Process integration study of tail-end Ca-Looping process for CO2 capture in cement plants

Abstract

In this work, the integration of Calcium looping (CaL) process into a cement plant for post-combustion CO2 capture is assessed via process simulations. In the proposed scheme, the carbonator of the CaL process is used as an end-of-pipe unit to capture the CO2 from the cement kiln gas.From the results obtained, it is demonstrated that CO2 capture efficiencies of the order of 90% are achievable, with CaL reactors operating in conditions not far from those demonstrated for application in power plants. The integration of the tail-end CaL process results in a significant increase of the total fuel consumption (about two to three times higher) compared to the benchmark cement plant without CO2 capture. On the other hand, the heat from the CaL process can be recovered by a steam cycle producing decarbonized electric power that may exceed the needs of the plant auxiliaries (including the ASU and the CO2 compression and purification unit), exporting in this way electricity to the grid and so resulting in CO2 emission credits from a life cycle perspective. The resulting specific primary energy consumption for CO2 avoided (SPECCA) highly depends on the reference power generation technology considered, and it ranges between 2.7 and 3.7 MJLHV/kgCO2 in a coal-fired power generation scenario.As for the retrofittability of existing cement plants, the operation of the suspension preheating tower after the implementation of the CaL unit, as well as the position of the CaL carbonator with respect to the raw mill, have been assessed. Based on the results obtained, no critical issues have been found from a technical point of view in the adoption of the tail-end CaL process in existing cement kilns.