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Show Case A and Case B, respectively. These estimates are fairly conservative as they are based largely on prototype plants employing commercially-available hardware; component optimization and improved system integration should yield some cost savings. This preliminary thermoeconomic analysis suggests that the addition of the proposed precombustion carbon dioxide removal system to a natural gas-fired power plant would increase the cost of electrical power generation by about 1.7 cents/kWh-net, i.e., by slightly less than 30% of the Base cost of exporting power. (The additional cost for the pre-combustion carbon dioxide removal system is referred to as "Environmental Cost" in Table 1.) Even under the most conservative scenario (with lower Base plant cost, higher fixed annual charge, and substantially higher costs for the reformer, carbon dioxide separation and liquefaction equipment, and disposal pipeline), the incremental cost would still be less than 50% of the Base cost Although the incremental cost for the pre-combustion carbon dioxide removal system applied to a methane (natural gas) power plant is considerably less than projected by other investigators (e.g., Golomb, et al., 1989; Groscurth and Kiimmel, 1990) for other carbon dioxide extraction processes, it should be emphasized that the earlier studies considered coal-frred power stations and therefore a direct comparison is not appropriate. Indeed, the economics of the precombustion carbon dioxide removal concept applied to coal-frred systems would be less favorable than for methane combustion due to the larger carbon:hydrogen ratio in coal- whereas a large methane-fired plant would emit only 0.5 kg CO2/kWh, a comparable coal-frred plant would produce 0.9 kg CO2/kWh (Golomb, et al., 1989). SUMMARY AND CONCLUSIONS A concept is proposed which has the potential to reduce substantially carbon dioxide emissions from stationary, industrial combustors that burn hydrocarbon fuels. Unlike flue gas treatment processes considered by other investigators, the present authors propose that carbon be removed from the fuel as carbon dioxide prior to combustion via oxidation with superheated steam on a catalyst followed by preferential absorption into a recyclable liquid solvent or by staged phase transformations of the carbon dioxide. Long-term containment would be accomplished by liquefying the carbon dioxide and discharging it into the deep ocean, probably at depths of -500 m. The hydrogen-rich gas that remains after the carbon dioxide is removed from the fuel would be combusted in place of the original hydrocarbon fuel. Since this concept is based largely on validated, commercial technologies, it can be implemented in the near-term. A modest degree of development is necessary to optimize the reformer and the gas separation system. The only area requiring significant study is disposal and containment of carbon dioxide in the ocean. Specifically, the long-term fate of the discharged carbon dioxide must be determined, and the optimum depth of release and potential effect on the marine ecosystem must be identified. Experimental and analytical investigations currently are being conducted to address these concerns. Detailed thermoeconomic analyses were performed on a hypothetical 500 MW methane combustion power plant to estimate the energy and cost requirements of the pre-combustion carbon dioxide removal concept Results suggest that application of the concept would increase in-plant power consumption (back-work) from 5% of the electric power generated to approximately 12% to 19%, and reduce plant thermal efficiency by about 7 to 10 percentage points. As a consequence, the cost of exporting electrical power would rise from 5.9 cents/kWh to about 7.5 cents/kWh, a moderate increase of less than 30%. Work is underway to extend the analysis to other fossil fuels, most notably, coal. The present countermeasure to rising atmospheric carbon dioxide concentrations targets largescale, stationary combustion systems in proximity with the deep ocean. It probably cannot be 8 |