Investigation of iron losses during desulphurisation of hot metal utilising nepheline syenite

Abstract

Iron losses during calcium carbide based hot metal desulphurisation have been studied via large scale investigations of slag from the slag pit as well as slag sampling during desulphurisation at SSAB EMEA in Luleå . The desulphurisation slag, after injection of calcium carbide, is normally solid and contains large amounts of iron. An alkali containing mineral, nepheline syenite, was mixed together with the calcium carbide to form a more fluid slag as the iron losses originate from enclosed metal droplets in the slag as well as drawn off hot metal during slag skimming. The slag amount after slag skimming decreased from 28?1 to 25?1 kg t 21 hot metal with addition of 5 wt-% nepheline syenite to the calcium carbide, and the magnetic fraction of the slag from the slag pit decreased from 2?5 to 1?9%. Finally, no negative effect on the reagent efficiency was observed during the trials with addition of nepheline syenite.

Effect of Nepheline Syenite on Iron Losses in Slags during Desulphurization of Hot Metal

“…This is due to significant increase splashes of hot metal during desulfurization. This result is in good agreement with the data obtained in the ref . Therefore, a minimization of iron losses with metal droplets in the slag in the trials with a NS injection should be done by an optimization of the gas injection.…”

“…Moreover, several plant trials showed that the injection of NS during desulphurization of the hot metal can significantly reduce the iron losses in slag. For instance, the magnetic fraction in the skimmed slag after desulfurization of hot metal, which correlates to the iron losses in this slag, decreases in the heats with an injection of NS by 54.5% on average for fractions of slag pieces in the size range from 5 to >300 mm . This decrease of the magnetic iron losses in the slag from 2.5 to 1.9% was explained by a more effective slag skimming in the trials with an addition of NS.…”

“…There are two common steps to remove sulfur from the hot metal: injection desulphurization agents to the melt and stirring of this melt to obtain an intensification of the desulphurization processes. Currently, the most common desulphurization agents used in the steelmaking industry are the following components: lime (CaO), calcium carbide (CaC 2 ), magnesium, or a mixture of those materials . Products of desulphurization reactions are made up of a mixture of oxides, such as CaO, SiO 2 , FeO, Al 2 O 3 as well as sulfides (CaS).…”

Characterization of Metal Droplets in Slag after Desulfurization of Hot Metal

“…Overall, the amount of iron losses in a slag only during desulfurization operations (Source 1) can reach from 30-60% 5) to 80% 4) (6-11 kg/t HM) from the summary iron losses during desulfurization of hot metal depending on the used technology. Therefore, the purposes of this study were: a) to characterize the metal droplets in the size range smaller than 5 mm in the slag just after desulfurization of hot metal, b) to consider the different mechanisms of involving of different metal droplets into the slag during the desulfurization process, c) to discuss the effects of some technological parameters of desulfurization on a possibility to decrease the amounts of different metal droplets in the slag.…”

“…Magnelöv et al 5) estimated the total iron losses and quotas of magnetic fractions having different sizes in the skimmed slag after desulfurization of hot metal by injection of CaC2 + 2 wt% cryolite (Campaign 1) and CaC2 + 5 wt% nepheline syenite (Campaign 2). The magnetic fractions in the skimmed slags after desulfurizations (Sources 1 and 2) in Campaign 1 (average reduction of S content in the iron was from 0.026% to 0.0051%) and Campaign 2 (average reduction of S content in the iron was from 0.044% to 0.0037%) were 2.5 and 1.9% of the total processed hot metal, respectively.…”