Why carbon capture and storage does not solve the climate problem of blast furnaces

Blast furnaces produce more carbon dioxide (CO2) than iron. Producing one tonne of steel with the blast furnace (BF) route releases 2.3 tonnes of CO2. Some steelmakers are proposing to use carbon capture and storage (CCS) as a solution, promising to reduce their blast furnace emissions in the decades ahead. A close look at the evidence leads us to conclude that carbon capture on coal-based blast furnaces is the wrong use of precious effort and investment — for a technology that falls far short of what the climate requires. 

Carbon capture on coal-based blast furnaces does not resolve the fundamental incompatibility between coal-based steel production and a near-zero emissions steel sector. 

Fitting carbon capture onto some of the gas streams at a blast furnace-basic oxygen furnace (BF-BOF) plant could prevent a fraction of emissions reaching the atmosphere. But the reduction in released emissions is far less than companies’ claims would lead you to believe. And far away from what is needed for a near-zero emissions steel sector and a stable climate. 

Commercial scale CCS on coal-based blast furnaces does not exist today. Developing and scaling it would consume substantial capital, political will, and time that should instead be directed toward deep decarbonisation. CCS reinforces continued dependence on coal-based steelmaking at precisely the moment the industry needs to transition away from it. 

Four major problems stand out. 

1. A “solution” that locks in coal is not a climate solution

The prospect of CCS is being used to justify continued investment in blast furnaces. CCS on coal-based blast furnaces is a multi-decade investment that entrenches coal-based steelmaking and its associated infrastructure, such as coke ovens and coal mines. Locking in coal dependency in turn locks in climate emissions and air pollution for decades to come. 

Reinforcing the coal-based infrastructure also reinforces inertia and builds political and institutional resistance to the transition out of coal. This entrenchment therefore doesn’t just freeze the current system in place; it actively resists change. Companies will not want their expensive CCS-equipped blast furnaces to become stranded assets, so they will logically argue for policies that protect their return on investment rather than policies that drive ambitious decarbonisation. 

Capital that could and should be directed toward near-zero emissions steelmaking is instead consumed by CCS. This means the cost reductions and technical learning on breakthrough technologies take longer, slowing the pace of the green steel transition.

The result is a vicious circle: more investment in coal makes the transition out of coal harder. The problem with CCS is not that the technology does nothing. It is that investing in it drives commitment to continued coal-based BF operation well beyond the point when near-zero alternatives must be scaling up.

2. Emissions reductions are less than steelmakers’ claims would have you believe

Steelmakers make ambitious claims for what CCS can deliver in the decades ahead, but actual emissions reductions achievable in a BF-BOF plant are significantly more limited than headline figures suggest.

Technically, capture rates above 90% are possible on a stream with high CO2 concentration. But a BF-BOF plant has multiple sources of emissions [1], from the blast furnace itself, the coke ovens, sintering plants, and power plants. The CO2 in the blast furnace gas is the most concentrated and easiest to capture, but capturing CO2 from other gas streams with lower concentrations is more difficult. 

Capture rates also say nothing about upstream emissions. For example, CCS does nothing to reduce upstream fugitive emissions from coal mining. 

Total emissions reductions are not the same as reported capture rates. A capture rate on one gas stream might be high, but the reduction in total emissions from the plant will be much smaller, and the reduction over the entire supply chain is even smaller still. 

No BF-BOF plant has commercially demonstrated CCS yet. Existing pilots and demonstrations rarely exceed 35% emissions reductions (across scopes 1–3). Looking over the next two to three decades, our assessment [2] is that total emissions reductions from CCS are unlikely in practice to go beyond 50%. 

So when large claims are made, the reduction will most likely cover only Scope 1 emissions, and potentially only a portion of those. Even in the most optimistic scenarios, total reductions fall well short of what the climate demands.

3. CCS is disproportionately expensive 

The economics associated with BF-BOF-CCS are deeply challenging and become increasingly so when larger emissions reductions are sought. 

Carbon capture requires significant energy. As CO2 concentration in gas streams decreases, more energy is required to capture the CO2. This is the energy penalty of carbon capture. Costs rise steeply once the relatively easy, high-concentration sources have been dealt with. The marginal cost of each additional tonne captured climbs sharply along a hockey-stick pattern, making anything approaching near-zero via CCS prohibitively expensive.  

CCS requires high capital investment and entails ongoing extra operating costs. So it consumes enormous financial and organisational resources, investment that could otherwise be directed toward scaling up near-zero alternatives which eliminates emissions at source. 

Combined with the structural reality of operating across multiple emission point sources, the result is a technology that is expensive to deploy, structurally ill-suited to BF-BOF systems, and increasingly uneconomical as emissions reduction ambitions rise.

4. Transport and storage remain major under-recognised challenges 

The challenges of transporting and permanently storing captured CO2 are too often absent from the case made for BF-BOF-CCS, but they represent serious practical constraints.

Captured CO2 must be transported to and injected into geological storage formations. Yet most existing coal-based steel plants are located far from suitable sites or established CO2 pipeline networks, adding significant infrastructure costs to an already expensive proposition. 

New pipeline and storage projects are being developed by public and private actors, but they are publicly-contested, require substantial investment to develop, and take many years to permit and build. Storage has to be paid for continually, year after year.  

Timing is another major problem. Developing sufficient transport and storage infrastructure for steelmaking would likely take us well past the point when steelmakers should already be scaling near-zero emissions production. 

Transport and storage are therefore not side issues. They are core challenges limiting the practicality, cost and timing of CCS deployment in BF-based steelmaking.

CCS on blast furnaces is simply the wrong choice

A blast furnace fitted with carbon capture will still drive substantial climate emissions. These emissions are economically inconvenient to avoid, not genuinely unavoidable. They could and should be avoided through the deployment of near-zero emissions iron and steel production instead. Technology to get there already exists, so the effort and investment should go into building and scaling near-zero emissions steel.

By 2050, truly unavoidable residual emissions across all sectors will need to be compensated by carbon dioxide removal (CDR). Carbon removal will be needed for emissions that are genuinely and demonstrably unavoidable, not for those that are merely economically inconvenient to avoid. 

Carbon capture on a blast furnace is a dubious financial choice to make. It requires huge investment, development over many years, and locks a company into coal-based operations, for an outcome that is unproven. It will add major costs to each tonne of steel, while the chance of recouping the money through any “green premium” is doubtful given the steel will still be made with coal.

Carbon capture on blast furnaces is a commercially unproven, expensive, and inadequate attempt to hide or prolong the dirtiest problem at the heart of iron and steelmaking: dependence on coal. Blast furnaces are dependent on coal, and with or without CCS, they are not compatible with near-zero emissions steelmaking. And that needs to be the starting point of how steelmakers make technological choices to head us into a net-zero future.

Notes

1. (1) the on-site power plant, (2) the blast-furnace hot stoves, (3) the sinter plant strand, (4) the coke-oven battery, (5) the lime kiln, (6) the rolling-mill reheating furnaces, and (7) the basic oxygen furnace. Whole-plant CCS addressing all seven sources requires separate capture units at each – with associated capital cost, space, energy, and operational complexity.
2. For example, from the ULCOS Top Gas Recycling Blast Furnace campaigns, van der Stel et al. present a maximum 75% reduction of CO2 emissions from the blast furnace, of which 24% comes from gas recycling, and assuming leakage-free transport and permanent storage. However, the authors note this 75% reduction drops to 60% direct CO2 emissions when considering the extra energy required to compensate for the decreased amount of blast furnace gas normally used in the plant and for operating the CO2-removal unit. Even when assuming the 60% covers coking and sintering, it remains an on-site Scope 1 emissions figure and therefore omits, among others: coal mine methane, the indirect emissions for oxygen production and CO2 compression, and the CO2 transport-and-storage chain itself – all of which would lower the net avoided emissions. SteelWatch estimates approximately a 37–45% reduction on a full Scope 1-3 GWP-100 basis depending on grid emissions intensity. Source: van der Stel, J., Louwerse, G., Sert, D., Hirsch, A., Eklund, N., & Pettersson, M. (2013). Top gas recycling blast furnace developments for ‘green’ and sustainable ironmaking. Ironmaking & Steelmaking, 40(7), 483–489.