Drainage Model of Multi-taphole Blast Furnaces

Abstract

A drainage model of a multi-taphole hearth of a (large) blast furnace operated by alternate tappings has been developed. The model, which is based on a simplified treatment of the pressure losses in the dead man, taphole entrance and taphole, can estimate the liquid levels and outflow rates of the two liquid phases in quasi-stationary and dynamic states. The sensitivity of the results to changes in the conditions, such as taphole length and diameter, dead-man porosity, as well as in the model parameters is illustrated. The effect of asymmetric conditions at the two tapholes, and dynamic responses of particular interest are also illustrated and discussed. The results of the model are finally compared with findings from a reference blast furnace where the outflows rates of iron and slag are routinely estimated, demonstrating that several of the typical outflow patterns observed in the furnace can be at least quantitatively reproduced. This demonstrates the feasibility of the model as a tool for gaining deeper insight into the complex drainage with alternating tappings and the evolution of the liquid levels in the hearth of large blast furnaces.

Experimental Study of Blast Furnace Hearth Drainage Based on Image Analysis

“…A varying slag-layer thickness at tap start can arise in a multitaphole BF due to an imbalance in the slag flow from the alternating tapholes, as reported in the literature. [11,12,17] To gain an understanding of some of these factors, a set of experiments were undertaken with the pilot model, as explained later.…”

“…In the practical operation, the initial l-l level can be sensed by observing the outflow orders of iron and slag from the furnace at the tappings, and the slag delay (i.e., the time of iron-only flow in the beginning of the tap) has been demonstrated to be an important indicator of the hearth state. [13,14,17,24]…”

“…A simple liquid-level model by Shao and Saxén [16] incorporated a model of the taphole, assuming a stratified flow of iron and slag. More recently, Roche et al [17] presented a drainage model of a multitaphole furnace based on a simplified treatment of the fluid flow and demonstrated that the model was able to explain outflow patterns observed in a large BF.…”

Dead-Man Behavior in the Blast Furnace Hearth—A Brief Review

“…The bottom shape and position of the dead man depend on the liquid levels in the hearth and on the force acting on the bed from above. In a normal tap cycle, the liquid levels vary with varying outflow rates of iron and slag, due to the intermittent tapping, as the taphole is eroded during tapping, and because of the "competition" between iron and slag flow in the taphole [24]. Mainly based on balance equations of mass and force, the liquid levels in the BF hearth with two different dead man floating states were estimated and are shown in Figure 2, where the corresponding filtered electromotive force (emf) signals measured at the hearth shell are also depicted [25].…”

“…A substantial pressure drop in the vicinity of the taphole can be formed as the high-viscosity slag is driven to flow through the dead man towards the taphole. As a result, the gas-slag interface is tilted down locally near the taphole [24,[59][60][61][62]. Thus, the overall gas-slag interface is above the taphole level at the moment when gas bursts out and the tap is terminated.…”