Decarbonisation of the steel and cement sectors faces significant challenges. They are some of the largest consumers of fossil fuels on the planet; fuels that are not easily substituted due to the high-temperature processes used.

‘Neither industry can get rid of coal or find an alternative easily, as it is an essential part of current processes. What’s more, electricity cannot be used as a direct heating source – which makes them hard-to-abate industries,’ explained Lars Erik Nicolaisen, Deputy Chief Executive Officer of Rystad Energy.

Furthermore, if the energy consumption is correlated with the carbon emissions associated with the industries respectively, cement, iron and steel are ‘outliers’ compared to other industrial sectors as they produce a higher proportion of emissions.

Rystad Energy estimates 38-40 Gt of CO₂ are released in total annually, of which about a quarter comes from industrial activity. Of that quarter, roughly half are attributable to steel and cement production. Half of these emissions originate from the combustion of coal, in order to achieve heat at high temperature; the other half come from the process itself and the chemical reactions associated.

Let’s look at both industrial processes in more detail.

Cement – CCUS will be vital 

The cement industry is the second largest emitter of emissions (after chemicals, which uses a lot of fossil fuels for feedstock) among the total industry sector, accounting for 18% of industrial emissions worldwide. For every tonne of cement produced there is almost an equal amount of CO₂ emitted – around 0.9 tonnes of CO₂ for every tonne of cement produced. That was equivalent to 2.3 Gt of emissions in 2019.

The Asia-Pacific accounts for over 50% of total cement industry emissions, primarily from China.

As mentioned, there are two sources of emissions – from the fuel combustion and from the chemical process itself. For the cement industry, process emissions amount to more than 50%, with over 40% contributed by combustion.

Cement production starts with mining limestone, which accounts for a small quantity of emissions. The limestone is ground up and passed through a rotary blender, then undergoes a process called calcination at up to 1,400oC, which forms cement clinker.

The clinker is mixed with gypsum and other materials, and after cooling and further grinding produces cement. The entire process accounts for 90% of the emissions in the cement industry.

Almost 100% of the emissions created during this process could be abated using carbon capture, use and storage (CCUS) technologies, suggested Yvonne Lame, Vice President, CCS, Rystad Energy. ‘Utilisation of the CO₂ will also improve the economics of the cement industry, giving it an incentive to use CCUS.’

Creation of novel cements could help reduce the emissions by about 90%, for example, using magnesium silicate as a highly reactive source of silica. Combustion emissions could also eventually be addressed by hydrogen for electricity, replacing about 40% of coal emissions in the sector.

In the meantime, many cement producers are improving process efficiency and energy consumption. There have also been initiatives to create a circular economy by recycling cement from demolished buildings to reduce emissions.

Aker Carbon Capture offers a technology called Big Catch, which uses a chemical absorption capture process. This approach is currently being used in the Norcem cement plant in Brevik, Norway, as part of the Northern Lights CCUS project.

Looking to the long-term, under Rystad Energy’s 1.6℃ scenario by 2050, about 40% of total CO₂ emitted needs to be captured using CCUS by mid-century and 30% by direct air capture.

Lame considered that CCS will have a significant impact on the cement sector ‘as 60% of carbon emissions come from process emissions, and CCS is a proven technology to capture CO₂ and store it in saline aquifers or abandoned oil and gas fields.’ She also noted that there ‘is also an opportunity for the sector to use hydrogen for effective decarbonisation of electricity or heat eventually’.

Lame recognised that it is early days and still very expensive to capture and store CO₂, especially for the industrial sector. According to Rystad Energy calculations, the levelised costs could come down to $75–100/t for carbon capture, transportation and storage by the mid-2030s.

‘We believe that a level of $100/t abatement costs for CCUS will be more appealing. However, looking at where CCUS is today, industrial players think it will often be cheaper to emit CO₂ rather than to do something with it.’ – Yvonne Lame, Vice President, CCS, Rystad Energy 

Steel sector – a more complex picture 

‘The emissions picture and abatement options are more complex for iron and steel,’ noted Jonny Scafidi, Hydrogen Analyst, Rystad Energy.

Iron and steel manufacture account for about a quarter of industrial emissions – about 7–8% of total global emissions in 2020, equivalent to 2.6 Gt of CO₂. Two alternative processes are used – blast furnaces or electric arc furnaces (EAF). EAFs have about one third of the emissions of blast furnaces.

The average emissions in 2020 were about 1.85 tonnes of CO₂ for every tonne of steel produced – split between using blast furnaces and EAFs, 85% and 15% respectively.

Looking more closely at each process, power can be decarbonised using low carbon electricity, CCS and/or hydrogen.

Starting with iron ore, the ore is processed into iron pellets, using low carbon electricity as one option. Limestone is used as a reactant in a blast furnace. Coal is converted to coke, which in the process emits CO₂ that could be captured using CCS. The process requires heat, which could be provided using hydrogen. ‘But its more complicated than simply replacing the coal and coke which goes into the blast furnace in the first place,’ commented Scafidi.

The blast furnace produces iron, which is then converted to steel using a lot of heat, in another process that could be addressed with hydrogen. Scrap metal can be added and, as a rule, the more scrap that is used, the lower the emissions. Over the last few decades, 20–40% scrap has been put into steel. But there is variation because higher grades of steel utilise little or no scrap.

The steel is then post-processed and products cast, which again requires heat – potentially from hydrogen to decarbonise the process.

The direct reduction of iron (DRI) or EAF routes also start with iron ore which is converted to iron pellets. Traditionally, coal or natural gas is used to reduce the iron ore to iron pellets plus CO₂. That process could be eliminated using hydrogen as an alternative reductant which produces water.

This produces sponge iron, which is then added to the EAF, which is run by electricity (as the name suggests) that could be generated from a renewable source. Again, scrap steel could be added prior to post-processing and casting.

About 2.3 tonnes of CO₂ are emitted for every tonne of steel produced in an unabated blast furnace. ‘Even a slightly more efficient process could eliminate 20% of emissions,’ said Scafidi. ‘If biofuels are used as a reactant instead of coke, emissions can be reduced up to 40%. On top of that, up to 60% of emissions could be eliminated using CCUS.’ Hydrogen blending could also have an impact.

An EAF is already based on electricity and accounts for 80% emissions reduction compared to using a blast furnace. However, utilisation of low carbon electricity could cut emissions a further 10%, topped up with hydrogen to reach 100%.

The world’s first commercial fossil-free steel operation, called HYBRIT (Hydrogen Breakthrough Ironmaking Technology), is located in Sweden. This plant is being run with renewable power and hydrogen to produce iron instead of coking coal. The iron pellets are then put in an EAF to produce steel, along with some recycling of scrap metal. The first fossil fuel-free steel was produced in 2021, and ingots were given out at COP26 in Glasgow. Commercial operations are scheduled to start by 2026.

Plans are also underway to develop hard rock hydrogen storage on the site. Successful use of HYBRIT is forecast to reduce Sweden’s CO₂ emissions by 10%.

Looking to the future, the blast furnace route is more suited to using CCS ‘as there’s a lot more CO₂ emitted, that can’t really be avoided’ suggested Scafidi. He continued: ‘Whereas DRI and EAF are looking towards hydrogen, taking into account how many furnaces there are, their age and the number of EAFs out there.’

For example, China has had a real building boom, so lots of steel factories were opened in the early 2000s, with an expected life of 50–75 years. ‘So it makes sense to add CCS to the mix to decarbonise those plants, as CCS can typically be amortised over 25 years,’ commented Scafidi. However, as plants are shutdown, new steel plants are likely to favour using hydrogen and DRI for emissions reduction.

An interesting initiative was also announced by Valborg Lundegaard, CEO of Aker Carbon Capture, who reckoned that: ‘CCS is at an inflection point and will really take off.’ Aker is involved in the Norcem cement CCS project, as well as delivering carbon capture for Twence’s waste-to-energy plant in Hengelo in the Netherlands.

Aker Carbon Capture has created a new business model of ‘carbon capture as a service’, based on its ‘Just Catch’ product, for capturing up to 100,000 t/y of CO₂. The service is applicable to cement facilities and other industrial plants, with a one-stop shop solution costing €70–150/t CO₂, including finance, insurance, delivery, CO₂ transport and storage, covering all the steps in the value chain by working with strategic partners.

Targeted at the medium-sized customers, Lundergaard, said: ‘This one-stop-shop approach is designed for organisations that find CCS very complicated as a completely new industry which they don’t understand.’