This work analyses a novel calcium looping process for cement plants, based on a reactor configuration that uses a double calcium chemical loop for CO2 capture and the calcination of CaCO3. This novel scheme employs a number of state-of-the-art cyclonic preheaters, where the solids exiting the carbonator reactor are overheated by being brought into direct contact with high-temperature gas streams before they enter the calciner. This reduces the energy demand in the calciner, which is fed by solids from a second calcium solid loop where solids are overheated by an external air-fired combustor, thereby transferring the heat required for CaCO3 calcination and avoiding the need for oxy-fired combustion. Two different process schemes, with different ranges of capture efficiency and complexity, emerge when considering the option of feeding the flue gases from the new air-fired combustor to the carbonator. The results of the energy and mass balances performed on the proposed schemes reveal that as much as 94% of the total amount of CO2 generated can be captured (equivalent to 92% CO2 avoided) with an increase in the overall process heat demand of just 1.1 GJth/tcement. Moreover, this value could be as low as 0.3 GJth/tcement if a second configuration is used to capture only the CO2 derived from the calcination of the CaCO3 in the raw meal of the cement plant, resulting in a CO2 capture efficiency of 58%. A preliminary economic analysis of both configurations indicates that the cost of cement increases from 74 $/tcement typical of a reference cement plant to 106 and 85 $/tcement, respectively, while the calculated avoided costs are of the order of 42 and 27 $/tCO2 avoided, respectively. The results obtained show that the configurations proposed could be feasible and competitive within certain operating windows that are discussed in this work.

B. Arias acknowledges the award of a Ramon y Cajal contract from the Spanish MINECO.

Peer reviewed