Direct Reduced Iron

Direct reduced iron (DRI), also called sponge iron is produced from the direct reduction of iron ore (in the form of lumps, pellets, or fines) to iron by a reducing gas or elemental carbon produced from natural gas or coal. Many ores are suitable for direct reduction.

Reduced iron derives its name from the chemical change that iron ore undergoes when it is heated in a furnace at a high temperature of 800 to 1200 °C in the presence of a reducing gas called syngas which is a mixture of hydrogen and carbon monoxide.

Direct reduction refers to processes which reduce iron oxides to metallic iron at temperatures below the melting point of iron. The product of such solid state processes is called direct reduced iron.

Process

Direct reduction processes can be divided roughly into two categories: gas-based, and coal-based. In both cases, the objective of the process is to drive off the oxygen contained in various forms of iron ore (sized ore, concentrates, pellets, mill scale, furnace dust, etc.), in order to convert the ore to metallic iron, without melting it (below 1200 °C).

The direct reduction process is comparatively energy efficient. Steel made using DRI requires significantly less fuel, in that a traditional blast furnace is not needed. DRI is most commonly made into steel using electric arc furnaces to take advantage of the heat produced by the DRI product.[3]

Benefits

In modern times, direct reduction processes have been developed to specifically overcome the difficulties of conventional blast furnaces. DRI is successfully manufactured in various parts of the world and enables production of specialized iron and steel based products in a decentralized manner (as distinct from the older, centralized Open Hearth Furnace based model of the so-called 'Integrated' Steel Plants).

Factors that help make DRI economical:

• Direct-reduced iron has about the same iron content as pig iron, typically around 90% total iron (depending on the quality of the raw ore) so it is an excellent feedstock for the electric furnaces used by mini mills, allowing them to use lower grades of scrap for the rest of the charge or to produce higher grades of steel.
• Hot-briquetted iron (HBI) is a compacted form of DRI designed for ease of shipping, handling and storage.
• Hot direct reduced iron (HDRI) is iron not cooled before discharge from the reduction furnace, that is immediately transported to a waiting electric arc furnace and charged, thereby saving energy.
• The direct reduction process uses pelletized iron ore or natural "lump" ore. One exception is the fluidized bed process which requires sized iron ore particles.
• The direct reduction process can use natural gas contaminated with inert gases, avoiding the need to remove these gases for other use. However, any inert gas contamination of the reducing gas lowers the effect (quality) of that gas stream and the thermal efficiency of the process.
• This method produces 97% pure iron.

Handling

Direct reduced iron is highly susceptible to oxidation and rusting if left unprotected, and is normally quickly processed further to steel. The bulk iron can also catch fire since it is pyrophoric. Unlike blast furnace pig iron, which is almost pure metal, DRI contains some siliceous gangue, which needs to be removed in the steel-making process.