New recycling centre for Eco Aggregates
DUO Equipment have supplied Eco Aggregates with a full washing and water-management plant for their operation at a disused quarry near Welwyn Garden City. This is a completely new venture for Eco Aggregates who specialize in the recycling of clean construction and demolition materials.
Having obtained temporary planning permission to recycle imported C&D waste from local sites, the project has been partly funded by a grant from WRAP. While the primary objective for Eco Aggregates is the restoration of the quarry using recovered silt and clay derived from the recycling operation, the processed aggregates will also allow Eco Aggregates to operate a recycling centre. The company will supply materials to the local market for use in asphalt and concrete production as well as for sub-base, capping and drainage materials.
Imported material is fed into a high-capacity, heavy-duty Powerscreen Warrior screen where it is dry screened into three sizes, with mid-sized material being directly fed into a Powerscreen Commander 1400 feed hopper to the wash plant. From the hopper, material is fed to a Powerscreen 12 x 5 static rinser via an inclined lattice-frame conveyor, complete with belt magnet. Featuring six spray bars on both the top and bottom decks, the vibrating top-deck screen rejects oversize material to an adjacent ground stockpile via a conveyor.
Mid-size material passes from the rinser and is discharged into a Powerscreen Powerscrub. This three-in-one machine provides a water bath, scrubber and final rinse. Capable of producing up to 120 tonnes/h of contaminant-free sand and gravel, the Powerscrub 120R unit comprises an inclined trough fitted with two counter-rotating axles with high-tensile exchangeable blades and an elevated spray-bar system. The unit mixes incoming feed, while milling and washing the material at the same time. Any lumps of earth or clay are broken down and carried away in the wash water, while lighter particles are floated off through specially designed outflow exits. Three spray bars mounted at the discharge end of the unit provide a final rinse.
Material is then fed, via a second inclined static transfer conveyor, to a final 12 x 5 dry screen. This screen splits the material into three single-sized products — 10mm, 20mm and 40mm.
Sand from the first screen is fed to a pre-wash system to remove the majority of the silt. The pre-washed sand is then fed into a Linatex twin-sand plant that removes further silt and dewaters the sand. The plant then delivers two grades of sand to stockpile via radial conveyors.
DUO also supplied a Tecnoidea multi-plate filter press complete with 68 plates. Located in a penthouse structure 5m above the ground, the press provides a fully automatic silt-management system that is specifically designed and sized to minimize operator input and maintain low running costs. The system also includes: a foul water pump, an automatic flocculant mixing and dosing plant with a SADF system that takes samples every 50s, a 7m diameter dynamic thickener tank with 140m3 storage, an 80m3 buffer sludge stocking tank with internal rake, a 43m3 lime silo with automatic mixing and dosing tank, and a fresh water tank.
Once in the thickener tank, silt settles to the bottom and is automatically discharged into a silt buffer tank where lime is added. The quantity of lime is automatically controlled using a rotary valve that feeds the lime on to a rotary screen, which in turn feeds it into a mixing tank. Water is added to create a solution that is automatically distributed into the silt buffer tank as required. The lime solution reacts with any clay material in the silt to facilitate water drainage in the press. The quantity of lime can be adjusted depending on the amount of clay in the silt to help maintain throughput through the filter press.
When the filter press has been filled and the water drained away, the silt cake drops down into a concrete bay below. The self-cleaning press is then prepared for the next cycle. The flocculant mixing and dosing system maintains a continuous supply of clean water and automatically mixes a batch of flocculant solution when the level drops.
Commenting on the success of the project, Paul Dalrymple, business development manager for Eco Aggregates, said: ‘Because we wanted to put a soil-washing plant in what is effectively Green Belt, the project has taken in excess of two years to become operational. Eco Aggregates and our parent company, Anderson Group, have worked closely with the county council’s planners and other regulators to deliver an environmentally friendly aggregate-recycling facility that will not only benefit the construction industry but also local communities, building companies and the environment.
‘The facility at Welwyn Garden City will recycle over 1.5 million tonnes of C&D waste and recover over 1 million tonnes of reusable aggregate during its time on site. Recycling at this level needs more than just a financial injection; it needs an environmental commitment and a long-term sustainable strategy. It’s fair to say that the success of this project has been heavily dependent on the support of Hertfordshire County Council, the Environment Agency and WRAP. Without them the majority of the feedstock material would have been lost to landfill.’
DUO Equipment Ltd, 1 Rye Hill Office Park, Birmingham Road, Allesley, Coventry CV5 9AB; tel: (0845) 222 2386; fax: (0845) 222 2387.
