How to Choose the Best Plastic Washing Line for Your Needs?

Selecting the optimal plastic recycling washing line is a critical investment decision for recyclers, significantly impacting efficiency, output quality, and operational costs. With diverse technologies available, understanding key factors ensures the chosen system aligns precisely with your specific requirements.

Determining Your Capacity Needs

Capacity planning is the cornerstone of selection, yet it is far from a simple numbers game. A common mistake many investors make is confusing "design capacity" with "actual effective capacity.

Scientific Formula for Capacity Calculation

To accurately assess the required equipment scale, you must perform a reverse derivation based on the bulk density of raw materials and the target output.

• Input vs. Output: After removing silt, labels, caps, and other impurities, the yield of a washing line typically ranges from 70% to 90% (depending on contamination levels).

• Formula: Target Output Capacity (kg/h) ÷ Yield Rate (%) = Required Input Capacity (kg/h)

• Case Study: If you plan to produce 1,000 kg of clean flakes per hour using agricultural film with 30% contamination, the throughput capacity of the upstream crushing and washing equipment must reach 1,429 kg/h (1,000 ÷ 0.7).

Bottleneck Analysis and Safety Margin Design

In industrial practice, we recommend that clients reserve a 20% safety margin for capacity.

• Maintenance Downtime: Considering blade sharpening, screen cleaning, and preventive maintenance, actual operating time is typically calculated at 20–22 hours per day.

• Impact of Bulk Density: For lightweight materials such as PE film, the feeding stage is often the bottleneck. Boxin Machinery recommends configuring a belt conveyor with a metal detector before the shredder, utilizing an automatic current-controlled feeding system. This system adjusts conveyor speed based on the main motor's current load, ensuring the equipment consistently operates at optimal load while avoiding idling or overloading.

Economies of Scale

• Small-scale Lines (500 kg/h): Suitable for the startup phase or processing specific post-industrial waste; offers high flexibility and a small footprint.

• Medium-scale Lines (1,000–2,000 kg/h): The industry-standard configuration, balancing energy consumption and labor costs, typically equipped with automated control systems.

• Large-scale Lines (3,000+ kg/h): Targeted at municipal-level waste processing centers. It is recommended to equip these with high-end auxiliary equipment, such as optical sorters and automatic balers with moisture monitoring, to minimize processing costs per ton through maximized economies of scale.

Choose the Type of Washing Line: Cold vs. Hot

Cold Washing Process: Limits of Physical Decontamination

Cold washing utilizes ambient temperature water and mechanical friction to remove physical attachments.

Application Scenarios:

• PE/PP Agricultural Films and Woven Bags: Primary contaminants include silt, soil, and organic roots. These impurities are water-insoluble but can be effectively stripped via the intensive centrifugal force (rotational speed > 2000 RPM) of a high-speed Friction Washer.

• Post-Industrial Scraps: Clean waste materials that have not come into contact with grease or adhesives.

Technical Advantages: Low energy consumption (no boiler or electric heating required) and simplified maintenance. Limitations: Ineffective against grease, stubborn adhesives, and persistent odors.

Hot Washing Process: Deep Purification via Chemical Modification

Hot washing is the critical process for producing high-quality recycled resins, particularly for food-grade or filament-grade applications.

Application Scenarios:

• PET Bottle Recycling: Essential for removing label adhesives (typically EVA or hot-melt) as well as residual beverages and oil stains.

• HDPE Milk/Detergent Bottles: Removal of protein residues and surface self-adhesive labels.

Detailed Process Parameters:

• Temperature Control: The optimal range is 85°C - 95°C. Insufficient heat results in incomplete adhesive softening, while temperatures exceeding 100°C lead to a surge in energy consumption and necessitate pressure vessels. Boxin’s hot washing tanks feature PID temperature control systems to ensure a variance within ±1°C.

• Chemical Additives:

  • Sodium Hydroxide (NaOH/Caustic Soda): Concentration is maintained at 1%-2% to break down adhesive molecular chains and corrode aluminum foil layers.

  • Surfactants (Detergents): Used to emulsify grease and prevent re-adsorption of contaminants onto the plastic surface.

• Retention Time: Designed for 15-30 minutes of reaction time based on contamination levels. Multi-stage series configurations (such as 1+2 or 2+1) are typically employed to guarantee sufficient chemical reaction duration.

Decide on the Quality of Output

The configuration of a washing line should be reverse-engineered based on the requirements of your target customers (downstream applications). Different applications demand distinct standards for purity, moisture content, and color.

PET Flake Grade Standards

Grade A (Filament/Sheet Grade):

• Moisture Content: < 1%

• PVC Content: < 50 ppm

• Adhesives/Impurities: < 100 ppm

• Required Configuration: Must include whole bottle pre-washing, optical sorters (to remove off-colors and non-PET materials), hot washing, and high-precision Zig-Zag air classifiers for fines and dust removal.

Grade B (Staple Fiber/Fiberfill Grade):

• Moisture Content: < 2%

• PVC Content: < 200 ppm

• Required Configuration: Standard hot washing and flotation configurations are generally sufficient to meet these requirements.

PE/PP Film Grade Standards

Pelletizing Grade:

• Moisture Content: This is the critical metric. Due to the high surface area of films, traditional centrifugal dryers can only achieve ~10% moisture, which leads to bubbling during the extrusion/pelletizing process.

• Recommended Configuration: A Squeezer (Drying Press) is highly recommended. It uses physical compression and frictional heat to reduce moisture to 3%–5% and semi-plasticizes (densifies) the material, significantly enhancing the feeding efficiency of the pelletizer.

Market Insight

With the 2025 implementation of mandatory global regulations regarding recycled content—such as the EU mandate for 25% PCR (Post-Consumer Recycled) material in packaging—the supply-demand gap for high-purity recycled resins is widening. Investing in a high-performance washing line is strategically equivalent to securing an "entry ticket" into premium global supply chains.

Evaluate Energy Efficiency

Amidst fluctuating energy prices today, OpEx (Operating Expenses) control is the key to washing line profitability. A high-efficiency design must maximize the reduction of water, electricity, and steam consumption while maintaining cleaning quality.

Energy-Saving Design Elements

• Variable Frequency Drive (VFD) Control: All motors across the Boxin line (crushing, friction, drying) are equipped with VFDs. This minimizes current surges during startup and automatically adjusts rotational speeds based on the load. For instance, when the feed rate decreases, the friction washer automatically slows down, achieving energy savings of 15-20%.

• Thermal Insulation System: Hot washing tanks utilize a double-layer stainless steel design filled with rock wool insulation. This effectively prevents heat loss and reduces the energy required for steam or electric heating.

• Wet Grinding: Injecting water into the crusher's cutting chamber serves as a pre-wash while utilizing water to dissipate frictional heat. This extends blade lifespan and prevents motor overloads caused by plastic melting.

Energy Consumption Benchmarks

• PET Washing Line (1,000 kg/h): Installed power is approximately 200–300 kW, with an actual operating power factor typically around 0.7.

• Electricity Consumption per Ton: A high-performance system should maintain consumption between 50–80 kWh/ton.

Consider Water Usage and Recycling

Plastic washing is essentially a water treatment process. A 1 ton/hour washing line without a circulation system could consume 10–20 tons of fresh water per hour, which is unsustainable both economically and environmentally.

Closed-Loop Water Circulation System

Modern washing lines are recommended to integrate a modular water treatment plant:

Tiered Treatment:

• Upstream Water (Pre-wash/Rinsing): High in silt and solids; reused after removing suspended solids via a Sedimentation Tank.

• Hot Washing Water: Contains alkali and detergents; recycled after removing grease and colloids via a Dissolved Air Flotation (DAF) unit. Chemical replenishment is used to maximize heat energy and reagent savings.

• Final Rinsing Water: Requires the highest purity. Fresh water is typically introduced here, and its overflow serves as makeup water for upstream processes, following the counter-current rinsing principle.

Water Consumption Metrics: Through high-efficiency circulation, Boxin systems can limit fresh water consumption to within 1–2 tons of water per ton of plastic.

Sludge Treatment: Equipped with screw dischargers or filter presses to dehydrate the sludge from the bottom of sedimentation tanks into cakes, ensuring compliant disposal.

Assess Maintenance and Reliability

Equipment downtime is the primary threat to plant profitability. During equipment selection, durability and maintenance accessibility must be rigorously evaluated.

Material Selection for Core Components

• Blade Materials: Crusher blades should be fabricated from D2 (Cr12Mo1V1) or SKD-11 alloy steel. Cryogenically treated blades can reach a hardness of HRC 58-60, offering 2–3 times the wear resistance of standard materials and extending sharpening intervals to 40–60 hours.

• Bearing Protection: Bearing housings for friction washers and crushers should utilize an external design equipped with multi-stage labyrinth seals. This provides physical isolation from water, preventing bearing seizure caused by moisture ingress.

• Stainless Steel Grades: All components in contact with water (tanks, screws, piping) must be constructed from SUS304 stainless steel to prevent corrosion and plastic contamination. For hot washing tanks exposed to strong alkalis, we recommend reinforced steel plates with a thickness exceeding 3mm.

Design for Maintainability

• Screen Replacement: Friction washers and dryers should feature hydraulic hood opening or quick-access doors, allowing operators to complete screen cleaning or replacement within 30 minutes.

• Blade Calibration: Boxin crushers are equipped with an external blade-setting jig, which reduces downtime for blade changes by 50%.

Conclusion

Selecting the optimal plastic washing line is a systematic endeavor that requires balancing capacity, quality, cost, and sustainability. By deeply understanding raw material characteristics (PET vs. PE/PP) and mastering core process parameters (temperature, retention time, and mechanical force), you will be able to build a plastic recycling line with robust market competitiveness.

Boxin Machinery is dedicated to providing one-stop solutions spanning crushing, washing, drying, and pelletizing. Whether your feedstock consists of massive volumes of PET bottles or heavily contaminated agricultural film, we offer proven technical solutions to help you maximize value.