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Towards purer products

There can be no argument that recycling is essential to protect the environment and make best use of finite natural resources.  However, setting targets and enacting legislation, the favoured tools of politicians and bureaucrats, will not achieve the desired result unless public money is thrown at the problem - and this seems unlikely to happen, especially in the current economic climate.

The solution lies in a combination of profit and technology: profit for the recycler using technology that works to a high level of efficiency

So, as is often the case, the solution lies in a combination of profit and technology: profit for the recycler using technology that works to a high level of efficiency. A number of UK companies have recognised the profit potential of recycling and are making significant investment in the latest technology.  This has encouraged the equipment manufacturers to invest in using the latest technology in the design and development of sophisticated separation and sorting systems able to deliver a good quality output that can be used in place of virgin material.

The hot topic in recycling is currently processing used PET and HDPE food and drink containers to a standard of purity suitable for use by the food industry, simply because consigning used plastic food and drink containers to landfill or export is too expensive, wasteful of a valuable resource and incompatible with environmental considerations.

There are a number of processes for chemically ‘super cleaning’ recycled PET to remove unwanted molecules, making the recyclate suitable for use for food packaging. Developed by the United Resource Recovery Corporation (URRC), the UnPET process, the most widely used method of chemically cleaning PET, produces recycled PET chip that is cleared by the US Food and Drug Administration (FDA) for 100% use in packaging in direct contact with food and drink.  According to US based URRC over 6 billion bottles have been produced from the 100% UnPET recycled PET processed at its plant. This and other cleaning processes are used by many recycling plants worldwide, including Closed Loop in the UK. 

Whichever process is used, the recyclate must be pure PET with all contamination including metal, unwanted colours and non-PET plastics removed.  To meet this requirement, S+S uses a combination of detection technologies to identify the different impurities and specially developed high speed, air ejection systems capable of removing up to 200,000 particles per minute to ensure that every piece of contamination is removed with the minimum of good material loss. By focussing on developing specific system solutions over the whole gamut of contaminant separation, from sorting systems for bottles and other recycled components through high sensitivity flake and granulates separation, S+S systems achieve great efficiency of both inspection and separation, producing higher yields and profits and giving an accelerated return on the investment in sorting systems.

The separation of polymers of different types at the ‘bottle stage’ of the recycling process has traditionally used Near Infra Red (NIR) technology but, as no single sorting technique will remove 100% of contamination, a number of different technologies have to be used after flaking.  Laser technology has been used with varying degrees of success and, while such systems can be effective, they are expensive to buy and to run. A more logical and cost effective step is to enhance the capabilities of the existing NIR technology by using special cameras, similar in concept to the full spectrum Charge Coupled Device (CCD) cameras used in the S+S colour sorting systems. At the flake stage, the precision of the latest systems allows the last small percentage of contamination to be removed producing a highly purified end product.

A by-product of the enhanced ability to separate a wider range of plastics with higher efficiency levels is the potential to recycle plastics that would hitherto have been consigned to landfill

A by-product of the enhanced ability to separate a wider range of plastics with higher efficiency levels is the potential to recycle plastics that would hitherto have been consigned to landfill. This opens up a whole new level of profitability for recyclers, and for the environment a further reduction in the amount of unrecycled waste. After pre-separation at the container stage, a number of flake sorters in sequence sort material by colour and type to leave a high quality product that can be put to a variety of uses, some back in the food chain and others in ancillary markets.

Identification of material, whether required or not, can be very close to 100% with the final fractions of a percent meaning the difference between profit and loss to the recycler. But this is only one half of the whole story. Firstly, products must be separated and secondly this must be done with the minimum loss of good product or residual contamination. Once more, a combination of technologies has been developed and is being enhanced to achieve the desired result. Using two separation stages in one sorter, although there can be disadvantages, removes one process stage and allows the use of a combination of technologies in the same sorting package to facilitate the removal of any remaining metals, off colour and unwanted plastic types.  Even so, 100% separation and total end product purity is a not a realistic proposition but it is now possible get to within fractions of 1% of this ideal.

The metal detection and optical sensors utilised today by S+S can identify very precisely where the inspected product item is located across the width of the sorter and in some cases, even the shape and size. This data, when combined with knowledge of the trajectory, allows a sophisticated digital evaluation system to activate one or more of over 200 solenoid valves to blow the flake or contaminant from the main product stream. Pneumatic valves are critical to the separation process; more valves having high precision controllability create a highly efficient separation process using less air per separation cycle reducing the system running cost to a minimum.

With Auto-Teach in and Auto Learn systems becoming ever more precise, the exact characteristics of a large number of product types can be ‘learned’ and held in non-volatile memory for instant recall when a similar product is to be processed at a later date, without the need for time consuming and expensive set up.

To be truly cost-effective, a separation system must function consistently and reliably with the minimum of operation monitoring

To be truly cost-effective, a separation system must function consistently and reliably with the minimum of operation monitoring. Current systems use intranet and extranet data communications to provide interactive feedback allowing systems to be monitored 24/7 from a remote location. Operating parameters can be adjusted, faults identified and, in many cases, rectified automatically or manually from any location. Operational data can be delivered to the user’s Process Management System allowing the process to be fine-tuned in real-time to achieve the best possible result from the material being processed.

Recyclers are trying to produce the proverbial ‘silk purse from a sow’s ear’ and, with the technology and operational sophistication now available, this objective is being reached in a manner that makes the operation both environmentally desirable and profitable.

Richard Lines is managing director of S+S Inspection

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