Accurate knowledge of slag level in iron-making processes is a key issue for scientific furnace control to increase productivity and ensure safe operation.
The level measurement method can be broadly divided into contact and non-contact. Contact methods are pressure, float, electric resistance and conduction methods and non-contact methods include microwave, ultrasonic and radiation. The level can be measured by selecting a suitable method with the characteristics of measurement objects and the measurement environments in consideration.
In the Hismelt process, the core is a smelting reduction vessel, where the molten steel is tapped in a continuous mode by a siphon front, unlike conventional blast furnaces, and the slag discharge is periodic. Contact methods are not suitable for measuring the slag level in a closed Hismelt furnace, but non-contact methods are needed. Radiation method is appropriate for measuring the level of boiling slag in a closed furnace like a Smelt Reduction Vessel (SRV).
With an attempt to evaluate the level of slag in a Smelt Reduction Vessel (SRV) where hot air is introduced into a closed furnace and iron ore is melted, Ri Hye Won, a researcher at the Institute of Analysis, proposed a method of level measurement. In this method, radiation source and radiation detectors are installed outside the furnace and each detector is operated like a relay.
He selected a 137Cs source with radioactivity of 3.2Ci as the radiation source and placed five NaI(Tl) scintillation detectors uniformly in the interval from the copper cooling box position to the hot wind lance, the interface of slag and molten metal, to measure the level of slag flow zone (2m).
The Monte Carlo simulation and experiments verified that slag levels in the range of 10~200cm from the copper cooling box could be estimated with accuracy of ±10cm.