Determining protective layer thickness of blast furnaces

A method of determining the thickness of a protective layer of solidified metal skull formed on the refractory hearth of a blast furnace wherein the refractory hearth has temperature probes embedded at spaced locations in radial directions from the center of the furnace and at various elevations across the thickness of the floor and walls thereof, comprising the steps of:

• a. periodically measuring temperatures at said spaced locations in said radial directions and across the thickness of the furnace hearth floor and walls by the temperature probes embedded therein;
• b. determining the maximum temperature recorded by each temperature probe since the beginning of a campaign of the furnace and the average temperature recorded by each temperature probe during a current time period;
• c. analyzing the relation of said campaign maximum and current average temperatures of said temperature probes embedded in the hearth walls correlated with the radial distance between the temperature probes and the center of the furnace and the relation of said campaign maximum and current average temperatures of said temperature probes embedded in the hearth floor correlated with the elevation distance between the location of the temperature probes in the hearth floor so as to predict the location of the wear line of the refractory hearth from the location of a solidification isotherm closest to a metal shell, and to predict the location of the inner surface of a solidified metal skull lining said refractory hearth from an isotherm closest to the hot side of the furnace remote from the metal shell, and
• d. determining the thickness of the protective layer of solidified metal skull from the distance between the predicted wear line of the refractory hearth and the predicted inner surface of the metal skull.