Size reduction of solids: An energy-intensive and highly inefficient process

The size reduction of solid particles is a major process used in industries-chemical, mining, pharmaceutical, metal, food, and coal power plants, among others. However, little success has been obtained in designing and optimal operation systems for this process without first performing full-scale experimentation. This lack is mainly due to the complex phenomena involved in operation, as well as inadequate characterization of particle strength (grindability). In this chapter, some of the available strength measurement procedures and standards for coal particles are examined. We show that the most common index for coal grindability (the Hardgrove Index, HGI) fails to predict the behavior of some of the coals (mainly the "younger" ones) in power plant grinders. Therefore, we introduce and examine some other strength measurement procedures such as compression of single particles (crush strength) and rotating drum tests.