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  • 1. Backman, Marjan Bozaghian
    et al.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Thyrel, Mikael
    Bergstrom, Dan
    Larsson, Sylvia H.
    Does Mechanical Screening of Contaminated Forest Fuels Improve Ash Chemistry for Thermal Conversion?2020Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 34, nr 12, s. 16294-16301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of mechanical screening of severely contaminated forest fuel chips was investigated, focusing on main ash-forming elements and slagging tendency and other properties with relevance for thermal conversion. In this study, screening operations were performed according to practice on an industrial scale by combining a star screen and a supplementary windshifter in six different settings and combinations. Mechanical screening reduced the amount of ash and fine particles in the accept fraction. However, the mass losses for the different screening operations were substantial (20-50 wt %). Fuel analyses of the non-screened and the screened fuels showed that the most significant screening effect was a reduction of Si and Al, indicating an effective removal of sand and soil contaminations. However, the tested fuel's main ash-forming element's relative concentration did not indicate any improved combustion characteristics and ash-melting behavior. Samples of the accept fractions and non-screened material were combusted in a single-pellet thermogravimetric reactor, and the resulting ashes' morphology and elemental composition were analyzed by scanning electron microscopy-energy dispersive X-ray spectrometry and the crystalline phases by powder X-ray diffraction. Results from both these analyses confirmed that screening operations had no, or minor, effects on the fuels' ash chemistry and slagging tendencies, i.e., the fuels' proneness to ash melting was not improved. However, the reduction of ash and fine particles can reduce slagging and other operational problems in smaller and more sensitive combustion units.

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  • 2.
    Bozaghian Bäckman, Marjan
    et al.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Ume.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    De La Fuente, Teresa
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Karjalainen, Mikko
    Luke Natural Resources Institute Finland, Kokkola, Finland.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Bergström, Dan
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Larsson, Sylvia H.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Does mechanical screening improve fuel properties?: Effects of mechanical screening of stored logging residue chips on ash chemistry and other parameters relevant for combustion2019Konferansepaper (Fagfellevurdert)
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    poster
  • 3.
    Holmgren, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wagner, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Molinder, Roger
    Energitekniskt Centrum, Piteå.
    Wiinikka, Henrik
    Energitekniskt Centrum, Piteå.
    Umeki, Kentaro
    Luleå Technical University.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Size, Shape and Density Changes of Biomass Particles during Devolatilization in a Drop Tube Furnace2014Inngår i: Impacts of Fuel Quality on Power Production October 26 –31, 2014, Snowbird, Utah, USA, 2014Konferansepaper (Annet vitenskapelig)
  • 4.
    Holmgren, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wagner, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Molinder, Roger
    Wiinikka, Henrik
    Umeki, Kentaro
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Size, shape, and density changes of biomass particles during rapid devolatilization2017Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 206, s. 342-351Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Particle properties such as size, shape and density play significant roles on particle flow and flame propagationin pulverized fuel combustion and gasification. A drop tube furnace allows for experiments athigh heating rates similar to those found in large-scale appliances, and was used in this study to carryout experiments on pulverized biomass devolatilization, i.e. detailing the first stage of fuel conversion.The objective of this study was to develop a particle conversion model based on optical informationon particle size and shape transformation. Pine stem wood and wheat straw were milled and sieved tothree narrow size ranges, rapidly heated in a drop tube setup, and solid residues were characterized usingoptical methods. Different shape descriptors were evaluated and a shape descriptor based on particleperimeter was found to give significant information for accurate estimation of particle volume. The opticalconversion model developed was proven useful and showed good agreement with conversion measuredusing a reference method based on chemical analysis of non-volatilized ash forming elements.The particle conversion model presented can be implemented as a non-intrusive method for in-situ monitoringof particle conversion, provided density data has been calibrated.

  • 5. Nordin, Andreas
    et al.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Elbashir, Sana
    Åmand, Lars-Erik
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Pettersson, Anita
    Co-Combustion of Municipal Sewage Sludge and Biomass in a Grate Fired Boiler for Phosphorus Recovery in Bottom Ash2020Inngår i: Energies, E-ISSN 1996-1073, Vol. 13, nr 7, artikkel-id 1708Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phosphorus has been identified as a critical element by the European Union and recycling efforts are increasingly common. An important phosphorus-containing waste stream for recycling is municipal sewage sludge (MSS), which is used directly as fertilizer to farmland. However, it contains pollutants such as heavy metals, pharmaceutical residues, polychlorinated bi-phenyls (PCBs) and nano-plastics. The interest in combustion of MSS is continuously growing, as it both reduces the volume as well as destroys the organic materials and could separate certain heavy metals from the produced ashes. This results in ashes with a potential for either direct use as fertilizer or as a suitable feedstock for upgrading processes. The aim of this study was to investigate co-combustion of MSS and biomass to create a phosphorus-rich bottom ash with a low heavy metal content. A laboratory-scale fixed-bed reactor in addition to an 8 MWth grate-boiler was used for the experimental work. The concentration of phosphorus and selected heavy metals in the bottom ashes were compared to European Union regulation on fertilizers, ash application to Swedish forests and Swedish regulations on sewage sludge application to farmland. Element concentrations were determined by ICP-AES complemented by analysis of spatial distribution with SEM-EDS and XRD analysis to determine crystalline compounds. The results show that most of the phosphorus was retained in the bottom ash, corresponding to 9-16 wt.% P2O5, while the concentration of cadmium, mercury, lead and zinc was below the limits of the regulations. However, copper, chromium and nickel concentrations exceeded these standards.

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  • 6.
    Persson, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Decomposition modeling using thermogravimetry with a multivariate approach2013Inngår i: European Biomass Conference and Exhibition Proceedings: 21st European Biomass Conference and Exhibition, ETA-Florens Renewable Energies , 2013, s. 1451-1455Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    There exists a need for simple and reliable characterization methods for biomass in several scientific areas. Not many publications report on multivariate statistical treatment of thermogravimetric data, and therefore the objectives of this study were to i) evaluate the potential for using a multivariate statistical approach for modeling degree of decomposition of thermally pretreated wood using data from conventional thermogravimetric analysis, ii) compare the predictions from the multivariate chemometric model with a gaussian curve fit approach made to the same data set, and iii) demonstrate the method comparison also for torrefied material from a pilot scale torrefaction plant, an application with relevance for bio-based energy systems under development. The results showed that the suggested method for decomposition modeling performed well, even though some limitations were discovered. It was also proven useful for the application tested.

  • 7.
    Skoglund, Nils
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Boström, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Elemental approaches to additives: mechanisms and dosage2019Konferansepaper (Annet vitenskapelig)
  • 8.
    Skoglund, Nils
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Perrin, Jonathan
    Anatomix Beamline, Synchrotron SOLEIL – L'Orme des Merisiers – Départementale 128, Saint-Aubin, France.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Characterisation of ash particles from co-combustion of bark and sludges from pulp and paper industry2023Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 340, artikkel-id 127597Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recycling phosphorus from waste streams for fertilization purposes could contribute to a sustainable society. The production in the pulp and paper industry results in several waste streams, among others nutrient-rich sludges in different forms. This study presents a detailed chemical and 3D characterization of ash from co-combustion of bark and two types of sludges from a paper mill; mixed sludge and biosludge. The combustion performance was investigated for these experiments and advanced analysis methods were used to characterise the ashes to correlate chemical and physical properties relevant for nutrient recycling. The elemental composition was determined by energy-dispersive X-ray spectroscopy; dominating crystalline phases by X-ray diffraction; and morphology, porosity, pore size distribution and active surface area of the slag were analysed with synchrotron-based X-ray micro-tomography and image analysis. Slag was formed in all combustion experiments to a large extent with increasing amounts with a higher proportion of sludge. Nutrient amounts indicate that slag particles from co-combustion of both biosludge and mixed sludge can be useful either as a soil improvement directly or for recovery processes. Slag from combustion of 30 wt% biosludge and 70 wt% bark contained the highest amount of phosphorus, 9 at% on a C and O free basis. Evaluation of tomography data showed that discrete and open pores could be distinguished on a micrometre scale. The porosity of the slag varied between the replicates and fuel mixtures, on average between 17 and 23 vol% for the bark and sludge mixtures. Open pore volume displayed large variations, on average 39–56 vol% of the pores were open pores connected to the surrounding volume. For all samples, 90 % of the pores were small, with an equivalent diameter under 30 μm, but the largest pore volume (80–90 %) consists of pores with an equivalent diameter over 75 μm. In soils, pores with a minimum equivalent diameter over 30 μm generally transmit water and the smaller pores store water. The slag particles have relatively thick walls, with few pore openings to the surroundings, indicating that the slag needs to be pre-treated by milling or crushing before application in the soil.

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  • 9.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fuel conversion and ash formation interactions: a thermochemical study on lignocellulosic biomass2018Doktoravhandling, med artikler (Annet vitenskapelig)
    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.

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  • 10.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Carlborg, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Boman, Christoffer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Ash formation and transformation during combustion of poplar wood pelletsManuskript (preprint) (Annet vitenskapelig)
  • 11.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Carlborg, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Boman, Christoffer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Ash Transformation During Single-Pellet Combustion of a Silicon-Poor Woody Biomass2019Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, nr 8, s. 7770-7777Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 12.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Predicting fuel properties of biomass using thermogravimetry and multivariate data analysis2017Inngår i: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 156, s. 107-112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simple and reliable characterization methods for determining fuel properties of biomass are needed for several different applications. This paper describes and demonstrates such a method combining thermogravimetric analysis with multivariate data analysis, based on the thermal decomposition behavior of the fuel. Materials used for the tests were milled samples of wood chips thermally pretreated under different conditions in a torrefaction pilot plant. The predictions using the multivariate model were compared to those from a conventional curve deconvolution approach. The multivariate approach showed better and more flexible performance, with error of prediction of 2.7% for Mass Yield prediction, compared to the reference method that resulted in 29.4% error. This multivariate method could handle samples pretreated under more severe conditions compared to the curve deconvolution methods. Elemental composition, heating value and volatile content were also predicted with even higher accuracies. The results highlight the usefulness of the method and also the importance of using calibration data of good quality. (C) 2016 Elsevier B.V. All rights reserved.

  • 13.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wagner, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Molinder, Roger
    Wiinikka, Henrik
    Umeki, Kentaro
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Effects of pyrolysis conditions and ash formation on gasification rates of biomass char2017Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, nr 6, s. 6507-6514Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 14.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Thyrel, Mikael
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Characterization of porosity and microstructure of phosphorus-rich ash particles with X-ray micro-tomography2019Konferansepaper (Fagfellevurdert)
    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.

  • 15.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Morphological characterisation of ash particles from co-combustion of sewage sludge and wheat straw with X-ray microtomography2021Inngår i: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 135, s. 30-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Combustion of phosphorus-rich residual streams can produce nutrient-rich ashes and these can be used either in further processing or as materials for direct nutrient recycling. The latter requires knowledge on morphological parameters of such ash particles that may impact plant growth, nutrient availability, and soil physical properties. The present work aims to determine the porosity, pore size, and specific surface area of ash particles, and discuss these properties in light of literature concerning interaction with soil water and plant roots. Bottom ash particles from combustion of sewage sludge and wheat straw and their co-combustion were analysed with X-ray microtomography. Image analysis provided information on morphology, specific surface area, porosity, and pore structure on a micrometre scale resolution. Co-combusting sewage sludge with wheat straw resulted in differences in ash particles' porosity and pore structure compared to combustion of pure fuels. Pure wheat straw ash displayed 62 vol% porosity while there was no apparent difference between 10 wt% or 30 wt% mixtures of sewage sludge, with a porosity of 29–31 vol%. Open pore volume comprise the largest part of the porosity (72–99 vol%) enabling interaction between surrounding pore water and nutrients.

    Overall, the ash particles display large open volume fractions and thin particle walls which may lead to rapid weathering and extensive interaction with soil water. The particles generally contained pore openings over 200 µm towards the surroundings, which provide opportunities for interaction with microbes and roots from a variety of plant species in addition to nutrient transport by soil water.

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  • 16.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, SE 901 83 Umeå, Sweden.
    Lestander, Torbjörn A.
    Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, SE 901 83 Umeå, Sweden.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Backman, Rainer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Time-Resolved Study of Silicate Slag Formation During Combustion of Wheat Straw Pellets2019Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, nr 3, s. 2308-2318Artikkel i tidsskrift (Fagfellevurdert)
    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.

    Fulltekst (pdf)
    fulltext
  • 17.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Thyrel, Mikael
    Swedish University of Agricultural Sciences.
    Lestander, Torbjörn A.
    Sveriges Lantbruksuniversitet, Institutionen för skogens biomaterial och teknologi.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Backman, Rainer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wheat straw pellet combustion – characterization with X-ray micro-tomography and SEM-EDS analysis2019Konferansepaper (Annet vitenskapelig)
  • 18.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Science, Department of Forest Biomaterials and Technology.
    Lestander, Torbjörn
    Swedish University of Agricultural Science, Department of Forest Biomaterials and Technology.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Backman, Rainer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Time-dependent studies of silicate slag formation during combustion of wheat strawManuskript (preprint) (Annet vitenskapelig)
  • 19.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Steinvall, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Morari, Adrian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Boman, Christoffer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Time-resolved understanding of the conversion of biochar and its properties during gasification2023Konferansepaper (Annet vitenskapelig)
  • 20.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Thyrel, Mikael
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Falk, Joel
    Energy Engineering, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden.
    Öhman, Marcus
    Energy Engineering, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Morphology and phosphate distribution in bottom ash particles from fixed-bed co-combustion of sewage sludge and two agricultural residues2024Inngår i: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 177, s. 56-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this study was to provide detailed knowledge of the morphological properties of ash particles, including the volumetric fractions and 3D distributions of phosphates that lay within them. The ash particles came from digested sewage sludge co-combusted with K- and Si-rich wheat straw or K-rich sunflower husks. X-ray micro-tomography were combined with elemental composition and crystalline phase information to analyse the ash particles in 3D.

    Analyses of differences in the X-ray attenuation enabled calculation of 3D phosphate distributions that showed high heterogeneity in the slag particles. This is underscored by a distinct absence of phosphates in iron-rich and silicon-rich parts. The slag from silicate-based wheat straw mixtures had lower average attenuation than that from sunflower husks mixtures, which contained more calcium. Calculated shares of phosphates between 7 and 17 vol% were obtained, where the highest value for a single assigned phosphate was observed in hard slag from wheat straw with 10 % sewage sludge. The porosity was notably higher for particles from pure wheat straw combustion (62 vol%), compared to the other samples (15–35 vol%). A high open pore volume fraction (60–97 vol%) indicates that a large part of the pores can be accessed by the surroundings. For all samples, more than 60 % of the discrete (closed) pores had an equivalent diameter < 30 μm, while the largest volume fraction consisted of pores with an equivalent diameter > 75 μm. Slag from sunflower husk mixtures had larger pore volumes and a greater relative number of discrete pores >75 µm compared to wheat straw mixtures.

    Fulltekst (pdf)
    fulltext
  • 21.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, SE 901 83, Sweden.
    Rudolfsson, M.
    Lestander, T. A.
    Backman, Rainer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Char conversion characterized by synchrotron based X-ray micro-tomography and SEM-EDS analysis2017Inngår i: European Biomass Conference and Exhibition Proceedings / [ed] Ek, L., Ehrnrooth, H., Scarlat, N., Grassi, A., Helm, P., ETA-Florence Renewable Energies , 2017, s. 485-491Konferansepaper (Fagfellevurdert)
    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.

  • 22.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Lestander, Torbjörn A.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Backman, Rainer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography2018Inngår i: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 176, s. 211-220Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 23.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wagner, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Molinder, Roger
    Energitekniskt Centrum, Piteå.
    Wiinikka, Henrik
    Energitekniskt Centrum, Piteå.
    Umeki, Kentaro
    Luleå Technical University.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Influence of Biomass Particle Properties and Pyrolysis Conditions on Char Reactivity2014Inngår i: Proceedings of Impacts of Fuel Quality on Power Production October 26 –31, 2014, Snowbird, Utah, USA, 2014Konferansepaper (Annet vitenskapelig)
  • 24.
    Wagner, David R.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wiinikka, Henrik
    Energitekniskt Centrum, Piteå.
    Molinder, Roger
    Energitekniskt Centrum, Piteå.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fate of Inorganic Species during Biomass Devolatilization in a Drop Tube Furnace2014Inngår i: Impacts of Fuel Quality on Power Production October 26–31, 2014, Snowbird, Utah, USA, 2014Konferansepaper (Annet vitenskapelig)
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