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 (CaCO ₃). 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 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 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 CO ₂ pressure will decrease the operating power consumption.