NewsNewsNewsNewsNewsNews

Day Aggregates

Powerscreen Washing Systems have recently supplied and installed equipment to Day Aggregates recycling facility at Murphy’s Wharf, Greenwich, London.

Located on a six acre site adjacent to the world famous Millennium Dome, the company operate a recycling plant which processes two materials; crushed glass and concrete wash out. Whilst the latter originates from an adjacent ready-mix business run by London Concrete, the glass is sourced from the local authorities waste stream, collection from the kerbside, pubs, clubs and restaurants in London. Unlike bottle banks where the glass is segregated by colour the supply is of a general mix and does contain other secondary waste providing the business with a waste stream of otherwise unwanted material by other recycling plants.

Day Aggregates currently recycle 25,000 tonnes of glass per annum and 20,000 tonnes of concrete wash out in an efficient and effective operation where the materials would have previously gone to landfill.

In processing the glass the system is fed by wheeled loader into a horizontal impact crusher to reduce the size of the glass. Passing under an overband magnet which removes any unwanted metal, the material is fed into the hopper of a Powerscreen Commander 1400 feeder complete with a remote control vibrating grid, this feeder can also perform as a secondary input for other materials as its position provides a bypass to the crusher. The material is then carried by transfer conveyor and discharged onto the main frame of the wash plant, it is then processed through a Powerscreen 16 x 5 two deck modular rinsing screen, fitted with rolling chutes and walkway and utilising a vibrating top deck which is fitted with online polyurethane screen mats. At this stage any waste material is rejected off the top deck into a waste bunker below for transfer to landfill. Material passing over the bottom deck of the screen transfers onto a horizontal conveyor which recirculates this material through a secondary crusher. All material is then fed into the Powerscreen Fines Master 120, a high capacity compact machine providing a throughput of 120tph. This robust machine is positioned directly under the wash plant and all the washed material is gravity fed into the two separate bucket wheel tanks which collect the product and discharge it onto a 12 x 5 high frequency dewatering screen producing two products. All the dirty water and fine material accumulates in a collection tank where it is pumped to twin 15” hydro cyclones which retain +75 micron material. As the two grades of material separately exit the system in a virtually dry condition, they are then fed onto separate stockpile conveyors. In the final process the waste water from the wash plant is discharged to a pond where it is pumped upwards into a Powerscreen Powersludge silt remover, then decanted and the clean water then returned to the primary holding tank for reuse.

As both incoming waste streams are processed at separate times, the concrete wash out process entails the belt reversal of the horizontal transfer conveyor, eliminating the use of the secondary crusher; then after passing through the Fines Master where the cement, sand and water is separated any thickened material is pumped to a multi-plate filter press where it produces a dry pressed cake which drops into a bunker directly below the machine where it is collected for landfill.

The process enables two waste streams to be efficiently recycled into finished products, utilising the Fines Master has provided the operation with an improved cut on fines and ensured a final dryer product providing Day Aggregates with more saleable product.

Recycling the bottles into a easily handled fine and course grade of sand which when mixed together is ideal for usage in street maintenance to lay paving stones, has provided a cheaper alternative to sand which is expensive in the London area. Other applications are also being considered, the fine grade can be utilised in golf courses and the course grade in drainage and shot-blasting. Additionally the wash out from the concrete plant which was previously dumped in landfill can now be re-used in the adjacent ready-mix plant as a primary aggregate replacement for non structural concrete.