CO2 Capture by Chemical Absorption: Kinetics and Combined Heat and Mass Transfer

Abstract

Currently, global warming is an alarming issue. Tremendous efforts are being made in the research area to develop new and improved CO2 capture technologies in recent years. Many small-scale pilot test rigs and semi-industrial plants and even a few industrial scale plants have been built and are in operation currently all over the world, almost all based on absorption with chemical reactions. The relatively high-energy penalty and the possible aerosols emissions are challenges for successful implementation of CO2 capture world-wide. Many researchers work on developing new low-energy penalty solvents, on cost efficient process modification, on aerosols emissions control and on scale-up standards of the process. To accelerate the development, commercialization and deployment of these carbon capture technologies, it is important to fill the gaps in process understanding and to develop a standard reference case, which can be used for comparing and analyzing new developments in technology. In a CO2 absorption process, rapid mass and heat transfer occur at several places, for example at the bottom of the absorber, in the water wash section and in the desorption column. The rate of CO2 absorption into aqueous amine solutions is enhanced by fast chemical reactions occurring in the liquid phase and this plays a major role in the process design. Precise and validated reaction kinetics and good fundamental models for the combined heat and mass transfer are crucial for optimized process design and operation.

The present work is devoted to developing and validating new kinetic and mass transfer models and testing and evaluating uncertainities in the exisiting models. Thereby a standard process modeling case can be developed that can be a guideline for characterizing new solvents and for fast deployement of new CO2 capture techonologies. The dissertation presents the following findings:

•Development of a mass transfer model with chemical reaction, based on rigorous thermodynamic, using penetration theory for the CO2 absorption with chemical reactions and implemented in MATLAB software.

•Development of new concentration and activity based kinetic models for the CO2 reaction with aqueous MEA solution based on the termolecular reaction mechanism using orthogonal collocation on finite elements (OCFE) method coupled with a global optimization technique.

•Validation of the kinetic models against experimental data from three independent sources.

•Evaluation of uncertainties and impact of critical model parameter estimation methods (VLE, solubility, reaction kinetics, diffusivities and viscosity) on the performance of the model.

•Development of a combined heat and mass transfer model to study the effect of water condensation and evaporation on the absorption process and a study of five different process cases.

•An experimental validation to check the applicability of enhancement factor models for CO2 capture into aqueous MEA solution. 24 different enhancement factor correlations were tested to represent laboratory scale experimental CO2 mass transfer rates from four different lab-scale experimental set-ups.