Ball mill recirculating

Several reactors are presently used for studying gas-solid reactions. These reactors should, in principle, be useful for studying gas-liquid-solid catalytic reactions. The reactors are the ball-mill reactor (Fig. 5-10), a fluidized-bed reactor with an agitator (Fig. 5-11), a stirred reactor with catalyst impregnated on the reactor walls or placed in an annular basket (Fig. 5-12), a reactor with catalyst placed in a stationary cylindrical basket (Fig. 5-13), an internal recirculation reactor (Fig. 5-14), microreactors (Fig. 5-16), a single-pellet pulse reactor (Fig. 5-17), and a chromatographic-column pulse reactor (Fig. 5-18). The key features of these reactors are listed in Tables 5-3 through 5-9. The pertinent references for these reactors are listed at the end of the chapter. 

When finer material is required, a ball mill is used in a closed circuit. The feed is ground and then classified to separate coarse from fine sohds. The coarse sohds, also called oversized particles, are returned back to the mill for further grinding. This is called the recirculation load and the circuit is considered a closed circuit. In a dry circuit, the classifier may be a set of vibrating screens. 

Particle degradation in recirculating loops is similar to rod and ball milling processes. 

The particle size of the precleaned coals was reduced to mean diameters near 10 jum by milling in a stirred-ball slurry attritor mill. Slurries containing 20% by weight coal dispersed in deionized water were milled for 2 minutes using 6.3 mm diameter stainless steel media (140 cc slurry/kg media) and an agitator shaft speed of 290 rpm (18). The slurries were then filtered and dried in a recirculating nitrogen atmosphere at 110°C for 3 hours. 

The centrifugal slurry pump is the workhorse of slurry flows. Chapter 7 briefed the reader about some important slurry circuits, and it was explained that the grinding circuits consume a fair portion of the power of a concentrator. One particular pump at the discharge of the SAG, ball, or other mills is called the mUl discharge pump. Wear in these pumps is particularly harsh, leading to frequent replacement of impellers and liners, because a fair portion of the solids remain fairly coarse until recirculated back through the classification circuit. 

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