Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
The effect of surface morphology on bed particle layer characteristics in fluidized bed combustion and gasification of woody biomass
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0003-1203-0410
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A critical process phenomenon in fluidized bed combustion and gasification is the bed particle layer formation which might be problematic in cases where it instigates bed agglomeration and bed material deposition or could improve the process performance in cases where it has a positive effect on tar reduction in biomass gasification. The interactions between ash forming matter for a wide variety of wood-derived fuels with different types of bed materials in fluidized bed combustion and gasification have been profusely studied, and the underlying mechanism of bed particle layer formation has been suggested. Howbeit, the influence of bed material’s surface properties on bed layer characteristics has not been elaborated in the literature.

In this thesis, the effect of surface morphology on the formation of bed particle layers and crack layers has been investigated for different bed material types in combustion and gasification of woody biomass. Samples were selected from different full-scale and bench-scale conversion units at different ages from the start-up to investigate the development of the bed layer at different surface morphologies over the bed particle. Natural sand samples (consisting mainly of quartz and K-feldspar) were taken from a 30 MWth bubbling fluidized bed (BFB30) combustion unit and a 90 MWth circulating fluidized bed (CFB90) combustion unit, K-feldspar and olivine bed samples were taken from a dual fluidized bed (DFB) gasification unit (consisting of a 2-4 MWth bubbling fluidized bed gasifier and a 12 MWth circulating fluidized bed combustor), and ilmenite bed samples were taken from a 5 kWth bench scale bubbling fluidized bed (BFB5)combustion unit. 

X-ray microtomography analysis (XMT) was utilized to inspect the bed layer distribution and determine surface morphology in 3D, including measurements of the bed particle layer thickness over the particle surface. Distribution of the crack layers inside the bed core was also observed through the XMT images. Moreover, scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) along with transmission electron microscopy (TEM) were employed to investigate the elemental compositional distribution and to support interpretation of XMT results.  

The results revealed that for all types of bed materials, regardless of the conversion process, both inner and outer layers could be observed over the convex-shaped regions on the bed particle surfaces after some days, while the concave-shaped regions are mainly covered with a thin inner layer. Consequently, a thicker overall layer could be observed over the convex-shaped regions compared to the concave regions. Results from the combustion processes units show that K-feldspar bed particles retain a thinner overall layer compared to quartz when both are exposed to the same process condition and fuel ash composition. Moreover, almost no tendency for crack layer formation was observed in K-feldspar particles while up to 19% and 32% of the quartz bed particle could be engaged by the crack layers in bed samples taken from the BFB30 and CFB90, respectively. It was also observed that the crack layers are initiated from the concave-shaped regions on the bed surface where gaseous alkali can penetrate into the bed core through the inward cracks in the thin inner layer.

In the BFB5 combustor, it was observed for the samples taken 6 and 12 hours after the start-up that a thin Fe-rich layer ascends over the convex areas over the ilmenite surface due to the outward migration of Fe from the bed particle core. Over time, this iron-rich layer is covered with a Ca-rich outer layer that obstructs further migration of the Fe through the convex areas. For the older particles (i.e., 30 and 42 hours from the start-up) high concentration of Fe was observed in the concaves and more porous areas inside the bed particle core. 

Measurement of the average overall layer thickness for typical K-feldspar and olivine bed particles from the DFB gasifier showed that the latter exhibits thinner overall bed layer thickness. The elemental composition of the bed layer over the concave and convex regions was observed to be different for both bed materials. A slightly higher Fe concentration was observed over the convex areas on olivine. A similar trend was likewise noticed for Mn on both bed types.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-93678ISBN: 978-91-8048-198-4 (print)ISBN: 978-91-8048-199-1 (electronic)OAI: oai:DiVA.org:ltu-93678DiVA, id: diva2:1705183
Presentation
2022-12-15, E231, Luleå tekniska univerisitet, Luleå, 13:30 (English)
Opponent
Supervisors
Available from: 2022-10-21 Created: 2022-10-21 Last updated: 2023-09-05Bibliographically approved
List of papers
1. 3-dimensional Morphology Analysis of Bed Particle Layers in Quartz Bed Particles from Fluidized Bed Combustion of Woody Biomass Using X-ray microtomography
Open this publication in new window or tab >>3-dimensional Morphology Analysis of Bed Particle Layers in Quartz Bed Particles from Fluidized Bed Combustion of Woody Biomass Using X-ray microtomography
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Research subject
Energy Engineering; Experimental Mechanics; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-93668 (URN)
Available from: 2022-10-21 Created: 2022-10-21 Last updated: 2023-09-05Bibliographically approved
2. Role of Surface Morphology on Bed Material Activation during Indirect Gasification of Wood
Open this publication in new window or tab >>Role of Surface Morphology on Bed Material Activation during Indirect Gasification of Wood
Show others...
2023 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 333, Part 1, article id 126387Article in journal (Refereed) Published
Abstract [en]

Olivine and alkali-feldspar were utilized in separate campaigns in an indirect dual fluidized bed gasification campaign with woody biomass as fuel. After three days, both bed materials were reported to be active towards tar removal and exhibited oxygen-carrying abilities and had formed an ash layer consisting of an outer ash deposition layer and an inner interaction layer.

X-ray microtomography analysis concluded that a preferred deposition of ash happens onto convex regions of the bed particles, which results in an increase in thickness of the ash layer over convex regions. This effect is most pronounced for the outer layer which is a product of ash deposition. The inner layer exhibits a homogeneous thickness and is probably formed by interaction of Ca from the outer layer with the particles. Transmission electron microscopy revealed the presence of Fe and Mn on the surface of the particles in a solid solution with Mg. The oxygen-carrying effect which is found for aged particles is therefore attributed to the presence of Fe and Mn on the surface of aged particles. Alkali were found on the surface of both particles which are likely contributing to the catalytic activity of the material towards tar removal.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Fluidized bed, Bed material, Layer formation, Olivine, Feldspar, Material characterization
National Category
Energy Engineering Bioenergy
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-93675 (URN)10.1016/j.fuel.2022.126387 (DOI)000880106400002 ()2-s2.0-85140309835 (Scopus ID)
Funder
Swedish Energy Agency, 50450-1, P46533-1
Note

Validerad;2022;Nivå 2;2022-11-02 (sofila);

This article has previously appeared as a manuscript in a thesis

Available from: 2022-10-21 Created: 2022-10-21 Last updated: 2024-04-19Bibliographically approved
3. Bed Layer Formation Characteristics in Quartz and K-Feldspar Bed Particles during Fluidized Bed Combustion of Woody Biomass: A comparative study Using X-ray Microtomography
Open this publication in new window or tab >>Bed Layer Formation Characteristics in Quartz and K-Feldspar Bed Particles during Fluidized Bed Combustion of Woody Biomass: A comparative study Using X-ray Microtomography
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-93676 (URN)
Available from: 2022-10-21 Created: 2022-10-21 Last updated: 2023-09-05Bibliographically approved
4. Effect of Ash Layer Thicknesses on the Oxygen Transport Capacity of Ilmenite
Open this publication in new window or tab >>Effect of Ash Layer Thicknesses on the Oxygen Transport Capacity of Ilmenite
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-93677 (URN)
Available from: 2022-10-21 Created: 2022-10-21 Last updated: 2023-09-05Bibliographically approved

Open Access in DiVA

fulltext(29569 kB)206 downloads
File information
File name FULLTEXT01.pdfFile size 29569 kBChecksum SHA-512
302407c6dd5687ff6d8a2d63ffd8f72c9e107e4bc400b4e6d80af213fe5a6ec0b66fa33a2e32171e3753c29a56b8a05e0fa46a327f3a20045d2ac8ffc7c4ff23
Type fulltextMimetype application/pdf

Authority records

Valizadeh, Ali

Search in DiVA

By author/editor
Valizadeh, Ali
By organisation
Energy Science
Energy Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 206 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 379 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf