Integrating economic, environmental, and social sustainability in Power-to-Ammonia plants: A multi-objective optimization methodology

Consistent with actual decarbonization efforts in the ammonia industry, this work addresses the process design of Power-to-Ammonia plants (i.e. industrial facilities producing “green” ammonia starting from renewable energy via water electrolysis) by introducing an innovative methodology based on the multi-objective optimization of the “three pillars of sustainability”: economic, environmental, and social. Specifically, the proposed criterion performs a brute-force but exhaustive search evaluating the sizes and operating schedules of key process sections characterizing Power-to-Ammonia facilities (e.g., the renewable power plant, the electrolyzer, electricity and hydrogen storage systems, etc.) to harmonize the three pillars (which are most often conflicting) as much as possible and identify the process configuration achieving the maximum attainable global sustainability. Indeed, thanks to the scalarization technique, the proposed methodology combines the three different objective functions into a global one by an appropriate set of user-assigned weights reflecting the relative importance among the pillars. For instance, proposing 60 %, 30 %, and 10 % weights to the economic (ECO), environmental (ENV), and social (SOC) pillars, respectively, leads to a Power-to-Ammonia plant achieving a Global Sustainability Score equal to 93 % (ECO: Ammonia production costs = 750.40 USD/tNH3; ENV: Global Warming Potential = 0.76 tCO2eq/tNH3; SOC: Fire and Explosion Index = 141.48). Valuable insights into the conceptual design of chemical processes integrating renewable energy and the associated sustainability assessment criteria are provided, and further industrial application opportunities are discussed.