Speaker
Description
The lowest part, the hearth, of the blast furnace is the most non-transparent region of the process as no measurements of the internal state are available due to extremely hostile conditions. Since the life of the hearth lining limits the furnace campaign length and the state of the hearth is of significant importance for maintaining an un-disturbed and well-controlled drainage of hot metal and slag and for the final composition of the hot metal, many attempts have been made to estimate the internal conditions based on indirect measurement information. The present paper presents an analysis of the hearth of a large blast furnace using a model of the lining wear, which is based on the solutions of a set of inverse heat conduction problems. The changes in the lining state throughout the campaign are estimated, and the findings are compared with independent measurements and observations of disturbances experienced in the operation. The hearth is demonstrated to perform efficiently during certain periods, while other periods are characterized by erratic behaviour with excessive growth of buildup material (“skull”) on the hearth wall and bottom. Furthermore, a recurring behaviour is noted, where periods showing skull melting are followed by strong skull formation. Such cyclic behavior has been reported by other investigators and it is hypothesized that a reason could be transition between a floating and sitting state of the hearth coke (“dead man”). An attempt is finally made to quantify the floating state of the dead man by a force-balance based analysis. The results indicate that a vertical motion of the hearth coke may be an underlying reason, but the factors that trigger these changes still remain largely unknown. This calls for a deeper analysis of the role of other variables in future research.