What It Is
Coal gasification is an alternative method of producing hydrogen for ammonia synthesis. Instead of using natural gas (as in Steam Methane Reforming), coal is converted into a synthesis gas (“syngas”) of hydrogen, carbon monoxide, and carbon dioxide. This hydrogen then feeds into the Haber–Bosch process to produce ammonia.
Coal gasification is used extensively in China, where natural gas is scarce but coal reserves are abundant.
How It Works
The process involves reacting coal with oxygen and steam at high temperatures under controlled conditions:
- Gasification Reaction
- C + H₂O + O₂ → CO + H₂ (+ CO₂)
- Water-Gas Shift Reaction
- CO + H₂O → CO₂ + H₂
The result is a mixture of hydrogen and carbon monoxide, with CO₂ separated out. The hydrogen stream is then purified and used to synthesize ammonia via Haber–Bosch.
Where It Happens
- China: The world leader in coal-based ammonia, accounting for more than half of its nitrogen fertilizer output.
- South Africa: Uses coal-to-chemicals processes on a smaller scale.
- Historically tested in other coal-rich nations but largely phased out elsewhere due to cost and emissions.
Environmental Considerations
Coal gasification is even more carbon-intensive than SMR:
- Produces roughly 2–3 times more CO₂ per tonne of ammonia compared with natural gas-based routes.
- Generates solid waste (slag, ash) in addition to air emissions.
- Highly water-intensive.
This makes coal-based ammonia one of the most environmentally damaging fertilizer production methods.
Why It Matters
Coal gasification allows China to maintain fertilizer self-sufficiency without relying on imported natural gas. It ties fertilizer prices in China more closely to coal markets than gas markets, creating a unique dynamic compared to the rest of the world.
However, this reliance also means Chinese fertilizer production has a much higher carbon footprint — a key concern in global decarbonisation debates.
Outlook
- Short term: China will continue to rely on coal gasification due to resource availability.
- Medium term: Pressure is mounting domestically and internationally to cut emissions.
- Long term: Transition toward green ammonia via electrolysis is expected, but cost remains a barrier.
Coal gasification highlights the trade-off between energy independence and environmental cost. As the world pushes toward low-carbon solutions, coal-based ammonia will be increasingly scrutinised and phased out — but for now, it remains a pillar of Chinese fertilizer production.
