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Since blow-in stage on 22nd November 2001, operating parameters analysis has highlighted that the ceramic cup wall was still inside after 7.5 years of operation (Figure 4). Residual Coranit brick thickness average was estimated to be around 100 mm.
Here, the global wear of brick lining is regular on all blast furnace cross- sections except for one measure detected at level 04 below the tuyere n°1. Based on this weak point, the ceramic cup wall lifetime has been reduced to 7.5 years even though residual thickness of Coranit brick is measured on the rest of the entire hearth circumference after more than 8 years (Figure 4).
Unfortunately, it was not possible to identify clearly blast furnace operating events to explain the wear below tuyere 1 level 4.
However, some abnormal events occurred soon after blast furnace blow-in were reported by the user:
- Immediately after blow-in, some hot spots with gas leakage within one tap-hole area and propagating in the interstitial space between the carbon lining and the steel shell were detected. This issue was stabilized by numerous grout injections from the outside in various shell locations.
- In 2003, tap-hole n°1 was blocked during several weeks. Significant operations were performed using oxygen lance through the emergency tap- hole to reconnect the tuyere/tap-hole. This is the most likely hypothesis mentioned for the user.
Difficulties observed on each tap-hole leading finally to a general stoppage for full tap-hole repair in April 2016 as illustrated Figure 5.
It seems reasonable to believe that these repairs (grout injection amount and property, local additional stress, etc.) or operational procedures would impact the lining stability and could certainly explain the weak point occurrence.
The refractory corrosion rate increases consistently with the BF elevation (Figure 6) putting forward the existence of an erosion gradient in this BF below the tap-hole to the bottom.
GRW thickness (meter)
BF n°4 level
BF
elevation (meter)
01 02 03 04
2.40 3.10 3.80 4.38
Initial
2.42 2.40 2.38 2.35
Average in-situ measure
2.68* 2.47* 2.16 2.06
Average wear evolution (%)
GRW
≈ 0% ≈ 0% 9%
13% CW (Coranit)
≈ 0% ≈ 0% 54% 74%
Figure 6: Average wear profile data measured 8 years after BF n°4 blow-in
A large number of modelling studies reported that heat flow distribution in the hearth and temperature distribution in the hot metal and in refractories [9, 10, 11, 12, 13] are significantly influenced by several often dependent factors, which are principally:
- The fluid flow resulting from daily tap-hole tapping [14]. In this process, significant local flow behavior in blast furnace hearth, especially in the coke free region, occurring also when all tap-holes are closed [15] and known to be responsible for refractory material erosion [16, 17].
BF n°1 level
BF
elevation (meter)
01 02 03 04 05 06
5.35 5.95 7.15 8.40 9.80 11.15
Initial
1.83 1.83 1.73 1.73 1.73 1.58
Average in-situ measure
1.83 1.80 1.58 1.60 1.59 1.39
- Dead man position and characteristics saturation) [15, 17, 18].
- Hot iron fluid characteristics: temperature, density and viscosity, fluid tilt during taping [19].
- Carbon dissolution impact, maximum in the high-speed zone near and around tap-hole [14].
Monitoring was accurate enough to detect when rapid wear occurred local to the tap-hole below tuyere 1 level 4 (Figure 5). It can be seen that the remaining Cup suddenly disappeared towards the end of 2009. In addition, over 400 mm of carbon rapidly disappeared at this time also (Figure 4); this rapid carbon wear characteristic has been already reported [20].
This was the start of a more local monitoring of the tap-hole areas which eventually led to the repair outage in 2016 for repairs. The repairs made in 2016 (almost 15 years after blow-in the Cup had eventually worn away) highlighted that the carbon thickness was generally close to original thickness. This can be seen in the photo of the repaired tap-hole (Figure 5).
Blast furnace operators of the Ceramic Cup concept should note once more the importance of the rapid carbon wear that was experienced on Dunkerque BF4 once the Cup disappeared. Even during periods of accelerated wear, such rapid loss was never experienced by the Ceramic Cup, only the carbon. This proves once again the protecting and attenuating aspect of the Cup during periods of BF operational instability.
ArcelorMittal – Fos-sur-Mer
In both blast furnaces (BF n°1 and BF n°2), a Coranit Al brick wall of 400 mm was installed. Thermocouples were installed regularly around the hearth with positions ranging from 5.3 m to 11.2 m (Figure 3). The design of both furnaces is rigorously the same.
BF n°1
No issues were detected over the first 8 years after blow-in (10th January 2008). Using Mothus wear profile model, Coranit Al brick wall remained inside the blast furnace on the entire circumference with no reported weak point (Figure 7).
GRW thickness (meter)
Average wear evolution (%)
CW GRW
≈ 0% 1% 9% 7% 8%
12%
(Coranit Al)
≈ 0% 5%
37% 31% 35% 48%
Figure 7: Wear profile data measured 8 years after BF n°1 blow-in (ArcelorMittal – Fos-sur-Mer)
If we consider the most corroded parts (level 03 to 06), 62% of initial Coranit Al thickness is still inside the hearth corresponding to a residual brick thickness around 248 mm.
The corrosion profile is quite regular all along the blast furnace elevation * It will be considered that a lining thickness superior to initial will be the result of iron pig solidification on brick surface (iron gangue). As a result the wear rate will be considered to be close to 0%. July 2017 Issue ENGINEER THE REFRACTORIES
Technical Paper (porosity, permeability,
23
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