PE film, encompassing low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), is ubiquitous in applications like shopping bags, agricultural films, and industrial wraps. Recycling is vital for reducing environmental impact, and the PE film washing line is central to this, cleaning and preparing used film for reuse. Industry standards, such as those from the Association of Plastic Recyclers (APR) – PE Film, guide design and processing to maximize recyclability.
Detailed Process Analysis
1. Feeding and Preliminary Size Reduction
The process begins by conveying PE film into shredders or crushers. If films are baled, a debaling system separates them. Due to the risk of tangling, films are reduced into small pieces (approximately 1-5 inches), ensuring smooth operation. Water is occasionally introduced to cool equipment during shredding and prevent clogging.
2. Wet Granulation
In the subsequent wet granulation stage, granulators cut the material into flakes ranging from 10-20 mm. Water injection at this step facilitates initial cleaning and cools blades, extending equipment life. Water’s presence significantly reduces frictional heat, preserving machinery integrity.
3. Pre-Washing
During pre-washing, paddle-type washers agitate flakes in water, effectively removing loose contaminants such as mud and sand. This stage significantly reduces the cleaning burden on subsequent processes, enhancing overall line efficiency.
4. Friction Washing
High-speed friction washers, typically operating around 1000 RPM, mechanically remove persistent contaminants like oils and adhesives. Heavily contaminated films may undergo multiple friction washing stages to ensure thorough cleanliness.
5. Hot Wash and Detergent Application (Optional)
Heavily soiled materials may require a hot washing stage utilizing hot water combined with detergents. This optional step breaks down challenging residues, including oils and waxes, significantly improving the cleanliness of the material.
6. Separation and Rinsing
Sink-float separation tanks effectively isolate floating plastic from heavier contaminants (e.g., sand, glass, and metals). Screw conveyors then remove these separated impurities. Following this, clean water rinsing ensures the removal of residual detergents or contaminants.
7. Dewatering
Excess water is efficiently removed through centrifugal dewatering machines or screw presses, which substantially reduces the energy requirements for subsequent drying processes.
8. Drying
Thermal drying involves circulating hot air within stainless steel tubes, reducing material moisture content below 2-4%. Cyclone separators then cool the dried flakes and extract fine particles, ensuring the material meets storage requirements.
9. Quality Control and Storage
Quality inspections focusing on moisture and purity standards confirm that processed flakes meet operational criteria. Once quality requirements are met, flakes are stored in silos. Some systems further integrate pelletizers, directly converting flakes into pellets, enhancing material usability.
Technical Specifications and Capacity Planning
Typical washing lines vary in capacity from 500 kg/h to 3000 kg/h. Key specifications are summarized below:
| Input Capacity | Required Space [L×W×H] | Operators | Installation Power | Water Circulation (T/H) |
|---|---|---|---|---|
| 500 kg/h | 40m x 15m x 6m | 2-3 | 250 KW | 2 |
| 1000 kg/h | 50m x 15m x 6m | 3-5 | 350 KW | 3 |
| 1500 kg/h | 60m x 30m x 6m | 4-6 | 470 KW | 3 |
| 2000 kg/h | 80m x 30m x 6m | 4-6 | 650 KW | 4 |
| 3000 kg/h | 80m x 40m x 6m | 5-8 | 850 KW | 5 |
These parameters support effective facility design and operation planning.
Additional Considerations: Industry Standards and Challenges
The Association of Plastic Recyclers (APR) standards provide critical guidance on designing PE film washing lines for maximum recyclability. Common industry challenges include managing high contamination levels (>80%), addressed through rigorous pre-sorting and selection of advanced equipment. Additionally, resource consumption, such as water and energy use, is increasingly mitigated by closed-loop systems and energy-efficient process designs.
Conclusion
The PE film washing line represents a complex yet highly efficient recycling process. Clear understanding and optimization of each stage—from initial size reduction through to drying and storage—support sustainable operations. By adhering to industry standards and proactively addressing challenges such as contamination, operational effectiveness can be consistently improved, fostering greater sustainability in plastic recycling.