Reaction kinetics of Ru/Ca(NH2)2 and Ru/Pr2O3, were modeled by the lab-scale experimental data in the temperature and pressure ranges shown in Table . For pressure, we extrapolated the model based on the available data at low pressure to reproduce the reaction performance at 50 bar since the catalysts are expected to be used at 50 bar in practical. The operation temperature in the reactor needs to be elevated to accelerate the reaction, although ammonia synthesis is an exothermic reaction. It means that as the reaction proceeds, the temperature increases to be close to the equilibrium, and the reactivity slows down. Therefore, the reactor needs to cool down when the temperature is too high. The plant generally employs a multi-bed reactor and removes the heat in the outlet of each reactor. The difference between inlet and outlet (ΔT) was kept less than 90 K for safety. In this study, three beds system was applied because the three-bed reactor system was found to be the most efficient in terms of NH3 production, energy savings, capital, and maintenance cost. The three-bed reactor system consisted of three reactors and two heat exchangers (Fig. ). In the case that the ammonia concentration is close to equilibrium, the reaction rate slowdowns and redundantly increases the reactor volume, resulting in high cost. Hence, the general way to determine the volume was employed, which stops the reaction when the product concentration reaches 90% of the equilibrium under adiabatic conditions. The reaction was stopped when the ΔT increased to = 90 K, or the ammonia concentration in a reactor reached 90% of the equilibrium, determining the reactor's volume. The reaction temperature ranges for each catalyst were determined by the optimization to obtain the lowest cost with the above criteria and available experimental data from literature.