Gas-Based DRI: The Direct Reduction Process
Gas-based DRI uses a shaft furnace and H2+CO gas reformed from natural gas. Midrex and HYL/Energiron processes, metallization, and vs coal-based DRI.
Gas-based DRI is the direct reduction of iron ore pellets or lump ore inside a shaft furnace using a reducing gas composed primarily of hydrogen (H2) and carbon monoxide (CO) derived from reformed natural gas, without any melting of the iron. The result is the same product as the coal-based route: porous metallic iron (sponge iron) used as a premium steelmaking feed in electric arc furnaces. Two commercial platforms dominate: the Midrex Process (Midrex Technologies) and HYL/Energiron (Tenova and Danieli). Together, shaft furnace gas-based DRI accounts for the majority of global production: Midrex plants alone produced 76.2 Mt in 2024, representing 54.1% of total world DRI output of 140.8 Mt [1].
Gas-based DRI: direct reduced iron produced in a counter-current shaft furnace by reacting iron ore with a hot H2+CO reducing gas, reformed from natural gas or hydrogen, without smelting. Also called gas-based sponge iron or shaft furnace DRI. See sponge iron production process for the full cross-route overview.
How the Midrex process works
The Midrex process reforms natural gas with recycled top gas from the shaft furnace to produce a hot reducing gas (approximately 55% H2 and 36% CO on a dry basis) that is injected into the middle of the reduction shaft at 850-950°C [2][3].
The reformer is a gas-tight, refractory-lined furnace containing alloy steel tubes packed with nickel-based catalyst. Fresh natural gas is blended with recycled shaft top gas and heated through the catalyst bed. The reforming reactions are:
CH4 + H2O → CO + 3H2 (steam reforming)
CH4 + CO2 → 2CO + 2H2 (dry reforming)
Where:
- CH4 = methane (from natural gas)
- H2O = steam; CO2 = carbon dioxide from recycled top gas
- Outlet H2/CO ratio: 1.5-1.8, reformer exit temperature 900-950°C [3]
The reformed gas enters the shaft furnace through a peripheral bustle pipe at mid-shaft height and flows counter-current upward through a descending packed bed of iron ore pellets or lump ore. Iron oxides are reduced to metallic iron between 800-900°C:
Fe2O3 + 3H2 → 2Fe + 3H2O (hydrogen reduction)
Fe2O3 + 3CO → 2Fe + 3CO2 (CO reduction)
The shaft furnace has three sections (top to bottom):
- Upper reduction zone: ore preheats and reduction begins; top gas (H2O + CO2 + unreacted H2/CO) exits the furnace top and is recycled to the reformer after CO2 removal.
- Lower reduction zone / transition zone: reduction to target metallization; residence time of 4-8 hours total in the shaft.
- Cooling zone (cold DRI) or direct hot-discharge (HDRI): cold DRI is cooled with inert gas before discharge at below 50°C for safe handling and transport; HDRI is discharged at approximately 650-700°C directly into adjacent EAF ladles, saving the energy cost of reheating.
Typical Midrex product specification: metallization approximately 92%, carbon content 0.5-2.5% (adjustable by controlling CO content in reducing gas) [4].
How the HYL / Energiron process works
The HYL/Energiron process is a pressurised shaft furnace route operating at approximately 0.6-0.8 MPa absolute (6-8 bar) that uses H2-rich reducing gas at approximately 1,080°C reduction temperature in its ZR (Zero Reformer) variant [5][6].
The original HYL process was developed by Hylsa in Mexico in the 1950s. The modern Energiron platform (Tenova + Danieli) uses internal autothermal reforming within the shaft furnace in the ZR variant, eliminating the separate external reformer and reducing capital cost. CO2 from the reduction reaction is scrubbed and recycled, enabling tight control of carbon content in the product.
Key Energiron ZR design case [5]:
- Metallization: approximately 94%
- Carbon content: 3.5% (controllable)
- Thermal energy input: 2.30 Gcal/t DRI (for hot DRI discharge)
- Operating pressure: 0.6-0.8 MPa
The elevated pressure approximately doubles productivity per unit furnace cross-section compared with near-atmospheric Midrex operation, reducing the footprint for a given capacity. The ZR variant's internal reforming also means it can operate on green hydrogen by bypassing the reforming step entirely, making it a platform for low-carbon ironmaking as renewable hydrogen costs fall.
Gas-based vs coal-based DRI: where each route fits
Gas-based DRI produces a higher-metallization, lower-ash product and emits less CO2 per tonne than coal-based sponge iron, but requires access to cheap natural gas or hydrogen. Coal-based suits regions with abundant non-coking coal and limited gas supply.
| Dimension | Gas-based (shaft furnace) | Coal-based (rotary kiln) |
|---|---|---|
| Reductant | Reforming gas (H2+CO from natural gas or H2) | Non-coking coal |
| Reactor type | Counter-current shaft furnace | Inclined rotary kiln |
| Typical metallization | 92-94% | 88-92% |
| Typical carbon content | 0.5-3.5% (controllable) | 0.1-0.3% |
| CO2 per tonne DRI | Lower (~1.0-1.5 t CO2/t DRI, gas route) | Higher (~3.0 t CO2/t DRI, coal route) |
| Scale per unit | 0.5-2.5 Mt/year per module | 50-500 TPD per kiln |
| Dominant geography | Middle East, North Africa, Russia, Mexico | India (~80% of Indian DRI) [7] |
| Decarbonisation path | H2-ready (MIDREX H2, Energiron ZR-H2) | Limited; green electricity for coal supply only partial fix |
Sources: Midrex 2024 [1]; IspatGuru [2][5]; TERI 2021 [7]; IEA Steel Breakthrough Agenda 2025 [8].
India is the world's largest DRI producer (54.7 Mt in 2024 [1]) but relies predominantly on coal-based kilns. Iran is the leading gas-based DRI producer at 34.7 Mt in 2024, enabled by domestic natural gas reserves [1]. For a detailed comparison of both routes on energy, quality, and economics, see coal-based vs gas-based DRI.
Key process parameters
| Process | Parameter | Midrex (NG) | Energiron ZR |
|---|---|---|---|
| Reduction temperature | °C | 800-900 | ~1,080 |
| Operating pressure | MPa abs | ~0.12 (near atm.) | 0.6-0.8 |
| Reducing gas H2 fraction (dry) | % | ~55 | Higher (ZR-H2: ~100) |
| Metallization | % | ~92 | ~94 |
| Carbon content | % | 0.5-2.5 | ~3.5 (typical) |
| Energy input (HDRI) | GJ/t DRI | ~10-11 [2] | ~9.6 [5] |
| 2024 production | Mt | 76.2 [1] | Not separately reported |
Common questions about this topic
The Midrex process reforms natural gas into a hot H2+CO reducing gas, injects it counter-current through a shaft furnace packed with iron ore pellets, and extracts DRI at approximately 92% metallization without melting the iron [2][3]. The top gas from the furnace is recycled back to the reformer, making the process energy-efficient. Midrex plants produced 76.2 Mt in 2024, the largest single-technology share of global DRI output [1]. For the broader context of where DRI fits in steelmaking, see [sponge iron production process](/en/blog/sponge-iron-production-process).
Gas-based DRI uses a shaft furnace and H2+CO reducing gas reformed from natural gas; [coal-based sponge iron production](/en/blog/coal-based-sponge-iron-production) uses an inclined rotary kiln and non-coking coal. Gas-based achieves higher metallization (92-94% vs 88-92%), lower ash content, and lower CO2 per tonne, but requires natural gas or hydrogen supply at competitive cost. Coal-based dominates in India because domestic non-coking coal is abundant; gas-based dominates the Middle East where gas is cheap. The [metallurgical industry](/en/industries/metallurgical) page covers both routes in the context of Oswal's kiln-sealing applications across DRI plants.
Yes. Both MIDREX H2 and the Energiron ZR-H2 variant can operate on green hydrogen, replacing the natural gas reformer entirely. When run on 100% H2, the reducing gas is pure hydrogen and the only by-product is water vapour -- the lowest-carbon ironmaking route commercially demonstrated at scale. The IEA's Steel Breakthrough Agenda 2025 identifies H2-DRI coupled with electric arc furnaces as the primary decarbonisation pathway for primary steel production [8].
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