Oxidschichtbildung und Materialprobleme metallischer Werkstoffe bei Verbrennungsprozessen mit Heizöl EL

Scope of the present work was the investigation of the oxide scale formation on metallic high-temperature alloys resulting during reaction with the atmosphere of the combustion of industrial gas oil (IGO). The Ni-Cr-based alloys 601 (2.4851), 602 (2.4633), 603, 693 and 617 (2.4663) were tested at elevated temperatures between 900°C and 1050°C in a burner rig equipped with a low-NOx recirculation burner by application as material of the burner flame tube. Further on, the oxide scale on a woven wire cloth made of a Ni-Cr-based alloy was analysed. The wire cloth was used as the hot surface of a radiant burner at temperatures of approximately 685°C for an operation time of 844 h. All alloys investigated in the low-NOx burner rig showed following oxide scale structure: a chromium oxide scale at the alloy surface and aluminium or silicon oxide (on alloy 603) beneath. Particles with a composition similar to that of the bulk alloy were found enclosed in the chromium oxide scale. Frequently these particles were located near the oxide-gas boundary indicating an impending local degradation of the chromium oxide scale. Aluminium oxide grew predominantly along grain boundaries in the depth of the bulk. During the test period of up to 3000 h no aluminium oxide scale was found. For longer investigation times accelerated internal oxidation of aluminium was observed.In contrast to aluminium, silicon formed an albeit noncontinuous scale of silicon oxide directly below the chromium oxide layer. The diffusion of chromium towards the surface was inhibited by the silicon scale, which resulted in a slower kinetic of the chromium oxide growth and consequently a thinner chromium oxide scale. However, as the silicon oxide scale was not protective. Mo-oxides formed in the bulk – Mo being an alloying element of alloy 603 – followed by breakaway oxidation. In case of the aluminium alloyed material the formation of nitrides in the bulk indicated the breakdown of the oxide scale. Failure of the alloys was related to massive inward nitrogen diffusion and the formation of aluminium nitrides in the bulk. Therefore it is assumed that in nitrogen rich atmospheres a high aluminium content is unfavourable due to the strong affinity of aluminium to nitrogen. In general it was observed, that at lower temperatures, as a result of a slower growth kinetic, the nitride formation began later.Short term tests of 50 hours of alloy 602, alloy 603 and alloy 693 showed, that a thicker and more uniform oxide layer formed when the burner was operated with standard quality IGO (1700 mg/kg S), compared with the oxide scale formed in the case of operation with fuel with reduced sulphur content (20 mg/kg S). Ventilation with air after burner shut down had no significant effect on chromium oxide scale thickness.The time dependence of the observed growth of the chromium oxide scale was fitted with a power law. A deviation from the parabolic law has been found indicating an oxide loss due to spallation.Reasonable estimation of life time was achieved by logarithmic plots of the time dependence of the chromium depletion measured by line scans on cross sections of the samples.The metallographic investigation of the hot surface of the radiant burner showed a thin continuous chromium oxide layer. No indication of damage of the scale, a small depth of internal oxidation and the absence of a significant chromium depletion zone were found. Hence, a long life time of the woven wire cloth can be expected.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Teneva-Kosseva, Guergana I.

Contributors dc:contributor

• Köhne, Heinrich

• info:eu-repo/classification/ddc/620
• Ingenieurwissenschaften
• Hochtemperaturoxidation
• Ni-Cr-Basislegierungen
• Verbrennung
• Oxidschichtbildung
• Lebensdauer
• high-temperature oxidation
• Ni-Cr-based alloys
• fuel oil combustion
• oxide scale formation
• life time

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122475%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:60785