Tunnel Kiln: A Technoeconomic Route of Sponge Iron Making

Abstract

The conventional coal-based sponge iron process (Rotary Kiln) used for the production of sponge iron (DRI- Directly Reduced Iron) requires high-grade ferruginous materials in the form of lump or pellets and quality coal. Moreover, these Rotary Kiln processes require pre-indurated pellets to sustain the mechanical abrasion during reduction and suffer from low thermal and chemical efficiency. To overcome these problems, CSIR-National Metallurgical Laboratory, Jamshedpur, has developed a process for production of sponge iron utilizing mining and steel plant ferruginous waste such as iron ore fines, mill scale, LD sludge, BF sludge, etc. and lean grade coal in Tunnel Kiln. Pellets were made utilizing these ferruginous wastes in their suitable proportion, and reduction kinetics studies were carried out with non coking coal in a muffle furnace simulating Tunnel Kiln conditions. Process parameters were optimized w.r.t. blending ratio, reduction temperature and time. Based on the laboratory scale investigation, pilot plant trials were carried out in a commercial tunnel kiln on a 5-tpd scale. Fine tuning of the process parameters was carried out to obtain optimum metallic yield in the commercial production. After fine tuning of the process parameters in the commercial tunnel kiln, continuous production at the rate of 18 TPD is carried out to ascertain the techno-economics of the process. Techno-economic evaluation of the process reveals that the sponge iron produced from the Tunnel Kiln process is much cheaper (30-40%) than the conventional process of sponge iron making. Patents have been filed, and technology has been transferred to user industries.