Hot Metal Desiliconization Station Begins Operation at Fukuyama

A newly constructed hot metal desiliconization station went into operation at NKK's Fukuyama Works in early March. The addition of this facility to remove silicon from hot metal means that the works is now on its way to achieve a 100% slag-less steelmaking operation, thereby minimizing the volume of slag formed in the process of steelmaking.

In the conventional steelmaking process in which hot metal pretreatment is not employed, removal of impurities such as phosphorus and silicon is carried out directly in a basic oxygen furnace (BOF). This required a large volume of lime consumed in the BOF to treat high-silicon hot metal at high temperatures, resulting in the formation of a greater volume of slag.

NKK's new slag-less steelmaking is an innovative process using ultralow-silicon hot metal, which is then effectively dephosphorized at a low temperature by adding a small amount of lime. As a result, almost no lime is required in the BOF and the formation of slag is greatly reduced. Less slag leads to a higher yield of ultra-clean steel and decreased consumption of ferro-alloys and other resources, realizing ultimate cost and quality improvements.

Since 1995, the Fukuyama Works has expanded low-silicon ironmaking in the blast furnace and hot metal dephophorization practices. However, the level of silicon content in the BF remained at around 0.16%, thereby limiting the application ratio of slag-less steelmaking to around 70% or 80%.

The new desiliconization station (capacity: 420,000 tons per month) enables the efficient mass removal of silicon in the hot metal ladle en route to the BOF, permitting a stable supply of hot metal with a silicon content below 0. 1%. Through the enhanced efficiency of hot metal pretreatment, the Fukuyama Works is set to begin complete slag-less steelmaking operations. As a result, the formation of slag in the BOF operation is almost eliminated, thus reducing the entire volume of slag formed in the steelmaking process to less than 30 kg per ton of steel produced, down from the usual 100 kg.