Fuels – Coal Rank vs. Calorific Value Among the listed types of coal, anthracite has the highest calorific value (highest fixed carbon and lowest volatile matter).

Introduction / Context:
Coal is categorized by rank based on fixed carbon, volatile matter, moisture, and mineral content. Calorific value typically increases with rank. Recognizing which coal yields more energy per unit mass is important for combustion system design and fuel selection.

Given Data / Assumptions:

• Standard coal ranks: peat, lignite, sub-bituminous, bituminous, anthracite.
• Higher fixed carbon and lower moisture/volatiles raise heating value.
• Comparison at similar reference conditions (as-received may vary).

Concept / Approach:

Anthracite, the highest rank coal, has the greatest fixed carbon content and the least volatile matter, leading to the highest gross calorific value among common coals. Peat and lignite are low-rank with high moisture and low heating value; bituminous is intermediate.

Step-by-Step Solution:

Verification / Alternative check:

Typical higher heating values: lignite ~10–20 MJ/kg, bituminous ~24–35 MJ/kg, anthracite ~30–35+ MJ/kg, with lower moisture making anthracite most energy-dense.

Why Other Options Are Wrong:

Peat/lignite are moisture-rich and energy-poor; bituminous is lower than anthracite; sub-bituminous is intermediate, not maximal.

Common Pitfalls:

Confusing “best flame stability” or “ease of ignition” with highest calorific value; considering as-received vs. dry basis inconsistently.

Final Answer:

Anthracite coal