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  • 1. Arm, Maria
    et al.
    Lindeberg, Johanna
    Rådin, Åsa
    Öhrström, Anna
    Backman, R
    Öhman, Marcus
    Boström, D
    Gasbildning i aska2006Report (Other academic)
  • 2. Backman, R
    et al.
    Sandelin, K
    Kouvo, P
    Öhman, Marcus
    Nordin, A
    Brus, E
    Reactions between trace elements and sand bed particles in fluidized bed combustion of biomass and waste based fuels2002Conference paper (Other academic)
  • 3. Backman, Rainer
    et al.
    Berg, Magnus
    Boström, Dan
    Hirota, Catherine
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrström, Anna
    Metalliskt aluminium i förbränningen: Metallic aluminum in combustion2007Report (Other academic)
    Abstract [sv]

    Projektet har visat att det är mycket svårt att få tunn aluminiumfolie, som normalt finns i bl.a. hushållsavfall, att oxidera oberoende av tid, temperatur och förbränningsatmosfärens sammansättning. Vidare har svävhastighetsmätningar visat att tunn plastbelagd aluminiumfolie lätt kan ryckas med rökgaserna vid normala rökgashastigheter (1-5 m/s).

  • 4. Berg, M
    et al.
    DeGeyter, S
    Öhman, Marcus
    Förbränning av biomassa i fluidiserad bädd: bäddmaterialets betydelse för agglomereringsrisken2005In: Nordisk Papper & Massa, ISSN 1651-2995, no 2, p. 9-10Article in journal (Other (popular science, discussion, etc.))
  • 5. Berg, Magnus
    et al.
    Andersson, Christer
    Ekvall, Annika
    Eskilsson, David
    Geyter, Sigrid de
    Helgesson, Anna
    Myringer, Åse
    Wikman, Karin
    Öhman, Marcus
    Förbränning av utsorterade avfallsfraktioner2005Report (Other academic)
    Abstract [sv]

    Projektet har visat på möjligheter och problem vid förbränning av utsorterade avfallsfraktioner bestående av papper, trä och plast i fluidbädd. Denna typ av bränslen kan antingen samförbrännas eller användas som enda bränsle i en avfallspanna. I båda fallen bör gällande gränsvärden för emissioner till luft kunna klaras men man får däremot räkna med ökade drift- och underhållskostnader, främst beroende på ökade problem med påslag och korrosion. Dessa problem är starkt kopplade till bränslets innehåll av oönskade ämnen såsom klor, alkali och vissa andra metaller. Innehållet av dessa ämnen varierar kraftigt mellan olika bränslefraktioner och därmed blir omfattningen av problemen beroende både av inblandningsgrad och av bränslets ursprung. Projektet har även visat att mängden påslag kan minskas genom tillsats av svaveladditiv samtidigt som den kemiska samansättningen i påslagen förändras på ett sådant sätt att även risken för korrosion bör minska.

  • 6.
    Bergström, Dan
    et al.
    Department of Forest Resource Management, Swedish University of Agricultural Sciences.
    Israelsson, Samuel
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dahlqvist, Sten-Axel
    Unit of Biomass Technology and Chemistry, SLU.
    Gref, Rolf
    Department of Forest Resource Management, Swedish University of Agricultural Sciences.
    Boman, Christoffer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Wästerlund, Iwan
    Department of Forest Resource Management, Swedish University of Agricultural Sciences.
    Effects of raw material particle size distribution on the characteristics of Scots pine sawdust fuel pellets2008In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 89, no 12, p. 1324-1329Article in journal (Refereed)
    Abstract [en]

    In order to study the influence of raw material particle size distribution on the pelletizing process and the physical and thermomechanical characteristics of typical fuel pellets, saw dust of Scots pine was used as raw material for producing pellets in a semi industrial scaled mill (∼ 300 kg h- 1). The raw materials were screened to a narrow particle size distribution and mixed into four different batches and then pelletized under controlled conditions. Physical pellet characteristics like compression strength, densities, moisture content, moisture absorption and abrasion resistance were determined. In addition, the thermochemical characteristics, i.e. drying and initial pyrolysis, flaming pyrolysis, char combustion and char yield were determined at different experimental conditions by using a laboratory-scaled furnace. The results indicate that the particle size distribution had some effect on current consumption and compression strength but no evident effect on single pellet and bulk density, moisture content, moisture absorption during storage and abrasion resistance. Differences in average total conversion time determined for pellet batches tested under the same combustion conditions was less than 5% and not significant. The results are of practical importance suggesting that grinding of saw dust particle sizes below 8 mm is probably needless when producing softwood pellets. Thus it seem that less energy could be used if only over sized particles are grinded before pelletizing.

  • 7. Boman, C
    et al.
    Nordin, A
    Boström, D
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Pettersson, Esbjörn
    Characterisation of inorganic particulate matter from domestic combustion of pelletized biomass fuels2001Conference paper (Other academic)
  • 8.
    Boman, Christoffer
    et al.
    Umeå universitet.
    Israelsson, S.
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundmark, B.
    Glommers Miljöenergi AB, Glommersträsk.
    Combustion properties and environmental performance during small scale combustion of pelletized white hardwood raw material2008In: Proceedings: World Bioenergy 2008 : [Conference & Exhibition on Biomass for Energy, 27 - 29 May 2008, Jönköping - Sweden] / [ed] Johan Vinterbäck, Stockholm: Swedish Bioenergy Association (SVEBIO) , 2008, Vol. Oral session, p. 241-246Conference paper (Refereed)
  • 9. Boman, Christoffer
    et al.
    Nordin, A
    Westerholm, R
    Öhman, Marcus
    Boström, D
    Emissions from small-scale combustion of biomass fuels: extensive quantification and characterization2005Report (Other academic)
  • 10.
    Boman, Christoffer
    et al.
    Umeå university.
    Nordin, Anders
    Umeå university.
    Boström, Dan
    Umeå university.
    Öhman, Marcus
    Characterization of inorganic particulate matter from residential combustion of pelletized biomass fuels2004In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 18, no 2, p. 338-348Article in journal (Refereed)
    Abstract [en]

    The increased focus on potential adverse health effects associated with exposure to ambient particulate matter (PM) motivates a careful characterization of particle emissions from different sources. Combustion is a major anthropogenic source of fine PM, and, in urban areas, traditional residential wood combustion can be a major contributor. New and upgraded biomass fuels have become more common, and fuel pellets are especially well-suited for the residential market. The objective of the present work was to determine the mass size distributions, elemental distributions, and inorganic-phase distributions of PM from different residential combustion appliances and pelletized biomass fuels. In addition, chemical equilibrium model calculations of the combustion process were used to interpret the experimental findings. Six different typical pellet fuels were combusted in three different commercial pellet burners (10-15 kW). The experiments were performed in a newly designed experimental setup that enables constant-volume sampling. Total-PM mass concentrations were measured using conventional filters, and the fractions of products of incomplete combustion and inorganic material were thermally determined. Particle mass size distributions were determined using a 13-step low-pressure cascade impactor with a precyclone. The PM was analyzed for morphology (using environmental scanning electron microscopy, ESEM), elemental composition (using energy-dispersive spectroscopy, EDS), and crystalline phases (using X-ray diffractometry, XRD). For complementary chemical structural characterization, time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy XPS and X-ray absorption fine structure (XAFS) spectroscopy were also used. The emitted particles were mainly found in the fine ( less than or equal 1 μm) mode with mass median aerodynamic diameters of 0.20 - 0.39 μm and an average PM1 of 89.5% ± 7.4% of total PM. Minor coarse-mode fractions (>1 μm) were present primarily in the experiments with bark and logging residues. Relatively large and varying amounts (28%-92%) were determined to be products of incomplete combustion. The inorganic elemental compositions of the fine particles were dominated by potassium, chlorine, and sulfur, with minor amounts of sodium and zinc. The dominating alkali phase was KCl, with minor but varying amounts of K3Na(SO4)2 and, in some cases, also K2SO4. The results showed that zinc is almost fully volatilized, subsequently and presumably forming a more complex solid phase than that previously suggested (ZnO). However, the formation mechanism and exact phase identification remain to be elucidated. With some constrains, the results also showed that the amounts and speciation of the inorganic PM seemed to be quite similar to that predicted by chemical equilibrium calculations.

  • 11. Boman, Christoffer
    et al.
    Nordin, Anders
    Westerholm, Roger
    Öhman, Marcus
    Boström, Dan
    Systematic characterization and quantification of gaseous and particulate emissions from present residential wood and pellet stoves and potentials for future technolgy2004In: Biomass for energy, industry and climate protection: Second World Biomass Conference ; proceedings of the world conference held in Rome, Italy, 10 - 14 May 2004 ; [held jointly with the 13th European Conference on Biomass for Energy, Industry and Climate Protection] / [ed] W. P. M. van Swaaij, ETA - Renewable Energies , 2004, Vol. Florence, p. 1439-1443Conference paper (Refereed)
  • 12. Boman, Christoffer
    et al.
    Pettersson, Esbjörn
    Lindmark, Fredrik
    Öhman, Marcus
    Nordin, Anders
    Westerholm, Roger
    Effects of temperature and residence time on the emissions of pic and fine particles during fixed bed combustion of conifer stemwood pellets2006In: Pellets 2006: proceedings of the Second World Conference on Pellets ; in Jönköping, Sweden, 30 May - 1 June 2006, Stockholm: Swedish Bioenergy Association (SVEBIO) , 2006, p. 187-193Conference paper (Refereed)
  • 13.
    Boman, Christoffer
    et al.
    Umeå university.
    Öhman, Marcus
    Nordin, Anders
    Umeå university.
    Trace element enrichment and behavior in wood pellet production and combustion processes2006In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 20, no 3, p. 993-1000Article in journal (Refereed)
    Abstract [en]

    The extensive and well-documented concerns regarding environmental dispersion of toxic trace metals constitute solid motives for a special focus of their fate and forms in fuel treatment and conversion processes. The potential enrichment of trace elements during fuel pellet production processes and behavior during combustion was, therefore, studied in a combined field sampling and chemical equilibrium modeling work. Raw materials, pellet fuels, and particulate matter in the drying gases in two different pelletizing plants were sampled and analyzed. In addition, chemical equilibrium model calculations were performed with variations in the content of trace elements, moisture, sulfur, and chlorine, at both oxidizing and reducing conditions. A significant enrichment of Zn, Cu, Cd, and Pb was documented when using bark combustion gases for direct drying of the sawdust and was also supported by the chemical equilibrium results. This is presumably caused by the volatilization of these elements from the bark fuel during combustion, subsequently forming fine particles in the flue gases and being captured by the sawdust during drying. The magnitude and importance for these trace elements were, however, found to be relatively small, regarding concentrations in different fuels as well as potential increased emissions to air during combustion compared to national total emission estimations. In addition, some alternative measures for prevention of trace metal contamination during fuel pellet production were suggested, including fuel quality aspects, high-temperature particle separation, and indirect drying processes.

  • 14.
    Boström, Dan
    et al.
    Umeå universitet.
    Boman, Christoffer
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Effect of fuel additive sorbents (kaolin and calcite) on aerosol particle emission and characteristics during combustion of pelletized woody biomass2008In: From Research to industry and markets: 16th European Biomass Conference & Exhibition ; proceedings of the international conference held in Valencia, Spain, 2 - 6 June 2008 / [ed] J. Schmid, Florence: ETA - Renewable Energies , 2008, p. 1514-1517Conference paper (Refereed)
  • 15.
    Boström, Dan
    et al.
    Umeå universitet.
    Boström, Markus
    Umeå universitet.
    Skoglund, Nils
    Umeå universitet.
    Boman, Christoffer
    Umeå universitet.
    Backman, Rainer
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ash transformation chemistry during energy conversion of biomass2010In: Proceedings of the International Conference on Impact of Fuel Quality on Power production and the Environment, 2010Conference paper (Other academic)
    Abstract [en]

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

  • 16.
    Boström, Dan
    et al.
    Umeå university.
    Broström, Markus
    Umeå university.
    Lindström, Erika
    Umeå university.
    Boman, Christoffer
    Umeå university.
    Backman, Rainer
    Umeå university.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grimm, Alejandro
    Ash transformation chemisty during energy conversion of agricultural biomass2009Conference paper (Other academic)
    Abstract [en]

    There is relatively extensive knowledge available concerning ash transformation reactions during energy conversion of woody biomass. Traditionally, these assortments have constituted the main resources for heating in Sweden. In recent decades the utilization of these energy carriers has increased, from a low technology residential small scale level to industrial scale (i.e. CHP plants). Along this evolution ash‐chemical related phenomena for woody biomass has been observed and studied. So, presently the understanding for these are, if not complete, fairly good. Briefly, from a chemical point of view the ash from woody biomass could be characterized as a silicate dominated systems with varying content of basic oxides and with relatively high degree of volatilization of alkali sulfates and chlorides. Thus, the main ash transformation mechanisms in these systems have been outlined. However, since the demand for CO2‐neutral energy resources has increased the last years and will continue to do so in the foreseeable future, other biomasses as for instance agricultural crops has become highly interesting. Globally, the availability of these shows large variation. In Sweden, for instance, which is a relatively spare populated country with large forests, these bio‐masses will play a secondary role, although not insignificant. In other parts of the world, more densely populated and with a large agricultural sector, such bio‐masses may constitute the main energy bio‐mass resource in the future. However, the content of ash forming matter in agricultural bio‐mass is rather different in comparison to woody biomass. Firstly, the content is much higher; from being about 0.3 – 0.5% (wt) in stem wood, it can amount to between 4 and 10 %(wt) in agricultural biomass. Furthermore, the composition of the ash forming matter is different . Shortly, the main difference is due to a much higher content of phosphorus which has major consequences on the ash‐transformation reactions. In many crops, the concentration of phosphorus and silicon is equivalent, which (depending on the concentration levels of basic oxides) may result in a phosphate dominated ash. The properties of this ash are in several aspects different from the silicate dominated woody biomass ash and will consequently behave differently in various types of energy conversion systems. The knowledge about phosphate dominated ash systems has so far been scarce. We have been working with these systems, both with basic and applied research, for about a decade know. Some general experiences and conclusions as well as some specific examples of our research will be presented.

  • 17.
    Boström, Dan
    et al.
    Energy Technology and Thermal Process Chemistry, Department of Applied Physics and Electronics, Umea University.
    Eriksson, Gunnar
    Boman, Christoffer
    Energy Technology and Thermal Process Chemistry, Department of Applied Physics and Electronics, Umea University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    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. An 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.

  • 18.
    Boström, Dan
    et al.
    Umeå universitet.
    Eriksson, Gunnar
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Boman, Christoffer
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bench-scale fluidized bed combustion of rapeseed meal2008In: From Research to industry and markets: 16th European Biomass Conference & Exhibition ; proceedings of the international conference held in Valencia, Spain, 2 - 6 June 2008 / [ed] J. Schmid, Florence: ETA - Renewable Energies , 2008, p. 1380-1385Conference paper (Refereed)
  • 19.
    Boström, Dan
    et al.
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Grimm, Alejandro
    Boman, Christoffer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Björnbom, Emilia
    Chemical Engineering and Technology, Royal Institute of Technology.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    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 microscopy/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 formed 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.

  • 20.
    Boström, Dan
    et al.
    Umeå universitet.
    Grimm, Alejandro
    Lindström, Erica
    Umeå universitet.
    Boman, Christoffer
    Umeå universitet.
    Björnbom, Emilia
    Kungliga tekniska högskolan, KTH.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Abatement of corrosion and deposits formation in combustion of oat2008In: From Research to industry and markets: 16th European Biomass Conference & Exhibition ; proceedings of the international conference held in Valencia, Spain, 2 - 6 June 2008 / [ed] J. Schmid, Florence: ETA - Renewable Energies , 2008, p. 1528-1534Conference paper (Refereed)
  • 21.
    Boström, Dan
    et al.
    Umeå universitet.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå universitet.
    Boman, Christoffer
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Broström, Markus
    Umeå universitet.
    Backman, Rainer
    Umeå universitet.
    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.

  • 22. Brus, E
    et al.
    Öhman, Marcus
    Nordin, A
    Skrifvars, B J
    Backman, R
    Bed material consumption in biomass fired fluidised bed biolers due to risk for bed agglomeration: coating formation and possibilities for regeneration2003In: Industrial Combustion, ISSN 2075-3071, E-ISSN 2075-3071, no 2, p. 1-12Article in journal (Refereed)
    Abstract [en]

    Previous studies have shown that many biomass fuels result in critical agglomeration temperatures in the same range as typical operating process temperatures for fluidised beds. As soon as a sufficiently thick coating on the bed particles has been formed, the risk for severe agglomeration and defluidisation is often significant. Frequent bed change is therefore the normally method applied to ensure problem-free operation, but this is associated with additional costs and not sustainable on a long-term basis.The objectives of the present work were therefore to; i) collect full-scale bed material samples to determine coating characteristics and growth as functions of time; ii) estimate the critical coating thickness/age of the bed particles by SEM/EDS analysis and experimental determinate the agglomeration temperatures for the collected bed material; iii) experimentally evaluate if size fractionation and mechanical treatment could be used to reduce the bed material consumption.Bed material samples from two bubbling and two circulating full-scale fluidised bed boilers, with previous documented bed agglomeration problems, were collected. All plants used typical wood-based fuel mixtures. The coating formation rates on the bed particles were found to be significant, with an initial rate of some mm per day, but decreasing with time. The coating material was generally found to consist of Ca- and Mg-silicates as well as P, although the form in which it was present was not determined. The experimentally determined fuel specific agglomeration temperatures were found to agree well with the corresponding critical temperatures for the full-scale bed materials, as well as with the experiences reported by the different plant operators. The critical coating thickness was found to be relatively thin (<10 mm), and was reached within a few days. Unfortunately, regeneration by sieving and bed removal at different heights seemed relatively ineffective. Mechanical treatment (soft grinding) resulted in a breakdown of the original quartz bed material particles and the desired selective scavenging of the coating could not be obtained.

  • 23.
    Brus, Elisabet
    et al.
    Umeå university.
    Öhman, Marcus
    Nordin, Anders
    Umeå university.
    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.

  • 24.
    Brus, Elisabet
    et al.
    Umeå university.
    Öhman, Marcus
    Nordin, Anders
    Umeå university.
    Boström, Dan
    Umeå university.
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Eklund, Anders
    ÅF Energi & Miljö AB.
    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.

  • 25. Burvall, J
    et al.
    Öhman, Marcus
    Undersökning av bäddagglomerering och beläggningstillväxt vid sameldning av torv och trädbränsle2000Report (Other academic)
  • 26. Burvall, Jan
    et al.
    Öhman, Marcus
    Samförbränning av torv och biobränslen: askrelaterade systemfördelar2006Report (Other academic)
  • 27.
    Carlborg, Marcus
    et al.
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Boström, Dan
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Backman, Rainer
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Reactions Between Ash Forming Elements and Two Mullite Based Refractories in Entrained Flow Gasification of Wood2014Conference paper (Refereed)
  • 28.
    Carlborg, Markus
    et al.
    Umeå universitet.
    Boström, Dan
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Backman, Rainer
    Umeå universitet.
    Reactions between ash and ceramic lining in entrained flow gasification of wood: exposure studies and thermodynamic considerations2013In: Proceedings of the 21st EU BC&E - Copenhagen 2013, Florence Italy, 2013, p. 446-449Conference paper (Other academic)
    Abstract [en]

    Gasification of biomass in the entrained flow process requires temperatures above 1000°C and pressures above 20 bar. Together with the ash forming elements, a harsh environment is created inside these reactors and degradation of construction material is likely to occur. This will lead to unplanned stops and increased maintenance work resulting in economic loss. In this work, two refractory materials (63 and 83 weight percent alumina) were exposed to synthetic ash composed of K2CO3, CaCO3 and SiO2 to study chemical attack on and interactions with the refractory materials. The exposure went on for 7 days in 1050°C and CO2­atmosphere in a muffle furnace. It was found that potassium (K) is the most active element in attack of the refractories and is transported fastest in the material. A melt composed of K, Ca and Si was formed that prevented penetration of K but it also dissolved aluminum from the refractory materials. X­ray diffraction showed that the crystalline phases leucite, kalsilite, kaliophilite, K(2­x)Al(2­x) SixO4 and wollastonite had formed. Formations of new phases in refractories will cause stress and eventually failure within refractories.

  • 29.
    Carlsson, Per
    et al.
    Energy Technology Centre, Piteå.
    Ma, Charlie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Molinder, Roger
    Energy Technology Centre, Piteå.
    Weiland, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Wiinikka, Henrik
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Energy Technology Centre, Piteå.
    Slag Formation During Oxygen Blown Entrained-Flow Gasification of Stem Wood2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 11, p. 6941-6952, article id 28Article in journal (Refereed)
    Abstract [en]

    Stem wood powders were fired in a mullite-lined pilot-scale oxygen-blown pressurized entrained-flow gasifier. During repeated campaigns involving increases in fuel load and process temperature, slag formations that eventuated in the blockage of the gasifier outlet were observed. These slags were retrieved for visual and chemical characterization. It was found that the slags had very high contents of Al and, in particular, high Al/Si ratios that suggest likely dissolution of the mullite-based refractory of the gasifier lining due to interactions with the fuel ash. Possible causes for the slag formation and behavior are proposed, and practical implications for the design of future stem wood entrained-flow gasifiers are also discussed

  • 30.
    Carvalho, Lara
    et al.
    Austrian Bioenergy Centre.
    Lundgren, Joakim
    Wopienka, Elisabeth
    Austrian Bioenergy Centre.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Challenges in small-scale combustion of agricultural biomass fuels2007In: 9th Conference on Energy for a Clean Environment: Clean Air 2007, 2007Conference paper (Refereed)
    Abstract [en]

    In the present work, several agricultural biomass fuels, namely straw, Miscanthus,maize whole crop and horse manure mixed with two bedding materials, woodshavings and straw, were reviewed in terms of fuel characteristics. Furthermore,these fuels were tested in several existing boiler technologies and the particulateand gaseous emissions were monitored. The ash was analysed visually in terms ofpresence of sintered material. As expected, all the fuels showed problems withash lumping and slag formation, especially straw and horse manure. Differentboiler technologies showed different operational performance regarding ash andslag management. Miscanthus was the best fuel tested regarding emissions. Maizeand horse manure are problematic fuels regarding NOx and particulate emissions.Due to the big variation of the fuel properties and therefore combustion behaviourof agricultural biomass, further R&D is required to adapt the existing small-scalecombustion systems for these new fuels. Improvements in the combustionchamber design, controlling technology and ash removal systems of small-scalecombustion systems are therefore essential.

  • 31. DeGeyter, S
    et al.
    Öhman, Marcus
    Eriksson, M
    Nordin, A
    Boström, D
    Berg, M
    Agglomeration characteristics using alternative bed materials for combustion of biomass2005In: Biomass for energy, industry and climate protection: 14th European Biomass Conference & Exhibition ; proceedings of the international conference held in Paris, France, 17 - 21 October 2005, Florence: ETA - Renewable Energies , 2005, p. 1343-1346Conference paper (Refereed)
    Abstract [en]

    The objective of the work was to evaluate differences in agglomeration characteristics between commercially available alternative bed materials and quartz-based bed materials, commonly used in fluidised bed combustion. Pure quartz bed materials. Magnesium oxide and foundry sand (natural sand with a clay coating) were used as alternative bed aterials. Carefully controlled bench-scale fluidised bed agglomeration experiments were performed, using calcium-rich bark and potassium-rich olive residue as model fuels with significantly different ash compositions, typical for forestry and griculture residues respectively. The resulting bed material particles and agglomerates were analysed with SEM/EDS. Analysis of bed material and agglomerates suggested that Mg and Al in the bed materials affect the agglomeration temperature positively for calcium-rich fuels. Al-rich foundry sand was found to decrease the agglomeration temperature in (Si, K)-rich systems. For combustion of olive residue in MgO bed, no attack layer was formed and agglomeration probably occurred via direct adhesion by partly melted alkali-silicates. The results suggest that the choice of bed material should take the intended fuel use into consideration.

  • 32. Eklund, A
    et al.
    Brus, E
    Öhman, Marcus
    Hedman, H
    Boström, D
    Nordin, A
    Utvärdering av hyttsand som bäddmaterial i FB-anläggningar: förstudie och laboratorieförsök2003Report (Other academic)
  • 33. Eklund, Anders
    et al.
    Öhman, Marcus
    Fullskaleförsök med hyttsand som bäddmaterial i 12 MW avfallseldad BFB-panna2004Report (Other academic)
    Abstract [en]

    Blast furnace slag from SSAB Merox has been used as bed material in two waste-fired 12 MWth BFB-boilers at Säverstaverket in Bollnäs. The results are positive in some aspects and negative in other aspects but the overall conclusion is that blast furnace slag can replace silica sand as bed material with no changes of the boiler conditions. The boiler performance has been improved with the blast furnace slag but boiler failure can and has occurred during the trials.

  • 34. Erhardsson, Thomas
    et al.
    Öhman, Marcus
    Geyter, Sigrid de
    Öhrström, Anna
    Bäddagglomereringsrisk vid förbränning av odlade bränslen (hampa, rörflen, halm) i kommersiella bäddmaterial2006Report (Other academic)
    Abstract [en]

    The market of forest products is expanding and thus resulting in more expensive biomass fuels. Therefore research within the combustion industry for alternative fuels is needed, for example cultivated fuels. Combustion and gasification research on these cultivated fuels are limited. The objectives of this work was to increase the general knowledge of silicon rich cultivated fuels by study the agglomeration characteristics for wheat straw, reed canary grass and industrial hemp in combination with commercial bed materials.Controlled fluidized bed agglomeration tests was conducted in a 5 kW, bench-scale, bubbling fluidized bed reactor. The tendencies of agglomeration were determined with the three cultivated fuels in combination with various minerals present in natural sand (quarts, plagioclase and potassium feldspar) and an alternative bed material (olivine). During the experiments bed samples and formed agglomerates were collected for further analyses with a scanning electron microscope (SEM) and with X-ray microanalysis (EDS).Wheat straw had the highest agglomeration tendency of the studied fuels followed by reed canary grass and industrial hemp. No significant layer formation was found around the different bed particles. Instead, the ash forming matter were found as individual ash sticky (partial melted) particles in the bed. The bed material mineralogical composition had no influence of the agglomeration process because of the non layer formation propensities of the used silicon rich fuels.

  • 35.
    Eriksson, Daniel
    et al.
    Swedish University of Agricultural Sciences, Vindeln Experimental Forest, Svartberget Research Station.
    Weiland, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Stenberg, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Lestander, Torbjörn A.
    Swedish University of Agricultural Sciences, Unit of Biomass Technology and Chemistry, Umeå.
    Bergsten, Urban
    Swedish University of Agricultural Sciences, Vindeln Experimental Forest, Svartberget Research Station.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Characterization of Scots pine stump-root biomass as feed-stock for gasification2012In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 104, p. 729-736Article in journal (Refereed)
    Abstract [en]

    The main objective was to explore the potential for gasifying Scots pine stump-root biomass (SRB). Washed thin roots, coarse roots, stump heartwood and stump sapwood were characterized (solid wood, milling and powder characteristics) before and during industrial processing. Non-slagging gasification of the SRB fuels and a reference stem wood was successful, and the gasification parameters (synthesis gas and bottom ash characteristics) were similar. However, the heartwood fuel had high levels of extractives (≈ 19%) compared to the other fuels (2 – 8%) and thereby ≈ 16% higher energy contents but caused disturbances during milling, storage, feeding and gasification. SRB fuels could be sorted automatically according to their extractives and moisture contents using near-infrared spectroscopy, and their amounts and quality in forests can be predicted using routinely collected stand data, biomass functions and drill core analyses. Thus, SRB gasification has great potential and the proposed characterizations exploit it.

  • 36.
    Eriksson, Gunnar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå universitet.
    Boström, Dan
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Combustion and fuel characterisation of wheat distillers dried grain with solubles (DDGS) and possible combustion applications2012In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 102, p. 208-220Article in journal (Refereed)
    Abstract [en]

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

  • 37. Eriksson, Gunnar
    et al.
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Department of Applied Physics and Electronics, Umea University.
    Backman, Rainer
    Energy Technology and Thermal Process Chemistry, Department of Applied Physics and Electronics, Umea University.
    Pettersson, Esbjörn
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    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%wtds) is comparable to wood; the moisture content (6.2−11.8%wt) is low; and the ash content (7.41 ± 0.286%wtds) 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%wtds) and the sulfur content is high (0.67−0.74%wtds). RM has high contents of nitrogen (5.0−6.4%wtds), phosphorus (1.12−1.23%wtds), and potassium (1.2−1.4%wtds). Fuel-specific combustion properties of typical RM were determined through combustion tests, with an emphasis on 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%wtds. 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 SO2 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 flue gases.

  • 38. Eriksson, Gunnar
    et al.
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Pettersson, Esbjörn
    Pommer, Linda
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Lindström, Erica
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Backman, Rainer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Rikard
    Energy Technology Centre, Piteå.
    Förbränningskarakterisering av rapsmjöl och förslag till optimalt nyttjande i olika förbränningsanläggningar2007Report (Other academic)
    Abstract [en]

    When rape oil is chemically extracted, rape seed meal, a solid residue remains. Currently, it is used as animal feed. Several plants for the production of rape methyl ester (RME, biodiesel) are in operation or under construction. Combustion properties have been studied for rape seed meal produced as a by product to rape-methyl esther (RME, biodiesel). Composition of the material has been measured, using proximate and ultimate analysis. The lower heating value was 18.2 ± 0,3 MJ/kg d.w. and the ash content was 7-8 percent d.w. The material is rich in nitrogen and sulphur. Concentrations of K, P, Ca and Mg are high in the fuel. Rape seed meal was mixed with bark and pelletised. Bark pellets were also used as a reference fuel. Pellets with 10 and 30 percent rape seed meal were produced. Material with 80 percent rape seed meal and 20 percent planer shavings was also pelletised. Wood had to be added to provide enough friction in the pelletising process, with adapted equipment rape seed meal could probably be easily pelletised). The material was studied using Thermo-Gravimetric Analysis (TGA), and compared with data from tests with wood powder. The pyrolysis of the rape seed meal has a characteristic temperature of 320oC. Devolatilisation starts at 150 oC (at a lower temperature than for wood powder), and proceeds within a rather wide temperature range. The probable cause is the difference in organic content, in particular protein content. The result does not suggest that the material will be difficult to ignite. Experiments in a bench-scale fluidised bed (5 kW) showed that pellets containing only bark, and the mixture rape seed meal/wood had a bed agglomeration temperature well over the normal operational bed temperature. For the fuel mixtures rape seed meal and bark, the agglomeration temperature was slightly over the operational temperature. Particle emissions from fluidised bed combustion and grate combustion were, the latter simulated using a commercial pellet burner, were roughly doubled with fuels containing rape seed meal compared to bark. In the powder burner tests, particle emissions increased with a factor 17 with rape seed meal compared to wood powder. The emitted particles were mainly found in the fine (< 1 µm) mode during grate and powder combustion. During fluidized bed combustion the total particulate matter consisted both of a coarse (>1 µm) and a fine mode fraction. The particles from grate combustion of bark contain mostly K, S, Na and Cl apart from oxygen and carbon. When rape seed meal is present, Cl and Na concentrations decrease considerably and the main contents of the particles are K and S (and O and C). The results from the X-ray Diffraction Spectroscopy (XRD) analyses showed the presence of crystalline K2SO4 och KCl. The fine particles (<1 µm) from powder combustion contain mainly K, P and S. The only identified crystalline phase was K2SO4, suggesting that most phosphorus was in the amorphous phase, i.d. most probably molten. The deposit formation on a cooled probe was studied during the fluidized bed and powder combustion experiments. The fine particles deposited during fluidised bed combustion contained K, Cl and S. When bark was combusted in the fluidised bed, the coarse fraction contained Ca and Si, when rape seed meal in different mixes was combusted this changed to P, K, Ca and Mg. The deposits formed during combustion of rape seed meal in the powder burner were mainly made up of phosphates (Ca-, Mg/K-, Ca/Mg-phosphates) and MgO. Sintered material (slag) from grate combustion of bark contained mainly Si, Ca, K and Al, probably as silicates. Adding rape seed meal tended to increase P, Ca and Mg while Si and Ca content tended to decrease. Through XRD a number o crystalline phases in the sintered material and the rest of the bottom ashes could be identified. NO emissions from the combustions tests increased two to four times with rape seed meal compared to typical wood fuels. For the fluidised bed test, SO2 concentrations were rather high for the rape seed meal pellets (with 20 percent wood), still only about 20 percent of the sulphur in the fuel formed SO2. For the grate combustion and powder burner combustion, 60 percent and 70 percent of the sulphur respectively formed SO2. HCl emissions were low for all tests. The rather high emissions of NOx and SOx mean that the material should be used in large-scale facilities with external SOx and NOx cleaning. In smaller facilities, the material may be used in small amounts mixed with other fuels. The risk of slagging is not very high, and should not rule out grate combustion of pellets with rape seed meal mixed with other fuels. The risk of corrosion of superheater surfaces during combustion is probably low since the smaller-size particles formed at fluidised bed combustion and grate combustion contain K2SO4. However, a large fraction of the particles formed in powder burner combustion probably contains low temperature melting K2PO4, making the risk for deposit formation significant. Rape seed meal for powder burner applications should be used with care. The content of phosphorus in the material may be an advantage when mixes of rape seed meal and other fuels are considered. The high affinity between potassium and phosphorus means that more sulphur in the fuel will be available for sulphatising of any KC. (formed from combustion of many forest and agricultural fuels). Use of rape seed meal as a sulphur containing additive could thus be an option. For grate combustion and fluidised bed combustion, addition of rape seed meal may reduce the risk of slagging and bed agglomeration, respectively. Full scale tests in fluidised beds or grate combustors with problematic biofuels (containing Cl and K) would be useful to test whether ash-reduced operational problems could be reduced through the addition of rape seed meal.

  • 39. Eriksson, Morgan
    et al.
    Wikman, Karin
    Berg, Magnus
    Öhman, Marcus
    Effekten av fluidiseringshastighet och kornstorlek på agglomereringsrisk vid biobränsleeldning i FB-pannor2004Report (Other academic)
    Abstract [sv]

    Effekten av bäddkornstorleken och fluidiseringshastigheten på agglomereringsrisken i biobränsleeldade BFB/CFB fullskaleanläggningar har studerats. De experimentella försöken visar på att ökad fluidiseringshastighet gör att bädden agglomererar vid en högre temperatur. Detta är mest markant vid relativt låga fluidiseringshastigheter, vilket ofta förekommer i t ex en BFB-panna eller recirkulationsbenet i en CFB.

  • 40. Eriksson, Morgan
    et al.
    Öhman, Marcus
    Nordin, Anders
    Wikman, Karin
    Berg, Magnus
    Effects of fluidization velocity and bed particle size on bed defluidization during biomass combustion2004In: Biomass for energy, industry and climate protection: Second World Biomass Conference ; proceedings of the world conference held in Rome, Italy, 10 - 14 May 2004 ; [held jointly with the 13th European Conference on Biomass for Energy, Industry and Climate Protection] / [ed] W. P. M. van Swaaij, Florence: ETA - Renewable Energies , 2004Conference paper (Refereed)
  • 41.
    Erlich, Catharina
    et al.
    Kungliga tekniska högskolan, KTH.
    Öhman, Marcus
    Björnbom, Emilia
    Kungliga tekniska högskolan, KTH.
    Fransson, Torsten H.
    Umeå university.
    Thermochemical characteristics of sugar cane bagasse pellets2005In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 84, no 5, p. 569-575Article in journal (Refereed)
    Abstract [en]

    Pelletisation facilitates utilisation of sugar cane bagasse as a fuel and storage for year-round electricity generation. The present work determines thermochemical characteristics of bagasse pellets of different sizes and origins, using various temperatures (600, 750 and 900°C) and gas flow rates (4,7 and 10 L/min) with varying concentrations of oxygen (5,10 and 15%) in mixtures with nitrogen. Of major interest are the effects of raw material, origin and size of pellets, and the treatment conditions on the rate of pyrolysis and the structure and reactivity of char in combustion. The char yield of the larger pellets of high-ash content bagasse was practically independent of treatment conditions. Smaller pellets gave better mechanical stability of the char but lower reactivity.

  • 42.
    Fagerström, Jonathan
    et al.
    Umeå universitet.
    Näzelius, Ida-Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dan, Boström
    Umeå universitet.
    Öhman, Marcus
    Boman, Christoffer
    Umeå universitet.
    Reduction of fine particle- and deposit forming alkali by co-combustion of peat with wheat straw and forest residues2010In: Proceedings of the International Conference on Impact of Fuel Quality on Power production and the Environment., 2010Conference paper (Other academic)
    Abstract [en]

    Combustion of ash rich biomass fuels like forest residues and wheat straw often cause severe fouling/deposits and high emissions of PM1, mainly related to alkali transformation. Due to technical and air pollution aspects, primary process/fuel related measures for reduction of volatilized alkali could therefore be of importance. Peat has been used extensively in e g Sweden and Finland since the early 80th due to its positive ash chemical effects. Earlier research with co-combustion of peat and biomass has mostly been focused on fluidized bed boilers and aspects of bed agglomeration and deposits/corrosion. It has also been shown that the content and form of ash forming elements in different peats can vary significantly. The objective with this work was to determine the potential reduction of fine particle- and deposit forming alkali during co-combustion of forest residue and wheat straw with four different peat types in a small scale (15 kW) grate fired pellet boiler. The results showed that significant reduction of fine particle- and deposit forming alkali is possible, either simply by "dilution" of K content (e.g for wheat straw) or by "capturing" of K to bottom ash/slag (e.g. for forest residues), most probably caused by reaction of K vapour from the biomass with reactive Si or clay minerals from the peat. The alkali reduction potential for different biomass fuels and peat mixtures is dicussed in relation to the slagging tendencies and general ash transformation processes

  • 43.
    Fagerström, Jonathan
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Näzelius, Ida-Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gilbe, Carl
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå University. Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boman, Christoffer
    Umeå University. 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.

  • 44.
    Fagerström, Jonathan
    et al.
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Rebbling, Anders
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Olwa, Joseph
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Steinvall, Erik
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Boström, Dan
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boman, Christoffer
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Control Strategies for Reduction of Alkali Release during Grate Combustion of Biomass: Influence of Process Parameters and Fuel Additives in a 40 kW Reactor2014Conference paper (Refereed)
  • 45.
    Faust, Robin
    et al.
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Hannl, Thomas Karl
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Berdugo Vilches, Teresa
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Kuba, Matthias
    Bioenergy2020+ GmbH, Güssing, Austria.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Seemann, Martin
    Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden.
    Knutsson, Pavleta
    Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden.
    Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood. 1. K-Feldspar2019In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 8, p. 7321-7332Article in journal (Refereed)
    Abstract [en]

    The choice of bed material for biomass gasification plays a crucial role for the overall efficiency of the process. Olivine is the material conventionally used for biomass gasification due to the observed activity of olivine toward cracking of unwanted tars. Despite its catalytic activity, olivine contains high levels of chromium, which complicates the deposition of used bed material. Feldspar has shown the same activity as olivine when used as a bed material in biomass gasification. As opposed to olivine, feldspar does not contain environmentally hazardous compounds, which makes it a preferred alternative for further applications. The interaction of bed material and ash heavily influences the properties of the bed material. In the present study interactions between feldspar and main ash compounds of woody biomass in an indirect gasification system were investigated. Bed material samples were collected at different time intervals and analyzed with SEM-EDS and XRD. The obtained analysis results were then compared to thermodynamic models. The performed study was divided in two parts: in part 1 (the present paper), K-rich feldspar was investigated, whereas Na-rich feldspar is presented in part 2 of the study (DOI: 10.1021/acs.energyfuels.9b01291). From the material analysis performed, it can be seen that, as a result of the bed materials’ interactions with the formed ash compounds, the latter were first deposited on the surface of the K-feldspar particles and later resulted in the formation of Ca- and Mg-rich layers. The Ca enriched in the layers further reacted with the feldspar, which led to its diffusion into the particles and the formation of CaSiO3 and KAlSiO4. Contrary to Ca, Mg did not react with the feldspar and remained on the surface of the particles, where it was found as Mg- or Ca-Mg-silicates. As a result of the described interactions, layer separation was noted after 51 h with an outer Mg-rich layer and an inner Ca-rich layer. Due to the development of the Ca- and Mg-rich layers and the bed material–ash interactions, crack formation was observed on the particles’ surfaces.

  • 46.
    Gabra, Mohamed
    et al.
    Energy Technology Centre, Piteå.
    Nordin, Anders
    Avdelningen för oorganisk kemi, Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kjellström, Björn
    Alkali retention/separation during bagasse gasification: a comparison between a fluidised bed and a cyclone gasifier2001In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 21, no 6, p. 461-476Article in journal (Refereed)
    Abstract [en]

    Biomass fuelled integrated gasification/gas turbines (BIG/GTs) have been found to be one of the most promising technologies to maximise electricity output in the sugar industry. However, biomass fuels contain alkali metals (Na and K) which may be released during the gasification processes and cause deleterious effects on the downstream hardware (e.g. the blades of gas turbines). Much research has therefore been focused on different kinds of gas cleaning. Most of these projects are using a fluidised bed gasifier and includes extensive gas cleaning which leads to a high capital investment. Increasing alkali retention/separation during the gasification may lead to improved producer gas quality and reduced costs for gas cleaning. However, very little quantitative information is available about the actual potential of this effect. In the present work, comparative bench-scale tests of bagasse gasification were therefore run in an isothermal fluidised bed gasifier and in a cyclone gasifier to evaluate which gasification process is most attractive as regards alkali retention/separation, and to try to elucidate the mechanisms responsible for the retention. The alkali retention in the fluidised bed gasifier was found to be in the range of 12-4% whereas in the cyclone gasifier the alkali separation was found to be about 70%. No significant coating of the fluidised bed's bed material particles could be observed. The SEM/EDS and the elemental maps of the bed material show that a non-sticky ash matrix consisting of mainly Si, Al and K were distributed in a solid form separated from the particles of bed material. This indicates the formation of a high temperature melting potassium containing silicate phase, which is continuously scavenged and lost from the bed through elutriation.

  • 47. Geyter, Sigrid De
    et al.
    Eriksson, Morgan
    Öhman, Marcus
    Nordin, Anders
    Boström, Dan
    Berg, Magnus
    Skillnader i bäddagglomereringstendens mellan alternativa bäddmaterial och olika mineraler i natursand2005Report (Other academic)
    Abstract [sv]

    Projektets resultat visar på skillnaderna i bäddagglomereringstendens mellan olika mineraler i natursand och ett antal alternativa bäddmaterial, t.ex. olivinsand, gjuterisand och hyttsand. Vid förbränning av ett bränsle med hög andel kalium, olivkross, visar försöken att K-fältspater har en högre benägenhet till bäddagglomerering. Detta kan även förklara skillnaden mellan ren kvartssand och Rådasand vilket innehåller en förhållandevis hög andel fältspater.

  • 48.
    Geyter, Sigrid De
    et al.
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Eriksson, Morgan
    Övik Energi.
    Nordin, Anders
    Energy Technology and Thermal Process Chemistry, Umeå University.
    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 full-scale 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.

  • 49. Gilbe, Carl
    et al.
    Lindström, Erica
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Backman, Rainer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Samuelsson, Robert
    Unit for Biomass Technology and Chemistry, Swedish University of Agricultural Sciences.
    Burvall, Jan
    Skellefteå Kraft AB.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    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 71 20), 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.

  • 50. Gilbe, Carl
    et al.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lindström, Erica
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Backman, Rainer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Samuelsson, Robert
    Unit for Biomass Technology and Chemistry, Swedish University of Agricultural Sciences.
    Burvall, Jan
    Skellefteå Kraft AB.
    Slagging characteristics during residential combustion of biomass pellets2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 5, p. 3536-43Article 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), stem 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 O2, 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 from 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.

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