Since 1999, the Thermographic Slag Detection system TSD is being operated successfully at converters. Here, the different emissivity of steel and slag is being analysed in the infrared range. This system does not need any sensors at or in the converter.
The transfer of BOF & EAF slag during the tap is recognized as an important issue in today’s steel-making process. In order to control slag transfer, it has to be measured. AMEPA’s new slag detection system, the TSD, measures this transfer by means of thermographic analysis.
The Laws of Physics state that electromagnetic energy is radiated when a body temperature is above absolute zero. The amount of energy radiated depends on factors such as composition, surface properties and temperature. Non-contact temperature readings are measured with this radiated energy. Radiation factors also allow items of the same temperature to be distinguished. This is possible because of the difference between the composition and/or surface properties.
When transferring molten metal, steel and slag approximately have the same temperature. But the composition and surface properties are different, so the slag flowing on the surface can be identified.
Human eyes distinguish between steel and slag by seeing a transition from white to yellow in the molten stream. But it is very difficult to identify this transition due to the high radiation intensity.
With a specialized infrared camera and sophisticated image processing, the molten metal stream can be illustrated to show a significantly greater contrast. For instance, the steel to slag contrast can be displayed as a transition from yellow to green.
A reliable slag detection system must identify the steel-slag transition under varying operating conditions. Influencing factors for the measurement principle include:
Steel tap temperature differences
Taphole changes that affect mass/energy, and surface conditions/emissivity levels
Changes in air humidity & dust levels that affect the transmission of infrared radiation
Radiation from other sources
A quality system must have the intelligence to recognize and suppress these influences.
The AMEPA System achieves this by directing the infrared camera signal to an industrial PC, where the image processing is done. This software solution allows the automatic identification and tracking of the tap stream.
Within the software, various algorithms identify changes to the tap stream emissivity, and stream-to-camera radiation transmission levels. The camera parameters are automatically adjusted in an adaptive manner. Optimal operation of the system is therefore achieved. In the tap pulpit, the molten stream is displayed on a suitable monitor for use by the BOF operators. A bar graph on the Tap Pulpit Monitor displays the percentage, or index, of slag in the visible stream area.
Since the TSD system generates a significant contrast between steel and slag, an alarm can be generated. The alarm limit is fully adjustable and can be readily set by operating personnel.
When the Slag Alarm occurs, the bar graph turns red and an audible alarm is set. The alarm signal can also be transmitted to other computer systems via analog or serial interface. This alarm is easily connected to taphole stopper or slidegate systems for automatic shut-off.
Each tap is recorded and relevant information can be transmitted to the customers computer database for viewing and storage. The stored tap images generated by the system are useful for training and documentation purposes.
System status, fault and diagnostic codes are reported and shown on the system’s monitors, and are stored in a daily log file.