Vernasca is a small village in Emilia-Romagna, Italy. It’s mostly known for its breathtaking Castello di Vigoleno, a vestige of Ancient Rome, but it is also home to an industrial plant producing 1.3 million tonnes of cement every year. This is where the future is at play: In October 2020, the EU-funded CLEANKER project inaugurated a brand-new technology called calcium looping and hopes to reduce the plant’s CO2 emissions by 90 %.
“Our technology presents several advantages for existing cement plants,” says Martina Fantini, coordinator of CLEANKER on behalf of LEAP – an Italian laboratory specialising in highly efficient, low environmental impact energy technology. “First, the retrofit does not imply any modification of the plant’s rotary kiln, which is the most critical equipment in any cement plant. Then, the sorbent produced at the end of the CO2 capture process is the same raw material used for clinker production (clinker is the main component of most cements). Finally, there is a wide range of possibilities for exploiting the heat produced by the CO2 capture process.”
As its name entails, calcium looping essentially works in a loop of repeating steps. The CO2 generated during clinker production is captured from the flue gases by means of the so-called carbonation reaction, which binds CO2 with solid calcium oxide (CaO) to form solid calcium carbonate (CaCO3). Then the resulting sorbent goes through the calcination process, which is pretty much the opposite of carbonation: CaCO3 is decomposed into CaO and gaseous CO2. The concentrated stream of CO2 is ready to be stored in suitable geological sites or used as a raw material for the synthesis of basic chemicals or fuels, while the former is made available again to continue the cement production and CO2 capture cycle.
The main difference between CLEANKER and other attempts to capture CO2 at cement production sites is the fact that the process takes place during combustion, not after. “Although being less advanced, CLEANKER can potentially achieve high CO2 capture efficiency with a low energy penalty and economic impact. This is thanks to the use of conventional raw meal as CO2 sorbent and tight thermal integration, which significantly reduces the fuel consumption,” Fantini explains.
Tests at Buzzi Unicem’s cement plant consist in processing 1 % of kiln flue gases. This is to prove the concept and to enable the development of a rigorous techno-economic assessment method that will eventually allow LEAP to exploit the technology at full-scale. Calcium looping is currently at Technology Readiness Level (TRL) 7, but Fantini is confident that – once the capacity of the sorbent is verified, the main governing parameters are fine-tuned and heat recovery is optimised – the technology will be ready for scale-up to TRL 8-9. Although the results from these tests won’t be known until sometime later, all simulations run so far estimate that capture efficiency will be close to 90 %.
Success of the calcium looping technology will be key to retrofitting cement plants for CO2 capture, which is itself crucial to meeting EU emission targets over the short to medium term. Most cement plants in Europe indeed date back to the 1980s and will not likely be rebuilt before 2050. As Fantini concludes, “CLEANKER should be able to retrofit its technology at full scale in about 3 years.”