Page 380 - Chemical Process Equipment - Selection and Design

12.4. EQUIPMENT FOR SIZE REDUCTION 343

LE 12.3. Operating Ranges for Commonly Used Size Reduction Equipment
Size of Power
Size of Feed Product Reduction Capacity Consum tion
Equipment (mm) (mm) Ratio (tons/hr) (kwy
~~ ~
Gyratory crushers 200-2000 25-250 8 100-500 100-700
Jaw crushers 100-1 000 25-1 00 8 10-1000 5-200
Cone crushers 50-300 5-50 8 10-1000 20-250
Impact breakers 50-300 1-10 40 10-1000 100-2000
Rod mills 5-20 0.5-2 10 20-500 100-4000
Ball mills 1-10 0.01-0.1 100 10-300 50-5000
Hammer mills 5-30 0.01-0.1 400 0.1-5 1-1013
Jet mills 1-113 0.003-0.05 300 0.1-2 2-1013

lumps. The performance data of Table 12.6(b) are for wet grinding; density 100 lb/cuft with a charge of 50 vol % of pebbles or 33 vol %
dry grinding capacities are 10-20% less. Segregation of balls by size of steel balls. The obvious advantage of batch grinding is that any
also is achieved in cylindrical shapes with spiral twists in the liner degree of fineness can be obtained by allowing sufficient time.
profile (Trelleborg AB). Roller mills [Figs. 12.4(a) and 12.6(f)]. Such equipment
Tube mill is the term applied to a mill of uniform diameter with employs cylindrical or tapered surfaces that roll along flatter
greater ratio of length to diameter, in the range of 4-5. Because of surfaces and crush nipped particles. In the ring-roller mill of Figure
the greater len,gth, and correspondingly greater residence time, a 12.4(a), spring-loaded rolls are forced against a rotating ring and
finer product can be obtained. Figure 12.5(e) shows a tube mill with crush the material that is thrown between them with ploughs. In
three compartrrients. another design the ring is stationary, and the assembly of rolls is
Pebble milts are single compartment tube mills with ceramic rotated and maintained in contact with the ring by centrifugal force.
balls as the grinding medium. They are used when contamination The unit shown is equipped with built-in air classification: as fines
with iron must be avoided, as for grinding and mixing of light are formed, they are removed with an air stream. For closer control
colored pigments, food products, and pharmaceuticals. Since the of size distribution, ring-roller mills often are operated with external
grinding rate is roughly proportional to the weight of the balls, the air classification similar to the process of Figure 12.4(d). The
grinding rate with pebbles is oniy about P/3 that with steel balls of performance data of Table 12.6(c) are for products ranging from 20
the same volume. This is clear from the data of Table 12.6(b). The to 200 mesh, with appropriate control of air rates. Ring roller milk
batch operating data of Table 12.6(c) are for grinding sand of are used widely for grinding of materials from coal to hard rock and
cement clinker; some applications are cited in Tables B2.5(b) and
12.10.
TABLE 12.4. Slize Reduction Equipment Commonly Used in Some special equipment is shown in Figure 12.6.
tlhe Chemical Process Industries
a. Gyratory crusher was described earlier. The sketch shows the
Material Equipment cone-shaped element rotating in a tapered passage. Gyratories
are made to handle even larger lumps than jaw crushers. Very
Asbestos and mica roll crushers, hammer, and jet mills large lumps are broken first by explosives or pneumatic hammers
Cement gyratory, jaw and roll crushers, roller, and ball before feeding to crushers.
mills b. The squirrel-cage disintegrator illustrated has four concentric
Clays pan crushers, ring-rollers, and bead mills
Coal roll crushers, pulverizers, ball, ring-roller, and cages with horizontal impact bars. The cages rotate in alternately
bowl mills opposite directions, strike the feed and disintegrate or tear it
Coke rod, ball, and ring-roller mills apart. Coal, other friable materials, and fibrous materials are
Colors and pigments hammer, jet, and ring-roller mills handled in this equipment.
Cosmetics and dispersion and colloid mills c. Disc-type attrition milk have surfaces that rotate past each other
pharmaceuticals with close clearance and high speed, usually in opposite
Cotton and leatber rotary cutters directions but sometimes in the same direction at different
Flour and feed meal roller, attrition, hammer, and pin mills speeds. Clearances are adjustable with spring loading in
Graphite ball, tub, ring-roller, and jet mills increments of 0.001in. Maximum feed sizes are 10-25mm,
Hard rubber roller mills
Lime and Shells hammer and ring-roller mills diameters 12-48 in., and speeds 1200-7000 rpm. Table 12.5(b) is
Metallic minerah gyratory and jaw crushers, tumbling mills a list of materials that have been ground in disc mills. Some data
Paper and plastics cutters and slitters are in Table 12.7(b).
Phosphates ball and ring-roller mills d. Colloid milk are used to grind and disperse solids in liquids and
Polymers pulverizers, attrition mills to prepare emulsions. Adjustable clearances are between 0.001
Pressed cakes hammer and attrition mills and 0.050 in., and peripheral speeds to 10,000 ft/min. They are
Refractories gyratory and jaw crushers, pan and ball mills used, for example, to make lubricating greases by dispersion of
Salts cage and hammer mills calcium stearate in hydrocarbon oils.
Soaps hammer, multicage, and screen mills e. Buhrstone mills are an ancient example of an attrition mill.
Starch hammer and pin mills Nowadays they are used mostly for fine grinding of paints, inks,
Stone and aggregate gyratory, jaw, and roll crushers
Sulfur ring-roller mills and pharmaceuticals.
Talc and soapstones roil crushers, ring-roller, pebble, and jet mills f. Roller mills, also called spindle mills, act by crushing nipped
materials between a rotating cylindrical or tapered surface and a