Date of Graduation
Statler College of Engineering and Mineral Resources
Chemical and Biomedical Engineering
Modern grids will include input from fossil-fueled power generation facilities as well as renewable energy sources, and these are expected to work together actively. One major problem with this integrated power production is that most renewable energy sources are intermittent and variable, and thus introduce a very challenging situation with regard to grid stability and reliability. Also, fossil-fueled power generation facilities have load cycles based on expected usage. A non-reliable power source cannot feasibly be used to supply the grid with proper amounts of energy needed in peak times. A solution to this dilemma is power storage. The sodium-sulfur battery has high potential for electrical storage at the grid level due to its high energy density, low cost of the reactants, and high open-circuit voltage. However, the use of sodium-sulfur batteries at the grid level requires high current density operation that can cause cell deterioration, leading to lower sulfur utilization and lower energy efficiency. In addition, it can result in undesired thermal runaway leading to potentially hazardous situations. A rigorous, dynamic model of a sodium-sulfur battery can be used to study these phenomena, design the battery for optimal transient performance, and develop mitigation strategies.;Most literature on sodium-sulfur batteries is concerned the dynamics of the sulfur electrode (a sodium-polysulfide melt). There is limited data in the open literature for dynamics of an entire cell. With this motivation, a first-principles dynamic model of a sodium-sulfur cell (with beta"-alumina electrolyte) has been developed.;The state of discharge (SOD) of a sodium-sulfur cell significantly affects the heat generation rate, rates of electrochemical reactions, and internal resistance. To capture these phenomena correctly, a fully coupled thermal-electrochemical model has been developed. The thermal model considers heat generation due to Ohmic loss, Peltier heat, and heat due to the entropy change. Species conservation equations are written in the sulfur electrode by considering the phase transition and change in the composition depending on the SOD. The electrochemical reactions are modeled by using Arrhenius-type rate equations with temperature-dependent terms and varying species concentration depending on the SOD. Species conservation equations are written in the beta"-alumina electrolyte for the ionic species by considering the change in composition due to diffusion and migration. In addition, the potential distribution, and the cell resistance for this spatially distributed system has been modeled. The physicochemical properties are considered to be temperature-dependent. The model is used to study both charging and discharging characteristics of the cell at varying current densities.;The PDE-based model is solved in Aspen Custom Modeler by using method of lines. Our work shows that an appropriate thermal management strategy is necessary for high current-density operation, especially in the case of high penetration of the renewable energy into the grid.
Caprio, Sarah, "Transient Studies of a Sodium Sulfur Cell" (2014). Graduate Theses, Dissertations, and Problem Reports. 5314.