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Distribution of temperature, H2O and atomic potassium during entrained flow biomass combustion: coupling in situ TDLAS with modeling approaches and ash chemistry
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. Energy Engineering, Department of Engineering Sciences & Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.ORCID iD: 0000-0002-5777-9241
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
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2018 (English)In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 188, p. 488-497Article in journal (Refereed) Published
Abstract [en]

Tunable diode laser absorption spectroscopy (TDLAS) is employed for simultaneous detection of gas temperature, water vapor (H2O) and gas-phase atomic potassium, K(g), in an atmospheric, research-scale entrained flow reactor (EFR). In situ measurements are conducted at four different locations in the EFR core to study the progress of thermochemical conversion of softwood and Miscanthus powders with focus on the primary potassium reactions. In an initial validation step during propane flame operation, the measured axial EFR profiles of H2O density-weighted, path-averaged temperature, path-averaged H2O concentration and H2O column density are found in good agreement with 2D CFD simulations and standard flue gas analysis. During biomass conversion, temperature and H2O are significantly higher than for the propane flame, up to 1500 K and 9%, respectively, and K(g) concentrations between 0.2 and 270 ppbv are observed. Despite the large difference in initial potassium content between the fuels, the K(g) concentrations obtained at each EFR location are comparable, which highlights the importance of considering all major ash-forming elements in the fuel matrix. For both fuels, temperature and K(g) decrease with residence time, and in the lower part of the EFR, K(g) is in excellent agreement with thermodynamic equilibrium calculations evaluated at the TDLAS-measured temperatures and H2O concentrations. However, in the upper part of the EFR, where the measured H2O suggested a global equivalence ratio smaller than unity, K(g) is far below the predicted equilibrium values. This indicates that, in contrast to the organic compounds, potassium species rapidly undergo primary ash transformation reactions even if the fuel particles reside in an oxygen-deficient environment.

Place, publisher, year, edition, pages
New York: Elsevier, 2018. Vol. 188, p. 488-497
Keywords [en]
Tunable diode laser absorption spectroscopy (TDLAS), Atomic potassium, Entrained flow reactor, Biomass combustion, Thermodynamic equilibrium calculations, Computational fluid dynamics (CFD)
National Category
Atom and Molecular Physics and Optics Chemical Process Engineering Inorganic Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-141456DOI: 10.1016/j.combustflame.2017.10.013ISI: 000424859100040OAI: oai:DiVA.org:umu-141456DiVA, id: diva2:1154855
Available from: 2017-11-06 Created: 2017-11-06 Last updated: 2018-10-05Bibliographically approved
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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Qu, ZhechaoHolmgren, PerSkoglund, NilsWagner, David R.Broström, MarkusSchmidt, Florian M.

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Combustion and Flame
Atom and Molecular Physics and OpticsChemical Process EngineeringInorganic Chemistry

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