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Slag Formation During Entrained Flow Gasification: Calcium Rich Bark Fuel with KHCO3 Additive
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå Universitet. (TEC-lab)
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå Universitet. (TEC-lab)
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå Universitet. (TEC-lab)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Managing slag properties is of utmost importance for successful operation of entrained flow gasifiers. The present study details some aspects of slag formed from a softwood bark fuel, and especially the situation with only small amounts of mineral contaminants, meaning composition is shifted from Si- towards P-dominated ash. Wood bark with and without KHCO3 additive was gasified between 850 °C and 1300 °C at O2 stoichiometric ratio (λ) 0.6 to study the resulting ash properties and the influence of the additive. The ash particles collided with a flat impact probe inside the hot reactor, with particle impact angles varied between 90° to 30°. The reactor and probe were constructed to allow for long-distance microscope data collection close to the surface of the probe. In situ PIV and SEM-EDS of deposit samples from lab scale entrained flow gasification experiments were used for evaluation, while XRD was used to characterize carbonates. High potassium release was found but numerous spherical ash particles indicated lower ash melting temperatures than expected from the bulk ash composition. These new findings propose a mechanism for melt formations involving carbonates rich in potassium and phosphorous, followed by K-release and calcination leading to solidification.

National Category
Inorganic Chemistry Energy Engineering
Identifiers
URN: urn:nbn:se:umu:diva-152329OAI: oai:DiVA.org:umu-152329DiVA, id: diva2:1252730
Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2018-10-04
In thesis
1. Entrained flow studies on biomass fuel powder conversion and ash formation
Open this publication in new window or tab >>Entrained flow studies on biomass fuel powder conversion and ash formation
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Partikelomvandling och askbildning i pulverflammor
Abstract [en]

Reducing the global dependence on fossil fuels is of paramount importance in tackling the environmental challenges we face, not only tomorrow, but already today. Biomass offers a renewable supply of CO2-neutral raw material that can be converted into many different forms of fuels and valuable chemicals, making it a prime candidate for the technologies of tomorrow. However, the heterogeneous nature and distinctly different elemental composition of biomass compared to traditional fossil sources present new challenges to be solved. When it comes to thermochemical technologies, key issues concern fuel conversion efficiency, ash formation, ash/fuel interactions and ash/reactor material interactions.

The objective of the present thesis was to provide new knowledge and insights into thermochemical fuel conversion, in particular its application in entrained flow technologies. A laboratory-scale reactor was constructed, evaluated and was used to study several aspects of high-temperature entrained flow biomass fuel conversion. Pulverized fuel particles from different biomass sources were used, and their physical and chemical interactions with the surrounding atmosphere, the concurrent ash element release, ash formation, and phase interactions were also studied in detail. In addition to the entrained flow reactor designed and constructed for this purpose, the main method for data collection was in situ optical studies of converting particles, either while entrained in the flow or when impacting upon surfaces. Elemental composition analysis of collected samples and gas analysis were also performed, allowing for a deeper understanding of ash element fractionation and interactions and thus explaining the observed properties of the resulting deposits or slag.

The degree of conversion of fuels with very low ash content, such as stem wood, was well described and modeled by a novel method using optical data, offering a non-intrusive and non-destructive alternative to traditional techniques. Coupling computational fluid dynamics with optical data allowed for improved experimental data interpretation and provided improved accuracy for fuel particle residence time estimations, which is an important parameter when studying fast chemical reactions such as those taking place in reactors for entrained flow conditions. The results from studies on ash formation gave new insights into the feasibility of using dry-mixed K-rich additives for improving slag properties during gasification of Ca-rich and Si-rich fuels. Interpretations of the experimental results were supported by thermodynamic equilibrium calculations, and the conclusions highlight both possibilities and challenges in gasification with high fuel flexibility while at the same time producing a flowing slag. Applications and future implications are discussed, and new topics of interest are presented.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2018. p. 63
Keywords
Thermochemical biomass conversion, particle image velocimetry, gasification, entrained flow reactor, ash transformation, equilibrium calculations, slag formation
National Category
Inorganic Chemistry Chemical Engineering Energy Engineering
Identifiers
urn:nbn:se:umu:diva-152332 (URN)978-91-7601-937-5 (ISBN)
Public defence
2018-10-26, N430, Naturvetarhuset, Umeå, 10:00 (English)
Opponent
Supervisors
Funder
Bio4EnergySwedish Research CouncilSwedish Energy Agency
Available from: 2018-10-05 Created: 2018-10-02 Last updated: 2018-10-18Bibliographically approved

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Holmgren, PerCarlborg, MarkusBroström, Markus

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