Effect of iron oxide feeding rate and hot metal temperature on dephosphorization rate in torpedo car

Abstract

In this study, the reduction behavior of iron oxide and the effects of the iron oxide feeding rate and hot metal temperature on the dephosphorization rate were investigated in laboratory experiments and industrial plant tests with the aim of increasing the dephosphorization rate. The results are summarized as follows: (1) When the iron oxide feeding rate was 400kg/min under a constant lime feeding rate, 61 % of the iron oxide is reduced by a transitory reaction zone, while 11 % is reduced by a permanent reaction in the effective reaction zone in the top slag. The remainder is not reduced and remains in the dead zone in the torpedo car in the form of iron oxide. (2) The iron oxide reduction rate in the transitory reaction zone is dependent on the hot metal temperature and iron oxide feeding rate. When the hot metal temperature was reduced from 1 653 to 1 563 K (Δ90°C), the iron oxide reduction rate decreased by 40%. The reduction ratio decreased by 20% when the iron oxide feeding rate was increased from 200 to 400 kg/min. (3) The apparent activation energy of iron oxide reduction was evaluated as 132 kJ/mol, which is slightly smaller than the temperature dependence of the diffusion coefficient of oxygen in FeO-CaO-SiO2 slag. (4) A new mathematical model of hot metal dephosphorization in the torpedo car was developed, which considers the effect of the hot metal temperature and iron oxide feeding rate on the oxygen supply rate. The results with this model showed good agreement with actual data from the torpedo car. © 2005 ISIJ.