Simulation of CO2 Capture by MEA Scrubbing with a Rate-Based Model

Abstract

The most commonly used process for CO2 capture is absorption by means of chemical solvents, such as alkanolamines. This consolidated technology can be applied to CO2 removal from exhaust gas of power plants, natural gas and refinery gas. This paper focuses on CO2 capture from exhaust gas by absorption with monoethanolamine (MEA). Thermodynamics, kinetics and mass transfer influence the chemical absorption process. Acidic gases and amines are weak electrolytes, which partially dissociate in the aqueous phase: the high non-ideality of the liquid phase must be properly taken into account when dealing with vapor-liquid equilibrium (VLE). Kinetics and mass transfer can be described using two different approaches: the “equilibrium-based stage efficiency” model or the “rate-based” one. The “equilibrium-based stage efficiency” approach corrects the performance of a theoretical stage by a factor called “stage efficiency”. The “rate-based” model analyzes the mass and heat transfer phenomena that occur on a real tray or actual packing height. In ASPEN Plus®, that has been chosen as framework for the model proposed in this work, the prediction of mass transfer coefficients is based on the film theory by Lewis and Whitman, while other theories can more conveniently be used, i.e. the Eddy Diffusivity theory. Experimental data of a pilot plant for the purification of exhaust gas from power plant have been used to validate the model.The obtained results show an improvement in the representation of the absorption phenomenon.