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Researchers at George Washington University have found a way to make lime cement using concentrated solar thermal power.
The technique could both cut the cost of production and release zero carbon dioxide.
Cement manufacture contributes around 5% of total greenhouse gas emissions: the second single largest source after coal-fuelled power plants. It produces 9kg of CO2 for every 10kg of cement – so the consequences of a switch to this new method of production could be huge.
Around one-third of the CO2 in conventional manufacture results from using fossil fuels to heat the limestone to melting point (to produce lime); the remainder is from the chemical reaction which ensues, where limestone (CaCO3) breaks down into lime (CaO) and CO2.
The process, which has been pioneered by a team from George Washington University in Virginia, harnesses concentrated solar thermal power to avoid generating the CO2 at both stages of the process. So, solar energy provides the heat for melting the limestone – and for a specially designed process of high-temperature electrolysis.
This results in a different chemical breakdown of the limestone: instead of separating into lime and carbon dioxide, it splits into lime, carbon monoxide (CO) and oxygen – thereby avoiding CO2 emissions altogether.
Carbon monoxide has a number of industrial applications – including in the manufacture of bulk chemicals. This gives it a market value of $550 a tonne, which could help offset the cost of the solar cement process. So far, the team has built a prototype which proves the process can work. The next stage is to take it to an industrial scale.
So, what are its commercial prospects? Martin Everett, materials advisor with construction group Skanska, said the process seemed to be “really good”. But he cautioned that the localised nature of much cement production, using local limestone rocks, might not encourage its take-up. Then there is the industry’s cautious approach to new techniques. A number of structures built using new materials and processes introduced around 30 years ago have been found to have developed some worrying faults.
“The industry has the scars from that, and will want to see if there are any negative results from long term testing.” – Andrew Collier