On-line Analysis of Cr₂O₃ Content of the Slag in Pilot Scale EAF by Measuring Optical Emission Spectrum of Electric Arc

摘要

Control of slag Cr_(2)O_(3) content is essential in stainless steelmaking electric arc furnace (EAF). Excessive Cr_(2)O_(3) content of slag lead to high Cr_(2)O_(3) content after the EAF tapping, since the solid precipitates forming in high Cr_(2)O_(3) contents are not reduced significantly during the tapping procedure. In this work the slag Cr_(2)O_(3) content during the EAF process was analysed by measuring the optical emission spectrum of the electric arc. The measurements were conducted in a pilot EAF situated in Aachen, Germany. Cr_(2)O_(3) content of the slag was increased with periodical additions of Cr_(2)O_(3) powder. The line ratios calculated from the optical emission spectra were compared to the results of the X-ray fluorescence (XRF) analysis of the slag samples taken from the furnace. The results indicate that best accuracy in a pilot scale can be obtained by using Ca I, Fe I or Mn I lines as reference for Cr I lines. By combining the most accurate line ratios of these three components, the Cr_(2)O_(3) composition of the slag could be measured with an average absolute error of 0.62%-points and a standard deviation of 0.49%-points. The results suggest that Fe I and Mn I lines are the most promising reference lines for analysing Cr_(2)O_(3) content of industrial EAF slag.