for 2000 and 2005 can already be met or exceeded by technology in commercial use today, although cost reduction remains an important objective. Because environmental control requirements show a strong tendency to become more stringent, and because DOE's emissions goals for the next decade already are being achieved with modern technology (see Chapter 3), it is not clear to the committee that the DOE goals will be adequate to meet all necessary environmental standards for coal plants a decade or more from now. The 2010 target of 1/10 NSPS represents a relatively demanding level of emissions reduction but one that should be achievable by a number of coal-based systems much sooner than 2010 (although not all advanced systems may be able to meet the objective readily for all pollutants). Whether DOE's emission goals will be adequate to meet regional and local environmental quality constraints—which tend to be the most demanding—cannot be foreseen.

Emissions control requirements for hazardous air pollutants (air toxics) have yet to be defined by the EPA (U.S. Environmental Protection Agency). The most likely need in this area will be for control of volatile species, such as mercury, which escape collection in existing gas cleaning systems. Studies are in progress to assess baseline emission levels for current and advanced technologies.

In the mid- to long-term periods a critical environmental issue for coal use is likely to be the need to reduce emissions of CO2 and other greenhouse gases. The committee concurs with DOE's primary strategy of reducing coal-related CO2 emissions by improving the energy efficiency of new power generating plants. The CO2 benefits of advanced technologies should be compared to the best commercial technologies currently available, which are more efficient than average U.S. plants (Table 10-3). The reductions actually achieved in the U.S. economy will depend on the rate of penetration of the advanced technology.

The DOE program plan includes the cross-cutting area of control technology, whose general goal is to achieve "ultra-low" emissions beyond the goals for 2010 (DOE, 1993a). No specific targets are set. However, the historical evidence (Appendix D) shows a strong trend toward requiring emissions from new coal plants to be reduced to the maximum extent achievable, within reasonable constraints on economic cost. Ideally, a risk-cost-benefit analysis would serve as the basis for determining environmental control regulations; discussion of this topic is beyond the scope of the present study. A possible vision for longer-term environmental R&D goals is to benchmark emissions of air pollutants from coal plants relative to cleaner but more costly competing fuels, particularly natural gas. With the exception of CO2 content, it is feasible to match the quality of natural gas by cleanup of coal-derived gas. Since natural gas will continue to be used, a consistent set of requirements for coal-derived gas and natural gas may be appropriate. To the extent that such a goal for ultra-low emissions can be achieved, the environmental acceptability of coal relative to competing energy sources will be enhanced. The long-term challenge for the DOE program, then, would be to develop systems that achieve targeted emissions reductions from coal plants at



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