Sponge iron is iron ore reduced directly in solid state using coal gasses, natural gasses or coke coal as reductants and is known as Directly Reduced Iron (DRI). It is a recognized alternative to Steel Scrap as a raw material for the manufacture of steel products. The process of making sponge iron aims at reducing oxygen levels in the raw iron ore. The quality of iron ore is determined by the amount of deoxidization performed. The final metallization percentage (ratio of metallic iron to the total iron) ascertains the grade of sponge iron.
At AMBA SHAKTI, we produce 200,000 tons of sponge Iron annually using coal based reduction techniques.
The main furnace used in the reduction process is the Rotary Kiln, which essentially a furnace, is a refractory lined, long inclined cylindrical structure, into which all the raw materials and reducing agent (coal) are fed, The kiln is injected with continuous hot air and oxygen at varying temperatures from all sides, depending on the temperature requirement. At startup, a light-up burner is used at the kiln discharge end, which is oil fired to heat up the kiln. Coal is then injected from the outlet of the kiln to ignite the kiln. Once the desired temperature is reached, iron ore, reduction coal and limestone (usually dolomite) are fed from the feed end.
Since the kiln is inclined (2.5%) from the feed and downwards to the discharge end and keeps on rotating, the fed iron ore keeps on mixing with the coal. With the help of continuous oxygen injection the iron ore slowly gets reduced as it goes through the system. The rotary speed of the kiln is adjusted to suit the feed rate and the required percentage of metallization. The following chemical reactions take place in the kiln.
C+O2 = CO2
C+O2 + C = 22CO
Fe2O3 +CO = Fe3O4+CO2
Fe3O4 +CO = FeO+CO2
FeO + CO = Fe (Metals)+CO2
Resulting in the following reduction chain:
2Fe2O3 -> 2Fe3O4 -> 6FeO -> 6Fe
(0%) (11%) (22%) (67%) -> 6Fe
This process gives out a lot of hot gasses. These gasses are recycled in the waste heat reduction boiler (WHRB), where they are processed and then sent off to the power plant. Here the gasses are used to rotate the turbines, thereby leading to generation of electricity. At AMBA SHAKTI, we have an installed captive plant capacity of 12 and 15MV at out integrated plants at Goa and Chandrapur respectively. The power generated at these plants is entirely through recycling waste gasses. This process leads to massive energy savings not only for the company, but for the society as well.
- More volumetric weight: Usually (10-100%) more than other types of scraps
- Known uniform composition: Less variations in chemical compositions
- Low sulphur and phosphorus levels.
- Low content of dissolved gasses.
- Foamy slag: Capability of gorming protective cover of foamy slag in the bath