Summary of Criteria and Main Applications

As previously discussed, one of the determinant factors for the right selection of size reduction equipment is consideration of the hardness of the material to be processed. The second factor of great relevance is the required capacity, either fixed or subjected to variations by process requirements. Taking these two main considerations along with a thorough analysis of as many other factors as necessary, flowcharts can be devised to select and locate the most suitable comminution units for a size reduction plant. The combination of different criteria may be summarized in charts, like the one given in Table 4.3, which includes some typical applications of the principal size reduction equipment. 

Calcite rocks of 2350 kg/m density are comminuted in crushing rolls, having 1 m diameter and 40 cm length. The faces of the rollers are separated by 1.25 cm in the narrowest point and operate at a rotation speed of 75 rpm. The angle of nip has been determined as 30°. Determine the maximum permissible size of fed particles and the capacity in ton/h, considering that it only represents 12% of the theoretical. 

As in the case of Example 4.2, in order to calculate the maximum permissible size of feed, the transposed form of Equation 4.7 could be used, considering that the angle a represents half the angle of nip. Thus cos a = cos(15°) = 0.9659. On the other hand, the radius of the roller, R, is 0.5 m, while the dimension d represents half the distance between rollers, that is, 0.00625 m. Substituting, then in the transposed form of Equation 4.7, 

Equation 4.8 can be used to compute the theoretical volumetric flow rate. Substituting all the terms. 

Since real capacity only represents 12% of theoretical, in reality the capacity would only be 0.00075 mVs. Also, the answer is required in ton/h, so using the density of the material in order to transform to mass flow (0.00071 mVs) (2350 kg/ m ) = 1.7625 kg/s. Finally, transforming to kg/h and then to ton/h, the required capacity of 6.345 ton/h is obtained. Thus, the results are maximum permissible size of fed particles in average = 5 cm optimum capacity = 6.3 ton/h. 

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