Cement Plants Could Combine Production With Direct Air Capture

Cement production causes around five to eight per cent of global CO₂ emissions. Researchers at ETH Zurich have now explored a way to reduce this impact. Their proposed system combines cement production with direct air capture (DAC). As a result, future cement plants could remove more CO₂ from the air than they emit.

Using The Same Calcium Cycle

The system uses calcium looping, a carbon capture method based on limestone. Cement plants already use this widely available raw material.

During cement production, manufacturers heat limestone to produce quicklime and CO₂. This process is called calcination. Conventional plants burn coal or gas to generate the required heat. The proposed system would instead use an electric kiln powered by low-carbon energy.

An electric kiln would prevent emissions from burning fossil fuels. It would also make it easier to collect the CO₂ released from limestone. The gas would remain separate from combustion fumes. According to the study, electric kilns and direct carbon capture could reduce cement’s climate impact by 78 per cent by 2050.

After calcination, producers add water to the quicklime. This creates slaked lime, which absorbs CO₂ when exposed to air. The material then turns back into limestone. Plants could repeat this cycle several times before using the material to make cement. Each cycle would remove more CO₂ from the atmosphere.

The cement itself would not store this captured carbon. Instead, operators would compress the CO₂ and transport it to underground storage sites.

Towards Net-Negative Cement

ETH Zurich worked with US company Heirloom Carbon Technologies on the research. Heirloom has operated a commercial calcium-looping DAC plant in California since 2023. The facility can capture 1,000 tonnes of CO₂ each year.

The researchers used data from real operations for their life-cycle assessment. They examined every stage of the process. These stages included raw material extraction, construction, operation and permanent CO₂ storage.

Their results suggest that the technology could achieve a net-negative carbon footprint. Its carbon-removal efficiency could reach between 85 and 96 per cent by 2050. For each tonne of stored CO₂, the full process would generate 40 to 150 kilograms of emissions. Plants powered by renewable energy would achieve the best results.

Opportunities For Lower-Carbon Construction

The technology could help reduce the embodied carbon of cement. This makes it relevant to architects, engineers and other construction professionals. It also uses existing cement infrastructure and established supply chains.

However, several challenges remain. The projections assume much cleaner electricity networks by 2050. Large electric calcination kilns are also not yet common in industry. In addition, the researchers have not yet completed a detailed cost analysis.

The study therefore shows the system’s climate potential. Further trials must now confirm whether cement producers can apply it at scale and at a viable cost.

Source & photo: ETH Zurich