OCR Text |
Show used to generate the coal-water slurry. What is vitally important, however, is one particular coal-rank parameter, namely, volatile matter content. As has already been mentioned, this parameter is strategically important in neat (dry) pulverized coal combustion as well. It is also becoming increasingly apparent to the author that the Murphy's Law ("If anything can go wrong it will") of coal-water slurry fuel preparation and its subsequent combustion is the following, as coined by the author: higher-volatile coals are easy to burn, but, with difficulty, make rather poorly pumpable and storable slurries - unless exotic particle sizings or expensive additives are used - whereas lower-volatile coals make rather more highly pumpable and storable slurries, but are more difficult to burn. In the author's opinion, this dilemma has remained sub rosa in discussions of coal-water slurry preparation techniques reported in the literature in spite of the fact that selected papers can be readily used to 5-9 prove its existence. For example, the data in Figure 1 have been gleaned from a very recent paper on coal slurry preparation. The re-evaluation of these data clearly demonstrates the relationship between a coal's volatility and the maximum amount of this coal that can be successfully slurried with water, even when additives are used. It is partially the result of the behavior illustrated in Figure 1 that the target maximum coal content for coal-water slurry vendors has been set at 65- 70% by the Electric Power Research Institute (EPRI) and the Department of Energy (DOE). Other examples of the relationship between coal volatility and the ease/difficulty of its water-slurrying have also been reported. For example, the rather extensive coal-water slurry preparation research at the Atlantic Research Corporation has revealed that a high-volatile (40.6%) coal was much more difficult to grind than a lower-volatile (29.9%) one. The more difficult a coal's grinding, the more difficult the preparation of its coal-water slurry becomes. No doubt this last reported behavior and that illustrated in Figure 1 are closely coupled to each other. As already discussed, the role of coal volatile matter in determining flame performance is much better characterized, and somewhat more obvious. This behavior is expected to carry over into coal-water slurry combustion as well. In fact, the Atlantic Research Corporation has set 20% as 17-7 |