On the optimal design of load flexible fixed bed reactors: Integration of dynamics into the design problem

The design of dynamically operated fixed bed reactors is a challenging task, especially for highly exothermic reactions. Fluctuations of process conditions such as inlet flow rate and composition can cause losses in product quality, wrong-way behavior or even a thermal runaway which damages reactor and catalyst. We present a methodology for the model-based design of dynamically operated, load flexible fixed bed reactors. Critical reactor dynamics are already considered during the reactor design and are integrated into the optimization problem. Instead of a steady state problem, the reactor is optimized for a worst case dynamic scenario. The optimization approach yields a design which allows for safe transitions from any flow rate to another within a predefined load range. The approach is introduced using the methanation of carbon dioxide as an important case study of high relevance for both research and society within the context of chemical energy storage of fluctuating renewable energy. A feasibility test demonstrates the safe reactor operation for a time horizon which includes a series of step-changes of the inlet flow rate as an approximation of a fluctuating hydrogen supply.