| 1. |
- Larsson, Ann-Charlotte, et al.
(författare)
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Targeting by Comparison with Laboratory Experiments the SCR Catalyst Deactivation Process by Potassium and Zinc Salts in a Large-Scale Biomass Combustion Boiler
- 2006
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 20:4, s. 1398-1405
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Tidskriftsartikel (refereegranskat)abstract
- The deactivation of a commercial selective catalytic reduction (SCR) catalyst of type V2O5−WO3/TiO2 has been studied in this work through comparisons of results from a full-scale biomass combustion plant with those from laboratory experiments. In the latter, the catalyst was exposed to KCl, K2SO4, and ZnCl2 by both wet impregnation with diluted salt solutions and deposition of generated submicrometer aerosol particles by means of an electrostatic field. The reactivity of freshly prepared and deactivated catalyst samples was examined in the SCR reaction, for which the influence of the different salts and the method of exposure were explored. Chemical and physical characterizations of the catalyst samples were carried out focusing on surface area, pore volume, pore size, chemical composition, and the penetration profiles of potassium and zinc. Particle-deposition deactivation as well as commercially exposed catalyst samples were shown to impact surface area and catalyst activity similarly and to have penetration profiles with pronounced peaks. Salt impregnation influenced pore sizes and catalyst activity more strongly and showed flat penetration profiles. Deposition of submicrometer-sized particles on the monolithic SCR catalyst has been shown to induce deactivation of the catalyst with characteristics resembling those obtained in a commercial biomass combustion plant; the laboratory process can be used to further assess the deactivation mechanism by biomass combustion.
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| 2. |
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| 3. |
- Almgren, Karin, et al.
(författare)
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Role of fibre-fibre and fibre-matrix adhesion in stress transfer in composites made from resin-impregnated paper sheets.
- 2009
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Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier BV. - 0143-7496 .- 1879-0127. ; 29:5, s. 551-557
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Tidskriftsartikel (refereegranskat)abstract
- Paper-reinforced plastics are gaining increased interest as packaging materials, where mechanical properties are of great importance. Strength and stress transfer in paper sheets are controlled by fibre-fibre bonds. In paper-reinforced plastics, where the sheet is impregnated with a polymer resin, other stress-transfer mechanisms may be more important. The influence of fibre-fibre bonds on the strength of paper-reinforced plastics was therefore investigated. Paper sheets with different degrees of fibre-fibre bonding were manufactured and used as reinforcement in a polymeric matrix. Image analysis tools were used to verify that the difference in the degree of fibre-fibre bonding had been preserved in the composite materials. Strength and stiffness of the composites were experimentally determined and showed no correlation to the degree of fibre-fibre bonding, in contrast to the behaviour of unimpregnated paper sheets. The degree of fibre-fibre bonding is therefore believed to have little importance in this type of material, where stress is mainly transferred through the fibre-matrix interface.
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| 4. |
- Mouzon, Johanne, et al.
(författare)
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Comparison between slip-casting and uniaxial pressing for the fabrication of translucent yttria ceramics
- 2008
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 43:8, s. 2849-2856
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Tidskriftsartikel (refereegranskat)abstract
- Slip casting and uniaxial pressing were compared as first consolidation stages prior to cold isostatic pressing (CIP) to produce translucent yttria ceramics. In the first step, yttria slurries suitable for slip casting were prepared. The viscosity was optimized with respect to the starting agglomeration state, amount of dispersant, milling time, and number of milling balls. Secondly, pellets were prepared either by slip casting or uniaxial pressing and then cold-isostatically pressed. Finally, the pellets were made translucent by a combination of pre-sintering and hot isostatic pressing (HIP). Although slip-cast and pressed samples exhibited similar green-body densities after CIP and pre-sintering, the samples prepared by slip casting were more homogeneous in terms of translucency and microstructure throughout their bodies. This was attributed to the ability of slip casting to minimize density gradients during packing, and to the beneficial effect of ball-milling to remove larger agglomerates before casting. Therefore, slip casting as a first consolidation stage prior to CIP appears to be more suitable than uniaxial pressing in order to prepare homogeneous optical ceramics.
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| 5. |
- Mangalaraja, Ramalinga Viswanathan, et al.
(författare)
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Sintering, microstructural and mechanical characterization of combustion synthesized Y2O3 and Yb3+-Y2O3
- 2009
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Ingår i: Journal of the Ceramic Society of Japan. - : Ceramic Soc of Japan. - 1882-0743 .- 1348-6535. ; 117:1371, s. 1258-1262
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Tidskriftsartikel (refereegranskat)abstract
- The present work highlights the microstructural features and mechanical properties of Y2O3 prepared with and without Yb3+ doping that processed through combustion synthesis involving various organic fuels such as urea, citric acid and glycine. Properties such as powder-now, particle packing, green density, % of shrinkage, sintered density, grain size, Vicker's microhardness (H-v) and fracture toughness (K-IC) were analyzed and compared with respect to the fuel sources. The as combusted precursors were calcined at 1100 degrees C for 4 h under oxygen atmosphere to obtain fully crystalline Y2O3 powders. Cylindrical pellets were fabricated as test specimens and sintered at 1600 degrees C for 3 h. The SEM images of the sintered yttria samples show an average grain size of < 3 mu m irrespective of the fuels. However, the mechanical properties show significant dependence on the fuels used. A maximum hardness of 6.8 +/- 0.1 and 7.0 +/- 0.1 GPa was obtained for Y2O3 and Yb3+ doped Y2O3 derived from glycine fuel. Whereas the maximum fracture toughness of 2.6 +/- 0.3 MPa m(1/2) was obtained for the samples derived from urea. The Yb3+ doping found to increase the bulk hardness of yttria from 0.2 to 0.6 GPa. The study contributes to appropriately select the fuels for obtaining high dense, mechanically stable yttria ceramics through combustion process.
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| 6. |
- Gourdon, Mathias, 1980, et al.
(författare)
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Scale formation and growth when evaporating black liquor with high carbonate to sulphate ratio
- 2008
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 23:2, s. 231-239
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Tidskriftsartikel (refereegranskat)abstract
- Scaling in black liquor evaporators has for longbeen recognised as a problem. Most problems are connected tothe precipitation of sodium salts. In the black liquor evaporation,as the black liquor gets concentrated, sodium carbonateand sodium sulphate will saturate and precipitate from the solution.When precipitation occurs the salts may crystallise on theheat transfer surface or adhere to the surface as well as they cancrystallise in the bulk. If crystals remain on the heat transfersurface an insulating layer of scales can quickly build up causingthe heat flux to drop and eventually forcing the evaporatorto be shut down for cleaning. The research in this paper focused primarily on scaling forblack liquors with high ratio of carbonate to sulphate, a conditionshown to be important in industrial black liquor evaporators(Frederick et al. 2004). The scaling behaviour was investigatedexperimentally in a falling film evaporator. The aim wasto find favourable operating conditions decreasing or eliminatingscaling. The examined parameters were different heat flux,circulation flow rate, internal residence time and black liquorfeed concentration. For the investigated operating conditions themain parameters affecting scaling were the circulation flow rateand heat flux whereas the scaling rate was seen independent ofthe internal residence time.
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| 7. |
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| 8. |
- Kulachenko, Artem, et al.
(författare)
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Reinventing mechanics of fibre network
- 2008
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Ingår i: Progress in Paper Physics Seminar. - Helsinki : Helsinki University Press. ; , s. 185-193
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Lindström, Stefan B, 1974-, et al.
(författare)
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A model for flexible fibres in viscous and inert fluid
- 2007
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Ingår i: 61st Appita annual conference and exhibition, Gold Coast, Australia, 6-9 May 2007, 2007 International paper physics conference, 6pp [Carlton, Australia: Appita, 2007. ; , s. 23-28, s. 23-28
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A model is proposed for simulating the motion of flexible fibres in fluid flow. Care has been taken to include typical papermaking conditions into the validity range of the model. Fibres are modelled as chains of fibre segments, whose motion is governed by Newton's second law. The fluid motion is calculated from the three-dimensional incompressible Navier-Stokes equations. By enforcing momentum conservation, the two-way coupling between the solids and fluid phase is taken into account. Fibre-fibre interactions as well as self-interactions include normal, frictional and lubrication forces. Furthermore, the model considers nonlaminar fibre-fluid interactions and particle inertia. Simulation results were compared with experimental data found in the literature. The model predicts very well the orbit period of rigid fibre motion in shear flow. Quantitative predictions were made for the amount of bending of flexible fibres in shear flow. It was also possible to reproduce the different regimes of motion of flexible fibres in shear flow, ranging from rigid motion to coiled motion and self-entanglement.
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| 10. |
- Lindström, Stefan B, 1974-, et al.
(författare)
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Evolution of the paper structure along the length of a twin-wire former
- 2009
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Ingår i: ADVANCES IN PULP AND PAPER RESEARCH, OXFORD 2009, VOLS 1-3. - Bury, UK : Pulp Paper Fund. Res. Soc.. - 9780954527266 ; , s. 207-245, s. 207-245
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Konferensbidrag (refereegranskat)abstract
- A particle-level numerical model is used to simulate forming with a twin-wire former configuration. The development of the paper structure along the length of the former is observed to explain the effects ofthe dewatering elements on the paper structure at different jet-to-wire speed ratios, consistencies, and target basis weights. The simulations indicate that most of the structure development takes place in the initial part of forming (forming roll) and, in some instances, at the drop to atmospheric pressure after the forming roll. Dramatic effects onthe through-thickness fibre orientation anisotropy are observed when the consistency is varied by changing the jet thickness, while changes in basis weight had less impact. The through-thickness concentration gradient was almost uniform throughout the forming process, except in the lower range of typical papermaking consistencies. This indicates that the dewatering mechanism is normally thickening, rather than filtration.
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