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  • 1.
    Boman, Christoffer
    et al.
    Umeå university.
    Nordin, Anders
    Umeå university.
    Boström, Dan
    Umeå university.
    Öhman, Marcus
    Characterization of inorganic particulate matter from residential combustion of pelletized biomass fuels2004In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 18, no 2, p. 338-348Article in journal (Refereed)
    Abstract [en]

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

  • 2.
    Boman, Christoffer
    et al.
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Pettersson, Esbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerholm, Roger
    Analytical Chemistry, Arrhenius Laboratory, Stockholm University.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Nordin, Anders
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Stove performance and emission characteristics in residential wood log and pellet combustion: Part 1: Pellet stoves2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 1, p. 307-314Article in journal (Refereed)
    Abstract [en]

    Stove performance, characteristics and quantities of gaseous and particulate emissions were determined for two different pellet stoves, varying fuel load, pellet diameter and chimney draught. This approach aimed at covering variations in emissions from stoves in use today. The extensive measurement campaign included CO, NOx, organic gaseous carbon, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions and inorganic composition. At high load, most emissions were similar. For stove B, operating at high residual oxygen and solely with primary air, the emissions of PMtot and particle numbers were higher while the particles were smaller. Lowering the fuel load, the emissions of CO and hydrocarbons increased dramatically for stove A, which operated continuously also at lower fuel loads. On the other hand for stove B, which had intermittent operation at lower fuel loads, the emissions of hydrocarbons increased only slightly lowering the fuel load, while CO emissions increased sharply, due to high emissions at the end of the combustion cycle. Beside methane, dominating VOCs were ethene, acetylene and benzene and the emissions of VOC varied in the range 1.1-47 mg/MJfuel. PAH emissions (2-340 µg/MJfuel) were generally dominated by phenantrene, fluoranthene and pyrene. PMtot (15-45 mg/MJfuel) were in all cases dominated by fine particles with mass median diameters in the range 100-200 nm, peak mobility diameters of 50-85 nm and number concentrations in the range 4×1013- 3×1014 particles/MJfuel. During high load conditions the particulate matter was totally dominated by inorganic particles at 15-25 mg/MJfuel consisting of potassium, sodium, sulfur and chlorine, in the form of K2SO4, K3Na(SO4)2 and KCl. The study shows that differences in operation and modulation principles for the tested pellet stoves, relevant for appliances in use today, will affect the performance and emissions significantly, although with lower scattering in the present study compared to compiled literature data.

  • 3.
    Boman, Christoffer
    et al.
    Umeå university.
    Öhman, Marcus
    Nordin, Anders
    Umeå university.
    Trace element enrichment and behavior in wood pellet production and combustion processes2006In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 20, no 3, p. 993-1000Article in journal (Refereed)
    Abstract [en]

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

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

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

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

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

  • 6.
    Boström, Dan
    et al.
    Umeå universitet.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå universitet.
    Boman, Christoffer
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Broström, Markus
    Umeå universitet.
    Backman, Rainer
    Umeå universitet.
    Ash transformation chemistry during combustion of biomass2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 1, p. 85-93Article in journal (Refereed)
    Abstract [en]

    There is relatively extensive knowledge available concerning ash transformation reactions during combustion of woody biomass. In recent decades, the use of these energy carriers has increased, from a low-technology residential small-scale level to an industrial scale. Along this evolution, ash chemical-related phenomena for woody biomass have been observed and studied. Therefore, presently the understanding for these are, if not complete, fairly good. However, because the demand for CO2-neutral energy resources has increased recently and will continue to increase in the foreseeable future, other biomasses, such as, for instance, agricultural crops, have become highly interesting. The ash-forming matter in agricultural biomass is rather different in comparison to woody biomass, with a higher content of phosphorus as a distinctive feature. The knowledge about the ash transformation behavior in these systems is far from complete. Here, an attempt to give a schematic but general description of the ash transformation reactions of biomass fuels is presented in terms of a conceptual model, with the intention to provide guidance in the understanding of ash matter behavior in the use of any biomass fuel, primarily from the knowledge of the concentrations of ash-forming elements. The model was organized in primary and secondary reactions. Restrictions on the theoretical model in terms of reactivity limitations and physical conditions of the conversion process were discussed and exemplified, and some principal differences between biomass ashes dominated by Si and P, separately, were outlined and discussed.

  • 7.
    Brus, Elisabet
    et al.
    Umeå university.
    Öhman, Marcus
    Nordin, Anders
    Umeå university.
    Mechanisms of bed agglomeration during fluidized-bed combustion of biomass fuels2005In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 19, no 3, p. 825-832Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Brus, Elisabet
    et al.
    Umeå university.
    Öhman, Marcus
    Nordin, Anders
    Umeå university.
    Boström, Dan
    Umeå university.
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Eklund, Anders
    ÅF Energi & Miljö AB.
    Bed agglomeration characteristics of biomass fuels using blast-furnace slag as bed material2004In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 18, no 4, p. 1187-1193Article in journal (Refereed)
    Abstract [en]

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

  • 9.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Iisa, Kristiina
    National Renewable Energy Laboratory.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Computational fluid dynamics simulations of raw gas composition from a black liquor gasifier: comparison with experiments2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 9, p. 4122-4128Article in journal (Refereed)
    Abstract [en]

    Pressurized entrained flow high temperature black liquor gasification can be used as a complement or a substitute to the Tomlinson boiler used in the chemical recovery process at kraft pulp mills. The technology has been proven on the development scale, but there are still no full scale plants. This work is intended to aid in the development by providing computational tools that can be used in scale up of the existing technology. In this work, an existing computational fluid dynamics (CFD) model describing the gasification reactor is refined. First, one-dimensional (1D) plug flow reactor calculations with a comprehensive reaction mechanism are performed to judge the validity of the global homogeneous reaction mechanism used in the CFD simulations in the temperature range considered. On the basis of the results from the comparison, an extinction temperature modification of the steam-methane reforming reaction was introduced in the CFD model. An extinction temperature of 1400 K was determined to give the best overall agreement between the two models. Next, the results from simulations of the flow in a 3 MW pilot gasifier with the updated CFD model are compared to experimental results in which pressure, oxygen to black liquor equivalence ratio, and residence time have been varied. The results show that the updated CFD model can predict the main gas components (H2, CO, CO2) within an absolute error of 2.5 mol %. CH4 can be predicted within an absolute error of 1 mol %, and most of the trends when process conditions are varied are captured by the model.

  • 10.
    Carlsson, Per
    et al.
    Energy Technology Centre, Piteå.
    Ma, Charlie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Molinder, Roger
    Energy Technology Centre, Piteå.
    Weiland, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Wiinikka, Henrik
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Energy Technology Centre, Piteå.
    Slag Formation During Oxygen Blown Entrained-Flow Gasification of Stem Wood2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 11, p. 6941−6952-, article id 28Article in journal (Refereed)
    Abstract [en]

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

  • 11.
    Dai, B.
    et al.
    China Rural Technology Development Center, Beijing, China.
    Zhu, W.
    Department of Pharmaceutical Engineering, China Pharmaceutical University, Nanjing, Jiangsu, China.
    Mu, Liwen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Guo, X.
    Ministry of Education Key Laboratory of Resource Chemistry, Shanghai Key Laboratory of Rare Earth Functional Materials, Department of Chemistry and Chemical Engineering, Shanghai Normal University, Shanghai, China .
    Qian, H.
    Department of Pharmaceutical Engineering, China Pharmaceutical University, Nanjing, Jiangsu, China.
    Liang, X.
    Department of Chemical and Biochemical Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
    Kontogeorgis, G.M.
    Department of Chemical and Biochemical Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
    Effect of the composition of biomass on the quality of syngas produced from thermochemical conversion based on thermochemical data prediction2019In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 6, p. 5253-5262Article in journal (Refereed)
    Abstract [en]

    Syngas produced from thermochemical conversion of biomass has been given more attention because it can be converted to a variety of fuels and chemicals as substitutes for petroleum-based chemicals via the Fischer–Tropsch process. In this study, one wheat straw and its element content fluctuation in the feasible range are selected as samples first to study the effect of the biomass composition on the quality of syngas produced. Then, the thermochemical data (standard molar enthalpy of formation, standard molar entropy, and heat capacity) of samples are predicted by highly accurate prediction models. Thermochemical conversions of the samples are simulated by the Gibbs energy minimization method based on the results of thermochemical data prediction. At last, the effect of the biomass composition on the resource index (amounts of CO and H2 and ratio of H2/CO) and energy index (lower heat value) of syngas is calculated and analyzed. This study provides a method to obtain the relationship between the composition of biomass and the quality of syngas produced.

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

    A future shortage of biomass fuel can be foreseen. The production of rapeseed oil for a number of purposes is increasing, among others, for biodiesel production. A byproduct from the oil extraction process is rapeseed meal (RM), presently used as animal feed. Further increases in supply will make fuel use an option. Several energy companies have shown interest but have been cautious because of the scarcity of data on fuel properties, which led to the present study. Combustion-relevant properties of RM from several producers have been determined. The volatile fraction (74 ± 0.06%wtds) is comparable to wood; the moisture content (6.2−11.8%wt) is low; and the ash content (7.41 ± 0.286%wtds) is high compared to most other biomass fuels. The lower heating value is 18.2 ± 0.3 MJ/kg (dry basis). In comparison to other biomass fuels, the chlorine content is low (0.02−0.05%wtds) and the sulfur content is high (0.67−0.74%wtds). RM has high contents of nitrogen (5.0−6.4%wtds), phosphorus (1.12−1.23%wtds), and potassium (1.2−1.4%wtds). Fuel-specific combustion properties of typical RM were determined through combustion tests, with an emphasis on gas emissions, ash formation, and potential ash-related operational problems. Softwood bark was chosen as a suitable and representative co-combustion (woody) fuel. RM was added to the bark at two levels: 10 and 30%wtds. These mixtures were pelletized, and so was RM without bark (for durability mixed with cutter shavings, contributing 1%wt of the ash). Each of these fuels was combusted in a 5 kW fluidized bed and an underfed pellet burner (to simulate grate combustion). Pure RM was combusted in a powder burner. Emissions of NO and SO2 were high for all combustion tests, requiring applications with flue gas cleaning, economically viable only at large scale. Emissions of HCl were relatively low. Temperatures for initial bed agglomeration in the fluidized-bed tests were high for RM compared to many other agricultural fuels, thereby indicating that RM could be an attractive fuel from a bed agglomeration point of view. The results of grate combustion suggest that slagging is not likely to be severe for RM, pure or mixed with other fuels. Fine-mode particles from fluidized-bed combustion and grate combustion mainly contained sulfates of potassium, suggesting that the risk of problems caused by deposit formation should be moderate. The chlorine concentration of the particles was reduced when RM was added to bark, potentially lowering the risk of high-temperature corrosion. Particle emissions from powder combustion of RM were 17 times higher than for wood powder, and the fine-mode fraction contained mainly K-phosphates known to cause deposits, suggesting that powder combustion of RM should be used with caution. A possible use of RM is as a sulfur-containing additive to biomass fuels rich in Cl and K for avoiding ash-related operational problems in fluidized beds and grate combustors originated from high KCl concentrations in the flue gases.

  • 13.
    Fagerström, Jonathan
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Näzelius, Ida-Linn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gilbe, Carl
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå University. Department of Applied Physics and Electronics.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boman, Christoffer
    Umeå University. Department of Applied Physics and Electronics.
    Influence of peat ash composition on particle emissions and slag formation in biomass grate co-combustion2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 5, p. 3403-3411Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Faust, Robin
    et al.
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Hannl, Thomas Karl
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Berdugo Vilches, Teresa
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Kuba, Matthias
    Bioenergy2020+ GmbH, Güssing, Austria.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Seemann, Martin
    Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden.
    Knutsson, Pavleta
    Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden.
    Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood. 1. K-Feldspar2019In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 8, p. 7321-7332Article in journal (Refereed)
    Abstract [en]

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

  • 15.
    Furusjö, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Stare, Ragnar
    Chemrec AB, Stockholm.
    Landälv, Ingvar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Löwnertz, Patrik
    Chemrec AB, Stockholm.
    Pilot Scale Gasification of Spent Cooking Liquor from Sodium Sulfite Based Delignification2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 12, p. 7517-7526Article in journal (Refereed)
    Abstract [en]

    This paper describes a pilot scale high pressure entrained flow gasification experiment with spent cooking liquor from a sodium sulfite based delignification process in the DP-1 black liquor gasifier in Piteå, Sweden. Approximately 92 tons of sulfite thick liquor were gasified during 100 h of operation without any operational problems despite the new feedstock. The syngas quality was found to be good for all operating points with the CH4 content below 0.3% and H2/CO ratio between 1.03 and 1.15. The experiment shows that the process capacity is limited by green liquor quality parameters primarily dependent on the presence of small amounts of unconverted carbon. The pilot plant capacity was found to be somewhat lower than for Kraft black liquor on mass basis but higher when measured as thermal load, due to the higher heating value of sulfite thick liquor. Mass and energy balances were made difficult by the unavailability of measured green liquor and syngas flow rates, which lead to the necessity of using alternative approaches for the estimation of these flows. Using these estimates, overall mass and energy balances were closed to within 5% for all operating points except one, and the process cold gas efficiency was 60-68% on sulfur-free lower heating value basis. Carbon balances indicate that 95-97% of feedstock carbon leaves with the syngas, mainly as CO and CO2 with the remainder being mostly green liquor carbonate. More than 95% of the feedstock sodium is found in green liquor, while 3-5% ends up in the gas condensate purge stream. The sulfur balance does not close as well as other elements but indicates that 70-73% of the feedstock sulfur ends up in the syngas as H2S and COS with the remainder being present in green liquor as dissolved sulfide salts.

  • 16.
    Geyter, Sigrid De
    et al.
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Eriksson, Morgan
    Övik Energi.
    Nordin, Anders
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Effects of non-quartz minerals in natural bed sand on agglomeration characteristics during fluidized bed combustion of biomass fuels2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 5, p. 2663-2668Article in journal (Refereed)
    Abstract [en]

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

  • 17. Gilbe, Carl
    et al.
    Lindström, Erica
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Backman, Rainer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Samuelsson, Robert
    Unit for Biomass Technology and Chemistry, Swedish University of Agricultural Sciences.
    Burvall, Jan
    Skellefteå Kraft AB.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Predicting slagging tendencies for biomass pellets fired in residential appliances: a comparison of different prediction methods2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 6, p. 3680-3686Article in journal (Refereed)
    Abstract [en]

    In this paper, a comparison between four different types (both empirical and theoretical) of techniques to predict the slagging tendencies in residential pellet combustion appliances was performed. The four techniques used were the standard ash fusion test (SS ISO-540) used in the Swedish pellet standard (SS 18 71 20), thermal analysis (TGA/DTA), thermochemical model calculations, and a laboratory-scale sintering test. The tests were performed with 12 pelletized biomass raw materials, and the results were compared with measured slagging tendencies in controlled combustion experiments in a commercial under-fed pellet burner (20 kW) installed in a reference boiler. The results showed significant differences in the prediction of slagging tendencies between different predicting techniques and fuels. The method based on thermal analysis (TGA/DTA) of produced slags must be further developed before useful information could be provided of the slagging behavior of different fuels. The used sintering method must also be further improved before the slagging tendency of fuels forming slags extremely rich in silicon (e.g., some grasses) can be predicted. Relatively good agreement was obtained between results from chemical equilibrium calculations and the actual slagging tendencies from the combustion tests. However, the model calculations must be further improved before quantitative results can be used. The results from the standard ash fusion test (SS ISO 540) showed, in general, relatively high deformation temperatures, therefore predicting a less problematic behavior of the fuels in comparison to the actual slagging tendencies obtained from controlled combustion experiments in commercial pellet burner equipment. Nevertheless, the method predicted, in most cases, the same fuel-specific slagging (qualitatively) trends as the corresponding combustion behavior.

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

    Limited availability of sawdust and planer shavings and an increasing demand for biomass pellets in Europe are pushing the market toward other, more problematic raw materials with broader variation in total fuel ash content and composition of the ash forming elements as well as in their slagging tendencies. The main objective in the present work was therefore to determine the influence of fuel-ash composition on residual ash and slag behavior. Twelve different biomass pellets were used: reed canary grass (two different samples), hemp (two different samples), wheat straw, salix, logging residues (two different samples), stem wood (sawdust) as well as spruce, pine, and birch bark. The different pellet qualities were combusted in a commercial under fed pellet burner (20 kW) installed in a reference boiler. Continuous measurements of O2, CO, CO2, HCl, SO2, and total particle matter mass concentrations were determined in the exhaust gas directly after the boiler. The collected slag deposits, the corresponding deposited bottom ash in the boiler and the collected particle matter were characterized with X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray analysis (SEM/EDS). For biomass fuel pellets rich in silicon (either inherent or contaminated with sand) and low content of alkaline earth metals the main part of the potassium reacted with the silicon rich ash-residual, forming sticky alkali-silicate particles, which were not entrained from the burner and thereby giving rise to/initiating slag formation. Silicon rich fuels, i.e. fuels were the ash characteristics were dominated by silicate-alkali chemistry, therefore generally showed relatively high slagging tendencies. Straw fuels have typically this ash composition but exceptions to these general trends exists (e.g., one of the hemp fuels used in this work). Wood derived fuels with a relatively low inherent silicon content therefore showed low or relatively moderate slagging tendencies. However, contamination of sand material to these fuels may greatly enhance the slagging tendencies.

  • 19.
    Grimm, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå universitet.
    Boström, Dan
    Umeå universitet.
    Boman, Christoffer
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Influence of phosphorus on alkali distribution during combustion of logging residues and wheat straw in a bench-scale fluidized bed2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 5, p. 3012-3023Article in journal (Refereed)
  • 20.
    Grimm, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Umeå university.
    Boström, Dan
    Umeå university.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bed agglomeration characteristics in fluidized quartz bed combustion of phosphorus-rich biomass fuels2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 3, p. 937-947Article in journal (Refereed)
    Abstract [en]

    The bed agglomeration characteristics during combustion of phosphorus-rich biomass fuels and fuel mixtures were determined in a fluidized (quartz) bed reactor (5 kW). The fuels studied (separately and in mixtures) included logging residues, bark, willow, wheat straw, and phosphorus-rich fuels, like rapeseed meal (RM) and wheat distillers dried grain with solubles (DDGS). Phosphoric acid was used as a fuel additive. Bed material samples and agglomerates were studied by means of scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDX), in order to analyze the morphological and compositional changes of coating/reaction layers and necks between agglomerated bed particles. Furthermore, bed ash particles were separated by sieving from the bed material samples and analyzed with SEM/EDS and powder X-ray diffraction (XRD). For logging residues, bark, and willow, with fuel ash rich in Ca and K but with low contents of P and organically bound Si, the bed layer formation is initiated by reactions of gaseous or liquid K compounds with the surface of the bed material grains, resulting in the formation of a potassium silicate melt. The last process is accompanied by the diffusion/dissolving of Ca into the melt and consequent viscous flow sintering and agglomeration. The addition of high enough phosphorus content to convert the available fuel ash basic oxides into phosphates reduced the amount of K available for the reaction with the quartz bed material grains, thus preventing the formation of an inner bed particle layer in the combustion of logging residues, bark, and willow. Some of the phosphate-rich ash particles, formed during the fuel conversion, adhered and reacted with the bed material grains to form noncontinuous phosphate−silicate coating layers, which were found responsible for the agglomeration process. Adding phosphorus-rich fuels/additives to fuels rich in K and Si (e.g., wheat straw) leads to the formation of alkali-rich phosphate−silicate ash particles that also adhered to the bed particles and caused agglomeration. The melting behavior of the bed particle layers/coatings formed during combustion of phosphorus-rich fuels and fuel mixtures is an important controlling factor behind the agglomeration tendency of the fuel and is heavily dependent on the content of alkaline earth metals in the fuel. A general observation is that phosphorus is the controlling element in ash transformation reactions during biomass combustion in fluidized quartz beds because of the high stability of phosphate compounds.

  • 21.
    Grimm, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lindberg, Therese
    LKAB.
    Fredriksson, Andreas
    LKAB.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Bed agglomeration characteristics in fluidized bed combustion of biomass fuels using olivine as bed material2012In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 7, p. 4550-4559Article in journal (Refereed)
    Abstract [en]

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

  • 22.
    Góger, Szabolcs
    et al.
    Department of General and Inorganic Chemistry, University of Pannonia. Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences.
    Szabo, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Czakó, Gábor
    Department of Physical Chemistry and Materials Science, Institute of Chemistry, University of Szeged.
    Lendvay, György
    Department of General and Inorganic Chemistry, University of Pannonia. Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Hungary.
    Flame Inhibition Chemistry: Rate Coefficients of the Reactions of HBr with CH3 and OH Radicals at High Temperatures Determined by Quasiclassical Trajectory Calculations2018In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 32, no 10, p. 10100-10105Article in journal (Refereed)
    Abstract [en]

    Reactions of HBr with radicals are involved in atmospheric chemistry and in the mechanism of operation of bromine-containing flame retardants. The rate coefficients for two such reactions, HBr + OH and HBr + CH3, are available from earlier experiments at near or below room temperature, relevant for atmospheric chemistry, and in this domain, the activation energy for both has been found to be negative. However, no experimental data are available at combustion temperatures. In this work, to provide reliable data needed for modeling the action of brominated flame suppressants, we used the quasiclassical trajectory (QCT) method in combination with high-level ab initio potential energy surfaces to evaluate the rate coefficients of the two title reactions at combustion temperatures. The QCT calculations have been validated by reproducing the experimental rate coefficients at room temperature. At temperatures between 600 and 3200 K, the QCT rate coefficients display positive activation energies. We recommend the following extended Arrhenius expressions to describe the temperature dependence of the thermal rate coefficients: k6 = (9.86 ± 2.38) × 10–16T(1.23±0.03) exp[(5.93 ± 0.33) kJ mol–1/RT] cm3 molecule–1 s–1 for the HBr + OH → H2O + Br reaction, and k–2 = (4.06 ± 2.72) × 10–18T(1.83±0.08) exp[(7.53 ± 0.18) kJ mol–1/RT] cm3 molecule–1 s–1 for the HBr + CH3 → CH4 + Br reaction. The latter is in very good agreement with the formula proposed by Burgess et al. [Burgess, D. R., Jr.; Babushok, V. I.; Linteris, G. T.; Manion, J. A. A Chemical Kinetic Mechanism for 2-Bromo-3,3,3-trifluoropropene (2-BTP) Flame Inhibition. Int. J. Chem. Kinet. 2015, 47, 533−619, DOI: 10.1002/kin.20923]. The conventional transition state theory has been tested against the rate data obtained by the QCT method and was found to overestimate not only the rate coefficients but also the activation energies

  • 23.
    Hannl, Thomas Karl
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Faust, Robin
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Kuba, Matthias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Bioenergy2020+ GmbH, Güssing, Austria. Institute of Chemical, Environmental & Bioscience Engineering, TU Vienna, Vienna, Austria. Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
    Knutsson, Pavleta
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Berdugo Vilches, Teresa
    Department of Space, Earth, and Environment, Chalmers University of Technology, Gothenburg, Sweden.
    Seemann, Martin
    Department of Space, Earth, and Environment, Chalmers University of Technology, Gothenburg, Sweden.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood. 2. Na-Feldspar2019In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 8, p. 7333-7346Article in journal (Refereed)
    Abstract [en]

    Selecting a suitable bed material for the thermochemical conversion of a specific feedstock in a fluidized bed system requires identification of the characteristics of potential bed materials. An essential part of these characteristics is the interaction of the bed material with feedstock ash in a fluidized bed, which leads to layer formation and morphology changes. For this purpose, the interaction of feldspar bed material with the main ash-forming elements in wood ash (Ca, K, Mg, Si) in an indirect gasification system was analyzed using SEM-EDS, XRD, and thermodynamic modeling. In part 1 of this work (DOI: 10.1021/acs.energyfuels.9b01291), the layer formation on K-feldspar dominated by Ca reaction and ash deposition was investigated. The aim of this second part of the work was to determine the time-dependent layer formation on Na-feldspar and compare the results with the findings for K-feldspar. Interaction of Na-feldspar with ash-derived elements resulted in different layers on Na-feldspar: K reaction layers, where K replaced Na and Si shares decreased; Ca reaction layers, where Ca enriched and reacted with the Na-feldspar; and ash deposition layers, where wood ash elements accumulated on the surface. Ca reaction layers were formed first and became continuous on the surface before K reaction layers and ash deposition layers were detected. Cracks and crack layer formation in the Na-feldspar particles were found after several days of operation. The layer compositions and growth rates indicate that the diffusion of Ca and K plays an essential role in the formation of Ca reaction and K reaction layers. The reaction with Ca and the crack formation coincide with the interaction previously found for quartz and K-feldspar. In contrast to K-feldspar, Na-feldspar showed high potential for reaction with K. The findings indicate that the reaction of Na-feldspar with ash-derived K makes Na-feldspar a less stable bed material than K-feldspar during the thermochemical conversion of K-rich feedstocks in a fluidized bed system.

  • 24.
    Hardi, Flabianus
    et al.
    Department of Environmental Science and Technology, Tokyo Institute of Technology.
    Imai, Akihisa
    Department of Transdisciplinary Science and Engineering, Tokyo Institute of Technology.
    Theppitak, Sarut
    Department of Transdisciplinary Science and Engineering, Tokyo Institute of Technology.
    Kirtania, Kawnish
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Furusjö, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Yoshikawa, Kunio
    Department of Environmental Science and Technology and ‡Department of Transdisciplinary Science and Engineering, Tokyo Institute of Technology.
    Gasification of Char Derived from Catalytic Hydrothermal Liquefaction of Pine Sawdust under a CO2 Atmosphere2018In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 32, no 5, p. 5999-6007Article in journal (Refereed)
    Abstract [en]

    The integration between K2CO3 catalytic hydrothermal liquefaction (HTL) and gasification is explored to improve the gasification process. In this study, the CO2 gasification characteristics and the activation energies of the chars derived from four kinds of HTL products, black liquor (BL), and virgin pine sawdust (PS) are investigated non-isothermally using a thermogravimetric analyzer. The complete conversion of BL char and HTL product chars was achieved at lower temperatures (1150 K) than that of PS char (1300 K). BL char showed the highest derivative thermogravimetric (DTG) peak, an indicator of high reactivity, followed by HTL product chars and PS char. HTL liquid product chars exhibited the lowest DTG peak temperature (1023–1058 K), which is advantageous for the low-temperature gasification. The activation energies were calculated isoconversionally using the Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Starink approximations. On the basis of the KAS method, the range of the activation energy for the HTL aqueous product char sample was 127–259 kJ/mol, which was wider than that for BL char (171–190 kJ/mol). The HTL process can improve the gasification feedstock reactivity, and the use of the HTL liquid product allows for the gasification at a low temperature.

  • 25.
    He, Hanbing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Time dependence of bed particle layer formation in fluidized quartz bed combustion of wood-derived fuels2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 6, p. 3841-3848Article in journal (Refereed)
    Abstract [en]

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

  • 26.
    He, Hanbing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå universitet, Energy Technology and Thermal Process Chemistry, Umeå University, Umeå university.
    Backman, Rainer
    Umeå university, Åbo Akademi, Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Mechanism of Quartz Bed Particle Layer Formation in Fluidized Bed Combustion of Wood-Derived Fuels2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 3, p. 2227−2232-Article in journal (Refereed)
    Abstract [en]

    Agglomeration is among one of the major problems in the operation of fluidized bed boilers. The formation of bed particle layers is thought to play an important role on the occurrence of agglomeration in wood-fired fluidized (quartz) beds. In spite of frequent experimental reports on the quartz bed particle layer characteristics, the underlying bed layer formation process has not yet been presented. By combining our previously experimental results on layer characteristics for samples with durations from 4 h to 23 days, with phase diagrams, thermochemical equilibrium calculations, and a diffusion model, a mechanism of quartz bed particle layer formation was proposed. For younger bed particles (

  • 27.
    He, Hanbing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Time-Dependent Crack Layer Formation in Quartz Bed Particles during Fluidized Bed Combustion of Woody Biomass2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 2, p. 1672-1677Article in journal (Refereed)
    Abstract [en]

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

  • 28.
    He, Hanbing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Skoglund, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Time-dependent layer formation on K-feldspar bed particles during fluidized bed combustion of woody fuels2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 11, p. 12848-12856Article in journal (Refereed)
    Abstract [en]

    Despite frequent reports on layer characteristics on quartz bed particles, few studies have been found focusing on the layer characteristics on K-feldspar bed particles. The layer characteristics of K-feldspar bed particles in fluidized bed combustion of woody biomass was therefore investigated by collecting bed material samples of different ages from large-scale bubbling and circulating fluidized bed facilities. Scanning electron microscopy/energy-dispersive spectroscopy was used to analyze the layer morphology and elemental composition. For particles with an age of 1 day, a thin layer rich in Si, Ca and Al was found. For particles older than some days, an inner more homogenous layer containing cracks and an outer more particle-rich layer were observed. The outer layer was thinner for K-feldspar bed particles sampled from circulating fluidized bed, compared to particles from bubbling fluidized bed. The concentration of Ca in the inner layer increases towards bed particle surface, the molar ratio of Si/Al is maintained, and the molar ratio of K/Al decreases compared to the K-feldspar. The inner layer thickness for quartz and K-feldspar bed particles collected at the same operation conditions was found to be similar. No crack layers, as have been observed in quartz particles, were found in the core of the K-feldspar bed particles. The results suggest that the diffusion and reaction of Ca2+ into/with the feldspar particle play an important role on the inner layer formation process.

  • 29.
    He, Qing
    et al.
    East China Univ Sci & Technol, Minist Educ, Key Lab Coal Gasificat & Energy Chem Engn, Shanghai 200237, Peoples R China.
    Guo, Qinghua
    East China Univ Sci & Technol, Minist Educ, Key Lab Coal Gasificat & Energy Chem Engn, Shanghai 200237, Peoples R China.
    Ding, Lu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gong, Yan
    East China Univ Sci & Technol, Minist Educ, Key Lab Coal Gasificat & Energy Chem Engn, Shanghai 200237, Peoples R China.
    Wei, Juntao
    East China Univ Sci & Technol, Minist Educ, Key Lab Coal Gasificat & Energy Chem Engn, Shanghai 200237, Peoples R China.
    Yu, Guangsuo
    East China Univ Sci & Technol, Minist Educ, Key Lab Coal Gasificat & Energy Chem Engn, Shanghai 200237, Peoples R China.
    Co-pyrolysis Behavior and Char Structure Evolution of Raw/Torrefied Rice Straw and Coal Blends2018In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 32, no 12, p. 12469-12476Article in journal (Refereed)
    Abstract [en]

    Combination of biomass and coal for energy production is conducive to the sustainable development of society and a clean-energy future. This study investigates co-pyrolysis behavior of raw/torrefied rice straw and coal blends. Mild torrefaction (250 degrees C) and severe torrefaction (300 degrees C) were taken into consideration. Samples of five mixing ratios were tested by thermogravimetric analyzer, and the resulting chars were characterized by Raman spectroscopy and SEM-EDS. The results show that co-pyrolysis had little effect on char yields. Decomposition rate curves showed two distinct peaks for raw/mildtorrefied rice straw and coal blends, and the reaction rate was enhanced below 380 degrees C. However, only one peak appeared for severely torrefied rice straw blended with coal. During co-pyrolysis, the secondary pyrolysis of coal around 700 degrees C was inhibited, and the graphitization degree of biomass char increased, while the crystalline structure of coal char was poorly organized. The activation energy of mixtures also changed in different pyrolysis stages.

  • 30.
    Jafri, Yawer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Furusjö, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kirtania, Kawnish
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Performance of a Pilot-Scale Entrained-Flow Black Liquor Gasifier2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 4, p. 3175-3185Article in journal (Refereed)
    Abstract [en]

    Pilot-scale entrained flow gasification experiments were carried out at the 3 MWth LTU Green Fuels black liquor gasification (BLG) plant, using ∼140 tons of Kraft black liquor (BL) with a dry solids content of ∼72.5%. Comprehensive mass and energy balances were performed to quantify process performance under varying pressure, load, and oxygen/fuel ratio. Carbon conversion efficiency of the BLG process was 98.3%–99.2% and did not vary systematically in response to process changes. The unconverted carbon is almost exclusively present as dissolved organic carbon in the green liquor (GL) stream. GL is an aqueous solution of sodium carbonate and sodium sulfide used to recover the inorganic pulping chemicals present in BL for reuse in the pulp mill. A small fraction of syngas CO is converted to formate ions dissolved in GL through reaction with hydroxide ions. Unconverted carbon present in GL solids is insignificant. Syngas produced is subsequently upgraded to methanol and dimethyl ether (DME) in an integrated fuel synthesis facility. Concentration of H2 in syngas is not significantly affected by operating point changes in the domain investigated, while CO and CO2 concentrations are. Syngas hydrocarbon concentration values are typically in the single-digit parts per million (ppm) with the exception of C6H6, which was present at 16–127 ppm. CH4 is present at 0.5%–1.2%, with lower concentrations at higher temperatures, and shows good correlation with C6H6. A quantity of 24%–27% of BL sulfur ended up in the syngas as 1.5%–1.7% H2S and 64–72 ppm COS. Cold gas efficiencies (CGEs) on a lower heating value (LHV) basis, when including syngas CH4, were 52%–55% and decreased at higher temperature. CGEs on an LHV basis, when considering only H2 and CO with a sulfur-free BL heating value relevant for catalytic syngas upgrading, were 58%–60% and showed the opposite temperature dependence. Good mass and energy balance closures show the figures presented to be reliable. The results obtained from this study demonstrate process stability at varying operating conditions and can be further used for techno-economic analysis and design purposes.

  • 31.
    Ji, Xiaoyan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Zhu, Chen
    Department of Geological Sciences, Indiana University.
    Modeling of phase equilibria in the H2S-H2O system with the statistical associating fluid theory2010In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 24, no 11, p. 6208-6213Article in journal (Refereed)
    Abstract [en]

    The phase equilibria of the binary system of H2S-H2O are represented using the statistical associating fluid theory. H2S is modeled as a molecule with four association sites, i.e., two sites of type S and two sites of type H, and sites of the same type do not associate with each other. The parameters of H2S are fitted to its vapor pressure and saturated liquid density. Cross-association between the site H in H2S and the site O in H2O is allowed, and two temperature-dependent parameters are used to describe this cross-association. A temperature-dependent binary interaction parameter is used to correct the cross-dispersive energy for this binary system. Cross-parameters are fitted to mole fractions in both H2S-rich/vapor and H2O-rich phases. The model is found to represent well the phase equilibria of the H2S-H2O system from 273 to 630 K and at pressures up to 200 bar

  • 32.
    Jonsson, Carrie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Stjernberg, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lindblom, Bo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Deposit formation in a grate-kiln plant for iron-ore pellet production: Part 1: Characterization of process gas particles2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 10, p. 6159-6170Article in journal (Refereed)
    Abstract [en]

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

  • 33.
    Klauser, Franziska
    et al.
    BIOENERGY 2020+ GmbH, Graz, Austria;Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
    Schmidl, Christoph
    BIOENERGY 2020+ GmbH, Graz, Austria.
    Reichert, Gabriel
    BIOENERGY 2020+ GmbH, Graz, Austria.
    Carlon, Elisa
    BIOENERGY 2020+ GmbH, Graz, Austria.
    Kistler, Magdalena
    Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
    Schwabl, Manuel
    BIOENERGY 2020+ GmbH, Graz, Austria.
    Haslinger, Walter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kasper-Giebl, Anne
    Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
    Effect of Oxidizing Honeycomb Catalysts Integrated in a Firewood Room Heater on Gaseous and Particulate Emissions, Including Polycyclic Aromatic Hydrocarbons (PAHs)2018In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 32, no 11, p. 11876-11886Article in journal (Refereed)
    Abstract [en]

    Residential wood combustion is linked to a significant extent of emissions of polycyclic aromatic hydrocarbons (PAHs), which represent highly toxic, semivolatile pollutants. The use of catalysts reveals an effective measure to reduce emissions, especially gaseous flue gas compounds (carbon monoxide (CO) and organic gaseous compounds (OGC)). Their effect on toxicologically relevant PAHs is not clarified yet. In this work, the impact of two commercially available oxidizing platinum/palladium catalysts with either metallic or ceramic honeycomb carriers was examined under real-life operating conditions of a firewood room heater. The catalytic effect on CO and OGC, total suspended particles (TSP), total carbon (TC), elemental carbon (EC), organic carbon (OC), and 19 different PAHs, including 16 EPA PAHs (PAHs defined by the Environmental Protection Agency as priority pollutants) was evaluated by parallel measurements of catalytically treated and untreated flue gas from firewood combustion. The metallic catalyst, having a reaction surface that is 3.5 times greater than the ceramic catalyst, leads to a more-pronounced impact. Both types, the ceramic and the metallic catalyst, led to distinct reductions of CO (-69%, -88%) and OGC (-27%, -39%). In the test with the metallic catalyst, TSP increased (+17%) and PAHs were clearly reduced (-63%). This reduction was exclusively related to the higher-molecular-weight PAHs, such as the particularly toxic benzo(a)pyrene. Carbonaceous fractions (TC, EC, and OC) were not affected significantly. The toxicity of emissions arising from EPA PAHs can be clearly reduced by catalytic treatment. Moreover, the increase of TSP opens new questions, which must be clarified before the investigated catalysts are recommended as suitable secondary measure for emission abatement.

  • 34.
    Kuba, Matthias
    et al.
    TU Wien.
    He, Hanbing
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kirnbauer, Freidrich
    Bioenergy 2020+.
    Skoglund, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hoffbauer, Herman
    TU Wien.
    Mechanism of Layer Formation on Olivine Bed Particles in Industrial-Scale Dual Fluid Bed Gasification of Wood2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 9, p. 7410-7418Article in journal (Refereed)
    Abstract [en]

    Utilization of biomass as feedstock in dual fluidized bed steam gasification is a promising technology for the substitution of fossil energy carriers. Experience from industrial-scale power plants showed an alteration of the olivine bed material due to interaction with biomass ash components. This change results mainly in the formation of Ca-rich layers on the bed particles. In this paper, a mechanism for layer formation is proposed and compared to the better understood mechanism for layer formation on quartz bed particles. Olivine bed material was sampled at an industrial-scale power plant before the start of operation and at predefined times after the operation had commenced. Therefore, time-dependent layer formation under industrial-scale conditions could be investigated. The proposed mechanism suggests that the interaction between wood biomass ash and olivine bed particles is based on a solid-solid substitution reaction, where Ca2+ is incorporated into the crystal structure. As a consequence, Fe2+/3+ and Mg2+ ions are expelled as oxides. This substitution results in the formation of cracks in the particle layer due to a volume expansion in the crystal structure once Ca2+ is incorporated. The results of this work are compared to relevant published results, including those related to quartz bed particles

  • 35.
    Kuba, Matthias
    et al.
    TU Wien, Institute of Chemical Engineering.
    He, Hanbing
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kirnbauer, Freidrich
    Bioenergy 2020+.
    Skoglund, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå University, Energy Technology and Thermal Process Chemistry.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hoffbauer, Herman
    TU Wien, Institute of Chemical Engineering.
    Thermal stability of bed particle layers on naturally occurring minerals from dual fluid bed gasification of woody biomass2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 10, p. 8277-8285Article in journal (Refereed)
    Abstract [en]

    The use of biomass as feedstock for gasification is a promising way of producing not only electricity and heat but also fuels for transportation and synthetic chemicals. Dual fluid bed steam gasification has proven to be suitable for this purpose. Olivine is currently the most commonly used bed material in this process due to its good agglomeration performance and its catalytic effectiveness in the reduction of biomass tars. However, as olivine contains heavy metals such as nickel and chromium, no further usage of the nutrient-rich ash is possible, and additional operational costs arise due to necessary disposal of the ash fractions. This paper investigates possible alternative bed materials and their suitability for dual fluid bed gasification systems focusing on the behavior of the naturally occurring minerals olivine, quartz, and K-feldspar in terms of agglomeration and fracturing at typical temperatures. To this end, samples of bed materials with layer formation on their particles were collected at the industrial biomass combined heat and power (CHP) plant in Senden, Germany, which uses olivine as the bed material and woody biomass as feedstock. The low cost logging residue feedstock contains mineral impurities such as quartz and K-feldspar, which become mixed into the fluidized bed during operation. Using experimental and thermochemical analysis, it was found that the layers on olivine and K-feldspar showed a significantly lower agglomeration tendency than quartz. Significant fracturing of particles or their layers could be detected for olivine and quartz, whereas K-feldspar layers were characterized by a higher stability. High catalytic activity is predicted for all three minerals once Ca-rich particle layers are fully developed. However, quartz may be less active during the buildup of the layers due to lower amounts of Ca in the initial layer formation

  • 36. Lindberg, Jenny
    et al.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Space discretization error of methane combustion simulations in turbulent flow2005In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 19, no 5, p. 1873-1878Article in journal (Refereed)
    Abstract [en]

    Numerical investigation of methane combustion in a pipe with turbulent flow is studied. The space discretization error is investigated quantitatively and qualitatively, using the Richardson extrapolation and profiles comparisons. Comparison of the profiles indicates that the solution converges to a grid-independent solution. The Richardson method gives unsatisfactory results to determine the grid error, because of the rigidity of the method. A second-order polynomial is used as an alternative to the Richardson method. The results are more stable and have a better goodness of fit. The results of the simulations are compared with those of a similar experiment and the corresponding analytical solution.

  • 37. Lindberg, Jenny
    et al.
    Hermansson, Roger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Modification of reaction rate parameters for combustion of methane based on experimental investigation at furnace-like conditions2004In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 18, no 5, p. 1482-1484Article in journal (Refereed)
    Abstract [en]

    A method for modifying reaction rate parameters in the Arrhenius rate equation for combustion of methane is proposed. Linear least-squares data fit to measured concentrations and temperatures is used to modify reaction rate parameters in the Arrhenius rate equation for combustion of methane in one step. The modified equation is compared to the one provided by the software Fluent by implementing both into a three-dimensional Fluent simulation. The modification of reaction rate parameters influences the result of computational fluid dynamics simulations to predict combustion at experimental conditions where the Fluent rate equation failed. With modified parameters, the size of the reaction zone increases to give better agreement with experiments than that obtained using the Fluent rate equation. This first test indicates that the method has the contingency of becoming a useful tool for modification of reaction rate parameters though it still needs further development.

  • 38.
    Lindström, Erica
    et al.
    Umeå university.
    Larsson, Sylvia
    Swedish University of Agricultural Sciences.
    Boström, Dan
    Umeå university.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Slagging characteristics during combustion of woody biomass pellets made from a range of different forestry assortments2010In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 24, no 6, p. 3456-3461Article in journal (Refereed)
    Abstract [en]

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

  • 39.
    Lindström, Erica
    et al.
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Sandström, Malin
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Energy Technology Centre in Piteå.
    Slagging characteristics during combustion of cereal grains rich in phosphorus2007In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 2, p. 710-717Article in journal (Refereed)
    Abstract [en]

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

  • 40.
    Lindström, Erica
    et al.
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Backman, Rainer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Influence of sand contamination on slag formation during combustion of wood derived fuels2008In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 22, no 4, p. 2216-2220Article in journal (Refereed)
    Abstract [en]

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

  • 41.
    Lundholm, Karin
    et al.
    Umeå university.
    Nordin, Anders
    Umeå university.
    Öhman, Marcus
    Boström, Dan
    Umeå university.
    Reduced bed agglomeration by co-combustion biomass with peat fuels in a fluidized bed2005In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 19, no 6, p. 2273-2278Article in journal (Refereed)
    Abstract [en]

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

  • 42.
    Ma, Charlie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Backman, Rainer
    Umeå university, Åbo Akademi, Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Thermochemical equilibrium study of slag formation during pressurized entrained-flow gasification of woody biomass2015In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 29, no 7, p. 4399-4406Article in journal (Refereed)
    Abstract [en]

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

  • 43.
    Ma, Charlie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Carlborg, Markus
    Energy Technology and Thermal Process Chemistry, Department of Applied Physics and Electronics, Umeå University.
    Hedman, Henry
    SP Energy Technology Center AB.
    Wennebro, Jonas
    SP Energy Technology Center AB.
    Weiland, Fredrik
    SP Energy Technology Center AB.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. SP Energy Technology Center AB.
    Backman, Rainer
    Energy Technology and Thermal Process Chemistry, Department of Applied Physics and Electronics, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ash Formation in Pilot-Scale Pressurized Entrained-Flow Gasification of Bark and a Bark/Peat Mixture2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 12, p. 10543-10554Article in journal (Refereed)
    Abstract [en]

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

  • 44.
    Ma, Charlie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Weiland, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Boström, Dan
    Umeå universitet.
    Backman, Rainer
    Umeå universitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Characterization of Reactor Ash Deposits from Pilot-Scale Pressurized Entrained-Flow Gasification of Woody Biomass2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 11, p. 6801−6814-Article in journal (Refereed)
    Abstract [en]

    Pressurized entrained-flow gasification of renewable forest residues has the potential to produce high-quality syngas suitable for the synthesis of transport fuels and chemicals. The ash transformation behavior during gasification is critical to the overall production process and necessitates a level of understanding to implement appropriate control measures. Toward this end, ash deposits were collected from inside the reactor of a pilot-scale O2-blown pressurized entrained-flow gasifier firing stem wood, bark, and pulp mill debarking residue (PMDR) in separate campaigns. These deposits were characterized with environmental scanning electron microscopy equipped with energy-dispersive X-ray spectrometry and X-ray diffractometry. The stem wood deposit contained high levels of calcium and was comparatively insubstantial. The bark and PMDR fuels contained contaminant sand and feldspar particles that were subsequently evident in each respective deposit. The bark deposit consisted of lightly sintered ash aggregates comprising presumably a silicate melt that enveloped particles of quartz and, to a lesser degree, feldspars. Discontinuous layers likely to be composed of alkaline-earth metal silicates were found upon the aggregate peripheries. The PMDR deposit consisted of a continuous slag that contained quartz and feldspar particles dispersed within a silicate melt. Significant levels of alkaline-earth and alkali metals constituted the silicate melts of both the bark and PMDR deposits. Overall, the results suggest that fuel contaminants (i.e., quartz and feldspars) play a significant role in the slag formation process during pressurized entrained-flow gasification of these woody biomasses.

  • 45.
    Näzelius, Ida-Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå universitet.
    Boman, Christoffer
    Umeå universitet.
    Hedman, Henry
    Energy Technology Centre, Piteå.
    Samuelsson, Robert
    Sveriges Lantbruksuniversitet.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Influence of peat addition to woody biomass pellets on slagging characteristics during combustion2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 7, p. 3997-4006Article in journal (Refereed)
    Abstract [en]

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

  • 46.
    Näzelius, Ida-Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå University, Energy Technology and Thermal Process Chemistry.
    Rebbing, Anders
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Boman, Christoffer
    Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Fuel Indices for Estimation of Slagging of Phosphorus-Poor Biomass in Fixed Bed Combustion2017In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 1, p. 904-915Article in journal (Refereed)
    Abstract [en]

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

  • 47.
    Näzelius, Ida-Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Fagerström, Jonathan
    Energy Technology and Thermal Process Chemistry, Umeå University, Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Boman, Christoffer
    Energy Technology and Thermal Process Chemistry, Umeå University, Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University, Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    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 are not welcomed, as it may cause technical and operational problems as well as extra costs. Increased understanding of the critical slagging sub-processes makes it easier to suggest semi-empirical models and fuel indexes for prediction of slagging tendency 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 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, 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 ending up with a proposed starting point for a new slagging index. The slag (ash particles > 3.15 mm) formed during the combustion experiments has been described according to fraction of fuel ash that forms slag (wt-%), visual sintering category (1-4) and viscosity predictions. The results explain that both the fraction of melt and its viscosity is critical for the slag formation process in phosphorus-poor biomasses. Additionally, fuels with low Si/K ratio along with higher Ca concentration may form a low viscous carbonate melt 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.

  • 48.
    Olwa, Joseph
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Pettersson, Esbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Boström, Dan
    Umeå universitet.
    Okure, Mackay
    Makerere University.
    Kjellström, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Potassium retention in updraft gasification of wood2013In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 27, no 11, p. 6718−6724-Article in journal (Refereed)
    Abstract [en]

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

  • 49.
    Pettersson, Esbjörn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boman, Christoffer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Westerholm, Roger
    Analytical Chemistry, Arrhenius Laboratory, Stockholm University.
    Boström, Dan
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Nordin, Anders
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Stove performance and emission characteristics in residential wood log and pellet combustion: Part 2: Wood stove2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 1, p. 315-323Article in journal (Refereed)
    Abstract [en]

    The characteristics and quantities of a large number of gaseous and particulate emission components during combustion in a residential wood log stove with variations in fuel, appliance and operational conditions were determined experimentally. The measurement campaign included CO, NOx, organic gaseous carbon (OGC), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions and inorganic composition. CO varied in the range of 1100 to 7200 mg/MJfuel, while OGC varied from 210 to 3300 mg/MJfuel. Dominating VOCs were methane, followed by ethene, acetylene and benzene. Methane varied from 9 to 1600 mg/MJfuel. The non-methane volatile organic compound (NMVOC) emissions were in the range of 20-2300 mg/MJfuel. The PAHtot emissions varied from 0.8 to 220 mg/MJfuel, in most cases dominated by phenantrene, fluoranthene and pyrene. PMtot were in all cases dominated by fine particles and varied in the range 38-350 mg/MJfuel. The mass median particle diameters and the peak mobility diameters of the fine particles varied in the range 200-320 nm and 220-330 nm respectively and number concentrations in the range of 1-4×1013 particles/MJfuel. Air starved conditions, at high firing intensity, gave the highest emissions, especially for hydrocarbons. This type of conditions is seldom considered, though it may occur occasionally. The emissions from Swedish wood stoves, comparing a Swedish field study, are covered fairly well with the applied methodology, but other field studies reports considerably higher emissions especially for diluted particle sampling.

  • 50.
    Pettersson, Esbjörn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lindmark, Fredrik
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Nordin, Anders
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Westerholm, Roger
    Analytical Chemistry, Stockholm University.
    Boman, Christoffer
    Energy Technology and Thermal Process Chemistry, Umeå University.
    Design changes in a fixed bed pellet combustion device: effects of temperature and residence time on emission performance2010In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 24, no 2, p. 1333-1340Article in journal (Refereed)
    Abstract [en]

    The use of wood fuel pellets has proven to be well-suited for the small-scale market, enabling controlled and efficient combustion with low emission of products of incomplete combustion (PIC). Still, a potential for further emission reduction exists, and a thorough understanding of the influence of combustion conditions on the emission characteristics of air pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and particulate matter (PM), is important. The objective of the present work was to determine the effect of design changes, i.e., increasing the temperature and/or residence time, on the emission performance and characteristics for a pellet combustion device using a laboratory fixed-bed reactor (<5 kW). The temperature and residence time after the bed section were varied according to statistical experimental designs (650-950 °C and 0.5-3.0 s) with the emission responses: CO, organic gaseous carbon (OGC), NO, volatile organic compounds (VOCs, 20 compounds), PAHs (43 compounds), PMtot mass concentration, fine particle mass/count median diameter (MMD and CMD), and number concentration. The temperature was negatively correlated with the emissions of all studied PIC, with limited effects of the residence time. The PMtot emissions of 15-20 mg/MJ were in all cases dominated by fine (<1 μm) particles of K, Na, S, Cl, C, O, and Zn. An increased residence time resulted in increased fine particle sizes (i.e., MMD and CMD) and decreased number concentrations. The importance of a high temperature (>850 °C) in the bed zone with intensive, air-rich, and well-mixed conditions was illustrated for wood pellets combustion with almost a total depletion of all studied PIC. The importance of the residence time was shown to be limited, and the results emphasize the need for further verification studies and technology development work.

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