Comminution equipment selection

Table 10.12. Selection of comminution equipment (after Lowrison, 1974)...

Table 10.13. Selection of comminution equipment for various materials (after Marshall, 1974) Note Moh s scale of hardness is given in Table 10.12... 

Table 10.14. Selection of Comminution Equipment for Various Materials (after Marshall, 1974)—Cont d... 

Comminution of the sample presents significant opportunity for contamination. Contamination of the sample from abrasion of the comminution equipment is fundamentally unavoidable, so efforts must be made to select the best possible equipment for each particular analytical task. Equipment is preferred in which the sample comes into contact only with surfaces fabricated from such high-purity plastics as polytetrafluoroethyl-ene (PTFE), since this permits the sample to be used without restriction for the determination of a large number of elements. Friability can be increased by deep-freezing or drying the sample prior to comminution. 

The most important factors that determine the selection of the size-reduction equipment are the mechanical characteristics (shear strength, ductility, etc.) of the feed material, as well as the size distribution of feed and comminuted product. From the aforementioned analysis, it is clear that the mechanical characteristics determine the acting force for size reduction and, consequently, the selection of the proper equipment. The size distribution of the feed stream and product determines the type of the corresponding equipment as well as the dimensions of feed and discharge openings. 

Grinding equipment used for comminution operations in chemical analysis varies in design and layout with application requirements, i.e., sample make-up, desired degree of particle size decrease, etc. The selection of the grinding kit to be used depends on... 

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. 

A(p) is the rate constant for attrition. The rate of attrition depends on the material to be granulated, the binder, the type of equipment used for granulation and the intensity of agitation. The rate of breakage may also be accounted for by the use of selection and breakage function as used in the simulation of population balances in comminution (see Chapter 12). 

---