Not everything entering a recycled paper mill becomes pulp.
During OCC pulping, screening and cleaning, paper mills continuously generate a complex waste stream containing ragger ropes, plastic films, residual paper fibers, wires, baling straps, rubber, sand and other contaminants.
These materials are commonly referred to as paper mill rejects.
For many recycled paper mills, the challenge is not simply how to remove these rejects from production. The real challenge is how to process a wet, heterogeneous and highly entangled waste stream reliably, without creating excessive disposal costs or frequent equipment downtime.
Landfilling remains expensive in many regions, while direct incineration is often inefficient because untreated paper mill rejects can contain metals, inert materials, excessive moisture and inconsistent combustible content.
A more practical approach is to separate recyclable metals and non-combustible contaminants first, then process the remaining combustible fraction into RDF (Refuse Derived Fuel) or SRF (Solid Recovered Fuel).
Wiscon designs modular shredding and separation systems specifically for this type of application.
Why Are Paper Mill Rejects Difficult to Process?Paper mill waste behaves very differently from conventional municipal solid waste.
The material is often tough, wet, flexible and heavily intertwined. A successful recycling system must therefore be designed around the physical characteristics of the waste rather than simply around the required throughput.
Ragger ropes are one of the most difficult materials produced during recycled paper pulping.
They typically contain a mixture of:
Because ragger ropes are long and highly tensile, they can easily wrap around high-speed rotors or shafts.
For this reason, paper mill rejects are usually better handled by low-speed, high-torque shredding technology capable of cutting, tearing and opening long entangled materials before downstream separation.
The goal of the first shredding stage is not to produce the final RDF size.
Its main function is to break open the material and make the different fractions easier to separate.
Recovered paper often enters the mill with steel baling wire, metal straps and other metallic contaminants.
If these materials are allowed to pass directly into secondary shredders or downstream fuel preparation equipment, they can increase:
Sand, stones, glass and other heavy inert materials also have little or no fuel value.
A properly designed paper mill waste recycling line should therefore do much more than simply reduce particle size.
A typical process is:
Primary shredding → metal separation → heavy fraction removal → combustible fraction cleaning → secondary shredding → RDF/SRF preparation
Paper mill rejects are not a standardized raw material.
Their composition can change depending on:
One batch may contain mainly plastics and fibers, while another may contain more wire, grit or wet pulp residue.
High-moisture pulp rejects and sludge require particular attention.
Moisture directly affects the net calorific value of the final fuel and may significantly influence transportation, storage and combustion performance.
Before designing an RDF/SRF line, Wiscon therefore recommends evaluating key material parameters such as:
In many projects, this material analysis is more important than selecting the shredder itself.
Wiscon uses a modular approach to paper mill waste recycling.
The exact equipment configuration depends on the incoming waste and the required final product, but a typical system includes several key stages.
Paper mill rejects are first introduced into the system through a heavy-duty conveyor or feeding unit.
The material then enters the primary shredder.
At this stage, the objective is to:
For rejects containing large amounts of ragger rope and flexible plastics, a low-speed twin-shaft shredder is often more suitable than a conventional high-speed grinder.
High torque helps the machine process difficult material while reducing the risk of uncontrolled wrapping.
After primary shredding, steel wire, baling straps and other ferrous metals become easier to release from the waste stream.
An overband magnet or another magnetic separation system can then remove these materials.
This stage serves two purposes.
First, it protects downstream shredders, screens and conveyors from unnecessary wear.
Second, recovered ferrous metals can be collected and sent to metal recycling.
Where significant quantities of aluminum or other non-ferrous metals are present, additional separation technology can be incorporated into the system.
The shredded waste still contains contaminants that are unsuitable for fuel production.
Depending on the waste composition, the line may include equipment such as:
These systems help remove stones, glass, grit and other non-combustible materials.
The aim is to concentrate the lighter combustible fraction, mainly consisting of:
plastic + residual paper fiber + other suitable combustible materials
Removing inert contaminants also helps reduce ash content in the final RDF/SRF.
Once metals and heavy contaminants have been removed, the combustible fraction can be sent to a secondary shredder.
This stage controls the final fuel size.
Depending on the receiving plant, the material may be processed into sizes in the range of approximately 30–100 mm, although there is no universal RDF particle size.
The correct size depends on the final application, including:
Where a narrow particle-size distribution is required, the system can also include screening and recirculation of oversized material.
RDF and SRF are often used interchangeably, but they are not exactly the same.
RDF is a broad term for fuel produced from processed waste.
SRF, by contrast, is generally associated with more defined and controlled fuel quality characteristics.
This means that shredded waste does not automatically qualify as SRF.
For a recovered fuel to be suitable for a specific industrial application, parameters such as the following may need to be evaluated:
For paper mill rejects, chlorine deserves particular attention.
Recovered paper streams may contain PVC, labels, adhesives, laminated packaging and other chlorine-bearing materials.
A fuel with a high calorific value may still be unsuitable for a particular cement kiln or industrial boiler if the chlorine content is too high.
The objective of a professional RDF/SRF preparation line is therefore not simply to make waste smaller.
The objective is to make the fuel more consistent, cleaner and easier to control.
Where Can RDF/SRF from Paper Mill Rejects Be Used?Once the combustible fraction has been properly processed, it can be evaluated for use in several industrial energy applications.
Cement production requires large amounts of thermal energy, making cement kilns one of the major users of alternative fuels.
After metal removal, contaminant separation and size reduction, combustible paper mill rejects may be used as an alternative fuel, provided they meet the receiving plant’s technical and regulatory requirements.
Typical acceptance parameters may include:
For this reason, RDF quality should always be matched to the requirements of the final user.
Properly prepared alternative fuel may also be accepted by industrial energy facilities equipped to handle RDF or SRF.
For paper mills operating their own suitable energy systems, on-site utilization may also be considered.
This can potentially reduce long-distance transportation of rejects and improve control over the mill’s waste stream.
However, RDF cannot simply be fed into any standard boiler.
Its use depends on the combustion system, permits, emission-control equipment and applicable local regulations.
The value of an RDF/SRF project should not be measured only by the selling price of the fuel.
A complete business case normally includes several different value streams.
By separating recyclable and combustible materials, the amount of waste requiring external disposal can be reduced.
This may lower:
The actual savings depend heavily on local waste management costs.
Steel wire, baling straps and other ferrous materials contained in paper mill rejects can be separated and recovered.
Although metal recovery may not be the largest revenue source in every project, it can create additional value while protecting downstream equipment.
Untreated mixed waste is difficult to use because its composition, particle size and contaminant level are unstable.
After processing, the combustible fraction becomes a more consistent alternative fuel.
This can make it easier to establish long-term supply relationships with:
Relying entirely on external disposal leaves a paper mill exposed to changing disposal prices, transportation constraints and waste acceptance policies.
Installing an in-house preprocessing system gives the mill greater control over how its rejects are handled.
There is no universal payback period for a paper mill waste recycling line.
The economics depend on several local factors.
A realistic ROI analysis should consider:
**Current disposal cost
This is why Wiscon does not recommend selecting an RDF line only by nominal throughput.
Two paper mills producing the same tonnage of rejects can require completely different process configurations.
No two paper mill waste streams are exactly the same.
One mill may generate mostly light plastic and paper fiber.
Another may produce a much more difficult mixture containing:
If the system is selected only according to tons per hour, common problems may include:
A more reliable approach is to evaluate the waste first and design the equipment around the material.
Wiscon can then determine the appropriate combination of:
For difficult applications, material testing can also be used to verify the processing concept before final system configuration.
Wiscon Paper Mill Waste Recycling SolutionsWiscon specializes in industrial waste shredding and recycling systems.
For paper mills, Wiscon can design modular RDF/SRF preparation lines based on the actual reject composition, plant capacity and final fuel requirements.
A typical system may include:
Heavy-duty feeding → Primary shredding → Magnetic separation → Screening → Air/heavy fraction separation → Secondary shredding → Product discharge
Additional modules can be integrated when required, including:
The key is not to install as many machines as possible.
Each stage should solve a specific processing problem.
First, reduce wrapping and oversized material.
Then remove metals.
Next, eliminate contaminants that do not contribute to fuel value.
Only after that should the material be finely shredded to the required final size.
This process logic helps improve line stability, reduce unnecessary wear and produce a more consistent RDF/SRF output.
No.
Combustible materials such as plastics and residual paper fibers may be suitable for RDF production, but metals, stones, glass and other inert contaminants must be removed.
High-moisture sludge or pulp residue should be evaluated separately because drying cost, ash content and calorific value can significantly affect project feasibility.
There is no universal RDF size.
The required particle size depends on the final fuel user and feeding system.
Some projects require material in the approximate range of 30–100 mm, while others may require a finer or coarser product.
Yes, but the shredder must be suitable for long, flexible and entangled material.
Low-speed, high-torque shredders are generally better suited to this application than conventional high-speed grinders.
Yes.
Primary shredding helps expose steel wire and baling straps so they can be removed by magnetic separation.
This protects downstream equipment and also allows the recovered metal to be recycled.
To evaluate a project, Wiscon typically needs:
Based on this information, Wiscon can recommend the appropriate shredding, separation and fuel preparation process.
Paper mill rejects should not automatically be treated as disposal waste.
With the right shredding and separation process, recyclable metals can be recovered and suitable combustible fractions can be prepared for RDF/SRF applications.
If your paper mill is currently dealing with ragger ropes, OCC rejects, plastic-fiber mixtures or other pulping residues, send Wiscon your material photos, composition, moisture content and required capacity.
Our engineering team can evaluate the waste stream and recommend a suitable paper mill waste recycling system.
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