(682a) Sustainable Ammonia Production through Process Synthesis and Optimization

Increasing the share of renewables is an important step in shifting toward a sustainable energy production and supply chain and reducing mankind’s dependency on fossil fuels. While a transition to fully renewable energy production looks possible in the future, the intermittent and distributed nature of the renewable energy resources make the conversion and storage of renewables into useful and transportable energy vectors is a necessity and hence an outstanding challenge [1].While hydrogen is a promising energy vector to store renewables due to its high gravimetric energy storage density (33 kWh/kg), its low volumetric storage density (3 Wh/L under ambient conditions) makes both storage and transportation problematic [2]. Ammonia is a promising vector due to its proven production and transportation infrastructure.It has a high capacity for hydrogen storage, 17.6 wt.% based on its molecular structure and a hydrogen volume density of 105.0 kg/m³, which is about 45 % higher than that of liquid hydrogen, which is reported as 71.2 kg/m³[3].

Renewable resources are geographically distributed and an optimal solution at a location might not be feasible let alone optimal for another location. The distributed nature of the resources necessitates the concept of decentralized energy production. With this work, we want to contribute a study on the production of ammonia from various renewable sources, such as municipal solid waste, biomass, solar energy, and wind energy. In order to determine the economic and technical feasibility of novel ammonia production methods, a global optimization-based process synthesis approach is used to determine the optimal process topologies while minimizing the annualized cost of ammonia production. A superstructure of process alternatives is modelled as a large-scale mixed-integer nonlinear optimization (MINLP) model, with simultaneous heat, power, and water integration. The nonconvex MINLP model is solved to global optimality by using a branch-and-bound global optimization algorithm. Several case studies will be examined to investigate the types of available renewable resource and production scale on topological decisions.

1. WW Tso, CD Demirhan, JB Powell, EN Pistikopoulos, 2018, Toward Optimal Synthesis of Renewable Ammonia and Methanol Processes (RAMP), Proceedings of Process Systems Engineering, PSE 2018, Accepted for Publication.
2. D Teichmann, W Arlt, P Wasserscheid, 2012, Liquid Organic Hydrogen Carriers as an efficient vector for the transport and storage of renewable energy, Int. J. Hydrogen Energy 37, 18118- 18132.
3. G Thomas, G Parks, 2006, Potential Roles of Ammonia in a Hydrogen Economy, DOE.