A KINETIC DESCRIPTION OF VAPOR-PHASE ALKALI TRANSFORMATIONS IN COMBUSTION SYSTEMS

A kinetic model was developed to predict concentrations of atomic and molecular sodium species existing in both flame and post-flame zones of pulverized coal combustors with and without chlorine. To date, the model has successfully predicted measured literature values of sodium species in the Na/H2/O2/N2 system. At temperatures above 1900 K, sodium hydroxide is predicted to be the dominant species at times longer than a few milliseconds. Atomic sodium levels decay rapidly, representing less than 1% of the total sodium species present at time greater than 5 msec for lean hydrogen flames. At lower temperatures, NaO2 forms in significant quantities as well, leading to decreases in the levels of atomic sodium. Addition of 1 ppm levels of chlorine generated approximately 10% sodium chloride in addition to sodium hydroxide at 1500 K, while addition of 1000 ppm levels yielded sodium chloride as the dominant species. Current understanding regarding the addition of sulfur chemistry to the matrix, and specifically the formation of vapor phase sodium sulfate, is also discussed. © 1990.