Dynamic Simulation and Optimization for Load Regulation Strategies of the Green Ammonia Synthesis Process

The green ammonia synthesis process driven by renewable electricity represents a highly regarded decarbonization pathway. Due to the inherent randomness, volatility, and intermittency of renewable energy sources, such as wind and solar power, the green power load fluctuates accordingly. Considering that large-scale storage of hydrogen and electricity could introduce economic and technical difficulties, a small-scale hydrogen storage system combined with dynamic load regulation of the ammonia synthesis unit is commonly adopted to accommodate these fluctuations. This green ammonia process results in more frequent transition state operations, such as load regulation scenarios, compared with traditional ammonia plants. Optimizing load regulation strategies can effectively reduce the transition time and enhance economic benefits. This work employs a rigorous dynamic simulation to examine potential infeasibilities and operational risks associated with various load regulation scenarios. The model's reliability is validated using industrial data. Based on this dynamic model, a two-step optimization approach is proposed to improve transition strategies. First, process optimization, considering process topology and control scheme modifications, is conducted to enhance the process stability and operability. Subsequently, operation optimization is performed to minimize the duration of operations based on the optimized process, enabling the system to swiftly reach a steady state and produce high-quality products. A case study of a realistically designed green ammonia synthesis process demonstrates the significant operational and economic benefits of the proposed methodology. Results indicate that energy costs, waste of the feed gas composed of carbon-free hydrogen and nitrogen, and hydrogen storage can be substantially reduced, while transition time is shortened by 27–30% using optimized load regulation strategies compared to the industrial standard strategies.