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- 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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| 2. |
- 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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| 3. |
- 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. |
- Jonsson, Torbjörn, 1970, et al.
(författare)
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The influence of KCl on the corrosion of an austenitic stainless steel (304L) in oxidizing humid conditions at 600 ºC: A microstructural study
- 2009
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 72:3, s. 213-239
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Tidskriftsartikel (refereegranskat)abstract
- The effect of KCl on the corrosion behavior of the austenitic stainless steel 304L was studied at 600 A degrees C in 5% O(2) + 40% H(2)O + N(2). The breakdown of the protective oxide was investigated. This was done through a detailed microstructural characterization of the oxide scales formed after 1, 24 and 168 h. The oxidized samples were investigated by SEM/EDX, FIB and STEM/EDX. The presence of KCl(s) causes a breakdown of most of the protective scale, even though it is not in direct contact with KCl(s) particles, starting after just 1 h exposure. A fast growing porous oxide formed in direct contact with (former) KCl(s) particles and an about 2 mu m thick scale covered most of the surface. Only some regions were covered by a thin scale. K(2)CrO(4) particles were randomly distributed all over the scale after 1 h exposure. The particles are situated above the oxide scale and are not in direct contact with the subjacent metal. The thin scale contains lower Cr levels than has been observed in corresponding scales formed in the absence of KCl. The breakdown of the protective scale is suggested to be caused primarily by the formation of K(2)CrO(4), depleting the protective oxide in chromium. In addition, chromia evaporation contributes to chromia depletion and breakdown of the protective scale. Very little or no transition metal chlorides were found after breakaway oxidation. Cl is suggested to play a minor role in the initial breakdown of the protective scale. The presence of KCl particles caused local rapid oxidation, which results in an outward growing Fe and Fe-Cr rich porous oxide.
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| 8. |
- Karlsson, Sofia, 1982, et al.
(författare)
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Alkali Induced High Temperature Corrosion of Stainless Steel: The Influence of NaCl, KCl and CaCl2
- 2012
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 78:1-2, s. 83-102
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Tidskriftsartikel (refereegranskat)abstract
- The influence of KCl, NaCl and CaCl2 on the oxidation of 304-type (Fe18Cr10Ni) stainless steel at 600 A degrees C in 5 %O-2 + 40 %H2O was investigated. Prior to exposure, a small amount of the preferred salt (cation equivalent: 1.35 mu mol/cm(2)) was deposited on the samples. Exposure time was 1-168 h. The oxidized samples were analyzed by SEM/EDX, XRD, FIB and IC. The presence of KCl and NaCl strongly accelerates high temperature corrosion of 304L. Corrosion attack is initiated by the formation of alkali chromate through the reaction of alkali with the protective oxide. Chromate formation is a sink for chromium in the oxide and leads to a loss of its protective properties. Subsequently a rapidly growing scale forms, consisting of an outer hematite layer with chromate particles on top and an inner spinel oxide layer. In contrast to NaCl and KCl, CaCl2 is not very corrosive. At temperature, CaCl2 is rapidly converted to CaO. Small amounts of CaCrO4 form where CaO is in direct contact with the scale. CaO also reacts with the scale to form Ca2Fe2O5.
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| 9. |
- Karlsson, Sofia, 1982, et al.
(författare)
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KCl-Induced High Temperature Corrosion of Austenitic Stainless Steel 304L – The Influence of SO2
- 2011
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Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 696, s. 224-229
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Tidskriftsartikel (refereegranskat)abstract
- The effect of SO2 on the oxidation of alloy 304L in O2+H2O and O2+H2O+KCl environment has been investigated at 600°C. Exposure time was 1-168 hours. The exposed samples were analyzed by SEM/EDX, XRD and IC. In dry O2, a protective and chromium-rich corundum-type oxide forms. In the presence of H2O(g), chromium is volatilized in the form of CrO2(OH)2(g). The corresponding chromium depletion of the protective oxide triggers a partial loss of protective properties resulting in the formation of oxide islands on the alloy grain centers. The oxide islands consist of an outward growing hematite layer and an inward growing FeCrNi spinel layer. By coating the samples with KCl the chromia depletion of the protective oxide dramatically increases due to the formation of K2CrO4. This leads to breakaway corrosion, a rapidly growing scale forming all over the surface. The resulting thick scale has a similar structure as the oxide islands formed in the absence of KCl. The addition of 300 ppm SO2 to the O2+H2O and O2+H2O+KCl environments results in a drastic reduction of corrosion rate. In O2+H2O environment the effect of SO2 is attributed to the formation of a thin sulphate film on the oxide surface that impedes chromium volatilization and decreases the rate of oxygen reduction on the oxide surface. In O2+H2O+KCl environment the corrosion mitigating effect of SO2 is mainly attributed to the rapid conversion of KCl to K2SO4. In contrast to KCl, K2SO4 does not deplete the protective oxide in chromium by forming K2CrO4. Keywords: Oxidation, Alkali, Breakaway Corrosion, 304L, Chromate, Sulphur
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| 10. |
- Pettersson, Carolina, 1980, et al.
(författare)
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KCl-Induced High Temperature Corrosion of the Austenitic Fe-Cr-Ni Alloys 304L and Sanicro 28 at 600 °C
- 2006
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Ingår i: Corrosion Science. ; 48:6, s. 1368-1378
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Tidskriftsartikel (refereegranskat)abstract
- The influence of KCl(s) on the high temperature oxidation of the austenitic alloys 304L and Sanicro 28 at 600 °C in O2 + H2O environment is reported. 0.10 mg/cm2 KCl(s) was added before exposure. The samples are investigated by grazing angle XRD, SEM/EDX, and AES. In the absence of KCl, both alloys show protective behaviour in dry O2. In O2 + H2O environment, alloy 304L suffers local breakaway corrosion while Sanicro 28 still shows protective behaviour. The oxidation of both alloys is strongly accelerated by KCl. KCl reacts with chromium in the normally protective corundum-type oxide, forming K2CrO4. This depletes the scale in chromia and leads to the formation of a non-protective, iron-rich scale. The significance of KCl-induced corrosion in real applications is discussed and the oxidation behaviour of the two steels is compared.
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