umu.sePublications
Change search
Refine search result
12345 101 - 150 of 209
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Mikkola, Jyri-Pekka
    et al.
    Umeå University.
    Tuuf, Jean-Christoffer
    Kirilin, Alexey
    Damlin, Pia
    Salmi, Tapio
    Ionic liquid-aided carboxymethylation of kraft pulp2010In: International journal of Chemical Reactor Engineering, ISSN 1542-6580, E-ISSN 1542-6580, Vol. 8, no A102Article in journal (Refereed)
    Abstract [en]

    Different ionic liquids containing the cation such as 1-N-butyl-3-methylimida-zolium (Bmim+) are able to efficiently dissolve cellulose. The ability of ionic liquids to truly dissolve cellulose is significant when cellulose derivatization is attempted. A series of experiments on etherification (carboxymethylation) of cellulose was performed, using both the conventional suspension approach (slurry) with 2-propanol as the principal reaction media and a totally homogenous reaction approach utilizing ionic liquids as a reaction media capable of dissolving cellulose. It was observed that a pre-treatment with the ionic liquid 1-N-butyl-3-methylimidazolium iodide ([Bmim][I]) seems to promote substitution in line with the conventional, heterogeneous suspension process. Under carefully chosen reaction conditions, a higher degree of substitution was obtained when wetting the cellulose with [Bmim][I] prior to classical derivatization than without this pre-treatment. It was also observed that the substitution pattern was changing upon use of the ionic liquid [Bmim][I]. Upon a totally homogenous etherification, it was found that the ionic liquid 1-N-butyl-3-methylimidazolium acetate ([Bmim][oAc]) gave the highest degree of substitution. The product obtained was water-soluble and had a DS (degree of substitution) of 0.59. The substitution pattern of the products obtained from the homogenous reactions follow the same substitution pattern as the products obtained from the conventional suspension process. This indicates that the properties of the products are in line with products prepared via the conventional reaction route.

  • 102.
    Miranda La Hera, Pedro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Rehman, Bilal Ur
    Sandberg, Anders
    Modeling an industrial flotation process: A case study at the mining company Boliden AB2012In: 2012 WORLD AUTOMATION CONGRESS (WAC), IEEE , 2012, p. 1-5Conference paper (Refereed)
    Abstract [en]

    We present results of modeling dynamics of a copper flotation pl'ocess, for which conventional system identification methods are applied. To this end, experimental studies are performed at an open pit mine belonging to the Swedish mining company Boliden AB. The main idea is to identify linear plants, that approximate dynamics of the process around neighborhoods of cost efficient working conditions. These models are intended to be applied for the design of model based control strategies, and to assess better studies of performance optimization. The results of simulation tests show a satisfactory agreement in between the identified models performance and the measured variables.

  • 103. Mohammadi, Marzieh
    et al.
    Shafiei, Marzieh
    Karimi, Keikhosro
    Abdolmaleki, Amir
    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
    Improvement of ethanol production from birch and spruce pretreated with 1-H-3-methylmorpholinium chloride2019In: Electronic Journal of Biotechnology, ISSN 0717-3458, E-ISSN 0717-3458, Vol. 41, p. 95-99Article in journal (Refereed)
    Abstract [en]

    Background: Pretreatment is the critically important step for the production of ethanol from lignocelluloses. In this study, hardwood birch (Betula pendula) and softwood spruce (Norway spruce) woods were pretreated with a newly synthesized morpholinium ionic liquid, 1-H-3-methylmorpholinium chloride ([HMMorph][Cl]), followed by enzymatic hydrolysis and fermentation to ethanol.

    Results: [HMMorph][Cl] was synthesized using inexpensive raw materials, i.e., hydrochloric acid and N-methyl morpholine, following a simple process. The influence of pretreatment time (2, 3, 5, and 8 h) and temperature (120 and 140°C) in terms of hydrolysis efficiency was investigated. Glucose yields from enzymatic hydrolysis were improved from 13.7% to 45.7% and 12.9% to 51.8% after pretreatment of birch and spruce woods, respectively, under optimum pretreatment conditions (i.e., at 140°C for 3 h) as compared to those from pristine woods. Moreover, the yields of ethanol production from birch and spruce were increased to 34.8% and 44.2%, respectively, while the yields were negligible for untreated woods.

    Conclusions: This study demonstrated the ability of [HMMorph][Cl] as an inexpensive agent to pretreat both softwood and hardwood.

  • 104. 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. 

  • 105. Murzin, D. Yu.
    et al.
    Murzina, E. V.
    Tokarev, A.
    Shcherban, N. D.
    Wärnå, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Salmi, T.
    Arabinogalactan hydrolysis and hydrolytic hydrogenation usingfunctionalized carbon materials2015In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 257, p. 169-176Article in journal (Refereed)
    Abstract [en]

    Hydrolysis of the hemicellulose arabinogalactan was studied in this work over several functionalized carbon materials, which were specifically treated to increase their acidities. Hydrolytic hydrogenation of arabinogalactan was investigated using the same materials in a mechanical mixture with ruthenium supported on active carbon. Application of these mixtures resulted in formation of polyols, suppressing simultaneously the generation of side products hydroxymethylfurfural (HMF) and furfural. Formation of high molecular weight compounds (aggregates of sugars and humins) was still quite substantial with a mechanical mixture of Ru/C and a carbon material prepared from sucrose by activation with zinc chloride to increase porosity. Post-treatment of this carbonaceous material with sulphuric acid significantly influenced kinetics of high molecular weight products formation resulting also in elevation of sugar alcohols yields.

  • 106.
    Navarro, Montserrat Perez
    et al.
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Ames, William M.
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Nilsson, Håkan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lohmiller, Thomas
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Pantazis, Dimitrios A.
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Rapatskiy, Leonid
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Nowaczyk, Marc M.
    Ruhr Univ Bochum, D-44780 Bochum, Germany.
    Neese, Frank
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Boussac, Alain
    CEA Saclay, CNRS, iBiTec S, UMR 8221, F-91191 Gif Sur Yvette, France.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lubitz, Wolfgang
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Cox, Nicholas
    Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany.
    Ammonia binding to the oxygen-evolving complex of photosystem II identifies the solvent-exchangeable oxygen bridge (µ-oxo) of the manganese tetramer2013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 39, p. 15561-15566Article in journal (Refereed)
    Abstract [en]

    The assignment of the two substrate water sites of the tetramanganese penta-oxygen calcium (Mn4O5Ca) cluster of photosystem II is essential for the elucidation of the mechanism of biological O-O bond formation and the subsequent design of bio-inspired water-splitting catalysts. We recently demonstrated using pulsed EPR spectroscopy that one of the five oxygen bridges (mu-oxo) exchanges unusually rapidly with bulk water and is thus a likely candidate for one of the substrates. Ammonia, a water analog, was previously shown to bind to the Mn4O5Ca cluster, potentially displacing a water/substrate ligand [Britt RD, et al. (1989) J Am Chem Soc 111(10):3522-3532]. Here we show by a combination of EPR and time-resolved membrane inlet mass spectrometry that the binding of ammonia perturbs the exchangeable mu-oxo bridge without drastically altering the binding/exchange kinetics of the two substrates. In combination with broken-symmetry density functional theory, our results show that (i) the exchangable mu-oxo bridge is O5 {using the labeling of the current crystal structure [Umena Y, et al. (2011) Nature 473(7345):55-60]}; (ii) ammonia displaces a water ligand to the outer manganese (Mn-A4-W1); and (iii) as W1 is trans to O5, ammonia binding elongates the Mn-A4-O5 bond, leading to the perturbation of the mu-oxo bridge resonance and to a small change in the water exchange rates. These experimental results support O-O bond formation between O5 and possibly an oxyl radical as proposed by Siegbahn and exclude W1 as the second substrate water.

  • 107. Nicholson, James
    et al.
    Azim, Syed
    Rebecchi, Mario J.
    Galbavy, William
    Feng, Tian
    Reinsel, Ruth
    Rizwan, Sabeen
    Fowler, Christopher J.
    Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Pharmacology.
    Benveniste, Helene
    Kaczocha, Martin
    Leptin Levels Are Negatively Correlated with 2-Arachidonoylglycerol in the Cerebrospinal Fluid of Patients with Osteoarthritis2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 4Article in journal (Refereed)
    Abstract [en]

    ` Background There is compelling evidence in humans that peripheral endocannabinoid signaling is disrupted in obesity. However, little is known about the corresponding central signaling. Here, we have investigated the relationship between gender, leptin, body mass index (BMI) and levels of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) in the serum and cerebrospinal fluid (CSF) of primarily overweight to obese patients with osteoarthritis. Methodology/Principal Findings Patients (20 females, 15 males, age range 44-78 years, BMI range 24-42) undergoing total knee arthroplasty for end-stage osteoarthritis were recruited for the study. Endocannabinoids were quantified by liquid chromatography - mass spectrometry. AEA and 2-AG levels in the serum and CSF did not correlate with either age or BMI. However, 2-AG levels in the CSF, but not serum, correlated negatively with CSF leptin levels (Spearman's. -0.48, P=0.0076, n=30). No such correlations were observed for AEA and leptin. Conclusions/Significance In the patient sample investigated, there is a negative association between 2-AG and leptin levels in the CSF. This is consistent with pre-clinical studies in animals, demonstrating that leptin controls the levels of hypothalamic endocannabinoids that regulate feeding behavior.

  • 108.
    Nilsson, Håkan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Substrate water binding to the oxygen-evolving complex in photosystem II2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Oxygenic photosynthesis in plants, algae and cyanobacteria converts sunlight into chemical energy. In this process electrons are transferred from water molecules to CO2 leading to the assembly of carbohydrates, the building blocks of life. A cluster of four manganese ions and one calcium ion, linked together by five oxygen bridges, constitutes the catalyst for water oxidation in photosystem II (Mn4CaO5 cluster). This cluster stores up to four oxidizing equivalents (S0,..,S4 states), which are then used in a concerted reaction to convert two substrate water molecules into molecular oxygen. The reaction mechanism of this four-electron four-proton reaction is not settled yet and several hypotheses have been put forward. The work presented in this thesis aims at clarifying several aspects of the water oxidation reaction by analyzing the mode of substrate water binding to the Mn4CaO5 cluster.

    Time-resolved membrane-inlet mass spectrometric detection of flash-induced O2 production after fast H218O labelling was employed to study the exchange rates between substrate waters bound to the Mn4CaO5 cluster and the surrounding bulk water. By employing this approach to dimeric photosystem II core complexes of the red alga Cyanidoschyzon merolae it was demonstrated that both substrate water molecules are already bound in the S2 state of the Mn4CaO5 cluster. This was confirmed with samples from the thermophilic cyanobacterium Thermosynechococcus elongatus. Addition of the water analogue ammonia, that is shown to bind to the Mn4CaO5 cluster by replacing the crystallographic water W1, did not significantly affect the exchange rates of the two substrate waters. Thus, these experiments exclude that W1 is a substrate water molecule.

    The mechanism of O-O bond formation was studied by characterizing the substrate exchange in the S3YZ● state. For this the half-life time of this transient state into S0 was extended from 1.1 ms to 45 ms by replacing the native cofactors Ca2+ and Cl- by Sr2+ and I-. The data show that both substrate waters exchange significantly slower in the S3YZ● state than in the S3 state. A detailed discussion of this finding lead to the conclusions that (i) the calcium ion in the Mn4CaO5 cluster is not a substrate binding site and (ii) O-O bond formation occurs via the direct coupling between two Mn-bound water-derived oxygens, which were assigned to be the terminal water/hydroxy ligand W2 and the central oxo-bridging O5.

    The driving force for the O2 producing S4→S0 transition was studied by comparing the effects of N2 and O2 pressures of about 20 bar on the flash-induced O2 production of photosystem II samples containing either the native cofactors Ca2+ and Cl- or the surrogates Sr2+ and Br-. While for the Ca/Cl-PSII samples no product inhibition was observed, a kinetic limitation of O2 production was found for the Sr/Br-PSII samples under O2 pressure. This was tentatively assigned to a significant slowdown of the O2 release in the Sr/Br-PSII samples. In addition, the equilibrium between the S0 state and the early intermediates of the S4 state family was studied under 18O2 atmosphere in photosystem II centers devoid of tyrosine YD. Water-exchange in the transiently formed early S4 states would have led to 16,18O2 release, but none was observed during a three day incubation time. Both experiments thus indicate that the S4→S0 transition has a large driving force. Thus, photosynthesis is not limited by the O2 partial pressure in the atmosphere.

  • 109.
    Nilsson, Håkan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Han, Guangye
    Shevela, Dmitriy
    Cournac, Laurent
    Boussac, Alain
    Rappaport, Fabrice
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lavergne, Jerome
    Estimation of the equilibrium constant of the molecular oxygen generating S4→S0 (S3+YZ→S0YZ) transition in photosystem IIManuscript (preprint) (Other academic)
  • 110.
    Nilsson, Håkan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Krupnik, Tomasz
    Kargul, Joanna
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae2014In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1837, no 8, p. 1257-1262Article in journal (Other academic)
    Abstract [en]

    The binding affinity of the two substrate–water molecules to the water-oxidizing Mn4CaO5 catalyst in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae was studied in the S2and S3 states by the exchange of bound 16O-substrate against 18O-labeled water. The rate of this exchange was detected via the membrane-inlet mass spectrometric analysis of flash-induced oxygen evolution. For both redox states a fast and slow phase of water-exchange was resolved at the mixed labeled m/z 34 mass peak: kf = 52 ± 8 s− 1 and ks = 1.9 ± 0.3 s− 1 in the S2 state, and kf = 42 ± 2 s− 1 and kslow = 1.2 ± 0.3 s− 1 in S3, respectively. Overall these exchange rates are similar to those observed previously with preparations of other organisms. The most remarkable finding is a significantly slower exchange at the fast substrate–water site in the S2 state, which confirms beyond doubt that both substrate–water molecules are already bound in the S2 state. This leads to a very small change of the affinity for both the fast and the slowly exchanging substrates during the S2 → S3 transition. Implications for recent models for water-oxidation are briefly discussed.

  • 111. 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.

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

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

  • 113.
    Näzelius, Ida-Linn
    et al.
    Luleå, Sweden.
    Fagerström, Jonathan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå, Sweden.
    Slagging in fixed-bed combustion of phosphorus-poor biomass: critical ash-forming processes and compositions2015In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 2, p. 894-908Article in journal (Refereed)
    Abstract [en]

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

  • 114.
    Ohlsson, K. E. Anders
    et al.
    Swedish University of Agricultural Sciences, Department of Forest Ecology and Management, Umeå, Sweden.
    Olofsson, Thomas
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Quantitative infrared thermography imaging of the density of heat flow rate through a building element surface2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 134, p. 499-505Article in journal (Refereed)
    Abstract [en]

    Infrared thermography is often used to record an image of the building envelope surface temperature, and thereby acquire qualitative information on its thermal insulation performance. Recently, a thermography method has evolved, which enables quantitative measurement of the 2-dimensional pattern of the density of heat flow rate (q) across the building element surface. However, based on previous estimates of its measurement uncertainty, the capacity of the thermography method to yield accurate results has been questioned. We present here an improved procedure for measurement of q, with an evaluation of measurement errors. The main improvement consists of the simultaneous measurement of surface temperature, surrounding radiative temperature, and air temperature, based on information included in one single thermal camera image. This arrangement allows for accurate measurements of small temperatures differences, and thereby reduced uncertainty in the measurement of q. The measurement bias was evaluated experimentally by a comparison of thermography results against a reference method. Under natural convective conditions, there was a 2.6 W m(-2) constant difference between the two methods. The measurement uncertainty u(q) was estimated as a function of q. Based on this, the lower limit of the measurement working range was determined to be 6 W m(-2), which corresponds to less than 10% relative uncertainty. In the case of forced convection, the thermography method yielded less reliable results. The reason for this was the sensitivity of the results to the choice of model for the convective heat transfer coefficient, and the difficulty to select the position for measurement of the wind speed, which is appropriate for this model.

  • 115. Olofsson, Ingemar
    et al.
    Strandberg, Martin
    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.
    Broström, Markus
    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.
    Oxygen enhanced torrefaction - An initial feasibility studyManuscript (preprint) (Other academic)
    Abstract [en]

    Upcoming world market prices on thermally treated and densified biomass to be feasible for coal replacement put a high demand on the process suppliers to deliver cost efficient and high energy yield conversion systems with a capacity to produce a high quality product. One of the more complex and vital parts in a torrefaction facility is the indirect or direct heat transfer system applied. This is a critical task that also may limit the scale-up potential and thus influence the economy of scale of a complete torrefaction system.

    In the present study, it was demonstrated that the torrefaction reactions in a rotary drum pilot reactor (20 kgDS/h) potentially may be operated autothermally by a low level injection of air directly into the reactor for controlled in-situ partial combustion of the released torrefaction gases. Both concurrent and countercurrent gas flow patterns were evaluated for different process temperatures. At higher temperatures (338°C) in countercurrent gas flow mode, steady-state torrefaction was reached without external heat supply. The resulting torrefied biomass had higher heating value, higher carbon content and lower milling energy consumption, compared to non-oxidative torrefied biomass with same mass yield. Condensation of torrefaction gas compounds is a suggested reason.No significant decrease in the combustibility of the torrefaction gas was experienced.  The demonstrated Oxygen Enhanced Torrefaction (OET) mode thus has the potential to improve the torrefaction systems in terms of scale-up performance with reduced investment and operational costs but further validation work is needed to confirm the present findings and also to identify working conditions.

  • 116. Persson, Kristoffer
    et al.
    Broström, Markus
    Carlsson, Jörgen
    Nordin, Anders
    Backman, Rainer
    High Temperature Corrosion in a 65 MW Waste-to-Energy Plant2006Conference paper (Refereed)
  • 117. Persson, Kristoffer
    et al.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Carlsson, Jörgen
    Nordin, Anders
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    High Temperature Corrosion in a 65 MW Waste-to-Energy Plant2006Conference paper (Other academic)
  • 118.
    Pettersson, Anita
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business (including The Swedish School of Textiles), Department of Resource Recovery and Building Technology.
    Nordin, Andreas
    University of Borås, Faculty of Textiles, Engineering and Business (including The Swedish School of Textiles), Department of Resource Recovery and Building Technology.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Åmand, Lars-Erik
    University of Borås, Faculty of Textiles, Engineering and Business (including The Swedish School of Textiles), Department of Resource Recovery and Building Technology.
    Phosphorous Rich Bottom Ash with Low Cadmium Content by Ash Design by means of Co-Combustion of Municipal Sewage Sludgein a 27MWth Grate Fired Boiler2019Conference paper (Refereed)
  • 119. Pezoa-Conte, Ricardo
    et al.
    Leyton, Allison
    Baccini, Andrea
    Ravanal, María Cristina
    Mäki-Arvela, Päivi
    Grénman, Henrik
    Xu, Chunlin
    Willför, Stefan
    Lienqueo, María Elena
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Abo Akad Univ, Ind Chem & React Engn, Johan Gadolin Proc Chem Ctr, Biskopsgatan 8, FI-20500 Turku, Finland.
    Aqueous Extraction of the Sulfated Polysaccharide Ulvan from the Green Alga Ulva rigida: Kinetics and Modeling2017In: Bioenergy Research, ISSN 1939-1234, E-ISSN 1939-1242, Vol. 10, no 3, p. 915-928Article in journal (Refereed)
    Abstract [en]

    The incentives for utilizing a versatile range of renewable feedstocks in novel ways are continuously increasing. Sulfated polysaccharides from green algae, such as ulvan, are interesting due to the rare sugar constituents which can be utilized for new materials and chemicals in industry. However, before valorization fractionation needs to be performed in a controlled way. In the current work, the kinetics of the aqueous extraction of ulvan was studied in the temperature range 60–130 °C. The highest yield of 97.6 wt.% was attained after 2 h of extraction at 130 °C, and the extraction efficiency was observed to be heavily temperature dependent. Interestingly, two regimes of extraction kinetics were observed, presumably due to the different ulvan fractions contained within the cell wall of green algae. The experimental data was modeled with first-order kinetics, and an apparent activation energy of 53.8 kJ mol−1 was obtained for the process. The algal residue was processed using simultaneous saccharification and fermentation, and 0.48 g ethanol g−1 of sugars was obtained.

  • 120.
    Phan, Duong Ngoc Chau
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Link between fly ash properties and polychlorinated organic pollutants formed during simulated municipal solid waste incineration2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 4, p. 2761-2769Article in journal (Refereed)
    Abstract [en]

    The relationship between the properties of fly ash generated during waste incineration and the thermal formation of persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs), was investigated on two artificial wastes using a laboratory incinerator. Fly ash particles were sampled in the post-combustion zone at approximately 300 degrees C and were characterized with the following complementary techniques: X-ray diffraction (XRD), scanning electron microscopy energy-dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Flue gas samples were collected at the same location and analyzed for Mo-OCDDs, Mo-OCDFs, Tri-DCBs, and Di-OCNs. A strong correlation between fly ash characteristics and waste composition exists for several of the elements considered in this work. For instance, the waste containing the highest levels of Al produced more abundant Al-bearing minerals and elemental Al in the resulting fly ashes. Copper, an especially important POP formation catalyst, was not detected in the top 10 nm surface of fly ash particles but rather occurred within the top 2 pm, indicating that surface copper of catalytic importance for POP formation reactions was not available. Important contributions of ferric iron present in the abundant fly ash-building hematite phase could have also played an important role, especially given its documented contributions in chlorination pathways. Orthogonal projections to latent structures (OPLS) modeling resolved the relationship between fly ash properties and the post-combustion POP formation. These efforts showed that low levels of ash-forming elements (i.e., Na, Mg, Fe, Ti, etc.) were associated with an increase in flue gas S levels, which, in turn, poison the Cl-2 production via the Deacon process. Wastes with depleted levels of fly-ash-building elements should therefore be favored for minimizing PCDD, PCDF, PCB, and PCN release caused by incineration.

  • 121. Phounglamcheik, Aekjuthon
    et al.
    Wang, Liang
    Romar, Henrik
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ramser, Kerstin
    Skreiberg, Øyvind
    Umeki, Kentaro
    Effects of pyrolysis oil recycling and reaction gas atmosphere on the physical properties and reactivity of charcoal from wood2018In: 22nd International Symposium on Analytical and Applied Pyrolysis, 2018Conference paper (Other academic)
  • 122.
    Piotrowska, Patrycja
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Rebbling, Anders
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lindberg, Daniel
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Öhman, Marcus
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Waste gypsum board and ash-related problems during combustion of biomass: 1. Fluidized bed2015In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 2, p. 877-893Article in journal (Refereed)
    Abstract [en]

    This paper is the first in a series of two describing the use of waste gypsum boards as an additive during combustion of biomass. This paper focuses on experiments performed in a bench-scale bubbling fluidized-bed reactor (5 kW). Three biomass fuels were used, i.e., wheat straw (WS), reed canary grass (RC), and spruce bark (SB), with and without addition of shredded waste gypsum board (SWGB). The objective of this work was to determine the effect of SWGB addition on biomass ash transformation reactions during fluidized bed combustion. The combustion was carried out in a bed of quartz sand at 800 or 700 degrees C for 8 h. After the combustion stage, a controlled fluidizedbed agglomeration test was carried out to determine the defluidization temperature. During combustion experiments, outlet gas composition was continuously measured by means of Fourier transform infrared spectroscopy. At the same place in the flue gas channel, particulate matter was collected with a 13-stage Dekati low-pressure impactor. Bottom and cyclone fly ash samples were collected after the combustion tests. In addition, during the combustion tests a 6-h deposit sample was collected with an air-cooled (430 degrees C) probe. All ash samples were analyzed by means of scanning electron microscopy combined with energy dispersive X-ray spectrometry for elemental composition and with X-ray powder diffraction for the detection of crystalline phases. Decomposition of CaSO4 originating from SWGB was mainly observed during combustion of reed canary grass at 800 degrees C. The decomposition was observed as doubled SO2 emissions. No significant increase of SO2 during combustion of SB and WS was observed. However, the interaction of SWGB particles with WS and SB ash forming matter, mainly potassium containing compounds, led to the formation of K2Ca2(SO4)(3).

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

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

  • 125. Qin, Danfeng
    et al.
    Xu, Ruiyu
    Shen, Hangjia
    Mamat, Xamxikamar
    Wang, Le
    Gao, Shanshuang
    Wang, Ying
    Yalikun, Nuerbiya
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Shiguo
    Yuan, Qunhui
    Li, Yongtao
    Hu, Guangzhi
    Protic salt-based nitrogen-doped mesoporous carbon for simultaneous electrochemical detection of Cd(II) and Pb(II)2017In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 59, p. 36929-36934Article in journal (Refereed)
    Abstract [en]

    Nitrogen-doped mesoporous carbon (NMC) derived from a single small-molecule protic salt (p-phenylenediamine bisulfate) is used for sensing toxic heavy metal ions. Using Nafion, bismuth and NMC to anchor the glassy carbon electrode surface, the fabricate electrode shows high sensitivity for detecting Cd(II) and Pb(II). The limits of detection (S/N = 3) are estimated to be 0.3 mu g L-1 for Cd(II) and 0.4 mu g L-1 for Pb(II), respectively, which are 10 and 25 times lower than the maximum acceptable content for drinking water recommended by the WHO. Furthermore, the sensor is successfully used to analyze Cd(II) and Pb(II) in tap-water with high anti-interference capability and good recovery.

  • 126.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Fagerström, Jonathan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Steinvall, Erik
    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.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Florian, Schmidt
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Real-time In-Situ Detection of Potassium Release during Combustion of Pelletized Biomass using Tunable Diode Laser Absorption Spectroscopy2014In: Impacts of Fuel Quality on Power Production October 26 –31, 2014, Snowbird, Utah, USA, 2014, p. 1-14Conference paper (Other academic)
    Abstract [en]

    Tunable diode laser absorption spectroscopy (TDLAS) was used for quantitative in-situ detection of gaseous elemental potassium (K) at distances 2-11 mm above biomass pellets combusted in a macro-thermogravimetric analyzer (macro-TGA). Single pellets of energy wood (EW) and wheat straw (WS) were converted in air at a furnace temperature of 850 °C and a carrier flow rate of 15 liters per minute. A second TDLAS system measured water vapor concentration and temperature above the pellets. In addition, semi-time-resolved K release data was obtained from conventional ICP-MS/AES analysis of fuel/ash residues collected at several occasions during devolatilization and char combustion. It was found that the fuels differ with respect to relative K-release and temporal release histories. Significant concentrations of K(g) were detected with TDLAS above the pellets during devolatilization, but no K(g) was observed during char combustion, independent of the fuel type. The amount of K(g)tot measured above the pellets during devolatilization was larger for EW than for WS, even though the total K content of WS was a factor of 60 higher. By combining TDLAS and ICP data, and supported by equilibrium calculations, these results indicate that, during devocalization, K is mainly released as KCl from wheat straw, whereas both KCl and KOH are released from energy wood.

  • 127.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Energy Engineering, Department of Engineering Sciences & Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Wagner, David R.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Distribution of temperature, H2O and atomic potassium during entrained flow biomass combustion: coupling in situ TDLAS with modeling approaches and ash chemistry2018In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 188, p. 488-497Article in journal (Refereed)
    Abstract [en]

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

  • 128.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Skoglund, Nils
    Wagner, David R.
    Broström, Markus
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Investigation of H2O, temperature and potassium in entrained flow biomass combustion – coupling in situ TDLAS with modelling2017In: Nordic Flame Days 2017, 10-11 October, Stockholm, 2017Conference paper (Refereed)
  • 129.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wagner, David R.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    TDLAS-based in situ detection of atomic potassium during combustion of biomass in an entrained flow reactor2016Conference paper (Other academic)
  • 130.
    Rebbling, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Näzelius, Ida-Linn
    Piotrowska, Patrycja
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ohman, Marcus
    Waste Gypsum Board and Ash-Related Problems during Combustion of Biomass. 2. Fixed Bed2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 12, p. 10705-10713Article in journal (Refereed)
    Abstract [en]

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

  • 131.
    Reyes Forsberg, Diana Carolina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Experimental study of alkalinisation of cellulose in industrial relevant conditions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Mercerisation of cellulose pulp with a solution of NaOH is the first step of manufacturing cellulose-based value-added products, e.g. viscose fibres and cellulose ethers. During this process, cellulose transforms into a swollen crystalline structure, alkali cellulose (Na-Cell). This increases the reactivity of the cellulose and makes it more accessible for reagents to penetrate and react with the hydroxyl groups. The mercerisation conditions are known to affect the degree of alkalinisation of cellulose as well as the final products. The main objective of this thesis is to investigate how the alkalinisation of softwood sulphite dissolving cellulose pulp is influenced by the co-variation of process variables in the mercerisation in industrial relevant conditions, for both viscose and cellulose ether production. This objective was achieved by quantitative analysis of the effect of simultaneous variation of a set of key parameters on the degree of alkalinisation (i.e. degree of activation, DoA) of the chosen dissolving pulp. Quantitative measurements were performed using Raman spectroscopy data, evaluated by partial least squares (PLS) regression. For mercerisation at viscose production conditions, the effect of studied variables on mass yield was also considered. In the case of mercerisation at ether processing conditions, formation of alkali cellulose at a fixed temperature was included. The knowledge obtained on mercerisation under ether processing conditions was then applied for preparation of the ionic cellulose ether carboxymethylcellulose (CMC).

    The overall results show that temperature has a strong effect on DoA and mass yield for mercerised samples under steeping conditions. Measured DoA decreases as the temperature increases from 20 to 70 °C. Mass yield correlates positively with the temperature up to 45-50 °C in the PLS model, after which the relation is negative. The [NaOH] and reaction time show a complex dependence of other variables. At mercerisation conditions for cellulose ether production, the NaOH/AGU stoichiometric ratio, denoted as (r), shows to be very important for DoA, with a positive correlation. At these mercerisation conditions, temperature shows no effect on DoA. The influence of the [NaOH] (which also refers to the concentration of water) shows a complex dependence on (r). As (r) increases and [NaOH] decreases, the measured DoA increases. Prolonged mercerisation time shows no significance in the modelled DoA. However, a gradual increase of the DoA over time was seen when mercerisation was performed with 30% and 40% [NaOH] at (r) = 0.8, suggesting a slow diffusion of NaOH and Na-Cell formation. 13C CP-MAS NMR measurements of samples produced at room temperature show that formation of the Na-Cell allomorph is mainly determined by the [NaOH]. However, in the transition area between Na-Cell I and Na-Cell II, (r) also seems to be of importance.  An increase of DS in the produced CMC samples also shows to be consistent at such conditions with the increase in the measured DoA and with increased (r) and decreased [NaOH]. However, these conditions also favour the formation of by-products. In the synthesised CMC samples, a DS of up to 0.7 was achieved. Measured solubility was lower than expected for any given DS. This, along with the non-statistical distribution of monomer units in the polymer chains, indicates high heterogeneity in the synthesised samples. The distribution of substituents within the AGU shows attachment to hydroxyl oxygens in the order O3 < O2 ≈ O6. The relative importance of the substitution at O3 indicates an increase at this position when [NaOH] increases.

    The models presented in this thesis will hopefully serve as a basis for predicting the effects of the studied variables on the DoA, as well as on the mass yield of cellulose pulp when mercerisation conditions are adjusted. Moreover, it is believed that the presented studies can give a better understanding of mercerisation at cellulose ether conditions, hence enabling further development of this process step.

  • 132. 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.

  • 133. Rissler, Jenny
    et al.
    Swietlicki, Erik
    Bengtsson, Agneta
    Boman, Christoffer
    Pagels, Joakim
    Sandström, Thomas
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Pulmonary Medicine.
    Blomberg, Anders
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Pulmonary Medicine.
    Löndahl, Jakob
    Experimental determination of deposition of diesel exhaust particles in the human respiratory tract2012In: Journal of Aerosol Science, ISSN 0021-8502, E-ISSN 1879-1964, Vol. 48, p. 18-33Article in journal (Refereed)
    Abstract [en]

    Diesel emissions are a major contributor to combustion-generated airborne ambient particles. To understand the role of diesel particulate emissions on health effects, it is important to predict the actual particulate dose deposited in the human respiratory tract, with respect to number, surface area and mass. This is complicated by the agglomerate nature of some of these particles. In this study the respiratory tract deposition fraction in the size range 10-500 nm, was determined for 10 healthy volunteers during both idling and transient engine running conditions of a heavy duty diesel engine. The aerosol was characterized with respect to both chemical and physical properties including size resolved particle effective density. The dominating part of the emitted particles had an agglomerate structure. For those formed during transient running conditions, the relationship between particle mass and mobility diameter could be described by a power law function. This was not the case during idling, most likely because of volatile compounds condensing on the agglomerates. The respiratory tract particle deposition revealed large intra-subject variability with some subjects receiving a dose that was twice as high as that of others, when exposed to the same particle concentration. Associations were found between total deposited fractions (TDF), and breathing pattern. There was a difference between the idling and transient cycle with TDF being higher with respect to number during idling. The measured size-dependent deposition fraction of the agglomerated exhaust particles from both running conditions was nearly identical and closely resembled that of spherical hydrophobic particles, if plotted as a function of mobility diameter. Thus, for the size range covered, the mobility diameter could well describe the diameter-dependent particle respiratory tract deposition probability, regardless of the agglomeration state of the particles. Whilst mobility diameter well describes the deposition fraction, more information about particle characteristics is needed to convert this to volume equivalent diameter or estimate dose with respect to surface area or mass. A methodology is presented and applied to calculate deposited dose by surface area and mass of agglomerated particles. The methodology may be useful in similar studies estimating dose to the lung, deposition onto cell cultures and in animal studies. (C) 2012 Elsevier Ltd. All rights reserved.

  • 134.
    Romão, Inês
    et al.
    Åbo Akademi University, Dept. of Chemical Engineering.
    Eriksson, Matias
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nduagu, Experience
    Åbo Akademi University, Dept. of Chemical Engineering.
    Fagerlund, Johan
    Åbo Akademi University, Dept. of Chemical Engineering.
    Gando-Ferreira, Licínio
    University of Coimbra, Dept. of Chemical Engineering.
    Zevenhoven, Ron
    Åbo Akademi University, Dept. of Chemical Engineering.
    Carbon dioxide storage by mineralisation applied to a lime kiln2012In: PROCEEDINGS OF ECOS 2012 / [ed] Enrico Sciubba, Giampaolo Manfrida, Umberto Desideri, Firenze: Firenze University Press, 2012, Vol. VI, p. 226-1-226-13Conference paper (Refereed)
    Abstract [en]

    This paper describes a design, for a pilot-scale application, of a two-staged process that is under study at Åbo Akademi University (ÅA), for Carbon dioxide Storage by Mineralisation (CSM). The ÅA route implies the production of brucite (besides Ca- and Fe- based by-products) from a magnesium/calcium silicate rock, using recoverable ammonium sulphate (AS), followed by carbonation of the Mg(OH)2 in a pressurised fluidised bed at ~ 500°C, 20-30 bar CO2 partial pressure. An assessment is reported for operating the CSM process on waste heat from a limekiln (lime production: 210 t/day) in Pargas, Southwest Finland, i.e. without external energy input apart from what is needed for crushing the rock to the required particle size (a few % of the overall CSM process energy requirement) and compressing the flue gas to be treated. Part of the off-gas from the limekiln (CO2 content ~21%-vol) will be processed without a CO2 separation step. The feature of operating without CO2 separation makes CSM an attractive and cost-competitive option when compared to conventional CCS involving underground storage of CO2. An exergy analysis is used to optimise process layout and energy efficiency, and at the same time maximise the amount of CO2 that can be bound to MgCO3 given the amount of waste heat available from the kiln. Also, experimental results are reported for producing Mg(OH)2 (and Fe,Ca(OH)2) from local rock material.

  • 135. 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.

  • 136.
    Rönnbäck, Marie
    et al.
    SP Sveriges Tekniska Forskningsinstitut.
    Gustavsson, Lennart
    SP Sveriges Tekniska Forskningsinstitut.
    Hermansson, Sven
    SP Sveriges Tekniska Forskningsinstitut.
    Skoglund, Nils
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Fagerström, Jonathan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Backman, Rainer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Näzelius, Ida-Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Förbränningskaraktärisering och förbränningsteknisk utvärdering av olika pelletsbränslen - syntes av projektet2011Report (Other academic)
  • 137. Salmi, Tapio O
    et al.
    Wärnå, Johan P
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Chemical reaction engineering and reactor technology2010Book (Other academic)
    Abstract [en]

    A Systematic Development of the Chemical Reaction Engineering Concept. The role of the chemical reactor is crucial for the industrial conversion of raw materials into products and numerous factors must be considered when selecting an appropriate and efficientchemical reactor. Chemical Reaction Engineering and Reactor Technology defines the qualitative aspects that affect the selection of an industrial chemical reactor and couples various reactor models to case-specific kinetic expressions for chemical processes. Offering a systematic development of the chemical reaction engineering concept, this volume explores:• essential stoichiometric, kinetic, and thermodynamic terms needed in the analysis of chemical reactors• homogeneous and heterogeneous reactors• residence time distributions and non-ideal flow conditions in industrial reactors• solutions of algebraic and ordinary differential equation systems• gas- and liquid-phase diffusion coefficients and gas-filmcoefficients• correlations for gas-liquid systems• solubilities of gases in liquids• guidelines for laboratory reactors and the estimation of kinetic parameters. The authors pay special attention to the exact formulations and derivations of mass energy balances and their numerical solutions. Richly illustrated and containing exercises and solutions covering a number of processes, from oil refining to the development of specialty and fine chemicals, the text provides a clear understanding of chemical reactor analysis and design.

  • 138. Salminen, Eero
    et al.
    Rujana, Luis
    Mäki-Arvela, Päivi
    Virtanen, Pasi
    Salmi, Tapio
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Åbo Akademi University, Department of Chemical Engineering, Process Chemistry Centre, Industrial Chemistry & Reaction Engineering, Åbo, Finland.
    Biomass to value added chemicals: Isomerisation of β-pinene oxide over supported ionic liquid catalysts (SILCAs) containing Lewis acids2015In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 257, p. 318-321Article in journal (Refereed)
    Abstract [en]

    The isomerisation of β-pinene oxide was studied over supported ionic liquid catalysts (SILCAs) consisting of Lewis acids in immobilized ionic liquid. SILCAs were demonstrated as efficient catalysts for the transformation of β-pinene oxide to myrtanal with the product distribution and activity being depend-ent on the nature of the ionic liquid and Lewis acid strength of catalytic species. With the catalystZnCl2/[N(3-OH-Pr)Py][NTf2]/ACC, the highest myrtanal molar yield obtained was 68%.

  • 139. Salminen, Eero
    et al.
    Virtanen, Pasi
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Åbo-Turku, Finland.
    Alkaline ionic liquids applied in supported ionic liquid catalyst for selective hydrogenation of citral to citronellal2014In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 2, article id 3Article in journal (Refereed)
    Abstract [en]

    The challenge in preparation of ionic liquids containing a strong alkaline anion is to identify a suitable cation which can tolerate the harsh conditions induced by the anion. In this study, a commercial quaternary ammonium compound (quat) benzalkonium [ADBA] (alkyldimethylbenzylammonium) was used as a cation in the synthesis of different alkaline ionic liquids. In fact, the precursor, benzalkonium chloride, is a mixture of alkyldimethylbenzylammonium chlorides of various alkyl chain lengths and is commonly used in the formulation of various antiseptic products. The prepared ionic liquids were utilized as Supported Ionic Liquid Catalysts (SILCAs). Typically, a SILCA contains metal nanoparticles, enzymes, or metal complexes in an ionic liquid layer which is immobilized on a solid carrier material such as an active carbon cloth (ACC). The catalysts were applied in the selective hydrogenation of citral to citronellal which is an important perfumery chemical. Interestingly, 70% molar yield toward citronellal was achieved over a catalyst containing the alkaline ionic liquid benzalkonium methoxide.

  • 140.
    Sandström, Karin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Weidemann, Eva
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Fluorine reactions in MSW combustion2019In: EUBCE 2019, 2019Conference paper (Other academic)
    Abstract [en]

    Fluorine is of increasing concern in waste combustion since fluorinated plastics constitute anincreasing share of waste fractions entering CHP plants. Alkali fluorides could potentially causesimilar problems as are well known for the corresponding chlorides. However, there are somefundamental differences in thermodynamic stabilities. Available literature essentially lacks theexperimental evidence needed to draw any further conclusions on the extent of any fluorine relatedproblems, but recently a MSW fired CHP reported alarming deposit growth rates, possibly relatedto a delivery of fluorine containing fuels. The objective of the present study was to experimentallyevaluate some of the thermodynamic considerations mentioned. Fuels were prepared by addingNaCl, NaF and S to softwood pellets. Deposit and aerosol samples were analyzed with SEM-EDSand XRD, and evaluated together with fundamental thermodynamic phase equilibriumconsiderations to provide new and important information on the ash forming reactions and theirimplications. The results from the combustion tests showed that the fluorine found on the depositprobe was in form of NaF and Na3F(SO4) in qualitative agreement with thermodynamicequilibrium calculations.

  • 141.
    Sandström, Karin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Eriksson, Matias
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Nordkalk AB.
    Estimating ash properties for new fuels in calcination kilns2019Conference paper (Other academic)
  • 142.
    Sandström, Karin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Weidemann, Eva
    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.
    Fluorides in Deposits2018Conference paper (Other academic)
  • 143.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Innovations in nanomaterials for proton exchange membrane fuel cells2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hydrogen technologies are rapidly receiving increased attention as it offers a renewable energy alternative to the current petroleum-based fuel infrastructure, considering that continued large-scale use of such fossil fuels will lead to disastrous impacts on our environment. The proton exchange membrane fuel cell should play a significant role in a hydrogen economy since it enables convenient and direct conversion of hydrogen into electricity, thus allowing the use of hydrogen in applications particularly suited for the transportation industry. To fully realize this, multiple engineering challenges as well as development of advanced nanomaterials must however be addressed.

    In this thesis, we present discoveries of new innovative nanomaterials for proton exchange membrane fuel cells by targeting the entire membrane electrode assembly. Conceptually, we first propose new fabrication techniques of gas diffusion electrodes based on helical carbon nanofibers, where an enhanced three-phase boundary was noted in particular for hierarchical structures. The cathode catalyst, responsible for facilitating the sluggish oxygen reduction reaction, was further improved by the synthesis of platinum-based nanoparticles with an incorporated secondary metal (iron, yttrium and cobalt). Here, both solvothermal and high-temperature microwave syntheses were employed. Catalytic activities were improved compared to pure platinum and could be attributed to favorably shifted oxygen adsorption energies as a result of successful incorporation of the non-precious metal. As best exemplified by platinum-iron nanoparticles, the oxygen reduction reaction was highly sensitive to both metal composition and the type of crystal structure. Finally, a proton exchange membrane based on fluorine and sulfonic acid functionalized graphene oxide was prepared and tested in hydrogen fuel cell conditions, showing improvements such as lowered hydrogen permeation and better structural stability. Consequently, we have demonstrated that there is room for improvement of multiple components, suggesting that more powerful fuel cells can likely be anticipated in the future.

  • 144.
    Sandström, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Annamalai, Alagappan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Boulanger, Nicolas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ekspong, Joakim
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mühlbacher, Inge
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Evaluation of Fluorine and Sulfonic Acid Co-functionalized Graphene Oxide Membranes in Hydrogen Proton Exchange Membrane Fuel Cell Conditions2019In: Sustainable Energy & Fuels, ISSN 2398-4902, Vol. 3, no 7, p. 1790-1798Article in journal (Refereed)
    Abstract [en]

    The use of graphene oxide (GO) based membranes consisting of self-assembled flakes with a lamellar structure represents an intriguing strategy to spatially separate reactants while facilitating proton transport in proton exchange membranes (PEM). Here we chemically modify GO to evaluate the role of fluorine and sulfonic acid groups on the performance of H2/O2 based PEM fuel cells. Mild fluorination is achieved by the presence of hydrogen fluoride during oxidation and subsequent sulfonation resulted in fluorine and SO3- co-functionalized GO. Membrane electrode assembly performance in low temperature and moderate humidity conditions suggested that both functional groups contribute to reduced H2 crossover compared to appropriate reference membranes. Moreover, fluorine groups promoted an enhanced hydrolytic stability while contributing to prevent structural degradation after constant potential experiments whereas sulfonic acid demonstrated a stabilizing effect by preserving proton conductivity.

  • 145. Schoen, Claudia
    et al.
    Hartmann, Hans
    Schwabl, Manuel
    Feldmeier, Sabine
    Dahl, Jonas
    Rathbauer, Josef
    Vega, Daniel
    Boman, Christoffer
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Oehman, Marcus
    New evaluation strategies regarding slag prediction in pellet boilers2014In: Papers of the 22nd european biomass conference: setting the course for a biobased economy, 2014, p. 368-372Conference paper (Refereed)
    Abstract [en]

    Pellet boilers are widely used for heat production. In most cases only wood pellets with low ash content are suitable for these appliances due to the increased risk of slagging. The ash fusion test (AFT) is the only standardized method currently available for the prediction of slagging but it frequently failed when solid biofuels were investigated. Therefore different laboratory methods for the prediction of slagging were applied in order to identify the most suitable method for reliable prediction of slagging tendencies. Three laboratory test methods were considered in this investigation: a rapid slag test (1), the so-called "CIEMAT method" (2) and the "slag analyser" (3). The suitability of the obtained results was validated by practical combustion tests in up to nine different pellet boilers. As the most promising method the slag analyser was identified. It will be further developed with the aim to be proposing as an additional standard method for determination of slag related problems in fixed bed combustion systems.

  • 146. 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.

  • 147.
    Sharifi, Tiva
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kwong, Wai Ling
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Berends, Hans-Martin
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Maghemite nanorods anchored on a 3D nitrogen-doped carbon nanotubes substrate as scalable direct electrode for water oxidation2016In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 1, p. 69-78Article in journal (Refereed)
    Abstract [en]

    A hybrid catalyst 3D electrode for electrochemical water oxidation to molecular oxygen is presented. The electrode comprises needle shaped maghemite nanorods firmly anchored to nitrogen doped carbon nanotubes, which in turn are grown on a conducting carbon paper that acts as efficient current collector. In 0.1 M KOH this hybrid electrode reaches a current density of 1 mA/cm(2) (geometric surface) at an overpotential of 362 mV performing high chronoamperometric stability. The electrochemical attributes point toward efficient catalytic processes at the surface of the maghemite nanorods, and demonstrate a very high surface area of the 3D electrode, as well as a firm anchoring of each active component enabling an efficient charge transport from the surface of the maghemite rods to the carbon paper current collector. The latter property also explains the good stability of our hybrid electrode compared to transition metal oxides deposited on conducting support such as fluorine doped tin oxide. These results introduce maghemite as efficient, stable and earth abundant oxygen evolution reaction catalyst, and provide insight into key issues for obtaining practical electrodes for oxygen evolution reaction, which are compatible with large scale production processes. 

  • 148. Shen, Gulou
    et al.
    Held, Christoph
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry & Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Biskopsgatan 8, 20500 Åbo-Turku, Finland.
    Lu, Xiaohua
    Ji, Xiaoyan
    Modeling the Viscosity of Ionic Liquids with the Electrolyte Perturbed-Chain Statistical Association Fluid Theory2014In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, no 52, p. 20258-20268Article in journal (Refereed)
    Abstract [en]

    In this work, the friction theory (FT) and free volume theory (FVT) were combined with the electrolyte perturbed-chain statistical association fluid theory (ePC-SAFT) in order to model the viscosity of pure ionic liquids (ILs) and IL/CO2 mixtures in a wide temperature and pressure (up to 3000 bar) range and with viscosities up to 4000 mPa center dot s. The ePC-SAFT pure-component parameters for the considered imidazolium-based ILs were adopted from our previous work. These parameters were used to calculate the density and residual pressure of the pure ILs. The density and pressure were then used as inputs for pure-IL viscosity modeling using FVT or FT, respectively. The viscosity-model parameters of FT and FVT were obtained by fitting to experimental viscosity data of imidazolium-based ILs and linearized with the molecular weight of the IL-cation. As a result, the FT viscosity model can more accurately describe the experimental viscosity data of pure ILs than the FVT model, at the cost of an increased number of parameters used in the FT viscosity model. Finally, FT and FVT were applied to model the viscosities of IL/CO2 mixtures in good agreement to experimental data by adjusting one binary viscosity-model parameter between the IL-anion and CO2. The application of FT required fitting the viscosity model parameters of pure ILs to experimental viscosity data of pure ILs and of IL/CO2 mixtures. In contrast, the FVT viscosity model parameters were adjusted to the experimental viscosity data of pure ILs only.

  • 149. Shen, Hangjia
    et al.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Le
    Qin, Danfeng
    Gao, Sanshuang
    Mamat, Xamxikamar
    Ren, Wei
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Chinese Acad Sci, Xinjiang Tech Inst Phys & Chem, Urumqi 830011, Peoples R China.
    Microwave-assisted synthesis of multimetal oxygen-evolving catalysts2017In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 81, p. 116-119Article in journal (Refereed)
    Abstract [en]

    Oxygen evolution reaction (OER) plays a pivotal role in water-splitting. Here, we report a facile method to synthesize multimetal supported on commercial carbon black via a time-saving microwave process. Crystalline FeNi3 nanoparticles homogeneously doped with Mo are formed via a microwave treatment and activated to metal oxyhydroxide in-situ during cyclic voltammetry test with overpotential of only 280 mV at 10 mA cm(-2) for OER in alkaline electrolyte, outperforming RuO2. Our synthesis methodology is a promising alternative for large-scale production, delivering a valuable contribution to catalyst preparation and electrocatalytic water oxidation research.

  • 150.
    Skoglund, Nils
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics, Energy Technology and Thermal Process Chemistry.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Återvinning av fosfor och energi ur avloppsslam genom termiskbehandling i fluidiserad bädd: Utvärdering och optimering av prestandaför slutprodukten2012Report (Other academic)
    Abstract [en]

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

12345 101 - 150 of 209
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf