Indicators of the Internal State of the Blast Furnace Hearth.

Abstract

The hearth is a crucial region of the blast furnace, since the life of its refractory may be decisive for the campaign length of the furnace. Excessive growth of skull on the hearth wall and bottom, in turn, reduces the inner volume of the hearth, causes drainage and other problems that limit productivity, and has a negative effect on hot metal temperature and chemistry. A set of indicators that reflect the internal state of the hearth has been developed. The motivation for the indicators is outlined and their application to hearth state detection is illustrated with several examples from the operation of two Finnish blast furnaces.KEY WORDS: blast furnace hearth; dead man state; erosion and skulling; slag delay. Indicators of the Hearth State Lining Wear and SkullingA model estimating the residual lining and the thickness of the skull layer on the hearth wall and bottom has been developed.7) The routine determines the location of the 1 150°C-isotherm that gives the best match between measured and calculated temperatures for a set of two-dimensional vertical cross-sections of the hearth (Fig. 1), aggregating the results into a three-dimensional representation of the internal profile, as shown in Fig. 2. The model describes the state of the lining and its results can be used as a basis for decisions on control and maintenance actions, e.g., whether a relining or injection of Ti-bearing materials to form protective skull on the hearth lining should be scheduled to avoid a breakout, or if a drop in hot metal production is necessary to avoid excessive hot metal velocities. By examining the evolution of the 3-D representation, it is possible to follow the progress of the erosion and skulling in time. However, when the results of the model are correlated with other process data, it may be more useful to study the evolution of quantities such as the available hearth volume, 6) calculated on the basis of the model's results (cf. Sec. 3). The Internal State of the Hearth CokeIn spite of its name, the dead man, i.e., the core of the hearth coke, is known to play an important role for the operation of the blast furnace. Its shape and permeability influence the hot metal and slag velocities and flow patterns in the hearth, and, therefore, also affect the erosion or formation of skull and the drainage of the two liquid phases. Heat and mass transfer between the slag and iron phases are also affected by the dead man state. Furthermore, the dead man may also have an impact on the conditions in the upper part of the furnace through its possible vertical motion along with changes in the levels of liquids in the hearth. In the following, some indicators of the state of the hearth coke are presented. Slag Delay and Hearth Coke VoidageA simple but extremely informative variable that reflects the internal state of the hearth is the slag delay, t slag , i.e., the time that elapses after the tap is started until slag enters the runner. The delay, which is roughly a function of the (extreme) levels of the iron-slag interface and the ta...

Model Analysis of the Operation of the Blast Furnace Hearth with a Sitting and Floating Dead Man

“…21) Hence, this state was taken as a reference case for a sitting dead man. Simulation on the data for Day 2 (cf.…”

“…5,21) Considerable variations in the slag delay were observed in BF B, showing a strong negative correlation with changes in the volume of the hearth. In BF A no correlation between slag delay and hearth volume has been observed, even though the hearth volume has varied considerably.…”

“…The difference between the furnaces is believed to depend mainly on the floating state of the dead men: In BF B indicators show that the dead man floats during parts of the campaign, while there are no such indications in the data from BF A. 21) In what follows, the model described in Sec. 2 is applied on data from BF B.…”

“…In BF A no correlation between slag delay and hearth volume has been observed, even though the hearth volume has varied considerably. 21) The measured slag delays and the estimated hearth volumes of the furnaces have been depicted in Fig. 7.…”

“…This observation applies for both BF A, where the dead man has been sitting during the whole campaign, and BF B during the first year after blow-in, when the hearth was unworn, but also during later periods when the hearth was clogged. 21) A one-hour slag delay is obtained if the initial iron level is Dz ir min £0.25 m below the taphole, varying somewhat with production rate, hearth cross-sectional area and coke voidage. As for the slag surface, its initial level cannot be measured or estimated accurately.…”