469399 A Theoretical Investigation of Sulfur Adsorption on Calcium Oxide

Sunday, November 13, 2016: 5:10 PM
Union Square 13 (Hilton San Francisco Union Square)
Benjamin Galloway1, Angel Maymi2, Alexandra Bland3 and Bihter Padak1, (1)Chemical Engineering, University of South Carolina, Columbia, SC, (2)Chemical Engineering, University of Puerto Rico Mayaguez Campus, Mayaguez, PR, (3)University of South Carolina, Columbia, SC

Sulfur capture on coal fly ash plays a critical role in limiting SOx emissions in power plants. The retention on the fly ash is heavily dependent on the alkali and alkaline earth metal (AAEM) species in coal such as Ca. In oxy-combustion, this mechanism becomes particularly important as the sulfur concentration (SO2 + SO3) in the flue gas can be several times greater than traditional air-combustion due to the unique staging required of oxy-fuel systems. While higher rates of sulfur capture on fly ash have been observed for oxy-combustion compared to air-combustion, this increased retention can create concerns in utilization of the fly ash for cement and concrete production.

Although there have been previous experimental studies, the surface mechanism of sulfur retention on Ca-based materials is not well understood. In this study, computational modeling was employed to examine the binding of SOx species to the most prominent AAEM species, calcium oxide. Density functional theory (DFT) calculations were performed using Vienna ab initio Simulation Package (VASP) to investigate the binding mechanism for SOx on a CaO(100) surface. Calculations were also run with various other co-adsorbates, including CO2, H2O and SOx, that are pre-adsorbed to the surface to examine the effect of their presence on any subsequent SOx reactions on the surface. The energetic, geometric and electronic properties of the simulated surfaces were analyzed to discern any possible trends in the SOx binding mechanism with respect to the specific pre-adsorbed molecule.  The results were then compared to experimental data where CaO was exposed to a variety of flue gas compositions. In this way, a more complete picture of the SOx binding mechanism on calcium oxide was determined allowing for a better understanding of the initial stages of sulfur capture in combustion systems.

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See more of this Session: Environmental Applications of Adsorption: Gas Phase
See more of this Group/Topical: Environmental Division