Traditional large integrated steel plants

From the end of the 19th century to the middle of the 20th century, almost all the world's steel was produced in integrated plants, which grew both in number and unit production capacity. These steelworks have virtually always been based on the production of pig iron from iron ore in blast furnaces and, for the past forty years, the conversion of this pig iron into steel using oxygen.

We are currently seeing competition with the other steel production sector, based on the smelting of scrap metal (often using cast iron and, increasingly, DRI) in an electric arc furnace. This is the basis of what are known as "mini mills" (see [M 7 110] and [M 7 130] ).

Integrated mills, the subject of this article, produce two-thirds of the world's steel. These plants, after evolving towards gigantism and the construction of 15, even 20 Mt/year steel complexes (a trend that continues in Asia), are tending in the "old industrial countries" to restructure towards more compact companies in the 2 to 10 Mt/year range. In fact, in 2007 (a record year, along with 2008, for the global steel industry), the 185 plants surveyed worldwide produced 933 Mt (including the few plants still based on Martin furnaces, which accounted for 33 Mt), i.e. an average of around 5 Mt/year per company.

Energy requirements have been greatly reduced over the past thirty years, and now stand at around 24 GJ/t of steel (crude and without scrap). These needs are essentially met by coal. However, if prices are right, some of this coal can be replaced by natural gas or fuel oil, which can reduce net requirements to around 17 GJ/t, or even less with the addition of scrap.

In any case, such mills release around 8 GJ/t of hot-rolled steel in waste gases that can, for example, be used to generate electrical energy not only for the company's own needs, but also for external sale if this is cost-effective in the local context.

Another major effort has been made to improve the profitability of these companies by reducing labor requirements:

• less than 1.5 h/t of hot-rolled steel, aiming for 1 h/t ;

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