Kinetic analysis and thermodynamic properties of air/steam gasification of agricultural waste

A. FERNANDEZ; L. A. RODRIGUEZ ORTIZ; D. ASENSIO; R. A. RODRIGUEZ; G. D. MAZZA

Journal of Environmental Chemical Engineering

Elsevier B.V.

Lugar: Amsterdam; Año: 2020 vol. 8 p. 1 - 13

2213-3437

The air/steamgasification of wood sawdust (SD), plum and olive pits (PP, OP) bio-wastes was studied using macro-thermogravimetric analysis at three heating rates (5, 10,15 K/min). Three stageswere identified during gasification process: water vaporization;de-volatilization and char gasification. The experimental data were analysed byapplying five model-free methods: Flynn-Wall-Ozawa (FWO), Distributed Activation Energy Model (DAEM),Friedman, Starink, and Kissinger-Akahira-Sunose (KAS), to evaluate the gasification kinetic parameters. TheFWO method exhibited the best fit to the experimental results. Thepre-exponential factor was estimated using the Kissinger?s expression. Theaverage apparent activation energy (E) for the char-gasification step was foundto be 218.27 (SD), 143.70 (PP) and 87.89 kJ mol-1 (OP). The pre-exponential factors were 6.93 1023(SD), 5.10 1014(PP), and 3.71 1009s-1 (OP). A kinetic model to predict the CO release during thebio-waste decomposition was also proposed and validated. The E values forglobal release of CO were 87.34 (SD), 67.19 (PP), and 133.23 kJ mol-1 (OP). In addition, the thermodynamic parameters ΔS, ΔHand ΔG were calculated from the FWO method. The positive values of ΔH evidencedthe global endothermicity of the gasification process over the whole range ofthe conversion degree. The average ΔG values were 130.53 (SD), 148.17 (PP)and 132.91 kJ mol-1 (OP). The average ΔS and ΔG values, togetherwith the Arrhenius kinetic coefficient showed that the reactivity forgasification decreased in the following order: SD > OP > PP. The resultsare in good agreement with previously reported data.