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Fuels - Part I |
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All the energy that we use in our everyday lives, namely, electricity, cooking gas, petrol, are generated from substances that may be termed as fuels. Fuels are those substances that when oxidized give rise to heat energy. This heat energy can be converted to other forms of energy like electricity or mechanical energy like vehicle motion. Even the food we consume can be termed as fuel, as it is converted in our body to give us energy to sustain, breathe, walk, have our hearts beating, brains functioning, Thus fuels form a very basic and important component in our lives. In this chapter we will see the chemistry of different types of fuels and how they alter on combustion. What we will
study in this chapter 1.
Classification
and sources
of fuels Solid fuels
: Examples of solid fuels are wood, coal, charcoal and coke. Fuels can also be divided into categories such as
primary and secondary fuels. Primary fuels
: Fuels that directly produce heat on ignition are called primary type
of fuels. They are Now
let us look at a few sources of fuel that we come across in our everyday
lives. We will study a sample of solid, liquid and gaseous fuels. Bio Mass :
Waste matter that is
organic in nature is called bio-mass. Cattle dung, wood, household vegetable
wastes, bagasse from sugar cane, all are termed as biomass. Dried animal
dung or cattle dung cakes are used directly as fuels in rural India in “chulhas”.
The use of biomass directly as fuel is not very efficient. It produces smoke
and has very low efficiency of burning. Biomass is a primary type of fuel.
Biomass can be used more usefully in producing secondary fuel likes gobar
gas or methane gas. This we shall see later in the chapter. Charcoal : Charcoal is produced when wood is heated in the absence of air.
Charcoal thus is a secondary fuel. Charcoal is pure carbon. Charcoal is
prepared from destructive distillation of wood. When wood is heated in the
absence of air, it looses all its volatile matter locked into wood,
including water. Wood is decomposed into simpler substances. This process is
called destructive distillation. The
apparatus for obtaining charcoal is shown below. Take
a hard glass tube and place some pieces of wood in it.
Take another hard glass tube and keep a bit of water in it. Connect
L-shaped tubes as shown in the figure. Start heating the wood with a burner.
You will notice that some gas is bubbling
and coming out of the tube. This is called wood gas. If you hold a
ignited matchstick near it, the gas will start burning. Wood gas is a
combination of many inflammable gaseous hydrocarbons, but is mainly methane.
As the wood is heated further, you will notice a black liquid deposit
collecting at the bottom of the water. This is called coal tar. If you smell
the water, you will get a distinct odour of acetic acid and methyl alcohol.
The destructive distillation is complete when the first test tube has
only black chunky residue left. This is called charcoal. Thus destructive
distillation of wood gives wood gas, tar, methyl alcohol, acetic acid, water
and charcoal. Wood contains cellulose (C6H10O5)n and charcoal contains only pure C. The efficiency of charcoal in producing heat is much more than wood. Also wood gives of a lot smoke which does not happen with charcoal. Charcoal is sold in chunks and is easy to handle and store when compared to wood. Charcoal also has higher calorific value when compared to wood or coal. Hence charcoal is a very useful fuel. But its input is wood, which leads to deforestation. This is the reason why charcoal is not very popular as fuel in rural or urban areas. |
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