Sponge Iron (DRI)

Direct-reduced iron (DRI), also called sponge iron, is produced from direct reduction of iron ore (in the form of lumps, pellets or fines) by a reducing gas produced from natural gas or coal. The reducing gas is a mixture majority of Hydrogen (H­₂) and Carbon Monoxide (CO) which acts as reducing agent. This process of directly reducing the iron ore in solid form by reducing gases is called direct reduction.

The conventional route for making steel consists of sintering or pelletization plants, coke ovens, blast furnaces, and basic oxygen furnaces. Such plants require high capital expenses and raw materials of stringent specifications. Coking coal is needed to make a coke strong enough to support the burden in the blast furnace. Integrated steel plants of less than one million tons annual capacity are generally not economically viable. The coke ovens and sintering plants in an integrated steel plant are polluting and expensive units.

Specification

Sponge Iron is mainly used as a raw material for speciality steel as well as substitute for scrap. Made from iron ore, sponge iron in itself is not used. It is further processed to make wrought iron. The rise in price of scrap and other factors have led to the increase in the use of sponge iron for making high quality steel.

The quality of sponge iron is primarily ascertained by the percentage of metallization (removal of oxygen), which is the ratio of metallic iron to the total iron present in the product. Sponge iron manufacture is highly sensitive to raw material characteristics.

Therefore, it is essential to examine the chemical and physical characteristics of raw materials, both individually and in combination.

The sponge iron is a key raw material for the manufacture of steel. The appropriate percentage of metallization (removal of oxygen) ensures the high quality of the sponge iron. The percentage of metallization is the ratio of metallic iron to the total iron present in the product.

 The features and specifications are mentioned below:

Use of sponge iron

Sponge iron is not useful in itself, but can be processed to create wrought iron. The sponge is removed from the furnace, called a bloomery, and repeatedly beaten with heavy hammers and folded over to remove the slag, oxidise any carbon or carbide and weld the iron together. This treatment usually creates wrought iron with about three percent slag and a fraction of a percent of other impurities. Further treatment may add controlled amounts of carbon, allowing various kinds of heat treatment (e.g. "steeling").

Today, sponge iron is created by reducing iron ore without melting it. This makes for an energy-efficient feedstock for specialty steelmanufacturers which used to rely upon scrap metal.