With the ever-increasing diversity of waste streams, the separation and segregation stage of the recycling process is crucial so that a saleable end product is achieved. Materials such as glass, rubber, plastics, municipal waste, wood and biomass are all examples where a cleaner end product can be worth so much more.
Cheshire-based Rotex Europe has been able to progressively demonstrate that, with efficient screening, products can drastically enhance their end value. Rubber and glass are two materials where such benefits can be had.
Tyre shredding is never easy. The process of shredding and granulating creates problems due to the internal webbing in tyres being shredded to the same size as the rubber. But the removal of this webbing not only cleans and enhances the appearance of the rubber product, but it can have a saleable value in its own right: when mixed with silica sand it can be used to create a stable riding surface for horse arenas, for example.
Gyratory motion screening, using specialised decks, balls up the fibre to a point where it can be aspirated away or discharged into skips, leaving an almost pure rubber product. Testing at the Rotex Europe headquarters lab has led to deck systems being developed that maximise the benefits of separation and produce good, clean products.
With glass, recycling has yet to reach the stage where all commercially collected glass is waste-free. Initial crushing has to be supplemented by screening to remove plastic caps, oversize glass, unwanted foreign bodies and so on. Traditional mesh screening simply lends itself to blinding and pegging, when the mesh openings gradually smear over and clog, or where particles wedge into the mesh, causing blockages. This usually needs constant monitoring by operators, which comes at a cost.
By selecting alternative screen deck profiles and screen motion, blockages can be eliminated and glass recovery maximised. The correct machine motion is essential to ensure the product is spread evenly across the screen, to give the best opportunity for accurate screening. Motions can be vibratory or gyratory; both can be effective. Usually kiln drying is needed to remove the final traces of paper and moisture, while secondary crushing or imploding is essential to create a raw product of either sharp or sharp-free glass.
From here on, screening is the driving factor in producing graded glass that can be used, for example, as shot blasting media, fillers, aggregate substitute and decorative coverings. In some cases, and to meet client needs, this can require frequent deck changes if a variety of outputs are needed. It is essential to look at machines that can accommodate this and offer swift deck changes because this will affect productivity - and production time gained helps to maximise profits.
Rotex is a screening company that operates in many other industries. It has observed that because waste is often non-uniform in size and composition, it needs to be treated differently to most other market sectors. The screen mesh needs to be specifically selected to minimise blinding and pegging, while screen motion can be crucial in creating maximum separation. Moisture and size are also major factors in determining how material can be separated - or if indeed it can.
Not every company has all the answers, so they tend to specialise in specific types of screening: wet, dry, large or small. It is therefore essential when considering waste separation to discuss with such companies exactly what you have and what you want to achieve. Bear in mind that screening usually determines the saleable product at the end.
Get it right at the outset and the chances are that you will maximise your potential. Get it wrong and, regardless of all the initial tearing, ripping and shredding, the end-of-line bagging plant operator may spend more time reading the latest issue of Nuts than you would like because there won’t be much to do.
Allan Thompson is UK and Ireland sales manager for Rotex Global