Mass transfer limitation in thermogravimetry of biomass gasification

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    Abstract

    In order to determine the intrinsic reactivity behavior from thermogravimetry studies, the experimental conditions should be such that the reactions are not mass transfer limited. Biomass char usually has a higher reactivity than coal chars. Therefore, mass transfer limitations may be more problematic when studying biomass char reactivity. Chemical reaction kinetics and mass transfer processes present in thermogravimetry are used for modeling the overall reaction rate for spruce bark CO2 gasification. Thermogravimetric experiments are carried out between 700 and 900 A degrees C, and the CO2 concentration is varied between 10 and 90 vol%. The intrinsic activation energy is found to be 120 kJ mol(-1). The transition temperature between regimes I and II is here defined when the fraction apparent to true activation energy equals 0.75. Higher external mass transfer (e.g., by decreasing the diffusion path through the crucible's freeboard), decreasing the sample amounts, and higher CO2 partial pressures for the Langmuir-Hinshelwood reaction type increase the transition temperature. The results show that the transition temperature between regimes I and II conditions is approx. 1,030 A degrees C for 90 vol% CO2.
    Original languageUndefined/Unknown
    Pages (from-to)183–192
    Number of pages10
    JournalJournal of Thermal Analysis and Calorimetry
    Volume111
    Issue number1
    DOIs
    Publication statusPublished - 2013
    MoE publication typeA1 Journal article-refereed

    Keywords

    • Char
    • CO2 gasification
    • Kinetic regime
    • Model
    • Spruce bark

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