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

Abstract

The drainage of the hearth plays an important role for the operation of the ironmaking blast furnace. An undisturbed extraction of the produced molten materials from the hearth is a prerequisite of a smooth operation of the high-temperature region, and a good mixing of liquid iron and slag in the taphole and runner helps desulfurize the iron. The flows of molten iron and slag in the blast furnace taphole have not received much attention, even though several investigators have studied the hearth drainage phenomena. In the present paper a two-fluid model of the taphole flow, based on an assumption of full stratification of the two liquids, is developed, and coupled with a simple material balance for the furnace hearth. Furthermore, the pressure loss of the liquids in the dead-man in front of the taphole inlet is considered. Simulations with the model are applied to illustrate how different factors affect the drainage, liquid levels and taphole flow. It is demonstrated that the in-furnace conditions play an important role for the flows and the flow distribution between iron and slag. The effects of key variables, such as coke-bed voidage and coke size, are illustrated and conclusions concerning their impact on the drainage are drawn.KEY WORDS: taphole; two-phase flow; hearth drainage; blast furnace.hearth drainage and taphole flow, paying special attention to the latter condition. A simultaneous flow of two immiscible liquids through a (slightly inclined) pipe is encountered in a variety of industrial processes, but usually the density and viscosity differences of the two liquids are not as big as for the molten materials in the BF taphole. Despite these differences, the model equations for fully stratified flow are known and can be rather readily applied to the present problem. [13][14][15][16] However, the pressure loss in the coke bed (dead-man) in front of the taphole for the two phases has also to be considered. The novelty of this work is to use a two-fluid (TF) model to describe the dynamic features of iron and slag flow in the taphole and to couple this with a simple description of the hearth drainage process. ModelingThe present study simulates the hearth drainage of a small or medium-size BF with a single taphole. According to the typical tap cycle, 17) the taphole is generally kept plugged for about 20-30 min to let the injected taphole mud solidify properly after the previous tapping operation. This section describes the main assumptions made in the modeling, as well as the arising equations of the model. Simplifying AssumptionsSince the conditions of dead-man and taphole are extremely complex during the tapping operation, some assumptions must be made in order to be able to simulate the tap cycle. The following simplifications are therefore introduced (where the 'iron level' and the 'slag level' refer to the overall vertical levels in the hearth of the iron-slag interface and the slag-gas interface, respectively): a) The dead-man sits at the bottom of hearth and its voidage is constant. b) The liquid v...

Pressure Drop in the Blast Furnace Hearth with a Sitting Deadman

“…According to our preliminary work, the flow length also depends on the geometry of the system, such as taphole diameter, hearth diameter and sump height, as mentioned by other authors. 12,13) Nevertheless, the present work has revealed some fundamental issues that can be useful in a more detailed modeling of the system.…”

The tap-hole - key to furnace performance

“…A detrimental feature reported for alternating tapping on BFs, where a zone of low permeability exists between tapholes, is the potential for the slag level to rise due to excessive pressure loss, which disrupts bosh gas flow (Iida et al, 2009;Shao, 2013;Shao and Saxen, 2011, 2013a, 2013b. Slag levels could conceivably fluctuate on SAFs similarly, owing to the presence of less permeable zones.…”

“…Similar two-phase liquid entrainment and an initial declination of the slag interface towards the tap-hole as tapping commences followed by a switch to initial inclination and even 'pumping' out of the tap-hole later in the tap has been modelled on BFs by CFD (Shao, 2013;Shao and Saxen, 2011, 2013a, 2013b. However, in the modelling of BF tapping, He and co-authors (2012) caution that the metal should not be maintained at a depth too low above the taphole, as one runs a risk of entraining process gas by 'viscous fingering' during tapping, especially (1) when the slag viscosity is high, or (2) in the presence of a permeable bed of solids through tapping occurs (e.g.…”

A Simulation Study of Two-liquid Flow in the Taphole of the Blast Furnace

“…[1][2][3][4][5][6][7][8][9] Most investigators have focused on the effect of various in-furnace conditions, including coke size, dead man porosity and coke-free zone on (gas, iron and slag) multiphase flow in the hearth. The two-liquid flow in the taphole, however, has received very little attention and was usually ignored or strongly simplified in these studies.…”

“…The validity of this assumption may be questioned, as large density and viscosity differences between the two phases would make it natural to assume the taphole flows to be stratified, which motivates a separate treatment of the two phases in the taphole. This treatment was adopted in the earlier work of the authors of the present paper, 9) where the drainage behavior of iron and slag in BF hearth was simulated by employing a two-fluid model (TM) to assess the pressure drops induced by two-liquid flows both in hearth and the taphole.…”