Abstract
Electric arc furnaces (EAFs) and ladle furnaces (LFs) are the main recycling units for scrap metal. With lower CO₂ emissions than traditional ore-based steelmaking, the importance of EAFs can be expected to increase in the future. Increasing steel production rates and demand for high-quality and special steels require innovative process control systems to be developed for the steel industry. However, the harsh conditions inside the furnaces set strict requirements for durability and viable data acquisition methods for online measurement systems.
In this thesis, the applicability of optical emission spectroscopy (OES) as an online measurement system for industrial EAFs and LFs is discussed, based on the results from pilot-scale and industrial EAFs, and an industrial LF.
The electric arc has been characterised with OES, plasma diagnostics, and image analysis in the pilot-scale EAF measurements. These studies highlighted the influence of slag composition on the overall properties of the electric arc, the electrical parameters of the furnace, and the arc length{voltage relation. The majority of the atomic emission lines in the electric arc OES spectra were observed to originate from the slag components.>
In the industrial EAF campaign, high alloyed steel grade was observed to have high-quality arc spectra within 30 mins before tapping and higher radiative heat transfer compared with the carbon steel grade. The spectra from the carbon steel grade, on the other hand, were used to observe how spectra evolve during slag foaming. Additionally, the molten bath surface temperature was estimated from the OES spectra. The slag composition was evaluated with OES in the industrial LF campaign, indicating that the CaF₂, MgO, and MnO content of the slag could be evaluated from the spectra
