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

Abstract

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...

A Simulation Study of Blast Furnace Hearth Drainage Using a Two-phase Flow Model of the Taphole

“…When the tapping starts, i.e., when the taphole is drilled open, iron and slag flow out through the dead-man and taphole. Many researchers [1][2][3][4][5][6][7][8][9][10] have studied this complex system, primarily concentrating their efforts on analyzing the effects of inhearth conditions, such as coke diameter, dead-man voidage, and extent of the coke free region, on the drainage behavior. As for the conditions in the taphole, most of these studies assumed either a constant pressure loss or assumed iron and slag to be a mixture of specified volume ratio and applied mean values of density and viscosity in describing the flow.…”

Research Status and Development Trend of Numerical Simulation on Blast Furnace Lining Erosion

“…In the early, researchers [27][28][29]32,[35][36][37][38][39][40] supposed the dead-man was cylinder or hemisphere, owed uniform voidage, and filled the hearth along the radial. The simulation results 29,32) revealed the volume of free coke in the hearth significantly affect the line erosion, the narrower the space, the faster the metal flow, the heavier the erosion.…”

“…And because there is no suitable measurements in the hearth at present, the numerical simulation, furnace dissection, 12,41) , physical model 13,15) and simple estimation 16) are the common ways to study the hearth. The early hearth model is decoupled with the heat transfer in the refractory, which only investigated the flow at first, gradually the natural convection, 17) carbon dissolve, [18][19][20][21][22] the effect of the dead-man, [22][23][24]26) taping and tap-hole, 23,35) flow stress profile, [27][28][29] etc. Latterly since Tachimori 30) and Ohno et al 31) undertook a pioneering effort to develop the relationship between hot metal flow and heat transfer in the hearth, and all kinds of comprehensive models were put forward, such as porous media model, VOF (Volume of Fluid) model and DEM (Discrete Element Method).…”

Heat Transfer Analysis and Estimation of Refractory Wear in an Iron Blast Furnace Hearth Using Finite Element Method

“…12) In the present investigation, an axisymmetric finite element heat transfer model has been formulated to calculate the temperature profile inside the hearth refractories and estimate the maximum (worst) hearth wear, and a computer program is developed based on the model. The model incorporates different types of boundary conditions in terms of prescribed temperature, prescribed heat flux and prescribed convection at the cold faces (side walls and underhearth) as well as hot metal-refractory interface.…”