| 1. |
- Cantatore, Valentina, 1986, et al.
(författare)
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Oxidation Driven Permeation of Iron Oxide Scales by Chloride from Experiment Guided First-Principles Modeling
- 2019
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:42, s. 25957-25966
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Tidskriftsartikel (refereegranskat)abstract
- In this comprehensive investigation, it is demonstrated how chloride ions may permeate a crack-free oxide scale, thus providing hitherto missing mechanistic insight as to the impacts of KCl(s) or HCl(g) exposures on the high-temperature corrosion of biomass- and waste-fired boilers. Guided by dedicated experimental analyses, mechanistic understanding is gained by means of density functional theory. Chloride ions, being accommodated in oxygen anion vacancies that are generated at the receding magnetite/alloy interface, are driven through the oxide scale by the oxidation process. Intermediate stabilities of quasi-homogeneous transient iron oxychloride species are found, employing potassium ferrite and goethite as complementary cation sinks for the KCl(s) and HCl(g) reactants, respectively. Spontaneous disproportionation of the supersaturated oxychlorides into two different types of chloride decorated magnetite grain boundaries is demonstrated. These motifs are proposed to explain loss of scale integrity as well as accelerated oxidation by offering short-circuiting transient pathways for ion diffusion.
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| 2. |
- Davidsson, Kent, 1967, et al.
(författare)
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Potassium, chlorine, and sulfur in ash, particles, deposits, and corrosion during wood combustion in a circulating fluidized-bed boiler
- 2007
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 21:1, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the addition of chlorine and/or sulfur to the fuel on fly ash composition, deposit formation, and superheater corrosion has been studied during biomass combustion in a circulating fluidized-bed boiler. The chlorine (HCl (aq)) and sulfur (SO2 (g)) were added in proportions of relevance for the potassium chemistry. The composition of the bottom and the fly ashes was analyzed. Gas and particle measurements were performed downstream of the cyclone before the convection pass and the flue gas composition was recorded in the stack with a series of standard instruments and an FTIR analyzer. At the position downstream of the cyclone, a deposit probe was situated, simulating a superheater tube. Deposits on the probe and initial corrosion were examined. It is concluded that addition of sulfur and chlorine increases the formation of submicron particles leading to deposition of potassium sulfate and chloride. The results compare well with earlier work based on laboratory-scale experiments concerning effects of chlorine and sulfur on potassium chemistry.
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| 3. |
- Eklund, Johan, 1991, et al.
(författare)
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Field exposure of FeCrAl model alloys in a waste-fired boiler at 600°C: The influence of Cr and Si on the corrosion behaviour
- 2019
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Ingår i: Materials and Corrosion. - : Wiley. - 0947-5117 .- 1521-4176. ; 70:8, s. 1476-1485
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Tidskriftsartikel (refereegranskat)abstract
- Materials and Corrosion WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The aim of this study was to examine the performance of FeCrAl model alloys in a waste-fired boiler and investigate the influence of chromium and silicon content on the corrosion behaviour. The investigation was executed by utilising an air-cooled probe, giving a material temperature of 600°C throughout a 672 hr exposure. The material loss measurements were performed by utilizing an ultrasonic thickness gauge in combination with scanning electron microscopy analysis. It was found that increasing the chromium content significantly reduced the overall material loss of the FeCrAl model alloys but further accelerated the corrosion attack on the windward side. Simultaneously, the increased chromium content caused embrittlement of the material. Minor additions of silicon drastically reduced the material loss of the FeCrAl model alloys, whereas the sample ring with no silicon present was completely deteriorated. The trends observed in this field study correlated well with what has been observed in previous laboratory studies. A state-of-the-art alloy in the present environment, Inconel 625, was simultaneously exposed and showed similar performance to the silicon-containing FeCrAl model alloys with ≥10 wt% Cr.
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| 4. |
- Eklund, Johan, 1991, et al.
(författare)
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The influence of silicon on the corrosion properties of FeCrAl model alloys in oxidizing environments at 600 °C
- 2018
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 144, s. 266-276
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the influence of Si on the high temperature corrosion behaviour of FeCrAl model alloys in O2, O2+H2O and O2+H2O + KCl at 600 °C for up to 168 h. The investigation by SEM/EDX showed that all alloys displayed a protective behaviour in dry O2. In the more corrosive environments (O2+H2O and O2+H2O + KCl) the addition of Si affected the oxidation properties in two ways; Alloys containing Si resisted breakaway oxidation caused by Cr-evaporation (O2+H2O) and the thickness of the oxide formed after breakaway oxidation decreased with increasing amount of Si (O2+H2O + KCl).
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| 5. |
- Folkeson, Nicklas, 1981, et al.
(författare)
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Fireside corrosion of stainless and low alloyed steels in a waste-fired CFB boiler; The effect of adding sulphur to the fuel
- 2008
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Ingår i: Materials Science Forum. ; 595-598, s. 289-297
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion field tests have been carried out in the superheater region of a commercial waste-fired 75MW CFBC boiler using air cooled probes. Exposure time was 24 and 1000 hours. The effect of adding sulphur to the fuel on the corrosion of two high alloyed steels and a low alloyed steel was studied. The fuel consisted of 50% household waste and 50% industrial waste. The exposed samples were analyzed by ESEM/EDX and XRD. Metal loss was determined after 1000 hours. Both materials suffered significant corrosion in the absence of sulphur addition and the addition of sulphur to the fuel reduced corrosion significantly. The rapid corrosion of the high alloyed steel in the absence of sulphur addition is caused by the destruction of the chromium-containing protective oxide by formation of calcium chromate. Adding sulphur to the fuel inhibited chromate formation and increased the sulphate/chloride ratio in the deposit. Iron(II) chloride formed on the low alloyed steel regardless of whether sulphur was added or not.
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| 6. |
- Herstad-Svärd, S., et al.
(författare)
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Ramprogram – Åtgärder för samtidig minimering av alkalirelaterade driftproblem, Etapp 2
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of an increasing amount of biofuel and waste woods has resulted in certainenvironmental advantages, including decreased emissions of fossil CO2, SO2 andmetals. On the other hand, a number of chloride and alkali related operational problemshave occurred which are related to combustion of these fuels.Alkali related operational problems have been studied in a project consisting of twoparts. The overall scope has been to characterise the operational problems and to studymeasures to minimise them. The first part was reported in Värmeforsk report 997 wherethe results were summarised in a table of different measures. In part two, additionalmeasures have been included in the test plan and initial corrosion has been studiedlinked to the different measures. The tests have also in part two been carried out at the12 MW CFB boiler at Chalmers. The effect of the selected measures has beeninvestigated concerning both deposit formation and bed agglomeration, and at the sametime emissions and other operational conditions were characterised.The second part of the project has among other things focused on:• To investigate measures which decrease the content of alkali and chloride in thedeposits, and consequently decrease the risk for corrosion (by investigating theinitial corrosion). Focus was also on trying to explain favourable effects.• To investigate if it is possible to combine a rather low dosage of kaolin and injectionof ammonium sulphate. This was done in order to reduce both bed agglomerationand problems from deposits during combustion of fuels rich in chlorine.• To investigate if co-combustion with sewage sludge, de-inking sludge or peat withhigh ash content, could give similar advantages as conventional additives.• Investigate if ash from PFBC is possible to use as an alternative bed material.By comparing the different measures in part two, it could be concluded that cocombustionof sewage sludge gave the best overall effect. The judgement was based onthe effects concerning bed agglomeration, level of alkali chloride in the flue gas,deposits and initial corrosion. Simultaneous addition of kaolin and ammonia sulphatealso had a favourable impact both in the bed and on the alkali chlorides in the gas phase.Dosage of kaolin did not reduce the effect of injected ammonium sulphate. Cocombustionof peat could also be a very attractive alternative, but it is critical to select asuitable peat type. It is of special concern to avoid peat with a high content of calcium,since it can increase the level of alkali chlorides by reacting with available sulphur.Change of bed material to ash from PFBC can decrease problems with bedagglomeration, but there is a risk of increased deposit formation and corrosion. A boileroperated with high steam data should consequently combine the change of bed materialwith injection of ammonium sulphate or another source of sulphur.Co-combustion of de-inking sludge from pulp and paper production can reduceproblems with bed agglomeration. There is, however, an increased chance of corrosiondue to the high content of calcium. Injection of sulphates may improve the situationconcerning corrosion. The results also showed that low potassium chlorine content in the flue gas decreasesthe risk of corrosion. Increased amount of potassium chlorine content in the flue gaswill not necessary give a high amount of chlorine content in the deposits if there is sulphur in the system.Key words: agglomeration, deposits, corrosion, alkali, kaolin, ammonium sulphate,sludge
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| 7. |
- Hoseini Hooshyar, Hamed, 1986, et al.
(författare)
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The Effect of H-2 and H2O on the Oxidation of 304L-Stainless Steel at 600 A degrees C: General Behaviour (Part I)
- 2016
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 85:3-4, s. 321-342
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Tidskriftsartikel (refereegranskat)abstract
- The effect of p(H2O) and p(H-2) on the oxidation of 304L stainless steel at 600 A degrees C has been investigated in the present study. The samples were analysed by means of X-ray diffraction, Auger spectroscopy, and scanning electron microscopy equipped with energy dispersive spectroscopy. The results showed that at fixed p(H-2), the corrosion rate increased considerably with increasing p(H2O). At fixed p(H2O), the corrosion rate decreased slightly with increasing p(H-2). Duplex oxide scales formed during the exposure in all environments. The outer and inner layer consisted of Fe3O4 and (Fe, Cr)(3)O-4, respectively. The latter was mainly in the form of internal oxidation. The Cr-rich oxide formation was observed at the initial oxidation process before oxide breakdown. The Auger analysis also suggested the presence of Cr-rich oxide layer just after the breakaway oxidation. The results indicated that the rate-determining step in the corrosion attack is surface controlled or diffusion controlled through an oxide layer with fixed thickness over time.
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| 8. |
- Ihlström, Carina, et al.
(författare)
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Introducing the e-Newspaper:Identifying Initial Target Groups
- 2007
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Ingår i: Journal of Media Business Studies. ; 4:3, s. 41-62
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates how audience groups differ with respect to the adoption of new media services. The authors expand the existing framework of early adopters, which is heavily directed towards the technological aspects of a product, by including users that are more interested in the social and content-related aspects of media services. The objective is to identify and explore important audience groups that can be used as initial target groups for the introduction of the enewspaper (a newspaper published on e-paper technology). Data was collected from in total 2976 respondents at the web sites of three Swedish newspapers.
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| 9. |
- Johansson, Jesper, 1989, et al.
(författare)
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A Novel Speculative Pseudo-Parallel \Delta\Sigma Modulator
- 2015
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Ingår i: 32rd NORCHIP 2014. ; , s. Article number 7004712-
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Konferensbidrag (refereegranskat)abstract
- We present a novel speculative pseudo-parallel \Delta\Sigma modulator structure, which almost halves the logic depthof the critical path in the pseudo-parallel Hatami structure. Following Hatami, our modulator calculates a block of n consecutive output bits in parallel, and then employs a parallelserial interface to output the bits at n times the modulator clock frequency. We circumvent the block-to-block dependence, which limits the clock speed of the Hatami structure, by speculatively calculating the outputs based on all possible output values of theprevious block, and then selecting the correct one. We present cost and performance estimates for an initial implementation of the modulator, synthesized towards an FPGA and an ASIC technology.
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| 10. |
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