Fossil Fuels: Coal

Definition

Coal is a combustible, sedimentary organic rock primarily composed of carbon, along with varying quantities of other elements—chiefly hydrogen, sulfur, oxygen, and nitrogen. It is classified as a non-renewable fossil fuel because it is formed from the remains of ancient vegetation over millions of years through geological processes.

Main Content

1. Geological Formation (Coalification)

• Coal originates from plant matter that accumulated in ancient swampy environments millions of years ago.
• Through a process known as coalification, layers of organic material are buried under sediment, where intense heat and pressure transform peat into higher-grade coal over geological epochs.

2. Classification by Rank

• Coal is categorized into ranks based on its carbon content and energy density: Lignite (lowest rank), Sub-bituminous, Bituminous, and Anthracite (highest rank).
• The "rank" of coal indicates the degree of transformation the plant material has undergone; higher ranks possess more energy and release fewer impurities when burned.

3. Coal as an Energy Source

• Coal acts as a chemical storage medium for solar energy that was captured by plants via photosynthesis millions of years ago.
• It is a primary feedstock for global electricity generation, providing a reliable, "baseload" power supply that does not fluctuate like weather-dependent renewables.

Working / Process

1. Extraction (Mining)

• Surface mining (strip mining) is used when coal seams are close to the surface, involving the removal of overlying soil and rock.
• Underground mining is employed for deeper deposits, where shafts or tunnels are drilled to reach the coal seams.

2. Combustion

• In a coal-fired power plant, coal is pulverized into a fine powder and burned in a boiler to create extreme heat.
• This heat converts water into high-pressure steam, which is directed toward a turbine.

3. Power Generation

• The high-pressure steam turns the blades of a turbine, which is connected to a generator that converts mechanical energy into electricity.
• The following diagram illustrates the basic cycle of a coal power plant:

[Coal] -> [Boiler] -> [Steam] -> [Turbine] -> [Generator] -> [Electricity]
             ^          |           |
             |__________|___________|
                    (Water Cycle)

Advantages / Applications

• Reliability: Coal provides a steady, consistent supply of electricity, essential for supporting the industrial electrical grid 24/7.
• Affordability: Coal is generally inexpensive to mine and transport compared to other energy sources, keeping energy costs stable in many regions.
• Versatility: Beyond electricity, coal is a vital raw material in the steel and cement industries, where it is used to produce coke for blast furnaces.

Summary

Coal is a dense, energy-rich fossil fuel formed from ancient organic matter that serves as a cornerstone of industrial energy production. While it provides critical baseload power and raw materials for manufacturing, its use is associated with significant environmental impacts due to carbon dioxide emissions and mining disruption.

Important terms to remember: Coalification, Carbon density, Rank, Pulverization, and Baseload power.