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  • 1.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Davis, C.
    Szakalos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. Vattenfall Res & Dev AB, Sweden.
    Corrosion of the low alloy steel 16Mo3 in the furnace region of used-wood fired boilersManuscript (preprint) (Other academic)
  • 2.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Initial Corrosion of Waterwalls Materials in a Waste Wood Fired Power PlantManuscript (preprint) (Other academic)
  • 3.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    The effect of co-firing of sewage sludge with waste wood on furnace wall corrosion2014In: International Symposium On High-Temperature Oxidation And Corrosion Hakodate, Hokkaido Japan, 2014, 23-27 June, 2014Conference paper (Refereed)
  • 4.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. Vattenfall Res & Dev AB, Sweden.
    Szakalos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Effect of temperature on corrosion of furnace walls in a waste wood fired boiler2015In: Materials at High Temperature, ISSN 0960-3409, E-ISSN 1878-6413, Vol. 32, no 1-2, p. 188-196Article in journal (Refereed)
    Abstract [en]

    One way of reducing the furnace wall corrosion is to lower the temperature of the wall by reducing the boiler pressure. To test this, four coupons of 16Mo3 were exposed in the furnace wall of a waste wood fired boiler for 1075 h. The temperatures of the samples were individually controlled in the range 280-410 degrees C. The corrosion rates and corrosion mechanism were investigated. The deposits were analysed by XRD and SEM/EDS. The corrosion fronts were studied by focused ion beam milling (FIB)/EDS. The environment was modelled by Thermo-Calc. The amount of potassium and chlorine in the deposit decreased with decreasing temperature. The FIB sections showed a distinctive iron chloride layer at the corrosion front, with an outer layer of iron oxide. The corrosion rate decreased with decreasing metal temperature, but the boiler pressure needs to be reduced to a low level to achieve this, which is not beneficial for the electrical efficiency and therefore not a viable way of reducing corrosion.

  • 5.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Szakalos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    The effect of a nickel alloy coating on the corrosion of furnace wall tubes in a waste wood fired power plant2014In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 65, no 2, p. 217-225Article in journal (Refereed)
    Abstract [en]

    The use of waste wood as a fuel in power plants is becoming more widespread in Europe, because it is a renewable energy source with a lower cost than forest fuel. However it is more corrosive than coal and corrosion problems have arisen in the furnace wall area of a low NOx heat and power boiler. The furnace walls are made of a low alloy steel which has been coated in some parts with a nickel alloy to reduce corrosion. In this work, furnace tubes coated with a nickel alloy were compared to the uncoated tubes of the low alloy steel 16Mo3 after 3 years of exposure in the boiler. The nickel alloy coating and uncoated material were also compared with more controlled testing on a corrosion probe lasting for about 6 weeks. The corrosion rates were measured and the samples were chemically analysed by SEM/EDS/WDS and XRD methods. The corrosive environment was also modelled with Thermo-Calc software. The corrosion rates measured from the probe and tube samples of 16Mo3 agreed well with each other, implying linear corrosion rates. The results also showed that the use of nickel alloy coatings changes the corrosion mechanism, which leads to a dramatic reduction in the corrosion rate. The results are discussed in terms of the corrosion mechanisms and thermodynamic stability of the corrosion products.

  • 6.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Talus, A.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. Vattenfall AB, Stockholm 169 92, Sweden.
    Norling, R.
    The effect of co-firing sewage sludge with used wood on the corrosion of an FeCrAl alloy and a nickel-based alloy in the furnace region2015In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 138, p. 805-813Article in journal (Refereed)
    Abstract [en]

    The effect of digested sewage sludge as a fuel additive to reduce corrosion of furnace walls has been studied. The nickel base alloy Alloy 625 and the iron-chromium-aluminium alloy Kanthal APMT™ were exposed for 14.25. h at the furnace wall in a power boiler burning 100% used (also known as waste or recycled) wood. The test was then repeated with the addition of sewage sludge to the waste wood. The samples were chemically analysed and thermodynamically modelled and the corrosion mechanisms were investigated. The results showed that the co-firing of sewage sludge with recycled wood leads to a reduction in the corrosion. Attack by a potassium-lead combination appeared to be the main corrosion mechanism in Alloy 625 during waste wood combustion, while attack by alkali chloride was found to be dominant in APMT alloy.

  • 7.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Viklund, Peter
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    The analysis of furnace wall deposits in a low-NOx waste wood-fired bubbling fluidised bed boiler2012In: VGB PowerTech Journal, ISSN 1435-3199, Vol. 92, no 12, p. 96-100Article in journal (Other academic)
    Abstract [en]

    Increasing use is being made of biomass as fuel for electricity production as the price of natural wood continues to rise. Therefore, more use is being made of waste wood (recycled wood). However, waste wood contains more chlorine, zinc and lead, which are believed to increase corrosion rates. Corrosion problems have occurred on the furnace walls of a fluidised bed boiler firing 100 % waste wood under low-NOx conditions. The deposits have been collected and analysed in order to understand the impact of the fuel.

  • 8.
    Henderson, Pamela
    Vattenfall research and Development.
    Högtemperaturkorrosion i barkpannor: Del 12007In: Nordisk Papper & Massa, ISSN 1652-9995, no 2, p. 58-59Article, review/survey (Other (popular science, discussion, etc.))
    Abstract [sv]

    Ökad eldning av retur- och avfallsbränslen i barkpannor har medfört att alltfler har fått problem med avlagringar och korrosion. Det finns ett stort intresse att minska kostnader för högtemperaturkorrosion genom att förlänga livslängden och att minska risken för oplanerade stopp. Samtidigt finns det starka drivkrafter att förbättra anläggningarnas elverkningsgrad genom högre ångdata.

  • 9.
    Henderson, Pamela
    Vattenfall Research and Development.
    Högtemperaturkorrosion i barkpannor: del 22007In: Nordisk Papper & Massa, ISSN 1652-9995, no 3/4, p. 83-85Article, review/survey (Other (popular science, discussion, etc.))
    Abstract [sv]

    Ökad eldning av retur- och avfallsbränslen i barkpannor har medfört att alltfler har fått problem med avlagringar och korrosion. Det finns ett stort intresse att minska kostnader för högtemperaturkorrosion genom att förlänga livslängden och att minska risken för oplanerade stopp. Samtidigt finns det starka drivkrafter att förbättra anläggningarnas elverkningsgrad genom högre ångdata.

  • 10.
    Henderson, Pamela
    et al.
    Vattenfall Research and Development.
    Andersson, Christer
    Vattenfall Research and Development.
    Szakalos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Kassman, Håkan
    Vattenfall Research and Development.
    Högberg, Jan
    Pettersson, Rachel
    Reducing superheater corrosion in wood-fired boilers2008In: Novel approaches to improving high temperature corrosion resistance: European Federation of Corrosion Publications number 47 / [ed] M Schütze and W.J. Quadakkers, Woodhead Publishing Limited, 2008, p. 428-444Chapter in book (Refereed)
    Abstract [en]

    In the last few years, there has been a move away from burning fossil fuels through the co-utilisation of biomass and coal and finally to 100% biomass such as wood and waste wood products. Unfortunately, burning of biomass causes widespread fouling of superheater tubes and corrosion can occur rapidly under the sticky alkali chloride deposits. Even at today's maximum steam temperatures of 500 to540°C there are some severe corrosion problems when burning  100% wood-based fuel. It is also desirable to be able to burn other environmental fuels such as straw, demolition wood or other wood-waste products, to reduce production costs and avoid dumping waste at landfill sites. This, however, makes the corrosion and fouling problems even more serious. 

     A complete set of superheaters for a 100 MW combined heat and power boiler costs in excess of 1 MEuro. The durability of superheaters is thus an important factor in determining the long-term production costs. Unplanned outages due to leaking superheaters are also very expensive. As well as causing corrosion problems, the build-up of deposits reduces the heat uptake to the superheaters which leads to lower efficiency. Consequently, ways are being sought to reduce superheater corrosion.

    Most biomass fuels have a high content of alkali metals and chlorine, but they contain very little sulphur compared to fossil fuels. Potassium chloride, KCl, is found in the gas phase, condenses on the superheater tubes and forms complex alkali salts with iron and other elements in the steels. These salts have low melting points and are very corrosive. Vattenfall has developed and patented an instrument for in-situ measurement of gaseous alkali chlorides which gives an indication of how corrosive the flue gases are.  This instrument is called an in-situ alkali chloride monitor (IACM).  Vattenfall has also developed and patented a concept with a sulphate containing compound called “ChlorOut” , which is sprayed into the flue gases after combustion is complete, but before the flue gases reach the superheaters, and effectively converts KCl into potassium sulphate, K2SO4.  This compound much less corrosive than KCl.  In the experiments reported here the sulphate used in ChlorOut was ammonium sulphate. This is also used for the reduction of NOx.

     This study reports on measures taken to reduce superheater corrosion in two fluidised bed boilers burning wood-based fuels, using the ChlorOut additive to control the KCl levels and by using more corrosion-resistant steels.

  • 11.
    Henderson, Pamela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Davis, Colin
    Montgomery, Melanie
    Karlsson, Asger
    In-situ fireside corrosion testing of superheater materials with coal, wood and straw fuels for conventional and asvanced steam temperatures2005In: VGB PowerTech, ISSN 1435-3199, Vol. 84, no 6, p. 53-59Article in journal (Refereed)
    Abstract [en]

    An increase in the steam temperature of a power station increases the electrical efficiency of the turbine. This in turn leads to a reduction in the cost of electricity and in environmental emissions produced per unit of electricity generated. However, higher steam temperatures give rise to more aggressive corrosive environments and the choice of material becomes more important. In addition, the aggressiveness of the fuels also depends on their chemical compositions.  As part of a European research programme (COST 522) fireside corrosion tests of superheater and waterwall materials have been performed in-situ in industrial boilers or combustion test facilities, simulating conventional and higher steam temperatures. The fuels used were, straw, wood (logging residues) and coal. Goals were  set at different maximum steam temperatures and lifetimes according to the fuel. The targets were: coal 650°C/100,000 h,  wood 580°C/40,000 h and straw 580°C/20,000 h .A wide range of materials was tested.  An overriding constraint was that the materials must be economically viable and not impose exceptional fabrication requirements. Some materials were tested in a number of combustion environments, allowing useful comparisons to be made. The results showed that for a given superheater alloy, temperature and fuel, the corrosion rate depended on the alloy’s position in a superheater bank. Tubes on the outside, exposed to the flue gas, corroded faster than those positioned deeper in a bank.  Tubes experiencing a greater heat flux will corrode more rapidly. Poorly controlled combustion will also increase corrosion. Straw was much more corrosive than wood (logging residues). The difference in corrosiveness increased with increasing temperature above a metal temperature of about 520°C. The corrosion rates of the alloys tested during wood-firing were only a little higher than those from firing coal with a medium to high chlorine content. Straw and wood are often collectively known as “biomass”, but the corrosion they cause can vary by a factor of 5 or more. No difference could be found in the fireside  corrosion rates of the steels TP 347H and TP 347HFG, when tested under similar conditions. Esshete 1250 also showed similar fireside corrosion rates to347 instraw and wood boilers and at temperatures below 650°Cin coal boilers.

    Several alloys were identified to resist corrosion in coal-fired plant at metal temperatures of680°C(steam temperatures650°C) and high heat fluxes.  Adequate high temperature creep strength remains more problematic.  At lower heat fluxes (resulting in lower corrosion rates) more candidate alloys exist.

    It is expected that the goals set can be achieved with the use of suitable alloys in the case of wood, waste and coal. For wood (logging residues) TP347, Esshete 1250 and 50Ni50Cr coatings showed sufficient corrosion resistance at the target temperatures. In the coal case  HR3C fulfills the requirements of strength and corrosion resistance with a high heat flux and  Super 304H and SAVE 25 if the heat flux is low. HR11N and IN671 are suitable for use as claddings on a substrate with the appropriate creep strength. The goal set for straw firing was ambitious, a steam temperature of580°C, and in this case a combination of material, combustion technology and boiler design are needed.

  • 12.
    Henderson, Pamela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Hjörnhede, Anders
    Vattenfall Power Consultant AB.
    Combating corrosion in biomass and waste-fired plant2010In: 9th Liege conference on Materials for Advanced Power engineering 2010 / [ed] J. Lecomte-Beckers et al, Forschungszentrum Jülich GmbH , 2010, p. 986-999Conference paper (Refereed)
    Abstract [en]

    Many biomass- or waste-fired plants have problems with high temperature corrosion especially if the steam temperature is greater than500°C.  An increase in the combustion of waste fuels means that an increasing number of boilers have had problems. Therefore, there is great interest in reducing the costs associated with high temperature corrosion and at the same time there exists a desire to improve the electrical efficiency of a plant by the use of higher steam temperatures.  Assuming that the fuel is well-mixed and that there is good combustion control, there are in addition a number of other measures which can be used to reduce superheater corrosion in biomass and waste fired plants, and these are described in this paper.  These include the use of fuel additives, specifically sulphur-containing ones; design aspects like placing superheaters in less corrosive positions in a boiler, using tube shielding, a wider pitch between the tubes; operational considerations such as more controlled soot-blowing and the use of better materials.

  • 13.
    Henderson, Pamela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Hjörnhede, Anders
    Vattenfall Power Conultant AB.
    Montgomery, Melanie
    Mekanik, DTU, Denmark.
    Preliminary experience with material testing at the oxyfuel pilot plant at Schwarzepumpe2010In: 9th Liege conference on Materials for Advanced Power engineering 2010 / [ed] J. Lecomte-Beckers et al, Forschungszentrum Jülich GmbH , 2010, p. 1244-1259Conference paper (Refereed)
    Abstract [en]

    Several material related issues may arise from oxyfuel combustion of coal due to the presence of CO2   but also as an effect of the partial recirculation of the flue gas. Two examples are increased corrosion and carburisation which may limit steam data, hence limiting the efficiency.

    A number of corrosion tests, in both conventional air-firing and oxyfuel mode, have been made in Vattenfalls 30 MW oxyfuel pilot plant located in Schwarze Pumpe, Germany. Internally cooled corrosion probes, equipped with ferritic, austenitic, super austenitic steels as well as Ni-based and FeCrAl alloys, simulating superheaters, economisers and air preheaters were exposed for up to 1500 hrs.

    The analyses show an indication of higher material wastage in oxyfuel compared to air combustion especially at the lower exposure temperatures. This may be due to increased sulphur concentration in corrosion front, increased heat flux, carburisation or other preciptate formations on austenitic steels and Ni-based alloys.

  • 14.
    Henderson, Pamela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Kassman, Håkan
    Andersson, Christer
    The use of fuel additives in wood and waste wood fired boilers to reduce corrosion and fouling problems2004In: VGB PowerTech, ISSN 1435-3199, Vol. 84, no 6, p. 58-62Article in journal (Refereed)
    Abstract [en]

    One of the major drawbacks to the implementation of 100% biomass in conventional power station boilers is the increase in the fouling and corrosion of superheaters. Rapid corrosion of superheaters leads to increased maintenance costs while fouling caused by widespread deposit formation gives rise to a decrease in efficiency of the turbine and an increase in unplanned outages. The purpose of this paper is to report on the effects of fuel additives to change the biofuel chemistry, thus making the fuel less problematic and reducing corrosion and fouling problems. Full-scale trials have been carried out in 35MWth and 105 MWth combined heat and power stations.

    Most biomass fuels have a high content of alkali metals and sometimes high chlorine levels, but they contain very little sulphur compared to fossil fuels. It is thought that the addition of sulphur to the fuel could help to reduce corrosion since a deposit containing only alkali sulphates has a higher first melting point than deposits containing alkali chlorides. Molten phases increase the corrosion and fouling rates and in this sense, sulphates are preferred to chlorides in the deposits.

    To investigate the effect fuel additives, trials were initially performed in a 35 MWth wood-fired circulating fluidised bed boiler, adding controlled amounts of sulphur and a newly developed compound additive, called ChlorOut, to the 100% wood fuel feed or flue gases. It was found that the compound additive, ChlorOut, had a greater effect in removing KCl from the flue gases that pure sulphur, whilst having only a marginal effect on the SOcontent of the flue gas and sulphate content and pH of the flue gas condensate.

    Long term tests with ChlorOut were then repeated in a 105 MWth boiler and in addition corrosion probe testing of superheater steels was performed with and without ChlorOut. The results showed that the ChlorOut additive effectively reduced KCl levels in the flue gas at the superheaters, removed chlorides from the deposits, reduced fouling problems and reduced the corrosion rates by about 50%.

  • 15.
    Henderson, Pamela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Lundberg, Mats
    Sandvik Materials Technology, 811 81 Sandviken, Sweden.
    A steam loop for materials testing at 600C in a biomass and waste fired boiler: results of corrosion testing2010In: 9th Liege conference on Materials for Advanced Power Engineering 2010 / [ed] J. Lecomte-Beckers, Q. Contrepois, T. Beck and B. Kunh, Forschungszentrum Jülich GMbH , 2010, p. 1140-1149Conference paper (Refereed)
    Abstract [en]

    A steam loop for corrosion testing was constructed in Esshete 1250 and attached to one of the superheaters in a 100 MWth bubbling fluidised bed (BFB) boiler. The loop raised the final steam temperature to about600°Cat 140 bar.  A number of different test materials were welded into the loop for evaluation at low temperature (500°Csteam) and high temperature (600°Csteam). Their wall thicknesses were measured with a high resolution ultrasonic probe before and after exposure. A number of sections were examined metallographically after exposure. The steam loop was in service for one firing season (about 5500 h) and the fuel mixture was initially a biomass mix co-firing with 15% coal. However halfway though the firing season the coal was replaced with 15% packaging waste containing plastic and aluminium.  The latter mixture (biomass and waste) was highly corrosive and accounted for most of the corrosion.

     

    The alloys with the highest Ni and Cr contents, Haynes230, AC66 and HR11N, showed negligible steam-side corrosion. The 11% chromium steel X20  and the nickel-base alloy HR11N were not tested at the higher steam temperature because of strength considerations. Regarding fireside corrosion at500°Csteam the alloys with the best corrosion resistance were  Haynes 230, HR11N, AC 66 and HR3C followed by Esshete 1250 and  TP347HFG.  The corrosion rate of X20 was unacceptably high and is totally unsuitable for this fuel mix.  At 600°C  Haynes 230 showed the lowest corrosion rates, followed by TP 347 HFG, HR3C, AC66, and  Esshete 1250. Large amounts of internal corrosion were seen.

  • 16.
    Henderson, Pamela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Lundberg, Mats
    Sandvik Materials Technology, Sandviken.
    Corrosion of superheaters at 600C steam in biomass-fired boilers2011In: EuroCorr 2011: developing solutions for the global challenge, 2011, p. 4656-Conference paper (Other academic)
    Abstract [en]

    A steam loop for corrosion testing was constructed in stainless steel and attached to one of the superheaters in a power station boiler which ran on a mixture of biomass and waste. The loop raised the final steam temperature to about600°Cat 140 bar and was in service for 5500 h. A number of different test materials were welded into the loop for evaluation. Their wall thicknesses were measured before and after exposure and a number of sections were examined metallographically after exposure to investigate steam-side oxidation and fire-side corrosion.

     

    The alloys with the highest Ni and Cr contents (over 30 and 20 wt% respectively) showed negligible steam-side oxidation. Regarding fireside corrosion a stainless steel containing 18%Cr and 11%Ni exhibited the second lowest corrosion rates, performing much better than all of the higher alloyed steels.  The corrosion rate for this steel was not temperature sensitive and appeared to decrease as the temperature increased.  Large amounts of internal or selective corrosion were seen in all the materials tested at 600°C steam.

  • 17.
    Henderson, Pamela
    et al.
    Vattenfall Research and Development.
    Szakalos, Peter
    Swedish Institute for Metals Research.
    Pettersson, Rachel
    Andersson, Christer
    Högberg, Jan
    Reducing superheater corrosion in wood-fired boilers2006In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 57, no 2, p. 128-134Article in journal (Refereed)
    Abstract [en]

    One of the major drawbacks to the combustion of 100% biomass in power station boilers is the increase in the fouling and corrosion of superheaters. Experience shows that conventional superheater steels last no more than 20 000 h or four operating years before they must be replaced, if 100% wood-based fuel is used and the steam temperature is higher than 480C. Rapid corrosion of superheaters leads to increased maintenance costs while widespread deposit formation gives rise to a decrease in efficiency of the turbine and an increase in unplanned outages.

    This paper reports on measures taken to reduce superheater corrosion. Most biomass fuels have a high content of alkali metals and chlorine, but they contain very little sulphur compared to fossil fuels. Potassium chloride, KCl, is found in the gas phase, condenses on the superheater tubes and forms complex alkali salts with iron and other elements in the steels. These salts have low melting points and are very corrosive. The corrosion can be mitigated by use of an instrument for in-situ measurement of alkali chlorides in the flue gases, in combination with the addition of ammonium sulphate.  An ammonium sulphate solution, specially developed for the reduction of corrosion was sprayed into the flue gases and effectively converted KCl into potassium sulphate, K2SO4, much less corrosive than KCl.

    Deposit probe tests and long-term corrosion probe tests have been performed in-situ in two biomass-fired fluidised bed boilers. One boiler, 105 MW tot, 540C steam, is the CHP plant in Nyköping,Sweden. The other producing 98 MWtot, 480C steam, is a bark-fired boiler at a pulp and paper mill in Munksund, also in Sweden. Tests have been performed with a range of steel types, ferritic and austenitic, with ammonium sulphate additive and under normal conditions (no additive). Corrosion rates have been measured, deposit chemistry analysed and flue gas chemistry and KCl content measured. The structure and composition of the oxide with and without ammonium sulphate has been investigated. The results show that ammonium sulphate reduced the KCl levels in the flue gases, removed the chlorides from the deposits and the metal/oxide interface, greatly reduced the deposition rates and halved the corrosion rates for superheater materials. The alkali chloride measuring system and the use of ammonium sulphate for the reduction of corrosion have now been patented.

  • 18. Talus, A.
    et al.
    Alipour, Yousef
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Norling, R.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Effect of sewage sludge addition on initial corrosion of 16Mo3 and 310S when exposed in a used wood fired boiler2016In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176Article in journal (Refereed)
    Abstract [en]

    With an expanding use of low quality bio fuels, corrosion problems on water wall tubes are increasing. In this study, the possible corrosion reducing effect when adding digested sewage sludge to the fuel in a used wood (also known as waste or recycled wood) fired furnace has been evaluated. The low alloyed steel 16Mo3 and the stainless steel 310S were exposed for 14.25h at the furnace wall position when firing only used wood and used wood with sewage sludge additions. The exposures were performed in a bubbling fluidized bed boiler and the metal temperature of the test samples was controlled to 350°C. Chemical analysis of the deposits and microscopic evaluation of the metallic samples showed reduced amount of alkali metals and chlorine in the deposit together with reduced initial corrosion for both materials when co-firing with digested sewage sludge. In the corrosion process, metal chlorides were formed for both materials when firing only used wood, iron chlorides for the low alloyed steel, and chromium chlorides for the stainless steel. When co-firing with sewage sludge, this behavior was suppressed.

  • 19. Talus, A.
    et al.
    Alipour, Yousef
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Norling, R.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. Vattenfall Res & Dev AB, Sweden.
    Initial corrosion of 16Mo3 and 310S when exposed in a used wood fired boiler with and without sewage sludge additionsManuscript (preprint) (Other academic)
  • 20.
    Viklund, Peter
    et al.
    Swerea KIMAB AB, Stockholm, Sweden.
    Hjörnhede, Anders
    Vattenfall Power Consultants AB, Göteborg, Sweden.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Stålenheim, Annika
    Vattenfall Research and Development AB, Stockholm, Sweden.
    Pettersson, Rachel
    Outokumpu Stainless AB, Avesta, Swden.
    Corrosion of superheater materials in a waste-to-energy plant2013In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 105, no SI, p. 106-112Article in journal (Refereed)
    Abstract [en]

    A major drawback when generating electricity from waste-fired boilers is the rapid corrosion of critical components such as superheater tubes. In this work a number of commonly-used superheater materials have been exposed on internally cooled probes in a waste-fired grate boiler. The investigated materials are the ferritic steel 13CrMo44, the ferritic-martensitic steel HCM12A, the austenitic steels Super 304, 317L and Sanicro 28, and the nickel-base alloys Hastelloy C-2000 and Inconel 625. Short-term exposures (3 h) for analysis of deposit composition and initial corrosion, as well as long-term exposures (1550 h) to investigate corrosion rates and corrosion characteristics have been made. Analysis revealed a deposit dominated by CaSO4, KCl and NaCl, but also appreciable amounts of low melting salt mixtures such as ZnCl2-KCl, PbCl2-KCl, FeCl2-KCl and NaCl-NiCl2. Metal loss measurements showed unacceptably high corrosion rates for 13CrMo44, HCM12A and Super 304. The corrosion attack for these alloys was manifested by the formation of mixed metal chloride/metal oxide scales. A different type of behaviour was seen for the higher alloyed austenitic steels and nickel-base alloys, which were able to form a chromium-enriched oxide next to the metal. However, these alloys suffered from some localised pitting attack. The behaviour is explained by oxide dissolution in the molten salts that are present in the deposit.

  • 21.
    Viklund, Peter
    et al.
    Swerea KIMAB AB, Stockholm, Sweden.
    Pettersson, Rachel
    Outokumpu Stainless AB, Avesta, Swden.
    Hjörnhede, Anders
    Vattenfall Power Consultants AB, Göteborg, Sweden.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Sjövall, P.
    SP Technical Research Institute of Swdedn, Borås, Sweden.
    Effect of sulphur containing additive on initial corrosion of superheater tubes in waste fired boiler2009In: Corrosion Engineering, Science and Technology, ISSN 1478-422X, E-ISSN 1743-2782, Vol. 44, no 3, p. 234-240Article in journal (Refereed)
    Abstract [en]

    The major drawback to generating electricity from waste fired boilers is the rapid corrosion of superheaters which increases the maintenance costs. Within the last few years, it has been shown that additions of ammonium sulphate to biomass fired boilers decrease the corrosion tendencies. This paper reports on the effects of ammonium sulphate on corrosion in a waste fired CFB boiler. Air cooled probes were exposed at a position corresponding to the one of superheater tubes. The probe temperature was 500 degrees C, corresponding to a steam temperature of similar to 450 degrees C. Both the austenitic steel EN1.4301 (Fe-18Cr-9Ni) and the low alloyed ferritic steel EN1.7380 (Fe-2.25Cr-1Mo) were tested. During exposure, the concentration of alkali chlorides in the flue gas was measured and a decrease was observed when adding ammonium sulphate. After 4 h of exposure, the probes were removed for detailed analysis with SEM-EDS, TOF-SIMS and XRD. The sides of the tubes facing the flue gas were covered with a calcium rich deposit, while relatively more sodium and potassium were present on the lee side. The results also show that ammonium sulphate shifted the deposit composition from chloride rich and highly corrosive, to one significantly less corrosive and dominated by sulphates of sodium, potassium and calcium. Metallography shows a marked difference in corrosion attack between the two steels. Iron chlorides accumulate at the metal/oxide interface of the ferritic steel, while the amounts of iron chlorides were significantly lower in the austenitic steel. These results indicate that ammonium sulphate has the potential to reduce corrosion in waste fired boilers and that austenitic stainless steels are more likely to resist corrosion in these environments than low alloyed ferritic steels.

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