CO2removal by absorption: challenges in modelling

The traditional method for large-scale CO2 removal is by absorption in a mixture of an amine and water. The tasks of modelling this process can be divided into descriptions of absorption and reaction kinetics, gas/liquid equilibrium, gas and liquid flows and pressure drop. Process simulation tools containing models for most of these tasks are commercially available, and the calculated results can be used as a basis for equipment dimensioning and economical optimization. A flowsheet calculation in the program Aspen HYSYS® is used as an example. Calculation convergence is important, especially the column convergence is critical. For some simplified conditions, calculation of stage efficiencies can give a satisfactory description of the absorption process. Computational fluid dynamics is an efficient tool for calculating flow conditions, pressure drop and temperature profiles, especially for one-fluid phase. An unsolved problem when using computational fluid dynamics for gas/liquid processes is the description of the gas/liquid interfacial area. A major challenge is to combine different models and calculation tools. An improved model for a specific task must be available and possible to combine with other calculation tools to be utilized by other programs. In an example, models for equilibrium and mass transfer efficiency are used in a flowsheet calculation including CO2 absorption and desorption, followed by economical optimization. The example illustrates some possibilities, limitations and challenges.