Technology Zone
Sensors, analyzers and software turn a recycling line into a measured process. This zone covers material identification, mass-flow and moisture measurement, radiation detection and the control software that ties them together.
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What this zone covers
Most recycling plants run on operator experience: the loader driver sees the pile, the line manager hears the shredder. Instrumentation makes that knowledge measurable — mass flow per stream, composition, moisture, machine load, purity — and control uses it to keep the line at its design point. The gains are in throughput stability, purity, energy and the ability to prove quality to a buyer.
Belt scales on every major conveyor give mass balance across the plant; radar level sensors in bunkers and hoppers keep feeders supplied; speed monitors, motor current and vibration sensors watch every drive. A mass balance that closes to within a few per cent is the foundation for every other measurement; without it, purity and recovery numbers are guesses.
Sensor-based sorters already carry NIR, VIS, X-ray and AI cameras; the same sensors mounted over a belt as monitors report the composition of the input and the product continuously. Moisture sensors on organics and RDF, metal detectors on product streams, and camera-based counting of contaminants (batteries, PVC, glass) turn manual sampling into a live signal. Laboratory sampling stays as the reference.
PLC and SCADA systems sequence the plant: interlocks (a conveyor runs only if the next one runs), metering control on the feed bunker, load-dependent speed on shredders, automatic reversing on jams, and recipe control on sorters. Data historians record every signal; dashboards show purity, throughput and downtime per shift; alarm management stops the operator drowning in nuisance alarms.
Scrap yards and incinerators screen incoming loads for radioactive sources with portal monitors; X-ray and AI cameras find lithium batteries at reception; gas detectors watch organic storage and landfill gas; thermal cameras and spark detectors feed the fire system. Safety functions run on dedicated safety controllers, separate from the process PLC.
| Parameter | Typical range | Rule of thumb |
|---|---|---|
| Belt scale accuracy | ±0.5–1 % with weekly zero check | Idler alignment and belt tension decide more than the electronics |
| Plant mass balance closure | Within 2–5 % over a shift | If it does not close, find the unmeasured stream |
| Radar level in bunkers | 80 GHz; ±5–10 mm; dust-tolerant | Aim away from the fill stream and the loader |
| Online moisture (organics, RDF) | NIR or microwave; ±1–2 % after calibration | Calibrate per material; heterogeneous waste scatters |
| Composition monitor | NIR/VIS camera over belt; results per minute | Trend, not absolute; verify with manual samples |
| Radiation portal | Alarm threshold a few % above background; vehicle speed ≤ 8 km/h | Every load, both directions of travel |
| Speed and rotation monitoring | Alarm below 80 % of nominal within seconds | Standard on every conveyor and elevator |
| Data logging | 1 s resolution for drives; 1 min for flows and levels | Keep at least a year for trend analysis |
| Symptom | Likely causes | What to do |
|---|---|---|
| Mass balance does not close | Unmeasured streams (fines, reject, rework); belt scale drift; double counting | Map every stream, calibrate scales, define measurement points |
| Level sensor in bunker gives wrong level | Sensor sees the loader or the fill stream; build-up; heap shape | Reposition, use two sensors, camera as backup |
| Nuisance alarms | Thresholds set at commissioning; sensors on unstable signals; no alarm management | Alarm review, deadbands and delays, prioritisation |
| Composition monitor disagrees with lab | Monitor sees surface only; burden depth; calibration set | Use as trend; calibrate against lab samples from the same time window |
| Shredder trips on overload | No load-dependent feed control; feed surges | Feed metering on motor current, automatic reversing, buffer bunker |
| Radiation alarms with no source found | Naturally occurring radioactive material (fertiliser, ceramics, some scrap); medical isotopes | Spectroscopic identification, procedure for isolation and re-check |
| Data collected but not used | No dashboards; no KPIs; nobody owns the data | Shift dashboards with purity, throughput, downtime, energy; weekly review |
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Xu Xifeng
Jiangsu Keson Environment Technology Co., Ltd.
Xu Xifeng, the founder of Keson and vice president of Jiangsu Low Carbon Environment Design Institute of China. He has been engaged…
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Questions and answers
With a mass balance: belt scales on the input, the main products and the residue, plus level sensors on the feed bunkers. Once the tonnes are known per stream and per shift, purity, recovery, energy per tonne and downtime become meaningful numbers, and every later sensor has something to be compared with.
Approximately: NIR and camera monitors above the input belt report the share of the main material classes in the surface layer every minute. Use them as trends and for detecting a change in the input, and keep manual sampling as the reference — the monitor sees the top of the burden, not the whole stream.
±0.5–1 % on a well-installed scale with aligned idlers, constant belt tension, a weekly zero check and a periodic span check with test weights or a material test. Sticky, wet material on the belt and misaligned idlers are the usual causes of drift; the electronics rarely are.
No. Emergency stops, guard interlocks, spark extinguishing, fire suppression and explosion protection belong on a certified safety controller with its own wiring and diagnostics; the process PLC receives their status. That separation is required by the machinery and ATEX rules and expected by insurers.
Throughput per stream, purity and recovery of the main products, downtime by cause, energy per tonne, filter and shredder condition indicators, and open alarms. Fewer numbers looked at every shift beat a hundred numbers nobody reads. Owning the data — one person responsible for each KPI — matters more than the software.
Radiation: portal monitors at the weighbridge that every load passes at low speed, with a procedure for isolating and identifying alarms. Batteries: visual inspection on the tipping floor supported by X-ray or AI camera systems on the reception conveyor, with a KPI on batteries found. Both are cheaper than the fire or the contaminated load they prevent.
A level sensor tells the operator when to load and lets the PLC hold the bunker in a band; the actual feed rate to the line comes from the metered discharge (floor or drum speed) and, ideally, a belt scale directly after the bunker that closes the loop. Level alone does not keep the burden depth constant.
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