Turnkey Solution for Gaskell Bros
CDE supply advanced recycling system to the North-West
Gaskell Bros, based at Winwick near Warrington, have experience in both the quarrying and recycling sectors. Their site, originally a quarry, is now used for landfill and recycling. The majority of material brought in is building, demolition, and public service waste from the surrounding Liverpool, Manchester, and Leigh areas. Gaskell directors Mike Broad and Mark Gaskell saw an opportunity for washing this waste and established their first system in 1999 using the standard aggregate and sand-washing systems popular at the time.
In 2002, however, Gaskell approached CDE for a solution to the excessive fines losses they were experiencing with their conventional bucket-wheel system. CDE supplied a 40 tonnes/h Compact Sands plant that improved the system’s performance with respect to fines recovery and sand dewatering. In 2004/2005 Gaskell decided to revise the complete operation with a view to replacing the existing system that had suffered wear in the harsh recycled aggregates environment.
After consultation with a number of leading plant suppliers Gaskell opted for a new turnkey system from CDE. Mike Broad commented: ‘I believe that this is the most advanced aggregate recycling system in the UK. I know of no other manufacturer capable of delivering such a complete system, specifically designed around my individual feed characteristics and output requirements. CDE offered the complete turnkey package from design to commissioning. We were regularly consulted and made important contributions throughout the project.’
The system has to manage a widely varied feedstock that can include plastics, paper and polystyrene in addition to organic contaminants such as soil, clay and wood. When the plant is not washing reclaimed materials at a rate of 120 tonnes/h, it is employed to wash the site’s own reserves of fine sand to produce commercial-grade building sand.
Waste is brought to site either by Gaskell’s own fleet of vehicles or directly by customers. On arrival at the weighbridge the load is viewed via a remote camera to check the material’s suitability for the washing plant. Unsuitable loads are directed to Gaskell’s licensed landfill site while appropriate material is diverted to the wash plant. Large pieces of rubble are broken down using a pulverizer fitted to an excavator with the majority of material then being transferred by the excavator to a track-mounted jaw crusher.
The feedstock first passes through a vibrating head to remove +100mm oversize before passing to the feed hopper fitted with an integrated belt feeder and inclined conveyor. This new CDE product was specifically designed to facilitate and speed-up installation and is delivered as a single unit. A further advantage is that the hopper’s belt feeder and the inclined conveyor are precision aligned during manufacture, significantly reducing potential spillage and housekeeping problems. Ferrous metals are removed by an over-band magnet mounted on the inclined conveyor as material is transferred to an R2M90 1.5m x 4m rinsing screen. Any –5mm slurry is passed to a Compact Sand plant that removes silts and clay below 75µm via an integrated hydrocyclone. The sand is typically dewatered to less than 13% moisture content. This approach to commercial-fines recovery means that there is no need to pre-screen or remove topsoil from the feedstock. This increases the number of potential saleable products by offering dewatered sharp sand that finds a ready market as cable and pipe bedding as well as in non-structural concrete manufacture.
As with any washing plant, properly managing the waste water is crucial, and in recycling systems this presents a technical challenge in view of the highly varied feedstock. Here a CDE high-rate thickener with an integrated polyelectrolyte dosing station is used. This rapidly settles out the excess fines to form a dense sludge that is then pumped to a remote bunded settling area. Clean water overflows the thickener and is filtered to remove any residual floating contaminants, such as styrofoam particles, before being passed to an adjacent storage tank. From here water can be readily recirculated to the washing system.
In August Gaskell’s will take delivery of a new 16m overhead-beam filter press capable of handling up to 30 tonnes/h of waste solids. This will complete the water-recycling circuit, creating a fully closed system with only dry, easily managed cake output as a by-product. This unit will be the largest machine of its type in the UK. The overhead-beam design was first used by CDE for a recycling project near Birmingham where it is proving much more robust than conventional sidebar presses. Its integrated washing system and fully automatic operation means it is particularly suited to the highly variable feed volumes and characteristics found in recycling projects. Referring back to his ongoing relationship with CDE, Mr Broad noted: ‘When it came to selecting the supplier for a heavy-duty filter press to complement this system CDE were the natural choice’.
Aggregates and dirt-bound particles pass directly from the primary rinsing screen to an 8m CDE 132/8 Rotomax log-washer. This features twin shafts fitted with chromo-molybdenum blades; each shaft has a diameter of 1,320mm tip to tip. The speed of the Rotomax is easily controlled to accommodate changing material characteristics as the unit features a single motor and gearbox. Mike Broad is particularly impressed with this unit having worked with several log-washers from other suppliers. This has been highlighted by the unit’s exceptional wear performance; blades have so far returned more than five times the wear time of units previously used by Gaskell. Light contaminants including clinker, plastics and organics, such as wood and grass, are actively floated off from the rear of the Rotomax before being passed to a trash removal screen that recovers water and fine particles to the sand-washing unit. Attritioned material is discharged to a dewatering screen fitted with CDE’s modular PU panels. Liberated fines and water pass through this screen to a ground sump complete with submersible pump. The sump also collects wash-down and groundwater, which is then pumped back to the rinsing screen, encouraging initial fluidization and reducing the fresh-water requirement while facilitating site management and safety.
Dewatered +5mm aggregates are conveyed from the dewatering screen to a D2M90 1.5m x 4m twin-deck dry screen for final size classification. The process currently provides five commercial products — sand, 5–10mm, 10–20mm, 20–40mm and 40–100mm — and these are sold throughout the North-West. Most of the products are used for pipe bedding and cable-laying work with the 20–40mm also sold as a gas membrane for new house builds. The +40mm is commonly used for pile capping or can be crushed to produce recycled MoT 1 product, as it is virtually free of plastic, wood, and other contaminants. Once the overhead-beam press is installed even the silt and clay fines are expected to find a market as puddling clay for canal and watercourse lining. The magnet-collected ferrous metals are passed to a skip to be sold as scrap.
According to CDE, washing adds much greater value to the final products than conventional dry processes. The ability to release quality sand that would otherwise be a waste by-product is another important advantage. This particular installation demonstrates how the correct application of the latest washing technologies means that water availability and waste-fines management are no longer significant barriers to efficiently realizing commercial products from former waste materials. It is now up to recycling and demolition operators to decide how best to capitalize on these new technologies, a commercial decision that has clearly paid dividends for Gaskell Bros.
