It is now widely accepted that carbon dioxide (CO2) capture and sequestration has become one of the defining problems of our time. Of all the ways that have been suggested to achieve this, our approach in collaboration with Calera Corporation (based in Los Gatos, California) is to mimic nature's way and mineralize carbon dioxide into calcium carbonate (limestone) particles at the emission sites. In particular, post-combustion stack gases at atmospheric pressure are reacted with subsurface geological brines in industrial reactors to form solid carbonates (so called supplementary cementitious material or SCM) that are suitable for use in the construction industry. This concept has the potential benefit of synergistically integrating the power generation and cement manufacturing industries to make a useful product out of harmful CO2.
In this research, the two scenarios of the Calera technology for capturing 90% CO2 are investigated: Case A) All alkalinity is provided by brine, Case B) 15% of alkalinity is provided by an electrochemistry process. Initially, a deeper understanding of the chemistry is developed by identifying the total numbers of independent chemical equations to fully describe the process in the domain of given species (ions and molecules) and elements . Subsequently, overall mass and energy balances are performed to estimate: (1) the quantities of sub-surface brines needed for capturing 90% CO2 and the subsequent amount of product produced (2) the energy penalty for the power plant while supporting the energy needs of the Calera carbon capture technology. Approximately 10% (energy penalty) of the total electric power produced is used by the process in Case A while 24% (energy penalty) of the total electric power produced is consumed in Case B. Note that the energy penalty for the liquid CO2 (i.e. CO2 separated from post-combustion stack gases in the form of a highly compressed and almost pure fluid ) route of carbon capture and storage can range from 20% to 40% with an average number around 29% of the electric power generated from the power plant . In addition, sensitivity analysis is carried out to identify feasible regimes of operation with respect to brine concentrations and dynamic depth, alkalinity contribution from electrochemistry, % CO2 capture, and % reaction conversion.
A deeper understanding of the mass transfer, reactions kinetics, and reaction rate laws, and thermodynamic behavior of CO2 absorption in to the brine solutions is currently underway and will be reported in the presentation. Sensitivity analyses are carried out to identify the process conditions that are favorable from a thermodynamic and kinetic point of view which will be utilized in designing the absorber. These will be used in finding process alternatives for the technology. For example, should absorption of CO2 into alkaline brine occur separately from reaction with hard brine (absorption followed by reaction & precipitation) or should it be performed simultaneously (absorption + reaction + precipitation).
 Gadewar S. B., Doherty M. F., and Malone M. F., A systematic method for reaction invariants and mole balances for complex chemistries, Comp. Chem. Eng., 2001, pp 1199-1217
 House KZ, Harvey CF, Aziz MJ and Schrag DP, The energy penalty of post-combustion CO2 capture & storage and its implications for retrofitting the U.S. installed base, Energy Environ. Sci., 2009, 2, pp 193 – 205.
See more of this Group/Topical: Topical G: Innovations of Green Process Engineering for Sustainable Energy and Environment