Finaal voordrag Franske version2
14
Franske Stenden Dr. J.P. Beukes Dr. P.G. van Zyl Mr. R.I. Glastonbury Final presentation, 14 November 2014 North-West University, Potchefstroom Honours project 2014 Chromium research: Characterisation of Söderberg electrodes using XRD and breaking strength
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Transcript of Finaal voordrag Franske version2
Franske StendenDr. J.P. BeukesDr. P.G. van ZylMr. R.I. Glastonbury
Final presentation, 14 November 2014North-West University, Potchefstroom
Honours project 2014 Chromium research:Characterisation of Söderberg electrodes using
XRD and breaking strength
Content
1. Introduction
2. Aim
3. Experimental Procedures
4. Results
5. Conclusion
Introduction & Background
• Electrodes: transmit electricity from transformers to ore mix
• Two types electrodes: Söderberg- and pre-baked electrodes
• Söderberg predominantly used – lower cost
• Sketch illustrating general functioning
Innvaer, R., Olsen, L., Vatland, A., 1984. Operational parameters for Söderberg electrodes from calculations, measurements and plant experience. In:Proceedings: Mintek, vol. 50, pp. 787–797 .[1] Innvær, R., 1992. A status for the Söderberg smelting electrode. In: Proc. of UIE,Electrotech 92. Montreal, Canada.[2]
Introduction & Background
B. Larsen, H. Feldborg, S.A Halvorsen. Minimizing thermal stress during shutdown of Söderberg electrodes. 2013.
• Poor electrode management: electrode breakage
• Almost no research published since 1970 in scientific journals
• Only conference contributions by electrode component manufacturers
Aim
The aim was to uncover means of improving electrode
management in the FeCr industry: centred on the
graphitisation occurring in a Söderberg electrode & breaking
strength changes of the region beneath the contact shoes.
Accepted by operation staff, the level of graphitisation and
strength of the Söderberg increases as the electrode is
presented to higher temperatures. This forms the general
consensus in terms of handling the Söderberg electrode,
these postulations are not supported in published scientific
studies. Research conducted in this study aims to examine
the authenticity of these assumptions.
Experimental Procedures
• 100mm core drill samples were drilled from the 1.3m diameter X 2.5m (long) electrodes
• Samples were drilled every 0.3m to 0.5m from the top of the electrode
• Only used: samples cut off 1m below the contact shoe, the top-most middle, and the bottom core drill samples
• A cutting machine was used to slice the core drill samples into 10mm thick slices
• The 10mm slices were drilled into smaller pellets: pellets then used for analysis
Sample technique
Experimental Procedures
X-ray diffraction (XRD)• The degree of graphitisation (DOG) was calculated using
XRD
Breaking strength testing• Tests the physical strength of the pellets
Scanning electron microscopy (SEM) • Reveals differences between calcined anthracite and coal
tar pitch.
Results
0
5000
10000
15000
Counts
Position [°2θ] (Copper (Cu))28 28.50 29
Displacement Corrected K-alpha2 substracted Original
X-ray diffraction (XRD)
• Subtracting K-alpha2 component, adding internal standard
• Applying 2θ peak maximum correction
Results
Position [°2θ] (Copper (Cu))25 30
Counts
0
10000
20000
30000
0
10000
20000
30000
0
10000
20000
30000
X-ray diffraction (XRD)
"a"
"b"
"c "
• XRD spectrum of three Söderberg electrode samples
• “a” top, “b” middle and “c” bottom core drill samples
• Degree of graphitisation virtually the same, i.e. 34.5%, 34.6% and 34.7% for samples "a", "b" and "c" respectively
Results
Breaking strength
0 200 400 600 800 1000 12000
0.2
0.4
0.6
0.8
1
1.2
Length vs load at maximum load
Length vs load at max load 24+ 100 Length vs load at max 166+100 Length vs load at max load 85+100
Length
Load
at m
axim
um lo
ad (k
N)
“a”
“b”
“c”
Results
0 200 400 600 800 1000 12000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1Length vs load at break
Length vs load at break 24+ 100Length vs load at break 166+ 100Length vs load at break 85+100
Length
Load
at b
reak
(kN
)
“a”
“b”
“c”
Breaking strength
Results
Scanning electron microscopy
Conclusion
• XRD showed that the the degree of graphitisation of the calcined anthracite stayed virtually the same.
• Shoulder developing: indicative of coal tar pitch graphitisation
• No substantial difference in breaking strength
• Future studies: graphitisation of coal tar pitch will be further investigated
