BEST PRACTICES IN PET INTERMEDIATE PROCESSING Sorting Systems: Introduction and Overview
Due to the increase in curbside collection programs that collect recyclables in a commingled fashion, there has been an increase in the need for reliable and effective sorting systems that separate post-consumer PET plastics from other plastic and non-plastic containers and to remove other contaminants that might be present To recover PET plastic bottles and containers from commingled recyclables, they must be delivered to a MRF and separated from other recyclable materials to prepare them for sale to an intermediate processor, PRF, reclaimer or end-user.
There are two generic types of sorting systems used at plastics recycling facilities. These are manual sorting systems and automated sorting systems. Manual systems rely on plant personnel who visually identify and physically sort plastic bottles traveling over a conveyor belt system. Automated systems employ a detection system, or combination of detection systems, that analyze one or more properties of the plastic bottles passing through and automatically sorts these plastics into several categories, either by resin type, color, or both.
The sorting system chosen for a particular facility is a function of several important factors. While cost factors influence system purchasing decisions, sorting system design is primarily a function of incoming plastic quality and level of commingling of plastic containers of different resin types. For example, bales of resin-segregated PET bottles and containers lend themselves to one type of sorting, while bales of two or more commingled plastic container types may require a different approach.
In addition, sorting system design will depend on whether the plastics recycling facility is baling or granulating the plastics they receive from their suppliers. For example, baling operations at MRFs, IPCs or PRFs generally use less expensive and less sophisticated sorting systems than PRFs that debale, sort and granulate incoming bales of plastic into individual resin and color categories for sale to reclaimers and end-users. PRFs that granulate PET plastic bottles and
containers often combine manual and automated sorting systems to ensure the highest level of quality control for the regrind they produce.
Regardless of the specific type of plastic recycling facility and the sorting system used, there are several design elements that can be incorporated into a sorting line that will help minimize the presence of contaminants that must be removed either manually or automatically and improve the overall quality of the PET recovered. Whether plastic bottles or containers are entering a facility in loose or baled form, most system designs will feed plastic bottles via an inclined conveyor system to a horizontal conveyor system from which containers will be sorted. A best practice for sorting system design is to install a screening device over which incoming material will pass prior to moving on to the next stage of the sorting process. Screening will remove grit, dirt, broken glass and other non-plastic contaminants and pieces of non-PET plastic caps, base- cups and bottles that can get trapped inside bottles and potentially contaminate regrind. This can be accomplished by using various commercially available screening devices, such as trommel screens, or vibrating screens (also called “shaker tables”) that the FET bottles and containers pass over before they are discharged onto the sorting line.
In some cases simpler systems can be used, for example, screen tables onto which incoming plastic bottles are placed and then raked across by plant personnel into the feed hopper of the sorting system. Screens can also be installed in the conveyor system where materials drop from one conveyor to another. This design feature can greatly reduce the amount of smaller contaminants that might be difficult to identify and remove later in the sorting process by either manual or automated systems.
What follows is a brief description and discussion of manual and automated sorting systems. This discussion is directed towards plastics intermediate processing facilities that are granulating PET plastic bottles and containers for sale to reclaimers or end-users. This is followed by Best Practices for each system category.
Manual sorting systems
Manual sorting systems use trained inspectors to visually identify and sort PET bottles and containers into designated categories from a stream of plastic bottles passing over a conveyor. Manual sorting systems are generally one of two types -- positive or negative sort systems. In a positive sort system, PET bottles and containers are removed from a stream of plastic containers being earned over a conveyor system. In a negative sort system, PET bottles and containers are left on the conveyor system and unwanted materials or contaminants are removed from the conveyor line.
When PET bottles and containers are removed in a positive, manual sort, they are either fed directly into a granulator or onto a second conveyor system that feeds into a granulator. The advantage of a system where line inspectors feed a second conveyor is that the second
conveyor can be designed to incorporate an automated sorting system as a final check for PVC prior to feeding the granulator.
Throughout the plastics recycling industry, positive sort systems are considered best in generating the highest quality materials. However, they may not always result in the most efficient system as positive sorts are generally more time consuming than negative sorts. The sorting capacity of plant personnel working on manual sorting lines is a function of the quality of incoming materials, system design and belt speed.
Negative manual sort systems are generally considered to have a potential for greater levels of contamination as many negative sort systems are configured to discharge materials left on the conveyor belt directly into a baler or grinder. If the removal of unwanted materials is not complete, these unwanted materials will enter the next stage of processing and possibly yield contaminated material. However, negative sort systems work well if materials have been “pre¬sorted” into specific categories. (Negative sort systems also work well for baling operations). For example, it is easier to pick out contaminants from a stream of predominantly PET soda bottles, rather than to pick out the soda bottles. Some negative sort systems are designed to have inspectors sort from both sides of a conveyor that feeds directly to a baler or grinder to increase material throughput.
Ultimately the choice between positive and negative sort system designs will depend on program budget and the supply characteristics of incoming materials. For example, mixed plastic bottles, whether loose or in bales, are best sorted with a positive sort system, whereas resin segregated plastic bottles may lend themselves towards a negative sort system.
Studies of commercial, manual, visual sortation systems conducted by Plastic Technologies, Inc. (PTI), of Toledo, Ohio, indicate that trained inspectors are capable of sorting 500 to 600 pounds of PET per hour and are more than 80% effective at dentifying and removing PVC from the line. However, sorting capability is always a function of the density of plastic bottles feeding the line, belt speed, and the number of plastic bottle types mixed in the stream.
It is often difficult to visually distinguish PVC bottles from PET bottles without individually inspecting a bottle for a characteristic molding mark or looking for crease marks that occur on PVC bottles when pinched. This is particularly true when a large number of bottles are passing over a conveyor surface and such individual bottle inspection is not cost effective. The efficiency of visual, manual sorting systems in removing PVC from PET can be improved through the use of ultraviolet (LTV) fight. While ultraviolet fight is not visible to the human eye, certain materials, because of their unique chemical structure, emit visible fight when exposed to ฟtraviolet fight which can then be detected by the human eye. When materials emit fight when exposed to uv fight they are said to fluoresce.
PET is fluorescent and appears blue when exposed to uv fight. The chemical structure of PVC does not cause fluorescence, but many of the additives used in the manufacture of PVC bottles do. These additives will cause PVC bottles and containers to appear yellow or green when exposed to uv light. By designing systems that expose bottles passing over a conveyor to ultraviolet lights, removal efficiencies for PVC by trained personnel can increase to as much as 99% under the proper conditions, according to PTI. Because of the concentration required by this kind of identification procedure, it is recommended that line inspectors work no more than two hours at a time.
However, there are limits to the effectiveness of sortation with uv light. “Pre-sorting” is necessary prior to uv sorting of PVC from PET. For example, green PET bottles must be sorted out, as green PET bottles will remain green when exposed to uv fight and can be confused with PVC. Because uv light can degrade certain plastics over time, many PVC and PET containers are manufactured with additives to absorb the uv portion of natural sunlight to protect the products contained in them. These containers will appear dark under uv light and are difficult to detect. Some blue tinted PVC bottles can fluoresce blue under uv tight and be confused with PET bottles, adding to its limitations. Finally, some forms of uv tight have been linked to the formation of cataracts and skin cancer. Although the type of uv tight used in sort systems is considered safe, systems should be designed with shields and viewing windows that filter out UV tight to prevent worker exposure and avoid any possible exposure risks.
Automated Sortins Systems
Automated sorting te
BEST PRACTICES IN PET INTERMEDIATE PROCESSING Sorting Systems: Introduction and OverviewDue to the increase in curbside collection programs that collect recyclables in a commingled fashion, there has been an increase in the need for reliable and effective sorting systems that separate post-consumer PET plastics from other plastic and non-plastic containers and to remove other contaminants that might be present To recover PET plastic bottles and containers from commingled recyclables, they must be delivered to a MRF and separated from other recyclable materials to prepare them for sale to an intermediate processor, PRF, reclaimer or end-user.There are two generic types of sorting systems used at plastics recycling facilities. These are manual sorting systems and automated sorting systems. Manual systems rely on plant personnel who visually identify and physically sort plastic bottles traveling over a conveyor belt system. Automated systems employ a detection system, or combination of detection systems, that analyze one or more properties of the plastic bottles passing through and automatically sorts these plastics into several categories, either by resin type, color, or both.สำหรับสิ่งอำนวยความสะดวกเฉพาะระบบเรียงลำดับคือ ฟังก์ชันของปัจจัยสำคัญหลายประการ ในขณะที่ต้นทุนปัจจัยอิทธิพลระบบซื้อตัดสินใจ การเรียงลำดับการออกแบบระบบเป็นฟังก์ชันหลักของคุณภาพพลาสติกขาเข้าและระดับของ commingling ของบรรจุภัณฑ์พลาสติกชนิดต่าง ๆ ยาง ตัวอย่าง ก้อนแยกเรซิน PET ขวดและบรรจุภัณฑ์ยืมตัวเองชนิดหนึ่งของการเรียงลำดับ ในขณะที่ก้อนสอง หรือมากกว่าสองชนิดบรรจุภัณฑ์พลาสติก commingled อาจต้องใช้วิธีที่แตกต่างกันนอกจากนี้ เรียงลำดับการออกแบบระบบจะขึ้นอยู่กับว่าพลาสติกบาลิง หรือ granulating พลาสติกรีไซเคิลสิ่งอำนวยความสะดวก ที่ได้รับจากซัพพลายเออร์ของตน บาลิงการดำเนินงานใน MRFs, IPCs หรือ PRFs โดยทั่วไปใช้ไม่แพง และมีความซับซ้อนน้อยกว่าระบบเรียง PRFs ที่ debale เรียงลำดับ และเม็ดเป็นเมล็ดเข้าก้อนพลาสติกเรซิ่นแต่ละและประเภทสีขาย reclaimers และผู้ใช้ PRFs ที่ขวดพลาสติก PET เม็ดเป็นเมล็ด และ ภาชนะบรรจุมักรวมระบบเรียงลำดับด้วยตนเอง และอัตโนมัติให้ regrind ผลิตควบคุมคุณภาพระดับสูงสุดโดยเฉพาะชนิดพลาสติกรีไซเคิลสิ่งอำนวยความสะดวกและระบบเรียงลำดับที่ใช้ มีองค์ประกอบการออกแบบต่าง ๆ ที่สามารถรวมเป็นเรียงลำดับบรรทัดที่จะช่วยลดของสารปนเปื้อนที่ต้องเอาออกด้วยตนเอง หรือโดยอัตโนมัติ และปรับปรุงคุณภาพโดยรวมของสัตว์เลี้ยงที่กู้คืน ว่าขวดพลาสติกหรือภาชนะใส่สิ่งอำนวยความสะดวกในแบบฟอร์มการหลวม หรือเสีย baled ออกแบบระบบส่วนใหญ่จะกินขวดพลาสติกผ่านระบบการลำเลียงเข้าใจกับระบบสายพานลำเลียงแนวนอนซึ่งจะเรียงลำดับบรรจุภัณฑ์ ควรเรียงลำดับการออกแบบระบบคือการ ติดตั้งอุปกรณ์คัดกรองผ่านวัสดุที่เข้ามาจะผ่านก่อนย้ายไประยะถัดไปของการเรียงลำดับในการ คัดกรองจะเอา grit สกปรก แก้ว และอื่น ๆ สารปนเปื้อนไม่ใช่พลาสติก และชิ้นส่วนของหมวกพลาสติกไม่ใช่ PET ฐานถ้วย และขวดที่สามารถได้รับการติดอยู่ภายในขวด และอาจปนเปื้อน regrind นี้สามารถดำเนินการ โดยใช้ต่าง ๆ ในเชิงพาณิชย์ตรวจอุปกรณ์ เช่นหน้าจอ trommel หรือระบบสั่นหน้าจอ (ยังเรียกว่า "ตารางที่เชคเกอร์") ว่า FET ขวดและบรรจุภัณฑ์ผ่านก่อนที่พวกเขาจะออกไปยังบรรทัดเรียงลำดับได้ในบางกรณีสามารถใช้ง่ายกว่าระบบ ตัวอย่าง ตารางหน้าจอลงในขวดพลาสติกที่เข้ามาอยู่แล้ว raked ข้ามโดยพืชในถังตัวดึงข้อมูลของระบบเรียงลำดับ หน้าจอสามารถยังติดตั้งระบบสายพานลำเลียงซึ่งปล่อยวัสดุจากเครื่องหนึ่งไปยังอีก คุณลักษณะการออกแบบนี้สามารถมากลดปริมาณสารปนเปื้อนที่มีขนาดเล็กที่อาจจะยากที่จะระบุ และลบออกในภายหลังในการเรียงลำดับด้วยตนเอง หรืออัตโนมัติระบบสิ่งต่อไปนี้เป็นคำอธิบายสั้น ๆ และสนทนาด้วยตนเอง และอัตโนมัติระบบเรียงลำดับ สนทนานี้อยู่โดยตรงต่อการอำนวยการประมวลผลกลางพลาสติกที่มี granulating PET ขวดพลาสติกและบรรจุภัณฑ์สำหรับการ reclaimers หรือผู้ขาย ตาม ด้วยแนวทางปฏิบัตินี้สำหรับแต่ละประเภทระบบระบบเรียงลำดับด้วยตนเองระบบเรียงลำดับด้วยตนเองใช้ฝึกอบรมผู้ตรวจสอบเพื่อระบุ และเรียงลำดับขวด PET และบรรจุภัณฑ์เป็นประเภทกำหนดจากกระแสของขวดพลาสติกที่ผ่านการลำเลียง ระบบเรียงลำดับด้วยตนเองเป็นโดยทั่วไปหนึ่งในสองชนิด - ระบบการจัดเรียงที่เป็นค่าบวก หรือค่าลบ ในระบบเรียงลำดับบวก ขวด PET และภาชนะบรรจุจะออกจากกระแสสุขภาพที่กำลังได้รับผ่านระบบสายพานลำเลียง ในระบบการจัดเรียงที่เป็นค่าลบ ขวด PET และภาชนะบรรจุจากระบบสายพานลำเลียง และวัสดุที่ไม่พึงประสงค์หรือสารปนเปื้อนจะถูกลบออกจากบรรทัดการลำเลียงWhen PET bottles and containers are removed in a positive, manual sort, they are either fed directly into a granulator or onto a second conveyor system that feeds into a granulator. The advantage of a system where line inspectors feed a second conveyor is that the secondconveyor can be designed to incorporate an automated sorting system as a final check for PVC prior to feeding the granulator.Throughout the plastics recycling industry, positive sort systems are considered best in generating the highest quality materials. However, they may not always result in the most efficient system as positive sorts are generally more time consuming than negative sorts. The sorting capacity of plant personnel working on manual sorting lines is a function of the quality of incoming materials, system design and belt speed.Negative manual sort systems are generally considered to have a potential for greater levels of contamination as many negative sort systems are configured to discharge materials left on the conveyor belt directly into a baler or grinder. If the removal of unwanted materials is not complete, these unwanted materials will enter the next stage of processing and possibly yield contaminated material. However, negative sort systems work well if materials have been “pre¬sorted” into specific categories. (Negative sort systems also work well for baling operations). For example, it is easier to pick out contaminants from a stream of predominantly PET soda bottles, rather than to pick out the soda bottles. Some negative sort systems are designed to have inspectors sort from both sides of a conveyor that feeds directly to a baler or grinder to increase material throughput.Ultimately the choice between positive and negative sort system designs will depend on program budget and the supply characteristics of incoming materials. For example, mixed plastic bottles, whether loose or in bales, are best sorted with a positive sort system, whereas resin segregated plastic bottles may lend themselves towards a negative sort system.Studies of commercial, manual, visual sortation systems conducted by Plastic Technologies, Inc. (PTI), of Toledo, Ohio, indicate that trained inspectors are capable of sorting 500 to 600 pounds of PET per hour and are more than 80% effective at dentifying and removing PVC from the line. However, sorting capability is always a function of the density of plastic bottles feeding the line, belt speed, and the number of plastic bottle types mixed in the stream.It is often difficult to visually distinguish PVC bottles from PET bottles without individually inspecting a bottle for a characteristic molding mark or looking for crease marks that occur on PVC bottles when pinched. This is particularly true when a large number of bottles are passing over a conveyor surface and such individual bottle inspection is not cost effective. The efficiency of visual, manual sorting systems in removing PVC from PET can be improved through the use of ultraviolet (LTV) fight. While ultraviolet fight is not visible to the human eye, certain materials, because of their unique chemical structure, emit visible fight when exposed to ฟtraviolet fight which can then be detected by the human eye. When materials emit fight when exposed to uv fight they are said to fluoresce.
PET is fluorescent and appears blue when exposed to uv fight. The chemical structure of PVC does not cause fluorescence, but many of the additives used in the manufacture of PVC bottles do. These additives will cause PVC bottles and containers to appear yellow or green when exposed to uv light. By designing systems that expose bottles passing over a conveyor to ultraviolet lights, removal efficiencies for PVC by trained personnel can increase to as much as 99% under the proper conditions, according to PTI. Because of the concentration required by this kind of identification procedure, it is recommended that line inspectors work no more than two hours at a time.
However, there are limits to the effectiveness of sortation with uv light. “Pre-sorting” is necessary prior to uv sorting of PVC from PET. For example, green PET bottles must be sorted out, as green PET bottles will remain green when exposed to uv fight and can be confused with PVC. Because uv light can degrade certain plastics over time, many PVC and PET containers are manufactured with additives to absorb the uv portion of natural sunlight to protect the products contained in them. These containers will appear dark under uv light and are difficult to detect. Some blue tinted PVC bottles can fluoresce blue under uv tight and be confused with PET bottles, adding to its limitations. Finally, some forms of uv tight have been linked to the formation of cataracts and skin cancer. Although the type of uv tight used in sort systems is considered safe, systems should be designed with shields and viewing windows that filter out UV tight to prevent worker exposure and avoid any possible exposure risks.
Automated Sortins Systems
Automated sorting te
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