Today India stands as the largest producer of coal based sponge iron through rotary kiln process using calibrated ore and non coking coal. However, Rotary kiln process suffers from serious limitations like low productivity and pollution. In this respect fixed bed Tunnel kiln furnace are evolving as an alternative to Rotary kiln process. Iron ore fines and the low grade beneficiated iron ore cake are directly used for manufacturing of sponge iron in tunnel kilns. The material bed in Tunnel kiln being stationary, it does not require high strength and thermal stability of the raw material. This gives the opportunity for charging composite pellets or briquettes which could possibly enhance kiln productivity and efficiency. In order to explore the efficacy of iron ore-coal composite pellets over indurated iron ore pellets, standard charging of concentric layers of separate iron ore, coal fines, or their mixture, these pellets were tested at 1200 C in the tunnel kiln. It was observed that metallization for indurated iron ore pellets, and concentric charging were limited to 80% to 83% where as composite pellets had a metallic iron of 88% to 89%. Thermal efficiency of tunnel kiln is quiet low and depends on the length of the kiln. Present experiment show that use of composite pellets in the present kiln could improve the thermal efficiency from 27% with standard practice to 37% with composite pellets. Similarly, carbon utilization efficiency could be increased from 48% with standard practice to 65% with composite pellets.

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http://eprints.nmlindia.org/7035/1/SC_khattoi_G.G.Roy_IIT_KGP_ARIM-10_53.pdf