Feedstock
The MIDREX® Shaft Furnace is designed to operate with virtually any blend of pellets and lump ores. This allows the plant operator to maximize productivity at the lowest cost. MIDREX® Plants have processed iron oxide pellets and lump ores from over 50 sources around the world. The figures in the table reflect general characteristics for widely traded iron ores. However, materials not meeting these characteristics may be acceptable, depending on economics.
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| Pellets | Lump |
One of the most significant innovations in direct reduction-grade iron ore has been oxide coating. By coating pellets with a thin layer of limestone, cement or bauxite, the reducing gas temperature can be increased significantly, resulting in a production increase of up to 20 percent. Many pellet suppliers are now coating DR-grade pellets, or it can be done by the plant operator.
Screened iron ore fines can make up 5-10 percent of the feed mix, depending on their size and reducibility.
Preferred Characteristics for DR-Grade Pellets and Lump Ore
| CHEMICAL CHARACTERISTICS | ||
| Pellets | Lumps | |
| Fe (%) | 67.0 min. | 67.0 min. |
| SiO2 | 3.0 max. | 3.0 max. |
| S (%) | 0.008 max. | 0.008 max. |
| P (%) | 0.03 max. | 0.03 max. |
| TiO2 | 0.15 max. | 0.15 max. |
| PHYSICAL CHARACTERISTICS | ||
| Pellets | Lumps | |
| Nominal Size | 6 x 16 mm | 10 x 35 mm |
| 10 x 35 mm (%) | - | 85 min. |
| 9 x 16 mm (%) | 95 min. | - |
| Minus 5 mm (%) | 3 max. | 5 max. |
| Compression Strength (kg) | 250 min. | - |
| Less than 50 kg (%) | 2 max. | - |
| REDUCTION CHARACTERISTICS | ||
| Pellets | Lumps | |
| Midrex Linder Test (760 degrees C) | ||
| Metallization (%) | 93 min. | 93 min. |
| Minus 3.36 mm (%) | 2 max. | 5 max. |
| Hot Load Test (815 degrees C) | ||
| Tumble Strength (% plus 6.74 mm) | 90 min. | 85 min. |
| Compression Strength (kg) | 100 min. | - |
| Clustering (% plus 25 mm after 10 rev.) | 0 | 0 |
