By replacing part of cement clinker with calcined (thermally activated) clay, CO2 emissions in cement production are lowered by up to 40%, according to thyssenkrupp Industrial Solutions AG (Essen, Germany; www.thyssenkrupp-industrial-solutions.com), which developed the technology known as “polysius activated clay.” Cimpor Global Holdings B.V. (Amsterdam, the Netherlands) will use the technology on an industrial scale at a new plant being built near the Cameroon sea port of Kribi. Upon completion in fall 2021, the plant will save more than 120,000 ton/yr of CO2 emissions. Thyssenkrupp is carrying out engineering, procurement, construction and commissioning of the new plant, which will produce 720 tons of activated clay per day. It is the second calcined clay project of Cimpor Global Holdings.
Carbon dioxide is a natural constituent of limestone, the main component of cement. For each ton of cement clinker produced, around 790 kg of process-related CO2 is emitted. Around two thirds of this results from the limestone used, which releases CO2 in a chemical reaction in the production process. At the same time, the process requires large amounts of energy, because for the production of cement clinker, limestone has to be heated with other aggregates to temperatures of more than 1,400°C.
With polysius activated clay, thyssenkrupp has developed a technology that allows around one third of the cement clinker to be replaced with activated clay. The clay is heated to around 800°C, which is significantly less heat than is needed to produce clinker. Thanks to the significant energy savings in the production of thermally activated clays and the changed chemical composition, CO2 emissions per ton of cement can be cut by up to 40%, says the company.