Thermodynamic and kinetic analysis of autothermal syngas-generating limestone calcination process for ammonia synthesis

A novel autothermal methane-reforming limestone-calcination process is analyzed through thermodynamic and kinetic investigations to yield syngas for direct ammonia production. A comprehensive correlation is developed to determine the required gaseous feed concentrations for near-autothermal reactor operation under varying conditions of temperature, pressure, and nitrogen/oxygen compositions. The study establishes critical operating boundaries to achieve complete limestone calcination while preventing coke formation. The process performance, evaluated through the syngas yield and quality metrics (H₂/CO and H₂/N₂ ratio), demonstrates that the optimal MRC calciner off-gas with a H₂/N₂ ratio of 3 can be produced at moderate CaCO₃/CH₄ molar feed ratio (0.2–0.3) with air oxygen concentrations around 40 vol%. Kinetic analysis in turbulent fluidized bed reactors reveals that appreciable sorbent calcination (>60 %) can be achieved at industrially relevant conditions (pressures up to 25 bar, temperatures below 900 °C), with enhanced performance at elevated temperatures and reduced pressures. The process generates syngas primarily composed of H₂, CO, and N₂ at tunable compositions, suitable for ammonia synthesis after the reverse water gas shift reaction without requiring cryogenic air separation.