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Show systems. For coal, the process is expected to include a gasification step that incorporates removal Jff ItJ of nitrogen and sulfur pollutants. To facilitate separation of carbon dioxide from the fuel gas and r to maintain high caloric value, the quantity of diluent nitrogen introduced during gasification should be minimized. The economics of carbon capture from coal or oil are expected to be less favorable than for methane due to their larger carbon:hydrogen ratios. The primary focus of the follow-on work is to identify a fuel refonning system that would yield the desired mixture of hydrogen and carbon dioxide without imposing prohibitively high cost or energy penalties. An assessment of the effectiveness of this concept to address the global warming problem also requires validation of the deep ocean containment strategy (refer to discussion in the following section). Retrofitting an existing power station with the pre-combustion carbon dioxide removal system can be accomplished without extensive modifications to the existing boiler furnace. Burners and controls need to be redesigned slightly to ensure the stability of the hydrogen-air flame and to minimize further thennal NOx production; their development can draw upon previous experience with hydrogen-rich town gas. Although the present study focuses on the retrofitting of a simple Rankine power cycle, the proposed carbon dioxide removal concept also is well suited to gas-turbine combined cycle plants. Indeed, combustion of hydrogen in air offers several efficiency, materials compatibility, and environmental advantages over combustion of conventional fossil fuels (Peschka, 1987; Peschka, 1988). In a combined cycle plant, the refonned hydrogen gas could be burned in the main combustor and in a reheater. The reheater would increase the temperature of the gas turbine exhaust to the 11000 C necessary to operate the refonner, and the temperature of the gas exiting the reformer exit should be sufficiently high to drive a steam power cycle. DISPOSAL AND CONTAINMENT OF CARBON DIOXIDE Following separation, measures must be taken to ensure that the captured carbon dioxide does not escape into the atmosphere. Two general options have been proposed for carbon dioxide containment: (1) injection into spent oil and gas wells or excavated salt caverns (Steinberg, et al., 1984) and (2) dissolution in ocean water (Marchetti, 1979; Mustacchi, et al., 1979; Baes, et al., 1980; Steinberg, et al., 1984; Golomb, et al., 1989). Because the latter is more widely applicable, it is the focus of this study. The oceans presently are a natural sink for carbon dioxide. This is a reversal of the role which they had played in the geochemical carbon cycle prior to the industrialization of human society (Sabine and MacKenzie, 1990). Estimating the strength of the oceanic sinks for anthropogenic carbon dioxide is a topic of current interest, vital to accurate modeling of the carbon cycle (Sabine and MacKenzie, 1990; Tans, et al., 1991; Berner and Lasaga, 1989). It is generally conceded that slow rates of transfer between the air and the ocean depths limit the effectiveness of natural transport of carbon dioxide from the atmosphere. Ocean disposal strategies for sequestering carbon dioxide attempt to bypass natural diffusion processes in exploiting the carbon storage capacity of the marine environment Four criteria should be satisfied in disposing carbon dioxide in the ocean: (1) the bulk of the discharged carbon dioxide must be prevented from escaping into the atmosphere for a length of time sufficient to stabilize or reduce the greenhouse warming trend (probably until most fossil fuel reserves are expended - in excess of a century); (2) parasitic power consumed in accomplishing the disposal must be reasonably low; (3) the impact on the marine ecosystem should be minimal; and (4) the process must be technically and economically sound. The pre-combustion carbon dioxide removal concept described above, coupled with the transporting of cold, pressurized liquid carbon dioxide through a bottom-anchored, offshore pipeline, and discharging through 5 |