Studying the effect of dynamic operation conditions on green ammonia production synthesis loop

The global challenges meeting hydrogen demands due to limited renewable resources urge the need for low-cost imports. Green ammonia, promising for its existing infrastructure, encounters inflexibility challenges in large-scale production with renewables. This study delves into ammonia synthesis loop flexibility amid renewable intermittencies. Utilizing an Aspen Plus® model of 1223 tonnes per day ammonia production capacity, the transient behavior under varied feed flow was investigated with Aspen Dynamics™ simulations. The findings indicated that effective strategies enabled managing a minimum load of 10 % or lower under stoichiometric conditions, constrained by the electrolysis system's lower load. The study also concluded that the ammonia synthesis unit's 20 %/hr feed flow ramp rate is restricted by the thermal cycling of the reactor catalyst; the consequences of fast ramp-up and ramp-down of the operational parameters such as feed flow or stoichiometric ratio are the primary limits in green ammonia production or dynamic operation of the plant. • Comprehensive Ammonia Synthesis Model : Developed a detailed ammonia synthesis model, including a catalyst model, based on a steady-state framework to investigate unit flexibility • Dynamic Simulations for Enlightening Flexibility Analysis : Transformed the steady-state model into dynamic flow-driven models using Aspen Dynamics™ to analyze transient behavior • Data Validation : Validated steady-state model data against academic literature and industrial sources before conducting dynamic simulations. • Dynamic Feed Simulation : Employed Aspen Dynamics™ simulations to evaluate the effects of dynamic feed conditions on process stability and operational flexibility. • Minimum Load Factor (turn-down ratio) : Demonstrated that the ammonia synthesis unit could achieve a minimum load factor of 12 % while maintaining stability and efficiency. • Practical Implications of Ramp Rate Constraints : Identified that the heating and cooling rates of the catalyst bed limited the maximum ramp rate of 20 % per hour. • Challenges with Purging and H 2 Ratio : We found that adjusting the H2 feed ratio and purging was impractical due to low inert content and the risk of hydrogen loss.