umu.sePublications
Change search
Refine search result
12 1 - 50 of 77
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Boman, Christoffer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Pettersson, Esbjörn
    Energy Technology Centre, Piteå, Sweden.
    Westerholm, Roger
    Department of Analytical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Stove performance and emission characteristics in residential wood log and pellet combustion: Part 1: Pellet stoves2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 1, p. 307-314Article in journal (Refereed)
    Abstract [en]

    Stove performance, characteristics, and quantities of gaseous and particulate emissions were determined for two different pellet stoves, varying fuel load, pellet diameter, and chimney draft. This approach aimed at covering variations in emissions from stoves in use today. The extensive measurement campaign included CO, NOx, organic gaseous carbon, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions, and inorganic composition. At high load, most emissions were similar. For stove B, operating at high residual oxygen and solely with primary air, the emissions of PMtot and particle numbers were higher while the particles were smaller. Lowering the fuel load, the emissions of CO and hydrocarbons increased dramatically for stove A, which operated continuously also at lower fuel loads. On the other hand for stove B, which had intermittent operation at lower fuel loads, the emissions of hydrocarbons increased only slightly lowering the fuel load, while CO emissions increased sharply, due to high emissions at the end of the combustion cycle. Beside methane, dominating VOCs were ethene, acetylene, and benzene and the emissions of VOC varied in the range 1.1−42 mg/MJfuel. PAH emissions (2−340 μg/MJfuel) were generally dominated by phenanthrene, fluoranthene and pyrene. The PMtot values (15−45 mg/MJfuel) were in all cases dominated by fine particles with mass median diameters in the range 100−200 nm, peak mobility diameters of 50−85 nm, and number concentrations in the range 4 × 1013 to 3 × 1014 particles/MJfuel. During high load conditions, the particulate matter was totally dominated by inorganic particles at 15−25 mg/MJfuel consisting of potassium, sodium, sulfur, and chlorine, in the form of K2SO4, K3Na(SO4)2, and KCl. The study shows that differences in operation and modulation principles for the tested pellet stoves, relevant for appliances in use today, will affect the performance and emissions significantly, although with lower scattering in the present study compared to compiled literature data.

  • 2.
    Borén, Eleonora
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Industrial Doctoral School for Research and Innovation, Umeå University, Umeå, Sweden.
    Larsson, Sylvia H.
    Biomass Technology Centre, Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Andreas, Averheim
    Mikael, Thyrel
    Biomass Technology Centre, Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Reducing VOC off-gassing during the production of pelletized steam-exploded bark: impact of storage time and controlled ventilation2018In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 32, no 4, p. 5181-5186Article in journal (Refereed)
    Abstract [en]

    Volatile organic compound (VOC) off-gassing behavior of thermally treated biomass intended for bioenergy production has recently been shown to be vastly different from that of untreated biomass. Simple measures to reduce emissions, such as controlled ventilation and prolonged storage time, have been suggested but not yet studied in detail. In the present study, we monitored how VOC off-gassing was reduced over time (24–144 h) in enclosed storage with and without ventilation. Steam-exploded bark was collected directly from a pilot-scale steam explosion plant as well as before and after subsequent pelletizing. Active Tenax-TA absorbent sampling of VOCs was performed from the headspaces of a bench-scale sample storage setup. The impact of storage time and ventilation on VOC levels was evaluated through multivariate statistical analysis. The results showed that relative VOC concentrations in the headspace were reduced by increased storage time, with heavier VOCs reduced at a higher rate. VOC composition was neither reduced nor shifted by controlled intermittent ventilation during storage; instead, VOC levels equilibrated at the same levels as those stored without ventilation, and this was independent of the process step, storage time, or number of ventilations.

  • 3.
    Borén, Eleonora
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå University Industrial Doctoral School for Research and Innovation.
    Yazdanpanah, Fahimeh
    Lindahl, Roger
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Schilling, Christoph
    Chandra, Richard P.
    Ghiasi, Bahman
    Tang, Yong
    Sokhansanj, Shahabaddine
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Larsson, Sylvia H.
    Off-gassing of VOCs and permanent gases during storage of torrefied and steam exploded wood2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 10, p. 10954-10965Article in journal (Refereed)
    Abstract [en]

    Thermal treatment for upgrading of low-value feedstocks to improve fuel properties has gained large industrial interest in recent years. From a storage and transport perspective, hazardous off-gassing could be expected to decrease through the degradation of reactive biomass components. However, thermal treatment could also shift chemical compositions of volatile organic components, VOCs. While technologies are approaching commercialization, off-gassing behavior of the products, especially in terms of VOCs, is still unknown. In the present study, we measured off-gassing of VOCs together with CO, CO2, CH4, and O2 depletion from torrefied and steam exploded softwood during closed storage. The storage temperature, head space gas (air and N2), and storage time were varied. VOCs were monitored with a newly developed protocol based on active sampling with Tenax TA absorbent analyzed by thermal desorption-GC/MS. High VOC levels were found for both untreated and steam exploded softwood, but with a complete shift in composition from terpenes dominating the storage gas for untreated wood samples to an abundance of furfural in the headspace of steam exploded wood. Torrefied material emitted low levels of VOCs. By using multivariate statistics, it was shown that for both treatment methods and within the ranges tested, VOC off-gassing was affected first by the storage temperature and second by increasing treatment severity. Both steam exploded and torrefied biomass formed lower levels of CO than the reference biomass, but steam explosion caused a more severe O2 depletion.

  • 4.
    Boström, Dan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Eriksson, Gunnar
    Division of Energy Engineering, Department of Applied Physics and Mechanical Engineering, Luleå Technical University.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Division of Energy Engineering, Department of Applied Physics and Mechanical Engineering, Luleå Technical University.
    Ash transformations in fluidized-bed combustion of rapeseed meal2009In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 23, no 5, p. 2700-2706Article in journal (Refereed)
    Abstract [en]

    The global production of rapeoil is increasing. A byproduct is rapeseed meal that is a result of the oil extraction process. Presently the rapeseed meal mainly is utilized as animal feed. An interesting alternative use is, however, energy conversion by combustion. This study was undertaken to determine the combustion properties of rapeseed meal and bark mixtures in a bubbling fluidized bed, with emphasis on gas emissions, ash formation, -fractionation and -interaction with the bed material. Due to the high content of phosphorus in rapeseed meal the fuel ash is dominated by phosphates, in contrast to most woody biomass where the ash is dominated by silicates. From a fluidized bed combustion (FBC) point of view, rapeseed meal could be a suitable fuel. Considering FBC agglomeration effects, pure rapeseed meal is in level with the most suitable fuels, as earlier tested by the methods utilized in the present investigation. The SO2 emission, however, is higher than most woody biomass fuels as a direct consequence of the high levels of sulfur in the fuel. Also the particulate matter emission, both submicron and coarser particles, is higher. Again this can be attributed the high ash content of rapeseed meal. The high abundance of SO2 is apparently effective for sulfatization of KCl in the flue gas. Practically no KCl was observed in the particulate matter of the flue gas. A striking difference in the mechanisms of bed agglomeration for rapeseed meal compared to woody biomass fuels was also observed. The ubiquitous continuous layers on the bed grains found in FBC combustion of woody biomass fuels was not observed in the present investigation. Instead very thin and discontinuous layers were observed together with isolated partly melted bed ash particles. The latter could occasionally be seen as adhered to the quartz bed grains. Apparently the bed agglomeration mechanism, that obviously demanded rather high temperatures, involved more of adhesion by partly melted ash derived potassium -calcium phosphate bed ash particles/droplets than direct attack of gaseous alkali on the quartz bed grains forming potassium -calcium silicate rich bed grain layers. Am explanation could be found in the considerable higher affinity for base cations of phosphorus than silicon. This will to a great extent withdraw the present basic oxides from attacking the quartz bed grains with agglomeration at low temperatures as a result.

  • 5.
    Boström, Dan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Grimm, Alejandro
    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.
    Björnbom, Emilia
    Chemical Engineering and Technology, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
    Öhman, Marcus
    Division of Energy Engineering, Luleå University of Technology, SE- 971 87 Luleå, Sweden.
    Influence of kaolin and calcite additives on ash transformations in small-scale combustion of oat2009In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 23, no 10, p. 5184-5190Article in journal (Refereed)
    Abstract [en]

    A growing interest has been observed for the use of cereal grains in small- and medium-scale heating. Previous studies have been performed to determine the fuel quality of various cereal grains for combustion purposes. The present investigation was undertaken in order to elucidate the potential abatement of low-temperature corrosion and deposits formation by using fuel additives (calcite and kaolin) during combustion of oat. Special emphasis was put on understanding the role of slag and bottom ash composition on the volatilization of species responsible for fouling and emission of fine particles and acid gases. The ash fractions were analyzed with scanning electron micro scopy/energy dispersive spectroscopy (SEM/EDS), for elemental composition, and with X-ray diffraction (XRD) for identification of crystalline phases. The previously reported K and Si capturing effects of kaolin additive were observed also in the present study using P-rich biomass fuels. That is, the prerequisites for the formation of low melting K-rich silicates were reduced. The result of using kaolin additive on the bottom ash was that no slag was formed. The effect of the kaolin additive on the formation of submicrometer flue gas particles was an increased share of condensed K-phosphates at the expense of K-sulfate and KCl. The latter phase was almost completely absent in the particulate matter. Consequently, the levels of HCl and SO2 in the flue gases increased somewhat. The addition of both calcite assortments increased the amount of farmed slag, although to a considerably higher extent for the precipitated calcite. P was captured to a higher degree in the bottom ash, compared to the combustion of pure oat. The effect of the calcite additives on the fine particle emissions in the flue gases was that the share of K-phosphate decreased considerably, while the content of K-sulfate and KCl increased. Consequently, also the flue-gas levels of acidic HCl and SO2 decreased. This implies that the low-temperature corrosion observed in small-scale combustion of oat possibly can be abated by employing calcite additives. Alternatively, if problems with slagging and deposition of corrosive matter at heat convection surfaces are to be avoided, kaolin additive can be utilized, on the condition that the higher concentrations of acidic gases can be tolerated.

  • 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.
    Branca, Carmen
    et al.
    Istituto di Ricerche sulla Combustione, C.N.R., P.le V. Tecchio, 80125 Napoli, Italy.
    Di Blasi, Colomba
    Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università degli Studi di Napoli “Federico II”, P.le V. Tecchio, 80125 Napoli, Italy.
    Galgano, Antonio
    Istituto di Ricerche sulla Combustione, C.N.R., P.le V. Tecchio, 80125 Napoli, Italy.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Effects of the Torrefaction Conditions on the Fixed-Bed Pyrolysis of Norway Spruce2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 9, p. 5882-5891Article in journal (Refereed)
    Abstract [en]

    Fixed-bed pyrolysis of Norway spruce wood previously subjected to torrefaction at temperatures between 533 and 583 K and retention times between 8 and 25 min was studied. Although the thermal pretreatment always results in an increased production of char at the expense of volatile products, appropriate torrefaction conditions give rise to maximum percentages of anhydrosugars, guaiacols possessing a carbonyl group, and phenols in the liquid fraction. Other carbohydrates (e.g., acetic acid, formic acid, hydroxyacetaldehyde, hydroxypropanone, furfural, and furfuryl alcohol) and the large majority of guaiacols show continuously decreasing values. The percentages of carbon monoxide and carbon dioxide in the gas product remain approximately the same, but that of methane slightly increases. The pyrolysis temperatures of torrefied wood are lower than those of the raw material, mainly because of the partial or complete absence of the exothermic contribution associated with extractives and hemicellulose degradation.

  • 8.
    Brus, Elisabet
    et al.
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics. Umeå University, Faculty of Science and Technology, Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Umeå University.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics. Umeå University, Faculty of Science and Technology, Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Mechanisms of bed agglomeration during fluidized-bed combustion of biomass fuels2005In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 19, no 3, p. 825-832Article in journal (Refereed)
    Abstract [en]

    The major ash-related problem encountered in fluidized beds is bed agglomeration, which, in the worst case, may result in total defluidization of the bed and unscheduled downtime. Because of the special ash-forming constituents of biomass fuels, several of these fuels have been shown to be especially problematic. Despite the frequent reporting, a precise and quantitative knowledge of the bed agglomeration process during fluidized bed combustion of biomass fuels has not yet been presented. Bed sampling versus operation time was performed in four different biomass-fired full-scale fluidized beds, as well as during controlled fluidized bed agglomeration tests in bench-scale testing of five representative biomass fuels. The bed materials and agglomerates were further analyzed using scanning electron microscopy, coupled with energy-dispersive spectroscopy SEM/EDS, to determine the characteristics of the formed bed particle layers. For typical wood fuels, coating-induced agglomeration with subsequent attack reaction and diffusion by calcium into the quartz was identified to be the dominating bed agglomeration mechanism. Low-melting calcium-based silicates (including minor amounts of, for example, potassium) were formed with subsequent viscous-flow sintering and agglomeration. For high-alkali-containing biomass fuels, direct attack of the quartz bed particle by potassium compounds in a gas or aerosol phase formed a layer of low-melting potassium silicate. Thus, formation and subsequent viscous-flow sintering and agglomeration seemed to be the dominating agglomeration mechanism for these fuels.

  • 9.
    Brus, Elisabet
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Nordin, Anders
    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.
    Hedman, Henry
    Energy Technology Centre, Piteå, Sweden.
    Eklund, Anders
    Bed agglomeration characteristics of biomass fuels using blast-furnace slag as bed material2004In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 18, no 4, p. 1187-1193Article in journal (Refereed)
    Abstract [en]

    Agglomeration of bed material may cause severe operating problems during fluidized bed combustion. The attack or coating layers that are formed on the bed particles during combustion play an important role in the agglomeration process. To reduce bed agglomeration tendencies, alternative bed materials may be used. In this paper, bed agglomeration characteristics during the combustion of biomass fuels using a relatively new bed material (iron blast-furnace slag) as well as ordinary quartz sand were determined. Controlled agglomeration tests lasting 40 h, using five representative biomass fuels (bark, olive residue, peat, straw, and reed canary grass) were conducted in a bench-scale fluidized bed. The bed materials and agglomerates were analyzed using SEM/EDS and X-ray diffraction. Chemical equilibrium calculations were performed to interpret the experimental findings. The results showed that blast-furnace slag had a lower tendency to agglomerate than quartz sand for most of the fuels. The quartz particles showed an inner attack layer more often than did the blast-furnace slag. The blast-furnace slag had a lower tendency to react with elements from the fuel. The outer coating layer had similar characteristics and thickness for both bed materials when the same fuel was combusted. However, the inner attack layer thickness was larger for quartz particles. SEM/EDS analyses of the agglomerates showed that the inner Ca-K-silicate-rich attack layer was responsible for the agglomeration of quartz sand. The composition of blast-furnace slag agglomerate was similar to the outer coating layer. Chemical equilibrium calculations showed that the original composition of the blast-furnace slag was close to the equilibrium composition, and hence there was no major driving force for reactions between that bed material and K and Ca from the fuel. The homogeneous silica-rich attack layer (with a low melting temperature) was not formed to the same extent for blast-furnace slag, thus explaining the lower bed agglomeration tendency.

  • 10. Capablo, Joaquin
    et al.
    Arendt Jensen, Peter
    Hougaard Pedersen, Kim
    Hjuler, Klaus
    Nikolaisen, Lars
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Frandsen, Flemming
    Ash properties of alternative biomass2009In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 23, p. 1965-1976Article in journal (Refereed)
    Abstract [en]

    The ash behavior during suspension firing of 12 alternative solid biofuels, such as pectin waste, mash from a beer brewery, or waste from cigarette production have been studied and compared to wood and straw ash behavior. Laboratory suspension firing tests were performed on an entrained flow reactor and a swirl burner test rig, with special emphasis on the formation of fly ash and ash deposit. Thermodynamic equilibrium calculations were performed to support the interpretation of the experiments. To generalize the results of the combustion tests, the fuels are classified according to fuel ash analysis into three main groups depending upon their ash content of silica, alkali metal, and calcium and magnesium. To further detail the biomass classification, the relative molar ratio of Cl, S, and P to alkali were included. The study has led to knowledge on biomass fuel ash composition influence on ash transformation, ash deposit flux, and deposit chlorine content when biomass fuels are applied for suspension combustion.

  • 11.
    de Geyter, Sigrid
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    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.
    Eriksson, Morgan
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Effects of non-quartz minerals in natural bed sand on agglomeration characteristics during fluidized bed combustion of biomass fuels2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 5, p. 2663-2668Article in journal (Refereed)
    Abstract [en]

    Most of the previous literature on fluidized bed agglomeration during biomass combustion is based on quartz as a bed material. Full-scale installations however often use natural sand, which apart from quartz may contain a high fraction of non-quartz minerals such as potassium feldspar and plagioclase. The objective of the present study was therefore to elucidate the effects of non-quartz minerals occurring in natural sand on the agglomeration behavior during fluidized bed combustion of biomass fuels. Three fuels typical for previously determined agglomeration mechanisms were chosen as model fuels: calcium-rich bark, potassium-rich olive residues, and silica- and potassium-rich wheat straw. Two different feldspar minerals were used: a potassium feldspar and a plagioclase, labradorite, which both occur in many commercial bed materials. Furthermore, olivine was used as a bed material as this mineral represents another type of bed material used in some fullscale installations. Quartz was used as a reference bed material. The effects of non-quartz minerals in natural sand on initial defluidization temperature were assessed during carefully controlled, bench-scale fluidized bed agglomeration experiments. Bed material samples and agglomerates were analyzed using scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) in order to explore the occurrence and chemical composition of coating and attack layers on the bed particles and necks between agglomerated particles. Significant differences in agglomeration characteristics were found for the different minerals when bark and olive residue were combusted. Potassium-feldspar was shown to lower the initial defluidization temperature for combustion of bark and olive residues. Plagioclase and olivine on the other hand were found to increase the initial defluidization temperature as compared to quartz for the combustion of olive residue, but for bark combustion, they did not differ significantly from quartz. During combustion of wheat straw, all bed materials agglomerated shortly after the startup of the experiment. For bark and olive residue samples, attack layers were found on all bed materials and the composition of the inner attack layer and agglomerate necks differed significantly with the fuel/bed material combination. For wheat straw however, no continuous attack layers were found, and the bed material composition was concluded not to influence the agglomeration characteristics for this biomass. The results were used to suggest possible mechanisms involved in layer formation for the different minerals.

  • 12.
    Diaz-Ramirez, Maryori
    et al.
    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.
    Sebastian, Fernando
    Royo, Javier
    Xiong, Shaojun
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash Characterization and Transformation Behavior of the Fixed-Bed Combustion of Novel Crops: Poplar, Brassica, and Cassava Fuels2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 6, p. 3218-3229Article in journal (Refereed)
    Abstract [en]

    New biofuel raw materials for energy pellet production are now being studied as potential energy sources for the heating market. Because of the complexity of the chemical and physical properties of novel fuels, such as some agricultural residues and energy crops, the study of their ash-related aspects is crucial for the sustainable development of this potential energy sector. Ash fractions formed during fixed-bed combustion of different pelletized novel crops; i.e., two Mediterranean crops (one herbaceous, brassica, and one woody species, poplar) and three Chinese cassava stems (cassava species from three different Chinese regions), and three Chinese cassava stems (cassava species from three different Chinese regions), were characterized, and their formation paths assessed in this study. Special emphasis was placed on elucidating the role of major ash-forming elements in the fractionation and transformation behavior, leading to the formation of bottom ash, deposits, and particulate emissions (fine and coarse ash particle fractions) on the basis of experimental data. In the Mediterranean fuels, the predominant ash fraction obtained was bottom ash, mainly characterized by silicates. Phosphates were found to be the main crystalline phases in the Chinese fuels. The slagging tendency was low for all of the fuels, although more significant for the cassava species under the studied conditions. Further, combustion of the studied Chinese energy crops resulted in a considerably finer particle fraction compared to the Mediterranean fuels. Deposits and particulate matter were dominated by K-sulfates as well as K-chloride in all fuels (except poplar), with the occurrence of K-phosphates for cassava pellets. Overall, this study showed fundamental differences in ash transformation behavior during combustion of P-rich fuels (i.e., cassava mixtures) compared to Si-rich fuels (i.e., poplar and brassica mixtures). Of major importance is the experimental verification of the higher thermodynamic stability of phosphates in relation to silicates. Furthermore, in P-rich fuels at high (K + Na)/(Ca + Mg) ratios, a significant degree of alkali metal volatilization occurs, which forms larger amounts of particulate matter, whereas this ratio has no/low effect in Si-rich fuels at high alkali metal ratios.

  • 13.
    Enestam, Sonja
    et al.
    Åbo Akademi.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Niemi, Jere
    Metso Power.
    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.
    Mäkele, Kari
    Metso Power.
    Hupa, Mikko
    Åbo Akademi.
    Occurrence of zinc and lead in aerosols and deposits in the fluidized bed combustion of recovered waste wood:  Part 1: Samples from boilers2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 4, p. 1396-1404Article in journal (Refereed)
    Abstract [en]

    Combustion of recovered waste wood (RWW) has led to increased fouling and corrosion of furnace walls, superheaters, and economizers. These problems have been associated mainly with chlorine, zinc, and lead in the deposits but also with sodium and titanium. The presence of lead and zinc compounds, especially lead and zinc chlorides, has been shown to increase the corrosivity of the deposits even at relatively low metal temperatures (230−450 °C). The present work determined experimentally the distribution and speciation of zinc and lead compounds in aerosol particles and deposits in the fluidized-bed combustion of RWW. Measurements were conducted in both a full-scale (20 MWth) plant with as-received RWW and in a pilot-scale (2 MWth) setup with as-received RWW and RWW doped with zinc and lead. The results show that the amount and speciation of zinc and lead in the deposits vary depending upon the fuel composition, flue gas temperature, and metal temperature. Both lead and zinc chlorides are found in temperature ranges typical for the primary superheater area. A caracolite-type compound [Na3Pb2(SO4)3Cl] was identified in deposits from the economizer area and K2ZnCl4 in the sub-micrometer aerosol particle fraction.

  • 14. Enestam, Sonja
    et al.
    Mäkelä, Kari
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hupa, Miko
    Occurrence of Zinc and Lead in Aerosols and Deposits in the Fluidized-Bed Combustion of Recovered Waste Wood. Part 2: Thermodynamic Considerations2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 4, p. 1970-1977Article in journal (Refereed)
    Abstract [en]

    In the present work, which is the second part in a series of two, multi-phase, multi-component equilibrium calculations were used to study the chemistry and deposition behavior of lead and zinc in the combustion of recovered waste wood (RWW). Particular attention was paid to the deposition behavior in different parts of the boiler under varying flue gas and material temperature conditions. In addition, the influence of fuel composition was considered by studying three different fuel compositions. The results from the calculations were compared to experimental results from two measurement campaigns, whose goal was to experimentally determine the distribution and speciation of zinc and lead compounds in aerosol particles and deposits in the fluidized-bed combustion of RWW. The results from the experimental work are presented in part 1 (10.1021/ef101478n) of this work.

  • 15.
    Eriksson, Gunnar
    et al.
    Division of Energy Engineering, Department of Applied Physics and Mechanical Engineering, Luleå University of Technology.
    Hedman, Henry
    Energy Technology Centre, Piteå, Sweden.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Pettersson, Esbjörn
    Division of Energy Engineering, Department of Applied Physics and Mechanical Engineering, Luleå University of Technology.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Division of Energy Engineering, Department of Applied Physics and Mechanical Engineering, Luleå University of Technology.
    Combustion characterization of rapeseed meal and possible combustion applications2009In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 23, no 8, p. 3930-3939Article in journal (Refereed)
    Abstract [en]

    A future shortage of biomass fuel can be foreseen. The production of rapeseed oil for a number of purposes is increasing, among others, for biodiesel production. A byproduct from the oil extraction process is rapeseed meal (RM), presently used as animal feed. Further increases in supply will make fuel use an option. Several energy companies have shown interest but have been Cautious because of the scarcity of data on fuel properties, which led to the present study. Combustion-relevant properties of RM from several producers have been determined. The volatile fraction (74 +/- 0.06%(wt ds)) is comparable to wood; the moisture content (6.2-11.8%(wt)) is lows and the ash content (7.41 +/- 0.286%(wt) (ds)) is high compared to most other biomass fuels. The lower heating value is 18.2 +/- 0.3 MJ/kg (dry basis). In comparison to other biomass fuels, the chlorine content is low (0.02-0.05%(wt ds)) and the sulfur content is high (0.67-0.74%(wt ds)). RM has high contents of nitrogen (5.0-6.4%(wt) (ds)) phosphorus (1.12-1.23%(wt) (ds)) and potassium (1.2-1.4%(wt) (ds)). Fuel-specific combustion properties of typical RM were determined through combustion tests. with an emphasis oil gas emissions, ash formation, and potential ash-related operational problems. Softwood bark was chosen as a suitable and representative co-combustion (woody) fuel. RM was added to the bark at two levels: 10 and 30%(wt) (ds). These mixtures were pelletized, and so was RM without bark (for durability mixed With cutter shavings, contributing 1%(wt) of the ash). Each of these fuels was combusted in a 5 kW fluidized bed and an underfed pellet burner (to simulate grate combustion). Pure RM was combusted in a powder burner. Emissions of NO and SO, were high for all combustion tests, requiring applications with flue gas cleaning, economically viable only at large scale. Emissions of HCl were relatively low, Temperatures for initial bed agglomeration in the fluidized-bed tests were high for RM compared to many other agricultural fuels, thereby indicating that RM could be an attractive fuel from a bed agglomeration point of view. The results of grate combustion Suggest that slagging is not likely to be severe for RM, pure or mixed with other fuels. Fine-mode particles from fluidized-bed combustion and grate combustion mainly contained sulfates of potassium, suggesting that the risk of problems caused by deposit formation should be moderate. The chlorine concentration of the particles was reduced when RM was added to bark, potentially lowering the risk of high-temperature corrosion. Particle emissions from powder combustion of RM were 17 times higher than for wood powder, and the fine-mode fraction contained mainly K-phosphates known to cause deposits, suggesting that powder combustion of RM should be used With Caution. A possible use of RM is as a sulfur-containing additive to biomass fuels rich in Cl and K for avoiding ash-related operational problems in fluidized beds and grate combustors originated from high KCl concentrations in the fuel gases.

  • 16.
    Fagerström, Jonathan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Näzelius, Ida-Linn
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Gilbe, Carl
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Influence of Peat Ash Composition on Particle Emissions and Slag Formation in Biomass Grate Co-combustion2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 5, p. 3403-3411Article in journal (Refereed)
    Abstract [en]

    Co-combustion by fuel blending of peat and biomass has shown positive effects on operational problems. However, peat ash compositions vary considerably, and this has been shown to affect the potential for operational problems in different fuel-blending situations. The present work used three different peat types with the objective to elucidate how the variation in peat ash composition influences both particle emissions and slag formation during co-combustion with three different biomasses in a small-scale pellet boiler. Estimations of potassium release and slag formation were performed and discussed in relation to fuel composition in the (K2O + Na2O) (CaO + MgO) (SiO2) system. All tested peat types reduced the fine particle emissions by capturing potassium into the bottom ash as one or several of the following forms: slag, sulfates, chlorides, and alumina silicates. However, there were considerable differences between the peat types, presumably depending upon both their content and mineral composition of silicon, calcium, aluminum, and sulfur. Some general important and beneficial properties of peat type in co-combustion situations with biomass are defined here, but the specific blending proportion of peat should be decided on an individual basis for each scenario based on the relative contents in the fuel mixture of the most relevant ash-forming elements.

  • 17. Gilbe, Carl
    et al.
    Lindström, Erica
    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.
    Samuelsson, Robert
    Burvall, Jan
    Ohman, Marcus
    Predicting slagging tendencies for biomass pellets fired in residential appliances: a comparison of different prediction methods2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 6, p. 3680-3686Article in journal (Refereed)
    Abstract [en]

    In this paper, a comparison between four different types (both empirical and theoretical) of techniques to predict the slagging tendencies in residential pellet combustion appliances was performed. The four techniques used were the standard ash fusion test (SS ISO-540) used in the Swedish pellet standard (SS 18 7120), thermal analysis (TGA/DTA), thermochemical model calculations, and a laboratory-scale sintering test. The tests were performed with 12 pelletized biomass raw materials, and the results were compared with measured slagging tendencies in controlled combustion experiments in a commercial under-fed pellet burner (20 kW) installed in a reference boiler. The results showed significant differences in the prediction of slagging tendencies between different predicting techniques and fuels. The method based on thermal analysis (TGA/DTA) of produced slags must be further developed before useful information could be provided of the slagging behavior of different fuels. The used sintering method must also be further improved before the slagging tendency of fuels forming slags extremely rich in silicon (e.g., some grasses) can be predicted. Relatively good agreement was obtained between results from chemical equilibrium calculations and the actual slagging tendencies from the combustion tests. However, the model calculations must be further improved before quantitative results can be used. The results from the standard ash fusion test (SS ISO 540) showed, in general, relatively high deformation temperatures, therefore predicting a less problematic behavior of the fuels in comparison to the actual slagging tendencies obtained from controlled combustion experiments in commercial pellet burner equipment. Nevertheless, the method predicted, in most cases, the same fuel-specific slagging (qualitatively) trends as the corresponding combustion behavior.

  • 18. Gilbe, Carl
    et al.
    Öhman, Marcus
    Lindström, Erica
    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.
    Samuelsson, Robert
    Burvalll, Jan
    Slagging characteristics during residential combustion of biomass pellets2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 5, p. 3536-3543Article in journal (Refereed)
    Abstract [en]

    Limited availability of sawdust and planer shavings and an increasing demand for biomass pellets in Europe are pushing the market toward other, more problematic raw materials with broader variation in total fuel ash content and composition of the ash forming elements as well as in their slagging tendencies. The main objective in the present work was therefore to determine the influence of fuel-ash composition on residual ash and slag behavior. Twelve different biomass pellets were used: reed canary grass (two different samples), hemp (two different samples), wheat straw. salix, logging residues (two different samples), stern wood (sawdust) as well as spruce, pine, and birch bark. The different pellet qualities were combusted in a commercial under fed pellet burner (20 kW) installed in a reference boiler. Continuous measurements of O-2, CO, CO2, HCl, SO2, and total particle matter mass concentrations were determined in the exhaust gas directly after the boiler. The collected slag deposits, the corresponding deposited bottom ash in the boiler and the collected particle matter were Characterized with X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray analysis (SEM/EDS). For biomass fuel pellets rich in silicon (either inherent or contaminated with sand) and low content of alkaline earth metals the main part of the potassium reacted with the silicon rich ash-residual. forming sticky alkali-silicate particles, which were not entrained front the burner and thereby giving rise to/initiating slag formation. Silicon rich fuels, i.e. fuels were the ash characteristics were dominated by silicate-alkali chemistry, therefore generally showed relatively high slagging tendencies. Straw fuels have typically this ash composition but exceptions to these general trends exists (e.g., one of the hemp fuels used in this work). Wood derived fuels with a relatively low inherent silicon content therefore showed low or relatively moderate slagging tendencies. However, contamination of sand material to these fuels may greatly enhance the slagging tendencies.

  • 19. Grimm, Alejandro
    et al.
    Ohrnan, Marcus
    Lindberg, Therese
    Fredriksson, Andreas
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Bed Agglomeration Characteristics in Fluidized-Bed Combustion of Biomass Fuels Using Olivine as Bed Material2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 7, p. 4550-4559Article in journal (Refereed)
    Abstract [en]

    The bed agglomeration characteristics during combustion of typical biomass fuels were determined in a bench-scale bubbling fluidized-bed reactor (5 kW) using olivine and quartz sand as bed material. The fuels studied include willow, logging residues, wheat straw, and wheat distiller's dried grain with solubles (wheat DDGS). Bed material samples and agglomerates were analyzed by means of scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), for morphology and elemental composition. Furthermore, bed ash particles were separated by sieving from the bed material samples and analyzed for elemental composition by SEM-EDS and for determination of crystalline phases by powder X-ray diffraction (XRD). Chemical equilibrium calculations were performed to interpret the experimental findings of layer formation and reaction tendencies in both bed materials. Significant difference in the agglomeration tendency between olivine and quartz was found during combustion of willow and logging residues. These fuels resulted in inner layers that were more dependent on the bed material composition, and outer layers that have a composition similar to the fuel ash characteristics. The elemental composition of the inner layer formed on the quartz bed particles was dominated by Si, K, and Ca. In the olivine bed, the inner layer consisted mainly of Mg, Si, and Ca. Chemical equilibrium calculations made for both bed materials showed a low chemical driving force for K to react and be retained by the olivine bed particles, which is in accordance to the experimental findings. For the quartz case, the inner layer was found responsible for the initiation of the agglomeration process. The composition of the fewer and more porous agglomerates found after the experiments in the olivine bed showed neck composition and characteristics similar to the individual bed ash particles found in the bed or outer bed particle coating composition. For DDGS (rich in S, P, K, and Mg) and wheat straw (rich in Si and K), no significant differences in the bed agglomeration tendency between olivine and quartz bed materials were found. The results show that the bed particle layer formation and bed agglomeration process were associated to direct adhesion of bed particles by partly molten fuel ash derived K Mg phosphates for DDGS and K-silicates for wheat straw.

  • 20.
    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.

  • 21.
    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.

  • 22.
    Hagman, Henrik
    et al.
    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.
    Co-combustion of Animal Waste, Peat, Waste Wood, Forest Residues, and Industrial Sludge in a 50 MWth Circulating Fluidized-Bed Boiler: Ash Transformation, Ash/Deposit Characteristics, and Boiler Failures2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 10, p. 5617-5627Article in journal (Refereed)
    Abstract [en]

    In strive to lower the energy conversion cost and CO2 net emission, more complex biofuels are used. The combustion of these fuels often creates aggressive and problematic fireside environments in boilers, resulting in reduced availability, which, in turn, may lead to increased usage of fossil fuel in backup boilers. The objective of the present work was to contribute to the efforts of maximizing the availability of a 50 MWth circulating fluidized-bed (CFB) boiler firing complex fuels with high amounts of P, Ca, S, Cl, N, K, and Na. In the present work, ash and deposit samples collected from the flue gas system of a CFB boiler were further analyzed with X-ray powder diffraction, complementing earlier analysis made on the same sample set with scanning electron microscopy equipped with energy-dispersive spectrometry. Thermodynamic calculations were also made. The results clarify details about the ash speciation and transformation as well as effects on boiler operation. A suggestion of a control strategy to minimize corrosion rates in superheaters and SO2 emission to downstream cleaning equipment in full-scale industrial boilers is made. An equation for rough estimation of fuel mix corrosion tendencies is also presented.

  • 23.
    Hagman, Henrik
    et al.
    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.
    Effects on a 50 MWth Circulating Fluidized-Bed Boiler Co-firing Animal Waste, Sludge, Residue Wood, Peat, and Forest Fuels2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 10, p. 6146-6158Article in journal (Refereed)
    Abstract [en]

    This work is a part of an effort to maximize the operational safety of a 50 MWth circulating fluidized-bed (CFB) boiler located in Perstorp, Sweden, co-firing animal waste, peat, waste wood, forest residues, and industrial sludge. An increase in the CFB boiler availability reduces the use of expensive fossil fuel (oil) in backup boilers during operational problems of the CFB boiler. The work includes a thorough mapping and analysis of the failure and preventive maintenance statistics, together with elemental analysis of boiler ash and deposits, flue gas, and fuel fractions. Correlations between boiler parameters and boiler availability are sought, and recommendations regarding boiler design and operation are made. An explicit description of the boiler is made to allow for the use of presented material as future reference material. It was observed that the failure frequency is especially high where (1) rapid chloride-rich windward deposit buildup is combined with (2) high construction material temperature and (3) windward soot blowing. In areas where one of these factors was absent, a more moderate material loss could be seen. The flue gas average elemental composition can be regarded as close to constant as it flows through the series of heat exchangers. Thus, the significant differences in deposit buildup of different flue gas cross-sections cannot be a result of changed average flue gas composition. The areas of the steam tubes suffering from rapid material loss are also exposed to high deposit rates. Downstream of a well-defined temperature threshold in the secondary superheater, neither material loss nor substantial deposit buildup could be seen. Tube deposits are dominated by Na, S, Ca, K, and P, but only Na, K, and S are enriched in the windward tube deposits relative to the fly ash bulk composition. The temperature of the flue gas is the major parameter governing the rate of deposit buildup in the boiler heat exchangers. Of the fuel nitrogen, 95 wt % leaves the process as N-2(g). Fuel mix ash content analysis via a separate ashing of different fuel fractions by heating to 550 degrees C does not reflect the ash content of the fuel mix correctly. The soot blowing angle of attack on the deposits should be regarded in areas with rapid deposit growth when boilers and soot blowers are designed to allow for efficient tube cleaning. The use of heterogeneous fuel in the boiler creates strong variations in fuel, flue gas, and particle composition and makes it increasingly important to have online measurements to be able to understand and control the furnace chemistry. The filter ash in the flue gas baghouse filter effectively sorbs HCl(g) and NH3(g) from the flue gas already without the addition of sorbents. Online flue gas measurement to control the furnace chemistry must therefore be installed upstream of the filter to enable accurate control. Also, a significantly larger filtration area can be installed in the baghouse filters with a slight increase in cost, to allow for efficient use of the ash as free of cost sorbent and lowered emission levels. Scanning electron microscopy analysis of the flue gas deposits shows that no pieces of ground bone, sand particles, or other relatively large flue gas particles contribute directly to the deposit buildup. White crystals rich in N and Cl, most likely ammonium chloride, precipitate downstream of the flue gas filter. The precipitation interferes with the dust emission measurement and forces a reduced usage of waste-derived fuels because of the exceedance of environmental limits. More expensive forest fuels are used to replace waste-derived fuels, resulting in a higher fuel cost.

  • 24.
    Hagman, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lundberg, Mats
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Alloy Selection for a Cofired Circulating Fluidized Bed Boiler Vortex Finder Application at 880 degrees C in a Complex Mixed Mode Corrosion Environment2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 11, p. 12857-12866Article in journal (Refereed)
    Abstract [en]

    X-ray diffraction and scanning electron microscopy (SEM) were used on a corroded industrial-scale circulating fluidized bed (CFB) boiler vortex finder (VF) 253MA alloy plate material to identify the dominating corrosion products and to enable a qualified selection of candidate alloys for the long-term, full-scale exposure study. Alloys 253MA, 310S, 800H/HT, Alloy DS, and Alloy 600 were chosen, and the alloy plates were exposed to the CFB boiler combustion atmosphere having an average temperature of approximately 880 degrees C, consisting of a moist globally oxidizing gas, burning hydrocarbons, CO2, CO, SO2, HCl, NH3, N-2, alkali species, and erosive particles. The exposure times used in this study were 1750, 8000, 12000, and 16000 operating hours. After exposure, the alloy samples were cut, and cross-sections were dry-polished and analyzed with an SEM-backscatter electron detector (BSD) setup to quantify material loss and penetration depth of the corrosion attack. This work suggests two novel concepts: heavily affected depth (HAD) enabling quantitative evaluation of heavily degraded alloys and remaining serviceable metal thickness (RSMT) enabling the use of long-term corrosion data from one alloy to make rough service life estimations of other alloys exposed for significantly shorter periods. The findings of this work show that there is no simple correlation between the heavily affected depth of the alloy and the nickel, chromium, or iron content. Instead, there seem to be two successful alloy composition principles that work well for this application. Furthermore, the work shows that major improvements can be made in terms of both technical life-span and the cost-effectiveness of the VF application if the most appropriate alloy is selected. In this study, a replacement of the frequently used Alloy 253MA with Alloy 310S doubled the lifespan of full-scale VFs, reducing the average VF maintenance cost to half.

  • 25. He, Hanbing
    et al.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ohman, Marcus
    Time Dependence of Bed Particle Layer Formation in Fluidized Quartz Bed Combustion of Wood-Derived Fuels2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 6, p. 3841-3848Article in journal (Refereed)
    Abstract [en]

    Formation of sticky layers on bed particles has been considered as a prerequisite for bed agglomeration in fluidized bed combustion of wood-derived fuels. The present investigation was undertaken to determine the quartz bed particle layer formation process in fluidized bed combustion of wood-derived fuels. Bed material samples from three different appliances, bench-scale bubbling fluidized bed, full-scale bubbling fluidized bed, and full-scale circulating fluidized bed, at different sampling times from startup with a fresh bed were collected. Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD) were used to explore layer morphology and chemical composition and to gain information on crystalline phases of the layers and coatings. Significant differences in layer morphology and composition were found for quartz bed particles with different ages. For bed samples with operational duration of less than 1 day, only one thin Ca-, Si-, O-, and K-rich homogeneous quartz bed particle layer that has a relatively high K/Ca molar ratio was found. For quartz bed particles with an age from around 1 day to 2 weeks, an outer more particle-rich coating layer was also found. During the initial days of this period, the layer growth rate was high but decreased over time, and decreasing K/Ca and increasing Ca/Si molar ratios in the inner bed particle layer were observed. For bed particles with age between 2 and 3 weeks, a much lower layer growth rate was observed. At the same time, the Ca/Si molar ratio reached high values and the K concentration remained on a very low level. In addition to these layer formation processes mentioned, also an inner-inner/crack layer was also formed in the circulating fluidized bed quartz bed particles simultaneously with the inner bed particle layer.

  • 26. He, Hanbing
    et al.
    Ji, Xiaoyan
    Boström, Dan
    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.
    Öhman, Marcus
    Mechanism of Quartz Bed Particle Layer Formation in Fluidized Bed Combustion of Wood-Derived Fuels2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 3, p. 2227-2232Article in journal (Refereed)
    Abstract [en]

    Agglomeration is among one of the major problems in the operation of fluidized bed boilers. The formation of bed particle layers is thought to play an important role on the occurrence of agglomeration in wood-fired fluidized (quartz) beds. In spite of frequent experimental reports on the quartz bed particle layer characteristics, the underlying bed layer formation process has not yet been presented. By combining our previously experimental results on layer characteristics for samples with durations from 4 h to 23 days, with phase diagrams, thermochemical equilibrium calculations, and a diffusion model, a mechanism of quartz bed particle layer formation was proposed. For younger bed particles (<around 1 day), the layer growth process is accelerated due to a high diffusion of calcium in a K-rich silicate melt. However, with continuous addition of calcium into the layer, the amount of melt decreases and crystalline Ca-silicates starts to form. Ca2SiO4 is the dominating crystalline phase in the inner layer, while the formation of CaSiO3 and possibly Ca3SiO5 are favored for younger and older bed particles, respectively. The decreasing amount of melt and formation of crystalline phases result in low diffusion rates of calcium in the inner layer and the layer growth process becomes diffusion controlled after around 1 day.

  • 27. 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.

  • 28. 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.

  • 29.
    Holmgren, Per
    et al.
    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.
    Slag Formation during Entrained Flow Gasification: Silicon Rich Grass Fuel with KHCO3 Additive2018In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029Article in journal (Refereed)
    Abstract [en]

    Prediction of ash particle adherence to walls, melting, and flow properties are important for successful operation of slagging entrained flow gasifiers. In the present study, silicon-rich reed canary grass was gasified at 1000 and 1200 °C with solid KHCO3 added at 0, 1, or 5 wt % to evaluate the impact and efficiency of the dry mixed additive on slag properties. The fuel particles collided with an angled flat impact probe inside the hot reactor, constructed to allow for particle image velocimetry close to the surface of the probe. Ash deposit layer buildup was studied in situ as well as ash particle shape, size, and velocity as they impacted on the probe surface. The ash deposits were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy, giving detailed information on morphology and elemental composition. Results were compared to thermodynamic equilibrium calculations for phase composition and viscosity. The experimental observations (slag melting, flow properties, and composition) were in good qualitative agreement with the theoretical predictions. Accordingly, at 1000 °C, no or partial melts were observed depending upon the potassium/silicon ratio; instead, high amounts of additive and a temperature of at least 1200 °C were needed to create a flowing melt.

  • 30. Jonsson, Carrie Y. C.
    et al.
    Stjernberg, Jesper
    Wiinikka, Henrik
    Lindblom, Bo
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Technology and Thermal Process Chemistry (ETPC).
    Ohman, Marcus
    Deposit Formation in a Grate-Kiln Plant for Iron-Ore Pellet Production. Part 1: Characterization of Process Gas Particles2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 10, p. 6159-6170Article in journal (Refereed)
    Abstract [en]

    Slag formation in the grate-kiln process is a major problem for iron-ore pellet producers. It is therefore important to understand the slag formation mechanism in the grate-kiln production plant. This study initiated the investigation by in situ sampling and identifying particles in the flue gas from a full-scale 40 MW grate-kiln production plant for iron-ore pelletizing. Particles were sampled from two cases of combustion with pulverized coal and heavy fuel oil. The sampling location was at the transfer chute that was situated between the traveling grate and the rotary kiln. The particle-sampling system was set up with a water-cooled particle probe equipped with nitrogen gas dilution, cyclone, and low-pressure impactor. Sub-micrometer and fine particles were size-segregated in the impactor, while coarse particles (>6 mu m) were separated with a cyclone before the impactor. Characterization of these particles was carried out with environmental scanning electron microscopy (ESEM), and the morphology of sub-micrometer particles was studied with transmission electron microscopy (TEM). The results showed that particles in the flue gas consisted principally of fragments from iron-ore pellets and secondarily of ashes from pulverized coal and heavy fuel oil combustions. Three categories of particle modes were identified: (1) sub-micrometer mode, (2) first fragmentation mode, and (3) second fragmentation mode. The sub-micrometer mode consisted of vaporized and condensed species; relatively high concentrations of Na and K were observed for both combustion cases, with higher concentrations of Cl and S from heavy fuel oil combustion but higher concentrations of Si and Fe and minor P, Ca, and Al from coal combustion. The first fragmentation mode consisted of both iron-ore pellet fines and fly ash particles; a significant increment of Fe (>65 wt %) was observed, with higher concentrations of Ca and Si during heavy fuel oil combustion but higher concentrations of Si and Al during coal combustion. The second fragmentation mode consisted almost entirely of coarse iron-ore pellet fines, predominantly of Fe (similar to 90 wt %). The particles in the flue gas were dominantly iron-ore fines because the second fragmentation mode contributed >96 wt % of the total mass of collected particles.

  • 31.
    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.

  • 32.
    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.

  • 33.
    Larsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Nordin, Anders
    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.
    Warnqvist, Björn
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Eriksson, Gunnar
    Influence of black liquor variability, combustion, and gasification process variables and inaccuracies in thermochemical data on equilibrium modeling results2006In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 20, no 1, p. 359-363Article in journal (Refereed)
    Abstract [en]

    The present work is a systematic sensitivity study of how inaccuracies in thermochemical data influence important parameters resulting from chemical equilibrium modeling of black liquor combustion and gasification processes. These effects have also been compared with those originating from normal variations in process variables and black liquor composition. Determination of the effects was achieved by performing a large number of equilibrium calculations structured according to statistical designs. Evaluation of the chemical equilibrium model calculations was facilitated by regression analysis. From the results, it can be concluded that uncertainties in thermochemical data of several key components have significant effects on important chemical and physical modeling responses in black liquor combustion and gasification. These effects are in many cases comparable to, or larger than, the effects from variation in fuel and process variables. Experimental redetermination of thermochemical data for Na2S, K2S, and gaseous NaOH is suggested.

  • 34. Lindstroem, Erica
    et al.
    Oehman, Marcus
    Backman, Rainer
    Bostroem, Dan
    Influence of sand contamination on slag formation during combustion of wood derived fuels2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 4, p. 2216-2220Article in journal (Refereed)
    Abstract [en]

    Previous investigations have suggested that sand contamination to woody biomass fuels enhances slag formation in residential combustion appliances. The objectives were therefore to observe the effect of soil contamination in different forestry assortments on the extent of slagging and to gain increased understanding in the ash and slag forming chemical processes. This was accomplished by studying the bottom ash and the slag compositions after 19 2 h of combustion in a residential pellet burner. Melted ash reacted with the admixed sand particles resulting in an increased amount of melt with an increased content of silicon. The results confirm earlier experiences that melted bottom ash from combustion of woody biomass, upon cooling, forms silicate phases. In the corresponding melted ash, sand minerals as quartz, plagioclase, and microcline are not thermodynamically stable but will react and form a more silica rich melt. This melt has presumably lower liquidus temperature, explaining the increased amount of melt observed in the combustion experiments of soil contaminated fuels.

  • 35.
    Lindström, Erica
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Larsson, Sylvia H.
    Unit of Biomass Technology and Chemistry, Swedish University of Agricultural Sciences, S-901 83 Umeå, Sweden.
    Boström, Dan
    Division of Energy Engineering, Luleå University of Technology, S-971 87 Luleå, Sweden.
    Öhman, Marcus
    Division of Energy Engineering, Luleå University of Technology, S-971 87 Luleå, Sweden.
    Slagging characteristics during combustion of woody biomass pellets made from a range of different forestry assortments2010In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 24, no 6, p. 3456-3461Article in journal (Refereed)
    Abstract [en]

    In this study, multivariate methods were used to select representative raw materials of the pellet assortments prior to combustion. The fuels were selected to form a range of expected slagging tendencies. During combustion, temperatures and O-2, CO, NO, and SO2 were measured continuously. The deposits (i.e., slag and bottom ash) were quantified after every experiment and collected for analysis to identify the crystalline phases and to study the morphology and elemental composition respectively. As expected, the slagging was most severe for the whole-tree assortments because of their content of branches, foliage, and twigs. In the most severe case over three-quarters of the total amount of ash melted to form slag. This study indicates that certain concentrations of silicon, inherent in the fuel but also as silicates from contamination, together with alkali metals, mainly potassium, are prerequisites for the initiation of and progress of slag formation. Generally the concentrations of silicon and potassium are low in stemwood but higher in bark, foliage, and living tissues of the tree. Also, the contamination from sand and/or soil is present in the bark and foliage.

  • 36.
    Lindström, Erica
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Larsson, Sylvia H
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Slagging tendencies during combustion of woody biomass pellets made from  a range of different forestry assortments2010In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 24, no 6, p. 3456-3461Article in journal (Refereed)
    Abstract [en]

    In this study, multivariate methods were used to select representative raw materials of the pellet assortments prior to combustion. The fuels were selected to form a range of expected slagging tendencies. During combustion, temperatures and O2, CO, NO, and SO2 were measured continuously. The deposits (i.e., slag and bottom ash) were quantified after every experiment and collected for analysis to identify the crystalline phases and to study the morphology and elemental composition respectively. As expected, the slagging was most severe for the whole-tree assortments because of their content of branches, foliage, and twigs. In the most severe case over three-quarters of the total amount of ash melted to form slag. This study indicates that certain concentrations of silicon, inherent in the fuel but also as silicates from contamination, together with alkali metals, mainly potassium, are prerequisites for the initiation of and progress of slag formation. Generally the concentrations of silicon and potassium are low in stemwood but higher in bark, foliage, and living tissues of the tree. Also, the contamination from sand and/or soil is present in the bark and foliage.

  • 37.
    Lindström, Erica
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Sandström, Malin
    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 tekniska universitet.
    Slagging characteristics during combustion of cereal grains rich in phosphorous2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 2, p. 710-717Article in journal (Refereed)
    Abstract [en]

    A residential cereal burner (20 kW) was used to study the slagging characteristics of cereal grains with and without lime addition. The deposited bottom ash and slag were analyzed using X-ray diffraction (XRD), to identify the crystalline phases, and environmental scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (ESEM/EDS), to study the morphology and elemental composition. Phase-diagram information was utilized to extract qualitative information about the behavior of cereal grain ashes under combustion conditions. Chemical equilibrium model calculations were used to interpret the experimental results. In addition, investigations of the melting behavior of the produced slags were conducted. The results showed significant differences in slagging characteristics between the fuels that were used. The slags consisted of high-temperature melting crystalline phases (calcium/magnesium potassium phosphates) and a potassium-rich phosphate melt for all cereal grains. For oat and barley, cristobalite was also identified in the slag. Furthermore, in these cases, the slags most probably contained a potassium-rich silica melt. The differences in the melting behaviors of the slags had a considerable effect on the performance of the burner. The addition of lime reduced the formation of slag for barley and totally eliminated it for rye and wheat. This occurs because lime contributes to the formation of high-temperature melting calcium potassium phosphates.

  • 38. Lundholm, K
    et al.
    Nordin, A
    Ohman, M
    Bostrom, D
    Reduced bed agglomeration by co-combustion biomass with peat fuels in a fluidized bed2005In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 19, no 6, p. 2273-2278Article in journal (Refereed)
    Abstract [en]

    Fluidized bed combustion is an energy conversion technology that is very suitable for biomass combustion because of its fuel flexibility and low process temperatures. However, agglomeration of bed material may cause severe operating problems. To prevent or at least reduce this, peat has been suggested as an additive to the main fuels. Nevertheless, the characteristics of peat fuels vary and there is limited information of the effect of different peat fuels and of the mechanisms behind the agglomeration prevention. The objectives of the present work were therefore to: (i) quantify the potential positive effect by co-combustion peat with forest fuels in terms of initial agglomeration temperatures; (ii) determine the amount of peat fuel that is needed to significantly reduce the agglomeration tendencies; and, if possible, (iii) elucidate the governing mechanisms. The results showed that all peat fuels prevented agglomeration in the studied interval of 760-1020 degrees C and even as little as 5% peat fuel was found to have significant effects. The results also indicated that the mechanism of the agglomeration prevention varies between different peat fuels. Possible mechanisms are the minerals in the peat fuel retain alkali, which then is either elutriated up from the bed or captured in the bed; calcium and other refractory elements increase the melting temperature and thereby counteract the melting of alkali; and sulfur reacts with alkali metals and the alkali sulfates is either elutriated up from the bed or prevents agglomeration by increased melting temperature and lowered viscosity. Results from elemental analysis of the coating on bed particles showed that all mixtures with peat fuel resulted in a decreased or unchanged fraction of potassium and an increased fraction of aluminum in the coatings. The results also indicated a complex relationship between the fuel inorganic contents and the agglomeration process.

  • 39. Lundholm, Karin
    et al.
    Rogers, Joseph M.
    Haynes, Brian S.
    Bostroem, Dan
    Nordin, Anders
    Fate of Cu, Cr, and As during the combustion stages of CCA-treated wood fuel particles2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 3, p. 1589-1597Article in journal (Refereed)
    Abstract [en]

    A safe end-of-life management of the abundant chromated copper arsenate (CCA) preserved materials is 14 demanded for several environmental and health reasons. Thermal treatment as a disposal method will allow for efficient energy recovery and more controlled separation of the CCA elements, and potentially decrease leaching of toxic compounds into soils, lakes, and groundwater in the vicinity of landfills. However, this also leads to a potential risk of increased trace element emissions into the atmosphere. Developments in combustion science and technology have focused on decreasing emissions of particulates, sulfur and nitrogen oxides, but to fully control the fate of the trace elements through the thermal process and the subsequent flue gas cleaning process, the partitioning of these elements during combustion must be understood, especially for CCA-treated materials. The fate of the CCA elements during the different stages of combustion of impregnated wood was therefore explored. This paper compares the predicted results from chemical equilibrium modeling with results from laboratory-scale single-particle batch experiments. The results showed that a significant volatilization of arsenic was obtained experimentally, which the equilibrium calculations suggest is mainly related to the volatilization stage of combustion. The chemical equilibrium analysis showed to describe the overall behavior and fate of the three elements relatively well, since both degree of volatilization and solid phase compositions were quite in agreement between model and experimental results.

  • 40. Ma, Charlie
    et al.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ohman, Marcus
    Thermochemical Equilibrium Study of Slag Formation during Pressurized Entrained-Flow Gasification of Woody Biomass2015In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 7, p. 4399-4406Article in journal (Refereed)
    Abstract [en]

    The potential slag formation behavior during pressurized entrained-flow gasification (PEFG) of woody biomass has been studied from a thermodynamic perspective with respect to compositional, temperature, and pressure variations. An ash transformation scheme was proposed on the basis of the melt formation potential that arises when gaseous K species are present with Si and Ca. Databases and models in FactSage 6.4 were used to carry out thermochemical equilibrium calculations within ChemSheet. It was found that increasing pressure and increasing Si content expanded the range of operating conditions that are conducive of melt formation, while increasing temperature and increasing Ca content diminished the range. The results from the calculations compared qualitatively well to experimental results and provide further information needed in the development of PEFG reactors for woody biomass.

  • 41. Ma, Charlie
    et al.
    Carlborg, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Hedman, Henry
    Wennebro, Jonas
    Weiland, Fredrik
    Wiinikka, Henrik
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ohman, Marcus
    Ash Formation in Pilot-Scale Pressurized Entrained-Flow Gasification of Bark and a Bark/Peat Mixture2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 12, p. 10543-10554Article in journal (Refereed)
    Abstract [en]

    Pressurized entrained-flow gasification (PEFG) of bark and a bark/peat mixture (BPM) was carried out in a pilot scale reactor (600 kW(th), 7 bar(a)) with the objective of studying ash transformations and behaviors. The bark fuel produced a sintered but nonflowing reactor slag, while the BPM fuel produced a flowing reactor slag. Si was enriched within these slags compared to their original fuel ash compositions, especially in the bark campaign, which indicated extensive ash matter fractionation. Thermodynamically, the Si contents largely accounted for the differences in the predicted solidus/liquidus temperatures and melt formations of the reactor slags. Suspension flow viscosity estimations were in qualitative agreement with observations and highlighted potential difficulties in controlling slag flow. Quench solids from the bark campaign were mainly composed of heterogeneous particles resembling reactor fly ash particles, while those from the BPM campaign were flowing slags with likely chemical interactions with the wall refractory. Quench effluents and raw syngas particles were dominated by elevated levels of K that, along with other chemical aspects, indicated KOH(g) and/or K(g) were likely formed during PEFG. Overall, the results provide information toward development of woody biomass PEFG and indicate that detailed understanding of the ash matter fractionation behavior is essential.

  • 42. Ma, Charlie
    et al.
    Weiland, Fredrik
    Hedman, Henry
    Boström, Dan
    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.
    Ohman, Marcus
    Characterization of Reactor Ash Deposits from Pilot-Scale Pressurized Entrained-Flow Gasification of Woody Biomass2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 11, p. 6801-6814Article in journal (Refereed)
    Abstract [en]

    Pressurized entrained-flow gasification of renewable forest residues has the potential to produce high-quality syngas suitable for the synthesis of transport fuels and chemicals. The ash transformation behavior during gasification is critical to the overall production process and necessitates a level of understanding to implement appropriate control measures. Toward this end, ash deposits were collected from inside the reactor of a pilot-scale O-2-blown pressurized entrained-flow gasifier firing stem wood, bark, and pulp mill debarking residue (PMDR) in separate campaigns. These deposits were characterized with environmental scanning electron microscopy equipped with energy-dispersive X-ray spectrometry and X-ray diffractometry. The stem wood deposit contained high levels of calcium and was comparatively insubstantial. The bark and PMDR fuels contained contaminant sand and feldspar particles that were subsequently evident in each respective deposit. The bark deposit consisted of lightly sintered ash aggregates comprising presumably a silicate melt that enveloped particles of quartz and, to a lesser degree, feldspars. Discontinuous layers likely to be composed of alkaline-earth metal silicates were found upon the aggregate peripheries. The PMDR deposit consisted of a continuous slag that contained quartz and feldspar particles dispersed within a silicate melt. Significant levels of alkaline-earth and alkali metals constituted the silicate melts of both the bark and PMDR deposits. Overall, the results suggest that fuel contaminants (i.e., quartz and feldspars) play a significant role in the slag formation process during pressurized entrained-flow gasification of these woody biomasses.

  • 43. Nazelius, Ida-Linn
    et al.
    Boström, Dan
    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.
    Hedman, Henry
    Samuelsson, Robert
    Ohman, Marcus
    Influence of Peat Addition to Woody Biomass Pellets on Slagging Characteristics during Combustion2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 7, p. 3997-4006Article in journal (Refereed)
    Abstract [en]

    Upgraded biofuels such as pellets, briquettes, and powder are today commonly used in small as well as large scale appliances. In order to cover an increasing fuel demand new materials such as bark, whole tree assortments, and peat are introduced. These materials have higher ash content which is why they are potentially more problematic compared with stem wood. In general, few studies can be found regarding cocombustion of peat and biomass and in particular where the slagging tendencies are discussed. The overall objective of this study was therefore to determine the influence of peat addition to woody biomass pellets on slagging characteristics. Two different peat assortments (peat A and B) were copelletized separately in four different dry matter levels (0-5-15-30 wt %) into stem wood and energy wood, respectively. Peat A was a traditional Scandinavian fuel peat, with a high ash and Si content (carex), and peat B had a low ash content and relatively high Ca/Si ratio (sphagnum) chosen for its special characteristics. The produced pellets were combusted in a commercial underfed pellet burner (15 kW) installed in a reference boiler. The collected deposits (bottom ash and slag) from the combustion experiments were chemically characterized by scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis (EDS) and X-ray diffraction (XRD) regarding the elemental distribution and morphology and phase composition, respectively. In addition, the bottom ashes were characterized according to inductively coupled plasma atomic emission spectroscopy (ICP-AES). To interpret the experimental findings chemical equilibrium model calculations were performed. The slagging tendency increased when adding peat into the woody biomasses. Especially sawdust with its relatively low ash and Ca content was generally more sensitive for the different peat assortments. Cofiring with the relatively Si and ash rich peat A resulted in the most severe slagging tendency. A significant increment of the Si, Al, and Fe content and a significant decrement of the Ca content in the slag could be seen when increasing the content of peat A in both woody biomasses. The slagging tendency increased when adding peat A because high temperature melting Ca-Mg oxides react to form more low temperature melting Ca/Mg-Al-K silicates. The slagging tendency was significantly lower when adding the more ash poor peat B, with relatively high Ca/Si ratio, into the woody biomass fuels compared with the peat A mixtures. The slag from the peat B mixings had a slightly higher Ca content compared with the Si content and a clearly higher content of Ca compared with the peat A mixtures. There were still Ca-Mg oxides left in the bottom ash i.e. a less amount of sticky low temperature melting K-silicate rich melt was formed when peat B was added to the woody biomasses.

  • 44. Nazelius, Ida-Linn
    et al.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Rebbling, Anders
    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
    Fuel indices for estimation of slagging of phosphorus-poor biomass in fixed bed combustion2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 1, p. 904-915Article in journal (Refereed)
    Abstract [en]

    The market for solid biofuels will grow rapidly during the coming years, and there will be a great demand for raw materials. This will force the existing fuel base to also cover wooden materials of lower qualities as well as agricultural raw materials and residues, which often show unfavorable ash-melting temperatures. This may lead to combustion-related problems. Thus, for the utilization of lower quality fuels, it is important to be able to predict potential fuel ash-related problems such as slagging. In light of this, the first objective of the present paper was to evaluate the applicability of previously defined indices for slagging of biomass fuels (phosphorus-poor) in fixed bed combustion. The evaluation showed that none of the previously suggested indices in the literature are suitable for qualitative (nor quantitative) prediction of slagging during fixed bed combustion of P-poor biomass fuels. Hence, a second objective was to develop improved novel fuel indices that can be applied to estimate the slagging of phosphorus-poor biomass in fixed bed combustion. The novel fuel indices give a qualitative prediction of the slagging tendency in biomass fixed bed combustion but still needs additional work to further extend the compositional range as well as to fine tune the indices' boundaries.

  • 45. Norheim, Arnstein
    et al.
    Lindberg, Daniel
    Hustad, Johan E
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Equilibrium calculations of the composition of trace compounds from biomass gasification in the solid oxide fuel cell operating temperature interval2009In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 23, no 2, p. 920-925Article in journal (Refereed)
    Abstract [en]

    The solid oxide fuel cell (SOFC), due to its high operating temperature and high fuel flexibility, may be fueled by biomass gasification producer gases. Based on the main gas components of typical producer gases (CO, CO(2), H(2), H(2)O, N(2), and light hydrocarbons), the expected SOFC performance will be in the range of cells that use, for example, reformed natural gas as fuel. However, other minor components such as compounds of S, Cl, Na, and K may form species that degrade the SOFC fuel electrode and thus have a negative influence on SOFC performance. Knowledge of the composition of the minor components and the expected level of these compounds is therefore of great importance to be able to perform a detailed experimental study and thus evaluate the expected SOFC performance. The present work comprises results from equilibrium calculations of the composition of biomass gasification gases from two types of biomass gasifiers, one that uses air as gasifying agent and one that uses steam, in the SOFC operating temperature interval (750-1000 degrees C). The major trace components present in biomass gasification producer gases have been identified for several levels of sulfur, potassium, chlorine, and sodium in the SOFC operating temperature interval. Sulfur is present mainly as H(2)S(g), whereas potassium is mainly present as KOH(g) and to some extent K(g), depending mainly on temperature. High chlorine content in the fuel favors KCl(g) production. In the temperature interval between 750 and 900 degrees C there are, in the cases investigated here, small amounts of carbonate-rich liquid phase and solid carbonates in equilibrium with the gasifier gas.

  • 46. Norheim, Arnstein
    et al.
    Waernhus, Ivar
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hustad, Johan E.
    Vik, Arild
    Experimental Studies on the Influence of H2S on Solid Oxide Fuel Cell Performance at 800 °C2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 2, p. 1098-1101Article in journal (Refereed)
    Abstract [en]

    Short-term tests showing the influence sulfur has on solid oxide fuel cell (SOFC) performance have been performed. The experiments were performed using two single-cell SOFC setups operated at 800 degrees C. In setup I, sulfur (H2S) was mixed into the fuel gas in concentrations ranging from 20 to 100 ppm. It was found that the performance decreased with increasing sulfur concentration up to 80 ppm. The performance loss at 80 and 100 ppm sulfur was equal. At a current density of 200 mA cm(-2), the operating voltage was reduced from 0.810 V at 0 ppm H2S to 0.790 V at 100 ppm H2S, corresponding to an increase in the area-specific cell resistivity (ASR) of 0.10 Omega cm(2). In setup II, sulfur levels of 80, 120, and 240 ppm were introduced. In all these three cases the ASR increased by around 0.13 Omega cm(2). Removing the sulfur impurity when the 240 ppm H2S exposure test was finished the cell performance fully recovered, indicating no irreversible changes in the cell structure.

  • 47.
    Nyström, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lindgren, Robert
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Avagyan, Rozanna
    Westerholm, Roger
    Lundstedt, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Influence of Wood Species and Burning Conditions on Particle Emission Characteristics in a Residential Wood Stove2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 5, p. 5514-5524Article in journal (Refereed)
    Abstract [en]

    Emissions from small-scale residential biomass combustion are a major source of indoor and outdoor particulate matter (PM) air pollution, and the performance of stoves, boilers, and fireplaces have been shown to be influenced both by fuel properties, technology, and user behavior (firing procedures). Still, rather scarce information is available regarding the relative importance of these variables for the particle characteristics and emissions of different particulate components, e.g., soot, polycyclic aromatic hydrocarbons (PAHs), oxy-PAH, and metals. In particular, the behavior of different wood fuels under varying firing procedures and combustion conditions has not been studied thoroughly. Therefore, the objective of this work was to elucidate the influence of wood species and combustion conditions on particle emission characteristics in a typical Nordic residential wood stove. The emissions from four different wood species were investigated at two controlled combustion conditions, including nominal and high burn rates, with a focus on physical and chemical properties of the fine particulate matter. Considerably elevated carbonaceous particle emissions (soot and organics) were found during high burn rate conditions, which were associated with a shift in particle number size distribution toward a higher fraction of larger particles. In some cases, as here seen for pine, the specific fuel properties can affect the combustion performance and thereby also influence particle and PAH emissions. For the inorganic ash particles, the content in the fuel, and not burning conditions, was found to be the main determining factor, as seen by the increased emissions of alkali salts for aspen. Wood stove emission data on 11 specific oxy-PAHs, together with 45 PAHs, were combined with controlled variations of burning conditions and fuels. The oxy-PAH/PAH ratio during a high burn rate was observed to increase, suggesting an enrichment of particulate oxy-PAH. Accordingly, the main influence on emission performance and particle characteristics was seen between different burn rates, and this study clearly illustrates the major importance of proper operation to avoid unfavorable burning condition, regardless of the wood species used.

  • 48.
    Näzelius, Ida-Linn
    et al.
    Luleå, Sweden.
    Fagerström, Jonathan
    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.
    Öhman, Marcus
    Luleå, Sweden.
    Slagging in fixed-bed combustion of phosphorus-poor biomass: critical ash-forming processes and compositions2015In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 2, p. 894-908Article in journal (Refereed)
    Abstract [en]

    Slagging in combustion facilities is not welcomed, because it may cause technical and operational problems, as well as extra costs. Increased understanding of the critical slagging subprocesses makes it easier to suggest semiempirical models and fuel indexes for predicting the slagging tendencies of different fuels. That could open the biomass market for potentially more troublesome raw materials. The objective of this work was to determine critical ash-forming processes and compositions in the fixed-bed combustion of phosphorus-poor biomass fuels. This was achieved by performing a systematic review of data and experience gathered from combustion experiments in a small grate burner of 36 different biomasses, as well as chemical analysis of their bottom ashes and slags. The paper presents a discussion of the slagging tendency in phosphorus-poor biomass by combining three different slagging classifications, culminating in a proposed starting point for a new slagging index. The slag (ash particles >3.15 mm in size) formed during the combustion experiments has been described according to the fraction of fuel ash that forms slag (expressed in terms of weight percent), the visual sintering category (1-4), and the viscosity predictions. The results explain that both the fraction of melt and its viscosity are critical for the slag formation process in phosphorus-poor biomasses. In addition, fuels with low Si/K ratio along with a higher Ca concentration may form a low viscous carbonate melt that is not prone to form slag. Increased Si and lowered Ca concentration will increase the amount of formed silicate melt formed, as well as its viscosity, thus resulting in a more sticky melt.

  • 49. Olwa, Joseph
    et al.
    Öhman, Marcus
    Esbjörn, Pettersson
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Okure, Mackay
    Kjellström, Björn
    Potassium Retention in Updraft Gasification of Wood2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 11, p. 6718-6724Article in journal (Refereed)
    Abstract [en]

    The release of compounds of K with producer gas during biomass gasification is known to play significant roles in fouling and high-temperature corrosion in boilers and high-temperature heat exchangers as well as blades in gas turbines that use producer gas as fuel. These phenomena are a major setback in the application of biomass fuel in combination with advanced process conditions. Updraft gasification provides gas filtering by the fuel bed with a gas cooling effect, conditions anticipated to create an avenue for K retention in the gasifier. The objective of this study was to determine the K retention potential of such gasifiers during wood gasification. Samples for the determination of the fate of K compounds included in the feedstock were collected from the generated producer gas using Teflon filters and gas wash bottles and also from wall deposits and ash residues. Analyses of samples were carried out using inductively coupled plasma atomic emission spectrometry/mass spectrometry and Xray diffraction methods. The finding was that about 99% of K was retained in the gasifier. K was found in the ash samples as a crystalline phase of K2Ca(CO3)(2)(s) (fairchildite). A possible reaction mechanism leading to the formation of K2Ca(CO3)(2) is discussed in the paper. The 1% K understood as released, equivalent to 1200 ppbw content of K entrained in the producer gas stream, exceeds a known limit for application of the gas in conventional gas turbines. This would suggest application of the gas in an externally fired gas turbine system, where some limited K and other depositions in the heat exchanger can be relatively easy to handle.

  • 50.
    Pettersson, Esbjörn
    et al.
    Luleå tekniska universitet och ETC Piteå.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Westerholm, Roger
    Stockholms universitet, Analytisk kemi.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Stove performance and emission characteristics in residential wood log and pellet combustion: Part 2: Wood stove2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 1, p. 315-323Article in journal (Refereed)
    Abstract [en]

    The characteristics and quantities of a large number of gaseous and particulate emission components during combustion in a residential wood log stove with variations in fuel, appliance and operational conditions were determined experimentally. The measurement campaign included CO, NOx, organic gaseous carbon (OGC), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions, and inorganic composition. CO varied in the range of 1100 to 7200 mg/MJfuel, while OGC varied from 210 to 3300 mg/MJfuel. Dominating VOCs were methane, followed by ethene, acetylene, and benzene. Methane varied from 9 to 1600 mg/MJfuel. The nonmethane volatile organic compound (NMVOC) emissions were in the range of 20−2300 mg/MJfuel. The PAHtot emissions varied from 1.3 to 220 mg/MJfuel, in most cases dominated by phenantrene, fluoranthene, and pyrene. PMtot were in all cases dominated by fine particles and varied in the range 38−350 mg/MJfuel. The mass median particle diameters and the peak mobility diameters of the fine particles varied in the range 200−320 and 220−330 nm, respectively, and number concentrations in the range of 1−4 × 1013 particles/MJfuel. Air starved conditions, at high firing intensity, gave the highest emissions, especially for hydrocarbons. This type of condition is seldom considered, though it may occur occasionally. The emissions from Swedish wood stoves, comparing a Swedish field study, are covered fairly well with the applied methodology, but other field studies report considerably higher emissions especially for diluted particle sampling.

12 1 - 50 of 77
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf