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.