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Strandberg, Anna, DrORCID iD iconorcid.org/0000-0003-0895-3474
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Publications (10 of 18) Show all publications
Strandberg, A., Carlborg, M., Boman, C. & Broström, M. (2019). Ash Transformation During Single-Pellet Combustion of a Silicon-Poor Woody Biomass. Energy & Fuels, 33(8), 7770-7777
Open this publication in new window or tab >>Ash Transformation During Single-Pellet Combustion of a Silicon-Poor Woody Biomass
2019 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 8, p. 7770-7777Article in journal (Refereed) Published
Abstract [en]

Biomass fuels with calcium and potassium as the main ash-forming elements are expected to form ash consisting mainly of carbonates and oxides. These carbonates are stable in a rather narrow temperature range, which in turn depends on the Ca/K ratio, as well as on the surrounding atmosphere. The objective of the present study was to perform a detailed characterization of ash formation and transformation at a single-pellet level during combustion of silicon-poor woody biomass fuel. Combustion tests were performed with poplar in a single-pellet isothermal thermogravimetric analyzer operated at different temperatures and atmospheres and quenched at different stages of fuel conversion. The char and residual ashes were characterized for morphology and chemical composition. The focus of the experimental work in this study was on the time (conversion) resolved ash formation and transformations at the late part of the char combustion phase. Thermodynamic equilibrium calculations were used both to design the experiments and to support the interpretation of experimental results. It was concluded that carbonates were, in general, stable at low temperatures (here, 600–800 °C), identified as CaCO3, K2Ca2(CO3)3, and K2Ca(CO3)2, and decomposed at higher temperatures. In addition, a combined carbonate and phosphate phase in the form of carbonate apatite, Ca9.9(PO4)6(CO3)0.9, was also found, mainly at lower temperatures. However, for char/ash samples quenched before full conversion, CaCO3 was still found at temperatures higher than expected, possibly explained by the stabilizing effect of locally higher CO2 partial pressure within the burning fuel particles. Thus, the results of the present study provide new insights into conversion-based ash formation and transformation in a burning fuel particle with relevance for combustion of Si-poor woody biomass fuels.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Bioenergy
Identifiers
urn:nbn:se:umu:diva-163274 (URN)10.1021/acs.energyfuels.9b00937 (DOI)000481569100090 ()2-s2.0-85070870382 (Scopus ID)
Available from: 2019-09-12 Created: 2019-09-12 Last updated: 2019-09-16Bibliographically approved
Strandberg, A., Skoglund, N. & Thyrel, M. (2019). Characterization of porosity and microstructure of phosphorus-rich ash particles with X-ray micro-tomography. In: : . Paper presented at Nordic Flame Days, Turku, Finland, 28-29 August, 2019.
Open this publication in new window or tab >>Characterization of porosity and microstructure of phosphorus-rich ash particles with X-ray micro-tomography
2019 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

A large proportion of the nutrients supplied from forest and agricultural sector are lost today, both through leaching and removing of produced biomass. Sustainable and efficient recycling of macro- and micro nutrients can be done by combustion / co-combustion of residual streams, which makes it possible to utilize for example the phosphorus-bound fraction in the produced ash for further processing and recycling. The porosity of the ash is important for, among other things, leaching and water-retaining ability when returning to the soil. The purpose of the project is to provide detailed knowledge of porosity and internal microstructure of ash particles from combustion of residual biomass streams, by using X-ray based micro-tomography and image analysis. The results provide new insights into how ash porosity and micro structure differs between different ashes, depending on fuel and the choice of conversion process.

National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:umu:diva-163277 (URN)
Conference
Nordic Flame Days, Turku, Finland, 28-29 August, 2019
Available from: 2019-09-12 Created: 2019-09-12 Last updated: 2019-10-23Bibliographically approved
Skoglund, N., Strandberg, A., Öhman, M. & Boström, D. (2019). Elemental approaches to additives: mechanisms and dosage. In: : . Paper presented at World Sustainable Energy Days, REFAWOOD workshop session, 28 February, 2019, Wels, Austria.
Open this publication in new window or tab >>Elemental approaches to additives: mechanisms and dosage
2019 (English)Conference paper, Oral presentation only (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:umu:diva-157287 (URN)
Conference
World Sustainable Energy Days, REFAWOOD workshop session, 28 February, 2019, Wels, Austria
Note

Funded by the ERA-NET project REFAWOOD

Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2020-02-24Bibliographically approved
Strandberg, A., Skoglund, N., Thyrel, M., Lestander, T. A., Broström, M. & Backman, R. (2019). Time-Resolved Study of Silicate Slag Formation During Combustion of Wheat Straw Pellets. Energy & Fuels, 33(3), 2308-2318
Open this publication in new window or tab >>Time-Resolved Study of Silicate Slag Formation During Combustion of Wheat Straw Pellets
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2019 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 3, p. 2308-2318Article in journal (Refereed) Published
Abstract [en]

Ash formation during single-fuel pellet combustion of wheat straw at 700 and 1000 °C was studied throughout fuel conversion by quench cooling and analysis at different char conversion degrees. The combination of X-ray microtomography analysis and scanning electronic microscopy with energy-dispersive X-ray spectroscopy showed that ash accumulated in rigid net structures at 700 °C with streaks or small beads surrounding the char, and the pellet mostly maintained its size during the entire fuel conversion. At 1000 °C, the ash formed high-density melts that developed into bubbles on the surface. As the conversion proceeded, these bubbles grew in size and covered parts of the active char surface area, but without entirely blocking the gas transport. The successive char conversion dissolved increasing amounts of calcium in the potassium silicate melts, probably causing differences in the release of potassium to the gas phase. Similarities were found with slag from a combustion experiment in a domestic boiler, with regard to relative composition and estimated and apparent viscosity of the slag. Complete char encapsulation by ash layers limiting char burnout was not found at the single pellet level, nor to any greater extent from the experiment performed in a small domestic boiler.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Inorganic Chemistry Other Environmental Engineering
Identifiers
urn:nbn:se:umu:diva-157725 (URN)10.1021/acs.energyfuels.8b04294 (DOI)000462260600064 ()
Projects
Bio4Energy
Funder
Swedish Research Council, 2014-5041Bio4Energy
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-08-30Bibliographically approved
Strandberg, A., Skoglund, N., Thyrel, M., Lestander, T. A., Broström, M. & Backman, R. (2019). Wheat straw pellet combustion – characterization with X-ray micro-tomography and SEM-EDS analysis. In: : . Paper presented at World Sustainable Energy Days, Wels, Austri, Febrary 28, 2019.
Open this publication in new window or tab >>Wheat straw pellet combustion – characterization with X-ray micro-tomography and SEM-EDS analysis
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2019 (English)Conference paper, Oral presentation only (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:umu:diva-157286 (URN)
Conference
World Sustainable Energy Days, Wels, Austri, Febrary 28, 2019
Funder
Swedish Research Council, 2014-5041Swedish Research Council Formas, 2017-01613
Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2020-02-05Bibliographically approved
Strandberg, A., Thyrel, M., Skoglund, N., Lestander, T. A., Broström, M. & Backman, R. (2018). Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography. Fuel processing technology, 176, 211-220
Open this publication in new window or tab >>Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography
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2018 (English)In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 176, p. 211-220Article in journal (Refereed) Published
Abstract [en]

Ash formation during thermochemical conversion of biomass-based pellets influences both char conversion rates and ash-related operational problems. The objective of the present study was to provide detailed insights into changes in fuel and ash properties during fuel conversion. Pellets of poplar wood and wheat straw were used as model biofuels, representing vastly different compositions of ash-forming elements. Pellet samples at different char conversion phases were analyzed by synchrotron-based 3D X-ray micro-tomography, to map and visualize the development of cracks, internal cavities, and ash layers during conversion. The analysis of ash layers was complemented by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. The results provide new insights into how large cracks and internal cavities are developed already during devolatilization, for example, the poplar wood pellets had a 64% void fraction after the devolatilization stage. As expected, there were large variations between the ash layer properties for the two fuels. A porous, low density, and calcium-rich ash was formed from the poplar fuel, whereas the wheat straw ash was a high-density silicate melt that developed into bubbles on the surface. As the conversion proceeded, the wheat straw ash covered parts of the active char surface area, but without blocking the gas transport.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
ash composition, pellet, thermochemical conversion, wheat straw, poplar, SEM-EDS
National Category
Chemical Process Engineering Bioenergy
Identifiers
urn:nbn:se:umu:diva-146673 (URN)10.1016/j.fuproc.2018.03.023 (DOI)000435062600027 ()2-s2.0-85044919238 (Scopus ID)
Projects
Bio4Energy
Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2020-01-14Bibliographically approved
Strandberg, A. (2018). Fuel conversion and ash formation interactions: a thermochemical study on lignocellulosic biomass. (Doctoral dissertation). Umeå: Umeå Universitet
Open this publication in new window or tab >>Fuel conversion and ash formation interactions: a thermochemical study on lignocellulosic biomass
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomass is considered to be CO2 neutral, and to be able to reduce the dependency on fossil fuels the need for expanded and sustainable biomass feedstock is increasing. Ash-related problems are some of the most important aspects of this increasing use of new biomass assortments in thermal energy conversion systems. An improved basic understanding of fuel conversion, ash formation, ash transformation and ash interactions with the converting fuel is therefore important.

In the present thesis, the main objective was to provide new knowledge on thermochemical fuel conversion, specifically on how ash formation interacts with fuel conversion for lignocellulosic biomasses. The main methods used were experimental characterization of decomposition behavior and analysis of morphology and elemental composition of samples, using different appliances, analytical methods and fuels. Multivariate data analysis was successfully used on thermogravimetric data for prediction of compositional data and fuel properties.

New, detailed explanations of structural changes in char morphology and ash properties during conversion were provided including descriptions of the influences of ash formation on fuel conversion rates under different conditions. The influences were found different depending on both particle size and ash composition. One implication of these findings is that for fuels with low temperature melting ash, the diffusion barrier formed causes difficulties for typical thermogravimetric experiments aiming at determination of reactivity in the kinetically controlled regime. This is recommended to carefully consider for future studies. On a single pellet level, char encapsulation was not found to dominate and limit gas transport and conversion for any of the fuels tested. In practical applications, however, the situation may be different with thick ash layers accumulating on a fuel bed surface. Another important finding was the extensive formation of cracks and internal cavities during combustion of pellets, providing new insights in the fundamentals of fuel conversion.

Clean woody fuels, rich in calcium, formed a porous ash layer with no sign of limiting char conversion rates. The phase chemical transformations involving carbonate and oxide formation from poplar pellets was studied in detail. For grassy fuels, on the other hand, low melting point silicates are expected to form. The physical properties of K-Ca-silicates from silicon rich straw fuels were also characterized, providing new insights on ash formation on micrometer scale resolution; at high temperature, the silicate melt formed bubbles on the surface that partially covered the char, while for lower temperature a more rigid net structure was formed.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2018. p. 66
Keywords
Char conversion, pyrolysis, devolatilization, ash transformation, biomass, fuel characterization, fuel composition, ash composition, silicate formation, carbonate formation, thermogravimetric analysis, micro-tomography
National Category
Energy Systems Chemical Process Engineering Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-147532 (URN)978-91-7601-871-2 (ISBN)
Public defence
2018-06-01, Carl Kempe salen (KBE 303), KBC-huset, Umeå, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2018-05-09 Created: 2018-05-07 Last updated: 2018-06-09Bibliographically approved
Strandberg, A., Thyrel, M., Rudolfsson, M., Lestander, T. A., Backman, R., Skoglund, N. & Broström, M. (2017). Char conversion characterized by synchrotron based X-ray micro-tomography and SEM-EDS analysis. In: Ek, L., Ehrnrooth, H., Scarlat, N., Grassi, A., Helm, P. (Ed.), European Biomass Conference and Exhibition Proceedings: . Paper presented at 25th European Biomass International Conference, JUN 12-15, 2017,Stockholm, SWEDEN (pp. 485-491). ETA-Florence Renewable Energies
Open this publication in new window or tab >>Char conversion characterized by synchrotron based X-ray micro-tomography and SEM-EDS analysis
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2017 (English)In: European Biomass Conference and Exhibition Proceedings / [ed] Ek, L., Ehrnrooth, H., Scarlat, N., Grassi, A., Helm, P., ETA-Florence Renewable Energies , 2017, p. 485-491Conference paper, Published paper (Refereed)
Abstract [en]

Fuel and ash properties were studied during fuel conversion by careful examination of char samples at different degrees of char oxidation. Two types of lignocellulosic pellets with different compositions of ash forming elements were used: poplar and straw from wheat. The charred pellets were investigated by synchrotron-based X-ray micro-tomography to create 3D images of the development of cracks, internal cavities, and ash layers during conversion. Furthermore, SEM-EDS was used to for detailed chemical and morphological information of the ash layers formed. The pore development during pellet conversion was found to deviate from what has previously been described for the structure of solid wood particles. Large cracks and internal cavities were formed extensively already during devolatilization. For poplar, no mobility of the ash forming elements were observed as the burnout proceeded. Ash layer properties varied between the two fuels: poplar formed a porous, permeable, low density and Ca rich ash, whereas wheat straw ash accumulated on the surface in the form of high density melt that develop into bubbles on the surface. As the conversion proceeded, the ash layer covered more of the active char surface area, but without totally blocking the gas transport.

Place, publisher, year, edition, pages
ETA-Florence Renewable Energies, 2017
Series
European biomass conference and exhibition proceedings, ISSN 2282-5819
Keywords
chemical composition, pellet, thermochemical conversion, wheat straw, poplar
National Category
Chemical Process Engineering Bioenergy
Identifiers
urn:nbn:se:umu:diva-167261 (URN)000461835100090 ()2-s2.0-85043759507 (Scopus ID)
Conference
25th European Biomass International Conference, JUN 12-15, 2017,Stockholm, SWEDEN
Available from: 2020-01-14 Created: 2020-01-14 Last updated: 2020-01-14Bibliographically approved
Strandberg, A., Thyrel, M., Rudolfsson, M., Lestander, T. A., Backman, R., Skoglund, N. & Broström, M. (2017). Char conversion characterizedby synchrotron based X-ray micro-tomograhy and SEM-EDS analysis. In: EUBCE 2017 – 25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden: . Paper presented at EUBCE 2017 – 25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden.
Open this publication in new window or tab >>Char conversion characterizedby synchrotron based X-ray micro-tomograhy and SEM-EDS analysis
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2017 (English)In: EUBCE 2017 – 25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden, 2017Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Fuel and ash properties were studied during fuel conversion by careful examination of char samples at different degrees of char oxidation. Two types of lignocellulosic pellets with different compositions of ash forming elements were used: poplar and straw from wheat. The charred pellets were investigated by synchrotron-based X-ray micro-tomography to create 3D images of the development of cracks, internal cavities, and ash layers during conversion.  Furthermore, SEM-EDS was used to for detailed chemical and morphological information of the ash layers formed. The pore development during pellet conversion was found to deviate from what has previously been described for the structure of solid wood particles. Large cracks and internal cavities were formed extensively already during devolatilization. For poplar, no mobility of the ash forming elements were observed as the burnout proceeded. Ash layer properties varied between the two fuels: poplar formed a porous, permeable, low density and Ca rich ash, whereas wheat straw ash accumulated on the surface in the form of high density melt that develop into bubbles on the surface. As the conversion proceeded, the ash layer covered more of the active char surface area, but without totally blocking the gas transport.

Keywords
chemical composition, pellet, thermochemical conversion, wheat straw, poplar
National Category
Energy Engineering Analytical Chemistry
Identifiers
urn:nbn:se:umu:diva-136274 (URN)10.5071/25thEUBCE2017-2BO.14.5 (DOI)978-88-89407-17-2 (ISBN)
Conference
EUBCE 2017 – 25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden
Funder
Bio4Energy
Available from: 2017-06-15 Created: 2017-06-15 Last updated: 2018-06-09
Strandberg, A., Holmgren, P., Wagner, D. R., Molinder, R., Wiinikka, H., Umeki, K. & Broström, M. (2017). Effects of pyrolysis conditions and ash formation on gasification rates of biomass char. Energy & Fuels, 31(6), 6507-6514
Open this publication in new window or tab >>Effects of pyrolysis conditions and ash formation on gasification rates of biomass char
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2017 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 6, p. 6507-6514Article in journal (Refereed) Published
Abstract [en]

Pyrolysis conditions and the presence of ash-forming elements significantly influence char properties and its oxidation or gasification reactivity. In this study, intrinsic gasification rates of char from high heating rate pyrolysis were analyzed with isothermal thermogravimetry. The char particles were prepared from two biomasses at three size ranges and at two temperatures. Reactivity dependence on original particle size was found only for small wood particles that had higher intrinsic char gasification rates. Pyrolysis temperature had no significant effect on char reactivity within the range tested. Observations of ash formation highlighted that reactivity was influenced by the presence of ash-forming elements, not only at the active char sites but also through prohibition of contact between char and gasification agent by ash layer formation with properties highly depending on ash composition.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-136565 (URN)10.1021/acs.energyfuels.7b00688 (DOI)000404691900079 ()
Projects
Bio4Energy
Available from: 2017-06-19 Created: 2017-06-19 Last updated: 2019-09-06Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0895-3474

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