Materials Recovery Sorting Line Product

Overview

A materials recovery facility (MRF) sorting line is a fully integrated automated system designed to process mixed residential and commercial recyclables (commingled "single-stream" waste) into separate commodity-grade streams ready for secondary processors or remelting. The machine combines mechanical size reduction, screening, magnetic and eddy-current separation, and advanced optical sorting to achieve 95%+ purity in individual output streams.

A modern MRF processes 15–25 tonnes per hour, sorting incoming material into 6–8 final products: corrugated cardboard, office paper, PET plastic (beverage bottles), HDPE plastic (milk jugs), ferrous metals (steel cans), aluminum, and glass. Each output is sufficiently pure that it commands commodity-market pricing, offsetting operating costs and generating positive economics for the facility operator.

How it works

Stage 1: Bag Breaking and Initial Reduction

Mixed recyclables arrive in compacted bags and bales. The [[mrf-sorting-line-bag-breaker|bag breaker shredder]] (30 kW motor, 300 rpm) fragments plastic bags and breaks material clusters into individual pieces. A [[mrf-sorting-line-shredder-screen|50 mm perforated screen]] sized discharge prevents material larger than 50 mm from proceeding. The shredded stream drops onto the first [[mrf-sorting-line-conveyor-system|conveyor stage]], moving material to the next processing step.

Stage 2: Disc Screen Classification

A [[mrf-sorting-line-disc-screen|disc screen classifier]] with rotating polyethylene discs (1800 rpm rotor) performs primary size separation. Material is fed onto the rotating discs; larger pieces ride the outer disc face and exit the oversize end (going to picking cabins for manual secondary sorting), while smaller material passes through the disc gaps and continues on the main stream.

Stage 3: Trommel Screen and Fines Removal

A large [[mrf-sorting-line-trommel-screen|trommel screen]] (1200 mm diameter, 3000 mm length, 12 mm perforations, 60 rpm rotation) further refines size classification. Material tumbles through the rotating perforated drum. Fines (<10 mm) and lightweight material fall through the bottom perforations; this undersize fraction is transported to a separate hopper for occasional manual inspection or disposal. Oversize material (bottles, cans, bulky items) exits the discharge end onto the next conveyor.

Stage 4: Ferrous Metal Extraction

An overhead [[mrf-sorting-line-ferrous-magnet|permanent-magnet belt]] (1.0 T field strength, 180 rpm belt speed) captures ferrous metals (steel cans, scrap). Steel-containing items are magnetically attracted upward and travel with the moving belt to a [[mrf-sorting-line-magnet-collection-chute|dedicated collection chute]], dropping ferrous material into a separate bin. Non-ferrous items fall back to the main conveyor.

Stage 5: Non-Ferrous Metal Recovery

An [[mrf-sorting-line-eddy-current-separator|eddy-current separator]] (3000 rpm rotor, 500 mm diameter permanent-magnet array) extracts aluminum and other non-ferrous metals. The rotor generates time-varying magnetic fields; eddy currents induced in non-ferrous metals create repelling forces, launching those items sideways onto a [[mrf-sorting-line-eddy-collection-chute|deflection chute]]. Ferrous-free, non-ferrous-free material continues straight through to the next stage.

Stage 6: Optical Sorting

Two [[mrf-sorting-line-optical-sorter|hyperspectral optical sorters]] positioned in series provide advanced material identification. Each sorter houses:

• A [[mrf-sorting-line-optical-camera|line-scan camera]] imaging material at 30 kHz (30,000 images/second) as it passes on a conveyor.
• Multispectral [[mrf-sorting-line-optical-led-bank|LED illumination]] (8 wavelengths, 400–1600 nm) enabling detection of material type and color.
• A real-time [[mrf-sorting-line-optical-processor|image processor]] running machine-learning models to classify each particle (PET plastic, HDPE plastic, polypropylene, aluminum, paper, cardboard, glass, etc.).
• Eight [[mrf-sorting-line-optical-ejector-valve|solenoid air ejector jets]] (6 bar supply) positioned downstream, each capable of firing in <5 ms.

When the camera detects a PET bottle, the processor triggers the jet corresponding to the PET collection bin, blowing the item sideways into the correct bin. This process repeats for each material type, achieving 95%+ purity.

The [[mrf-sorting-line-optical-compressor|3 kW air compressor]] (600 L tank, 8 bar delivery) supplies all ejector jets and pneumatic vibrators on the line.

Stage 7: Manual Picking Stations (Secondary Sorting)

Two [[mrf-sorting-line-picking-cabin|operator workstations]] receive oversize or contaminated material from earlier stages. Each cabin has:

• An adjustable-speed [[mrf-sorting-line-cabin-belt|sorting belt]] (0.1–0.5 m/s) allowing operators to view material at controlled speed.
• Multiple quick-swap [[mrf-sorting-line-cabin-bin-support|bin holders]] for different material types.
• [[mrf-sorting-line-cabin-light|LED work lights]] (500 lux) ensuring visibility.

Operators manually sort material, removing contaminants (non-recyclables, hazardous items) and consolidating items for specific reprocessing routes. Typical processing rate is 200–300 kg/hour per operator.

Control and Safety System

A [[mrf-sorting-line-control-system|programmable logic controller]] (16 inputs, 16 outputs) coordinates all motors, conveyors, and safety systems. The PLC:

• Monitors all conveyor motors via current relays, stopping the system if a belt jams.
• Manages start/stop sequences for sequential activation of each stage.
• Communicates with optical sorter [[mrf-sorting-line-optical-processor|image processors]] via Ethernet, receiving real-time material classifications.
• Controls solenoid ejector valves, firing them at the correct instant as items reach collection points.

All motor contactors are rated 480 VAC 3-phase, sized for individual motor loads (30 kW for shredder, 7.5 kW for disc screen, etc.). A central [[mrf-sorting-line-control-enclosure|NEMA 4X stainless-steel control cabinet]] houses the PLC, relays, and soft-start drives.

An [[mrf-sorting-line-emergency-stop|emergency stop button]] (40 mm red mushroom, dual-channel safety-rated) halts all motion instantly. [[mrf-sorting-line-interlock-switch|Interlock switches]] on each access door break motor circuits if guards are opened during operation.

Material Flow Diagram

''' Input (Mixed Recyclables) ↓ [Bag Breaker Shredder] → Oversize Waste Bin ↓ [Disc Screen] → Picking Cabin 1 (Oversize) ↓ [Trommel Screen] → Fines Bin (<10 mm) ↓ [Ferrous Magnet] → Ferrous Metal Bin ↓ [Eddy-Current] → Aluminum Bin ↓ [Optical Sorter 1] → PET Bin, HDPE Bin, etc. ↓ [Optical Sorter 2] → Paper Bin, Cardboard Bin ↓ [Picking Cabin 2] (Final QC) ↓ [Output Bins] (6–8 commodity streams) '''

Maintenance

Daily: Visually inspect all [[fastener-set|fasteners]] on screens and conveyors. Check [[pressure-sensor|air pressure gauge]] (should read 7.5–8.0 bar); if low, inspect compressor and check for solenoid leaks. Test the [[mrf-sorting-line-emergency-stop|emergency stop button]] to verify circuit break.

Weekly: Drain moisture from the [[mrf-sorting-line-optical-compressor|air compressor]] tank by opening the manual drain valve for 10 s. Inspect all [[drive-belt|conveyor belts]] for tracking and fraying; adjust belt tension (deflection should be 10–15 mm midspan). Replace any worn [[mrf-sorting-line-conveyor-belt|nylon belts]] showing cracks or missing sections.

Monthly: Change the [[mrf-sorting-line-optical-compressor|air compressor]] oil and element filter (if not automatic filter trap). Clean the [[mrf-sorting-line-disc-rotor-assembly|disc rotor]] polyethylene discs with warm water and mild detergent to remove buildup. Inspect [[mrf-sorting-line-optical-camera|camera lens]] on optical sorters for dust or condensation; clean with lens tissue if needed.

Quarterly: Perform calibration run on both [[mrf-sorting-line-optical-sorter|optical sorters]] using reference samples of known material types (PET, HDPE, paper, cardboard, glass). Accuracy should remain >95%; if below 90%, contact equipment manufacturer for recalibration. Grease all [[mrf-sorting-line-conveyor-roller|roller bearings]] via zerk fittings if present.

Annually: Have the [[mrf-sorting-line-magnet-belt-assembly|permanent-magnet belt]] field strength measured with a gaussmeter (should read 0.95–1.05 T). Magnets degrade over time; if field drops below 0.8 T, replace the belt. Change hydraulic or drive-fluid in the [[mrf-sorting-line-trommel-gearbox|trommel gearbox]] and [[mrf-sorting-line-eddy-gearbox|eddy transmission]] every 2000 operating hours.

Economic Benefit

A single-stream MRF (25 tonne/hour capacity, 16 operating hours/day, 250 working days/year) processes approximately 100,000 tonnes annually. At typical commodity pricing:

• Cardboard: $90/tonne
• Office paper: $120/tonne
• PET: $350/tonne
• HDPE: $280/tonne
• Ferrous: $200/tonne
• Aluminum: $1200/tonne

A material recovery of 90 tonnes of mixed commodities (weighted average $280/tonne) generates $25.2 million/year in gross material sales before operating costs (labor, maintenance, utilities, processing). This revenue covers facility expenses and generates positive returns for the operator, making MRF automation economically justified.

Environmental Impact

By automating sorting to >95% purity, a MRF sorting line ensures:

• Paper and cardboard are reused by paper mills, avoiding landfill and virgin tree harvesting.
• Plastics are melted into new packaging or textiles without virgin plastic blend.
• Aluminum is remelted into new cans, reducing bauxite mining and smelting energy (95% energy savings vs. virgin aluminum).
• Glass is crushed and mixed into fiberglass or new containers.
• Ferrous metals are scrap-melted for rebar and structural steel.

Contamination prevention (achieved via high purity) is critical: a single ceramic tile mixed into a cardboard bale can damage paper-mill equipment. Optical sorting prevents this costly contamination.