The Iron and Steel sector covers the manufacture of steel into basic shapes and forms that then can be used to create products. The sector is divided into two basic types of production that each represents approximately half of domestic production. Integrated steel mills use a three-step process to produce steel from coal, involving cokemaking, ironmaking (using a blast furnace), and Basic Oxygen Furnace (BOF) technology. Alternatively, “mini-mills” produce steel from metal scrap using Electric Arc Furnace (EAF) technology, without operations for coking or ironmaking.
Coke, which is the fuel and carbon source at integrated mills, is produced by heating coal in the absence of oxygen at high temperatures in coke ovens. Pig iron is then produced by heating the coke, iron ore, and limestone in a blast furnace. In a BOF, molten iron from the blast furnace is combined with flux and scrap steel where high-purity oxygen is injected. This processâ€”with cokemaking, ironmaking, steelmaking, and subsequent forming and finishing operationsâ€”is referred to as â€œfully integrated production.â€ Alternatively, in an EAF the input material is primarily scrap steel, which is melted and refined by passing an electric current from the electrodes through the scrap.
The percentage of steel produced by EAFs is significant and growing. In 2001, 125 minimills generated 47.5 percent of the steel produced domestically, consuming 75 million tons of ferrous scrap to do so. Nearly 200 mills make up this sector, employing more than 150,000 people. The mills are concentrated geographically in Great Lakes states, although the South also has a large number of mini-mills. Principal consumers of the steel generated from these millsÂ are auto manufacturers and the construction industry.
The sector has multi-media impacts, including air emissions (CO, SOx, NOx, PM2), wastewater contaminants, hazardous wastes, and solid wastes. The major environmental impacts from integrated steel mills are from coking and ironmaking, although U.S. steelmakers are turning to new technologies to decrease the sources of pollution from, and their reliance on, coke.
As an industry, mini-mills are the largest U.S. consumers of recycled steel scrap, but also face issues related to contaminants in scrap products. The energy used by mini-mills generates greenhouse gas emissions from power generation. An emerging trend to generate heat on-site by burning carbon will improve energy efficiency but will also increase emissions.