Material Recovery Facilities (MRF)

Copyright Anders Damgaard & Morton A. Barlaz, NC State University 1

Material Recovery Facilities (MRF)


Lecture Objectives

• Explains MRFs and understand all the different types of separation equipment

• Define design parameters• C&D Waste


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


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


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


Drop-off Centers


Technologies in a MRF

• Separation – separation according to a single or combined characteristic– bag opening

• Size reduction – reducing particle size

• Compaction – increasing bulk density


Technology: Size reduction

• Hammer mills• Impact crushers• Cutters /shredders• Cascade mills• Jaw crushers

9Copyright: Anders Damgaard & Morton A. Barlaz, NC State University

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


Hammers for a hammer mill


Jaw crusher


Roll crusher


Shredder


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)


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)


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


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


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


Trommels


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


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


Bucket screen


Size Separation - Screens

Vibrating Screens useful for dry materials broken glass and dirt removal


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


Disk screen


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


Star Screen


Star and Disc Screens

• Design Parameters– Distance between disks on axle– Distance between axles– Incline

• Limitations– Wet weather/humidity– Wire/string on shaft


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


Material passing under a magnet


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

Material Recovery Facilities (MRF)

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