Robust NMPC for a Benchmark Fed-Batch Reactor with Runaway Conditions

A nonlinear model predictive control (NMPC) formulation is used to prevent an exothermic fed-batch chemical reactor from thermal runaways even in the case of total cooling failure. Detailed modeling of the reaction kinetics and insight into the process dynamics led to the formulation of a suitable optimization problem with safety constraints which is then successively solved within the NMPC scheme. Although NMPC control-loops can exhibit a certain degree of inherent robustness, an explicit consideration of process uncertainties is preferable not only for safety reasons. This is approached by reformulating the open-loop optimization problem as a min-max problem. This corresponds to a worst-case approach and leads to even more cautious control moves of the NMPC in the presence of uncertain process parameters. All results are demonstrated in simulations for the esterification process of 2-butyl.