Public defence 30.10.2020

Friday, October 30, 2020

Candidate:  Henri Pauna

Place: L5, Linnanmaa

Remote connection: Zoom

Date & time: 30.10.2020 12:00

Topic: Electric arc characterisation and furnace process monitoring with optical emission spectroscopy and image analysis

Opponent: Valentina Colla

Custos: Professor Timo Fabritius

Light as the source of process information for more environmentally friendly steelmaking

New information on the recycled metal-based steelmaking in electric arc furnaces and ladle furnaces can be acquired by studying the light of the electric arc. In Henri Pauna’s doctoral dissertation, the light from the arc has been measured with optical emission spectroscopy (OES), which has the potential to work as amuch needed real-time analysis method in process control. On the industrial scale, it has prospects to increase resourceand energy efficiency.

CO2emission reductions set for 2050 will most probably lead to a transition from an iron ore-based blast furnace process to electric steel production in electric arc furnaces and ladle furnaces. In these furnaces, recycled metal and sponge iron reduced by hydrogen aremelted by a high-energy electrical discharge whose light contains a huge amount of information.

The main significance of the dissertation research is in the development of real-time process control with OES, which measures the light emitted by the arc and the melt surface. The arc forms a plasma in which compounds decompose into both charged and neutral atoms and molecules. The high energy of the plasma excites particles, causing them to emit light, or photons, at wavelengths characteristic to the particle. Atoms and molecules can be identified from the spectra based on the wavelengths ofthephotons, and e.g. plasma and melt surface temperature, plasma composition, and the effect of the atmosphere onthespectra can be evaluated from the data.

Characterisation of the pilot-scale furnace arc with OES and image analysis has helped to understand the behavior of the arc during the melting process, and the high impact of slag on arc properties is one of the main results of the study. In industrial OES spectra, on the other hand, the slag foamingandthe time-evolutionofthe temperature ofboththe charge material andthemelt temperatures can be monitored together with the evaluation of theslagcomposition. Industrial measurements have proven that OES is also suitable for studying industrial processes.

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Last updated: 27.10.2020