Fuel gas composition: Coke-oven gas produced during coal carbonisation consists mainly of which constituents?

Introduction / Context:
Coke-oven gas (COG) is a valuable by-product of high-temperature coal carbonisation in coke plants. Its composition determines calorific value, safety considerations, and treatment steps (e.g., tar, ammonia, benzol recovery, and gas cleaning for use as fuel or feedstock).

Given Data / Assumptions:

• High-temperature by-product coke ovens (about 900–1100°C).
• Typical plant-average gas after initial tar/condensate removal.
• We seek the principal constituents by volume.

Concept / Approach:
COG is characteristically rich in hydrogen and methane with smaller fractions of carbon monoxide, carbon dioxide, nitrogen, and light hydrocarbons. Thus the pair that best represents the dominant components is hydrogen (H2) and methane (CH4).

Step-by-Step Solution:
Identify major species in COG → H2 (often 50–60% v/v) and CH4 (~25–30% v/v).Minor components include CO, CO2, N2, and C2–C6 hydrocarbons.Therefore, the principal pair is H2 and CH4.

Verification / Alternative check:
Standard coke-plant references list H2 and CH4 as the two largest fractions, aligning with the selected option.

Why Other Options Are Wrong:
CO and CO2 are present but not dominant; H2 and CO together omit methane, a key constituent; CH4 and CO omit the dominant hydrogen fraction.

Common Pitfalls:

• Confusing COG with blast-furnace or basic oxygen furnace gases, which are CO-rich and H2-poor.
• Using site-specific numbers as universal; ranges vary but qualitative dominance persists.

Final Answer:
H2 and CH4