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Förutsättningar för ökad livslängd av sandlåsöverhettare
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
2018 (Swedish)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesisAlternative title
Conditions for increased life time of superheaters in loop seals (English)
Abstract [en]

Superheaters suffer large material loss during combustion of waste and biomass, causing a short life time for these expensive components. During combustion, corrosive ash particles are formed and erosion is caused by circulating bed material and sand particles, all contributing to the material loss. This study examines whether corrosion or erosion has the largest effect on this material loss by investigating two superheaters in loop seal during biomass and waste combustion of an 85 MW, Circulating Fluidized Bed (CFB) boiler in Händelö.

The samples were investigated by SEM/EDX and XRD with regard to material loss and corrosion products. The superheaters have different thermal conditions since the material temperature in the first superheater that the steam passes is lower than in the one that comes after. In this report, a model to determine the tube temperature in steam boiler superheaters is also described due to the fact that the local tube temperature is of great importance of condensation of corrosive gases such as KCl and NaCl.

Material loss was significantly greater on the cooler superheater compared with the warmer. The material temperatures on the outside of the tubes, were calculated to be about 574 °C for the cooler superheater and about 617°C for the warmer superheater. Overall, all analyzes showed low levels of corrosive substances, although there was a certain corrosion tendency, which indicates that material loss of the superheaters is caused by corrosion-assisted erosion. Lower material temperature of the superheater resulted in a higher degree of condensation of corrosive species such as alkali chlorides, which might have accelerated the erosion.

The conclusion is that the dominant mechanism of material loss on the superheaters is erosion. 

Place, publisher, year, edition, pages
2018. , p. 49
Series
UPTEC K, ISSN 1650-8297 ; 18003
Keywords [en]
corrosion, erosion, loop seal, cfb, cfb boiler
Keywords [sv]
korrosion, erosion, sandlåsöverhettare, överhettare, cfb, intrexöverhettare, intrex, p15, händelöverket, cirkulerande fluidiserande bädd, fluidiseringshastighet, fluidisering, eon, värmeöverföring
National Category
Corrosion Engineering
Identifiers
URN: urn:nbn:se:uu:diva-343511OAI: oai:DiVA.org:uu-343511DiVA, id: diva2:1186253
Subject / course
Chemistry
Educational program
Master Programme in Chemical Engineering
Supervisors
Examiners
Available from: 2018-02-28 Created: 2018-02-27 Last updated: 2018-11-21Bibliographically approved

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