The Coal Grinding Task Group basically characterized coal grinding technology (June 1982) with an emphasis on identifying any needs related to producing very fine coal (<325 mesh). The underlying assumption was that future coal usage in non-designed-for-coal-applications will depend on coal being free of ash (and perhaps sulfur), or capable of behaving in a fluid-like manner, or both. One common step toward both of these attributes is the fine grinding of coal. Of the various types of fine grinding devices identified, two were found to appear superior from the standpoints of energy consumption and operational lifetime. These are the attritor (a special embodiment of which is the Drais Direct Dispersion System), and the Fluid Energy Reduction Mill. There are two widely regarded theories that relate energy consumption to product particle size. The first was developed by Rittinger about 1867 and holds that, ''The work required to reduce particle size is directly proportional to the new surface area produced.''The second theory, developed by Kick in 1885, was based on plastic deformation, ''The work required for crushing a given quantity of material is constant for the same reduction ratio, irrespective of the original size.''Neither of these theories has been found to be exactly applicable; however, the Rittinger theory appears reasonably usable in the range of 10 to 100 microns. The Kick theory appears better matched to larger particle sizes. Another approach, known as the Bond theory, fits between the two. The conclusion is that cost, scale of available hardware and technology, and the ability to make reliable predictions relative to producing any UCCWM that requires particles below the 10-micron size should be approached with great caution.