Garry R. Kenny, Mitchell G. Roe, Felix A. HottensteinR'99, February 2-5, 1999, Switzerland

Abstract

A fundamental change in plastic bottlerecycling has occurred during the last two years – more plastic bottles are nowsorted using automated equipment than are being sorted by manual means. New configurationsof automated plastic separation equipment are now available as well as new sensor systems.This paper presents the current status of automated plastics separation, new sorting andsensor systems, and details the economics of automated versus manual sorting systems.

Background

Development of systems to auto-matically sortpost consumer plastic bottles began in 1989 at Rutgers Uni-versity (1). Thefirst commercial systems to separate PVC from PET utilizing x-rays were introduced in 1991(2,3). Also in 1991, MSS introduced a multi-resin system for separation of PVC,clear and colored PET, natural HDPE and PP, and pigmented HDPE plastic bottles usingabsorption of x-ray, visible and near infrared electro-magnetic radiation. Other MSSseparation technology developments have also been reported (4,5).

The use of automated plastic bottle separationequipment by processors of recycled plastics has increased substantially since that time.In the last two years at least seven complete automated plastic bottle systems forindustrial applications have been installed worldwide. These systems, in conjunction withindividual separation modules, have increased the automated plastics sorting capacity bynearly 100,000 tons per year (220,000,000 lbs/yr). Currently over 200 process lines orseparation modules are operating world wide to automatically separate plastic bottles byresin type or color.

Primary Needs for Plastics Recycling

Two dominant needs must currently be addressedin order for plastics recycling to continue to increase. The first need is an increase inthe availability of post consumer plastics. Due to the increased usage of plastics inpackaging applications, particularly PET, the actual percentage of plastics recycling hasdeclined in several countries, most notably the United States. Significant price swingsover the past few years contributed to a reduction in the number of cities collectingrecyclable materials. Additionally, a general decrease in public interest in recycling hasalso contributed to a slowing in the rate of increase of recyclable plastics collection.

Recovery of recyclable metal, glass, and paper frommunicipal waste and collection systems has been practiced for a number of years, butplastics recovery has been limited to collection systems. Plastics recycling, with a morerestricted supply source, are at greater risk from market downturns than the abovematerials as the recycling infrastructure is not as mature.

Plastics Supply

A potential new source is the recovery of recyclableplastics from mixed municipal waste. Such a facility has been placed in operation sinceJuly 1998 in the Crisp County Facility in Cordeal, Georgia, USA. It is located in a ruralarea and provides collection to 21 different counties. The member counties are relativelysparsely populated and as such do not provide curbside collection of recyclable materials.

The facility has a processing capacity of 1,000 tonsof municipal waste per day and uses a combination of separation equipment to process raw,mixed municipal waste into recyclable components. The process includes, trommel screens,magnetic separators for ferrous metal, eddy current separators for nonferrous metal, andan automated system for separation of plastic containers. An extensive composting processis also integral to the facility.

The recovery of post consumer plastic containersfrom mixed municipal waste represents a new source of recycled plastics. The plasticseparation equipment recovers an average of 40 tons per day or 14.000 tons per year ofseparated plastics.

The plastics separation system was designed by MSSto separate the plastic into five components: 1) PVC, 2) Clear PET, 3) Colored PET, 4)Natural HDPE, and 5) Mixed Color HDPE. The separation system utilizes x-ray-based sensorsfor PVC identification, in addition to using near infrared and visible light sensors forthe remaining sorts. The separation system has passed performance tests with respect tothe designed capacity of 2,200 kg/hr (5,000 lbs/hr) while providing plastic puritieswithin specifications.

The installation of ten Crisp county typeinstallations would increase the amount of post consumer plastics available for recyclingby nearly 30 percent in the U.S. alone. In addition, installation of Crisp county typefacilities are being considered in a number of countries where relatively low populationdensities favor this approach to municipal waste processing with recyclable recovery.

Cost Savings and Economic Analysis

The second need for significant increase of plasticsrecycling is a reduction in processing costs, and ultimately the cost of the end product-- clean, recycle plastic flake. Recycle plastic must compete directly with virgin resinin both quality and price. Variations in plastics demand versus production capacity leadsto significant variations in the price of virgin resin. This resulting virgin pricevariation has made profitability very difficult to achieve for recycle plastics producers.As a result decreases in processor production costs are critical to the viability ofplastics recycling in the future.

The introduction of automated plastics sortingequipment has both improved the quality and reduced the cost of plastics recycling overthe past seven years. The cost saving over manual separation varies with the specific mixof plastics. In general, the more complex the mixture, the greater the saving due toautomation.

In the case of separation of PVC and PET plastics,cost saving is secondary to the quality of the separation. It has been shown that manualseparation of PVC from PET is not adequate, and that automated separation is required foracceptable PET quality. Plant operating experience has shown that a single PVC sepa-rationunit can produce average PET purities of 100 to 200 ppm (PVC content). Most recentinstallations, however, utilize two PVC separation units in series, which reduces averagePVC content to 20 to 30 ppm. The addition of a flake PVC separation equipment to the abovebottle removal equipment, such as the MSS VYDAR system, can reduce PVC levels topreviously unobtainable levels of 3 to 5 ppm range.

A study performed by the engineering firm of R. W.Beck (6), conducted in 1994, showed cost savings of 20% to 28% for an MSSautomated sorting system versus a manual sorting line operation. In addition, recentanalysis of operational and planned automated PET sorting facilities in Switzerlandsubstantiates a reduction in sorting costs of between 15% to 50% for automated versusmanual sorting. This improvement over the 1994 study results is predominantly due toimprovements in the efficiency of the automated equipment. These improvements include useof mass sorting technology as opposed to singulating type systems, and improved sensortechnology. The detailed results of the analysis are given in Table 1.

MRF Sorting Applications

The primary supply of recycled plastics to thereclaimers in the U.S., France, Germany, Canada, and some other countries are MaterialRecycling Facilities (MRF’s). These facilities function to accept mixed recyclablescollected at the curbside or deposited in dropoff boxes. The MRF’s function is toprovide the basic separations required to add value to the individual recyclablecomponents such as ferrous and nonferrous metals, plastics, paper and cardboard.

The degree to which the plastics are sorted by resinand/or color type depends upon the individual MRF. Additionally, the number of manualsorters required is higher for non-automated MRF’s than would be required ifautomated equipment were employed. For example, in the Allied Waste facility in Chicago,Illinois, USA the number of persons required to separate the plastic waste was reduced by4 to 6 persons after automated plastic sorting was installed. This resulted in costsavings such that the automated equipment payback time was less than sixteen months.

In addition to the cost savings, the quality of thePET plastic was improved significantly with respect to PVC content. Although the pricepaid for the reclaimed PET has not increased at this point in time, the ability to sellthe PET in down markets has improved.

A new plastics separation module has been developedspecifically to fit in MRF systems. The unit is designated the MFR-0-Matic™ and isable to separate PET and natural HDPE from a mixed bottle stream. The module provides ahigh purity output stream to minimize the requirement for final quality control. It isdesigned with a small footprint to facilitate installation in existing MRF facilities.Modules with capacities of 1,000 and 2,000 kg/hr (2,200 and 4,400 lbs/hr), respectively,are available.

New Systems for DSD Material

The separation cost of plastic materials inthe German DSD system is currently relatively high. A significant portion of this cost isdue to the high cost of manual sorting. To reduce these costs, automated sorting moduleshave been introduced to the German DSD sorting plants.

Two basic types of systems are currently availablefor this application:

1. all plastics away from other materials
2. aseptic packaging away from other materials.

Over the past year approximately 50 such systemshave been installed in DSD plants. The labor saving due to these installations has beensignificant, and additional automation will further reduce cost.

Two companies currently provide modules that fit theDSD type sorting plant applications, MSS and TiTech (7). The MSS systems areprovided under the names of PlasticSort™ and CartonSort™ respectively. TheTiTech systems are provided under the name of AutoSort™. Both systems utilizereflective near infrared sensors for identification of plastic and aseptic packagingmaterials, and as such are able to be positioned over an existing or new conveyor system.After identification, the selected material is ejected either downward or upwardperpendicular to the flow of the feed stream by an array of air jet ejectors. The systemshave a capacity of between 2 and 2.5 tons/hr (4,400 to 5,500 lbs/hr) with a sortingaccuracy of 80% to 90% depending upon the feedstream and the material removed.

Flake Analysis Systems

The ability to identify and separate plasticresin in a flake or granulated form has the potential to save plastics processorssignificant costs, both in processing and quality control costs. MSS recently completed astudy for an analysis system which can quantify the amount of PEN plastic (PolyethyleneNaphthalate) present in PET flake. The American Plastics Council, under the direction ofthe Naphthalate Stewardship Council sponsored the study.

Work is currently underway by MSS to develop asystem to identify PVC content in parts per million of PVC in granulated PET. The systemis designed to provide online PVC measurements at a rate of 25 to 30 kg/hr. Applicationsinclude batch testing of processed PET as well as real time online analysis of granulatedPET streams.

The availability of equipment to enable sorting ofplastic flake by resin type would in many cases eliminate the need to bale the plasticbottles, and then debale them at a processing facility, thereby significant reducinghandling costs. The cost of such flake separation systems will however be relatively high.System feed rate will be limited by the need to separate the individual flakes cleanly,rather than removing a few flakes at ppm level as a contaminant.

New Sensor Technologies

From a technical standpoint it is desirable todevelop and apply one single sensor type to identification and separation of all plasticresin types and colors. However, experience in recycling facilities shows that bottlesthrown away by consumers are often significantly distorted and covered or filled bycontamination or labels. We have found that resin specific sensors in general providebetter separation than any single sensor currently available. One example is thedevelopment by MSS of a specific sensor for identification of PEN resins.

The development of a sensor to identify PEN andPEN/PET blends in a stream of PET bottles follows this philosophy. The sensor developmentwas partially funded by AMOCO and Shell Chemical, who recognized that recycling of PETbottles was a large and viable industry which could potentially be impacted by theintroduction of PEN bottles.

This support is noteworthy in that it was providebefore introduction of PEN to the market, thereby insuring that a system for PENseparation was available when it was needed.

Two generations of PEN sensor systems wereextensively field-tested at the Wellman recycling facility in Johnsonville S.C. Wellmanprovided the equipment and support to expose the PEN test containers to the typicalrecycle conditions of baling, debaling, and materials handling. The test PEN containerswere also provided with simulated labels.

The results of the testing of the PEN separationsystem shows an identification accuracy of between 92% and 99% depending upon the type ofbottle tested. The presence of food contamination or labels reduced the system sortingaccuracies by only a small amount.

MSS recently completed work on the development of asensor system for identification of PAN (Polyacrylonitrile) plastic bottles. This work hasbeen partially funded by BP Chemical. Laboratory testing of the system shows anidentification accuracy of 92% to 98% for test bottles. Both the PEN and PAN separationsystems, utilizing the developed sensor, is now commercially available.

Conclusions

Currently the dominant requirements to insureviability of plastics recycling are new sources of plastics, lower processing costs, andhigher quality available through newly available technologies. These requirements arebeing addressed through a combination of new process systems and equipment. The impact ofnew plastic packaging resins, such as PEN and PAN, on the recycling infrastructure isbeing addressed by the development of new sensors and their associated sorting systems.Development in plastic flake identification and separation promises advances in the abovecritical areas in the future. And finally, experience with operating automated plasticsseparation facilities demonstrates a significant cost advantage over manual separation.

References

1. Rutgers University Center for Plastics Research
2. Govoni Simbianca
3. National Recovery technologies, Inc.
4. High Speed Plastic Bottle Identification - Industry Review and New Developments in Plastics Sorting - IdentiPlast Conference, Brussels, Belgum, October,1997, G. Kenny, M. Roe, R. Bruner.
5. New Challenges and Developments in Plastic Sorting - R97 Conference, Geneva, Switzerland, February 1997, G. Kenny and C. Crow.
6. R. W. Beck
7. TiTech, Norway