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Glendinning, the West Country’s largestindependent quarry operators, have completedphase1 of a major upgrade at their Linhay Hill

Quarry, at Ashburton, in Devon. The quarry lies on thesouth-eastern edge of Dartmoor, within close proximityto themain A38 trunk road running throughDevon andCornwall.The limestone quarried at the site is late-Devonian

in age, some 360–380 million years old, and ischaracterized by its fine-grained medium to darkgrey colouring. Linhay Hill produces over 500,000tonnes of this limestone annually, with productsranging fromaggregates, coated stone and ready-mixedconcrete to building blocks, decorative and industrialpaving and hardcore, agricultural lime and wallingstone.Major investment in a new state-of-the-art asphalt

plant from Benninghoven was part of an £8 millionupgrade of the existing asphalt and crushing and

screening plants, to increase operating efficiency andrealign output with changing market requirements.Commenting on the new plant and its selection,

operations director Ian Glendinning said: ‘The projectteam,who actively involved employees fromall aspectsof the business, spent a great deal of time and effortevaluating the options shortlisted to ensure the plantselected provided us with the required flexibility andperformance criteria. It was also vital that we gainedthe necessary assurance from the manufacturer withregard to build quality, delivery and erection time-scales,after-sales support and, most importantly, theirapproach to, and focus, on health and safety.’Designed to provide significant operational benefits

and cost savings, the new Benninghoven modelTBA3000UE plant is able to produce a wide range ofhigh-specification coatedmaterials, includingmodernthin-surfacing stone-mastic asphalts and otherspecialized mixes. The plant is rated to produce

Glendinning CompleteMajor Quarry UpgradeNew Benninghoven asphalt plant for Linhay Hill Quarry

The new Benninghoven model TBA3000UE asphalt plant at Linhay Hill Quarry

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200 tonnes/h at 3% initial moisture (DBM) and 160tonnes/h at 5% initial moisture (SMA).The aggregate cold feed consists of an in-line set of

eight bins with belt feeders, discharging on to a 6.5mcollecting conveyor, which, in turn, feeds on to a 30minclined conveyor. The fully covered inclined conveyoris mounted on trestles with safety pull wires along itswalkways. An 18m long x 800mm wide transferconveyor transports material on to a short reversibleslinger conveyor, which feedsmaterials directly into thedryer.The aggregate dryer drum,whichmeasures 2.4m in

diameter x 9m in length, is fully laggedwith 70mmthickinsulation and aluminium clad for heat retention andnoise reduction. The drum is friction driven by foursupport rollers through individual 18.5kW gearedmotor units.The burner is a Benninghoven model Rax Jet oil 4-

3 OFU type, designed to burn both gas oil and Eco oil.This is equippedwith a full range of operating and safetydevices to deliver high-efficiency fuel usage. An air-inletsilencer is connected to the burner to suppress noiselevels. The burner and silencer aremounted on a track

to allow the unit to slide back from the dryer for routineservicing.The plant’s dust collection system, which is rated at

64,000Nm3/h, is sized for the dryer andmixing sectionscavenging, and achieves emission levels of less than20mg/m3. A primary skimmer unitmounted alongsidethe dryer separates any coarse dust from the airstream,which passes to the hot-stone elevator feed boot via agravity flap valve and chute. The secondary cassette-type filter system collects any remaining dust andtransfers it, via two screwconveyors, to the filler elevator.A dustmonitormounted on the exhaust stack providesa remote readout in the operator’s cabin. As a result,the plant meets the most stringent dust controlregulations.Any excess dust collected can be discharged from the

reclaimed dust silo through a rotary valve into a twin-shaft paddle conditioner, where water is introduced toprovide an environmentally friendlymethod of purgingthe dust. Any excess filler can also be directly loadedinto road tankers.Hot aggregates are transported from the dryer up to

the screen by a 28m vertical bucket-type elevator. This

Eight-compartment coveredcold-feed unit

2.4m diameter fully lagged and clad aggregate dryer Benninghoven Rax Jet oil 4-3 OFU burner

Asphalt Plant

January 2011 www.Agg-Net.com 9

is totally enclosed and features a heavy-duty double-strand chain and wear-resistant steel buckets withreplaceable liner plates at impact points. Elevator driveis by a 37kW geared motor and toothed chain wheelsat the elevator head. The elevator features externallylocated bearings and a safety backstop facility. A wideplatform provides access for maintenance.Material discharged from the elevator passes into a

six-deck screen featuring twin-shaft drive via two19kW‘bolt on’ low-maintenance vibratingmotors. These driveunits are mounted outside the screen housing toallow thehigh-temperature screening ofmaterials.Wideaccess doors, together with a rollaway chute, provideaccess to all screen decks. An extraction fan ensuresnegative pressure ismaintained in the screen housingfor optimum dust control.The hot storage section has a total capacity of 80

tonnes and comprises six bins. All the bins areinsulated and clad and each is fitted with continuouslevel indicators and an overflow chute. Discharge is bya pneumatically operated radial door, which accuratelyregulatesmaterial flow to the aggregateweigh hopper,fromwhere the aggregates are discharged directly intothe mixer.Accurate weighing out of ingredients is achieved by

separate load-cell-mounted weigh hoppers, whichcomprise a 3,000kg capacity aggregate hopper, 600kgfiller weigh hopper, and 350-litre capacity weigh vesselfor bitumen.Mixing takes place in an insulated 3,000kgcapacity twin-shaft paddle mixer, with drive providedby two 37kWgearedmotor units through synchronizedgears. A radiation pyrometer is situated at the mixerdischarge to indicate mix temperature.Mixedmaterial discharged from themixer falls into

a 3,000kg skip unit, which runs on horizontal tracks anddistributes the material into a 200-tonne capacitysilo, arranged in four 50-tonne compartments. All fourcompartments are equipped with high-level warningindicators and are insulated and fittedwith electric traceheating around the discharge doors. A 6-tonne directload-out hopper is positioned beneath themixer. All binsaremounted on load-cells to ensure accuratematerialloading.

Bitumen is stored in two vertical tanks (70m3 and100m3 capacity) located adjacent to the plant, both ofwhich are Benninghoven’s latest electric high thermalefficiency units that deliver low running costs due to theirstepped heating system design. An in-built loading

Skimmer and cassette-typedust-collection filter

Two vertical high thermalefficiency bitumen tanks

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systemwith high-level probes offers fail-safe fillingwithno possibility of spillage and ensures compliance withthe latest RBA standards.Filler is stored in an external two-compartment

vertical silo holding approximately 60m3 of reclaimedfiller and 40m3 of imported material. Both silos areequipped with level indicators and shut-off valves.A gravimetric additive system is also incorporated

within the plant to feed granulatedmaterial froma30m3

silo. Each batch of granulate is accurately weighed ina load-cell-mounted weigh hopper before beingdischarged through a butterfly valve to themixer. A 3m3

silo for pigment, which is filled from bags, is situatedalongside.A RAP system has been incorporated in the facility

to deliver precise percentages directly into the plantmixer. The system comprises a steep-sided, 10m3

capacity feed hopper fittedwith an oversize grid and twovibrators. A 4kW belt feeder mounted beneath the

hopper discharges the RAP on to a 30m long coveredconveyor equippedwith a belt weigher to give accuratebatches proportional to the weight of aggregates. TheRAP is transported up to themixer level via a recyclingelevator. An automatic vent duct at the mixer allowsrapid extraction of steam during recycling operations.The plant is controlled by a Benninghoven Online

Batcher 3000 computer system that displays all plantfunctions via colour graphics. The system, which ishoused in an existing control cabin adjacent to the plant,is modem linked and provides storage for up to 500asphalt mix recipes.

AAcckknnoowwlleeddggeemmeennttss Thanks are due to Ian Glendinning, operations director;Barry Wilson, managing director; and Richard Webb,operations manager, of E&JW Glendinning; as well asNigel Moreton of Benninghoven UK Ltd, for their helpin preparing this report.

Asphalt Plant

Fully sheeted tower with two-compartment, 100m3 capacityfiller silo

RAP feed hopper, conveyor and elevator to mixer level Benninghoven OnLine Batcher 3000 plant control system