Traditional ironmaking melts iron ore in a blast furnace, consuming massive energy and emitting CO2. The direct reduced iron market offers a different approach: reducing iron ore in the solid state (without melting) using a reducing gas.

The Shaft Furnace (MIDREX, HYL/ENERGIRON)

Most DRI is produced in a shaft furnace. The sponge iron market describes the process: (1) Iron ore pellets (or lump ore) are fed into the top of the furnace, (2) Reducing gas (CO and H2) is injected at the bottom, (3) The gas flows upward, reducing the iron oxide to metallic iron, (4) The reduced iron (DRI) is discharged at the bottom. The furnace is tall (many meters). The process is continuous. The temperature is around 900-1050°C (below iron's melting point).

The Reducing Gas (Natural Gas Reform)

The reducing gas is produced by reforming natural gas (methane) with steam and oxygen. The iron briquette market explains: CH4 + H2O → CO + 3H2 (endothermic). The resulting syngas (CO+H2) is then injected into the furnace. The CO and H2 react with iron oxide: Fe2O3 + 3H2 → 2Fe + 3H2O; Fe2O3 + 3CO → 2Fe + 3CO2. The off-gas (H2O, CO2) is recycled (after CO2 removal). The reformer is a large unit.

The Iron Ore Pellet (Quality Requirements)

DRI requires high-quality iron ore pellets (high iron content, low impurities). The hot briquetted iron market notes that pellets must have: (1) High compressive strength (to survive the shaft), (2) Low reducibility (to control reduction), (3) Low fines (dust). The pellets are made from iron ore concentrate. The pelletizing plant is often co-located with the DRI plant. The pellet quality directly affects DRI quality.

Sponge Iron (DRI) Characteristics

DRI is porous (like a sponge), hence "sponge iron". The steel raw materials market describes DRI: (1) High iron content (90-94%), (2) Low impurities (sulfur, phosphorus, silicon), (3) Low carbon content (0.5-2%), (4) Porous (surface area). The porous nature makes DRI reactive. It can reoxidize (rust) and can generate heat if exposed to moisture. Therefore, DRI is often briquetted (HBI) for transport.

The HYL/ENERGIRON Process (Alternative)

The HYL (now Energiron) process uses a similar shaft furnace but with a different reducing gas composition. The HBI market notes that Energiron can use hydrogen-rich gas and can recycle CO2. It also produces DRI with higher carbon content (for EAF use). The process is patented. Several plants use this technology.

The MIDREX Process (Dominant)

The MIDREX process is the most common. The direct reduced iron market estimates that a large portion of global DRI is produced by MIDREX. The process uses a shaft furnace with counterflow of gas and solids. The reducing gas is produced in a reformer. The DRI is discharged at a certain temperature. The process is reliable and efficient.

Carbon in DRI (For EAF Use)

EAF steelmakers need carbon in the DRI to: (1) Help melt the iron (carbon lowers the melting point), (2) Provide a foaming slag (to protect the furnace walls), (3) Aid in reduction (if there is residual oxygen). The sponge iron market can produce DRI with carbon content (1-3%) by controlling the gas composition. The carbon is present as iron carbide (Fe3C). High-carbon DRI is valuable.

Cooling and Handling DRI

DRI at the furnace discharge is hot. The iron briquette market uses: (1) A cooling conveyor (to cool the DRI) or (2) A briquetting machine (to make HBI). If the DRI is to be shipped, it must be briquetted. If used directly in a nearby EAF, it can be hot-charged (hot DRI). Hot charging saves energy (no reheating). The DRI must be transported via a covered conveyor (to prevent reoxidation).

The Challenge of DRI Fines

DRI is friable (can break into fines). The steel raw materials market warns that fines: (1) Are difficult to feed into the EAF, (2) Can reoxidize quickly, (3) Can be lost (dust). To reduce fines, DRI is screened. Fines can be briquetted (cold briquetting) or recycled. The briquetting process also reduces fines.

Reoxidation of DRI (Pyrophoric)

Fresh DRI can reoxidize exothermically (spontaneously combust) if exposed to air and moisture. The hot briquetted iron market explains that the reaction is Fe + O2 + H2O → Fe2O3 + heat. This can cause fires in storage or shipping. To prevent this, DRI is: (1) Passivated (coated with a lime slurry), (2) Stored in a nitrogen atmosphere, (3) Briquetted (HBI). HBI is much safer.

Water and Hydrogen (Reaction)

The reoxidation reaction requires water. The sponge iron market notes that DRI shipped by sea must be kept dry. The ship's hold must be ventilated (to prevent condensation). Cargo holds are monitored for temperature and gas (hydrogen). If the DRI is not properly passivated, it can overheat. There have been incidents of DRI cargoes catching fire.

The Cost of DRI vs. Pig Iron

DRI is more expensive than pig iron (blast furnace) in many regions. The direct reduced iron market attributes this to: (1) Natural gas cost (vs. coal), (2) Higher grade ore cost, (3) Capital cost of the DRI plant. However, DRI has lower emissions. As carbon pricing increases, DRI will become more competitive. Some steelmakers integrate DRI into their steelmaking (to secure feedstock).

The Transition to Hydrogen

To reduce CO2 emissions, the direct reduced iron market is transitioning from natural gas to hydrogen (green or blue). The iron briquette market has pilot plants using up to 100% hydrogen. The hydrogen DRI process is similar to natural gas (H2 as reducing agent). The main difference is the reformer (not needed). The product is low-carbon DRI. The cost is currently high.

The Future: Hot DRI (HDRI) Direct Charging

To save energy, DRI can be charged directly into the EAF while hot. The sponge iron market uses a hot transport system (e.g., a covered conveyor or a pneumatic transfer). The HDRI is at around 700°C. This saves electricity (the EAF uses less energy to melt). The EAF also has higher productivity. Hot charging is used in integrated DRI-EAF plants. The direct reduced iron market is evolving. And the sponge iron market continues to improve DRI quality, reduce fines, and lower emissions, providing the steel industry with a low-carbon iron feedstock.

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