Development of a new CO2 sequestration process utilizing the carbonation of waste cement

We propose a new sequestration process for anthropogenic carbon dioxide (CO2) that uses waste cement. The proposed process consists of two main reactions. The first is the extraction of calcium ions (Ca2+) from waste cement particles by pressurized carbon dioxide (several megapascals of pressure). The second is the precipitation of calcium carbonate (CaCO3). Ca2+ extracted from waste cement is deposited as CaCO3 when the pressure is reduced. CaCO3 is disposed of directly, or recycled as a raw material for cement production. In the latter case, the same amount Of CO2 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 CO2 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 CO2 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 CO2 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 CO2 pressure will decrease the operating power consumption.