An estimated 30% of today's world steel production is through the electric arc furnace (EAF) steel-making route. This contribution to world steel production is likely to continue, given that EAF steel-making is more environment friendly and there is availability of a huge stock of scrap steel on earth, waiting to be recycled. It is, therefore, important that EAF steel making improves in terms of efficiency and productivity.
As a chemical reactor in steel making, EAF is quite slow compared to the basic oxygen furnace (BOF) route. The conditions that drive chemical reactions between slag and metal are impaired by insufficient intermixing of slag and metal during the process. That's not all. There is an additional limitation. The design of an EAF is such that there is always a possibility of slag flowing out through the slag-door early in the process. Early flowing out of slag is a huge problem and is seen in EAF operations where awareness about the resultant losses is poor. It could also be because the operators are not trained well enough to take countermeasures. In some organisations, there is no system of monitoring, analysing and reducing these losses. While slag is basically a solution of metallic oxides required for refining of steel, it is also a sink for iron – in the form of iron oxide (FeO) – the valuable metal that we strive to recover. Loss of unreduced slag is a direct loss of iron (Fe). In addition, early loss of slag adversely affects arc stability, refractory life, heat insulation of bath, power consumption, electrode consumption, etc. The importance of slag in the EAF process makes it imperative that the approach to EAF steel making should focus on the following:
Holding slag inside EAF;
Extracting iron and all other benefits from it; and
Finally, releasing it through the slag door.
There are technologies that are presently being developed to achieve this end. These technologies are likely to improve consistency of the benefits.
However, trained and knowledgeable EAF operators have achieved this type of operation with the help of homegrown interventions.
Every technology that develops, over a period, into a sophisticated electro-mechanical-auto-software combo, has its roots in simple, manual applications. So is the case of the initiative to increase the residence time of slag in EAFs. The following suggested homegrown methodology involves tweaking the furnace refractory pattern to create extra working volume through the following steps:
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