A MULTI-PHYSICS STUDY ON GAS DIFFUSION AND CHEMICAL REACTIONS IN CEMENT MATERIAL WITH CO2 SORPTION
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Abstract
Emission control and storage of carbon dioxide (CO¬2) from fossil fuel combustion is an emerging and frontier research area to counter likely global climate changes. Although the carbon dioxide separation techniques are quite mature, there is still an issue of excessive carbon dioxide being emitted into the atmosphere. Carbon sequestration as mineral carbonates is an attractive and novel method with the potential to be implemented with acceptable economics to dispose carbon dioxide in large scale. This study suggests innovative research in using building materials (cement and concrete) for CO2 storage and presents two new tools for the development of this technology. The tools are developed so that a quantitative measure of the sorption potential of the futuristic building material can be determined.The Constant Temperature Pressurized Reaction Chamber (CTPRC) testing technique is a cylindrical structure that allows mineral sequestration and embedment of CO2 within a highly porous, calcium rich material. The material allows high diffusion and maximizes chemical sorption. Test setup involves the measurement of the amount of CO2 being absorbed using the ideal gas law. Because of the porosity, the actual sorption process engages multi-physical processes including complex diffusion behavior, elastic material deformation under pressure and over seven chemical reactions. Environmental scanning electron microscopy (ESEM) and X-ray powder diffraction (XRD) were used to validate the forming of carbonates with the test specimens. A numerical model is developed to help understand the sorption process, which over seven stoichiometric equations have been derived. This dissertation summarized the hazards of carbon dioxide to the environment and society, the source of carbon dioxide in atmosphere and the current control technologies in the world. Laboratory experiments were conducted to demonstrate the CTPRC testing technique and the sorption potential. The theory behind the mineral carbonation mechanism is investigated including the complicated dynamic behavior about porous material deformation, carbon dioxide gas diffusion and chemical reactions. The coupled system involved in the laboratory study is then simulated with the multi-physical model. The main contributions and results are as follows:(1) An experimental technique, CTPRC (Constant Temperature Pressurized Reaction Chamber) is developed to quantify the carbon dioxide mineral carbonation and a series of six experiments were reported to determine critical factors involved in the sorption process including initial gas pressure, initial sample porosity and initial sample water-binder ratio. These factors influenced the rate of carbonation reaction.(2) The hydration and carbonation reactions involved in the cement based porous material were reasonably simplified in the numerical simulation and each component quantity changes were analyzed. According to mass conservation involved in the process of chemical reaction and diffusion, the reaction rate equations were established and were summarized into seven reaction rates. Ten kinds of component concentration field and CO2 gas diffusion velocity field with different water-binder ratios, initial CO2 pressure and initial sample porosities were simulated by the numerical modeling. The impact of the three factors on the component concentration field was investigated.(3) The results involving the carbon dioxide sorption process using both physical and chemical sorption of the porous cement material conclusively indicate a hopeful sequester of a maximum 50% of the injected CO2 within initial 48 hours.This research work reported can be the foundation for future works that may involve further optimization of sorption potential of the cementitious material. Additional studies involved the utilization of fly ash have also been performed, which add further values to the futuristic material development enabling a sustainable environment that can be free of wastes of gas, liquid and solid forms.