Can we cut carbon emissions from steel and cement production to zero?

There are effective ways to reduce emissions from producing steel and cement. Let’s start with cement. Cement is the mineral glue that holds together the sand, gravel and stones (aggregates) that form the bulk of concrete, and most of the emissions from concrete are from making cement. Well and poorly made concrete can differ hugely in strength, and better mixed concrete with properly sized and dispersed aggregates can be stronger and use less cement. It is therefore possible to use less cement in concrete by substituting 25-90% of it with other “cementious” minerals (e.g. up to 50% with ground limestone and heated clays), and the resulting concrete can be stronger.

There are also some higher technology means for reducing emissions from cement production. Most of the emissions (60%) are from heating limestone (CaCO₃) to 800°C, producing calcium oxide (CaO) (or “quicklime”), which is then mixed with other minerals and heated to 1450°C to make cement. This liberates CO₂, which we currently vent to the atmosphere. By redesigning the kiln, the CO₂ can potentially be concentrated and either reused by other sectors or disposed underground, a common practice in the oil and gas sector. Some companies are already adding waste CO₂ to cement and concrete when it is poured. The rest of the emissions from making cement are from process heat, which could come from biofuels or eventually hydrogen. Finally, new cement chemistries are being tested and being sold for limited use that produce much lower emissions, and some speculative chemistries could be carbon negative, removing CO₂ from the air.

When it comes to steel making, there are several prototype ways to decarbonize the process based on either capturing the CO₂ waste and reusing or disposing of it, or by using electricity or hydrogen instead of coal. New primary steel – that which isn’t recycled – is made from iron ore by first removing the attached oxygen (“reduction”), and then melting it and alloying it with other metals to make steel. Currently, a purified form of coal is used for removing the oxygen and process heat in the most common steel-making process through a b last furnace (BF) &  basic oxygen furnace (BOF). A first step is to replace some of the coal with methane or hydrogen, both of which are being piloted, which could potentially reduce emission by 40%. Considering alternative reduction methods are needed, such as melting and alloying processes that allow carbon capture and utilization or storage, or the use of decarbonized hydrogen or electricity. Both paths are being followed by using several different technologies.

Historically, there has been no demand for low emissions for steel or cement. This needs to change. Although the adoption of new production processes for steel and cement face several hurdles, they must be tackled directly by policymakers if we are to meet our emissions goals. 

Policies that will drive low emissions of these industries into the market place will require several components, such as accelerated R&D, lead or niche markets supported by public procurement, content regulations or temporary subsidies, carbon pricing and protections for competitiveness (e.g. standards or border carbon adjustments), potential “sunset” regulations to retire facilities that cannot be retrofitted, and finally, supporting institutions for a just transition for workforces and affected communities.

For more information, read the report “Low and zero emissions in the steel and cement industries: Barriers, technologies and policies” recently prepared for the 2019 Green Growth and Sustainable Development Forum, to be held on 26-27 November in Paris, France.