DRI / HBI

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, the majority of which is hydrogen (H2) and carbon monoxide (CO) which act as reducing agents. This process of 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.

Direct Reduced Iron (DRI) is a manufactured metallic material produced by the reduction (removal of oxygen) of iron oxide at temperatures below the melting point of iron (1536° C or 2797° F). The iron oxide in either lump, conceptrate, or pellet form is reduced at 800-1050 ° C (1472-1922 ° F) by interaction with reductants (H2+CO) derived from natural gas or coal.

DRI lump, pellets, and cold-molded briquettes have an apparent density of less than 5.0 g/cm3 (312 lbs/ft3). Cold-molded briquettes are formed at a temperature less than 650° C (1202° F).

Hot Briquetted Iron (HBI) is a compacted form of DRI with enhanced physical characteristics, which make it ideal for handling, shipping, and storing as a merchant product. See HBI page for more details.

DRI fines are generated during the production and handling of DRI and HBI and can have up to 75 percent metallic content. Particle size can range from less than 6.35 mm (0.25 inch) to 12 mm (0.5 inch). Moisture content can be as much as 12 percent (by weight).

Process

Direct reduction, an alternative route of iron making, has been developed to overcome some of these difficulties of conventional blast furnaces. DRI is successfully manufactured in various parts of the world through either natural gas or coal-based technology. Iron ore is reduced in solid state at 800 to 1,050 °C (1,470 to 1,920 °F) either by reducing gas (H2+CO) or coal. The specific investment and operating costs of direct reduction plants are low compared to integrated steel plants and are more suitable for many developing countries where supplies of coking coal are limited.

The direct reduction process is energy efficient, but most competitive with the Blast Furnace (BF) when it can be integrated with Electric Arc Furnace (EAF) to take advantage of the latent heat produced by the DRI product[2], more information on this in “DRI – The EAF Energy Source of the Future?”

Factors that help make DRI economical:

  • Direct-reduced iron has about the same iron content as Pig Iron (MPI), typically 90–94% total iron (depending on the quality of the raw ore) as opposed to about 93% for molten pig iron, 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. Few ores are suitable for direct reduction.

  • 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.

  • Supplies of powdered ore and raw natural gas are both available in areas such as Northern Australia, avoiding transport costs for the gas. In most cases the DRI plant is located near natural gas source as it is more cost effective to ship the ore rather than the gas.

  • this method produces 97% pure iron.

Hot Briquetted Iron (HBI) is a premium form of Direct Reduced Iron (DRI)* that has been compacted at a temperature greater than 650° C at time of compaction and has a density greater than 5000 kilograms per cubic meter (5000 kg/m3).

HBI is a premium quality, high density steel industry raw material containing 90-94% total iron (Fe) in a nearly pure form, which is used in Electric Arc Furnace (EAF) and Basic Oxygen Furnace (BOF) steelmaking, Blast Furnace (BF) ironmaking, and foundry applications.


Hot Briquetted Iron (HBI) Advantages:

● High bulk density of 2500-3300 kg/m3 (156-206 lbs/ft3).
● Known, consistent chemistry certified by the producer.
● Minimal (trace) amounts of undesirable chemical elements (Cu, Ni, Cr, Mo, Sn, Pb, and V).
● High thermal and electrical conductivity
● Low reactivity with fresh and saltwater (reoxidation).

Typical Chemistry of Hot Briquetted Iron (HBI)


Weight: 0.2-3.0 kg (0.5-6.6 lbs)
Apparent Density: > 5000 kg/m3 (> 312 lbs/ft3)
Bulk Density: 2500-330 kg m3 (156-206 lbs/ft3)
Length: 50-140 mm (1.97-5.5 in)
Width: 40-100 mm (1.6-3.9 in)
Thickness: 20-50 mm (0.79-1.97 in)
Fines: (under 6.35 mm) not to exceed 5%

Reduction

Iron oxide, in pellet or lump form, is introduced through a proportioning hopper at the top of the shaft furnace. At VENPRECAR in Venezuela, the feed mix is 65% pellets, 32% lump ore, and the rest is recycled remet.

As the ore descends through the furnace by gravity flow, it is heated and the oxygen is removed from the iron (reduced) by counter flowing gases, which have a high H2 and CO content. In the VENPRECAR plant, the process gas is 60% H2 and 35% CO on a dry basis. These gases react with the Fe2O3in the iron ore and convert it to metallic iron, leaving H2O and CO2.

For production of cold DRI, the reduced iron is cooled and carburized by counter flowing cooling gases in the lower portion of the shaft furnace. The DRI also can be discharged hot and fed to a briquetting machine for production of HBI, or fed hot, as HDRI, directly to an EAF using the HOTLINK Systemor insulated transfer vessels.