Jae K. (Jim) Park, Professor Dept. of Civil and Environmental Engineering University of Wisconsin-Madison 1

Materials Recovery Facilities Often referred to as “Intermediate Processing Facilities or Centers (IPFs or IPCs) Designed to process recyclables and prepare the materials for sale to end users (SWANA, 1991) Aimed to receive, sort, process, and store recovered materials efficiently and safely for eventual shipment to the markets Consists of both mechanical and manual processing; sometimes use other methods of processing, e.g., optical scanning SWANA: Solid Waste Association of North AmericaSolid Waste Association of North America 2

MRFs - Activities Receiving: deposit collected materials in a building prior to processing Processing: determine degree of processing by  Degree and quality of separation of the recyclables;  Quality of materials delivered to the processing facility; and  Market specifications for secondary materials to be produced Preparation for shipment: bale, compact, or prepare materials in other ways to enable shipment Storage: store sufficient recovered materials to meeting shipping and customer quantity requirements 3

MRF in Calumet, IL 4

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Eddy Current Separator 10

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Eddy Current Separator 13

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Typical MRF Operation Unload recyclables in a tipping area adjacent to the MRF processing lines Separate paper designated for recycling from other recyclables in advance Manually sort paper products such as corrugated paper Feed rest of the commingled materials onto a conveyer system which moves the material through the MRF where handpicking platforms, magnets, and other mechanical devices are used for separation 21

Unit Operations in MRFs Size reduction: hammer-mill, shear shredders, tub grinder  Size separation: reciprocating screen, trommel screen, disc screen  Density separation: air classification, stoner, flotation, heavy media separation  Electric and magnetic field separation  Densification (compaction) Development and implementation of MRFs 22

Unit Operations for MSW Processing Size reduction  Reduce size, blend constituents, more uniform for processing, compaction more efficient  Chippers used to process wood, brush, trees - selection based on max diameter of material to be processed  Hammer mills used to process logs, brush, stumps, plastic, tires, glass, C&D materials, asphalt, shingles  Vertical grinders (tub grinder)-fed vertically which can result in material fly away and safety problems 23

Stationary Size Reduction Equipment Crushers Impactors Grinders (hammer mills) Shear Shredders Chippers 24

Shredders Hammer Mills  Vertical Shaft  Horizontal Shaft Horizontal Grinder Cutter Mills 25

Separation Processes Hand Picking (Manual) Screening Air Classification Magnets Optical separation Eddy current Flotation 26

Material Separation Binary -two output streams Polynary-more than two output streams Separation Processes  Picking (Hand Sorting)  Screens Used to:  Remove fines from material prior to processing  Grade ground or crushed materials particularly concrete  Separate glass, Al cans, cardboard  Post-process compost to ensure complete degradation  Opening size based on desired separation  Removes under/over sized material, light/heavy components Trommel  Cascading  Cataracting 27

Material Separation Separation Efficiency Recovery of:Component X = R (x1) = X 1 /X 0 x 100% Component Y = R (y2) = Y 1 /Y 0 x 100% Purity of:Component X = X 1 /(X 1 + Y 1 ) x 100% Component Y = Y 2 /(X 2 + Y 2 ) x 100% Efficiency : E(x,y)= (X 1 /X 0 - Y 1 /Y 0 ) x 100% = (X 2 /X 0 – Y 2 /Y 0 ) x 100% 28 Binary Separation 1 2 X 0 + Y 0 X 1 + Y 1 (Want x) X 2 + Y 2 (Want y)

Screens Trommel Screens Vibratory Screens Disk Screens 29

Trommel 30 This is a trommel prior to installation. Notice the different size openings in different sections of the trommel.

Density Separation Based on the density and aero dynamic characteristics Applied to the separation of shredded MSW into  Light fraction; paper, plastics and organics  Heavy fraction; metals, wood, etc. 31

Air Classifier Lighter materials transport to the top of chute by the upward airflow Control factors include waste loading, airflow rate, and the cross sectional area of chute Type of classifier  Straight  Zigzag: creates turbulence and allows bunched materials to be broken up  Pulsed air: can achieve a greater discrimination 32

Stoner Consists of a vibrating porous deck through which air is blown Initially designed to remove stones and other heavy rejects  Separate heavy grit from organic material in trommel underflow streams Called inert separator Actual separating criterion is terminal velocity, not density or weight. Important operation variables are deck slope and air volumes 33

Floatation Employs a fluid to separate two components of different densities.  Using water Sink to bottom: glass chips, rocks, bricks Float: light organics, plastics, ….  Change the liquid, we can separate in a different density. 34

Heavy Media Separation Shredded feedstock is dumped into a liquid stream that has a high specific gravity.  Aluminum separation (floating in a liquid)  After ferrous metal and glass have been removed  Disadvantage Optimum-size requirement: 2000~3000 ton/d of feedback Shredded feedstock is dumped into a liquid stream that has a high specific gravity. 35

Density Separation – Selection of Equipment Factors to be considered  Characteristics of material produced by the device: particle size, shape, bulk specific weight, moisture content, particle size distribution, clumping tendency, fiber content  Material specifications for light fraction: particle size and its distribution  Air classifier design parameters: air/solids ratio, fluidizing velocity, unit capacity, total air flow  Stoner design parameters: bet slope, fluidizing air, exhaust air  Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, noise, air emission  Site considerations: floor space and height, access 36

Magnetic and Electric Field Separation Magnetic separation  Based on magnetic permeability  Separate ferrous from nonferrous metals Electrostatic separation  Based on differing surface charge characteristics  Separate plastics from paper Eddy current separation  Varying magnetic fields are used to induce eddy currents in nonferrous metals such as aluminum 37

Magnetic and Electric field Separation – Performance Characteristics Performance criteria  Recovery, Purity, Efficiency  Magnetic separation devices Generally, very high efficiency (<95%) Design criteria  Based on mass loading and power consumption  Permanent magnets, comparing with electromagnets Reduce operating cost, but need more capital costs 38

Magnetic and Electric field Separation – Selection of Equipment Factors to be considered  Characteristics of material to be separated: particle size, shape, moisture content, material consumption  Materials specifications for separated materials, purity, recovery and efficiency requirement  Device design parameters: unit capacity, power requirements (voltage and amperage), magnet strength, electrostatic field strength  Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, noise, air emission  Site considerations: floor space and height, access 39

Mechanical Separation Techniques for Specific Materials Ferrous metal-magnetism (most successful and efficient unit process) Glass-froth flotation, optical separation tried in ‘70s but not efficient Non-ferrous metals-flotation, electromagnetic eddy current, electrostatic separation tried, concentration and efficiency low Plastics: Mo mechanical separation device in US source separation or hand picking, proprietary means used in Europe 40

Eddy Current Separator A rotor comprised of magnet blocks, either standard ferrite ceramic or the more powerful rare earth magnets depending on application, are spun at high revolutions (over 3000 rpm) to produce an ‘eddy current’. This eddy current reacts with different metals, according to their specific mass and resistivity, creating a repelling force on the charged particle. If a metal is light, yet conductive such as aluminum, it is easily levitated and ejected from the normal flow of the product stream making separation possible. 41

Eddy Current Separator 42

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Densification (Compaction) Unit operation which increases the density of waste materials  Reduction of storage requirements of recyclables  Reduction of volume for shipping  Preparation of densified refuse-derived fuels (RDF) Type of equipment  Stationery compactor  Prior to landfilling or combustion to reduce haul costs  Baling machine (Baler)  Processing recovered materials prior to sale  Cubing and pelleting equipment  Preparation of densified RDF 44

Stationary Compactor Compactor is categorized into stationery or movable  Mechanism is same as that in a collection vehicle Usage of stationary compactor  Light duty  Commercial and light industry  Heavy industry  Transfer station  Low-pressure (< 100lb/inch 2 )  High-pressure (> 100lb/inch 2 ) 45

Bailing Equipment Operating under high pressure  Typically, 100 to 200 lb/inch 2 Target materials  Cardboard, newsprint, plastic, PET bottles, Aluminum can Baled materials  Easy to load with forklifts and economically shipped 46

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Cubing and Pelleting Technology that can be used to produced densified refuse-derived fuels Waste paper or shredded RDF is extruded through extrusion dies with and eccentric rotating press -wheel 48

Performance criteria Percentage volume reduction Volume reduction = (V i –V f )/V i V i : initial volume of wastes before compaction V f : final volume of waste after compaction Compaction ration Compaction ratio = V i /V Final specific weight Cubing and pelleting equipment Unit specific weight: for an individual cube or pellet Bulk specific weight: for a fixed volume of cubes or pellets 49 Densification – Performance Characteristics

Densification – Selection of Equipment Factors to be considered  Purpose of densification: compaction, cubing and pelleting, baling  Characteristics of material to be processed: particle size and its distribution, shape, moisture content, material composition, specific weight  Equipment design parameters: unit capacity, power requirements (voltage, amperage, horsepower), compaction ratio, unit specific weight, bulk specific weight, bale weight, operating pressure  Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, noise, air emission  Site considerations: floor space and height, access 50

Development and Implementation of MRFs Engineering consideration  Definition of the functions of the MRF  Selection of the materials to be separated (now and future)  Identification of the material specifications  Development of separation process flow diagram  Determination of process loading rates  Layout and design of the physical facilities  Selection of the equipment and facilities  Environmental controls and aesthetics considerations Non-engineering implementation issues  Siting  Environmental emissions: traffic, noise, odor, dust, airborne debris, liquid discharge, visual unsightliness, vector control  Public health and safety: workers, public access  Economics 51

1 Conveyor2 Manual sorting station3 Rejects/negative sort 4 Paper baler5 Magnetic separator6 Ferrous baler 7 Inclined sorting table 8 Aluminum baler9 Eddy current separator 10 Plastics sorting station 11 PET baler12 HDPE baler 13 Glass sorting station 14 Glass crusher/storage bunker Typical MRF Process Line 52 See next slide

Typical MRF Process Line Medium Technology Processing 53

Typical MRF Process Line High Technology Processing 54

Siting Similar to the siting of any other solid waste management facility Siting issues: convenience to the collection system, transporting corridors, zoning compatibility, public acceptance, and building code and permit requirements Many states do not define MRFs as a solid waste management facilities, thereby eliminating a state environmental requirement. Property in a zoned industrial area is the preferred location since traffic and transportation corridors are already established to service the industrial establishment. Provide sufficient space for drop-off facilities, office, buffer zones, and landscaping. 55

Typical Design Scale and scalehouse: accommodate collection vehicles at peak periods of the day Tipping floor/unloading area: space for unloading the recyclables. Constructed of concrete with slopes for drainage and protective materials to withstand the movement of equipment Storage area: either under roof or in the open to store processed materials; sufficient space Process lines: consists of a variety of equipment to move, sort, separate and prepare the recyclables for their respective markets. 56

Typical Buildings Normally enclosed in buildings which house the tipping floor, the process lines, and some storage. Designed to allow safe and easy access. Sufficiently large and high doors to accommodate vehicles normally using MRF 57 Reference material: