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Material Recovery Facilities (MRF)
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Lecture Objectives
• Explains MRFs and understand all the different types of separation equipment
• Define design parameters• C&D Waste
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Purpose of a MRF
• Where does a MRF fit in solid waste management?• A MRF performs mechanical treatment/separation
– affects mechanical or physical characteristics, no conversion• The MRF should have recyclable material as an end product (as
well as a residual stream)• A MRF is by necessity also a transfer station• Role of environmental engineer
– Bid specs
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MRF design will depend on..
• How many types of recyclables are handled?• Are recyclables presorted or to be sorted at MRF?
– (single/dual stream)• Are recyclables separated from mixed waste?• Endless combinations of materials to be processed
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Simplest MRF – Drop-Off Centers
• Drop-off centers in central locations– Shopping centers – Schools– Transfer stations
• Participation is an issue– Substitute for curbside recycling in areas that do not provide this
service• Maintaining neatness is critical
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Drop-off Centers
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Technologies in a MRF
• Separation – separation according to a single or combined characteristic– bag opening
• Size reduction – reducing particle size
• Compaction – increasing bulk density
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Technology: Size reduction
• Hammer mills• Impact crushers• Cutters /shredders• Cascade mills• Jaw crushers
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Hammer Mill - Glass
A miniature hammer mill installed in a chute below a sorting conveyor used to reduce the
volume of glass for shipment in bins or large boxes
installation is based on transport, storage economics and market requirements
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Hammers for a hammer mill
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Jaw crusher
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Roll crusher
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Shredder
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Technology: SeparationBag OpeningScreens (size separation)• Trommel screens• Oscillating screens• Bucket screens• Ballistic screens• Disc screensAir classifiers (heavy / light separation)• Zig-zag air classifiers• Rotary or cross current air classifiers• Suction hoods (maybe manually assisted)
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Technology: SeparationMetal separators
– Magnets– Eddy current (repels Al in alternating magnetic field)
Optical sortersLiquid-based (water) separation
– Flotation– Sedimentation– Hydrocyclones
Manual sorting– Positive sorting (removing the product)– Negative sorting (removing the dirt and contaminants)
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Bag opening
Typically applies to mixed wasteSlitter/Trommel• Bags fed by conveyor to a slitter
– Cut by 2 rotating blades– Wheels with spikes
• Dropped onto a trommel where 75 - 95% of material (MSW or yard waste) is removed
• Trommel may have knives in front section
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Bag Opening
AugersBags are dropped onto an auger by a loader or from a hopper• Auger is at a 25o angle• Glass breakage is 5%• 98% of contents are removed• Auto-reverse feature to protect equipment
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Size Separation - Trommels
Uses• bag opening• broken glass/fines removal from commingled stream • cleaning paper• removal of materials from mixed (MSW)
– can have multiple openings along length• container separation• food waste/fines removal
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Trommels
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Size Separation - Trommels
Sizing is difficult Separation efficiencies are estimates Example Sizing
These sizes are based on estimates from one vendor
Ton/hr (TPH) 10 30-50 70-100
Diam. (ft) 5-6 10 12Length (ft.) 15-20 30-50 60-70
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This is a trommel prior to installation. Notice the different size openings in different sections of the trommel
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Bucket screen
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Size Separation - Screens
Vibrating Screens useful for dry materials broken glass and dirt removal
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Size Separation - Screens
Disk Screens• rotating disks with an interval between them to allow one
component to fall between the disks while another component is carried over the top
• works well for separation of paper from containers or OCC from other paper
• the small material may be compostable in a mixed waste MRF
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Disk screen
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Size Separation – Star Screens
• Star Screens - modification of disk screen• Uses:
– Loosen up a fiber stream to ease manual sorts of mixed paper– Separate OCC from ONP– Separate fiber from containers when recyclables are collected
as a single stream
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Star Screen
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Star and Disc Screens
• Design Parameters– Distance between disks on axle– Distance between axles– Incline
• Limitations– Wet weather/humidity– Wire/string on shaft
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Magnetic Separation
• Recovery of ferrous metal from– A mixture of tin and aluminum cans– Commingled recyclables– Shredded MSW – mixed waste MRF
• Depending on purity of inlet stream, two magnets in series, or a double throw magnet may be used
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Material passing under a magnet
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Eddy Current Separation
• Use of magnetic fields to separate aluminum from other components
• Aluminum is repelled by magnetic force due to generation of a charge of opposite polarity
• Can be used to pull aluminum out of a stream of commingled recyclables or at the end of a belt to separate aluminum from residuals
35Copyright: Anders Damgaard & Morton A. Barlaz, NC State University
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