INTEGRATED CARBONATION: A NOVEL CONCEPT TO DEVELOP A CO2 SEQUESTRATION MODULE FOR VISION 21 POWER PLANTS

The greatest challenge to achieve no environmental impact or zero emissions for the Vision 21 plants is probably greenhouse gases, especially CO{sub 2} emissions that are inevitably associated with fossil fuel combustion. Mineral carbonation, that involves the reaction of CO{sub 2} with non-carbonate minerals to form stable mineral carbonates, has been lately proposed as a promising CO{sub 2} sequestration technology due to the vast natural abundance of the raw minerals, the long term stability of the mineral carbonates formed, and the overall process being exothermic, and therefore, potentially economic viable. However, carbonation efficiency is being considered a major hurdle for the development of economically viable sequestration technologies, where present studies require extensive mineral particle communition, high pressures and prior capture of the CO{sub 2}. Consequently, mineral carbonation will only become a viable cost-effective sequestration technology through innovative development of fast reaction routes under milder regimes in a continuous process. The objective of the proposed novel active carbonation concept is to promote and accelerate reaction rates and efficiencies through surface activation to the extent that extensive mineral particle communition and high temperatures and pressures are not required. In this research program, serpentine was used as the carbonation feedstock material. Physical and chemical surface activation studies were conducted to promote its inherent carbonation reactivity. The activated materials were characterized by a battery of analytical techniques to determine their surface properties and assess their potential as carbonation minerals. Active carbonation studies were conducted and the carbonation activity was quantitatively determined by the increase of the weight of solid products and the percent of stoichiometric conversion. This work has shown that chemical activation was more effective than the physical activation in terms of increasing the surface area (330 vs. 17m{sup 2}/g). The steam activated serpentine had a 73% conversion to magnesite at 155 C and 1850 psig after 1 hour reaction, while under the same operating conditions, the parent sample only had 8% conversion. However, heat treatment is very energy intensive, and therefore, this steam activation route was not further considered. For the chemical activation, the most effective acid used was sulfuric acid, that resulted in surface areas of over 330 m{sup 2}/g, and more than 70% of the magnesium was dissolved from the serpentine (100{micro}m), and therefore, made available for carbonation. As a consequence, the subsequent carbonation reaction could be conducted at ambient temperatures (20 C) and low pressures (600psi) and it was possible to achieve 73% conversion after only 3 hours. This is indeed a significant improvement over previous studies that required temperatures over 185 C and very high pressures of around 1950 psig. Finally, this project has been awarded a Phase II, where the active carbonation process developed during this Phase I will be optimized in order to design a CO{sub 2} sequestration module.