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  • 1.
    Fagerström, Jonathan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Näzelius, Ida-Linn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Gilbe, Carl
    Boström, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Öhman, Marcus
    Boman, Christoffer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Influence of Peat Ash Composition on Particle Emissions and Slag Formation in Biomass Grate Co-combustion2014Ingår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, nr 5, s. 3403-3411Artikel i tidskrift (Refereegranskat)
    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.

  • 2. Falk, Joel
    et al.
    Berry, Robert J.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Larsson, Sylvia H.
    Mass flow and variability in screw feeding of biomass powders: relations to particle and bulk properties2015Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 276, s. 80-88Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Biomass powders often have high cohesiveness, low bulk density and poor material flow characteristics which cause interruptions and variations in feeding systems. In this study, a range of biomasses – commercial charcoal, torrefied Norway spruce stem wood, non-treated Norway spruce stem wood, and reed canary grass – were milled (screen size: 1 mm) using two different methods; cutting mill and hammer mill, to form eight types of biomass powders. The powders were analyzed for loose bulk density, Hausner ratio, compression ratio, angle of repose and for size and shape distributions. Size and shape were determined by mechanical sieving and optical particle size and shape analysis. Additionally, yield loci and wall yield loci were determined through standard bulk solid testing methods. Screw feeding properties of the eight biomass powders were determined by feeding the materials in a twin screw feeder — at constant rpm and at a constant feeding rate of 1 kg/h. Correlation analysis and principal component loadings were used to describe relations between material properties and feeding characteristics. When materials were fed at a constant rpm, feeding variability was closely correlated to the powder's angle of repose (long time) and Hausner and compression ratios (short time).

  • 3.
    Kristoffersson, Stina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Effekt av karbonatisering med biogas på aska från trädbränslen2015Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    It is essential to reuse- and recycles residues to decrease the amount of deposit materials and reach sustainable energy use. Two ways to work towards this is to recycle wood ashes to the forest as nutrient compensation and extract biogas from combustion of biomass.

    The aim with this study was to decide whether wood ashes that been used for biogas upgrading with accelerated carbonation also can be used as a nutrient compensation in the woods according to recommendations from the Swedish Forest Agency (Skogsstyrelsen).

    The ashes that were used in this study came from Johan Andersson who works at JTI in Uppsala, who also treated the ashes with biogas. The ashes have, in both untreated and treated condition, been analyzed in this study according to contents of elements, leaching properties, hardening properties and contents of crystalline phases, to evaluate what impact carbonation with biogas has on the ashes.

    The accelerated carbonation led to hardening of the ash, and decreased amount of CaO- and increased amount of CaCO3. The CO2-uptake also entails a dilution of the elements, and the content of nutrients and trace elements decreases. However the results show an indication of an uptake of S from the biogas to the ash, since the dilution had a smaller impact on S than the rest of the elements. No conclusions could be made according to what affect carbonation has on the leaching properties.

    This study showed that the ashes from biomass incineration that were analyzed in this study can be used both for biogas upgrading and nutrient compensation in the woods; since the results confirm that the ashes that been treated with biogas fulfills all the limits from the Swedish Forest Agency. 

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  • 4. Nazelius, Ida-Linn
    et al.
    Boström, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Boman, Christoffer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Hedman, Henry
    Samuelsson, Robert
    Ohman, Marcus
    Influence of Peat Addition to Woody Biomass Pellets on Slagging Characteristics during Combustion2013Ingår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, nr 7, s. 3997-4006Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    Wiklund Lindström, Susanne
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Nilsson, David
    Nordin, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Nordwaeger, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Ingemar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Pommer, Linda
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Geladi, Paul
    Quality assurance of torrefied biomass using RGB, visual and near infrared (hyper) spectral image data2014Ingår i: Journal of Near Infrared Spectroscopy, ISSN 0967-0335, E-ISSN 1751-6552, Vol. 22, nr 2, s. 129-139Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Visible and near infrared imaging techniques for analysing characteristics of torrefied biomass were evaluated for possible use in future online process control. The goal of such a control system is to identify products with the desired properties and reject products outside the specification. Two pushbroom hyperspectral cameras with different wavelength regions and a commercial digital colour camera were evaluated. The hyperspectrat cameras, short wave infrared (SWIR) and visible-near infrared (VNIR), covered the ranges of 1000-2500 nm and 400-1000 nm, respectively. The biomass was produced according to an experimental design in a torrefaction pilot plant at different temperatures, residence times, and nitrogen and steam flow rates to obtain a wide range of different characteristics and qualities of torrefied material. Chemical characteristics, heating values and milling energy of the different torrefied materials were analysed or calculated using standardized procedures and were used for calibration. For the hyperspectral images, a principal-component analysis was performed on the absorbance spectra. The score plots and score images were used interactively to separate background, outlier pixels and shading effects from sample signal. Averaged spectra of individual torrefied woodchips were used. Partial least-squares regression was used to relate average spectra to heating values and chemical characteristics of the torrefied biomass. Owing to the small size of the data sets, cross-validation using leave-one-out validation was used for testing the models. The ratio of standard error of prediction to sample standard deviation (RPD) values were used for comparing the imaging techniques. For ROB images, all RPD values were 4 or lower. The RPD values for the VNIR technique were all below 5, while the SWIR images produced RPD values above 5 for eight of the 13 properties. The promising results of the SWIR technique strongly suggested that the torrefied biomass undergoes changes to chemical structures, which are not necessarily manifested as changes to the colour of the material.

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