A robust nonlinear model predictive controller for a post-combustion CO2 capture absorber unit

Abstract

This study presents the design of a robust nonlinear model predictive controller (NMPC) for the absorber unit of a post-combustion CO2 capture process operating downstream from a coal-fired power plant. The controller employs a dynamic mechanistic model for this process, which allows for a precise treatment of the sources of uncertainty. In the case of the absorber, the model enables explicit consideration of uncertainty in the process operating conditions dictated by upstream units and in physical property parameters associated with phenomenological descriptions of the process. Using the multi-scenario approach, discrete realizations of the uncertain parameters inside a given uncertainty region can be incorporated into the controller to produce control actions that result in a robust operation in closed-loop. The multi-scenario controller was tested under several disturbance rejection scenarios of varying complexity and their performance was assessed against that of single-scenario NMPCs. The benefits of the robust NMPC approach were most evident for longer simulations and, considering the continuous nature of a power plant and its emissions, make the robust NMPC approach suitable for the operation of this process in the presence of uncertainty and disturbances.