(499c) Binding of SO3 to Fly Ash Components: CaO, MgO, Na2O and K2O

Authors: 
Galloway, B., University of South Carolina
Sasmaz, E., University of California, Irvine
Padak, B., University of South Carolina

Oxy-combustion proposes to incorporate carbon capture and storage technologies into existing coal-fired power plants to lower carbon emissions.  It does so by separating out the N2 prior to combustion, resulting in a concentrated CO2 as a final product that can be easily captured and stored.  Sulfur oxide (SOX) emissions can be lowered due to high concentrations of SO3in the oxy-combustion flue gas resulting in sulfur retention on fly ash and ash deposits in the furnace. It has been shown that the extent of sulfur retention is heavily dependent on the alkali and alkaline earth metal (AAEM) species in coal such as Na, K, Mg and Ca and the sulfur retention increases as the AAEM:S molar ratio increases. While higher sulfur retention on the ash particles reduces the emission rates, it creates problems utilizing the fly ash for cement and concrete production.

 Although there have been previous experimental studies, the mechanism of sulfur retention on fly ash is not well understood. In this study, a variety of computational and experimental methods were employed to examine the binding of SOX species to the AAEM species.  Firstly, density functional theory (DFT) calculations were performed using Vienna ab initio Simulation Package (VASP) to investigate the binding mechanism for SO3 on several metal oxides that compose fly ash, namely CaO, MgO, Na2O, and K2O.  Calculations were also run where SO3 was co-adsorbed with H2O to examine if its presence would facilitate further reaction of the SO3 on the oxide surface.  Secondly, FTIR spectroscopy will be employed to investigate the AAEM oxides after exposure to a SO2/SO3 mixture plus a variety of other flue gas components. FTIR results along with DFT calculations will be used to create a more complete picture of the SOX binding mechanism on the metal oxides.