High-temperature tube corrosion upon ash deposition during oxy-firing of victorian brown coal

Lian Zhang, Iman Jabaz, Juan Chen, Yoshihiko Ninomiya, Barbara Etschmann

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Abstract

This study has examined the corrosion of tubes exposed to Victorian brown coal fly ash under the oxy-fuel combustion mode. The temperature of 650ºC, flue gas composition (steam 30 vol%, O2 5%, SO2 3000 ppm, HCl 1000 ppm, N2 5% and CO2 balanced), and an exposure time of 50 hrs were employed. Through the joint use of advanced instruments such as synchrotron X-ray adsorption spectroscopy and thermodynamic equilibrium calculation, it has been confirmed that, from both mass loss and penetration rate perspectives, the corrosion of low-Cr tubes under the oxy-firing mode is severe compared to the respective air-firing mode. Both flue gas-related and ash-related corrosions are responsible for tube corrosion. In contrast, the corrosion rate of high-Cr tubes (~20% for SUS304 and SUS347) is comparable between the two modes, due to the protective effect of Cr-oxide. The existence of fly ash on tube surface suppressed the chlorination reaction. Oxygen is the principal element permeating into tube under the air-firing mode, whereas both oxygen and sulphur penetrated into the tube under the oxy-firing mode, accelerating sulfation/sulfidation reactions for a rapid corrosion. Although Cr2O3 forms a protective layer under the air-firing mode, it broke down due to the accelerated corrosion attack caused by sulfates/sulphide under the oxy-firing mode. The interaction between ash and tube surface promoted the formation of pure oxides and oxide complexes with the involvement of Na and Ca as well. The presence of alkali sulfates in ash promoted the sulfidation reaction, the extent of which is however tube-specific and correlates little with Cr content. The use of advanced material SUS347 was found to be the most suitable candidate for heat-exchange tubes to be used in the oxy-firing boiler burning low-rank coal such as Victorian brown coal which is rich in alkali and alkaline earthmetals.
Original languageEnglish
Title of host publicationChemeca 2016
Subtitle of host publicationChemical Engineering - Regeneration, Recovery and Reinvention
Place of PublicationMelbourne Vic Australia
PublisherEngineers Australia
Pages252-260
Number of pages9
ISBN (Print)9781922107831
Publication statusPublished - 2016
EventChemeca: Australasian Conference on Chemical Engineering 2016 - Adelaide, Australia
Duration: 25 Nov 201628 Nov 2016
Conference number: 44th

Conference

ConferenceChemeca: Australasian Conference on Chemical Engineering 2016
Abbreviated titleCHEMECA 2016
CountryAustralia
CityAdelaide
Period25/11/1628/11/16

Keywords

  • Victorian brown coal
  • Oxy-fuel combustion
  • Ash deposition
  • Tube corrosion

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