Modelling and simulation of intermediate temperature solid oxide fuel cells and their integration in hybrid gas turbine plants

Abstract

Solid oxide fuel cells (SOFCs) are gaining prominence as power sources amongst other types of fuel cells due to their high electric energy efficiencies, their ability to integrate with other energy cycles in a hybrid system, fuel choice flexibility and low pollutant emissions. Operation of an SOFC involves complex coupling of the electrochemical reactions, chemical reactions and transport phenomena simultaneously in the cell’s main components consisting of gas channels, porous electrodes and the dense ceramic electrolyte. Consequently, mathematical modelling of these processes becomes an essential research tool aiming to provide detailed insight, while reducing cost, time and the effort associated with experimentation. The main aim of this thesis is to develop mathematical models in the cell and at system level to better understand the complex operation of SOFCs and its associated cycle under practical conditions with the aim of enhancing the power output and efficiency of the cell. At the cell level, a two dimensional along the channel micro-scale isothermal model of a SOFC is developed and validated against experimental data and other simulated result from literature. The steady state behaviour of the cell was determined by numerical solution of the combined transport, continuity and kinetic equations. The model is capable of predicting the cell performance including polarisation behaviour and power output. The model is used to study the effect of the support structure, geometric parameters and the effect of operating conditions on cell performance. Several parametric studies, such as the effect of operating conditions and geometric parameters on cell performance with a view to optimising the cell. Also, at the cell level, a two dimensional along the channel model was developed which integrates a heat transfer model and direct internal reforming kinetics into the earlier developed isothermal model. This non-isothermal model was also validated against experimental data. The developed model not only predicts the performance of the SOFC at different design and operating conditions, it also provides an insight on the different phenomena and the distributions of current density, temperature and gas pressures within the cell. Microstructural parametric studies of the reaction layer were also carried out.Solid oxide fuel cells (SOFCs) are gaining prominence as power sources amongst other types of fuel cells due to their high electric energy efficiencies, their ability to integrate with other energy cycles in a hybrid system, fuel choice flexibility and low pollutant emissions. Operation of an SOFC involves complex coupling of the electrochemical reactions, chemical reactions and transport phenomena simultaneously in the cell’s main components consisting of gas channels, porous electrodes and the dense ceramic electrolyte. Consequently, mathematical modelling of these processes becomes an essential research tool aiming to provide detailed insight, while reducing cost, time and the effort associated with experimentation. The main aim of this thesis is to develop mathematical models in the cell and at system level to better understand the complex operation of SOFCs and its associated cycle under practical conditions with the aim of enhancing the power output and efficiency of the cell. At the cell level, a two dimensional along the channel micro-scale isothermal model of a SOFC is developed and validated against experimental data and other simulated result from literature. The steady state behaviour of the cell was determined by numerical solution of the combined transport, continuity and kinetic equations. The model is capable of predicting the cell performance including polarisation behaviour and power output. The model is used to study the effect of the support structure, geometric parameters and the effect of operating conditions on cell performance. Several parametric studies, such as the effect of operating conditions and geometric parameters on cell performance with a view to optimising the cell. Also, at the cell level, a two dimensional along the channel model was developed which integrates a heat transfer model and direct internal reforming kinetics into the earlier developed isothermal model. This non-isothermal model was also validated against experimental data. The developed model not only predicts the performance of the SOFC at different design and operating conditions, it also provides an insight on the different phenomena and the distributions of current density, temperature and gas pressures within the cell. Microstructural parametric studies of the reaction layer were also carried out.Solid oxide fuel cells (SOFCs) are gaining prominence as power sources amongst other types of fuel cells due to their high electric energy efficiencies, their ability to integrate with other energy cycles in a hybrid system, fuel choice flexibility and low pollutant emissions. Operation of an SOFC involves complex coupling of the electrochemical reactions, chemical reactions and transport phenomena simultaneously in the cell’s main components consisting of gas channels, porous electrodes and the dense ceramic electrolyte. Consequently, mathematical modelling of these processes becomes an essential research tool aiming to provide detailed insight, while reducing cost, time and the effort associated with experimentation. The main aim of this thesis is to develop mathematical models in the cell and at system level to better understand the complex operation of SOFCs and its associated cycle under practical conditions with the aim of enhancing the power output and efficiency of the cell. At the cell level, a two dimensional along the channel micro-scale isothermal model of a SOFC is developed and validated against experimental data and other simulated result from literature. The steady state behaviour of the cell was determined by numerical solution of the combined transport, continuity and kinetic equations. The model is capable of predicting the cell performance including polarisation behaviour and power output. The model is used to study the effect of the support structure, geometric parameters and the effect of operating conditions on cell performance. Several parametric studies, such as the effect of operating conditions and geometric parameters on cell performance with a view to optimising the cell. Also, at the cell level, a two dimensional along the channel model was developed which integrates a heat transfer model and direct internal reforming kinetics into the earlier developed isothermal model. This non-isothermal model was also validated against experimental data. The developed model not only predicts the performance of the SOFC at different design and operating conditions, it also provides an insight on the different phenomena and the distributions of current density, temperature and gas pressures within the cell. Microstructural parametric studies of the reaction layer were also carried out.