Combustion plasma electrical conductivity model validation for oxy-fuel MHD applications: Spectroscopic and electrostatic probe studies

Abstract

The U.S. Department of Energy has a renewed interest in direct power extraction (DPE) technologies, such as a magnetohydrodynamic (MHD) generator, in conjunction with oxy-fuel combustion. As a topping cycle, this configuration can enable efficient CO2 capture, while offsetting oxygen separation penalties. In order to appropriately evaluate these cycles in the context of modern plant configurations, validated modeling tools are needed. In a prior publication (Bedick et al., 2016), an electrical conductivity model was presented for oxy-fuel MHD applications. However, rigorous validation of the model could not be performed due to a lack of high-quality experimental data at relevant conditions.In this publication, validation experiments were performed and relevant parameters quantified using spectroscopic and electrostatic probe diagnostics. Oxygen-methane flames were generated using a Hencken burner and seeded with K2CO3 to increase ionization and electrical conductivity. The electrical conductivity model from Bedick et al. (2016) was integrated into a 3D CFD simulation of a single burner quadrant and a reaction mechanism including potassium kinetics and ionization was utilized. Lineshape fitting techniques were implemented to determine atomic potassium concentration and gas temperature, while appropriate electrostatic probe theory was applied to derive potassium ion concentrations from experimental current-voltage characteristics. Measured quantities are compared to CFD predictions as a function of seed rate and spatial location within the flame, showing good overall agreement. Indirect validation of electrical conductivity predictions is performed using measured quantities, with results falling well within the bounds of measurement uncertainty.