Fundamental Principles of Comminution

The objective of comminution is to produce small particles from larger ones. Smaller particles are the desired product either because of their large surface or because of their shape, size, and number. The energy efficiency of the operation can be related to the new surface formed by the reduction in size. The geometric characteristics of particles, both alone and in mixtures, are important in evaluating a product from comminution. In an actual process, a given unit does not yield a uniform product, whether the feed is uniformly sized or not. The product normally consists of a mixture of particles, which may contain a wide variety of sizes and even shapes. In comminuted products, the term diameter is generally used to describe a characteristic dimension related to particle size. As described in Chapter 2, the shape of an individual particle is conveniently expressed in terms of the sphericity which is independent of particle size. For spherical particles, O, equals unity, while for many crushed materials, its value lies between 0.6 and 0.7. 

The different types of particle size distributions have been discussed extensively in Chapter 2. No single distribution applies equally well to all comminuted products, particularly in the range of coarser particle sizes. For finer particles, however, the most commonly found distribution follows a log-normal function (Herdan, 1960), which is the most useful one among the different types of functions (Beddow and Meloy, 1980). 

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