Energy integration and techno-economic performance of coal to ammonia system coupled with green hydrogen

There is an urgent need for energy conservation and carbon reduction in coal-to-ammonia production, while the stable and economical operation of electricity-to-ammonia production remains constrained by the volatility of renewable energy sources. Therefore, constructing a synthetic ammonia system based on the coupling of coal-to‑hydrogen and green hydrogen production is considered an ideal low-carbon transition path for ammonia production that balances environmental benefits and operational stability. A multi-objective optimization algorithm is employed to optimize the waste heat recovery unit of the coal-to-ammonia system. By comprehensively balancing the system techno-economic performance, the optimal design conditions for coal-to-ammonia coupled with green hydrogen are determined, and the impact of different green hydrogen coupling ratios on system energy integration and techno-economic performance are investigated. The results indicate that the heat demand of amine-based acid gas removal unit is the dominant factor limiting the energy integration, while coupling green hydrogen can effectively reduce its energy consumption. When the green hydrogen coupling ratio increases from 0% to 70%, the system energy efficiency improves from 50% to 52.7%, while reducing carbon emissions from 3.2 kgCO₂/kgNH₃ to 1 kgCO₂/kgNH₃. And when the green‑hydrogen coupling ratio reaches 34.6%, the required capacity of the air separation unit is minimized, and the by-product shifts from nitrogen to oxygen. Due to the lack of by-product revenue, the ammonia production cost is the highest under this operating condition. The effects of electricity price, carbon tax, AWE investment cost, and byproduct revenue on the feasible green hydrogen coupling ratio range are evaluated based on a 10-year payback threshold.