Accretion growth on single-pipe tuyeres: Part II. Model results and discussion

Abstract

A mathematical model of accretion growth on single-pipe injectors has been used to analyze the process of accretion growth during copper converting and inert gas stirring of steel. A sen-sitivity analysis of the model developed in Part I of this article revealed that the critical unknown factor controlling the growth process is the local bath velocity. It is likely that the asymmetric forms seen in accretions are due primarily to nonuniformity in bath flow around the accretion. The important factors controlling the size of accretions in copper converting are bath superheat, gas flow rate, and oxygen content. Blockage of the tuyeres in the converter is a function of wall and bath superheat and likely is a result of the freezing of matte in the pipe. The effect of gas-flow rate on accretion size is clearly shown in the case of inert gas injection into steel. The transition between the different accretion types found on single-pipe tuyeres, pipes, porous pipes, and hemispheres, depends on events at the tuyere-pipe tip. Conditions of high back-attack frequency, low superheat, and small tuyere diameters tend to lead to accretions forming over the tip. If this takes place at high injection pressures and with a relatively ductile material, a “porous plug” will form, on which a hemisphere will grow. Under other conditions, it may result in a blockage. The presence of accretions at a tuyere has a strong influence on the thermal profile in the surrounding refractory and tuyere pipe. Steep thermal gradients near the tip in both regions will likely lead to refractory deterioration and pipe distortion.