Coal-Based vs Gas-Based DRI: Which Process for Which Market
Coal-based DRI dominates India via rotary kilns; gas-based DRI dominates MENA via shaft furnaces. Compare feedstock, scale, metallization, emissions.
Coal-based DRI and gas-based DRI both reduce iron ore to solid metallic iron below the melting point, but they differ in feedstock, process equipment, scale, metallization, carbon footprint, and geographic viability in ways that determine which route suits a given market and resource environment. In 2024, world DRI production reached 140.8 Mt: shaft furnaces (predominantly gas-based) produced approximately 72% and rotary kilns (predominantly coal-based) approximately 24% [1]. India accounted for 54.8 Mt of global output in 2024, approximately 80% of it coal-based [2][1]. This piece sets out the decision frame for comparing the two routes.
Two routes to the same product
Both routes start with iron ore pellets or lump ore and a reducing agent, and both aim to strip oxygen from the iron oxides below the melting point of iron (~1,538°C for pure iron) to produce a solid metallic product. The reactor, the reductant, and the scale differ substantially.
Coal-based route. A rotating inclined cylindrical kiln (typically 60-100 m in length, 4-6 m in diameter) heats a bed of iron ore and non-coking coal. The coal combusts in a controlled way in the freeboard, generating a CO-rich gas that penetrates the ore bed and reduces the iron oxides over an 8-12 hour residence time [3]. The product exits at approximately 200-400°C into a rotary cooler. India's 285-plant DRI industry is built almost entirely on this technology, with individual kiln capacities of 50-500 TPD [3][4].
Gas-based route. Iron ore pellets or lump ore descend through a counter-flow vertical shaft furnace (the Midrex or ENERGIRON/HYL configuration). A hot reformed gas (CO + H2, typically 90-92% reducing gas) passes upward through the descending ore, reducing it over a 5-8 hour residence [5][6]. The product is discharged hot (HDRI, around 700°C) for direct EAF charging or cooled (CDRI) for bulk handling and storage. Single-module capacity ranges from 0.5 Mt/y to 2.5 Mt/y (ENERGIRON, Nucor Steel) [6].
Decision-frame comparison
| Parameter | Coal-Based (Rotary Kiln) | Gas-Based (Shaft Furnace) |
|---|---|---|
| Primary reductant | Non-coking coal | Reformed natural gas; or hydrogen (emerging) |
| Key processes / licensors | SL/RN (LKAB/Outokumpu heritage), TISCO, Indian variants | Midrex (Kobe/Primetals); ENERGIRON (Tenova/Danieli) |
| Typical unit capacity | 50-500 TPD per kiln | 0.5-2.5 Mt/y per module |
| Reactor type | Rotary kiln, 60-100 m length | Counter-flow vertical shaft furnace |
| Metallization | 88-92% | 92-95% |
| Carbon in product | 0.08-0.2% | 1.0-2.5% (tunable via cooling gas methane) |
| Specific energy | 4.1-5.3 Gcal/t DRI (17-22 GJ/t) [4] | ~10-12 GJ/t (gas input) [5] |
| GHG intensity | 1,391-1,880 kg CO2/t DRI [7] | 815-1,160 kg CO2/t DRI (NG); under 100 kg/t (H2-DRI) [7][8] |
| Capex profile | Lower (modular, coal-side infrastructure) | Higher (gas reforming, large-module civil works) |
| Gas / power dependency | Low (coal only) | High (natural gas supply; pipeline infrastructure) |
| Geographic stronghold | India (dominant), South Africa, China (legacy) | MENA, Iran, Russia, Mexico, USA, Europe (green steel) |
| Transition to H2 | Not feasible (reactor incompatible with gas-phase reductant) | Yes, MIDREX Flex and ENERGIRON ZR are H2-ready |
The coal-based route: why India chose the rotary kiln
India adopted the coal-based rotary kiln because the country has no commercially viable indigenous supply of metallurgical coking coal (required for blast furnaces) but does have substantial reserves of non-coking coal, and the rotary kiln is modular enough to serve the small and medium electric furnace steel producers that dominate Indian DRI consumption [2][3][4].
India is the world's largest DRI producer: 54.8 Mt in 2024 (World Steel Association) [2], approximately 80% of which was coal-based [3]. The 285 DRI plants in India mostly operate 100 TPD kilns, supplying induction furnace and mini EAF customers in the secondary steel sector [4]. The SL/RN process and its Indian adaptations are the dominant technology.
Specific coal consumption for the rotary kiln route is approximately 950-1,000 kg coal per tonne of DRI, with specific energy consumption typically 4.1-5.3 Gcal/t-DRI (17-22 GJ/t-DRI) [4]. This is substantially higher than the gas-based route on a per-tonne basis, reflecting the inherent inefficiency of burning coal to generate both process heat and reducing gas in the same vessel.
The scale constraint is fundamental. A single Midrex or ENERGIRON shaft furnace module at 1-2.5 Mt/y cannot economically serve the scattered 50-500 TPD demand pattern of India's induction furnace belt. The rotary kiln's lower minimum economic scale (50 TPD) is an enabling feature for the Indian market structure.
Quality consequences of the coal-based route are covered in coal-based sponge iron production and sponge iron quality control. The key quality trade-off: coal-based DRI delivers 88-92% metallization and 0.08-0.2% carbon, while gas-based delivers 92-95% metallization and 1.0-2.5% tunable carbon. For the sponge iron production process in full, see the C9 cornerstone piece.
The gas-based route: why MENA and green-steel developers chose the shaft furnace
Gas-based DRI via shaft furnace dominates MENA, Iran, Russia, Mexico, and is the route of choice for new green-steel projects in Europe and North America, because these regions have abundant and relatively cheap natural gas, and the large-module shaft furnace delivers higher metallization, a tunable carbon product, and a clear pathway to green steel via hydrogen [1][5][6].
MIDREX is the leading licensor. Its plants produced 76.2 Mt in 2024, 54.1% of all DRI produced globally and a new annual record [1]. The 7.5 m diameter Super Megamod shaft furnace produces 2.2 Mt/y of DRI from a single module [5]. Qatar Steel's 5.0 m module has produced over 28.7 Mt of cumulative DRI since 1978 [1]. SULB (United Steel Company, Bahrain) operates a 1.5 Mt/y HDRI/CDRI combination plant and surpassed 15 Mt cumulative output [1].
ENERGIRON (Tenova/Danieli joint venture). The largest single-module ENERGIRON installation is Nucor Steel's 2.5 Mt/y plant in the United States [6]. The process is notable for its self-reforming feature: the reactor uses the ore bed as the reforming catalyst, reducing capital cost relative to external-reformer designs.
The gas-based shaft furnace is the only commercially proven DRI reactor that can transition to hydrogen-based reduction. MIDREX Flex and ENERGIRON ZR designs can blend increasing proportions of hydrogen into the reducing gas as hydrogen costs fall. At 100% H2, MIDREX Flex operation reduces CO2 emissions by approximately 97% relative to blast furnace-BOF steelmaking [8].
Gas-based DRI product also carries more carbon per tonne of product: 1.5-2.5% carbon, tuned by adjusting methane content in the cooling gas. Each kilogram of carbon entering the EAF bath provides approximately 2.3 kWh of chemical energy, reducing electrical energy demand. This is a steelmaking quality advantage the coal-based route cannot match structurally.
Emissions and the green steel transition
Gas-based DRI emits roughly 33-41% less CO2 than coal-based DRI at current natural gas mix; the gap widens to approximately 97% with hydrogen-based operation [7][8].
Measured as kg CO2 per tonne of DRI produced:
| Route | GHG intensity (kg CO2/t DRI) | Source |
|---|---|---|
| Coal-based DRI (rotary kiln, India conditions) | 1,391-1,880 | Biswas et al. (2022) LCA [7] |
| Gas-based DRI (NG reforming, MIDREX) | 815-1,160 | Biswas et al. (2022) LCA [7] |
| Gas-based DRI (H2-DRI, MIDREX Flex at 100% H2) | ~60-100 (estimated) | Midrex [8] |
| Blast furnace-BOF (for reference) | 1,800-2,000 kg CO2/t steel | World Steel Assoc [9] |
India's coal-based DRI plants face a structural decarbonisation challenge: the rotary kiln cannot switch to hydrogen feedstock. Any transition to lower-emission ironmaking for Indian plants will require greenfield gas-based or hydrogen-based shaft furnaces, not retrofits of existing kilns. This is beginning to appear in Ministry of Steel India discussions on a net-zero steel roadmap, though the timeline remains unclear.
For the MENA and European operators, the gas-based route is already positioned as the transition vehicle: the same plant that runs on natural gas today can progressively blend in hydrogen as renewable supply expands. That optionality is the primary strategic advantage of the gas-based route at a new-investment decision point.
Kiln sealing implications for each route
Both routes require effective sealing at the reactor inlet and outlet, but the failure consequences differ [10][11].
Coal-based rotary kilns. The kiln inlet and outlet seals are the primary barriers against false air ingress and product re-oxidation. At the discharge end (200-400°C), the sponge iron is reactive and porous. A seal failure at the outlet hood or cooler interface causes direct metallization loss: a persistent 5-10% false air ingress can suppress metallization by 2-4 percentage points, pushing product below IS 15774:2018 Grade 1 specification. Seal integrity in coal-based plants is a product quality issue, not merely an energy-efficiency issue.
Gas-based shaft furnaces. The shaft furnace operates under positive reducing gas pressure, which means minor ambient air leakage is less likely to penetrate the reactor bed. Sealing at the gas offtake, product discharge lock-hopper, and cooling gas circuit is engineering-critical, but the process is inherently more forgiving of small atmospheric air contact than the coal-based rotary kiln. The quality control mechanism in gas-based plants is primarily the CO/H2 gas composition rather than the physical atmosphere seal.
The duplex kiln sealing system is particularly applicable to coal-based DRI kilns where continuous campaign operation between planned maintenance windows creates sustained exposure to wear-driven seal degradation. The double-barrier design maintains atmosphere integrity at the discharge end even as the primary seal approaches its service limit. Oswal serves the metallurgical industry with sealing systems for both DRI and other kiln applications in the sector. For more on the sealing case specifically, see why kiln sealing matters in DRI plants.
Common questions about this topic
Gas-based DRI (shaft furnace) consistently achieves higher metallization: 92-95%, compared with 88-92% for coal-based rotary kiln DRI [2][5]. The shaft furnace uses a tightly controlled reducing gas (CO + H2) that is optimised for the target metallization degree; the rotary kiln's reducing conditions are harder to control uniformly along the kiln length. Air ingress at the kiln seals in coal-based plants can further suppress metallization below the kiln's design target, adding process variability that the gas-based route does not face in the same way.
Not imminently in India, where the coal-based route accounts for approximately 80% of production and the sector's small-scale structure (100-500 TPD kilns supplying induction furnace customers) makes large gas-based shaft furnaces economically impractical for most operators [3][4]. However, the coal-based route has a substantially higher emissions footprint and cannot transition to hydrogen. Long-term, Indian DRI capacity additions at larger scale are likely to favour gas-based or hydrogen-based shaft furnaces. The coal-based fleet will probably operate until the end of its economic life rather than being converted.
No. The two routes use fundamentally different reactors. A coal-based plant uses a rotary kiln; a gas-based plant uses a counter-flow shaft furnace with a gas-reforming unit upstream. Switching requires building a new plant. The capital intensity of a Midrex or ENERGIRON module (and the gas infrastructure it requires) means transition decisions are made at the new-investment stage, not as retrofits to existing kilns. Indian producers evaluating capacity expansion above approximately 0.5 Mt/y are increasingly examining gas-based options, particularly as LNG import infrastructure develops.
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