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High temperature corrosion during waste incineration: characterisation, causes and prevention of chlorine-induced corrosion
Swerea KIMAB AB, Stockholm, Sweden.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Waste-fired boilers suffer severely from corrosion of critical components such as superheater tubes. In this work the high temperature corrosion of candidate superheater alloys have been investigated by detailed laboratory studies and controlled field exposures in full-scale boilers.

In a laboratory study the detrimental effect of gaseous hydrochloric acid (HCl) on three  different ground surface and preoxidised austenitic stainless steels was investigated. Exposures were conducted in an environment comprising N2-10O2-5H2O-0.05HCl at both 400 °C and 700 °C. A positive effect of preoxidation is evident when the alloys are exposed at 400 °C. Oxide layers formed during preoxidation effectively suppress chlorine ingress and lower the corrosion rate for all three materials while accelerated corrosion and chlorine accumulation at the metal/oxide interface is detected for ground surface specimens. The positive effect of preoxidation is lost at 700 °C and corrosion resistance is dependent on alloying level. At 700 °C metal chloride evaporation contributes significantly to the material degradation. Based on the results, high temperature corrosion in the presence of gaseous HCl is discussed in general terms.

 In two different waste-fired boilers measures for counteracting superheater corrosion were investigated. In a grate-boiler the deposit formation and high temperature corrosion of some candidate superheater materials were studied. Metal loss measurements showed unacceptably high corrosion rates for the lower alloyed ferritic steels 13CrMo44 (Fe-1Cr-0.5Mo) and HCM12A (Fe-11Cr-2W), as well as for the austenitic Super 304 (Fe-18Cr-9Ni-3Cu). 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, the alloys suffered from localised pitting attack. Since analyses of the deposit revealed appreciable amounts of low melting salt mixtures such as ZnCl2-KCl, PbCl2-KCl, FeCl2-KCl and NaCl-NiCl2, oxide dissolution in these molten salts is the probable reason for pitting attack. In a waste-fired boiler ammonium sulphate solution was added to the flue gas and the effect on flue gas and deposit composition was evaluated. It was evident that the sulphur-rich additive reduced the amount of alkali chlorides in both the flue gas and the deposit. Results also indicated that the initial corrosion rates were lowered with the use of ammonium sulphate. It was concluded that using the additive could be a possible strategy for changing the flue gas chemistry so that superheater corrosion is mitigated.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 50 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:18
Keyword [en]
high temperature corrosion, waste incineration, superheater tubing, steel, alkali, chlorine, suphur
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-32412OAI: oai:DiVA.org:kth-32412DiVA: diva2:410556
Presentation
2011-04-08, Ytkemiska Institutet, Drottning Kristinas väg 51, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20110414

Available from: 2011-04-14 Created: 2011-04-14 Last updated: 2013-11-07Bibliographically approved
List of papers
1. HCl-induced high temperature corrosion of austenitic stainless steels under thermal cycling conditions and the effect of preoxidation
Open this publication in new window or tab >>HCl-induced high temperature corrosion of austenitic stainless steels under thermal cycling conditions and the effect of preoxidation
2011 (English)In: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 76, no 1/2, 111-126 p.Article in journal (Refereed) Published
Abstract [en]

Gaseous HCl released during combustion is one reason for the severe materials degradation often encountered in power generation from waste and biomass. In this study, three stainless steels (the low alloyed EN 1.4982, the standard EN 1.4301 and the higher alloyed EN 1.4845) were tested by repeated thermal cycling in an environment comprising N2–10%O2–5%H2O–0.05%HCl at both 400 and 700 °C. The materials were exposed with ground surfaces and preoxidised at 400 or 700 °C. A positive effect of preoxidation is evident when alloys are exposed at 400 °C. Oxide layers formed during preoxidation effectively suppress chlorine ingress for all three materials, while chlorine accumulation at the metal/oxide interface is detected for surface ground specimens. The positive effect of preoxidation is lost at 700 °C and corrosion resistance is dependent on alloying level. At 700 °C metal chloride evaporation contributes significantly to the material degradation. Based on the results, high temperature corrosion in chlorinating environments is discussed in general terms.

National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-120439 (URN)10.1007/s11085-010-9227-1 (DOI)000294691800008 ()2-s2.0-79960315001 (ScopusID)
Note

QC 20130408

Available from: 2013-04-05 Created: 2013-04-05 Last updated: 2013-11-07Bibliographically approved
2. Corrosion of superheater materials in a waste-to-energy plant
Open this publication in new window or tab >>Corrosion of superheater materials in a waste-to-energy plant
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2013 (English)In: Fuel processing technology, ISSN 0378-3820, Vol. 105, no SI, 106-112 p.Article in journal (Refereed) Published
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.

Keyword
high temperatur corrosion, waste incineration, deposits
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-32407 (URN)10.1016/j.fuproc.2011.06.017 (DOI)000312414400015 ()2-s2.0-84869089947 (ScopusID)
Note

QC 20130110

Available from: 2011-04-14 Created: 2011-04-14 Last updated: 2013-04-08Bibliographically approved
3. Effect of sulphur containing additive on initial corrosion of superheater tubes in waste fired boiler
Open this publication in new window or tab >>Effect of sulphur containing additive on initial corrosion of superheater tubes in waste fired boiler
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2009 (English)In: Corrosion Engineering, Science and Technology, ISSN 1478-422X, Vol. 44, no 3, 234-240 p.Article in journal (Refereed) Published
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.

Keyword
Waste fired boilers, Superheaters, Power generation, High temperature corrosion
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-32408 (URN)10.1179/174327809X419203 (DOI)000269201500010 ()
Note

QC 20110414

Available from: 2011-04-14 Created: 2011-04-14 Last updated: 2013-04-08Bibliographically approved

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