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  • 1.
    Samuelsson, Lina N.
    et al.
    KTH Royal Institute of Technology.
    Bäbler, Matthaus U.
    KTH Royal Institute of Technology.
    Moriana, Rosana
    KTH Royal Institute of Technology.
    A single model-free rate expression describing both non-isothermal and isothermal pyrolysis of Norway Spruce2015Ingår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 161, s. 59-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A strictly isoconversional rate expression has been derived for pyrolysis of biomass. This rate expression, derived from non-isothermal thermogravimetric experiments using heating rates 2-10 K/min, can successfully predict the conversion rates of experimental data at heating rates 1-100 K/min and quasiisothermal experiments at 539-650 K. The methodology used is based on an extension of the incremental integral method by Vyazovkin (2001). Being able to derive an intrinsic reaction rate expression from non-isothermal data, without any assumption regarding the chemical processes present, opens up for the possibility to model industrial pyrolysis reactors, with a variety of temperature profiles.

  • 2.
    Samuelsson, Lina N.
    et al.
    KTH Royal Institute of Technology.
    Bäbler, Matthäus U.
    KTH Royal Institute of Technology.
    Brännvall, Elisabet
    KTH Royal Institute of Technology.
    Moriana, Rosana
    KTH Royal Institute of Technology.
    Pyrolysis of kraft pulp and black liquor precipitates derived from spruce: Thermal and kinetic analysis2016Ingår i: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 149, s. 275-284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The potential of seven kraft cook materials to become functional char materials and fuels is investigated. Thermogravimetric analysis was used to study the thermal properties while a model-free isoconversional method was used to derive kinetic rate expressions. Black liquor precipitates had lower thermal stability (20-60 K lower) than pulps and spruce wood and the precipitates decomposed in a wider temperature range, producing chars with similar or higher thermal stability than char from pulps, but lower than those from spruce wood. Samples suitable to produce char were identified based on char yield, devolatilization rate and charring temperature. The highest char yield (46%), achieved from a precipitate, was more than twice as high as that from spruce powder. Under the studied conditions none of the materials had a pyrolysis process that for the whole conversion range could be described with a single set of kinetic parameters. The apparent activation energy varied between 170-260 kJ/mol for the pulps and 50-650 kJ/mol for the precipitates. The derived kinetic parameters were validated by predicting the conversion at a heating rate outside the range used for its derivation and at quasi isothermal conditions. Both these tests gave satisfactory results in good agreement with experimental data.

  • 3.
    Samuelsson, Lina Norberg
    et al.
    KTH Royal Institute of Technology.
    Moriana, Rosana
    KTH Royal Institute of Technology.
    Bäbler, Matthäus U.
    KTH Royal Institute of Technology.
    Ek, Monica
    KTH Royal Institute of Technology.
    Engvall, Klas
    KTH Royal Institute of Technology.
    Model-free rate expression for thermal decomposition processes: The case of microcrystalline cellulose pyrolysis2015Ingår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 143, s. 438-447Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We explore the possibility to derive a completely model-free rate expression using isoconversional methods. The Friedman differential method (Friedman, 1964) and the incremental integral method by Vyazovkin (2001) were both extended to allow for an estimation of not only the apparent activation energy but also the effective kinetic prefactor, defined as the product of the pre-exponential factor and the conversion function. Analyzing experimental thermogravimetric data for the pyrolytic decomposition of microcrystalline cellulose, measured at six different heating rates and three different initial sample masses (1.5-10 mg), revealed the presence of secondary char forming reactions and thermal lag, both increasing with increased sample mass. Conditioning of the temperature function enables extraction of more reliable prefactors and we found that the derived kinetic parameters show weak dependence on initial sample mass. Finally, by successful modeling of quasi-isothermal experimental curves, we show that the discrete rate expression estimated from linear heating rate experiments enables modeling of the thermal decomposition rate without any assumptions regarding the chemical process present. These findings can facilitate the design and optimization of industrial isothermal biomass fed reactors.

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