Robust economic MPC of the absorption column in post-combustion carbon capture through zone tracking

TL;DR

This paper introduces a robust economic Model Predictive Control method with zone tracking for absorption columns in post-combustion CO2 capture, effectively managing uncertainties and operational constraints to improve efficiency.

Contribution

It develops a multi-objective EMPC with zone tracking using ellipsoidal invariant sets and back-off strategies for large-scale absorption columns.

Findings

Effective zone tracking under uncertainties demonstrated in simulations

Prevents solvent overcirculation and flooding

Applicable to large-scale systems

Abstract

Several studies have reported the importance of optimally operating the absorption column in a post-combustion CO2 capture (PCC) plant. It has been demonstrated in our previous work how economic Model Predictive Control (EMPC) has a great potential to improve the operation of the PCC plant. However, the use of a general economic objective such as maximizing the absorption efficiency of the column can cause EMPC to drive the state of the system close to the constraints. This may often than not lead to solvent overcirculation and flooding which are undesirable. In this work, we present an EMPC with zone tracking algorithm as an effective means to address this problem. The proposed control algorithm incorporates a zone tracking objective and an economic objective to form a multi-objective optimal control problem. To ensure that the zone tracking objective is achieved in the presence of model uncertainties and time-varying flue gas flow rate, we propose a method to modify the original target zone with a control invariant set. The zone modification method combines both ellipsoidal control invariant set techniques and a back-off strategy. The use of ellipsoidal control invariant sets ensure that the method is applicable to large scale systems such as the absorption column. We present several simulation case studies that demonstrate the effectiveness and applicability of the proposed control algorithm to the absorption column in a post-combustion CO2 capture plant.