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cleaning has also been conducted by those oil companies involved in coal production.
State of the Art
Coal preparation technologies are widely practiced by the coal industry. Recent R&D efforts (Feeley et al., 1994; Killmeyer et al., 1994; Hucko et al., 1994) have been aimed at developing processes that will further reduce both the sulfur and ash contents of coals. Coal cleaning techniques for the fine fractions also are now commercial. Many of these same techniques have been utilized to produce the very clean coals required for coal-liquid mixtures (see below). Sustained investigations into chemical and biological coal preparation techniques that remove organic as well as inorganic sulfur have not, however, produced any systems with a strong potential for commercialization, largely because of their high costs. Indeed, from the perspective of many coal users, the higher cost of coals subjected to advanced levels of preparation makes them unattractive relative to naturally occurring coals with lower sulfur and ash contents. Furthermore, many of the advanced power and fuel systems are designed to be fuel flexible, so there are limited markets for highly cleaned coals in the power generation sector.
DOE currently performs or funds the majority of coal preparation R&D in the United States. This activity falls primarily within the Advanced Clean Fuels Research Program. The FY (fiscal year) 1994 program budget of $11.3 million included $4.6 million for work on technologies for producing premium fuels and removal of air toxic precursors; $2.25 million for continued testing of high-efficiency processes; and $4.1 million for continuation of in-house bench-scale and characterization research at PETC related to advanced physical and chemical cleaning concepts (DOE, 1994a). In addition to the direct funding of the coal preparation program, the AR&TD (advanced research and technology development) component of the DOE budget supports a number of closely allied programs of a more basic nature, such as the $1.9 million program on the bioprocessing of coal for sulfur and nitrogen removal, which is part of DOE's Advanced Manufacturing Technology program. This program recently shifted its emphasis to the removal of SOx and NOx from combustion gases, rather than from coal.
For FY 1995, DOE has proposed a 52 percent reduction in funding for coal preparation, to a total of $5.5 million. The main thrusts of the program include continued research on advanced physical coal cleaning methods to produce premium coal fuels very low in ash, sulfur and air toxic precursors at the proof-of-concept scale of technology development ($2.6 million), and continued in-house research on bench-scale development of advanced cleaning concepts ($2.0 mil-