Page 221 - Materials Chemistry, Second Edition

CAT3525_C07.qxd 1/29/2005 9:57 AM Page 192
192 Waste Management Practices: Municipal, Hazardous, and Industrial

FIGURE 7.21 Tub grinder for yard wastes.

FIGURE 7.22 A new hammer for a horizontal hammermill.

rotate at high speeds within a large steel housing. The input enters at the top and flows downward
by gravity. The housing is cone-shaped and tapers down to a narrow throat section. The rotating
hammers create a vortex, or fan effect which, in addition to gravity, pulls wastes downward into the
unit. Some size reduction occurs as the waste is milled in the upper portion. Farther down the rotor
shaft more hammers are attached. Once the feed passes the throat section it is further reduced by
the action of the lower hammers and the breaker bars on the housing walls. Adjusting the spacing
between the hammers and the walls controls particle size. It is in the lower portion of the unit that
most of the size reduction occurs. When the input waste reaches the bottom it has been sufficiently
reduced in size such that a grate is not needed. The final shredded product is forced out through the
discharge chute.