Detection and Quantification of the Dead Man Floating State in the Blast Furnace
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THE hearth is a crucial part of the blast furnace because the furnace campaign is often limited by the life of the hearth lining and its repair cannot be undertaken without a long stoppage. The operation of the hearth also plays a crucial role in liquids drainage, hot metal temperature and composition.[1,2] In practice, avoiding problems in the hearth is critical, and one primary means for achieving this goal is to keep the hearth coke, the dead man, in an active and permeable state. Because no on-line measurements of the dead man state are available, it has to be estimated through interpretation of available indirect measurements, and mathematical models of the internal phenomena can be used with advantage to extract essential information hidden in the measurements from the lower furnace. If the liquid bath in the hearth is deep enough, the buoyancy force acting on the submerged coke bed may lift the dead man from the hearth bottom. A floating dead man state is more likely to occur in small rather than in large blast furnaces: In the former, the size of the raceway regions, and therefore, the gas buoyancy force, is relatively larger compared with the total burden weight. Both experimental and mathematical models of the liquid flow behavior in the hearth have demonstrated that, under idealized isothermal conditions, even a partial floating of the dead man considerably affects the flow patterns.[3,4,5] The change in flow pattern as a result of a transition from a sitting to a floating dead man state may have both positive and negative effects on JOHNNY BRA¨NNBACKA, formerly with Heat Engineering Laboratory, A˚bo Akademi University, FIN-20500 A˚bo, Finland, is Research Engineer, Mittal Steel USA R&D, East Chicago, IN 46312. HENRIK SAXE´N, Professor, is with Heat Engineering Laboratory, A˚bo Akademi University. Contact e-mail: hsaxen@abo.fi. DAVE POMEROY, Principal Researcher, is with Dofasco Inc., L8N 3J5, Hamilton, ON, Canada. Contact e-mail: dave_pomeroy@ dofasco.ca Manuscript submitted November 16, 2006. Article published online June 15, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
the operation of the furnace. A floating dead man generally improves the drainage of the liquids and prevents a clogging of the dead man, but at the same time, the increased iron flow at the bottom of the hearth accelerates the lining erosion and also leads to increased (intercast) variation in the hot metal composition. From an operational point of view, it is important to know the state of the dead man to be able to take appropriate control actions to promote or prevent floating, and to predict and prevent a rapid erosion of the lining, but very few methods for detecting the dead man motion have been proposed in the literature. A rising heat load on the wall and bottom due to an increased peripheral flow may be detected by studying thermocouple readings.[6,7] This method does not, however, provide any explanation for the change in flow pattern, so an increased peripheral flow as a cause of a transition into a partially floating dead man
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