MHD seed recovery and regeneration

Abstract

An MHD topping system generates electric power by sending a hightemperature gas stream through a magnetic field. The gas stream is "seeded with potassium to increase its electrical conductivity. Seeding with potassium carbonate will also capture the sulfur released during combustion to prevent air pollution. The potassium is recovered as K2SO4 in the spent seed but must be regenerated into a form suitable for reuse in order for the MHD process to be economical. A proposed seed regeneration process based on reduction of sulfate followed by separation of the sulfur and potassium is presented in this paper. Bench-scale evaluations of key steps in the process were performed to demonstrate technical feasibility. The conditions required to achieve 70% sulfur reduction in a rotary kiln were determined. The vapor pressure of H2S over solutions of sodium and potassium bisulfides were also determined. Overall recovery efficiency is better than 90% with a purity of about 95% K2CO3. Thermodynamic studies of possible impurities in the recovered K2CO3 showed no significant effect at the 10% level on the MHD channel performance. The sulfur is recovered as a marketable by-product.