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| 2. |
- Gilbe, Carl, et al.
(författare)
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Predicting slagging tendencies for biomass pellets fired in residential appliances : a comparison of different prediction methods
- 2008
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Ingår i: Energy & Fuels. - Washington : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 22:6, s. 3680-3686
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a comparison between four different types (both empirical and theoretical) of techniques to predict the slagging tendencies in residential pellet combustion appliances was performed. The four techniques used were the standard ash fusion test (SS ISO-540) used in the Swedish pellet standard (SS 18 7120), thermal analysis (TGA/DTA), thermochemical model calculations, and a laboratory-scale sintering test. The tests were performed with 12 pelletized biomass raw materials, and the results were compared with measured slagging tendencies in controlled combustion experiments in a commercial under-fed pellet burner (20 kW) installed in a reference boiler. The results showed significant differences in the prediction of slagging tendencies between different predicting techniques and fuels. The method based on thermal analysis (TGA/DTA) of produced slags must be further developed before useful information could be provided of the slagging behavior of different fuels. The used sintering method must also be further improved before the slagging tendency of fuels forming slags extremely rich in silicon (e.g., some grasses) can be predicted. Relatively good agreement was obtained between results from chemical equilibrium calculations and the actual slagging tendencies from the combustion tests. However, the model calculations must be further improved before quantitative results can be used. The results from the standard ash fusion test (SS ISO 540) showed, in general, relatively high deformation temperatures, therefore predicting a less problematic behavior of the fuels in comparison to the actual slagging tendencies obtained from controlled combustion experiments in commercial pellet burner equipment. Nevertheless, the method predicted, in most cases, the same fuel-specific slagging (qualitatively) trends as the corresponding combustion behavior.
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| 3. |
- Gilbe, Carl, et al.
(författare)
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Slagging characteristics during residential combustion of biomass pellets
- 2008
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 22:5, s. 3536-43
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Tidskriftsartikel (refereegranskat)abstract
- Limited availability of sawdust and planer shavings and an increasing demand for biomass pellets in Europe are pushing the market toward other, more problematic raw materials with broader variation in total fuel ash content and composition of the ash forming elements as well as in their slagging tendencies. The main objective in the present work was therefore to determine the influence of fuel-ash composition on residual ash and slag behavior. Twelve different biomass pellets were used: reed canary grass (two different samples), hemp (two different samples), wheat straw, salix, logging residues (two different samples), stem wood (sawdust) as well as spruce, pine, and birch bark. The different pellet qualities were combusted in a commercial under fed pellet burner (20 kW) installed in a reference boiler. Continuous measurements of O2, CO, CO2, HCl, SO2, and total particle matter mass concentrations were determined in the exhaust gas directly after the boiler. The collected slag deposits, the corresponding deposited bottom ash in the boiler and the collected particle matter were characterized with X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray analysis (SEM/EDS). For biomass fuel pellets rich in silicon (either inherent or contaminated with sand) and low content of alkaline earth metals the main part of the potassium reacted with the silicon rich ash-residual, forming sticky alkali-silicate particles, which were not entrained from the burner and thereby giving rise to/initiating slag formation. Silicon rich fuels, i.e. fuels were the ash characteristics were dominated by silicate-alkali chemistry, therefore generally showed relatively high slagging tendencies. Straw fuels have typically this ash composition but exceptions to these general trends exists (e.g., one of the hemp fuels used in this work). Wood derived fuels with a relatively low inherent silicon content therefore showed low or relatively moderate slagging tendencies. However, contamination of sand material to these fuels may greatly enhance the slagging tendencies.
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| 5. |
- Hedman, Björn, et al.
(författare)
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Emissions from small-scale energy production using co-combustion of biofuel and the dry fraction of household waste
- 2005
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Ingår i: Waste Management. - New York, N.Y. : Pergamon. - 0956-053X .- 1879-2456. ; 25:3, s. 311-321
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Tidskriftsartikel (refereegranskat)abstract
- In sparsely populated rural areas, recycling of household waste might not always be the most environmentally advantageous solution due to the total amount of transport involved. In this study, an alternative approach to recycling has been tested using efficient small-scale biofuel boilers for co-combustion of biofuel and high-energy waste. The dry combustible fraction of source-sorted household waste was mixed with the energy crop reed canary-grass (Phalaris Arundinacea L.), and combusted in both a 5-kW pilot scale reactor and a biofuel boiler with 140–180 kW output capacity, in the form of pellets and briquettes, respectively. The chlorine content of the waste fraction was 0.2%, most of which originated from plastics. The HCl emissions exceeded levels stipulated in new EU-directives, but levels of equal magnitude were also generated from combustion of the pure biofuel. Addition of waste to the biofuel did not give any apparent increase in emissions of organic compounds. Dioxin levels were close to stipulated limits. With further refinement of combustion equipment, small-scale co-combustion systems have the potential to comply with emission regulations.
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| 6. |
- Hedman, Björn, et al.
(författare)
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PCDD/F in source-sorted waste fractions and emissions from their co-combustion with reed canary-grass
- 2007
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Ingår i: Waste Management. - Oxford : Pergamon Press. - 0956-053X .- 1879-2456. ; 27:11, s. 1580-1592
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Tidskriftsartikel (refereegranskat)abstract
- The dry combustible fraction of source-sorted household waste, including material that would otherwise be recycled, was mixed with the energy crop reed canary-grass (Phalaris arundinacea L.), and combusted as briquettes in 150 and 600 kW biofuel-boilers without advanced cleaning systems. The source-sorted waste was further sorted and characterized according to its material and chemical contents. The bulk of the waste’s chlorine content came from the non-package plastic fraction, whereas 90–95% of ∑PCDD/F (74–90% of WHO-TEQ) originated from the textile fraction. The sources of the dioxins in the waste fractions are discussed. The balance of dioxin levels was negative, i.e., the amounts of dioxins output in the flue gas were lower than those input in the fuel, except when there were operational disturbances in the combustion. In one of the combustion trials the total levels of dioxins in the flue-gas and ashes were also lower than the input levels. The use of additional cleaning equipment will be needed to ensure that emissions of dioxins and hydrochloric acid will be below legal limits.
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| 8. |
- Pommer, Linda, et al.
(författare)
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Mechanisms behind the positive effects on bed agglomeration and deposit formation combusting forest residue with peat additives in fluidized beds
- 2009
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 23:9, s. 4245-4253
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Tidskriftsartikel (refereegranskat)abstract
- A compilation was made of the composition of peat from different areas in Sweden, of which a selected set was characterized and co-combusted with forest residue in controlled fluidized-bed agglomeration tests with extensive particle sampling. The variation in ash-forming elements in the different peat samples was large; thus, eight peat samples were selected from the compilation to represent the variation in peat composition in Sweden. These samples were characterized in terms of botanical composition, analyzed for ash-forming elements, and oxidized using a low-temperature ashing procedure, followed by characterization using scanning electron microscopy/electron-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD). The selected peat samples had in common the presence of a small fraction of crystalline phases, such as quartz, microcline, albite, and calcium sulfate. The controlled fluidized-bed agglomeration tests that co-combusted forest residue with peat resulted in a significant increase in agglomeration temperatures compared to combusting forest residue alone. Plausible explanations for this were an increase of calcium, iron, or aluminum in the bed particle layers and/or the reaction of potassium with clay minerals, which prevented the formation of low-melting bed particle layers. The effects on particle and deposit formation during co-combustion were reduced amounts of fine particles and an increased number of coarse particles. The mechanisms for the positive effects were a transfer and/or removal of potassium in the gas phase to a less reactive particular form via sorption and/or a reaction with the reactive peat ash (SiO2 and CaO), which in most cases formed larger particles (>1 μm) containing calcium silicon and potassium.
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| 9. |
- Reza, Salim, 1985-
(författare)
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Phase-Contrast and Spectroscopic X-ray Imaging for Paperboard Quality Assurance
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The end-use performance of a paperboard depends on its quality.The major properties of a good quality paperboard include consistencyin the expected ratio between the thickness of the core andthe coating layers, and the uniformity in the coating layer. Measurementsystems using X-rays to monitor these properties could assistthe paperboard industries to assure the quality of their products in anon-destructive and automatic manner. Phase Contrast X-ray Imaging (PCXI) has been used successfullyto look inside a wide range of objects using synchrotron radiationsources. Recent advancements in the grating interferometer basedPCXI technique enables high quality phase-contrast and dark-fieldimages to be obtained using conventional X-ray tubes. The darkfieldimages map the scattering inhomogeneities inside objects andis very sensitive to micro-structures, and thus, can reveal useful informationabout the object’s inner structures, such as, the fibre structuresinside paperboards. In this thesis, methods, using spectroscopic X-ray imaging andPCXI technique have been demonstrated to measure paperboard quality.The thicknesses of the core and the coating layers on a paperboardwith the coating layer on only one side can be measured usingspectroscopic X-ray imaging technique. However, the limitedspectral and spatial resolution offered by the measurement systembeing used led to the measured thicknesses of the layers being lowerthan their actual thicknesses in the paperboard sample. Suggestionshave been made in relation to overcoming these limitations and toenhance the performance of the method. The dark-field signals from paperboard samples with different qualityindices are analysed. The isotropic and the anisotropic scatteringcoefficients for all of the samples have been calculated. Basedon the correlation between the isotropic coefficients and the qualityindices of the paperboards, suggestions have been made for paperboardquality measurements.
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