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  • 1. Bergström, Dan
    et al.
    Israelsson, Samuel
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Dahlqvist, Sten-Axel
    Gref, Rolf
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Wästerlund, Iwan
    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 (similar to 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.

  • 2. Bergström, Dan
    et al.
    Israelsson, Samuel
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Dahlqvist, Sten-Axel
    Gref, Rolf
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Wästerlund, Iwan
    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 (similar to 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.

  • 3.
    Broström, Markus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash fractionation and slag formation during entrained flow biomass gasification2018Conference paper (Other academic)
  • 4. Buss, Wolfram
    et al.
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wurzer, Christian
    Masek, Ondrej
    Synergies between BECCS and Biochar-Maximizing Carbon Sequestration Potential by Recycling Wood Ash2019In: ACS SUSTAINABLE CHEMISTRY & ENGINEERING, ISSN 2168-0485, Vol. 7, no 4, p. 4204-4209Article in journal (Refereed)
    Abstract [en]

    Bioenergy carbon capture and storage (BECCS) and biochar are key carbon-negative technologies. In this study, synergies between these technologies were explored by using ash from wood combustion, a byproduct from BECCS, as an additive (0, 5, 10, 20, and 50 wt %) in biochar production (wood pyrolysis at 450 degrees C). The addition of wood ash catalyzed biochar formation and increased the yield of fixed carbon (FC) (per dry, ash-free feedstock), i.e., the sequestrable carbon per spruce wood input. At the highest ash addition (50%), 45% less wood was needed to yield the same amount of FC. Since the land area available for growing biomass is becoming scarcer, our approach significantly increases biochar's potential to sequester carbon. However, increasing the feedstock ash content results in less feedstock carbon available for conversion into FC. Consequently, the yield of FC per pyrolysis run (based on dry feedstock) in the 50% ash-amended material was lower than in the control. An economic analysis showed that the 20% ash-amended biochar brings the biggest cost savings over the control with a 15% decrease in CO2-abatement costs. Biochar-ash composites increase the carbon sequestration potential of biochar significantly, reduce the CO2-abatement costs, and recycle nutrients which can result in increased plant growth in turn and more biomass for BECCS, bringing synergies for BECCS and biochar deployment.

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

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

  • 6.
    Gandla, Madhavi Latha
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. KBC Chemical-Biological Centre, Umeå University.
    Martin, Carlos
    Umeå University, Faculty of Science and Technology, Department of Chemistry. KBC Chemical-Biological Centre, Umeå University.
    Jönsson, Leif J.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. KBC Chemical-Biological Centre, Umeå University.
    Analytical Enzymatic Saccharification of Lignocellulosic Biomass for Conversion to Biofuels and Bio-Based Chemicals2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 11, article id 2936Article, review/survey (Refereed)
    Abstract [en]

    Lignocellulosic feedstocks are an important resource for biorefining of renewables to bio-based fuels, chemicals, and materials. Relevant feedstocks include energy crops, residues from agriculture and forestry, and agro-industrial and forest-industrial residues. The feedstocks differ with respect to their recalcitrance to bioconversion through pretreatment and enzymatic saccharification, which will produce sugars that can be further converted to advanced biofuels and other products through microbial fermentation processes. In analytical enzymatic saccharification, the susceptibility of lignocellulosic samples to pretreatment and enzymatic saccharification is assessed in analytical scale using high-throughput or semi-automated techniques. This type of analysis is particularly relevant for screening of large collections of natural or transgenic varieties of plants that are dedicated to production of biofuels or other bio-based chemicals. In combination with studies of plant physiology and cell wall chemistry, analytical enzymatic saccharification can provide information about the fundamental reasons behind lignocellulose recalcitrance as well as about the potential of collections of plants or different fractions of plants for industrial biorefining. This review is focused on techniques used by researchers for screening the susceptibility of plants to pretreatment and enzymatic saccharification, and advantages and disadvantages that are associated with different approaches.

  • 7.
    García López, Natxo
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Biomass utilization for energy purposes in Kenya: Fuel characteristics and thermochemical properties2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Around forty percent of the world´s population, mostly inhabitants of countries with developing economies, rely on the traditional usage of biomass for energy purposes. The major negative consequences are environmental and health effects. Additionally, the most remarkable social consequence is rural poverty which is directly linked to lack of access to electricity. This places the questions related to biomass utilization for energy production at the core of global welfare.

    The present work was performed as a part of a larger research project funded by Formas and which involves Swedish and Kenyan partners. The aim of this study was to gather basic knowledge about the characteristics of relevant biomass from sub-Saharan Africa, more specifically from Kenya. Eight different types of biomass, including agroforestry trees, agricultural residues, and water hyacinth, were evaluated according to fuel characteristics and thermochemical properties. Ultimate and proximate analyses of the collected biomass were carried out, in addition to heating values analyses. Moreover, the biomass was pelletized and a thermogravimetric analysis was performed in a single pellet reactor.  Finally, the composition of the residual ashes was determined. The results show that there was a large variation in the fuel characteristics and thermochemical behaviour of the studied agricultural residues and water hyacinth biomass types, whereas agroforestry trees had rather similar properties and thermochemical behaviour when combusted at the same temperature. In addition, results from the ash composition analyses showed large differences among the studied biomass types, which can be used to better predict and solve problems related to the combustion of these biomass types. 

  • 8. Gilbe, Carl
    et al.
    Lindström, Erica
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Samuelsson, Robert
    Burvall, Jan
    Ohman, Marcus
    Predicting slagging tendencies for biomass pellets fired in residential appliances: a comparison of different prediction methods2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 6, p. 3680-3686Article in journal (Refereed)
    Abstract [en]

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

  • 9.
    Hagman, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Co-combustion of Animal Waste, Peat, Waste Wood, Forest Residues, and Industrial Sludge in a 50 MWth Circulating Fluidized-Bed Boiler: Ash Transformation, Ash/Deposit Characteristics, and Boiler Failures2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 10, p. 5617-5627Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 11.
    Jonsson, Leif J.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Martin, Carlos
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pretreatment of lignocellulose: Formation of inhibitory by-products and strategies for minimizing their effects2016In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 199, p. 103-112Article, review/survey (Refereed)
    Abstract [en]

    Biochemical conversion of lignocellulosic feedstocks to advanced biofuels and other commodities through a sugar-platform process involves a pretreatment step enhancing the susceptibility of the cellulose to enzymatic hydrolysis. A side effect of pretreatment is formation of lignocellulose-derived by-products that inhibit microbial and enzymatic biocatalysts. This review provides an overview of the formation of inhibitory by-products from lignocellulosic feedstocks as a consequence of using different pretreatment methods and feedstocks as well as an overview of different strategies used to alleviate problems with inhibitors. As technologies for biorefining of lignocellulose become mature and are transferred from laboratory environments to industrial contexts, the importance of management of inhibition problems is envisaged to increase as issues that become increasingly relevant will include the possibility to use recalcitrant feedstocks, obtaining high product yields and high productivity, minimizing the charges of enzymes and microorganisms, and using high solids loadings to obtain high product titers.

  • 12.
    Jönsson, Leif J.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Alriksson, Björn
    Nilvebrant, Nils-Olof
    Bioconversion of lignocellulose: inhibitors and detoxification2013In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 6, article id 16Article in journal (Refereed)
    Abstract [en]

    Bioconversion of lignocellulose by microbial fermentation is typically preceded by an acidic thermochemical pretreatment step designed to facilitate enzymatic hydrolysis of cellulose. Substances formed during the pretreatment of the lignocellulosic feedstock inhibit enzymatic hydrolysis as well as microbial fermentation steps. This review focuses on inhibitors from lignocellulosic feedstocks and how conditioning of slurries and hydrolysates can be used to alleviate inhibition problems. Novel developments in the area include chemical in-situ detoxification by using reducing agents, and methods that improve the performance of both enzymatic and microbial biocatalysts.

  • 13. Kirtania, Kawnish
    et al.
    Haggstrom, Gustav
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Umeki, Kentaro
    Furusjo, Erik
    Cogasification of Crude Glycerol and Black Liquor Blends: Char Morphology and Gasification Kinetics2017In: Energy Technology, ISSN 2194-4288, Vol. 5, no 8, p. 1272-1281Article in journal (Refereed)
    Abstract [en]

    In this study, we assessed the feasibility of black liquor/glycerol blends as a potential gasification feedstock. The char gasification reactivity and kinetics were studied at T=750, 800, 850, and 900 degrees C for 20 and 40% blends of glycerol with black liquor. Three qualities of glycerol were used including two industrial-grade crude glycerols. The gasification rates were similar for all blends; therefore, the alkali-metal catalysis is also sufficient for the char blends (alkali/C atomic ratio between 0.45 and 0.55). The blends with the most impure glycerol (containing K) had the lowest activation energies (approximate to 120 kJ mol(-1)) and reaction times for char gasification and, therefore, had fuel properties suitable for gasification. The char particles from different blends showed surface morphologies similar to those of black liquor chars with an even surface distribution of alkali elements. A loss of alkali (mainly K) from the fuel blends during pyrolysis indicated the necessity to perform gas-phase studies of alkali release. Overall, these results encourage the use of glycerol as a potential gasification feedstock for catalytic-gasification-based biorefineries.

  • 14. Lage, Sandra
    et al.
    Kudahettige, Nirupa P.
    Ferro, Lorenza
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Matsakas, Leonidas
    Funk, Christiane
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rova, Ulrika
    Gentili, Francesco G.
    Microalgae Cultivation for the Biotransformation of Birch Wood Hydrolysate and Dairy Effluent2019In: Catalysts, E-ISSN 2073-4344, Vol. 9, no 2, article id 150Article in journal (Refereed)
    Abstract [en]

    In order to investigate environmentally sustainable sources of organic carbon and nutrients, four Nordic green microalgal strains, Chlorella sorokiniana, Chlorella saccharophila, Chlorella vulgaris, and Coelastrella sp., were grown on a wood (Silver birch, Betula pendula) hydrolysate and dairy effluent mixture. The biomass and lipid production were analysed under mixotrophic, as well as two-stage mixotrophic/heterotrophic regimes. Of all of the species, Coelastrella sp. produced the most total lipids per dry weight (~40%) in the mixture of birch hydrolysate and dairy effluent without requiring nutrient (nitrogen, phosphorus, and potassium—NPK) supplementation. Overall, in the absence of NPK, the two-stage mixotrophic/heterotrophic cultivation enhanced the lipid concentration, but reduced the amount of biomass. Culturing microalgae in integrated waste streams under mixotrophic growth regimes is a promising approach for sustainable biofuel production, especially in regions with large seasonal variation in daylight, like northern Sweden. To the best of our knowledge, this is the first report of using a mixture of wood hydrolysate and dairy effluent for the growth and lipid production of microalgae in the literature.

  • 15.
    Larsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Warnqvist, Björn
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Eriksson, Gunnar
    Influence of black liquor variability, combustion, and gasification process variables and inaccuracies in thermochemical data on equilibrium modeling results2006In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 20, no 1, p. 359-363Article in journal (Refereed)
    Abstract [en]

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

  • 16. Lienqueo, María Elena
    et al.
    Ravanal, María Cristina
    Pezoa-Conte, Ricardo
    Cortínez, Victoria
    Martínez, Loreto
    Niklitschek, Tomas
    Salazar, Oriana
    Carmona, René
    García, Alejandro
    Hyvärinen, Sari
    Mäki-Arvela, Päivi
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry and Reaction Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, Åbo-Turku, Finland.
    Second generation bioethanol from Eucalyptus globulus Labill and Nothofagus pumilio: ionic liquid pretreatment boosts the yields2016In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 80, p. 148-155Article in journal (Refereed)
    Abstract [en]

    The depletion of petroleum reserves and the high level of pollution caused by fossil fuels have led to enhancing renewable energy and fuel production from biomass. Eucalyptus globulus and Nothofagus pumilio residues could constitute an interesting source of biomass for second generation biofuel production. Lenga residues were pretreated with the ionic liquid (IL) 1-N-ethyl-3-methylimidazolium chloride (C2mimCl), followed by subsequent fermentation using both the strategy of Simultaneous Saccharification and Fermentation (SSF) as well as Separate Hydrolysis and Fermentation (SHF). The SHF process yielded 0.134 g ethanol/g glucose (26.3 wt-% of the theoretical yield) compared to the SSF process which yielded 0.173 g ethanol/g glucose (33.9 wt-% of the theoretical yield) within the first 24 h of fermentation. In case of Eucalyptus residues, another IL, 1-N-ethyl-3-methylimidazolium acetate (C2minOAc) was applied. The SSF process was applied for a period of three days. As a result, 3.7 g ethanol/L (corresponding to a yield of 0.19 g of ethanol/g of glucose or 38.0 wt-% of the theoretical maximum) was obtained at 72 h. When fresh Lenga and Eucalyptus residues were fermented without any pretreatment, the SSF process yielded 0.017 and 0.002 g of ethanol/g of glucose, respectively (3.33 wt-% and 0.48 wt-% of the theoretical maximum, respectively). Thus, the pretreatment procedures resulted in a significant increase in ethanol production, therefore justifying the need of pretreatment prior to the co-enzyme hydrolysis and fermentation for this type of biomass. Further, the combination of IL pretreatment and use of SSF process demonstrated the high potential for bioethanol production from Lenga and Eucalyptus residues. Nevertheless, further improvement by optimization of operational conditions is required to maximize the ethanol yield.

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

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

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

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

  • 19. Martinsson, J
    et al.
    Eriksson, A C
    Nielsen, I Elbaek
    Berg Malmborg, V
    Ahlberg, E
    Andersen, C
    Lindgren, R
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nyström, Robin
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nordin, E Z
    Brune, W H
    Svenningsson, B
    Swietlicki, E
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Pagels, J H
    Impacts of Combustion Conditions and Photochemical Processing on the Light Absorption of Biomass Combustion Aerosol2015In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 24, p. 14663-14671Article in journal (Refereed)
    Abstract [en]

    The aim was to identify relationships between combustion conditions, particle characteristics, and optical properties of fresh and photochemically processed emissions from biomass combustion. The combustion conditions included nominal and high burn rate operation and individual combustion phases from a conventional wood stove. Low temperature pyrolysis upon fuel addition resulted in "tar-ball" type particles dominated by organic aerosol with an absorption Angstrom exponent (AAE) of 2.5-2.7 and estimated Brown Carbon contributions of 50-70% to absorption at the climate relevant aethalometer-wavelength (520 nm). High temperature combustion during the intermediate (flaming) phase was dominated by soot agglomerates with AAE 1.0-1.2 and 85-100% of absorption at 520 nm attributed to Black Carbon. Intense photochemical processing of high burn rate flaming combustion emissions in an oxidation flow reactor led to strong formation of Secondary Organic Aerosol, with no or weak absorption. PM1 mass emission factors (mg/kg) of fresh emissions were about an order of magnitude higher for low temperature pyrolysis compared to high temperature combustion. However, emission factors describing the absorption cross section emitted per kg of fuel consumed (m(2)/kg) were of similar magnitude at 520 nm for the diverse combustion conditions investigated in this study. These results provide a link between biomass combustion conditions, emitted particle types, and their optical properties in fresh and processed plumes which can be of value for source apportionment and balanced mitigation of biomass combustion emissions from a climate and health perspective.

  • 20. Mohammadi, Marzieh
    et al.
    Shafiei, Marzieh
    Abdolmaleki, Amir
    Karimi, Keikhosro
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry & Reaction Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, Åbo-Turku, Finland.
    Larsson, Christer
    A morpholinium ionic liquid for rice straw pretreatment to enhance ethanol production2019In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 139, article id 111494Article in journal (Refereed)
    Abstract [en]

    Rice straw was successfully pretreated with a novel and inexpensive morpholinium ionic liquid, 1-H-3-methylmorpholinium chloride ([HMMorph][Cl]). The influence of water (30, 40, 50% w/w) and dimethyl sulfoxide (DMSO) (10, 30% w/w), as co-solvents, pretreatment time (2, 3, 5 h), temperature (90, 105, 120 °C), solid loading (5, 6.7, 10% w/w), and straw particle size (<0.177, 0.177–0.841 mm, and 0.841–2 mm) were investigated for maximum ethanol production. The best results were obtained in 50% water, at 120 °C and 5% (w/w) solid loading for 5 h from 0.177 – 0.841 mm straw particles. The hydrolysis yield was increased from 33.2% to 70.1%, while ethanol production yield was improved from 21.9% to 64% of the theoretical maximum. The performance of the IL was comparable to 1-ethyl-3-methylimidazolium acetate. Simple synthesis process and dilute solution required for the pretreatment with [HMMorph][Cl] offers cost reductions in the use of ILs in biofuel production.

  • 21. Moradian, Farzad
    et al.
    Tchoffor, Placid A.
    Davidsson, Kent O.
    Pettersson, Anita
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Thermodynamic equilibrium prediction of bed agglomeration tendency in dual fluidized-bed gasification of forest residues2016In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 154, p. 82-90Article in journal (Refereed)
    Abstract [en]

    Dual fluidized-bed (DFB) gasification is one of the recently developed technologies for production of heat, power, transportation fuels and synthetic chemicals through steam gasification of biomass. Bed agglomeration is a serious ash-related problem that should be taken into account when biomass-based fuels are selected for fluidized bed gasification and combustion. This study developed a thermodynamic equilibrium model to assess the risk of bed agglomeration in gasification and combustion reactors of a DFB gasifier using biomass (forest residues) as feedstock. The modelling approach combined thermodynamic equilibrium calculations with chemical fractionation technique to predict the composition and melting behaviour of the fuel-derived ash as well as bed particles coating layer in the gasification and combustion reactors. FactSage was employed for the thermodynamic equilibrium calculations. The modelling results were then compared with experimental data obtained from a full-scale DFB gasifier to estimate the reliability and validity of the predictive model. In general, a good agreement was found between the modelling results and experimental observations. For the forest residues as feedstock and olivine as bed material, the modelling results indicate a low risk of bed agglomeration in the DFB gasifier, as long as the dominant temperature in the combustion zone is below 1020 degrees C. In contrast, quartz as bed material in the DFB gasifier was shown to significantly increase the risk of bed agglomeration through coating-induced agglomeration mechanism. 

  • 22. Mäkelä, Mikko
    et al.
    Wai Kwong, Chi
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Yoshikawa, Kunio
    Hydrothermal treatment of grape marc for solid fuel applications2017In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 145, p. 371-377Article in journal (Refereed)
    Abstract [en]

    The treatment and disposal of grape marc, a residue from grape processing, represents a significant economic and environmental challenge for the winemaking industry. Hydrothermal treatment of grape marc could be an efficient way for producing solid fuels on-site at the wineries. In this work the effects of treatment temperature and liquid pH on grape marc char and liquid properties were determined based on laboratory experiments and the combustion characteristics of char were assessed through thermogravimetric analysis and fuel ash classification. The results showed that hydrothermal treatment increased the energy and carbon contents and decreased the ash content of grape marc. The effect of liquid pH was statistically significant (p < 0.05) only for the determined carbon yield of liquid samples. The energy yield from grape marc was maximized at lower treatment temperatures, which also decreased the content of less thermally stable compounds in the attained char. Higher treatment temperatures decreased grape marc solid, carbon and energy yields and led to an increase in thermally labile compounds compared to lower temperatures likely due to the condensation of liquid compounds or volatiles trapped in the pores of char particles. The alkali metal contents of char ash were reduced coupled with an increase in respective phosphorus. Overall the results support the use of hydrothermally treated grape marc in solid fuel applications, if elevated levels of ash phosphorus can be tolerated.

  • 23. Nielsen, Ingeborg E.
    et al.
    Eriksson, Axel C.
    Lindgren, Robert
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Martinsson, Johan
    Nyström, Robin
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nordin, Erik Z.
    Sadiktsis, Ioannis
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nojgaard, Jacob K.
    Pagels, Joakim
    Time-resolved analysis of particle emissions from residential biomass combustion: Emissions of refractory black carbon, PAHs and organic tracers2017In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 165, p. 179-190Article in journal (Refereed)
    Abstract [en]

    Time-resolved particle emissions from a conventional wood stove were investigated with aerosol mass spectrometry to provide links between combustion conditions, emission factors, mixing state of refractory black carbon and implications for organic tracer methods. The addition of a new batch of fuel results in low temperature pyrolysis as the fuel heats up, resulting in strong, short-lived, variable emission peaks of organic aerosol-containing markers of anhydrous sugars, such as levoglucosan (fragment at m/z 60). Flaming combustion results in emissions dominated by refractory black carbon co-emitted with minor fractions of organic aerosol and markers of anhydrous sugars. Full cycle emissions are an external mixture of larger organic aerosol-dominated and smaller thinly coated refractory black carbon particles. A very high burn rate results in increased full cycle mass emission factors of 66, 2.7, 2.8 and 1.3 for particulate polycyclic aromatic hydrocarbons, refractory black carbon, total organic aerosol and m/z 60, respectively, compared to nominal burn rate. Polycyclic aromatic hydrocarbons are primarily associated with refractory black carbon-containing particles. We hypothesize that at very high burn rates, the central parts of the combustion zone become air starved, leading to a locally reduced combustion temperature that reduces the conversion rates from polycyclic aromatic hydrocarbons to refractory black carbon. This facilitates a strong increase of polycyclic aromatic hydrocarbons emissions. At nominal burn rates, full cycle emissions based on m/z 60 correlate well with organic aerosol, refractory black carbon and particulate matter. However, at higher burn rates, m/z 60 does not correlate with increased emissions of polycyclic aromatic hydrocarbons, refractory black carbon and organic aerosol in the flaming phase. The new knowledge can be used to advance source apportionment studies, reduce emissions of genotoxic compounds and model the climate impacts of refractory black carbon, such as absorption enhancement by lensing. 

  • 24.
    Nilsson, Håkan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cournac, Laurent
    Rappaport, Fabrice
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lavergne, Jerome
    Estimation of the driving force for dioxygen formation in photosynthesis2016In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1857, no 1, p. 23-33Article in journal (Refereed)
    Abstract [en]

    Photosynthetic water oxidation to molecular oxygen is carried out by photosystem II (PSII) over a reaction cycle involving four photochemical steps that drive the oxygen-evolving complex through five redox states S-i (i = 0, ... , 4). For understanding the catalytic strategy of biological water oxidation it is important to elucidate the energetic landscape of PSII and in particular that of the final S-4 --> S-0 transition. In this short-lived chemical step the four oxidizing equivalents accumulated in the preceding photochemical events are used up to form molecular oxygen, two protons are released and at least one substrate water molecule binds to the Mn4CaO5 cluster. In this study we probed the probability to form S-4 from S-0 and O-2 by incubating YD-less PSII in the S-0 state for 2-3 days in the presence of O-18(2) and (H2O)-O-16. The absence of any measurable O-16,18(2) formation by water-exchange in the S-4 state suggests that the S-4 state is hardly ever populated. On the basis of a detailed analysis we determined that the equilibrium constant K of the S-4 --> S-0 transition is larger than 1.0 x 10(7) so that this step is highly exergonic. We argue that this finding is consistent with current knowledge of the energetics of the S-0 to S-4 reactions, and that the high exergonicity is required for the kinetic efficiency of PSII.

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

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

  • 26.
    Nyström, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lindgren, Robert
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Avagyan, Rozanna
    Westerholm, Roger
    Lundstedt, Staffan
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Influence of wood species and burning conditions on particle emission characteristics in a residential wood stoveManuscript (preprint) (Other academic)
    Abstract [en]

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

  • 27.
    Nyström, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lindgren, Robert
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Avagyan, Rozanna
    Westerholm, Roger
    Lundstedt, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Influence of Wood Species and Burning Conditions on Particle Emission Characteristics in a Residential Wood Stove2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 5, p. 5514-5524Article in journal (Refereed)
    Abstract [en]

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

  • 28.
    Nzayisenga, Jean Claude
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Eriksson, Karolina
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Sellstedt, Anita
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Mixotrophic and heterotrophic production of lipids and carbohydrates by a locally isolated microalga using wastewater as a growth medium2018In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 257, p. 260-265Article in journal (Refereed)
    Abstract [en]

    The biomass production and changes in biochemical composition of a locally isolated microalga (Chlorella sp.) were investigated in autotrophic, mixotrophic and heterotrophic conditions, using glucose or glycerol as carbon sources and municipal wastewater as the growth medium. Both standard methods and Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) analysis of data acquired by Fourier-transform IR (FTIR) spectrometry showed that autotrophic and mixotrophic conditions promoted carbohydrate accumulation, while heterotrophic conditions with glycerol resulted in the highest lipid content and lowest carbohydrate content. Heterotrophic conditions with glycerol as a carbon source also resulted in high oleic acid (18:1) contents and low linolenic acid (18:3) contents, and thus increasing biodiesel quality. The results also show the utility of MCR-ALS for analyzing changes in microalgal biochemical composition.

  • 29.
    Olofsson, Martin
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Lamela, Teresa
    Necton SA, Olhao, Portugal.
    Nilsson, Emmelie
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Bergé, Jean-Pascal
    IFREMER, Nantes, France.
    del Pino, Victória
    Necton SA, Olhao, Portugal.
    Uronen, Pauliina
    Neste Oil, Ctr Technol, Porvoo, Finland.
    Legrand, Catherine
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Combined Effects of Nitrogen Concentration and Seasonal Changes on the Production of Lipids in Nannochloropsis oculata 2014In: Marine Drugs, ISSN 1660-3397, E-ISSN 1660-3397, Vol. 12, no 4, p. 1891-1910Article in journal (Refereed)
    Abstract [en]

    Instead of sole nutrient starvation to boost algal lipid production, we addressed nutrient limitation at two different seasons (autumn and spring) during outdoor cultivation in flat panel photobioreactors. Lipid accumulation, biomass and lipid productivity and changes in fatty acid composition of Nannochloropsis oculata were investigated under nitrogen (N) limitation (nitrate:phosphate N:P 5, N:P 2.5 molar ratio). N. oculata was able to maintain a high biomass productivity under N-limitation compared to N-sufficiency (N:P 20) at both seasons, which in spring resulted in nearly double lipid productivity under N-limited conditions (0.21 g L−1 day−1) compared to N-sufficiency (0.11 g L−1 day−1). Saturated and monounsaturated fatty acids increased from 76% to nearly 90% of total fatty acids in N-limited cultures. Higher biomass and lipid productivity in spring could, partly, be explained by higher irradiance, partly by greater harvesting rate (~30%). Our results indicate the potential for the production of algal high value products (i.e., polyunsaturated fatty acids) during both N-sufficiency and N-limitation. To meet the sustainability challenges of algal biomass production, we propose a dual-system process: Closed photobioreactors producing biomass for high value products and inoculum for larger raceway ponds recycling waste/exhaust streams to produce bulk chemicals for fuel, feed and industrial material.

  • 30.
    Olofsson, Martin
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Lindehoff, Elin
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Frick, Brage
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Svensson, Fredrik
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Legrand, Catherine
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Baltic Sea microalgae transform cement flue gas into valuable biomass2015In: Algal Research, ISSN 2211-9264, Vol. 11, p. 227-233Article in journal (Refereed)
    Abstract [en]

    We show high feasibility of using cement industrial flue gas as CO2 source for microalgal cultivation. The toxicity of cement flue gas (12-15% CO2) on algal biomass production and composition (lipids, proteins, carbohydrates) was tested using monocultures (Tetraselmis sp., green algae, Skeletonema marinoi, diatom) and natural brackish communities. The performance of a natural microalgal community dominated by spring diatoms was compared to a highly productive diatom monoculture S. marinoi fed with flue gas or air-CO2 mixture. Flue gas was not toxic to any of the microalgae tested. Instead we show high quality of microalgal biomass (lipids 20-30% DW, proteins 20-28% DW, carbohydrates 15-30% DW) and high production when cultivated with flue gas addition compared to CO2-air. Brackish Baltic Sea microalgal communities performed equally or better in terms of biomass quality and production than documented monocultures of diatom and green algae, often used in algal research and development. Hence, we conclude that microalgae should be included in biological solutions to transform waste into renewable resources in coastal waters. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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

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

  • 32. Riittonen, Toni
    et al.
    Eränen, Kari
    Mäki-Arvela, Päivi
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rautio, Anne-Riikka
    Kordas, Krisztian
    Kumar, Narendra
    Salmi, Tapio
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Åbo Akademi University, Process Chemistry Centre, Laboratory of Industrial Chemistry & Reaction Engineering, Turku/Åbo, Finland.
    Continuous liquid-phase valorization of bio-ethanol towards bio-butanol over metal modified alumina2015In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 74, p. 369-378Article in journal (Refereed)
    Abstract [en]

    Commercial mixed-phase aluminum oxide was used as a heterogeneous catalyst support, providing slightly basic properties which are well-suited for the condensation of bio-ethanol to C-4 hydrocarbons, such as 1-butanol. Different metals (Cu, Ni and Co), at various metal loadings were deposited on the support. Consequently, the catalytic reactions were carried out in a continuous laboratory-scale fixed bed reactor operated at 240 degrees C and 70 bar. The catalysts were characterized by means of XRD, TEM, FT-IR, XPS and ICP-OES. Different metals were found to give entirely different product distributions. With the best catalysts, the selectivities towards 1-butanol close to 70% were reached, while the ethanol conversion typically varied between 10 and 30% - strongly depending on the metal applied. It was observed that low loading of copper and high loading of nickel were responsible for the formation of 1-butanol, whereas cobalt and high loading of copper resulted in the production of ethyl acetate. The reaction was found to be extremely sensitive to catalyst preparation conditions and procedures such as metal loading, calcination/reduction temperature and, thereby, to the formation of corresponding crystallite structure.

  • 33. Rudolfsson, Magnus
    et al.
    Borén, Eleonora
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Pommer, Linda
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lestander, Torbjörn A.
    Combined effects of torrefaction and pelletization parameters on the quality of pellets produced from torrefied biomass2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 191, p. 414-424Article in journal (Refereed)
    Abstract [en]

    A combined torrefaction and pelletization study was performed at industrially relevant settings using a factorial design. First, wood chips of Scots pine were torrefied at high temperatures (291-315 degrees C) and short residence times (6-12 min), facilitating high throughput in a continuous pilot-scale torrefaction process. Then the torrefied materials were pelletized, also in pilot-scale, using varying moisture contents (MCs) (10-14%), sieve sizes (4-6 mm), and press channel lengths (PCLs) (25 and 30 mm), in all 19 batches, each of 400 kg. The resulting so called black pellets exhibited bulk densities of 558-725 kg m(-3), durabilities of 46.3-86.5%, and fines contents of 3.8-85.8%. Through multiple linear regression modelling of all 11 responses, it was found that the parameter with the greatest influence on the responses was the torrefaction temperature, followed by torrefaction time, MC, and PCL. Longer PCL and higher MC resulted in higher pellet quality, with less fines and greater bulk density and durability. Furthermore, a low torrefaction degree decreased the amount of power required for pelletization. The energy required to grind pellets into a powder (<0.5 mm) decreased with increasing torrefaction degree as expected, but also with decreasing MC before pelletizing. Pyrolysis-GC/MS analysis of thermal degradation products from the pellets revealed correlations with the torrefaction temperature and time, but no correlations with the pelletization process. These results are useful for mapping chemical changes in torrefied materials and identifying complementary torrefaction and pelletization settings. Specifically of interest is adjustment of PCLs at low intervals to better match friction properties of torrefied materials.

  • 34. Sepman, Alexey
    et al.
    Ögren, Yngve
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wiinikka, Henrik
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå University.
    Real-time in situ multi-parameter TDLAS sensing in the reactor core of an entrained-flow biomass gasifier2017In: Proceedings of the Combustion Institute, ISSN 1540-7489, E-ISSN 1873-2704, Vol. 36, no 3, p. 4541-4548Article in journal (Refereed)
    Abstract [en]

    Tunable diode laser absorption spectroscopy (TDLAS) was used to measure several important process parameters at two different locations inside the reactor of an atmospheric, air-blown 0.1 MWth biomass gasifier. Direct TDLAS at 2298 nm was employed for carbon monoxide (CO) and water vapor (H2O), calibration-free scanned wavelength modulation spectroscopy at 1398 nm for H2O and gas temperature, and direct TDLAS at 770 nm for gaseous elemental potassium, K(g), under optically thick conditions. These constitute the first in situ measurements of K(g) and temperature in a reactor core and in biomass gasification, respectively. In addition, soot volume fractions were determined at all TDLAS wavelengths, and employing fixed-wavelength laser extinction at 639 nm. Issues concerning the determination of the actual optical path length, as well as temperature and species non-uniformities along the line-of-sight are addressed. During a 2-day measurement campaign, peat and stem wood powder were first combusted at an air equivalence ratio (lambda) of 1.2 and then gasified at lambdas of 0.7, 0.6, 0.5, 0.4 and 0.35. Compared to uncorrected thermocouple measurements in the gas stream, actual average temperatures in the reactor core were significantly higher. The CO concentrations at the lower optical access port were comparable to those obtained by gas chromatography at the exhaust. In gasification mode, similar H2O values were obtained by the two different TDLAS instruments. The measured K(g) concentrations were compared to equilibrium calculations. Overall, the reaction time was found to be faster for peat than for stem wood. All sensors showed good performance even in the presence of high soot concentrations, and real-time detection was useful in resolving fast, transient behaviors, such as changes in stoichiometry. Practical implications of in-situ TDLAS monitoring on the understanding and control of gasification processes are discussed.

  • 35.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Combustion of biosolids in a bubbling fluidized bed part 1: main ash forming elements and ash distribution with a focus on phosphorus2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 2, p. 1183-1190Article in journal (Refereed)
    Abstract [en]

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

  • 36.
    Strandberg, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Carlborg, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ash Transformation During Single-Pellet Combustion of a Silicon-Poor Woody Biomass2019In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 8, p. 7770-7777Article in journal (Refereed)
    Abstract [en]

    Biomass fuels with calcium and potassium as the main ash-forming elements are expected to form ash consisting mainly of carbonates and oxides. These carbonates are stable in a rather narrow temperature range, which in turn depends on the Ca/K ratio, as well as on the surrounding atmosphere. The objective of the present study was to perform a detailed characterization of ash formation and transformation at a single-pellet level during combustion of silicon-poor woody biomass fuel. Combustion tests were performed with poplar in a single-pellet isothermal thermogravimetric analyzer operated at different temperatures and atmospheres and quenched at different stages of fuel conversion. The char and residual ashes were characterized for morphology and chemical composition. The focus of the experimental work in this study was on the time (conversion) resolved ash formation and transformations at the late part of the char combustion phase. Thermodynamic equilibrium calculations were used both to design the experiments and to support the interpretation of experimental results. It was concluded that carbonates were, in general, stable at low temperatures (here, 600–800 °C), identified as CaCO3, K2Ca2(CO3)3, and K2Ca(CO3)2, and decomposed at higher temperatures. In addition, a combined carbonate and phosphate phase in the form of carbonate apatite, Ca9.9(PO4)6(CO3)0.9, was also found, mainly at lower temperatures. However, for char/ash samples quenched before full conversion, CaCO3 was still found at temperatures higher than expected, possibly explained by the stabilizing effect of locally higher CO2 partial pressure within the burning fuel particles. Thus, the results of the present study provide new insights into conversion-based ash formation and transformation in a burning fuel particle with relevance for combustion of Si-poor woody biomass fuels.

  • 37.
    Strandberg, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Predicting fuel properties of biomass using thermogravimetry and multivariate data analysis2017In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 156, p. 107-112Article in journal (Refereed)
    Abstract [en]

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

  • 38.
    Strandberg, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Thyrel, Mikael
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lestander, Torbjörn A.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography2018In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 176, p. 211-220Article in journal (Refereed)
    Abstract [en]

    Ash formation during thermochemical conversion of biomass-based pellets influences both char conversion rates and ash-related operational problems. The objective of the present study was to provide detailed insights into changes in fuel and ash properties during fuel conversion. Pellets of poplar wood and wheat straw were used as model biofuels, representing vastly different compositions of ash-forming elements. Pellet samples at different char conversion phases were analyzed by synchrotron-based 3D X-ray micro-tomography, to map and visualize the development of cracks, internal cavities, and ash layers during conversion. The analysis of ash layers was complemented by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. The results provide new insights into how large cracks and internal cavities are developed already during devolatilization, for example, the poplar wood pellets had a 64% void fraction after the devolatilization stage. As expected, there were large variations between the ash layer properties for the two fuels. A porous, low density, and calcium-rich ash was formed from the poplar fuel, whereas the wheat straw ash was a high-density silicate melt that developed into bubbles on the surface. As the conversion proceeded, the wheat straw ash covered parts of the active char surface area, but without blocking the gas transport.

  • 39. Svanberg, Martin
    et al.
    Olofsson, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Flodén, Jonas
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Analysing biomass torrefaction supply chain costs2013In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 142, p. 287-296Article in journal (Refereed)
    Abstract [en]

    The objective of the present work was to develop a techno-economic system model to evaluate how logistics and production parameters affect the torrefaction supply chain costs under Swedish conditions. The model consists of four sub-models: (1) supply system, (2) a complete energy and mass balance of drying, torrefaction and densification, (3) investment and operating costs of a green field, stand-alone torrefaction pellet plant, and (4) distribution system to the gate of an end user. The results show that the torrefaction supply chain reaps significant economies of scale up to a plant size of about 150-200 kiloton dry substance per year (kton(DS)/year), for which the total supply chain costs accounts to 31.8 euro per megawatt hour based on lower heating value ((sic)/MWLHV). Important parameters affecting total cost are amount of available biomass, biomass premium, logistics equipment, biomass moisture content, drying technology, torrefaction mass yield and torrefaction plant capital expenditures (CAPEX).

  • 40. Tranvik, AC
    et al.
    Öhman, Marcus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Sanati, M
    Bed material deposition in cyclones of wood fuel fired circulating fluidized beds (CFBs)2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 1, p. 104-109Article in journal (Refereed)
    Abstract [en]

    Bed material samples were collected at different times from a full-scale combustion boiler, and bed material deposits were taken from the cyclone and the riser at two different occasions from a wood-fired circulating fluidized bed boiler (104 MWth). The bed materials and the bed material deposits were analyzed with environmental scanning electron microscopy/energy-dispersive X-ray spectroscopy (ESEM/EDXS) to determine the characteristics of the formed bed particle layers and bed material deposits. On the basis of their elemental composition, the corresponding melting behavior was estimated, using data extracted from phase diagrams. The bed material was also fractionated by sieving, and the alkali metal concentration dependence on the particle size was determined. The bed material deposits found in the cyclone and the riser consisted of bed particles embedded in a low-temperature melting (sticky) alkali metal silicate (K and Na) that resemble the composition of the layer found around the cracks in older quartz bed particles. The alkali silicate formation, which is in progress in the vicinity of the formed cracks of older quartz bed particles, significantly transforms a large part of the bed particle and makes it less resistant against fragmentation. The results therefore suggest that elutriated alkali silicate-rich fragments from old quartz bed particles are responsible for bed material depositions in cyclones of wood-fired circulating fluidized beds (CFBs).

  • 41. Weiland, Fredrik
    et al.
    Nordwaeger, Martin
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Olofsson, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wiinikka, Henrik
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Entrained flow gasification of torrefied wood residues2014In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 125, p. 51-58Article in journal (Refereed)
    Abstract [en]

    In this work, four different fuels were gasified in a pressurized entrained flow pilot plant gasifier at approximately 270 kW(th). The different fuels were; two torrefied wood residues, one raw wood residue and one torrefied stem wood. The system pressure and oxygen equivalence ratio (lambda) were held constant for all four gasification experiments. It was found that the torrefaction pretreatment significantly reduced the milling energy consumption for fuel size reduction, which in turn contributed to increased gasification plant efficiency. Furthermore, the results indicate that the carbon conversion efficiency may be enhanced by an intermediate torrefaction pretreatment, whereas both less severe torrefaction and more severe torrefaction resulted in reduced carbon conversions. The results also indicate that the CH4 yield was significantly reduced for the most severely torrefied fuel.

  • 42. Whitty, Kevin
    et al.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hupa, Mikko
    Influence of pressure on pyrolysis of black liquor: 1. Swelling2008In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 99, no 3, p. 663-670Article in journal (Refereed)
    Abstract [en]

    This is the first of two papers concerning the behavior of black liquor during pyrolysis under pressurized conditions. Two industrial kraft liquors were pyrolyzed in a laboratory-scale pressurized single particle reactor and a pressurized grid heater at temperatures ranging from 650 to 1100 degrees C and at pressures between 1 and 20 bar. The dimensions of the chars produced were measured and the specific swollen volume was calculated. Swelling decreased roughly logarithmically over the pressure range 1-20 bar. An expression is developed to predict the specific swollen volume at elevated pressure when the volume at 1 bar is known. The bulk density of the char increased with pressure, indicating that liquors will be entrained less easily at higher pressures.

  • 43. Whitty, Kevin
    et al.
    Kullberg, Mika
    Sorvari, Vesa
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hupa, Mikko
    Influence of pressure on pyrolysis of black liquor: 2. Char yields and component release2008In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 99, no 3, p. 671-679Article in journal (Refereed)
    Abstract [en]

    This is the second in a series of papers concerning the behavior of black liquor during pyrolysis at elevated pressures. Two industrial black liquors were pyrolyzed under pressurized conditions in two laboratory-scale devices, a pressurized single-particle reactor and a pressurized grid heater. Temperatures ranging between 650 and 1100 degrees C and pressures in the range 1-20 bar were studied. Char yields were calculated and based on analysis of some of the chars the fate of carbon, sodium, potassium and sulfur was determined as a function of pyrolysis pressure. At temperatures below 800 degrees C little variation in char yield was observed at different pressures. At higher temperatures char yield increased with pressure due to slower decomposition of sodium carbonate. For the same reason, sodium release decreased with pressure. Sulfur release, however, increased with pressure primarily because there was less opportunity for its capture in the less-swollen chars.

  • 44. Wiinikka, Henrik
    et al.
    Grönberg, Carola
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Emissions of heavy metals during fixed-bed combustion of six biomass fuels2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 2, p. 1073-1080Article in journal (Refereed)
    Abstract [en]

    Few studies examine heavy metal emissions during the small-scale combustion of various solid biofuels. This issue may become more important, as one can expect new regulations governing such emissions from biomass combustion similar to those governing waste incineration. This paper investigates the emissions of particulate-associated heavy metals (i.e., Sb, As, Cd, Co, Cr, Cu, Pb, Mn, Ni, Tl, V, Hg, and Zn) during the fixed-bed combustion of six solid biofuels (i.e., stemwood from birch and pine/spruce, bark from birch and pine, salix, and oat grains) and of peat and bituminous coal for comparison. The results indicate that the flue gas concentration (normalized to 11% O-2) of the sum of all measured metals (Zn excluded) during the biomass combustion tests ranged from 57 mu g Nm(-3) for birch stemwood to 198 mu g Nm(-3) for birch bark. The concentration of Zn in the flue gas was generally considerably higher than those of the other metals, ranging from 646 mu g Nm(-3) for spruce/pine stemwood to 7948 mu g Nm(-3) for birch bark. Compared with coal and peat, the biomass fuels produced higher Zn emissions, but lower or similar emissions of the sum of the other metals. The volatile behavior and concentration of the metal in the flue gases as a function of the heavy metal in the fuel are also presented for selected heavy metals.

  • 45. Zevenhoven-Onderwater, Maria
    et al.
    Öhman, Marcus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Skrifvars, Bengt-Johan
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry. Åbo Akademi University.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Hupa, Mikko
    Bed agglomeration characteristics of wood-derived fuels in FBC2006In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 20, no 2, p. 818-824Article in journal (Refereed)
    Abstract [en]

    The agglomeration tendency of five Scandinavian forest-derived biomass fuels was studied using an advanced fuel analysis, i.e., a combination of chemical fractionation analysis, controlled bed defluidization tests, and SEM/EDX analysis of bed samples. It is shown that all five fuels have a tendency to form bed agglomerates when fired in a fluidized bed with silica sand as the bed material. The agglomeration appeared to proceed by formation of a sticky layer on bed particles gluing them together. The layers on the bed particles contained Si, Ca, and K, and, in some cases, P. The combination of advanced fuel analysis by SEM/EDX showed that the soluble fraction of Ca and K (i.e., leachable from the fuel with water and acetate) may be responsible for the formation of the layer. Silicon may mainly come from the bed particles.

  • 46.
    Zhu, Youjian
    et al.
    School of Energy and Power Engineering, Zhengzhou University of Light Industry, Zhengzhou, Henan 450002, People’s Republic of China.
    Piotrowska, Patrycja
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    van Eyk, Philip Joseph
    School of Chemical Engineering, University of Adelaide, Adelaide, South Australia 5005, Australia.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wu, Xuehong
    School of Energy and Power Engineering, Zhengzhou University of Light Industry, Zhengzhou, Henan 450002, People’s Republic of China.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Zhang, Jun
    School of Energy and Power Engineering, Zhengzhou University of Light Industry, Zhengzhou, Henan 450002, People’s Republic of China.
    Kwong, Chi Wai
    School of Chemical Engineering, University of Adelaide, Adelaide, South Australia 5005, Australia.
    Wang, Dingbiao
    School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou, Henan 450001, People’s Republic of China.
    Cole, Andrew J
    MACRO, the Centre for Macroalgal Resources and Biotechnology, James Cook University, Townsville, Queensland 4811, Australia.
    de Nys, Rocky
    MACRO, the Centre for Macroalgal Resources and Biotechnology, James Cook University, Townsville, Queensland 4811, Australia.
    Gentili, Francesco G.
    Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences (SLU), 901 83 Umeå, Sweden.
    Ashman, Peter J.
    School of Chemical Engineering, University of Adelaide, Adelaide, South Australia 5005, Australia.
    Fluidized bed co-gasification of algae and wood pellets: gas yields and bed agglomeration analysis2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 3, p. 1800-1809Article in journal (Refereed)
    Abstract [en]

    Algae utilization in energy production has gained increasing attention as a result of its characteristics, such as high productivity, rapid growth rate, and flexible cultivation environment. In this paper, three species of algae, including a fresh water macroalgae, Oedogonium sp., a saltwater macroalgae, Derbersia tenuissima, and a microalgae species, Scenedesmus sp., were studied to explore the potential of using smaller amounts of algae fuels in blends with traditional woody biomasses in the gasification processes. Co-gasification of 10 wt % algae and 90 wt % Swedish wood pellets was performed in a fluidized bed reactor. The effects of algae addition on the syngas yield and carbon conversion rate were investigated. The addition of 10 wt % algae in wood increased the CO, H2, and CH4 yields by 3–20, 6–31, and 9–20%, respectively. At the same time, it decreased the CO2 yield by 3–18%. The carbon conversion rates were slightly increased with the addition of 10 wt % macroalgae in wood, but the microalgae addition resulted in a decrease of the carbon conversion rate by 8%. Meanwhile, the collected fly ash and bed material samples were analyzed using scanning electron microscopy combined with an energy-dispersive X-ray detector (SEM–EDX) and X-ray diffraction (XRD) technique. The fly ashes of wood/marcoalgae tests showed a higher Na content with lower Si and Ca contents compared to the wood test. The gasification tests were scheduled to last 4 h; however, only wood and wood/Derbersia gasification experiments were carried out without significant operational problems. The gasification of 10 wt % Oedogonium N+ and Oedogonium N– led to defluidization of the bed in less than 1 h, and the wood/Scenedesmus (WD/SA) test was stopped after 1.8 h as a result of severe agglomeration. It was found that the algae addition had a remarkable influence on the characteristics and compositions of the coating layer. The coating layer formation and bed agglomeration mechanism of wood/macroalgae was initiated by the reaction of alkali compounds with the bed particles to form low-temperature melting silicates (inner layer). For the WD/SA test, the agglomeration was influenced by both the composition of the original algae fuel as well as the external mineral contaminations. In summary, the operational problems experienced during the co-gasification tests of different algae–wood mixtures were assigned to the specific ash compositions of the different fuel mixtures. This showed the need for countermeasures, specifically to balance the high alkali content, to reach stable operation in a fluidized bed gasifier.

  • 47. Zhu, Youjian
    et al.
    van Eyk, Philip J.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Kirtania, Kawnish
    Piotrowska, Patrycja
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    de Nys, Rocky
    Bhattacharya, Sankar
    Gentili, Francesco G.
    Ashman, Peter J.
    Preliminary understanding on the ash behavior of algae during co-gasification in an entrained flow reactor2018In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 175, p. 26-34Article in journal (Refereed)
    Abstract [en]

    Algae are considered as a promising alternative fuel to produce energy due to its advantages such as high production yield, short growth cycle and flexible growing environment. Unfortunately, ash-related issues restrict its thermochemical utilization due to the high ash content and especially the high alkali metal concentration. In this paper, the gasification performance and ash behavior were experimentally analysed for three macro- and micro-algal species. Clear differences in the proximate and ultimate compositions were found between the cultivated algae used in this study and macroalgae (seaweed) harvested from the marine environments. Algal biomass generally contained higher Na and P contents than lignocellulosic biomass. Microalgae also had a relatively high mineral content due to the impurities in the harvesting process which included centrifugal pumping followed by sedimentation. Co-gasification of 20 wt% algae with softwood was investigated using an entrained flow reactor. The addition of both macroalgal species Derbersia tenuissima and Oedogonium to softwood had a limited influence on the gas yields and carbon conversion. On the other hand, the addition of the microalgal species Scenedesmus significantly decreased the main gas yields and carbon conversion. Moreover, the addition of algae clearly changed the residual ash composition of the base fuel. Finally, a preliminary understanding of the ash behavior of the tested algae blends was obtained through the analysis of the fuel ashes and the collected residual ashes. Fouling and corrosion were presumably occurred during the co-gasification of wood/macroalgae blends in view of the high alkali metal content. Microalga Scenedesmus had a high mineral content which could potentially capture the alkali metal in the ash and mitigate fouling when gasified with softwood. The growing environment and harvesting method were found to be significantly affecting the ash behavior implying the need for careful consideration regarding co-gasification process.

  • 48.
    Åberg, Katarina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Pommer, Linda
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nordin, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Syngas production by combined biomass gasification and in situ biogas reforming2015In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 6, p. 3725-3731Article in journal (Refereed)
    Abstract [en]

    For small- to medium-sized streams of biogas (methane) produced at a biorefinery site where cost-efficient reforming by traditional methods are unavailable, combined biomass gasification and methane reforming could facilitate co-conversion and increase the H-2/CO ratio in the syngas from the gasification plant. In the present work, co-gasification of biomass with CH4 was evaluated by means of a parametric chemical equilibrium study for both wood/CH4 and black liquor/CH4 feedstocks and bench-scale fluidized-bed gasification experiments for a wood/peat/CH4 fuel mixture. The parametric study indicated that high-temperature, and steam and oxygen addition all facilitate a high conversion rate, i.e., methane reforming. Evaluating the influence of the gasification temperature on CH4 reforming and increasing the H-2/CO ratio experimentally demonstrated that high temperatures are required for efficient co-conversion.

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