Presentation on Liquid Fuels. Properties and uses

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Presented By:
Yasir Gul
Abdul Wahab
M.Rizwan
Izaz Ahsan
Habib Ullah
M.Farooq Siddique
Ihsan Ullah
Salman Khan
M.Asad
LIQUID FUELS

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 Introduction
 Occurrence and Processing of fossil fuels
 Properties of Liquid Fuels
 Liquid fuels other than Petroleum products
 Combustion of Liquid Fuels
 Liquid Fuel Burners
 Advantages and Disadvantages
Agenda

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• Liquid fuels are combustible or energy-generating
molecules that can be harnessed to create mechanical
energy, usually producing kinetic energy.
• These also must take the shape of their container. It is
the fumes of liquid fuels that are flammable instead of
the fluid.
• Most liquid fuels in widespread use are derived
from fossil fuels; however, there are several types, such
as hydrogen fuel (for automotive uses), ethanol,
and biodiesel, which are also categorized as a liquid fuel.
Introduction

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 The basic source of liquid fuels is crude oil, which
occurs in strata of sedimentary rocks.
 Gaseous, liquid and semi-solid materials are
separated at the well head, but the liquid fuels which
are burned in practice are first processed in a refinery.
The most significant of the refinery processes is
distillation.
Occurrence and Processing

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 The crude oil is flashed (i.e. it undergoes a sudden
drop in pressure) into a column.
 The main part of the column is at atmospheric
pressure with a vacuum section producing the heavier
products.
 The vaporized oil travels up the column which has a
vertical temperature gradient with the top of the
column being the coolest part
Contd…

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 The fraction of the oil which vaporizes in the column
will condense out at the appropriate level in the
column.
 A system of bubble caps and trays is used to
facilitate this.
Contd…

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Fractional Distillation of Petroleum

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 Table 8.1 gives some physical properties of the
commercially important fuel oils.
 Some explanatory notes about the properties in the
table follow.
Properties of Liquid Fuels

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Flash Point
This gives an indication of the flammability of the fuel.
Its significance is in the safety aspects of storing and handling
the fuel.
Viscosity
This is a measure of resistance to flow.
It reflects the energy required to pump the oil through
pipework and it has an important bearing on the atomization
process in burners. It is measured in a standard U-tube
viscometer at 38 .
℃
Pour Point
This is complementary to viscosity in that it gives an indication
of the temperature at which the oil will start to flow freely.
Contd…

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 Calorific Value
The calorific value of a liquid fuel is measured in a
bomb calorimeter, which measure directly the gross
calorific value at constant volume.
It can be seen that the less volatile oils have lower
calorific values.
 Sulfur content
Sulfur exists in all liquid fuels, but it is present to a
significant degree in residual fuel oils.
When burnt, sulfur forms SO2 and SO3 which are major
sources of air pollution.
Contd…

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Liquefied petroleum gas (LPG)
 LP gas is a mixture of propane and butane, both of
which are easily compressible gases under standard
atmospheric conditions.
It offers many of the advantages of compressed
natural gas (CNG), but does not burn as cleanly, is
denser than air and is much more easily compressed.
 Commonly used for cooking and space heating, LP gas
and compressed propane are seeing increased use in
motorized vehicles; propane is the third most
commonly used motor fuel globally.
Liquid Fuels other than Petroleum

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Non-petroleum fossil fuels
 When petroleum is not easily available, chemical
processes such as the Fischer-Tropsch process can be
used to produce liquid fuels from coal or natural gas.
 Synthetic fuels from coal were strategically important
during World War II for the German military.
 Today synthetic fuels produced from natural gas are
manufactured, to take advantage of the higher value of
liquid fuels in transportation.
Contd…

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Bio-Diesel
Biodiesel is similar to diesel, but has differences akin to those
between petrol and ethanol. For instance, biodiesel has a
higher cetane rating (45-60 compared to 45-50 for crude-oil-
derived diesel) and it acts as a cleaning agent to get rid of dirt
and deposits.
It has been argued that it only becomes economically feasible
above oil prices of $80 per barrel. This does however depend on
locality, economic situation, government stance on biodiesel and
a host of other factors- and it has been proven to be viable at
much lower costs in some countries. Also, it yields about 10%
less energy than ordinary diesel.
Analogous to the use of higher compression ratios used for
engines burning higher octane alcohols and petrol in spark-
ignition engines, taking advantage of biodiesel's high cetane
rating can potentially overcome the energy deficit compared to
ordinary Number 2 diesel.
Contd…

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Alcohols
 Generally, the term alcohol refers to ethanol, the
first organic chemical produced by humans, but any alcohol
can be burned as a fuel. Ethanol and methanol are the
most common, being sufficiently inexpensive to be useful.
Methanol
Methanol is the lightest and simplest alcohol, produced
from the natural gas component methane. Its application is
limited primarily due to its toxicity (similar to gasoline),
but also due to its high corrosivity and miscibility with
water.
 Small amounts are used in some gasolines to increase
the octane rating. Methanol-based fuels are used in some
race cars and model airplanes.
Contd…

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Ethanol
 Ethanol, also known as grain alcohol or ethyl alcohol, is
commonly found in alcoholic beverages. However, it may
also be used as a fuel, most often in combination with
gasoline.
 For the most part, it is used in a 9:1 ratio of gasoline to
ethanol to reduce the negative environmental effects of
gasoline.
 There is increasing interest in the use of a blend of 85% fuel
ethanol blended with 15% gasoline. This fuel blend called
E85, has a higher fuel octane than most premium gasolines.
When used in a modern Flexible fuel vehicle, it delivers
more performance to the gasoline it replaces at the expense
of higher fuel consumption due to ethanol's lesser specific
energy content.
Contd…

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Butanol
 Butanol is an alcohol which can be used as a fuel in
most gasoline internal combustion engines without
engine modification.
 It is typically a product of the fermentation
of biomass by the bacterium Clostridium
acetobutylicum (also known as the Weizmann
organism).
 This process was first delineated by Chaim
Weizmann in 1916 for the production
of acetone from starch for making cordite, a smokeless
gunpowder.
Contd…

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Hydrogen
 Liquefied hydrogen is the liquid state of the
element hydrogen.
 It is a common liquid rocket
fuel for rocket applications and can be used as a fuel
in an internal combustion engine or fuel cell.
 Various concept hydrogen vehicles have been lower
volumetric energy, the hydrogen volumes needed for
combustion are large.
Hydrogen was liquefied for the first time by James
Dewar in 1898.
Contd…

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Ammonia
 Ammonia (NH3) has been used as a fuel before at
times when gasoline is unavailable (e.g. for buses in
Belgium during WWII).
 It has a volumetric energy density of 17 Mega-joules
per liter (compared to 10 for hydrogen, 18 for
methanol, 21 for dimethyl ether and 34 for gasoline).
 It must be compressed or cooled to be a liquid fuel,
although it does not require cryogenic cooling as
hydrogen does to be liquefied.
Contd…

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 For efficient combustion, a liquid fuel must be
broken up into a stream of droplets to maximize the
surface area-to-volume ratio.
 The various types of burner accomplish this in
different ways, but the objective of all types of burner
is to produce a spray of droplets which are small, and
which have a narrow size distribution.
 The combustion process consists of evaporation of
the droplet, driven by heat transfer from its
surroundings, with the vapor subsequently burning in a
diffusion flame.
Combustion of Liquid Fuels

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 A classical analysis of this situation where the heat
transfer to the droplet is by convection shows that the
rate of mass transfer (and hence the combustion rate of
the droplet) is inversely proportional to the diameter.
 Because evaporation of the droplet is the controlling
influence on the combustion rate, liquids with low
latent heats of evaporation will burn more quickly.
 The combustion of a liquid fuel spray is more complex
than is indicated above: in particular, heat transfer to
the droplet will be by radiation as well as convection.
Contd…

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 The combustion of oil is a two phase process.
 Intimate mixing of the fuel and air is an important
requirement hence the fuel is broken up into a fine
spray, or atomized.
 Three common oil burners with different atomization
methods are reviewed below.
Contd…

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 The simplest form of pressure jet consists of a swirl
chamber through which the fuel passes before issuing
through the final orifice (Fig 8.2).
 Angular velocity is imparted to the liquid by
tangential slots or ports.
Pressure Jet Burners

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 The fuel emerges from the jet as a conical sheet
which subsequently breaks up into droplets of between
10 and 200 μm diameter.
 The oil supply pressure is usually greater than 500
kPa.
 The simplest and most common type of oil burner
incorporates the pressure jet, and this is shown
diagrammatically in Fig. 8.3.
 Pressure jet burners span a wide range of ratings,
from domestic units of about 25 kW up to 2.5 MW.
Classes C, D, and E oils can be burned.
Contd…

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 The supply of oil is fed onto a rotating surface (usually
a cup or disk) and the atomization is achieved when the
fluid is flung off the cup by centrifugal force.
 These atomizers tend to give a narrow size range of
droplets and are ideally suited to the more viscous liquid
fuels, as pumping pressures are much lower than those
for pressure jet burners.
 The cup rotates at 4,000-6,000 rpm to atomize a class
G residual fuel oil, although much higher speeds are
used in some applications.
 The air supply to this type of burner is split into two
streams: 15% is supplied as primary air around the
atomizer itself, the remainder being admitted
subsequently as secondary air.
Rotary Cup Burners

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 A second fluid (typically air or steam) is used to
produce the shear necessary to break up the oil into
droplets.
 The nozzle is essentially similar to that of the pressure
jet burner with the addition of an extra set of
tangential ports on the inside or outside of the oil flow
passage.
 In an air-blast atomizer about 2-10% of the combustion
air is supplied at a high pressure
(20-100 kPa).
 This type of atomizer is more expensive to operate
than the other types but it is capable of much greater
load modulation, achieving turndown ratios up to 5:1,
which can make the extra expense worthwhile.
Twin-fluid Atomizers

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 They possess higher calorific value per unit mass than
solid fuels.
 They burn without forming dust, ash, clinkers etc.
Their firing is easier and also fire can be extinguished
easily by stopping the liquid fuel supply.
 They are easy to transport through pipes.
 They can be stored indefinitely without any loss.
 The flame produced by burning liquid fuels can easily
be controlled by adjusting the liquid fuel supply.
 Liquid fuels are generally handled by pipes and one
man can easily regulate a large number of furnaces
simultaneously.
Advantages of Liquid Fuels

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 They are clean in use and economic in labour.
 Loss of heat to chimney is very low due to grater
cleanliness.
 They require less excess of air for complete
combustion.
 They require less furnace space for combustion.
 There is no wear and tear of grate bars and cleaning
of fires unlike solid fuels.
 They can be used as internal combustion fuels.
Contd…

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 The cost of liquid fuel is relatively much higher as
compared to solid fuels.
 Costly special storage tanks are required for storing
liquid fuels.
 There is greater risk of fire hazards, particularly in
case of highly inflammable and volatile liquid fuels.
 Liquid fuels give bad odour.
 For efficient burning of liquid fuels, specially
constructed burners and spraying apparatus are
required.
 Choking for sprayers is a drawback of oil firing.
Disadvantages of Liquid Fuels

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[1]. Sharma, S.P. and Mohan, C., 1984. Fuels and combustion.
[2]. Gupta, O.P., 1997. Elements of fuels, furnaces and
refractories. Khanna Publishers.
[3]. George E. Totten, (2003). Fuels and lubricants handbook :
technology, properties, performance, and testing (2nd
printing. ed.). West Conshohocken, Pa.: ASTM
International. ISBN 9780803120969.
[4]. Wikipedia contributors. (2018, March 23). Liquid fuel.
In Wikipedia, The Free Encyclopedia. Retrieved 09:00, April
9, 2018, from https://en.wikipedia.org/w/index.php?
title=Liquid_fuel&oldid=831996659
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