Seiji Nabeshima

Development of Slag Recycling Process in Hot Metal Desulfurization with Mechanical Stirring

In order to develop an environment-friendly steelmaking process, a slag recycling process for hot metal desulfurization by mechanical stirring was designed. The process was developed with 70 kg-scale hot metal experiments and actual plant tests. The recycled slag has a 70% desulfurization ability compared with that of virgin flux (CaO-5%CaF2). The lower efficiency of the recycled slag was caused by SiO2 contamination carried over from the previous process. There is no particular size requirement for the recycled slag, as the effect of the recycled slag size on the desulfurization ability is small. The ratio of CaO in the recycled slag to total CaO should be less than 60% in order to prevent an increase in the amount of slag. Slag recycling operation can be repeated more than twice when the optimum conditions are applied. The slag recycling process was established in an industrial operation, and consumption of desulfurization flux decreased by 40% with the process compared with that without slag recycling. Slag hot recycling was adopted at another plant where consumption of desulfurization flux decreased by 50% compared to operation without slag recycling. The positive effect of hot slag recycling is estimated to be a result of the temperature of the recycled slag.