Towards technology, economy, energy and environment oriented simultaneous optimization of ammonia production process: Further analysis of green process.

Ammonia is one of the most produced chemicals around the world due to its various uses. However its traditional production process is associated with high fossil fuel consumption. To avoid this, the production of green ammonia can be done, and one of the considered production methods is water electrolysis, where the hydrogen needed for the manufacturing of ammonia is produced using solar energy. In this work, multi-objective optimization (MOO) is carried out for two ammonia synthesis processes with water electrolysis. One process uses solar energy to generate electricity for the whole process (Green ammonia), while the other uses natural gas for the same purpose (non-green ammonia) on a small production scale. The process is simulated using ProMax 5.0 and MOO is done using Excel-based MOO with I-MODE algorithm. Several MOO cases are solved with different objectives like CO emissions and energy (ENG) minimization, and Profit and Purity maximization in two and three objective cases. To conduct the work, several decision variables are selected like the operating temperatures and pressures of different streams in addition to the flow rate of nitrogen and water. Some constraints regarding the purity and reactors temperature are considered as well. The obtained results showed that the profit of green ammonia process (ranges between 0.7 and 80 M$/yr) is lower compared to the non-green process (ranges between 0.8 and 4.4 M$/yr). On the other hand, huge CO emissions (up to 38000 tons/yr) are produced in the non-green process compared to almost zero emissions with the green process. In most cases, water and nitrogen flow rates showed a high influence on the results and caused conflict between the objectives.