The circular chemistry that could make cement carbon-negative
By closing the loop on the same reaction that makes cement, researchers say plants could capture more CO2 than they release.
Cement, a widely-used man-made material, accounts for around 8% of global carbon dioxide emissions. Researchers from ETH Zurich and Heirloom Carbon Technologies have proposed a novel method to significantly reduce emissions from cement factories. By capturing and storing carbon dioxide, the process could slash climate impact by 78% by 2050.
The team's solution involves using existing technologies to achieve this. They suggest powering cement kilns with clean electricity instead of fossil fuels, thereby cutting heat production emissions. Concurrently, the kiln emissions of carbon dioxide would be captured using a direct air capture technology called calcium looping from Heirloom Carbon. This technology works by cycling calcium between two compounds, calcium carbonate and calcium hydroxide, repeatedly.
Limestone, or calcium carbonate, serves as the starting point for cement production. When heated, it converts into calcium oxide, or quicklime, and carbon dioxide. The proposed system then adds water to the quicklime, enabling the quicklime to absorb more carbon dioxide from the atmosphere and revert to limestone. This continuous loop, called calcium looping, can potentially make cement production carbon-negative.
The researchers calculated that implementing electrified kilns and calcium-looping DAC could decrease the climate impact of cement production by 78% by 2050. Currently, Heirloom operates a plant in California that captures 1,000 tonnes of carbon dioxide annually. Vittoria Bolongaro, a graduate student and lead author of the paper, expressed excitement about Heirloom's partnership, noting that the company is already employing commercial-scale calcium looping DAC systems.
The team assessed various energy scenarios, including the current US electricity mix, a clean electricity mix consisting of wind and solar energy, and a fully autonomous clean-energy system with photovoltaic panels and battery storage. Their analysis concluded that the technology has a net-negative carbon footprint, meaning that a commercial calcium looping DAC plant with carbon dioxide storage removes more carbon dioxide than it generates over its entire lifecycle.
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