Kinetics of MSWI fly ash thermal degradation. 2. Mechanism of native carbon gasification

A generalized kinetic model for fly ash native carbon oxidation is develope d. It is shown that the conversion of fly ash native carbon to CO2 is the r esult of two simultaneous processes taking place on fly ash surface: the fi rst pro cess (rate constant k(2)) is the direct oxygen transfer from a meta l oxide site to a vacant carbon active site leading to immediate carbon gas ification; the second one is dissociative oxygen chemisorption (k(1)) follo wed by C(O) complex intermediate uncatalyzed gasification (k(3)). The model is validated using the kinetic data from model systems and those reported in Part 1 for four different fly ashes. The rate constants, k(1), k(2), and k(3), together with activation and thermodynamic parameters are calculated . For each fly ash, the rate determining step is the complex intermediate o xidation. The nature of the interaction between native carbon and the fly a sh surface is the key factor for C and C(O) complex formation and gasificat ion.