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Abstract
The level of slag foaminess in an electric arc furnace has emerged as a critical variable in electric arc steelmaking, as a good foaming slag contributes significant efficiency benefits to the process. Many arc furnaces utilise harmonics generated in the electrical supply by the arcs as a foaming slag monitor, as a better foaming slag leads to a more stable arc and fewer harmonics. Monitoring via sound and light emissions from the EAF have also been attempted as a method of foam monitoring.
This study examines EAF mass inputs and some outputs, EAF energy inputs and some outputs, the potential to monitor the quality of the foaming slag using sound analysis, and the interdependence of an electrical harmonic –based foaming indicator and the increase of the steel temperature during refine. It was found that a broad trend exists between increasing metal refine power and increasing averages of foaming slag indicators during refine which could be used to adjust the foaming indicator such that it can be used to gauge the heating rate of the steel. A method for examining the relationship between actual electrical harmonics and metal refine power is proposed.
As the furnace studied used both normal coke injection and a rubber and coke blend as foaming slag agents, a comparative analysis of the coke-injectant and rubber/coke-injectant heats also took place. Analysis of input and output energy found that heats using a rubber/coke blend as inject carbon were more efficient in energy consumption than heats using the standard inject coke. Analysis of the energy released from combustion of the inject carbon types found that the combustion of rubber could not account for all of the savings in specific electrical energy consumption that were recorded, indicating that the improvement in electrical efficiency of the EAF seen when a rubber/coke injectant blend is used arrives from better slag foaming increasing heat transfer from the arc to the steel, not from substitution of electrical energy by combustion energy. On the whole, foaming indicator trends appeared better for heats using a blend of rubber and coke for inject carbon.