Question

Which of the following fuels has the lowest calorific value?

• A. Bituminous coal
• B. Coke oven gas
• C. Lignite
• D. Pulverized coal

Hint:

Remember the "Coal Ladder": Peat $\rightarrow$ Lignite $\rightarrow$ Bituminous $\rightarrow$ Anthracite. Energy value increases as you go up the ladder. Lignite is near the bottom, so it has a low CV.

Answer 1

The Correct Option is C

Concept: The Calorific Value (CV) of a fuel is the total quantity of heat liberated by the complete combustion of a unit unit mass or volume of the fuel. For solid fuels like coal, the calorific value depends heavily on the carbon content and the stage of coalification.

Step 1: Analyze the ranking of coal types.
Coal forms over millions of years through a process called coalification. As the process progresses, the carbon content increases and the moisture/volatile content decreases, leading to higher calorific values:
• Peat: Lowest carbon content, highest moisture.
• Lignite (Brown Coal): Next stage, still has high moisture and low carbon (approx. 25-35%).
• Sub-bituminous Bituminous: Higher carbon content and energy density.
• Anthracite: Highest carbon content and highest calorific value.

Step 2: Evaluate the options.

• Bituminous coal: A high-rank coal with significant energy density.
• Coke oven gas: A gaseous fuel which typically has a much higher calorific value per unit mass than solid coal.
• Lignite: A low-rank coal with the highest moisture content among the solid options, resulting in the lowest calorific value.
• Pulverized coal: This is just finely ground coal (usually bituminous), so its CV is similar to the source coal.