Comparing packed columns and membrane absorbers for carbon dioxide capture

In recent years the capture of carbon dioxide (CO2 ) from flue gases has received a considerable amount of attention. In addition to the environmental reasons for studying CO2 absorption processes, there are a number of industrial applications that also benefit from the research. This thesis explores an emerging membrane technology that has the potential for widespread application in mass transfer applications. Gas absorption membrane (GAM) systems are gaining momentum as a feasible alternative to traditional contacting devices. In the case of CO2 removal from flue gases, GAM systems are being explored as a possible option to replace traditional packed column absorbers.; The primary focus of this thesis was to conduct a proper comparison of the absorption performance achieved in packed columns with that obtained in GAM systems. Bench scale CO2 absorption experiments were conducted to measure the volumetric overall mass transfer coefficient (K Gav) obtained in each system. Aqueous solutions of monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP) were used as the absorption solvent. The packed column contained Sulzer DX structured packing while the GAM system tested microporous polypropylene (PP) and polytetrafluoroethylene (PTFE) hollow fibre membranes. Testing was conducted under a variety of operating conditions with a total of nineteen (19) packed column experiments and two hundred and fifteen (215) runs in the GAM system. Results showed that the GAM system performed better than the packed column, but the degree of improvement depended on the operating conditions and system characteristics.; Studies were also conducted to evaluate the GAM system under various operating conditions. The best performance was obtained in a counter-current flow regime with the liquid flowing in the hollow fibre lumen. The addition of extra membrane modules was shown to improve the overall absorption rate. Durability tests of the PP and PTFE membranes showed that PTFE membranes are the most suitable. Three different sizes of PTFE membranes were tested. As the inside diameter of the membrane reduces, the surface area per module volume increases, but the system become less conducive for liquid flow on the fibre lumen-side.; Modeling work was conducted to prove that a model originally developed for randomly packed columns could be modified and used to simulate the performance of a GAM system. The rigorous computer model was first adapted for Sulzer DX structured packing by applying an appropriate correlation to calculate the effective packing surface area. The model was then expanded to simulate the GAM system by including appropriate mass transfer correlations.; This thesis provides a number of contributions to the research area. These are discussed in detail in the thesis. Some of the important contributions include: (1) a proper comparison of the mass transfer performance in packed columns and GAM systems, (2) a good database on GAM system performance coming from a large number of GAM experimental data, and (3) a new GAM system design that allows for the connection of modules in series, intermediate data sampling points, and removable membrane cartridges.