The Tunnel Kiln Process for producing Sponge Iron (Direct Reduced Iron, DRI) in India is an alternative to the more common Rotary Kiln and Gas-Based DRI methods. This process is suitable for small to medium-scale production and is particularly useful where natural gas or high-grade coal is scarce.
Tunnel Kiln Process for Sponge Iron Production in India
# 1. Overview
– The tunnel kiln is a continuous, straight furnace where iron ore (pellets/lumps) and coal are loaded in crucibles or saggars.
– The charge moves slowly through different temperature zones (preheating, reduction, cooling) inside the kiln.
– Sponge iron is produced by solid-state reduction of iron ore using coal as a reductant.
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# 2. Key Steps in Tunnel Kiln Process
1. Raw Material Preparation
– Iron ore (lumps/pellets with 65-68% Fe)
– Non-coking coal (as reductant & heat source)
– Dolomite/limestone (as desulfurizing agent)
2. Charging into Crucibles/Saggars
– Alternate layers of iron ore and coal are loaded into refractory-lined crucibles.
3. Movement Through Kiln Zones
– Preheating Zone (~800°C) – Moisture & volatile matter removal.
– Reduction Zone (~1050-1100°C) – Hematite (Fe₂O₃) reduces to magnetite (Fe₃O₄), then to wustite (FeO), and finally to sponge iron (~90-92% metallization).
– Cooling Zone – Reduced sponge iron is cooled before discharge.
4. Discharge & Separation
– Sponge iron is separated from coal char and other residues.
– Magnetic separation may be used to improve purity.
5. Briquetting (Optio
)
– Sponge iron fines can be briquetted for ease of handling.
# 3. Advantages of Tunnel Kiln Process in India
✔ Suitable for small-scale plants (30,000–100,000 TPA capacity).
✔ Lower capital cost compared to rotary kilns/gas-based plants.
✔ Can use low-grade non-coking coal (abundant in India).
✔ Better control over reduction conditions compared to rotary kilns