The Concept of Fuels

Fuel is combustible substance burning in air to produce energy. Example heat energy and light energy.

Since combustion is chemical process so fuel is also called chemical fuel

Categories of fuels

Fuels are classified according to;

i. Occurrence (preparation)

ii. Physical state

According to Occurrence (preparation)

According to occurrence fuel classified into two groups of fuels which are;

i. Natural/primary fuels

ii.Artificial/secondary fuels

Natural fuels

By dfn: Natural fuel is the fuel which occurs naturally. Example wood, coal, peat, petroleum and natural gas

Artificial fuel

By dfn: Artificial fuel is the fuel manufacture in industries or fining from natural fuel. Example coke, kerosene, petrol, coal gas and producer gas

Physical state

According to physical state fuel classified into three fuels which are;

i. Solid fuel

ii. Liquid fuel

iii. Gaseous fuel

Characteristics of a Good Fuels

A good fuel should have the following characteristcs

High energy value

A good fuel should have a high energy value. Energy value is determined by the amount of energy produced per unit mass of the fuel. This is called heat value

High rate of combustion

A good fuel should have high rate of burns and moderate rate for a continuous supply of heat

Have Average ignition point

By dfn: ignition point is the temperature needed to burn fuel. A good fuel should have average ignition point.

This is because

i.                    Low ignition is risk due to fire hazard

ii.                 High ignition point makes difficult to start a fire. But fuels with high ignition point are safe to transport and store.

Low Non-combustible material content

A good fuel should have low or no contents of non-combustible material. For example, Ashes.

Non-combustible materials are those materials which cannot get burnt.

Note that.

i. Non-combustible materials lower the heat

value of the fuel and are left in form of ash.

Not produce poisonous gas

A good fuel should not give off poisonous gases and also it should give off very little or no smoke.

Highest pyrometric burning effect

By dfn:

Pyrometric burning effect is the highest temperature reached by burning a fuel. A good fuel should have highest Pyrometric burning effect.

➔ Gaseous fuels have high

Pyrometric burning effect

Readily available

A good fuel should be readily available in large quantities.

Affordable.

A good fuel should be affordable to most people. i.e. should be cheap.

Ease to transport and store

A good fuel should be easy and safe to transport and store.

Have no effect on environment

A good fuel should not have harmful effect on the environment. Example Fossil fuels which produce carbon monoxide on burning are major contributor to global warming

Destructive distillation

By dfn: Destruction distillation is the process whereby organic fuel is decomposed by heating in the absence of air (oxygen) to obtain useful product.

Organic fuels include wood, coal and oil shale. The useful product that can be formed include coke, charcoal, oil and gases.

Solid fuels

This is the kind of fuel which exist as solid.

Solid fuels include

i. Coal

ii. Charcoal

Coal

By dfn: Coal is the fossil energy formed by anaerobic (without oxygen) decay of plants that lived millions of years ago.

Fossil energy is the energy formed by anaerobic (without oxygen) decay of plants that lived millions of years ago.

Energy remain in the coal is Solar energy stored in plants

Composition of coal

Coal is composed by four components which are;

i. Moisture

ii. Volatile matter

iii. Ash

iv. Coke

CHARCOAL

Charcoal is made from dry distillation of wood at 94000 – 4500 in an earth-pit kiln or earth-mound kiln. Charcoal burns with non-luminous flame and is easily ignited

Earth-pit kiln

Consider the process takes in earth-pit kiln

1st. The wood is heaped in hemispherical pile in a central pit

2nd. Then it is covered by with earth and sod, leaving small air holes near the bottom

3rd. Wood is lit at the centre and allowed to burn until the whole pile is on fire.

In fact, Smouldering combustion takes place, utilizing oxygen and hydrogen components of the wood fibre

·       The product of Smouldering combustion is water, carbon dioxide and volatile organic compound

4th. Small hole closed until the fire goes off and charcoal cool

This process yields about 20% charcoal by weight and 75% by volume

Earth-mound kiln

It works as earth-pit kiln but earth-mound kiln has not a pit but the wood is heaped in a pile above the ground surface

Keep in mind

i. Earth-mound kiln is Preferred if the soil occupied by rocky (stones)

ii. Earth-mound kiln is Preferred if the soil water table is close to the surface

Characteristics of good charcoal

i. Should be porous

ii. Should be Brittle

iii. Should be retained in the form of the wood