Abstract
The condition and state of the hearth of the blast furnace is of considerable importance since the life length of the refractories governs the campaign length of the furnace, but it is also of significance as it affects the drainage of iron and slag and the hot metal temperature and composition. The paper analyses the hearth of a blast furnace using a model of the lining wear based on the solution of an inverse heat conduction problem, studying the changes in the lining state throughout the campaign. Different operation states are detected, characterized by smooth and efficient hot metal production and by erratic behavior with large disturbances in the hearth state. During the periods of poor performance, the hearth exhibits a cycling state with stages of excessive skull growth on the unworn refractory, followed by periods of dissolution of the skull and lining erosion. An explanation of the transitions is sought by a stating and solving a force balance for the deadman with the aim to clarify whether it is floating or sitting. A connection between the thermal cycles in the hearth and the hot metal sulfur content is finally demonstrated.
Highlights
THE hearth is a crucial part of the blast furnace because its refractory lining is subjected to harsh conditions, but it cannot be repaired without a full stoppage of the furnace.[1]
The hearth of a two-taphole blast furnace has been studied by a two-dimensional wear model, which estimates the progress of the erosion line and the formation of build-up material (‘‘skull’’) on the hearth wall and bottom
After some initial erosion followed by a period skull formation, a time period of very efficient and smooth operation follows, with low coke rate and high PCI rate. The hearth during this period is estimated to be slowly eroding, but the refractory lining is protected by a thin skull layer
Summary
THE hearth is a crucial part of the blast furnace because its refractory lining is subjected to harsh conditions, but it cannot be repaired without a full stoppage of the furnace.[1]. The wear of the lining, and growth of build-up material, skull, may occur. The erosion during the full campaign has to be scanned to detect the ‘‘worst case’’ at every location,[4] and any decrease in the lining temperature from this point would indicate skull growth. Skull may occur in some regions of the hearth simultaneously as other regions experience erosion. This calls for a systematic treatment of the problem. The analysis of the present paper applies a two-dimensional wear model[7] based on a regularized inverse heat conduction problem to yield an overall view of the hearth wear and skull formation in three dimensions.
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