Sponge Iron

What is Sponge Iron?

Sponge Iron at a glance
Alternative Name Direct Reduced Iron (DRI)
Variants Hot Briquette Iron (HBI)
Prime use As feedstock in steel making process

Sponge Iron/Direct Reduced Iron (DRI) is the resulting product (with a metalization degree greater than 82%) of solid state reduction (in Blast furnace reduction takes place in molten or liquid state) of iron ores or agglomerates (generally of high grade), the principal constituents of which are metallic iron, residual iron oxides, carbon and impurities such as phosphorous, sulphur, and gangue (principally silica and alumina). The final product can be in the form of fines, lumps, briquettes or pellets. Sponge iron when briquetted in hot condition at elevated temperature is called hot briquette iron (HBI).

Sponge Iron Technology in India and abroad

 In India, a modest beginning in the field of sponge iron making was only be made in mid 80’s by setting up the country’s first coal based demonstration-cum-production unit of 30,000 TPA (Tonnes per annum) capacity at Kothagudam, Andhra Pradesh based on M/s Lurgi’s SL/RN technology under UNDP/UNIDO assistance programme

In the mean while another technology shaped by Allis Chalmers in the US.  And Torsteel Research Foundation in India Ltd., wanted to adopt this process for their first commercial plant to be set up in style and name of Orissa Sponge Iron Ltd (OSIL). This technology facilitated production of Sponge Iron in a Ported Rotary Reactor with coal, diesel oil or Natural gas singly or in combination. Later however the process which was unsuccessful, was modified and patented  by OSIL as OSIL PROCESS taking coal as the only feed stock for fuel and reductant. Through an experience of operation and development over decade, OSIL perfected its process and ventured in to market hither to dominated by giants like LURGI, KRUPP and DAVY. It started by providing technological advice and trouble shooting in Sponge Iron Plant setup with other technologies. Finally OSIL provide total consultancy in collaboration with MECON and first Sponge Iron Plant was built by LLOYDS METALS AND ENGINEERS LIMITED based on OSIL PROCESS. Thus the first indigenous Sponge iron technology transfer was executed.

This plant has been an eye opener to the flexibility of OSIL PROCESS towards accommodating the low quality coal available in India. Coal based Sponge Iron technology is no longer in the domain of International giants and available in India. It is this perspective that OSIL has standardized a series of economic modules and has prepared a set of profiles for use of Promotional Institutions, Technocrats, Potential Promoters, Industrialists in mini steel sector who want to integrate backwards, so that they can take a decision to promote such units.

Process of making Sponge Iron

Sponge Iron production using coal involves reducing iron ore with coal or lignite. The reduction is carried out in a Rotary Kiln at a pre-determined temperature and controlled atmosphere. The input raw material i.e. iron ore, coal and limestone in the required calibrated sizes are fed into the rotary kiln which is inclined and rotates at a required range of speeds. Due to the inclination and the rotary motion of the kiln, the raw materials move from the feed end to the discharge end. In the process it gets pre-heated and reduced to sponge iron.  The material discharged from the kiln is taken into a rotary cooler where the material is cooled. The cooled product at about a temperature of 800oC is discharged from the cooler and taken to the product separation and handling system. The product, which consists of sponge iron and non-magnetic such as char etc., is screened to different size fractions and then magnetically separated by means of magnetic separators. Sponge iron is taken to a storage bin for dispatch.  The char, which is not magnetic and contains a certain amount of carbons, is taken into a separate bin and can be recycled if found suitable or alternatively sold as fuel for applications such as in brick making and so on.

Uses of Sponge Iron

Some of the most important uses of sponge iron are

  1. Full or part raw material for the manufacture of Pig Iron and Steel
  2. Manufacture of Steel to rigid specifications
  3. Ideal for deep drawing stock where absolute freedom from the presence of such impurities as copper, Nickel, Molybdenum, Tin and Arsenic are required.
  4. Production of commercial quality Steel directly from the compressed block of sponge iron powder in EAF.
  5. Reduction of nitrogen content in the steel to the very minimum. The greater the amount of sponge iron used in the charge the lower the nitrogen content of the finished product. The presence of nitrogen has an important bearing on high temperature brittleness, magnetic properties and the shock resisting qualities of steel.
  6. Precipitating agent in the metallurgy of copper and lead

Advantage of Using Sponge Iron  

  1. Chemical Composition is uniform and known exactly.
  2. Contains no undesirable metallic impurities.
  3. Permits dilution with low cost scrap.
  4. Easy to handle and transport
  5. Automatic continuous charging in Arc-furnace.
  6. More predictable price structure.
  7. Less noise during melt – down