A model has been developed to simulate and analyse the overall performance of the blast furnace hearth. The model is based on a set of simplifying assumptions concerning the inflow and outflow rates of iron and slag, and on a hypothesis concerning the general operating principles of liquid drainage. These assumptions have, in earlier studies, proved to be adequate for capturing the overall behaviour of hearths in industrial blast furnaces. The model, which also considers the case where the 'dead man coke' floats in the iron bath, can be used for what-if analysis of how, for example, hearth geometry, sump depth, production rate, slag ratio, and tapping time influence the drainage procedure. A set of simple equations for certain special cases is presented. The model is illustrated by examples of how changes in boundary and internal conditions affect the performance of the hearth.

The phenomena in the blast furnace hearth are extremely complex and the possibilities to directly measure its internal state are practically non-existent. In order to control the process to achieve smooth operation and long campaigns, a thorough understanding of the conditions in the hearth is required. Such knowledge can be gained through mathematical modeling of the internal conditions. Since the properties of the dead man are known to considerably affect the hearth conditions, a model describing the operation of the hearth with a sitting, partially or completely floating dead man has been developed. Simulation of the tap cycle of a one-taphole blast furnace shows the effect of boundary conditions, hearth geometry, coke voidage and dead-man floating state on the evolution of the liquid levels and the slag delay. On the basis of the computed inner geometry of the hearth, the model has been applied to data from a six-year period of a Finnish blast furnace, and it has been found to accurately predict the long-term variations in the slag delay.KEY WORDS: blast furnace hearth; tap cycle; dead man floating; slag delay. scend further to a certain (given or calculated) level below the taphole at the end of each tap. Under these assumptions, the voidage of the dead man can be estimated once in every tap cycle from produced and tapped quantities of iron.According to Zulli, 13) a coke-free zone at the bottom of the hearth does not influence the cyclic behavior of the liquid levels as long as its volume is constant and it does not extend above the surface of the iron phase. However, if a coke-free zone below the dead man exists, the reason must be that the dead man is (at least partially) floating, so the position of the dead man, and thus also the size of the free space below it, depends on the volume of the liquids in the hearth. From this it follows that it is likely that the volume of the free space varies and affects the liquid levels. Therefore, the methods for estimating the dead-man voidage reviewed above apply only for a hearth with a sitting dead man. This is one of the motivations behind the modeling effort presented in the present paper, where the effect of a floating dead man on the liquid levels is investigated. In particular, the implications of dead-man floating on the slag delay, t sl , i.e., the time of iron-only flow in the beginning of the tap, is studied. Modeling The Tap CycleIn blast furnaces with one taphole, the tapping of iron and slag from the hearth follows a typical cycle, schematically illustrated in Fig. 1. When the taphole is closed both iron and slag accumulate in the hearth because of the progress of reduction and smelting of iron and slag formation. In the hearth the two liquids form separate layers, the dense iron on the bottom and the light slag layer floating on top of the iron bath. The taphole is generally kept plugged for at least 20-30 min to let the injected taphole mud solidify properly. Thus, as the tapping begins the iron-slag interface, henceforth called the iron level, is us...

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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...

A model for estimation of the profiles of erosion and buildup material in the hearth of an ironmaking blast furnace has been developed. The model is based on thermocouple readings in the hearth wall and bottom and solves an inverse heat transfer problem for two-dimensional slices of the hearth geometry to estimate the inner profile. Special attention has been paid to the mathematical formulation of the problem at hand, yielding a general model optimized for fast computation. This includes a flexible formulation of the boundary conditions, a generic setup of the lining materials applied in the hearth refractory, and a sophisticated iterative procedure in the estimation of the location of the internal profile. These steps have led to a model that facilitates process analysis with estimation and reestimation of the furnace hearth conditions over whole campaigns using different parameter settings. The model has been applied to study the evolution of the hearth erosion and buildup formation processes in several industrial furnaces.

The drainage of a blast furnace hearth is analyzed on the basis of measurements of the instantaneous mass flow rates of tapped iron and slag, obtained from radar level measurements in the iron ladles and a pressure signal from the slag granulation drum. The measurements are used in a model estimating the levels of liquids in the blast furnace hearth, where correction terms have been introduced to prevent the level estimates from excessive drift. When applying the model on data from two Finnish blast furnaces, it was found that the estimated iron level exhibited strong correlation with the electromotive force (emf ) measured between two electrodes at the furnace shell. The results of the model are in general agreement with results reported by other investigators. The performance of the model is illustrated by some examples, and a procedure for considering the case of a floating dead man is proposed.KEY WORDS: blast furnace; iron and slag levels; hearth drainage; tap rates.

A mathematical model has been developed to provide realtime information about the important stages of the tapping operation of the ironmaking blast furnace (BF). The model tracks the levels of molten iron and slag inside the hearth based on a continuous analysis of produced and tapped liquid quantities, further considering the internal state of the hearth, including its geometry and the state of the coke bed. Because of inaccuracies in the model and in the measurements from the process, an optimal filtering method, the extended Kalman filter, is applied to provide reasonable liquid level estimates. For real-time predictions, the model additionally utilizes measurements of the electromotive force (emf) between two electrodes attached to the furnace shell, and predicts the occurrence of important events in the tap cycle, such as the duration of the present tap. The model has been found to provide valuable information about the crucial steps in the tap cycle.

The lower part, the hearth, is a crucial region of the ironmaking blast furnace. The life length of it often determines the campaign length of the furnace and the thermal state and permeability of the hearth exert strong influence on liquids drainage and hot metal chemistry. In order to operate the furnace efficiently, the hearth state should be controlled, but the conditions in the hearth are extremely hostile with little possibility to carry out direct measurements. This article presents a set of methods and models through which the floating of the hearth coke bed, the dead man, can be assessed. Data from three industrial blast furnaces illustrate how a systematic analysis of available measurements, in combination with results of mathematical models of the phenomena in the hearth, can successfully detect and quantify the dead man floating state.