Decarb/Desal: Separation of Carbon Dioxide from Flue Gas with Simultaneous Fresh Water Production

Abstract

If fossil fuels continue to be a major part of the world's energy supply, effective means must be developed to deal with the carbon emissions. Geologic sequestration of supercritical CO{sub 2} is expected to play a major role in mitigating this problem. Separating carbon dioxide from other gases is the most costly aspect of schemes for geologic sequestration. That cost is driven by the complexity and energy intensity of current chemical-stripping methods for separating carbon dioxide. Our experience in water treatment technology indicated that an entirely new approach could be developed, taking advantage of water's propensity to separate gases that ionize in water (like CO{sub 2}) from those that do not (like N{sub 2}). Even though water-based systems might not have the extreme selectivity of chemicals like substituted amines used in industrial systems today, they have the potential to tolerate NO{sub x}, SO{sub x}, and particulates while also producing clean drinking water as a valuable byproduct. Lower capital cost, broader range of applicability, environmental friendliness, and revenue from a second product stream give this approach the potential to significantly expand the worldwide application of carbon separation for geologic sequestration. Here we report results for separation of CO{sub 2} from flue more » gas by two methods that simultaneously separate carbon dioxide and fresh water: ionic pumping of carbonate ions dissolved in water, and thermal distillation. The ion pumping method dramatically increases dissolved carbonate ion in solution and hence the overlying vapor pressure of CO{sub 2} gas, allowing its removal as a pure gas. We have used two common water treatment methods to drive the ion pumping approach, reverse osmosis and electrodialysis to produce pure CO{sub 2}. This novel approach to increasing the concentration of the extracted gas permits new approaches to treating flue gas, because the slightly basic water used as the extraction medium is impervious to trace acid gases that destroy existing solvents, and no pre-separation is necessary. Thermal distillation uses boiling water to steam strip solid sorbents - the steam is recovered as fresh water. We anticipate that our method will compete favorably with current chemical stripping systems used for CO{sub 2} separation at power plants, which incur a 35% energy penalty. Thus we expect to offer a dramatically improved solution for removing carbon from hydrocarbon combustion. Our method can be demonstrated on small sources, which will enable us to conduct the demonstrations required to build confidence in the method. If successful, we will be in a position to advance a follow-on proposal for a demonstration at the 10-MW scale. « less