Coal Washers Of The Classifier Type (Chapter 10)

THEORY HYDRAULIC classification as explained by Rittinger and others was largely restricted to conditions wherein the free-falling velocities of the particles were conceived as governing the separations effected (see chapter 9). The laws governing classification under free-falling conditions have been summarized by Chapman and Mott as follows: 1 Nomenclature r represents, in a particle of irregular shape, the round-hole screen through which the particle would pass, or some other linear dimen¬sion of the particle equivalent to d, the diameter of a sphere. s, the specific gravity of the particle. 1, the specific gravity of the water used as a medium. K, a constant. W, the velocity of the water. In an Upward Current of Water 1. A particle will move upward if [W > KVr(s-1)] and, by suitably regulating the speed of the water current, the larger and heavier particles may be made to fall downward against the current, leaving the smaller, lighter particles in suspension in the current. 2. Particles such that [T1= s2-1] cannot be separated in an upward-current classifier with any one velocity of current. Coal particles having a specific gravity of 1.35 cannot be separated from refuse particles of 2.5 sp. gr. Unless 2.5-1 the ratio of diameters is less than [1.35-1 or 4.3 to 1,] and the raw coal must be screened to size limits within this ratio if they are to be separated. Cone¬-shaped vessels or vessels of other shapes that allow the use of&apos; different velocities of current at different points in the flow are used to modify this limitation. 3. During the initial stages of motion, coal particles ascend more rapidly than refuse particles of the same size. 4. A particle will ultimately fall if [W < KVr(s-1).] If particles of