Modeling and simulation of packed-bed absorbers for post-combustion capture of carbon dioxide by reactive absorption in aqueous monoethanolamine solutions

Abstract

Capture of carbon dioxide (CO2) from flue gases by reactive absorption in aqueous monoethanolamine (MEA) solutions can be regarded as a mature base-line technology for mitigation of greenhouse gas emissions at fossil fuel-fired power plants. Reliable modeling and simulation of the required packed-bed absorber is important for the design, scale-up, control, and optimization of post-combustion CO2 capture processes. Three types of rate-based models have been used for the simulation of CO2 packed-bed absorbers: the continuous differential contactor model, the nonequilibrium stage model, and the continuous film reaction model. This paper begins with a comparative review of previous works in which these rate-based models have been used for the simulation of the reactive absorption of CO2 in aqueous MEA solutions. The continuous differential absorber model (proposed by Pandya in 1983) stands out as the kind of rate-based model more often used in previous works. However, in order to obtain a consistent formulation of the differential equations that describe the material and energy balances for the liquid phase in the packed-bed absorber, we provide here a revised mathematical derivation of Pandya's model. By making a judicious selection of the most suitable correlations (or methods) currently available for the calculation of the liquid-phase speciation, the reaction rate constant, the mass-transfer enhancement factor, the density, heat capacity, viscosity, and surface tension of CO2-loaded aqueous MEA solutions, the heat of reactive absorption of CO2 in aqueous MEA, the gas-phase and liquid-phase mass transfer coefficients, the effective interfacial area, and the packing liquid holdup, we show from the computer simulation of our revised version of Pandya's model that it is possible to obtain accurate predictions of the absorber temperature profiles that were measured in a recently published and well-documented pilot-plant study.