Energy crisis of the world has increased due to the high consumption and low productL To adjust this imbalance, fossil fuels like coal a_ ure used. Fossil fuels are divided into three categories liquid and gaseous. In the first is the coal second is the petroleum and in the third category fall the natural gases. The value of a fuel lies primarily in its calorific value. A fuel with higher proportion of hydrogen has higher calorific value. The liquid and gaseous fuels have high hydrogen and they give out far more heat on combustion than solid fuels.
Majority of fuels come directly or indirectly from carbo-hydrates (photosynthetic products of green plants). In this sense, we owe most of our fuels to the sun. When we burn wood, we are merely recovering recent solar energy. When we burn coal, oil or city gas we are distributing ancient solar energy.
COAL
Coal is an important source of heat and energy. Coal may be defined as plant debris that has been subjected to various bio-chemical and geological processes. As a result, the plant debris has undergone many changes in physical properties and chemical composition. The changes are mainly
1. darkening of colour
2. an increase in hardness and compactness
3. loss of moisture
4. loss of volatiles like carbondioxide, hydrogen and oxygen and
5. an increase in carbon conten.
Coal is a principal 'mineral fuel' which occurs abun¬dantly in the earth's crust. Coal cannot be strictly con sidered as a mineral as it is not a homogenous substance. The coal contains plant materials and a variety of minerals in the form of ash. However, in trade and industry it is regarded as a mineral.
Based on the various stages in the transformation of a
plant material into coal, coal is classified into Peat, Lignite,
Bituminous Coal and Anthracite Coal. All are related to one
another and sometimes called 'humoliths'. The first two
peat, and Lignite - are generally termed 'Low rank' coals-ghd
the last two Bituminous and Anthracite - as 'High rank'
coals.
The main chemical constituents of coal are carbon, hydrogen and a small amount of nitrogen and sulphur. The proportion of these elements, starting from the plant material to anthracite, is given in the table.
Based on the nature of the original plant material from pi-Inch coals are formed, coals are divided into two types.
Humic Coalsjyfoody Coals) and sapropelic coals. (non-Woody coals). The humic coals are very important and they kare mainly formed by the wood and bark of land and Bwampy plants. They are sometimes called "humolith,s". The Sapropelic coals are derived from non-woody matters Kkv leaves, spores cuticle, etc., of plants as well as from Aigae, Fungi and planktons. This coal, on distillation, yields petroleum. The sapropelic coals may be considered as a more or less transistory stage between true coal and petroleum.
They are sometimes called 'Sapropelites'.
