Development of a Continuous High-Pressure CO2 to Precipitated Calcium Carbonate Reactor

The US National Academy of Sciences has reported that CO2 mineral carbonation is among the largest, most energy-efficient CO2 utilization technologies closest to commercial scale due to its thermodynamic favorability and end-product market size. However, the natural rate of reaction is generally slow in terms of kinetics, whereby only by dramatically increasing the CO2 dissolution rate can a major impact on the rate of reaction for CO2 mineral carbonation happen. Hence, despite the clear advantages of CO2 mineral carbonation over other options in Carbon Capture and Sequestration CCS technologies, the current research gaps highlighted here should be addressed to ensure future technology deployment success. Therefore, this study investigated the feasibility of the design, operation and experimental improvement of a continuous high-pressure CO2 reactor in producing and optimizing high-quality precipitated calcium carbonates PCC synthesized for consumer and industrial application. A novel mineral carbonation reactor is hereby proposed, in which, by incorporating the application of a high-pressure or supercritical CO2 phase into the reactor, CO2 diffusion can be increased into the continuously fine-sprayed aqueous reaction media within the reactor to form PCC. The effective reactor volume can be simultaneously decreased from the reduced high-pressure CO2 volume. Next, by incorporating a backpressure regulator, a continuous flow of the liquid phase in and out of the reactor can be controlled. The initial reactor design had undergone successful start-up, but experimental improvement alone was unable to provide the anticipated particle size of the calcium carbonate precipitate PCC. Optimized design of the new reactor to limit internal dead flow zones was proven to successfully reduce the particle size of precipitated calcium carbonate PCC from an initially P50/P90 of 87/131 μm to 3.8/9.1 μm. Additionally, a continuous 100 h stable run was successfully executed to thoroughly investigate the three main factors influencing the quality of PCC synthesized, in which the reactant flow rate and feedstock concentration were found to be significant, with the exception of CO2 gas pressure. The overall 3D surface trend of the particle size spread P50/P90 of the PCC synthesized was plotted over the experimental range and found to meet most of the industrial requirements and technical specifications, except for TiO2 replacement which requires sub-micron quality. Instantaneous electricity power consumption was also measured at various operating points. Performance-wise, the continuous high-pressure CO2 mineral carbonation reactor in this work was calculated to be able to process a maximum of 4200 g/h lime CaO feedstock at a lime concentration of 7 g/L and flow rate of 10 g/L, using a 40 L internal volume vessel, effectively increasing the productivity of lime CaO production by several fold from what was reported by peer studies assuming similar electricity costs were used for all productivity factors under consideration.