The continuous oxidation of scrap iron in the presence of a constant CO2-rich waste gas stream and water is evaluated as a means of sequestering anthropogenic CO2 as well as generating hydrogen gas and electricity. The stoichiometry of the net reaction, Fe-0 + CO2 + H2O --> FeCO3 + H-2, and assumptions about reaction rates, reactant and product prices/values and overhead costs suggest that CO2 might be mitigated at a net profit in excess of $30/tonne CO2. The principle profit center of the process would be hydrogen production, alone providing a gross income of >$160/tonne CO2 reacted. However, the realization of such fuel cell economics depends on a number of parameters including: (1) the rate at which the reaction can be sustained, (2) the areal and volumetric density with which H-2 and electricity can be produced, (3) the purity of the H-2 produced, (4) the transportation costs of the reactants (Fe, CO2 and H2O) and products (FeCO3 or Fe(HCO3)(2)) to/from the cells and (5) the cost/benefit trade-offs of optimizing the preceding variables in a given market and regulatory environment. Because of the carbon intensity of conventional iron metal production, a net carbon sequestration benefit for the process can be realized only when waste (rather than new) iron and steel are used as electrodes and/or when Fe(HCO3)(2) is the end product. The used electrolyte could also provide a free source of Fe2+ ions for enhancing iron-limited marine photosynthesis and, thus, greatly increasing the CO2 sequestration potential of the process. Alternatively, the reaction of naturally occurring iron oxides (iron ore) with CO2 can be considered for FeCO3 formation and sequestration, but this foregoes the benefits of hydrogen and electricity production. Use of Fe/CO2 fuel cells would appear to be particularly relevant for fossil fuel gasification/steam reforming systems given the highly concentrated CO2 they generate and given the existing infrastructure they provide for producing and handling H2 and/or electricity. (C) 2003 Elsevier Ltd. All rights reserved.
