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FURNACES
• There were empty spaces and gaps in the carbon blocks close to tap hole. • Steam penetration of the level V top surface of carbon blocks. Visible roughness on carbon surface. • Vertical cracks in carbon blocks. As a result of a visual survey of both repaired tap holes the scope of relining was extended to an additional three blocks in level VI on both spots. Extra sidewalls were dismantled to remove blocks with discontinuities in structure. A decision was taken to shorten virgin blocks to avoid intensive projection in relation to the existing hearth profile and resultant mechanical stresses. Installation started with the cleaning of the top surface of the carbon block (layer V) and partial machining to improve the flatness of existing carbon blocks. This operation is visible in Fig. 9. Following installation of first three blocks in relation to layer VI, parallel works involving the installation of mortar bricks were started. UCAR bricks have been glued with graphite mortar directly to the staves to achieve a good heat transfer to the cooling system. Cold phase layers have been built using NMD type bricks (~70W/m°K) and hot phase with NMA bricks (~18W/m°K) which have higher wear resistance. In terms of quality parameters, it was important to secure proper thickness of mortar joints,
Fig 6. Sample of core drilling
Fig 7. Tap hole engineering done by Pirson
but not greater than 2mm. Second, tight insertion of each brick with connection to the old lining was performed using hydraulic pumps. This installation method was continued until the last level of large carbon blocks (level 9). Starting from the newly created flat surface the entire lining up to the tuyeres level was built with only UCAR material. On reaching the tuyeres level, however, the project team decided to cast parts of the protective ceramics with a high alumina material above both tap holes. This solution satisfied the requirements of short-time application and created good, solid protection by the time fresh slag made skull. All new tap hole blocks were equipped with thermocouples to establish continuous monitoring of the thermal state. Some spot grouting was necessary to stabilise blast furnace gas leakages. Currently, blast furnace no. 2 is operating under stable conditions. Conclusion The relining took 37 days and 18 hours,
meeting the target and becoming a great planning and organisational success. Not a single lost time injury occurred, which is significant taking into account 300,000 working hours. Since the outlined method of tap hole relining took place, blast furnace number 2 has proved reliable. There have been no hot spots and no tap hole has shown any signs of failure or reduced reliability. Hot burden removal has proved that with a proper level of risk assessment it can be done in a safe way securing the remaining carbon lining and avoiding water quenching.
Acknowledgments The author wishes to thank all those who supported what was a difficult relining project. He extends special thanks to Andrzej Chyzy, Yves de Langhe, Patrick Negro and the entire blast furnace and engineering department at ArcelorMittal and wishes to express his gratitude to Pirson Group, SGL Group, Graftech and HPR Centrex.
Layer X - 249mm IX - 577mm VII - 563mm VII - 510mm VI - 704mm
Virgin blocks
Average wear profile
Fig 8. Hearth survey prepared by SGL
March 2016
Furnaces arcelormittal.indd 3
Fig 9. Levelling of layer VI
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