About Unit Operation Of Separation In A Material Recovery Facilities

grinding equipment, cleared level ground with equipment to form and turn windrows, screening equipment (optional)

High-end system

>20

Feedstock derived from source-separated yard waste or processing of commingled wastes; facilities include enclosed building with concrete floors, in vessel composting reactors; enclosed building for curing of compost product; equipment for processing (e.g. screening and bagging); and marketing compost product

Source: H. Leverenz, G. Tchobanoglous, and D. B. Spencer, "Recycling," in G. Tchobanoglous and F. Kreith (Eds.), Solid Waste Handbook, 2nd ed., McGraw-Hill, New York, 2002, Chapter 8.

Source: H. Leverenz, G. Tchobanoglous, and D. B. Spencer, "Recycling," in G. Tchobanoglous and F. Kreith (Eds.), Solid Waste Handbook, 2nd ed., McGraw-Hill, New York, 2002, Chapter 8.

be developed. In developing MRF process flow diagrams, the following factors must be considered: (1) identification of the characteristics of the waste materials to be processed, (2) consideration of the specifications for recovered materials now and in the future, and (3) the available types of equipment and facilities. For example, specific waste materials cannot be separated effectively from commingled MSW unless bulky items such as lumber and white goods and large pieces of cardboard are first removed and the plastic bags in which waste materials are placed are broken open and the contents exposed. The specifications for the recovered material will affect the degree of separation to which the waste

TABLE 3.14 Typical Methods and Equipment Used for Processing and Recovery of Individual Waste Components from MSW

Processing Options

Description

Manual sorting

Size reduction

Size separation

Magnetic field separation

Densification (compaction)

Materials handling

Automated sorting

Unit operation in which personnel physically remove items from the waste stream. Typical examples include (1) removal of bulky items that would interfere with other processes and (2) sorting material off an elevated conveyor into large bins located below the conveyor.

Unit operation used for the reduction of both commingled MSW and recovered materials. Typical applications include (1) hammermills for shredding commingled MSW, (2) shear shredders for use with commingled MSW and recycled materials such as aluminum, tires, and plastics, and (3) tub grinders used to process yard wastes.

Unit operation in which materials are separated by size and shape characteristics, most commonly by the use of screens. Several types of screens are in common use, including

(1) reciprocating screens for sizing shredded yard wastes,

(2) trommel screens used for preparing commingled MSW prior to shredding, and (3) disc screens used for removing glass from shredded MSW.

Unit operations in which ferrous (magnetic) materials are separated from nonmagnetic materials. A typical application is the separation of ferrous from nonferrous materials (e.g., tin from aluminum cans).

Densification and compaction are unit operations used to increase the density of recovered materials to reduce transportation costs and simplify storage. Typical applications include (1) the use of baling for cardboard, paper, plastics, and aluminum cans and (2) the use of cubing and pelletizing for the production of densified RDF.

Unit operations used for the transport and storage of MSW and recovered materials. Typical applications include (1) conveyors for the transport of MSW and recovered materials, (2) storage bins for recovered materials, and

(3) rolling stock such as fork lifts, front-end loaders, and various types of trucks for the movement of MSW and recovered materials.

Unit operation in which materials are separated by material characteristics. Typical examples include (1) optical sorting of glass by color, (2) X-ray detection of polyvinyl chloride (PVC), and (3) infrared sorting of mixed resins.

Source: G. Tchobanoglous, H. Theisen, and S. Vigil, Integrated Solid Waste Management: Engineering Principles and Management Issues, McGraw-Hill, New York, 1993.

Separation Concerns Principle

FIGURE 3.16 Typical manual separation of waste components at a materials recovery facility: (a) separating cardboard, paper, plastic, film plastic, glass, tin cans, and aluminum cans from mixed municipal solid waste at a facility with a current capacity of 400 tons/day with room to expand to 1200 ton/day by adding two more sorting lines and (b) separating contaminants from source separated compostable wastes before preprocessing (size reduction) and placement in piles in long rows (windrows) for composting. (See Figure 3.20(b).) (Courtesy H. Leverenz.)

FIGURE 3.16 Typical manual separation of waste components at a materials recovery facility: (a) separating cardboard, paper, plastic, film plastic, glass, tin cans, and aluminum cans from mixed municipal solid waste at a facility with a current capacity of 400 tons/day with room to expand to 1200 ton/day by adding two more sorting lines and (b) separating contaminants from source separated compostable wastes before preprocessing (size reduction) and placement in piles in long rows (windrows) for composting. (See Figure 3.20(b).) (Courtesy H. Leverenz.)

Recovery Flow Diagram
FIGURE 3.17 Process flow diagram for MRF used to further process source-separated waste. (Source: H. Leverenz, G. Tchobanoglous, and D. B. Spencer, "Recycling," in G. Tchobanoglous and F. Kreith (Eds.), Solid Waste Handbook, 2nd ed., McGraw-Hill, New York, 2002, Chapter 8.)

material is subjected. Three typical MRF process flow diagrams are presented in Figures 3.17, 3.18, and 3.19 for source-separated recyclable material, for mixed paper and cardboard, and commingled solid waste, respectively.11

Technical Considerations in the Planning and Design of MRFs

Technical consideration in the planning and design of MRFs involves three basic steps: (1) feasibility analysis, (2) preliminary design, and (3) final design. These planning and design steps are common to all major public works projects such as landfills or wastewater treatment plants. In some cases, the feasibility analysis has

Mixed paper and cardboard

Mixed paper and cardboard

Unit Operations Mrf

Shipping

FIGURE 3.18 Process flow diagram for MRF used to separate mixed paper and cardboard. (Source: H. Leverenz, G. Tchobanoglous, and D. B. Spencer, "Recycling," in G. Tchobanoglous and F. Kreith (Eds.), Solid Waste Handbook, 2nd ed., McGraw-Hill, New York, 2002, Chapter 8.)

Shipping

FIGURE 3.18 Process flow diagram for MRF used to separate mixed paper and cardboard. (Source: H. Leverenz, G. Tchobanoglous, and D. B. Spencer, "Recycling," in G. Tchobanoglous and F. Kreith (Eds.), Solid Waste Handbook, 2nd ed., McGraw-Hill, New York, 2002, Chapter 8.)

already been accomplished as part of the integrated waste management planning process. These topics are considered further in Table 3.15.11

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