Reducing carbon emissions in cement production through solarization of the calcination process and thermochemical energy storage

The conceptual design of a novel cement production process has been developed during the SolCement research project. Fossil fuels used for limestone calcination are replaced by concentrated solar energy. Also, a Thermochemical energy Storage Reactor - TSR is used for transferring energy between daytime and nighttime operation. Additionally, the process enables energy recovery from waste gases and integration with carbon capture systems by isolating the rich carbon dioxide stream produced by the decomposition of limestone. A computational study simulates and compares a conventional with two different versions of the SolCement process (with and without the TSR). Simulations show that the use of a solar calciner operated at 1000 degrees C increases energy savings, while shifting the production capacity towards daytime improves the overall performance. The proposed scheme can lead to a 33 % reduction in fossil fuel consumption, but only a 9 % reduction in overall emissions, corresponding to 493 kg CO2/tonne clinker, since most of the carbon dioxide is produced due to limestone calcination. However, with storage and further utilization of the CO2 rich gaseous outlet stream, the predicted reduction of emissions may reach 82 %. The TSR provides 22 % of the energy required for preheating during the night operation, while simple Rankine cycles can recover from the otherwise rejected hot gas streams, 49 % and 40 % of the electrical energy required for compressing the produced carbon dioxide during daytime and nighttime operation, respectively. This results in 33 kg CO2-eq per tonne of clinker less, or an additional 0.6 % emissions reduction.