| 1. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Investigation of Chromium Volatilization from FeCr Interconnects by a Denuder Technique
- 2010
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 157:9, s. B1295-B1300
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Tidskriftsartikel (refereegranskat)abstract
- A technique is presented for accurate and time-resolved quantification of chromium volatilization from alloys at high temperature. A denuder tube which is coated with Na2CO3 is placed downstream of the samples. CrO2(OH)(2) that evaporated from the samples is collected on the denuder and converted to the thermally stable Na2CrO4. The chromate is then dissolved in water and determined quantitatively. Three commercially available ferritic 22% Cr steels intended for use as solid oxide fuel cell interconnect materials (Sanergy HT, Crofer 22 APU, and ZMG 232) have been investigated with respect to chromium volatilization and oxidation rate. The effect on chromium volatilization of a submicrometer cobalt coating on the steel surface is reported. Comparisons are made with a conventional thick ceramic coating. The experiments are carried out at 850 degrees C in N-2 - 20% O-2 - 3% H2O atmosphere. The submicrometer Co coatings proved to be very efficient, reducing Cr volatilization by 1 order of magnitude. Microscopic studies show that both uncoated steel and steel coated with a submicrometer cobalt film develop two-layered oxide scales with the bottom part consisting of a Cr-rich corundum-type oxide. The uncoated samples develop a top layer consisting of (Cr, Mn)(3)O-4 oxide, whereas the Co-coated samples exhibit a top layer consisting of Co-rich spinel oxide. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3462987] All rights reserved.
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| 2. |
- Gourdon, Mathias, 1980, et al.
(författare)
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Pulp mill biorefineries
- 2013
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Ingår i: International Process Integration Jubilee Conference, Gothenburg, Sweden, March 18-20 2013.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Canovic, Sead, 1979, et al.
(författare)
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Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation
- 2013
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 215, s. 62-74
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Tidskriftsartikel (refereegranskat)abstract
- The effect of novel Co and Ce nanocoatings on oxidation behaviour and chromium volatilization from a commercial Fe-22Cr steel (Sanergy HT) developed for solid oxide fuel cell interconnect applications is investigated. Three different coatings (10 nm Ce, 640 nm Co and 10 nm Ce + 640 nm Co) are studied. Uncoated and nanocoated samples are exposed isothermally at 850 C in the air with 3% H2O for 168 h. The detailed microstructure of the different coatings is investigated. The surface morphology and microstructure of the oxide scales are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX). Cross-section TEM thin foils are prepared by using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument. A 640 nm cobalt coating strongly inhibits Cr volatilization but has only minor effects on oxidation rate. In contrast, a 10 nm Ce coating decreases the oxidation rate but has no significant effects on chromium volatilization. Combining the two coatings, i.e., applying a 640 nm Co coating on top of the 10 nm Ce, effectively reduces Cr evaporation and slows down the rate of alloy oxidation.
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| 4. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Long term study of Cr evaporation and high temperature corrosion behaviour of Co coated ferritic steel for solid oxide fuel cell interconnects
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 220, s. 217-227
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation behaviour of the uncoated ferritic Fe-22Cr steel Sanergy HT is compared with an 640 nm Co coated version of the same material. The materials have been subject to corrosion and Cr volatilization measurements in air for up to 3000 h at 850 degrees C. Oxidation tests have been carried out both isothermal and discontinuously. The volatilization measurements were carried out using a recently developed denuder technique, which allows to quantify Cr evaporation in a time resolved manner. The oxidation process is studied from very initial phases (>15 s) to long term behaviour (3000 h). The formed oxide scales are analysed by XRD, SEM/EDX as well as TEM/EDX.The results show that both materials form an oxide scale with an inner layer of Cr2O3 and a spinel layer on top. In the case of the uncoated material, the spinel layer is of (Cr,Mn)(3)O-4 type while in the presence of a Co coating a (Co,Mn,Fe)(3)O-4 is formed. The Cr evaporation measurements show that despite the fact that the Co coating is very thin (640 nm) it effectively blocks Cr evaporation for at least 3000 h. This is in line with TEM analysis showing that after 3000 h there is only a low Cr content in the outer oxide scale. This long term stability indicates the suitability of the coated material as solid oxide fuel cell (SOFC) interconnect.
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| 5. |
- Khanzadi, M Reza, 1983, et al.
(författare)
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On Models, Bounds, and Estimation Algorithms for Time-Varying Phase Noise
- 2011
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Ingår i: 5th International Conference on Signal Processing and Communication Systems (ICSPCS2011). - 9781457711800 ; , s. Art Nr. 6140897-
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Konferensbidrag (refereegranskat)abstract
- In this paper, first, a new discrete-time model of phase noise for digital communication systems, which is a more accurate model compared to the classical Wiener model, is proposed based on a comprehensive continuous-time representation of time-varying phase noise, and statistical characteristics of this model are derived. Next, the non-data-aided (NDA) and decision-directed (DD) maximum-likelihood (ML) estimators of time-varying phase noise, using the proposed discrete-time model are derived. To evaluate the performance of the proposed estimators, the Cramer-Rao lower bound (CRLB) for each estimation approach is derived and by using Monte-Carlo simulations it is shown that the mean-square error (MSE) of the proposed estimators converges to the CRLB at moderate signal-to-noise ratios (SNR). Finally, simulation results show that the proposed estimators outperform existing estimation methods as the variance of the phase noise process increases.
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| 6. |
- Lundberg, Valeria, 1984, et al.
(författare)
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Converting a kraft pulp mill into a multi-product biorefinery: techno-economic analysis of a case mill
- 2014
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Ingår i: Clean Technologies and Environmental Policy. - : Springer Science and Business Media LLC. - 1618-954X .- 1618-9558. ; 16:7, s. 1411-1422
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Tidskriftsartikel (refereegranskat)abstract
- In this case study, we investigated the conversion of an existing Swedish kraft pulp mill to the production of dissolving pulp, with export of electricity, lignin, and a hemicellulose stream suitable for upgrading. By increasing the level of heat integration of the mill, it was possible to achieve self-sufficiency in terms of steam and to produce significant amounts of excess steam. The excess steam could facilitate the integration of a lignin separation plant or be used for power generation. The production of dissolving pulp requires a higher input of wood that is required for the same level of pulp production as is achieved with kraft pulp. For the studied mill, the batch digester was the main limitation for pulp production. Nevertheless, if the digester capacity was increased, then the level of pulp production could be maintained. In addition, the recovery boiler, causticization plant, and evaporation plant had sufficient capacities for preserving the same production level upon conversion, and could easily be upgraded to a certain degree through relatively simple measures for an increase in pulp production. However, increasing pulp production beyond that limit required extensive upgrades or investments in new equipment, which negatively affected annual earnings. Annual earnings were found to be also dependent upon the level of heat integration, type of by-product, and the costs for lignin and electricity. However, our results suggest that the optimal process configuration is more dependent upon other factors, such as the long-term vision of the company and policy instruments.
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| 7. |
- Nelsson, Erik, 1983-, et al.
(författare)
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Improved energy efficiency in thermomechanical pulping through co-optimixation of intensity by segment design and wood softening by sulfonation
- 2014
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Ingår i: International mechanical pulping conference IMPC 2014. - : PI.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A mill scale trial was performed where chips were mechanically pretreated and impregnated with sodium sulfite (<7.2 g/kg). Pretreated chips were refined in two parallel double disc refiners (RGP68DD) using two different conditions: Turbine™ segment at higher production rate (higher intensity) and Low Shive™ segment at normal production rate (lower intensity). By combining the Turbine segments with chip pretreatment using a sodium sulphite charge of 3.6 g/kg it was possible to reduce the specific energy consumption by 15%, while maintaining pulp properties, compared with the lower intensity refining without pretreatment.
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| 8. |
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| 9. |
- Tahmasebi Toyserkani, Arash, 1978, et al.
(författare)
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A Complexity Adjustable Scheduling Algorithm for Throughput Maximization in Clusterized TDMA Networks
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424425198
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Konferensbidrag (refereegranskat)abstract
- We consider clustered wireless networks, wheretransceivers in a cluster use a time-slotted mechanism (TDMA) to access a wireless channel that is shared among several clusters.Earlier work has demonstrated that a significant increase innetwork throughput can be achieved if all the schedules areoptimized jointly. However, a drawback of this approach is the prohibitive level of computational complexity is required when a network with a large number of clusters and time-slots is to be scheduled. In this paper, we propose a modification to our previously proposed algorithm which allows for the complexityto be adjusted to the available processing power, provided some minimum processing power is available. This is achieved by carefully reducing the number of interfering clusters considered when scheduling a cluster. In addition, we propose and evaluatetwo heuristic methods of discarding the less significant clusters.While the optimality of the obtained schedule is not proven, our results demonstrate that large gains are consistently attainable.
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