The recycling plant at Springwell Quarry is handling skip waste and C&D waste. The initial screening split is at 40mm using a large Trommel screen. For many years the 40mm down product was acceptable for use as a cover material not only on Thompson's own landfill site but other landfill sites in the area. Due to the tightening legislation the material could no longer be used for this purpose. The presence of paper, plastic, cardboard and polystyrene meant it became subject to landfill tax and when you're producing around 25 tons per hour it's a bitter pill to swallow.
 
The problem was discussed at length with Aubrey Telfer, Thompson's Operations Manager, and Craig Bateson the Site Manager at Springwell and a two stage operation was decided on.
Firstly we had to screen the material for a second time. A split at around 12 to 15mm would be ideal leaving a soil-like product with perfectly acceptable levels of contaminates for it to be used as a cover material with no tax penalty. The choice of screen for this operation was critical as not only did it have to produce the required product, but it needed to be able to operate on constantly changing materials with differing moisture contents. A vibrating mesh screen or another trommel were out of the question. Screening at such a small aperture the mesh would blind over when the material became damp. A tension deck was considered but should you need to change the size you wish to screen at there is the down time to be considered. This only really left the option of using a star screen.

After considering a number of different makes of star screens an excellent demonstration from Chris Pearson of Pearsons Separation Machinery ensured the inclusion of the Pearson Screen in the plant.
 
The Pearson Screen features a unique adjustment mechanism which allows the operator to set the ‘fines’ to be removed between 10mm and 50mm. This is achieved by a simple mechanical linked system, and adjustments can be made with the machine still in operation. Thus, if the operator decides that the small fraction is too large or too small, he can make the change instantly with no down time lost. Consisting of 18 rotating star shafts 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 if required. The shafts run in sealed bearings, and there is no maintenance required on the machine other than a periodical cleaning of the star shafts. The stars are moulded from robust polyurethane, giving long service whilst retaining flexibility which helps to break down wet and matted materials, thus allowing more ‘fines’ to be screened. These features give the operator total control over ‘fines’ extraction.
 
Once all the 15mm down material had been removed we were going to be left with a 40 - 15mm material containing bricks, concrete, stones, wood, paper, plastics, cardboard, and polystyrene. We had already reduced the weight of the material going to landfill by 40/45 % but there was still a considerable amount of valuable product left. All that had to be done was separate the light material from the heavy material and we would be left with a useful inert fill material. A density separator was chosen to achieve this. It is a simple process whereby the remaining material that comes over the starscreen is fed onto a vibrating feed table and over a defusing plate. High velocity air is blown up through the waste stream which has effect of raising the light material to the top of the stream. The material is then fed over an airknife which will blow all the lights out leaving the heavy fraction to drop down onto a stockpiling conveyor. With the airflow to both the defuser plate and the airknife being infinitely variable it is possible determine the exact quality of the product you extract. If you wish to have a very clean heavy fraction it is possible to turn the air up and blow out all the sticks and small pieces of wood. Small stones will be lost to the lights pile but a screening effeciency of 95% + can be achieved. Alternatively a little less air will put the small stones and some of the wood into the heavies pile. If this is acceptable for use as a rough hardcore/fill material then there is even less weight going to landfill. It is possible to safely change these settings while the machine is in operation.