Eco Aggregates establish recycling centre with the help of DUO

DUO Equipment has recently supplied Eco Aggregates with a full washing and water-management plant which will operate at a previously disused quarry near Welwyn Garden City.

This is a completely new venture for Eco Aggregates who are part of the Anderson Group and specialise in the cost effective recycling of clean construction and demolition materials. 

Having obtained temporary planning permission to recycle imported C&D waste etc, from local sites, the project has been partly funded by a grant from WRAP (the Waste and Resources Action Programme) 

Whilst the primary objective of Eco Aggregates is the restoration of the quarry from the recovered silt and clay derived from the recycling operation; the resulting processed aggregates will enable Eco Aggregates to operate a recycling centre. The company will then supply materials to the local construction materials market which will be used for asphalt and concrete production as well as for sub-base, capping and drainage materials.
 
Production Process.

The imported material is fed by excavator into a high capacity, heavy duty, Powerscreen Warrior. Acting as the primary screen the material is dry screened into 3 sizes, with the midsize being directly fed into the Powerscreen Commander 1400 feed hopper of the wash plant.

From the hopper material is fed onto an inclined lattice frame feed conveyor complete with belt magnet; this conveyor delivers material onto the primary screen, a Powerscreen 12 x 5 static rinser. Featuring six spray bars on both top and bottom decks the vibrating top deck of the screen rejects all oversize material and delivers this via a stock conveyor to an adjacent ground stockpile.

Any midsize material passes from the rinser and is discharged into a Powerscreen Powerscrub which is basically a three-in-one machine which 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 during this process and carried away in the wash water, while any lighter particles are floated off through specially designed outflow exits. Three spray bars are mounted at the discharge end of the unit to provide a final rinse.

Midsize material is fed onto a second inclined static transfer conveyor which provides material to the final 12 x 5 dry screen. This screen splits the material into three final single-size products - 10mm, 20mm and 40mm which are then delivered to their respective ground stockpiles by three radial conveyors.
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 to further remove silt and dewater the sand. This plant then delivers the two grades of sand to stockpile via radial conveyors.

Water Management

Being an essential part of the project DUO supplied a Tecnoidea multi-plate filter press complete with 68 plates. Situated in a penthouse structure 5m from the ground the press provides a fully automatic silt management system that is specifically designed and sized to minimise operator input and maintain low running costs. As well as the press, the system includes the foul water pump, automatic flocculent mixing and dosing plant with a SADF system which samples every 50 seconds, 7m diameter dynamic thickener tank with 140m³ storage in cone, 80m³ buffer sludge stocking tank with internal rake, 43m3 lime silo with automatic mixing and dosing tank and fresh water tank.

Once in the thickener the silt settles to the bottom of the cone and is automatically discharged into a silt buffer tank where the lime is added.
The quantity of lime is automatically controlled using a rotary valve which then feeds the lime onto a rotary screw which in turn feeds the lime into a mixing tank. At this point water is added to the lime to create a solution which is automatically distributed into the silt buffer tank as required. The lime solution reacts with any clay material in the silt to facilitate the water drainage in the press.

The quantity of lime can also be adjusted depending on the quantity of clay in the silt to maintain throughput through the press.
When the press has filled and drained the water, it opens and the silt cake drops down into a concrete bay below; the press then self-cleans itself ready for another cycle. As in any application, DUO selected the correct size of press and took into account such factors as the silt content, clay content and settlement rate of the raw material. The flocculent mixing and dosing system maintains a continuous supply of clean water and automatically mixes a batch of flocculent solution when the level drops. An operator only has to add the powder to a storage bin.

The installation of the new washing plant has been very beneficial for Eco Aggregates.

Commenting on the success of the project, Paul Dalrymple, Business Development Manager said "Because we wanted to put a soils washing plant in what is effectively the 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 reuseable aggregate during it’s 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 Herts County Council, the Environment Agency and WRAP, without them the majority of the feedstock material would have been lost to landfill."

Further information:

DUO (Europe) PLC
DUO Equipment Ltd,
1, Rye Hill Office Park,
Birmingham Road,
Allesley,
Coventry
CV5 9AB
Tel: 0845 22 22 386    
Fax: 0845 22 22 387
Email: info@duoplc.com 
Web: www.duoplc.com