analysis, developing instrumentation for process control, including computerized on-line analyzers, and improving dewatering for both fine high-rank coals as well as low-rank coals. However, the R&D and demonstration planning should use market-based decision tools and have extensive industrial participation.
DOE has contributed to the development of the fine coal cleaning technology that is now commercially available. Applied research to improve current commercial preparation processes may help such technology compete more effectively, especially in international markets. Advanced power and fuel systems are being designed for fuel flexibility and high-efficiency sulfur removal and may be unlikely to require coals that have been subjected to coal preparation beyond current commercial practice.
Reduction of trace element concentrations in coal representing air toxic precursors may offer an R&D opportunity for meeting future, as yet undefined, hazardous air pollutant emission standards. Work in this area is addressed in the DOE's proposed program for FY 1995.
Coal-liquid mixtures consist of finely ground coal suspended in a liquid, such as oil or water, together with small amounts of chemical additives to improve stability and other physical properties. The primary purpose of coal-liquid mixtures is to make solid coal behave as an essentially liquid fuel that can be transported, stored, and burned in a manner similar to heavy fuel oil. The most mature coal-liquid mixture technologies are those using coal-oil and coal-water mixtures (CWM). Several of these technologies already have been offered commercially. Since coal-liquid mixtures are intended as a substitute for oil, their market penetration is heavily dependent on oil prices.
Initial development work on coal-oil mixtures (COMs) dates back to the last century (DOE, 1988). Extensive COM research was conducted in the United States during the 1940s because of wartime constraints on oil supply. More recent interest in COMs followed the 1973 OPEC oil embargo and the oil price hikes of the late 1970s. Utility and industrial boiler demonstrations using COMs were conducted in the United States, Japan, Sweden, and England between 1977 and 1981. Over 20 COM preparation plants are currently operating or have been operated in various countries.