How to open recycled plastic granulation compound factory using twin screw extruder

How to open recycled plastic granulation compound factory using twin screw extruder

Feasibility first: the four gates every project must pass

Opening a recycled plastic granulation compound factory using a twin screw extruder is not primarily a machine-buying decision. It is a feasibility decision about feedstock, a positioning decision about which pellet grades you will sell, a facility decision about power, water and permits, and only then an equipment decision. Projects that fail almost never fail because the extruder was wrong. They fail because the feedstock supply dried up, because the target grade could not meet the buyer’s acceptance specification, or because the site could not legally or physically support the process. This guide walks through the whole build sequence in the order an experienced project engineer would tackle it.

Kerke, a Wanplas factory, has spent more than 12 years designing, manufacturing and commissioning parallel co-rotating twin screw compounding extruders. From a 19,997+ square meter plant, with more than 2,000 machines running in over 70 countries and a technical team of 100+ specialists, Kerke has supported masterbatch producers, engineering compounders and recycled-pellet plants through exactly this build sequence. Recognized as a top-five twin screw extruder supplier in China, the factory works to a single stated principle: “We Know Compounding Extruder.” That accumulated project experience is the backbone of the planning framework below.

Before any layout drawing is produced, force the project through four gates. Each gate is a question with a hard pass condition. If a gate fails, the correct action is to change the plan, not to buy a bigger machine and hope the problem disappears downstream.

Gate	Core question	Pass condition	Red flag that should stop the project
1. Feedstock security	Can I secure a consistent tonnage of one or two dominant waste streams for at least 12 months?	Two or more independent suppliers can each cover 40 percent or more of monthly demand, with a documented grade description	Supply depends on a single collector, or the material description changes every delivery
2. Product definition	Do I know exactly which pellet grade I sell, and against which acceptance indicators?	Written target specification covering melt flow rate window, ash, moisture, mechanical minimums, color tolerance and odor level	Plan is “make recycled pellets and find buyers later”
3. Site and utilities	Can the site legally and physically carry the process, the load and the emissions?	Confirmed three-phase capacity, water circulation, waste water route, exhaust treatment path and fire compartment plan	Transformer capacity below installed demand, or no permitted discharge route for washing effluent
4. Process and machine fit	Does the chosen process route actually convert my feedstock into my product specification?	Trial run on the real feedstock produces pellets that meet the target specification at rated output	Configuration selected from a catalog without a sample trial on actual material

Gate four deserves special emphasis, because it is the gate that a machinery partner can help you close before capital is committed. Recycled feedstock is heterogeneous by nature: bulk density varies bale to bale, residual moisture varies with weather, contamination varies with the collection region, and additive history is unknown. A configuration that is perfect for virgin compounding may starve, surge or degrade on the same nominal resin in recycled form. The only reliable way to close gate four is to send real material and run it on a real machine, which is why sample trial runs are a standard part of the Kerke pre-order workflow rather than an optional extra.

A second point about sequencing: decide your product grade before you decide your capacity, and decide your capacity before you decide your building. Many first-time operators do the reverse, renting a building first and then discovering that the roof height will not accept a strand pelletizing platform, or that the available transformer will not carry a 315 kW main drive plus auxiliaries. Correcting a building decision after the lease is signed is far more expensive than correcting a machine decision before the order is placed.

Defining your product: which recycled grades to target

The single most profitable decision in a recycled granulation business is choosing the right grade to make. Plain washed regrind pelletized without modification competes on price alone. Compounded recycled grades, where the twin screw extruder adds fillers, impact modifiers, compatibilizers, stabilizers or color, sell into a technical specification and hold a much stronger position. The twin screw extruder is what makes the second business model possible; a single-screw remelting line is structurally limited to the first.

Below is a positioning table of the main recycled streams, with the technical characteristics that determine whether you can serve them and the acceptance indicators that downstream buyers will actually test on arrival.

Target grade	Typical feedstock	Key downstream buyers	Critical acceptance indicators	Technical difficulty
Recycled PP pellet, natural or gray	Post-industrial PP scrap, woven bags, rigid PP packaging, automotive bumper regrind	Injection molders of crates, housewares, pails; pipe and profile extruders	Melt flow rate window, ash content, notched impact, odor grade, black speck count	Low to Medium
Recycled LDPE / LLDPE film pellet	Post-consumer and post-industrial film, agricultural film, liners	Film blowing plants, garbage bag makers, drip irrigation pipe	Melt flow rate, gel count, moisture, tensile at break, color consistency	Medium (low bulk density, high volatile load)
Recycled HDPE pellet	Bottle regrind, drum and crate regrind, pipe scrap	Pipe extrusion, blow molding of non-food containers, injection molding	Melt flow rate, density, environmental stress crack resistance, ash	Low to Medium
Filled PP or PE compound (CaCO3, talc)	Recycled polyolefin plus mineral filler at 20 to 70 percent	Injection molders, sheet and board extruders, building products	Filler loading accuracy, dispersion quality, flexural modulus, ash, density	Medium to High (abrasive, needs side feeding)
R-PET flake compounding and re-pelletizing	Washed PET bottle flake, PET thermoform trim, fiber-grade scrap	Strapping, fiber, sheet, engineering compound producers	Intrinsic viscosity, moisture below 50 ppm, acetaldehyde, color b-value, dust	High (crystallizing, drying, hydrolysis control)
Recycled ABS and PS compound	Appliance and electronics housings, sheet trim, toy scrap	Appliance parts, consumer goods, sheet extrusion	Notched impact, Vicat softening temperature, color delta E, flame retardancy where declared	Medium to High (color and impact recovery)
Recycled PA6 / PA66 compound	Fiber waste, industrial scrap, glass-fiber reinforced part regrind	Automotive under-hood parts, electrical components, cable ties	Moisture, relative viscosity, tensile strength, glass content, heat deflection temperature	High (hygroscopic, needs strict drying and devolatilization)
Recycled PVC compound	Profile and pipe scrap, cable insulation scrap	Profile extrusion, footwear, floor and sheet products	Thermal stability time, plasticizer content, hardness, color hold	High (thermal degradation and corrosion risk)

Read that table as a strategy map, not a menu. A new plant should launch with one dominant stream and one adjacent stream, not with seven. The dominant stream builds operator competence, formula stability and buyer trust; the adjacent stream absorbs feedstock fluctuation. Adding a third and fourth stream is a year-two decision, and it is far easier if the extruder was specified with a modular barrel and an interchangeable screw element system from the beginning, so that changing configuration is a shift-length job instead of a machine replacement.

Note also the difference between a specification you publish and a specification you can hold. A buyer’s purchase order will state a melt flow rate window such as 8 to 12 g/10 min, and your process must land inside that window batch after batch. Recycled feedstock will not do that by itself. Holding a window requires incoming batch testing, blending of feedstock lots to average out variation, loss-in-weight feeding accuracy, and a stable thermal profile in the extruder. Every one of those four is a design requirement that must be built into the plant, not a habit that can be added later.

Feedstock supply radius, stability and screening discipline

Feedstock economics in recycling are dominated by transport and by contamination, and both are functions of distance. Waste plastic has low bulk density, so a truck fills by volume long before it fills by weight. That single physical fact means the practical collection radius for loose film or unbaled rigid scrap is far shorter than most business plans assume, unless baling or pre-shredding happens at the source.

Supply radius band	Practical feedstock forms	Logistics burden	Supply stability risk	Recommended action
Within 50 km	Loose rigid scrap, unbaled film, factory trim, in-house scrap	Low	Low if multiple sources exist	Anchor the plant here; sign annual offtake with two or more collectors
50 to 150 km	Baled film, baled bottles, washed flake, densified agglomerate	Medium	Medium; seasonal for agricultural film	Require baling at source; set minimum bale density in the purchase agreement
150 to 400 km	Washed and dried flake, agglomerate, sorted regrind only	High	Medium to High; price-driven diversion to other buyers	Buy only pre-processed material; specify moisture and contamination limits per lot
Beyond 400 km	Washed flake and pellet-grade intermediates only	Very High	High	Treat as a buffer source for peak demand, never as the base load

Once the radius is set, the second discipline is incoming screening. Contamination that reaches the melt stage costs far more to remove than contamination rejected at the gate. A practical incoming control routine has five checks that a trained receiving operator can perform in under fifteen minutes per load: visual grade verification against a retained reference sample, a sink-float or density check on a representative handful, a moisture reading on the flake, a metal detection pass, and a small-scale melt test on a laboratory extruder or melt flow rate tester to confirm the resin identity and rough viscosity band.

Metal is the highest-consequence contaminant because it damages screw elements, barrel liners and cutting tools. A recycled granulation plant should carry magnetic separation ahead of the crusher, a second magnet plus an all-metal detector on the conveyor feeding the extruder hopper, and, for streams with a history of embedded metal, an eddy current separator. This layered approach is standard practice; skipping it to save on the initial installation reliably costs more in wear parts within the first year.

Non-metallic contaminants matter in a different way. Paper, wood and label residue char and appear as black specks; sand and grit accelerate wear; cross-polymer contamination such as PP in a PET stream forms unmelted inclusions; and PVC in a polyolefin stream releases hydrogen chloride at compounding temperature, corroding tooling and degrading the batch. A written incoming acceptance limit for each of these, tied to a rejection right in the purchase agreement, is the cheapest quality tool a recycling plant owns.

Site selection, building envelope and utility planning

The building has to hold three things: the process line, the feedstock inventory, and the finished-goods inventory. Most first-time operators size the building for the line and then find that raw material bales consume the aisle space. A workable planning ratio is roughly one third of the floor area for the process line and its auxiliaries, one third for incoming feedstock, and one third for finished pellets, quality laboratory, workshop and offices.

Line capacity tier	Total building area	Clear height	Floor loading	Installed three-phase capacity	Cooling water circulation
100 to 200 kg/h (pilot / niche compound)	400 to 600 m²	5.0 to 5.5 m	1.0 to 1.5 t/m²	120 to 200 kW	10 to 18 m³/h
300 to 500 kg/h (entry commercial)	800 to 1,200 m²	6.0 to 7.0 m	1.5 to 2.0 t/m²	350 to 500 kW	25 to 45 m³/h
600 to 900 kg/h (mid-scale)	1,400 to 2,000 m²	7.0 to 8.0 m	2.0 t/m²	550 to 850 kW	45 to 70 m³/h
1,000 to 1,500 kg/h (industrial)	2,000 to 3,000 m²	8.0 m	2.0 to 2.5 t/m²	900 to 1,300 kW	70 to 110 m³/h
2,000 kg/h and above (large scale)	3,500 to 5,500 m²	9.0 to 10.0 m	2.5 t/m²	1,600 to 2,400 kW	120 to 190 m³/h

Treat the installed capacity figures as planning envelopes that include the main drive, barrel heating, vacuum pumps, feeders, pelletizer, dryer, chiller and cooling tower, air compressor, conveying blowers and lighting, with a reserve margin. Actual running demand is normally 55 to 70 percent of installed capacity, because barrel heaters draw heavily at start-up and then cycle at a fraction of rated power once the melt is generating shear heat. Sizing the transformer to running demand instead of installed demand is one of the most common and most disruptive planning errors, because it shows up only during the first cold start of a full line.

Clear height matters more than plan area for certain layouts. Strand pelletizing with an elevated water bath, gravimetric feeders mounted on a platform above the feed throat, and silo or big-bag discharge stations all consume vertical space. If the twin screw extruder is fed from loss-in-weight feeders on a mezzanine, plan 3.5 to 4.5 meters of clear space above the feed throat, and confirm crane hook height for screw and barrel removal. Screw shafts on a large machine can be several meters long; the maintenance aisle must allow the shaft to be withdrawn axially without dismantling the surrounding structure.

Water, air and exhaust

Cooling water serves the barrel cooling circuits, the gearbox oil cooler, the pelletizer water loop, the vacuum system, and the chiller condensers. A closed circuit with a cooling tower plus a plate heat exchanger is the standard arrangement, with a separate chilled loop where pellet quality demands tighter water temperature. Pelletizing water carries fines, so the loop needs a settling tank and a filtration stage; without it, fines circulate and abrade pump seals and spray nozzles.

Compressed air is needed for pneumatic conveying assists, screen changer actuation, vibrating screen operation, valve control and cleaning. A 300 to 500 kg/h line typically calls for a 15 to 22 kW screw compressor with a receiver and a refrigerated dryer; larger lines scale roughly in proportion. Process exhaust deserves careful attention. Devolatilization vents pull moisture, low-molecular volatiles, and odor compounds out of the melt. The vacuum discharge must go to a condenser and then to an exhaust treatment stage, which is typically a water scrubber followed by activated carbon adsorption for odor control, sized to the permitted emission limits of the jurisdiction.

Waste water, solid waste and fire compartments

If the plant includes a washing stage, waste water is the single largest compliance topic. Washing effluent carries suspended solids, residual detergent, and organic load, and it requires a treatment train, typically screening, dissolved air flotation, coagulation and sedimentation, followed by biological or membrane polishing depending on the discharge standard. Sludge from that train, together with spent melt filter screens and the caked residue from the screen changer, is normally classified as controlled industrial waste and must be handled by a licensed contractor with documented manifests.

Fire protection design is driven by the storage areas rather than the machinery. Baled plastic is a high-calorific-value fuel with a large surface area, so the feedstock yard is usually placed in a separate fire compartment, physically separated from the process hall, with limited pile heights, defined aisle widths, and appropriate detection and suppression. Finished pellets in big bags carry a lower but still significant load. Local codes govern the details; the planning point is that the fire strategy influences the site layout from the first sketch and cannot be retrofitted cheaply.

Process route design: from bale to bagged pellet

A recycled granulation compound plant is a sequence of unit operations, and each one exists to protect the operation downstream of it. Sorting protects the crusher, washing protects the dryer, drying protects the melt, devolatilization protects the pellet, filtration protects the die, and screening protects the customer. Understanding the process as a chain of protections makes it obvious why cutting one stage to save on the initial build tends to reappear as a quality or maintenance problem later.

The canonical route for post-consumer or post-industrial plastic into a compounded pellet runs: sorting and metal removal, crushing, washing, dewatering and drying, metered feeding, twin screw melting and mixing, vacuum devolatilization, melt filtration through a screen changer, pelletizing, vibrating screen classification, homogenizing in a blending silo, and packing. The table below sets out each step with its function, the parameters that must be controlled, and the failure mode that appears when control is lost.

Step	Equipment	Function	Key control parameters	Common problem when out of control
1. Sorting and inspection	Sorting belt, magnetic separator, metal detector, optional eddy current and color sorter	Remove metal, cross-polymer, wood, paper, oversize contaminants	Belt speed, staffing per meter of belt, detector sensitivity, reject rate log	Metal reaches the screw; black specks and unmelted inclusions in the pellet
2. Size reduction	Shredder for bulky items, crusher or granulator with screen	Reduce to a uniform flake size that conveys and feeds consistently	Screen aperture 8 to 16 mm typical, rotor speed, blade clearance 0.2 to 0.5 mm	Excessive fines, blade heat, feed surging into the extruder
3. Washing	Pre-wash tank, friction washer, hot wash tank, float-sink separation tank	Remove dirt, oil, label adhesive, and separate resins by density	Water temperature 60 to 85 degrees Celsius for hot wash, detergent dosing, residence time, water renewal rate	Residual adhesive causes gels and odor; poor density split leaves cross-polymer
4. Dewatering and drying	Centrifugal dewatering machine, thermal dryer, dehumidifying dryer for hygroscopic resins	Bring surface and bound moisture down to the level the melt stage tolerates	Centrifuge speed, air temperature, residence time, outlet moisture measurement	Steam in the melt, porous strands, hydrolytic chain scission in PET and PA
5. Metered feeding	Loss-in-weight feeder, volumetric feeder, side feeder, crammer feeder, liquid feeder	Deliver the formula at accurate and constant mass rate into the process section	Feeder calibration, refill logic, hopper bridging control, feed rate stability within plus or minus 1 percent	Formula drift, melt flow rate scatter, torque surging, motor trips
6. Melting and mixing	Co-rotating parallel twin screw extruder with segmented barrel and modular screw	Convey, melt, disperse, distribute, homogenize and build pressure	Barrel zone temperatures, screw speed, specific energy input, torque percentage, melt temperature	Degradation, poor dispersion, unmelted particles, color shift
7. Devolatilization	Atmospheric vent plus one or two vacuum vents with condenser and vacuum pump	Strip moisture, monomer, solvent residue and odor compounds from the melt	Vacuum level typically minus 0.06 to minus 0.095 MPa, vent depth, melt seal integrity	Vent flooding, porous pellets, odor complaints, foaming at the die
8. Melt filtration	Double-station or continuous screen changer, or laser-drilled continuous filter for heavy contamination	Capture char, gel, sand, paper residue and unmelted particles	Screen mesh 40 to 200 depending on grade, pressure differential trigger, changeover interval	Pressure spikes, die freeze, contamination carried into the pellet
9. Melt pressure stabilization	Gear-type melt pump with closed-loop control	Decouple die pressure from extruder surging; stabilize output	Inlet pressure setpoint, pump speed ratio, differential pressure limit	Strand diameter variation, pellet length scatter, throughput drift
10. Pelletizing	Strand pelletizing, water-ring die-face hot cutting, underwater pelletizing, air-cooled die-face cutting	Convert melt into a defined pellet geometry and cool it	Water temperature, cutter speed, blade clearance, strand tension, die hole layout	Tails and fines, twins, irregular length, strand breakage
11. Classification	Vibrating screen with oversize and fines decks, optional dedusting	Remove agglomerates, twins, tails and dust	Deck aperture, amplitude, feed distribution, reject collection	Customer complaints on fines and off-spec pellet geometry
12. Homogenizing	Blending silo or batch mixer with recirculation	Average out batch-to-batch variation before packing	Silo volume relative to hourly output, blend cycles, sampling point	Lot-to-lot melt flow rate and color variation reaching the buyer
13. Packing and traceability	Big-bag or 25 kg bag station with weighing and sealing, lot labeling	Package to the buyer’s requirement with lot identity retained	Weighing accuracy, moisture barrier, lot number linkage to production log and retained sample	No traceability when a complaint arrives; disputes cannot be resolved

Note that steps one to four are upstream preparation. Many granulation plants begin by buying washed flake from an external supplier and installing only steps five to thirteen, then integrate washing later once the volume justifies it. That staged approach is sound: it lowers the initial complexity, shortens commissioning, and lets the team build competence on the melt side before taking on effluent treatment. When the washing stage is added, Wanplas supplies matched washing and drying lines that feed directly into Kerke pelletizing systems, so the upstream and downstream sections share a single control philosophy and a single service contact.

Whichever route is chosen, insist on buffer capacity between stages. A surge hopper between the dryer and the feeders, and a blending silo between the pelletizer and packing, absorb the small stoppages that are inevitable in a recycling plant. Without buffers, one blocked chute stops the entire line, and a plant that stops six times per shift will never reach its nameplate output no matter how good the extruder is.

Twin screw extruder fundamentals for recycled compounding

The co-rotating parallel twin screw extruder is the standard compounding machine because it separates two functions that a single screw must combine: conveying and mixing. In a single-screw extruder, output and mixing are both driven by drag flow in one channel, so improving one degrades the other. In a co-rotating twin screw extruder, the intermeshing screws convey positively while the kneading sections apply controlled shear, which means throughput can be set independently by the feeder and the mixing intensity can be set independently by the screw configuration and screw speed.

Three characteristics make this architecture particularly suited to recycled feedstock. First, the machine is starve-fed: material enters at a rate set by the feeder, not by the screw, so a low bulk density flake such as film regrind can be accepted without the flood-feeding surges that plague single-screw remelting. Second, the intermeshing geometry is self-wiping, so the screw flights continuously clean each other, which limits stagnation zones where degraded material would otherwise accumulate and later release as black specks. Third, the barrel is segmented and the screw is modular, so vent ports, side feed ports, and liquid injection ports can be placed exactly where the process needs them and moved later when the product mix changes.

Characteristic	Single-screw extruder	Co-rotating parallel twin screw extruder	Consequence for recycled granulation
Feeding mode	Flood fed from hopper	Starve fed by loss-in-weight or volumetric feeder	Low bulk density film and fluffy regrind can be metered reliably
Output versus mixing	Coupled; raising output reduces mixing time	Decoupled; screw speed and feed rate set independently	Dispersion quality can be held while throughput changes
Self-cleaning	Limited; stagnation zones common	Intermeshing self-wiping profile	Fewer black specks; faster color changeover
Devolatilization	One vent, limited surface renewal	Multiple vents with strong surface renewal in the melt	Moisture, odor and volatiles removed effectively
Additive and filler addition	Pre-blend only	Main feed, side feed, downstream feed, liquid injection	High filler loading and heat-sensitive additives handled properly
Configuration flexibility	Fixed screw geometry	Modular elements on splined shafts	One machine serves many recipes across the product roadmap
Typical role in a recycling plant	Plain remelting of clean, single-resin scrap	Compounding, modification, filling, devolatilizing, upgrading	Determines whether the plant sells commodity regrind or specification compound

Kerke’s screw assemblies are computer-aided designed with a kneading co-type geometry that provides an excellent self-cleaning function and good interchangeability between elements. In practical terms the screw is engineered to realize seven distinct duties along its length: material transport, plasticizing, shearing, dispersion, homogenization, exhaust, and pressure building. Understanding which section of the screw performs which duty is the key to configuring a machine for a specific recycled stream rather than accepting a generic layout.

Screw configuration, L/D and specific torque class

Three specification decisions determine whether a twin screw extruder will succeed on your feedstock: the length-to-diameter ratio, the specific torque class, and the screw element arrangement. These are more important than nominal screw diameter, because diameter mainly sets the size band while these three set the capability inside that band.

Choosing the L/D ratio

L/D is the ratio of the process length to the screw diameter. It defines how much residence time and how many functional zones are available. More length means more room for melting, mixing, side feeding and vacuum devolatilization, but it also means more thermal history and more specific energy input, which matters for heat-sensitive recycled material.

L/D range	Typical zone layout	Best suited to	Cautions
28 to 32	Feed, melt, one atmospheric vent, pressure build	Clean single-resin regrind pelletizing, PVC compounding where heat history must be minimized	Little room for side feed or deep vacuum; limited mixing length
32 to 36	Feed, melt, mixing, one vacuum vent, pressure build	Standard recycled PP and PE pelletizing with moderate volatile load	Marginal for high filler loading or twin vacuum layouts
36 to 40	Feed, melt, side feed, mixing, vacuum vent, homogenizing, pressure build	Filled recycled compounds up to about 50 percent filler; color and additive compounding	Requires a properly designed melt seal ahead of the vent
40 to 44	Feed, melt, first vent, side feed, mixing, second vacuum vent, homogenizing, pressure build	Post-consumer film with high volatile load, glass-fiber reinforced recycled compounds, two-stage filler addition	Higher installed power; specific energy must be managed by screw speed control
44 to 48	Extended mixing with multiple side feeds and twin deep vacuum vents	Reactive extrusion, chain extension of R-PET, very high filler loading above 60 percent, heavily contaminated post-consumer streams	Longest thermal history; not appropriate for thermally fragile formulas

Specific torque and why it defines the machine class

Specific torque, expressed in newton meters per cubic centimeter (Nm/cm³), normalizes the torque a gearbox can transmit against the free volume of the screw. It is the honest way to compare two extruders of the same nominal diameter, because it tells you how much work the machine can do per unit of material inside it. Higher specific torque means the machine can process a higher-viscosity or higher-filler formula at a given screw speed, or reach a target output at a lower screw speed and therefore with less shear heating.

Specific torque class	Indicative range	Typical application	Behavior on recycled feedstock
Standard	About 5 to 7 Nm/cm³	Low-viscosity masterbatch, simple pelletizing	Adequate for clean polyolefin regrind; struggles when filler loading rises
High	About 8 to 9 Nm/cm³	General compounding, filled polyolefins, recycled engineering plastic	Good headroom against feedstock viscosity swings; the common choice for recycling plants
Very high	About 10 to 12 Nm/cm³	High filler loading, glass-fiber reinforced compound, high-viscosity engineering resin	Allows low-speed high-torque operation, which protects heat-sensitive recycled material

For a recycled granulation plant the practical guidance is to specify a high or very high torque class even if the launch formula does not demand it. Recycled feedstock viscosity drifts upward when the input contains more heavily degraded or more heavily filled material than expected, and a machine running at 95 percent torque has no room to absorb that drift. A machine that normally runs at 60 to 75 percent torque has both a stability reserve and a route to higher output later.

Screw element strategy

The screw is assembled from elements on splined shafts, and the arrangement is what converts a generic machine into a process-specific one. The main element families and their duties are as follows.

• Conveying elements — forward-flighted elements of varying pitch. Long pitch in the feed zone maximizes intake for low bulk density flake; shorter pitch downstream builds fill level and pressure. These elements transport material and set residence time distribution.
• Kneading blocks at 30 and 45 degrees (KB45) — moderate offset angle, forward-conveying, primarily distributive with useful dispersive action. The workhorse element for melting and for blending additives without excessive shear heating.
• Kneading blocks at 60 degrees (KB60) — higher offset, longer residence, stronger dispersive shear. Used where pigment agglomerates or filler clusters must be broken down.
• Kneading blocks at 90 degrees (KB90) — neutral conveying, maximum residence and shear intensity, and an effective melt seal. Used for the hardest dispersion tasks and to seal ahead of a vacuum vent.
• Reverse-flighted elements and reverse kneading blocks — deliberately restrict flow, raising fill level and pressure locally. They create a strong melt seal before a vacuum port, and they force a fully filled zone where dispersion must be guaranteed.
• Toothed mixing and gear-type elements — high distributive efficiency at low shear, valuable for heat-sensitive recycled compounds and for late-stage color homogenization.
• Discharge elements — short-pitch conveying to build stable pressure into the screen changer, melt pump and die.

A typical configuration for post-consumer polyolefin film at 40 L/D reads as follows: long-pitch conveying at the feed throat for intake, a first melting block combining KB45 and KB60, a conveying stretch to relieve pressure at the first atmospheric vent, a side feed port for filler introduction, a second mixing block dominated by KB45 with a short reverse element to guarantee fill, a KB90 melt seal, a deep vacuum vent, a distributive toothed section for final homogenization, and short-pitch discharge elements. For a high-filler recycled compound, the mixing block after the side feed is strengthened and the reverse element lengthened; for a thermally fragile stream, dispersive blocks are shortened and toothed distributive elements are substituted.

Devolatilization, melt filtration and pressure stabilization

Three subsystems determine whether the pellets leaving your plant look and behave like a specification product or like reprocessed waste: the vacuum devolatilization section, the melt filtration system, and the melt pump. They are also the three subsystems most often under-specified in a first-time plant.

Vacuum devolatilization

Recycled feedstock carries moisture from washing, absorbed water in hygroscopic resins, residual printing ink solvent, adhesive residue from labels, degradation products, and the odor compounds absorbed during the material’s first life. All of these must be removed while the polymer is molten, because that is the only stage where the volatiles can diffuse to a free surface and be extracted.

A two-vent layout is the standard for post-consumer material. The first vent, placed shortly after the melting section, operates at atmospheric pressure or under light vacuum and removes the bulk of the water vapor and air. The second vent, placed after the mixing section, operates under deep vacuum, typically in the range of minus 0.06 to minus 0.095 MPa, and removes the residual moisture and the low-molecular volatiles that carry odor. Between the mixing section and the vacuum port, a melt seal formed by reverse elements or a KB90 block prevents vacuum from pulling melt backward and flooding the vent.

Practical design points that separate a working vacuum section from a troublesome one: use a generously sized vent insert so the vapor has cross-sectional area to escape; fit a water-cooled condenser between the vent and the vacuum pump so condensable vapor does not reach the pump; select a liquid ring pump or a dry pump appropriate to the vapor load; and provide a vent stuffer or wiper on streams that tend to push melt into the port. Odor grading is increasingly a purchase specification for recycled pellets used in consumer goods, and vacuum performance is the primary lever on it.

Melt filtration and screen changing

Melt filtration is where the contamination that survived sorting and washing is finally removed. The selection question is how much contamination the stream carries and how much production interruption the plant can tolerate.

Filtration option	Working principle	Contamination tolerance	Production interruption	Best fit
Manual plate screen changer	Single screen pack, manual slide change	Low	Line stop for every change	Clean post-industrial scrap, laboratory and pilot lines
Hydraulic double-station screen changer	Two screen cavities; one filters while the other is serviced	Low to Medium	Brief pressure disturbance at changeover	Most recycled polyolefin and engineering compound lines
Continuous backflush screen changer	Screen segments cleaned by reverse melt flow without stopping	Medium to High	Effectively none	Post-consumer film and mixed rigid streams running long campaigns
Laser-drilled continuous rotary filter	Rotating perforated drum with continuous scraping and discharge of contaminant	High to Very High	None; contaminant discharged automatically	Heavily contaminated post-consumer material, paper and wood residue

Mesh selection follows the product. A coarse 40 to 60 mesh pack suits filled compounds and construction-grade pellets; 80 to 120 mesh is common for general-purpose recycled polyolefin; 150 to 200 mesh or finer is used where surface quality matters, such as film-grade or fiber-grade recycled material. Finer screens raise the pressure differential and shorten the interval between changes, so the plant must balance cleanliness against interruption. A pressure transducer before and after the screen, with a logged differential trend, converts screen changing from a guess into a scheduled maintenance task.

Melt pump and pressure stabilization

A gear-type melt pump installed between the screen changer and the die decouples die pressure from upstream fluctuation. In a recycling plant this matters more than in a virgin compounding plant, because feed density variation causes torque and pressure to oscillate. Without a pump, that oscillation shows up as strand diameter variation and pellet length scatter. With a pump under closed-loop control on inlet pressure, the die sees a near-constant flow, strand diameter stabilizes, pellet geometry tightens, and the extruder can often be run at a lower head pressure, which reduces specific energy and melt temperature.

The pump also enables a useful operating strategy: the extruder is optimized purely for mixing quality while the pump takes responsibility for pressure generation. That division of labor allows a shorter, lower-shear discharge section on the screw, which protects heat-sensitive recycled polymers from the extra thermal input that pressure building would otherwise impose.

Process adaptation by recycled resin stream

No single machine setting serves all recycled streams. Each polymer family brings a different combination of thermal sensitivity, moisture behavior, viscosity and contamination profile, and the twin screw extruder must be configured accordingly. The table below summarizes the practical adaptation for the streams most commonly processed in a recycled granulation compound plant.

Recycled stream	Screw configuration emphasis	Barrel temperature profile	Vacuum requirement	Drying requirement	Output correction factor
PP / PE film regrind (post-consumer)	Long-pitch intake, crammer or side feeder for low bulk density, moderate KB45 melting, distributive finish	170 to 230 degrees Celsius rising then flat	One atmospheric plus one deep vacuum vent	Mechanical dewatering plus hot air drying to below 0.3 percent	0.55 to 0.75 of the rated polyolefin output, limited by intake volume
Rigid PP / HDPE regrind	Standard melting block, single vacuum vent, short discharge	180 to 235 degrees Celsius	One vacuum vent at minus 0.06 to minus 0.08 MPa	Surface moisture removal only, below 0.5 percent	0.90 to 1.00 of rated output
Filled PP / PE compound (CaCO3 or talc, 20 to 70 percent)	Side feeder for filler, strong KB45 and KB60 dispersion block, reverse element for fill, wear-resistant elements	170 to 220 degrees Celsius, lowered late to limit shear heat	One deep vacuum vent after the filler mixing zone	Filler pre-dried; polymer surface dry	1.10 to 1.35 of the unfilled rate on a mass basis due to filler density
R-PET bottle flake	Low-shear melting, minimal dispersive blocks, twin deep vacuum, optional chain extender via side feed	255 to 285 degrees Celsius, tightly controlled	Two vents, second at minus 0.09 to minus 0.095 MPa	Crystallizing dryer then dehumidifying dryer, dew point about minus 40 degrees Celsius, moisture below 50 ppm	0.75 to 0.90 of polyolefin rated output
Recycled ABS / PS	Moderate dispersion, careful color homogenization, toothed distributive elements late	190 to 240 degrees Celsius for ABS; 180 to 220 for PS	One deep vacuum vent for residual styrene and moisture	Dehumidifying dryer, moisture below 0.05 percent for ABS	0.80 to 0.95 of rated output
Recycled PA6 / PA66, including glass-fiber reinforced	Downstream glass fiber feeding to protect fiber length, gentle dispersion, high torque reserve	240 to 290 degrees Celsius depending on grade	Two vents, deep vacuum mandatory	Dehumidifying dryer, moisture below 0.1 percent; hydrolysis risk is severe	0.70 to 0.85 of rated output
Recycled PVC (rigid and flexible)	Low shear throughout, no aggressive kneading, corrosion-resistant screw and barrel surfaces, short residence time	150 to 190 degrees Celsius, narrow window	Light vacuum only; avoid pulling stabilizer volatiles excessively	Surface dry; avoid high-temperature pre-drying	0.60 to 0.80 of rated output
Mixed polyolefin with compatibilizer	Compatibilizer via side or liquid feed, strong distributive mixing, moderate dispersive shear	180 to 225 degrees Celsius	One to two vents depending on contamination level	Drying to below 0.3 percent	0.70 to 0.90 of rated output

The output correction factors in the final column matter for capacity planning. A machine rated at 500 kg/h on clean polyolefin will not produce 500 kg/h on post-consumer film, because low bulk density limits intake volume long before torque or thermal capacity becomes the constraint. Sizing the extruder against the nominal rating rather than the corrected rating is one of the most common causes of a new plant failing to hit its production target in the first quarter. Where intake volume is the limiting factor, the correct remedies are a crammer feeder, a twin-screw side feeder used as a main feed, densification of the film before feeding, or a larger machine size.

PET deserves a separate note because it is chemically different from the polyolefins. PET is a polyester and undergoes hydrolytic chain scission when melted in the presence of water; every 100 ppm of residual moisture measurably reduces intrinsic viscosity. That is why crystallizing before drying is mandatory — amorphous PET flake softens and agglomerates in a hot dryer unless it has been crystallized first — and why the dew point specification of about minus 40 degrees Celsius is not negotiable for grades where intrinsic viscosity must be preserved. Where a chain extender is used to rebuild molecular weight, it should be introduced through a dedicated feed port into a fully filled, well-mixed zone, with sufficient residence time downstream for the reaction to complete before the die.

Quality control system and laboratory build-out

A recycled granulation plant sells consistency. The physical pellet is easy to produce; the certificate of analysis that a buyer will accept lot after lot is the difficult part. Build the quality system at the same time as the production line, not afterward, because retrofitting traceability into an operating plant is painful and because early customers are the ones who decide whether the business survives.

Test	What it controls	Typical instrument	Sampling frequency	Action when out of specification
Melt flow rate (MFR)	Molecular weight, degradation, batch consistency	Melt flow index tester with standard load and temperature per resin	Every 1 to 2 hours and every feedstock lot change	Adjust melt temperature, screw speed, or blend ratio of incoming lots
Moisture content	Hydrolysis risk, pellet porosity, downstream processing defects	Loss-on-drying balance or Karl Fischer for low-level work	Every dryer batch and every finished lot	Extend drying time, verify dew point, check vacuum vent function
Ash content	Filler loading accuracy, inorganic contamination	Muffle furnace burn-off	Every shift for filled grades; daily otherwise	Recalibrate side feeder; check feedstock for sand and mineral load
Tensile strength and elongation	Mechanical performance for the downstream part	Universal testing machine with injection-molded specimens	Every production campaign and on customer request	Review degradation, contamination, and compatibilizer dosing
Notched impact strength	Toughness, especially for recycled ABS, PP and PA	Izod or Charpy impact tester	Every campaign; more often for impact-modified grades	Increase impact modifier, reduce shear, review cross-polymer contamination
Color difference (delta E)	Color consistency lot to lot	Spectrophotometer with plaque or pellet fixture	Every lot for colored grades	Adjust pigment dosing; check for carryover from the previous campaign
Black speck and gel count	Cleanliness, degradation, filtration performance	Cast film or pressed plaque inspection against a reference chart	Every 2 hours during production	Change the screen pack, review dead zones, purge and inspect the die
Odor grade	Suitability for consumer-facing applications	Standardized sealed-jar sensory panel	Every lot for consumer-goods grades	Deepen vacuum, verify condenser, review feedstock source
Pellet geometry and fines	Feeding behavior at the customer’s machine	Sieve analysis and manual count of tails and twins	Every lot	Adjust cutter speed, blade clearance and water temperature; re-screen
Bulk density	Packing, conveying and dosing behavior downstream	Standard bulk density cup	Every lot	Review pellet size distribution and fines content

Two supporting practices multiply the value of this laboratory. First, retain a sealed sample of every production lot for at least twelve months, cross-referenced to the production log, the feedstock lots consumed, and the process parameters used. When a complaint arrives eight months later, the retained sample is the only way to establish whether the problem originated in your plant or downstream. Second, run a laboratory twin screw extruder for formula development and incoming-material screening. Trialing a new feedstock or a new additive package on a laboratory machine costs a few kilograms of material and one hour; trialing it on the production line costs a shift of output and a contaminated screen pack.

Kerke KTE Series twin screw extruder

The KTE Series is Kerke’s parallel co-rotating twin screw extruder family and the core machine around which a recycled granulation compound plant is built. The range spans KTE-16B through KTE-135D, covering laboratory-scale formula development at around 30 kg/h up to high-capacity industrial compounding. Every machine in the series is built on the same design logic: a segmented barrel, a modular screw assembled from interchangeable elements on splined shafts, a high-torque distribution gearbox, and a control system that logs the process parameters an operator needs to reproduce a formula.

What makes the series suitable for recycled feedstock specifically is that the aspect ratio, barrel structure, screw arrangement, exhaust configuration, feeding system and electrical control are all optimizable per project rather than fixed. A plant that starts on rigid PP regrind and later adds filled compound or post-consumer film does not need a new machine; it needs a revised screw configuration and, in some cases, an additional barrel section and side feeder. The kneading co-type screw geometry provides an excellent self-cleaning function, which shortens color changeover and limits the stagnation zones that generate black specks in recycled material.

Model	Screw diameter	L/D ratio (configurable)	Max screw speed	Main motor power	Specific torque class	Indicative output on recycled polyolefin
KTE-16B	About 16 mm	32 to 48	500 to 600 rpm	2.2 to 4 kW	High	1 to 10 kg/h (laboratory and formula trials)
KTE-20B	About 21 mm	32 to 48	500 to 600 rpm	4 to 7.5 kW	High	5 to 25 kg/h
KTE-35D	About 35.6 mm	32 to 48	500 to 600 rpm	15 to 22 kW	High to Very High	30 to 120 kg/h
KTE-52D	About 51.4 mm	32 to 48	500 to 600 rpm	45 to 75 kW	High to Very High	150 to 400 kg/h
KTE-65D	About 62.4 mm	32 to 48	500 to 600 rpm	90 to 132 kW	High to Very High	300 to 700 kg/h
KTE-75D	About 71 mm	32 to 48	500 to 600 rpm	132 to 200 kW	High to Very High	500 to 1,000 kg/h
KTE-95D	About 93 mm	32 to 48	450 to 600 rpm	250 to 400 kW	High to Very High	1,000 to 2,000 kg/h
KTE-135D	About 133 mm	32 to 48	400 to 600 rpm	630 to 900 kW	High to Very High	2,500 to 5,000 kg/h

The output column is deliberately labeled indicative. Real throughput on a recycled stream depends on bulk density, filler loading, moisture load, the number of vacuum vents, and the pelletizing method, which is why the correction factors in the resin adaptation table should be applied before a capacity commitment is made. Kerke confirms the achievable rate for a specific feedstock during the sample trial run, and the confirmed rate — not the catalog figure — is what appears in the production capacity guarantee.

Feeding system options on the KTE Series

Because recycled feedstock is difficult to meter, the feeding system is as important as the extruder itself. The KTE Series supports a full range of feeding configurations, and most recycled granulation plants use two or three of them on the same machine.

• Loss-in-weight feeder — gravimetric control that measures mass rate directly and corrects continuously. This is the accuracy standard for formula-critical work and the only reliable way to hold a filler loading or additive dosage across bulk density variation.
• Volumetric metering system — simpler and lower cost, appropriate for a single-component feed of consistent bulk density, or as a pre-feeder ahead of a gravimetric stage.
• Twin-screw side feeder — introduces filler, glass fiber or a second polymer downstream of the melting section. Essential for high filler loading, and equally useful for protecting fiber length and heat-sensitive additives.
• Crammer feeder — force-feeds low bulk density material such as film flake, fluff and fiber waste into the feed throat, directly addressing the intake-volume limit that caps output on those streams.
• Liquid feeder — injects oil, plasticizer, liquid color or liquid additives directly into the melt through a metering pump and an injection nozzle.

Kerke pelletizing systems, SE Series and double-stage extrusion

The pelletizing system determines pellet geometry, fines generation and how tolerant the line is of melt viscosity variation. Kerke supplies six cutting and pelletizing configurations, and the right choice depends on the resin, the viscosity, the output tier, and the operator skill level available at start-up.

Pelletizing system	Working principle	Suited resins	Practical output range	Pellet quality	Operator skill demand
Water-cooled strand pelletizing	Strands drawn through a water bath, air-knife dried, then cut by a rotating blade set	PP, PE, ABS, PS, PA, filled compounds, most engineering grades	30 to 2,000 kg/h	Uniform cylindrical pellet, low fines when set correctly	Low to Medium; easiest to train
Air-cooled strand pelletizing	Strands cooled on a chilled air conveyor, then cut	Moisture-sensitive and water-reactive compounds	30 to 500 kg/h	Good; avoids water pickup entirely	Medium
Water-ring die-face hot cutting	Blades cut at the die face inside a water ring that immediately quenches the pellet	Low-viscosity and sticky recycled melt that breaks as strands	100 to 1,500 kg/h	Slightly lenticular pellet; very low strand-break risk	Medium
Eccentric water mist hot cutting	Die-face cutting with a controlled water mist quench	Adhesive and tacky formulations, some elastomer compounds	50 to 600 kg/h	Good separation, low agglomeration	Medium to High
Air-cooled die-face hot cutting	Die-face cutting with air quench and pneumatic transport	Hot-melt adhesives, wax compounds, low-output specialty grades	20 to 300 kg/h	Spherical to lenticular	Medium
Underwater pelletizing	Cutting chamber fully flooded; pellets cut and transported in a temperature-controlled water loop	PET, PA, high-output polyolefin, engineering compounds	300 to 5,000 kg/h and above	Highest geometric uniformity, lowest fines	High; benefits from an experienced operator

For a first plant, the pragmatic default is water-cooled strand pelletizing for rigid regrind and engineering compounds, and water-ring die-face hot cutting for post-consumer film and low-viscosity streams that cannot hold a strand. Plants moving above roughly 1,000 kg/h, or entering R-PET work where moisture pickup and pellet uniformity are critical, should plan for underwater pelletizing from the start, because retrofitting it later means changes to the die, the water loop, the dryer and the floor layout.

SE Series single screw extruder and the KTE-SE double-stage system

Not every job needs a twin screw extruder, and not every job can be done on one machine. Kerke’s SE Series single screw extruder covers 30 kg/h to 800 kg/h and is used mainly for plastic recycling where the task is straightforward remelting and pelletizing of a clean, single-resin stream. Where a plant handles both simple regrind and specification compound, running an SE Series line alongside a KTE Series line lets each machine do what it does best: the single screw absorbs high-volume commodity work at low specific energy, while the twin screw is reserved for the compounded grades that carry the technical specification.

The KTE-SE double-stage extrusion system — a mother-baby arrangement in which a twin screw first stage feeds a single screw second stage — solves a different problem. Some materials cannot be processed satisfactorily on a single-stage machine because the requirements conflict: the first stage needs high shear and deep vacuum for mixing and devolatilization, while the second stage needs low shear and stable pressure for pelletizing. Heavily contaminated post-consumer film, high-volatile streams, and heat-sensitive filled compounds are typical cases. Separating the two duties into two machines allows the twin screw to be optimized purely for compounding and devolatilization, while the single screw second stage builds die pressure gently and drives a large-area filtration system without imposing extra shear on the polymer.

Configuration	Model reference	Screw arrangement	Typical L/D	Indicative output	Primary duty in a recycling plant
Laboratory twin screw	KTE-16B / KTE-20B	Co-rotating parallel twin screw, modular	32 to 44	1 to 25 kg/h	Formula development, incoming feedstock screening, customer sample production
Production twin screw	KTE-52D to KTE-135D	Co-rotating parallel twin screw, modular, multi-vent	36 to 48	150 to 5,000 kg/h	Compounding, filling, modification, devolatilization of recycled streams
Single screw recycling line	SE Series	Single screw, vented, with screen changer	30 to 36	30 to 800 kg/h	Plain remelting and pelletizing of clean single-resin scrap
Double-stage mother-baby system	KTE-SE Series	Twin screw first stage feeding a single screw second stage	First stage 36 to 44; second stage 12 to 16	200 to 2,000 kg/h	Heavily contaminated or high-volatile streams; heat-sensitive compounds
Triple screw extruder	KTE-T Series	Three-screw arrangement	Project specific	Project specific	Special materials requiring distinctive mixing behavior

Kerke also supplies the auxiliary equipment that surrounds these machines — high-speed mixers for pre-blending, plastic granulators and pulverizers for size reduction, water chillers for the cooling loops, and extruder core parts including screw elements, barrel liners and shafts. Sourcing the core wear parts from the machine builder matters more in recycling than in virgin compounding, because abrasive and contaminated feedstock consumes screw elements and barrel liners faster, and dimensional consistency between replacement elements and the original assembly is what keeps the self-wiping geometry intact.

Downstream applications for recycled pellets

A recycled granulation compound factory does not sell pellets; it sells an input to somebody else’s molding or extrusion process. Understanding what happens to the pellet after it leaves your gate is what allows you to write a specification your buyer will accept and to price your grade against the value it creates. The application areas below are the recurring destinations for recycled compound produced on twin screw lines.

Downstream industry	End products	Recycled grade required	Critical property the buyer tests	Process note
Injection molded housewares	Storage boxes, buckets, crates, hangers, stools, plant pots	Recycled PP or HDPE, natural or pigmented, often lightly filled	Melt flow rate window, impact at low temperature, color consistency	Tight melt flow rate control is the main purchase criterion; wide scatter causes short shots and flash
Pipe extrusion	Drainage pipe, cable protection pipe, agricultural irrigation pipe, corrugated pipe	Recycled HDPE or PP, controlled density and melt flow rate	Melt strength, environmental stress crack resistance, ash, gel count	Gels and unmelted particles create wall defects; fine melt filtration is essential
Sheet and board extrusion	Pallet decking, protective sheet, construction board, hollow profile board	Filled recycled PP or PE at 20 to 60 percent mineral loading	Flexural modulus, ash accuracy, dispersion quality, flatness behavior	Filler dispersion determines surface quality; side feeding and KB60 blocks matter
Packaging (non-food contact)	Industrial liners, garbage bags, shrink hood film, strapping	Recycled LDPE, LLDPE or R-PET depending on product	Gel count, tensile at break, dart impact, intrinsic viscosity for strapping	Film-grade recycled pellet demands the finest filtration in the plant
Automotive interior and under-body	Wheel arch liners, battery trays, interior brackets, sound insulation carriers	Filled and impact-modified recycled PP; recycled PA for under-hood	Notched impact, heat deflection temperature, odor grade, emission behavior	Odor and emission specifications make deep vacuum devolatilization non-negotiable
Construction and formwork	Plastic formwork panels, cable trays, scaffolding parts, geo-products	Heavily filled recycled polyolefin, often with compatibilizer	Flexural modulus, dimensional stability, weathering behavior	High filler loading requires a very high torque class and wear-resistant elements
Textile and fiber	Staple fiber, strapping tape, non-woven feedstock	R-PET with controlled intrinsic viscosity, or recycled PP fiber grade	Intrinsic viscosity, moisture, dust content, filtration cleanliness	Underwater pelletizing and fine filtration are typically specified
Cable and wire compounds	Insulation and sheathing compounds using recycled base resin	Recycled PE or PVC compound with stabilizer and filler package	Dielectric behavior, thermal stability, hardness, cleanliness	Contamination tolerance is very low; laser filtration or fine screens required

These downstream markets also map directly onto the application industries Kerke serves with the KTE Series: masterbatch production including color, filler, additive, black and textile masterbatch; plastic compounding including engineering plastic, biodegradable plastic, cable compounding, PVC compounding, thermoplastic elastomer and wood-plastic composite; and specialized work including R-PET flake recycling. A recycled granulation plant that positions itself as a compounder rather than a re-pelletizer is competing in those same value pools, which is precisely why the twin screw extruder rather than a plain remelting line is the strategic equipment choice.

Requirement to model selection guidance

The table below translates a plant’s operating requirement into a starting machine recommendation and screw configuration direction. Treat it as a first pass for budgeting and layout; the final configuration is confirmed after a sample trial run on the actual feedstock.

Target output	Feedstock type	High filler or reinforcement?	Recommended Kerke model	Screw configuration direction	Suggested pelletizing system
Formula trials only, 1 to 25 kg/h	Any; small sample quantities	Either	KTE-16B or KTE-20B laboratory twin screw	36 to 44 L/D, quick-change elements, one vacuum vent	Water-cooled strand pelletizing, laboratory scale
30 to 120 kg/h	Clean post-industrial PP / PE regrind, niche engineering compound	No	KTE-35D	36 L/D, moderate KB45 melting, single vacuum vent	Water-cooled strand pelletizing
150 to 400 kg/h	Rigid PP / HDPE regrind, general recycled compound	No	KTE-52D	36 to 40 L/D, one deep vacuum vent, loss-in-weight main feed	Water-cooled strand pelletizing
150 to 400 kg/h	Post-consumer film, low bulk density	No	KTE-52D with crammer feeder	40 L/D, long-pitch intake, atmospheric plus deep vacuum vent	Water-ring die-face hot cutting
300 to 700 kg/h	Recycled PP / PE with mineral filler 20 to 50 percent	Yes	KTE-65D with twin-screw side feeder	40 to 44 L/D, KB45 plus KB60 dispersion block, reverse element, wear-resistant elements	Water-cooled strand pelletizing or water-ring hot cutting
300 to 700 kg/h	Washed R-PET flake	No	KTE-65D with crystallizing and dehumidifying drying upstream	40 L/D, low-shear melting, twin deep vacuum vents, optional chain extender port	Underwater pelletizing
500 to 1,000 kg/h	Mixed post-consumer polyolefin with compatibilizer	Moderate	KTE-75D	44 L/D, distributive-dominant mixing, liquid feeder for compatibilizer, twin vents	Water-ring die-face hot cutting or underwater pelletizing
500 to 1,000 kg/h	Heavily contaminated post-consumer film with high volatile load	No	KTE-SE double-stage system based on KTE-75D first stage	First stage 40 to 44 L/D for mixing and devolatilization; single screw second stage for pressure and large-area filtration	Water-ring die-face hot cutting
1,000 to 2,000 kg/h	Industrial-scale recycled polyolefin compound	Yes	KTE-95D	44 L/D, dual side feed, twin deep vacuum, melt pump and continuous screen changer	Underwater pelletizing
2,500 kg/h and above	Large-scale single-stream recycled compound	Yes	KTE-135D	44 to 48 L/D, multiple side feeds, twin deep vacuum, melt pump, laser filtration	Underwater pelletizing
Any output, plain remelting of clean single-resin scrap	Post-industrial trim, single-color regrind	No	SE Series single screw extruder	30 to 36 L/D, single vent, screen changer	Water-cooled strand pelletizing

Two selection habits are worth adopting. First, size the machine to the corrected output for your worst-case feedstock rather than to the average, so that a bad month of low bulk density input does not put the plant below its committed volume. Second, buy one size band of headroom in torque class rather than in diameter. Torque headroom lets you run richer formulas and higher filler loadings later without changing machine size; diameter headroom mainly increases the minimum viable batch, which is the wrong flexibility for a plant whose product mix is still evolving.

Staffing, start-up SOP, energy and yield ramp-up

Equipment defines the ceiling of a plant’s performance; operating discipline defines how close to that ceiling it actually runs. Three operational topics decide the first year: staffing structure, a written start-up procedure, and an honest ramp-up plan for yield and energy.

Shift staffing structure

Role	Headcount per shift, 300 to 600 kg/h line	Headcount per shift, 1,000 to 1,500 kg/h line	Core responsibility
Shift leader / extruder operator	1	1	Process parameters, torque and pressure monitoring, screen change decisions, shift log
Feeding and formula operator	1	1 to 2	Feeder calibration and refill, formula verification, additive weighing, lot recording
Pelletizing and screening operator	1	1	Cutter blade condition, water temperature, strand handling, screen deck monitoring
Packing and material handling	1 to 2	2 to 3	Big-bag and bag filling, labeling, palletizing, warehouse movement
Sorting and pre-processing (if washing is in-house)	2 to 4	4 to 6	Belt sorting, contaminant rejection, crusher and washer tending
Quality technician (shared across shifts)	1 per plant, day shift	1 to 2 per plant	Melt flow rate, moisture, ash, color and impact testing; certificate of analysis issuance
Maintenance technician (shared across shifts)	1 per plant	1 to 2 per plant	Preventive maintenance, wear-part replacement, gearbox oil, electrical faults

The headcount does not scale linearly with output, which is the main labor argument for building at a meaningful scale rather than starting with the smallest possible line. Moving from a 300 kg/h line to a 1,000 kg/h line roughly triples output while raising shift headcount by only two or three people, so labor input per kilogram falls substantially. That is a real operating advantage, provided the feedstock supply can actually keep the larger line fed.

Start-up SOP

A written and posted start-up sequence prevents the two most expensive first-year events: a cold start that damages the screw, and a start on wet material that produces an unsellable first batch. The essential sequence is as follows.

1. Verify barrel zone temperature setpoints against the formula record and confirm every zone has reached setpoint, then hold a soak period so the metal mass is uniformly heated. Never rotate the screw before soak-out is complete.
2. Confirm gearbox oil level, oil temperature and cooling water flow to the gearbox cooler and the feed throat jacket.
3. Verify the cooling water loop, pelletizer water temperature and the chiller setpoint.
4. Check the vacuum system: condenser water on, vacuum pump ready, vent inserts clean and fitted.
5. Verify feeder calibration for every component against the recorded formula; run a static weigh check before production.
6. Install a fresh screen pack and record the starting pressure differential.
7. Start the screw at low speed, purge with a compatible purge or virgin material, and confirm clean melt at the die before switching to recycled feedstock.
8. Introduce feedstock gradually, raising screw speed and feed rate together while watching torque, melt pressure and melt temperature.
9. Once stable, take a first sample for melt flow rate, moisture and visual inspection, and only then start production lot recording.
10. Log the stable parameter set into the recipe management system so the next start-up begins from a known point.

Shutdown discipline matters equally. Purge the machine before stopping, especially after a filled, colored, or thermally sensitive compound, and never leave PVC or PA in a hot barrel. Degraded material left in the machine overnight becomes the black specks in tomorrow’s first lot.

Energy indicators and yield ramp-up

Specific energy consumption, expressed in kilowatt-hours per kilogram of pellet, is the cleanest operating benchmark a compounding plant has. It captures screw configuration efficiency, thermal management, and the appropriateness of screw speed in a single number, and it can be tracked shift by shift without any special instrumentation beyond an energy meter on the line.

Product type	Typical specific energy at the extruder	Whole-line energy including auxiliaries	Main energy lever
Plain recycled PP / PE pelletizing	0.15 to 0.25 kWh/kg	0.28 to 0.45 kWh/kg	Screw speed discipline; avoid running faster than the formula needs
Filled polyolefin compound	0.18 to 0.30 kWh/kg	0.32 to 0.52 kWh/kg	Side feeding instead of main-feed filler; correct dispersion block length
Post-consumer film with deep vacuum	0.22 to 0.38 kWh/kg	0.45 to 0.70 kWh/kg	Upstream drying efficiency; vacuum pump sizing; intake improvement
R-PET compounding with crystallizing and drying	0.20 to 0.32 kWh/kg	0.55 to 0.85 kWh/kg	Dryer heat recovery; correct dew point rather than excess drying
Recycled engineering compound (ABS, PA)	0.22 to 0.35 kWh/kg	0.42 to 0.65 kWh/kg	Melt temperature control; avoid excess shear from over-long dispersive sections

Yield follows a predictable learning curve, and planning against an honest curve prevents the demoralizing experience of missing an unrealistic target. In the first month, expect first-pass yield in the 70 to 82 percent band as operators learn feed control, screen-change timing, strand handling and color changeover. By month three, with a documented formula library, a written SOP and a stabilized feedstock supply, 88 to 93 percent is a normal level. By month six, with preventive maintenance running on schedule and incoming material screening enforced, 94 to 97 percent is achievable on stable streams. The residual loss is mostly start-up and changeover purge, screen-change transition material, and off-spec fines, all of which can be reprocessed internally rather than discarded, which is why an in-house regrind loop back into the feed system should be part of the original layout.

Compliance, permits and product standards

Recycling is a permitted activity in most jurisdictions, and the permit process usually takes longer than the equipment lead time. Starting the compliance track in parallel with the equipment specification, rather than after commissioning, is what keeps a project on schedule.

Compliance area	What is typically required	Trigger	Planning note
Environmental impact assessment	Assessment report and approval covering emissions, effluent, noise and solid waste	Any new plastic processing facility	Begin early; approval conditions often dictate exhaust treatment and layout
Waste water discharge permit	Permitted discharge point, treatment train, monitoring and reporting	Any in-house washing operation	If no discharge route exists, plan a closed-loop water system or buy washed flake instead
Process exhaust and odor control	Condenser, scrubber and activated carbon stage sized to permitted limits	Vacuum devolatilization and hot processing	Odor complaints from neighbors are a common cause of forced shutdowns
Solid and controlled waste management	Registration, licensed disposal contractor, manifest records for sludge and spent screens	Washing sludge, filter residue, contaminated reject	Keep manifests filed; they are the first documents an inspector requests
Fire protection design	Compartmentation, pile height limits, detection and suppression for storage areas	Bulk storage of baled plastic and finished pellets	Drives the site layout; cannot be added economically after construction
Occupational health and safety	Noise, dust and heat exposure control; lockout procedures; machine guarding	All operating plants	Hot melt, rotating screws and high-voltage drives require formal lockout discipline
Quality management system	ISO 9001 certification with documented procedures and traceability	Industrial and automotive customers	Most B2B buyers treat this as a minimum qualification, not a differentiator
Recycled resin product standards	Conformity to recognized specifications for recycled material characterization and testing	Contractual supply to specification buyers	ASTM D7209 covers recycled PE terminology and practice; regional GB/T and EN specifications apply by market
Machine conformity	CE marking where the destination market requires it; electrical safety documentation	Imported machinery into regulated markets	Confirm the required conformity package at the order stage, not at customs

A practical compliance sequence runs: confirm the site zoning permits plastic recycling; commission the environmental impact assessment; design the effluent and exhaust systems to the assessment conditions; obtain fire protection design approval on the layout; register waste streams and appoint a licensed disposal contractor; install and commission; then build the ISO 9001 documentation during the ramp-up period so that certification audit can take place once real production records exist. Attempting to certify a quality system before there is production data to audit rarely works.

On the product side, be careful about food-contact claims. Recycled material intended for food contact is subject to a distinct and much stricter approval pathway involving decontamination process validation, and it should never be claimed on the basis of a general recycling permit. A new plant is far better served by targeting non-food industrial and consumer applications first, and treating food-contact grades as a later, separately engineered project.

Service and support from Kerke

The gap between a specification on paper and a plant that produces saleable pellets is closed by engineering support, and that support should be defined before the order is placed rather than negotiated after a problem appears. Kerke, as a Wanplas factory, provides the following support framework, which is shared across the Wanplas brand.

• Sample trial run on your feedstock — send real material, and the achievable output, screw configuration and process window are established on a production machine before you commit. For recycled streams this is the single most valuable pre-order step, because catalog outputs assume clean, uniform material and your material is neither.
• Configuration engineering — L/D ratio, barrel structure, screw element arrangement, vent placement, feeding system and electrical control are specified around your resin stream and target grade rather than sold as a fixed package.
• Factory testing before shipment — machines are run without load to verify mechanical and electrical function, and then run with material to confirm the process behavior recorded during the trial. Test records travel with the machine.
• Installation and commissioning — engineers attend site for mechanical installation supervision, electrical connection verification, water and vacuum system checks, first start-up and trial production.
• Operator and maintenance training — covering the start-up and shutdown SOP, screw configuration changes, screen changing, feeder calibration, wear-part inspection, and the fault-finding logic for torque, pressure and temperature deviations.
• Spare parts policy — the Wanplas group commitment of USD 500 free parts every year, plus free replacement of parts damaged within the warranty period. For recycling plants the practical recommendation is to hold a working stock of screw elements from the highest-wear zones, spare barrel liner sections, screen packs, pelletizer blades and die plates, because those are the items that determine how long an unplanned stop lasts.
• Remote technical support — process parameter review and fault diagnosis with the plant’s own data, so that a formula problem can often be resolved without a site visit.
• Open factory policy — customers are welcome to visit the plant, inspect machines under construction, and witness trial runs in person before shipment.

Two further group commitments are relevant to a plant being financed against a production plan: a transportation guarantee, and a production capacity guarantee tied to the configuration confirmed during the trial run. Because the guaranteed capacity is based on your actual material rather than a generic figure, it is a number that can be carried into a business plan with confidence.

Frequently Asked Questions

Do I need a twin screw extruder to open a recycled plastic granulation factory, or is a single screw enough?

A single-screw extruder is adequate when the job is pure remelting of a clean, single-resin, single-color stream into a commodity pellet, and Kerke’s SE Series covers that duty from 30 kg/h to 800 kg/h. A twin screw extruder becomes necessary as soon as the plant must devolatilize moisture and volatiles, disperse fillers or pigments, add impact modifiers or compatibilizers, blend two resins, or hold a tight melt flow rate window across variable post-consumer input. Most granulation businesses migrate toward compounding within the first two years, because compounded grades sell into a technical specification while plain regrind competes on price alone.

What building area and installed electrical capacity does a recycled granulation plant need?

As a planning rule, a 300 to 500 kg/h line needs roughly 800 to 1,200 square meters including feedstock and finished-goods storage, 6 to 7 meters clear height under the crane hook, and a three-phase installed capacity of about 350 to 500 kW. A 1,000 to 1,500 kg/h line typically needs 2,000 to 3,000 square meters, 8 meters clear height and 900 to 1,300 kW installed. Running demand is usually 55 to 70 percent of installed capacity, but the transformer must be sized to the installed figure because barrel heaters draw heavily during a cold start. Storage area, not machine footprint, is what most first-time operators underestimate.

What L/D ratio should I choose for a recycled compounding twin screw extruder?

For straightforward PP or PE regrind pelletizing with one vent, 32 to 36 L/D is sufficient. For filled or reinforced recycled compounds with side feeding and two vents, 40 to 44 L/D is the practical standard. For heavily contaminated post-consumer film, filler loading above 60 percent, reactive extrusion or PET chain-extension work, 44 to 48 L/D provides the residence time and free volume required. Longer is not automatically better, because additional length adds thermal history and specific energy input, which is exactly what a heat-sensitive recycled stream does not need.

How dry does PET flake have to be before it enters the twin screw extruder?

PET must be crystallized first, then dried in a dehumidifying dryer at a dew point of about minus 40 degrees Celsius, with moisture brought below 50 ppm before the melt stage if intrinsic viscosity is to be preserved. Crystallizing before drying is mandatory because amorphous flake softens and agglomerates in a hot dryer. A well-designed twin vacuum devolatilization section extends the tolerance somewhat, but any residual moisture at melt temperature causes hydrolytic chain scission, and the resulting intrinsic viscosity drop must either be accepted in the grade specification or compensated with a chain extender introduced through a dedicated feed port.

Which pelletizing method should a recycled granulation plant use?

Water-cooled strand pelletizing is the most forgiving and the easiest to train operators on, and it suits PP, PE, ABS, PS and most engineering compounds. Water-ring die-face hot cutting handles low-viscosity and sticky recycled melt that will not hold a strand. Underwater pelletizing gives the highest geometric uniformity and the lowest fines, and it is the usual choice above roughly 1,000 kg/h and for R-PET and moisture-sensitive engineering grades. Air-cooled die-face cutting suits hot-melt and low-output specialty work. Choose before the layout is fixed, because retrofitting underwater pelletizing later affects the die, the water loop, the dryer and the floor plan.

How many operators does a recycled pelletizing plant need per shift?

A single 300 to 600 kg/h compounding line typically runs with four to five people per shift: one shift leader and extruder operator, one feeding and formula operator, one pelletizing and screening operator, and one to two packing and material handling staff. A quality technician and a maintenance technician are normally shared across shifts on the day shift. If washing and sorting are in-house, add two to four sorting and pre-processing staff per shift. Headcount rises only modestly with output, which is why a larger line shows a clearly better labor input per kilogram.

How long does it take for a new recycled granulation factory to reach stable yield?

A realistic ramp-up puts first-month first-pass yield around 70 to 82 percent while operators learn feed control, screen-change timing and strand handling. Month three, with a fixed formula library and a written start-up SOP, normally reaches 88 to 93 percent. Month six, with disciplined incoming screening and preventive maintenance on schedule, reaches 94 to 97 percent on stable input streams. Feedstock variability rather than machine capability dominates the curve, so the fastest route to the month-six band is a written incoming acceptance standard and blending of feedstock lots before production.

What certifications and permits does a recycled granulation compound factory need?

Typical requirements include an environmental impact assessment and discharge permit covering waste water and process exhaust, a solid and controlled waste management registration for sludge and spent filter screens, fire protection design approval for the storage areas, and an occupational health and safety plan with lockout procedures. Commercially, ISO 9001 quality system certification is expected by most industrial buyers, and product conformity is usually demonstrated against recycled-resin specifications such as ASTM D7209 for recycled PE terminology and practice, together with regional GB/T or EN requirements. Food-contact recycled material follows a separate and much stricter approval pathway and should not be claimed on the basis of a general recycling permit.

Can one twin screw extruder handle several different recycled materials?

Yes, provided the machine is specified for it. Because the KTE Series uses a segmented barrel and a modular screw built from interchangeable elements, one machine can be reconfigured between recycled polyolefin, filled compound and engineering compound work by changing the screw arrangement and, where necessary, adding a side feeder or a second vent. The practical limits are corrosive materials such as PVC, which are best kept to a dedicated machine with corrosion-resistant surfaces, and highly pigmented or black formulations, which should be scheduled after light colors to reduce changeover purge.

What spare parts should a recycled granulation plant hold in stock?

Prioritize the items that stop production and have the longest replacement lead time: screw elements from the highest-wear zones such as the dispersive kneading blocks and the elements immediately after a side feed, spare barrel liner sections, screen packs in the meshes you run, pelletizer blades and blade holders, die plates and die inserts, and the seals and thermocouples that fail without warning. Abrasive recycled feedstock consumes wear parts faster than virgin material, so track wear-part life in running hours from the first month and use that data rather than a generic interval to set reorder points.

Conclusion

Opening a recycled plastic granulation compound factory using a twin screw extruder is a project with a clear critical path. Secure the feedstock before anything else, because everything downstream is sized against it. Define the pellet grade you intend to sell and the acceptance indicators you must hold, because that decides whether you need compounding capability or only remelting capability. Lock the site utility envelope — transformer capacity, water circulation, effluent route, exhaust treatment and fire compartments — before signing a lease, because those are the four attributes that cannot be changed later. Then design the process route as a chain of protections, and only then specify the machine.

On the machine itself, the three decisions that matter most are L/D ratio, specific torque class, and screw element arrangement. Specify torque headroom you do not yet need, because recycled feedstock viscosity drifts. Specify the vent layout for the worst volatile load you expect, not the average. Choose the pelletizing method before the layout is fixed. And confirm the whole configuration with a sample trial run on your real material, because catalog output figures assume a uniformity that post-consumer feedstock never has.

Kerke, a Wanplas factory with more than 12 years of specialization in parallel co-rotating twin screw compounding extruders, a 19,997+ square meter plant, over 2,000 machines running in more than 70 countries and a 100+ strong technical team, supports this entire path — from formula trials on a laboratory KTE-16B, through production configurations across the KTE Series up to KTE-135D, SE Series single screw lines and KTE-SE double-stage systems, to the pelletizing, screening and auxiliary equipment that completes the plant. Where the project also needs upstream preparation, Wanplas supplies matched washing and drying lines that feed directly into Kerke pelletizing systems.

If you are planning a recycled granulation compound plant, the most useful next step is a trial. Send a representative sample of your actual feedstock — a few bags of flake or regrind that genuinely reflect what you will buy every week — together with your target output and the specification your buyers demand. Kerke will run the material, establish the achievable rate and process window, and return a configuration proposal built on the trial result rather than a catalog assumption. Share your production target and product roadmap and the configuration will be tailored around them. Customers are also welcome to visit the factory in person to inspect machines under construction and witness the trial run.