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Role of Surface Morphology on Bed Particle Layer Formation During Thermal Conversion of Woody Biomass in Fluidized Beds
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.ORCID-id: 0000-0003-1203-0410
2024 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Bed particle layer formation is a crucial aspect of fluidized bed conversion of woody biomass, which can positively and negatively impact the process performance. The layer formation may lead to issues such as bed agglomeration and bed material deposition or reduced oxygen transport capacity of oxygen carriers. However, bed layer formation may positively affect the product gas composition in gasification. While extensive research has been conducted on the interactions between the ash-forming constituents from various wood-derived fuels and different bed materials, the influence of the bed particle surface properties on the bed layer characteristics remains largely unexplored in the existing literature.

This thesis thoroughly studied the role of bed particle surface morphology on the bed layer formation and its characteristics across different bed particle types within various fluidized bed conversion processes of woody biomass. The bed particle samples were collected from different bench-scale, semi-industrialscale, and industrial-scale conversion units at different time intervals from the start-up to assess the bed particle layer formation process throughout the bed particle age in different conversion processes of woody biomass. Natural sand bed 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 were obtained from a dual fluidized bed (DFB12-4) indirect gasification unit comprising a 12 MWth circulating fluidized bed combustor and a 2-4 MWth bubbling fluidized bed gasifier. Different types of ilmenite samples were taken from a 5 kWth bench-scale bubbling fluidized bed (BFB5) and a 12 MWth circulating fluidized bed (CFB12) combustion unit. Additionally, quartz and natural sand samples (comprising mainly quartz, K-feldspar, and Na-feldspar) were gathered from three different industrial fast pyrolysis plants. Bed particles found in the samples were subjected to different analysis methods. Scanning electron microscopy (SEM), coupled with energy dispersive spectroscopy (EDS), served as a primary tool for obtaining information regarding the morphology and elemental composition of different layers present on the surface of bed particles and inside the bed particle core. In instances where layers were too thin to be adequately examined via SEM/EDS, transmission electron microscopy (TEM) was employed as a complementary analysis method. X-ray microtomography (XMT) was also utilized to explore the distribution of bed particle layers on the particle surfaces. This method facilitated both qualitative and quantitative assessments, including observation of the surface morphology of the bed particles, analysis of the bed layer distribution on the bed particle surface, along with measurements of bed particle layer thickness and the volume fraction of various features throughout the bed particles.

Comprehensive analysis of the results from different characterization techniques showed that for all studied bed particles, regardless of their chemical composition, the inner layer (i.e., the Ca-reaction layer) was thicker on convex areas and thinner or entirely missing in the concave regions. The outer layer, mainly consisting of Ca compounds (i.e., the ash-deposition layer), was more likely to be found on the convex areas of the bed particle surface. Overall, the total bed particle layer thickness (inner and outer layer) was larger on the convex areas compared to the concaves. Consequently, the concave regions can facilitate mass transfer to and from the bed particle core even after the full development of the Ca-rich inner layer. Therefore, in the case of using quartz and Na-feldspar particles where there was a high chemical potential to react with fuel-derived gaseous alkali, the inner-inner layer and the crack layers (together referred to as the K-reaction layers) were connected to concaves on the bed particle surface. For the studied oxygen carrier (i.e., ilmenite), where most of the convex regions at the bed particle surface were covered with the Ca-rich layer, Fe could still migrate to the bed particle surface through concaves.

Bed particle layer characteristics observed in the fast pyrolysis plants were, to some extent, different compared to those in the combustion and gasification of woody biomass. In general, the layers were considerably thinner in the fast pyrolysis process, with a similar exposure time compared to combustion and gasification. Crack layers were not detected in quartz and Na-feldspar bed particles in any of the studied fast pyrolysis plants, and the inner layer had a lower Ca concentration than that in the combustion or gasification. Further, only the Ca-reaction layer was identified on feldspar bed particles. However, the distribution pattern of the bed particle layers at different morphologies on the bed particle surface resembled that in combustion and gasification.

The findings indicated that apart from the chemical composition, the surface morphology of the bed particles plays a vital role in determining their performance throughout the fuel conversion process in the fluidized bed. Specifically, as the crack layer formation in quartz bed particles is linked to the concave-shaped areas on the bed particle surface, quartz bed particles characterized by fewer concaves experience less fragmentation during the conversion process. Conversely, when employing ilmenite as an oxygen carrier, the presence of concaves on the particle surface facilitates the outward migration of Fe over prolonged exposures, albeit potentially compromising the structural integrity of the bed materials. Thus, a trade-off exists between achieving a desired oxygen-carrying capacity and maintaining structural integrity over extended durations. Previous studies have suggested that the formation of a Ca-rich layer on bed particles can positively influence the composition of the product gas in the gasification process. Results from this work showed that the Ca-rich layer on bed particles intended for gasification, such as K-feldspar and olivine, is thicker and more evenly distributed on particles possessing a surface morphology featuring more frequent convex shapes.

sted, utgiver, år, opplag, sider
Luleå: Luleå University of Technology, 2024.
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
HSV kategori
Forskningsprogram
Energiteknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-105164ISBN: 978-91-8048-546-3 (tryckt)ISBN: 978-91-8048-547-0 (digital)OAI: oai:DiVA.org:ltu-105164DiVA, id: diva2:1852879
Disputas
2024-06-11, E632, Luleå University of Technology, Luleå, 09:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2024-04-19 Laget: 2024-04-19 Sist oppdatert: 2024-05-21bibliografisk kontrollert
Delarbeid
1. Role of surface morphology in bed particle layer formation on quartz bed particles in fluidized bed combustion of woody biomass
Åpne denne publikasjonen i ny fane eller vindu >>Role of surface morphology in bed particle layer formation on quartz bed particles in fluidized bed combustion of woody biomass
Vise andre…
2024 (engelsk)Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 357, nr part A, artikkel-id 129702Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The influence of quartz bed particle surface morphology on the bed particle layer and crack layer formation process in fluidized bed combustion of woody biomass was investigated in this work. Bed material samples were collected at different sampling times from the startup with a fresh bed in industrial scale bubbling fluidized bed (BFB) and circulating fluidized bed (CFB) boilers, both utilizing woody biomass. X-ray microtomography (XMT) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) were employed to characterize bed particle layers and crack layers in the samples. Results showed that there is a noticeable difference between the bed layer characteristics over the so-called “concave” and “convex”-shaped morphologies on the bed particle surface with respect to layer formation. The concave areas are mainly covered with a thin inner layer, whilst the convex display a comparably thick inner layer and an outer layer. In addition, 3D images of the particles revealed that the crack layers mainly originate from concave areas where the particle is less protected by an outer bed particle layer in conjunction with cracks in the inner layer.

sted, utgiver, år, opplag, sider
Elsevier Ltd, 2024
Emneord
Bed material, Industrial-scale, Time-resolved, X-ray tomography
HSV kategori
Forskningsprogram
Energiteknik; Experimentell mekanik; Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-101365 (URN)10.1016/j.fuel.2023.129702 (DOI)001070700200001 ()2-s2.0-85170026881 (Scopus ID)
Forskningsfinansiär
Swedish Energy Agency, no. 46533-1
Merknad

Validerad;2023;Nivå 2;2023-09-18 (joosat);

CC BY 4.0 License;

For correction, see: Valizadeh A., Skoglund N., Forsberg F., Lycksam H., Öhman M., (2024). Corrigendum to “Role of surface morphology in bed particle layer formation on quartz bed particles in fluidized bed combustion of woody biomass” [Fuel 357(Part A) (2024) 129702]. Fuel. 364 131320. doi https://doi.org/10.1016/j.fuel.2024.131320

Tilgjengelig fra: 2023-09-18 Laget: 2023-09-18 Sist oppdatert: 2024-04-19bibliografisk kontrollert
2. A comparative study in 3D of bed particle layer characteristics in quartz and K-feldspar from fluidized bed combustion of woody biomass using X-ray microtomography
Åpne denne publikasjonen i ny fane eller vindu >>A comparative study in 3D of bed particle layer characteristics in quartz and K-feldspar from fluidized bed combustion of woody biomass using X-ray microtomography
Vise andre…
2023 (engelsk)Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 342, artikkel-id 127707Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Bed particle layer and crack layer characteristics at different ages were studied for quartz and K-feldspar bed particles from a 30 MWth bubbling fluidized bed and a 90 MWth circulating fluidized bed, both using woody biomass as fuel. X-ray microtomography (XMT) was utilized to determine the bed particle layer distribution on the bed particles' surface. For each bed particle type, the average bed particle layer thickness as well as average volume fractions of the bed particle layer and crack layers to the entire bed particle volume were determined at three different bed particle ages by utilizing XMT analysis. Comparison of the two different bed particle types showed that K-feldspar retains a thinner bed particle layer in both conversion processes compared to quartz. Crack layers were observed extensively in quartz bed particles to the extent of 19.3 vol% and 32.1 vol% after 13 days in the BFB and the CFB, respectively, which could cause deposition of the bed particle fragments. On the contrary, K-feldspar has almost no tendency toward forming crack layers.

sted, utgiver, år, opplag, sider
Elsevier Ltd, 2023
Emneord
Bed particle layer formation, Combustion, Fluidized bed, Woody biomass, X-ray microtomography
HSV kategori
Forskningsprogram
Energiteknik; Experimentell mekanik; Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-95819 (URN)10.1016/j.fuel.2023.127707 (DOI)000946690800001 ()2-s2.0-85148664496 (Scopus ID)
Konferanse
28th International Conference on the Impact of Fuel Quality on Power Production and the Environment, Åre, Sweden, September 19-23, 2022
Forskningsfinansiär
Swedish Energy Agency, 46533-1
Merknad

Godkänd;2023;Nivå 0;2023-03-08 (joosat);Konferensartikel i tidskrift

Part of special issue: 28th International Conference on the Impact of Fuel Quality on Power Production and the Environment, Edited by Flemming J. Frandsen, Stanley Harding, Terry Wall, Markus Broström, Maria Zevenhoven

Licens fulltext: CC BY License

Tilgjengelig fra: 2023-03-08 Laget: 2023-03-08 Sist oppdatert: 2024-04-19bibliografisk kontrollert
3. Role of Surface Morphology on Bed Material Activation during Indirect Gasification of Wood
Åpne denne publikasjonen i ny fane eller vindu >>Role of Surface Morphology on Bed Material Activation during Indirect Gasification of Wood
Vise andre…
2023 (engelsk)Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 333, Part 1, artikkel-id 126387Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier, 2023
Emneord
Fluidized bed, Bed material, Layer formation, Olivine, Feldspar, Material characterization
HSV kategori
Forskningsprogram
Energiteknik
Identifikatorer
urn:nbn:se:ltu:diva-93675 (URN)10.1016/j.fuel.2022.126387 (DOI)000880106400002 ()2-s2.0-85140309835 (Scopus ID)
Forskningsfinansiär
Swedish Energy Agency, 50450-1, P46533-1
Merknad

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

This article has previously appeared as a manuscript in a thesis

Tilgjengelig fra: 2022-10-21 Laget: 2022-10-21 Sist oppdatert: 2024-04-19bibliografisk kontrollert
4. Effect of time-dependent layer formation on the oxygen transport capacity of ilmenite during combustion of ash-rich woody biomass
Åpne denne publikasjonen i ny fane eller vindu >>Effect of time-dependent layer formation on the oxygen transport capacity of ilmenite during combustion of ash-rich woody biomass
Vise andre…
2023 (engelsk)Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 353, artikkel-id 129068Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Oxygen carrier aided combustion (OCAC) is a novel technology that aims to enhance combustion of heterogenous fuels by replacing the inert bed material with an active oxygen carrier. One of the promising oxygen carriers is natural ilmenite which shows decent oxygen transport capacity and mechanical stability under OCAC operating conditions. However, interactions between ilmenite and woody biomass ash lead to the formation of a calcium-rich ash layer, which affects the ability of the oxygen carrier (OC) to transfer oxygen throughout the boiler and subsequently decreases the combustion efficiency. This paper focuses on the time-dependent morphological and compositional changes in ilmenite bed particles and the consequence effects on the oxygen transport capacity and reactivity of ilmenite. Ilmenite utilized in this study was investigated in a 5 kW bubbling fluidized bed combustion unit, utilizing ash-rich bark pellets as fuel. A negative effect of iron migration on the oxygen transport capacity was observed in ilmenite bed particles after 6 h of operation in the bubbling fluidized bed reactor. The decrease in the oxygen transport capacity of ilmenite was found to correlate with the increased exposure time in the fluidized bed reactor and was caused by the migration and subsequent erosion of Fe from the ilmenite particles. On the other hand, the older bed particles show an increase in reaction rate, presumably due to the catalytic activity of the calcium-enriched outer layer on the bed particle surface.

sted, utgiver, år, opplag, sider
Elsevier Ltd, 2023
Emneord
Ash layer, Ilmenite, OCAC, Oxygen transport
HSV kategori
Forskningsprogram
Energiteknik
Identifikatorer
urn:nbn:se:ltu:diva-99289 (URN)10.1016/j.fuel.2023.129068 (DOI)001047077300001 ()2-s2.0-85164690459 (Scopus ID)
Forskningsfinansiär
Swedish Energy Agency, P46533-1
Merknad

Validerad;2023;Nivå 2;2023-08-08 (joosat);

Tilgjengelig fra: 2023-08-08 Laget: 2023-08-08 Sist oppdatert: 2024-04-19bibliografisk kontrollert
5. Role of Particle Geometry on the Structural Integrity of Sand and Rock Ilmenite Used as Oxygen Carrier in Combustion of Woody Biomass
Åpne denne publikasjonen i ny fane eller vindu >>Role of Particle Geometry on the Structural Integrity of Sand and Rock Ilmenite Used as Oxygen Carrier in Combustion of Woody Biomass
Vise andre…
2024 (engelsk)Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029Artikkel i tidsskrift (Fagfellevurdert) Epub ahead of print
Abstract [en]

The role of particle geometry in the structural integrity of sand and rock ilmenite bed particles was studied under prolonged exposure to oxygen carrier-aided combustion (OCAC) conditions in a 12 MWth circulating fluidized bed (CFB) boiler. Woody biomass was used as fuel. Bed particles were collected at different stages of the exposure. Fresh bed particles were used as reference samples. All the materials were examined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray microtomography (XMT). The obtained results showed that over time, sphericity diminishes in sand ilmenite, whereas the sphericity of rock ilmenite particles remains unchanged. For both bed types, it was noticed that cracks are mainly connected to the concave areas on the bed particle surface. It was also observed that in sand ilmenite, the bed particle layer predominantly forms on convex areas, resulting in nonuniform distribution, whereas in rock ilmenite, with infrequent convex and concave features, the layer is thicker and exhibits a more uniform distribution. Consequently, the bed particle layer in rock ilmenite plays a higher protection against the outward migration of iron. This, coupled with a lower frequency of concave areas, contributes to a reduced average volume fraction of porous regions and cracks, which makes rock ilmenite structurally more resistant to breakage than sand ilmenite. Notably, the difference in the structural integrity of the two bed types becomes even more pronounced with longer exposure times.

sted, utgiver, år, opplag, sider
American Chemical Society (ACS), 2024
HSV kategori
Forskningsprogram
Energiteknik; Experimentell mekanik
Identifikatorer
urn:nbn:se:ltu:diva-105155 (URN)10.1021/acs.energyfuels.4c00658 (DOI)2-s2.0-85192850521 (Scopus ID)
Forskningsfinansiär
Swedish Energy Agency, P46533-1Swedish Research Council, 2023-03500
Merknad

Full text: CC BY license;

This article has previously appeared as a manuscript in a thesis.

Tilgjengelig fra: 2024-04-19 Laget: 2024-04-19 Sist oppdatert: 2024-05-27
6. Layer Characteristics on Quartz and Feldspar Bed Particles DuringIndustrial-Scale Fast Pyrolysis of Woody Biomass
Åpne denne publikasjonen i ny fane eller vindu >>Layer Characteristics on Quartz and Feldspar Bed Particles DuringIndustrial-Scale Fast Pyrolysis of Woody Biomass
Vise andre…
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
HSV kategori
Identifikatorer
urn:nbn:se:ltu:diva-105163 (URN)
Tilgjengelig fra: 2024-04-19 Laget: 2024-04-19 Sist oppdatert: 2024-04-19

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