture and ash content should be low
...
Porosity: Coke should have high porosity
...

3
...

4
...

5
...

6
...

Difference between coal and coke
Coal

Coke

1
...


1
...


2
...


2
...


3
...


3
...


4
...

and volatile matter
...
Coal has lesser calorific value
...

5
...

6
...


6
...


Coal Vs Coke in metallurgical process
Coal cannot be used for metallurgical purposes because

a) Coal does not produce as much strength and porosity as coke
...

c) Coal burns with a long flame, which is suitable only for reverbatory furnaces
...
6
...

Carbonization of coal can be carried out at low temperature or high temperature
...

High temperature carbonization (above 900∞C): In high temperature carbonization,
coal is heated to a high temperature to 900-1200 ∞C, and the coke obtained has desired
porosity, strength, purity and hardness
...

Comparison of High Temperature and Low temperature carbonization
Characteristics

Low temperature

High temperature

carbonization

carbonization

1

Heating temperature

450-750∞C

900-1200∞C

2

Yield of coke

75−80%

65−75%

3
...


Coke produced

Soft

Hard

5
...


Mechanical strength

Poor

Good

7
...


Uses

Domestic

Metallurgy

1
...
5 MANUFACTURE OF METALLURGICAL COKE
Metallurgical coke can be manufactured by two methods
...
Beehive’s oven method and
2
...


1
...
5
...

Construction: The oven has a dome shaped brick structure about 4m wide and 2
...
It has two openings which can be opened and closed as desired
...
The side door, also act as air inlet
...
60
...
Some air is supplied through the side door and coal is ignited
...
Thus, heat for
carbonization is supplied by the burning of volatile matter and partly by coal itself
...
Complete
carbonization takes place in 3-4 days
...
The yield of coke is about 75% of charged
coal
...
By products are not recovered in this method
...
1 Beehive’s oven
Disadvantages:
∑

Useful by-products are not recovered
...


∑

Yield of coke is lower due to partial combustion

1
...
5
...
The main advantages of this process are i) recovery
of valuable by products like coal gas, ammonia, benzene etc ii) regenerative
system of heat economy increases the thermal efficiency of carbonization process
...


Figure 1
...
Oven
The oven consists of a number of narrow silica chambers
...
4-0
...
Chambers are tightly closed so that no air is
admitted
...

2
...
The oven works on heat regenerative
principle
...

3
...

4
...
The air and gas are preheated
by sending them through 2nd and 3rd regenerators
...


For economical heating, the direction of inlet gases and flue gases are changed
frequently
...
Each oven holds about 20 tonnes of
coal charge and the time taken for carbonization is about 12-20 hours
...

5
...

Wet quenching: Wet quenching is done by spraying water
...

6
...
This consists of tar,
ammonia, moisture, aromatic hydrocarbons (naphthalene, benzene), H2S etc
...

Recovery of tar: The flue gas is first passed through a tower in which ammonia
sprayed tar gets condensed
...
The ammonia is used again
...

Recovery of ammonia: The flue gas is then passed through a tower in which water is
sprayed
...

NH3 +H2O→ NH4OH
Use: Recovered ammonia is dissolved in dil
...

Use: Naphthalenes are used as solvents
Recovery of benzene: The gases are again passed through another tower in where
petroleum ether is sprayed, here benzene gets condensed
...
Here H2S is retained
...
can be recovered
fully
...
Complete carbonisation takes about 12 hours
...


∑

1
...


LIQUID FUELS

Liquid fuels are becoming more and more important these days due to their usefulness,
convenience in handling, high calorific value etc
...
Most of the other liquid fuels such as
petrol, diesel, kerosene etc are derived from petroleum
...

Advantage of liquid fuels
∑

Liquid fuels have higher calorific value than solid fuels
...
Fuels can be easily transported through
pipes
...


∑

Liquid fuels product less ash during combustion
...


Disadvantages of liquid fuels
∑

Liquid fuels are costlier than solid fuels
...


1
...
1 PETROLEUM
Petroleum (also known as crude oil) is found in nature at varying depths below the
earth’s surface
...
According to modern theory, petroleum was formed by the anaeorbic
decay marine animals over millions of years
...

1
...
2 COMPOSITION OF PETROLEUM
Crude petroleum is a complex mixture of paraffin, cycloparaffin, aromatic hydrocarbon
and nitrogen and carbon containing compounds
...
Depending on the source of crude petroleum, color,
composition and appearance change widely
...

1
...
3 MINING OF CRUDE OIL
Crude oil is found deep below the earth crust
...
Usually natural gas is found
above petroleum deposits
...

1
...
4 REFINING OF PETROLEUM
Petroleum that comes from the ground is a viscous, dark colored, foul smelling liquid
...
After the removal of water and other
impurities, the crude oil is subjected to fractional distillation
...
The process
of removing impurities and seperating the crude oil into various fractions having different
boiling points is called refining of petroleum
...

Step 1:

Seperation of water (Cottrell’s process)

Crude oil from oil well is a stable emulsion of oil and salt water
...

Step 2:

Removal of harmful sulphur compounds

Sulphur compounds are removed by treating crude oil with copper oxide
...

Step 3:

Fractional distillation

The purified crude oil is then heated to about 4000C in an iron retort, where the oil gets
vapourised
...
The fractionating column is a tall cylindrical tower containing a number of
horizontal stainless steel trays at short distances
...
When the vapours of the oil go up in the fractionating
column, they become cooler and get condensed at different trays
...
Various fractions are collected depending on
their boiling points
...
3

Fractional distillation of crude petroleum

Various crude oil fractions and their uses

1
...
5 CHEMICAL PROCESSING OF PETROLEUM
Primary distillation of crude oil yeilds about 25% of striaght run petrol only
...
So, another portion of refining
includes the convertion of molecules of different size and shapes to the required
demand
...

1
...

Cracking is usually done in high temperature (liquid phase or vapour
phase) in presence of catalyst
...

2
...

Here the molecular weight of the product is higher than the reactant
...
Reforming: Reforming involves the rearrangement of the molecular
structure to alter the chemical behaviour
...
By reforming octane number of the
gasoline can be improved
...


1
...
6 CRACKING
The process of breakdown of high molecular weight hydrocarbons of high boiling points
into simple, lower molecular weight hydrocarbons of low boiling point
...

Higher paraffin → lower paraffin + olefin
Alkyl naphthene → naphthene + olefin
Alkyl aromatics → aromatics + olefin
The important cracking process are
∑

Thermal cracking
a) Liquid phase thermal cracking
b) Vapour phase thermal cracking

∑

Catalytic cracking
a) Fixed bed catalytic cracking
b) Moving bed catalytic cracking

1
...
6
...
Cracked products are cooled and fractionally distilled to
get gasoline and other fragments of lower molecular mass
...

Thermal cracking of heavier hydrocarbons depends on the thermal stability of the
molecules
...
Consider the thermal
cracking of decane (C10H20)
...


c) Termination
Free radicals can combine to give final products in the termination reaction

Thermal cracking may be carried out in a) liquid phase b) vapour phase
...
The products obtained are separated in a fractionating column
...

Vapour phase thermal cracking: In vapour phase thermal cracking, heavy oil is
cracked at a temperature of 600-700∞C under low pressure (10-20 kg/cm2)
...
Yield of petrol is about 70%
and octane rating is about 70
...

1
...
6
...
The use of
catalyst increases the rate of cracking and the process is carried out at lower
temperature and pressure
...

a) Less severe conditions of temperature and pressure is employed
...

c) The products of cracking have better anti-knocking property as it contains higher
percentage of aromatics
...

e) More economical method
...
Fixed bed catalytic cracking
2
...
Fixed bed catalytic cracking
A simple sketch of fixed bed catalytic cracking is shown in the figure below
...

The heavy oil vapour is heated to 420 – 450∞C in a preheater
...
5 kg/cm2
pressure, where catalysts (artificial clay mixed with zirconium oxide), are kept in fixed
beds
...
After 8-10 hours, the catalyst loses its activity due to the
deposition of carbon
...
Cracking
reaction yields LPG, petrol etc
...
4

Fixed bed catalytic cracking

2
...
Catalyst can be handled like
a fluid system and can be pumped like liquid
...

The feed oil is mixed with finely powdered solid catalysts which is passed to a reactor
maintained at 500∞C and a pressure of 5 kg/cm 2, where cracking takes place
...
In cooler, the vapours are condensed to liquid gasoline
along with some dissolved gases
...
Catalyst is regenerated by heating to 600∞C
(to burn off carbon) and reused
...
5

Moving bed catalytic cracking

Advantages of catalytic cracking over thermal cracking
∑

Catalytic cracking can be done at lower temperature and pressure
...


∑

Better control of reaction and choice of product
...


∑

Limited amount of external fuel is necessary
...


∑

Better octane value for gasoline produced
...
7
...
Here the molecular weight of the product is higher than the reactant
...

These are polymerized into liquid gasoline by heating alone or heating in presence
of catalysts like phosphoric acid
...

Polymerization can be achieved by heating or in the presence of a catalyst at lower
temperatures
...

Catalytic polymerization
Olefins can be easily polymerized by means of an acid catalyst
...
The
reaction is exothermic
...

Polymerization combines two or more olefins together to yield polymer gasoline
...
Thus, the product may still have a double
bond
...


Figure 1
...
7
...
The molecular weight and
boiling point of the product does not vary much from that of the feed hydrocarbons
...
The anti-knock
characteristics of gasoline is thus
...

Following reactions happens during reforming
a) Dehydrogenation
b) Dehydrocyclisation
c) Hydrocracking
d) Isomerization

Reforming is carried out either thermally or in presence of a catalyst
...
7
...
1

THERMAL REFORMING

This involves heating of straight run gasoline in a reactor at 500-600∞C under
pressure of 70-80 atmospheres in the absence of catalyst
...
Degree of
reforming is controlled by quenching(cooling) of the products vapours by a cold oil
spray
...


The amount and quality of gasoline largely depends upon the temperature of the
furnace
...
The octane number of gasoline achieved by thermal
refining process is only 65-80
...


Figure 1
...
7
...
2

Thermal reforming process

CATALYTIC REFORMING

Catalytic reforming refers to conversion of low octane gasoline to high octane gasoline
in the presence of a catalyst
...
Increase
in octane number of gasoline occurs through structural modifications where straight
chain hydrocarbons are converted into branched chain, cyclic and aromatic
hydrocarbons
...

This process can be carried out in a fixed bed or a moving bed reactor
...

In this process, straight run naphtha is fractionated to remove the low boiling fractions
...
This
fraction is preheated and compressed with hydrogen and heated to about 500∞C before
it comes into contact with catalyst in the reactor
...
Gases are passed through an

absorption tower containing diethanol amine (DEA) to remove H2S
...


Figure 1
...
No
1
...

2
...


Gasoline obtained has low octane Gasoline obtained has high octane
number (65-80)

3
...


4
...


Less effective and less economical

Highly effective and more economical

1
...
9 REFINING OF GASOLINE
Gasoline obtained by fractional distillation, cracking or reforming may still contain some
undesirable constituents
...
Unsaturated hydrocarbons may undergo oxidation or polymerization
leading to gum and sludge formation during storage
...

H2S can be removed by the treatment with diethanol amine
...
The process of removal of sulphur compounds and
mercaptans is known as “sweetening”
...
This
process converts sulphur compounds into disulphides
...
Black PbS formed is removed by filtration and
disulphides are removed by solvent extraction
...
After refining of gasoline, some inhibitors are added which retard the oxidation
of gasoline on storage
...

1
...
10

SYNTHETIC PETROL

Petroleum is likely to exhaust in few decades
...
On the other hand, requirement of
petrol is always on the rise
...
Petrol obtained synthetically from coal is known as
synthetic petrol
...
They
are a) Bergius process and b) Fischer-Tropsch process
1
...
10
...


∑

The paste is pumped along with hydrogen gas into the converter, where the
paste is heated to 400 – 450°C under a pressure of 200 – 250 atm for about 2
hours
...


∑

Vapours leaving the convertor upon condensation give crude oil or synthetic
petroleum
...


∑

The middle oil is further hydrogenated in vapour phase in presence of catalyst to
yield more gasoline
...
The yield of gasoline is about 60% of the coal used
...
9

Bergius process

Advantages of Bergius process
∑

Direct liquefaction of coal

∑

Decent yield of petrol

∑

Experimental set up is easier

1
...
10
...


∑

In this process coal is first converted into coke which is free moisture, nitrogen
and sulphur compounds
...


∑

C + H2O → CO + H2
Coke steam (water gas)
The water gas is mixed with hydrogen and the mixture is purified by passing

through Fe2O3 (to remove H2S) and then into a mixture of Fe2O3 + Na2CO3 (to
remove organic sulphur compounds)
...
The converter is provided
with a catalyst bed consisting of a mixture of 100 parts cobalt, 5 parts thoria, 8
parts magnesia and 200 parts keiselguhr earth
...
The crude oil is fractionated to yield (i) gasoline and (ii) heavy oil
...


Figure 1
...
No
1
...


used for the production of water gas
...


Direct method

Indirect method

3
...


breakdown of coal
4
...
8

Moderate yield

Moderate yield

KNOCKING

The basic principle of an internal combustion engine is that when a mixture of air and
petrol is injected, compressed (17:1) and ignited by a spark, this mixture should burn
smoothly
...
All these steps should occur uniformly and
simultaneously, ie, injection, compression, ignition, combustion and expansion of gases
and movement of piston should be uniform (synchronize)
...
Due to this pre ignition shock waves
are produced within the cylinder
...

Thus, Knocking is the unwanted rattling sound produced by the uneven combustion
(pre ignition) of petrol vapors inside the spark ignition (SI) engine
...
The tendency
to knock is in the following order
Straight chain hydrocarbons > Branched hydrocarbons > Olefins > cycloparaffins
> Aromatics
Problems caused by knocking
• Efficiency of internal combustion engine is reduced
...

• Life of the machine is reduced
...

• Knocking causes wastage of fuel
...

• Driving and travelling becomes unpleasant
...
8
...
It involves the formation of free radicals,
peroxy compounds etc
...
The accumulated peroxides decompose suddenly and burst into
flames producing shock waves
...


Antiknocking agents- Terta ethyl lead (TEL) and Tetra methyl lead (TML): Knocking
of petrol may be reduced by the addition of some organo- lead compounds into it
...
(i) Tetra ethyl lead (TEL), (C2H5)4Pb , (ii)
Tetra methyl lead (TML), (CH3)4Pb and a mixture of TEL and TML is used as
antiknocking agent
...

TEL and TML produces ethyl and methyl free radicals by dissociation
...
Thus, chain reaction is prevented
...

When leaded petrol is used, lead and lead oxide will be deposited inside the cylinder
...
In order to
prevent this, ethylene bromide is added to petrol
...
But these lead halides are
harmful to living organisms
...
By the use tetraethyl lead (TEL) or tetramethyl lead (TML)
...
Methyl t-butyl ether or ethyl t-butyl ether can be used as antiknocking agents
...

3
...

4
...

1
...
2 OCTANE NUMBER
The knocking characteristic of a petrol engine is normally expressed in terms of octane
number
...
n-heptane burns
very fast due to its straight chain structure (anti-knocking value 0)
...
Iso octane is 2,2,4Trimethyl pentane
...


Example: A fuel sample is said to have an octane number 80, if its knocking property is
similar to a mixture of 80% iso-octane and 20% n-heptane
...

Chemical structure and knocking
The octane number of a hydrocarbon depends upon its structure
...

• Branched-chain alkanes, alkenes and aromatic hydrocarbons have high octane
numbers
...

• Straight chain alkanes have low octane numbers, the value of which decreases
with the increase in the length of the chain
...


• Cyclic alkanes have higher octane numbers than the corresponding straight chain
alkanes
...

1
...
3

KNOCKING IN A DIESEL ENGINE

Diesel oil is a fraction obtained between 250-320°C and is a mixture of C15–C18
hydrocarbons
...
It is used as diesel engine fuel
...
In diesel engine there is no spark
plug
...
Compression is followed by a
rise in temperature to about 500°C
...
Diesel gets vaporized and attains self ignition
temperature and burns
...

If vaporization and combustion are instantaneous, the fuel burns smoothly and
efficiently
...
Due to the delay, vapor is accumulated in engine and when
ignited explosion results
...
In short, delayed ignition causes
knocking in diesel engines
...

1
...
4 CETANE NUMBER
The resistance to knocking offered by diesel is expressed in terms of an arbitrary scale
called cetane number
...


Cetane number is the percentage by volume of cetane (n-hexadecane) present in a
mixture of cetane and α-methyl naphthalene which has the same knocking
characteristic (ignition delay) as the fuel under test
...

Greater the cetane number of diesel, more resistant is the fuel towards knocking
...
By using diesel with high cetane number – containing more straight chain
hydrocarbons
...
Certain organic additives such as ethyl nitrite, iso amyl nitrite etc can improve
knocking
...
Thus, a fuel of high octane
number has low cetane number and vice-versa
...
No
1
...


2
...


3
...

diesel
...

lead (TEL)
...


Hydrocarbons which are poor diesel fuels Hydrocarbons which are poor gasoline
are good gasoline fuels
...


5
...


fuels, as they have high cetane numbers
...
No

Gasoline(Petrol) oil

High boiling fraction of petroleum
...


It contains C15–C18 hydrocarbons
...


2
...


Fuel for spark ignition engine
...


It is cheaper
...


4
...


rating
...


Anti knocking is improved by the addition Anti knocking is improved by the addition
of alkyl nitrates
...


of TEL
...


7
...


of pollutants
...


1
...


GASEOUS FUELS

Gaseous fuels are widely used as industrial and domestic fuel
...

a) High calorific value
...

d) Can be used in internal combustion engines
e) No soot, smoke or ash produced during combustion
...

b) They are highly inflammable
...


c) Gaseous fuels are expensive when compared to solid and liquid fuels
...

Except natural gas all other gaseous fuels are artificially prepared
...
9
...
It is colorless
and has a characteristic odor
...
Its
calorific value is about 4900 Kcal/m3
...
9
...
1

H2
50

35

10

5

MANUFACTURE OF COAL GAS

Coal gas is obtained by carbonization of coal (heated in absence of air) at about 1300∞C
in coke ovens or gas retorts
...


Figure 1
...
It is heated by producer gas to a
temperature of 1300∞C
...
Tar is removed by cooling
the gas in a big water cooling heat exchanger called condenser
...
Benzol, naphthalene etc are removed by scrubbing with creosote oil
...


Fe2O3 + 3 H2S → Fe2S3 + 3 H2O
Iron oxide can be regenerated later on exposure to air
Fe2S3 + 3 H2O → Fe2O3 + 3 H2S
Purified coal gas be stored in tanks
...


∑

Domestic and commercial illumination
...


∑

In metallurgical operations to provide reducing atmosphere
...
9
...
It burns with a smoky flame and has a
characteristic golden color
...

The average composition of coal gas is
Constituent

CH4

CO

CO2

Percentage %

1
...
2
...
Cracking is usually
done is strong iron retorts enclosed in coal fired furnace
...

The retort is heated to red hot and a stream of kerosene oil is allowed to fall on the
bottom of red hot retort
...

The gas rises and goes to the hydraulic main( a tank containing water) through the
bonnet, where tar gets condensed
...


Figure 1
...


∑

Oil gas is mixed with water gas to improve the calorific value of water gas
...


REVIEW QUESTIONS
1
...
Account also for the
recovery of by-products
...
Discuss the recovery of by-products
...
6
...
1
2
...

Refer Section 1
...
5
...
Write notes on the following:
(i)

Classification of coal (Refer Section 1
...
2)

(ii)

Metallurgical coke [R
...
U
...
6
...
1)

4
...
7
...
Write notes on the following:
(iii)

Synthetic petrol [R
...
U
...
7
...
T
...
2012, 2015] (Refer Section 1
...
6)

6
...
9
...
Differentiate the characteristic of solid, liquid and gaseous fuels
...
2
8
...

Refer Section 1
...
10
...
What is knocking in IC engine? How it is related to the structure of constituent
hydrocarbons? Define octane number
Refer Section 1

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