Solar calcium looping cycle for CO2 capturing in a cement plant. Definition of process parameters and reactors selection

Technologies to capture carbon dioxide (CO2) from industrial processes are needed to reach the climate change goals. In case of the cement industry, calcium looping cycle (CaL cycle) for CO2 capturing has gained more attention not only because it can be integrated in an existent cement plant, but also because the calcination step of the CaL cycle can be carried out using renewable energy sources such as concentrated solar power (CSP). However, material issues associated with the continuous cycling processing of particles, such as reduction of sorption capacity and particles attrition, are the bottleneck of CaL cycle. We studied the performance of cycled limestone under real CO2 capture conditions related to cement industries using Thermogravimetric Analysis (TGA). We found that not all limestone samples can be used for this purpose, since the calcination reaction can be strongly hindered after the first calcination-carbonation step is performed. Based on TGA results as well as on reactor analysis, a solar rotary kiln and a modified rotary kiln were defined as the two reactors to enable the implementation of a solar CaL cycle into a cement plant, where the spent and crushed sorbent is directly used in the subsequent cement production process. The solar calciner has to be operated at approximate to 950 degrees C to achieve feasible residence times of the treated solid material of less than 12 min. A temperature gradient of around 50 K inside the carbonator (carbonation temperature 600-650 degrees C), can favour the removal of almost all CO2 content in the flue gas.