(214s) SOx Binding On Fly Ash Components for Oxy-Coal Combustion

The United States is responsible for emitting 1.5 billion tons of carbon dioxide (CO₂) per year from the combustion of coal in the generation of electricity.  These CO₂ emissions have been garnering greater attention in recent years due to CO₂’s classification as a greenhouse gas and its role in global warming.  One technology being developed to combat this problem is oxy-coal combustion where oxygen, not air, is used as the oxidizer in the boiler.  The elimination of nitrogen produces a concentrated CO₂stream that can be captured and compressed for transport and sequestration.  For the existing conventional power plants to be retrofitted, the operational and environmental impacts of oxy-coal combustion need to be evaluated.

Previous research has shown that sulfur dioxide (SO₂) emissions can be lowered by employing oxy-coal technology.  The higher oxygen concentration and recycle stream leads to greater oxidation of SO₂ to sulfur trioxide (SO₃) resulting in sulfur retention on fly ash and ash deposits in the furnace.  While the increased sulfur retention on the ash particles decreases SO₂ emissions, it creates problems utilizing the fly ash for cement and concrete production. To address this problem and aid in making oxy-coal combustion a viable technology, one must first examine the binding of sulfur oxides (SO_X) on the various components of fly ash, e.g. calcium oxide (CaO), magnesium oxide (MgO) etc. To better understand the sulfur retention mechanism, density functional theory (DFT) calculations were performed using plane wave basis sets to investigate these earth metal oxides.  A slab model was used to simulate clean CaO(100), MgO(100), Na₂O(100), and K₂O(100) surfaces for SO₃ binding.  Energies and density-of-states were calculated for a variety of binding sites and adsorbate orientations to examine the binding mechanism and dominant species on these surfaces.