Ammonia (NH₃) synthesis gas from natural gas — Which primary process step generates the H₂-rich make-up gas fed to the Haber–Bosch loop?

Introduction:
Ammonia manufacture requires a hydrogen-rich synthesis gas combined with nitrogen at about 3:1 molar ratio. For natural-gas–based plants, the front-end process determines efficiency, CO₂ capture load, and impurity control.

Given Data / Assumptions:

• Feedstock: natural gas (primarily methane).
• Target: H₂ + N₂ mixture for Haber–Bosch loop.
• Standard industrial practice considered.

Concept / Approach:
Steam reforming converts methane with steam to synthesis gas: CH4 + H2O ⇌ CO + 3H2 (endothermic). A water–gas shift then increases H₂: CO + H2O ⇌ CO2 + H2. CO₂ is removed, and residual CO/CO₂ are further decreased (e.g., methanation) before compression and mixing with N₂ (from air separation or secondary reformer). Partial oxidation is used in heavy-oil routes or as an autothermal variant, but classical natural-gas plants rely on steam reforming as the primary step.

Step-by-Step Solution:
Identify NG front-end → primary steam reformer.Apply shift conversion to raise H₂ and convert CO to CO₂.Remove CO₂ and polish impurities; send H₂ to synthesis loop with N₂.

Verification / Alternative check:
Block flow diagrams of ammonia plants universally show primary steam reforming followed by shift, CO₂ removal, and methanation when natural gas is the feed.

Why Other Options Are Wrong:

• Thermal cracking yields unsaturated hydrocarbons/soot and insufficient H₂.
• Partial oxidation alone is not typical for NG (autothermal combines both but still includes reforming chemistry).
• Hydrogenation of CO₂ produces methane, not NH₃ syngas.
• Electrolysis is unrelated to NG reforming route.

Common Pitfalls:
Confusing autothermal reforming with pure POX; assuming the nitrogen source is from the front-end rather than air addition later.

Final Answer:
Steam reforming of natural gas (followed by shift and purification)