A model for estimation of erosion and skull profiles of the blast furnace hearth is presented. The model, which is based on thermocouple measurements in the hearth bottom and wall lining, estimates the most severe erosion of the lining experienced during the campaign and also the present thickness of the skull material. The model is illustrated on process data from two Finnish blast furnaces. Complementary measurements and calculations are used to verify the results. Based on the findings, conclusions are drawn about the internal state of the blast furnace hearth, for instance, whether the dead man floats or sits at the bottom. Finally, some suggestions on how to control the state of the furnace hearth are given.KEY WORDS: erosion and skull profiles; blast furnace hearth; dead man. sitting dead man. Hood 7) reported on the use of the skull thickness to monitor the hearth lining and to take control actions against erosion.To be able to estimate the state of the hearth, a model for calculating the remaining sound lining and the amount of skull on the bottom and wall based on thermocouple readings has been developed. The model solves an inverse heatconduction problem to determine the erosion and skull profiles using time averages of thermocouple signals from the lining. By monitoring the results from these wear profile calculations, indications may be obtained on the need to adapt the operation towards conditions less prone to cause erosion. In case of severe damage, the results can even be thought to trigger the planning of a relining of the hearth. The estimates from the skull calculations, in turn, can be used to assist in the interpretation of the internal state of the hearth. In this work, the calculated amount of skull has been verified by correlating this estimate with other key variables, such as production rate, hearth coke voidage, and pressure loss of the furnace. Some suggestions on how to control the amount of skull on the hearth wall, primarily by adjusting the cooling rate in this region, are finally presented. Model for Calculation of Hearth Wear and SkullingThe calculation of the hearth wear and the amount of skull on the hearth wall is based on the commonly accepted procedure of estimating the location of the 1 150°C isotherm in the hearth lining: Carbon saturated pig iron cannot exist below this temperature in liquid form, so this isotherm corresponds to the maximum hot metal penetration in the lining. The erosion profile is usually estimated as the most severe location of this isotherm experienced during the furnace campaign. If, in turn, the estimated location of the isotherm falls inside the erosion line, the volume between these two is considered to be filled with skull material.The general ideas outlined above are followed in the present model, the kernel of which is a routine for calculating the temperature distribution in the hearth lining. To estimate the location of the 1 150°C isotherm, the position of it that gives the best fit between the calculated temperature distribution and the te...

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 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 two-dimensional mathematical model of steelmaking ladles is presented. The model can be used as a design tool, by which a number of variables such as holding time, material choice, and refractory layer thicknesses can be studied with regard to their influence on the steel temperature evolution during casting. In addition, the model can act as a decision support and as a basis for automation of temperature control. Temperature measurements from an operational steelmaking ladle are compared to simulation results obtained with the model, demonstrating its feasibility and applicability to steelmaking. I. BACKGROUNDwas done by numerical integration of the heat-conduction equation for the ladle wall. [4,5,[11][12][13][14] Due to the intricate IN modern steelmaking, after the introduction of the conboundary-condition changes for the equation as the ladle tinuous casting process and new refractory materials, steel cycles through various stages of secondary metallurgy, onetemperature control within the narrow bounds called for by dimensional solutions at different height positions in the quality requirements has become increasingly demanding.refractory have been adopted as a sufficient means for steel As holding times for steel in the ladle have increased and temperature prediction. [14,15] Although this approach is process logistics often over-rule thermal-and energyappropriate for on-line simulation, more powerful modeling efficiency aspects, improved strategies for heat-loss estimaand simulation tools are required to achieve a deeper undertion for the steel are necessary. Contemporary refractory standing of thermal phenomena in the ladle cycle, e.g., materials, with improved durability and longer campaign through parametric studies. life, are thermally inferior to traditional brick material, i.e.,Another application of thermal modeling of metallurgical their heat conductivity and specific heat are larger, resulting ladles is the design of refractory configurations. [16,17,18] This in increased heat losses from the steel. Over multiple ladle has been a growing field, with the advent of new materials cycles, this can also lead to unacceptably high shell temperacapable of withstanding longer campaigns and higher temtures for the ladle, introducing problems with shell buckling peratures but, unfortunately, having less-advantageous and lining separation. thermal properties. Traditionally, engineering of ladle refractories has been done by confirming, with steady-state calculations, that the refractory and shell temperature stayed II. INTRODUCTION within permissible temperature bounds. Although this Over the years, a number of thermal models for ladle mostly produced acceptable lining-material assemblies, systems has been presented. Early contributions feature simsince the steady state would give substantially overestimated ulation of heat losses and refractory temperature profiles on temperatures, it was hard to foresee long-term effects over an analog computer. [1,2] More-recent approaches range in multiple ladle cycl...

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