Optimum taphole length and flow induced stresses

The flow induced shear stress on the wall of a blast furnace hearth has bee n computed by solving the Navier-Stokes and Darcy flow equations in the hea rth numerically. The Navier-Stokes equations were used to compute the flow field in the coke free zone, while the Darcy flow equation was used for the flow of liquid metal in the coke packed porous zone (known as the deadman) . The computed velocity field was utilised to determine the shear stresses on the side wall of the hearth for various lengths of taphole and different types of deadman when the hearth is filled with liquid metal. It was found that the peak stress on the wall of the blast furnace reduces significantl y as the length of the taphole increases. However, the peak stress again in creases above a certain length of taphole, for a floating deadman, indicati ng an optimum taphole length to be used to minimise the fluid induced shear stress. For the case of a sitting deadman the increase of peak stress with taphole length, above the optimum length, is marginal, but it was possible to determine a clearly defined optimum taphole length. For the case of no deadman the peak stress was found to decrease continuously with increase in taphole length; hence, an optimum taphole length could not be determined. It was also found that the location of the maximum equivalent sheer stress shifts in the increasing direction of 0 almost linearly with an increase in taphole length. (C) 2001 loM Communications Ltd.