Figure shows the system boundary of this study. An ammonia production plant consists of hydrogen and nitrogen production and an ammonia synthesis loop. We focused on the ammonia synthesis loop because the purpose was to evaluate the impact of the mild reaction condition achieved by Ru/Ca(NH2)2 and Ru/Pr2O3 on the ammonia synthesis loop. In addition, the loops with the commercialized iron-based catalysts, KM1R (Fe), and conventional Ru-based catalyst, Ru/C, were also investigated as a comparison. Although the cost of the hydrogen and nitrogen production process is inevitable, it does not change the conclusion of the comparison among all plants because the amount of hydrogen and nitrogen gas is the same. Therefore, the cost calculation for the ammonia synthesis loop is sufficient for the comparison (Figure ). Cryogenic air separation is suitable for preparing nitrogen gas because of the high purity of nitrogen, since the catalysts for ammonia synthesis are readily poisoned by H2O and O2. Pressure swing adsorption is not suitable because it cannot achieve high purity for the ammonia synthesis, although it seems preferable for small-scale production. We assumed to utilize the cold heat of O2 and N2 in the cryogenic air separation to cool down ammonia for the separation. Aspen Plus © was employed to simulate the whole processes of the ammonia synthesis loop. The loop was based on the template of the ammonia synthesis plant in Aspen Plus © with some modifications (Fig. ). The properties of gas and liquid were from the database in Aspen Plus © . The loop scales were 5-1000 tonnes/day. The inlet gas is the stoichiometric ratio of ammonia, H2/N2 = 3.