Skip firm loses weight, but gains pounds
A star screen is helping to shed the amount of construction waste going to landfill for a skip hire firm, and increasing profitability as a result
Thompson’s of Prudhoe has reduced the amount of construction waste going to landfill by up to 90%, by weight, thanks to a redesign of its screening operations
Thompson’s plant at Springwell Quarry handles skip and C&D waste. Incoming material used to initially be split over a 40mm Trommel screen, with the 40mm down product used as cover material for local landfill sites. However this material then became subject to landfill tax as it contained paper, plastic, cardboard and polystyrene.
As there was a throughput of 25 tonnes an hour of this type of material, it was considered viable to re-screen the fines. A split which took out material at around 12 to 15mm would be ideal, since this soil-like material could be used for cover material with no tax penalty.
The choice of screening method became critical as the screening module would be required to operate with constantly changing materials and widely variable moisture conditions. Thompson’s chose a star screen from Pearson Separation Machinery for the job.
The Pearson screen module consists of 18 rows of rotating stars within a 5m long chassis. Each shaft is 1560mm wide and is driven by independent electric motor, the speed of which can be controlled by an inverter.
The shafts run in sealed bearings, so little maintenance is required, other than a periodical cleaning of the star shafts. The stars are moulded from robust polyurethane which gives long service, while retaining the flexibility which helps to break down wet and matted materials, to allow more fines to be screened.
Adjust for flexibility
The Pearson unit also features an adjustment mechanism which allows the operator to set the fines to be removed between 10mm and 50mm. The combination of variable apertures and variable shaft speeds on the star screen means the plant is capable of infinite adjustment – a key consideration when handling this type of waste as no two loads are exactly the same.
With the 15mm down material removed, a 40 >15mm sample of material containing bricks, concrete, stones, wood, paper, plastics, cardboard, and polystyrene remains. The removal of this fines material had already reduced the weight of the material going to landfill by up to 45%, but there was still a considerable amount of valuable product left.
The next stage was to separate the light material from the heavy material to leave a useful inert fill material and a density separator was chosen to achieve this. Having decided on the layout of the new waste handling line, it was necessary to combine these components in a robust structure.
As a result, Master Magnets was employed to design and manufacture the support structure, including access stairways, walkways and safety guarding. In addition, two belt conveyors were designed to fit within the operating area to efficiently transport the material.
Pearson Separation Machinery
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