THERMOGRAVIMETRIC COMBINED WITH MASS-SPECTROMETRIC STUDIES ON THE OXIDATION OF CALCIUM SULFIDE

The oxidation of CaS particles has been investigated by means of a the rmogravimetric analyzer combined with a mass spectrometer, especially under fluidized bed combustion conditions. The products are CaSO4 or b oth CaSO4 and CaO, depending on the temperature and O-2 concentration. The oxidation reaction results in the evolution of SO2 when CaO is fo rmed in the products. The conditions under which the undesirable SO2 w ill be released: or not, have been obtained. There is always an overal l sample weight gain, even when SO2 is evolved during the reaction. Th e investigation of the kinetics of the CaS oxidation in the no SO2 rel easing conditions shows that the oxidation reaction is of first order with respect to O-2, and a higher conversion can be achieved at higher temperature and by reducing the particle size. The maximum conversion of CaS to CaSO4 is 48.67% in 60 min at 865 degrees C and 4 vol% O-2 i n N-2 for 17 mu m CaS particles. The rate constant and the effective p roduct layer diffusivity are 4.1 x 10(-4)-2.88 x 10(-3) m s(-1) and 3. 15 x 10(-11)-4.39 x 10(-10) m(2) s(-1) at 500-865 degrees C in the lig ht of the shrinking unreacted core model for gas-solid reaction, the f ormer yielding an activation energy of 39.5 kJ mol(-1) for the CaS oxi dation reaction. (C) 1997 Elsevier Science B.V.