COAL
Coal is the most abundantly available fossil fuel in India and the world. It is a highly combustible, black or brownish-black sedimentary rock composed primarily of carbon, along with variable quantities of other elements like hydrogen, sulphur, oxygen, and nitrogen. It forms the backbone of the energy sector, providing a substantial portion of the nation’s electricity generation and serving as a crucial raw material for industries like iron and steel.
1. Origin of Coal (How is it formed?)
The formation of coal is a slow, natural process that takes millions of years. This process of conversion of dead vegetation into coal is called carbonisation.
Because coal was formed from the remains of vegetation, it is classified as a fossil fuel. The step-by-step process of its origin is as follows:
- Prehistoric Forests: About 300 million years ago, the Earth had dense forests in low-lying wetland areas and swamps.
- Burial: Due to natural processes like flooding, earthquakes, and tectonic shifts, these forests were buried under the soil. Over time, more and more soil deposited over them, compressing the organic matter.
- Heat and Pressure: As the vegetation sank deeper underground, the temperature and pressure rose significantly. In this oxygen-poor environment, the dead plants were prevented from decaying normally.
- Chemical Transformation: The intense heat and pressure over millions of years slowly squeezed out the water and oxygen from the plant remains, leaving behind carbon-rich deposits. This gradual transformation resulted in the formation of coal.
2. Geological Age of Coal in India
In India, rock systems are classified based on their geological age. Coal occurs in rock series of two main geological ages: Gondwana and Tertiary.
Understanding the age of coal is important because older coal has generally been subjected to more heat and pressure, making it richer in carbon and better in quality.
Gondwana Coal:
- Age: This is the older variety of coal, formed around 250 million years ago (during the Permian period).
- Significance: It is the most important and extensive coal resource in India. It accounts for nearly 98% of the total coal reserves and 99% of India’s total coal production.
- Location: These deposits are mainly found in peninsular India, within the river valleys of Damodar (Jharkhand-West Bengal), Mahanadi (Odisha-Chhattisgarh), Godavari (Telangana), and Wardha. Major coalfields like Jharia, Raniganj, and Bokaro belong to this age.
Tertiary Coal:
- Age: This is relatively younger coal, formed about 15 to 60 million years ago (during the Eocene to Miocene periods).
- Significance: Because it is younger, the carbonisation process is less complete. It has a lower carbon content and higher moisture content compared to Gondwana coal.
- Location: These deposits are mostly found in the extra-peninsular regions of India, such as Assam, Meghalaya, Nagaland, Arunachal Pradesh, and parts of Jammu and Kashmir.
3. Characteristics of Coal
The quality and efficiency of coal as a fuel depend on its physical and chemical characteristics. The main characteristics include:
- Carbon Content: This is the most important factor. The higher the carbon content, the greater the heating value (calorific value) of the coal. High-carbon coal burns hotter and longer.
- Moisture Content: The presence of water reduces the heating efficiency of coal because energy is wasted in evaporating the moisture during combustion. Older coal generally has less moisture.
- Volatile Matter: These are gases (like methane) trapped within the coal. Coal with high volatile matter catches fire easily and burns with a long flame, but it may also produce more smoke.
- Ash Content: Ash is the non-combustible mineral residue left behind after coal is completely burned.
- Note on Indian Coal: A defining characteristic of Indian coal is its high ash content (often ranging from 20% to 30% or more) and low sulphur content. High ash content is a disadvantage because it reduces the heating value, increases transportation costs, and poses environmental challenges regarding ash disposal.
Coal in India – Geological Age, Characteristics, and Distribution
Geological Age | Age (Approx.) | Description | Location |
Gondwana | ~200 million years | – Major coal resources of India – Includes metallurgical coal used in industry – Formed by deep burial and compression of plant material over geological time | – Damodar Valley (West Bengal & Jharkhand) – Coalfields: Jharia, Raniganj, Bokaro – Other regions: Godavari, Mahanadi, Son, Wardha valleys |
Tertiary | ~55 million years | – Younger coal deposits – Limited in extent – Lower quality compared to Gondwana coal | – Found in northeastern states: Meghalaya, Assam, Arunachal Pradesh, Nagaland |
