Comparation of char gasification kinetics studied by micro fluidized bed and by thermogravimetric analyzer

The isothermal gasification kinetics of coal char with CO₂ was separately studied using a so-called micro-fluidized bed reaction analyzer (MFBRA) and a thermogravimetric analyzer (TGA). With minimized effects of heat and mass transfer, the reaction rate in MFBRA is much higher than that in TGA. And the maximal rate appears at a conversion of about 0.15 in MFBRA but at 0.45 in TGA. The shrinking core model can well describe the char gasification reaction both in MFBRA and in TGA. In the temperature range of 760~1 000 ℃, the char gasification reaction is investigated in two stages. At lower temperatures, the activation energy from MFBRA and TGA is very close, validating the reliability of MFBRA for gas-solid reaction kinetic studies. At higher temperatures, the estimated activation energy by MFBRA is obviously higher, showing a lower diffusion limitation in MFBRA. It is found that the measured frequency factor for the Arrhenius equation by MFBRA is much higher than that by TGA, complying with the higher reaction rate in MFBRA. As a consequence, MFBRA and TGA differ in diffusion and heating behavior, which can greatly affect the measurement of (apparent) kinetics.