Development of a New CO₂ Sequestration Process Utilizing the Carbonation of Waste Cement

We propose a new sequestration process for anthropogenic carbon dioxide (CO 2 ) that uses waste cement. The proposed process consists of two main reactions. The first is the extraction of calcium ions (Ca 2+ ) from waste cement particles by pressurized carbon dioxide (several megapascals of pressure). The second is the precipitation of calcium carbonate (CaCO 3 ). Ca 2+ extracted from waste cement is deposited as CaCO 3 when the pressure is reduced. CaCO 3 is disposed of directly, or recycled as a raw material for cement production. In the latter case, the same amount of CO 2 is considered to be sequestered because the net amount of virgin limestone mined can be reduced. The power consumption and cost of the proposed sequestration process for CO 2 emitted from a 100 MW thermal power plant were evaluated, on the basis of laboratory-scale experimental results. The power consumption for the operating process strongly depended on the operating conditions such as the cement/water ratio, the CO 2 pressure, and the average cement diameter. The minimum power consumption was 25.9 MW/100 MW of power generation when optimized within the operating conditions studied experimentally, and the sequestration cost associated with the power consumption (excluding capital and maintenance) would be about $22.6/t of carbon dioxide. This result indicates that the present process is highly competitive with previously reported CO 2 sequestration scenarios such as ocean sequestration. Sensitivity analysis of the operating parameters was carried out on the operating power consumption, and it was found that a smaller ratio of waste cement to water and a lower CO 2 pressure will decrease the operating power consumption.