On-line analysis of process conditions in ilmenite smelting with optical emission spectrometry

摘要

Ilmenite smelting in EAF (electric arc furnace) is the main process used in producing TiO_2 slag. The slag is used as a raw material by the pigment industry for the production of pure TiO_2 powder. The most important control parameters in ilmenite smelting are the ratio between ilmenite feed and electrical power input, as well as the ratio between ilmenite feed and carbon input. Deviation from optimal values of these control parameters destabilizes the process, which is observed as changes in slag composition and temperature.In order to analyze the changes in these process parameters, in situ measurement of optical emission spectrum of electric arc and slag in DC-arc furnace was conducted. Optical emission spectrometry is a method which relies on optical transitions of atoms and ions in the arc plasma. In addition to these transitions, emission spectrometry provides insight on the thermal radiation emitted by .the measured material.The measurements were conducted with a pilot-scale DC-arc furnace in Outotec Research Center, located in Pori, Finland. In these measurements the optical emission was gathered with an optical fiber attached on the furnace roof, and the analysis was conducted remotely with a commercial spectrometer. The optical fiber was protected with a measurement head, which was purged with nitrogen.The best quality data was obtained when the feed was off during the manual slag height and temperature measurement pauses. Multiple transitions lines of Ti I and Fe I were observed from the arc emission spectrum. Comparison to ICP-OES-analyzed slag samples shows that it is possible to measure FeO amount of the slag by using the described method with an average error of ± 1.4 percentage points. The slag surface temperatures measured with the optical emission spectrometer were also found to correspond to changes in process conditions. The accuracy of the FeO-content analysis could be further increased with more sophisticated spectrum analysis tools or process models.