Recyclers who have specialized in the separation and sorting of mixed plastics have implemented some of the newest advances in these technologies.
As the recovery and separation of plastics from consumer and commercial waste streams becomes more of a global priority, at least one industry expert says it’s become virtually impossible for material recovery facilities (MRFs) to continue to sort polymers by hand.
That’s the belief of Sebastien Petithuguenin, deputy managing director of Paris-based Paprec Group, a leading French recycling company with some 80 sites and 3,500 employees. Paprec Group handles more than 5 million tonnes of waste and recovers 3 million tonnes of recyclables.
“Automatic sorting will sooner be mandatory to sort plastics from households,” Petithuguenin says. “As a lot of different materials appear in a MRF, and as the material coming into the MRF will always be variable, optical sorting can adapt to these changes. Optical sorting is, therefore, the most used and the most mature for the households MRF.”
Etiene De Beauval, an officer with Paprec Group, says the positioning of optical sorters in a MRF depends highly on what type of MRF is handling the plastic. Those dedicated to processing mixed materials, he says, first need to separate plastics from nonplastics. “Then, at the end of the facility, the sorters will separate the mixed plastic into different streams.”
More specialized MRFs would require a different setup, he says.
“In a MRF dedicated to plastics, the best place to put the sorters is at the beginning of the line,” says De Beauval. “Further recycling stages would need a very pure material.”
Increasing Options in Plastics Sorting
Near-infrared (NIR) sorting technology is one of the most commonly used methods the world over when it comes to sorting mixed plastics. However it is certainly not the only choice out there, notes Etienne De Beauval, an officer with France-based Paprec Group.
De Beauval says three main optical technologies remain key for sorting plastics: bichromatic colour sorters that can separate by colour or shape; NIR cameras that can recognize polymers; and X-ray fluorescence technology that can analyse the molecular structure, enabling the machine to sort by additive.
“In terms of colour, bichromatic colour sorters are mature now and can separate flakes from colour into different streams,” he says. He explains that the method uses halogen lamps to illuminate the flakes. The reflected light is detected by a sensor, the information is sent to a processing unit and control valves then eject objects in two or three categories, by colour families or by shape.
Meanwhile near-infrared cameras can recognize specific polymers and optimize the purity of the material. “Near-infrared spectroscopy is based on the analysis of a reflection spectrum whose signature reveals the structure of molecules,” he says. After information is processed, nozzles eject objects into two or three categories. “The limit is that NIR cannot read brown or dark objects,” De Beauval notes.
And X-ray fluorescence technology is being used to analyze the molecular structure of the plastic, thus enabling the sorter to sort the polymer by additive, De Beauval says. “The identification by X-ray fluorescence is mainly used for negative sorting: it is to remove undesirable products such as bromated or chlorinated PVC (polyvinyl chloride) from a presorted feed.”
When it comes to sorting plastics from WEEE (waste electrical and electronic equipment), De Beauval says recyclers can use NIR technology as well as various flotation methods to achieve maximal purity. Additionally, electrostatic separation technology can be employed.
Some of the most technologically advanced sorting methods are happening in facilities that specialize in the recycling of mixed plastics.
As one example, Hanbury Plastics Recycling (HPR), headquartered in Stoke-on-Trent in the U.K., is a new company that has implemented some of the newest separation technology. The company was set up in mid-2011 specifically to create a number of high quality plastic feedstock materials by sorting commingled postconsumer scrap into separated polymer streams. The company plans to begin sorting commercial scrap in future months, but presently most of the material comes from kerbside collections, says Managing Director Rick Devine.
“We see ourselves sitting between a MRF and a plastic reprocessor,” says Devine. “We segregate the materials into the different polymers and even by different colours and then supply them to plastic reprocessors for further processing.”
One of the company’s newest technologies in use is a three-way sorting unit, manufactured by Redwave, Gleisdorf, Austria, that was installed in 2012 and brings the number of HPR’s near-infrared sorting units to five.
HPR processes some 40,000 tonnes per year of mixed kerbside collected plastic material. The company brings in a variety of baled mixed plastics, including bottles, tubs and trays, from various sources throughout the U.K. and produces a range of end products that includes film, natural HDPE (high-density polyethylene), natural PET (polyethylene terephthalate), coloured HDPE, coloured PET and PP (polypropylene). But all of those grades are typically mingled together in the bales that HPR receives on the front end.
After bales are broken open and metals are removed, the material goes through a series of five near-infrared sorters. According to Devine, much of the material has been subjected to only basic levels of sorting.
Devine says all of the sorters have basically the same function: picking out different types of plastic, and all can be tuned to sort for a variety of polymers. The company has two sorters made by Titech, Mühlheim-Kärlich, Germany, and three Redwave sorting units, including the three-way machine. The plastic sorting line then feeds into a fully automatic twin-ram baler. The line is rated at 5 tonnes per hour, Devine says, and is operated 24 hours a day, seven days a week.
The first two optical sorters, both from Titech, are 2-metre-wide sorters fed from a vibrating table. The first sorter takes out PP and the second pulls clear and light blue PET, Devine explains. Next is the new three-way unit that can select, or positively sort, two different types of plastics.
“It has two sets of valve blocks,” says Devine, “so once the material passes under the spectrum of light, the computer can select two different materials to be ejected separately.” He says one valve block is slightly before the other, enabling the machine to segregate two different materials at once.
“We can change the settings on any of the near-infrareds to pick out any different plastic that we need,” he says. Currently, he adds, the three-way unit is picking out natural HDPE and coloured or green PET. Devine notes that this new machine can be tuned to detect solid white HDPE bottles used by some milk bottlers. “There’s a setting on the Redwave that these are missed, so that we just get pure translucent milk bottles.” In that case, the white bottles are kept with the coloured HDPE.
Fourth is a cleanup sorter, and the fifth sorter picks out coloured HDPE. Any residual material gets sent back to the beginning of the line for another look, Devine says. “Because near-infrared sorters typically have a hit rate of somewhere around 90% to 92%, they are missing 8% or 10% of what has come through; this material then gets sent back to the beginning of the process.”
Devine says HPR decided to install the new sorter after witnessing the new machine in action at another facility in Austria. It also has received a guarantee from the manufacturer of sorting with 93% purity. “We actually exceeded that on the trials,” Devine says of the equipment.
Devine says that while no specific additions are planned, there is room for another line to be added within the facility. He also says any black plastic that comes across the lines ends up as residue.
While black plastics cannot be positively sorted, he says HPR is looking into the feasibility of segregating them via shredding and flotation.
From Bales to Bottles
Another sizable plastics recycler in the U.K. is ECO Plastics Ltd. based in Hemswell, in Lincolnshire. Jonathan Short, managing director of the company, says ECO Plastics processes 150,000 tonnes per year of mixed post-consumer plastics from kerbside collections. The company operates what it calls one of the largest and most technologically advanced mixed plastic bottle sorting facilities in Europe. According to the company’s website, it is currently the only U.K. business producing food-grade quality PET pellets.
The company’s Hemswell plastic bottle sorting facility has numerous Titech optical sorters on the front end of the sorting operation that sort the mixed plastics both by colour and by polymer into individual streams, using near-infrared technology to detect polymer type and cameras to detect colour. “We have 20 in total and decided to introduce the high specification multifunction units to afford us full flexibility,” Short explains. The company then washes and extrudes the PET into food-grade recycled PET pellets.
One offshoot of the company’s work is its involvement with Continuum Recycling, ECO Plastics’ award-winning joint venture with Coca-Cola Enterprises Ltd. of the U.K. Continuum’s centerpiece is its high-end extrusion machine that has been approved to make a food-grade material from plastic scrap and has passed Coca-Cola’s validation program so that the pellets can be used to make PET bottles for Coca-Cola in Great Britain, Short says.
While that equipment has gotten a lot of attention, Short says the success of that joint venture depends heavily upon the processes that occur well before the material ever hits the extruder. “We go through four different sort processes before we even go into the wash process,” explains Short. “By going through all of those sort processes, we ensure that all of the cross-polymer contamination, such as the mixed plastics mixed in with the PET, is kept to an absolute minimum.”
But the sorting doesn’t stop there, Short says. A hot wash process of the sorted granulated PET bottles takes care of half of any cross-contamination, Short says. Then the half-inch flake is sent through an ultra-high resolution flake sort module to remove any remaining cross-contamination. The module utilizes colour sort technology from Bühler Sortex of Uzwil, Switzerland, and near-infrared detection from Titech.
“We take out any colours that shouldn’t be in there,” says Short, “and we also have a polymer sort.” Short describes the module as a major investment in ground-breaking technology that delivers a food-grade PET flake for the extruder.
“That is what you’ve got to get to in order to ensure that you then have a world-class pellet,” says Short. “You’ve got to get all of your pre-processes right first, then it will work.”
Of the 150,000 tonnes of mixed plastics that ECO Plastics processes each year, says Short, “the most PET we would expect to get from our mix would be around 65,000 tonnes per year,” he says. The company’s two extrusion machines offer a combined 40,000 tonnes of extrusion capacity, he says.
The author is managing editor of Recycling Today Global Edition and can be reached at firstname.lastname@example.org.