Natural gas composition — Which constituent contributes the most to the heating value of typical natural gas?

Introduction:
Natural gas is a valuable fuel whose calorific value is mainly determined by its combustible hydrocarbons. Identifying the key contributor is essential for combustion calculations and gas quality control.

Given Data / Assumptions:

• Typical pipeline natural gas composition is predominantly methane, with smaller amounts of ethane, propane, butanes, CO₂, N₂, and traces of others.
• Heating value arises from combustibles; inerts lower the value.

Concept / Approach:
Methane typically comprises 80–95% of natural gas on a volume basis and has a high heat of combustion. Therefore, even though heavier hydrocarbons have higher heats per mole, methane’s dominant mole fraction makes it the principal contributor to overall calorific value.

Step-by-Step Solution:
Identify major component: CH₄ is the bulk of natural gas.Note that CO₂ and N₂ are inerts (no calorific contribution).CO and H₂ may be present in trace amounts; their contributions are minor in natural gas.Conclude CH₄ is the primary source of heating value.

Verification / Alternative check:
Gas quality specifications and tariff billing (therms) closely track methane number and its mole fraction, underscoring methane’s role.

Why Other Options Are Wrong:

• CO₂ and N₂: inerts, reduce CV.
• CO and H₂: limited presence in natural gas streams; overall impact is small compared to methane.

Common Pitfalls:
Overemphasising heavier hydrocarbons due to higher per-mole heats while ignoring their lower fractions.

Final Answer:
Methane (CH₄)