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Torrefaction and gasification of lignocellulosic hydrolysis residue from bio-ethanol production
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Bioendev AB.
Sigma Industry.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Production of lignocellulosic ethanol through hydrolysis (acid or enzymatic) combined with fermentation generate a large amount of residue consisting of mainly lignin and un-ydrolyzed cellulose. The significant amount of energy retained in this residue require further conversion as a measure to ensure economic viability for the total process. Thermal conversion of the hydrolysis residue through gasification for syngas production would improve the fuel yield in addition to the overall plant efficiency. Also, torrefaction of various biomass feedstocks has been shown to significantly improve biomass fuel characteristics in addition to having substantial positive effect on the energy consumption of the particle size reduction. The present work was an evaluation of hydrolysis residue and torrefied hydrolysis residue as gasification feedstocks in a bench-scale fluidized bed gasifier, based on syngas composition, particle formation, tar production and volatilization behavior. In addition, the effects of torrefaction on hydrolysis residue material characteristics were separately evaluated, including the influence of the process parameters on milling energy consumption and morphology. All torrefaction data was fitted to multiple linear regression models with good reproducibility and fit. The results confirm the previously reported improved feedstock characteristics resulting from torrefaction of biomass, however residence time was proved the most influential process parameter on the torrefaction severity, most likely derived from the lack of hemicellulose in the residue. The resulting syngas composition and quality indicated that both non-torrefied and torrefied hydrolysis residue were suitable gasification feedstocks. The hydrolysis residue product gas had elevated tar concentration but the torrefied residue demonstrated a significant reduction in the tar content (particularly the heavy tar components), compared to both raw hydrolyis residue and the wood reference feedstock. Hence, torrefaction may significantly reduce tar related problems in downstream equipment/processes.

Keyword [en]
torrefaction, gasification, enzymatic hydrolysis, bio-ethanol, lignocellulosic biomass, hydrolysis residue
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:umu:diva-139834OAI: oai:DiVA.org:umu-139834DiVA: diva2:1143784
Available from: 2017-09-22 Created: 2017-09-22 Last updated: 2017-09-28Bibliographically approved
In thesis
1. Biomass conversion through syngas-based biorefineries: thermochemical process integration opportunities
Open this publication in new window or tab >>Biomass conversion through syngas-based biorefineries: thermochemical process integration opportunities
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The replacement of fossil resources through renewable alternatives is one way to mitigate global climate change. Biomass is the only renewable source of carbon available for replacing oil as a refining feedstock. Therefore, it needs to be utilized not just as a fuel but for both biochemical and thermochemical conversion through biorefining. Optimizing and combining various conversion processes using a system perspective to maximize the valorization, biomass usage, and environmental benefits is of importance. This thesis work has evaluated the integration opportunities for various thermochemical conversion processes within a biorefinery system.

The aim for all evaluated concepts were syngas production through gasification or reforming. Two potential residue streams from an existing biorefinery were evaluated as gasification feedstocks, thereby combining biochemical and thermochemical conversion. Torrefaction as a biomass pretreatment for gasification end-use was evaluated based on improved feedstock characteristics, process benefits, and integration aspects. A system concept, “Bio2Fuels”, was suggested and evaluated for low-temperature slow pyrolysis as a way to achieve simultaneous biomass refinement and transport driven CO2 negativity.

Syngas was identified as a very suitable intermediate product for residue streams from biochemical conversion. Resulting syngas composition and quality showed hydrolysis residue as suitable gasification feedstock, providing some adjustments in the feedstock preparation. Gasification combined with torrefaction pretreatment demonstrated reduced syngas tar content. The co-gasification of biogas and wood in a FBG was successfully demonstrated with increased syngas H2/CO ratio compared to wood gasification, however high temperatures (≥1000°C) were required for efficient CH4 conversion. The demonstrated improved feedstock characteristics for torrefied biomass may facilitate gasification of biomass residue feedstocks in a biorefinery. Also, integration of a torrefaction unit on-site at the biorefinery or off-site with other industries could make use of excess low-value heat for the drying step with improved overall thermal efficiency. The Bio2Fuels concept provides a new application for slow pyrolysis. The experimental evaluation demonstrated significant hydrogen and carbon separation, and no significant volatilization of ash-forming elements (S and Cl excluded)  in low-temperature (<400°C) pyrolysis. The initial reforming test showed high syngas CH4 content, indicating the need for catalytic reforming.

The collective results from the present work indicate that the application of thermochemical conversion processes into a biorefinery system, making use of by-products from biochemical conversion and biomass residues as feedstocks, has significant potential for energy integration, increased product output, and climate change mitigation.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2017. 67 p.
Keyword
Biomass, biorefinery, thermochemical conversion, torrefaction, slow pyrolysis, gasification, process integration, carbon negativity
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-139839 (URN)978-91-7601-427-1 (ISBN)
Public defence
2017-10-20, N430, Naturvetarhuset, Umeå, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2017-09-29 Created: 2017-09-22 Last updated: 2017-09-29Bibliographically approved

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