Fully Automatic Blowing Technique in BOF Using Slag Formation Control System

Abstract

Blow end control technique for carbon content and temperature in BOF has been remarkably improved by sublance. However it is necessary to develop technique for slag formation control for the purpose of obtaining over 90% simultaneous hitting ratio for carbon content and temperature and controlling of phosphorous content.
In Mizushima Works, for continuous detection of slag formation in BOF, various experiments such as measurement of furnace vibration, calculation with waste gas analysis, and measurement of sound were performed. Thus, the best reliability in the continuous monitoring of slag foaming height was found by measuring lance vibration during blowing. This technique is based on the principle that degree of lance vibration is correlated with lance length immerzed into foaming slag and oxygen flow rate. When slag foaming height is continuously detected, slag formation control can be realized by the correction of lance height or oxygen flow rate by computer. Combining this slag formation control technique with program blowing and blow end control ones, fully automatic blowing system was established. The system improved the hitting ratio and yield of steel, reduced reblowing ratio and lengthened furnace life.