(357g) Cost Efficiency Vs. Energy Utilization: How the Techno-Economic Optimization of Green Ammonia Production Illustrates Novel Influences for an Electrified Chemical Industry

Decarbonization of the chemical industry through electrification with renewable energy will require the re-optimization of conventional chemical processes considering the novel constraints imposed by renewable energy. Of principal importance is the intermittency of solar and wind energy, which is contrary to the steady supply of fossil-fuels for the chemical industry today. Ammonia production is responsible for ~45% of emissions in primary chemicals production,¹ making its electrification to green ammonia production essential to decarbonizing the chemical industry. Further, the well-known Haber-Bosch process for producing ammonia is customarily operated at steady-state, thereby challenging it integration with intermittent solar and wind energy.² Therefore, the production of green ammonia using hydrogen generated by water electrolysis, nitrogen separated from air and power from solar/wind energy is a case study which exemplifies the novel constraints faced when electrifying chemical processes.

In this work, by optimizing the techno-economics of green ammonia production with a widespread range of solar and wind energy profiles across Europe, it is shown that intermittent energy reverses the conventional paradigm which pairs increased energy utilization with decreased cost. Chemical processes have for many years been optimized and integrated to maximize the utilization of energy at steady-state. However, daily/seasonal intermittency in renewable energy supply causes the wasting of energy (i.e. curtailment) to be optimal for economic green ammonia production – sometimes exceeding greater than 50% of energy curtailed. Unlike in the case of curtailed energy on the grid, this curtailment is primarily dictated by limitations in the storage capacity of the process rather than the power capacity, which produces unique cost drivers compared to an electrical grid. To facilitate this optimization, neural networks are trained and implemented, illustrating how AI can promote the incorporation of vast spatial-temporal data associated with renewable solar and wind energy.

To assess measures which simultaneously decrease curtailment and cost, this work further optimizes green ammonia production with a combination of solar and wind energy and adjusting (i.e. ramping) the production level of the Haber-Bosch process. While curtailment generally decreases with both process modification, it is unable to completely remove seasonal energy intermittency in all but the ideal locations. Further, when considering energy intermittency at the time-scale of multiple years rather than seasonal intermittency, it is shown that the optimal curtailment and capacity deviates significantly from that predicted from seasonal intermittency due to the unique cost drivers for optimizing constant chemical production with intermittent energy supply. Therefore, this work demonstrates the novel influences which emerge at the process and system level when electrifying a steady-state chemical process with dynamic solar and wind energy.

1. Sanchez, D.P., Collina, L., and Voswinkel, F. (2023). Chemicals. https://www.iea.org/energy-system/industry/chemicals.
2. Smith, C., and Torrente-Murciano, L. (2024). The importance of dynamic operation and renewable energy source on the economic feasibility of green ammonia. Joule 8. 10.1016/j.joule.2023.12.002.