On the fast pyrolysis of torrefied woody biomass

Alexander Charnchai Louwes

    Research output: ThesisPhD Thesis - Research UT, graduation UT

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    Abstract

    Producing biofuels from woody biomass via torrefaction and fast pyrolysis can play a key role in the transition to a sustainable economy. Products like bio-coal and bio-oil have the potential to replace fossil fuels for the production of energy as well as chemicals and materials. However, bio-coal and bio-oil do not have the same properties as their fossil counterparts. For example, bio-oil from fast pyrolysis has a lower quality in terms of heating value, acidity, viscosity, and storage stability. A combination of a torrefaction pre-treatment with subsequent fast pyrolysis could improve the bio-oil’s quality, in the direction of fossil fuels.

    This thesis investigates combining torrefaction and fast pyrolysis to produce higher quality bio-oil from woody biomass. Torrefaction (200-300°C, 15-60 min) produces a coal-like biofuel called bio-coal. Fast pyrolysis (500°C, seconds) produces a liquid called bio-oil. Bio-oil has low quality compared to fossil fuels. Combining torrefaction and fast pyrolysis could improve bio-oil quality.

    A torrefaction reactor was built to produce bio-coal from beech wood and straw. Bio-coal had 40% higher heating value but 65% lower mass compared to raw biomass, and was compositionally and grindability-wise similar to coal. An existing cyclonic thermogravimetric analyzer was upgraded to measure fast pyrolysis kinetics and yields from raw and torrefied beech wood. An analytical model was developed to describe single particle conversion - the model accurately predicted conversion times.

    Further fast pyrolysis experiments were carried out to compare bio-oils from raw and torrefied woods. Torrefied bio-oils had reduced oxygen, increased heating value, and coal-like elemental composition. However, torrefied bio-oils were more viscous and unstable during aging. Torrefaction pretreatment was energetically favorable over post-treatment for deoxygenation.

    Economic analysis of a torrefaction + fast pyrolysis route vs. conventional wood combustion route for electricity in Brazil/Netherlands showed higher profitability for the torrefaction and fast pyrolysis process as well as lower CO2 emissions, but high sensitivity to feedstock and electricity prices.

    In conclusion, this thesis shows the technical feasibility and economic viability of the combination of a torrefaction pre-treatment with fast pyrolysis for the production of bio-oils of improved quality. More research is needed on bio-oil applications and optimization.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • University of Twente
    Supervisors/Advisors
    • Brem, Gerrit, Supervisor
    • Pozarlik, Artur K., Co-Supervisor
    Award date29 Nov 2023
    Place of PublicationEnschede
    Publisher
    Print ISBNs978-90-365-5890-7
    Electronic ISBNs978-90-365-5891-4
    DOIs
    Publication statusPublished - 29 Nov 2023

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