ABSTRACT
INTRODUCTION Three potential control points (C02 removal sites) are available for regulating the concentration of CO2 in the atmosphere: (1) the atmosphere itself, (2) the surface waters of the oceans, and (3) the stacks of fossil-fuel power plants. The latter site has the advantage of providing a source of relatively high CO2 concentration, while the first two provide more flexibility for site selection and simpler disposal or recovery and reuse logistics. A choice of control point limits the available choices of CO2 removal processes and will reflect on the size of the operation, the number of required sites, energy requirements, the comparative economics, and the overall feasibility of operation. A most important factor is the energy required to remove, recover, and dispose of CO2• The CO2 concentration ranges of the three control points are listed in Table 5.1.1 Since the concentration of CO2 in flue gas is significantly greater (by a factor of 5(0) than that in the atmosphere or the ocean, the energy required to remove CO2 from flue gas should be appreciably lower than for the other two control points. The minimum theoretical energy (the thermodynamic free energy) to separate CO2 from each of the three sources is also listed in Table 5.1. Based on these theoretical values, it would take about three times more energy to separate CO2 from the atmosphere than from flue gas. It should be noted that the practical energy required for separation is usually on the order of magnitude by a factor of 10 or more greater than the thermodynamic minimum.
