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  • 1.
    Albán Reyes, Diana Carolina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden .
    Svedberg, Anna
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sundman, Ola
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    The influence of different parameters on the mercerisation of cellulose for viscose production2016In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 23, no 2, p. 1061-1072Article in journal (Refereed)
    Abstract [en]

    A quantitative analysis of degree of transformation from a softwood sulphite dissolving pulp to alkalised material and the yield of this transformation as a function of the simultaneous variation of the NaOH concentration, denoted [NaOH], reaction time and temperature was performed. Samples were analysed with Raman spectroscopy in combination with multivariate data analysis and these results were confirmed by X-ray diffraction. Gravimetry was used to measure the yield. The resulting data were related to the processing conditions in a Partial Least Square regression model, which made it possible to explore the relevance of the three studied variables on the responses. The detailed predictions for the interactive effects of the measured parameters made it possible to determine optimal conditions for both yield and degree of transformation in viscose manufacturing. The yield was positively correlated to the temperature from room temperature up to 45 A degrees C, after which the relation was negative. Temperature was found to be important for the degree of transformation and yield. The time to reach a certain degree of transformation (i.e. mercerisation) depended on both temperature and [NaOH]. At low temperatures and high [NaOH], mercerisation was instantaneous. It was concluded that the size of fibre particles (mesh range 0.25-1 mm) had no influence on degree of transformation in viscose processing conditions, apparently due to the quick reaction with the excess of NaOH.

  • 2.
    Almqvist, Jonna
    et al.
    SP Processum.
    Westin, Gunnar
    SP Processum.
    Öberg, Christian
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Luleå University of Technology, Department of Department of Engineering Sciences and Mathematics, Energy Science.
    Samförbränning av bioslam från massaindustrin i bubblande fluidiserad bädd2016Report (Other (popular science, discussion, etc.))
  • 3.
    Boman, Christoffer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash transformation chemistry in biomass fixed beds with focus on slagging and aerosols: 20 years of research and new developments2017In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Article in journal (Other academic)
  • 4.
    Boström, Dan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Ash transformation chemistry during energy conversion of biomass2010In: Impacts of Fuel Quality on Power Production & Environment: 29/08/2010 - 03/09/2010, Impacts of Fuel Quality , 2010Conference paper (Refereed)
    Abstract [en]

    There is relatively extensive knowledge available concerning ash transformation reactions during energy conversion of woody biomass. Traditionally, these assortments have constituted the main resources for heating in Sweden. In recent decades the utilization of these energy carriers has increased, from a low technology residential small scale level to industrial scale (e.g. CHP plants). Along this evolution ash-chemical related phenomena for woody biomass has been observed and studied. So, presently the understanding for these are, if not complete, fairly good. Briefly, from a chemical point of view the ash from woody biomass could be characterized as a silicate dominated systems with varying content of basic oxides and with relatively high degree of volatilization of alkali sulfates and chlorides. Thus, the main ash transformation mechanisms in these systems have been outlined. Here, an attempt to give a general description of the ash transformation reactions of biomass fuels is presented, with the intention to provide guidance in the understanding of ash matter behavior in the utilization of any biomass fuel, primarily from knowledge of the concentrations of ash forming elements but also by considering the physical condition in the specific combustion appliance and the physical characteristic of the biomass fuel. Furthermore, since the demand for CO2-neutral energy resources has increased the last years and will continue to do so in the foreseeable future, other biomasses as for instance agricultural crops has become highly interesting. Globally, the availability of these shows large variation. In Sweden, for instance, which is a relatively spare populated country with large forests, these bio-masses will play a secondary role, although not insignificant. In other parts of the world, more densely populated and with a large agricultural sector, such bio-masses may constitute the main energy bio-mass resource in the future. However, the content of ash forming matter in agricultural bio-mass is rather different in comparison to woody biomass. Firstly, the content is much higher; from being about 0.3 – 0.5% (wt) in stem wood, it can amount to between 2 and 10 %(wt) in agricultural biomass. In addition, the composition of the ash forming matter is different. Shortly, the main difference is due to a much higher content of phosphorus (occasionally also silicon) which has major consequences on the ash-transformation reactions. In many crops, the concentration of phosphorus and silicon is equivalent, which (depending on the concentration levels of basic oxides) may result in a phosphate dominated ash. The properties of this ash are in several aspects different from the silicate dominated woody biomass ash and will consequently behave differently in various types of energy conversion systems. The knowledge about phosphate dominated ash systems has so far been scarce. We have been working with these systems, both with basic and applied research, for about a decade know. Some general experiences and conclusions as well as some specific examples of our research will be presented.

  • 5.
    Boström, Dan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash transformation chemistry during combustion of biomass, theory and technical applications2017In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Article in journal (Other academic)
  • 6.
    Boström, Dan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Grimm, Alejandro
    Luleå Univ Technol, Div Energy Sci, SE-97187 Luleå, Sweden.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå Univ Technol, Div Energy Sci, SE-97187 Luleå, Sweden.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash Transformation Chemistry during Combustion of Biomass2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 1, p. 85-93Article in journal (Refereed)
    Abstract [en]

    There is relatively extensive knowledge available concerning ash transformation reactions during combustion of woody biomass. In recent decades, the use of these energy carriers has increased, from a low-technology residential small-scale level to an industrial scale. Along this evolution, ash chemical-related phenomena for woody biomass have been observed and studied. Therefore, presently the understanding for these are, if not complete, fairly good. However, because the demand for CO2-neutral energy resources has increased recently and will continue to increase in the foreseeable future, other biomasses, such as, for instance, agricultural crops, have become highly interesting. The ash-forming matter in agricultural biomass is rather different in comparison to woody biomass, with a higher content of phosphorus as a distinctive feature. The knowledge about the ash transformation behavior in these systems is far from complete. Here, an attempt to give a schematic but general description of the ash transformation reactions of biomass fuels is presented in terms of a conceptual model, with the intention to provide guidance in the understanding of ash matter behavior in the use of any biomass fuel, primarily from the knowledge of the concentrations of ash-forming elements. The model was organized in primary and secondary reactions. Restrictions on the theoretical model in terms of reactivity limitations and physical conditions of the conversion process were discussed and exemplified, and some principal differences between biomass ashes dominated by Si and P, separately, were outlined and discussed.

  • 7. Bozaghian, Marjan
    et al.
    Rebbling, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Larsson, Sylvia H.
    Thyrel, Mikael
    Xiong, Shaojun
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering, S-971 87 Luleå, Sweden.
    Combustion characteristics of straw stored with CaCO3 in bubbling fluidized bed using quartz and olivine as bed materials2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 212, p. 1400-1408Article in journal (Refereed)
    Abstract [en]

    The addition of Ca-containing compounds can reduce mass loss from agricultural biomass during storage. The resulting alkaline environment is detrimental to microorganisms present in the material. Theoretical analysis of Ca-containing biomass suggests that combustion properties are improved with respect to slagging. To validate the theoretical calculations, barley straw was utilized as a typical model agricultural biomass and combustion characteristics of straw pre-treated with 2 and 4 w/w% CaCO3 for combined improvement of storage and combustion properties were determined through combustion at 700 degrees C in a bench-scale bubbling fluidized-bed reactor (5 kW) using quartz and olivine sand as bed materials. The combustion characteristics were determined in terms of elemental composition and compound identification in bed ash and bed material including agglomerates, fly ash, particulate matter as well as flue gas measurements. The addition of CaCO3 to straw had both positive and negative effects on its combustion characteristics. Both additive levels raised the total de fluidization temperature for both quartz and olivine, and olivine proved to be less susceptible than quartz to reactions with alkali. With Ca-additives, the composition of deposits and fine particulate matter changed to include higher amounts of KCl potentially leading to higher risk for alkali chloride-induced corrosion. Flue gas composition was heavily influenced by CaCO3 additives by significantly elevated CO concentrations likely related to increased levels of gaseous alkali compounds. The results suggest that it is necessary to reduce gaseous alkali compounds, e.g. through kaolin or sulphur addition, if alkali-rich straw is to be co-combusted with Ca-rich biomass or large amounts of Ca-additives.

  • 8.
    Bozaghian, Marjan
    et al.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Rebbling, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Larsson, Sylvia H.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Xiong, Shaojun
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Combustion characteristics of barley straw stored with CaCO3 using olivine and quartz as bed materials in fluidized bed combustion2017Conference paper (Refereed)
  • 9.
    Bozaghian, Marjan
    et al.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Rebbling, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Larsson, Sylvia H.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Xiong, Shaojun
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Combustion characteristics of barley straw stored with CaCO3 using quartz and olivine as bed materials in fluidized-bed combustion2017Conference paper (Other academic)
  • 10.
    Brännvall, Evelina
    et al.
    Luleå Tekniska Universitet.
    Nilsson, Malin
    Luleå Tekniska Universitet.
    Sjöblom, Rolf
    Luleå Tekniska Universitet.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Kumpiene, Jurate
    Luleå Tekniska Universitet.
    Effect of residue combinations on plant uptake of nutrients and potentially toxic elements2014In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 132, p. 287-295Article in journal (Refereed)
    Abstract [en]

    The aim of the plant pot experiment was to evaluate potential environmental impacts of combined industrial residues to be used as soil fertilisers by analysing i) element availability in fly ash and biosolids mixed with soil both individual and in combination, ii) changes in element phytoavailability in soil fertilised with these materials and iii) impact of the fertilisers on plant growth and element uptake.

    Plant pot experiments were carried out, using soil to which fresh residue mixtures had been added. The results showed that element availability did not correlate with plant growth in the fertilised soil with. The largest concentrations of K (3534 mg/l), Mg (184 mg/l), P (1.8 mg/l), S (760 mg/l), Cu (0.39 mg/l) and Zn (0.58 mg/l) in soil pore water were found in the soil mixture with biosolids and MSWI fly ashes; however plants did not grow at all in mixtures containing the latter, most likely due to the high concentration of chlorides (82 g/kg in the leachate) in this ash. It is known that high salinity of soil can reduce germination by e.g. limiting water absorption by the seeds. The concentrations of As, Cd and Pb in grown plants were negligible in most of the soils and were below the instrument detection limit values.

    The proportions of biofuel fly ash and biosolids can be adjusted in order to balance the amount and availability of macronutrients, while the possible increase of potentially toxic elements in biomass is negligible seeing as the plant uptake of such elements was low.

  • 11.
    Bäfver, Linda
    et al.
    Pöyry SwedPower.
    Renström, Caroline
    Pöyry SwedPower.
    Fahlström, Johan
    Ragn-Sells.
    Enfält, Patrik
    EasyMining Sweden.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmén, Erik
    ENA Energi.
    Slambränsleblandningar: Förbränning och fosforutvinning2013Report (Other academic)
    Abstract [en]

    For sustainable phosphorus recycling, the phosphorus in sewage sludge needs to be recovered, as it is a major phosphorus-source. However, all sludge is not suitable for direct recycling on agricultural land, e.g. when the content of heavy metals is too high. To achieve an increased recycling of phosphorus from sewage sludge there is a need of research and development of alternative methods to return the phosphorus from sewage sludge to agricultural land.

    The aim of the project is to show that sewage sludge can be co-combusted with demolition wood in existing boilers, and that the ash can be processed for extraction of phosphorus, together with valuable by-products from the process. Further effects of the project will be the development of new knowledge about combustion with a high sludge to demolition wood ratio in a grate boiler (up to 45 % sludge with respect to wet mixture), which has not been studied in full-scale combustion earlier. The project's goal is to demonstrate mixing and combustion of fuel mixtures of sludge and demolition wood, and subsequent extraction of phosphorus from ash. The target groups for this work are energy companies, suppliers of grate boilers, municipalities, wastewater treatment plants and authorities.

    The project involves the mixing of sewage sludge and demolition wood, combustion-tests of the fuel mixtures and laboratory experiments on bottom ash and fly ash for phosphorus extraction using EasyMining Sweden's method for phosphorus extraction from ash. Extensive analyses have been carried out on fuel, bottom ash and fly ash, as well as thermodynamic equilibrium calculations on the formed compounds containing phosphorus.

    The experience of preparing sludge fuel mixtures shows that the mixtures should be prepared in the near future to when they are to be combusted, to avoid a composting process in the fuel. The project shows that it is possible to combust sludge fuel mixtures with an admixture of up to 45 % sludge relative wet fuel, in an existing grate boiler during one day. However, to combust sludge fuel mixtures over a longer period of time and at a higher load, modifications of the de-ashing system and the flue gas cleaning system are needed. The results indicate a reduced tendency of slagging on the fuel bed at the combustion of sludge mixtures. The analyses of the fly ash showed a trend towards less corrosive ash at combustion of sludge mixtures. The phosphorus content in the ash in this work was 3-4 %. For process economics and from the phosphorus extraction point, as high phosphorus content as possible in the ash is preferable. Higher phosphorus content can be accomplished by mixing sludge with a fuel with lower ash content than demolition wood, co-combustion with a fuel with higher phosphorus content than demolition wood, or by increasing the percentage of sewage sludge in the fuel mixture. Still, a higher proportion of sludge in the mixture would require a higher dry matter content of the sludge in order to get proper combustion conditions. It is primarily bottom ash that is suitable for phosphorus extraction using Easy Mining Sweden's method. If fly ash are to be used for phosphorus extraction, an optimization of the dissolution conditions is required, which was not included in this project. In this project, phosphorus is extracted as ammonium phosphate. The purity of ammonium phosphate is very high, which means that unwanted substances and heavy metals in sewage sludge will not be returned to contaminate fields.

  • 12.
    Edo Gimenez, Mar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Engineering, Department of Engineering Sciences & Mathematics, Luleå University of Technology, Luleå, Sweden.
    Gao, Qiuju
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per-Erik
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Fate of metals and emissions of organic pollutants from torrefaction of waste wood, MSW, and RDF2017In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 68, p. 646-652Article in journal (Refereed)
    Abstract [en]

    Torrefaction of municipal solid waste (MSW), refuse-derived fuel (RDF), and demolition and construction wood (DC) was performed at 220°C and a residence time of 90 min in a bench-scale reactor. The levels of toxic polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) contained in emission from the torrefaction process were evaluated. In addition, main ash-forming elements and trace metals in the raw feedstock and char were determined. The use of MSW in fuel blends with DC resulted in lower PCDD and PCDF emissions after torrefaction, compared with the RDF blends. The migration of chlorine from the feedstock to the gas phase reduces the chlorine content of the char which may reduce the risk of alkali chloride-corrosion in char combustion. However, trace metals catalytically active in the formation of PCDD and PCDF remain in the char, thereby may promote PCDD and PCDF formation during subsequent char combustion for energy recovery; this formation is less extensive than when the feedstock is used.

  • 13.
    Eriksson, Gunnar
    et al.
    Swedish Univ Agr Sci, Dept Forest Resource Management, S-90183 Umea, Sweden.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Combustion and fuel characterisation of wheat distillers dried grain with solubles (DDGS) and possible combustion applications2012In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 102, p. 208-220Article in journal (Refereed)
    Abstract [en]

    The present transition to a sustainable global energy system requires that biomass is increasingly combusted for heat and power production. Agricultural fuels considered include alkali-rich fuels with high phosphorus content. One such fuel is wheat distiller’s dried grain with solubles (wheat DDGS) from wheat-based ethanol production. Further increases in ethanol production may saturate the current market for wheat DDGS as livestock feed, and fuel uses are therefore considered. Fuel properties of wheat DDGS have been determined. The ash content (5.4 ± 1.6 %wt d.s.) is similar to many agricultural fuels. In comparison to most other biomass fuels the sulphur content is high (0.538 ± 0.232 %wt d.s.), and so are the contents of nitrogen (5.1 ± 0.6 %wt d.s.), phosphorus (0.960. ± 0.073 %wt d.s.) and potassium (1.30 ± 0.35 %wt d.s.). To determine fuel-specific combustion properties, wheat DDGS and mixes between wheat DDGS and logging residues (LR 60 %wt d.s. and DDGS 40 %wt d.s.), and wheat straw (wheat straw 50 %wt d.s., DDGS 50 %wt d.s.) were pelletized and combusted in a bubbling fluidised bed combustor (5 kW) and in a pellets burner combustor (20 kW). Pure wheat DDGS powder was also combusted in a powder burner (150 kW). Wheat DDGS had a high bed agglomeration and slagging tendency compared to other biomass fuels, although these tendencies were significantly lower for the mixture with the Ca-rich LR, probably reflecting the higher first melting temperatures of K–Ca/Mg-phosphates compared to K-phosphates. Combustion and co-combustion of wheat DDGS resulted in relatively large emissions of fine particles (<1 μm) for all combustion appliances. For powder combustion PMtot was sixteen times higher than from softwood stem wood. While the Cl concentrations of the fine particles from the the mixture of LR and wheat DDGS in fluidised bed combustion were lower than from combustion of pure LR, the Cl- and P-concentrations were considerably higher from the wheat DDGS mixtures combusted in the other appliances at higher fuel particle temperature. The particles from powder combustion of wheat DDGS contained mainly K, P, Cl, Na and S, and as KPO3 (i.e. the main phase identified with XRD) is known to have a low melting temperature, this suggests that powder combustion of wheat DDGS should be used with caution. The high slagging and bed agglomeration tendency of wheat DDGS, and the high emissions of fine particles rich in K, P and Cl from combustion at high temperature, mean that it is best used mixed with other fuels, preferably with high Ca and Mg contents, and in equipment where fuel particle temperatures during combustion are moderate, i.e. fluidised beds and possibly grate combustors rather than powder combustors.

  • 14.
    Falk, Joel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Grimm, Alejandro
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Difference in phosphate speciation between sewage sludge and biomass ash from fluidized bed combustion2018In: 27th International Conference of Impacts of Fuel Quality on Power Production and the Environment, September 23–28 September, 2018, Lake Louise, Canada, 2018Conference paper (Refereed)
    Abstract [en]

    The role of phosphorus in biomass combustion is a topic that has become increasingly relevantin recent years. Due to the demand for new sources of renewable energy and recovery of phosphorus from waste streams such as sewage sludge, research into the behavior of phosphorus during combustion is necessary for a continued development. This study aims to investigate potential differences in phosphate behavior during co-combustion of sewage sludge compared to other phosphorus-rich biomass or additives. The investigation was carried out in a bench scale bubbling fluidized bed, co-combusting six biomass blends of similar ash composition and combustion conditions but with different phosphorus association (logging residues (LR) or wheat straw (WS) with sewage sludge (SS), dried distiller’s grain (DG), or phosphoric acid (PA)). After combustion, bed ash samples, fly ash deposits and cyclone ash were collected and analyzed for elemental composition (SEM-EDS) and phase composition (XRD). Based on the XRD phase analyses, a significant difference in phosphate speciation were foundbetween biomass blends containing SS compare to DG or PA. Only two phosphate phases were identified in the ash from SS blends compared to a large variety of phosphates in ash from DG or PA blends. The difference in speciation could not be explained by a difference in ash fractionation as the elemental composition of the analyzed ash fractions were similar. Rather, the results indicate that the behavior of phosphorus in SS may be different to that in DG or PA.

  • 15.
    Grimm, Alejandro
    et al.
    Lulea Univ Technol, Dept Engn Sci & Math, SE-97187 Lulea, Sweden.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Lulea Univ Technol, Dept Engn Sci & Math, SE-97187 Lulea, Sweden.
    Influence of phosphorus on alkali distribution during combustion of logging residues and wheat straw in a bench-scale fluidized bed2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 5, p. 3012-3023Article in journal (Refereed)
    Abstract [en]

    The influence of phosphorus on the alkali distribution in fluidized (quartz) bed combustion using two different typical biomasses (logging residues and wheat straw) was studied. Phosphoric acid (H3PO4) was used as an additive. The produced ash fractions were analyzed for morphology and elemental composition by scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), and crystalline phases by powder X-ray diffraction (P-XRD). For both fuel assortments tested, a reduction of volatilized deposit and fine particle-forming matter, containing mainly KCl, was achieved by adding phosphorus. For the wheat straw, this effect was considerable at medium and high phosphorus addition. As a consequence, an increased amount of potassium was found in the coarse ash particle fractions, principally as CaKPO4, KMgPO4, and CaK2P2O7, at the same time that the levels of HCl and SO2 in the flue gases increased. Generally, the addition of phosphorus to the studied biomasses changed the alkali distribution from being dominated by amorphous K-silicate coarse ash fractions and fine particulate KCl, to a system dominated by crystalline coarse ash of K-Ca/Mg-phosphates and fine particulate K2SO4. This implies that the fouling and high-temperature corrosion observed in industrial-scale combustion of problematic biofuels can possibly be reduced by employing additives rich in reactive phosphorus, on the condition that the higher concentrations of acidic gases can be tolerated. In order to achieve these effects, the relationship between alkali and alkaline-earth metals (i.e., (K + Na)/(Ca + Mg)) in the overall fuel ash must be considered. With respect to this, the formation of low-temperature-melting alkali-rich phosphates should not be promoted, to avoid potential increases in bed agglomeration tendencies and phosphorus release from the bed.

  • 16.
    Grimm, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bed agglomeration characteristics in fluidized quartz bed combustion of phosphorus-rich biomass fuels2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 3, p. 937-947Article in journal (Refereed)
    Abstract [en]

    The bed agglomeration characteristics during combustion of phosphorus-rich biomass fuels and fuel mixtures were determined in a fluidized (quartz) bed reactor (5 kW). The fuels studied (separately and in mixtures) included logging residues, bark, willow, wheat straw, and phosphorus-rich fuels, like rapeseed meal (RM) and wheat distillers dried grain with solubles (DDGS). Phosphoric acid was used as a fuel additive. Bed material samples and agglomerates were studied by means of scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDX), in order to analyze the morphological and compositional changes of coating/reaction layers and necks between agglomerated bed particles. Furthermore, bed ash particles were separated by sieving from the bed material samples and analyzed with SEM/EDS and powder X-ray diffraction (XRD). For logging residues, bark, and willow, with fuel ash rich in Ca and K but with low contents of P and organically bound Si, the bed layer formation is initiated by reactions of gaseous or liquid K compounds with the surface of the bed material grains, resulting in the formation of a potassium silicate melt. The last process is accompanied by the diffusion/dissolving of Ca into the melt and consequent viscous flow sintering and agglomeration. The addition of high enough phosphorus content to convert the available fuel ash basic oxides into phosphates reduced the amount of K available for the reaction with the quartz bed material grains, thus preventing the formation of an inner bed particle layer in the combustion of logging residues, bark, and willow. Some of the phosphate-rich ash particles, formed during the fuel conversion, adhered and reacted with the bed material grains to form noncontinuous phosphate−silicate coating layers, which were found responsible for the agglomeration process. Adding phosphorus-rich fuels/additives to fuels rich in K and Si (e.g., wheat straw) leads to the formation of alkali-rich phosphate−silicate ash particles that also adhered to the bed particles and caused agglomeration. The melting behavior of the bed particle layers/coatings formed during combustion of phosphorus-rich fuels and fuel mixtures is an important controlling factor behind the agglomeration tendency of the fuel and is heavily dependent on the content of alkaline earth metals in the fuel. A general observation is that phosphorus is the controlling element in ash transformation reactions during biomass combustion in fluidized quartz beds because of the high stability of phosphate compounds.

  • 17.
    Grimm, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Diaz, Maryori
    Eriksson, Gunnar
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Effects of phosphorus addition by additives or co-firing on the ash transformation processes such as bed agglomerations and deposit formation during combustion of ash-rich biomass fuels2009In: 17th European Biomass Conference & Exhibition - Proceedings: From Research to Industry and Markets, 2009Conference paper (Refereed)
  • 18.
    Grimm, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Eriksson, Gunnar
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Effekter av fosfortillsats vid förbränning av biomassa2010Report (Other academic)
    Abstract [sv]

    Resultaten från försöken visar att fosforrika additiv kan vara intressanta för att reducera beläggningsbildning och högtemperaturkorrosion utan att i någon större omfattning öka slaggnings- och bäddagglomereringstendensen hos typiska biobränslen. För att erhålla en märkbar positiv effekt av kaliumbindning till fosfater krävs att mängden kalcium och magnesium i den slutgiltiga bränslemixen inte är alltför hög relativt mängden fosfor, då framför allt Ca men till viss del även Mg reagerar med P innan K binds in effektivt. Generellt behövs troligen inblandningsgrader motsvarande en molkvot P/(K+Na+2/3Mg+2/3Ca) i bränslemixen som närmar sig 1. För att erhålla en molkvot på 1 i ett typiskt halm-, salix- eller grotbränsle innebär det i praktiken en fosfortillsats motsvarande 12, 4.7 respektive 3.7 gram rent P per kg torrt bränsle.

  • 19. He, Hanbing
    et al.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Engineering, Division of Energy Science, Luleå University of Technology, Luleå, Sweden.
    Öhman, Marcus
    Time-Dependent Crack Layer Formation in Quartz Bed Particles during Fluidized Bed Combustion of Woody Biomass2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 2, p. 1672-1677Article in journal (Refereed)
    Abstract [en]

    Bed agglomeration during combustion and gasification of woody biomass fuels in quartz beds has been frequently studied, and chemical mechanisms responsible for bed agglomeration have been suggested: However, few studies have focused on the bed material deposition on walls, in cyclones, and return legs in fluidized bed combustion. Part of these bed material depositions originates from sticky fragments of alkali-rich silicates formed after crack formation in older quartz bed particles. The crack layer formation in quartz bed particles in fluidized bed combustion of woody biomass was therefore investigated by collecting bed material samples of different ages from full-scale bubbling and circulating fluidized bed facilities. Scanning electron microscopy/energy-dispersive spectroscopy was used to analyze the crack morphology and composition of the layer surrounding the cracks. For quartz bed particles with an age of some days, a crack in the quartz bed particle was observed in connection to the irregular interface between the inner layer and the core of the bed particle. The crack layer composition is similar for quartz particles with different ages and for samples taken from different fluidized bed techniques. Their composition is dominated by Si, K, Ca, and Na (except O). These crack layers become deeper, wider, and more common as bed particle age increases. The crack layers eventually connect with each other, and the whole quartz particle is transformed into smaller quartz cores surrounded by crack layers, which were observed in particles older than 1 week. From the characterization work, a crack formation process including three phases is proposed on the basis of the presumption that the initial crack layer formation resulted from the presence of induced cracks in the inner quartz bed particle layer. Fragmentation after the third phase is likely responsible for the formation of sticky alkali silicate deposit formation, and a weekly complete exchange of the bed is therefore recommended to avoid problematic deposits in combustion of woody-type biomass in fluidized bed combustion.

  • 20. He, Hanbing
    et al.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Engineering, Division of Energy Science, Luleå University of Technology, Luleå SE-971 87, Sweden.
    Öhman, Marcus
    Time-Dependent Layer Formation on K-Feldspar Bed Particles during Fluidized Bed Combustion of Woody Fuels2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 11, p. 12848-12856Article in journal (Refereed)
    Abstract [en]

    Despite frequent reports on layer characteristics on quartz bed particles, few studies have focused on the layer characteristics of K-feldspar bed particles. The layer characteristics of K-feldspar bed particles were therefore investigated by collecting bed material samples of different ages from fluidized bed combustion of woody fuels in large-scale bubbling and circulating fluidized bed facilities. Scanning electron microscopy/energy-dispersive spectroscopy was used to analyze the layer morphology and elemental composition. Bed particles aged 1 day displayed a thin layer rich in Si, Ca, and Al. Inner layers had a more homogeneous composition than the outer layers, which instead were more heterogeneous and sometimes contained discernible fuel ash particles. The outer layer was thinner for K-feldspar bed particles sampled from circulating fluidized bed, as compared to particles from bubbling fluidized bed. The concentration of Ca in the inner layer increases toward the bed particle surface, the molar ratio of Si/Al is maintained, and the molar ratio of K/Al decreases as compared to the K-feldspar. The inner layer thickness for quartz and K-feldspar bed particles collected at the same operation conditions was found to be similar. No crack layers, as have been observed in quartz particles, were found in the core of the K-feldspar bed particles. The results suggest that the diffusion and reaction of Ca2+ into/with the feldspar particle play an important role in the inner layer formation process.

  • 21.
    Hedayati, Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Lindgren, Robert
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Ash transformation during single-pellet combustion of agricultural biomass fuels – focus on K and P2018Conference paper (Refereed)
  • 22.
    Häggström, Gustav
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Wagner, Katharina
    Bioenergy 2020+ GmbH, Wienerstraße 49, A-7540 Güssing, AustriaInstitute of Chemical, Environmental & Bioscience Engineering, TU Wien, Getreidemarkt 9/166, A-1060 Vienna, Austria.
    Kuba, Matthias
    Bioenergy 2020+ GmbH, Wienerstraße 49, A-7540 Güssing, AustriaInstitute of Chemical, Environmental & Bioscience Engineering, TU Wien, Getreidemarkt 9/166, A-1060 Vienna, Austria.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Effect on P-mineralization in fluidized bed combustion of chicken litter with wheat straw and bark residues2018Conference paper (Refereed)
  • 23.
    Kuba, Matthias
    et al.
    Technische Universität Wien, Institute of Chemical Engineering.
    He, Hanbing
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Kirnbauer, Friedrich
    Technische Universität Wien, Institute of Chemical Engineering.
    Skoglund, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Hofbauer, Hermann
    Technische Universität Wien, Institute of Chemical Engineering.
    Mechanism of Layer Formation on Olivine Bed Particles in Industrial-Scale Dual Fluid Bed Gasification of Wood2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 9, p. 7410-7418Article in journal (Refereed)
    Abstract [en]

    Utilization of biomass as feedstock in dual fluidized bed steam gasification is a promising technology for the substitution of fossil energy carriers. Experience from industrial-scale power plants showed an alteration of the olivine bed material due to interaction with biomass ash components. This change results mainly in the formation of Ca-rich layers on the bed particles. In this paper, a mechanism for layer formation is proposed and compared to the better understood mechanism for layer formation on quartz bed particles. Olivine bed material was sampled at an industrial-scale power plant before the start of operation and at predefined times after the operation had commenced. Therefore, time-dependent layer formation under industrial-scale conditions could be investigated. The proposed mechanism suggests that the interaction between wood biomass ash and olivine bed particles is based on a solid–solid substitution reaction, where Ca2+ is incorporated into the crystal structure. As a consequence, Fe2+/3+ and Mg2+ ions are expelled as oxides. This substitution results in the formation of cracks in the particle layer due to a volume expansion in the crystal structure once Ca2+ is incorporated. The results of this work are compared to relevant published results, including those related to quartz bed particles.

  • 24.
    Kuba, Matthias
    et al.
    Technische Universität Wien, Institute of Chemical Engineering.
    He, Hanbing
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Kirnbauer, Friedrich
    Technische Universität Wien, Institute of Chemical Engineering.
    Skoglund, Nils
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Hofbauer, Hermann
    Technische Universität Wien, Institute of Chemical Engineering.
    Thermal stability of bed particle layers on naturally occurring minerals from dual fluid bed gasification of woody biomass2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 10, p. 8277-8285Article in journal (Refereed)
    Abstract [en]

    The use of biomass as feedstock for gasification is a promising way of producing not only electricity and heat but also fuels for transportation and synthetic chemicals. Dual fluid bed steam gasification has proven to be suitable for this purpose. Olivine is currently the most commonly used bed material in this process due to its good agglomeration performance and its catalytic effectiveness in the reduction of biomass tars. However, as olivine contains heavy metals such as nickel and chromium, no further usage of the nutrient-rich ash is possible, and additional operational costs arise due to necessary disposal of the ash fractions. This paper investigates possible alternative bed materials and their suitability for dual fluid bed gasification systems focusing on the behavior of the naturally occurring minerals olivine, quartz, and K-feldspar in terms of agglomeration and fracturing at typical temperatures. To this end, samples of bed materials with layer formation on their particles were collected at the industrial biomass combined heat and power (CHP) plant in Senden, Germany, which uses olivine as the bed material and woody biomass as feedstock. The low cost logging residue feedstock contains mineral impurities such as quartz and K-feldspar, which become mixed into the fluidized bed during operation. Using experimental and thermochemical analysis, it was found that the layers on olivine and K-feldspar showed a significantly lower agglomeration tendency than quartz. Significant fracturing of particles or their layers could be detected for olivine and quartz, whereas K-feldspar layers were characterized by a higher stability. High catalytic activity is predicted for all three minerals once Ca-rich particle layers are fully developed. However, quartz may be less active during the buildup of the layers due to lower amounts of Ca in the initial layer formation.

  • 25.
    Kumpiene, Jurate
    et al.
    Luleå University of Technology.
    Brännvall, Evelina
    Luleå University of Technology.
    Wollters, Martin
    Skoglund, Nils
    Energy Engineering, Department of Engineering Sciences & Mathematics, Luleå University of Technology, SE-97187 Luleå, Sweden.
    Čirba, Stasys
    Aksamitauskas, Vladislovas Česlovas
    Phosphorus and cadmium availability in soil fertilized with biosolids and ashes2016In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 151, p. 124-132Article in journal (Refereed)
    Abstract [en]

    The recycling of hygienized municipal sewage sludge (biosolids) to soil as the source of phosphorus (P) is generally encouraged. The use of biosolids, however, has some concerns, such as the presence of elevated concentrations of potentially toxic trace elements, and the possible presence of pathogens, hormones and antibiotics. Organic substances are destroyed during combustion whereas trace elements could partly be separated from P in different ash fractions. Biomass combustion waste (ash) can instead be considered as an alternative P source. This study evaluates and compares the impact of biosolids and their combustion residues (ashes), when used as fertilizers, on P and Cd solubility in soil, plant growth and plant uptake of these elements. Biosolids were also amended with K and Ca to improve the composition and properties of P in ashes, and incinerated at either 800 °C or 950 °C. Combustion of biosolids improved the Cd/P ratio in ashes by 2–5 times, compared with the initial biosolids. The low Cd content in ashes (4–9 mg Cd (kg P)−1) makes this material a particularly attractive alternative to mineral fertilizers. Significantly higher pore water P (as well as total N) was measured in soils containing biosolids, but plants produced a higher biomass in soil fertilized with ashes. The K and Ca amendments prior to biosolids combustion generally decreased the total Cd in ash, but had little effect on P and Cd uptake and biomass growth. Similarly, the combustion temperature had negligible effect on these factors as well.

  • 26.
    Pettersson, Anita
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business (including The Swedish School of Textiles), Department of Resource Recovery and Building Technology.
    Nordin, Andreas
    University of Borås, Faculty of Textiles, Engineering and Business (including The Swedish School of Textiles), Department of Resource Recovery and Building Technology.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Åmand, Lars-Erik
    University of Borås, Faculty of Textiles, Engineering and Business (including The Swedish School of Textiles), Department of Resource Recovery and Building Technology.
    Phosphorous Rich Bottom Ash with Low Cadmium Content by Ash Design by means of Co-Combustion of Municipal Sewage Sludgein a 27MWth Grate Fired Boiler2019Conference paper (Refereed)
  • 27.
    Piotrowska, Patrycja
    et al.
    Åbo Akad Univ, Proc Chem Ctr, Inorgan Chem Lab, Turku, Finland.
    Grimm, Alejandro
    Luleå Univ Technol, Dept Engn Sci & Math, S-95187 Luleå, Sweden.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Luleå Univ Technol, Dept Engn Sci & Math, S-95187 Luleå, Sweden.
    Zevenhoven, Maria
    Åbo Akad Univ, Proc Chem Ctr, Inorgan Chem Lab, Turku, Finland.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hupa, Mikko
    Åbo Akad Univ, Proc Chem Ctr, Inorgan Chem Lab, Turku, Finland.
    Fluidized-Bed Combustion of Mixtures of Rapeseed Cake and Bark: The Resulting Bed Agglomeration Characteristics2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 4, p. 2028-2037Article in journal (Refereed)
    Abstract [en]

    The bed agglomeration characteristics resulting from the combustion of 11 mixtures of rapeseed cake and spruce bark were studied in a bench-scale bubbling fluidized-bed reactor (5 kW). The objective was to determine the defluidization temperatures and the prevailing bed agglomeration mechanism as functions of the fuel mixture. Controlled fluidized-bed agglomeration tests were performed for each mixture with quartz sand as the bed material. The total defluidization temperatures and the initial defluidization temperatures were determined based on the measured pressure and temperature profiles in the bed. After combustion, bottom ash samples, agglomerates, and fly ash samples were analyzed by means of scanning electron microscope combined with energy dispersive X-ray detector (SEM-EDX). The composition of the ash-forming matter produced by the combustion of rapeseed cake is significantly different from that produced by the combustion of bark, resulting in different bed agglomeration tendencies. Bark contains ash-forming matter dominated by calcium, with some silicon and potassium, whereas rapeseed cake is rich in phosphorus, potassium, and sodium. The total defluidization temperature for pure bark was above 1045 degrees C, whereas, for rapeseed cake, defluidization occurred during combustion (800 degrees C). During the combustion of bark, the formation of a potassium-rich layer on the silica-bed grains was found to be a crucial for the formation of agglomerates. The low defluidization temperature for the rapeseed cake can be attributed to the formation of sticky ash, which is dominated by phosphates. Two main phosphate forms were observed in the neck between the silica grains: calcium-potassium/sodium phosphates, and magnesium potassium phosphates. As the proportion of bark increased, the Ca/P ratio increased in the fuel mixture, and the formation of high-temperature melting phosphates in the ash was favored. However, the addition of bark also favored the formation of a potassium-rich layer on the silica bed material, leading to the coexistence of both bed agglomeration mechanisms. In the present work, mixtures with a minimum of 60 wt % bark resulted in significantly increased defluidization temperatures and reduced bed agglomeration tendencies, compared to what occurs in rapeseed cake monocombustion.

  • 28. Piotrowska, Patrycja
    et al.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Zevenhoven, Maria
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hupa, Mikko
    Agglomeration Tendency in Fluidized-Bed Combustion of Rapeseed Cake and Bark Mixtures2011Conference paper (Other academic)
  • 29. Piotrowska, Patrycja
    et al.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Zevenhoven, Maria
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hupa, Mikko
    Systematic Studies of Ash Composition During the Co-Combustion of Rapeseed Cake and Bark2012In: Proceedings of the 21st International Conference on Fluidized Bed Combustion, Naples, Italy, June 3-6, 2012, 2012, p. 219-226Conference paper (Refereed)
    Abstract [en]

    Agglomeration occurring during the firing of phosphorus-rich biomass is not fully understood. It has become clear that the ash-forming matter in agricultural biomass (e.g., rapeseed cake) is phosphorus dominated and that phosphate species are involved in agglomeration. Understanding the agglomeration mechanisms would provide valuable insight into possible strategies for preventing defluidization. The objective of this work was to study the ash composition resulting from the combustion of a phosphorus-rich fuel, in particular, the phosphorus compounds formed; the focus was the effect of ash composition on the formation of sticky ash particles, which cause defluidization. Eleven mixtures of rapeseed cake and bark with varying Ca/P molar ratio were studied. Using a 5 kW quartz BFB reactor operated at approximately 800 °C, eight‐hour combustion tests were performed prior to each agglomeration experiment. Fly ash and bottom ash samples were extensively analyzed with SEM/EDX, and the fuel properties were also determined. Rapeseed cake ash consists of particles containing different K/Na-Ca/Mg-P compounds. The ash composition responsible for low defluidization temperatures was found to lie in the region of the ternary diagram containing 30-40 mol% P2O5, 20-40 mol% (CaO+MgO), and 30-50 mol% (K2O+Na2O). Sodium probably formed CaNaPO4, but it was also found in mixtures with other phosphates. The addition of bark favoured the formation of orthophosphates containing 40-50 mol% (CaO+MgO), which increased the first melting temperature of the ash.

  • 30.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Engineering, Department of Engineering Sciences & Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Wagner, David R.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Distribution of temperature, H2O and atomic potassium during entrained flow biomass combustion: coupling in situ TDLAS with modeling approaches and ash chemistry2018In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 188, p. 488-497Article in journal (Refereed)
    Abstract [en]

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

  • 31.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Skoglund, Nils
    Wagner, David R.
    Broström, Markus
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Investigation of H2O, temperature and potassium in entrained flow biomass combustion – coupling in situ TDLAS with modelling2017In: Nordic Flame Days 2017, 10-11 October, Stockholm, 2017Conference paper (Refereed)
  • 32.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wagner, David R.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    TDLAS-based in situ detection of atomic potassium during combustion of biomass in an entrained flow reactor2016Conference paper (Other academic)
  • 33.
    Rebbling, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Luleå University of Technology, Department of Engineering Sciences & Mathematics, Energy Engineering.
    Understanding reactivity using fuel design - phosphorus vs kaolin in combustion of stem wood2016Conference paper (Other academic)
    Abstract [en]

    The fate of various ash-forming elements determine how well a fuel will perform in a given thermochemical energy conversion process. In order understand ash-related process problems it is particularly important in which compounds alkali metal ions, for biomass this primarily means K+ and Na+, are bonded. Their low charge and relatively large ionic radii leads to poor bond strengths in compounds where they provide the only Lewis acid component, i.e. electron acceptor. This can be remedied by trying to bond alkali metal ions to stronger, predominantly molecular Lewis bases which is the case in for instance arkanite, K2SO4 – the targeted reaction product when (NH4)2SO4 is added in the flue gas to reduce KCl formation. Another approach is to bond alkali in bottom or bed ash, by including Lewis base forming elements such as phosphorus or the additive kaolin which is dominated by kaolinite. This route attempts to promote formation of high-temperature melting compounds with at least one alkali metal ion per phosphate or other starting molecule.

    While the understanding of how phosphorus reacts in combustion process is increasing it is valuable to understand how it will react in presence of other elements or molecules that play an important role for alkali capture. This will be of interest in situations where the base fuels may be combusted with addition of sulphur or kaolin, for instance. If the base fuels has a high concentration of phosphorus the amount of additive may need to be adjusted according to what phosphates will form, and if they will form even in the presence of the amending additives. Using the inherent composition of the fuel to decide suitable strategies for additive choice or possibly co-combustion is a key component of fuel design.

    The aim of this study is to investigate the relative Lewis base potential for capture of alkali metal ions between phosphates and kaolin. This is made by adding highly available phosphorus in the form of di-ammonium hydrogen phosphate, (NH4)2HPO4, and kaolin, a mineral where kaolinite is the main constituent for capturing alkali to the fuel blend. The fuel chosen is stem wood where the amount of Lewis acid forming elements greatly surpass that of Lewis base forming elements found in the ash forming matter.

  • 34.
    Rebbling, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Näzelius, Ida-Linn
    Piotrowska, Patrycja
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ohman, Marcus
    Waste Gypsum Board and Ash-Related Problems during Combustion of Biomass. 2. Fixed Bed2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 12, p. 10705-10713Article in journal (Refereed)
    Abstract [en]

    This paper is the second of two describing the use of shredded waste gypsum board (SWGB) as an additive during combustion of biomass. The focus of this paper is to determine whether SWGB can be used as a fuel additive providing CaO and SO2/SO3 for mitigation of ash-related operational problems during combustion of biomass and waste derived fuels in grate fired fixed bed applications. The former study in this series was performed in a fluidized bed and thus allow for comparison of results. Gypsum may decompose at elevated temperatures and forms solid CaO and gaseous SO2/SO3 which have been shown to reduce problems with slagging on the fixed bed and alkali chloride deposit formation. Three different biomasses, spruce bark (SB), reed canary grass (RG), and wheat straw (WS), were combusted with and without addition of SWGB in a residential pellet burner (20 kWth). Waste derived fuel with and without the addition of SWGB was combusted in a large scale grate-fired boiler (25 MWth). The amount of added SWGB varied between 1 and 4 wt %. Ash, slag, and particulate matter (PM) were sampled and subsequently analyzed with scanning electron microscopy/ energy dispersive spectroscopy and X-ray diffraction. Decomposition of CaSO4 originating from SWGB was observed as elevated SO2 emissions in both the large scale and small scale facilities and significantly higher than was observed in the fluidized bed study. Slag formation was significantly reduced due to formation of calcium-silicates in small scale application, but no conclusive observations regarding calcium reactivity could be made in the large scale application. In the small scale study the formation of K2SO4 was favored over KC1 in PM, while in the large scale study K3Na(SO4)(2) and K2Zn2(SO4)(3) increased. It is concluded that SWGB can be used as a source of CaO and SO2/SO3 to mitigate slag formation on the grate and chloride-induced high temperature corrosion and that fixed bed applications are likely more suitable than bubbling fluidized beds when using SWGB as an additive.

  • 35.
    Rönnbäck, Marie
    et al.
    SP Sveriges Tekniska Forskningsinstitut.
    Gustavsson, Lennart
    SP Sveriges Tekniska Forskningsinstitut.
    Hermansson, Sven
    SP Sveriges Tekniska Forskningsinstitut.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Fagerström, Jonathan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Näzelius, Ida-Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Förbränningskaraktärisering och förbränningsteknisk utvärdering av olika pelletsbränslen - syntes av projektet2011Report (Other academic)
  • 36.
    Salehi, Shahrbanoo
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Energy Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Investigation of phase diagram with relevance for thermal conversion of biomass2014In: KBC-days, Umeå university, 2014Conference paper (Other academic)
  • 37. Sepman, Alexey
    et al.
    Jansson, Kjell
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wiinikka, Henrik
    Combustion characterization of five recyclable metal fuels2018Conference paper (Refereed)
  • 38.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash chemistry and fuel design focusing on combustion of phosphorus-rich biomass2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biomass is increasingly used as a feedstock in global energy production. This may present operational challenges in energy conversion processes which are related to the inorganic content of these biomasses. As a larger variety of biomass is used the need for a basic understanding of ash transformation reactions becomes increasingly important. This is not only to reduce operational problems but also to facilitate the use of ash as a nutrient source for new biomass production.

    Ash transformation reactions were examined in the present work using the Lewis acid-base concept. The model presented in Paper I was further extended and discussed, including the definition of tertiary ash transformation reactions as reaction steps where negatively charged molecular ions, Lewis bases, other than hydroxides are present in the reactants. The effect of such reactions for bonding of various metal ions, Lewis acids, were discussed. It was found that the formation of various phosphates through secondary and tertiary ash transformation reactions is important for the behaviour of biomass ash in combustion. The suggested model was supported by findings in Papers II-VIII.

    The experimental findings in Papers II-VIII were discussed in terms of ash transformation reactions. The fuel design choices made to investigate the effect of phosphorus in particular on ash transformation reactions were high-lighted. Addition of phosphoric acid to woody-type and agricultural biomasses showed that phosphate formation has a large influence on the speciation of Si, S, and Cl. Co-combustion of a problematic agricultural residue with other biomasses showed that the relation between phosphorus, alkali and alkaline earth metal content is important. Co-combustion of biosolids with wheat straw was shown to greatly improve the combustion properties of wheat straw.

    It was suggested that fuel analyses should be presented using molar concentration (mole/kg) in diagrams based on ash transformation reactions and elements forming Lewis acids or bases. This may facilitate the assessment of the combustion behaviour of a fuel. Some comments were made on fuel design and additives, specifically pointing out that phosphorus content should always be carefully considered in relation to alkali and alkaline earth metals in fuels and fuel blends.

  • 39.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Inorganic chemistry and bioenergy - an unexpected match?2019Conference paper (Other academic)
  • 40.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Återvinning av fosfor och energi ur avloppsslam genom termiskbehandling i fluidiserad bädd: Utvärdering och optimering av prestandaför slutprodukten2012Report (Other academic)
    Abstract [en]

    Combustion of pelletized sewage sludge in a fluidized bed allows the production of ash pellets with high P availability for plants. Co-combustion with biofuels, e.g. agricultural residues, is a suitable approach to raise the levels of K and Ca. The bed temperature used should be as high as possible without putting plant availability at risk in order to volatilize potentially harmful elements. Residence time for the ash pellet in the bed should be made as short as possible to improve ash recovery.

  • 41.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Brännvall, Evelina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Waste Science & Technology.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Kumpiene, Jurate
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Waste Science & Technology.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Combustion of Biosolids in a Bubbling Fluidized Bed Part 2: Environmental Aspects of Ash from Combustion of Biosolids for Application as FertilizerManuscript (preprint) (Other academic)
  • 42.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology.
    Bäfver, Linda
    Fahlström, Johan
    Holmén, Erik
    Renström, Caroline
    Fuel design in co-combustion of demolition wood chips and municipal sewage sludge2016In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 141, no 2, p. 196-201Article in journal (Refereed)
    Abstract [en]

    Municipal sewage sludge (MSS) is a waste stream resource which contains both energy and elements such as phosphorus which could be recycled. If these two aspects of this waste stream resource are to be used to their full potential the sludge should not be used in landfills or road construction. There is some use of sludge in agriculture today but not all MSS produced is suitable for direct use on arable land due to its content of potentially harmful elements, pathogens or anthropogenic chemicals. By combusting sludge that is not used directly in agriculture the problematic organic content could be destroyed. The combustion process also produces an ash that possibly could be used either directly in agriculture or as a raw material for recovering phosphorus and energy could be recovered. Building mono-combustion plants for sewage sludge is not economically feasible in all parts of the world so it is of interest to investigate how MSS can be introduced together with other fuels in existing infrastructure which already have extensive cleaning systems for potentially harmful elements. To investigate this possible path, demolition wood chips (DWC) were co-combusted with municipal sewage sludge (MSS) in a grate-fired combined heat and power plant running at 50% capacity producing 25 MWth and 9 MWel. The amount of MSS that was suitable to introduce in blends was determined using a "fuel fingerprint" based on the composition of the raw materials. Thermodynamic equilibrium calculations were made to evaluate potential problems with slagging based on the ash content prior to the combustion experiments. The fuels were introduced as a reference case with only demolition wood and pre-blended fuel mixtures in two ratios; 65 w/w-% DWC/35 w/w-% MSS and 55 w/w-% DWC/45 w/w-% MSS and were fired for 12 h. The high water content of the MSS affected how much MSS that could be introduced without compromising the heat and power production. The fuel blends worked nicely for 12 h of continuous combustion with small adjustments where the primarily the air inlet configuration was changed. The main problems encountered related to cleaning of the flue gases and to some extent ash removal. The bed ash and fly ash produced was analysed both using ICP-AES (elemental) and XRD (speciation) and the bottom ash was subjected to ash melting tests. The major nutrient phosphorus was mainly found in bottom ash (80 w/w-%) as whitlockites with some hydroxyapatite whereas fly ash (20 w/w-%) contained larger amounts of hydroxyapatite, especially for the reference fuel. The amount of alkali chloride in the fly ash was reduced in favour of alkali sulphate formation.

  • 43.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Bäfver, Linda
    Fahlström, Johan
    Holmén, Erik
    Renström, Caroline
    Full-scale Co-combustion of Municipal Sewage Sludge and Demolition Wood Chips in a Combined Heat and Power Plant2014In: Impacts of Fuel Quality on Power Production October 26 –31, 2014, Snowbird, Utah, USA, 2014, 2014Conference paper (Other academic)
  • 44.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Combustion of biosolids in a bubbling fluidized bed part 1: main ash forming elements and ash distribution with a focus on phosphorus2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 2, p. 1183-1190Article in journal (Refereed)
    Abstract [en]

    This is the first in a series of three papers describing combustion of biosolids in a 5-kW bubbling fluidized bed, the ash chemistry, and possible application of the ash produced as a fertilizing agent. This part of the study aims to clarify whether the distribution of main ash forming elements from biosolids can be changed by modifying the fuel matrix, the crystalline compounds of which can be identified in the raw materials and what role the total composition may play for which compounds are formed during combustion. The biosolids were subjected to low-temperature ashing to investigate which crystalline compounds that were present in the raw materials. Combustion experiments of two different types of biosolids were conducted in a 5-kW benchscale bubbling fluidized bed at two different bed temperatures and with two different additives. The additives were chosen to investigate whether the addition of alkali (K2CO3) and alkaline-earth metal (CaCO3) would affect the speciation of phosphorus, so the molar ratios targeted in modified fuels were P:K = 1:1 and P:K:Ca = 1:1:1, respectively. After combustion the ash fractions were collected, the ash distribution was determined and the ash fractions were analyzed with regards to elemental composition (ICP-AES and SEM-EDS) and part of the bed ash was also analyzed qualitatively using XRD. There was no evidence of zeolites in the unmodified fuels, based on low-temperature ashing. During combustion, the biosolid pellets formed large bed ash particles, ash pellets, which contained most of the total ash content (54%–95% (w/w)). This ash fraction contained most of the phosphorus found in the ash and the only phosphate that was identified was a whitlockite, Ca9(K,Mg,Fe)(PO4)7, for all fuels and fuel mixtures. With the addition of potassium, cristobalite (SiO2) could no longer be identified via X-ray diffraction (XRD) in the bed ash particles and leucite (KAlSi2O6) was formed. Most of the alkaline-earth metals calcium and magnesium were also found in the bed ash. Both the formation of aluminum-containing alkali silicates and inclusion of calcium and magnesium in bed ash could assist in preventing bed agglomeration during co-combustion of biosolids with other renewable fuels in a full-scale bubbling fluidized bed.

  • 45.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Effects on ash chemistry when co-firing municipal sewage sludge and wheat straw in a fluidised bed: Influence on the ash chemistry by fuel mixing2012Conference paper (Refereed)
    Abstract [en]

    Municipal sewage sludge (MSS) is of interest for co-combustion with problematic fuels, such as agricultural residues, due to its high content of inorganic elements which may improve combustion properties of such problematic fuels. Ash transformation when co-combusting MSS with the agricultural residue wheat straw was examined using a bench-scale bubbling fluidised bed (5 kW). Wheat straw pellets were combusted with MSS both in a co-pelletized form and co-firing of separate fuel particles. This was done to examine whether there is any advantage to either approach of introducing MSS together with a problematic fuel.

    Co-combusting wheat straw with MSS changed the bed agglomeration characteristics from being caused by the formation of low-temperature melting potassium silicates in the fuel ash to being caused by a higher-temperature melting bed ash. This shift in ash chemistry had a significant positive effect on the initial defluidisation temperature. The cyclone ash and fine particulate matter changed from being dominated by alkali in general and alkali chlorides in specific to an increased phosphate and sulphate formation which reduces the risk of alkali-related fouling and corrosion. The influence of aluminosilicates may also play a role in the improvement of fuel ash behaviour.

  • 46.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Grimm, Alejandro
    Energy Engineering, Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Öhman, Marcus
    Energy Engineering, Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Effects on Ash Chemistry when Co-firing Municipal Sewage Sludge and Wheat Straw in a Fluidized Bed: Influence on the Ash Chemistry by Fuel Mixing2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 10, p. 5725-5732Article in journal (Refereed)
    Abstract [en]

    Municipal sewage sludge (MSS) is of interest for co-combustion with problematic fuels, such as agricultural residues, because of its high content of inorganic elements, which may improve combustion properties of such problematic fuels. Ash transformation when co-combusting MSS with the agricultural residue wheat straw was examined using a bench-scale bubbling fluidized bed (5 kW). Wheat straw pellets were combusted with MSS in both a co-pelletized form and co-firing of separate fuel particles. This was performed to examine whether there is any advantage to either approach of introducing MSS together with a problematic fuel. Co-combusting wheat straw with MSS changed the bed agglomeration characteristics from being caused by the formation of low-temperature melting potassium silicates in the fuel ash to being caused by a higher temperature melting bed ash. This shift in ash chemistry had a significant positive effect on the initial defluidization temperature. The cyclone ash and fine particulate matter changed from being dominated by alkali in general and alkali chlorides in specific to an increased phosphate and sulfate formation, which reduces the risk of alkali-related fouling and corrosion. The influence of aluminosilicates may also play a role in the improvement of fuel ash behavior.

  • 47.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Kuba, Matthias
    BioEnergy2020+.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Effects of Bed Material Type and Fuel Ash Composition on Layer Formation and Bed Agglomeration in Thermo-chemical Conversion of Biomass and Waste Streams in Fluidized Beds2018In: 23rd International Conference on Fluidized Bed Conversion, 13-17 May 2018, Seoul, Korea, 2018Conference paper (Refereed)
    Abstract [en]

    The role of fluidized beds is increasingly important for challenging and ash-rich fuels, such as fast-growing biomass and waste streams. From a biomass perspective, the relatively homogeneous woody-type fuels are most commonly used in fluidized beds today whereas the fuel feedstock for waste streams is more heterogeneous. A key issue in enabling a broader fuel feedstock for existing and planned fluidized beds is how the fuel ash interacts with bed materials of different types during combustion or gasification. The resulting bed particle coating, layers, and cracks formed in bed grains are responsible for bed agglomeration and bed material deposition mechanisms, but studies have suggested that there is a possibility to affect melting temperatures of bed ash and reduce interaction between fuel ash and bed material through additives or by fuel blend design. Furthermore, it is of interest to extend the life-time of bed materials in the reactor to reduce the amount of material that is generated as waste streams, as well as increase the timespan between bed replacements.The aim of this review is therefore to summarize some of our previous research in this topic, to discuss current knowledge concerning layer formation and bed agglomeration mechanisms, address the benefit for different bed materials, and discuss how fuel ash composition can be used to reduce bed agglomeration issues. This is achieved by comparing studies from different combustion and gasification facilities using different biomasses as well as agricultural residues and waste streams. In particular, the possibility of using fuel blend design to reduce interaction of fuel ash with bed material will be highlighted. Using such approaches, coupled with a fundamental understanding of how differences between bed materials affect layer formation mechanisms, has the potential to reduce operational issues caused by interactions between fuel ash and bed materials as well as increase the potential fuel feedstock.

  • 48.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Strandberg, Anna
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Engineering.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Elemental approaches to additives: mechanisms and dosage2019Conference paper (Other academic)
  • 49.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Engineering, Department of Engineering Sciences & Mathematics, Luleå University of Technology, Luleå, Sweden.
    Werner, Kajsa
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nylund, Göran M.
    University of Gothenburg, Department of Marine Sciences - Tjärnö.
    Pavia, Henrik
    University of Gothenburg, Department of Marine Sciences - Tjärnö.
    Albers, Eva
    Chalmers University of Technology, Department of Biology and Biological Engineering, Division Industrial Biotechnology.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Combustion of seaweed: a fuel design strategy2017In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 165, p. 155-161Article in journal (Refereed)
    Abstract [en]

    The high ash content and varying ash composition in algal biomass is often mentioned as problematic if to beused for thermal energy conversion. This paper suggests an approach where detailed information on ash compositionand predicted ash formation reactions are basis for successful remedies enabling the use of fuels consideredto be difficult. The procedure is demonstrated on seaweed (Saccharina latissima) cultivated for biorefinery purposes. The ash composition of the seaweed was found suitable for co-combustion with Miscanthus x giganteus, an energy crop high in alkali and silicon. Fuel mixtures were combusted in a bubbling fluidized bed reactorand ash samples were analyzed by SEM-EDS and XRD. The results showed that Ca from the seaweed was veryreactive and thus efficient in solving the silicatemelting problems. The fuel design approach was proven successfuland the potential for using otherwise difficult seaweed fuels in synergetic co-combustion was demonstrated.

  • 50.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash transformation reactions for phosphorus-rich biomass and waste streams2017In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Article in journal (Other academic)
12 1 - 50 of 65
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