Laser-induced breakdown spectroscopy for advanced characterisation and sorting of steel scrap (LCS) : final report

The use of laser-induced breakdown spectroscopy (LIBS) for scrap analysis and sorting has been industrially evaluated in this project. A LIBS prototype was developed and installed for scrap analysis at the output of an industrial shredder (conveyor belt velocity 1 m/s) and at a pendulum conveying trough (0.3 to 5.5 m/min, width x depth approx. 2 m x 1 m) feeding an electrical arc furnace (EAF). The steel scrap throughput in both applications is within the range of 10 to 100 tonnes per hour, typically. The capability of the developed prototype for robust automated chemical scrap analysis in an industrial environment was shown. For example, the online measurement of silicon content shows good agreement with slag and steel analysis of the EAF melt, although the developed prototype detected only a fraction of the scrap load surface, due to the restricted measuring volume of 600 × 600 × 180 mm3. Increasing the measuring volume should further improve the performance. Furthermore, sorting trials were carried out with a lab-scale LIBS sorting system at 3 m/s with a projected throughput of 10 tonnes per hour to evaluate its sorting potential. The technique's high capability to recover FeMn steels from a flow of stainless steel and also the ability to sort out objects containing copper from a ferrous iron flow was demonstrated. Expert systems for scrap classifications have been investigated and the algorithms show high fidelity for sorting applications.