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Sand Processing














Material is sent via a 42m long inclined conveyor to the three-deck AggreSand 206 modular wash plant.
Material is sent via a 42m long inclined conveyor to the three-deck AggreSand 206 modular wash plant.

Sand, gravel plant brings quarry new lease of life

A modular wash plant and sand recovery unit has boosted the working life of a quarry that has only been back in full working order for the past couple of years.

Owned and operated by NRS Aggregates, Saredon Hill Quarry at Shareshill, near Wolverhampton, was brought back into full working order about four years ago, at which time the site’s original washing plant was sufficient to cope with the demand for sand and gravel.

However, with a major customer looking for increased supplies of sharp sand for three concrete plants, and with a further two plants about to come online, NRS Aggregates decided to upgrade its production capabilities at the quarry.

After researching the market, NRS Aggregates awarded the contract to specialist washing equipment supplier DUO Equipment to supply and install a new Terex AggreSand 206 modular wash plant, a Terex Finesmaster 120C sand recovery unit and a TC1000 cone crusher, together with an associated water/tailings management system.

“The new plant has given us the scope to improve efficiency and increase the production of high value products to match demand,” NRS Aggregates’ operations manager Stephen Graham said. “At this point we are operating at about 58 per cent capacity, processing 10,000 tonnes per week and selling 8000 tonnes across the weighbridge.”

High tonnage plant

Capable of processing more than 250 tonnes per hour (tph), the plant is generally fed by wheel loader via a 50-tonne feed hopper with tipping grid.

From here the material is sent, via a 42m long inclined conveyor, to the three-deck AggreSand 206 modular wash plant, which utilises individually controlled spray bars on each deck. The two-bearing 6m x 2m (20’ x 6’) screenbox is fitted with polyurethane modular media on all three decks, with the top deck rejecting any +20mm oversize material.

"The plant has been performing efficiently since then, providing the company with much more control and flexibility over its production, and allowing the company to satisfy the increased demand for sharp sand."

This is fed, via a chute, on to a 32m long crusher feed conveyor that discharges into a 25m3 capacity surge bin. From here the oversize is delivered onto a vibratory feeder that automatically choke feeds the TC1000 cone crusher. The crushed material is then returned to the screen feed conveyor for further processing.

“This closed circuit arrangement has worked very well and has proved to be a very good investment,” Graham said. “We have a rotary crusher at our other site, but I prefer the cone as it’s very efficient.”

The AggreSand 206 screen decks split the raw material into the required 10mm and 20mm aggregate products, which are sent to stockpiles via conveyors. However, the bottom deck is split and provides a 0-2mm fraction, which is delivered to the Finesmaster 120C static sand recovery unit. This single-chassis unit, complete with centrifugal slurry pump, hydrocyclone, collection tank and a 3m x 1.5m (12’ x 5’) dewatering screen, produces a soft sand that is stockpiled by radial conveyor.

Meanwhile, the 0-4mm fraction from the bottom deck is fed to the AggreSand 206 sand plant to produce a sharp sand. This sand plant incorporates a high energy 4m x 2m (14’ x 6’) dewatering screen capable of dewatering rates up to 200 tph, while two 45kW 200/150 pumps, one G4-660mm cyclone and one G4-500mm cyclone complete the specification to produce the clean, in-specification sharp sand.

“The Terex AggreSand system is delivered pre-wired and pre-plumbed, and combines aggregate washing and screening with sand processing on an easily installed modular chassis, which was the ideal solution for NRS Aggregates,” DUO managing director Luke Talbot said.

“It brings together tried and trusted Terex Washing Systems components in an innovative design that is very appealing in terms of access, serviceability and modularity. Quite simply, it sets itself apart from other washing systems in the marketplace.”

Water, tailings management

The water treatment plant at Saredon serves two purposes: first, to clarify and recycle the dirty water from the washing process, and second, to concentrate the resulting slime. This is achieved through the addition of a polymer flocculant solution, which is prepared/dosed and controlled/adjusted by Dosafloc and Controlfloc systems respectively.

The dirty water coming from the cyclone overflow is mixed with the flocculant solution prepared by the Dosafloc.

An additional and final dilution of the flocculant solution through cyclonic spreaders optimises this mixing solution in the flocculation box (fitted with baffle plates). Once prepared, the water is directed by gravity into the central feed shaft.

The Aggresand splits the raw material via its two decks.
The Aggresand splits the raw material via its two decks.

At this point the flocculation controller takes a sample of flocculated water from the central shaft and the Controlfloc, a glass tube fitted with optical cells, measures the settling speed. This information is then transferred to the programmable logic controller (PLC), which automatically adjusts the flow from the flocculant dosing pump (according to the settings entered during the commissioning stage) to optimise the flocculation efficiency and consumption. After each measure, the glass tube is automatically rinsed.

Samples taken with a vacuum system avoid the use of a pump that would distort the measure by breaking the flocculants. The optic cells also determine the turbidity of the recycled water and therefore adjust the coagulant dosing accordingly.

The resulting slime settles to the bottom of a 14m diameter thickener tank and is drawn off by a pump capable of handling silt at rates of up to 40 tph. The slime pumping cycles are controlled according to the measure of the resisting torque applied on the scraper that is interpreted by the PLC.

This gives reliable information about the quantity and consistency of the slime at the bottom of the thickener, and also offers safety in case of a “build up” inside the thickener. If the inverter detects an overload, the scraper is automatically fully lifted to its upper position and then progressively lowered down to dilute the sludge.

Meanwhile, the clarified water that overflows the thickener tank is discharged into a 10m diameter clean water storage tank for recirculation back to the washing plant.

The whole plant is controlled by a PLC, with a touch-screen providing synoptic displays and allowing access to the plant settings. Situated on a static bridge above the thickener tank, the control/ technical room also houses the main switchgear and electrical control panel, the flocculant preparation, dosing and control units, and the thickener tank scraper drive unit.

Commissioned in mid-2016, NRS Aggregates says the plant has been performing efficiently since then, providing the company with much more control and flexibility over its production, and allowing the company to satisfy the increased demand for sharp sand.

In Australia, the distributors of Terex Washing Systems’ Aggresand and Finesmaster plant and equipment are Terex Jaques (east coast states and South Australia) and OPS Screening and Crushing Equipment (Western Australia and the Northern Territory).

Article courtesy of Quarry Management Journal. Visit agg-net.com




















Monday, 20 August, 2018 03:04pm
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