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Low-temperature slow pyrolysis of biomass for H2-enriched syngas production and carbon negativity
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

To optimally utilize biomass resources as feedstock for fuels and chemicals production as well as for a potential substantial carbon sink, a dedicated process and system concept is suggested. The desired outcome of the process is a hydrogen-enriched pyrolysis gas and a carbon-enriched char, also retaining the ash-forming elements. To obtain a transport-driven large-scale CO2 negative system, the char is suggested as co-firing fuel in a facility with carbon capture and storage technology. In the present work, the basis for this Bio2Fuels separation concept was evaluated by 1) analysis of previously published empirical data for pyrolysis, and 2) chemical equilibrium calculations. The former analysis indicated on the potential for a significant separation of H and C to the pyrolysis gas and char respectively, with ~80% of the hydrogen and 40-60% of the carbon from the raw feedstock present in the pyrolysis gas product. Based on analyzed thermochemical driving forces, most of the ash-forming elements can be expected to be retained in the char, and an ash and alkali-free gas may be achieved at temperatures below 500°C. In addition, chemical equilibrium modelling of the pyrolysis gas reforming demonstrated a significantly increased H2/CO ratio in the syngas compared to gasification of the raw biomass.

Keyword [en]
biomass, slow pyrolysis, carbon negativity, hydrogen, pyrolysis gas reforming, syngas
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:umu:diva-97525OAI: oai:DiVA.org:umu-97525DiVA: diva2:773657
Available from: 2014-12-19 Created: 2014-12-19 Last updated: 2017-09-28Bibliographically approved
In thesis
1. Syngas production by integrating thermal conversion processes in an existing biorefinery
Open this publication in new window or tab >>Syngas production by integrating thermal conversion processes in an existing biorefinery
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The use of carbon from fossil-based resources result in changes in the earth’s climate due to emissions of greenhouse gases. Biomass is the only renewable source of carbon that may be converted to transportation fuels and chemicals, markets now fully dominated by traditional oil supply. The biorefinery concept for upgrading and refinement of biomass feedstocks to value-added end-products has the potential to mitigate greenhouse gas emissions and replace fossil products. Most biorefineries use biochemical conversion processes and may have by-product streams suitable as feedstocks for thermal conversion and production of syngas. Further synthesis to value-added products from the syngas could increase the product output from the biorefinery.

The application of thermal conversion processes integrated into an existing biorefinery concept has been evaluated in this licentiate thesis work. Two by-product streams; hydrolysis (lignin) residue from an ethanol plant and biogas from wastewater treatment, have been investigated as gasification/reforming feedstocks. Also, the pre-treatment method torrefaction has been evaluated for improved gasification fuel characteristics and integration aspects. A new process and system concept (Bio2Fuels) with potential carbon negative benefits has been suggested and evaluated as an alternative route for syngas production by separating biomass into a hydrogen rich gas and a carbon rich char product.

The evaluation demonstrated that hydrolysis residue proved a suitable feedstock for gasification with respect to syngas composition. Biogas can be further reformed to syngas by combined biomass gasification and methane reforming, with promising results on CH4 conversion rate and increased H2/CO ratio at temperatures ≥1000°C. The pre-treatment method torrefaction was demonstrated to improve fuel qualities and may thus significantly facilitate entrained flow gasification of biomass residue streams. Also, integration of a torrefaction plant at a biorefinery site could make use of excess heat for drying the raw material before torrefaction. The Bio2Fuels concept was evaluated and found feasible for further studies.

The application of thermal conversion processes into an existing biorefinery, making use of by-products and biomass residues as feedstocks, has significant potential for energy integration, increased product output as well as for climate change mitigation.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2014. 27 p.
Keyword
biorefinery, biofuels, syngas, gasification, torrefaction, methane reforming, H2/CO ratio, system analysis, CO2 negativity
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-92860 (URN)978-91-7601-101-0 (ISBN)
Presentation
2014-09-05, N460, Naturvetarhuset, Umeå Universitet, Umeå, 13:00 (Swedish)
Supervisors
Available from: 2014-12-19 Created: 2014-09-08 Last updated: 2014-12-19Bibliographically approved
2. 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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