Most PET bottle washing lines underperform for a boring reason. They got spec’d for the wrong bottle. Someone bought a line rated for clean post-industrial scrap, then fed it baled post-consumer bottles with labels, caps, sand, and last month’s ketchup still inside. Six weeks later the line is running at half capacity and the flake won’t sell above floor price.
This article walks through what a PET bottle washing line actually does, stage by stage, with the numbers that matter. Not the brochure version. The version you see on the floor at 2 p.m. when something’s jammed.
What a PET Washing Line Is Really For
A washing line does one job: turn dirty baled bottles into clean, dry PET flake that a buyer will pay a premium for. Everything else is detail. The flake goes to pelletizing (for strapping, fiber, sheet) or straight back into bottles if it’s food-grade.
The gap between “clean flake” and “food-grade flake” is where most buyers get burned. Clean flake might be 98% pure. Food-grade needs 99.5% plus, with PVC under 50 ppm and no detectable glue or oil. That second number is the difference between selling at $800/ton and $1,400/ton. Same machine category. Very different result.
The Process, Stage by Stage
Here’s the actual flow. Skip a stage and you pay for it downstream.
1. Bale Breaking
Bottles arrive compressed into 400–600 kg bales held together with steel wire or PET strap. A bale breaker tears them open and feeds a sorting conveyor. Simple machine, but it sets the pace for the whole line. If your breaker stalls, everything behind it stops.
2. Pre-Sort (the step people skip)
Manual or optical sorting at the front removes non-PET items: PVC bottles, HDPE jugs, metal cans, rocks, the occasional boot. This is where you catch contamination before it enters the wash and ruins your sink-float separation later. We’ve seen plants try to skip this and “sort at the end.” You can’t sort flake as well as you can sort whole bottles. Don’t do that.
3. Pre-Washing
A trommel or rotating drum knocks off loose dirt, sand, and small debris with cold water. Sounds trivial. It isn’t. Skip it and you sandblast your hot washer and clog your water treatment in a month.
4. Label Removal
Full-sleeve labels are the enemy. A label remover (or friction washer) strips them off. The plastic label goes to the float fraction; the PET bottle body stays. If you run PET with PVC sleeves and don’t remove them, your PVC count climbs and your food-grade claim dies.
5. Wet Shredding
Single shaft shredder, often with water injection, cuts bottles into 30–50 mm flake. Wet shredding cuts dust and starts the wash early. Output feeds the hot washer directly.
| Shredder Model | Chambre (mm) | Motor | Débit | Use Case |
|---|---|---|---|---|
| D1000 | 1 015 × 780 | 37 kW × 2 | 1 200 à 2 500 kg/h | Mid-size bottle lines |
| D1200 | 1 220 × 1 000 | 45 kW × 2 | 2 000 à 4 000 kg/h | Standard commercial lines |
| D1400 | 1 420 × 1 000 | 55 kW × 2 | 3 000 à 6 000 kg/h | High-volume operations |
6. Hot Washing (non-negotiable for food grade)
90°C water with caustic soda. This is what dissolves glue, oil, and food residue that cold water leaves behind. You need it if you’re chasing bottle-to-bottle quality. A line without hot wash tops out at 98–99% purity. Fine for strapping and fiber. Not fine for food contact.
7. Friction Washing
High-speed rotor (1,500–3,000 RPM) scrubs each flake surface to knock off ink and fine dirt. Think of it as a car wash for plastic. The flake comes out looking like flake, not like something that was in a landfill.
8. Sink-Float Separation
Here’s the physics that makes or breaks your line. PET sinks (density ~1.38). Caps, rings, and labels (PP/PE) float (density ~0.9). Flake goes into a water tank; the float fraction skims off the top, PET drops to the bottom. Get this stage right and your PVC and polyolefin contamination drops to near zero.
9. Rinse and Dry
Clean water rinse, then centrifugal dryer gets moisture under 1–2%. Wet flake jams pelletizers and ruins extrusion. Dry it.
10. Optical Sorting (optional, increasingly expected)
NIR or hyperspectral sorter catches the last PVC flakes and off-color material. If your buyer demands ≤50 ppm PVC, this isn’t optional. It’s the final gate before the flake gets certified.
| Scène | Removes | Skippable? |
|---|---|---|
| Bale break | Wire, strapping | Non |
| Pre-sort | Non-PET items | Not if feed is mixed |
| Pre-wash | Sand, loose dirt | Risky to skip |
| Label removal | Sleeves, glue-backed labels | No, for food grade |
| Hot wash | Glue, oil, food residue | No, for food grade |
| Sink-float | PP/PE caps, PVC (mostly) | Non |
| Optical sort | Residual PVC, color | Only if not food grade |
Cold Wash vs Hot Wash, Decided by Your Buyer
Don’t pick based on what’s cheaper upfront. Pick based on who’s buying your flake.
| Lavage à froid | Lavage à chaud | |
|---|---|---|
| Water temp | Ambient | 85–95 °C |
| Glue & oil removed? | Non | Oui |
| Energy cost | Faible | High (water heating dominates) |
| Purity | 98–99% | 99.5%+ |
| Sells to | Fiber, strapping, sheet | Bottle-to-bottle, food-grade |
If your customer is a fiber producer, cold wash is fine and you save on energy. If your customer is a bottle maker under EU PPWR rules, you need hot wash and optical sorting or you don’t have a product they can use.
Line Performance: What Good Looks Like
| Metric | Typical (1,000–2,000 kg/h line) |
|---|---|
| Throughput (real, not nameplate) | 800–1,700 kg/h |
| Water use (with recirculation) | 0.3–1.5 m³/ton |
| Energy use | 18–30 kWh/ton |
| Flake moisture after drying | <1–2% |
| PVC content (food grade) | <50 ppm |
| Final purity | 99.5%+ with optical sort |
Real throughput runs 60–80% of nameplate. Anyone quoting you “2,000 kg/h” on a machine spec’d at 2,000 kg/h is selling you the brochure, not the floor.
Mistakes That Kill PET Lines
Buying cold wash for food-grade ambition. You can’t add hot wash cheaply later. The heat exchanger, insulated tanks, and caustic dosing aren’t bolt-ons. Spec them upfront or replace the line.
Ignoring water treatment. A washing line without closed-loop water recirculation drinks 3+ m³ of water per ton and dumps contaminated wastewater. In most places that’s a permit violation within weeks. Budget 15–25% of line cost for water treatment. It pays back fast.
Undersizing the pre-sort. If contamination hits your hot washer, you’re cooking glue into flake instead of off it. Front-end sorting is cheaper than backend reprocessing. Always.
Matching machines by nameplate. A 2,000 kg/h shredder plus a 2,000 kg/h washer doesn’t make a 2,000 kg/h line. Size each stage 20–30% above target. Real lines run at 60–80% anyway.
FAQ
How much does a PET bottle washing line cost?
A basic cold-wash line at 1,000–2,000 kg/h runs $150,000–$300,000. Add hot wash, sink-float, and drying and you’re at $200,000–$400,000. Add optical sorting and closed-loop water treatment and the full food-grade line lands at $350,000–$600,000. Add 15–25% for water treatment and commissioning.
Can I start with cold wash and upgrade later?
Technically yes, practically no. Hot wash needs heat exchangers, insulated tanks, and caustic handling that cold-wash lines don’t have. Retrofitting costs more than building it in. If food grade is even a maybe in your plan, spec hot wash now.
Why does sink-float matter so much?
Because PET sinks and everything you don’t want (caps, rings, labels, most PVC) floats. One tank does more contamination removal than three manual sorters. Miss it and your flake carries polyolefin and PVC that kills its value.
What purity do I need for food-grade PET?
99.5% plus, PVC under 50 ppm, no glue or oil detectable. That’s the bottle-to-bottle bar. Below that you’re selling to fiber or strapping at a discount.
How long to install and commission?
Build 30–60 days, ship 15–45 days, install and commission 2–4 weeks with supplier support. Plan 3–4 months from order to first flake. Longer if customs or foundation work slips.
What Streamline Eco Tech Builds
We build PET bottle washing lines from 500 kg/h to 3,500 kg/h, modular so you can add hot wash, optical sorting, or water treatment as your market demands. Every line ships with closed-loop water recirculation as standard, not an upsell. Send us a bale sample and your target purity. We’ll run it, tell you what’s actually achievable, and quote the line that hits it. No brochure math.
More Questions
Do I need optical sorting on day one?
Only if you’re selling food grade from the start. If you’re supplying fiber or strapping first and moving up later, buy a line with the conveyor section and sensor ports ready for a sorter. Drop it in when the contract demands it. Don’t pay for it before you need it.
What’s the single most common failure?
Wrong feed assumption. A line built for clean post-industrial bottle scrap can’t handle baled post-consumer waste with labels, caps, and dirt. Know your actual feed before you buy the machine. Test it if you can.
How do I know if my flake is good enough?
Lab test it. Send a sample to a plastics lab for PVC content, moisture, and melt index. Don’t trust visual inspection. Flake that looks clean can still carry 200 ppm PVC and fail a food-grade buyer’s spec.