Size reduction is the unit operation used to reduce the size of the materials in MSW. Size reduction is used to process materials for direct use, such as mulch or compost, or as part of a materials recovery facility. The types, performance characteristic, design criteria, and selection of size reduction equipment are considered in the following discussion.
Several types of size reduction units are in common use:
(1) the hammermill, which is very effective with brittle material;
(2) the shear shredder, which uses two opposing counterrotating blades to cut ductile materials in a scissor like action;
(3) the tub grinder, which is widely used in the processing of yard wastes.
Each type of shredder has unique properties that suit it to specific applications. These properties can be used to meet different size reduction goals, depending on the requirements of downstream processes such as air classifiers or screens.
Selection of Size Reduction Equipment
Factors that must be considered in the selection of size reduction equipment are summarized below:
(1) Materials to be shredded
(2) size requirements for shredded material by components
(3) Method of feeding shredder
(4) Operational characteristics
(5) Site considerations
(6) Materials storage and conveyance requirements
