Gasification Kinetics of Biomass- and Fossil-Based Fuels: Comparison Study Using Fluidized Bed and Thermogravimetric Analysis

In this work, the influence of experimental setup on derived kinetic data for the heterogeneous Boudouard gasification reaction is studied. A thermogravimetric analyzer (TGA) and a small-scale fluidized bed reactor (FBR) are used. The two systems differ basically in their fuel heating rates and fuel bed configurations. The kinetic study was performed in both reactors for the same temperatures and partial pressures of CO2 at ambient pressure using same-batch fuel samples (biomass, brown coal, and petcoke). Kinetic data are reported, and the influence of the thermal history of the fuel particle prior to the char gasification process is discussed. In general, the activation energies derived from both systems are lower for the brown coal fuels as compared to the wood char fuels. This finding may be explained by the high ash content of the brown coal fuels with multiple catalytic components in the ash. Both experimental setups used in this study agree well in their results for the carbon conversion rate and kinetic parameters for fuels with low volatile content, whereas fuels with high volatile content show different results in the two experimental setups. This may be explained by the physical and chemical structure of the fuel particle not being changed significantly during the in situ pyrolysis prior to gasification for the low volatile fuels. The char properties of the high volatile fuels may differ significantly due to system dependent different heating rates and gas atmospheres during the in situ pyrolysis prior to gasification. Hence, the observed reactivity becomes system dependent. In conclusion, the results show that knowledge of the thermal history of the fuel particle prior to the gasification process is most important for the interpretation of kinetic data as well as for the design of experiments for generation of kinetic data.