UC Irvine

Comprehensive computational models are developed to explore the application of flameless combustion for two significant components of a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid power system: an off-gas burner, and an eductor. Flameless combustion, a regime in which fuel reacts with a high temperature low oxygen content oxidizer, is appropriate for these applications given a characteristically low stable adiabatic flame temperature and reduced pollutant emissions.

In this study, the operation of an off-gas burner and an eductor in the non-traditional flameless combustion regime are explored and investigated. For the off-gas burner application, highlight while alternatives to flameless combustion, such as porous media and catalytic off-gas burner designs, have produced promising results for the stable conversion of diluted SOFC off-gases, the systems are complex and expensive. For the eductor application, the high temperature recycled anode off-gas is mixed with low-oxygen content fuel. Facilitating these optimal conditions within the eductor promotes removal of oxygen in the mixed gas stream, thereby eliminating or reducing the size of an expensive catalytic oxidizer between the eductor and the SOFC inlet. The present research involves developing chemical kinetic models and computational fluid dynamic (CFD) models, simulating operation in the flameless combustion regime, and performing statistical analyses of the results to determine statistically significant design factors. Numerical modeling using chemical reactor networks (CRNs) was validated based on literature data and then used to analyze the associated chemical kinetics for flameless combustion within each component. Higher dimensional modeling, performed using updated CFD models, incorporated both the CRN results as well as important turbulent combustion and physics.

For the aforementioned applications, an increase in temperature and/or pressure promoted key reactions for producing and sustaining flameless combustion. Optimal design criteria for inlet mass flow rates for the off-gas burner application, and inlet stream temperatures for the eductor reactor application, are established utilizing a systematic method and significant statistical analysis tools. Insight from chemical kinetic modeling is essential for exploring the practical limits of the flameless combustion regime as they are uniquely tied to application-specific operating conditions such as residence time, temperature, pressure, and reactant composition.