Robust model-based control of a packed absorption column for the natural gas sweetening process

The sweetening units are the most important in natural gas processing. Packed bed absorption columns are widely used in the sweetening process; however, their operation and control are not simple due to their highly non-linear behavior derived from their distributed nature and interaction between multiple physical phenomena. In this work, two robust model-based control schemes are implemented to regulate the CO2 concentration at the outlet of a packed bed absorption column in the gas sweetening process. The model of an industrial-scale absorption column and the structure of the controllers, i) control based on modeling error compensation (MEC) ideas, and ii) nonlinear model predictive control (NMPC) are described. Numerical results show that the proposed robust model-based controllers can regulate the controlled variable to the desired reference despite external disturbances, set-point changes, and uncertainties in the absorption column model.