Basic Concept of FuelCourse - 3131 : Fuel Technology

3rd Year : Odd Semester

Chapter : 1

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Course Outline

6. Role of fixed C, N, S, O and ash content on calorific value in fuels.

1. Definition, classification and essential requirements of fuel

2. Primary and secondary fuel

3. Solid, liquid and gaseous fuel, advantages and disadvantages.

4. Classification of gaseous fuel, composition and calorific value of fuel.

5. Determination of calorific value (Direct and indirect method)

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Fuel

A fuel is anything that can produce energy/power.

A substance that produces useful energy when it undergoes a chemical or

nuclear reaction. Fuel such as coal, wood, oil, or gas provides energy when

burned. Compounds in the body such as glucose are broken down into

simpler compounds to provide energy for metabolic processes. Some

radioactive substances, such as plutonium and tritium, provide energy by

undergoing nuclear fission or fusion.

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Basic Concept of Fuel

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A fuel is any combustible substances which may be burnt to supply heat forpractical applications without the formation of excessively objectionable

byproducts.

Example- Petroleum, coal, wood, peat, dung, natural gas,

gasoline, kerosene, LPG, gas oil etc.

Modern Concept of Fuel

It is now well established that combustion is not necessary for a fuel to give

out energy. For example electrical energy when used as a source of heat is

also called fuel. Nuclear energy may also be used as source of heat. Chemical

compounds, such as power alcohol, ammonia etc. are used as fuels.

According to the modern concept-

A fuel is any fissionable material, chemical or reactant which produces energy

in a form that can be used for producing power. Example- Electrical E, Nuclear

E, Fuel cell etc.

A fuel cell is an electrochemical device that combines hydrogen and oxygen to produce electricity

4 May 2016 5Source: E-books

Composition of Fuel

Solid Fuel:

Carbon, Hydrogen, Oxygen, Sulfur, Moisture, Ash

Wood Coal Straw

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Composition of FuelLiquid/Gaseous Fuel:Carbon mono-oxide, Hydrogen, Methane, Ethane, Propane Ethylene, Butane,

Hydrogen Sulfide, Nitrogen, Sulfur, Carbon Di-Oxide

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Primary Fuel: Fuels that directly produce heat energy on ignition.

Ex: Wood, Coal, Petroleum, Natural Gas, Animal Dung etc.

Secondary Fuel: Fuels that processed & prepared from primary

fuel. Ex: Charcoal, Coke, Petrol, Diesel, Kerosene etc.

Classification of Fuel

According to Origin

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Classification of Fuel

According to physical state

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Type of Fuel Primary (natural) Secondary (artificial)

Solid fuelswood, coal, peat, dung,

etc.coke, semi-coke, charcoal

Liquid fuels petroleumdiesel, gasoline, kerosene, LPG, gas oil,

coaltar, naphtha, ethanol

Gaseous fuels natural gashydrogen, propane, coal gas, water gas, producer

gas, blast furnace gas, coke oven gas, CNG

Essential Requirements of Fuel

1. Reasonably high velocity of combustion

2. Release high value of thermal energy

7. Safe to transport or in case of accident

3. Proper ignition temperature

4. Low percentage of non-combustibles

5. Reasonable cost

6. Low toxicity with contact

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Solid Fuel: Advantage & DisadvantageAdvantages

1. Solid fuel can be very conveniently stored due to their high ignition temp.

2. They are comparatively cheap

3. Safe to transfer

4. Easy to handle

5. Their cost of production is low

Disadvantages

1. Large portion of heat is wasted due to lack of proper surface contact

2. A large amount of unburnt fuel is also wasted along with clinker, cinder etc.

3. Cannot stored in open area

4. Large area need for store.

5. Also produce smoke and ash

6. Their combustion operation cannot be controlled easily.

7. Their cost of handling is high

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Liquid Fuel: Advantage & DisadvantageAdvantages

1. Handling of liquid fuel is easy and they require less storage space

2. Liquid fuels can be fired easily and maximum temperature is attained in time.

3. Can use directly to produce energy.

4. Does not produce smoke and ash.

5. Easily burn and mixed with air.

Disadvantages1. They can pollute our environment during burning.

2. They require special type of burners

3. Costly special storage tanks are required for storing liquid fuels

4. Ignition temperature is low

5. The cost of liquid fuel is relatively much higher as compared to solid fuel

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Gaseous Fuel: Advantage & DisadvantageAdvantages

1. It contains no ash

2. There is no smoke/ash problem and hence much less labor

3. They are burned easily and readily mixed with air

4. Much higher fuel economy because of regenerative heating

5. Easy to transport

6. Everywhere can use (Industrial furnace, domestic use, internal combustion of engine etc.

Disadvantages

1. Comparatively dangerous to store due to their low ignition temperature

2. Need container to store

3. Handling is not so easy

4. Extra care need to take during storing, transferring and also using.

5. Danger of explosion and large scale of fire it may cause.

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Properties of Fuels1. Calorific Value

2. Specific Heat of Combustion

3. Ignition Temperature

4. Flame Temperature

5. Flash Point

6. Fire Point

7. Aniline Point

8. Knocking

9. Specific Gravity

10. Pour Point

11. Cloud Point

12. Coke Number

13. Viscosity

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Reference: Industrial Chemistry- by- B.K. Sharma

Properties of liquid fuels

Density

• Ratio of the fuel’s mass to its volume at 15 oC,

• kg/m3

• Useful for determining fuel quantity and quality

Viscosity

• Measure of fuel’s internal resistance to flow

• Most important characteristic for storage and use

• Decreases as temperature increases

4 May 2016 15Source: E-books

Flash point

• Lowest temperature at which a fuel can be heated so that the vapour gives

off flashes when an open flame is passes over it

• Flash point of furnace oil: 66oC

Pour point

• Lowest temperature at which fuel will flow

• Indication of temperature at which fuel can be pumped

Properties of liquid fuels

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Calorific value

• Heat or energy produced

• Gross calorific value (GCV): vapour is fully condensed

• Net calorific value (NCV): water is not fully condensed

Specific gravity

• Ratio of weight of oil volume to weight of same water volume at a given temperature

• Specific gravity of water is 1

• Hydrometer used to measure

Properties of liquid fuels

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Sulphur content

• Depends on source of crude oil and less on the refining process

• Furnace oil: 2-4 % sulphur

• Sulphuric acid causes corrosion

Ash content

• Inorganic material in fuel

• Typically 0.03 - 0.07%

• Corrosion of burner tips and damage to materials /equipments at high

temperatures

Properties of liquid fuels

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Carbon residue

• Tendency of oil to deposit a carbonaceous solid residue on a hot surface

• Residual oil: >1% carbon residue

Water content

• Normally low in furnace oil supplied (<1% at refinery)

• Free or emulsified form

• Can damage furnace surface and impact flame

Properties of liquid fuels

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Ignition Temperature

Factors affecting the Ignition Temperature

1. Nature of Fuel

2. Combustion environment

3. Presence of moisture

4. Pressure over the Fuel

5. Size and shape of burning unit

6. Particle size of Fuel

7. Presence of foreign matter

The lowest temperature at which a combustible substance will spontaneously ignite in a

normal atmosphere and continues to burn without an external source of ignition —called

also autogenous ignition temperature

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Reference: Industrial Chemistry- by- B.K. Sharma

Calorific ValueCalorific Value:

The quantity of heat produced by the complete combustion of a given mass of a fuel.

It is usually expressed in J/Kg.

Method for determining calorific value:

a) Direct Method

b) Indirect Method

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Calorific Value

The calorific value of solid fuels is expressed as British Thermal Units per Pound (B.T.U. per 1b)

or Kilogram Centigram Unit per Kilogram (K.C.U. per kg.).

Taking both above definitions of these units, a correlation between them can be written as;

1 B.T.U = 252 cals

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a) Direct Method

A calorimeter is used to measure the calorific value of a fuel called bomb calorimeter. The principle is

look like a bomb that is why the calorimeter is known as bomb calorimeter.

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Reference: E-Books

a) Direct Method

Procedure of bomb calorimeter experiment

1. A known quantity of fuel sample is taken in a crucible.

2. The stirrer is then started and note the initial temperature of water is noted down.

3. Current flow is started through crucible and let fuel sample to burn in presence of oxygen.

4. Heat release during combustion of fuel is taken by water and temperature of it rises.

5. Final steady state temperature of water is noted down.

Calorific Value =M

1+M

2X Tc+T

2−T

1X Cw

Mf

Where,

M1 and M2 are mass of water & water equivalent of

bomb calorimeter

Mf is mass of fuel sample.

T2 and T1 are final and initial temperature of water

sample.

Tc is temperature correction for radiation losses.

Cw is specific heat of water

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b) Indirect Method

Calorific value can be determined from the elements of the fuels. It is

assumed that the heating value of a fuel is equal to the sum of the heating value

of the elements present in fuel at free state.

Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur

Reference: Applied Chemistry-Volume-2, by V.M. Balsaraf (Google Books)

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b) Indirect Method

Calorific value: According to Dulong, the calorific value of a fuel is the sum

total of calorific values of its constituents elements. The calorific values of

some elements are as follows:

Total Calories/gm. =% 𝐶 𝑋 8080 + %𝐻 −

%𝑂

8𝑋 34500+% 𝑆 𝑋 2240

100

C + O2 CO2 + 96960 Calories ( 96960/12 = 8080 Cals.)

H2 + 1/2O2 H2O + 69000 Calories (69000/2 = 34500 Cals.)

Reference: Applied Chemistry-Volume-2, by V.M. Balsaraf (Google Books)

S + O2 SO2 + 71680 Calories (71680/32 = 2240 Cals.)

Dulong Equation

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Calorific Value

The quantity known as lower heating value (LHV) (net calorific value or lower calorific value -

LCV) is determined by subtracting the heat of vaporization of the water vapor from the higher

heating value.

NCV = GCV- Heat of vaporization of water

[Heat of vaporization of water = 0.09 H X 587 cal/gm.]

Reference: Applied Chemistry-Volume-2, by V.M. Balsaraf (Google Books)

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Criteria for Selecting a Fuel

There are some important criteria that are to be considered for a particular

type of purpose.

1. Suitability to process

2. Supply position

3. Cost of fuel

4. Calorific value

5. Transportation and labor

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Role of Different Element on CV

Different element/content present in a fuel plays an important role on

calorific value. Such as:

1. Fixed Carbon

2. Sulfur

3. Nitrogen

4. Oxygen

5. Ash content

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Role of Fixed Carbon on Calorific Value

It indicates the organic matter that does not undergo volatilization When a

known weight of the powdered solid fuel is combusted at a fixed

Temperature (950° ± 20° ) for a fixed period (7 Mins.)

The percentage of fixed carbon can be calculated by subtracting the weight

of ash from the residue. Suppose the weight of residue left after

subtracting the weight of ash is ‘a’ grams then-

Fixed carbon increases the calorific value of fuels.

% of fixed carbon =𝒂

𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐅𝐮𝐞𝐥X 100

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Role of Nitrogen on Calorific Value

Actually nitrogen does not have any calorific value. Nitrogen act as a

detergent in fuel engine and thus increases the calorific value indirectly.

Reference: Applied Chemistry-Volume-2, by V.M. Balsaraf (Google Books)

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Role of Sulfur on Calorific Value1. High sulfur levels in fuel, when combined with water vapor can also cause corrosive wear

on valve guides and cylinder lines, which can lead to premature engine failure.

2. Sulfur reduces catalytic efficiency in modern vehicles.

3. Sulfur in gasoline may degrade the performance of oxygen sensors, which may also result

high emissions.

4. High sulfur level in gasoline may also impair the performance of some vehicles.

5. Low sulfur level can reduces the natural lubricating properties of the diesel fuel.

6. Reduction of sulfur level can changes the overall chemical composition of the fuel and it

can affect fuel pump seals, engine seals etc.

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Role of Oxygen on Calorific Value

Oxygen present in the fuel normally as moisture or some oxygen is used to

burn the combustibles of the fuel. Heat will lose for burning. As a result low

amount of heat will be produced, because oxygen combine with hydrogen

to form water. So higher the oxygen level lowers the calorific value of fuel.

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Role of Ash Content on Calorific Value

% Ash =𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐀𝐬𝐡

𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐅𝐮𝐞𝐥X 100

Ash is non-combustibles materials and reduce the calorific value of fuel. Ash

also cause hindrance to flow of air and heat. Ash reduce the rate of

combustion. Hence lower the ash content, better the grade of fuel.

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Conclusion

Fuel crisis in Bangladesh and it’s remedy……..

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