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The Sponge Iron Production Process

Prior to the invention of the blast furnace, the primary source of iron in the world was sponge iron. Sponge iron or Directly Reduced Iron (DRI) is now mainly used as a scrap substitute and as raw material in specialty steel production. The processes for producing sponge iron are either coal- or gas-based.

  1. Global Production

    • Globally, approximately 49.5 million tons of sponge iron are produced annually, comprising roughly 3 to 4 percent of total iron production. The leaders in sponge iron production are India, Mexico, Venezuela and Iran. India is the largest producer, contributing an estimated 11.85 million tons each year from 118 plants. The United States produces 0.21 million tons of sponge iron each year.

    Production Process

    • Producing sponge iron involves the reduction of physically- and thermally-stable iron ore. This is achieved by using either a carbon substance, such as non-coking coal, or reformed natural gas, which acts as a reducing agent. Thus, sponge iron production plants are set on the foundation of these two reducing agents, coal-based rotary kilns or gas-based shaft furnace reactors. Coal and gas also fulfill the energy requirements for the process.

    Coal-based Process

    • In India, 115 of its 118 plants are coal-based, contributing to 65 percent of sponge iron production. The sponge iron pellets produced via this process are more stable and capable of long-term storage. The process occurs in a horizontal rotary kiln kept at temperatures ranging between 1,472 and 1,922 degrees Fahrenheit. The discharge produced is purified magnetically, and the sponge iron is sorted according to sizes above and below 3 millimeters.

    Gas-based Process

    • Approximately 95 percent of global sponge iron production is gas-based. Sponge iron produced via this process requires immediate use and can only be stored upon conversion to Hot Briquetted Iron (HBI). The gas mixture used includes hydrogen and carbon monoxide, and production occurs in a vertical retort. As gases move up, the discharge move downward via gravity and is cooled for use or storage as HBI since no magnetic separation is necessary.

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