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Analysis of a double calcium loop process configuration for CO2 capture in cement plants

Diego, M.E., Arias, B., Abanades, J.C.
Journal of cleaner production 2016 v.117 pp. 110-121
calcium, calcium carbonate, carbon dioxide, cement, combustion, economic analysis, energy, flue gas, heat
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.