Technical Paper
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Figure 13: Wear profile evolution of the hearth lining of Schwelgern blast furnace n°2 (1993 -2014) [3]
As a consequence, for this blast furnace, the combination of both a special format (small-size bricks) and an improved holding system were used within this target [3].
Since blow-in on 28th October 1993, operating parameters showed that the ceramic cup wall was still inside the hearth for 9 years and further 12 additional years for the carbon lining [3]. This entire furnace campaign of 21 years was recognized to exceed by far customer’s expectations (Figure 13).
Thanks to this result, it can be stated that Saint-Gobain Ceramic Cup concept was validated and a direct consequence is that it is considered in future to modify the design by increasing the ceramic side wall thickness by 50%. Under stable conditions the carbon wall, when protected can last many years. However, under unstable conditions it has been shown that rapid carbon loss can occur [20]. It is hoped that by increasing the Ceramic Cup wall thickness the lifetime can be extended on a pro-rata basis since it less affected than carbon by unstable operating conditions.
DISCUSSION
Thanks to a close collaboration with our ceramic cup customers, thermocouple and software data were collected directly from the field and analysed to evaluate the wear profile of the hearth lining. The Saint-Gobain Ceramic Cup, made of Coranit or Coranit Al walls, undergoes a regular wear from the blow-in stage throughout the BF campaign. It can be stated that the Saint-Gobain Sialon bonded lining is still present inside the blast furnace hearth over a period of time superior to 7.5 years, contrasting with the performance that could be reported for alternative ceramic linings [23, 24].
The Ceramic Cup wear is principally characterized by a regular erosion profile all along the diameter. The sensitivity and accuracy of the software programmes were able to detect localised premature wear positions. These localised wear areas reduced the overall lifetime of the whole or average ceramic wall such as observed for BF n°4 when operational difficulties were encountered. However, even during periods of operational difficulty the localised wear on the Ceramic Cup whilst worrying was not considered to be significant. Only when the Ceramic Cup wall disappeared was a really significant wearing observed (over 400 mm carbon disappeared in a few months).
The Ceramic Cup wear profile is quite homogeneous with slightly higher wear rate below the tuyere area. This is not really surprising as this area is known to be the hottest zone of the hearth in direct contact with highly corrosive slags. Less pronounced, an excess of erosion is underlined in the elephant foot zone where the mechanical stresses are the highest. This observation is common for each analysed BF and confirmed by the final Schwelgern II wear profile. It will be interesting to study the final wear characteristic after the CC has disappeared in this zone for ArcelorMittal blast furnaces in Fos-sur-Mer to determine whether this mechanism is more pronounced in ceramic or in carbon lining.
Based on the wear rate, it appears that the ceramic wall protects efficiently the carbon over the first 7.5 years. This observation can reasonably be attributed to the Sialon bonded ceramic properties especially its high resistance to iron and slag contact combined with excellent stability to the various chemical attacks. For the latter point, many customers reported that the brittle layer is generally localised and visible in the residual carbon layer during a blast furnace dismantling [15, 25]. This phenomenon seems to be reduced with a ceramic wall [15] by maintaining the isothermal of alkali condensation inside the ceramic brick rather than inside the carbon layer. Our knowledge of wear profiling is increasing and is leading towards a new design with increased Ceramic Cup brick thickness to maintain the isotherms as long as possible inside the ceramic lining and benefit from the superior wear characteristics of the Sialon-bonded corundum to increase BF lifetime campaign.
CONCLUSIONS
Since Saint-Gobain started to promote the new concept of Sialon-bonded Ceramic Cup, more than 20 years of intensive collaboration were necessary to follow, track and measure the benefit of our innovation.
In this paper, the consolidated and factual data highlight the real benefit of having a Saint-Gobain designed Ceramic Cup protection in front of carbon lining. We can now reasonably state that this ceramic lining resists with its whole integrity for a period of time superior to 7.5 years inside the hearth, fully assuming its role of carbon lining protection.
These benefits, shared by most of our customers, incite the most audacious and innovative of them to henceforth envision a new design based on an increased ceramic cup thickness and to request a new material generation
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ENGINEER THE REFRACTORIES
July 2017 Issue
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