On the influence of different experimental systems on measured heterogeneous gasification kinetics

The objective of this study was to gain further insight into the characteristic behavior of reaction systems for establishment of intrinsic and effective particle gasification kinetics. A wood-derived char was subjected to the carbon dioxide-containing atmospheres of four different reaction systems: a thermogravimetric analyzer (TGA), a fluidized-bed reactor (FBR), a fixed-bed reactor (FFB) and a drop-tube reactor (DTR). All systems contained the same CO₂ partial pressure of 800 mbar at atmospheric pressure. A temperature span from 700 to 1600 °C and residence times from 200 ms to over 8 h were investigated. Reactivities spanning five orders of magnitude were observed. The gasification experiments resulted in the identification of four fundamentally different reaction domains; two were classified as true particle behavior, while the observed reaction rates of the other two domains are mainly dominated by the characteristics of the reaction system applied. The domains were referred to as: chemical control, particle diffusion control, bed diffusion control, and system response control. Within the present work, the occurrence of these reaction domains is discussed in regard to the physical nature of the experiments, and implications towards the measurement of reliable particle kinetics are formulated.