PET Bottle Washing Recycling Line (bottle-to-flake)

PET bottle washing recycling line (bottle-to-flake)

A PET bottle washing line has one job: take baled or loose post-consumer bottles that arrive wearing labels, caps, glue, sand and the occasional stone, and hand back clear flake that a fibre spinner, a sheet extruder or a bottle-to-bottle plant can actually run. Everything between those two points is contamination removal.

What makes PET harder than most polymers is that the buyer does not judge the flake by how clean it looks. They judge it by parts per million — of PVC, of PE and PP, of everything else — because a few hundred ppm of the wrong polymer is enough to yellow a melt or drop the intrinsic viscosity below spec. That is why this line runs twelve stages rather than four, and why several of them exist purely to remove one specific contaminant that nothing else on the line can touch.

The sequence below is the standard bottle-to-flake configuration, sized from 500 to 3,000 kg/h.

What this line runs on

The feed is post-consumer PET drink bottles, delivered either as wire-bound bales from a sorting facility or loose from a local collection round. Both work. What differs is how much work the front of the line has to do before crushing starts.

Baled feed arrives compacted, which is good for freight and bad for everything else: the bottles are locked together, and a bale breaker has to open them before a trommel screen can shake anything loose. Loose feed skips that problem but usually carries more tramp material — caps, stones, sand, the odd length of steel strapping — because it has not been through a baling press that sheds some of it on the way.

The contamination that decides the line configuration is not the dirt, it is the other polymers. Soil and dust come off in the wash. PVC bottles, PE caps and coloured bottles do not — they have to be physically identified and pulled out, which is why this line carries a sorting belt with metal detection ahead of the crusher and a sink-float tank behind it. Skip either one and the ppm figures at the end of the line stop being achievable.

Before

Three typical infeed conditions. Anything in this range goes on the conveyor; what changes is how hard the pre-treatment section has to work behind it.

After

Washed and dried PET flake as it leaves the hot-air dryer — clear and pale blue chips at 12–20 mm, below 1% moisture, with labels, caps and glue gone.

How the line is laid out

Material enters at the conveyor, moves through pre-treatment and sorting, then through crushing, then through three separate cleaning principles in sequence, then through two stages of water removal before it reaches the silo. The layout can be run straight or folded into a U, and the choice is usually made by the building rather than by the process.

A straight run is the easier line to operate: fewer transfer points, and wet flake hangs up at transfer points. A U-shape fits a shorter building and puts the infeed and the bagging station near each other, which matters if the same team covers both.

On site, the two halves of the line look quite different. The dry pre-treatment end is conveyors and rotating drums; the wet end is tanks, agitators and access platforms, and it is the half that decides where your drains and your water treatment have to go.

Line capacity and what each tier costs you

Five standard models, from 500 kg/h up to 3,000 kg/h. Input capacity is the number most buyers start from, but it is rarely the number that settles the purchase.

Two things are worth reading off that table before you pick a model. Installed power scales far slower than output — six times the throughput needs only about three and a third times the connected load, because the big motors on a PET line are sized for the material they can grip rather than the tonnes they pass. That is the good news.

Water does not behave the same way. Supply runs 4–5 m³/h on the BKL-500 and 20–30 m³/h on the BKL-3000, which tracks output almost one for one. A site on a limited water connection will hit that ceiling long before it hits any electrical limit, and no amount of recirculation removes the need for the flow itself.

Manpower is the third axis and the one most often underestimated. Even the smallest line needs 4–6 people and the largest needs 12–16 — and most of them are not operating machines. They are on the sorting belt, because no automated sorter yet matches a trained eye for pulling a PVC bottle out of a PET stream.

Water, power and the people the line needs

A PET washing line is a wet process, and water is the utility that most often decides whether a site can host one. Four stages draw on it: wet crushing in the granulator, the high speed friction washer, the flotation tank and the hot washer. Between them they need 4–5 m³/h at 500 kg/h and 20–30 m³/h at 3,000 kg/h.

That water leaves the line carrying three different loads, and each needs a different answer. The flotation tank sheds sunk plastics and grit. The hot washer sheds caustic solution at 1–3% concentration together with the oil and glue it has lifted off. The friction washers shed fine dirt and label fibre. Only the first of those is straightforward to settle out; the caustic circuit needs neutralising before discharge, and that has to be designed in before commissioning rather than bolted on after.

Power is more predictable: 150 kW installed on the BKL-500 rising to 500 kW on the BKL-3000. That is connected load, not measured draw. Actual consumption sits lower, because the crusher, the friction washers and the hot wash heating never peak at the same moment. Note that the hot washer itself can be heated by gas, diesel, petrol or LPG rather than electrically, which for many sites is the difference between an affordable electrical supply and an expensive one.

Key equipment, stage by stage

Twelve machines, in the order material passes through them, grouped into the four things the line actually does: get bottles in and open them up, take out what does not belong, cut what is left and wash it, then take the water back out.

Belt conveyor

Belt material is rubber, PVC or metal chain depending on where in the line it sits. Fitted with wheels for easy moving and a tightening device.

The wheels sound like a detail and are not. A washing line gets re-arranged more often than anyone expects in the first two years, and a conveyor that can be rolled to a new position is the difference between an afternoon and a shutdown.

Bale breaker (opener)

Opens the tight bales of PET bottles.

Nothing downstream can work on a bale. The trommel cannot shake sand out of compressed bottles, the sorting belt cannot present them one layer deep, and the label remover needs individual bottles to rub against each other. This machine exists so that every stage after it sees loose material.

Trommel screen (rotary-drum separator)

Separates stones, caps, sand and any other possible contaminants off the bottle stream.

This is the cheapest contamination removal on the whole line, and it protects the most expensive parts of it. Every stone that leaves here is a stone that never reaches the crusher knives.

Label remover

A dry friction system that removes 80–90% of labels and caps before crushing.

Note the word dry, and note the word before. Taking labels off while the bottles are still whole means the label material leaves as recognisable sheets that are easy to collect. Crush first and the same labels become flakes the same size as the PET flakes, and separating them afterwards is a far harder job.

Sorting belt with metal detector

Removes non-PET materials — PVC, metals and coloured bottles. The metal detector finds and removes metal fragments before they can reach the crusher chamber.

This is the stage that protects both the product and the machine. PVC pulled out here never gets a chance to contaminate the flake; metal pulled out here never gets a chance to destroy a set of knives.

Granulator / crusher with force feeder

Grinds PET bottles to 12–20 mm flakes. Improved knife structure for higher output, running as a wet crusher.

Crushing under water does two jobs at once: it sizes the material, and the water immediately carries away the dust and grit that crushing releases — grit that would otherwise ride downstream embedded in the flake.

High speed friction washer

Removes stubborn contaminants by friction scrubbing combined with flushing water.

Flotation washing tank (sink-float tank)

Gravity and density separation. PET sinks; PVC and PE do not behave the same way, and the difference is what pulls them out of the stream.

This is the only stage on the line that separates by density rather than by force, and it is the one that decides the PVC and PE/PP figures on the final flake spec. Nothing downstream can do this job, and no amount of extra washing substitutes for it.

Hot washing machine / steam washer

Runs at 85–95 °C with 1–3% detergent or soda concentration, using mechanical agitation for deep cleaning. Removes surface dirt, oil and glue, including the adhesives that hold labels on. Heated by gas, diesel, petrol or LPG.

Hot caustic wash is what separates a PET line from a general plastics line. Bottle label adhesive is designed to survive rain, refrigeration and handling; cold water and friction will not shift it. The 85–95 °C window matters in both directions — too cool and the glue stays, too hot and PET flake starts to soften and clump.

Horizontal dewatering machine (dehydrator / centrifugal dryer)

Runs at 1500 RPM and brings moisture down to 0.5–2%. It appears twice on the line: once in the middle, to strip the alkaline liquid off the flake after hot washing, and once at the end, to remove surface water before final drying.

The mid-line unit is the one people forget to budget for, and it is arguably the more important of the two. Carrying caustic solution forward into the rinse stages means diluting it with clean water instead of removing it mechanically — which costs water, and leaves residue on the flake.

Hot-air dryer

Electrically heated, bringing final moisture below 1%.

Centrifuging throws off free water. What it cannot reach is the moisture held in the cupped and folded shapes that bottle wall flake naturally forms. That is the gap this stage closes, and it is the difference between flake that ships and flake that grows mould in a bulk bag.

Zig-zag label separator with rotary valve (air classifier)

Further removal of labels and dust, using air rather than water or friction.

This is the second label removal stage, and it exists because the first one is only 80–90% effective. Whatever survived the dry friction stage arrives here as light fragments among heavy flake, and a rising air stream sorts them by weight in a way that no wet stage can.

Electrical control cabinet

Controls and monitors the whole PET bottle washing line from one point.

On a twelve-stage line, single-point control is not a convenience feature. Stages have to be started and stopped in sequence, and an operator who has to walk the line to shut down a blocked crusher will flood the section behind it before they get there.

What comes out, and where it goes

The line produces one product: clean PET flake. What varies is how clean, and the specification below is what the standard configuration reaches on typical post-consumer feed.

Read that specification from the bottom up. Particle size and moisture are set by the machines — the crusher screen decides one, the dryer decides the other, and both are repeatable. The three impurity figures are different: they are set by how well the sorting belt and the flotation tank did their jobs, and they move with the incoming material. Real quality data depends on the real material situation as well, and any supplier who quotes ppm figures without asking what your feedstock looks like is quoting a brochure rather than a result.

Where the flake goes from there falls into three markets. Textiles take the largest share, drawn into polyester fibre for clothing and carpet. Packaging takes it as strapping, sheet and non-food containers. Industrial users take it into automotive parts and construction materials.

Those three routes have different tolerances, and that is worth knowing before you size the line. Fibre spinning is the least forgiving of PVC contamination and the most forgiving of colour. Sheet extrusion is the reverse. Customers can run this line to produce flake for sale, for drawing filament, for pelletising into PET granules, or for blowing new bottles — the machinery is the same, the acceptance limits are not.

See the line running

Models & specification

Final PET flake quality: final moisture < 1-2%; total impurity < 200ppm; PVC content < 100ppm; PE/PP content < 100ppm; particle size < 14-16mm. Final products real quality data is up to the real material situation, too.

Frequently asked questions