Molten iron dephosphorization method

A molten iron dephosphorization method that uses a top and bottom blown converter charged with molten iron and slag, and that, to perform dephosphorization of the molten iron by blowing an oxygen-containing gas from a top-blowing lance,

• supplies the oxygen-containing gas as a main gas from an inlet of one or more blowing main holes that are disposed so as to extend through an outer shell of the top-blowing lance, and
• supplies a control gas from an opening disposed in an inner wall surface of the blowing main hole toward an axial center of the blowing main hole through a control gas supply passage,
• characterized in that
• the method comprises:
• a slag top-surface position measurement step of, with a position of a top surface of the molten iron having been measured in advance, continuously or intermittently measuring an arbitrary position in a top surface of the slag present on the molten iron;
• a slag top-surface difference calculation step of calculating a slag thickness that is a difference between the measured top-surface positions of the molten iron and the slag;
• and
• a jetting condition adjustment step of, using the obtained slag thickness, adjusting a range of a jetting condition of the oxygen-containing gas jetted from the top-blowing lance, wherein
• the oxygen-containing gas jetted from the top-blowing lance penetrates through the slag on the molten iron and reaches the top surface of the molten iron,
• a depth of a depression in the molten iron made by the oxygen-containing gas having penetrated through the slag is less than 10% of the thickness of the slag, and
• the slag is foaming during blowing of the oxygen-containing gas.