NSF Award
1236761
Carbon dioxide emissions from combustion of fossil fuels is of great concern for global warming. A technology being considered for carbon capture and sequestration in power plants is oxy-coal combustion. Thus, the operational and environmental impacts of oxy-coal combustion need to be evaluated. Sulfur dioxide emissions can also be reduced with oxy-firing compared to air combustion due to high concentrations of sulfur trioxide in the flue gas resulting in sulfur retention on fly ash and ash deposits in the furnace. Higher sulfur retention on the ash particles reduces the sulfur dioxide emission rates, on the other hand it creates problems utilizing the fly ash for cement and concrete production. Further research regarding the sulfur dioxide emissions under oxy-firing conditions needs to be performed, specifically to investigate the fly ash retention. In comparison to the emissions of nitrogen and sulfur oxides, the subject of trace metal emissions in oxy-fuel combustion has not received much attention in the literature and little information has been reported on the mercury transformations under oxy-fired conditions. One area of concern is that the pollutants such as mercury and sulfur trioxide cause corrosion in carbon dioxide compressors and recirculation lines. The characteristics of oxy-combustion and air-combustion are fairly different and this results in changes in the behavior of pollutants in the flue gas, thus the emissions. As research in this area is beginning to grow, the fundamental understanding of pollutant formation remains to be elucidated and before developing removal technologies, one needs to understand the speciation and behavior of these pollutants under oxy-fired conditions. The objective of this project is to investigate the differences in pollutant behavior under air- and oxy-fired conditions. This research is unique in the fact that it will be the first comprehensive investigation of pollutant formation during oxy-fuel combustion at a fundamental level combining bench-scale experiments, kinetic modeling and molecular modeling. Two major milestones that will be achieved by the end of this project are the following: 1) Gas phase chemistry of sulfur oxides and trace metals will be elucidated by both bench-scale experiments and kinetic modeling and effects of other flue gas constituents and the recycling will be determined 2) Heterogeneous chemistry of sulfur oxides and trace metals on fly ash will be investigated by bench-scale experiments and molecular modeling and the mechanism of sulfur retention on fly ash will be identified.<br/><br/>This research will provide useful information for the oxy-fired power plants regarding the risk of corrosion associated with the pollutants in the flue gas as well as the extent of sulfur retention on fly ash that could prevent them selling the fly ash to concrete producers. Besides the practical knowledge, it will also provide a fundamental understanding of the pollutant chemistry that is taking place in the flue gas and on the fly ash surface. Experimental data that will be produced from this project will be made available in the literature and could be used to validate the existing models in the literature. Additionally, the graduate and undergraduate students working on this project will gain an in-depth knowledge of combustion chemistry as well as excellent experimental and modeling skills.
