Faced with increased demand for concrete sand, a UK producer has been boosted by the commissioning of a quality wash plant and water and silt management system.
Owned and operated by NRS Aggregates, Saredon Hill Quarry is located at Shareshill near Wolverhampton, in Central England. Following a period of six months when the site was reinstated into working order, sand processing quickly followed and has been in operation for the past three and a half years. With current planning permissions in place until 2032, there are also further options for extensions in the future.
Processing was originally handled by a washing plant which at the time was sufficient to cope with the sales, but with rising demand from a major customer to supply sharp sand for three concrete plants, and with a further two coming on-line, a decision was made to upgrade its production capabilities. After some research, specialist washing equipment distributor Power X was duly awarded the order for a new washing plant and a water and silt management system.
As the England and Wales dealer for Terex Washing Systems (TWS), Power X provides cohesive, innovative wash plant solutions for all material and mineral washing needs. For this project, Power X proposed an AggreSand 206 modular wash plant, which is part of the TWS modular, mobile and static wash plant range that focuses specifically on solutions for the quarrying, aggregate and C&D recycling industries.
“The new plant has given us the scope to increase production and improve efficiency and production of high value products to match demand,” Stephen Graham, the operations manager for NRS Aggregates, said. “At this point we are operating at about 58 per cent capacity and processing 10,000 tonnes per week and selling 8000 tonnes per week across the weighbridge.
“With a mixed feed from three sources the material is mixed like a cake and blended in metre layers until five metres in height is achieved, this is then levelled off with a dozer with another layer added which provides a better mixture, eliminating any gaps in the grading.”
SAND AND GRAVEL PLANT
Capable of processing more than 250 tonnes per hour (tph), the plant is fed by a wheel loader into a 50-tonne hopper (with tipping grid) via access up a wide ramp. The width of this ramp also allows the plant to be fed by a dump truck if there are any problems with the loader.
Material is then fed via a 42m long inclined conveyor onto the 6m x 2m (20’ x 6’) aggregate rinsing screen of the Terex AggreSand 206 modular wash plant. This three-deck version utilises individually controlled spray bars on each deck and the two-bearing screen is fitted with polyurethane modular media on all three decks with the top deck rejecting any +20mm material. This oversize material is fed via a chute onto the 32m long crusher feed conveyor which feeds a 25m³ surge bin. Material is then delivered onto a vibratory feeder which 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 do have a rotary crusher at our other site but I prefer the cone as it’s very efficient.”
The screen decks then split the required products of 10mm and 20mm which is stockpiled via conveyors. The bottom deck is split and provides a 0-2mm material which is delivered to a Finesmaster 120C, a static sand recovery unit on one chassis complete with centrifugal slurry pump, hydrocyclone, collection tank and a 3.6m x 1.5m (12’ x 5’) dewatering screen. This produces a soft sand which is then stockpiled by radial conveyor.
The 0-4mm off the bottom deck is fed to the AggreSand 206 sand plant to produce a sharp sand. Chute work on the 206 employs the well tested “dead box” system which results in a rock on rock set-up which provides excellent wear properties.
The AggreSand 206 sand plant at Saredon consists of a high energy 4m x 2m (14’ x 6’) dewatering screen which can dewater up to 200 tph. Two 45kW 200/150 pumps and one G4-660mm and one 500mm cyclones complete the specification to produce a 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,” Luke Talbot, the managing director at Power X, said. “It brings together tried and trusted TWS 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.
“TWS have continually demonstrated their commitment to providing outstanding innovative products, customer support and expertise in the field,” Talbot added. “As their English and Welsh dealer, Power X is dedicated in providing reliable, high quality and very productive TWS equipment to meet our clients’ materials and mineral washing needs that meet today’s stringent specifications of clean material.”
WATER AND SILT MANAGEMENT SYSTEM
The water treatment plant at Saredon receives dirty water from the washing plant and has two purposes. The first is to clarify and recycle the water and the second is to concentrate the sludge. This is achieved by the addition of a polymer which attracts the silt particles, forming larger, heavier particles known as flocculants which congeal and sink to allow both targets to be achieved. Delivered as a white powder, the process involves two stages: mixing with a low speed agitator, and secondly by maturation that takes place in a second tank where it is dosed by a pump with a frequency variator.
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 then 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.
At this point, the flocculation controller takes a sample of flocculated water from the central shaft and the settling speed is measured by the Controlfloc (a glass tube fitted with optical cells). 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 which 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.
SLUDGE CONCENTRATION, EVACUATION
The sludge settles quickly at the bottom of the thickener where it is concentrated and gathered into the pumping cone, due to the slow movement of the scraper. The sludge is then drawn by a pump which is located alongside the 14m diameter thickener tank which is sized to handle up to 40 tph of silt.
The sludge pumping cycles are controlled according to the measure of the resisting torque applied on the scraper which is interpreted by the PLC. This gives reliable information about the quantity and consistency of the sludge at the bottom of the thickener, and also offers a safety in case of a “build up” inside the thickener.
If an overload is detected by the inverter, the scraper is automatically fully lifted to its upper position and then progressively lowered down to dilute the sludge.
The transfer and pumping of recycled waters is achieved with the overflowing waters being discharged into the 10m diameter clarified storage tank, where the plant feed water pump delivers it back to the washing plant.
The whole plant is controlled from the technical room (sited on the static bridge) by the PLC; via a touch screen which displays the synoptic and allows access to the settings.
The main switch and control panel are also located inside the technical room which contains the flocculant preparation, dosing unit and controller, the main switch, control panel, scraper driving unit and the fresh water box.
Since its commissioning, the plant has performed efficiently, providing NRS with more control and flexibility over its production and enabling the company to satisfy the increased demand.
In Australia, Terex Jaques is the distributor of Terex Washing Systems modular washing plant solutions. Visit terex.com/washing/en/Australia/aggresand-206
Source: Terex Washing Systems