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Torr Works limestone quarry inSomerset, located approximately mid-way between Frome and Shepton Mallet,covers an area of some 200ha and

includes 60ha that have been landscaped toblend in with the surrounding countryside.Previously owned by Foster Yeoman, thequarry is now operated by Bardon Aggregatesas part of the Aggregate Industries UKbusiness. Much of the quarry’s annual output of

Carboniferous limestone is despatched by rail,

with up to 70 trains a week leaving the siteeach carrying, on average, 1,500 tonnes; localmarkets are also served within a 60–70kmradius.Production at Torr Works revolves around

the use of a 1,200-tonne ‘walking’ primarycrusher – the only one of its type in use inthe UK today. Commissioned in 1986 andstanding as tall as a seven-storey building, itcomprises a 54in gyratory crusher mountedin a ‘walking’ frame manufactured by O&K.Capable of walking at 32m per hour, it ‰

Adding value atTorr WorksDUO Equipment install largest washing and water-management plant in Europe

The new washing plant at Torr Works is one of the largest facilities of its kind in Europe, handling 600 tonnes/h of waste scalpings

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typically moves a few metres each dayfollowing the working of the quarry face. The walking crusher is linked to a flexible

conveyor system that transports the crushedrock across the quarry floor to an 85,000-tonne capacity primary stockpile, which isaround mile away from the furthest face.Following a recent decision to wash and

process the quarry’s large and growingstockpiles of primary scalpings to provideadditional ‘added-value’ products, AggregateIndustries commissioned DUO (Europe) toprovide a complete washing and water-management plant. Operating under CDMregulations as principal contractor on theturnkey project, DUO were responsible for allstructural calculations, bespoke structuralsteelwork and the provision of conveyors,which were supplied by DUO Manufacturing.Believed to be the largest facility of its kind

in Europe, the new plant currently handles 600 tonnes/h of waste scalpings and producesone grade of aggregate and two grades ofsand, although it has been designed with thecapability to produce several sizes of aggregatewith a just few minor modifications to thedischarge chutes and the addition of furtherstockpile conveyors.Material is drawn from the scalpings

stockpiles and fed into a 50-tonne capacityfeed hopper, which in turn feeds on to a

1,200mm wide x 27m long inclined beltconveyor. This feeds the material through atwo-way discharge chute on to two in-lineCedarapids 6.0m x 1.8m three-deck primaryrinsing screens. Supplied through the DUOdealership and well suited to large-scaleproduction, these screens are the first of theirtype to be installed in the UK.The inclusion of Cedarapids flat screens

within the plant is said to provide significantlygreater throughput compared with similar-sized inclined screens. Additionally, the use offlat screens provides easier access formaintenance and keeps the overall height ofthe plant to a minimum.The design of the screen vibrator

mechanism allows the angle of throw andamplitude of stroke to be adjusted, whileadjustable pitched motor pulleys provide foreasy speed adjustments to accommodatechanges from coarse to fine material screeningoperations. The deck frames are huck-bolted to side

sheets for greater durability under aggressivevibration, while high-strength alloy steel sidesheets with spherical clamp bolt washerseliminate weld stresses. The flat-deck screenswere also specially designed to accommodateeasily interchangeable modular polyurethanedecks.Any mid-size material from the rinsing ‰

View of the washing plantshowing the Cedarapids flatscreens and Greystone log-washers

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screens is discharged into two Greystone log-washers, which mix the incoming feed whilescrubbing and washing the material at thesame time. Any lumps of earth or clay arebroken down during this process and carriedaway in the wash water.Featuring a spiral paddle along the log shaft,

the Greystone log-washers provide continuousagitation of the material, delivering maximumscrubbing action, reducing energyrequirements and eliminating intermitentshock loading on the shaft and gearbox.Heavy-duty flex couplings prevent anymisalignment and provide maximumproduction and long wear life, as well as easyremoval of the log shaft for maintenance orrepair.The special paddle base design features

three bolt holes per paddle, while the Ni-Hardwear-resistant paddles themselves deliverextra strength to protect against breakage andmaximize wear life. Shoe paddles mounted tothe bases with Grade 8 bolts are installed atthe proper angle to the extra-heavy ASTMseamless steel log shaft for maximum washingaction and service life with minimummaintenance requirements.The heat-treated shaft is fitted into a hard,

stainless steel spacing sleeve and equippedwith a heavy-duty rubber gasket that fits

snugly between the seal retainer and tub. Aspecially designed slinger fits perpendicular tothe shaft between the roller bearing andsleeve and turns with the shaft, addingprotection to the outboard bearing andpreventing potential bearing failure due to sealleakage.The log-washer shaft is driven by twin

helical synchronized precision gears, which aretotally enclosed within an oil bath gearbox.The unit is designed with externally mountedbearings for easy pressure lubrication, serviceand maintenance. Standard electric motorsallow for a change of washing action with asimple change of the drive pulley on themotor, while shaft-mounted speed reducerswith durable cast iron, corrosion-resistanthousings provide positive gear alignment. Thehelical design of the gear teeth has a soft corethat resists shock loads and provides a 98.5%efficiency rating per gear set. Dual-outputshafts with timed gears allow for theinterlocking of the paddles. In order to keepdirt out and oil in, the reducers are sealedwith metallic double-lip seals.Mid-size material is fed from the log-

washers on to a final pair of in-line 6.0m x1.8m Cedarapids part-rinser screens, whichprovide a final rinse. The resulting clean5–20mm product is delivered to ground ‰

Two radial conveyors deliverthe clean 5-20mm product tostockpile

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stockpiles by two 800mm wide x 24m longradial stockpile conveyors fitted with walkwaysalong their full length and around the headdrums. Meanwhile, –5mm sand and water from the

primary rinsing screens, log-washers and finalpart-rinsers is collected in two tanks locatedbeneath the plant and pumped 170m acrossthe site and up into a boiling box. From here itis fed under gravity into two PowerscreenFinesmaster 200 machines which classify anddewater the material to produce two gradesof sand.Water management – an essential part of

the process – is dealt with by five Tecnoideamulti-plate filter presses, which providemaximum flexibility and throughput with rapidopening and closing times. Situated on agalvanized structure mounted 5.0m above theground, these five presses provide anautomatic silt-management system specificallydesigned and sized to minimize operator inputand maintain low running costs.As well as the five presses, the system

includes three 7.0m diameter deep-conethickeners to clarify the water, a 7.0mdiameter deep-cone clarified water storagetank, an automatic flocculant mixing plant andan automatic flocculant dosing system, whichregularly adjusts the volume of flocculant sentto the thickeners depending on the quantity ofsilt. Five in-line 80m3 capacity sludge buffertanks with internal rakes complete the line-up.Within each thickener tank the silt settles

to the bottom of the cone and is automatically

discharged into a silt buffer tank once it hasreached the required density for pumping tothe plate presses. In order to maintainthroughput through the five presses, lime canbe added if a large quantity of clay is presentwithin the silt.Lime addition is automatically controlled by

means of a rotary valve. This feeds the lime onto a rotary screw, which in turn feeds it into amixing tank; at this point water is added tocreate a lime solution. This is automaticallydistributed into the silt buffer tanks, asrequired, where it reacts with any clay materialin the silt to facilitate water drainage in thepress.Once each press has been filled and the

water drained, opening of the press allows theresulting silt cake to drop into a concrete baybelow. The press then goes through a self-cleaning routine ready for another cycle. As inall such applications, DUO carefully selectedthe size of presses for Torr Works taking intoaccount factors such as the silt content, claycontent and settlement rate of the rawmaterial.In designing the whole plant, DUO also

studied in detail the requirements for plantmaintenance. In particular, maintenance of thefive presses can be achieved with ease owingto the installation of fixed overhead liftingbeams complete with electrically operatedhoists, while accessto the plate presses is viatwo staircases situated at each side of thestructure with further access via wide, fullygalvanized walkways.

The water-management plantincorporating five Tecnoideamulti-plate filter presses