Why steel and cement are the hard cases

Steel and cement together produce roughly one-seventh of global carbon dioxide emissions — around 7% from steel and a similar share from cement. Both are used in enormous volumes, both rely on high temperatures, and neither has an obvious drop-in replacement. That is why they are usually described as "hard to abate", and why green hydrogen attracts so much attention as a possible answer.

In steelmaking, coal and coke do two jobs at once: they provide heat and they strip oxygen from iron ore. In cement, the fuel provides heat, but most of the emissions come from the limestone itself, which releases carbon dioxide as it is converted to clinker. That difference explains why hydrogen fits each industry in quite different ways.

Green hydrogen in steelmaking

The most developed route replaces the blast furnace with a direct reduced iron (DRI) shaft furnace. Iron ore pellets are heated to around 800–900°C in a stream of hydrogen, which pulls oxygen out of the ore and leaves metallic "sponge" iron. That sponge iron then goes into an electric arc furnace, powered by low-carbon electricity, to become steel.

Because the reduction is done chemically by hydrogen rather than by carbon, the main by-product is water vapour instead of carbon dioxide. Plants being designed today can usually start on natural gas and switch to increasing shares of hydrogen as supply becomes available, which de-risks the investment.

• Ore quality matters enormously: direct reduction needs high-grade pellets, generally above 67% iron with low gangue content.
• A fully hydrogen DRI route consumes roughly 50–60 kilograms of hydrogen per tonne of steel.
• The electric arc furnace adds a large new electricity load, typically 500–700 kWh per tonne of steel.

Green hydrogen in cement kilns

Cement is a different puzzle. Raw meal of limestone and clay is fed into a kiln and heated to about 1450°C so that clinker forms, with flame temperatures nearer 2000°C. Hydrogen can reach those temperatures, but its flame behaves differently: it burns faster, produces more water vapour, and tends to form more nitrogen oxides, so burners and kiln control systems need rethinking. Radiative heat transfer also changes, which affects how evenly the material is heated.

Even so, the harder truth is that fuel switching alone cannot decarbonise a cement plant. Roughly 60% of its emissions come from the calcination of limestone, which releases carbon dioxide no matter what is burned. Green hydrogen therefore sits alongside carbon capture, clinker substitution with materials such as ground granulated blast furnace slag or calcined clay, and greater use of alternative raw materials.

The barriers that keep coming up

High temperatures and heat transfer. Both industries need sustained, intense heat, and existing equipment was designed around the combustion behaviour of coal, coke and gas. Retrofitting burners, refractory linings and control systems takes time and capital, and pilot plants often reveal surprises that laboratory work does not.

Continuous supply. Cement kilns typically run for months without stopping, and DRI plants prefer steady operation too. Renewable electricity is variable, so a plant needs either large-scale hydrogen storage, a pipeline connection to a diversified production cluster, or enough renewable capacity to ride through calm, cloudy spells. Each option carries cost, and storage in salt caverns or pressurised vessels is not cheap.

Cost competitiveness. Green hydrogen currently costs several times more than the grey hydrogen made from natural gas, and an electrolyser needs around 50–55 kWh of electricity per kilogram produced. Electricity price is the dominant factor. For steel, fuel switching can add a fifth or more to production costs; for cement, hydrogen also competes with cheaper waste-derived fuels.

What practical progress looks like

• Blend before you switch: running kilns on 20–30% hydrogen by volume uses existing infrastructure and builds operator confidence.
• Cluster production: sharing a hydrogen network between steel, cement, refining and chemical plants spreads the cost of electrolysers and storage.
• Design for flexibility: plants that can run on gas today and hydrogen tomorrow are more investable than single-fuel designs.
• Support demand: contracts for difference, public procurement and advance market commitments for low-carbon steel and cement give producers confidence to invest.
• Be honest about accounting: hourly matched renewable electricity and clear emissions reporting stop green hydrogen claims from outrunning reality.

Where this leaves us

Green hydrogen is technically credible in both steel and cement, and the engineering is moving faster than many expected. But it is not a single fix. In steel it can replace the reductant and most of the fuel; in cement it can cut the fuel-related share while carbon capture handles the process emissions. The deciding factors over the next decade will be cheap renewable electricity, shared infrastructure, and steady demand for genuinely low-carbon materials. Get those right, and hydrogen becomes a workhorse rather than a niche. Get them wrong, and it stays expensive, intermittent and confined to demonstration projects.