Modeling potassium-sulfur interactions across secondary combustor in a coal-fired magnetohydrodynamics (MHD) system

The addition of a sulfur-free potassium salt as a seed material is one of the unique characteristics of a coal-fired Magnetohydrodynamics (MHD) power generation system. This potassium seed serves a two-fold purpose— to increase the electrical conductivity of the plasma formed in the primary combustor of an MHD system, and to reduce sulfur-containing pollutant emissions from the flue gas by the formation of spent seed K₂SO₄. The optimization of performance conditions of an MHD system will eventually depend on how well the interaction of potassium and sulfur in the system is understood. This thesis is focused on modeling the potassium-sulfur interactions in a typical coal-fired MHD power generation system: the Coal-Fired Flow Facility (CFFF) at the University of Tennessee Space Institute (UTSI).

Thermodynamic and kinetic computer codes were used to carry out extensive parametric calculations for the CFFF system. Calculation parameters were chosen based on meaningful operating conditions. Gas and particulate samples from selected locations at the CFFF were collected and analyzed. These results are then compared with those from the calculations. An overall potassium-sulfur interaction model is then postulated. An empirical equation which correlates SO₂ concentration with its major influencing factors is also presented.

According to the model, flame radical/sulfur chemistry and potassium oxidation chemistry are the dominant chemical reactions taking place before the secondary combustion. Potassium-sulfur reaction chemistry becomes dominant after the secondary combustion. From the derived empirical equation, SO₂ concentration is found to depend exponentially on the temperature of secondary combustion gases.