Sponge Iron

Sponge iron, is the product of reducing iron oxide in the form of iron ore and steel plant wastes into metallic iron, below the melting point of iron and typically in the range of 800–1200 °C.

Iron Ore Pellet is used for reduction. After reduction of iron ore pellet the product resembles sponge because of pores left behind after removal of oxygen. As such it is called Sponge Iron.

Sponge iron making is a process in which iron ore lumps (typically 5mm-18mm size) are tumbled with a 'select' grade of iron-coking coal little dolomite inside an inclined rotary kiln and control combusted in the presence of air for about 12 hours before the products are air cooled, magnetically separated and screened.

Sponge iron is formed through the reduction of iron ore to metallic iron through reaction with carbon in the form of coal, etc. at approx. 1100 degree Celsius. Over the years, the shortage of expensive melting scrap has made sponge iron a significant raw material for manufacturing high quality steel.

Sponge iron is used in the iron and steel industry as a substitute for scrap in induction and electrical arc furnaces. Over the years, the shortage of expensive melting scrap has made sponge iron a significant raw material for manufacturing high quality steel.

Capacity: 2,31,000 Metric Tonnes Per Annum (Two Lakh Thirty One Thousand Metric Tonnes Per Annum).

Coal-Based Process:

  • This process utilizes non-coking coal as reducing agent along with lumpy rich grade iron ore.
  • The reduction is carried out in an inclined horizontal rotary kiln, which rotates at a predetermined speed. A temperature profile ranging from 800-1050 degree centigrade is maintained along the length of the kiln at different zones and as the material flows down due to gravity the ore is reduced.
  • The hot reduced sponge iron along with semi-burnt coal, discharged from kiln is cooled in water-cooled cylindrical rotary cooler to a temperature of 100–200 degree centigrade.
  • The discharge from cooler consisting of sponge iron, char other contaminations are passed on through magnetic separators so that sponge iron can be separated from other impurities.

The basic reactions in this process is as follows:
 C + O2 = CO2
 CO2 + C = 2CO
 Fe2 O3 + CO = Fe3O4 + CO2
 Fe2 O4 + CO = FeO + CO2
 FeO + CO = Fe + CO2

Raw Material Requirements
As in case of any process, here also quality of raw materials plays a vital role in obtaining the rated capacity and product quality. The iron ore shall have resistance for physical & thermal de-crepitation and good reducibility and the coal should be of reactive nature along with the characteristics of high fusion temperature and less amount of ash.

  • Chemical and Physical Composition of Iron Ore
  • Constituent

    Chemical Composition   %
    Total iron 65 - 67 %
    Sio2 + al2 o3 2 - 3 %
    Cao + mgo 0.5 - 1 %
    Sulphur 0.02 % max.
    Phosphorous 0.04 % max.

    Physical Composition  
    Size 5 - 20 mm
    Shatter Index + 95 %
    Tumbler Index + 88 %
    Abrasion Index + 5 % max
    Reducibility Index + 94 %
    Thermal Degradation Index 5 %

  • Typical Chemical Analysis of Coal
  • Constituent %
    Moisture8% max
    VM27-30%
    Ash23-25%
    Fixed Carbon+ 40%
    Size0-20%
    Ash Softening Point1250 deg cent
    Calorific Value5200 k . Cals / mole
    Reactivity2.2 co / gm . Deg c

  • Typical Chemical Analysis
  • Cao40 - 45 %
    L.O.I.40 - 45 %
    Insolubles5 - 7 %
    Size0.5 - 4 mm

  • Typical Analysis of Sponge Iron Produced in Coal Based Process
  • Total Iron90 - 93 %
    Metallic Iron80 - 84 %
    Metallisation90 - 92 %
    Gangue3 - 4 %
    Carbon0.25 %
    Sulphur0.02 - 0.03 %
    Phosphorous0.035 - 0.05 %

    SPECIFICATION OF SPONGE IRON

    S/No SPECIFICATION SI DRCLO SI BACHELI (NORMAL) SI PELLETS
    1SIZE0-200-2020-Mar
    2Fe(M)82±0.5%80.5±0.5%80±1%
    3Fe(Mz)898888
    4NON MAG.MAX.1.25±0.25%1.5±0.25%0.75±0.25%
    5CARBON MAX.0.200.200.20
    6SULPHUR MAX0.0400.0400.040
    7PHOSPHORUS MAX0.0500.0600.080
    8(-1mm) MAX15%±5%20%±5%±5%