EU lend support to improving C&D waste recycling capability

A new processing plant for construction, demolition and excavation waste is currently undergoing final commissioning in Stuttgart, Germany and will be operational by June 2014. The plant has been installed on the site by materials washing specialists, CDE Global and includes a series of product developments aimed at improving the quality of recycled sand and aggregates produced from CD&E waste.

Supported by the Eco-Innovation Fund from the European Union the new advanced processing system for CD&E waste includes new product developments from CDE which include the feed arrangement to the plant, enhanced mobility, reduced plant footprint, improved maintenance access and developments at the sludge management stage of the process. The project will operate under the acronym of ‘CANDY’ which stands for ‘CompAct, highly mobile, Next generation, CD&E waste recoverY system.

The process

The process begins with the R2500 primary scalping unit – a new machine from CDE designed specifically for this project. Material is delivered to the R2500 hopper, which has a capacity of 20 tonnes. The +100 material is removed while the -100mm material is delivered to the M2500 mobile washing plant.

The R2500 comes fitted with an apron feeder which eliminates the danger of belt piercing due to the presence of metals or impact from large oversize material. The large capacity of the feed hopper allows for the plant operator to charge fill the plant and still be able to undertake additional work on site. “By using the R2500 operational efficiencies can be significantly improved as you do not require a dedicated vehicle for loading the plant” explains Gareth Kenwell, Senior R&D Engineer at CDE Global.

The R2500 also includes the latest laminate side wall design on the integrated ProGrade screen. This patent pending technology results in a stronger, but lighter screen which reduces the power requirement while enhancing screening performance. The screen is a bolted design which is a feature of the CDE ProGrade screen range. “Bolted structures are much more robust than welded structures” explains Gareth Kenwell. “Throughout the ProGrade screen range there is minimal use of welding which significantly reduces stress and therefore increases plant life.”

From the R2500 the -100mm material is delivered to the M2500 mobile washing plant. An extended feed boot on the M2500 feed conveyor ensures maximum material retention and from here the material is delivered to the integrated ProGrade P2-75 rinsing screen. The top deck of the screen removes the 45-100mm material to an oversize stockpile. The bottom deck of the screen collects the 8-45mm material for delivery to the AggMax portable logwasher.

The 0-8mm material gathers in the ProGrade sump before being pumped to the integrated EvoWash sand washing plant. The EvoWash dewatering screen is split to allow the production of 2 sand products. The 0-8mm material is first delivered directly to one side of the dewatering screen where a 2-8mm material is dewatered and stockpiled via an integrated 9m stockpile conveyor with a stockpile capacity of 150m3. The 0-2mm material falls through to the EvoWash sump before being pumped to the hydrocyclone which removes the -63 micron material. The 0-2mm sand slurry is discharged via the cyclone underflow to the EvoWash dewatering screen before being dewatered and stockpiled via another integrated 9m stockpile conveyor.

Production of clean, recycled aggregates is delivered by the AggMax portable logwasher which accepts the 8-45mm material from the bottom deck of the ProGrade screen. An overband magnet on the feed conveyor to the AggMax removes any ferrous metals which are subsequently discharged to a skip positioned underneath the feed conveyor.

The AggMax includes the RotoMax RX80 logwasher, a triple deck ProGrade sizing screen and trash screen. Material enters the RotoMax and is subjected to high attrition from the two counter rotating shafts each fitted with high cast chrome paddles. This subjects the C&D waste material to the level of attrition required to ensure effective breakdown of clays, liberation of silt and fine sand particles and efficient removal of lightweight and organic contaminants. The AggMax includes both side and rear discharge points for water, sand and silt removal and this ensures the minimum level of fines reach the main discharge point at the front of the machine. This waste discharge is delivered to the integrated trash screen which dewaters the material and discharges to a skip. Any liberated fines are returned to the EvoWash sand washing plant to maximise material recovery.

The scrubbed 8-45mm recycled aggregates are discharged from the RotoMax to a triple deck ProGrade P3-36 sizing screen. This screen includes spray bars to give the washed recycled aggregates a final rinse before being stockpiled. Any fines that make it to this stage of processing are once again returned to the EvoWash. There is a large focus on maximising plant life on the AggMax with a number of features including rubber lined product chutes, a rubber lined feed box and replaceable impact plates at the point of delivery from the RotoMax to the ProGrade sizing screen. The recycled aggregates are stockpiled as 8-16mm, 16-32mm and 32-45mm products.

The wastewater containing the -63micron material is then delivered to the AquaCell Sludge Concentrator. This is another of the new product developments from CDE Global included on the CANDY project and is a development of their AquaCycle thickener technology. The AquaCell is a rectangular unit measuring 12m x 2.4m. The upper tank accepts the waste feed from the plant which is dosed with flocculent. There are 4 separate collection cones where the settled sludge gathers before being delivered to a buffer tank. Tests conducted during plant commissioning reveal a sludge concentration of 663g/ltr of solids in the sludge discharged from the AquaCell. From the buffer tank the sludge is then delivered to a decanter centrifuge for further dewatering. A screw conveyor discharges the centrifuge cake to a stockpile.

Global potential

Following final commissioning of the CANDY project CDE will continue to gather performance data from the plant which will process a range of different waste materials. Through a partnership with Stuttgart University extensive material testing will be conducted to establish the suitability of the recycled sand and aggregates from the plant for use in high value construction applications such as concrete and asphalt.

Speaking about the project CDE Regional Manager for UK & Ireland, Matt Bunting said “We have pioneered these systems in the UK over the last decade and have proven the capability for the machines to move recycled sand and aggregates up the value chain. Through this partnership project with the EU we will be able to show that systems employed extensively in the UK market are the most advanced processing systems available for construction, demolition and excavation waste.”

According to Mr Bunting the CDE washing plants for construction, demolition and excavation waste currently operational in the UK are diverting more than 5 million tonnes of this material from landfill every year. “The product developments included within the CANDY project will offer significant potential for both our existing customers and other C&D waste processors to further improve the quality of the recycled sand and aggregate products they are producing. This will increase the commercial value of this material and deliver a much quicker return on investment.”

Rising transport costs, pressure on natural reserves and limited landfill capacity are all issues which have to be addressed by the aggregates industry in the years ahead. Marc Jennings is the Programme Manager for the CANDY project and he believes that the advances in processing technology will help to build confidence in the potential that recycled sand and aggregates offer when the appropriate technologies are employed. “The CANDY project involves research partnerships which will provide evidence as to the suitability of our products for high value construction applications” he explains. “This will be invaluable to the industry as a whole and will be critical to further adoption of this technology in the UK and the expansion of these advanced processing systems into other countries in Europe and beyond.”

CDE will be organising several open week events for the CANDY project over the coming months and further information will be published on the dedicated project website at www.cdecandyproject.com as well as www.cdeglobal.com.