vanced PFBC systems; it is one way to achieve higher efficiencies with advanced IGCC systems. Hot gas desulfurization technology similarly remains to be developed for advanced IGCC systems. While current hot gas cleanup devices achieve very low levels of SO2 and particulate emissions, to date neither hot gas particulate removal nor hot gas desulfurization systems have approached the durability and reliability requirements needed for a commercial system. Furthermore, current hot gas cleanup systems do not control volatile air toxics or nitrogen oxides (NOx). DOE remains optimistic that these critical problems will be solved through continued R&D. Nonetheless, the promise of advanced PFBC and the potential efficiency gains of IGCC and IGFC systems will not be realized until significant progress is demonstrated. For gasification-based systems, existing or improved cold gas cleanup systems can meet anticipated environmental requirements but at an efficiency penalty of about two percentage points.
To achieve larger or more rapid reductions in CO2 emissions than can be achieved by improving the thermal efficiency of coal-based power plants, technological options for the removal and storage of CO2 from conventional and advanced power systems could also be needed. The current DOE plan provides for such a contingency, in its objective of demonstrating by 2010 the capability to reduce and sequester CO 2 emissions by about 80 percent at a cost premium of not more than 20 percent (DOE, 1993a). Given the current state of technology in this area, the most pressing need is for research related to CO2 storage.
One of the most demanding long-term technical challenges for the DOE coal program is the reduction or elimination of solid wastes—a major environmental concern—through innovative and cost-effective recycle and reuse options, perhaps as part of an integrated "coal refinery."5 At present, DOE has only a relatively small program ($2.4 million per year) in solid waste management. At least one of DOE's advanced coal technologies—the second-generation PFBC system—generates more solid waste than today's best commercial plants meeting stringent standards for SO2 removal (98 percent or more). This underscores the need to find effective solutions that will allow coal to compete environmentally with alternative fuels for power generation.