Accurate knowledge of char oxidation rate parameters is of paramount importance in modeling coal combustion behavior. Generally, an isothermal thermogravimetric analyzer (TGA) is used to determine the intrinsic rate parameters. However, despite operating in a kinetic controlled regime, i.e., at relatively lower reaction temperatures, the char reactivity profile (reaction rate versus burnoff) has often been observed to go through a maximum. The existence of a maximum in the reactivity profile poses a difficulty in extracting the intrinsic rate parameters. This present paper attempts to investigate the conditions that may lead to such a maximum and recommends a method to deduce the kinetic parameters from such a profile. To address this matter, a high volatile bituminous coal is pyrolzyed in a drop tube reactor (DTR) at different furnace temperatures and in a TGA. Physical and structural properties of the char samples generated in DTR were measured, and the reactivity of the resultant char samples was determined in a TGA. The results demonstrate that both the pyrolysis history and char oxidation temperature have a significant effect on the shape of the rate profile obtained in a TGA. It is proposed that such an occurrence of a maximum is due to a transition from a intraparticle diffusion controlled zone to a kinetic controlled zone. This was further confirmed by observation of similar estimated activation energy values at several conversion levels after the maximum.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology