Home > Duo Group News > Equipment Division News
Situated approximately 7km south of Lancaster, Ellel Crag Quarry has a long history of sandstone and shale extraction dating back to the 1940's.
Installation of the new plant is providing Ellel Recycling with the ability to supply clean washed 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.
With production of recycled aggregates currently at 100 tph, on site material is fed by excavator into the tipping grid of a mobile Powerscreen Chieftain tracked 1400 rinser. This machine is unique in that it has a patented 11' 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 material is then fed to a conical sump where any lightweight contaminants overflow into a trash screen. Any coarse sand is then pumped to the Fines Master 120. Material passing through the integral screen decks is then conveyed under a magnet onto a folding side conveyor providing a stockpile of +40, and a further direct feed onto the latest design of Powerscreen Recycling Logwasher.
Capable of producing up to 120 tonnes of contaminant-free sand and gravel, the new 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. Two spray bars are also mounted at the discharge end of the unit to provide a final rinse.
Exiting the logwasher the material is then fed onto an 8 x 4 single deck vibrating part rinser, fitted with four sets of spray bars and polyurethane screen modules. The material is washed to recover all the sand and then fed onto a static inclined transfer conveyor which feeds the material directly into the feed hopper of a second Powerscreen Chieftain 1400 dry screen. Conveyed material passes underneath a magnet and is then sized and stockpiled through its three integral conveyors to provide stockpiles of +40/+20/+10mm.
In the production process any material from both the bottom of the recycled logwasher and part rinser is then fed into a Fines Master 120 twin grade, static sand recovery unit where it is classified and dewatered. Working for maximum sand grade flexibility, the Fines Master 120 produces a combined total of around 120 tonnes/h; comprising twin 15" hydro cyclones, 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. Any silt or lightweight waste being sent to a trash screen 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 operating up to 15 tph.
Ideally suited for recycling operations the 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.
As well as the centrifuge, the water management system includes a foul water pump, automatic flocculent mixing and dosing station for the thickener system, 6m diameter deep cone thickener tank with pneumatic discharge valve, sludge and fresh water tank; and all the support framework, structure, walkways and access platforms.
Operating principle.
The waste water (-75 micron) from the top of the cyclones of the Fines Master 120 gravity flows into a steel sump tank adjacent to the Fines Master, which is then pumped to the top of the deep cone thickener. Simultaneously, the batching pumps automatically inject flocculent solution into the delivery pipes to mix with the material. As a result, inside the thickener tank, the sludge drops 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 is pumped into a sludge buffer tank with internal rake to keep it agitated. The thickened sludge is then pumped directly to the centrifuge system which subjects the solution to an artificial force of gravity. By means of centrifugation, the solids are forced onto a drum and an internal screw conveys the solids to the discharge end. The water exits through the opposite end of the centrifuge and is pumped back to the thickener. The dry silt cake is then conveyed into a stocking bay to be removed by a loading shovel and dump truck.
The system supplied to Ellel Recycling is a closed looped system which recycles as much water as possible back into the wash plant.
With the project at Ellel Crag Quarry, 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 Ellel Recycling as they can now sell three BS specified products of +20-40/+10-20/-10mm as well as two sand products. This has provided new markets for the sale of these construction materials to construction companies at a local level.
Commenting on the success of the project, Peter Slater - Director, said "We are very pleased with the materials that are coming off the plant, which are up to the high standards required by the construction industry. The Gennaretti centrifuge is proving to be an excellent piece of equipment, providing dry manageable cake whilst keeping up with production. Our target was to produce high end recycled aggregates, which we are doing, the challenge now is to increase our presence in the market and establish recycled aggregates as an alternative."