An Innovative Process Design for Ammonia Synthesis Based on Self-Heat Recuperation Technology

Ammonia is not only an important chemical raw material in industry, but also a potential energy carrier for on-board vehicular hydrogen storage. The modern ammonia synthesis process is mainly based on Haber-Bosch process, which involves the reaction of gaseous nitrogen with hydrogen on Fe-based catalysts at high temperature and high pressures. Due to the thermodynamically limited low conversion rate (usually 10%–20%) of hydrogen-nitrogen mixture to ammonia, ammonia synthesis plants are commonly implemented as recycle process, in which the unreacted reactants are separated and recycled.

    The energy requirement of ammonia synthesis process strongly depends on the loop design of ammonia synthesis. As the conversion rate is just 10 to 20%, to produce 1 kg ammonia, 4- 6 kg nitrogen and hydrogen gas is usually recycled in the process. Thus, a large amount of energy is required for the ammonia synthesis compressor and refrigeration cycle compressor, even in the modern heat-integrated processes. Therefore, to reduce the energy consumption of ammonia synthesis is desirable.

    In this study, we investigated the feasibility of applying self-heat recuperation technology to the ammonia synthesis process, and proposed a novel ammonia synthesis process from an energy saving viewpoint. Both thermal and cold energy were circulated in the process, largely reduced the exergy destruction. The conventional and proposed ammonia synthesis processes were simulated with a commercial software, PRO II 9.2. The  results showed that the energy requirement for the proposed ammonia synthesis process was reduced by around 50% against the conventional process.