The difference between cold washing and hot ...

The recycling of PET (Polyethylene Terephthalate) plastic bottles has become an essential part of the plastic recycling industry. PET bottles, commonly used for beverages like soda, water, and other drinks, are collected, processed, and converted back into valuable materials through various recycling techniques. Among these techniques, the washing process is crucial in ensuring the quality and purity of the recycled PET bottle flakes. This article delves into the differences between cold washing and hot wash

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The recycling of PET (Polyethylene Terephthalate) plastic bottles has become an essential part of the plastic recycling industry. PET bottles, commonly used for beverages like soda, water, and other drinks, are collected, processed, and converted back into valuable materials through various recycling techniques. Among these techniques, the washing process is crucial in ensuring the quality and purity of the recycled PET bottle flakes. This article delves into the differences between cold washing and hot washing of PET bottle flakes, their respective advantages, and their impact on the recycling process.

Understanding the PET Bottle Recycling Process

The PET plastic bottle recycling process involves several steps designed to efficiently convert used bottles into clean, reusable PET flakes. The primary steps include:

Collection and Sorting: Discarded PET bottles are collected from various sources such as households, businesses, and recycling centers. These bottles are then sorted based on their material type, color, and quality to ensure a uniform feedstock for the recycling process.

Separation: The collected bottles are separated from non-PET materials, such as caps and labels. This separation can be achieved through manual sorting or automated methods, including air classification and density separation.

Crushing: The clean, sorted bottles are crushed into small pieces or flakes. This size reduction facilitates more efficient cleaning and processing in subsequent steps.

Washing: The crushed PET flakes undergo a series of washing steps to remove contaminants such as dirt, oil, adhesives, and other impurities. This step is critical in determining the final quality of the recycled PET flakes.

Drying: After washing, the PET flakes are thoroughly dried to remove any residual moisture, ensuring they are ready for further processing or sale.

Extrusion and Pelletizing: The clean, dry PET flakes can be melted and extruded into pellets, which serve as raw materials for producing new PET products, such as fibers, films, and bottles.

Cold Washing of PET Bottle Flakes

Cold washing is a straightforward process primarily used for initial cleaning of PET bottle flakes. It involves rinsing the flakes in cold water to remove surface dirt, light impurities, and loose contaminants. The steps involved in cold washing include:

Initial Rinsing: After crushing, the PET flakes are transferred to a rinsing tank filled with cold water. This initial rinse helps to remove loose dirt and debris from the surface of the flakes.

Float-Sink Separation: The flakes undergo float-sink separation to remove floating contaminants, such as bottle caps and labels, which are made from materials with lower density than PET.

Cold Water Scrubbing: The flakes are subjected to high-speed friction and scrubbing in cold water, which helps to dislodge more stubborn contaminants and improve the overall cleanliness of the flakes.

Rinsing and Dewatering: After scrubbing, the flakes are thoroughly rinsed with clean cold water to remove any remaining contaminants. The rinsed flakes are then dewatered to remove excess moisture.

Advantages of Cold Washing

Energy Efficiency: Cold washing requires less energy compared to hot washing since it does not involve heating water to high temperatures. This makes it a cost-effective and environmentally friendly option.

Simplicity: The cold washing process is relatively simple and easy to implement, making it suitable for small-scale recycling operations or as a preliminary cleaning step in larger recycling facilities.

Reduced Risk of Material Degradation: Cold washing poses a lower risk of degrading the PET material, as it does not expose the flakes to high temperatures that could potentially affect their physical properties.

Limitations of Cold Washing

Limited Effectiveness on Stubborn Contaminants: Cold washing may not be as effective in removing stubborn contaminants, such as grease, adhesives, and certain types of dirt, which may require more intensive cleaning methods.

Residual Contamination: While cold washing can remove surface dirt and light impurities, it may leave behind residual contamination that can affect the quality of the final recycled PET flakes.

Hot Washing of PET Bottle Flakes

Hot washing is a more intensive cleaning process that involves heating the PET flakes in water, often with the addition of cleaning agents or alkali, to remove stubborn contaminants. The steps involved in hot washing include:

Pre-Soaking: The crushed PET flakes are pre-soaked in warm water to loosen and soften any attached contaminants.

Heating and Agitation: The pre-soaked flakes are transferred to a heating tank where they are boiled at temperatures typically ranging from 85-95°C. During this process, alkali or cleaning agents are added to enhance the cleaning effectiveness.

High-Temperature Scrubbing: The flakes undergo high-speed friction and scrubbing in the hot water, which helps to dislodge and dissolve stubborn contaminants such as grease, glue, and sticker paper.

Hot Rinsing: After scrubbing, the flakes are rinsed with hot water to remove any remaining cleaning agents and dissolved contaminants.

Final Rinse and Dewatering: The cleaned flakes are subjected to a final rinse with clean water to ensure all residues are removed. The rinsed flakes are then dewatered and dried to remove any remaining moisture.

Advantages of Hot Washing

Superior Cleaning Effectiveness: Hot washing is highly effective in removing stubborn contaminants, such as grease, adhesives, and other residues, resulting in higher-quality PET flakes.

Enhanced Purity: The use of hot water and cleaning agents helps to achieve a higher level of cleanliness and purity in the recycled PET flakes, making them suitable for high-value applications.

Improved Material Quality: Properly controlled hot washing can enhance the physical properties of the PET flakes, such as color and viscosity, by effectively removing impurities that could affect their performance in subsequent processing.

Limitations of Hot Washing

Higher Energy Consumption: Hot washing requires more energy to heat the water to the necessary temperatures, making it a more energy-intensive and costly process compared to cold washing.

Complexity: The hot washing process is more complex and requires careful control of temperature, time, and chemical usage to avoid degradation of the PET material.

Potential for Material Degradation: If not properly controlled, the high temperatures and chemicals used in hot washing can potentially degrade the PET material, affecting its quality and usability.

Deep Cold Washing for Residual Chemical Removal

After hot washing, PET bottle flakes may still retain some residual chemical components from the cleaning agents used. To ensure thorough cleanliness and remove any remaining residues, a deep cold washing step is often employed. This involves multiple rinses in cold water to effectively remove any residual chemicals and achieve the highest level of purity.

Steps in Deep Cold Washing

Initial Cold Rinse: The hot-washed PET flakes are subjected to an initial cold rinse to remove the bulk of the residual chemicals.

Multiple Rinses: The flakes are then transferred to additional cold water tanks for further rinsing. Typically, 2-3 rinses are conducted to ensure thorough removal of any remaining contaminants.

Final Rinse and Dewatering: The flakes undergo a final rinse with clean cold water to ensure all residues are removed. The rinsed flakes are then dewatered and dried to remove any remaining moisture.

Importance of Deep Cold Washing

Ensuring Purity: Deep cold washing ensures the removal of any residual chemicals that could affect the quality and safety of the recycled PET flakes.

Preventing Contamination: Thorough rinsing prevents the possibility of chemical contamination in the final product, ensuring that the recycled PET flakes meet stringent quality standards.

Maintaining Material Integrity: Cold rinsing helps to maintain the physical properties of the PET flakes, ensuring they remain suitable for high-value applications.

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Choosing Between Cold and Hot Washing

The choice between cold washing and hot washing depends on several factors, including the degree of contamination of the PET bottle flakes, the desired level of cleanliness, and the specific requirements of the recycling process. Key considerations include:

Degree of Contamination: Heavily contaminated PET bottle flakes may require hot washing to effectively remove stubborn impurities, while lightly contaminated flakes can often be adequately cleaned with cold washing.

Quality Requirements: If the recycled PET flakes are intended for high-value applications that require a high level of purity and cleanliness, hot washing followed by deep cold washing may be necessary to achieve the desired quality.

Energy and Cost Considerations: Cold washing is more energy-efficient and cost-effective, making it suitable for operations where energy consumption and costs are a concern. However, the trade-off may be a lower level of cleanliness compared to hot washing.

Process Complexity: Hot washing is a more complex process that requires careful control of temperature, time, and chemical usage. Recycling operations must have the necessary infrastructure and expertise to effectively implement hot washing.

Conclusion

The washing process is a critical step in the recycling of PET bottle flakes, with cold washing and hot washing offering distinct advantages and limitations. Cold washing provides a simple, energy-efficient, and cost-effective method for initial cleaning, while hot washing offers superior cleaning effectiveness for heavily contaminated flakes. The choice between these methods depends on the specific requirements of the recycling process, the degree of contamination, and the desired quality of the recycled PET flakes. By understanding the differences between cold washing and hot washing, recycling operations can optimize their processes to produce high-quality, clean PET flakes suitable for a wide range of applications.

Our complete PET bottle washing line is an ideal solution for anyone looking to start or improve their plastic bottle recycling business. This fully automated, turnkey solution processes baled PET bottles into contaminant-free PET flakes. These plastic flakes can be sold for high prices to manufacturers of polyester staple fiber or can be pelletized into granules for use in manufacturing other PET products.

While our standard PET bottle washing lines are sufficient for most facilities, custom setups with additional machinery and increased capacity can be designed for your specific needs.

WORKING PRINCIPLE

Our turnkey PET bottle washing line consists of a series of our plastic recycling machines connected using various types of conveyor systems.

Debaler Machine: The first step in our plastic bottle washing line is to break the compacted bales of PET bottles into a free flowing stream. Once the bales are &#;busted&#;, the bottles can move freely onto the next machine.

Trommel: An optional piece of equipment, the trommel is a slowing rotating tunnel lined with small holes. The holes are slightly smaller than the PET bottles so small pieces of contamination (such as glass, metals, rocks/dirt, paper, etc&#;) can fall through while the PET bottles move onto the next machine.

Wet Plastic Granulator: Sometimes referred to as a plastic crusher, our plastic granulator machine cuts the PET bottles into small flakes between 10-15mm in size. With water constantly spraying into the cutting chamber, this wet granulation process pre-treats and partially cleans the material before moving onto the next equipment.

Air Classifier: Air classification is a way to separate lighter materials from heavier ones. The main purpose of using the air classifier is to remove contaminations such as paper, cardboard, and plastic labels away from on PET flakes.

Sink / float Separation Tank: Using water as a medium, materials that float are separated from materials that sink. In the case of plastic bottle recycling, PET plastic will sink while plastic film (bottle labels) and PP/PE plastic (bottle caps) will float. A screw conveyor at the bottom of the sink float separation tank moves the PET plastic to the next piece of equipment.

Hot Washer System: Hot washed PET flakes are of higher value because this process dissolves glues (used to glue labels onto the bottles) and leftover beverages/foods that are difficult to remove in a cold wash process. Although you can just use water in the hot washer system, adding washing agents can added for better results.

Friction Washer: A efficient piece of cold water washing equipment, the high speed friction washer uses friction as a mechanical way to remove any hard to remove dirt and debris from the PET flakes.

Dewatering Machine: The first step in the drying process, our centrifugal dewatering machine uses centrifugal force to remove a large portion of water within the PET flakes before moving forward onto our thermal dryers.

Thermal Dryer: PET flakes are vacuumed out of the dewatering machine into the thermal dryer where it travels down a series of stainless steel tubes mixed with hot air. This process removes any remaining moisture by dehydration. An attached cyclone separator mixes the PET flakes with cool air preparing it for storage in the product silo.

Product Silo: A storage tank for the clean, dry PET flakes.

Pelletizer / Extruder: For the most part, PET flakes are used as is particularly in manufacturing polyester fibers. However, we do have customers requiring plastic pelletizing machines such as our single-screw extruder pelletizers and twin-screw extruder pelletizers.

TECHNICAL SPECIFICATIONS

Input Capacity500 kg/h kg/h kg/h kg/h kg/hRequired Space [LxWxH]42mx10mx6m50mx15mx6m55mx16mx6m60mx18mx6m100mx20mx6mOperators3-5 people6-8 people7-9 people8-10 people10-12 peopleInstallation Power150KW250KW370KW450KW750KWWater Circulation (T/H)*CE certification available.
*Larger, more powerful models available based on your request.

HIGH QUALITY PET FLAKES

Our PET washing line produces high-quality PET flakes that are clean and contamination free. Below are typical benchmarks for PET flakes produced from this recycling line:

1. Moisture: < 1-2%
2. Bulk Density: < 0.3G/CM3
3. Total Impurity: < 320ppm
   • PVC Content: < 100ppm
   • Metal Content: < 20ppm
   • PE/PP Content: < 200ppm
4. Particle Size: < 14-16mm

ADDITIONAL VIDEOS & IMAGES

WARRANTY & INSTALLATION

All recycling machinery comes with a limited warranty

We offer installation packages where our engineers travel to your facility to guide your through the installation process the. Routine maintenance teams and operations consultants can also be arranged to ensure your PET recycling plant runs smoothly year and year.

INQUIRIES

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