Reduccion directa

Presented here is an excerpt from the Ironmaking Volume of The Making, Shaping and Treating of Steel. More information about this book can be found on p 80.
This Article Available On-Line www.aise.org

Chapter 11

Direct Reduction and Smelting Processes
J. Feinman, President, J. Feinman and Associates, Inc. (Retired U.S. Steel Corp.)
©1998. The Steel Foundation. Reprinted with permission.All rights reserved.

11.5 Reduction Smelting Processes
In the late 1950s and early 1960s, the concept of producing liquid iron or semi-steel directly from ore fines or concentrates and an inexpensive and plentiful fuel and reductant such as pulverized coal was the subject of considerable pilot plant development activity. These projects, which encountered serious technical, process and/ormechanical problems, were reviewed briefly in the second general reference in the bibliography. In recent years, interest has been renewed in developing such concepts to commercial viability, stimulated in part by prospects of long term shortages of high quality metallurgical coals, by increasing environmental problems associated with coke ovens, agglomeration plants and other operations ancillary toblast furnace ironmaking and by strong incentives to decrease the high capital requirements associated with blast furnace ironmaking. The most prominent projects representing this renewed interest are the KR process developed by Voest-Alpine AG and their subsidiary Korf Engineering in a pilot plant at Kehl, West Germany (now known commercially as the COREX process), the Direct Iron Ore Smelting(DIOS) process under development in Japan, the AISI direct steelmaking process studied in a pilot plant at Universal, Pennsylvania and the HIsmelt process originally developed in Germany and now being pursued cooperatively by Rio Tinto and Kvaerner Metals. Although there have been significant worldwide efforts to develop reduction smelting processes based on coal and ore directly during the pastdecade, no demonstration or commercial plants have been built as of 1998 with the exception of COREX. The basic principles and process parameters have been demonstrated through laboratory and pilot plant studies; however, until larger scale operations that demonstrate the long term performance of processes are established, COREX is likely to remain the only commercial reduction smelting alternative tothe blast furnace. The original objectives to go directly to steel or semi-steel in these concepts also remain to be demonstrated even on a pilot scale.

nace is produced by partial combustion of coal with oxygen in the fluidized bed of the smelter-gasifier. The energy needed to complete the reduction of the DRI and produce the hot metal and slag is provided by the partial combustion. Theliquid products are tapped periodically and partially spent offgas from the shaft reducer is exported along with excess gas produced in the smelter-gasifier.
Iron ore

Coal/ limestone

Top gas
Reduction shaft furnace

Export gas
Top gas cooler

Reduction gas
Coal feed bin Hot dust cyclone Gas cooler

Raw gas

Cooling gas

Smelter-gasifier

Oxygen Hot metal/slag
Fig. 11.16 Schematicrepresentation of the COREX process.

11.5.1 COREX Process33,34 The COREX process, shown schematically in Fig. 11.16, is a two-stage operation in which DRI from a shaft furnace like that used in the Midrex and HYL process is charged into a final smelter-gasifier. Reducing gas for the shaft furJune 1999

The smelter-gasifier operates at 3–5 bars and comprises an upper fluidized bed zone atapproximately 1500°C (2730°F) and a lower melting and liquid collection zone at approximately 1550°C (2820°F). Coal and limestone are injected into the freeboard above the fluidized bed zone
Iron and Steel Engineer 75

where they are heated rapidly to 1000–1200°C (1830–2190°F). The volatile matter is driven off and shattered fixed carbon particles fall into the gasification zone where a gas...