Development of Model and Model-Predictive Control of an MEA-Based Postcombustion CO₂ Capture Process

This work focuses on the development of a dynamic model for an MEA-based CO 2 capture process for a 550 MWe postcombustion, supercritical, pulverized coal (PC) plant. The dynamic model also provides the design of controllers for both traditional proportional-integral-derivative (PID) and advanced linear model predictive control (LMPC), using Aspen Plus and Aspen Plus Dynamics. To represent accurately the dynamics of the rigorous rate-based calculations provided in the steady-state simulator, the equilibrium dynamic model was exported from an optimized rate-based, steady-state model. Subsequently, modifications to the Murphree efficiencies in the columns and a rigorous pressure drop calculation method were implemented in the dynamic model to ensure consistency between the design and off-design results from the steady-state and dynamic models. The results from the steady-state model indicate that between three and six parallel trains of CO 2 capture processes are required to capture 90% CO 2 from a 550 MWe supercritical PC plant depending on the maximum column diameter used and the approach to flooding under the design condition. However, in this work, only two parallel trains of CO 2 capture process are modeled and integrated with a 550 MWe postcombustion, supercritical PC plant in the dynamic simulation because of the high calculation expense of simulating more than two trains. In the control studies, the performance of the PID- and LMPC-based approaches are evaluated for maintaining the overall CO 2 capture rate at the desired level in the face of typical disturbances in flue gas flow rate and composition as well as change in the power loadings and variable CO 2 capture rate. Scenarios considered include cases when different parallel trains have different efficiencies to mimic conditions in real industrial processes. In all cases, the LMPC-based approach gave superior results compared to those of the PID-based one. Different flooding control strategies for the situation when the flue gas flow rate increases are also covered in this work.