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

Abstract

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 CO 2 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.

Investigation of the Olive Mill Solid Wastes Pellets Combustion in a Counter-Current Fixed Bed Reactor

“…where Y coke is the mass fraction of carbon in the coke, which is approximately 0.85 for lignocellulosic biomass coke [51,52]. HHV coke then is approximately 30.80 MJ/kg.…”

Kinetic study of biomass char combustion in a low temperature fluidized bed reactor

“…Besides, the au thors also mentioned that the difference in char reactivity in the flui dized bed reactor and in the TGA is less significant at higher gasification temperatures. Mueller et al [39] also reported that, during the gasifi cation of high volatiles coal char with CO 2 for temperatures above 1073 K, the fluidized bed reactor shows significantly higher carbon conversion rate and reactivity than the TGA. They explained this phe nomenon by thermal annealing during the heat up of the char particles in the TGA which decreases the reactivity.…”

“…Several researchers [11,38,39] observed that the reactivity of char in gasification or combustion is dependent on the type of reactors. For instance, in the case of coal char gasification with CO 2 , the authors [38,39] agreed that the reaction rate is higher in the fluidized bed than in the TGA. Zeng et al [38] explained this phenomenon by the switching gas method in the TGA which leads to a non uniform CO 2 partial pressure at the beginning of the reaction.…”

Investigation of the apparent kinetics of air and oxy-fuel biomass combustion in a spout fluidised-bed reactor

“…Aside from these techniques, other researchers (Fennell et al, 2009;Gövert et al, 2017) have proposed using a bench-scale fluidised-bed reactor (FBR) with a fast-response gas analyser to investigate the kinetics of char combustion. This method can provide homogeneous temperature and bulk gas composition, high heating rates (around 10 4 K/s), sufficient residence time, flexible temperature and gas compositions and an approximate carbon mass balance (Kim et al, 2017;Li et al, 2015;Mueller et al, 2015).…”

“…However, this method relies on any reaction of the sample being inferred by measuring the gas composition rather than directly measuring the weight change of the sample itself, thus opening itself up to errors. It is also difficult to extract and quench fuel samples during a combustion experiment to permit the analysis of morphology and composition evolution, which are possible for EFR and DTR (Kim et al, 2017;Mueller et al, 2015).…”