Case study - Nottinghamshire Recycling
DUO Equipment delivered and installed a new full washing and water management plant for Nottinghamshire Recycling Ltd (NRL). Based in Worksop, Nottinghamshire, NRL is a sustainable waste solution provider processing C & D waste, green waste, wood and recycled aggregates.
The new washing and water management plant (which includes a Gennaretti centrifuge system) will provide NRL with the ability to divert recycled aggregates from landfill and supply high quality clean washed materials to the local construction materials market.
When deciding which processing plant to purchase NRL focused on the quality of the equipment, bespoke plant design and specification for their site, back up service and support and a proven ability to process difficult recycled materials.
With production of recycled aggregates currently at 100 tph, on site material is fed by excavator into a static Chieftain 1400 feed hopper featuring a single-deck, live head grid and an electric variable speed feeder.
Material is then fed from the hopper onto an inclined conveyor which conveys it under a belt magnet to remove the ferrous metal and delivers onto a 10 x 5 static rinser screen. Fitted with polyurethane modules on all decks the rinser screen box incorporates 6 top and 6 bottom deck spray bars with plastic nozzles.
This machine is unique in that it has a patented 10' x 5' four bearing 'free floating' screen box which eliminates the need for any fine tuning; acting as the primary screen the rinser facilitates the removal of more sand and silt out of the material. This fine sand is then fed to a conical sump where any lightweight contaminants overflow into a self cleaning filter. Any fine sand is then pumped to the Fines Master 120 Compact twin grade plant. The coarse sand is also fed to the opposite side of the sand plant. Material passing over the integral screen decks is then fed onto a T4026 conveyor to stockpile, and a further direct feed into the latest design of Powerscreen Recycling Logwasher.
Capable of producing up to 120 tonnes of contaminant-free sand and gravel, the Powerscreen Recycling Logwasher 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 onto a 6 x 2 trash screen fitted with polyurethane modules.
The scrubbed gravel is discharged onto an 8 x 4 dewatering screen fitted with polyurethane modules and three spray bars to provide a final rinse, with water and sand gravity flowing into an adjacent Powerscreen Finesmaster. Clean material is then conveyed via a transfer conveyor to a 10 x 5 double-deck dry screen. This dry screen grades the material into three sizes of 10mm, 20mm, and 40mm which are conveyed and stocked by three further radial stockpile conveyors.
In the production process any material from both the bottom of the recycled logwasher is then fed into a Fines Master 120 compact twin grade, static sand recovery unit where it is classified at approximately 75 micron and dewatered. Working for maximum sand grade flexibility, the Fines Master 120 compact can produce a combined total of around 120 tonnes/h; comprising a 15' fines cyclone and a 24' course cyclone, a centrifugal slurry pump, a collection tank and a high-frequency 12 x 5 dewatering screen fitted with polyurethane dewatering modules mounted on a single carrier chassis. The machine delivers one grade of course sand and one grade of fine sand to stockpile with the flexibility to blend the fine and coarse sand to maximise either sand grading. Any silt or lightweight waste being sent to a filter which feeds to a sump, with silt sent to the thickener.
Water Management and Centrifuge operation:
As water management was an essential part of the project DUO Equipment in conjunction with their partner Gennaretti supplied a GHT 503 variable speed centrifuge system which is capable of processing up to15 tph.
As well as the centrifuge, the water management system includes a foul water pump, automatic flocculent mixing and dosing station for the thickener system, 7m diameter deep cone thickener tank with pneumatic discharge valve, sludge and fresh water tank; and all the support framework, structure, walkways and access platforms.
The Waste water and silt from the top of the cyclones on the Fines Master gravitates flow into a steel sump tank adjacent to the Fines Master and through an in-line screw filter to remove organic material and polystyrene. The silty water is then pumped to the top of the deep cone thickener. Simultaneously the batching pumps automatically inject the flocculent solution into the delivery pipes to mix with the material. As a result, inside the thickener tank, the sludge will drop to the bottom of the cone while the clean water weirs over the top of the thickener into the clarified water tank. This water is then re-used by the wash plant for continuous cleaning of the material.
The underflow from the thickener then gravity feeds into a sludge tank with an internal rake. This material is then pumped directly to the centrifuge system to be dewatered and stockpiled into an allocated bay. The clarified water is then pumped back into the system via the deep cone thickener.
The whole process is based upon a complete closed loop system which enables recycling of as much water as possible back into the wash plant.
DUO Equipment of Coventry has a huge amount of in-house expertise in the field of materials processing and when it came to selecting the best method of dewatering sludge from the recycled aggregate washing plant the inclusion of a Gennaretti Decanter Centrifuge was an obvious choice as the machine is ideally suited for recycling operations.
Gennaretti variable drive models are compact in design relative to their output capabilities and efficiently process sludge with variable solids content such as that from washing recycled aggregates.
Fintan McKeever, Director - DUO Equipment, commented,' The inclusion of the Gennaretti Decanter Centrifuge was an obvious choice for this project. The Gennaretti Centrifuge has proved very successful in processing silts from recycled aggregates, sand & gravel, and limestone and offers a continuous process incorporating an automatic variable speed control to handle large fluctuations in feed material.'
With the NRL project, DUO Equipment delivered a fully automatic silt management system that was specifically designed and sized for the process, minimising operator input and maintaining low running costs.
DUO took into account such factors as the silt content, clay content and settlement rate of the raw material. The flocculent mixing and dosing system installed 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 and water management system has been very beneficial for NRL, Kevin Burgess - Managing Director commented, 'The choice of the plant was based on the need to utilise a closed loop water treatment system and the ability to produce a consistent product to a very demanding market specification. We have significant amounts of Powerscreen machines across all of our recycling sites and expect and receive guaranteed service support from DUO and Powerscreen.'
The new aggregate washing plant will help to maintain Nottinghamshire Recycling's position as one of the major suppliers of quality recycled aggregates in the Midlands.'