
The type of material you process ultimately determines the type of plant system you install. Getting it wrong can have a significant effect on productivity and profitability, but getting it right can pay dividends.
The downturn in the construction industry is already having a knock on effect to the skip industry as the credit crunch bites.
As a skip yard manager, the types of material more commonly seen and prized would be aggregates, wood, metal and plastics sourced from construction, demolition and excavation contracts. As recycling has been brought to the forefront of commercial and industrial life, a number of wily entrepreneurs are diversifying into mixed recyclable collections in a bid to keep up with the changing face of waste management, and to stave off the worst effects of the economic downturn.
Separation is the key to achieving high quality, decontaminated material from recyclable collections for selling to reprocessors and this can be achieved through a variety of plant components. For the purposes of this article, I’ve split plant systems into two categories, “light” and “heavy” – heavy being the more usual systems for processing CD&E mixed waste.
“Light” Plant System Components
Comingled recyclables are becoming bigger business as more local authorities pass out bins to local residents for everything from plastic bottles to glass to green waste, but what about commercial and industrial operations? Yes, they have their waste collections, but recycling from offices and the like has been much slower to get off the ground than household recycling.
Andrew Mills, of Ken Mills Engineering, has already seen this coming: “We’re finding more and more companies are looking to diversify into comingled processing and we have set up a number of plants to do just that in traditional skip yards. With the credit crunch biting the industry’s usual customer base so hard we believe more companies will look to process mixed recyclables from commercial and industrial contracts over the next 6-12 months.”
But only with the right machinery! Setting up comingled recycling collection services for local businesses can provide valuable streams of material, but the recycling streams must be separated to ensure maximum payout on material going to reprocessors.
Initial Separation
Ballistic separators, disc and ‘V’ screens do essentially the same job, splitting recycling streams into flat, 2D materials (paper and card) and rolling or 3D materials (plastic bottles, cans, etc). Used front end to begin the separation process they each have advantages depending on the size of your yard, incoming material and budget.
Disc screens sort material by shape and size and are very efficient separating card from other materials. Generally more suited to be further down the processing line, they can be used as an initial separator but can have problems sorting flattened plastic bottles from flat paper and card.
The ‘V’ screen has a smaller footprint and, according to Andrew, a capacity up to around 20TPH. Essentially a disc screen bent in the middle to form the unusual V, shape the quality of separation can be easily controlled by the touch of a button adjusting the angle of the machine and discs and the speed of the discs. However, long materials, such as film, cables, etc, can get wrapped around the disc shafts requiring more daily maintenance.
Ballistic separators have the same ability to fine tune the separation process but a larger footprint, although fines are removed through the perforated deck. Materials are sorted by shape and weight with heavier 3D material moving down the paddles of the machine and the lighter, flatter material moving up. Capacity can be increased with multiple decks which also gives a cleaner separation of material. Ballistic separators can be more costly than ‘V’ screens but, with less moving parts, maintenance time and costs are lower.
Trommels separate by size alone and are more common in “heavy” applications involving construction, demolition and excavated material. The rugged build of a trommel makes them more suited to heavier applications of mixed waste rather than comingled recyclables.
Down The Line
Further down the processing line, components could include the more usual overband magnets and eddy current magnets for ferrous and non-ferrous metal recovery. Other types of material can be separated into even finer recycling streams with the use of optical sorting technology, which can be quicker and more accurate than using pickers at a picking station.
Optical sorters using Near Infra Red (NIR) can be configured to separate plastics by polymer or by colour. I’ve seen these in action and the speed the material flows through the system and gets sorted is phenomenal. Separating up to three different fractions at a time is a breeze. More recently MIR (Mid Infra Red) technology has been used to analyse types of paper and card separating them into their various streams based on their grammage.
Even on a “light” system, pickers may be needed; either at the front end, to remove large contaminants, or at the back end, to make sure all contaminants are removed. But the more advanced technology gets, the less picking stations and associated staffing costs will be necessary.
“Heavy” Plant System Components
Processing mixed skip waste and CD&E waste can see a huge variety of materials going through your system. The initial separation of large contaminants, previously carried out by staff on the floor, can be carried out by machinery designed specifically for this purpose.
Already seen in many skip and waste processing organisations, trommels and finger screens help to prevent the need for these “ground teams” – increasing your Health & Safety credentials and saving money in terms of staffing costs. The rugged construction of these front end machines helps them stand up to the inevitable wear and tear of highly abrasive material like CD&E waste.
Mixed waste, or CD&E waste, enters the system via the trommel or fingerscreen; both machines sort by size alone, useful for removing fines before the main part of the separation process. Air separators remove the bulk of lighter material, paper, etc, and overband magnets recover ferrous metals.
The main bulk of the separating process really lies with the picking station. Pickers remove materials from the conveyor belt for further recovery, such as wood, plastics, etc. It can be useful to have another air separator at the end of the picking conveyor removing those last bits of light material before the cleaned hardcore exits the system.
Whether you’re going for a light system or a heavy system totally depends on the material you are processing. It’s no good putting in a disc screen at the front end of a plant system that is going to be processing CD&E waste – it just wouldn’t work. As commercial and industrial organisations look more closely at their social responsibility to recycle more of their waste, it’s a fairly safe bet that many skip companies can jump on the recyclable band wagon and benefit from providing a recyclable collection service.