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2020 / 2021 Edition

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New Wash Plant for Frimstone

First published in the August 2016 issue of Quarry Management

DUO Equipment supply new Terex AggreSand washing plant for busy new sand and gravel operation in Norfolk

Breck Farm (part of the Stody Estate) is one of eight sand and gravel sites operated by Frimstone Ltd in the East Anglia region. A family-owned business with more than 70 years’ experience in mineral extraction, the company supplies a range of mineral products including sharp and soft sands, gravel, rockery stone, decorative ‘slate’ aggregate and screened topsoil to the general public, businesses, local authorities and the construction industry, including a five-year supply contract with a national concrete supplier.

With potential reserves of sand and gravel well in excess of 10 million tonnes, the new Breck Farm site is currently producing 150,000 tonnes per annum of soft and sharp sands as well as 10mm, 20mm, 40mm and +40mm aggregate products.

Development of the new greenfield site started two years ago with construction of the haul road. This was followed by the laying of concrete pads for the washing plant, installation of the weighbridge and development of the silt lagoons. With all the site infrastructure complete, Frimstone researched the washing systems market and, following a successful tender bid, selected DUO Equipment to supply a new plant based around the AggreSand system from Terex Washing Systems (TWS).

The main elements of the plant consist of a TWS AggreSand 165 modular wash plant and a PowerScrub 120R log-washer. The AggreSand plant is a pre-wired, pre-plumbed, easily installed modular concept that facilitates quick installation; a combination that makes it appealing to many operators in terms of its access, serviceability and modularity.

Frimstone plant manager Richard Blowers commented: ‘It’s a very neat, compact plant incorporating an in-line system with ‘as raised’ ballast being fed by loading shovel into the feed hopper. With pumps installed, we are responsible for the wash water going in and the dirty slurry water coming out of the plant into the lagoons, so it’s a very simple and effective set-up.’

Currently operating at 130 tonnes/h, the plant incorporates a bespoke feed system comprising a 12m3 feed hopper and double-deck vibrating grid; both the feeder and the vibrating grid are electric/hydraulically powered. Material is delivered on to a main inclined feed conveyor driven by two 11kW electric motors via Bonfiglioli gearboxes mounted either side of the drive drum.

AggreSand 165

The AggreSand 165 unit at Breck Farm is a two-bearing, twin-deck version which utilizes eight individually controlled spray bars on each deck, both of which are equipped with polyurethane modular screen media. The top deck acts as a protection deck removing any +40mm material which is fed, via an on-board conveyor, to stockpile. The split bottom deck (2mm and 5mm) provides the feed to produce the required two sands. All chutework on the AggreSand 165 utilizes dead boxes, thereby ensuring effective rock-on-rock contact and excellent wear properties.

To produce two clean in-spec sands, the AggreSand 165 sand plant incorporates a 45kW 200/150 pump and G4-500mm cyclone for coarse sand, and a 150/125 pump and G4-375mm cyclone for soft sand. A specially designed rubber-lined catch box allows blending to take place so that an acceptable coarse and fine sand ratio can be achieved. The two sands are delivered to separate radial conveyors for stockpiling. Any –40mm +5mm material is fed by inclined conveyor to the PowerScrub 120R log-washer for scrubbing and the removal of clay agglomerates.

PowerScrub 120R

The PowerScrub 120R consists of a 6.5m long hull fitted with twin rotating shafts equipped with 30mm abrasion-resistant blades. The blades convey the material from the feed end of the unit to an 8ft x 4ft aggregate rinsing/sizing screen. As the material travels through the hull the abrasive stone-on-stone action scrubs the material and breaks up any clay agglomerates. Any organics or plastics are floated off and dewatered by the PowerScrub’s 6ft x 2ft trash screen. Underflow from the trash screen discharges into a catch box under the screen and is gravity fed to a sump tank under the hull.

Scrubbed aggregate exits the main discharge of the PowerScrub 120R to the 8ft x 4ft part-rinsing screen. The initial section of this screen is fitted with spray bars to remove any sand or grit residues produced during scrubbing. This is captured in a partial catch box under the screen and is piped to the sump tank below the hull to join the trash screen underflow. This sump tank is fitted with a 100/100 centrifugal pump which pumps the dirty water back to the AggreSand 165 sand plant to recover any remaining sand and maximize the use of internal process water.

Meanwhile, the washed material is fed, via transfer conveyor, on to Frimstone’s existing three-way-split screener to produce clean –40mm +20mm, –20mm +10mm and –10mm +4mm aggregate grades for stockpiling.

The control system for Frimstone’s AggreSand wash plant is housed in a centralized on-site cabin, which is one of the options offered by DUO, through TWS, on all AggreSand installations. Alternatively, the control panel can be mounted on the pre-wired machine, highlighting the flexibility of TWS and DUO, and the AggreSand concept, to suit individual customer needs or preferences.

Since the plant was commissioned Frimstone say it has proved very successful, providing them with consistent quality products. Plant manager Richard Blowers said: ‘I can’t fault the material that comes off the end of the belts – it’s very clean and saleable material, it’s fantastic!’

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